Abstract: A method is disclosed to separate the effect of the ambient lighting from the effects of surface reflectance to better analyze the surface properties of materials. The method uses the data sensed by N+1 sensor classes to define a finite dimensional approximation of a surface reflectance function at each image point, and a finite dimensional approximation of the ambient light.The ambient light reflected from a surface will cause a strength of response in the k.sup.th class of sensor, at position x, according to the formula.rho..sub.k.sup.x =.intg.E(.lambda.)S.sup.x (.lambda.)R.sub.k (.lambda.)d.lambda.We assume that there are P classes of sensor, and we represent the responses of all the sensors at location x by a vector,.rho..sup.x =(.rho..sub.1.sup.x . . . .rho..sup.x.sub.p)We use two approximating formulas, one to simplify the description of the ambient light and a second to simplify the description of the surface reflectance.