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Hardware User Guide
CSC Manual Programming
The equations performed by the CP CSC are as follows:
CSC Channel A
⎡
A1
[
=
×
Out
_
A
In
_
A
⎢ ⎣
4096
CSC Channel B
⎡
B1
[
12
=
×
Out
_
B
In
_
A
⎢ ⎣
4096
CSC Channel C
⎡
C1
[
12
=
×
Out
_
C
In
_
A
⎢ ⎣
4096
As can be seen from Equation 4, Equation 5, and Equation 6, the A1, A2, A3; B1, B2, B3; and C1, C2, C3 coefficients are used to scale the
primary inputs. The values of A4, B4, and C4 are added as offsets. The CSC_SCALE[1:0] bits allows the user to implement conversion
formulain which the coefficients exceed the standard range of [-4095/4096 .. 4095/4096]. The overall range of the CSC is [0..1] for
unipolar signals (for example, Y, R, G, and B) and [−0.5 ... +0.5] for bipolar signals (for example, Pr and Pb).
Note: The bipolar signals must be offset to midrange, for example, 2048.
To arrive at programming values from typical formulas, the following steps are performed:
1.
Determine the dynamic range of the equation.
The dynamic range of the CSC is [0 ... 1] or [−0.5 ... +0.5]. Equations with a gain larger than 1 need to be scaled back. Errors in the
gain can be compensated for in the gain stages of the follow on blocks.
•
Scale the equations, if necessary.
2.
Check the value of each coefficient. The coefficients can only be programmed in the range [−0.99 ... +0.99].
3.
To support larger coefficients, the CSC_SCALE[1:0] function should be used.
4.
Determine the setting for CSC_SCALE[1:0] and adjust coefficients, if necessary.
5.
Program the coefficient values. Convert the float point coefficients into 12-bit fixed decimal format. Convert into binary format,
using twos complement for negative values.
•
Program A1 to A3, B1 to B3, C1 to C3.
6.
Program the offset values. Depending on the type of CSC, offsets may have to be used.
•
Program A4, B4, C4.
CSC Example
The following set of equations gives an example of a conversion from a gamma corrected RGB signal into a YCbCr color space signal.
⎡
A1
[
=
×
Out
_
A
In
_
A
⎢ ⎣
4096
⎡
B1
[
12
=
×
Out
_
B
In
_
A
⎢ ⎣
4096
⎡
C1
[
12
=
×
Out
_
C
In
_
A
⎢ ⎣
4096
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.
12
:
] 0
A2
[
12
:
] 0
+
×
+
In
_
B
In
4096
:
] 0
B2
[
12
:
] 0
+
×
+
In
_
B
In
4096
:
] 0
C2
[
12
:
] 0
+
×
+
In
_
B
In
4096
12
:
] 0
A2
[
12
:
] 0
+
×
+
In
_
B
In
4096
:
] 0
B2
[
12
:
] 0
+
×
+
In
_
B
In
4096
:
] 0
C2
[
12
:
] 0
+
×
+
In
_
B
In
4096
⎤
A3
[
12
:
] 0
×
+
_
C
A4
[
12
:
] 0
⎥ ⎦
4096
⎤
B3
[
12
:
] 0
×
+
×
_
C
B4
[
12
:
] 0
⎥ ⎦
4096
⎤
C3
[
12
:
] 0
×
+
×
_
C
C4
[
12
:
] 0
⎥ ⎦
4096
⎤
A3
[
12
:
] 0
×
+
×
_
C
A4
[
12
:
] 0
⎥ ⎦
4096
⎤
B3
[
12
:
] 0
×
+
×
_
C
B4
[
12
:
] 0
⎥ ⎦
4096
⎤
C3
[
12
:
] 0
×
+
×
_
C
C4
[
12
:
] 0
⎥ ⎦
4096
Rev. A | Page 113 of 204
×
CSC
_
scale
2
(4)
CSC
_
scale
2
(5)
CSC
_
scale
2
(6)
CSC
_
scale
2
CSC
_
scale
2
CSC
_
scale
2
UG-237
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