如何以编程方式绘制UIImage的直方图？

import UIKit

func drawHistogram(for image: UIImage) -> UIImage? {
    guard let cgImage = image.cgImage else {
        return nil
    }
    
    let width = cgImage.width
    let height = cgImage.height
    
    // 创建图像上下文
    UIGraphicsBeginImageContextWithOptions(CGSize(width: width, height: height), false, 0.0)
    guard let context = UIGraphicsGetCurrentContext() else {
        return nil
    }
    
    // 绘制UIImage
    context.draw(cgImage, in: CGRect(x: 0, y: 0, width: width, height: height))
    
    // 获取像素数据
    guard let data = context.data else {
        return nil
    }
    
    let buffer = data.bindMemory(to: UInt8.self, capacity: width * height * 4)
    
    // 统计像素值的频率
    var histogram = [Int](repeating: 0, count: 256)
    for i in 0..<(width * height * 4) {
        let pixelValue = buffer[i]
        histogram[Int(pixelValue)] += 1
    }
    
    // 绘制直方图
    let barWidth = 1
    let barSpacing = 0
    let maxFrequency = histogram.max() ?? 1
    
    for i in 0..<256 {
        let barHeight = Int(Double(histogram[i]) / Double(maxFrequency) * Double(height))
        let barRect = CGRect(x: i * (barWidth + barSpacing), y: height - barHeight, width: barWidth, height: barHeight)
        context.setFillColor(UIColor.red.cgColor)
        context.fill(barRect)
    }
    
    // 获取绘制后的UIImage
    guard let histogramImage = UIGraphicsGetImageFromCurrentImageContext() else {
        return nil
    }
    
    // 结束图像上下文
    UIGraphicsEndImageContext()
    
    return histogramImage
}

// 使用示例
let image = UIImage(named: "example.jpg")
if let histogramImage = drawHistogram(for: image) {
    // 在这里使用绘制后的直方图图像
}