EFFECT OF LIGHT SCATTER ON HALF-TONE COLOR

The scattering of light within paper can affect the color of a halfton e image. Because of scattering, a photon may enter and emerge from the paper in different regions of the halftone microstructure. The micros tructure of a halftone print consists of a number of dots of ink of va rying color and size. The color of the halftone image is the partitive mixture of the colors of the microstructure-the colors of the dots, t he colors of the dot overlaps, and the color of the bare paper. In the present study the tristimulus values of the color of a halftone print are calculated in terms of the halftone microstructure. The analysis includes the effects of the scattering of light within the paper, an e ffect known as optical dot gain or the Yule-Nielsen effect. The tristi mulus values are expressed as the trace of the product of two matrices -one a matrix that expresses the different colors of the microstructur e that contribute to the partitive mixture and is a function of the in k transmittances and the paper reflectance and the other a matrix that expresses the amount of each color that contributes. The relative amo unt of each color is equal to the probability of the scattering proces s that gives rise to that color. These probabilities are calculated in terms of the dot shapes and sizes and in terms of the photon migratio n in the paper. As a result of the scattering, several ''new'' colors contribute to the partitive mixture. (C) 1998 Optical Society of Ameri ca.