Objective-C: convert UIImage to greyscale

- (UIImage *)convertImageToGrayScale:(UIImage *)image
	// Create image rectangle with current image width/height
	CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height);

	// Grayscale color space
	CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

	// Create bitmap content with current image size and grayscale colorspace
	CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone);

	// Draw image into current context, with specified rectangle
	// using previously defined context (with grayscale colorspace)
	CGContextDrawImage(context, imageRect, [image CGImage]);

	// Create bitmap image info from pixel data in current context
	CGImageRef imageRef = CGBitmapContextCreateImage(context);

	// Create a new UIImage object  
	UIImage *newImage = [UIImage imageWithCGImage:imageRef];

	// Release colorspace, context and bitmap information

	// Return the new grayscale image
	return newImage;