SwiftUI实现黑白反转且保留颜色的PDF图片深色适配

针对你需要将PDF转换的UIImage在SwiftUI中适配深色模式（地图背景转黑/深灰，保留原色彩）的需求，这里提供几种可行的实现方案：

方案一：优化SwiftUI图层混合（快速调整） #

之前的ZStack方案中黄色变绿是因为.color混合模式导致色相偏移，换成.colorBurn并调整滤镜参数可以修正这个问题，同时保留深色背景和原色彩：

ZStack {
    // 深色灰度底图：反转+去饱和+增强对比度让背景更纯粹
    Image(uiImage: self.mapImage!)
        .resizable()
        .scaledToFill()
        .colorInvert()
        .saturation(0)
        .contrast(1.2)
        .brightness(-0.1)
    
    // 原色彩层：用colorBurn混合模式保留原色相，增强饱和度让色彩更突出
    Image(uiImage: self.mapImage!)
        .resizable()
        .scaledToFill()
        .blendMode(.colorBurn)
        .saturation(1.1)
}
.clipped() // 裁剪超出边界的内容

这个方案不需要额外的CoreImage处理，纯SwiftUI API即可实现，调整contrast、brightness和saturation的数值可以适配不同的PDF内容。

方案二：用CoreImage模拟Affinity的图层组合 #

SwiftUI的blendMode确实没有"Add"模式，但CoreImage提供了CIAdditionCompositing滤镜，可以完全复刻你在Affinity中实现的效果：

1. 先写几个CoreImage工具函数 #

// 给图片应用单个CoreImage滤镜
private func applyFilter(to image: UIImage, filter: CIFilter) -> UIImage? {
    guard let ciImage = CIImage(image: image) else { return nil }
    filter.setValue(ciImage, forKey: kCIInputImageKey)
    
    guard let outputCI = filter.outputImage else { return nil }
    let context = CIContext(options: [.useSoftwareRenderer: false])
    guard let outputCG = context.createCGImage(outputCI, from: outputCI.extent) else { return nil }
    return UIImage(cgImage: outputCG)
}

// 生成反转+黑白的图片
private func invertedGrayscaleImage(from image: UIImage) -> UIImage? {
    let invertFilter = CIFilter(name: "CIColorInvert")!
    let grayFilter = CIFilter(name: "CIColorControls")!
    grayFilter.setValue(0, forKey: kCIInputSaturationKey)
    
    guard let inverted = applyFilter(to: image, filter: invertFilter) else { return nil }
    return applyFilter(to: inverted, filter: grayFilter)
}

// 用Add混合模式合成两张图片
private func addComposite(base: UIImage, overlay: UIImage) -> UIImage? {
    guard let baseCI = CIImage(image: base), let overlayCI = CIImage(image: overlay) else { return nil }
    let addFilter = CIFilter(name: "CIAdditionCompositing")!
    addFilter.setValue(baseCI, forKey: kCIInputImageKey)
    addFilter.setValue(overlayCI, forKey: kCIInputBackgroundImageKey)
    
    guard let outputCI = addFilter.outputImage else { return nil }
    let context = CIContext(options: [.useSoftwareRenderer: false])
    guard let outputCG = context.createCGImage(outputCI, from: outputCI.extent) else { return nil }
    return UIImage(cgImage: outputCG)
}

2. 在SwiftUI中处理并渲染 #

@State private var processedImage: UIImage?

var body: some View {
    Group {
        if let processedImage = processedImage {
            Image(uiImage: processedImage)
                .resizable()
                .scaledToFill()
        } else if let mapImage = mapImage {
            // 加载中可以显示原图或者占位符
            Image(uiImage: mapImage)
                .resizable()
                .scaledToFill()
        }
    }
    .onAppear {
        guard let original = mapImage else { return }
        // 复刻Affinity的三个图层逻辑
        guard let layer3 = invertedGrayscaleImage(from: original),
              let layer2 = addComposite(base: layer3, overlay: layer3),
              let darkenFilter = CIFilter(name: "CIDarkenBlendMode") else { return }
        
        darkenFilter.setValue(CIImage(image: original), forKey: kCIInputImageKey)
        darkenFilter.setValue(CIImage(image: layer2), forKey: kCIInputBackgroundImageKey)
        
        processedImage = applyFilter(to: original, filter: darkenFilter)
    }
}

如果觉得部分文本可读性差，可以在最后给processedImage再叠加一层亮度调整：

// 调整文本可读性
if let processedImage = processedImage {
    Image(uiImage: processedImage)
        .resizable()
        .scaledToFill()
        .brightness(0.1)
        .contrast(1.1)
}

方案三：极简单图层调整 #

如果不需要完全复刻Affinity的效果，只想快速适配深色模式，可以用单图层的滤镜组合：

Image(uiImage: mapImage!)
    .resizable()
    .scaledToFill()
    .colorInvert()
    .saturation(0.3) // 保留少量色彩，同时灰度化背景
    .colorMultiply(Color.black.opacity(0.8)) // 加深背景
    .brightness(0.1) // 提亮文本
    .blendMode(.screen) // 让彩色内容更醒目

内容的提问来源于stack exchange，提问作者Fez Vrasta