Rotate Newly Created iOS Image 90 Degrees Prior to Saving as PNG

Question

I have read numerous answers related to this, but I still can't get it to work.

I have a view where a user can sign their name. Here's how it looks: http://d.pr/i/McuE

I can successfully retrieve this image and save it to the file system, but I need to rotate it 90 degrees before saving so the signature reads from left-to-right.

// Grab the image
UIGraphicsBeginImageContext(self.signArea.bounds.size);
[self.signArea drawRect: self.signArea.bounds];
UIImage *signatureImage = UIGraphicsGetImageFromCurrentImageContext();

//-- ? -- Rotate the image (this doesn't work) -- ? --
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextRotateCTM(context, M_PI_2);

UIGraphicsEndImageContext();

//Save the image as a PNG in Documents folder
[UIImagePNGRepresentation(signatureImage) writeToFile:[[PPHelpers documentsPath] stringByAppendingPathComponent:@"signature-temp.png"] atomically:YES];

How can I rotate the image prior to saving?

Thanks in advance for your help. I'm on Xcode 5 using the iOS 7 SDK.

Answer 1

I finally got this to work using one of the answers on this post: How to Rotate a UIImage 90 degrees?

I used this method:

- (UIImage *)imageRotatedByDegrees:(UIImage*)oldImage deg:(CGFloat)degrees{
  //Calculate the size of the rotated view's containing box for our drawing space
  UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,oldImage.size.width, oldImage.size.height)];
  CGAffineTransform t = CGAffineTransformMakeRotation(degrees * M_PI / 180);
  rotatedViewBox.transform = t;
  CGSize rotatedSize = rotatedViewBox.frame.size;

  //Create the bitmap context
  UIGraphicsBeginImageContext(rotatedSize);
  CGContextRef bitmap = UIGraphicsGetCurrentContext();

  //Move the origin to the middle of the image so we will rotate and scale around the center.
  CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

  //Rotate the image context
  CGContextRotateCTM(bitmap, (degrees * M_PI / 180));

  //Now, draw the rotated/scaled image into the context
  CGContextScaleCTM(bitmap, 1.0, -1.0);
  CGContextDrawImage(bitmap, CGRectMake(-oldImage.size.width / 2, -oldImage.size.height / 2, oldImage.size.width, oldImage.size.height), [oldImage CGImage]);

  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  return newImage;
}

And then called it like this:

//Rotate it
UIImage *rotatedImage = [self imageRotatedByDegrees:signatureImage deg:90];

Thanks, everyone.