title: CIImage size extent zero?
body: <p>I have create this category to convert <code>CIImage</code> to <code>UIImage</code>. The <code>CIImage</code>s I am using are coming from <code>CIFilter</code>s.</p>
  
  <pre><code>-(UIImage *)obtainImageWithRetinaScale:(CGFloat)scale
  {
    CIContext *context = [CIContext contextWithOptions:nil];
  
    //CGRect frame = CGRectMake(0,0,700,392);
    CGImageRef processedCGImage = [context createCGImage:self
                                                fromRect:[self extent]];
  
    UIImage *returnImage = [UIImage imageWithCGImage:processedCGImage
                                      scale:scale
                                orientation:UIImageOrientationUp];
    CGImageRelease(processedCGImage);
  
    return returnImage;
  }
  </code></pre>
  
  <p>When this runs, <code>[self extent]</code> gives a rect with garbled numbers, that is barely (0, 0, infinity, infinity) ... really huge numbers there.</p>
  
  <p>Obviously processed image is nil.</p>
  
  <p>When I force a frame with the correct size, the image is correctly produced.</p>