Datasheet

ADV7320/ADV7321
Rev. A | Page 54 of 88
For lengths of 16 to 240 points, the gamma correction curve is
calculated as follows:
y = xγ
where:
y = gamma corrected output.
x = linear input signal.
γ = gamma power factor.
To program the gamma correction registers, calculate the seven
values for
y using the following formula:
16)16240(
)16240(
)16(
+−×γ
⎥
⎦
⎤
⎢
⎣
⎡
−
=
−n
n
x
y
where:
x
(n − 16)
= value for x along x-axis at points n.
n = 24, 32, 48, 64, 80, 96, 128, 160, 192, or 224.
y
n
= value for y along the y-axis, which must be written into the
gamma correction register.
For example,
y
24
= [(8/224)0.5 × 224] + 16 = 58
y
32
= [(16/224)0.5 × 224] + 16 = 76
y
48
= [(32/224)0.5 × 224] + 16 = 101
y
64
= [(48/224)0.5 × 224] + 16 = 120
y
80
= [(64/224)0.5 × 224] + 16 = 136
y
96
= [(80/224)0.5 × 224] + 16 = 150
y
128
= [(112/224)0.5 × 224] + 16 = 174
y
160
= [(144/224)0.5 × 224] + 16 = 195
y
192
= [(176/224)0.5 × 224] + 16 = 214
y
224
= [(208/224)0.5 × 224] + 16 = 232
where the sum of each equation is rounded to the nearest
integer.
The gamma curves in
Figure 71 and Figure 72 are only examples;
any user-defined curve is acceptable in the range of 16 to 240.
LOCATION
0
0
50
100
150
200
250
300
50 100 150 200 250
0.5
SIGNAL INPUT
GAMMA CORRECTED AMPLITUDE
SIGNAL OUTPUT
GAMMA CORRECTION BLOCK OUTPUT TO A RAMP INPUT
05067-071
Figure 71. Signal Input (Ramp) and Signal Output for Gamma 0.5
LOCATION
0
0
50
100
150
200
250
300
50 100 150 200 250
GAMMA CORRECTED AMPLITUDE
GAMMA CORRECTION BLOCK TO A RAMP INPUT FOR
VARIOUS GAMMA VALUES
0.3
0.5
1.5
1.8
S
I
G
N
A
L
I
N
P
U
T
05067-072
Figure 72. Signal Input (Ramp) and Selectable Output Curves