A set of pattern headers is used to replicate repeating patterns used in digitally-simulated halftone screens. The use of pattern headers is suited to digital processing systems which are most efficient when processing data having dimensions which are an integer power of two, yet permits generation of repeating patterns having dimensions which are other than an integer power of two. A complete repeating pattern is stored as a one-dimensional-array pattern header. The repeating pattern is generated from that pattern header by suitable shifting of the pattern header. The repeating pattern may be arbitrarily smaller than the pattern header and may, for example, comprise a binary bit pattern useful in driving a binary rendering device or a pattern of integer values representing tonal intensities of the digitally-simulated halftone screen useful in driving a variable-dot-size rendering device.