1. A data compaction system used in computer image generation of a complex image, said complex image being divided into a plurality of blocks, each of said blocks including an identical grid pattern for location of shapes within the block, said data compaction system comprising: a reference memory storing a limited number of a plurality of simple shapes from which a subset of said shapes are selected to generate a portion of said complex image for a specific location of the grid pattern in any one of said plurality of blocks, each of said simple shapes being assigned shape numbers and stored with their assigned shape number; a buffer memory storing bit string patterns for each of said plurality of blocks, each bit string pattern having a sequence corresponding to said shape numbers and indicating which of the simple shapes of said limited number of a plurality of simple shapes are to be generated for a specific location of the grid pattern to produce that portion of said complex image in the block, one or more simple shapes being selected for generation at the specific location with each selected shape adding a different feature to the specific location in the grid pattern; and output means for supplying data words derived from said reference memory and said buffer memory for each of said blocks, each said data word including an address field specifying stored simple shape patterns in said reference memory, said simple shape patterns being used repeatedly at different locations in said grid pattern to reduce the overall volume of data required to define an entire pattern of said complex image.