尝试更新tiff图像上的标签时出现问题

Question

注意：创建LibTiff.Net库从未改变的新tiff图像时，可以使用LibTiff.Net库添加/更改标签而不会出现问题（第一次）。

在我使用LibTiff.Net库改变tiff标签后，当我尝试第二次更改它们时，图像变得腐败。标签似乎很好，但图像本身显示为黑色图像（损坏）。

这是目前在我的课堂上使用我的标签扩展...

private static Tiff.TiffExtendProc m_parentExtender; 
private static List<TIFFTAGS_TAG> m_lTagsToWrite; 

private static void TagExtender(Tiff tif) 
{ 
    List<TiffFieldInfo> tfInfo = new List<TiffFieldInfo>(); 
    Int16 readCount = 0; 
    Int16 writeCount = 0; 
    bool okToChange = false; 
    bool passCount = false; 

    //Make sure to create a new tiff field info for all the tags to be written 
    foreach (TIFFTAGS_TAG ttTag in m_lTagsToWrite) 
    { 
     switch (ttTag.TagType) 
     { 
      case TIFFTAGS_TAG_DATATYPE.ASCII: 
       readCount = -1; 
       writeCount = -1; 
       okToChange = true; 
       passCount = false; 

       break; 
      case TIFFTAGS_TAG_DATATYPE.LONG: 
      case TIFFTAGS_TAG_DATATYPE.RATIONAL: 
      case TIFFTAGS_TAG_DATATYPE.SHORT: 
       readCount = 2; 
       writeCount = 2; 
       okToChange = false; 
       passCount = true; 

       break; 
     } 

     if (ttTag.TagType != TIFFTAGS_TAG_DATATYPE.UNKNOWN) 
     { 
      //Add the new item to the list 
      tfInfo.Add(new TiffFieldInfo((TiffTag)ttTag.TagNumber, readCount, writeCount, (TiffType)ttTag.TagType, FieldBit.Custom, okToChange, passCount, ttTag.TagName)); 
     } 
    } 

    //Turn the list into an array again 
    TiffFieldInfo[] tfInfoArray = tfInfo.ToArray(); 

    //Add the fields to the main field info area 
    tif.MergeFieldInfo(tfInfoArray, tfInfoArray.Length); 

    //Propergate the chain if needed 
    if (m_parentExtender != null) 
     m_parentExtender(tif); 
} 

，这是目前使用我的函数，在给定的TIFF

public static bool SetTiffTags(string sFileName, List<TIFFTAGS_TAG> ttTagsInfo) 
{ 
    //Sets all the tiff tags in the image given. 
    //Returns true if successful or false if error occured 

    //Check if the file exists 
    if (!File.Exists(sFileName)) 
    { 
     //File does not exist 
     return false; 
    } 

    try 
    { 
     //Set the tag info so that it can be carried over to the extender callback 
     m_lTagsToWrite = new List<TIFFTAGS_TAG>(); 
     m_parentExtender = Tiff.SetTagExtender(TagExtender); 
     m_lTagsToWrite = ttTagsInfo; 

     using (Tiff tImage = Tiff.Open(sFileName, "a")) 
     { 
      if (tImage != null) 
      { 
       //Go to the first page 
       tImage.SetDirectory(0); 

       foreach (TIFFTAGS_TAG ttTag in ttTagsInfo) 
       { 
        switch (ttTag.TagType) 
        { 
         case TIFFTAGS_TAG_DATATYPE.ASCII: 
          try 
          { 
           //string 
           string sValue = ttTag.Value.ToString(); 
           tImage.SetField((TiffTag)ttTag.TagNumber, sValue); 
          } 
          catch 
          { 
           //Could not convert to a string 
           return false; 
          } 
          break; 
         case TIFFTAGS_TAG_DATATYPE.LONG: 
          try 
          { 
           //long 
           int[] iValues; 
           if (ttTag.Value.GetType().ToString() == "System.Int32") 
           { 
            iValues = new int[] { (int)ttTag.Value }; 
           } 
           else if (ttTag.Value.GetType().ToString() == "System.Int32[]") 
           { 
            iValues = (int[])ttTag.Value; 
           } 
           else return false; 
           tImage.SetField((TiffTag)ttTag.TagNumber, iValues.Count(), iValues); 
          } 
          catch 
          { 
           //Could not convert to a long 
           return false; 
          } 
          break; 
         case TIFFTAGS_TAG_DATATYPE.SHORT: 
          try 
          { 
           //short 
           Int16[] iValues; 
           if (ttTag.Value.GetType().ToString() == "System.Int16") 
           { 
            iValues = new Int16[] { (Int16)ttTag.Value }; 
           } 
           else if (ttTag.Value.GetType().ToString() == "System.Int16[]") 
           { 
            iValues = (Int16[])ttTag.Value; 
           } 
           else return false; 
           tImage.SetField((TiffTag)ttTag.TagNumber, iValues.Count(), iValues); 
          } 
          catch 
          { 
           //Could not convert to a short 
           return false; 
          } 
          break; 
         case TIFFTAGS_TAG_DATATYPE.RATIONAL: 
          try 
          { 
           //float 
           Single[] iValues; 
           if (ttTag.Value.GetType().ToString() == "System.Single") 
           { 
            iValues = new Single[] { (Single)ttTag.Value }; 
           } 
           else if (ttTag.Value.GetType().ToString() == "System.Single[]") 
           { 
            iValues = (Single[])ttTag.Value; 
           } 
           else return false; 
           tImage.SetField((TiffTag)ttTag.TagNumber, iValues.Count(), iValues); 
          } 
          catch 
          { 
           //Could not convert to a single 
           return false; 
          } 
          break; 
         default: 
          //This type of tag is not supported so error out 
          return false; 
        } 
       } 

       //Write the information to the tiff 
       tImage.CheckpointDirectory(); 
      } 
      else 
      { 
       //Restore previous tag extender 
       Tiff.SetTagExtender(m_parentExtender); 

       return false; 
      } 
     } 

     //Restore previous tag extender 
     Tiff.SetTagExtender(m_parentExtender); 
    } 
    catch 
    { 
     //Restore previous tag extender 
     Tiff.SetTagExtender(m_parentExtender); 

     return false; 
    } 

    //Return success 
    return true; 
} 

Answer 1

快看看设置TIFF标记您的代码让我觉得问题的原因是呼叫tImage.CheckpointDirectory();

通过这个调用，您可以有效地将目录数据写入文件，而不必考虑可能会被读取的内容你放在那里。

我想早晚通过调用CheckpointDirectory写入的目录开始占用比先前分配给文件中的目录数据更多的空间，并且栅格数据的开始被覆盖。

请尝试改用RewriteDirectory方法。