In display systems, the relation between the intensity of color or brightness of an area occupied by an element or an image and the intensity of the area not occupied by that element or image. Deprecated synonym brightness ratio. 2. In optical character recognition, the difference between color or shading of the printed material on a document and the background on which it is printed. 3. In display systems, the extent to which the various luminance values in a picture are mapped to very dark and very light values. Note: A high-contrast picture is dominated by black and white and few values between. A low-contrast picture has many middle tones without many very dark or very light areas.