CIGaussianBlur Quality: Banding & Artifacts

Question

I am trying to blur the AVCaptureVideoPreviewLayer on applicationWillResignActive just as in the stock iOS Camera App.

Since rasterizing AVCaptureVideoPreviewLayer and blurring itself produces an empty frame, I approached it by keeping a CIImage from didOutputSampleBuffer and upon applicationWillResignActive, I take the CIImage -> Apply CIFilter CIGaussianBlur to it, add a UIImageView to AVCaptureVideoPreviewLayer and make that UIImageView's Image to be the UIImage version of the blur I applied the CIGaussianBlur to.

This seem to be working okay so far... However, it seem to produce quite a bit of banding, displaying quality issues on the Gaussian Blur.

Grabbing the Frame:

func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {

            let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer)
            CVPixelBufferLockBaseAddress(imageBuffer!, CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))

            let baseAddress = CVPixelBufferGetBaseAddress(imageBuffer!)

            let bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer!)
            let width = CVPixelBufferGetWidth(imageBuffer!)
            let height = CVPixelBufferGetHeight(imageBuffer!)

            let colorSpace = CGColorSpaceCreateDeviceRGB()

            let bitmap = CGBitmapInfo(rawValue: CGBitmapInfo.ByteOrder32Little.rawValue|CGImageAlphaInfo.PremultipliedFirst.rawValue)
            let context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                bytesPerRow, colorSpace, bitmap.rawValue)
            let quartzImage = CGBitmapContextCreateImage(context!)
            CVPixelBufferUnlockBaseAddress(imageBuffer!,CVPixelBufferLockFlags(rawValue: CVOptionFlags(0)))

            self.cameraBufferImage = CIImage(CGImage: quartzImage!)
}

Applying the CIGaussianBlur:

func blurPreviewWindow() {
    let previewLayer = self.previewView.layer as? AVCaptureVideoPreviewLayer
    previewLayer?.connection.enabled = false

    let context = CIContext(options: nil)
    let inputImage = self.cameraBufferImage!.imageByApplyingOrientation(6)

    let clampFilter = CIFilter(name: "CIAffineClamp")
    clampFilter!.setDefaults()
    clampFilter!.setValue(inputImage, forKey: "inputImage")

    if let currentFilter = CIFilter(name: "CIGaussianBlur") {
        currentFilter.setValue(clampFilter!.outputImage, forKey: "inputImage")
        currentFilter.setValue(50.0, forKey: "inputRadius")

        if let output = currentFilter.outputImage {
            if let cgimg = context.createCGImage(output, fromRect: inputImage.extent) {
                let processedImage = UIImage(CGImage: cgimg)
                self.previewBlurImageView = UIImageView(frame: self.previewView.bounds)
                self.previewBlurImageView?.alpha = 0
                self.previewView.addSubview(self.previewBlurImageView!)
                self.previewBlurImageView?.image = processedImage
                self.previewBlurImageView?.contentMode = .ScaleToFill
                self.previewBlurImageView?.layer.filters = [currentFilter]

                UIView.animateWithDuration(0.2, delay: 0.0, options: [.BeginFromCurrentState], animations: {
                                                () -> Void in
                    self.previewBlurImageView?.alpha = 1
                }, completion: { _ in })
            }
        }
    }
}

May be there's a whole different approach to this of this iOS 10 era?

UPDATE:

Could this be a colorspace issue? Since the test device is iPhone 7, which has wide color?

Answer 1

It was CIContext.

Changed:

let context = CIContext(options: nil)

To:

let context = CIContext(options: [kCIContextWorkingColorSpace: CGColorSpaceCreateDeviceRGB(),
                                  kCIContextOutputColorSpace: CGColorSpaceCreateDeviceRGB(), 
                                  kCIContextUseSoftwareRenderer: false])

No more banding or artifacts!!!