Datasheet

Confidential for truly Only
color CMOS QSXGA (5 megapixel) image sensor with OmniBSI™ technology
OV5647
proprietary to OmniVision Technologies PRELIMINARY SPECIFICATION version 1.0
4.6 AEC/AGC steps
The AEC and AGC work together to obtain adequate exposure/gain based on the current environmental illumination. In
order to achieve the best signal-to-noise ratio (SNR), extending the exposure time is always preferred rather than raising
the gain when the current illumination is getting brighter. Vice versa, under dark conditions, the action to decrease the
gain is always taken prior to shortening the exposure time.
4.6.1 auto exposure control (AEC)
The function of the AEC is to calculate the necessary integration time of the next frame and send the information to the
timing control block. Based on the statistics of previous frames, the AEC is able to determine whether the integration time
should increase, decrease, fast increase, fast decrease, or remain the same.
In extremely bright situations, the LAEC activates, allowing integration time to be less than one row. In extremely dark
situations, the night mode activates, allowing integration time to be larger than one frame.
To avoid image flickering under a periodic light source, the integration time can be adjusted in steps of integer multiples
of the period of the light source.
4.6.2 LAEC
If the integration time is only one row period but the image is too bright, AEC will enter LAEC mode. LAEC ON/OFF can
be set in register bit 0x3A00[6].
4.6.3 banding mode ON with AEC
In Banding ON mode, the exposure time will fall in steps of integer multiples of the period of light intensity.
Banding ON/OFF can be set in register 0x3A00[5].
For a given light flickering frequency, the band step can be expressed in units of row period.
The band steps for 50Hz and 60Hz light sources can be set in registers {0x3A08[1:0], 0x3A09[7:0]} and {0x3A0A[1:0],
0x3A0B[7:0]}, respectively.
• Banding mode OFF with AEC
• When banding mode is OFF, integration time increases/decreases as normal. It is not necessarily multiples of band
steps.
4.6.4 night mode
The OV5647 supports long integration time such as 1 frame, 2 frames, 3 frames, 4 frames, 5 frames, 6 frames, 7 frames,
and 8 frames in dark conditions. This is achieved by slowing down the original frame rate and waiting for exposure. Night
mode ceiling can be set in register bits 0x3A02[15:8], 0x3A03[7:0]. Night mode can be disabled by setting register bit
0x3A00[2] to 0. Also, when in night mode, the increase and decrease step can be based on band or frames, depending
on register 0x3A05[6]. The minimum increase/decrease step can be one band. The step can be based both on bands
and frames.
4.6.5 auto gain control (AGC)
Unlike prolonging integration time, increasing gain will amplify both signal and noise. Thus, AGC usually starts after AEC
is full. However, in cases where adjacent AEC step changes are too large (>1/16), AGC steps should be inserted in
between. The AGC ceiling can be set in {0x3A18[1:0], 0x3A19[7:0]}.