Stimulus examples used in the image analysis.

The bumpy surfaces were rendered using the BRDFs in the MERL database (100 BRDFs). The left panel shows the images rendered under a point light source with a slant of 0°, and the right panel shows the images rendered under an HDR environment map. Each panel includes 100 images rendered with different BRDFs. The same geometry is used for the rendered images in the left and right panels. From each rendered image, the direction and the magnitude maps of the intensity gradient were computed.