How to pixellate a UIImage

Paul Hudson    February 13th 2018    @twostraws

Core Image has a number of interesting filters baked in, and an easy one to use is CIPixellate – it pixellates images, making them appear blocky. You have control over how big each pixel block should be, so it’s suitable for a range of tasks.

Below is some sample code to get you started. To use it you should:

1. Change yourUIImage to be whatever input UIImage you want to use.
2. Change the value of 12 for however strong your pixellation effect should be.
3. Change the print(processedImage.size) line at the end for something more interesting – maybe you want to display the pixellated image somewhere?

Here’s the code:

guard let currentCGImage = yourUIImage.cgImage else { return }
let currentCIImage = CIImage(cgImage: currentCGImage)

let filter = CIFilter(name: "CIPixellate")
filter?.setValue(currentCIImage, forKey: kCIInputImageKey)
filter?.setValue(12, forKey: kCIInputScaleKey)
guard let outputImage = filter?.outputImage else { return }

let context = CIContext()

if let cgimg = context.createCGImage(outputImage, from: outputImage.extent) {
    let processedImage = UIImage(cgImage: cgimg)
    print(processedImage.size)
}

Note: if you intend to run pixellation several times you’ll find it more efficient to save your CIContext rather than keep recreating it.

Available from iOS 8.0

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