[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):

 == Here is a recap of the current situation

 We have 4 types of Indexed images
 - Indexed Color w/o Alpha
 - Indexed Color with Alpha
 - Greyscale Indexed w/o Alpha
 - Greyscale Indexed with Alpha

 1. `png8` destroy the alpha channel
 2. We have not found a mechanism to identify alpha in images to separate
 them from non-alpha
 3. We consider that preserving alpha is important, but the increase in
 size is a pain point
 4. Moreover, the increase in processing time with `getImageColors` is a
 pain point


 === Current opinions

 @nosilver4u considers that we should go full quantize again for indexed
 and aren't concerned about the processing time and the increase in size.

 Personally, I agree that we should not destroy the alpha of indexed
 images, and if this means an increase in size because we don't have a
 solution to separate Indexed images with alpha and without alpha, this is
 a sacrifice we should take, but, contrarily to @nosilver4u, I would stick
 to 256 colours to at least, not sacrifice in processing time (despite
 relative larger images, in very edge cases)

 === Possible Solution to progress

 I think that this report can get blocked until someone finds a solution to
 separate the Alpha (or maybe Imagick happens to release something).
 Perhaps we should report this upstream (Imagick) and see if we can find
 some additional help?

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Ticket URL: <https://core.trac.wordpress.org/ticket/63448#comment:79>
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