Image quality taken by iPhone camera using AVCaptureVideoDataOutputSampleBufferDelegate

I use iPhone camera to capture images in my iOS APP.

AVCaptureVideoDataOutputSampleBufferDelegate

AVCaptureDevice *videoDevice = [AVCamViewController deviceWithMediaType:AVMediaTypeVideo preferringPosition:AVCaptureDevicePositionBack]; 
AVCaptureDeviceInput *videoDeviceInput = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error]; 
if (error) { NSLog(@"%@", error); } 
if ([session canAddInput:videoDeviceInput]) 
{ 
  [session addInput:videoDeviceInput]; [self setVideoDeviceInput:videoDeviceInput];
   dispatch_async(dispatch_get_main_queue(),    ^{ 
   [[(AVCaptureVideoPreviewLayer *)[[self previewView] layer] connection] setVideoOrientation:(AVCaptureVideoOrientation)[self interfaceOrientation]]; }); 
}

The quality of the image taken by

AVCaptureVideoDataOutputSampleBufferDelegate and that of the image taken iPhone's camera app are much different. How can I adjust the image quality to have the same or closer quality as camera app.