RESOLVED DUPLICATE of bug 200026 Bug 269669
Unpremultiplied alpha workflow with canvas and transferFromImageBitmap is incorrect 
https://bugs.webkit.org/show_bug.cgi?id=269669
Summary Unpremultiplied alpha workflow with canvas and transferFromImageBitmap is inc...
Felix Herbst
Reported 2024-02-18 07:00:35 PST
Created attachment 469951 [details] Safari readback result When using transferImageBitmap on a bitmaprenderer canvas context, and then converting that to PNG, the premultipliedAlpha: none flag is not respected. Instead, the resulting image has garbled RGB data. The behavior is correct in Chrome. The behavior is wrong in all WebKit implementations I tested. Reproduction page: https://unpremultiplied-readback.glitch.me/ - Click "Download original" below. - Then, click "Download readback". You'll get 2 PNG files – their content should be identical. To check, - open them in Photopea (photopea.com) or another app that allows seeing the RGB channel independent from the Alpha channel - select Layer / Raster Mask / From Transparency - slect Layer / Raster Mask / Delete The results should be identical! There should be a cat in each of them, no weird pixels.
Attachments
Safari readback result (54.84 KB, image/png)
2024-02-18 07:00 PST, Felix Herbst 		no flags
Details
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Radar WebKit Bug Importer
Comment 1 2024-02-25 07:01:38 PST
<rdar://problem/123595818>
Karl Dubost
Comment 2 2024-03-05 20:49:27 PST
Felix, thanks for the report! This is a duplicate of Bug 200026 *** This bug has been marked as a duplicate of bug 200026 ***
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