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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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4
examples/vwebp.c
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@ -377,6 +377,7 @@ static void Help(void) {
" -nofancy ..... don't use the fancy YUV420 upscaler.\n"
" -nofilter .... disable in-loop filtering.\n"
" -dither <int> dithering strength (0..100). Default=50.\n"
" -noalphadither disable alpha plane dithering.\n"
" -mt .......... use multi-threading.\n"
" -info ........ print info.\n"
" -h ....... this help message.\n"
@ -399,6 +400,7 @@ int main(int argc, char *argv[]) {
return -1;
}
config->options.dithering_strength = 50;
config->options.alpha_dithering_strength = 100;
kParams.use_color_profile = 1;
for (c = 1; c < argc; ++c) {
@ -411,6 +413,8 @@ int main(int argc, char *argv[]) {
config->options.no_fancy_upsampling = 1;
} else if (!strcmp(argv[c], "-nofilter")) {
config->options.bypass_filtering = 1;
} else if (!strcmp(argv[c], "-noalphadither")) {
config->options.alpha_dithering_strength = 0;
} else if (!strcmp(argv[c], "-dither") && c + 1 < argc) {
config->options.dithering_strength = strtol(argv[++c], NULL, 0);
} else if (!strcmp(argv[c], "-info")) {