Real-time blur for UIImage by sliding on iOS

Question

How to achieve the real time blurring for UIImage on sliderValueChanged(_:)?

@IBOutlet weak var imageView: UIImageView!

@IBAction func sliderValueChanged(sender: UISlider) {
    let blurRadius = sender.value
    var img = imageView.image

    // some image processing for img

    //blurring for img

    // some another image processing for img

    imageView.image = img   
}

I don't fit the blurring for UIImageView due to the presence of other image processing.

Thanks!

Answer 1

For maximum performance, you should use GLKView with CIFilter instead of UIImageView .

One of the simplest implementation would be something like this (Xcode6/Swift1.2):

import UIKit
import GLKit

class BlurImageView: GLKView {
    let clampFilter = CIFilter(name: "CIAffineClamp")!
    let blurFilter = CIFilter(name: "CIGaussianBlur")!
    let ciContext:CIContext

    override init(frame: CGRect) {
        let glContext = EAGLContext(API: .OpenGLES2)
        ciContext = CIContext(
            EAGLContext: glContext,
            options: [
                kCIContextWorkingColorSpace: NSNull()
            ]
        )
        super.init(frame: frame, context: glContext)
        enableSetNeedsDisplay = true
    }

    required init(coder aDecoder: NSCoder) {
        let glContext = EAGLContext(API: .OpenGLES2)
        ciContext = CIContext(
            EAGLContext: glContext,
            options: [
                kCIContextWorkingColorSpace: NSNull()
            ]
        )
        super.init(coder: aDecoder)
        context = glContext
        enableSetNeedsDisplay = true
    }

    @IBInspectable var inputImage: UIImage? {
        didSet {
            inputCIImage = inputImage.map { CIImage(image: $0)! }
        }
    }

    @IBInspectable var blurRadius: Float = 0 {
        didSet {
            blurFilter.setValue(blurRadius, forKey: "inputRadius")
            setNeedsDisplay()
        }
    }

    var inputCIImage: CIImage? {
        didSet { setNeedsDisplay() }
    }

    override func drawRect(rect: CGRect) {
        if let inputCIImage = inputCIImage {
            clampFilter.setValue(inputCIImage, forKey: kCIInputImageKey)
            blurFilter.setValue(clampFilter.outputImage!, forKey: kCIInputImageKey)
            let rect = CGRect(x: 0, y: 0, width: drawableWidth, height: drawableHeight)
            ciContext.drawImage(blurFilter.outputImage!, inRect: rect, fromRect: inputCIImage.extent())
        }
    }
}

Then, you can use this like:

class ViewController: UIViewController {

    @IBOutlet var imageView: BlurImageView!

    override func viewDidLoad() {
        super.viewDidLoad()
        imageView.inputImage = UIImage(named:"testImage")!
    }

    @IBAction func sliderValueChanged(sender: UISlider) {
        imageView.blurRadius = sender.value
    }
}

See An Introduction to Core Image - objc.io and it's sample code for more explanations and examples.