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Have you played with Mozjpeg? (image optimization)
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Have you played with Mozjpeg? (image optimization)
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Have you played with Mozjpeg? (image optimization)
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02-02-2015, 12:46 AM
Post: #1
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Have you played with Mozjpeg? (image optimization)
If you don't know, Mozjpeg is a modified version of libjpeg-turbo-tools that will compress jpeg images more than standard jpegtran/jpegoptim without loss of any quality (lossless).
But what's really magical about Mozjpeg is the utility cjpeg which compresses the jpeg files - this is where you can really save bytes without losing much quality. You can read more about mozjpeg here: http://calendar.perfplanet.com/2014/mozjpeg-3-0/ I've been playing around with mozjpeg (mostly cjpeg) to see if I can't optimize my client's images kinda automatic without much loss of quality. In this example, I'm only using one image for quality checks. This jpeg image is of 99% quality factor and is 500kB (huge). The jpeg image is a huge background image in a "hero" area in above the fold. Here are the results of my experiments: Code: -rw-r--r-- 1 sigurdur sigurdur 480142 feb 1 11:34 home-page-image-big-1jpegtranmozjpeg.jpgSo originally, the image is 502793, and if we use jpegtran/jpegoptim to losslessly optimize it, it shrinks to 481715 bytes. If we use Mozjpeg 3.0 jpegtran the image losslessly shrinks to 480142 bytes (~1.5kB smaller than original jpegtran) The image is still friggin' huge (because of quality factor 99%) Well, after testing various things on this image and how it affects the size, quality and download speed, I've found that using 90% quality with mozjpeg (or 85% quality using "normal" compression tools) is probably the best in regards to quality/size. The difference between "normal" jpeg quality 85 and mozjpeg quality 90 is huge, quality wise. Even when only comparing the quality between Mozjpeg Q85 and normal Q85, it looks to me as if it has fewer artifacts (due to some smoothing algorithm or my internal bias). If we calculate how much download time difference there is with Q85 and Q90 (31kB) on Cable (5mbps), we find that we only add about 60ms.. 31÷(5000×.85÷8) = 0,058352941 Of course if there were multiple files like this needed for the initial download, then the 60ms aren't worth it, but since this is the only big image then it's worth it. TL;DR Mozjpeg is better at losslessly compressing (0-10% better than jpegoptim) jpeg files cjpeg from Mozjpeg is a fantastic way to do an extreme lossy compression without losing much quality. Have you played with Mozjpeg? ------------ All websites deserve to load fast. |
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02-02-2015, 02:09 AM
Post: #2
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RE: Have you played with Mozjpeg? (image optimization)
Ha!
Interesting. I am modifying my automation script to optimize images that are above 90% quality, and was testing the "identify" command from ImageMagick.. Look at what it thinks about the 90% quality file from cjpeg vs a "normal" 90% quality file: Code: sigurdur@sigurdur-ThinkPad-W510 ~/tmp $ identify -format "%Q" home-page-image-big-1mozjpegcjpeg90.jpgThe identify tool reverse engineers the image to figure out the quality setting .. but it doesnt seem to figure out how to deal with mozjpeg's modification .. (I need to post a msg to the imagemagick group) That sparked another test idea in my mind .. what would happen if I used the same quality setting as the original image ..? (99%) Code: sigurdur@sigurdur-ThinkPad-W510 ~/tmp $ mozjpeg/cjpeg -quality 99 -optimize -progressive -outfile home-page-image-big-1mozjpegcjpeg99.jpg home-page-image-big.jpg Same quality factor in the construction, but calculated quality factor is different (-1) What if we measure the actual difference? Code: sigurdur@sigurdur-ThinkPad-W510 ~/tmp $ compare home-page-image-big.jpg home-page-image-big-1mozjpegcjpeg99.jpg 99diff.pngless than 0.3% difference Well .. what if we try creating a "normal" 98% quality image and measure the difference.. Code: sigurdur@sigurdur-ThinkPad-W510 ~/tmp $ cp home-page-image-big.jpg home-page-image-big-q98.jpgSo that produces a slightly smaller file with a slightly more changes than the mozjpeg 99% conversion. So .. mozjpeg effectively is reducing the quality (based on reverse engineering the quantization tables), but keeps visual quality high compared to "normal" quality conversion. Well, I see no reason to not use mozjpeg, in fact I see every reason to use it to optimize images .. maybe a mozjpeg developer can chime in? ------------ All websites deserve to load fast. |
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02-03-2015, 10:36 PM
Post: #3
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RE: Have you played with Mozjpeg? (image optimization)
Kornel (the creator of imageoptim and pngquant) replied to my question about JPG quality (as assumed by in ImageMagick).
Hat's off to him for doing that. He also created a comparison utility to compare human perceived visual quality between images. Quote:Internally JPEG doesn't actually use a single number for quality. It uses quantization tables which are like 64 individual quality settings per channel, affecting different kinds of details in the image. ------------ All websites deserve to load fast. |
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04-04-2015, 01:59 PM
Post: #4
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RE: Have you played with Mozjpeg? (image optimization)
Hi sig, have you played around with jpegmini at all? It tends to do a great job but it hides the settings it uses.
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04-04-2015, 09:19 PM
Post: #5
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RE: Have you played with Mozjpeg? (image optimization)
Hey avalanch,
Yeah .. they use a patent-pending algorithm to change the quantification tables somehow. I think they change the q-tables on the fly and select the best tables by analyzing the image and choosing to use high quality compression in areas where the eye is likely to be watching, and low quality compression where the eye won't look. So, this is kinda like how mozjpeg is doing things, but it seems to go further than mozjpeg. It's kinda like if you would mix Kornel's dssim tool with mozjpeg to find the ultimate mix of quality and compression. Here are some very intelligent answers about the jpegmini compression on Quora: http://www.quora.com/How-does-JPEGmini-r...ny-quality ------------ All websites deserve to load fast. |
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