Image brightness

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The concept of image brightness can be interpreted as illuminance E (unit lux or lumen / m² ) in the image plane of an imaging system or as a gray value (no units, with 8 bit gray levels a value between 0 and 255) in a digital image . For the subjective quality of an image, in addition to image brightness, above all, sufficient contrast is necessary.

Mathematically, the image brightness of a gray value image can be defined as the mean value of all gray values, the contrast as the variance of all gray values.