Gray level requantization

A distance measure between pictures, that enables comparison of images with different gray level ranges, is described. With such measure halftoning can be treated as an optimization problem. Based on this measure, an algorithm for reducing the number of gray levels of a picture with minimal visual degradation is developed. The algorithm can even produce a binary halftone of the picture, which is needed for many hard copy devices. The complexity of the algorithm is high, and it is not recommended as a daily halftoning method. However, the method provides a well-defined mathematical approach for comparing images.