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Old 13th April 2011, 14:11   #1  |  Link
LigH
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Wanted: Perceptual adaptive JPEG encoder (optimizer)

Do you know any other, preferably free, software which is able to save JPEG images with perceptual per-macroblock adaptive quantization — except the good old "xat.com JPEG Optimizer 3.15" (which is not freeware, though, except I missed the official public release of the installer code)?

No, please do not post the code here. Although it is not exactly "secret" anymore, anyway...
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Old 31st March 2018, 22:27   #2  |  Link
LigH
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After hearing about "Pingo": No, I don't believe this tool can compete.

MagiCompress™ in xat.com JPEG Optimizer 3.15 is lossy and adaptive to the visual complexity per block. This is what I want.

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Old 31st March 2018, 22:34   #3  |  Link
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I do not know if it serves you:

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Old 31st March 2018, 22:38   #4  |  Link
LigH
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Yes, this sounds promising. I hope it is also publicly useable. If there is at least a CLI encoder with moderate CPU instruction set requirements, I may test it. Let's see what Jamaika published in the last months in "Crazy family JPEG formats".
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Old 4th April 2018, 08:32   #5  |  Link
LigH
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I compiled a guetzli JPEG encoder successfully. To compare the quality/size ratios of different optimizers, I wonder if there is a tool similar to MSU VQMT, just for a pair of still images, which would report PSNR, SSIM, MSE, and other metrics. Somehow I feel the more keywords I give Google, the more it derails the results away from image comparison tools and towards video comparison. And creating 1-frame video clips to be able to use VQMT would be a detour if simpler tools for still images exist.
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Old 8th April 2018, 04:52   #6  |  Link
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Hey, here's some related information from CÚdric, the creator of Pingo: https://css-ig.net/support/messages/...#comment-title
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Old 8th April 2018, 16:31   #7  |  Link
LigH
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Nice, thank you for pointing at it. I already tested guetzli, and it takes a lot of time to optimize a JPEG really thoroughly. It took several tries to produce a guetzli JPEG with a similar size as a xat.com MagiCompress™ result, and it had a better SSIM value (according to ffmpeg), and the difference image (bias grey128) appeared visually "flatter". In case of Lenna, guetzli -q93 had a similar size, guetzli -q92 had a similar SSIM value as xat q98 with probably 50% MagiCompress (one button click), compared to an original libJPEG -q100 (YUV 4:2:0). I will have to check more different material (especially some with low contrast and low sharpness, e.g. smoky/cloudy areas) to get a better feeling where advantages or disadvantages of different methods are. I believe xat MagiCompress may more probably produce obvious artifacts (banding) in such areas, or reduce details with faint regular patterns. That will cost some efforts ... but I thank you for good suggestions.
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Old 9th April 2018, 08:24   #8  |  Link
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As a side question (my curiosity), what does MozJpeg do to optimize a JPEG and how is that different to what you're looking for ?
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Old 9th April 2018, 08:39   #9  |  Link
LigH
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I read that MozJpeg provides a lossless compression optimization based on jpgcrush; I would allow lossy compression with variable quantization across all DCT blocks in the image.
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Old 9th April 2018, 16:48   #10  |  Link
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MozJpeg is lossy... 'just' an optimized libjpeg
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Old 9th April 2018, 17:37   #11  |  Link
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Read the whole mozjpeg build instructions and guetzli is still doing it's first 1920x1200 px png.... Build mozjpeg. Converted about 10 images from png to jpeg using mozjpeg (cjpeg) and guetzli still working...

This one https://transfer.sh/iSwqb/test.png
seems good (maybe transparent) with
Code:
mozjpeg -quality 90 -rgb test.png > out.jpg
edit: Not even close to transparent, heavy banding in bottom-left quadrant. edit2: Looks pretty much the same as default libjpeg (assuming imagemagick uses that) at same size, so I'am probably missing some magic switch?

Edit: This is what guezly did eventually (Way to slow to be useful)
https://transfer.sh/mHlK7/testguetzli.jpg

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Old 9th April 2018, 18:26   #12  |  Link
LigH
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@dipje: With "lossless", here I mean "no additional loss compared to libjpeg with the same quality level", no coarser quantization. But I would allow a coarser quantization as long as it won't be easily noticed. MagiCompress definitely raises the quantization, by different amounts for each DCT block. The result will not have the same quantizer all over the whole image.

The goal is adaptive quantization per DCT (macro?) block.
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