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Communications of the ACM

Communications of the ACM

A scan conversion algorithm with reduced storage requirements

Most graphics systems using a raster scan output device (CRT or hardcopy) maintain a display file in the XY or random scan format. Scan converters, hardware or software, must be provided to translate the picture description from the XY format to the raster format. Published scan conversion algorithms which are fast will reserve a buffer area large enough to accommodate the entire screen. On the other hand, those which use a small buffer area are slow because they require multiple passes through the XY display file. The scan conversion algorithm described here uses a linked list data structure to process the lines of the drawing in strips corresponding to groups of scan lines. A relatively small primary memory buffer area is used to accumulate the binary image for a group of scan lines. When this portion of the drawing has been plotted, the buffer is reused for the next portion. Because of the list processing procedures used, only a single pass through the XY display file is required when generating the binary image and only a slight increase in execution time over the fully buffered core results. Results show that storage requirements can be reduced by more than 80 percent while causing less than a 10 percent increase in execution time.

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