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Old 27th May 2010, 14:39   #1  |  Link
-horn-
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Video-codec rater by image comparison algorithm?

Hi,

perhaps anyone knows if this is possible.
comparing image quality is almost imposible to describe without subjective influences. When someone rates an image quality as good there is at least one person, that doesn't think so.
human preferences are always different.

So, I would like to know if there is away to "rate" the image quality by an algorithm that compares the original image to the produced one in following issues

- colour change(difference pixel by pixel
- blur rate
- artifacts and macroblocking

the first one would be the easiest one because you could check just the diffeence in colours and can give 3 values in +- of each hex-value
both last once I don't know if this is possible, but the blocking could be detected by edge-finding.

and the king's quest would be to do that for more then just one image, because video is done with several frames.

perhaps you expert programmers could tell me, if such an automated algo can be done to bring some objective measurement divice into rating image quality. this could perhaps calm down some h.264 is better than x264 and better than vp8 and blaaah people

Andreas

1st posted here http://www.hdtvtotal.com/PNphpBB2-viewtopic-t-1795.html
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Old 27th May 2010, 17:17   #2  |  Link
pandy
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some thing are common and quite independent - search for some books for psycho-optics - they describe characteristic of the human vision - all you need to to do is translate what we know about us (our perception) to the algorithm + add some magic yet undiscovered by science
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Old 27th May 2010, 17:26   #3  |  Link
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PSNR, SSIM ...

It's all well known stuff.
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Old 27th May 2010, 23:54   #4  |  Link
LoRd_MuldeR
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Some interesting reading:
http://www.ece.uwaterloo.ca/~z70wang...ions/SPM09.pdf
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Old 28th May 2010, 00:25   #5  |  Link
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Although people might disagree with visual comparison, mathematical comparison where the actual differences are calculated can also be unsuitable. If you had an original image or video, and compressed/encoded it with Psy optimisations on (with various adjustments), and had the same image or video with those optimisations off, but otherwise had them compressed to roughly the same file size, the human and mathematical comparisons should actually give opposite results!

The mathematical comparison gives the truest results in the difference between the original and the encoding, which favours the image with psy off. Visually people will most likely favour the encoding with psy on. The reason for this is psy uses tricks to improve perceptible quality and encoding efficiency and results in altering the output from the original.
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