AK8851 Datasheet, PDF (28/80 Pages) Asahi Kasei Microsystems – NTSC/PAL/SECAM Digital Video Decoder

ASAHI KASEI
[AK8851]
20.Image Quality Adjusting Function
The AK8851 has Image Quality Adjusting functions that include Contrast, Brightness, Sharpness , Color Saturation and
Hue adjustments.
By default, the Image Quality adjustment function is invalid during the Vertical Blanking period. However Contrast and
Brightness adjustments can be enabled by setting [VBIIMGCTR]-bit of [Image Control Register].
(1) Contrast Adjustment
Contrast Adjustments are made by multiplying the Luminance signal (Y) by the gain factor set by [Contrast Control
Register](R/W)[Sub Address 0x0E].
Contrast factor is processed on the 8-bit data after 601 level conversion as shown in the following equation.
Yout = CONT* (YIN-128)+128; where Yout : Contrast arithmetic result
Yin : Contrast level before arithmetic operation
CONT: Contrast factor (register set value)
Adjustable range of the Contrast Gain factor is from 0 ~ 1.99 (1/128 step).When the result exceeds the specified range, it is
clipped to upper limit (254) or lower limit (1) ( output result ranges from 16 to 235 with 601 limit-bit at “1”).
Bit allocation of [Contrast Control Register] is as follows.
Sub Address 0x0E
bit 7
bit 6
CONT7
CONT6
1
0
bit 5
CONT5
0
bit 4
bit 3
CONT4
CONT3
Default Value
0
0
bit 2
CONT2
0
Default Value : 0x80
bit 1
bit 0
CONT1
CONT0
0
0
(2) Brightness Control
Brightness adjustment is accomplished by adding to the Luminance signal (Y) a value
Register](R/W)[Sub Address 0x0F].
Brightness factor is processed on the 8-bit data after 601 level conversion as follows.
set by [Brightness Control
Yout = Yin + BR
where Yout : Brightness arithmetic result
Yin : Brightness before arithmetic operation
BR: Brightness Factor ( register set value )
The Adjustable range of Brightness is from –127 to +127.The value setting is done in 2’s complement number.
When the result exceeds the specified range, it is clipped to the upper limit ( 254 ) or the lower limit ( 1 ).( output result
ranges from 16 to 235 with 601 limit-bit at “1”).
Bit allocation of [Brightness Control Register] is shown as follows.
Sub Address 0x0F
Default Value : 0x00
bit 7
bit 6
bit 5
bit 4
bit 3
bit 2
bit 1
bit 0
BR7
BR6
BR5
BR4
BR3
BR2
BR1
BR0
Default Value
0
0
0
0
0
0
0
0
MS0244-E-03
28
Confidential
2005 / 07