text: ///////////////////////////////////////////////////////////////////////////
  //
  // Copyright (c) 2003, Industrial Light & Magic, a division of Lucas
  // Digital Ltd. LLC
  // 
  // All rights reserved.
  // 
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
  // met:
  // *       Redistributions of source code must retain the above copyright
  // notice, this list of conditions and the following disclaimer.
  // *       Redistributions in binary form must reproduce the above
  // copyright notice, this list of conditions and the following disclaimer
  // in the documentation and/or other materials provided with the
  // distribution.
  // *       Neither the name of Industrial Light & Magic nor the names of
  // its contributors may be used to endorse or promote products derived
  // from this software without specific prior written permission. 
  // 
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  //
  ///////////////////////////////////////////////////////////////////////////
  
  
  //-----------------------------------------------------------------------------
  //
  //	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
  