[Webkit-unassigned] [Bug 258686] New: [iOS 17] PNG image transparency is broken

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258686

            Bug ID: 258686
           Summary: [iOS 17] PNG image transparency is broken
           Product: WebKit
           Version: Safari 17
          Hardware: iPhone / iPad
                OS: Other
            Status: NEW
          Severity: Major
          Priority: P2
         Component: Images
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: jmgoldman at google.com
                CC: sabouhallawa at apple.com

Created attachment 466867

  --> https://bugs.webkit.org/attachment.cgi?id=466867&action=review

iOS 17.0 in Safari navigated to https://jsbin.com/rowohenaji?html,css,output

PNGs with any alpha channel set below around 0.5 has no effect. Pixels with an alpha channel of 0 are still visible, breaking transparent backgrounds. All PNGs seem to be impacted across the entire web.

Example: https://jsbin.com/rowohenaji?html,css,output. See attachment for iOS 17.0 reproduction showing pink overlays on all elements.

Only reproducible on iOS 17.0, cannot reproduce on macOS Ventura 13.4 with Safari Release 172 (Safari 17.0, WebKit 18616.1.17.3). I am unable to reproduce this on iOS outside of WebKit (verified in Safari and WKWebView).

See also:
* highly visible bug in Google Ads: https://redd.it/14kda07
* similar bug reported on Amazon.com: https://bugs.webkit.org/show_bug.cgi?id=258454.

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