Swift：自定义相机将修改后的元数据与图像一起保存

Question

我正在尝试将图像样本缓冲区中的一些元数据与图像一起保存。

我需要：

• 将图像旋转到元数据中的方向
• 从元数据中删除方向
• 将拍摄日期保存到元数据中
• 将该图像与元数据一起保存到文档目录中

我尝试从数据中创建 UIImage，但这会删除元数据。我尝试使用数据中的 CIImage 来保留元数据，但我无法旋转它然后将其保存到文件中。

private func snapPhoto(success: (UIImage, CFMutableDictionary) -> Void, errorMessage: String -> Void) {
    guard !self.stillImageOutput.capturingStillImage,
        let videoConnection = stillImageOutput.connectionWithMediaType(AVMediaTypeVideo) else { return }

    videoConnection.fixVideoOrientation()

    stillImageOutput.captureStillImageAsynchronouslyFromConnection(videoConnection) {
        (imageDataSampleBuffer, error) -> Void in
        guard imageDataSampleBuffer != nil && error == nil else {
            errorMessage("Couldn't snap photo")
            return
        }

        let data = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageDataSampleBuffer)

        let metadata = CMCopyDictionaryOfAttachments(nil, imageDataSampleBuffer, CMAttachmentMode(kCMAttachmentMode_ShouldPropagate))
        let metadataMutable = CFDictionaryCreateMutableCopy(nil, 0, metadata)

        let utcDate = "\(NSDate())"
        let cfUTCDate = CFStringCreateCopy(nil, utcDate)
        CFDictionarySetValue(metadataMutable!, unsafeAddressOf(kCGImagePropertyGPSDateStamp), unsafeAddressOf(cfUTCDate))

        guard let image = UIImage(data: data)?.fixOrientation() else { return }
        CFDictionarySetValue(metadataMutable, unsafeAddressOf(kCGImagePropertyOrientation), unsafeAddressOf(1))

        success(image, metadataMutable)
    }
}

这是我保存图像的代码。

func saveImageAsJpg(image: UIImage, metadata: CFMutableDictionary) {
    // Add metadata to image
    guard let jpgData = UIImageJPEGRepresentation(image, 1) else { return }
    jpgData.writeToFile("\(self.documentsDirectory)/image1.jpg", atomically: true)
}

Answer 1

我最终弄清楚了如何让一切按照我需要的方式工作。对我帮助最大的事情是发现 CFDictionary 可以转换为 NSMutableDictionary。

这是我的最终代码：

如您所见，我在 EXIF 字典中添加了一个属性，用于数字化日期，并更改了方向值。

private func snapPhoto(success: (UIImage, NSMutableDictionary) -> Void, errorMessage: String -> Void) {
    guard !self.stillImageOutput.capturingStillImage,
        let videoConnection = stillImageOutput.connectionWithMediaType(AVMediaTypeVideo) else { return }

    videoConnection.fixVideoOrientation()

    stillImageOutput.captureStillImageAsynchronouslyFromConnection(videoConnection) {
        (imageDataSampleBuffer, error) -> Void in
        guard imageDataSampleBuffer != nil && error == nil else {
            errorMessage("Couldn't snap photo")
            return
        }

        let data = AVCaptureStillImageOutput.jpegStillImageNSDataRepresentation(imageDataSampleBuffer)

        let rawMetadata = CMCopyDictionaryOfAttachments(nil, imageDataSampleBuffer, CMAttachmentMode(kCMAttachmentMode_ShouldPropagate))
        let metadata = CFDictionaryCreateMutableCopy(nil, 0, rawMetadata) as NSMutableDictionary

        let exifData = metadata.valueForKey(kCGImagePropertyExifDictionary as String) as? NSMutableDictionary
        exifData?.setValue(NSDate().toString("yyyy:MM:dd HH:mm:ss"), forKey: kCGImagePropertyExifDateTimeDigitized as String)

        metadata.setValue(exifData, forKey: kCGImagePropertyExifDictionary as String)
        metadata.setValue(1, forKey: kCGImagePropertyOrientation as String)

        guard let image = UIImage(data: data)?.fixOrientation() else {
            errorMessage("Couldn't create image")
            return
        }

        success(image, metadata)
    }
}

以及用于保存带有元数据的图像的最终代码：

很多守卫语句，我讨厌，但它比强制展开要好。

func saveImage(withMetadata image: UIImage, metadata: NSMutableDictionary) {
    let filePath = "\(self.documentsPath)/image1.jpg"

    guard let jpgData = UIImageJPEGRepresentation(image, 1) else { return }

    // Add metadata to jpgData
    guard let source = CGImageSourceCreateWithData(jpgData, nil),
        let uniformTypeIdentifier = CGImageSourceGetType(source) else { return }
    let finalData = NSMutableData(data: jpgData)
    guard let destination = CGImageDestinationCreateWithData(finalData, uniformTypeIdentifier, 1, nil) else { return }
    CGImageDestinationAddImageFromSource(destination, source, 0, metadata)
    guard CGImageDestinationFinalize(destination) else { return }

    // Save image that now has metadata
    self.fileService.save(filePath, data: finalData)
}

这是我更新的save 方法（与我写这个问题时使用的不完全相同，因为我已经更新到 Swift 2.3，但概念是一样的）：

public func save(fileAt path: NSURL, with data: NSData) throws -> Bool {
    guard let pathString = path.absoluteString else { return false }
    let directory = (pathString as NSString).stringByDeletingLastPathComponent

    if !self.fileManager.fileExistsAtPath(directory) {
        try self.makeDirectory(at: NSURL(string: directory)!)
    }

    if self.fileManager.fileExistsAtPath(pathString) {
        try self.delete(fileAt: path)
    }

    return self.fileManager.createFileAtPath(pathString, contents: data, attributes: [NSFileProtectionKey: NSFileProtectionComplete])
}

Answer 2

我对上面的代码做了一个大大简化的版本。它确实制作了一个图像文件，但正如 Carlos 所指出的，当您再次加载文件时，文件中没有自定义元数据。根据其他线程，这根本不可能。

func saveImage(_ image: UIImage, withMetadata metadata: NSMutableDictionary, atPath path: URL) -> Bool {
    guard let jpgData = UIImageJPEGRepresentation(image, 1) else {
        return false
    }
    // make an image source
    guard let source = CGImageSourceCreateWithData(jpgData as CFData, nil), let uniformTypeIdentifier = CGImageSourceGetType(source) else {
        return false
    }
    // make an image destination pointing to the file we want to write
    guard let destination = CGImageDestinationCreateWithURL(path as CFURL, uniformTypeIdentifier, 1, nil) else {
        return false
    }

    // add the source image to the destination, along with the metadata
    CGImageDestinationAddImageFromSource(destination, source, 0, metadata)

    // and write it out
    return CGImageDestinationFinalize(destination)
}