UIImageWriteToSavedPhotosAlbum() doesn't save cropped image - ios

Question

I'm trying to save a cropped image to the camera roll.
(I need to do it programmatically, I can't have the user edit it)
This is my (still quite basic) cut and save code:
- (void)cutAndSaveImage:(UIImage*)rawImage
{
CIImage *workingImage = [[CIImage alloc] initWithImage:rawImage];
CGRect croppingRect = CGRectMake(0.0f, 0.0f, 3264.0f, 1224.0f);
CIImage *croppedImage = [workingImage imageByCroppingToRect:croppingRect];
UIImage *endImage = [UIImage imageWithCIImage:croppedImage scale: 1.0f orientation:UIImageOrientationRight];
self.testImage.image = endImage;
UIImageWriteToSavedPhotosAlbum(rawImage, self, #selector(image:didFinishSavingWithError:contextInfo:) , nil);
UIImageWriteToSavedPhotosAlbum(endImage, self, #selector(image:didFinishSavingWithError:contextInfo:) , nil);
}
The method is called within:
- (void)imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info
I first create a CIImage using the raw UIImage.
Then I get a cropped CIImage using an instance method of the first one.
After that I create a new UIImage using the cropped CIImage.
At this point, to have some feedback, I set the new cropped UIImage as the backing image of a UIImageView. This works, and I can clearly see the image cropped exactly how I desired.
When I try to save it to the camera roll, however, things stop working.
I can't save the newly created endImage.
As you can see, I added a line to save the original UIImage too, just for comparison. The original one saves normally.
Another confusing thing is that the NSError object passed to the image:didFinishSavingWithError:contextInfo: callback is nil. (the callback is normally executed for both saving attempts)
EDIT:
Just made an experiment:
NSLog(#"rawImage: %# - rawImage.CGImage: %#", rawImage, rawImage.CGImage);
NSLog(#"endImage: %# - endImage.CGImage: %#", endImage, endImage.CGImage);
It looks like only the rawImage (coming from the UIImagePickerController) possesses a backing CGImageRef. The other one, created from a CIImage, doesn't.
Can it be that UIImageWriteToSavedPhotosAlbum works using the backing CGImageRef?

Answer 1

Can it be that UIImageWriteToSavedPhotosAlbum works using the backing CGImageRef?
Correct. A CIImage is not an image, and a UIImage backed only by a CIImage is not an image either; it is just a kind of wrapper. Why are you using CIImage at all here? You aren't using CIFilter so this makes no sense. Or if you are using CIFilter, you must render through a CIContext to get the output as a bitmap.
You can crop easily by drawing into a smaller graphics context.

Answer 2

If the UIImage object was initialized using a CIImage object, the
value of the property is NULL.
You can generate UIImage from CIImage like this:
let lecturePicture = UIImage(data: NSData(contentsOfURL: NSURL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!)!)!
let controlsFilter = CIFilter(name: "CIColorControls")
controlsFilter.setValue(CIImage(image: lecturePicture), forKey: kCIInputImageKey)
controlsFilter.setValue(1.5, forKey: kCIInputContrastKey)
let displayImage = UIImage(CGImage: CIContext(options:nil).createCGImage(controlsFilter.outputImage, fromRect:controlsFilter.outputImage.extent()))!
displayImage