///////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2003, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
//
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//
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///////////////////////////////////////////////////////////////////////////
//-----------------------------------------------------------------------------
//
// CIE (x,y) chromaticities, and conversions between
// RGB tiples and CIE XYZ tristimulus values.
//
//-----------------------------------------------------------------------------
#include <ImfChromaticities.h>
namespace Imf {
Chromaticities::Chromaticities (const Imath::V2f &red,
const Imath::V2f &green,
const Imath::V2f &blue,
const Imath::V2f &white)
:
red (red),
green (green),
blue (blue),
white (white)
{
// empty
}
Imath::M44f
RGBtoXYZ (const Chromaticities chroma, float Y)
{
//
// For an explanation of how the color conversion matrix is derived,
// see Roy Hall, "Illumination and Color in Computer Generated Imagery",
// Springer-Verlag, 1989, chapter 3, "Perceptual Response"; and
// Charles A. Poynton, "A Technical Introduction to Digital Video",
// John Wiley & Sons, 1996, chapter 7, "Color science for video".
//
//
// X and Z values of RGB value (1, 1, 1), or "white"
//
float X = chroma.white.x * Y / chroma.white.y;
float Z = (1 - chroma.white.x - chroma.white.y) * Y / chroma.white.y;
//
// Scale factors for matrix rows
//
float d = chroma.red.x * (chroma.blue.y - chroma.green.y) +
chroma.blue.x * (chroma.green.y - chroma.red.y) +
chroma.green.x * (chroma.red.y - chroma.blue.y);
float Sr = (X * (chroma.blue.y - chroma.green.y) -
chroma.green.x * (Y * (chroma.blue.y - 1) +
chroma.blue.y * (X + Z)) +
chroma.blue.x * (Y * (chroma.green.y - 1) +
chroma.green.y * (X + Z))) / d;
float Sg = (X * (chroma.red.y - chroma.blue.y) +
chroma.red.x * (Y * (chroma.blue.y - 1) +
chroma.blue.y * (X + Z)) -
chroma.blue.x * (Y * (chroma.red.y - 1) +
chroma.red.y * (X + Z))) / d;
float Sb = (X * (chroma.green.y - chroma.red.y) -
chroma.red.x * (Y * (chroma.green.y - 1) +
chroma.green.y * (X + Z)) +
chroma.green.x * (Y * (chroma.red.y - 1) +
chroma.red.y * (X + Z))) / d;
//
// Assemble the matrix
//
Imath::M44f M;
M[0][0] = Sr * chroma.red.x;
M[0][1] = Sr * chroma.red.y;
M[0][2] = Sr * (1 - chroma.red.x - chroma.red.y);
M[1][0] = Sg * chroma.green.x;
M[1][1] = Sg * chroma.green.y;
M[1][2] = Sg * (1 - chroma.green.x - chroma.green.y);
M[2][0] = Sb * chroma.blue.x;
M[2][1] = Sb * chroma.blue.y;
M[2][2] = Sb * (1 - chroma.blue.x - chroma.blue.y);
return M;
}
Imath::M44f
XYZtoRGB (const Chromaticities chroma, float Y)
{
return RGBtoXYZ (chroma, Y).inverse();
}
} // namespace Imf