Bug 269669

Summary:

Unpremultiplied alpha workflow with canvas and transferFromImageBitmap is incorrect

Product:

WebKit

Reporter:

Felix Herbst <felix.herbst>

Component:

Canvas

Assignee:

Nobody <webkit-unassigned>

Status:

RESOLVED DUPLICATE

Severity:

Normal

CC:

dino, felix.herbst, karlcow, webkit-bug-importer

Priority:

Keywords:

BrowserCompat, InRadar

Version:

Safari 17

Hardware:

All

OS:

All

URL:

https://unpremultiplied-readback.glitch.me/

Attachments:

Description	Flags
Safari readback result	none

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
View All Add attachment proposed patch, testcase, etc.

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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