AK8856 Datasheet, PDF (33/105 Pages) Asahi Kasei Microsystems – NTSC/PAL Digital Video Decoder

ASAHI KASEI
[ AK8856 ]
Picture Quality Adjust Process Function
Picture Quality Adjustments such as contrast, brightness, color saturation and color hue are integrated in the
AK8856.
(1) Contrast
Contrast is adjusted by multiplying the Luminance signal (Y) by a gain value which is set by
Contrast Control Register ( R/W ) [ Sub Address 0x06].
CNTSEL bit = 0
YOUT = CONT* (YIN – 128) + 125
YOUT : contrast arithmetic operation result
YIN : before contrast arithmetic operation
CONT : contrast coefficient (register value)
It is also possible to define the equation by setting the register:
CNTSEL bit = 1
YOUT = CONT* (YIN – 128) + 16
YOUT : contrast arithmetic operation result
YIN : before contrast arithmetic operation
CONT : contrast coefficient (register set value)
Setting is done with the [CNTSEL] bit of Control 2 Register (R/W) [Sub Address 0x04]
The range of the contrast gain coefficient varies from 0 to 1.99 (1/128 step), and when the arithmetic operation
result exceeds this range, it is clipped to the upper-limit of 254, or the lower-limit of 1 (the output result
ranges from 16 to 235 when the 601 limit-bit is 1).
Bit allocation of Contrast Control Register:
Sub Address 0x06
bit 7
bit 6
CONT7
CONT6
1
0
bit 5
CONT5
0
bit 4
bit 3
CONT4
CONT3
Default Value
0
0
Sub Address 0x04
bit 7
bit 6
CNTSEL
NSIGDEF
0
0
bit 5
ODEV
0
bit 4
bit 3
FRMRT1
FRMRT0
Default Value
0
0
bit 2
CONT2
0
bit 2
COLKIL
0
Default Value: 0x80
bit 1
bit 0
CONT1
CONT0
0
0
Default Value: 0x00
bit 1
bit 0
ACC
AGC
0
0
[CNTSEL] bit
This bit sets the changeover point of the contrast adjustment.
[CNTSEL]-bit
Function
0
To be adjusted at Luminance 125 as a center point
1
To be adjusted at Luminance 16 as a center point.
Condition
Rev-01
33
2007/03