PhotoDemon 6.0 is now live at photodemon.org

The final splash screen for version 6.0.  Thank you again to all the talented contributors that made this release possible!
The final splash screen for version 6.0. Thank you again to all the talented contributors that made this release possible!

After a successful (and relatively bug-free!) beta testing session, PhotoDemon 6.0 has been deemed “ready for mass consumption”. Normally this is where I would put a download link, but let me instead refer you to the new home of all things PhotoDemon: photodemon.org

I thought it was finally time for PD to get its own online home, and photodemon.org is the result. The site still has a few pieces left to assemble (most notably the Features section, which is only about half done), but I didn’t want that to delay the availability of 6.0’s release.

You can download version 6.0 from the “Downloads” section of the new site, or from this direct link:

Download PhotoDemon 6.0 (.zip file, 6.3 mb)

Functionally, this release is very similar to the 6.0 beta that launched two weeks ago. The primary changes from the beta are miscellaneous bug fixes, performance improvements, and cosmetic adjustments.

If you are upgrading from version 5.4, you’re going to notice a lot of new things! You can get a full write-up of all the improvements here, or if you’re in a hurry, here is the abbreviated list of updates:

  • All tools now support save/load presets, reset to default, randomize, and automatic save/load of last-used settings.
  • Italian language support.
  • Vastly improved support for non-US locales and non-English users.
  • Advanced selection tools, including rectangular, elliptical, and line selections.
  • All selection types now support feathering, live move/resize, interior/exterior/border types, and antialiasing.
  • Selection actions are fully integrated into Undo/Redo, and selections can be saved to disk.
  • Full preservation of all types of image metadata (EXIF, XMP, IPTC, etc). Metadata can be browsed via a new metadata browser.
  • Official RAW image format support; more than 20 RAW filetypes are now supported.
  • Three new blur tools: motion, radial, and zoom blur. Also, big improvements to Gaussian and Box Blur.
  • A new chroma key (“green screen”) tool with performance comparable to professional tools, including full support for edge blending.
  • New Perspective tool, with support for forward and reverse transforms.
  • New Photo Filter tool, with support for 50 digital photo filters (Wratten-type).
  • New Curves tool. Supports adding, moving, and removing an unlimited number of nodes.
  • New Channel Mixer tool.
  • New Canvas Resize tool.
  • New Spherize tool (for wrapping images around spheres).
  • New Vibrance tool.
  • New Pan and Zoom, Poke, Shear, and Squish distortion tools.
  • A new Language Editor for translators.
  • New variable-strength Sharpen tool.
  • New Oil Painting tool.
  • Many improvements to the Batch Wizard, including dedicated options for batch resizing.
  • Minor improvements to many tools, including polar coordinate conversion, wave distort, ripple distort, figured glass, tile image, posterize, rotate, custom filters, histogram, resize.
  • Any tool with a “color” option now allows you to pick a color directly from the image by clicking the preview.
  • Much better support for high-DPI screens, including tablets.
  • Support for transparent clipboard images, allowing you to move layered images between GIMP and PhotoDemon.
  • Filters and other long-running actions can now be canceled mid-action by pressing ESC.

Acknowledgments

This 6.0 release represents six months of hard work from a variety of contributors. While I am very grateful to all of PhotoDemon’s talented contributors, a few deserve special mention. Thank you to:

  • Audioglider for contributing three new tools: Channel Mixer, Vibrance, and Exposure. Audioglider also reported a number of issues, and motivated me to implement preset support for every PD tool.
  • Frank Donckers for again providing the German, French, and Dutch translations, and for contributing many pieces of code to the new Language Editor, including the Google Translate interface. Amazing stuff.
  • GioRock for the Italian translation, and for detailed testing of many small translation items. It takes a ton of work to get all of PD’s text translating properly, and GioRock debugged many items for me, which benefits users of every language.
  • Kroc Camen for a new IDE-safe mouse interface class, derived from his own open-source VB project. Kroc also reviews many of PD’s individual commits, where he catches many small items I overlook.
  • Robert Rayment for helping me profile and optimize a number of PD’s more taxing functions, and for many suggestions on tweaks and improvements. Many of the performance improvements available in this new version are a result of Robert’s help. Please check out his own VB image editor if you can.

Enjoy!

I hope you enjoy version 6.0. If you have any feedback, please send me a message. I’d love to hear from you.

 

This site - and its many free downloads - are 100% funded by donations. Please consider a small contribution to fund server costs and to help me support my family. Even $1.00 helps. Thank you!

PhotoDemon 6.0 beta is live

Chroma key (green screen) is one of many new tools in this release.
Chroma key (green screen) is one of many new tools in this release.

Download

Remember: if you’re an advanced user, you never have to wait for a beta release. You can always download PhotoDemon’s latest development release from its GitHub page (source code), or from this nightly build permalink (program only).

PhotoDemon is funded by donations from users like you.
Please consider a small donation to fund development and to help me support my family.
Even $1.00 helps. Thank you!

Overview

It’s taken nearly six months, but PhotoDemon 6.0 is finally ready for release. I’ve already talked about some of the great features this release includes, like powerful selection tools, metadata (EXIF) support, Curves and other new tools, so I’d recommend glancing through the linked article if you’re curious.

Since that article, a number of other features have been added or improved:

  • All tools now support save/load presets, reset to default, randomize, and automatic save/load of last-used settings. These items are all accessible from a new “command bar” at the bottom of each tool dialog.
  • From left-to-right, the command bar includes buttons for: reset, randomize, saved presets, and save current settings as preset.  Last-used settings are automatically saved and loaded by the dialog.
    From left-to-right, the command bar includes buttons for: reset, randomize, saved presets, and save current settings as preset. Last-used settings are automatically saved and loaded by the dialog.
  • Three new blur tools: motion, radial, and zoom blur. These tools outperform similar tools in GIMP and Paint.NET.
  • PhotoDemon's new radial blur tool is 4x faster than Paint.NET's, and 30x faster then GIMP's - and at high angles, it produces significantly better output.
    PhotoDemon’s new radial blur tool is 4x faster than Paint.NET’s, and 30x faster then GIMP’s – and at high angles, it produces significantly better output.
  • Much faster Gaussian and Box blur tools (20x improvement!)
  • The updated Gaussian Blur tool now provides quality settings for improved performance.  For most photos, the difference between "good" and "best" will be indistinguishable, but "good" will be some 20x faster.
    The updated Gaussian Blur tool now provides quality settings for improved performance. For most photos, the difference between “good” and “best” will be indistinguishable, but “good” will be some 20x faster.
  • A new chroma key (“green screen”) tool with performance comparable to professional tools, including full support for edge blending. Find it in the Image -> Transparency -> Make color transparent menu.
  • Before color removal; image courtesy http://dimula73.blogspot.com/2013/03/new-user-interface-for-krita-color-to.html
    Before color removal; image courtesy http://dimula73.blogspot.com/2013/03/new-user-interface-for-krita-color-to.html
    After color removal.  Note that the tool creates a 32bpp image, which you can then composite using any photo editing software.
    After color removal. Note that the tool creates a 32bpp image, which you can then composite using any photo editing software.
  • A new Language Editor makes contributing new translations fast and easy.
  • The new Language Editor makes it easier than ever to get involved in translation.  Please contact me if you can help!  (You will receive full credit for your work.)
    The new Language Editor makes it easier than ever to get involved in translation. Please contact me if you can help! (You will receive full credit for your work.)
  • New variable-strength Sharpen tool
  • Previously, PhotoDemon only provided set "Sharpen" and "Sharpen More" functions.  The new tool allows for floating-point adjustments, which allow for much more nuanced fixes.  (Unsharp Masking is still available too, obviously!)
    Previously, PhotoDemon only provided set “Sharpen” and “Sharpen More” functions. The new tool allows for floating-point adjustments, which allow for much more nuanced fixes. (Unsharp Masking is still available too, obviously!)
  • New Oil Painting tool
  • Same photo as the screenshot at the top of this page, but oil-ified.
    Same photo as the screenshot at the top of this page, but oil-ified.
  • Minor improvements to many tools, including polar coordinate conversion, perspective correction, wave distort, ripple distort, figured glass, tile image, posterize, rotate, custom filters, histogram.
  • The perspective tool now supports both forward and reverse transforms.  Reverse transforms allow you to simply trace a crooked object, and have it automatically straightened by the program.
    The perspective tool now supports both forward and reverse transforms. Reverse transforms allow you to simply trace a crooked object, and have it automatically straightened by the program.
    The histogram offers new render options, which can be helpful for identifying areas of channel overlap.
    The histogram offers new render options, which can be helpful for identifying areas of channel overlap.
  • Any tool with a “color” option now allows you to pick a color directly from the image by clicking the preview.
  • Much better support for high-DPI screens, including tablets.
  • Faster viewport rendering for 32bpp images.

Again, these new features are only a fraction of what 6.0 includes. Please check out the 6.0 preview article for news on all the other new tools and improvements.

Acknowledgments

This 6.0 release represents six months of hard work from a variety of contributors. While I am very grateful to all of PhotoDemon’s talented contributors, a few deserve special mention. Thank you to:

  • Audioglider for contributing three new tools: Channel Mixer, Vibrance, and Exposure. Audioglider also reported a number of issues, and motivated me to implement preset support for every PD tool.
  • Frank Donckers for again providing the German, French, and Dutch translations, and for contributing many pieces of code to the new Language Editor, including the Google Translate interface. Amazing stuff.
  • GioRock for the Italian translation, and for detailed testing of many small translation items. It takes a ton of work to get all of PD’s text translating properly, and GioRock debugged many items for me, which benefits users of every language.
  • Kroc Camen for a new IDE-safe mouse interface class, derived from his own open-source VB project. Kroc also reviews many of PD’s individual commits, where he catches many small items I overlook.
  • Robert Rayment for helping me profile and optimize a number of PD’s more taxing functions, and for many suggestions on tweaks and improvements. Many of the performance improvements available in this new version are a result of Robert’s help. Please check out his own VB image editor if you can.

Known bugs

  • EXIF data is not maintained with certain combinations of preferences (delay loading EXIF + export full data when saving). This is caused by a metadata caching issue, and will be fixed by release. Fixed!
  • ExifTool plugin is slightly out of date. It will be updated to its latest version upon 6.0’s release. Fixed!
  • Metadata menus sometimes become disabled even when metadata is available. This will be fixed by release. Fixed!
  • OK and Cancel buttons are not currently translated. This will be fixed by release. Fixed!
  • Some hotkeys don’t fire unless the main form is first clicked. This is a known problem with VB, and will hopefully be fixed by release. Fixed!
  • Master language file is missing a few minor text entries. This will be fixed by release.

