contrast

Definition: (1) Of ambient light: brightness range in scene: difference between highest luminance and lowest. High contrast indicates large subject brightness range. (2) Of film: rate at which density builds up with increasing exposure over mid-portion of characteristic curve of film/development combination. Also known as gamma: equal to slope of straight portion of curve. Objective measures: G-bar or contrast index. * May also refer to slope of other parts of curve ie toe or shoulder region. (3) Of light-source or quality of light: directional light e.g. spotlights give high contrast lighting with hard shadows; diffuse light or large light source give low-contrast lighting with soft shadows. (4) Of printing paper: grade of paper e.g. high-contrast paper is grade 4 or 5, grade 1 is low-contrast. (5) Of lens performance or image quality: usually in reference to measured MTF: high-contrast lens delivers image of object with high MTF. Also subjective evaluation of image quality: high-contrast usually preferred to low contrast. (6) Of colour: colours opposite each other on the colour wheel are regarded as contrasting e.g. blue and yellow, green and red; colours of adjacent hues do not contrast as strongly.

Related Terms: MTF

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