Land's Retinex theory

The assumptions of the Retinex theory:

• The visual system performs the same computation in each of 3 independent color channels. The absorbance profiles of the four types of photoreceptors in the human retina (3 types of cones and one type of rods) are illustrated here.
• In each channel, the intensity signal I is proportional to the product of illumination s and surface reflectance r:

  

• The illumination has no specular components, and the color channels have been chosen properly.

Hint: use the information around intensity edges.