Capture Controls (OV5640)

This page applies to the OV5640. The VD66GY has no on-sensor control loops; its exposure and white balance are handled by the image signal processor, described in The Global Shutter Camera.

The OV5640 runs three automatic control loops: exposure, gain and white balance. Each re-meters every frame. Classical vision algorithms generally require fixed capture settings, since a colour threshold or a barcode contrast tuned under one metering result changes under the next. The camera object exposes the controls.

#Holding the current values

Disabling an automatic loop retains its last converged value rather than resetting to a default:

camera.setAutoExposure(false);
camera.setAutoGain(false);
camera.setAutoWhiteBalance(false);

The camera is pointed at a representative scene, allowed to settle for about a second, and the loops are then disabled. Subsequent frames are exposed identically.

#Explicit values

camera.setAutoExposure(false);
camera.setExposureUs(4000);      // 4 ms
camera.setAutoGain(false);
camera.setGain(2.0f);            // 2x

Exposure is in microseconds and is clamped to the current mode's frame period. Gain is a multiplier.

#Exposure and gain interaction

Automatic exposure controls image brightness towards a target and uses whichever actuator remains enabled. If only exposure is locked, gain compensates and the image returns to the same brightness within a frame. The exposure value is held; the brightness is not. Both are locked for a reproducible image.

The one-sided case has a use: a short fixed exposure with automatic gain freezes motion at the cost of noise.

#Methods

Methods return 0 on success and a negative value when the sensor does not support the control. They may be called at any time after Vision.begin().

#Host controls

With an OV5640 fitted, Neuro Studio shows a Camera Controls panel with the same controls. The board reports its capabilities through controlCaps(); on a sensor without them, such as the VD66GY, the panel is not shown. Host changes take effect immediately and are not persisted. Values that must survive a reboot are placed in the sketch or stored as an asset.

#Autofocus

The OV5640 module has a voice coil lens and a focus coprocessor. cfg.af sets the mode at start and camera.autoFocus() changes it later. The first use loads focus firmware into the sensor and takes about one second.

AF_CONTINUOUS refocuses as the scene changes. AF_SINGLE from loop() refocuses on demand. Fine detail such as QR codes, barcodes and AprilTags requires focus; a blurred code does not decode.

#Strobe

Carriers with a flash LED connect it to the sensor's strobe pin. STROBE_ENABLED pulses the LED with each exposure. The LED cannot be held on continuously. On a carrier without the LED the call has no effect.

#VD66GY

The VD66GY outputs raw Bayer data and has no on-chip automatic loops. Exposure and white balance are handled by the STM32N6's image signal processor, configured through cfg.isp_enabled. The methods on this page return -1 on that sensor. See The Global Shutter Camera.