ios - 如何使用 CIFilter 在 Swift 中将 UIImage 转换为灰度？

Question

到目前为止，我正在为 iOS 应用程序构建扫描仪组件，结果图像已裁剪并处于正确的视角。现在我需要将彩色图像转换为黑白“扫描”文档。

我尝试使用 - “CIPhotoEffectNoir”，但它比全黑和白更灰度。我希望获得 100% 黑色和 100% 白色的全对比度图像。

我怎样才能做到这一点？谢谢

Answer 1

您可以使用 CIColorControls 并设置 Contrast Key kCIInputContrastKey 来增加黑白对比度，如下所示:

Xcode 9 • Swift 4

extension String {
    static let colorControls = "CIColorControls"
}

---

extension UIImage {
    var coreImage: CIImage? { return CIImage(image: self) }
}

---

extension CIImage {
    var uiImage: UIImage? { return UIImage(ciImage: self) }
    func applying(contrast value: NSNumber) -> CIImage? {
        return applyingFilter(.colorControls, parameters: [kCIInputContrastKey: value])
    }
    func renderedImage() -> UIImage? {
        guard let image = uiImage else { return nil }
        return UIGraphicsImageRenderer(size: image.size,
                                       format: image.imageRendererFormat).image { _ in
            image.draw(in: CGRect(origin: .zero, size: image.size))
        }
    }
}

---

let url = URL(string: "/image/Xs4RX.jpg")!
do {
    if let coreImage = UIImage(data: try Data(contentsOf: url))?.coreImage,
        let increasedContrast = coreImage.applying(contrast: 1.5) {
        imageView.image = increasedContrast.uiImage
        // if you need to convert your image to data (JPEG/PNG) you would need to render the ciimage using renderedImage method on CIImage   
    }
} catch {
    print(error)
}

---

要从颜色转换为灰度，您可以将饱和键 kCIInputSaturationKey 设置为零:

extension CIImage {
    func applying(saturation value: NSNumber) -> CIImage? {
        return applyingFilter(.colorControls, parameters: [kCIInputSaturationKey: value])
    }
    var grayscale: CIImage? { return applying(saturation: 0) }
}

---

let url = URL(string: "/image/Xs4RX.jpg")!
do {
    if let coreImage = UIImage(data: try Data(contentsOf: url))?.coreImage, 
        let grayscale = coreImage.grayscale {
        // use  grayscale image here
        imageView.image = grayscale.uiImage
    }
} catch { 
    print(error) 
}