Media: Ensure Imagick quality is set correctly

[adamsilverstein]

Summary

Imagick does not properly set image quality for AVIF images.

A user reported an issue in the Performance Lab plugin "wp_editor_set_quality not changing image quality for AVIF images". Link: ​https://github.com/WordPress/performance/issues/1331. When investigating this issue I found that the quality setting being applied in core doesn't work correctly when outputting AVIF images. When we added AVIF support in 6.5 we ​suggested using the wp_editor_set_quality filter control the AVIF quality setting, but this currently doesn't work (at least with Imagick).

Steps to reproduce

Here are the testing instructions:

1. Test on a server with Imagick enabled AVIF support. Check under Tools->Siet Health->Info to verify Imagick has AVIF in list of supported types.
2. Upload an AVIF image, verify all of the sub-sized (AVIF) images are created.
3. Add the following code snippet in your theme or an mu plugin:

   function filter_avif_quality( $quality, $mime_type ) {
   	if ( 'image/avif' === $mime_type ) {
   		return 15;
   	}
   	return $quality;
   }
   add_filter( 'wp_editor_set_quality', 'filter_avif_quality', 10, 2 );
   

4. Upload the same image as in step 2. the filter should be applied and the very low quality (15) should be used.
5. Expected result: the generated AVIF images are much smaller sized and lower quality looking (noticeable artifacts).Actual result: the generated images from step 2 are the same as the images generated in step 4 - the quality setting has no effect.

Previous Discussion

In this ​post the author encounters the same issue. The answer that resolves the issue is below:

I found the solution, Thanks to Danack from Imagick ​https://github.com/Imagick/imagick/.
There are two functions to set the compression quality:
setImageCompressionQuality
setCompressionQuality
According to the online documentation
​https://www.php.net/manual/en/imagick.setcompressionquality.php ... setCompressionQuality is for new images, and setImageCompressionQuality for already
existing ones.

Solution

I discovered that adding
$this->image->setCompressionQuality( $quality ); where we currently call setImageCompressionQuality already fixes the issue.

I am not clear if this issue affects other formats in any way (it didn't in my initial testing). However adding the additional quality setting call seems like a safe change to add and this will fix the issue for AVIFs.

Trac ticket: https://core.trac.wordpress.org/ticket/61614