The beta version was released before these small items were fixed, so it still contains these bugs. Developers can download updated source code, with these fixes, from GitHub.

Official release timeline

Barring any major bugs, the official 6.0 release should happen within several weeks. Feature-wise, it will be identical to this beta release. The only changes will be minor bug fixes and performance improvements. Automatic update notifications for existing PhotoDemon installs will also go live at that point.

Blur Filter performance: PhotoDemon vs GIMP vs Paint.NET

(Note before I begin: the PhotoDemon 6.0 beta should be live by the end of this week. Sorry it took so long to prepare!)

See what kind of fun charts we get to discuss?  And here I thought the days of 17-minute photo editing actions died with the Pentium III...
See what kind of fun charts we get to discuss? And here I thought the days of 17-minute photo editing actions died with the Pentium III…

The latest nightly build of PhotoDemon (download it here) includes a bunch of new and improved blur filters. Blur filters are among the most computationally demanding filters in a photo editor, because for each pixel in an image, a bunch of other pixels must also be examined in order to calculate the blur. (Blurs generally work by averaging together groups of pixels. Motion blur averages pixels in a line, radial blur averages pixels in an arc, and normal blur averages pixels in a box or circle shape.)

As a simple example, consider a basic blur with a 200 pixel radius, applied to a 10 megapixel digital photo. For each pixel in the photo (all ten million of them), an area of 200 pixels in each direction must be averaged together. Using a simple box blur, that means a box of 200 pixels left, right, up and down must be tallied (for a net area of 400 * 400, or 160,000 pixel comparisons) in order to calculate the blur. Thus, such an algorithm would require:

10,000,000 pixels * 160,000 calculations per pixel = 1.6 trillion total calculations

Even on a modern processor, that’s an enormous undertaking. Fortunately, mathematicians and coders have developed many clever ways to optimize blur functions. Many of these optimizations appear in the newest PhotoDemon build, so I thought it would be fun to speed-test four of PhotoDemon’s blur tools against two other free photo editors: GIMP and Paint.NET. The results were surprising enough that I thought them worth sharing.

A brief overview of each photo editor:

  • PhotoDemon: open-source, written in VB6, nightly build 893 (6.0 beta)
  • GIMP: open-source, written primarily in C, v2.8.6
  • Paint.NET: closed-source, written primarily in C# (and the .Net framework, per the name), v3.5.11

As benchmarking goes, this was very informal. PhotoDemon reports timing automatically in nightly builds, but for GIMP and Paint.NET I had to resort to using a stopwatch. Normally this is a terrible idea, but the algorithms involved take a very long time to run, so a stopwatch was sufficient for broad timing. (10ths of a second don’t matter much when an algorithm takes twenty minutes to finish…)

All tests were done on Windows 7 (64-bit), on my Core i5 650 (3.2ghz) desktop PC with 8gb of RAM. My PC was middle-of-the-road when I bought it back in 2010, so I’d consider reasonably representative of an “average” PC. All the tools in question appear to be heavily CPU-bound anyway, so it’s doubtful newer processors or more cores would make a meaningful difference.

The test photo I used was a 10 megapixel photo, 3872×2592 specifically, in JPEG format:

10 megapixel test photo

With the exception of some very long timings (10+ minutes), all timings were checked twice to make sure results were representative. Very long ones were only checked once due to the wait involved, though I did initiate a second attempt just to make sure my PC wasn’t acting up. (It wasn’t.)

Here are the timing results for four separate blur types, with some notes on my implementation, and what I know or can potentially infer about GIMP and/or Paint.NET’s implementations.

(Due to the large size of the images involved, I saw no reason to upload the output images of each test. Anyone interested can easily reproduce this test on their own PC with images of their choosing.)

Gaussian Blur

Two notes - PhotoDemon used the "good" quality setting, which is a Gaussian estimation using a modified 3x box blur, and GIMP used the IIR method.
Two notes – PhotoDemon used the “good” quality setting, which is a Gaussian estimation using a modified 3x box blur, and GIMP used the IIR method.

Gaussian Blur provides an excellent starting point. Gaussian blur works by averaging a square chunk of pixels, and giving pixels close to the center more weight than pixels far away. It is the most common type of blur tool in photo editing software, probably because its results are aesthetically pleasing, and it is an easy blur function to optimize.

Instead of a naive approach, which would involve the 1.6 trillion calculations mentioned above, most photo editors implement Gaussian Blur using a separable implementation, which cuts the calculations to a much more pleasant 8 billion calculations. Unfortunately, 8 billion calculations is still a lot. (PhotoDemon’s “best quality” option on its Gaussian tool applies a pure Gaussian using separable kernels. On large images, it’s slow. Very slow.)

An even faster approach takes advantage of a neat mathematical relationship between box filters and Gaussian filters: if you keep applying a box filter to a set of data, the result will eventually approach a Gaussian distribution. (Excellent charts available here, courtesy of Nghia Ho.) The Central Limit Theorem shows that repeating a box blur three times results in a function that’s ~97% identical to a true Gaussian.

PhotoDemon uses this as the basis for its three quality settings for Gaussian blur (good, better, and best). Good is a 3x box blur approximation, Better is a 5x, and Best is a true Gaussian. For the chart above, I used the “good” setting because it is by far the fastest. (Note that there’s a bit more to it than just repeating a box blur – how you calculate the box blur size matters; I use a variation of the W3 recommendation available here.)

Take-home message: GIMP’s IIR implementation is excellent – very fast, and it produces a true Gaussian, no estimations. PhotoDemon is surprisingly competitive for a single-threaded VB6 app. Paint.NET’s Gaussian is quite poor both in quality and final result. Its resulting blur is muddier than a true Gaussian, and much slower than you’d expect for a box-blur approximation… so I honestly have no idea how they’ve implemented it.

Motion Blur

PhotoDemon used "Quality" mode instead of "Speed", meaning bilinear interpolation was applied to the rotated image.  No extra options are available for this tool in GIMP or Paint.NET.
PhotoDemon used “Quality” mode instead of “Speed”, meaning bilinear interpolation was applied to the rotated image. Also, “blur symmetrically” was checked. No extra options are available for this tool in GIMP or Paint.NET.

Motion blur is a bit more problematic than Gaussian blur, because it doesn’t work in a square pattern. A naive approach would have you use something like Bresenham’s algorithm on each pixel, tracing a line at the specified angle and averaging interpolated values as you go.

A much better approach is to simply rotate the image by the requested angle, apply a (very fast) horizontal blur, then rotate the image back into place. If you use a fast rotation algorithm (like the famous 3-shear technique), this can make motion blur very quick.

My PhotoDemon implementation does not use the fast 3-shear technique; it uses a naive, geometric rotation (reverse-mapped) with bilinear interpolation. I expected this to make it quite a bit slower than comparable tools in GIMP and Paint.NET, but I was surprised to discover that both software packages are… well, pretty damn terrible.

Based on a brief perusal of GIMP’s source code, they appear to use the naive Bresenham approach, which explains why it’s so slow.

Once again, Paint.NET’s execution time makes no sense to me. For a software package that claims: “extensive work has gone into making Paint.NET the fastest image editor available“, methinks they need a bit more “extensive work” on this particular tool…

Radial Blur

As before, PhotoDemon uses the "quality" setting for bilinear interpolation.  Paint.NET was applied at quality setting 2 out of 5, the default setting.  (This results in a noticeably lower-quality image than PhotoDemon or GIMP.)  GIMP does not provide any additional options for this tool.
As before, PhotoDemon uses the “quality” setting for bilinear interpolation. Paint.NET was applied at quality setting 2 out of 5, the default setting. GIMP does not provide any additional options for this tool.

And so we move to Radial Blur, where we find a surprising role reversal: Paint.NET gives a much better showing here, while GIMP turns in the worst performance yet. Again, a brief look at GIMP’s source code for this function shows a questionable nested-loop approach to the problem. Tracing an arc-like path for each pixel is a bad idea, and while bilinear interpolation is used to improve the output quality – same as PhotoDemon – the time required makes this tool pretty much unusable.

PhotoDemon’s implementation is nothing particularly special, which makes its relative performance so surprising. I use a well-known trick where I convert the image to polar coordinates, apply a horizontal blur, then convert the image back to Cartesian coordinates. A small amount of image quality is lost by the two coordinate conversions, but because we are blurring the image anyway, this doesn’t matter much. That said, for small angles (< 5 degrees), both GIMP and Paint.NET produce better-looking output. At larger radii, however, PhotoDemon's is much better. Both GIMP and Paint.NET produce Moire patterns, presumably from sampling at discrete intervals, while PhotoDemon’s output is clean and smooth. This can probably be fixed in Paint.NET by using a higher quality setting, but quality setting 2/5 was already slow enough!

The top-left corner of the image after PhotoDemon's radial blur.  Buttery smooth, and accurate edge handling.
The top-left corner of the image after PhotoDemon’s radial blur. Buttery smooth, and accurate edge handling.
Same corner, but from Paint.NET's radial blur.  Nasty Moire patterns, and problematic handling in the corner - from an algorithm that took 4x longer to run.
Same corner, but from Paint.NET’s radial blur. Nasty Moire patterns, and problematic handling in the corner – from an algorithm that took 4x longer to run.

Zoom Blur

No, that huge green bar is not an error.  GIMP took a whopping 17 minutes to render a 200px zoom blur.  PhotoDemon's "traditional" mode was used to provide comparable output.  Paint.NET does not offer any specialized options for this tool.
No, that huge green bar is not an error. GIMP took a whopping 17 minutes to render a 200px zoom blur. PhotoDemon’s “traditional” mode was used to provide comparable output. Paint.NET does not offer any specialized options for this tool.

Last up is Zoom Blur, and we have a surprising winner! Paint.NET’s zoom blur implementation is excellent – great quality, very fast, and overall a huge improvement from their other blur tools. I have no idea why Zoom Blur is significantly faster than their Gaussian Blur implementation at a comparable pixel size, so I can only assume that some kind of specialized optimizations have been added. Nice work, Paint.NET team!

GIMP… I don’t even know what to say. It’s possible that I triggered some sort of problem with GIMP’s tile-based processing system, because there is no good way to explain a 17-minute processing time for such a straightforward function. Even a naive implementation shouldn’t take anywhere near that long. Their implementation has loops nested five-deep (dear god), and while bilinear interpolation is used to improve output, that algorithm is so poorly written that I frankly think they should consider removing it completely. Even at very low distances, rendering takes forever. The original copyright date on the source file is 1997, so perhaps someone familiar with GIMP’s internals should give this one a second look.

