iOS - AVCaptureDevice - Autofocus & Exposure with camera capture - ios

Question

I have been implementing Custom Camera using AVCaptureDevice, which require AutoFocus & Exposure to work nicely. I am using the following code to do the camera initialisation
- (void) initializeCamera {
AVAuthorizationStatus status = [AVCaptureDevice authorizationStatusForMediaType:AVMediaTypeVideo];
if(status == AVAuthorizationStatusAuthorized) { // authorized
[self.captureVideoPreviewLayer removeFromSuperlayer];
self.captureSession = [[AVCaptureSession alloc] init];
self.captureSession.sessionPreset = AVCaptureSessionPresetPhoto;
[self removeDeviceObserverForFocus];
self.captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
[self addDeviceObserverForFocus];
NSError *error = nil;
[self.captureDevice lockForConfiguration:nil]; //you must lock before setting torch mode
[self.captureDevice setSubjectAreaChangeMonitoringEnabled:YES];
[self.captureDevice unlockForConfiguration];
//Capture layer
self.captureVideoPreviewLayer = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.captureSession];
self.captureVideoPreviewLayer.bounds = CGRectMake(0, 0, CGRectGetWidth([UIScreen mainScreen].bounds), CGRectGetHeight([UIScreen mainScreen].bounds));
self.captureVideoPreviewLayer.position = CGPointMake(CGRectGetMidX(self.captureVideoPreviewLayer.bounds), CGRectGetMidY(self.captureVideoPreviewLayer.bounds));
[self.captureVideoPreviewLayer setVideoGravity:AVLayerVideoGravityResizeAspectFill];
self.captureVideoPreviewLayer.connection.enabled = YES;
[self.viewCamera.layer insertSublayer:self.captureVideoPreviewLayer atIndex:0];
//Capture input
self.captureInput = [AVCaptureDeviceInput deviceInputWithDevice:self.captureDevice error:&error];
if (!self.captureInput) {
[self capturePhoto];
}
else {
if ([self.captureSession canAddInput:self.captureInput]) {
[self.captureSession addInput:self.captureInput];
}
}
self.captureOutput = [[AVCaptureStillImageOutput alloc] init];
[self.captureOutput setOutputSettings:#{AVVideoCodecKey : AVVideoCodecJPEG}];
[self.captureSession addOutput:self.captureOutput];
//THIS LINE
[self.captureSession setSessionPreset:AVCaptureSessionPresetPhoto];
// setup metadata capture
AVCaptureMetadataOutput *metadataOutput = [[AVCaptureMetadataOutput alloc] init];
CGRect visibleMetadataOutputRect = [self.captureVideoPreviewLayer metadataOutputRectOfInterestForRect:self.vwCamera.bounds];
metadataOutput.rectOfInterest = visibleMetadataOutputRect;
[self.captureSession addOutput:metadataOutput];
dispatch_async(dispatch_get_main_queue(), ^{
[self.captureSession startRunning];
});
}
else if(status == AVAuthorizationStatusNotDetermined){ // not determined
//Try for getting permission
[AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
[self performSelectorOnMainThread:#selector(initializeCamera) withObject:nil waitUntilDone:NO];
}];
}
}
- (void)removeDeviceObserverForFocus {
#try {
while ([self.captureDevice observationInfo] != nil) {
[self.captureDevice removeObserver:self forKeyPath:#"adjustingFocus"];
}
}
#catch (NSException *exception) {
NSLog(#"Exception");
}
#finally {
}
}
- (void)addDeviceObserverForFocus {
[self.captureDevice addObserver:self forKeyPath:#"adjustingFocus" options:NSKeyValueObservingOptionNew context:nil];
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if( [keyPath isEqualToString:#"adjustingFocus"] ){
BOOL adjustingFocus = [ [change objectForKey:NSKeyValueChangeNewKey] isEqualToNumber:[NSNumber numberWithInt:1] ];
if (adjustingFocus) {
[self showFocusSquareAtPoint:self.viewCamera.center];
}
}
}
To monitor focus by movement of camera I am doing the following..
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(avCaptureDeviceSubjectAreaDidChangeNotification:) name:AVCaptureDeviceSubjectAreaDidChangeNotification object:nil];
#pragma mark - AVCaptureDeviceSubjectAreaDidChangeNotification
-(void)avCaptureDeviceSubjectAreaDidChangeNotification:(NSNotification *)notification{
CGPoint devicePoint = CGPointMake( 0.5, 0.5 );
[self focusWithMode:AVCaptureFocusModeContinuousAutoFocus exposeWithMode:AVCaptureExposureModeContinuousAutoExposure atDevicePoint:devicePoint monitorSubjectAreaChange:NO];
[self showFocusSquareAtPoint:self.vwCamera.center];
}
- (void)focusWithMode:(AVCaptureFocusMode)focusMode exposeWithMode:(AVCaptureExposureMode)exposureMode atDevicePoint:(CGPoint)point monitorSubjectAreaChange:(BOOL)monitorSubjectAreaChange
{
dispatch_async( dispatch_get_main_queue(), ^{
AVCaptureDevice *device = self.captureDevice;
NSError *error = nil;
if ( [device lockForConfiguration:&error] ) {
// Setting (focus/exposure)PointOfInterest alone does not initiate a (focus/exposure) operation.
// Call -set(Focus/Exposure)Mode: to apply the new point of interest.
if ( device.isFocusPointOfInterestSupported && [device isFocusModeSupported:focusMode] ) {
device.focusPointOfInterest = point;
device.focusMode = focusMode;
}
if ( device.isExposurePointOfInterestSupported && [device isExposureModeSupported:exposureMode] ) {
device.exposurePointOfInterest = point;
device.exposureMode = exposureMode;
}
device.subjectAreaChangeMonitoringEnabled = monitorSubjectAreaChange;
[device unlockForConfiguration];
}
else {
NSLog( #"Could not lock device for configuration: %#", error );
}
} );
}
Everything works as expected when I use this [self.captureSession setSessionPreset:AVCaptureSessionPresetPhoto];
If I change the camera preset to something else like AVCaptureSessionPresetHigh AutoFocus and Exposure doesn't work well as expected..
Anyone who has come across such situation?
Thank you for help.

Answer 1

Are you trying to take a picture or record video? Cause the High preset is for video and the exposure and focus work differently(I believe). Here is info on the different presets in the docs - AVCaptureSessionPresets