Measuring the Relationship between Perceived Image Contrast and Surround Illumination

While an image’s relative surround luminance increases from dark to light, the perceived contrast of the image will increase. For this reason, projected transparencies are made with higher physical contrast than reflection prints, which are intended to be viewed in an illuminated environment. Previous research shows that the surround effect is important for color appearance and device-independent imaging. An experiment was designed to investigate the effects of surround color and luminance on apparent image contrast. An LED illuminated lab was built to perform this experiment. Within the RGB 24-bit gamut of the LEDs, the surround color and luminance in this lab can be freely adjusted. The method of adjustment was used in this experiment. Results show general agreement with previous tone reproduction and lightness scaling research. However the surround effect on image contrast is not obvious for nonexpert observers. Because the perceived image contrast not only depends on the image luminance but also upon image spatial structure and the observer’s cognitive system, nonexpert observers might not notice the contrast changes caused by the surround effect when the images have complicated spatial structure and “flat” contrast.