In order to study the perceptual scaling of chroma, perceived chroma-differences of colour chips are subjectively estimated by means of ratio estimation method under standard illuminant A and daylight D
65.
The subjectively estimated values are compared with their colorimetric colour-differences in the CIE 1976
L*
u*
v* and
L*
a*
b* uniform colour spaces.
The set of calour chips used in the experiment consists of eight hues (5R, 5YR, 5Y, 7.5GY, 3.5G, 10BG, 2.5PB, and 5RP) with constant value 6, and chromas are from 0.3 to 13.7 at intervals of abaut 0.5 in the Munsell renotation system.
Results obtained are summarized as follows:
(1) Relative values of perceived colour-differences change little even when the illuminant changes from the daylight D
65 to the illuminant A, and the constancy of perceived colour-difference holds as well as in the case of hue-difference.
(2) Colorimetric chroma-differences in the
L*
u*
v* and
L*
a*
v* spaces generally do not change much when the illuminant is changed.
But, because of the insufficient compensation for chromatic adaptation, those for colours of 3.5G in both spaces change slightly.
(3) Except for colours of 5 Y and 3.5G, relative values of perceived colour-differences to colorimetric ones tend to become small generally with the increase in saturation.
(4) For colours of 5Y and 7.5GY, the correlation between perceived colour-differences and colorimetric ones is slightly low in both colour spaces irrespective of the illuminant.
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