PhotoDemon uses the same trick here as with radial blur. The image is converted to polar coordinates (with swapped x and y values compared to the radial blur conversion), a horizontal blur is applied, then the image is converted back. Again, there is quality loss at low values, and both Paint.NET and GIMP provide better-quality output at very small radii. To mitigate this, I provide a second style on that dialog, which uses an iterative image-sized alpha blend to generate a blur. One of the neat things about that approach is that the image can be zoomed-out as well as zoomed-in.

I doubt there is a legitimate use for zoom-blur-outward like this, but it wasn't any extra work to implement.  :)
I doubt there is a legitimate use for zoom-blur-outward like this, but it wasn’t any extra work to implement. :)

Conclusions

Blur algorithm performance is hugely variable in both GIMP and Paint.NET. I’ll admit – I find it a bit amusing that my little PhotoDemon project, written with a 15-year-old programming language and compiler, outperforms them so handily in multiple areas, despite my implementations being generally lazy, single-threaded, and heavily CPU-bound. I also call “bullshit” on Paint.NET’s claim about “extensive work going into making Paint.NET the fastest image editor available.” I think the Paint.NET team does great work, and their software is a wonderful improvement over many free and paid photo editors, but its performance is greatly lacking in a number of areas.

Then there is GIMP. While I am very grateful for their software, and have learned to love its many quirks, there’s no denying that whole swaths of its source code are in desperate need of a revamp. I imagine there is no point revisiting items like blur until they complete their migration to GEGL – perhaps then we will see big improvements in the performance of these various blur functions.

If there’s a take-home message to all this, it’s that algorithms will always be more important than programming languages. A well-written algorithm in a “slow” language will often outperform a poorly written algorithm in a “fast” language. VB6 may be forgotten and nearly dead, but I’m happy to see it staying competitive with the titans of the “free photo editor” world. :)

If you read the article all the way to here, I hope you’ll give PhotoDemon a look:

http://www.tannerhelland.com/photodemon/#download

For a free, open-source photo editor, it has a lot of nice features, and I can empirically state that it outperforms GIMP and Paint.NET in at least a few areas! (The current nightly build is pretty much how the next stable release (6.0) will look, minus a few minor bugfixes still to complete.)

PhotoDemon 6.0 preview and progress report

PhotoDemon's new splash screen.  I'd say this is a "huge" improvement over the old one, but that might be understating it... :)
PhotoDemon’s new splash screen. I’d say this is a “huge” improvement over the old one, but that might be understating it…

overview

It’s been awhile since I posted any news on PhotoDemon, but not because work has slowed – just the opposite, in fact! The development version of PD is cranking ahead full-steam, and thanks to a number of outside contributors, the next version will include a wider set of improvements than any previous version. There’s still quite a bit of testing and fine-tuning to do, so this article does not include a downloadable beta release – rather, the article is meant to serve as a preview of the upcoming 6.0 release and all the cool new features it provides. (Of course, developers or anyone with access to Visual Basic 6.0 can compile the latest version themselves by visiting PhotoDemon’s GitHub page. New testers and contributors are always welcome!)

First, an explanation on why the next PhotoDemon release will be version 6.0 instead of the expected 5.6. The next release will break backward compatibility with a number of PhotoDemon files, including any saved macros or filters. This break is necessary to implement a large overhaul of PhotoDemon’s internals – an overhaul that makes the program faster, smaller, more stable, and much easier to develop and maintain. The goal is to have all of PhotoDemon’s specialized file formats (including macros) use XML for storage. This allows both users and other software developers to read and edit PhotoDemon files from any general-purpose text editor. This change will also make it much easier to add new macro features without breaking old macro files. (The current macro format was developed over a decade ago, when the program was only meant for personal use, and it is extremely flimsy and difficult to extend – hence the need for a redesign.)

The downside of this change is that any current macros will need to be re-recorded in version 6.0, as version 4.X and 5.X macros will no longer be supported. I apologize for this inconvenience, and I promise to do my best to avoid breaking backward compatibility in the future.

The 6.0 release will also include important interface changes – such as a redesigned main menu and tool window – further supporting the switch to a new major version number, and for developers, the program’s central action processor has been redesigned from the ground up, making it easier than ever to get involved in development.

So with that out of the way, let’s talk about the good stuff, namely: what’s coming in 6.0? Here is a list of features and updates that are already finished and available in the current development build (again, downloadable at https://github.com/tannerhelland/PhotoDemon).

Italian language support

Courtesy of talented contributor GioRock is a new Italian language option for PhotoDemon. Many thanks to GioRock for this huge contribution.

Other internationalization improvements

With the help of GioRock and Frank Donckers (you may remember Frank as the brilliant developer behind PhotoDemon’s language translation engine), a number of other improvements are now available for international PhotoDemon users:

  • The comma “,” is now supported as a decimal separator in all tools. Previously, use of a comma could lead to critical errors.
  • Translated text is now automatically resized if it is larger than its tool window. This helps text in verbose languages remain fully readable.
  • Translations that span multiple lines (such as long tooltips) are now automatically handled by the program. This reduces the burden on translators to manually fit translated text longer than its English equivalent.
Here is the Options panel in full Italian.  The text of the bottom checkbox on the right-hand panel originally extended past the edge of the dialog, but PhotoDemon has detected that and shrunk the text accordingly.  This requires no work on the part of the translator!
Here is the Options panel in full Italian. The text of the two checkboxes on the right-hand panel originally extended past the edge of the dialog, but PhotoDemon has detected that and shrunk the text accordingly. (This required no work on the part of the translator!)

New feature: advanced selection tools

The new elliptical selection tool, with live feathering (feathering is the softened selection edges).
The new elliptical selection tool, with live edge feathering.

PhotoDemon 6.0 includes a completely redesigned selection tool engine. At present, the following dedicated selection tools are available:

  • Rectangular and Square selections (with optional rounded corners, including variable corner radii)
  • Elliptical and Circular selections
  • Line selections: unique to PhotoDemon, this tool allows you to select a line-shaped area, very helpful for things like tilt-shift effects (see below)
PhotoDemon's line selection tool was combined with Gaussian Blur to simulate this fake miniature photograph of the city of Jodhpur.  (Photograph and concept taken from this Wikipedia article.)
PhotoDemon’s line selection tool was combined with Gaussian Blur to simulate this fake miniature photograph of the city of Jodhpur. (Photograph and concept taken from this Wikipedia article.)

Each selection tool supports the following features:

  • Live selection coordinate and size display
  • On-canvas resizing by click-dragging nodes
  • Selections can be nudged or moved via text entry
  • Shift can be held to lock a 1:1 aspect ratio (e.g. squares or circles)
  • Live smoothing options: none, antialiased, or variable radius feathering (live feathering is only available on Windows 7)
  • Live selection types: interior, exterior, or bordered, with live border radius selection

In addition to these dedicated tools, a new Selection menu is available with additional selection-related features.

PhotoDemon's new Select menu
PhotoDemon’s new Select menu
  • Select All and Select None
  • Invert Selection (switch selected and un-selected pixels, with full feathering support!)
  • Grow/Shrink Selection
  • Border selection, which takes the current selection and selects only its border
  • Feather and sharpen selection
  • Load and save selections

Thanks to the selection engine redesign, these features will automatically work with future selection tool implementations, including polygon/free-draw and “magic wand” selections.

Another huge improvement is integrating all selection actions into the Undo/Redo engine. If you create, move, resize, or apply any other action to a selection, you can now Undo/Redo that operation.

Selections are now fully integrated into the Record Macro tool.

Copy and Crop now support selections of any shape, making it trivial to crop circular or rounded-rectangle regions, or copy them for use in another program. (Feathered selections are automatically converted to 32bpp images, with the feathering applied in the alpha channel.)

Finally, the core Selection tools have been rewritten to use vector coordinates. This means that selections loaded from file are automatically resized to fit the current image, making them extremely useful for Batch Processing operations.

New image metadata (EXIF, XMP, IPTC) support

PhotoDemon now includes the marvelous ExifTool project as an optional plugin. ExifTool is the most comprehensive image metadata handler currently available, and PhotoDemon makes full use of its ability to handle every known type of image metadata, from the popular EXIF format (used in JPEGs) to obscure maker notes for all major DSLR brands.

PhotoDemon's new custom-built Image Metadata browser.  This image is a RAW-format file from an Olympus DSLR.  ExifTool allows us to peruse all the custom Olympus data entries.
PhotoDemon’s new custom-built Image Metadata browser. The metadata in question comes from a RAW-format photo taken with an Olympus DSLR camera. Note that ExifTool allows us to peruse all the non-standard Olympus data entries.

A new integrated metadata browser automatically sorts metadata by category, and it allows the user to see actual or human-friendly metadata tags. The browser fully integrates with ExifTool’s multilanguage capabilities, sparing translators from any extra work!

When saving images, the Preferences manager now provides options for metadata embedding:

PhotoDemon's new metadata handling preferences.
PhotoDemon’s new metadata handling preferences.

Unique to PhotoDemon is a privacy-centric metadata option, which aims to remove any personally identifying metadata entries, like serial numbers or GPS coordinates. By default, the “preserve all relevant metadata” option is recommended, which will remove any metadata not relevant to a file format (such as removing maker notes when saving RAW files to JPEG), but retain all other metadata entries. Metadata can also be fully stripped from exported files.

Also fun is a new Image -> Metadata -> Map GPS Coordinates option, which becomes available if an image contains GPS data. This option will automatically map the photo’s location in Google Maps.

New tools: too many to mention!

