GPUImagePoissonBlendFilter produces weird result

Question

I am trying to use GPUImage (Objective-C) pod in order to blend two images with GPUImagePoissonBlendFilter in Swift project. The result is kinda weird and I don't understand how to fix it.

Sample project:

Back image

Front image

Result image

What is going on in code:

1. Load Back image into backImage

2. Load Front image into frontImage

3. Blend images with GPUImagePoissonBlendFilter

4. Result put to imageView

    class ViewController: UIViewController {
   
    private let imageView: UIImageView = {
        let image = UIImage(named: "back")
        let imageView = UIImageView(image: image)
        imageView.contentMode = .scaleAspectFill
        imageView.clipsToBounds = true
        imageView.translatesAutoresizingMaskIntoConstraints = false
        imageView.layer.borderWidth = 1
        imageView.layer.borderColor = UIColor.green.cgColor
        return imageView
    }()
   
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor.black
        view.addSubview(imageView)
        NSLayoutConstraint.activate([
            imageView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 10),
            imageView.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor)
        ])
   
        guard let backImage = imageView.image else { return }
        guard let frontImage = UIImage(named: "front") else { return }
   
   
        let backImageSource = GPUImagePicture(image: backImage)
        let frontImageSource = GPUImagePicture(image: frontImage)
   
        let poisionFilter = GPUImagePoissonBlendFilter()
        poisionFilter.mix = 0.9
        poisionFilter.numIterations = 100
        backImageSource?.addTarget(poisionFilter, atTextureLocation: 0)
        frontImageSource?.addTarget(poisionFilter)
        backImageSource?.processImage()
        frontImageSource?.processImage()
        poisionFilter.useNextFrameForImageCapture()
        let filterResult = poisionFilter.imageFromCurrentFramebuffer()
        imageView.image = filterResult
    }}
   

Can anyone point what I am doing wrong here ?

Thanks in advance !