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
This commit is contained in:
Clément Foucault 2020-02-17 14:14:30 +01:00
parent 5231d06d4c
commit 852cdd476b
Notes: blender-bot 2023-02-14 08:42:53 +01:00
Referenced by issue #78056, Increased Sampling Noise when Rendering the World Background in Cycles.
Referenced by issue #73834, Rendering a scene without light: result is not completely black
4 changed files with 35 additions and 15 deletions

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@ -115,9 +115,20 @@ vec4 curvemapping_evaluate_premulRGBF(vec4 col)
return result;
}
/* Using a triangle distribution which gives a more final uniform noise.
* See Banding in Games:A Noisy Rant(revision 5) Mikkel Gjøl, Playdead (slide 27) */
/* GPUs are rounding before writting to framebuffer so we center the distribution around 0.0. */
/* Return triangle noise in [-1..1[ range */
float dither_random_value(vec2 co)
{
return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453) * 0.005 * dither;
/* Original code from https://www.shadertoy.com/view/4t2SDh */
/* Uniform noise in [0..1[ range */
float nrnd0 = fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453);
/* Convert uniform distribution into triangle-shaped distribution. */
float orig = nrnd0 * 2.0 - 1.0;
nrnd0 = orig * inversesqrt(abs(orig));
nrnd0 = max(-1.0, nrnd0); /* Removes nan's */
return nrnd0 - sign(orig);
}
vec2 round_to_pixel(sampler2D tex, vec2 uv)
@ -128,7 +139,7 @@ vec2 round_to_pixel(sampler2D tex, vec2 uv)
vec4 apply_dither(vec4 col, vec2 uv)
{
col.rgb += dither_random_value(uv);
col.rgb += dither_random_value(uv) * 0.0033 * dither;
return col;
}
@ -151,10 +162,6 @@ vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
col = OCIO_to_display_linear_with_look(col, lut3d_texture);
if (dither > 0.0) {
col = apply_dither(col, noise_uv);
}
if (overlay) {
col *= 1.0 - col_overlay.a;
col += col_overlay; /* Assumed unassociated alpha. */
@ -162,6 +169,10 @@ vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
col = OCIO_to_display_encoded(col, lut3d_display_texture);
if (dither > 0.0) {
col = apply_dither(col, noise_uv);
}
return col;
}

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@ -317,19 +317,27 @@ MINLINE int compare_rgb_uchar(const unsigned char col_a[3],
return 0;
}
/* Using a triangle distribution which gives a more final uniform noise.
* See Banding in Games:A Noisy Rant(revision 5) Mikkel Gjøl, Playdead (slide 27) */
/* Return triangle noise in [-0.5..1.5[ range */
MINLINE float dither_random_value(float s, float t)
{
static float vec[2] = {12.9898f, 78.233f};
float value;
value = sinf(s * vec[0] + t * vec[1]) * 43758.5453f;
return value - floorf(value);
/* Original code from https://www.shadertoy.com/view/4t2SDh */
/* The nois reshaping technique does not work on CPU.
* We generate and merge two distribution instead */
/* Uniform noise in [0..1[ range */
float nrnd0 = sinf(s * 12.9898f + t * 78.233f) * 43758.5453f;
float nrnd1 = sinf(s * 19.9898f + t * 119.233f) * 43798.5453f;
nrnd0 -= floorf(nrnd0);
nrnd1 -= floorf(nrnd1);
/* Convert uniform distribution into triangle-shaped distribution. */
return nrnd0 + nrnd1 - 0.5f;
}
MINLINE void float_to_byte_dither_v3(
unsigned char b[3], const float f[3], float dither, float s, float t)
{
float dither_value = dither_random_value(s, t) * 0.005f * dither;
float dither_value = dither_random_value(s, t) * 0.0033f * dither;
b[0] = unit_float_to_uchar_clamp(dither_value + f[0]);
b[1] = unit_float_to_uchar_clamp(dither_value + f[1]);

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@ -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]);

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@ -5683,7 +5683,8 @@ static void rna_def_scene_render_data(BlenderRNA *brna)
prop = RNA_def_property(srna, "dither_intensity", PROP_FLOAT, PROP_NONE);
RNA_def_property_float_sdna(prop, NULL, "dither_intensity");
RNA_def_property_range(prop, 0.0f, 2.0f);
RNA_def_property_range(prop, 0.0, FLT_MAX);
RNA_def_property_ui_range(prop, 0.0, 2.0, 0.1, 2);
RNA_def_property_ui_text(
prop,
"Dither Intensity",