Brightness indention: a novel compression mechanism in the luminance-brightness mapping.

In a previous study, Schouten and Blommaert (1995) explicitly showed that brightness constancy implies a substantial compression in the luminance-brightness mapping. Here it is argued that additional compression mechanisms are required for scenes with large luminance ranges. To trace these, a series of experiments was conducted which involved expansion of the luminance range. We used a simple spatial configuration consisting of a disk on a contourless homogeneous surround (Ganzfeld). The contrast between the disk and Ganzfeld acted as the independent variable, while the size of the disk was parametrically varied. Sequential dichoptical brightness matches with a reference were carried out for both the disk and the surround. The results reveal a compression mechanism which we term brightness indention. This indention, which has not previously been reported in the literature, only occurs if the Ganzfeld is less luminous than the disk, and it takes the form of a brightness decrease of the immediate surroundings of the disk.