[wp-trac] [WordPress Trac] #36477: Responsive images (srcset) can include images larger than the full size

[WordPress Trac]

#36477: Responsive images (srcset) can include images larger than the full size
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 Reporter:  peterdavehello                       |       Owner:  pbearne
     Type:  defect (bug)                         |      Status:  assigned
 Priority:  normal                               |   Milestone:  Future
                                                 |  Release
Component:  Media                                |     Version:  4.4.2
 Severity:  normal                               |  Resolution:
 Keywords:  has-patch needs-testing dev-         |     Focuses:
  feedback needs-unit-tests                      |  performance
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Comment (by nosilver4u):

 @adamsilverstein My patch mostly replaces that from @pbearne, but his has
 the unit tests, though they may need some tweaking still. I'll let him
 speak to that further so I'm not making commitments for him :)

 As for WebP/AVIF, that doesn't solve the problem of reducing the palette
 back to the original number of colors. I tested WebP, and while it does
 admirably in some cases, it can still double or triple the file size
 without the palette reduction in place.

 With palette reduction included via quantizeImage(), the WebP file size is
 even smaller than the resized & indexed PNGs, except for test8.png that
 Imagick likes to force into grayscale mode rather than indexed. I don't
 know what the equivalent fix is for WebP, but I had to force the PNG8
 format for that particular case.

 GD does suffer from the same issue, though it looks like there was a
 potential fix, but it didn't work for me: https://github.com/WordPress
 /wordpress-develop/blob/ac84bd53c6ab38cb6d808d30bc985ae84de2f0dc/src/wp-
 includes/class-wp-image-editor-gd.php#L525
 The imageistruecolor() and imagecolorstotal() functions should run on the
 original image, and not the resized one, otherwise it doesn't convert the
 image back to palette/indexed. But even when you do, transparency is
 completely lost, so that's no good. That's as much as I care to mess with
 GD, so I wouldn't block this for lack of a GD fix which may not even be
 possible.

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Ticket URL: <https://core.trac.wordpress.org/ticket/36477#comment:62>
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