colorTransformMatrix

Gateway routine that returns various color space transformation matrices

  result = colorTransformMatrix(matrixtype,spacetype)
 
 The routine returns a 3x3 color matrix, MAT, suitable for use with
 rgbLinearTransform, to convert an NxMx3 color image from one color
 space to another. 

 Suppose a point is represented by the row vector, p = [R,G,B].
 The matrix transforms each color point, p, to an output vector pT

 This routine works with colorTransformMatrix, which provides color transformation matrices
 so that the call

   T = colorTransformMatrix('lms2xyz');
   xyzImage = rgbLinearTransform(lmsImage,T)

 returns an NxMx3 xyz Image as expected

 matrixtypes are:
    'lms2opp' -- cone coordinate to opponent (Poirson & Wandell 1993)
    'opp2lms' -- inverse of the above matrix
    'xyz2opp' -- xyz to opponent (CIE1931 2 degree XYZ)
    'opp2xyz' -- inverse of the above matrix
    'hpeCones2xyz' -- Hunt-Pointer-Estevez transformation from cone
                 to XYZ, normalized for D65 (lms=[100 100 100] for D65).
    'xyz2hpeCones' -- inverse of hpeCones2xyz.
    'xyz2yiq' -- convert from XYZ to YIQ
    'yiq2xyz' -- inverse of the abvoe matrix
    'rgb2yuv' -- convert from RGB to YUV (YCbCr) for JPEG compression
    'yuv2rgb' -- inverse of the above matrix
    'xyz2srgb' -- from XYZ to sRGB values
    'srgb2xyz' -- inverse of the above matrix
             (the above are not dependent on device calibration)
    We added lrgb, which does the same as srgb, to be a little
    clearer about the fact that this matrix is really in linear (0,1) space,
    not in the framebuffer (0,255) nonlinear space.
    'xyz2lrgb' -- from XYZ to lRGB values
    'lrgb2xyz' -- inverse of the above matrix
    'cmy2rgb'  -- converts cyan, magenta, yellow to RGB

 Examples:
  A red stimulus
    p = [70,70,40]; chromaticity(p)
    T = colorTransformMatrixNew('xyz2lrgb')
    p*T

    (luminance, red-green, blue-yellow)
    T = colorTransformMatrixNew('xyz2opp')
    p*T

  Make an image of the XYZ matching functions:
    XYZ = vcReadSpectra('XYZ.mat',370:730); imXYZ = zeros(361,20,3);
    for ii=1:3, imXYZ(:,:,ii) = repmat(XYZ(:,ii),1,20); end
    T = colorTransformMatrix('xyz2srgb');
    imRGB = imageLinearTransform(imXYZ,T);
    imagescRGB(imRGB);

 Copyright ImagEval Consultants, LLC, 2003.