[FFmpeg-cvslog] swscale: add two spatially stable dithering methods
Øyvind Kolås
git at videolan.org
Tue Mar 25 13:58:14 CET 2014
ffmpeg | branch: master | Øyvind Kolås <pippin at gimp.org> | Sun Mar 23 02:13:26 2014 +0100| [3e6016622e6fc5967e55d41e8074558d43bc33c0] | committer: Michael Niedermayer
swscale: add two spatially stable dithering methods
Both of these dithering methods are from http://pippin.gimp.org/a_dither/ for
GIF they can be considered better than bayer (provides more gray-levels), and
spatial stability - often more than twice as good compression and less visual
flicker than error diffusion methods (the methods also avoids error-shadow
artifacts of diffusion dithers).
These methods are similar to blue/green noise type dither masks; but are
simple enough to generate their mask on the fly. They are still research work
in progress; though more expensive to generate masks (which can be used in a
LUT) like 'void and cluster' and similar methods will yield superior results
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=3e6016622e6fc5967e55d41e8074558d43bc33c0
---
doc/scaler.texi | 8 ++++
libswscale/options.c | 10 +++--
libswscale/output.c | 83 ++++++++++++++++++++++++++++++++---------
libswscale/swscale_internal.h | 2 +
libswscale/utils.c | 2 +-
5 files changed, 82 insertions(+), 23 deletions(-)
diff --git a/doc/scaler.texi b/doc/scaler.texi
index f043ffd..23d6393 100644
--- a/doc/scaler.texi
+++ b/doc/scaler.texi
@@ -112,6 +112,14 @@ bayer dither
@item ed
error diffusion dither
+
+ at item a_dither
+arithmetic dither, based using addition
+
+ at item x_dither
+arithmetic dither, based using xor (more random/less apparent patterning that
+a_dither).
+
@end table
@end table
diff --git a/libswscale/options.c b/libswscale/options.c
index 9e8703f..5433d55 100644
--- a/libswscale/options.c
+++ b/libswscale/options.c
@@ -69,10 +69,12 @@ static const AVOption swscale_options[] = {
{ "dst_v_chr_pos", "destination vertical chroma position in luma grid/256" , OFFSET(dst_v_chr_pos), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 512, VE },
{ "dst_h_chr_pos", "destination horizontal chroma position in luma grid/256", OFFSET(dst_h_chr_pos), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 512, VE },
- { "sws_dither", "set dithering algorithm", OFFSET(dither), AV_OPT_TYPE_INT, { .i64 = SWS_DITHER_AUTO }, 0, NB_SWS_DITHER, VE, "sws_dither" },
- { "auto", "leave choice to sws", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_AUTO }, INT_MIN, INT_MAX, VE, "sws_dither" },
- { "bayer", "bayer dither", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_BAYER }, INT_MIN, INT_MAX, VE, "sws_dither" },
- { "ed", "error diffusion", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_ED }, INT_MIN, INT_MAX, VE, "sws_dither" },
+ { "sws_dither", "set dithering algorithm", OFFSET(dither), AV_OPT_TYPE_INT, { .i64 = SWS_DITHER_AUTO }, 0, NB_SWS_DITHER, VE, "sws_dither" },
+ { "auto", "leave choice to sws", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_AUTO }, INT_MIN, INT_MAX, VE, "sws_dither" },
+ { "bayer", "bayer dither", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_BAYER }, INT_MIN, INT_MAX, VE, "sws_dither" },
+ { "ed", "error diffusion", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_ED }, INT_MIN, INT_MAX, VE, "sws_dither" },
+ { "a_dither", "arithmetic addition dither", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_A_DITHER}, INT_MIN, INT_MAX, VE, "sws_dither" },
+ { "x_dither", "arithmetic xor dither", 0, AV_OPT_TYPE_CONST, { .i64 = SWS_DITHER_X_DITHER}, INT_MIN, INT_MAX, VE, "sws_dither" },
{ NULL }
};
diff --git a/libswscale/output.c b/libswscale/output.c
index ddb0d0c..f41b32a 100644
--- a/libswscale/output.c
+++ b/libswscale/output.c
@@ -1508,24 +1508,71 @@ static av_always_inline void yuv2rgb_write_full(SwsContext *c,
case AV_PIX_FMT_RGB8:
{
int r,g,b;
- R >>= 22;
- G >>= 22;
- B >>= 22;
