C#LibTiff.Net-MultiTIFF更改标记值

public static void setRequiredTags(string outputFilePath)
    {
        using (Tiff image_MultiTIFF = Tiff.Open(outputFilePath, "a"))
        {
            for (int i = 0; i < image_MultiTIFF.NumberOfDirectories(); i++)
            { 
                // Load the Next Sub-TIFF
                   image_MultiTIFF.SetDirectory((short)i);  
                // setting custom tag  
                // image_MultiTIFF.SetField(TiffTag.PAGENUMBER, i, image_MultiTIFF.NumberOfDirectories());
                // image_MultiTIFF.SetField(TiffTag.DATETIME, DateTime.Now); 

                // rewrites directory saving new tag
                   image_MultiTIFF.CheckpointDirectory();
            }  
        }
}