It’s simple to convert an UIImage to his negative image. Only use this code:


UIGraphicsBeginImageContext(renderImage.size);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
[renderImage drawInRect:CGRectMake(0, 0, renderImage.size.width, renderImage.size.height)];
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeDifference);
CGContextSetFillColorWithColor(UIGraphicsGetCurrentContext(),[UIColor whiteColor].CGColor);
CGContextFillRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, renderImage.size.width, renderImage.size.height));
renderImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();