ADV7314KST Analog Devices Inc, ADV7314KST Datasheet - Page 49

• Manufacturer Part Number: ADV7314KST
• Manufacturer: Analog Devices Inc

Specifications of ADV7314KST

• Number Of Dac's: 6
• Adc/dac Resolution: 14b
• Screening Level: Commercial
• Package Type: LQFP
• Pin Count: 64
• Lead Free Status / RoHS Status: Compliant

Gamma Correction
[Subaddress 24h–37h for HD, Subaddress 66h–79h for SD]
Gamma correction is available for SD and HD video. For each
standard there are 20 8-bit registers. They are used to program
the gamma correction curves A and B. HD gamma curve A is
programmed at Addresses 24h–2Dh, HD gamma curve B at
2Eh–37h. SD gamma curve A is programmed at addresses
66h–6Fh, and SD gamma curve B at Addresses 70h–79h.
Generally, 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 wher-
ever nonlinear processing is used.
Gamma correction uses the function
where
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 time, only one of these curves can be used.
The response of the curve is programmed at 10 predefined
locations. In changing the values at these locations, the gamma
curve can be modified. Between these points linear interpolation
is used to generate intermediate values. Considering the curve
to have a total length of 256 points, the 10 locations are at 24,
32, 48, 64, 80, 96, 128, 160, 192, and 224. Location 0, 16,
240, and 255 are fixed and cannot be changed.
REV. 0
= gamma power factor.
300
250
200
150
100
50
0
0
GAMMA CORRECTION BLOCK OUTPUT TO A RAMP INPUT
Figure 40. Signal Input (Ramp) and
Signal Output for Gamma 0.5
50
Signal
SIGNAL INPUT
OUT
100
LOCATION
=
0.5
(
Signal
SIGNAL OUTPUT
150
IN
)
g
200
250
–49–
For the length of 16 to 240, the gamma correction curve has to
be calculated as follows:
where:
y = gamma corrected output.
x = linear input signal.
To program the gamma correction registers, the seven values for
y have to be calculated using the following formula:
where:
x
n = 24, 32, 48, 64, 80, 96, 128, 160, 192, or 224.
y
For example:
*rounded to the nearest integer
The gamma curves in Figure 41 are examples only; any user
defined curve is acceptable in the range of 16 to 240.
(n–16)
n
= gamma power factor.
= value for y along the y-axis, which has to be written into
the gamma correction register.
= value for x along x-axis at points.
300
250
200
150
100
50
0
y
y
y
y
y
y
y
y
y
y
0
24
32
48
64
80
96
128
160
192
224
Figure 41. Signal Input (Ramp) and
Selectable Gamma Output Curves
y
= [(8 / 224)
= [(16 / 224)
= [(32 / 224)
= [(48 / 224)
= [(64 / 224)
= [(80 / 224)
GAMMA CORRECTION BLOCK TO A RAMP INPUT FOR
= [(112 / 224)
= [(144 / 224)
= [(176 / 224)
= [(208 / 224)
n
=
È
Í
Í
Î
50
(
240 16
x
(
n
VARIOUS GAMMA VALUES
–16
-
0.5
0.5
0.5
0.5
0.5
0.5
)
100
y = x
0.5
0.5
0.5
0.5
)
˘
˙
˙
˚
LOCATION
224] + 16 = 58*
g
224] + 16 = 76*
224] + 16 = 101*
224] + 16 =120*
224] + 16 =136*
224] + 16 = 150*
¥
224] + 16 = 174*
224] + 16 = 195*
224] + 16 = 214*
(
1.5
224] + 16 = 232*
0.3
1.8
0.5
240 16
150
-
)
ADV7314
200
+
16
250