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

There's a CoreImage filter for this. CIColorControls Just set the inputSaturation to < 1.0 to desaturate or > 1.0 to increase saturation...

eg. Here's a method I've added in a category on UIImage to desaturate an image.

-(UIImage*) imageDesaturated {
    CIContext *context = [CIContext contextWithOptions:nil];
    CIImage *ciimage = [CIImage imageWithCGImage:self.CGImage];
    CIFilter *filter = [CIFilter filterWithName:@"CIColorControls"];
    [filter setValue:ciimage forKey:kCIInputImageKey];
    [filter setValue:@0.0f forKey:kCIInputSaturationKey];
    CIImage *result = [filter valueForKey:kCIOutputImageKey];
    CGImageRef cgImage = [context createCGImage:result fromRect:[result extent]];
    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    return image;
}