How can I do fast image processing from the iPhone camera?

Question

I am trying to write an iPhone application which will do some real-time camera image processing. I used the example presented in the AVFoundation docs as a starting point: sett

Answer 1

Set sessionPresent of capture session to AVCaptureSessionPresetLow as shown in the below sample code, this will increase the processing speed, but image from the buffer will be of low quality.

- (void)initCapture {
    AVCaptureDeviceInput *captureInput = [AVCaptureDeviceInput 
                                          deviceInputWithDevice:[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo] 
                                          error:nil];
    AVCaptureVideoDataOutput *captureOutput = [[AVCaptureVideoDataOutput alloc] init] ;
    captureOutput.alwaysDiscardsLateVideoFrames = YES; 
    captureOutput.minFrameDuration = CMTimeMake(1, 25);
    dispatch_queue_t queue;
    queue = dispatch_queue_create("cameraQueue", NULL);
    [captureOutput setSampleBufferDelegate:self queue:queue];
    dispatch_release(queue);
    NSString* key = (NSString*)kCVPixelBufferPixelFormatTypeKey; 
    NSNumber* value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA]; 
    NSDictionary* videoSettings = [NSDictionary dictionaryWithObject:value forKey:key]; 
    [captureOutput setVideoSettings:videoSettings]; 
    self.captureSession = [[AVCaptureSession alloc] init] ;
    [self.captureSession addInput:captureInput];
    [self.captureSession addOutput:captureOutput];
    self.captureSession.sessionPreset=AVCaptureSessionPresetLow;
    /*sessionPresent choose appropriate value to get desired speed*/

    if (!self.prevLayer) {
        self.prevLayer = [AVCaptureVideoPreviewLayer layerWithSession:self.captureSession];
    }
    self.prevLayer.frame = self.view.bounds;
    self.prevLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
    [self.view.layer addSublayer: self.prevLayer];

}