CIImage的PNG/JPEG表示总是返回nil [英] PNG/JPEG representation from CIImage always returns nil

问题描述

我目前正在制作照片编辑应用.

I'm currently making a photo editing app.

用户选择了照片后，将使用以下代码将其自动转换为黑白:

When a photo is selected by the user, it is automatically converted into black and white using this code:

func blackWhiteImage(image: UIImage) -> Data {
    print("Starting black & white")

    let orgImg = CIImage(image: image)
    let bnwImg = orgImg?.applyingFilter("CIColorControls", withInputParameters: [kCIInputSaturationKey:0.0])

    let outputImage = UIImage(ciImage: bnwImg!)

    print("Black & white complete")

    return UIImagePNGRepresentation(outputImage)!
}

此代码存在的问题是我不断收到此错误:

The problem I am having with this code is that I keep getting this error:

fatal error: unexpectedly found nil while unwrapping an Optional value

我的代码配置稍有不同，但是到达UIImagePNG/JPEGRepresentation(xx)部分时，它仍然会中断.

I have had my code in a slightly different configuration, but it still breaks when it gets to the UIImagePNG/JPEGRepresentation(xx) section.

是否有任何方法可以从CIImage获取PNG或JPEG数据以用于图像视图(通常仅是UIImage)?

Are there any ways to get the PNG or JPEG data from a CIImage for use in an image view / just UIImage in general?

其他任何方法都没有为应该使用什么代码提供足够的细节.

Any of the other methods don't go into enough detail for what code should be used.

推荐答案

只需开始一个新的图形上下文并在其中绘制灰度图像. iOS 10或更高版本，您可以使用UIGraphicsImageRenderer，对于较旧的iOS版本语法，请检查编辑历史记录:

Just begin a new graphics context and draw your grayscale image there. iOS 10 or later you can use UIGraphicsImageRenderer, for older iOS version syntax please check edit history:

Xcode 11•Swift 5.1

func blackWhiteImage(image: UIImage, isOpaque: Bool = false) -> Data? {
    guard let ciImage = CIImage(image: image)?.applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey: 0]) else { return nil }
    let format = image.imageRendererFormat
    format.opaque = isOpaque
    return UIGraphicsImageRenderer(size: image.size, format: format).image { _ in
        UIImage(ciImage: ciImage).draw(in: CGRect(origin: .zero, size: image.size))
    }.pngData()
}

您还可以扩展UIImage以返回灰度图像:

You can also extend UIImage to return a grayscale image :

extension UIImage {
    var ciImage: CIImage? { CIImage(image: self) }
    func grayscale(isOpaque: Bool = false) -> UIImage? {
        guard let ciImage = ciImage?.applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey: 0]) else { return nil }
        let format = imageRendererFormat
        format.opaque = isOpaque
        return UIGraphicsImageRenderer(size: size, format: format).image { _ in
             UIImage(ciImage: ciImage).draw(in: CGRect(origin: .zero, size: size))
        }
    }
}

---

let profilePicture = UIImage(data: try! Data(contentsOf: URL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!))!

if let grayscale = profilePicture.grayscale(), let data = grayscale.pngData() {  // or Swift 4.1 or earlier -> let data = UIImagePNGRepresentation(grayscale)
    print(data.count)   //  689035
}

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