CompuServe Thread

Actually, printers that don't do continuous tone (such as ink-jets, thermal-transfer, solid-ink, etc.) use a dithering pattern to simulate more colors. This cuts down the usable resolution. In effect, they only have ten possible colors at the full resolution (white [no ink], cyan, magenta, yellow, orangeish-red [M+Y], green [C+Y], indigo-blue [C+M], muddy brown [C+M+Y], black, and registration black [C+M+Y+K]). 3-ink printers can only do seven colors (white, cyan, magenta, yellow, orangish-red, green, indigo blue, and a muddy black). To get more colors, resolution must be sacrificed on the altar of the great gods Halftoning or Dithering. Because of this, the actual resolution you need to image to get full color is nowhere near the full resolution of the printer. Assuming an 8×8 halftone cell to get 65 possible levels of each primary, you would need only 1/8th the specified resolution in both dimensions! This would reduce your area resolution (and file size) to 1/64th of the original! So, if you have a 600dpi color printer that is not continuous tone, and you use a diffusion dithering pattern that effectively chops the usable resolution to 1/4, you would need only 150 dpi files, scaled 4x (400%) on printing. The file would thus need to be only 1500×1200, not 6000×4800, to fill an A-sized page. Continuous-tone printers, on the other hand, can print full color to the full resolution. They therefore need full-sized images for best results.