CoreImage has long been a staple on OS X, and was added to iOS a few years ago. It's an incredibly feature-packed image processing API that can apply just about any type of filter or image manipulation you can dream of. Let's take a look at applying a simple color tint to an image:

func applyFilterToImage(image: UIImage) -> UIImage {
  guard let inputImage = image.CIImage else { return image }

  let tintColor = CIColor(red: 0.55, green: 0.33, blue: 0.22)

  let filter = CIFilter(
    name: "CIColorMonochrome",
    withInputParameters: [
      "inputImage" : inputImage,
      "inputColor" : tintColor,
      "inputIntensity" : 1.0
    ]
  )

  return UIImage(CIImage: filter!.outputImage)
}

CoreImage works on CIImages not UIImages, so we convert our image to a CIImage, and use guard since the CIImage property on UIImage is optional. CoreImage also doesn't use UIColor, so we create a CIColor instead.

Then the fun part, we create our filter by name. CoreImage has literally 100's of different filters available, and instead of subclasses, you instantiate them by name.

CIFilters also don't have explicit class properties, you instead supply values for "Input Parameters" on your filter.

Lastly, we apply the filter by simply asking for it's outputImage.