来自CIImage的PNG/JPEG表示始终返回nil

Question

我目前正在制作照片编辑应用.

当用户选择照片时,使用以下代码将其自动转换为黑白照片:

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)!
}

我对此代码的问题是我一直收到此错误:

fatal error: unexpectedly found nil while unwrapping an Optional value

我的代码略有不同,但是当它到达该UIImagePNG/JPEGRepresentation(xx)部分时它仍然会中断.

是否有任何方法可以从CIImage中获取PNG或JPEG数据,以便在图像视图/ UIImage中使用？

任何其他方法都没有详细说明应该使用什么代码.

Answer 1

只需开始一个新的图形上下文并在那里绘制灰度图像:

func blackWhiteImage(image: UIImage) -> Data? {
    guard let ciImage = CIImage(image: image)?.applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey: 0]) else { return nil }
    return UIGraphicsImageRenderer(size: image.size, format: image.imageRendererFormat).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:

extension UIImage {
    var ciImage: CIImage? { CIImage(image: self) }
    var grayscale: UIImage? {
        guard let ciImage = ciImage?.applyingFilter("CIColorControls", parameters: [kCIInputSaturationKey: 0]) else { return nil }
        return UIGraphicsImageRenderer(size: size, format: imageRendererFormat).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
}