如何在 Swift 中从 UIImage 转换为 HEIF / HEIC 数据？

Question

是NSKeyedArchiver适当的转换UIImage来Data？

do {
    let data = try NSKeyedArchiver.archivedData(withRootObject: UIImage(named: somePath), requiringSecureCoding: true)
    ...
} catch {
    print(error)
}

或者是矫枉过正，使用pngData()更合适？

let image = UIImage(named: somePath)
let data = image?.pngData()

以及如何从UIImageHEIF / HEIC转换Data？

目标是将图像保存到设备的文件系统。

Answer 1

不。永远不要使用 NSKeyedArchiver 将您的图像转换为数据。选择一种图像格式（HEIC、PNG、JPEG 等）并获取其数据表示。在保存要在 UI 中使用的图像时，您应该只使用 PNG。大多数时候 jpeg 是首选。如果设备支持 HEIC，考虑到图像质量和减少的数据大小，这是一个选项。

如果您需要检查用户设备是否支持 HEIC 类型，您可以按如下方式进行：

var isHeicSupported: Bool {
    (CGImageDestinationCopyTypeIdentifiers() as! [String]).contains("public.heic")
}

如果您需要将图像转换为 HEIC，则需要CGImage从您的图像中获取 aUIImage并将您的UIImage'simageOrientation转换CGImagePropertyOrientation为在创建其数据表示时保留方向：

extension UIImage {
    var heic: Data? { heic() }
    func heic(compressionQuality: CGFloat = 1) -> Data? {
        guard
            let mutableData = CFDataCreateMutable(nil, 0),
            let destination = CGImageDestinationCreateWithData(mutableData, "public.heic" as CFString, 1, nil),
            let cgImage = cgImage 
        else { return nil }
        CGImageDestinationAddImage(destination, cgImage, [kCGImageDestinationLossyCompressionQuality: compressionQuality, kCGImagePropertyOrientation: cgImageOrientation.rawValue] as CFDictionary)
        guard CGImageDestinationFinalize(destination) else { return nil }
        return mutableData as Data
    }
}

extension CGImagePropertyOrientation {
    init(_ uiOrientation: UIImage.Orientation) {
        switch uiOrientation {
            case .up: self = .up
            case .upMirrored: self = .upMirrored
            case .down: self = .down
            case .downMirrored: self = .downMirrored
            case .left: self = .left
            case .leftMirrored: self = .leftMirrored
            case .right: self = .right
            case .rightMirrored: self = .rightMirrored
        @unknown default:
            fatalError()
        }
    }
}

extension UIImage {
    var cgImageOrientation: CGImagePropertyOrientation { .init(imageOrientation) }
}

无损压缩的用途：

if isHeicSupported, let heicData = image.heic {
    // write your heic image data to disk
}

或为您的图像添加压缩：

if isHeicSupported, let heicData = image.heic(compressionQuality: 0.75) {
    // write your compressed heic image data to disk
}