UIImage scale and rotate based on exif flag

gistfile1.m

UIImage *scaleAndRotateImage(UIImage *image)
{
	int kMaxResolution = 1920;
	
	CGImageRef imgRef = image.CGImage;
	
	CGFloat width = CGImageGetWidth(imgRef);
	CGFloat height = CGImageGetHeight(imgRef);
	
	
	CGAffineTransform transform = CGAffineTransformIdentity;
	CGRect bounds = CGRectMake(0, 0, width, height);
	if (width > kMaxResolution || height > kMaxResolution) {
		CGFloat ratio = width/height;
		if (ratio > 1) {
			bounds.size.width = kMaxResolution;
			bounds.size.height = bounds.size.width / ratio;
		}
		else {
			bounds.size.height = kMaxResolution;
			bounds.size.width = bounds.size.height * ratio;
		}
	}
	
	CGFloat scaleRatio = bounds.size.width / width;
	CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
	CGFloat boundHeight;
	UIImageOrientation orient = image.imageOrientation;
	switch(orient) {
			
		case UIImageOrientationUp: //EXIF = 1
			transform = CGAffineTransformIdentity;
			break;
			
		case UIImageOrientationUpMirrored: //EXIF = 2
			transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
			transform = CGAffineTransformScale(transform, -1.0, 1.0);
			break;
			
		case UIImageOrientationDown: //EXIF = 3
			transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
			transform = CGAffineTransformRotate(transform, M_PI);
			break;
			
		case UIImageOrientationDownMirrored: //EXIF = 4
			transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
			transform = CGAffineTransformScale(transform, 1.0, -1.0);
			break;
			
		case UIImageOrientationLeftMirrored: //EXIF = 5
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
			transform = CGAffineTransformScale(transform, -1.0, 1.0);
			transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
			break;
			
		case UIImageOrientationLeft: //EXIF = 6
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
			transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
			break;
			
		case UIImageOrientationRightMirrored: //EXIF = 7
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeScale(-1.0, 1.0);
			transform = CGAffineTransformRotate(transform, M_PI / 2.0);
			break;
			
		case UIImageOrientationRight: //EXIF = 8
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
			transform = CGAffineTransformRotate(transform, M_PI / 2.0);
			break;
			
		default:
			[NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];
			
	}
	
	UIGraphicsBeginImageContext(bounds.size);
	
	CGContextRef context = UIGraphicsGetCurrentContext();
	
	if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
		CGContextScaleCTM(context, -scaleRatio, scaleRatio);
		CGContextTranslateCTM(context, -height, 0);
	}
	else {
		CGContextScaleCTM(context, scaleRatio, -scaleRatio);
		CGContextTranslateCTM(context, 0, -height);
	}
	
	CGContextConcatCTM(context, transform);
	
	CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
	UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	
	return imageCopy;
}