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Use deterministic random-dithering during RGB->YUV conversion

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-> helps debanding (sky, gradients, etc.)

This dithering can only be triggered when using -preset photo
or -pre 2 (as a preprocessing). Everything is unchanged otherwise.

Note that this change is likely to make the perceived PSNR/SSIM drop
since we're altering the input internally.

Change-Id: Id8d4326245d9b828141de162c94ba381b1fa5813
This commit is contained in:
skal
2013-10-17 22:36:49 +02:00
parent 8a2fa099cc
commit 0b2b05049f
7 changed files with 136 additions and 43 deletions
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6
src/enc/config.c
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@@ -58,11 +58,13 @@ int WebPConfigInitInternal(WebPConfig* config,
config->sns_strength = 80;
config->filter_sharpness = 4;
config->filter_strength = 35;
config->preprocessing &= ~2; // no dithering
break;
case WEBP_PRESET_PHOTO:
config->sns_strength = 80;
config->filter_sharpness = 3;
config->filter_strength = 30;
config->preprocessing |= 2;
break;
case WEBP_PRESET_DRAWING:
config->sns_strength = 25;
@@ -72,10 +74,12 @@ int WebPConfigInitInternal(WebPConfig* config,
case WEBP_PRESET_ICON:
config->sns_strength = 0;
config->filter_strength = 0; // disable filtering to retain sharpness
config->preprocessing &= ~2; // no dithering
break;
case WEBP_PRESET_TEXT:
config->sns_strength = 0;
config->filter_strength = 0; // disable filtering to retain sharpness
config->preprocessing &= ~2; // no dithering
config->segments = 2;
break;
case WEBP_PRESET_DEFAULT:
@@ -111,7 +115,7 @@ int WebPValidateConfig(const WebPConfig* config) {
return 0;
if (config->show_compressed < 0 || config->show_compressed > 1)
return 0;
if (config->preprocessing < 0 || config->preprocessing > 1)
if (config->preprocessing < 0 || config->preprocessing > 3)
return 0;
if (config->partitions < 0 || config->partitions > 3)
return 0;