imageOrientation returns Up, but photo shows up upsidedown

Question

I'm grabbing some photos from the iPad photo library. I took a few test photos in landscape mode, both with the iPad home button on the left side, and then the right side.

So in my app, for some reason some of the photos show up upsidedown. I checked their imageOrientation property, and they are all 0 (meaning they are UIImageOrientationUp). So that means I can't even tell which photos I need to rotate.

What's going on, and how can I tell which photos need to be rotated? Thanks

Answer 1

A UIImage has a property imageOrientation, which instructs the UIImageView and other UIImage consumers to rotate the raw image data. There's a good chance that this flag is being saved to the exif data in the uploaded jpeg image, but the program you use to view it is not honoring that flag.

To rotate the UIImage to display properly when uploaded, you can use a category like this: In .h file

UIImagefixOrientation.h

@interface UIImage (fixOrientation)

- (UIImage *)fixOrientation;

@end

UIImagefixOrientation.m

@implementation UIImage (fixOrientation)

- (UIImage *)fixOrientation {

    // No-op if the orientation is already correct
    if (self.imageOrientation == UIImageOrientationUp) return self;

   // We need to calculate the proper transformation to make the image upright.
   // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
  CGAffineTransform transform = CGAffineTransformIdentity;

  switch (self.imageOrientation) {
      case UIImageOrientationDown:
      case UIImageOrientationDownMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height);
         transform = CGAffineTransformRotate(transform, M_PI);
          break;

    case UIImageOrientationLeft:
    case UIImageOrientationLeftMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, 0);
        transform = CGAffineTransformRotate(transform, M_PI_2);
        break;

    case UIImageOrientationRight:
    case UIImageOrientationRightMirrored:
        transform = CGAffineTransformTranslate(transform, 0, self.size.height);
        transform = CGAffineTransformRotate(transform, -M_PI_2);
        break;
}

switch (self.imageOrientation) {
    case UIImageOrientationUpMirrored:
    case UIImageOrientationDownMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.width, 0);
        transform = CGAffineTransformScale(transform, -1, 1);
        break;

    case UIImageOrientationLeftMirrored:
    case UIImageOrientationRightMirrored:
        transform = CGAffineTransformTranslate(transform, self.size.height, 0);
        transform = CGAffineTransformScale(transform, -1, 1);
        break;
}

// Now we draw the underlying CGImage into a new context, applying the transform
// calculated above.
CGContextRef ctx = CGBitmapContextCreate(NULL, self.size.width, self.size.height,
                                         CGImageGetBitsPerComponent(self.CGImage), 0,
                                         CGImageGetColorSpace(self.CGImage),
                                         CGImageGetBitmapInfo(self.CGImage));
CGContextConcatCTM(ctx, transform);
switch (self.imageOrientation) {
    case UIImageOrientationLeft:
    case UIImageOrientationLeftMirrored:
    case UIImageOrientationRight:
    case UIImageOrientationRightMirrored:
        // Grr...
        CGContextDrawImage(ctx, CGRectMake(0,0,self.size.height,self.size.width), self.CGImage);
        break;

    default:
        CGContextDrawImage(ctx, CGRectMake(0,0,self.size.width,self.size.height), self.CGImage);
        break;
}

// And now we just create a new UIImage from the drawing context
CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return img;
}

@end

And call this function during capture image save or select image from the gallery.