如何在 Swift 中从 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)
}

还是矫枉过正，使用pngData()更合适？

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

以及如何从UIImage转换为HEIF/HEICData？

目标是将映像保存到设备的文件系统。

Answer 1

No.切勿使用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，才应使用 PNG。大多数情况下，jpeg 是首选。如果设备支持 HEIC，则考虑图像质量和减小的数据大小是一个选项。

如果您需要检查用户设备是否支持 HEIC 类型，您可以执行以下操作：

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

如果您需要将图像转换为 HEIC，则需要从UIImage获取CGImage，并将UIImage的imageOrientation转换为CGImagePropertyOrientation以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
}
}

<小时 />

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()
}
}
}

<小时 />

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

---

无损压缩的用法：

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

或为图像添加压缩：

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