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WebPagetest Forums - Image compression results

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Full Version: Image compression results
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I get results that I hardly understand about image compression :

But nor Jpegtran nor ImageMagick does allow better compression of this image:

Original : 50.497 bytes
jpegtran -copy none -optimize : 53.244 bytes
jpegtran -copy none -progressive : 50.497 bytes
convert -strip : 53.273 bytes
convert -strip -interlace Plane : 50.550 bytes

I made the same constation on a lot of others images...

Could somebody tell me what tool could be used to obtain the gain displayed par the result page (about 20Kb !!!) ?

Try By far the best jpeg compression tool ever.
You're right, it's pretty good! But maybe I should rephrase my question:

How WebPageTest can make such an assessment (ie, state that a gain of 40% is achievable as well known tools as jpegtrans, imagemagick can not even win one byte)?

It should be based on some specific tool/library that would be very interesting to know in order to try to achieve the above result (unless WebPageTest use JPEGMini? Smile).
jpegtrans and imagemagick were trying to do lossless optimizations (stripping exif data, etc). WebPagetest checks jpegs for lossy savings by recompressing them at a quality level of 85 using libjpeg which is actually pretty conservative. Hand-tuning you should actually be able to get significantly better than that.
All is clear now, thanks for your answer!
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