Comparing UIImage

Question

How can I compare an image to another one?

Thanks!

Answer 1

This is what I use in my unit tests to compare images. Unlike other methods (e.g., UIImagePNGRepresentation), it works even if the images have a different color space (e.g., RGB and grayscale).

@implementation UIImage (HPIsEqualToImage)

- (BOOL)hp_isEqualToImage:(UIImage*)image
{
    NSData *data = [image hp_normalizedData];
    NSData *originalData = [self hp_normalizedData];
    return [originalData isEqualToData:data];
}

- (NSData*)hp_normalizedData
{
    const CGSize pixelSize = CGSizeMake(self.size.width * self.scale, self.size.height * self.scale);
    UIGraphicsBeginImageContext(pixelSize);
    [self drawInRect:CGRectMake(0, 0, pixelSize.width, pixelSize.height)];
    UIImage *drawnImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return UIImagePNGRepresentation(drawnImage);
}

@end

It's not very efficient, so I would recommend against using it in production code unless performance is not an issue.