% convertRGB.m - obsolete - see rgb2lms.m
%
% Takes a vector of RGB numbers and calculates CIE XYZ and Yxy coordinates,
% as well as approximate LMS and MacLeod-Boynton Yrb coordinates.
%
% RGB numbers must be in the range 0->255.
% *** Requires a linearized (gamma corrected) monitor. Results are grossly inaccurate without it. ***
%
% Uses Sony Trinitron XYZ coodinates from a Sony monitor driver color profile (www.sony.com).
%
% Assumes:
% - no color temperature adjustments by video card or monitor
% - no color management by application used to display RGB image
% - accurate phosphor chromaticity coordinates
% - no interaction between phosphors
% Conversion to LMS and Yrb uses estimates of chromaticity coordinates of cone primaries by
% Smith & Pokorny (1975) (accurate?), and arbitrary normalization so that L+M is luminance and S/(L+M)
% is equal 1.0 for a 400nm spectral stimulus. See Y. Nakano's color vision math tutorial
% in Kaiser & Boynton's COLOR VISION.
%
% maximum luminance is at Y = 1
% equal-energy white ends up at LMS = Y * [0.6654 0.3346 0.0161],
%                            or  rb = [0.6654 0.0161]
%
% 1/6/2001 rdb  Wrote it.
% 12/14/2001 rdb Changed yourXYZ calculation to simple weighting of phosphor XYZ coordinates
%                Corrected error in Yrb calculation b=S/(L+M), not M/(L+M)
%
maxRGB = 255;

yourRGB=input('Enter an RGB vector, e.g. [255 128 128]: ');
yourRGB = yourRGB./maxRGB;

% Sony Trinitron phosphor XYZ coordinates
rXYZ = [0.390503 0.209930 0.012619];
gXYZ = [0.31950 0.676605 0.078995];
bXYZ = [0.254196 0.113449 0.733276];
% whitepoint
wXYZ = rXYZ + gXYZ + bXYZ;
wYxy = [wXYZ(2) wXYZ(1)./(wXYZ(1)+wXYZ(2)+wXYZ(3)) wXYZ(2)./(wXYZ(1)+wXYZ(2)+wXYZ(3))]

% phosphor chromaticity coordinates
xr = rXYZ(1) ./ (rXYZ(1) + rXYZ(2) + rXYZ(3));
yr = rXYZ(2) ./ (rXYZ(1) + rXYZ(2) + rXYZ(3));
zr = rXYZ(3) ./ (rXYZ(1) + rXYZ(2) + rXYZ(3));
xg = gXYZ(1) ./ (gXYZ(1) + gXYZ(2) + gXYZ(3));
yg = gXYZ(2) ./ (gXYZ(1) + gXYZ(2) + gXYZ(3));
zg = gXYZ(3) ./ (gXYZ(1) + gXYZ(2) + gXYZ(3));
xb = bXYZ(1) ./ (bXYZ(1) + bXYZ(2) + bXYZ(3));
yb = bXYZ(2) ./ (bXYZ(1) + bXYZ(2) + bXYZ(3));
zb = bXYZ(3) ./ (bXYZ(1) + bXYZ(2) + bXYZ(3));

% from Kaiser & Boynton:
RGBXYZ = [[xr./yr xg./yg xb./yb]              % phosphor coordinate (RGB) to XYZ conversion matrix
          [1      1      1     ]
          [zr./yr zg./yg zb./yb]];
k = [[0.2535 0       0      ]                 % arbitrary scaling
     [0      -0.4000 0      ]
     [0      0       0.01327]];
SP75 = [[0.7465 1.4000  0.1748]               % Smith and Pokorny (1975) copunctual points for dichromats
        [0.2535 -0.4000 0.0000]
        [0.0000 0.0000  0.8252]];
XYZLMS = k * inv(SP75);                       % XYZ to LMS conversion matrix

% using Sony Trinitron phosphor coordinates:
yourXYZ = RGB(1).* rXYZ + RGB(2).* gXYZ + RGB(3).* bXYZ;

% conversions
XYZ = yourXYZ;
Yxy = [XYZ(2) XYZ(1)./(XYZ(1)+XYZ(2)+XYZ(3)) XYZ(2)./(XYZ(1)+XYZ(2)+XYZ(3))]
LMS = XYZLMS * XYZ
Yrb = [LMS(1)+LMS(2) LMS(1)./(LMS(1)+LMS(2)) LMS(3)./(LMS(1)+LMS(2))]