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Image compression results
07-13-2012, 11:12 PM
Post: #1
Image compression results
I get results that I hardly understand about image compression :

http://www.webpagetest.org/result/120713...ess_images

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 !!!) ?

Thanks!
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07-14-2012, 06:37 AM
Post: #2
RE: Image compression results
Try http://jpegmini.com By far the best jpeg compression tool ever.
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07-14-2012, 09:56 AM
Post: #3
RE: Image compression results
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).
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07-15-2012, 12:38 PM (This post was last modified: 07-15-2012 12:39 PM by pmeenan.)
Post: #4
RE: Image compression results
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.
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07-17-2012, 12:58 AM
Post: #5
RE: Image compression results
All is clear now, thanks for your answer!
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