[wp-trac] [WordPress Trac] #33642: Improve default Imagick compression settings

[WordPress Trac]

#33642: Improve default Imagick compression settings
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 Reporter:  joemcgill    |       Owner:  joemcgill
     Type:  enhancement  |      Status:  assigned
 Priority:  normal       |   Milestone:  4.5
Component:  Media        |     Version:
 Severity:  normal       |  Resolution:
 Keywords:  has-patch    |     Focuses:
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Changes (by joemcgill):

 * keywords:  needs-patch => has-patch


Comment:

 [https://core.trac.wordpress.org/attachment/ticket/33642/33642.patch
 33642.patch] simply changes the default quality setting in
 `WP_Image_Editor` from 90 to 82, which is the quality setting for
 ImageMagick suggested by @dnewton in his
 [https://www.smashingmagazine.com/2015/06/efficient-image-resizing-with-
 imagemagick/ Smashing Magazine article] to closely match the output of
 Photoshop's 'high' quality setting for JPEG images.

 After experimenting with his suggested settings, I noticed that the most
 noticeable difference in file size came from changing this quality
 setting, while many of the settings resulted in no change in file size.

 I resized several different images using this setting and compared the
 image quality using Kornel Lesiński's implementation of
 [https://github.com/pornel/dssim DSSIM] to calculate perceived differences
 between the current default quality and images compressed using a quality
 of 82. I found both Imagick and GD produced DSSIM scores between 0.0014
 and 0.0023 in my test cases, which is well under the score (0.015) shown
 to be acceptable in [http://www.radware.com/neurostrata-fall2014/ research
 released in 2014] (requires signup to view,
 [http://calendar.perfplanet.com/2014/little-rgb-riding-hood-a-jpegs-tale/
 summary here]).

 Further enhancements to compression is possible (e.g., stripping some
 metadata, playing with different compression algorithms, etc.) but
 changing the quality alone would be a nice enhancement.

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Ticket URL: <https://core.trac.wordpress.org/ticket/33642#comment:22>
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