How to rotate an image correctly?

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];
}

I'd guess that the issue lies in the contentMode of the imageView - the rotated image do not fit the imageView anymore so it is downscaled. — Mr. Hedgehog, Apr 27 '17 at 17:29
@matt `UIGraphicsBeginImageContextWithOptions(rotatedSize, NO, self.scale);` I have changed and with no result also edited the question and added an image which illustrate the problem — astrolka, Apr 27 '17 at 17:55
@matt I have changed it to YES and uploaded another image hope it will show my problem — astrolka, Apr 27 '17 at 18:27
Make sure the `backgroundColor` of the `UIImageView` is set to `[UIColor clearColor]`. — Sulthan, Apr 27 '17 at 18:46
@Sulthan the problem is in that that image is getting smaller after the second rotation — astrolka, Apr 27 '17 at 18:48
Could you specify exactly what result you _want_ to get? How big should the resulting `image` be, precisely, and how should the drawn picture of the kittens lie within it? — matt, Apr 27 '17 at 19:05
@matt I got this code from this answer http://stackoverflow.com/a/11667808 — astrolka, Apr 27 '17 at 19:06
@matt wow to rotate the original image is really good idea! but to rotate only image view I cannot as the user will share this image. Thank you! — astrolka, Apr 27 '17 at 19:08

score 1 · Accepted Answer · answered Apr 27 '17 at 19:57

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.

the problem is this: `- (IBAction)rotateAction:(id)sender { self.imageView.image = [self.imageView.image rotateImageByDegree:22]; }` all I needed to do was to store actual angle and rotate initial image: `- (IBAction)rotateAction:(id)sender { self.angle += 22; self.imageView.image = [[UIImage imageNamed:@"kittens"] rotateImageByDegree:self.angle]; }` Please update the answer I'll accept it — astrolka, Apr 27 '17 at 20:13

How to rotate an image correctly?

1 Answers1