All of the wedge shaped sectors in the Kanizsa figures in the top figure (above red line) are identical; the same is true for the bottom figure (although they are darker than the top figure). When the two images on the left are cross fused (or right two images divergently fused), a strong lightness and opacity covariation is observed. In the image on the top left, the diamond looks relatively opaque and very light, while the corresponding segments in the figure on the lower top-left appear almost completely transparent but quite dark. On the bottom figure, the pattern inverts: the top left figure looks wispy and light, and the bottom left figure looks relatively opaque and dark. Lightess illusions can also be experienced in the reverse depth configuration (right two columns cross fused), but the difference in the pair of images is smaller. A brief description of these results can be found here, and a more detailed account in my 1997 Perception article (sorry, no pdfs, see publications page).