Creating UIImage from CIImage

I am using some CoreImage filters to process an image. Applying the filter to my input image results in an output image called filterOutputImage of type CIImage.

I now wish to display that image, and tried doing:

self.modifiedPhoto = [UIImage imageWithCIImage:filterOutputImage];
self.photoImageView.image = self.modifiedPhoto;

The view however is blank – nothing is being displayed.

If I add logging statements that print out details about both filterOutputImage and self.modifiedPhoto, those logging statements are showing me that both those vars appear to contain legitimate image data: their size is being reported and the objects are not nil.

So after doing some Googling, I found a solution that requires going through a CGImage stage; vis:

CGImageRef outputImageRef = [context createCGImage:filterOutputImage fromRect:[filterOutputImage extent]];
self.modifiedPhoto = [UIImage imageWithCGImage:outputImageRef scale:self.originalPhoto.scale orientation:self.originalPhoto.imageOrientation];
self.photoImageView.image = self.modifiedPhoto;
CGImageRelease(outputImageRef);

This second approach works: I am getting the correct image displayed in the view.

Can someone please explain to me why my first attempt failed? What am I doing wrong with the imageWithCIImage method that is resulting in an image that seems to exist but can't be displayed? Is it always necessary to "pass through" a CGImage stage in order to generate a UIImage from a CIImage?

Hoping someone can clear up my confusion 🙂

H.