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

Question

我正在为 iOS 应用程序构建一个扫描仪组件，到目前为止，我已经裁剪了结果图像并以正确的视角显示。现在我需要将彩色图像变成黑白 "Scanned" 文档。

我尝试使用 - "CIPhotoEffectNoir" 但它的灰度等级高于全黑和白色。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 black/white 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: "https://i.stack.imgur.com/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，您可以将饱和度键 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: "https://i.stack.imgur.com/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) 
}

Answer 2

去饱和会将您的图像转换为灰度图像
增加对比度会将那些灰色推向极端，即黑色和白色。

你可以CIColorControls:

let ciImage = CIImage(image: image)!
let blackAndWhiteImage = ciImage.applyingFilter("CIColorControls", withInputParameters: ["inputSaturation": 0, "inputContrast": 5])

原文：

与inputContrast = 1（默认）：

与inputContrast = 5:

Answer 3

在 Swift 5.1 中，我为 OSX 编写了一个扩展方法，它也可以与 NSImage 相互转换。它使用饱和度和输入对比度来转换图像。我抽象了一个黑白函数。

extension NSImage {

    func blackAndWhite () -> NSImage?
    {
        return applying(saturation: 0,inputContrast: 5,image: self)
    }

    func applying(saturation value: NSNumber, inputContrast inputContrastValue: NSNumber, image:NSImage) -> NSImage? {

        let ciImage = CIImage(data: image.tiffRepresentation!)!
        let blackAndWhiteImage = ciImage.applyingFilter("CIColorControls", parameters: ["inputSaturation": value, "inputContrast": inputContrastValue])
        let rep: NSCIImageRep = NSCIImageRep(ciImage: blackAndWhiteImage)
        let nsImage: NSImage = NSImage(size: rep.size)
        nsImage.addRepresentation(rep)

        return nsImage
    }

}

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

How can I convert an UIImage to grayscale in Swift using CIFilter?

core-image

ios

cifilter

swift