Implementing Exif Features

The Exif file format supports more complex comments than other formats. For a list of the comments, refer to Exif File Comments.

This example demonstrates how to handle Exif comments that are not stored as strings. (For a simpler example for saving strings, refer to the WriteComment method.)

This example does the following:

1.	Loads an image.
2.	Updates the comment array by loading comments from the existing file.
3.	Reverses the image and creates a RasterCommentMetadataType.UserComment comment that says that the image has been reversed.
4.	Saves the file. (All of the comments are saved, including the one that we updated.)
5.	Reads and displays two of the comments from the saved file. One of them is the comment that we created. The other is comment that uses the Exif RasterTagMetadataDataType.URational data type.
6.	Clean up the comment array.

Private Sub WriteCommentsTest() 
   Dim codecs As New RasterCodecs() 
             
   Dim srcFileName As String = "C:\LEADTOOLS21\Resources\Images\Image1.cmp" 
   Dim destFileName As String = "C:\LEADTOOLS21\Resources\Images\Exif.tif" 
             
   Dim tempImage As RasterImage = codecs.Load(srcFileName) 
             
   ' Flip the image. 
   Dim flipCmd As New FlipCommand(True) 
   flipCmd.Run(tempImage) 
             
   ' Add a user comment to the file and save it in another name. 
   Dim comment As New RasterCommentMetadata() 
   comment.Type = RasterCommentMetadataType.UserComment 
   Dim comments As String = "The image has been flipped" 
   Dim data() As Char = comments.ToCharArray(0, comments.Length) 
   Dim dataComments(8 + comments.Length - 1) As Byte 
             
   ' when you need to write a user comment the first 8 bytes  
   ' must contain the "Ascii" word. 
   dataComments(0) = 41 
   dataComments(1) = 53 
   dataComments(2) = 43 
   dataComments(3) = 49 
   dataComments(4) = 49 
   dataComments(5) = 0 
   dataComments(6) = 0 
   dataComments(7) = 0 
             
   For i As Integer = 0 To comments.Length - 1 
      dataComments(8 + i) = CType(AscW(data(i)), Byte) 
   Next 
             
   ' set the data property in the comment object to the dataComments array. 
   comment.FromByte(dataComments) 
             
   ' add the user comment to the comments collection of the image 
   tempImage.Comments.Add(comment) 
   codecs.Options.Save.Comments = True 
   codecs.Save(tempImage, destFileName, RasterImageFormat.Exif, 24) 
   tempImage.Dispose() 
             
   ' read the user comments and display it 
   comment = codecs.ReadComment(destFileName, 1, RasterCommentMetadataType.UserComment) 
   dataComments = comment.GetData() 
   Dim msg As String = "User comments = " 
   For i As Integer = 0 To dataComments.Length - 7 
      msg = msg + dataComments(i + 8).ToString 
   Next 
             
   MessageBox.Show(msg, "Notice") 
End Sub

private void WriteCommentsTest() 
{ 
   RasterCodecs codecs = new RasterCodecs(); 
             
   string srcFileName = @"C:\LEADTOOLS21\Resources\Images\Image1.cmp"; 
   string destFileName = @"C:\LEADTOOLS21\Resources\Images\Exif.tif"; 
             
   RasterImage tempImage = codecs.Load(srcFileName); 
             
   // Flip the image. 
   FlipCommand flipCmd = new FlipCommand(true); 
   flipCmd.Run(tempImage); 
                 
   // Add a user comment to the file and save it in another name. 
   RasterCommentMetadata comment = new RasterCommentMetadata(); 
   comment.Type = RasterCommentMetadataType.UserComment; 
   string comments = "The image has been flipped"; 
   char[] data = comments.ToCharArray(0, comments.Length); 
   byte[] dataComments = new byte[8 + comments.Length]; 
             
   // when you need to write a user comment the first 8 bytes  
   // must contain the "Ascii" word. 
   dataComments[0] = 41; 
   dataComments[1] = 53; 
   dataComments[2] = 43; 
   dataComments[3] = 49; 
   dataComments[4] = 49; 
   dataComments[5] = 0; 
   dataComments[6] = 0; 
   dataComments[7] = 0; 
                 
   for(int i = 0; i < comments.Length; i++) 
      dataComments[8 + i] = (byte)data[i]; 
             
   // set the data property in the comment object to the dataComments array. 
   comment.FromByte(dataComments); 
             
   // add the user comment to the comments collection of the image 
   tempImage.Comments.Add(comment); 
   codecs.Options.Save.Comments = true; 
   codecs.Save(tempImage, destFileName, RasterImageFormat.Exif, 24); 
   tempImage.Dispose(); 
                 
   // read the user comments and display it 
   comment = codecs.ReadComment(destFileName, 1, RasterCommentMetadataType.UserComment); 
   dataComments = comment.GetData(); 
   string msg =  "User comments = "; 
   for(int i = 0; i < (dataComments.Length - 8); i++) 
      msg += (char)dataComments[i + 8]; 
             
   MessageBox.Show(msg, "Notice"); 
}