如何在Swift中将UIImage转换为HEIF / HEIC数据？

Question

NSKeyedArchiver是否适合将UIImage转换为Data？

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

或者是矫kill过正，使用pngData()更合适吗？

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

以及如何从UIImage转换为HEIF / HEIC Data？

目标是将图像保存到设备的文件系统。

Answer 1

没有您永远不要使用NSKeyedArchiver将图像转换为数据。您应该选择图像格式（HEIC，PNG，JPEG等）并获取其数据表示形式。保存图像以在UI中使用时，仅应使用PNG。大多数情况下，jpeg是首选。如果设备支持HEIC，则可以选择考虑图像质量和减小的数据大小。

如果需要检查用户设备是否支持HEIC类型，可以按照以下步骤进行：

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

[如果需要将图像转换为HEIC，则需要从CGImage中获取UIImage并将UIImage的imageOrientation转换为CGImagePropertyOrientation以在创建其数据表示形式时保留方向：] >

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: imageOrientation.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.Orientation {
    var cgImageOrientation: CGImagePropertyOrientation { .init(self) }
}
无损压缩的用法：

if isHeicSupported, let heicData = image.heic {
    // write your heic image data to disk
}
或添加压缩图像：

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