Grayscale is a single channel colour mode that uses up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black). Images produced using black-and-white or grayscale scanners typically are displayed in Grayscale mode.
A grayscale image can also be the basis of a toned image such as a monotone where colour references of tone can be from light to dark of the same hue. Variations of this can be duotone (two-color), tritone (three-color), and quadtone (four-color). Instead of black and white or single hue, two to four custom colours can be used.
