libobs,obs-filters: Align HDR to SDR disparity

Adjust colors from BT.1886 to sRGB.

libobs/data/color.effect

@@ -42,14 +42,12 @@ float3 rec2020_to_rec709(float3 v)
 	return float3(r, g, b);
 }
 
-float reinhard_channel(float x)
-{
-	return x / (x + 1.);
-}
-
 float3 reinhard(float3 rgb)
 {
-	return float3(reinhard_channel(rgb.r), reinhard_channel(rgb.g), reinhard_channel(rgb.b));
+	rgb /= rgb + float3(1., 1., 1.);
+	rgb = pow(rgb, float3(1. / 2.4, 1. / 2.4, 1. / 2.4));
+	rgb = srgb_nonlinear_to_linear(rgb);
+	return rgb;
 }
 
 float linear_to_st2084_channel(float x)

plugins/obs-filters/data/color.effect

@@ -8,6 +8,16 @@ float3 srgb_linear_to_nonlinear(float3 v)
 	return float3(srgb_linear_to_nonlinear_channel(v.r), srgb_linear_to_nonlinear_channel(v.g), srgb_linear_to_nonlinear_channel(v.b));
 }
 
+float srgb_nonlinear_to_linear_channel(float u)
+{
+	return (u <= 0.04045) ? (u / 12.92) : pow((u + 0.055) / 1.055, 2.4);
+}
+
+float3 srgb_nonlinear_to_linear(float3 v)
+{
+	return float3(srgb_nonlinear_to_linear_channel(v.r), srgb_nonlinear_to_linear_channel(v.g), srgb_nonlinear_to_linear_channel(v.b));
+}
+
 float3 rec709_to_rec2020(float3 v)
 {
 	float r = dot(v, float3(0.62740389593469903, 0.32928303837788370, 0.043313065687417225));
@@ -24,14 +34,12 @@ float3 rec2020_to_rec709(float3 v)
 	return float3(r, g, b);
 }
 
-float reinhard_channel(float x)
-{
-	return x / (x + 1.);
-}
-
 float3 reinhard(float3 rgb)
 {
-	return float3(reinhard_channel(rgb.r), reinhard_channel(rgb.g), reinhard_channel(rgb.b));
+	rgb /= rgb + float3(1., 1., 1.);
+	rgb = pow(rgb, float3(1. / 2.4, 1. / 2.4, 1. / 2.4));
+	rgb = srgb_nonlinear_to_linear(rgb);
+	return rgb;
 }
 
 float linear_to_st2084_channel(float x)