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image compression: how does webpagetest check if an image can be compressed??!? - Printable Version

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image compression: how does webpagetest check if an image can be compressed??!? - dlam - 04-19-2014 05:30 AM

hey! I was wondering how exactly webpagetest figures out if an image could be more compressed or not, so I could test/tweak stuff see if my site is generating the "right" sized images

i gave a shot at looking at the source and found this constant in wpt_test.cc:37 which looks like maybe a clue... ->

wpt_test.cc
37:static const BYTE JPEG_DEFAULT_QUALITY = 30;


HuhAngelSmile


RE: image compression: how does webpagetest check if an image can be compressed??!? - dlam - 04-25-2014 10:38 AM

*bump bump*


RE: image compression: how does webpagetest check if an image can be compressed??!? - pmeenan - 04-29-2014 04:25 AM

The code you're looking for is actually here: https://github.com/WPO-Foundation/webpagetest/blob/master/agent/wpthook/optimization_checks.cc#L327

It recompresses jpegs at a quality level of 85 which is pretty generous (usually you can go down to 75 without even thinking about it). The process also strips out meta-data like exif tags.


RE: image compression: how does webpagetest check if an image can be compressed??!? - dlam - 05-06-2014 03:09 PM

cool! thanks Pat! Big Grin Smile Wink Angel