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MB86R02 'Jade-D' Hardware Manual V1.64
18.6.6 Programmable YCbCr/RGB conversion for L1-layer display
L1-layer can display video data in YCbCr format but RGB conversion coefficients are hard-wired and
fixed about previous products. MB86R02 'Jade-D' can program RGB conversion coefficients by
registers.
YCbCr data is converted by following expression.
×Y + a
×(Cb−128) + a
R = a
11
12
×Y + a
×(Cb−128) + a
G = a
21
22
×Y + a
×(Cb−128) + a
B = a
31
32
a
---- 11bit signed real (lower 8bit is fraction, two's complement)
ij
b
----- 9bit signed integer (two's complement)
i
It is represended by matrix operation.
R
Y
A
G
Cb-128
=
B
Cr-128
These parameters are set on registers shown bellow.
L1YCR0 (a
,a
), L1YCR1(b
12
11
L1YCG0 (a
a
), L1YCG1(b
22,
21
L1YCB0 (a
a
), L1YCB1(b
32,
31
Same conversion with previous products is applied by initial values of these registers after reset.
The register values just after reset is as follow.
a
= 0x12b (299/256) , a
11
a
= 0x12b (299/256), a
21
a
= 0x12b (299/256), a
31
b
= b
= b
= 0x1f0 (-16)
1
2
3
It is possible to control brightness, contrast, hue , color saturation by change these parameters.
Addition of a constant value into
Multiplication of a constant scalar value greater than one into
Two dimentional rotation of Cb-128 and Cr-128 means change of hue.
Color saturation is intensity of color, relative to Y-component.
New coefficients including these changes can be got by following expression.
×(Cr−128) + b
13
×(Cr−128) + b
23
×(Cr−128) + b
33
a
11
b
A
where
a
+
=
21
a
31
a
)
1,
13
a
)
2,
23
a
)
3,
33
= 0x0, a
= 0x198 (408/256)
12
13
= 0x79c (-100/256), a
22
= 0x204 (516/256), a
32
b
means inclease of brightness.
1
2
3
a
a
b
12
13
1
, b
a
a
b
=
22
23
2
a
a
b
32
33
3
= 0x72f (-209/256)
23
= 0x0
33
A
means increase of contrast.
18-27
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