Hi On Sat, Dec 31, 2022 at 01:11:54PM +0100, Clément Bœsch wrote: > On Sun, Nov 06, 2022 at 06:30:22PM +0100, Michael Niedermayer wrote: > > On Sun, Nov 06, 2022 at 06:09:41PM +0100, Michael Niedermayer wrote: > > > On Sat, Nov 05, 2022 at 04:26:02PM +0100, Clément Bœsch wrote: > > > > Hi, > > > > > > > > This patchset essentially fixes a few core problems in these filters and > > > > switches to a perceptual model. > > > > > > > > I've generated a report for each key commit on this (temporary) page: > > > > http://big.pkh.me/pal/ (warning: heavy page, ~500M; I did try to add > > > > some lazy > > > > loading of the images but I'm not sure it's actually working as > > > > expected). > > > > > > i just looked at file00 and 16 and 64 colors with dither for it and they > > > look > > > different, some areas look better before and some better afterwards > > > > looked at more of the 16 color cases with dither > > (16 colors as i asumed fewer would magnify any issues ) > > file 01, IMHO current looks better than last (variance per axis) > > file 02, IMHO current looks better than last (variance per axis) > > file 03, IMHO VPA looks better but both really are quite off in terms of > > color, > > thats not the color of the original image. > > file 04, VPA is not good thats not the correct color > > > > It seems th last (variance per axis) is more pale and looses color > > So I did a lot of experiments, and the explanation for the desaturated > output at low number of colors can be found at the end of this article: > http://blog.pkh.me/p/39-improving-color-quantization-heuristics.html
interresting and its impressive how much reseacrh you did here i hope this will get applied also i hape a bit that it will get extended to include clustering as in ELBG cuz it seems a bit odd to have this sort of alternative filters neither does all .... > > I still think it's acceptable to lean toward desaturated colors when > reducing the number of colors, but you may disagree. I think a key aspect of desaturation has not been mentioned. That is mixing, i mean dithering is some sort of mixing, in the sense of an artist mixing several pigment/dyes/colors. If you have black and white a 50% mixture gives 50% gray. other ratios would give us all values between white and black though with dithering some ratios work better like 50% looks good while ratios very close to 0 and 100% but not exacty 0 and 100 look bad with few highly vissible black or white pixels in a see of the opposing color. Now this results in 2 things at least. 1. We should be able to improve color quantization by this. If we have colors A and B the (A+B)/2 point is basically free, its dither pattern looks good on any high resolution display and if we consider such points there are more of course like maybe (A+B+C+D)/4 we can cover more output colors with a smaller palette. 2. desaturation happens in dithered images because colors are simply not representable, the same way a artist cant paint 100% white if the brightest color she has is 80% white. She cant mix that with anything to make it brighter. An algorithm which would ensure that the colors from the palette form a convex hull around all the colors of the input would ensure all colors are representable and no desaturation should happen. it of course may look bad, i dont know, A convex hull likely is not the global optimum from a perceptual POV. But one only needs 8 colors to gurantee all colors are representable with dithering Another way to maybe see this is that if you have 1 color the best place is teh one where it minimizes the distance to all. But as more points are added average points between them become usable in a dithered image so the thing starts filling up while the perimeter and outside is harder to represent One could also say that with 2 colors all points on the line joining them can be represented and so distance to that line could be minimized but as not really all points on that line form pleasing dither patterns iam hesitant about this representation but it can be extended to a triangle and so forth with more points Now i hope i have not given any ideas that make you spend more months on this if you dont enjoy it :) But i find the whole myself a bit interresting [...] thx -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Any man who breaks a law that conscience tells him is unjust and willingly accepts the penalty by staying in jail in order to arouse the conscience of the community on the injustice of the law is at that moment expressing the very highest respect for law. - Martin Luther King Jr
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