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我想使用 swift 将灰度线条艺术的所有白色背景更改为透明。我为 swift 实现了 RGB 色键文档：https ://developer.apple.com/documentation/coreimage/applying_a_chroma_key_effect

色调范围最初是绿色，有 R、G、B 和 alpha 参数

self.ChromaKeyFilter(fromHue: 0.3, toHue: 0.4)

，但对于灰度，根据苹果文档只有 2 个：白色，阿尔法。我想将极端的白色更改为透明，所以我只是将色调范围设置为 1。

class ChromaKey{

    //Hue range

    let whiteRange: CGFloat = 1

    func getHue(white: CGFloat) -> CGFloat{
        let color = UIColor(white: white, alpha: 1)
        var hue: CGFloat = 0
        color.getHue(&hue, saturation: nil, brightness: nil, alpha: nil)
        return hue
    }

    func chromaKeyFilter(ridHue:CGFloat) -> CIFilter? {
        let size = 64
        var cubeGrey = [Float]()

        for z in 0 ..< size{
            let white = CGFloat(z)/CGFloat(size-1)

            let hue = getHue(white: white)
            let alpha: CGFloat = (hue == ridHue) ? 0:1

            cubeGrey.append(Float(white * alpha))
            cubeGrey.append(Float(alpha))

        }
        let data = Data(buffer: UnsafeBufferPointer(start: &cubeGrey, count: cubeGrey.count))

        let colorCubeFilter = CIFilter(name: "CIColorCube", parameters: ["inputCubeDimension": size, "inputCubeData":data])
        return colorCubeFilter
    }

func filterPixels(foregroundCIImage: CIImage) -> CIImage {
        let chromaCIFilter = self.chromaKeyFilter(ridHue: whiteRange)
        chromaCIFilter?.setValue(foregroundCIImage, forKey: kCIInputImageKey)
        let sourceCIImageWithoutBackground = chromaCIFilter?.outputImage
        var image = CIImage()
        if let filteredImage = sourceCIImageWithoutBackground{
            image = filteredImage
        }
        return image
    }

chromakey 的函数。当我应用函数时，什么都没有出现。

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