CIDetector and UIImagePickerController

Question

I\'m trying to implement the built-in iOS 5 face detection API. I\'m using an instance of UIImagePickerController to allow the user to take a photo and then I\'

Answer 1

@tonyc Your solution only works for a specific case that is "UIImageOrientationRight". The problem comes from the difference between the orientation in UIImage and CIDetectorImageOrientation. From iOS docs:

CIDetectorImageOrientation

A key used to specify the display orientation of the image whose features you want to detect. This key is an NSNumber object with the same value as defined by the TIFF and EXIF specifications; values can range from 1 through 8. The value specifies where the origin (0,0) of the image is located. If not present, the default value is 1, which means the origin of the image is top, left. For details on the image origin specified by each value, see kCGImagePropertyOrientation.

Available in iOS 5.0 and later.

Declared in CIDetector.h.

So the problem now is the conversion between these two orientations, here is what I did in my code, I tested and it worked for all orientations:

int exifOrientation;
switch (self.image.imageOrientation) {
    case UIImageOrientationUp:
        exifOrientation = 1;
        break;
    case UIImageOrientationDown:
        exifOrientation = 3;
        break;
    case UIImageOrientationLeft:
        exifOrientation = 8;
        break;
    case UIImageOrientationRight:
        exifOrientation = 6;
        break;
    case UIImageOrientationUpMirrored:
        exifOrientation = 2;
        break;
    case UIImageOrientationDownMirrored:
        exifOrientation = 4;
        break;
    case UIImageOrientationLeftMirrored:
        exifOrientation = 5;
        break;
    case UIImageOrientationRightMirrored:
        exifOrientation = 7;
        break;
    default:
        break;
}

NSDictionary *detectorOptions = @{ CIDetectorAccuracy : CIDetectorAccuracyHigh }; // TODO: read doc for more tuneups
CIDetector *faceDetector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil options:detectorOptions];

NSArray *features = [faceDetector featuresInImage:[CIImage imageWithCGImage:self.image.CGImage]
                                          options:@{CIDetectorImageOrientation:[NSNumber numberWithInt:exifOrientation]}];