As always, the next release will include a host of new image editing tools. Here’s a small sampling of the latest additions to PhotoDemon’s repertoire:

PhotoDemon's new interactive perspective correction tool.  Drag the corner nodes to re-visualize the image in real-time, allowing you to do things like fix crooked buildings, as in this photograph from a recent trip to San Francisco.
PhotoDemon’s new interactive perspective correction tool. Drag the corner nodes to re-visualize the image in real-time, allowing you to do things like fix crooked buildings, as in this photograph from a recent trip to San Francisco.
PhotoDemon's new Photo Filter browser.  To my knowledge, this is the most comprehensive collection of post-production Wratten filters in any software, ever.  The interactive photo filter browser provides 50 custom-built photo filters for fixing every possible lighting situation.
PhotoDemon’s new Photo Filter browser. To my knowledge, this is the most comprehensive collection of digital Wratten filters in any software, ever. The interactive photo filter browser provides 50 filters, allowing you to make an infinite number of post-production lighting adjustments.
PhotoDemon's new Curves tool.  It supports unlimited curve points, a live histogram overlay, removal of points by right-clicking them, and fully antialiased curve rendering.  In my opinion, this is the loveliest tool in the program, and the loveliest Curves dialog of any mainstream photo editor.
PhotoDemon’s new Curves tool. It supports unlimited nodes, removing nodes by right-clicking, a live histogram overlay, and fully antialiased curve rendering. In my opinion, this is the loveliest tool in the program, and the loveliest Curves dialog of any mainstream photo editor.
PhotoDemon's new Channel Mixer.  This tool comes courtesy of outside contributer audioglider, who contributes multiple tools to this release - please shower him with praise!  (The subject of this photo is the latest addition to my family, a beautiful Australian Shepherd / Shetland Sheepdog mix named Yosuke.)
PhotoDemon’s new Channel Mixer. This tool comes courtesy of outside developer audioglider, who built multiple tools in this release – so please shower him with praise! (The subject of this photo is the latest addition to my family, a beautiful Australian Shepherd / Shetland Sheepdog puppy named Yosuke.)
PhotoDemon finally includes a Canvas Resize tool.
PhotoDemon finally includes a Canvas Resize tool.
PhotoDemon's new Sphere tool lies more in the "Fun" category than the "Practical" one, but that's okay.  For a bit of extra style, the program can render matching background rays onto the canvas, as shown in the screenshot above.
PhotoDemon’s new Sphere tool lies more in the “Fun” category than the “Practical” one, but that’s okay. For a bit of extra style, the program can render matching background rays onto the canvas, as shown in the screenshot above.

For sake of brevity, I’ll forgo images of the rest of the new tools, namely:

  • Max/min channel
  • Pan and zoom
  • Poke
  • Shear
  • Squish
  • Vibrance (developed by audioglider)

Other improvements and additions for end-users

PhotoDemon's batch wizard now includes dedicated options for common batch operations, such as resizing.  The wizard has also been further streamlined to make batch processing as easy and quick as possible.
PhotoDemon’s batch wizard now includes dedicated options for common batch operations, such as resizing. The wizard has also been further streamlined to make batch processing as easy and quick as possible.
The Resize Tool has undergone a significant redesign.  Resampling options are now human-friendly, and several how-to-fit options are now provided when changing an image's aspect ratio.  This makes it possible to resize images to a new aspect ratio without unsightly distortion.
The Resize Tool has undergone a significant redesign. Resampling options are now human-friendly, and several how-to-fit options are now provided when changing an image’s aspect ratio. This makes it possible to resize images to a new aspect ratio without unsightly distortion.
When flattening an image with transparency (alpha channel), you can now select a background color.  Previously the software always defaulted to white.
When flattening an image with transparency (alpha channel), you can now select a background color. Previously the software always defaulted to white.
  • Transparent images can now be copied/pasted between PhotoDemon and other software. This means you can take an image with multiple layers in GIMP and paste it into PhotoDemon fully composited.
  • Official RAW image format support; more than 20 RAW filetypes are now supported.
  • 30-40% speed improvements to Gaussian Blur, Smart Blur, and Unsharp Masking thanks to an Integer-only rewrite of the blur engine.
  • Filters and other long-running actions can now be canceled mid-action by pressing ESC.
  • Revamped main window interface, as you can see in the screens above. The left-hand toolbar is now images-only, while the right-hand one has been expanded.
  • Better validation for all text controls. Invalid entries are automatically circled in red.
  • Alt+T will now let you switch between preview and non-preview modes in all tools.
  • Many miscellaneous bug fixes, optimizations, and other improvements. For a full list, see the commit log at https://github.com/tannerhelland/PhotoDemon/commits/master

Improvements and additions for developers and contributors

  • PhotoDemon can now provide timing reports for all actions passed through the central software processor. Simply enable the DISPLAY_TIMINGS constant when compiling.
  • New custom slider/text and up/down controls make it easy to utilize PD’s existing validation and translation abilities in your own tool dialogs.
  • A new string-based filter parameter class makes it easy to tie complex tools with many parameters into the software processor (and thus into recorded macros). No longer do you have to convert param lists to complex custom Variant embeddings.
  • PhotoDemon now includes a high-performance font rendering class, which makes custom font rendering (with AA) much easier to implement.
  • Dev builds, including build number, are now automatically detected by the program, making it easy to see which build you’re currently working with.
  • Support tools, including the custom plugin compressor and master translation file generator, are now synched to GitHub in the /Support subfolder.
  • A public histogram-generation routine is now available, so you can tap into PhotoDemon’s highly optimized histogram generator for any of your own tools.

Contributors, developers, and translators still welcome!

As always, PhotoDemon can never have enough external contributors, developers, and translators. If you can help with any aspect of the 6.0 release, don’t hesitate to get in touch. Many features in the 6.0 release wouldn’t be possible without outside help, and I’d love to add you to the ever-growing list of talented contributors that make PhotoDemon possible!

If you can’t contribute with coding or translations, donations are another great way to help. Thanks in advance for your small monetary contribution to this completely open-source project, which provides a full-featured photo editor (comprising 60,000 lines of code and more than 50,000 words of translated text in five languages) completely free of charge.

PhotoDemon 5.4.1 is now live

PhotoDemon 5.4.1 provides fixes for several issues found in version 5.4 (released two days ago). If you have automatic updates enabled, you will automatically be notified up the update, or you can manually download it here.

5.4.1 fixes the following bugs:

  • FIXED: Some controls do not display text correctly on Windows XP
  • FIXED: Some dialogs load very slowly when a translation is active
  • FIXED: Some edge detection methods fail to initiate when a translation is active
  • FIXED: Left-hand toolbox text formatting looks poor when a translation is active
  • FIXED: Tooltips not showing for picture box objects when a translation is active
  • FIXED: When the last-used folder in the batch process tool contains many images (1000+), the batch tool loads slowly on subsequent uses
  • FIXED: Minor typographical errors in translation files

This update also includes a few minor modifications and additions:

  • MODIFIED: In the batch process tool, when a selected image is removed from the batch list, its preview is now erased to prevent confusion
  • ADDED: further optimizations to translation engine. Program performance should now be much better while translations are active.
  • ADDED: batch process tool now displays the number of images in the current batch list

Once again, you can download the update here.

PhotoDemon 5.4 is live – now with German, French, and Dutch language support

Summary

PhotoDemon 5.4 is complete. New features include language support (German, French, and Dutch), a full-featured batch processing wizard, shadow/highlight correction, nine new distort tools, vignetting, median noise removal, JPEG and PNG optimization, and more. Download it here.

Kaleidoscope is probably the least practical (but most fun!) new tool in 5.4.  :)
Kaleidoscope is probably the least practical (but most fun!) new tool in 5.4. Also, German!

Highlight feature: support for multiple languages!

This is the biggest addition in version 5.4, and I can only claim partial credit for it. Primary credit goes to Frank Donckers, a fellow VB programmer who prototyped the initial translation engine for me. As if that isn’t incredible enough, Frank also supplied the translations for French, German, and Dutch (Flemish), so I owe him an enormous debt of gratitude. Thank you, Frank!

One of the neatest aspects of this feature is the ability to change the language at run-time via the Language menu. Unlike every program I have ever used, no restart is required. PhotoDemon will dynamically change the program’s entire language immediately, and if you change your mind, you can switch to any other language at any time.

I hope these three languages are only the beginning. If you speak a language other than English, please consider contributing a new PhotoDemon translation! No programming knowledge is required, and you will receive full credit for your work. Contact me for more details.

Nine new Distort-style tools

Add and remove lens distortion. Swirl. Ripple. Pinch and whirl. Waves. Kaleidoscope. Polar conversion (both directions). Figured glass (dents).

The new Ripple tool.  All distort tools use resampling for improved image quality, and all provide real-time previews.
The new Ripple tool. All distort tools use resampling for improved image quality, and all provide real-time previews.
The new Figured Glass tool uses Perlin Noise to provide a warped glass look to images.
The new Figured Glass tool uses Perlin Noise to provide a warped glass look to images. (Note: the source image is a promotional photo for ABC’s Once Upon a Time.)

Vastly improved file format support

The new JPEG export dialog.  Optimization is a lossless way to reduce file size - very handy for JPEGs headed to the web.
The new JPEG export dialog. Optimization is a lossless way to reduce file size – very handy for JPEGs headed to the web.

JPEGs now support automatic EXIF rotation on import, and a variety of options on export (Huffman table optimization, progressive scan, thumbnail embedding, specific subsampling). TIFFs support CMYK encoding and a number of compression schemes (none, PackBits, LZW, CCITT 3 and 4, zLib, and more). PNG exporting supports variable compression strength, interlacing, and background color chunk preservation. PPMs can be exported with RAW or ASCII encoding. BMP and TGA files now support RLE encoding. And for icons, animated GIFs, and multipage TIFFs, all images inside a file can now be loaded (instead of just the first one).

These format settings can be accessed from the Tools -> Options menu, and the new Batch Process tool also provides direct access.

Revamped standard tools, including Box Blur, Gaussian Blur, Smart Blur, and Unsharp Masking.

Smart blur can be used to smooth out specific features, like skin, while leaving edges and fine details intact.  (Image of the lovely and talented Rashida Jones, via Glamour)
Smart blur can be used to smooth out specific features, like skin, while leaving edges and fine details intact. (Image of the lovely and talented Rashida Jones, via Glamour)

PhotoDemon is now a much better photo editor, thanks to the revamp of its core convolution filters. Larger tool dialogs make it easier to see the result of your actions. Better performance means real-time previews, even at enormous radii (up to 200px for all filters, plus 500px for box blur!). And all convolution algorithms now use specialized edge handling code to make sure every part of the image – from center to border – is handled correctly.

Also, the program’s Gaussian Blur is now a true gaussian blur. There are no shortcuts, no estimations, and it’s still fast enough to preview in real-time.

New advanced color tools, including Shadow/Midtone/Highlight adjustments, color balancing, and monochrome-to-grayscale recovery

Shadow / Midtone / Highlight correction allows for detailed recovery of light and dark parts of an image.  Thanks to deviantart user deviantsnark for the sample image.
Shadow / Midtone / Highlight correction allows for detailed recovery of light and dark sections of an image. Thanks to dA user deviantsnark for the Borderlands wallpaper.
Color balance provides a per-color way to adjust the hue of an image (versus hue / saturation adjustments, which apply equally to all colors).  Thanks to dA user LadyGT for the beautiful artwork.
Color balance provides a per-color way to adjust the hue of an image (versus hue / saturation adjustments, which apply equally to all colors). Thanks to dA user LadyGT for the beautiful Tomb Raider artwork.

