From Wikipedia, the free encyclopedia
Video
black level
is defined as the level of brightness at the darkest (black) part of a visual image or the level of
brightness
at which no light is emitted from a screen, resulting in a pure black screen.
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).
The voltage of the black level varies across different television standards.
PAL
sets the black level the same as the blanking level, while
NTSC
sets the black level approximately 54 mV above the
blanking level
.
User misadjustment of black level on monitors is common. It results in darker colors 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 interdependence of controls, so a control sometimes needs adjustment more than once.
In
digital video
black level usually means the range of
RGB
values in video signal, which can be either [0..255] (or "normal"; typical of a computer output) or [16..235] (or "low"; standard for video).
See also
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References
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