Table 4.1

Values of lightness for spectral colours

LA, cd/m2								White D65
	450	490	500	520	550	580	650
Y=10
20	22.53	24.33	24.80	25.48	26.74	28.69	32.21	28.24
50	22.43	24.39	24.86	25.55	26.82	28.78	32.32	28.32
100	22.31	24.43	24.91	25.61	26.88	28.85	32.42	28.39
200	22.21	24.47	24.97	25.67	26.96	28.94	32.53	28.47
Y=50
20	54.52	59.08	60.22	61.86	64.88	69.55	77.94	68.49
50	54.19	59.11	60.27	61.93	64.96	69.65	78.06	68.57
100	53.82	59.13	60.3	61.98	65.02	69.73	78.18	68.64
200	53.48	59.16	60.35	62.03	65.10	69.81	78.29	68.71
Y=100
20	79.50	86.31	87.97	90.36	94.75	101.52	113.63	100.00
50	78.92	86.27	87.95	90.00	94.75	101.53	113.64	100.00
100	78.30	86.22	87.92	90.35	94.76	101.54	113.68	100.00
200	77.72	86.17	87.90	90.34	94.76	101.55	113.70	100.00

It is seen from pictures and table, that:

• the change of adaptation luminance results in the perceptible changes of the perceived color, namely mainly lightness , colorfulness and hue in CAM02-UCS space, however, less than change of lightness , colorfulness and hue in CIECAM02 space;

• with increase of relative stimulus luminance dependence of colour variation on adaptation luminance carries stable character and changes with variation of , and this dependence is nonlinear.

Combined influence of surround and adapting luminance. On Figures 4.9‒4.18 the projections of chromaticity diagram are presented in CAM02-UCS space on the plane of coordinates . The figures demonstrate change of colour appearance depending on surround (dark, dim, average) and adapting lightness of for given stimulus luminance relative values Y.

As follows from figures, the change of surround may substantially influence on colour appearance, as it is visible from dependence of projection of chromaticity diagram on the plane of coordinates , and this influence shows up in a most degree at large stimulus luminance levels, and change of both colorfulness and perceived hue takes place.

These changes of colour appearance can be critical for video applications in that viewing conditions substantially differ on transmitting and receiving ends, that results in impairment of colour rendition.

General evaluation of colour appearance change

It is possible to give more complete quantitative evaluation of possible colour appearance changes with change of adapting luminance and surround, by evaluation of the change of chromaticity coordinates in CAM02-UCS space as distance between points on the plane of coordinates for different combinations of adapting luminance and of surround for the compared stimuli. Examples of quantitative evaluation of values of parameters and distance are presented an in Tables 4.2‒4.11.

In Table 4.2 the values of colorfulness of spectral color samples with given reference luminance for different adapting luminance levels are presented. The Table shows in what degree perceived colorfulness for different sample colours depends on .

The dependence of perceived colours on may be shown with use the criterion:

, (4/82)

where , , ‒ differences of coordinates of color space , , for adapting luminance levels and .

The values of are shown in the Table 4.3.