CIBlendWithMatte.swift

class CIBlendWithMatte : CIFilter {
    var inputImage: CIImage?
    var backgroundImage: CIImage?
    var color: CIVector?
    
    override var outputImage: CIImage? {
        guard let inputImage = inputImage
            , let backgroundImage = backgroundImage
            , let color = color else { return nil}
        
        // 写真に合わせてMatte画像のスケールを拡大
        let scaleFilter = CIFilter.lanczosScaleTransform()
        let matteHeight = inputImage.extent.height
        let photoHeight = backgroundImage.extent.height
        scaleFilter.inputImage = inputImage
        scaleFilter.scale = Float(photoHeight / matteHeight)
        scaleFilter.aspectRatio = 1.0
        
        // マット画像の色・アルファを変更
        let colorFilter = CIFilter.colorClamp()
        colorFilter.inputImage = scaleFilter.outputImage!
        colorFilter.maxComponents = color
        
        // Matte画像自身をマスクにして写真と合成
        let blendFilter = CIFilter.blendWithMask()
        blendFilter.inputImage = colorFilter.outputImage!
        blendFilter.backgroundImage = backgroundImage
        blendFilter.maskImage = scaleFilter.outputImage!
        
        return blendFilter.outputImage!
    }
}