How to rotate an image correctly? - ios

Question

What is wrong with this method? The problem is that rotated image has transparent box after rotation. How can I get rid of it?
#implementation UIImage (RotationMethods)
static CGFloat getRadianFromDegree(CGFloat degrees)
{return degrees * M_PI / 180;};
- (UIImage *) rotateImageByDegree:(CGFloat)degrees
{
UIView *rotatedImageView = [[UIView alloc] initWithFrame:CGRectMake(0,0,self.size.width, self.size.height)];
CGAffineTransform t = CGAffineTransformMakeRotation(getRadianFromDegree(degrees));
rotatedImageView.transform = t;
CGSize rotatedSize = rotatedImageView.frame.size;
UIGraphicsBeginImageContextWithOptions(rotatedSize, YES, self.scale);
CGContextRef bitmap = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);
CGContextRotateCTM(bitmap, getRadianFromDegree(degrees));
CGContextScaleCTM(bitmap, 1.0, -1.0);
CGContextDrawImage(bitmap, CGRectMake(-self.size.width / 2, -self.size.height / 2, self.size.width, self.size.height), [self CGImage]);
UIImage *rotatedImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return rotatedImage;
}
#end
EDIT1
EDIT2
Here is the code of rotate action:
- (IBAction)rotateAction:(id)sender {
self.imageView.image = [self.imageView.image rotateImageByDegree:22];
}

Answer 1

The problem is caused by code you are not showing us.
How do I know? I ran your code, the code you did show — and there is no gap between the rotated image and the image boundary:
In that screen shot, the main view background is red, and I have deliberately set the image view background to white so that you can see that the corners of the rotated kittens picture meet the containing image edges.
If we set the image view background to clear, the white disappears and we see the rotated kittens on the red background.
Thus we may conclude that the "shrinkage" you are complaining about is something you are doing, something that you have not revealed in your question.