New stylize tools, including Film Grain, Vignetting, Modern Art, Trace Contour, Film Noir, and Comic Book

Vignetting refers to the rounded halo around the edges of the image.  The new tool allows you to add halos of any size, softness (how blurry the edges are), transparency, and color, and it can automatically fit the effect to any aspect ratio.  Thanks to dA user chrismickens for the great Mad Men artwork.
Vignetting refers to the rounded halo around the edges of the image. The new tool allows you to add halos of any size, softness (how blurry the edges are), transparency, and color, and it can automatically fit the effect to any aspect ratio. Thanks to dA user chrismickens for the great Mad Men artwork.
PhotoDemon now allows you to add artificial film grain to any image.  This effect was famously used in the Mass Effect trilogy of games to create a more gritty, realistic look.
PhotoDemon now allows you to add artificial film grain to any image. This effect was famously used in the Mass Effect trilogy to create a more gritty, realistic look.
Contour tracing uses a stack of unique algorithms to "paint" the edges of an image.  It is also a useful edge detection tool.
Contour tracing uses a unique stack of algorithms to “paint” the main features of an image. It is also a useful edge detection tool.

Noise removal via Median Filtering

Median filtering serves two main purposes: removal of image noise (unwanted pixel variance), and recovery of damaged images.  The severely damaged image above is courtesy Wikipedia; the after image is pure PhotoDemon (note that it recovers better than the Wikipedia example!).
Median filtering serves two main purposes: removal of image noise (unwanted pixel variance), and recovery of damaged images. The severely damaged image above is courtesy Wikipedia; the after image is PhotoDemon’s correction (note that it recovers more than the Wikipedia example!)

Automatic image cropping

If an image has empty space around the edges - like this Firefox wallpaper - Autocrop can automatically crop it for you.  The feature supports thresholding, so it works equally well on lossy formats like JPEG.
If an image has empty space around the edges – like this Firefox wallpaper – Autocrop can automatically remove it for you. Autocrop supports thresholding, so it works just fine on JPEGs.

New Batch Process Wizard

If I had to pick a personal “favorite” new feature in this release, it would be the brand-new batch processing wizard. This tool is a highlight of PhotoDemon’s emphasis on usability, and I researched more than a dozen other image batch processing tools while building it. I could be biased, but I believe PhotoDemon is now the best general-purpose image batch processor available on the web.

The first page of the new Batch Process wizard.  This step is by far the most intricate, and a ton of work went into exposing full functionality without overwhelming the user.  To my knowledge, PhotoDemon is the only batch processor that allows you to create your own batch list from any number of source directories spread across any number of drives.
The first page of the new Batch Process wizard. This step is by far the most intricate, and a ton of work went into exposing full functionality without overwhelming the user. To my knowledge, PhotoDemon is the only batch processor that allows you to create your own batch list from any number of source directories spread across any number of drives.

Drag-and-drop is now supported when building the list of images to be processed – not only from within the dialog, by dragging between list boxes, but also from Windows Explorer. Live previews make it much easier to find the images you want, while helpful instructions on the left-hand side expose some of the more nuanced functionality.

Once a list of images has been created, you can optionally choose to apply photo editing actions to each image.  Unlike other batch processors, PhotoDemon allows you to use any photo editing actions provided by the program.
Once a list of images has been created, you can optionally choose to apply photo editing actions to each image. Unlike other batch processors, PhotoDemon allows you to use any photo editing actions provided by the program – not just a tiny subset.

Page 2 is the barest page of the new wizard. The current version allows you to skip photo editing actions (if you want to just do a batch rename or format conversion, for example), or you can apply any recorded macro. In the next release, I will add a set of “one-click” presets for common actions, like resizing, or optimizing images for the web.

Once you've created a list of images and chosen any photo editing actions, an output image format can be set.  New to this version, PhotoDemon can retain original image formats - allowing you to apply actions to mixed PNG/JPEG collections, for example.  Alternatively, you can select a single output format, with access to the program's full range of detailed format settings.
Once you’ve created a list of images and chosen any photo editing actions, an output image format can be set. New to this version, PhotoDemon can retain original image formats – allowing you to apply actions to mixed PNG/JPEG collections, for example.

Page 3 asks you to choose an output format. If you want to retain original image formats, that’s cool too – PhotoDemon now supports this! Alternatively, you can select a single output format, with access to the program’s full range of detailed format settings. In the example above, you can see all the options available for JPEGs, including new support for optimization (lossless file size reduction), thumbnails, progressive encoding, and specific subsampling.

The last step of the wizard asks you to choose a location to save all the processed files.  If desired, a number of rename options are also available.
The last step of the wizard asks you to choose a location to save all the processed files. If desired, a number of rename options are also available.

The final page asks you to select an output folder where PhotoDemon can save the processed images. New to this release is a wide range of renaming options – things like adding custom text to each filename, removing text from each filename, changing case, and replacing spaces with underscores for web-bound images. Additionally, original filenames can be retained, or PhotoDemon can just use ascending numbers.

So that’s the new batch wizard! I’d love feedback from power users, as there are a lot of moving parts to the batch tool, and while I have been very thorough in my own testing, it’s impossible to test every combination of variables. So if you find anything that doesn’t work, please let me know.

Improved features: Gamma Correction, Dilate, Erode, Monochrome Conversion, Histogram and Printing

As is usual with each PhotoDemon update, a number of existing tools received redesigns or new features. Gamma correction now displays live gamma curves, and each color component (red, green, and blue) can be adjusted individually. Dilate and Erode use a new algorithm that’s significantly more optimized, meaning sizes up to 200px radius can be previewed in real-time. Monochrome conversion supports any two color (not just black and white), while the printing and histogram dialogs were completely overhauled to make them more user-friendly.

The new gamma correction dialog.  The old dialog forced users to correct only one channel at a time.  The new one allows for correcting all three, with a live preview of the new curves.  Thanks to dA user Kouken for the Persona fan art.
The new gamma correction dialog. The old dialog forced users to correct only one channel at a time. The new one allows for correcting all three, with a live preview of the new curves. Thanks to dA user Kouken for the Persona fan art.

Universal color depth support at import and export time

PhotoDemon can now write 1, 4, 8, 24, and 32bpp variations of every supported file format. By default, when saving images, color depth detection is completely automated – the program will count the number of colors in an image and automatically select the most appropriate color depth for the output file. Alternatively, you can set a preference to manually specify color depth at save time. This also works for grayscale images; for example, the JPEG encoder will now detect grayscale images and write out 8bpp JPEGs accordingly. Alpha thresholding is also available when saving 32bpp images to 8bpp (e.g. PNG to GIF).

When saving a 32bpp image with a complex alpha channel to a simple format like GIF, the program has to reduce the alpha channel to binary values.  A new threshold dialog helps you find the perfect value.
When saving a 32bpp image with a complex alpha channel to a simple format like GIF, the program has to reduce the alpha channel to binary values. A new threshold dialog helps you find the perfect value.

This feature was a nightmare to implement, as PhotoDemon supports a huge variety of file formats, and each one has a detailed list of color depths it does or does not support. Full support for transparency adds a whole other layer of complexity. But now that the feature is completely implemented and rigorously tested, I can’t imagine it any other way. Color depth is not something users should have to worry about, and automatic handling should be a feature of every photo editor (rather than pestering you for color depth every time you save… *cough* GIMP *cough*).

New feature: pngnq-s9 plugin for optimizing PNG files

At the request of a good friend, PhotoDemon now provides integrated support for the pngnq-s9 variety of the famous pngnq library. For the uninitiated, pngnq provides a way to reduce 32bpp PNG files to 8bpp while still preserving complex alpha channels, allowing for file size reductions of up to 75%. Pngnq provides superior results over other tools by using a neural network to reduce image colors, unlike the brute-force median cut algorithm used by software like pngquant. See here for a gallery of sample images if you’re curious.

Pngnq-s9 is a further improvement over stock pngnq, including cool features like YUV color space matching for better results, and the ability to preserve alpha values of 0 and 255. When saving 32bpp PNG files to 8bpp, PhotoDemon will now lean on pngnq-s9 to do the heavy lifting.

In the next version of PhotoDemon, pngnq-s9 support will be integrated into the batch process wizard as a new “optimize for web” option. For now, if you want to test out the feature, head to Tools -> Options -> Saving, and change the “set outgoing color depth” option to “ask me what color depth I want to use”. Then save a 32bpp PNG image to 8bpp and compare the file size.

New plugin manager and plugin downloader

Sometimes it makes sense for PhotoDemon to use an existing open-source project instead of me writing a new feature from scratch. These support libraries are included as “plugins”, and there are four of them in current version. Each one provides indispensable features (like scanner support) at a fraction of the cost involved to write such a feature from scratch.

Some of these plugins expose additional functionality, but it has always been a challenge for PhotoDemon to expose these additional features to the user. So the program now has a detailed plugin manager, where advanced users can change settings on a per-plugin basis, including activating or deactivating plugins as necessary. The manager also tracks availability and version numbers of each plugin.

It is now much, much easier for the program to keep its plugins up-to-date.  Advanced users may also find it useful to enable or disable plugins while testing various features.  All changes happen in real-time - no restart required.
It is now much, much easier for the program to keep its plugins up-to-date. Advanced users may also find it useful to enable or disable plugins while testing various features. All changes happen in real-time – no restart required.
The pngnq-s9 page of the plugin manager.  Advanced or esoteric plugin features can be adjusted here, which keeps the program's main preferences dialog uncluttered.
The pngnq-s9 page of the plugin manager. Advanced or esoteric plugin features can be adjusted here, which helps keep the main “Options” dialog uncluttered.

Many canvas and interface improvements

Larger effect and tool previews. Persistent zoom-in/zoom-out buttons. Image URLs and files can now be directly pasted as new images. Improved drag/drop support, including drag/drop from common dialogs. New “Safe” save behavior to avoid overwriting original files. New Close All Images menu. New algorithms for auto-zoom when images are loaded, meaning much better results at all screen sizes. Tool and file panels can now be hidden. Higher-quality dynamic icons for the program, taskbar, child windows, and Recent Images list. Improved support for low screen resolutions.

Program-wide performance improvements

More aggressive memory management means lower resource usage. Program loading has been heavily streamlined, and now happens in less than a second on modern hardware. Image loading is much faster and more robust, including better support for damaged or incomplete image files.

More robust and comprehensive error handling

When loading multiple images, the program will now suppress warnings and failures (such as invalid files) until all images have been loaded. Many subclassing issues have been resolved – so no more surprise crashes! Overall this release should be extremely stable.

Many miscellaneous bug fixes and improvements

This article is already way too long, so I won’t bore you with a list of all the minor fixes and improvements. For a full list, see the commit log at https://github.com/tannerhelland/PhotoDemon/commits/master

In Conclusion…

This release was a lot bigger than I’d like future releases to be. The biggest delay came from adding language support, as that affected every piece of text in every part of the program (nearly 10,000 words in total!). Now that language support is complete, I foresee future releases being much tidier and quicker.

