Phase gratings with deep rectangular grooves have been successfully used in the zero diffraction order as transmission color filters. They form the basis of the ZOD microimage system for recording color images as surface-relief structures. ZOD images can be inexpensively replicated by hot embossing in a transparent sheet of plastic and read-out using conventional slide projectors or microfilm viewers. In this paper we use rigorous diffraction theory to derive optimum grating parameters for gratings with periods d < 2 μm to produce the three subtractive primary colors, cyan, magenta, and yellow, and also green. The theoretical results are in good agreement with the experiment.
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