CIFilter不会在触摸位置应用过滤器

Question

我正在使用下面的代码将图像滤镜应用于具有设定半径的触摸位置，但滤镜位于错误的位置。 x坐标似乎很接近，但y坐标反转，距离我的触摸有400多个像素。如果我将手指向上移动，则过滤器向下移动，反之亦然。我是否错误地使用了kCIInputCenterKey：CIVector参数？如何将滤镜半径的中心放在触摸位置？

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {

    let filter = CIFilter(name: "CIPixellate")!
    let inputImage = CIImage(image: originalImage)!
    filter.setValue(inputImage, forKey: kCIInputImageKey)
    let fullPixellatedImage = filter.outputImage
    var maskImage: CIImage!
    let radialGradient = CIFilter(name: "CIRadialGradient",
        withInputParameters: [
            "inputRadius0" : 30,
            kCIInputCenterKey : CIVector(x: (touches.first?.locationInView(self.view).x)!, y: (touches.first?.locationInView(self.view).y)!)
        ])!
    let radialGradientOutputImage = radialGradient.outputImage!.imageByCroppingToRect(inputImage.extent)
    if maskImage == nil {
        maskImage = radialGradientOutputImage
    } else {
        maskImage = CIFilter(name: "CISourceOverCompositing",
            withInputParameters: [
                kCIInputImageKey : radialGradientOutputImage,
                kCIInputBackgroundImageKey : maskImage
            ])!.outputImage
    }
    let blendFilter = CIFilter(name: "CIBlendWithMask")!
    blendFilter.setValue(fullPixellatedImage, forKey: kCIInputImageKey)
    blendFilter.setValue(inputImage, forKey: kCIInputBackgroundImageKey)
    blendFilter.setValue(maskImage, forKey: kCIInputMaskImageKey)
    let blendOutputImage = blendFilter.outputImage!
    let blendCGImage = context.createCGImage(blendOutputImage, fromRect: blendOutputImage.extent)
    mainImageView.image = UIImage(CGImage: blendCGImage)

}