A system for generating a set of bit masks arrays is provided (350-0 to 350-255) where the bit mask arrays (350-0 to 350-255) are such that clusters of entries of different types are spread across each array and entries of different types within the arrays are either part of a larger cluster of entries of that type or are immediately adjacent to a cluster of entries of that type. When a multi-level image (200) is converted to a half-tone image (300) utilizing the bit mask arrays (350-0 to 350-255) a half-tone image (300) which limits the occurrence of small isolated printed or unprinted areas is generated. The bit mask arrays (350-0 to 350-255) are therefore particularly suitable for use with laser printers (28,32) which have difficulty rendering half tone images which comprise small isolated printed and unprinted areas.