Abstract: An image processing technique in which illumination effects are reduced by subtraction of spatially weighted masks which are formed substantially simultaneously on an analog smoothing grid. Haloing are reduced by using a mask whose spatial weighting is non-linear at the boundary of image segments whose intensities differ by more than would be predicted by the Rule of Twenty which predicts that the ratio of naturally found reflectances seldom exceeds a factor of twenty. A color image is processed by forming differently scaled masks, each of which is related to a spectral component of the original image. The masks are subtracted from the image to form a composite image. The saturation level in each smoothing grid is selected to minimize adverse effects of illumination in that spectral component by causing segmentation of image areas whose intensity differences exceed natural reflectance ratios. The transfer functions of each grid may also separately adjusted to enhance the composite image.