UIKit rotation category on UIImage

UIImage+Rotate.h

//
//  UIImage+Rotate.h
//
//  Created by Foundry on 21/09/2013.
//

#import <UIKit/UIKit.h>

@interface UIImage (Rotate)

- (UIImage*) rotateExifToOrientation:(UIImageOrientation)orientation;

- (UIImage*) rotateBitmapToOrientation:(UIImageOrientation)orientation;

@end

UIImage+Rotate.m

//
//  UIImage+Rotate.m
//
//  Created by Foundry on 21/09/2013.
//
//see also http://blog.logichigh.com/2008/06/05/uiimage-fix/
//see also http://blog.9mmedia.com/?p=932
//see also http://stackoverflow.com/questions/14484816/force-uiimagepickercontroller-to-take-photo-in-portrait-orientation-dimensions-i/14491293#14491293
//see also http://stackoverflow.com/questions/13971491/captured-photo-automatically-rotated-during-upload-in-ios-6-0-or-iphone/13974815#13974815

/*
 
 typedef enum { 
   0 UIImageOrientationUp,           // landscapeLeft
   1 UIImageOrientationDown,         // landscapeRight
   2 UIImageOrientationLeft,         // portraitUpsideDown
   3 UIImageOrientationRight,        // portrait
   4 UIImageOrientationUpMirrored,   // as above but image mirrored along
     // other axis. horizontal flip
   5 UIImageOrientationDownMirrored,  // horizontal flip
   6 UIImageOrientationLeftMirrored,  // vertical flip
   7 UIImageOrientationRightMirrored, // vertical flip
 } UIImageOrientation;
 
 Orientation

 Apple/UIImage.imageOrientation     Jpeg/File kCGImagePropertyOrientation

 UIImageOrientationUp    = 0  =  Landscape left  = 1
 UIImageOrientationDown  = 1  =  Landscape right = 3
 UIImageOrientationLeft  = 2  =  Portrait  down  = 8
 UIImageOrientationRight = 3  =  Portrait  up    = 6

 */

#import "UIImage+Rotate.h"

@implementation UIImage (Rotate)

- (UIImage*) rotateExifToOrientation:(UIImageOrientation)orientation 
{
    return [[UIImage alloc] initWithCGImage:self.CGImage
                                      scale:self.scale
                                orientation:orientation];
}


-(UIImage*) rotateBitmapToOrientation:(UIImageOrientation)orientation
{
    UIImage* image = [self rotateExifToOrientation:orientation];
    CGImageRef imgRef = image.CGImage;
    CGSize imageSize = CGSizeMake(  CGImageGetWidth(imgRef)
                                  , CGImageGetHeight(imgRef));
    UIGraphicsBeginImageContext(imageSize);
    [image drawAtPoint:CGPointMake(0, 0)];
    UIImage *img=UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return img;
}



@end

A category extension on UIImage to rotate images -
(1) via the Exif (TIFF) Orientation metatag,
(2) by rewriting the bitmap.

The Exif method is highly efficient, but fails if passing to devices that strip metadata or don't bother reading it.

The bitmap method rearranges the actual image pixels so will work across all platforms, but is far less efficient to process. (around 200 times slower in my tests)