[Webkit-unassigned] [Bug 205568] New: JPEG 2000 images with alpha have begun looking strange

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=205568

            Bug ID: 205568
           Summary: JPEG 2000 images with alpha have begun looking strange
           Product: WebKit
           Version: Safari 13
          Hardware: All
                OS: iOS 13
            Status: NEW
          Severity: Critical
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: e at ericportis.com

In recent versions of iOS/MacOS/WebKit, the fully (and almost-fully) transparent bits of JPEG2000 images, which looked fine in previous versions, have begun turning green when placed on non-white backgrounds.

Here is a test page with three source JP2s: https://ericportis.com/etc/jp2-transparency-bug/

Here is what it looks like in iOS 12, when *not* exhibiting the problem: 
https://slack-files.com/T03FFDY8K-FRP9BRB9R-58950a5715
Here is what it looks like in iOS 13, when exhibiting the problem: 
https://slack-files.com/T03FFDY8K-FS2K01D63-8eb9fde71b

Notes:
- The problem occurs in Catalina/desktop Safari, as well as in Mobile Safari.
- We have only seen the problem in WebViews/Safari; we have not seen it in Preview, Photos, or other system software.
- We have only seen it in recent versions of things: Catalina + Safari 13, or iOS 13 + Safari 13.
- The error is not 100% consistently reproducible. Some iPhones/Macs running the same Safari version will show different results, sometimes.
- It does not affect all JP2s. All of the JP2s in the example above were generated from PNG source files, using Cloudinary (which uses Kakadu under the hood). When running these same source files through Preview and Exporting as JP2, we have yet to see the issue. We will continue to test with other encoders, and different encoder settings...
- When ignoring alpha entirely, the images also "turn green" -- that is, the RGB color of these images is green for some reason (presumably something to do with encoder efficency), and the Alpha, which is near 100%, is being ignored or multiplied incorrectly or something by some part of the display chain (again, they always look fine on white). Here's what one of the problematic JP2s looks like with its Alpha channel simply ignored: https://slack-files.com/T03FFDY8K-FRY0UFWUQ-6681080f44

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