如何在swift中将灰度图像转换为二值图像？

import UIKit
import CoreImage

func convertToBinaryImage(from image: UIImage) -> UIImage? {
    guard let ciImage = CIImage(image: image) else {
        return nil
    }
    
    let grayFilter = CIFilter(name: "CIColorControls")
    grayFilter?.setValue(ciImage, forKey: kCIInputImageKey)
    grayFilter?.setValue(0, forKey: kCIInputSaturationKey)
    grayFilter?.setValue(0, forKey: kCIInputBrightnessKey)
    grayFilter?.setValue(1, forKey: kCIInputContrastKey)
    
    guard let grayImage = grayFilter?.outputImage else {
        return nil
    }
    
    let binaryFilter = CIFilter(name: "CIColorMonochrome")
    binaryFilter?.setValue(grayImage, forKey: kCIInputImageKey)
    binaryFilter?.setValue(CIColor.white, forKey: kCIInputColorKey)
    binaryFilter?.setValue(1, forKey: kCIInputIntensityKey)
    
    guard let binaryImage = binaryFilter?.outputImage else {
        return nil
    }
    
    let context = CIContext()
    guard let cgImage = context.createCGImage(binaryImage, from: binaryImage.extent) else {
        return nil
    }
    
    UIGraphicsBeginImageContextWithOptions(image.size, false, image.scale)
    UIImage(cgImage: cgImage).draw(in: CGRect(origin: .zero, size: image.size))
    let binaryUIImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    
    return binaryUIImage
}

// 使用示例
let originalImage = UIImage(named: "gray_image.png")
let binaryImage = convertToBinaryImage(from: originalImage)