ColorManagement: Dithering Improvement

- Unlock property range.
- Use triangular noise to keep perceptual noise error more uniform.
  Remap range to preserve perceptual intensity.
- Center noise distribution around 0 for GPU implementation because of
  rounding.
- Do dithering after merging overlays.

Effect of using triangular noise is not really noticeable if you don't use
really low bitdepth. But doing a test in the shader were we artificially
reduce the bitdepth (`col = (col * 16) / 16;`) reveals the real difference.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D6850

1 files changed, 2 insertions, 2 deletions

diff --git a/source/blender/imbuf/intern/divers.c b/source/blender/imbuf/intern/divers.c
index aa49453d68c..07bbec9e15c 100644
--- a/source/blender/imbuf/intern/divers.c
+++ b/source/blender/imbuf/intern/divers.c
@@ -75,7 +75,7 @@ MINLINE void ushort_to_byte_dither_v4(
     uchar b[4], const unsigned short us[4], DitherContext *di, float s, float t)
 {
 #define USHORTTOFLOAT(val) ((float)val / 65535.0f)
-  float dither_value = dither_random_value(s, t) * 0.005f * di->dither;
+  float dither_value = dither_random_value(s, t) * 0.0033f * di->dither;
 
   b[0] = ftochar(dither_value + USHORTTOFLOAT(us[0]));
   b[1] = ftochar(dither_value + USHORTTOFLOAT(us[1]));
@@ -88,7 +88,7 @@ MINLINE void ushort_to_byte_dither_v4(
 MINLINE void float_to_byte_dither_v4(
     uchar b[4], const float f[4], DitherContext *di, float s, float t)
 {
-  float dither_value = dither_random_value(s, t) * 0.005f * di->dither;
+  float dither_value = dither_random_value(s, t) * 0.0033f * di->dither;
 
   b[0] = ftochar(dither_value + f[0]);
   b[1] = ftochar(dither_value + f[1]);