Data Sheet

10.13.2009 PRODUCT SPECIFICATION proprietary to OmniVision Technologies
5-1
5 image sensor processor digital functions
5.1 white balance control
The OV7675/OV7175 supports Automatic White Balance (AWB) function. The AWB circuit automatically adjusts red,
green and blue gain to a make white target be white regardless of the lighting. The OV7675/OV7175 supports both
automatic and manual mode. In AWB mode, after the initial pixel level adjustment, the Red and Blue channel gains are
optimized to the Green channel to set the white balance. When AWB function is disabled, the user can also manually
adjust red, green and blue gain to make image White Balanced. Following is the summery the two White Balance modes.
• Manual mode: Red, Green and Blue gain are set manually
• Automatic mode: Red, Green and Blue gain are controlled by the AWB circuit. The AWB circuit adjusts the gain to
make red, green and blue average values equal based on a grey world assumption
5.2 automatic white balance
In general, the white balance is done in two steps: by first adjusting the Red/Blue gain to match the green channel and
then by controlling the AWB response time.
table 5-1 is the common control registers of White Balance.
table 5-1 white balance control registers
sub register
address
default
value description
COM8 0x13
Bit[1]: AWB enable
0: Disable AWB, White Balance is in manual mode
1: Enable AWB, White Balance is in auto mode
COM16 0x41
Bit[3]: AWB gain enable has to be enabled in both manual and
automatic white balancing mode. When AWB gain is bypassed,
image output will be based on the default R/G/B gain (1x).
0: Bypass AWB gain
1: AWB gain enabled
BLUE 0x01
Bit[7:0]: Blue gain
Auto mode: gain value updates automatically
Manual mode: gain value determined by user.
Blue Gain = BLUE[7:0] / 0x40, BLUE[7:0] ≥ 0x40
RED 0x02
Bit[7:0]: Red gain
Auto mode: gain value updates automatically
Manual mode: gain value determined by user.
Red Gain = RED[7:0] / 0x40, RED[7:0] ≥ 0x40
GREEN 0x6A
Bit[7:0]: Green gain
Auto mode: gain value updates automatically
Manual mode: gain value determined by user.
Green Gain = GREEN[7:0] / 0x40, GREEN[7:0] ≥ 0x40
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