Abstract: A raster-scan display device (which may be part of a combined raster-scan/calligraphic display) has a store (8) which is loaded (calculators 2, 4, 5, and 7) with image data. Processing of the data to assemble and output sets of values corresponding to successive lines of the display is performed by line processors (10, 11, 12, etc.): during output of one line or part-line by a processor, image data for a subsequent line or part of a line is being processed by another processor, so that a processing time in excess of one line duration is available. One application of such devices is in flight simulators.

Abstract: In a calligraphic scene display, occulting or masking of information stored in a data base can take place due to occulting surfaces. To determine whether occulting occurs for any given data item, a comparison is made first with data held in a surface memory circuit (34) indicating generally the area occupied by the surface. When occulting is indicated, a more detailed check is made against data held in a line memory circuit (36) and addressed with the aid of an address held in the surface memory circuit. If the line check indicates occulting, the occult logic (50) is instructed accordingly.