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
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@ -115,9 +115,20 @@ vec4 curvemapping_evaluate_premulRGBF(vec4 col)
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return result;
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}
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/* Using a triangle distribution which gives a more final uniform noise.
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* See Banding in Games:A Noisy Rant(revision 5) Mikkel Gjøl, Playdead (slide 27) */
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/* GPUs are rounding before writting to framebuffer so we center the distribution around 0.0. */
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/* Return triangle noise in [-1..1[ range */
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float dither_random_value(vec2 co)
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{
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return fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453) * 0.005 * dither;
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/* Original code from https://www.shadertoy.com/view/4t2SDh */
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/* Uniform noise in [0..1[ range */
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float nrnd0 = fract(sin(dot(co.xy, vec2(12.9898, 78.233))) * 43758.5453);
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/* Convert uniform distribution into triangle-shaped distribution. */
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float orig = nrnd0 * 2.0 - 1.0;
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nrnd0 = orig * inversesqrt(abs(orig));
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nrnd0 = max(-1.0, nrnd0); /* Removes nan's */
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return nrnd0 - sign(orig);
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}
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vec2 round_to_pixel(sampler2D tex, vec2 uv)
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@ -128,7 +139,7 @@ vec2 round_to_pixel(sampler2D tex, vec2 uv)
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vec4 apply_dither(vec4 col, vec2 uv)
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{
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col.rgb += dither_random_value(uv);
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col.rgb += dither_random_value(uv) * 0.0033 * dither;
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return col;
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}
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@ -151,10 +162,6 @@ vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
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col = OCIO_to_display_linear_with_look(col, lut3d_texture);
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if (dither > 0.0) {
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col = apply_dither(col, noise_uv);
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}
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if (overlay) {
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col *= 1.0 - col_overlay.a;
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col += col_overlay; /* Assumed unassociated alpha. */
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@ -162,6 +169,10 @@ vec4 OCIO_ProcessColor(vec4 col, vec4 col_overlay, vec2 noise_uv)
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col = OCIO_to_display_encoded(col, lut3d_display_texture);
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if (dither > 0.0) {
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col = apply_dither(col, noise_uv);
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}
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return col;
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}
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@ -317,19 +317,27 @@ MINLINE int compare_rgb_uchar(const unsigned char col_a[3],
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return 0;
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}
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/* Using a triangle distribution which gives a more final uniform noise.
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* See Banding in Games:A Noisy Rant(revision 5) Mikkel Gjøl, Playdead (slide 27) */
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/* Return triangle noise in [-0.5..1.5[ range */
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MINLINE float dither_random_value(float s, float t)
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{
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static float vec[2] = {12.9898f, 78.233f};
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float value;
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value = sinf(s * vec[0] + t * vec[1]) * 43758.5453f;
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return value - floorf(value);
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/* Original code from https://www.shadertoy.com/view/4t2SDh */
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/* The nois reshaping technique does not work on CPU.
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* We generate and merge two distribution instead */
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/* Uniform noise in [0..1[ range */
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float nrnd0 = sinf(s * 12.9898f + t * 78.233f) * 43758.5453f;
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float nrnd1 = sinf(s * 19.9898f + t * 119.233f) * 43798.5453f;
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nrnd0 -= floorf(nrnd0);
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nrnd1 -= floorf(nrnd1);
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/* Convert uniform distribution into triangle-shaped distribution. */
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return nrnd0 + nrnd1 - 0.5f;
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}
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MINLINE void float_to_byte_dither_v3(
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unsigned char b[3], const float f[3], float dither, float s, float t)
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{
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float dither_value = dither_random_value(s, t) * 0.005f * dither;
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float dither_value = dither_random_value(s, t) * 0.0033f * dither;
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b[0] = unit_float_to_uchar_clamp(dither_value + f[0]);
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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(
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uchar b[4], const unsigned short us[4], DitherContext *di, float s, float t)
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{
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#define USHORTTOFLOAT(val) ((float)val / 65535.0f)
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float dither_value = dither_random_value(s, t) * 0.005f * di->dither;
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float dither_value = dither_random_value(s, t) * 0.0033f * di->dither;
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b[0] = ftochar(dither_value + USHORTTOFLOAT(us[0]));
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b[1] = ftochar(dither_value + USHORTTOFLOAT(us[1]));
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@ -88,7 +88,7 @@ MINLINE void ushort_to_byte_dither_v4(
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MINLINE void float_to_byte_dither_v4(
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uchar b[4], const float f[4], DitherContext *di, float s, float t)
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{
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float dither_value = dither_random_value(s, t) * 0.005f * di->dither;
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float dither_value = dither_random_value(s, t) * 0.0033f * di->dither;
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b[0] = ftochar(dither_value + f[0]);
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b[1] = ftochar(dither_value + f[1]);
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@ -5683,7 +5683,8 @@ static void rna_def_scene_render_data(BlenderRNA *brna)
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prop = RNA_def_property(srna, "dither_intensity", PROP_FLOAT, PROP_NONE);
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RNA_def_property_float_sdna(prop, NULL, "dither_intensity");
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RNA_def_property_range(prop, 0.0f, 2.0f);
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RNA_def_property_range(prop, 0.0, FLT_MAX);
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RNA_def_property_ui_range(prop, 0.0, 2.0, 0.1, 2);
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RNA_def_property_ui_text(
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prop,
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"Dither Intensity",
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