Parallel Resampling of (VCL-) Bitmaps
I have made my parallel resampling of bitmaps now as fast as I can get it. Now I would find it interesting to know, how the algorithm performs on other systems, and it would be super to get suggestions for improvement.
The procedures can be found in the unit uScale under Algorithms in the attached zip.
I have tested against Windows StretchBlt-Half_Tone, WICImage and Graphics32. On my PC (AMD Ryzen 7 1700, 8-core) I see a substantial improvement in speed.
The threads are based on TThread rather than TTask or TParallel, because I had failures using the latter two, whereas the oldfashioned threads haven't failed me ever in gazillions of runs.
If you want to compile and run the comparison project, you need to include the source folder of Graphics32 (latest version) in your search path. For convenience it is included in the zip under Algorithms. I couldn't find a way to divvy out only the units needed for resampling.
The test against Graphics32 might be slightly unfair, because of bitmaps being assigned to TBitmap32 before the processing.
Right now, the procedure itself cannot be run in concurrent threads, because the array of TThreads is a global variable, I need to change the design (ideas welcome).
There might be still room for improvement by minimizing the cache misses, but my head can't handle it at the moment.
Hope you find it useful.
Renate
Bitmap Scaling.zip
I have update the repo on GitHub
https://github.com/rmesch/Parallel-Bitmap-Resampler
Changes made to the "modern" VCL- and FMX-version in the folder BitmapScaling:
New resampling filters: Mitchell, Robidoux, RobidouxSharp, RobidouxSoft.
Simplified and corrected MakeGaussContributors in uScaleCommon.pas. @Anders Melander: It will pass the uniform color tests now. But it will fail the Gauss-RMS, since I changed to RadiusToSigma back.
Tried to make Gamma-correction a little more precise. I tried nonetheless. You already spent so much time digging through that ancient attachment, give the repo a shot. I also added the option in DemoScale.dpr to use a test-bitmap similar to yours. I can't see any of the color-artefacts you describe, though.
Simplified and corrected MakeGaussContributors in uScaleCommon.pas. @Anders Melander: It will pass the uniform color tests now. But it will fail the Gauss-RMS, since I changed to RadiusToSigma back.
Tried to make Gamma-correction a little more precise. I tried nonetheless. You already spent so much time digging through that ancient attachment, give the repo a shot. I also added the option in DemoScale.dpr to use a test-bitmap similar to yours. I can't see any of the color-artefacts you describe, though.