A developer’s work is never done, and a roadmap for version 5.6 is already being worked on. Some features that didn’t make the cut for 5.4 – like improvements to the selection tool, or a “smart resize” option – were cut at the last minute, and they will be among the first features added to 5.6. The batch process wizard will see a number of additions, and I’d love to add some advanced multilanguage features, like a way for casual users to fix or adjust translations on-the-fly. I also think I’m finally ready to tackle the monumental task of writing a user manual… should be fun!

As always, the best way to stay abreast of PhotoDemon development is the official code repository at https://github.com/tannerhelland/PhotoDemon

But for now, I hope you enjoy all the new features in 5.4, and please remember to donate if you find the software useful.

PhotoDemon 5.4 Beta Now Available

  1. Summary
  2. Download
  3. List of what’s new and improved
  4. Known bugs

Summary

PhotoDemon 5.4 is nearing completion, and I need help testing it. Version 5.4 provides a bunch of new features, including French, German, and Dutch (Flemish) language support. If you can help translate PhotoDemon into another language, please let me know! The translation process is very simple, and it requires no programming experience or special software.

Version 5.4 also includes nine new distort tools, tons of new file format features including specialized PNG and JPEG optimization, improved memory management, a new plugin manager, real-time Gaussian, Smart, and Box blur tools with variable radius, a full Unsharp Mask tool, vignetting, median filtering, adding film grain, automatic cropping, contour tracing, a new Batch Wizard, redesigned tool interfaces, and more. Please download the beta and let me know if you find any bugs.

Download

The PhotoDemon 5.4 beta comes in two flavors:

Remember – if you are an advanced user, you can always download the most recent development build of PhotoDemon’s source code from its GitHub page.

PhotoDemon is funded by donations from users like you.
Please consider a small donation to fund development and to help me support my family.
Even $1.00 helps. Thank you!

List of what’s new and improved in v5.4 (so far)

  • Official support for multiple languages. This is the biggest addition in version 5.4, and I can only claim partial credit for it. Primary credit goes to Frank Donckers, a fellow VB programmer and the one who prototyped the initial translation engine. Frank also supplied the translations for French, German, and Dutch (Flemish), so I owe him an enormous debt of gratitude.
  • Vastly improved file format support. JPEGs now support automatic EXIF rotation on import, and a variety of options on export (Huffman table optimization, progressive scan, thumbnail embedding, specific subsampling). TIFF exporting supports CMYK encoding and a number of compression schemes (none, PackBits, LZW, CCITT 3 and 4, zLib, and more). PNG exporting supports variable compression strength, interlacing, and background color chunk. PPM exporting supports RAW or ASCII encoding. BMP and TGA now support RLE encoding. For ICO files, all icons inside the file can now be loaded (instead of just the first one).
  • Nine new Distort-style tools. Add and remove lens distortion. Swirl. Ripple. Pinch and whirl. Waves. Kaleidoscope. Polar conversion (both directions). Figured glass (dents).
  • New and improved standard tools, including Box Blur, Gaussian Blur, Smart Blur, and Unsharp Masking. Each of these functions now supports variable radii (up to hundreds of pixels), and all have been heavily optimized. Gaussian Blur is the fastest VB-only true gaussian ever written. (Not a joke.)
  • Tons of new tools, including Film Grain, Color Balance, Vignetting, Autocrop, Median, Modern Art, Trace Contour, Shadow/Midtone/Highlight, Monochrome -> Grayscale conversion, Film Noir, and Comic Book. All tools include real-time previews. A number of existing tools received big updates as well – particularly Gamma Correction, Dilate, Erode, Monochrome Conversion, and Printing.
  • New Batch Process wizard. This replaces the old Batch Convert tool, which was an interface nightmare. The new tool supports a number of new features, including drag/drop support of batch lists, live image previews, and tons of file renaming options (prefix, suffix, case conversion, removing text, conversion of spaces to underscores for web).
  • Universal color depth support at import and export time. PhotoDemon can now write 1, 4, 8, 24, and 32bpp variations of every supported file format. Color depth detection is automatic at save time – the program will count the number of colors in an image and automatically save to the most appropriate color depth. Alternatively, you can set a preference to manually specify color depth at save time. This also works for grayscale images; for example, the JPEG encoder will now detect grayscale images and write out 8bpp JPEGs accordingly. Alpha thresholding is also available when saving 32bpp images to 8bpp (e.g. PNG to GIF).
  • New pngnq-s9 plugin for optimizing PNG files. Pngnq-s9 is an optimized and feature-rich variant of the original pngnq optimization library. Pngnq-s9 works by converting 32bpp PNG files to 8bpp with a heavily optimized palette, including support for variable alpha channels. File size savings of over 50% are common. See the Options -> Plugin Manager -> pngnq-s9 menu for a full list of tunable parameters.
  • New plugin manager and plugin downloader. Plugins can now be individually enabled/disabled, and missing plugins can be automatically downloaded. All plugin installation and activation/deactivation can be applied without a program restart.
  • Many canvas and interface improvements. Larger effect and tool previews. Persistent zoom-in/zoom-out buttons. Image URLs and files can now be directly pasted as new images. Improved drag/drop support, including drag/drop from common dialogs. New “Safe” save behavior to avoid overwriting original files. New Close All Images menu. New algorithms for auto-zoom when images are loaded, meaning much better results at all screen sizes. Tool and file panels can now be hidden. Higher-quality dynamic icons for the program, taskbar, child windows, and Recent Images list. Improved support for low screen resolutions.
  • Many performance improvements. More aggressive memory management means lower resource usage. Program loading has been heavily streamlined, and now happens in less than a second on modern hardware. Image loading is much faster and more robust, including better support for damaged or incomplete image files.
  • Much more robust and comprehensive error handling. When loading multiple images, the program will now suppress warnings and failures (such as invalid files) until all images have been loaded. Many subclassing issues have been resolved – so no more surprise crashes! Overall this release should be extremely stable.
  • Many miscellaneous bug fixes and improvements. For a full list, see the commit log at https://github.com/tannerhelland/PhotoDemon/commits/master

Known bugs

Here is a list of known bugs with the current beta. These bugs will be fixed before the final release.

  • When a new language is selected, some text may not be translated. This is not a problem with the translation engine – it is a problem with the translation files, which are still being finalized. All text will be translated in the final release.
  • When using a language other than English, some text may overflow its boundaries or disappear off the page. This is a known problem that is still being worked on. All text – in any language – should fit properly in the final release.

Coming to PhotoDemon 5.4: Language Support. Translators welcome!

Today I made an interesting discovery: my PhotoDemon release dates are slipping further and further apart.

  • PhotoDemon 4.3 – 10 August 2012
  • PhotoDemon 4.4 – 21 August 2012 (11 days later)
  • PhotoDemon 5.0 – 21 September 2012 (31 days later)
  • PhotoDemon 5.2 – 28 November 2012 (68 days later)
  • PhotoDemon 5.4 – …? (76 days and counting)

If I throw together a quick chart for the delay between releases, a clear trend emerges:

Not my favorite correlation...
Shame on me…

According to the chart, I still have a good for or five months available to work on the next release…

Actually, PhotoDemon 5.4 is rapidly nearing completion! My excuse for this latest delay is a good one, and I imagine you already inferred it from the title of the article… but in case you didn’t:

The next PhotoDemon release will include support for multiple languages, with French, German, and Dutch (Vlaams) officially supported at release.

Language support has been a monster to implement on account of the large amount of text in the project, not to mention classic VB’s utter lack of usable translation libraries. As a result, an entirely novel language engine was written from scratch, with (quite lovely) XML files being used to supply the actual translation data.

To give you an idea of the scope: as part of the translation process, I wrote a separate program whose sole purpose was to extract all necessary text from the PhotoDemon source code so that a “master” language file could be assembled. According to it, PhotoDemon contains almost 1400 unique phrases, with a total of more than 7800 words. Every one of those phrase occurrences needed code added to handle the actual text substitution, and then there’s the obvious challenge of the translation itself.

Fortunately, I didn’t tackle this project alone. An absolutely amazing contributor by the name of Frank Donckers contacted me with the initial prototype of the translation engine, and it is Frank who is supplying the French, German, and Dutch translation text. I could not have built this feature without him – so thank you, Frank!

At present, the translation engine is pretty much complete in terms of base functionality – all program text is translated on the fly, and the user is free to change languages at run-time at their leisure (no restart required!). The coding solution behind this is quite elegant, if I might say so, and users shouldn’t experience any noticeable performance hit while a translation is active. The only noticeable delay might be an additional second or two of start-up time on older machines, on account of the translation XML file being loaded and parsed. I’ve got some ideas for speeding up this process, however, so even that delay may disappear by release time.

I would love to include official support for additional languages. If you are fluent in a language other than English, please consider contributing a new translation!

No programming experience or specialized software is required to translate. I’ve got a master translation file ready to go – all that’s needed is to plug in the translated text in whatever language you might speak.

Here is how the French language file looks.  All a translator needs to do is place a translation between the translation XML tags - easy peasy!
Here is how the French language file looks in the free Notepad++ editor. All a translator needs to do is place a translation between the translation XML tags – easy peasy!

If you’re familiar with XML or HTML, you can see how simple the translation document is. Each phrase consists of original text and translated text, and that’s all there is to it. The lines in green are just comments added for convenience, in this case comments written by the language extraction tool. Translators can safely ignore these.

Before wrapping up, I should mention one rather large caveat with multiple language support – at present, only “ANSI” (Windows-1252) languages are supported. I apologize for this, but one of the problems with classic VB is its inability to handle unicode characters without major hacking – and by major hacking, I mean replacing every user interface aspect of the project, as well as every string library. If I ever port PhotoDemon to another programming language (something I often consider), Unicode support would be much more feasible, but I’m afraid it’s not on the present roadmap.

I need at least a couple more weeks to hammer out a few remaining issues with version 5.4, which leaves plenty of time for any ambitious translators out there to pitch in and contribute a new translation before release day. If it helps, note that your name will be visibly displayed as the translator in not only the language source file, but I’ll also add you to the special thanks section of the program, the PhotoDemon website, and the README file.

I can always be reached via this contact form – so that’s the place to go if you’re willing to help. Thank you in advance!

Hooking modern Windows common dialogs: some notes

Background: common dialog hooking is used to append your own controls to a Windows common dialog box.

A good friend recently sent me a number of resources related to hooking common dialog controls. I’ve been interested in common dialog hooking for PhotoDemon, as it would allow me to add support for image previewing right in the dialog itself. This isn’t as necessary in modern versions of Windows (7 in particular includes a number of GDI+ improvements, making Explorer very robust with standard formats), but it can be helpful for unsupported formats like RAW photographs.

