[wp-trac] [WordPress Trac] #21668: WordPress still does not save jpeg as progressive jpeg

[WordPress Trac]

#21668: WordPress still does not save jpeg as progressive jpeg
-------------------------+-----------------------------
 Reporter:  _ck_         |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  normal       |  Milestone:  Awaiting Review
Component:  Media        |    Version:  3.4.1
 Severity:  normal       |   Keywords:
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 Every time WordPress does `imagejpeg` it should be doing `imageinterlace`
 beforehand to set progressive mode, but it's not.

 http://php.net/manual/en/function.imageinterlace.php

 Progressive jpeg has been supported by ALL browsers since 2001 or so.

 progressive demo: http://bbshowcase.org/progressive/

 Note that even if an ancient browser is listed somewhere as not rendering
 progressive, progressive jpeg still will be displayed, simply showing it
 all at once rather than gradual.

 IE6 for example WILL load progressive jpeg, it will just not render it
 progressively, instead it will load the entire image and then render all
 at once at the end.

 Progressive algorithm will also make slightly smaller jpeg as a side
 effect in most cases.

 ie. in `media.php`
 `
 imageinterlace($newimage,1);
 imagejpeg( $newimage, ...
 `

 This update is years overdue.

 It might be possible to futureproof this by adding a filter to `$newimage`
 before the final `imagejpeg`. I am uncertain if that would work since
 filters would not pass `$newimage` by reference and instead make a copy -
 while newimage is only a pointer to php/gd memory. Can apply_filters be
 forced to work somehow by reference instead of a copy? Maybe that should
 be another feature idea.

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Ticket URL: <http://core.trac.wordpress.org/ticket/21668>
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