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7. Image Menu
Black level
∆
G
∆Β
∆
R
R
G
B
Image 7-25
One can conclude here that a good c
olor tracking can only be met by using three previously (input) balanced
color signals
Analog Digital Conversion
The analog color signals
must pass through an Analog/Digital conversion circuit prior to any digital processing in the PMP.
A typical ADC transforms the analog value into an 8 bit coded digital signal.
The graphic shows that when converting a signal containing a DC offset component the range of the converter is not optimally used.
Black level
∆
R
ADC
0
255
i1 : superfluous information
i2 : video information
Image 7-26
One can conclude here thata good data conversion can only bemet by using three previously (input) balanced
color signals
The objective of input balancing
The objective in input balancing is to “set” the same black level and the same white level for the three colors of a particular input
source.
Black level setting : brightness
White level setting : contrast
The
same absolute black and white level for the three colors allows the same reference for Brightness and contrast control of the
picture !
These two references also set the range in which the ADC will work for that particular source ( this explains also why each input
balance setting is linked to a particular source and thus saved in the image file).
How can it be done ?
T
o balance the three color signals of a particular source there are conditions; in fact we must know the black and the white level of
the source i.e. :
1. the source in question must be able to generate a white signal, ideally a 100% white (background) full screen pattern
2. th
e source in question must be able to generate a black signal, ideally a 100 % black (background) full screen pattern
70
R5976367 BARCOIQ GRAPHICS 500 01/02/2007