Contrast is a function that alters the brightness values in an image. It can be thought of as how different (or contrasting) the brightest and darkest values in an image are. Low contrast means there is little difference between light and dark areas and high contrast means there is a large difference. When contrast is reduced to its minimum the result is an even gray because there is no difference at all between values, and high contrast turns an image into black and white with no gray shades in between.

Examples of the same photo with varying contrast. The squares at the bottom show a simplified graph of how input values (along the bottom) map to output values (along the left side).

Low contrast creates a less distinct, softer appearance to an image, while higher contrast creates a harsher, grittier feel. High contrast is popular with street photographers because it adds a raw tone to candid pictures.

Sample image: detail of photo of an unidentified farmer at a Kansas auction in 1938, taken from the Library of Congress photo archives.