修改元数据后图像尺寸减小，即（EXIF，GPS，TIFF）

Question

我试图修改图像的元数据，但似乎原始图像的文件大小显着减少，这让我太烦了。如果图像大小为6MB，则修改后大小为3.2MB。我知道它很奇怪，但并非不可能。有没有人帮助我解决这个问题。我们将不胜感激。 这是我用swift 2.0编写的代码，工具是Xcode 7.3.1。

 func writeProperties(url:NSURL, override: Bool) -> NSURL?{
    guard let directory = url.URLByDeletingLastPathComponent else { return nil }
    guard let base = url.URLByDeletingPathExtension?.lastPathComponent else { return nil }
    guard let ext = url.pathExtension else { return nil }
    let newName = override ? url.lastPathComponent! : "\(base)_modified.\(ext)"
    let newPath = directory.URLByAppendingPathComponent(newName, isDirectory: false)
    print("writeProperties to \(newPath)")
    guard let imageSource = CGImageSourceCreateWithURL(url, nil) else { return nil }
    let imageType = CGImageSourceGetType(imageSource)!
    let data = NSMutableData()
    guard let imageDestination = CGImageDestinationCreateWithData(data, imageType, 1, nil) else { return nil }
    CGImageDestinationAddImageFromSource(imageDestination, imageSource, 0, saveProperties)
    CGImageDestinationFinalize(imageDestination)
    if let _ = try? data.writeToURL(newPath, options: NSDataWritingOptions.AtomicWrite) {
      let alert = NSAlert()
      alert.messageText = "Image Saved"
      alert.informativeText = "Image saved to \(newPath.path!)"
      alert.runModal()
      return newPath
    }
    return nil
  }