Described is a method for processing image data to determine if a portion of the imaged environment is exposed to high illumination, such as sunlight. In some implementations, image data from multiple different imaging devices may be processed to produce for each imaging device a respective illumination mask that identifies pixels that represent a portion of the environment that is exposed to high illumination. Overlapping portions of those illumination masks may then be combined to produce a unified illumination map of an area of the environment. The unified illumination map identifies, for different portions of the environment, a probability that the portion is actually exposed to high illumination.