Black level
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Video displays generally need to be calibrated so that the displayed black is true to the black information in the [video] signal. If the black level is not correctly adjusted visual information in a video signal could be displayed as black, or black information could be displayed as above black information (gray).
User misadjustment of black level on monitors is common. It results in darker colours having their hue changed, it affects contrast, and in many cases causes some of the image detail to be lost.
Black level is set by displaying a testcard image and adjusting display controls. With CRT displays:
- 'brightness' adjusts black level
- 'contrast' adjusts white level
- CRTs tend to have some interdependance of controls, so a control sometimes need adjustment more than once.
