Methods of Measurement
- contrast of direct-view displays
- contrast of projection displays
Depending on the nature of the display under test (direct-view or projection) the contrast is evaluated as a quotient of luminance values (direct-view) or as a quotient of illuminance values (projection displays) if the properties of the projection screen is separated from that of the projector. In the latter case, a checkerboard pattern with full-white and full-black rectangles is projected and the illuminance is measured at the center of the rectangles. The standard ANSI IT7.215-1992 defines test-patterns and measurement locations, and a way to obtain the luminous flux from illuminance measurements, it does not define however a quantity named "ANSI lumen".
If the reflective properties of the projection screen (usually depending on direction) are included in the measurement, the luminance reflected from the centers of the rectangles has to be measured for a (set of) specific directions of observation.
Luminance, contrast and chromaticity of LCD-screens is usually varying with the direction of observation (i.e. viewing direction). The variation of electro-optical characteristics with viewing direction can be measured sequentially by mechanical scanning of the viewing cone (gonioscopic approach) or by simultaneous measurements based on conoscopy.
Read more about this topic: Display Contrast
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