Influence of area effect in color appearance at the pictorial image observation.

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"Area, effect of color" is the phenomenon that saturation and lightness of color appearance of a chromatic field will increase, as the area of the field becomes larger. The purpose of this research project is to understand characteristics of this area effect and investigate factors of the area effect of color.The first step we did in this research was "Quantification of Area Effect of Color." We exhibited a pair of chromatic fields in a single color as visual stimuli, those were equal colorimetrically, but area size was different. The observer adjusted a color of a small matching stimulus so that the color appearance of the matching stimulus became the same as a large test stimulus. As the result of matching task in each area size of test stimuli, we calculated the magnitude of area effect in lightness and saturation directions. In the result, increment of the lightness and saturation as the area effect was observed as expected. But we observed the dependency for hue in the area effect, and the area effect of red-green direction was stronger than blue direction.As the second step, we performed "examination of spatial characteristic of the area effect of color" to clarify factors of area effect. In this experiment, we divided the large test field to small color chips by dark lines. We performed the same experiment except using this stimulus. As the result, we found that the area effect decreased with the divided test stimulus. The hue dependency in the area effect observed in large test stimulus was also preserved, and the decline of the lightness and saturation increments was approximately proportional in all condition. It means that small color patches caught by fovea are insufficient to hold the area effect.It is required to perform the new experiment that will incorporate nonlinear space summation effect in modeling of the area effect in future.