Data Sheet

CMOS VGA (640 x 480) image sensor with OmniPixel3-HS™ technology
OV7675/OV7175
proprietary to OmniVision Technologies PRODUCT SPECIFICATION version 2.0
4.4.7 gain control
The OV7675/OV7175 supports both automatic gain control (AGC) and manual gain control modes.
4.4.7.1 manual gain control
The manual gain control mode allows for the companion backend processor to control the OV7675/OV7175 gain
value. The companion backend chip can write gain values to register {0x03[7:6],0x00[7:0]} according to its gain
control algorithm. The formula to calculate gain from register value is:
The gain to register value correlation is shown in table 4-7.
4.4.8 automatic gain control (AGC)
The AGC function allows the image sensor to adjust image luminance by changing gain without external command or
control. Register setting 0x13[2] enables or disables AGC function. When AGC function is enabled, gain is automatically
adjusted and the result is saved in register 0x00[6:0]. The maximum gain is limited by gain ceiling (refer to
table 4-7).
When the AGC function is disabled, the gain control is still active, and user can change the gain setting.
The AGC uses the same algorithm as the AEC and shares most of the control registers with the AEC. table 4-7
summarizes the general controls for the AGC. To achieve best image quality, the sensor always increases exposure time
prior to gain and reduces gain prior to exposure time.
table 4-7 AGC general control registers
address register name description
0x13 REG13
Bit[2]: AGC function auto/manual selection
0: manual gain control
1: automatic gain control enable
0x00 GAIN
Bit[7:0]: Gain setting. Read-only when AGC is enabled. When AGC
is disabled, these registers can be programmed manually
.
0x03 VREF
Bit[7:6]: Gain setting. Read-only when AGC is enabled. When AGC
is disabled, these registers can be programmed manually
.
0x14 REG14
Bit[6:4]: Automatic gain ceiling - maximum AGC value
000: 2x
001: 4x
010: 8x
011: 16x
100: 32x
101 64x
110: 128x
111: Not used
gain = (0x03[7] + 1) x (0x03[6] + 1) x (0x00[7] + 1) (0x00[6] + 1) x
(0x00[5] + 1) x (0x00[4] + 1) x ( + 1)
0x00[3:0]
16
gain = (0x03[7] + 1) x (0x03[6] + 1) x (0x00[7] + 1) (0x00[6] + 1) x
(0x00[5] + 1) x (0x00[4] + 1) x ( + 1)
0x00[3:0]
16
gain = (0x03[7] + 1) x (0x03[6] + 1) x (0x00[7] + 1) (0x00[6] + 1) x
(0x00[5] + 1) x (0x00[4] + 1) x ( + 1)
0x00[3:0]
16
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