Cut a UIImage into a circle

Make sure to import QuarzCore if needed.

 func maskRoundedImage(image: UIImage, radius: CGFloat) -> UIImage {
        let imageView: UIImageView = UIImageView(image: image)
        let layer = imageView.layer
        layer.masksToBounds = true
        layer.cornerRadius = radius
        UIGraphicsBeginImageContext(imageView.bounds.size)
        layer.render(in: UIGraphicsGetCurrentContext()!)
        let roundedImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return roundedImage!
    }

Xcode 11 • Swift 5.1 or later

edit/update: For iOS10+ We can use UIGraphicsImageRenderer. For older Swift syntax check edit history.

extension UIImage {
    var isPortrait:  Bool    { size.height > size.width }
    var isLandscape: Bool    { size.width > size.height }
    var breadth:     CGFloat { min(size.width, size.height) }
    var breadthSize: CGSize  { .init(width: breadth, height: breadth) }
    var breadthRect: CGRect  { .init(origin: .zero, size: breadthSize) }
    var circleMasked: UIImage? {
        guard let cgImage = cgImage?
            .cropping(to: .init(origin: .init(x: isLandscape ? ((size.width-size.height)/2).rounded(.down) : 0,
                                              y: isPortrait  ? ((size.height-size.width)/2).rounded(.down) : 0),
                                size: breadthSize)) else { return nil }
        let format = imageRendererFormat
        format.opaque = false
        return UIGraphicsImageRenderer(size: breadthSize, format: format).image { _ in
            UIBezierPath(ovalIn: breadthRect).addClip()
            UIImage(cgImage: cgImage, scale: format.scale, orientation: imageOrientation)
            .draw(in: .init(origin: .zero, size: breadthSize))
        }
    }
}

Playground Testing

let profilePicture = UIImage(data: try! Data(contentsOf: URL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!))!
profilePicture.circleMasked

---

UIImage extension:

extension UIImage {

    func circularImage(size size: CGSize?) -> UIImage {
        let newSize = size ?? self.size

        let minEdge = min(newSize.height, newSize.width)
        let size = CGSize(width: minEdge, height: minEdge)

        UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
        let context = UIGraphicsGetCurrentContext()

        self.drawInRect(CGRect(origin: CGPoint.zero, size: size), blendMode: .Copy, alpha: 1.0)

        CGContextSetBlendMode(context, .Copy)
        CGContextSetFillColorWithColor(context, UIColor.clearColor().CGColor)

        let rectPath = UIBezierPath(rect: CGRect(origin: CGPoint.zero, size: size))
        let circlePath = UIBezierPath(ovalInRect: CGRect(origin: CGPoint.zero, size: size))
        rectPath.appendPath(circlePath)
        rectPath.usesEvenOddFillRule = true
        rectPath.fill()

        let result = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return result
    }

}

Usage:

UIImageView:

@IBDesignable class CircularImageView: UIImageView {

    override var image: UIImage? {
        didSet {
            super.image = image?.circularImage(size: nil)
        }
    }

}

UIButton:

@IBDesignable class CircularImageButton: UIButton {

    override func setImage(image: UIImage?, forState state: UIControlState) {
        let circularImage = image?.circularImage(size: nil)
        super.setImage(circularImage, forState: state)
    }

}