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add alpha dithering for lossy

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new options:
 dwebp -alpha_dither
 vwebp -noalphadither

When the source was marked as quantized, we use a threshold-averaging
filter to smooth the decoded alpha plane.
Note: this option forces the decoding of alpha data in one pass, and
might slow the decoding a bit.

The new field in WebPDecoderOptions struct is 'alpha_dithering_strength'
(0 by default, means: off). Max strength value is '100'.

Change-Id: I218e21af96360d4781587fede95f8ea4e2b7287a
This commit is contained in:
skal
2014-06-14 00:06:16 +02:00
parent 790207679d
commit bbe32df1e3
11 changed files with 308 additions and 21 deletions
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3
examples/dwebp.c
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@ -557,6 +557,7 @@ static void Help(void) {
" -nofilter .... disable in-loop filtering\n"
" -nodither .... disable dithering\n"
" -dither <d> .. dithering strength (in 0..100)\n"
" -alpha_dither use alpha-plane dithering if needed.\n"
" -mt .......... use multi-threading\n"
" -crop <x> <y> <w> <h> ... crop output with the given rectangle\n"
" -scale <w> <h> .......... scale the output (*after* any cropping)\n"
@ -623,6 +624,8 @@ int main(int argc, const char *argv[]) {
format = YUV;
} else if (!strcmp(argv[c], "-mt")) {
config.options.use_threads = 1;
} else if (!strcmp(argv[c], "-alpha_dither")) {
config.options.alpha_dithering_strength = 100;
} else if (!strcmp(argv[c], "-nodither")) {
config.options.dithering_strength = 0;
} else if (!strcmp(argv[c], "-dither") && c < argc - 1) {