1 A distinction between things being compared, or an emphasis on the distinction between things that are juxtaposed.
2 In perception, an enhancement of the perceived differences between stimuli resulting from juxtaposing them. In simultaneous contrast the stimuli are presented together; in successive contrast they are presented sequentially. See colour contrast, lightness contrast, warmth contrast. See also contrast ratio.
3 In statistics, a comparison of two or more means calculated by forming a weighted linear combination of means. For example, the contrast ½(Mean 1) + ½(Mean 2) − (Mean 3) could be used to test the null hypothesis that the average of Mean 1 and Mean 2 is equal to Mean 3 in the population. In most cases it is necessary for statistical reasons for the contrast to be orthogonal (3), with the coefficients summing to zero, as are the coefficients of ½, ½, and −1 in this example.
4 The degree to which areas of an optical image, such as those in television or photographic pictures, differ in luminance, often indexed by (Lmax − Lmin)/(Lmax + Lmin), where Lmax is a measure of the luminance of the brightest area and Lmin the luminance of the darkest area. See also contrast ratio, contrast threshold.
5 Exaggerating or increasing the discrepancy between one's own attitude and that of a source of a persuasive communication or message. See also assimilation-contrast theory. Compare assimilation (4). [From Latin contra opposite to + stare to stand]