shader tweak for LUT application

README.md

@@ -256,3 +256,5 @@ If neither variable is set, the workflow falls back to the repo-local defaults u
 - better shader search UI
 - LUT applicator
 - More comprehensive greenscreen shader
+- 16bit float render target, linear compositing?
+- add 10bit output path decklink

shaders/lut-apply/shader.json

@@ -1,7 +1,7 @@
 {
   "id": "lut-apply",
   "name": "3D LUT Apply",
-  "description": "Applies the packaged 33-point .cube LUT to the incoming video using trilinear interpolation.",
+  "description": "Applies the packaged 33-point .cube LUT to the incoming video using tetrahedral interpolation and optional output dithering.",
   "category": "Color",
   "entryPoint": "shadeVideo",
   "textures": [
@@ -38,6 +38,15 @@
       "max": 2.0,
       "step": 0.01
     },
+    {
+      "id": "ditherAmount",
+      "label": "Output Dither",
+      "type": "float",
+      "default": 0.5,
+      "min": 0.0,
+      "max": 1.0,
+      "step": 0.01
+    },
     {
       "id": "clampInput",
       "label": "Clamp Input",

shaders/lut-apply/shader.slang

@@ -30,13 +30,35 @@ float3 applyLut33(float3 color)
     float3 c011 = sampleLutCell(float3(baseIndex.r, nextIndex.g, nextIndex.b));
     float3 c111 = sampleLutCell(float3(nextIndex.r, nextIndex.g, nextIndex.b));
 
-    float3 c00 = lerp(c000, c100, blend.r);
-    float3 c10 = lerp(c010, c110, blend.r);
-    float3 c01 = lerp(c001, c101, blend.r);
-    float3 c11 = lerp(c011, c111, blend.r);
-    float3 c0 = lerp(c00, c10, blend.g);
-    float3 c1 = lerp(c01, c11, blend.g);
-    return lerp(c0, c1, blend.b);
+    if (blend.r > blend.g)
+    {
+        if (blend.g > blend.b)
+            return c000 + blend.r * (c100 - c000) + blend.g * (c110 - c100) + blend.b * (c111 - c110);
+        if (blend.r > blend.b)
+            return c000 + blend.r * (c100 - c000) + blend.b * (c101 - c100) + blend.g * (c111 - c101);
+        return c000 + blend.b * (c001 - c000) + blend.r * (c101 - c001) + blend.g * (c111 - c101);
+    }
+
+    if (blend.b > blend.g)
+        return c000 + blend.b * (c001 - c000) + blend.g * (c011 - c001) + blend.r * (c111 - c011);
+    if (blend.b > blend.r)
+        return c000 + blend.g * (c010 - c000) + blend.b * (c011 - c010) + blend.r * (c111 - c011);
+    return c000 + blend.g * (c010 - c000) + blend.r * (c110 - c010) + blend.b * (c111 - c110);
+}
+
+float hash12(float2 value)
+{
+    float3 p = frac(float3(value.xyx) * 0.1031);
+    p += dot(p, p.yzx + 33.33);
+    return frac((p.x + p.y) * p.z);
+}
+
+float3 outputDither(float2 pixel)
+{
+    float r = hash12(pixel + float2(17.0, 31.0)) - hash12(pixel + float2(83.0, 47.0));
+    float g = hash12(pixel + float2(29.0, 71.0)) - hash12(pixel + float2(53.0, 19.0));
+    float b = hash12(pixel + float2(61.0, 11.0)) - hash12(pixel + float2(7.0, 97.0));
+    return float3(r, g, b) / 255.0;
 }
 
 float4 shadeVideo(ShaderContext context)
@@ -49,6 +71,7 @@ float4 shadeVideo(ShaderContext context)
     float3 lutColor = applyLut33(inputColor);
     float3 graded = lerp(inputColor, lutColor, lutStrength);
     graded = (graded - 0.5) * postContrast + 0.5;
+    graded += outputDither(context.uv * context.outputResolution) * ditherAmount;
 
     return float4(saturate(graded), source.a);
 }