Add perceptual color distance function.

src/nvimage/CMakeLists.txt

@@ -2,29 +2,18 @@ PROJECT(nvimage)
 
 SET(IMAGE_SRCS	
     nvimage.h
-    FloatImage.h 
-    FloatImage.cpp
-    Filter.h
-    Filter.cpp
-    Image.h
-    Image.cpp
-    ImageIO.h
-    ImageIO.cpp
-    ColorBlock.h
-    ColorBlock.cpp
-    BlockDXT.h
-    BlockDXT.cpp
-    DirectDrawSurface.h
-    DirectDrawSurface.cpp
-    Quantize.h
-    Quantize.cpp
-    NormalMap.h
-    NormalMap.cpp
-    PsdFile.h
-    TgaFile.h
+    BlockDXT.h BlockDXT.cpp
+    ColorBlock.h ColorBlock.cpp
+    DirectDrawSurface.h DirectDrawSurface.cpp
+    Filter.h Filter.cpp
+    FloatImage.h FloatImage.cpp
+    Image.h Image.cpp
+    ImageIO.h ImageIO.cpp
+    NormalMap.h NormalMap.cpp
     PixelFormat.h
-    ColorSpace.h
-    ColorSpace.cpp)
+    PsdFile.h
+    Quantize.h Quantize.cpp
+    TgaFile.h)
 
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})
 

src/nvmath/Color.h

@@ -175,6 +175,16 @@ namespace nv
         return Vector4(c.r * scale, c.g * scale, c.b * scale, c.a * scale);
     }
 
+
+    inline float perceptualColorDistance(Vector3::Arg c0, Vector3::Arg c1)
+    {
+        float rmean = (c0.r + c1.r) * 0.5f;
+        float r = c1.r - c0.r;
+        float g = c1.g - c0.g;
+        float b = c1.b - c0.b;
+        return sqrtf((2 + rmean)*r*r + 4*g*g + (3 - rmean)*b*b);
+    }
+
 } // nv namespace
 
 #endif // NV_MATH_COLOR_H

src/nvtt/CompressionOptions.cpp

@@ -86,7 +86,7 @@ void CompressionOptions::setQuality(Quality quality)
 
 
 /// Set the weights of each color channel. 
-/// The choice for these values is subjective. In many case uniform color weights 
+/// The choice for these values is subjective. In most cases uniform color weights
 /// (1.0, 1.0, 1.0) work very well. A popular choice is to use the NTSC luma encoding 
 /// weights (0.2126, 0.7152, 0.0722), but I think that blue contributes to our 
 /// perception more than a 7%. A better choice in my opinion is (3, 4, 2).