2017-09-23 19:18 GMT+02:00 Mateusz <mateu...@poczta.onet.pl>: > W dniu 2017-09-23 o 17:01, Michael Niedermayer pisze: >> On Fri, Sep 22, 2017 at 02:10:01AM +0200, Mateusz wrote: >>> To reduce bit depth in planar YUV or gray pixel formats >>> ffmpeg uses DITHER_COPY macro. >>> Now it makes images greener and with visible dither pattern. >>> >>> In my opinion there is no point to use dither tables for >>> destination bit depth >= 9, we can use simple down-shift >>> which is neutral in full and limited range -- result images >>> are with the same brightness and with the same colors. >> >> Theres no reason why dither should mess up the average color tone. > > In theory -- yes, I agree. > In reality -- current version of DITHER_COPY mess up the > average color tone. > It's one of the reasons why I sending these patches. > >> And if the user asks for >= 9 bit depth and has >= 10 bit >> input the user likely wants to get the best quality. >> Thats more so in a world where computers get faster >> every few years, this isnt 1995 where shaving off a add >> or a multiply per pixel was actually making a difference >> in being able to play something in realtime >> More so coverting between bit depths might be memory >> speed limited and not limited by arithmetic computations >> once its done in SIMD > > Yes, I agree. Now I can't write patches in NASM syntax, but > I started reading and learning. > I hope I'll back in a few months...
I strongly suspect there should be agreement over the C code first, asm optimizations can be done once C code is agreed upon. Thank you for the samples, Carl Eugen _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
