Integrate YCoCg color space conversion by Jim Tilander.

src/nvimage/CMakeLists.txt

@@ -25,7 +25,9 @@ SET(IMAGE_SRCS
 	NormalMipmap.h
 	NormalMipmap.cpp
 	PsdFile.h
-	TgaFile.h)
+	TgaFile.h
+	ColorSpace.h
+	ColorSpace.cpp)
 
 INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})
 

src/nvimage/ColorSpace.cpp

@@ -0,0 +1,66 @@
+#include "ColorSpace.h"
+#include <nvmath/Color.h>
+#include <nvimage/Image.h>
+#include <nvcore/nvcore.h>
+
+namespace nv
+{
+	void ColorSpace::RGBtoYCoCg_R(Image* img)
+	{
+		const uint w = img->width();
+		const uint h = img->height();
+		
+		for( uint y=0; y < h; y++ )
+		{
+			for( uint x=0; x < w; x++ )
+			{
+				Color32 pixel = img->pixel(x, y);
+				
+				const int r = pixel.r;
+				const int g = pixel.g;
+				const int b = pixel.b;
+				
+				const int Co = r - b;
+				const int t  = b + Co/2;
+				const int Cg = g - t;
+				const int Y  = t + Cg/2;
+				
+				// Just saturate the chroma here (we loose out of one bit in each channel)
+				// this just means that we won't have as high dynamic range. Perhaps a better option
+				// is to loose the least significant bit instead?
+				pixel.r = clamp(Co + 128, 0, 255);
+				pixel.g = clamp(Cg + 128, 0, 255);
+				pixel.b = 0;
+				pixel.a = Y;
+			}
+		}
+	}
+	
+	void ColorSpace::YCoCg_RtoRGB(Image* img)
+	{
+		const uint w = img->width();
+		const uint h = img->height();
+		
+		for( uint y=0; y < h; y++ )
+		{
+			for( uint x=0; x < w; x++ )
+			{
+				Color32 pixel = img->pixel(x, y);
+				
+				const int Co = (int)pixel.r - 128;
+				const int Cg = (int)pixel.g - 128;
+				const int Y  =      pixel.a;
+				
+				const int t = Y - Cg/2;
+				const int g = Cg + t;
+				const int b = t - Co/2;
+				const int r = b + Co;
+				
+				pixel.r = r;
+				pixel.g = g;
+				pixel.b = b;
+				pixel.a = 1;
+			}
+		}
+	}
+}

src/nvimage/ColorSpace.h

@@ -0,0 +1,20 @@
+
+#ifndef NV_IMAGE_COLORSPACE_H
+#define NV_IMAGE_COLORSPACE_H
+
+namespace nv 
+{
+	class Image;
+	
+	// Defines simple mappings between different color spaces and encodes them in the 
+	// input image.
+	namespace ColorSpace
+	{
+		void RGBtoYCoCg_R(Image* img);
+		void YCoCg_RtoRGB(Image* img);
+	}
+}
+
+
+
+#endif

src/nvtt/Compressor.cpp

@@ -34,6 +34,7 @@
 #include <nvimage/Filter.h>
 #include <nvimage/Quantize.h>
 #include <nvimage/NormalMap.h>
+#include <nvimage/ColorSpace.h>
 
 #include "Compressor.h"
 #include "InputOptions.h"
@@ -482,6 +483,17 @@ bool Compressor::Private::initMipmap(Mipmap & mipmap, const InputOptions::Privat
 		premultiplyAlphaMipmap(mipmap, inputOptions);
 	}
 
+	// Apply gamma space color transforms:
+	if (inputOptions.colorTransform == ColorTransform_YCoCg)
+	{
+		ColorSpace::RGBtoYCoCg_R(mipmap.asMutableFixedImage());
+	}
+	else if (inputOptions.colorTransform == ColorTransform_ScaledYCoCg)
+	{
+		// @@ TODO
+		//ColorSpace::RGBtoYCoCg_R(mipmap.asMutableFixedImage());
+	}
+
 	return true;
 }
 

src/nvtt/nvtt.h

@@ -156,8 +156,10 @@ namespace nvtt
 	enum ColorTransform
 	{
 		ColorTransform_None,
-		ColorTransform_Linear,
-		ColorTransform_Swizzle
+		ColorTransform_Linear,      ///< Not implemented.
+		ColorTransform_Swizzle,     ///< Not implemented.
+		ColorTransform_YCoCg,       ///< Transform into r=Co, g=Cg, b=0, a=Y
+		ColorTransform_ScaledYCoCg, ///< Not implemented.
 	};
 	
 	/// Extents rounding mode.