Abstract
When a row of five squares varying in reflectance from black to white is suspended in midair and illuminated by a spotlight, there is a dramatic compression in the perceived range of grays, with the black square appearing light middle gray. Prior work has shown that this compression is eliminated by a coplanar white border surrounding the five squares, but not by a coplanar black border, and that the compression varies inversely with the number of squares in the group, an effect called articulation. To test the effect of a non-coplanar but retinally adjacent background one group of 10 observers was presented with the five-square display against a white remote background while a separate group viewed the display against a black background. Unlike the pronounced effect of the coplanar white or black background, the luminance of the remote background had no effect on the amount of compression. In Experiment 2 we studied the role of articulation by asking whether it is the number of rectangles in the display that is crucial, or the number of different gray shades. A separate group of 11 observers was shown each of three Mondrian displays presented in the spotlight: (1) 4 rectangles of 4 gray shades, (2) 46 rectangles of 13 gray shades, and (3) 46 rectangles of 4 gray shades. The compression was substantially reduced with 46 rectangles, compared to 4, and the black target was seen as significantly darker (t(20)=2,38, p=0.027; t(20)=2.15; p=0.044. But number of gray shades made no difference. We conclude that gamut compression is strongly influenced by the surrounding luminance when it is coplanar with the test display but not when it is located in a far depth plane, and that the compression depends on the number of elements, but not the number of gray shades, in the display.
NSF: BCS0236701 NIH: BM60826-02