Gray-scale graphics using dot matrix printers

Gray-scale graphics can be printed on conventional dot matrix printers by varying the dot density, rather than the dot intensity. The technique described here takes advantage of the high-contrast print possible with these printers and the increased resolution available using compressed character sets. The reflectance of individual characters and symbols was measured with a photometer, and a character set was selected that increased from dark to light in equal logarithmic steps of reflectance. Various criteria for choosing dot patterns are discussed, and the technique is applied to two-dimensional visual field maps.