[wp-trac] [WordPress Trac] #63448: Image quality significantly degrades for resized PNGs with transparency in WordPress 6.8.1

[WordPress Trac]

#63448: Image quality significantly degrades for resized PNGs with transparency in
WordPress 6.8.1
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 Reporter:  elvismdev                            |       Owner:
                                                 |  adamsilverstein
     Type:  defect (bug)                         |      Status:  reopened
 Priority:  normal                               |   Milestone:  6.8.2
Component:  Media                                |     Version:  6.8
 Severity:  critical                             |  Resolution:
 Keywords:  has-patch has-test-info dev-         |     Focuses:
  feedback has-unit-tests commit fixed-major     |
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Comment (by SirLouen):

 Replying to [comment:81 siliconforks]:
 > Replying to [comment:79 SirLouen]:
 > > 2. We have not found a mechanism to identify alpha in images to
 separate them from non-alpha
 >
 > Did you ever try using the Imagick `getImageChannelDepth()` method?
 I've been experimenting with it and it seems to work for me - see
 https://github.com/WordPress/wordpress-develop/pull/8933
 >
 > (Honestly this PR is getting a bit more complicated than I would like,
 but it's mostly just rearranging things to work with the original image
 before resizing, rather than after.)

 Interesting, I think I have not seen this function before.

 With this result, things change significantly:

 If it's indexed, and it doesn't have what you call "true alpha
 transparency", then you can go straight with `png8`

 For the rest, Quantization is required to avoid losing the Alpha.

 If you can add this modification, I think it's ready to go.

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Ticket URL: <https://core.trac.wordpress.org/ticket/63448#comment:82>
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