How to read the average color of a UIImage using CIAreaAverage

Paul Hudson    October 26th 2018    @twostraws

Core Image has a filter that resample an image down to 1x1 pixels so you can read the average color, although it’s a weirdly hard to use.

To simplify things, here’s an extension on UIImage that returns an optional UIColor – it will be nil only if something went wrong while reading your image, but otherwise it will contain the average color for the entire image:

extension UIImage {
    var averageColor: UIColor? {
        guard let inputImage = CIImage(image: self) else { return nil }
        let extentVector = CIVector(x: inputImage.extent.origin.x, y: inputImage.extent.origin.y, z: inputImage.extent.size.width, w: inputImage.extent.size.height)

        guard let filter = CIFilter(name: "CIAreaAverage", parameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: extentVector]) else { return nil }
        guard let outputImage = filter.outputImage else { return nil }

        var bitmap = [UInt8](repeating: 0, count: 4)
        let context = CIContext(options: [.workingColorSpace: kCFNull])
        context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: CGRect(x: 0, y: 0, width: 1, height: 1), format: .RGBA8, colorSpace: nil)

        return UIColor(red: CGFloat(bitmap[0]) / 255, green: CGFloat(bitmap[1]) / 255, blue: CGFloat(bitmap[2]) / 255, alpha: CGFloat(bitmap[3]) / 255)
    }
}

Available from iOS 9.0

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to choose a photo from the camera roll using UIImagePickerController
• How to render a UIView to a UIImage
• How to scan a barcode
• How to control the pitch and speed of audio using AVAudioEngine
• UIImageWriteToSavedPhotosAlbum(): how to write to the iOS photo album

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.