Unfortunately, several days of research have shown that it is not possible to hook a Vista or Windows 7 style dialog and maintain the modern layout. Let me explain with pictures:

This is the standard common dialog control in Windows Vista and 7 (and presumably 8 as well, though I haven't verified this myself).  The biggest improvements over past common dialogs include breadcrumb navigation at the top, a dedicated refresh button, and a persistent search bar.
This is the standard common dialog control in Windows Vista and 7 (and presumably 8 as well, though I haven’t verified this myself). The biggest improvements over past common dialogs include a dedicated left-hand file tree, breadcrumb navigation at the top, and a persistent search bar.

The common dialog above comes directly from PhotoDemon’s current common dialog implementation. This is the native common dialog control on Vista and 7. I very much like it. As a comparison, here is the same dialog in Windows XP:

Same folder as the previous image.  The XP common dialog provides no breadcrumb nav, folder tree, dedicated refresh, or search bar.  Note also how many TIFF formats do not display correctly - including XP not recognizing the MINISWHITE flag on the CCITT TIFF files.  Kinda interesting.
Same folder and images as the previous image. There is no breadcrumb nav, dedicated refresh, or search bar. Note also how many TIFF formats do not display correctly – including XP not recognizing the MINISWHITE flag on the CCITT TIFF files. Kinda interesting.

I strongly prefer the Vista/7-style dialog, particularly the breadcrumb nav and the persistent folder tree on the left.

Unfortunately, it is impossible to hook the Vista/7 dialog and maintain the native Vista/7 appearance. If you attempt to hook it, Windows will ALWAYS drop back to a previous generation common dialog. Here are some images to demonstrate, using a basic image preview hook:

This is what happens when you attempt to hook a dialog, and all you provide is the OFN_ENABLEHOOK flag.  Not pretty (and the hook doesn't even work right).
This is what happens when you attempt to hook a dialog, and all you provide is the OFN_ENABLEHOOK flag. Not pretty (and the hook doesn’t even work correctly).
Here is the same dialog, but with the OFN_EXPLORER flag set.  Note that hooking now works properly, but the common dialog itself has been reduced to XP style - the left-hand folder tree is gone, and the top bar has no breadcrumbs or search.
Here is the same dialog, but with the OFN_EXPLORER flag set. Note that hooking now works properly, but the common dialog itself has been reduced to XP style – the left-hand folder tree is gone, and the top bar has no breadcrumbs or search.

Note that the image above uses an older version of the OPENFILENAME struct, namely (this is its declaration in VB):

Private Type OPENFILENAME
    lStructSize       As Long
    hwndOwner         As Long
    hInstance         As Long
    lpstrFilter       As String
    lpstrCustomFilter As String
    nMaxCustFilter    As Long
    nFilterIndex      As Long
    lpstrFile         As String
    nMaxFile          As Long
    lpstrFileTitle    As String
    nMaxFileTitle     As Long
    lpstrInitialDir   As String
    lpstrTitle        As String
    Flags             As Long
    nFileOffset       As Integer
    nFileExtension    As Integer
    lpstrDefExt       As String
    lCustData         As Long
    lpfnHook          As Long
    lpTemplateName    As String
End Type

If you modify the struct to its newest version (as described here), you can slightly improve the dialog to look like this:

The newest version of the OPENFILENAME struct enables the places bar on the left.  I don't find this particularly useful - certainly not as useful as a folder pane - but perhaps some might find it preferable.
The newest version of the OPENFILENAME struct enables the places bar on the left. I don’t find this particularly useful – certainly not as useful as a folder pane – but perhaps some might find it preferable.

That is the best you can get if you want to hook a common dialog in Vista or 7.

Reasons for this have been speculated on by more qualified individuals than I. Over at stackoverflow, David H explains:

The reason for this is that MS completely re-organised the file dialogs for Vista. Hooks are used to extend a file dialog by supplying a resource file. This gives the customiser too much power. They can all too easily modify standard elements of the dialog and indeed many apps did so. The reorganisation of the dialogs would have broken many apps that used hooks. Those would have tried to manipulate elements of the dialog that were not there, or were implemented differently. Legacy versions of the dialogs remain for such apps to “get their hooks into”.

You are correct that it is impossible to get the new look when you use a hook. Instead you need to use the IFileDialogCustomize interface to customise the dialog. This is less powerful but does result in appearance and behaviour that is more consistent with the standard part of the dialog.

(More information is available here for those who are interested.)

Unfortunately, I am not aware of any way to access the iFileDialogCustomize interface in classic VB. If someone knows how, I’d love to hear it.

The take home message of all this is – if you work in classic VB and you want to hook a common dialog, you need to be content with an XP-style dialog. There is currently no way to maintain a Vista/7 style dialog while hooking.

For this reason, I’m going to stick with the stock common dialog control in PhotoDemon. I may look at a dedicated “browse” window in the future, which would allow for full image previewing, but I’m afraid such a feature is not on the roadmap for the next few versions.

All hooking-related screenshots were created using Carles PV’s iBMP project, which made it very easy to modify various hooking parameters and test the output. Thanks, Carles!

Image Dithering: Eleven Algorithms and Source Code

Dithering: An Overview

Today’s graphics programming topic – dithering – is one I receive a lot of emails about, which some may find surprising. You might think that dithering is something programmers shouldn’t have to deal with in 2012. Doesn’t dithering belong in the annals of technology history, a relic of times when “16 million color displays” were something programmers and users could only dream of? In an age when cheap mobile phones operate in full 32bpp glory, why am I writing an article about dithering?

Actually, dithering is still a surprisingly applicable technique, not just for practical reasons (such as preparing a full-color image for output on a non-color printer), but for artistic reasons as well. Dithering also has applications in web design, where it is a useful technique for reducing images with high color counts to lower color counts, reducing file size (and bandwidth) without harming quality. It also has uses when reducing 48 or 64bpp RAW-format digital photos to 24bpp RGB for editing.

And these are just image dithering uses – dithering still has extremely crucial roles to play in audio, but I’m afraid I won’t be discussing audio dithering here. Just image dithering.

In this article, I’m going to focus on three things:

  • a basic discussion of how image dithering works
  • eleven specific two-dimensional dithering formulas, including famous ones like “Floyd-Steinberg”
  • how to write a general-purpose dithering engine

Update 11 June 2016: some of the sample images in this article have been updated to better reflect the various dithering algorithms. Thank you to commenters who noted problems with the previous images!

Dithering: Some Examples

Consider the following full-color image, a wallpaper of the famous “companion cube” from Portal:

This will be our demonstration image for this article.  I chose it because it has a nice mixture of soft gradients and hard edges.
This will be our demonstration image for this article. I chose it because it has a nice mixture of soft gradients and hard edges.

On a modern LCD or LED screen – be it your computer monitor, smartphone, or TV – this full-color image can be displayed without any problems. But consider an older PC, one that only supports a limited palette. If we attempt to display the image on such a PC, it might look something like this:

This is the same image as above, but restricted to a websafe palette.
This is the same image as above, but restricted to a websafe palette.

Pretty nasty, isn’t it? Consider an even more dramatic example, where we want to print the cube image on a black-and-white printer. Then we’re left with something like this:

At this point, the image is barely recognizable.
At this point, the image is barely recognizable.

Problems arise any time an image is displayed on a device that supports less colors than the image contains. Subtle gradients in the original image may be replaced with blobs of uniform color, and depending on the restrictions of the device, the original image may become unrecognizable.

Dithering is an attempt to solve this problem. Dithering works by approximating unavailable colors with available colors, by mixing and matching available colors in a way that mimicks unavailable ones. As an example, here is the cube image once again reduced to the colors of a theoretical old PC – only this time, dithering has been applied:

A big improvement over the non-dithered version!
A big improvement over the non-dithered version!

If you look closely, you can see that this image uses the same colors as its non-dithered counterpart – but those few colors are arranged in a way that makes it seem like many more colors are present.

As another example, here is a black-and-white version of the image with similar dithering applied:

The specific algorithm used on this image is "2-row Sierra" dithering.
The specific algorithm used on this image is “2-row Sierra” dithering.

Despite only black and white being used, we can still make out the shape of the cube, right down to the hearts on either side. Dithering is an extremely powerful technique, and it can be used in ANY situation where data has to be represented at a lower resolution than it was originally created for. This article will focus specifically on images, but the same techniques can be applied to any 2-dimensional data (or 1-dimensional data, which is even simpler!).

The Basic Concept Behind Dithering

Boiled down to its simplest form, dithering is fundamentally about error diffusion.

Error diffusion works as follows: let’s pretend to reduce a grayscale photograph to black and white, so we can print it on a printer that only supports pure black (ink) or pure white (no ink). The first pixel in the image is dark gray, with a value of 96 on a scale from 0 to 255, with zero being pure black and 255 being pure white.

Here is an example of the RGB values in the example.
Here is a visualization of the RGB values in our example.

When converting such a pixel to black or white, we use a simple formula – is the color value closer to 0 (black) or 255 (white)? 96 is closer to 0 than to 255, so we make the pixel black.

At this point, a standard approach would simply move to the next pixel and perform the same comparison. But a problem arises if we have a bunch of “96 gray” pixels – they all get turned to black, and we’re left with a huge chunk of empty black pixels, which doesn’t represent the original gray color very well at all.

Error diffusion takes a smarter approach to the problem. As you might have inferred, error diffusion works by “diffusing” – or spreading – the error of each calculation to neighboring pixels. If it finds a pixel of 96 gray, it too determines that 96 is closer to 0 than to 255 – and so it makes the pixel black. But then the algorithm makes note of the “error” in its conversion – specifically, that the gray pixel we have forced to black was actually 96 steps away from black.

When it moves to the next pixel, the error diffusion algorithm adds the error of the previous pixel to the current pixel. If the next pixel is also 96 gray, instead of simply forcing that to black as well, the algorithm adds the error of 96 from the previous pixel. This results in a value of 192, which is actually closer to 255 – and thus closer to white! So it makes this particular pixel white, and it again makes note of the error – in this case, the error is -63, because 192 is 63 less than 255, which is the value this pixel was forced to.

As the algorithm proceeds, the “diffused error” results in an alternating pattern of black and white pixels, which does a pretty good job of mimicking the “96 gray” of the section – much better just forcing the color to black over and over again. Typically, when we finish processing a line of the image, we discard the error value we’ve been tracking and start over again at an error of “0” with the next line of the image.

