Locking AE/AF/AWB

Exposure, Focus and White-Balance are typically automatically adjusted as the scene changes. For pro-Camera apps, you can manually adjust Exposure Duration/ISO, Focus Lens Position and White-Balance Temperature and Tint Value and lock them in-place, if the device supports it.

Setting specific values

Setting custom Exposure Duration/ISO

If the CameraDevice supports Exposure Locking (see supportsExposureLocking) you can set a custom Exposure Duration/ISO via setExposureLocked(...):

const controller = ...
const format = ...
if (controller.device.supportsExposureLocking) {
  const exposureDuration = 1 / 60
  const iso = 200
  await controller.setExposureLocked(exposureDuration, iso)
}

Setting custom Focus Lens Position

If the CameraDevice supports Focus Locking (see supportsFocusLocking) you can set a custom Focus Lens Position via setFocusLocked(...):

const controller = ...
if (controller.device.supportsFocusLocking) {
  const lensPosition = 0.5
  await controller.setFocusLocked(lensPosition)
}

Setting custom White Balance Temperature and Tint

If the CameraDevice supports White-Balance Locking (see supportsWhiteBalanceLocking) you can set custom White Balance Temperature and Tint values via setWhiteBalanceLocked(...):

const controller = ...
if (controller.device.supportsWhiteBalanceLocking) {
  const temperature = 4500
  const tint = 20
  await controller.setWhiteBalanceLocked(temperature, tint)
}

Getting current values

At any point in time you can get the Camera's current Exposure, Focus or White-Balance values.

Getting current Exposure Duration/ISO

To get the current exposure values (for example to use VisionCamera as a light meter) use exposureDuration or iso:

const controller = ...
console.log(controller.exposureDuration)
console.log(controller.iso)

Getting current Focus Lens Position

To figure out how far away the current focus point is, simply get the current lensPosition:

const controller = ...
console.log(controller.lensPosition) // between 0...1

Getting current White Balance Gains

Lastly, the CameraController also exposes its current White-Balance Gains via whiteBalanceGains:

const controller = ...
console.log(controller.whiteBalanceGains)

Locking current values

To lock the current Exposure/Focus/White-Balance values at their current value (for example, after a tap to focus action), use lockCurrentExposure(), lockCurrentFocus() or lockCurrentWhiteBalance():

const controller = ...
const meteringPoint = ...
await controller.focusTo(meteringPoint, {
  autoResetAfter: null
})

if (controller.device.supportsExposureLocking) {
  await controller.lockCurrentExposure()
}
if (controller.device.supportsFocusLocking) {
  await controller.lockCurrentFocus()
}
if (controller.device.supportsWhiteBalanceLocking) {
  await controller.lockCurrentWhiteBalance()
}

To reset Exposure/Focus/White-Balance back to auto, use resetFocus():

const controller = ...
await controller.resetFocus()

Reacting to subject area changes

Once you lock AE/AF/AWB, the Camera keeps those values frozen no matter what the user points the device at. That's usually fine for a deliberate tap-to-focus, but if the user pans the Camera away from the subject, the scene becomes very under- or over-exposed and out-of-focus; so the locked values no longer make sense.

VisionCamera fires an onSubjectAreaChanged() listener whenever the scene substantially changes - for example, when the focus point drifts off the previously-focused subject. You can listen for this event and automatically reset AE/AF/AWB back to continuously auto-adjusting via resetFocus():

function App() {
  const camera = useRef<Camera>(null)

  return (
    <Camera
      style={StyleSheet.absoluteFill}
      isActive={true}
      device="back"
      ref={camera}
      onSubjectAreaChanged={() => {
        camera.current?.resetFocus()
      }}
    />
  )
}

function App() {
  const camera = useCamera({
    isActive: true,
    device: 'back',
    onSubjectAreaChanged: () => {
      camera?.resetFocus()
    }
  })
}

const session = ...
const controller = await session.configure(...)
const listener = controller.addSubjectAreaChangedListener(() => {
  controller.resetFocus()
})