I use the following code to draw a subimage

UIImage* subIm = getSubImage( large, rect );
[subIm drawInRect:self.bounds];

where getSubImage is defined as follows

    UIImage* getSubImage(UIImage* uim, CGRect rc){
      CGImageRef imref  = CGImageCreateWithImageInRect(uim.CGImage, rc); 
      UIImage*   sub = [UIImage imageWithCGImage:imref];
      CGImageRelease(imref);
        NSLog(@"subimage retainCount=%d", [sub  retainCount]); // is 1
      return sub;
   }//getSubImage

Is the code correct?

Is it safe to "CGImageRelease" imref?

Has sub "CGImageRetained" imref?

Should I release subIm (I get an error if I do)?

Is subIm contained in the autorelease-pool, and , if so, how do I know this?

In general, can one check if an object is contained in the autorelease pool (for debugging purpose)?