Page 117 - Computational Colour Science Using MATLAB

104 CHROMATIC-ADAPTATION TRANSFORMS AND COLOUR APPEARANCE

Table 6.3 Data for testing implementations of CMCCAT2000. Tristimulus values (XYZ)
under illuminant A are shown for four Munsell surfaces with the corresponding values
(X C Y C Z C ) for illuminant D65 for the 1964 standard observer. The parameters L T , L W and F
are fixed at 100, 100, and 1, respectively
X 34.1827 52.1707 11.9082 43.4214
Y 39.2556 35.6248 11.3118 43.2444
Z 14.8082 2.0716 12.0749 4.1055
D 0.9441 0.9441 0.9441 0.9441
29.7512 41.6879 12.7603 33.9602
X C
40.3041 33.5491 11.9818 42.8973
Y C
43.2750 7.5182 34.3499 13.5004
Z C
The samples that were used to test CMCCAT97 (Table 6.2) have also been used
to test CMCCAT2000 (Table 6.3) for comparison.

6.4.2 Computing colour appearance

The forward mode of the CIECAM97s CAM has been implemented by the
function ciecam97s. The format for this function is

[j,c,h,m,hq,s,q,cd] = ciecam97s(xyz,xyzw,la,yb,p),

where xyz and xyzw are 361 column matrices containing the tristimulus values
of the colour stimulus and the adopted white, respectively, under the test
illuminant, la is the luminance of the achromatic background in units of cd/m ,
2
yb is the Y value of achromatic background, and the parameter p is a 461
column matrix containing the four surround parameters F, c, F and N . The
LL C
ciecam97s function outputs eight variables. The first seven variables correspond
to the lightness (j), chroma (c), hue quadrature (hq), colourfulness (m), hue
angle (h), Saturation (s) and brightness (q) of the colour stimulus under the
reference illuminant. The eighth output parameter, cd, is a string that contains
the colour descriptor.

Box 17: ciecam97s.m

function [j,c,hq,m,h,s,q,cd] = ciecam97s(xyz,xyzw,
la,yb,para)

% function [j,c,hq,m,h,s,q,cd] = ciecam97s(xyz,xyzw,
% la,yb,para)