Need to modify image before displaying on AVCaptureVideoPreviewLayer - iphone

Question

I'm using AVCaptureSession to capture video from my iPhone 3G and I need to capture the image and change it before displaying on my AVCaptureVideoPreviewLayer. In my current implementation, I am simply implementing the captureOutput: method and displaying the UIImage in a UIImageView, but that does not work for some reason.
Any ideas? Subclass AVCaptureSession somehow?
Thanks!

Answer 1

Check out this https://developer.apple.com/library/ios/#samplecode/SquareCam/Introduction/Intro.html
I think it does this.
It draws face boxes onto faces.
- (void)drawFaceBoxesForFeatures:(NSArray *)features forVideoBox:(CGRect)clap orientation:(UIDeviceOrientation)orientation// videoMirrored:(const BOOL)ISVIDEOMIRRORED
{
NSArray *sublayers = [NSArray arrayWithArray:[previewLayer sublayers]];
NSInteger sublayersCount = [sublayers count], currentSublayer = 0;
NSInteger featuresCount = [features count], currentFeature = 0;
[CATransaction begin];
[CATransaction setValue:(id)kCFBooleanTrue forKey:kCATransactionDisableActions];
// hide all the face layers
for ( CALayer *layer in sublayers ) {
if ( [[layer name] isEqualToString:#"FaceLayer"] )
[layer setHidden:YES];
}
if ( featuresCount == 0 || !detectFaces ) {
[CATransaction commit];
return; // early bail.
}
CGSize parentFrameSize = [previewView frame].size;
NSString *gravity = [previewLayer videoGravity];
//BOOL isMirrored = isVideoMirrored;
#warning Deprecated
const BOOL isMirrored = [previewLayer isMirrored]; // deprecated
CGRect previewBox = [SquareCamViewController videoPreviewBoxForGravity:gravity
frameSize:parentFrameSize
apertureSize:clap.size];
for ( CIFaceFeature *ff in features ) {
// find the correct position for the square layer within the previewLayer
// the feature box originates in the bottom left of the video frame.
// (Bottom right if mirroring is turned on)
CGRect faceRect = [ff bounds];
// flip preview width and height
CGFloat temp = faceRect.size.width;
faceRect.size.width = faceRect.size.height;
faceRect.size.height = temp;
temp = faceRect.origin.x;
faceRect.origin.x = faceRect.origin.y;
faceRect.origin.y = temp;
// scale coordinates so they fit in the preview box, which may be scaled
CGFloat widthScaleBy = previewBox.size.width / clap.size.height;
CGFloat heightScaleBy = previewBox.size.height / clap.size.width;
faceRect.size.width *= widthScaleBy;
faceRect.size.height *= heightScaleBy;
faceRect.origin.x *= widthScaleBy;
faceRect.origin.y *= heightScaleBy;
if ( isMirrored )
faceRect = CGRectOffset(faceRect, previewBox.origin.x + previewBox.size.width - faceRect.size.width - (faceRect.origin.x * 2), previewBox.origin.y);
else
faceRect = CGRectOffset(faceRect, previewBox.origin.x, previewBox.origin.y);
CALayer *featureLayer = nil;
// re-use an existing layer if possible
while ( !featureLayer && (currentSublayer < sublayersCount) ) {
CALayer *currentLayer = [sublayers objectAtIndex:currentSublayer++];
if ( [[currentLayer name] isEqualToString:#"FaceLayer"] ) {
featureLayer = currentLayer;
[currentLayer setHidden:NO];
}
}
// create a new one if necessary
if ( !featureLayer ) {
featureLayer = [CALayer new];
[featureLayer setContents:(id)[square CGImage]];
[featureLayer setName:#"FaceLayer"];
[previewLayer addSublayer:featureLayer];
[featureLayer release];
}
[featureLayer setFrame:faceRect];
switch (orientation) {
case UIDeviceOrientationPortrait:
[featureLayer setAffineTransform:CGAffineTransformMakeRotation(DegreesToRadians(0.))];
break;
case UIDeviceOrientationPortraitUpsideDown:
[featureLayer setAffineTransform:CGAffineTransformMakeRotation(DegreesToRadians(180.))];
break;
case UIDeviceOrientationLandscapeLeft:
[featureLayer setAffineTransform:CGAffineTransformMakeRotation(DegreesToRadians(90.))];
break;
case UIDeviceOrientationLandscapeRight:
[featureLayer setAffineTransform:CGAffineTransformMakeRotation(DegreesToRadians(-90.))];
break;
case UIDeviceOrientationFaceUp:
case UIDeviceOrientationFaceDown:
default:
break; // leave the layer in its last known orientation
}
currentFeature++;
}
[CATransaction commit];
}