Statistical Separation of Objects in Shadows from Objects in Daylight in an Aerial Scene

Objects photographed in an aerial scene are ordered into frequency histograms in terms of log exposure on the film. A statistical analysis shows that each distribution actually contains two separate distributions; one of objects in daylight, the other of objects in shadows. The difference is due to a variation in apparent luminance of the objects. For example, as an asphalt road passes in and out of a shadow, its absolute reflectance doesn\u27t change but its apparent luminance does. It is also shown that the ratio of the derived shadow distribution to the daylight distribution is exactly the same as the ratio of skylight to daylight illumination