Terms to know

epi - elements per inch.

spi - spots per inch. Refers to points used for input by scanners and digital cameras. You cannot see a spot. When a scanner has a resolution of 3,000 x 3,000, the numerals refer to spots per inch horizontally and vertically.

dpi - dots per inch. Refers to the spots made by desktop printers.

ppi - pixels per inch. This refers to resolution of a computer monitor. You can see a pixel. Pixels consists of discreet units that render tonal values.

lpi - lines per inch. Refers to the relative size of halftone dots. High screen rulings, such as 175 and 200 lpi, have relatively small dots. Low rulings, such as 85 and 100 lpi, have relatively large dots.

High-end scanners have resolutions of 8,000 x 3,000 spi or greater.

Low-end scanners might have resolutions of 600 x 1,200 or even 300 x 600.

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