Question

I am trying to use CoreImage’s face detection in iOS 5 but it is not detecting anything. I am trying to detect faces in an image that was just captured by the camera using this code:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
    UIImage *image = [info objectForKey:@"UIImagePickerControllerOriginalImage"];
    NSDictionary *detectorOptions = [[NSDictionary alloc] initWithObjectsAndKeys:CIDetectorAccuracyHigh, CIDetectorAccuracy, nil];     
    CIDetector *faceDetector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil options:detectorOptions];
    NSArray *features = [faceDetector featuresInImage:image.CIImage];
    NSLog(@"Features = %@", features);
    [self dismissModalViewControllerAnimated:YES];
}

This compiles and runs fine but it the features array is always empty regardless of what’s in the image… Any ideas?

Answer 1

I can’t reply to your @14:52 comment directly Vic320, but I’ve been playing with the front camera for face detection – I went round and round in circles since I couldn’t get the front camera to pick up my face at all…

Turns out it’s very sensitive to rotation – I noticed that when holding my iPad2 in portrait (as you’d expect while using the front camera) I was getting less than 10% recognition accuracy. On a whim, turned it sideways and was getting 100% recognition with the front camera.

Simple fix for this if you’re using the front camera always in portrait is to add this little snippet:

NSDictionary* imageOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithInt:6] forKey:CIDetectorImageOrientation];
NSArray* features = [detector featuresInImage:image options:imageOptions];

That 6 in there forces the detector to operate in portrait mode. Apple’s SquareCam Sample has a whole bunch of utility methods to figure out what orientation you’re in if you need it to dynamically figure out your orientation.