Here is an example of the cube image from above with this exact algorithm applied – specifically, each pixel is converted to black or white, the error of the conversion is noted, and it is passed to the next pixel on the right:

This is the simplest possible application of error diffusion dithering.
This is the simplest possible application of error diffusion dithering.

Unfortunately, error diffusion dithering has problems of its own. For better or worse, dithering always leads to a spotted or stippled appearance. This is an inevitable side-effect of working with a small number of available colors – those colors are going to be repeated over and over again, because there are only so many of them.

In the simple error diffusion example above, another problem is evident – if you have a block of very similar colors, and you only push the error to the right, all the “dots” end up in the same place! This leads to funny lines of dots, which is nearly as distracting as the original, non-dithered version.

The problem is that we’re only using a one-dimensional error diffusion. By only pushing the error in one direction (right), we don’t distribute it very well. Since an image has two dimensions – horizontal and vertical – why not push the error in multiple directions? This will spread it out more evenly, which in turn will avoid the funny “lines of speckles” seen in the error diffusion example above.

Two-Dimensional Error Diffusion Dithering

There are many ways to diffuse an error in two dimensions. For example, we can spread the error to one or more pixels on the right, one or more pixels on the left, one or more pixels up, and one or more pixels down.

For simplicity of computation, all standard dithering formulas push the error forward, never backward. If you loop through an image one pixel at a time, starting at the top-left and moving right, you never want to push errors backward (e.g. left and/or up). The reason for this is obvious – if you push the error backward, you have to revisit pixels you’ve already processed, which leads to more errors being pushed backward, and you end up with an infinite cycle of error diffusion.

So for standard loop behavior (starting at the top-left of the image and moving right), we only want to push pixels right and down.

Apologies for the crappy image - but I hope it helps illustrate the gist of proper error diffusion.
Apologies for the crappy image – but I hope it helps illustrate the gist of proper error diffusion.

As for how specifically to propagate the error, a great number of individuals smarter than I have tackled this problem head-on. Let me share their formulas with you.

(Note: these dithering formulas are available multiple places online, but the best, most comprehensive reference I have found is this one.)

Floyd-Steinberg Dithering

The first – and arguably most famous – 2D error diffusion formula was published by Robert Floyd and Louis Steinberg in 1976. It diffuses errors in the following pattern:


       X   7
   3   5   1

     (1/16)

In the notation above, “X” refers to the current pixel. The fraction at the bottom represents the divisor for the error. Said another way, the Floyd-Steinberg formula could be written as:


           X    7/16
   3/16  5/16   1/16

But that notation is long and messy, so I’ll stick with the original.

To use our original example of converting a pixel of value “96” to 0 (black) or 255 (white), if we force the pixel to black, the resulting error is 96. We then propagate that error to the surrounding pixels by dividing 96 by 16 ( = 6), then multiplying it by the appropriate values, e.g.:


           X     +42
   +18    +30    +6

By spreading the error to multiple pixels, each with a different value, we minimize any distracting bands of speckles like the original error diffusion example. Here is the cube image with Floyd-Steinberg dithering applied:

Floyd-Steinberg dithering
Floyd-Steinberg dithering

Not bad, eh?

Floyd-Steinberg dithering is easily the most well-known error diffusion algorithm. It provides reasonably good quality, while only requiring a single forward array (a one-dimensional array the width of the image, which stores the error values pushed to the next row). Additionally, because its divisor is 16, bit-shifting can be used in place of division – making it quite fast, even on old hardware.

As for the 1/3/5/7 values used to distribute the error – those were chosen specifically because they create an even checkerboard pattern for perfectly gray images. Clever!

One warning regarding “Floyd-Steinberg” dithering – some software may use other, simpler dithering formulas and call them “Floyd-Steinberg”, hoping people won’t know the difference. This excellent dithering article describes one such “False Floyd-Steinberg” algorithm:


   X   3
   3   2

   (1/8)

This simplification of the original Floyd-Steinberg algorithm not only produces markedly worse output – but it does so without any conceivable advantage in terms of speed (or memory, as a forward-array to store error values for the next line is still required).

But if you’re curious, here’s the cube image after a “False Floyd-Steinberg” application:

Much more speckling than the legit Floyd-Steinberg algorithm - so don't use this formula!
Much more speckling than the legit Floyd-Steinberg algorithm – so don’t use this formula!

Jarvis, Judice, and Ninke Dithering

In the same year that Floyd and Steinberg published their famous dithering algorithm, a lesser-known – but much more powerful – algorithm was also published. The Jarvis, Judice, and Ninke filter is significantly more complex than Floyd-Steinberg:


             X   7   5 
     3   5   7   5   3
     1   3   5   3   1

           (1/48)

With this algorithm, the error is distributed to three times as many pixels as in Floyd-Steinberg, leading to much smoother – and more subtle – output. Unfortunately, the divisor of 48 is not a power of two, so bit-shifting can no longer be used – but only values of 1/48, 3/48, 5/48, and 7/48 are used, so these values can each be calculated but once, then propagated multiple times for a small speed gain.

Another downside of the JJN filter is that it pushes the error down not just one row, but two rows. This means we have to keep two forward arrays – one for the next row, and another for the row after that. This was a problem at the time the algorithm was first published, but on modern PCs or smartphones this extra requirement makes no difference. Frankly, you may be better off using a single error array the size of the image, rather than erasing the two single-row arrays over and over again.

Jarvis, Judice, Ninke dithering
Jarvis, Judice, Ninke dithering

Stucki Dithering

Five years after Jarvis, Judice, and Ninke published their dithering formula, Peter Stucki published an adjusted version of it, with slight changes made to improve processing time:


             X   8   4 
     2   4   8   4   2
     1   2   4   2   1

           (1/42)

The divisor of 42 is still not a power of two, but all the error propagation values are – so once the error is divided by 42, bit-shifting can be used to derive the specific values to propagate.

For most images, there will be minimal difference between the output of Stucki and JJN algorithms, so Stucki is often used because of its slight speed increase.

Stucki dithering
Stucki dithering

Atkinson Dithering

During the mid-1980’s, dithering became increasingly popular as computer hardware advanced to support more powerful video drivers and displays. One of the best dithering algorithms from this era was developed by Bill Atkinson, a Apple employee who worked on everything from MacPaint (which he wrote from scratch for the original Macintosh) to HyperCard and QuickDraw.

Atkinson’s formula is a bit different from others in this list, because it only propagates a fraction of the error instead of the full amount. This technique is sometimes offered by modern graphics applications as a “reduced color bleed” option. By only propagating part of the error, speckling is reduced, but contiguous dark or bright sections of an image may become washed out.


         X   1   1 
     1   1   1
         1

       (1/8)

Atkinson dithering
Atkinson dithering

Burkes Dithering

Seven years after Stucki published his improvement to Jarvis, Judice, Ninke dithering, Daniel Burkes suggested a further improvement:


             X   8   4 
     2   4   8   4   2

           (1/32)

Burkes’s suggestion was to drop the bottom row of Stucki’s matrix. Not only did this remove the need for two forward arrays, but it also resulted in a divisor that was once again a multiple of 2. This change meant that all math involved in the error calculation could be accomplished by simple bit-shifting, with only a minor hit to quality.

Burkes dithering
Burkes dithering

Sierra Dithering

The final three dithering algorithms come from Frankie Sierra, who published the following matrices in 1989 and 1990:


             X   5   3
     2   4   5   4   2
         2   3   2
           (1/32)


             X   4   3
     1   2   3   2   1
           (1/16)


         X   2
     1   1
       (1/4)

These three filters are commonly referred to as “Sierra”, “Two-Row Sierra”, and “Sierra Lite”. Their output on the sample cube image is as follows:

Sierra (sometimes called Sierra-3)
Sierra (sometimes called Sierra-3)
Two-row Sierra
Two-row Sierra
Sierra Lite
Sierra Lite

Other dithering considerations

If you compare the images above to the dithering results of another program, you may find slight differences. This is to be expected. There are a surprising number of variables that can affect the precise output of a dithering algorithm, including:

  • Integer or floating point tracking of errors. Integer-only methods lose some resolution due to quantization errors.
  • Color bleed reduction. Some software reduces the error by a set value – maybe 50% or 75% – to reduce the amount of “bleed” to neighboring pixels.
  • The threshold cut-off for black or white. 127 or 128 are common, but on some images it may be helpful to use other values.
  • For color images, how luminance is calculated can make a big difference. I use the HSL luminance formula ( [max(R,G,B) + min(R,G,B)] / 2). Others use ([r+g+b] / 3) or one of the ITU formulas. YUV or CIELAB will offer even better results.
  • Gamma correction or other pre-processing modifications. It is often beneficial to normalize an image before converting it to black and white, and whichever technique you use for this will obviously affect the output.
  • Loop direction. I’ve discussed a standard “left-to-right, top-to-bottom” approach, but some clever dithering algorithms will follow a serpentine path, where left-to-right directionality is reversed each line. This can reduce spots of uniform speckling and give a more varied appearance, but it’s more complicated to implement.

For the demonstration images in this article, I have not performed any pre-processing to the original image. All color matching is done in the RGB space with a cut-off of 127 (values <= 127 are set to 0). Loop direction is standard left-to-right, top-to-bottom.

Which specific techniques you may want to use will vary according to your programming language, processing constraints, and desired output.

I count 9 algorithms, but you promised 11! Where are the other two?

So far I’ve focused purely on error-diffusion dithering, because it offers better results than static, non-diffusion dithering.

But for sake of completeness, here are demonstrations of two standard “ordered dither” techniques. Ordered dithering leads to far more speckling (and worse results) than error-diffusion dithering, but they require no forward arrays and are very fast to apply. For more information on ordered dithering, check out the relevant Wikipedia article.

Ordered dither using a 4x4 Bayer matrix
Ordered dither using a 4×4 Bayer matrix
Ordered dither using an 8x8 Bayer matrix
Ordered dither using an 8×8 Bayer matrix

With these, the article has now covered a total of 11 different dithering algorithms.

Writing your own general-purpose dithering algorithm

Earlier this year, I wrote a fully functional, general-purpose dithering engine for PhotoDemon (an open-source photo editor). Rather than post the entirety of the code here, let me refer you to the relevant page on GitHub. The black and white conversion engine starts at line 350. If you have any questions about the code – which covers all the algorithms described on this page – please let me know and I’ll post additional explanations.

That engine works by allowing you to specify any dithering matrix in advance, just like the ones on this page. Then you hand that matrix over to the dithering engine and it takes care of the rest.

The engine is designed around monochrome conversion, but it could easily be modified to work on color palettes as well. The biggest difference with a color palette is that you must track separate errors for red, green, and blue, rather than a single luminance error. Otherwise, all the math is identical.

 

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