W dniu 2017-09-25 o 22:53, Carl Eugen Hoyos pisze: > 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
I've sent C code patch 2017-09-06 (and nothing) so I thought that the problem is with speed. For simplicity I've attached this patch. This code full-fill all rules (for limited and for full range): white -> white black -> black white-1 -> gray (it means white-1 -> white usually but sometimes white-1 -> white-1) black+1 -> gray (it means black+1 -> black usually but sometimes black+1 -> black+1) increase bitdepth & decrease bitdepth = identity About code: limited range (shiftonly == 1) tmp = (src + dither)>>shift; dst = tmp - (tmp>>dst_depth); In theory it is enough to make only dst = (src + dither)>>shift; -- white in limited range has 0 on bits to remove (235*4 for example) so overflow is impossible. For files with full range not marked as full range overflow is possible (for dither > 0) and white goes to black. tmp - (tmp>>dst_depth) undoing this overflow. full range (shiftonly == 0) dst = (src - (src>>dst_depth) + dither)>>shift; If we want to remove 2 bits from source (for example 10-bit -> 8-bit) white in full range: ...111|11 white-1 in full range: ...111|10 so we should subtract dither for rule 'white-1 -> gray' black in full range: ...000|00 black+1 in full range: ...000|01 so we should add dither for rule 'black+1 -> gray' (src>>dst_depth) is 0 for small values (close to black) and max possible dither for big values (close to white) For rule 'increase bitdepth & decrease bitdepth = identity' in full range, we have increase bitdepth: (v<<(dst_depth-src_depth)) | (v>>(2*src_depth-dst_depth)) so (src - (src>>dst_depth))>>shift is exactly inverse operation when we decreasing bitdepth. For full range when 'src' is from increased 'v' (src - (src>>dst_depth)) is equal 'v' shifted only, so we are as in limited range. And overflow is impossible in operation (src - (src>>dst_depth) + dither). Mateusz
From fd9e271ea531d25bc5a708d0dfeb1be5415b90d0 Mon Sep 17 00:00:00 2001 From: Mateusz <mateu...@poczta.onet.pl> Date: Wed, 6 Sep 2017 09:05:02 +0200 Subject: [PATCH] fix DITHER_COPY macro according to shiftonly state --- libswscale/swscale_unscaled.c | 73 ++++++++++++++++++++++--------------------- 1 file changed, 38 insertions(+), 35 deletions(-) diff --git a/libswscale/swscale_unscaled.c b/libswscale/swscale_unscaled.c index ef36aec..e3e375a 100644 --- a/libswscale/swscale_unscaled.c +++ b/libswscale/swscale_unscaled.c @@ -110,24 +110,6 @@ DECLARE_ALIGNED(8, static const uint8_t, dithers)[8][8][8]={ { 112, 16,104, 8,118, 22,110, 14,}, }}; -static const uint16_t dither_scale[15][16]={ -{ 2, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,}, -{ 2, 3, 7, 7, 13, 13, 25, 25, 25, 25, 25, 25, 25, 25, 25, 25,}, -{ 3, 3, 4, 15, 15, 29, 57, 57, 57, 113, 113, 113, 113, 113, 113, 113,}, -{ 3, 4, 4, 5, 31, 31, 61, 121, 241, 241, 241, 241, 481, 481, 481, 481,}, -{ 3, 4, 5, 5, 6, 63, 63, 125, 249, 497, 993, 993, 993, 993, 993, 1985,}, -{ 3, 5, 6, 6, 6, 7, 127, 127, 253, 505, 1009, 2017, 4033, 4033, 4033, 4033,}, -{ 3, 5, 6, 7, 7, 7, 8, 255, 255, 509, 1017, 2033, 4065, 8129,16257,16257,}, -{ 3, 5, 6, 8, 8, 8, 8, 9, 511, 511, 1021, 2041, 4081, 8161,16321,32641,}, -{ 3, 5, 7, 8, 9, 9, 9, 9, 10, 1023, 1023, 2045, 4089, 8177,16353,32705,}, -{ 3, 5, 7, 8, 10, 10, 10, 10, 10, 11, 2047, 2047, 4093, 8185,16369,32737,}, -{ 3, 5, 7, 8, 10, 11, 11, 11, 11, 11, 12, 4095, 4095, 8189,16377,32753,}, -{ 3, 5, 7, 9, 10, 12, 12, 12, 12, 12, 12, 13, 8191, 8191,16381,32761,}, -{ 3, 5, 7, 9, 10, 12, 13, 13, 13, 13, 13, 