- SS-HQ1 Application Notes -
Ver.1.0.0 January 7, 2005
105
Fig 10.4-5 Chroma Variable Gamma
Note: The curves shown in “
Chroma variable gamma”, are model curves. They do not represent
actual measurements.
If CKNEE (or UCKNEE) = 0[h]~5[h] is selected, 48 different curves may be selected, through a combination of
eight different nonlinear regions selected by setting CGAMMA (or UCGAMMA) to 0[h]~7[h] for input levels up
to 100% (1024[d] converted to digital), and six different linear regions based on CKNEE (or UCKNEE) for
higher levels.
If CGAMMA (or UCGAMMA) is set to 4[h] and CKNEE (or UCKNEE) is set to 3[h], then the result will be the
closest to gamma = 0.45 (the inverse of standard CRT gamma = 2.2), and the output level for 100% input level
will be 78% (400/511[d]).
Note that the input signals for the chroma variable gamma circuit are equivalent to the following:
Input signal inside DSP (CXD3172AR): RGB signal after white balance correction
Output signal: RGB signal before R-Y and B-Y color difference conversion
Note that neither of these signals can be measured directly.
Also note that chroma variable gamma output at high input levels may overflow in the R-Y and B-Y color
difference conversion process in a later step, and may be clipped or suppressed at specific levels.
0
CGAM
MA
=0
CGAMMA=7
CKNEE=0
CKNEE=5
100 [%]
78 [%]
INPUT Level
OU
TP
UT Lev
el
100 [%]
200 [%]