An intra-oral optical scanning method for intra-oral optical scanning including projecting a pattern, the pattern including at least a first area illuminated by a first color of light and a second area illuminated by a second color of light and at least one non-illuminated area onto an intra-oral feature, making a first image of the first area, the second area and the non-illuminated area differentiating between the first color of light and the second color of light in the first image of the projected pattern, and determining from the image of the non-illuminated area at least one of an ambient light level, a level of scattered light, a level of light absorption and a level of light reflected from at least one of the first area and the second area. Related apparatus and methods are also described.