iPhone - CGBitmapContextCreateImage Leak, Anyone else with this problem? - iphone

Question

Has anyone else come across this problem? I am resizing images pretty often with an NSTimer. After using Instruments it does not show any memory leaks but my objectalloc just continues to climb. It points directly to CGBitmapContextCreateImage.
Anyone know of a solution? or Even possible ideas?
-(UIImage *) resizedImage:(UIImage *)inImage : (CGRect)thumbRect : (double)interpolationQuality
{
CGImageRef imageRef = [inImage CGImage];
CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);
if (alphaInfo == kCGImageAlphaNone)
alphaInfo = kCGImageAlphaNoneSkipLast;
// Build a bitmap context that's the size of the thumbRect
CGContextRef bitmap = CGBitmapContextCreate(
NULL,
thumbRect.size.width,
thumbRect.size.height,
CGImageGetBitsPerComponent(imageRef),
4 * thumbRect.size.width,
CGImageGetColorSpace(imageRef),
alphaInfo
);
// Draw into the context, this scales the image
CGContextSetInterpolationQuality(bitmap, interpolationQuality);
CGContextDrawImage(bitmap, thumbRect, imageRef);
// Get an image from the context and a UIImage
CGImageRef ref = CGBitmapContextCreateImage(bitmap);
UIImage* result = [UIImage imageWithCGImage:ref];
CGContextRelease(bitmap); // ok if NULL
CGImageRelease(ref);
return [result autorelease];
}

Answer 1

Should you be releasing imageRef?
CGImageRelease(imageRef);

Answer 2

Just a sanity check: are you releasing the return UIImage -- normally i would expect a function that allocating a new object (in this case a UIImage) to have create in the name?
Perhaps you want
return [result autorelease]
?

Answer 3

Why not use the simpler UIGraphicsBeginImageContext?
#implementation UIImage(ResizeExtension)
- (UIImage *)resizedImageWithSize:(CGSize)newSize interpolationQuality:(CGInterpolationQuality)interpolationQuality;
#end
#implementation UIImage(ResizeExtension)
- (UIImage *)resizedImageWithSize:(CGSize)newSize interpolationQuality:(CGInterpolationQuality)interpolationQuality
{
UIGraphicsBeginImageContext(newSize);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetInterpolationQuality(context, interpolationQuality);
[image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
UIImage *result = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return result;
}
#end
Also, this will return an image retained by the current autorelease pool; if you are creating many of these images in a loop, allocate and drain an NSAutoreleasePool manually.

Answer 4

Ok, the problem here is that we are defining the return from CGBitmapContextCreateImage as CGImageRef, it should be CGImage. The reason your allocations (im assuming malloc) are perpetually increasing is becuase the CGImage itself is never getting released. Try the below code. Also, there is no need to autorelease the result since it is never 'Alloc'd.
After you make the changes run in insturments with allocation again, this time you will hopefully not see an continual increase in the live bytes.
I typed this on PC so there may be a syntax error if you drop it into XCode; however, this should do the trick.
// Get an image from the context and a UIImage
CGImage cgImage = CGBitmapContextCreateImage(bitmap);
UIImage* result = [UIImage imageWithCGImage:cgImage];
CGContextRelease(bitmap); // ok if NULL
CGImageRelease(cgImage);
return result;

Answer 5

If you're using garbage collection, use CFMakeCollectable(posterFrame). If you're using traditional memory management, it's very straightforward:
return (CGImageRef)[(id)posterFrame autorelease];
You cast the CFTypeRef (in this case, a CGImageRef) to an Objective-C object pointer, send it the -autorelease message, and then cast the result back to CGImageRef. This pattern works for (almost) any type that's compatible with CFRetain() and CFRelease().