How can I change the saturation of an UIImage?

Question

I have an UIImage and want to shift it\'s saturation about +10%. Are there standard methods or functions that can be used for this?

Answer 1

Here is an implementation of Bessey's hack (put this code in a UIImage category). It ain't fast and it definitely shifts hues, but it sort of works.

+ (CGFloat) clamp:(CGFloat)pixel
{
      if(pixel > 255) return 255;
      else if(pixel < 0) return 0;
      return pixel;
}

- (UIImage*) saturation:(CGFloat)s
{
      CGImageRef inImage = self.CGImage;
      CFDataRef ref = CGDataProviderCopyData(CGImageGetDataProvider(inImage)); 
      UInt8 * buf = (UInt8 *) CFDataGetBytePtr(ref); 
      int length = CFDataGetLength(ref);

      for(int i=0; i

Anyone have any ideas on how to improve this without doing a full HSV conversion? Or better yet, a true implementation for:

- (UIImage*) imageWithHueOffset:(CGFloat)h saturation:(CGFloat)s value:(CGFloat)v