- R += (7*err[0] + 1*c->dither_error[0][i] + 5*c->dither_error[0][i+1] + 3*c->dither_error[0][i+2])>>4;
- G += (7*err[1] + 1*c->dither_error[1][i] + 5*c->dither_error[1][i+1] + 3*c->dither_error[1][i+2])>>4;
- B += (7*err[2] + 1*c->dither_error[2][i] + 5*c->dither_error[2][i+1] + 3*c->dither_error[2][i+2])>>4;
- c->dither_error[0][i] = err[0];
- c->dither_error[1][i] = err[1];
- c->dither_error[2][i] = err[2];
- r = R >> (isrgb8 ? 5 : 7);
- g = G >> (isrgb8 ? 5 : 6);
- b = B >> (isrgb8 ? 6 : 7);
- r = av_clip(r, 0, isrgb8 ? 7 : 1);
- g = av_clip(g, 0, isrgb8 ? 7 : 3);
- b = av_clip(b, 0, isrgb8 ? 3 : 1);
- err[0] = R - r*(isrgb8 ? 36 : 255);
- err[1] = G - g*(isrgb8 ? 36 : 85);
- err[2] = B - b*(isrgb8 ? 85 : 255);
+
+ switch (c->dither) {
+ default:
+ case SWS_DITHER_AUTO:
+ case SWS_DITHER_ED:
+ R >>= 22;
+ G >>= 22;
+ B >>= 22;
+ R += (7*err[0] + 1*c->dither_error[0][i] + 5*c->dither_error[0][i+1] + 3*c->dither_error[0][i+2])>>4;
+ G += (7*err[1] + 1*c->dither_error[1][i] + 5*c->dither_error[1][i+1] + 3*c->dither_error[1][i+2])>>4;
+ B += (7*err[2] + 1*c->dither_error[2][i] + 5*c->dither_error[2][i+1] + 3*c->dither_error[2][i+2])>>4;
+ c->dither_error[0][i] = err[0];
+ c->dither_error[1][i] = err[1];
+ c->dither_error[2][i] = err[2];
+ r = R >> (isrgb8 ? 5 : 7);
+ g = G >> (isrgb8 ? 5 : 6);
+ b = B >> (isrgb8 ? 6 : 7);
+ r = av_clip(r, 0, isrgb8 ? 7 : 1);
+ g = av_clip(g, 0, isrgb8 ? 7 : 3);
+ b = av_clip(b, 0, isrgb8 ? 3 : 1);
+ err[0] = R - r*(isrgb8 ? 36 : 255);
+ err[1] = G - g*(isrgb8 ? 36 : 85);
+ err[2] = B - b*(isrgb8 ? 85 : 255);
+ break;
+ case SWS_DITHER_A_DITHER:
+ if (isrgb8) {
+ /* see http://pippin.gimp.org/a_dither/ for details/origin */
+#define A_DITHER(u,v) (((((u)+((v)*236))*119)&0xff))
+ r = (((R >> 19) + A_DITHER(i,y) -96)>>8);
+ g = (((G >> 19) + A_DITHER(i + 17,y) - 96)>>8);
+ b = (((B >> 20) + A_DITHER(i + 17*2,y) -96)>>8);
+ r = av_clip(r, 0, 7);
+ g = av_clip(g, 0, 7);
+ b = av_clip(b, 0, 3);
+ } else {
+ r = (((R >> 21) + A_DITHER(i,y)-256)>>8);
+ g = (((G >> 19) + A_DITHER(i + 17,y)-256)>>8);
+ b = (((B >> 21) + A_DITHER(i + 17*2,y)-256)>>8);
+ r = av_clip(r, 0, 1);
+ g = av_clip(g, 0, 3);
+ b = av_clip(b, 0, 1);
+ }
+ break;
+ case SWS_DITHER_X_DITHER:
+ if (isrgb8) {
+ /* see http://pippin.gimp.org/a_dither/ for details/origin */
+#define X_DITHER(u,v) (((((u)^((v)*237))*181)&0x1ff)/2)
+ r = (((R >> 19) + X_DITHER(i,y) - 96)>>8);
+ g = (((G >> 19) + X_DITHER(i + 17,y) - 96)>>8);
+ b = (((B >> 20) + X_DITHER(i + 17*2,y) - 96)>>8);
+ r = av_clip(r, 0, 7);
+ g = av_clip(g, 0, 7);
+ b = av_clip(b, 0, 3);
+ } else {
+ r = (((R >> 21) + X_DITHER(i,y)-256)>>8);
+ g = (((G >> 19) + X_DITHER(i + 17,y)-256)>>8);
+ b = (((B >> 21) + X_DITHER(i + 17*2,y)-256)>>8);
+ r = av_clip(r, 0, 1);
+ g = av_clip(g, 0, 3);
+ b = av_clip(b, 0, 1);
+ }
+
+ break;
+ }
+
if(target == AV_PIX_FMT_BGR4_BYTE) {
dest[0] = r + 2*g + 8*b;
} else if(target == AV_PIX_FMT_RGB4_BYTE) {
diff --git a/libswscale/swscale_internal.h b/libswscale/swscale_internal.h
index 5ce54d0..8c2dc79 100644
--- a/libswscale/swscale_internal.h
+++ b/libswscale/swscale_internal.h
@@ -66,6 +66,8 @@ typedef enum SwsDither {
SWS_DITHER_AUTO,
SWS_DITHER_BAYER,
SWS_DITHER_ED,
+ SWS_DITHER_A_DITHER,
+ SWS_DITHER_X_DITHER,
NB_SWS_DITHER,
} SwsDither;
diff --git a/libswscale/utils.c b/libswscale/utils.c
index f2e4167..483b0b2 100644
--- a/libswscale/utils.c
+++ b/libswscale/utils.c
@@ -1250,7 +1250,7 @@ av_cold int sws_init_context(SwsContext *c, SwsFilter *srcFilter,
if (c->dither == SWS_DITHER_AUTO)
c->dither = (flags & SWS_FULL_CHR_H_INT) ? SWS_DITHER_ED : SWS_DITHER_BAYER;
if (!(flags & SWS_FULL_CHR_H_INT)) {
- if (c->dither == SWS_DITHER_ED) {
+ if (c->dither == SWS_DITHER_ED || c->dither == SWS_DITHER_A_DITHER || c->dither == SWS_DITHER_X_DITHER) {
av_log(c, AV_LOG_DEBUG,
"Desired dithering only supported in full chroma interpolation for destination format '%s'\n",
av_get_pix_fmt_name(dstFormat));
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