What Are Lightness Illusions and Why Do We See Them?
Figure 1
Synthetic “Dead-Leaves” Stimuli
(A) “Dead-leaves” example, composed of occluding circular disks with radius r and distribution 1/r3. The intensity of each “leaf” is independently drawn from a uniform distribution.
(B) Reflectance matrix (R), which represents a 20 × 20 subsection randomly chosen from the larger “dead-leaves” stimulus. Typically, between 40 and 60 “leaves” were at least partially visible in each reflectance map.
(C) The light falling on a typical surface will come from many sources, so we model illumination with a more gradual change across space than for reflection (see Methods for details). The example illumination matrix (I) shown here is a 20 × 20 section chosen from a similar map as R but with larger disks than with reflection maps, typically containing 10–15 leaves. These were then heavily blurred producing maps of typically 200–400 distinct levels of intensity, but with a high level of spatial correlation.
(D) Stimulus intensity matrix (S), which is the pixel-wise product of B and C: S = I × R. All the values are in the range 0…1.