13, 14,16383,16383,32765,}, -{ 3, 5, 7, 9, 10, 12, 14, 14, 14, 14, 14, 14, 14, 15,32767,32767,}, -{ 3, 5, 7, 9, 11, 12, 14, 15, 15, 15, 15, 15, 15, 15, 16,65535,}, -}; - static void fillPlane(uint8_t *plane, int stride, int width, int height, int y, uint8_t val) @@ -1502,24 +1484,45 @@ static int packedCopyWrapper(SwsContext *c, const uint8_t *src[], } #define DITHER_COPY(dst, dstStride, src, srcStride, bswap, dbswap)\ - uint16_t scale= dither_scale[dst_depth-1][src_depth-1];\ - int shift= src_depth-dst_depth + dither_scale[src_depth-2][dst_depth-1];\ - for (i = 0; i < height; i++) {\ - const uint8_t *dither= dithers[src_depth-9][i&7];\ - for (j = 0; j < length-7; j+=8){\ - dst[j+0] = dbswap((bswap(src[j+0]) + dither[0])*scale>>shift);\ - dst[j+1] = dbswap((bswap(src[j+1]) + dither[1])*scale>>shift);\ - dst[j+2] = dbswap((bswap(src[j+2]) + dither[2])*scale>>shift);\ - dst[j+3] = dbswap((bswap(src[j+3]) + dither[3])*scale>>shift);\ - dst[j+4] = dbswap((bswap(src[j+4]) + dither[4])*scale>>shift);\ - dst[j+5] = dbswap((bswap(src[j+5]) + dither[5])*scale>>shift);\ - dst[j+6] = dbswap((bswap(src[j+6]) + dither[6])*scale>>shift);\ - dst[j+7] = dbswap((bswap(src[j+7]) + dither[7])*scale>>shift);\ + unsigned shift= src_depth-dst_depth, tmp;\ + if (shiftonly) {\ + for (i = 0; i < height; i++) {\ + const uint8_t *dither= dithers[shift-1][i&7];\ + for (j = 0; j < length-7; j+=8){\ + tmp = (bswap(src[j+0]) + dither[0])>>shift; dst[j+0] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+1]) + dither[1])>>shift; dst[j+1] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+2]) + dither[2])>>shift; dst[j+2] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+3]) + dither[3])>>shift; dst[j+3] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+4]) + dither[4])>>shift; dst[j+4] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+5]) + dither[5])>>shift; dst[j+5] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+6]) + dither[6])>>shift; dst[j+6] = dbswap(tmp - (tmp>>dst_depth));\ + tmp = (bswap(src[j+7]) + dither[7])>>shift; dst[j+7] = dbswap(tmp - (tmp>>dst_depth));\ + }\ + for (; j < length; j++){\ + tmp = (bswap(src[j]) + dither[j&7])>>shift; dst[j] = dbswap(tmp - (tmp>>dst_depth));\ + }\ + dst += dstStride;\ + src += srcStride;\ + }\ + } else {\ + for (i = 0; i < height; i++) {\ + const uint8_t *dither= dithers[shift-1][i&7];\ + for (j = 0; j < length-7; j+=8){\ + tmp = bswap(src[j+0]); dst[j+0] = dbswap((tmp - (tmp>>dst_depth) + dither[0])>>shift);\ + tmp = bswap(src[j+1]); dst[j+1] = dbswap((tmp - (tmp>>dst_depth) + dither[1])>>shift);\ + tmp = bswap(src[j+2]); dst[j+2] = dbswap((tmp - (tmp>>dst_depth) + dither[2])>>shift);\ + tmp = bswap(src[j+3]); dst[j+3] = dbswap((tmp - (tmp>>dst_depth) + dither[3])>>shift);\ + tmp = bswap(src[j+4]); dst[j+4] = dbswap((tmp - (tmp>>dst_depth) + dither[4])>>shift);\ + tmp = bswap(src[j+5]); dst[j+5] = dbswap((tmp - (tmp>>dst_depth) + dither[5])>>shift);\ + tmp = bswap(src[j+6]); dst[j+6] = dbswap((tmp - (tmp>>dst_depth) + dither[6])>>shift);\ + tmp = bswap(src[j+7]); dst[j+7] = dbswap((tmp - (tmp>>dst_depth) + dither[7])>>shift);\ + }\ + for (; j < length; j++){\ + tmp = bswap(src[j]); dst[j] = dbswap((tmp - (tmp>>dst_depth) + dither[j&7])>>shift);\ + }\ + dst += dstStride;\ + src += srcStride;\ }\ - for (; j < length; j++)\ - dst[j] = dbswap((bswap(src[j]) + dither[j&7])*scale>>shift);\ - dst += dstStride;\ - src += srcStride;\ } static int planarCopyWrapper(SwsContext *c, const uint8_t *src[], -- 2.7.4
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