Effect of Spatial-Frequency Distribution on Brightness Perception in Light Environment

Abstract

We conducted a psychophysical experiment using pictures of a light environment as image stimuli. Brightness perception in light environment depends on not only the illumination or mean luminance but also the luminance distribution of the scene. We analyzed the data from the viewpoint of spatial-frequency information processing to estimate the effects of non-uniform luminance distribution on brightness perception. We modified still pictures of scenes of a room (reference images) using two-dimensional frequency analysis. Lowpass-filtering and contrast-gain control operations in the spatial-frequency dimension provided the test images. By adjusting the brightness of the reference images to that of the test images, we derived equi-brightness pairs of the reference and test images. The results showed that even though the mean luminance values of the two images (reference and test stimuli) were equal, the brightness of the lower contrast image was substantially lower and that of the lowpass-filtered image was slightly lower. This suggests that all spatial-frequency channels affect brightness perception and that low spatial-frequency components of non-uniform images are critical factors for increasing brightness.