8. Image Menu
Incase of information contained in the amplitude of the signals which is the case of data color signals (R, G, B),image 8-33 , we are
quitesure that the am plitude of these color signals is subject to alterations.
Anexample of alteration may be a DC component added tothe signal, in the form of a DC offset repositioning the black level, since
thisbla ck level (“brightness”) will become crucial later on (clamping circuit) it will result in “black not being black”.
Anothervalue that is subject to alteration is the amplitude of the signal, resulting in an altered “Gain” of the signal (“white level” or
contrast).
Thealterations of the three color signals will happen independently i.e. the colors will end to be unbalanced, image 8-34
BBlack level
0.7V
Image8-33
Black level
∆
G
∆Β
∆
R
R
GB
Image8-34
Onecan conclude h ere that a good color tracking can only be met by using three previously (input) balanced
color signals
Analog Digital Conversion
Theanalog color signals must pass through an Analog/Digital conversion circuit prior to any digital processing in the PMP.
Atypical ADC transforms the an alogvalue into an 8 bit co ded digitals ignal.
Thegraphic 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
Image8-35
Onecan conclude here that a good data conversion can only be met 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.
78 R5976815 RLM G5I PERFORMER 02/06/2006