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ADV7190/ADV7191
–42–
REV. 0
GAMMA CORRECTION REGISTERS 0–13
(GAMMA CORRECTION 0–13)
(Address (SR5–SR0) = 26H–32H)
The Gamma Correction Registers are fourteen 8-bit-wide regis-
ters. They are used to program the gamma correction Curves A
and B.
Gamma correction is applied to compensate for the nonlinear
relationship between signal input and brightness level output (as
perceived on the CRT). It can also be applied wherever nonlin-
ear processing is used.
Gamma correction uses the function:
Signal
OUT
= (Si
gnal
IN
)
γ
where
γ
= g
amma power factor
Gamma correction is performed on the luma data only. The
user has the choice to use two different curves, Curve A, or
Curve B. At any one time only one of these curves can be used.
The response of the curve is programmed at seven prede
fi
ned
locations. In changing the values at these locations the gamma
curve can be modi
fi
ed. Between these points linear interpolation
is used to generate intermediate values. Considering the curve
to have a total length of 256 points, the seven locations are at:
32, 64, 96, 128, 160, 192, and 224.
Values at Location 0, 16, 240, and 255 are
fi
xed and cannot be
changed.
For the length of 16 to 240 the gamma correction curve has to
be calculated as below:
y
= x
γ
where
y
= gamma corrected output
x
= linear input signal
γ
= gamma power factor
To program the gamma correction registers, the seven values for
y
have to be calculated using the following formula:
y
n
= [
x
(
n–
16)
/(240
–
16) ]
γ
×
(240
–
16) + 16
where
x
(
n-
16) =
Value for x along x-axis
y
n
into the gamma correction register
n
= 32, 64, 96, 128, 160, 192, or 224
Example:
y
32
= [(16/224)
0
.5
×
224] + 16
=
76
*
y
64
= [(48/224)
0
.5
×
224] + 16 =120
*
=
Value for y along the y-axis, which has to be written
y
96
= [(80/224)
0
.5
×
224] + 16 = 150
*
y
128
= [(112/224)
0
.5
×
224] + 16 = 174
*
*
Rounded to the nearest integer.
The above will result in a gamma curve shown below, assuming
a ramp signal as an input.
250
200
150
100
50
0
300
250
200
150
100
50
300
SIGNAL OUTPUT
SIGNAL INPUT
0.5
GAMMA CORRECTION BLOCK OUTPUT
TO A RAMP INPUT
G
–
C
0
50
100
150
200
250
LOCATION
Figure 85. Signal Input (Ramp) and Signal Output for
Gamma 0.5
250
200
150
100
50
0
300
SIGNAL OUTPUTS
SGNALINPUT
0.5
GAMMA CORRECTION BLOCK OUTPUT
TO A RAMP INPUT FOR VARIOUS GAMMA VALUES
G
–
C
0
50
100
150
200
250
LOCATION
0.3
1.5
1.8
Figure 86. Signal Input (Ramp) and Selectable Gamma
Output Curves
The gamma curves shown above are examples only, any user-
de
fi
ned curve is acceptable in the range of 16
–
240.
DNR27
DNR26
DNR25
DNR24
DNR23
DNR22
DNR21
DNR20
BLOCK OFFSET
DNR DNR DNR DNR
27 26 25 24
0
0
0
0
0
0
1
1
1
1
1
1
0
0
1
0
1
1
0
1
0
1
0
1
0 PIXEL OFFSET
1 PIXEL OFFSET
2 PIXEL OFFSET
13 PIXEL OFFSET
14 PIXEL OFFSET
15 PIXEL OFFSET
DNR INPUT SELECT
DNR DNR DNR
22 21 20
0
0
0
1
0
1
1
0
1
0
1
0
FILTER A
FILTER B
FILTER C
FILTER D
0
1
DNR MODE
DNR
SHARPNESS
MODE
DNR23
DNR MODE
CONTROL
Figure 84. DNR Register 2