A thin strip of paper or film containing 15:20 shades of gray, increasing in density (typically in a logarithmic, not linear, fashion) from white to black, used to analyze and optimize the contrast of color and black-and-white images.
Gray scales come in a variety of different forms, for different types of reproduction. A gray scale can be supplied on film, as either continuous tones or halftone dots. If it is on film and comprises discrete stages of gray, it is called a step tablet. If it is on film and comprises a single continuous strip of progressively dense gray, it is called a continuous wedge. If it is on film and comprises halftone dots in discrete levels of gray, it is called a halftone scale. Gray scales are often printed beyond the trim boundaries of printed pages as a means of ensuring the consistency of the print characteristics.
On a computer monitor, gray scales are produced by varying the intensity of the pixels, on a scale of white to black. Images saved in the TIFF file format convert gray scale information into printer commands, which instruct the printer to construct a bit map plotting all the levels of gray for each spot in the output. The more levels of gray that a computer and printer can discern, the smoother and more realistic the image.