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4. Program the offset values.
Depending on the type of CSC, offsets may have to be used.
Program A4, B4, C4.
8.4.5.2 CSC Example
The following set of equations gives an example of a conversion from a gamma corrected RGB
signal into a YCrCb color space signal.
⎡
A
=
∗
_
_
Out
A
In
A
⎢ ⎣
⎡
[ 1
B
=
∗
_
_
Out
B
In
A
⎢ ⎣
⎡
[ 1
C
=
∗
_
_
Out
C
In
A
⎢ ⎣
Note: The original equations give offset values of 128 for the Pr and Pb components. The value of
128 equates to half the range on an 8-bit system. It must be noted that the CSC operates on a 12-bit
range. The offsets, therefore, must be changed from 128 to half the range of a 12-bit system, which
equates to 2048.
The maximum range for each equation, that is, each output data path, can only be [0 ... 1] or [-0.5 ...
+0.5]. Equations with a larger gain must be scaled back into range. The gain error can be
compensated for in the gain stage of the follow on blocks.
The ranges of the three equations are:
Equation
Minimum Value
Y
0 + 0 + 0 = 0
Pb
(-0.34) + (-0.17) = -0.51
Pr
(-0.43) + (-0.08) = -0.51
As can be seen from this table, the range for the Y component fits into the CSC operating range.
However, the Pb and Pr ranges slightly exceed the range. To bring all equations back into the
supported range, they should be scaled back by 1/1.02.
If equations fall outside the supported range, overflow or underflow can occur and undesirable wrap
around effects (large number overflowing to small ones) can happen.
. 0
59
0
3 .
=
∗
+
∗
Y
G
. 1
02
. 1
02
−
−
. 0
34
. 0
=
∗
+
Pb
G
. 1
02
. 1
02
Rev. F August 2010
[ 1
12
:
] 0
[ 2
A
+
∗
_
In
B
4096
4096
12
:
] 0
[ 2
12
B
+
∗
_
In
B
4096
4096
12
:
] 0
[ 2
12
C
+
∗
_
In
B
4096
4096
. 0
11
+
∗
=
∗
. 0
58
R
B
G
. 1
02
17
. 0
51
∗
+
∗
+
2048
R
B
. 1
02
12
:
] 0
[ 3
12
A
+
∗
_
In
C
4096
:
] 0
[ 3
12
B
+
∗
_
In
C
4096
:
] 0
[ 3
12
C
+
∗
_
In
C
4096
Maximum Value
0.59 + 0.3 + 0.11 = 1
0.51
0.51
+
∗
+
∗
. 0
29
. 0
11
R
B
=
−
∗
−
. 0
33
. 0
17
G
214
⎤
:
] 0
+
∗
[ 4
12
:
] 0
2
A
⎥ ⎦
⎤
:
] 0
+
∗ ⎥
[ 4
12
:
] 0
2
CSC
B
⎦
:
] 0
⎤
+
∗ ⎥
[ 4
12
:
] 0
2
CSC
C
⎦
Range
[0 ... 1] = 1
[-0.51 ... 0.51] = 1.02
[-0.51 ... 0.51] = 1.02
∗
+
∗
+
0
5 .
2048
R
B
ADV7604
_
CSC
scale
_
scale
_
scale
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