Retinex Land's model simulates human colour vision - Applying Retinex to GIF images to equalise colours.

Left: the original image; right: the transformed image.

The original image is an 8 bit GIF picture (80K), the transformed is 24 bit SGI (400K)

Applying Retinex to special patterns simulates colour illusion effects.

Josef Albers has explored some visual illusions due to colour contrast.

The first couple of images are taken from the cover of the paperback edition of Albers book: Interaction of Colours. The small brown square on the upper half seems to have a different saturation from the lower one.

The second couple of images is another Albers' original example of a smooth changing green pattern with a surrounding lighter grey cross: the visual illusions (see left) makes the grey cross to appear as non uniform.

The right hand images confirm the illusion: you can check by testing the HSV value.

See:
- Marini D. Rizzi A. "Colour Constancy and Optical Illusions: a computer simulation with Retinex Theory", 7th ICIAP, Bari (1993)
- Marini D.,Marini L. & Rizzi A. "Towards a Computational Model of Colour Perception", Internal Report, DSI-Unimi (1995)
- Marini D., Marini L. "A computational model for quantification of colour perception and its heuristic role in colour study", The Trieste Symposium on Perception and Cognition, Trieste, October (1995)
- Marini D., Rizzi A., Carati C., "Color constancy effects measurements of the Retinex Theory",Proc. SPIE EI-99, San Jose (1999)A. Rizzi, C. Gatta, D. Marini, Experiments on new contrast patterns, ECVP 2001, Kusadasi, August 2001, Turkey