Question

I am performing rotation on an UIImageView and then i try to crop a part of it and save it as an UIImage. The UIImageView rotates however it always crops the same part of the photo. So the cropping does not take into account the image rotation. What am i doing wrong?

//rotate image 
CGRect new = CGRectMake(0, 0, 100, 50);
CGAffineTransform rotation = CGAffineTransformMakeRotation(5);
[photo setTransform:rotation];

// crop image 
CGImageRef imageRef = CGImageCreateWithImageInRect([photo.image CGImage], new);
UIImage *croppedImage = [UIImage imageWithCGImage:imageRef]; 
CGImageRelease(imageRef);

// display crop bounds 
UIView* faceBounds = [[UIView alloc] initWithFrame:new];
faceBounds.layer.borderWidth = 2;
faceBounds.layer.borderColor = [[UIColor redColor] CGColor];

Answer 1

Use the following snippet for rotating image data.

The input data is inAngle (angle in radians) and inImage (UIImage instance).

What this does, it creates an image context, applies the transformation to it and draws the original image into that context. The resulting image data will now be stored in resultImage.

The first three lines handle the calculation of the bounding result image frame.

UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, inImage.size.width, inImage.size.height)];
rotatedViewBox.transform = CGAffineTransformMakeRotation(inAngle);
CGSize rotatedSize = rotatedViewBox.frame.size;

UIGraphicsBeginImageContext(rotatedSize);
CGContextRef bitmap = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(bitmap, rotatedSize.width / 2.0f, rotatedSize.height / 2.0f);
CGContextRotateCTM(bitmap, inAngle);
CGContextScaleCTM(bitmap, 1.0f, -1.0f);
CGContextDrawImage(bitmap, CGRectMake(-inImage.size.width / 2.0f,
                                      -inImage.size.height / 2.0f,
                                      inImage.size.width,
                                      inImage.size.height),
                                      inImage.CGImage);
UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();