iOS: How to retrieve image dimensions without loading CGImage into memory

Image.m

// This method requires ImageIO.framework
#import <ImageIO/ImageIO.h>

- (CGSize)sizeOfImageAtURL:(NSURL *)imageURL
{
    // With CGImageSource we avoid loading the whole image into memory
    CGSize imageSize = CGSizeZero;
    CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)imageURL, NULL);
    if (source) {
        NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:NO] forKey:(NSString *)kCGImageSourceShouldCache];
        CFDictionaryRef properties = (NSDictionary *)CGImageSourceCopyPropertiesAtIndex(source, 0, (CFDictionaryRef)options);
        if (properties) {
            NSNumber *width = [(NSDictionary *)properties objectForKey:(NSString *)kCGImagePropertyPixelWidth];
            NSNumber *height = [(NSDictionary *)properties objectForKey:(NSString *)kCGImagePropertyPixelHeight];
            if ((width != nil) && (height != nil))
                imageSize = CGSizeMake(width.floatValue, height.floatValue);
            CFRelease(properties);
        }
        CFRelease(source);
    }
    return imageSize;
}