adv7390 Analog Devices, Inc., adv7390 Datasheet - Page 54

• Manufacturer Part Number: adv7390
• Description: Low Power, Chip Scale 10-bit Sd/hd Video Encoder
• Manufacturer: Analog Devices, Inc.

ADV7390/ADV7391/ADV7392/ADV7393
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 to have 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 = gamma correction factor
DESIRED
INPUT
x
Figure 72. Signal Input (Ramp) and Signal Output for Gamma 0.5
DESIRED
= linear input signal
300
250
200
150
100
= 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 54 of 96
To program the gamma correction registers, calculate the
10 programmable curve values using the following formula:
where:
γ
point n on the gamma correction curve
n = 24, 32, 48, 64, 80, 96, 128, 160, 192, or 224
γ = 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 72 and Figure 73 are examples only;
any user-defined curve in the range from 16 to 240 is acceptable.
n
= value to be written into the gamma correction register for
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 73. 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 = 195
× 224] + 16 = 214
× 224] + 16 = 232
VARIOUS GAMMA VALUES
×
(
240
100
LOCATION
−
n
16
values:
)
1.5
0.3
0.5
1.8
⎞
⎟
⎟
⎠
150
+
16
200
250