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.

Did you draw your image to the CGContext with CGContextDrawImage()? — Stephen Johnson, Dec 24 '13 at 18:16
You need to convert degrees to radians when calling CGContextRotateCTM — yurish, Dec 24 '13 at 19:07
What are those 'numerous answers,' exactly? List several of them, please. — El Tomato, Dec 24 '13 at 20:58
@StephenJohnson I'm not entirely sure. I just have a view that enables "drawing" with touch, so the image isn't created until the beginning of the above code with `UIGraphicsBeginImageContext`. This stuff is pretty foreign to me. — Clifton Labrum, Dec 24 '13 at 23:55
Here are some of the other things I tried with no success, mostly because I'm generally lost with this stuff. This is an isolated bit of functionality in my app and I'm new to image manipulation. — Clifton Labrum, Dec 24 '13 at 23:56
http://stackoverflow.com/questions/10307521/ios-png-image-rotated-90-degrees — Clifton Labrum, Dec 24 '13 at 23:57
http://stackoverflow.com/questions/6326720/objective-c-how-can-you-rotate-text-for-uibutton-and-uilabel — Clifton Labrum, Dec 24 '13 at 23:57
http://stackoverflow.com/questions/16766111/rotate-image-using-cgcontextdrawimage — Clifton Labrum, Dec 24 '13 at 23:58
I don't know if iOS SDK has the radians function, but you can convert degrees to radians easily without it, see radians definition. 90 degrees in radians is M_PI_2 constant from math.h — yurish, Dec 25 '13 at 07:14
@CliftonLabrum do you have any code where your comment for "rotate the image" is? Or is the all the code you have? — Stephen Johnson, Dec 26 '13 at 20:56
This is what I have under "rotate the image": `CGContextRef context = UIGraphicsGetCurrentContext(); CGContextRotateCTM(context, M_PI_2);` — Clifton Labrum, Dec 27 '13 at 20:49
I updated my code in the question to reflect what I have so far. — Clifton Labrum, Dec 27 '13 at 20:52

score 18 · Accepted Answer · edited May 23 '17 at 11:51

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.

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

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