contrast

Six renditions of a rocky shore photo with incremental contrast levels, clockwise from bottom leftContrast is the difference in luminance or color that makes an object (or its representation in an image or display) distinguishable from a background. Human vision is more sensitive to relative differences than to absolute luminance, so perceived appearance can remain fairly stable despite large changes in illumination.

The maximum contrast of an image is termed the contrast ratio or dynamic range. In images where the contrast ratio approaches the maximum possible for the medium, there is a conservation of contrast. In such cases, increasing contrast in certain parts of the image will necessarily result in a decrease in contrast elsewhere. Brightening an image increases contrast in darker areas but decreases it in brighter areas; conversely, darkening the image will have the opposite effect. Bleach bypass reduces contrast in the darkest and brightest parts of an image while enhancing luminance contrast in areas of intermediate brightness.