210 // by http://www.sixtemia.com/journal/2010/06/23/uiimage-negative-color-effect/

   211 -(UIImage *)convertToNegative {

   212     UIGraphicsBeginImageContext(self.size);

   213     CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);

   214     [self drawInRect:CGRectMake(0, 0, self.size.width, self.size.height)];

   215     CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeDifference);

   216     CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(),[UIColor whiteColor].CGColor);

   217     CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, self.size.width, self.size.height));

   218     UIImage *result = UIGraphicsGetImageFromCurrentImageContext();

   219     UIGraphicsEndImageContext();

   220     return result;

   221 }

   222