adv7344 Analog Devices, Inc., adv7344 Datasheet - Page 57

• Manufacturer Part Number: adv7344
• Description: Multiformat Video Encoder Six 14-bit Noise Shaped Video Dacs
• Manufacturer: Analog Devices, Inc.

SD gamma correction is enabled using Subaddress 0x88, Bit 6.
SD Gamma Correction Curve A is programmed at Subaddress
0xA6 to Subaddress 0xAF, and SD Gamma Correction Curve B
is programmed at Subaddress 0xB0 to Subaddress 0xB9.
Gamma correction is performed on the luma data only. The
user can choose one of two correction curves, Curve A or
Curve B. Only one of these curves can be used at a time. For
ED/HD gamma correction, curve selection is controlled using
Subaddress 0x35, Bit 4. For SD gamma correction, curve
selection is controlled using Subaddress 0x88, Bit 7.
The shape of the gamma correction curve is controlled by
defining the curve response at 10 different locations along the
curve. By altering the response at these locations, the shape of
the gamma correction curve can be modified. Between these
points, linear interpolation is used to generate intermediate
values. Considering the curve has a total length of 256 points,
the 10 programmable locations are at points 24, 32, 48, 64, 80,
96, 128, 160, 192, and 224. Locations 0, 16, 240, and 255 are
fixed and cannot be changed.
From 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:
where:
x
x
γ is gamma correction factor.
DESIRED
INPUT
x
Figure 70. Signal Input (Ramp) and Signal Output for Gamma 0.5
DESIRED
is the linear input signal.
300
250
200
150
100
is the desired gamma corrected output.
50
0
0
GAMMA CORRECTION BLOCK OUTPUT TO A RAMP INPUT
= ( x
INPUT
50
)
γ
SIGNAL INPUT
100
LOCATION
0.5
SIGNAL OUTPUT
150
200
250
Rev. 0 | Page 57 of 88
To program the gamma correction registers, calculate the
10 programmable curve values using the following formula:
where:
γ
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
where the sum of each equation is rounded to the nearest integer.
The gamma curves in Figure 70 and Figure 71 are examples only;
any user-defined curve in the range from 16 to 240 is acceptable.
n
is the value to be written into the gamma correction register
y
y
y
y
y
y
y
y
y
y
γ
24
32
48
64
80
96
128
160
192
224
n
300
250
200
150
100
Figure 71. Signal Input (Ramp) and Selectable Output Curves
50
= [(8/224)
= [(16/224)
= [(32/224)
= [(48/224)
= [(64/224)
= [(80/224)
=
0
= [(112/224)
= [(144/224)
= [(176/224)
= [(208/224)
0
⎛
⎜
⎜
⎝
⎛
⎜
⎝
240
GAMMA CORRECTION BLOCK TO A RAMP INPUT FOR
n
−
−
16
0.5
16
50
0.5
0.5
0.5
0.5
0.5
× 224] + 16 = 58
⎞
⎟
⎠
0.5
0.5
0.5
0.5
× 224] + 16 = 76
× 224] + 16 = 101
× 224] + 16 = 120
× 224] + 16 = 136
× 224] + 16 = 150
γ
× 224] + 16 = 174
× 224] + 16 = 214
× 224] + 16 = 232
VARIOUS GAMMA VALUES
× 224] + 16 = 195
×
(
240
100
LOCATION
−
n
16
values:
)
1.5
0.3
1.8
0.5
⎞
⎟
⎟
⎠
150
+
16
200
ADV7344
250