ADV8005 Hardware Reference Manual
UG-707
generate intermediate values. Considering that the curve has a total length of 256 points, the 10 programmable locations are at the following
points: 24, 32, 48, 64, 80, 96, 128, 160, 192, and 224. The following locations are fixed and cannot be changed: 0, 16, 240, and 255.
From the curve locations, 16 to 240, the values at the programmable locations and, therefore, the response of the gamma correction curve, should
be calculated to produce the following result:
x
DESIRED
= (x
INPUT
)
γ
where:
x
DESIRED
is the desired gamma corrected output.
x
INPUT
is the linear input signal.
γ is the gamma correction factor.
To program the gamma correction registers, the 10 programmable curve values are calculated using
16
)
16
240
(
16
240
16
+
−
×
−
−
=
γ
γ
n
n
Equation 29: Gamma Correction Calculation
where:
γ
n
is the value to be written into the gamma correction register for point
n
on the gamma correction curve.
n
= 24, 32, 48, 64, 80, 96, 128, 160, 192, or 224.
γ
is the gamma correction factor.
For example, setting γ = 0.5 for all programmable curve data points results in the following
y
n
values:
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, these must then all be converted to hex.
The gamma curves in
and
are examples only; any user defined curve in the range from 16 to 240 is acceptable.
Figure 120: Signal Input (Ramp) and Signal Output for Gamma 0.5
LOCATION
0
0
50
100
150
200
250
300
50
100
150
200
250
0.5
SIGNAL INPUT
G
AM
M
A
CO
RRE
CT
E
D
AM
P
L
IT
UDE
SIGNAL OUTPUT
GAMMA CORRECTION BLOCK OUTPUT TO A RAMP INPUT
06398-
071
Rev. A | Page 263 of 317
