Read and Write Exif Tags and Comments - C# .NET 6

This tutorial shows how to read and write Exif tags and comments in a C# .NET 6 application using the LEADTOOLS SDK.

Required Knowledge

Get familiar with the basic steps of creating a project by reviewing the Add References and Set a License tutorial, before working on this tutorial.

Create the Project and Add LEADTOOLS References

Start with a copy of the project created in the Add References and Set a License tutorial. If you do not have that project, follow the steps in that tutorial to create it.

The references needed depend upon the purpose of the project. References can be added by one or the other of the following two methods (but not both).

If using NuGet references, this tutorial requires the following NuGet package:

If using local DLL references, the following DLLs are needed.

The DLLs are located at <INSTALL_DIR>\LEADTOOLS23\Bin\net:

• Leadtools.dll
• Leadtools.Core.dll
• Leadtools.Codecs.dll

For a complete list of which DLL files are required for your application, refer to Files to be Included in your Application.

Set the License File

The License unlocks the features needed for the project. It must be set before any toolkit function is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.

There are two types of runtime licenses:

• Evaluation license, obtained at the time the evaluation toolkit is downloaded. It allows the toolkit to be evaluated.
• Deployment license. If a Deployment license file and developer key are needed, refer to Obtaining a License.

Add the Read/Write Exif Comments Code

With the project created, the references added, and the license set, coding can begin.

In the Solution Explorer, open Program.cs. Add the following statements to the using block at the top of Program.cs:

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing; 

Add two new string variables to the Main method named _srcFile and _destFile above the call to the SetLicense method. Set _srcFile equal to the file path containing the source EXIF file and set _destFile equal to the file path to export the EXIF file containing the added comment.

Add a new method to the Program class named ReadAndWriteExifComments(string _srcFile, string _destFile, RasterCodecs _codecs). Call this method below the call to the SetLicense method, inside a using statement initiating a new instance of RasterCodecs, as shown below.

static void Main(string[] args) 
{ 
   string _srcFile = @"FILE PATH TO SOURCE EXIF FILE"; 
   string _destFile = @"FILE PATH TO OUTPUF EXIF FILE"; 
 
   InitLEAD(); 
 
   using RasterCodecs _codecs = new RasterCodecs(); 
 
   ReadAndWriteExifComments(_srcFile, _destFile, _codecs); 
   ReadAndWriteExifTags(_srcFile, _codecs); 
 
   Console.WriteLine("Press any key to exit"); 
   Console.ReadKey(true); 
} 

Add the below code to the ReadAndWriteExifComments method to flip the loaded image, write a tag to the file stating that the image has been flipped, and then read the user comment created.

static void ReadAndWriteExifComments(string _srcFile, string _destFile, RasterCodecs _codecs) 
{ 
   using RasterImage _image = _codecs.Load(_srcFile); 
   // Write Comment 
   // Flip the image. 
   FlipCommand flipCmd = new FlipCommand(true); 
   flipCmd.Run(_image); 
 
   // Add a user comment to the file and save it in another name. 
   RasterCommentMetadata comment = new RasterCommentMetadata(); 
   // When writing a user comment, the first 8 bytes must contain the "ASCII" word followed by 3 null characters. 
   comment.Type = RasterCommentMetadataType.UserComment; 
   string commentString = "ASCII\0\0\0"; 
   commentString += "The image has been flipped."; 
 
   // Convert the string to byte array and set the bytes into the comment 
   byte[] bytes = System.Text.Encoding.ASCII.GetBytes(commentString); 
   comment.FromByte(bytes); 
   // Add the user comment to the comments collection of the image 
   _image.Comments.Add(comment); 
   _codecs.Options.Save.Comments = true; 
   _codecs.Save(_image, _destFile, RasterImageFormat.Exif, 24); 
 
   // Read the comments 
   RasterCommentMetadata commentRead = _codecs.ReadComment(_destFile, 1, RasterCommentMetadataType.UserComment); 
   byte[] commentBytes = commentRead.GetData(); 
   string commentStringRead = System.Text.Encoding.ASCII.GetString(commentBytes, 8, commentBytes.Length - 8); 
 
   Console.WriteLine($"User comments = {commentStringRead}"); 
} 

Add the Read/Write Exif Tags Code

Add a new method to the Program class named ReadAndWriteExifTags(string _srcFile, RasterCodecs _codecs). Call this method below the call to the ReadAndWriteExifComments method, inside a using statement initiating a new instance of RasterCodecs, as shown in the previous section. Add the code below to the ReadAndWriteExifTags method to write a private tag then read all the tags from the designated file.

static void ReadAndWriteExifTags(string _srcFile, RasterCodecs _codecs) 
{ 
   RasterImageFormat format; 
 
   using CodecsImageInfo info = _codecs.GetInformation(_srcFile, false); 
   format = info.Format; 
 
 
   // Load the tags 
   List<RasterTagMetadata> tags = null; 
 
   if (!RasterCodecs.TagsSupported(format)) 
   { 
      Console.WriteLine("File Format Does Not Support Tags"); 
      return; 
   } 
   int PhoneNumber = 0x8001; // Add a private (custom) "Phone Number" tag 
   byte[] bytes = System.Text.Encoding.ASCII.GetBytes("+1-800-637-4699"); 
   RasterTagMetadata tag = new RasterTagMetadata(PhoneNumber, RasterTagMetadataDataType.Ascii, bytes); 
   _codecs.WriteTag(_srcFile, 1, tag); 
 
   tags = new List<RasterTagMetadata>(_codecs.ReadTags(_srcFile, 1)); 
 
   string txtFileName = "_metadata.txt"; 
 
   using StreamWriter writer = File.CreateText(txtFileName); 
   // List the tags into a text file 
   ExportTags(writer, "Tags", tags); 
} 

Add a new method to the Program class named ExportTags(StreamWriter writer, string name, List<RasterTagMetadata> tags). Call this method inside the ReadAndWriteExifTags method, as shown above. Add the code below to the ExportTags method to list the tags read to a TXT file.

static void ExportTags(StreamWriter writer, string name, List<RasterTagMetadata> tags) 
{ 
   writer.WriteLine("{0}:", name); 
 
   if (tags != null) 
   { 
      foreach (RasterTagMetadata tag in tags) 
      { 
         writer.WriteLine("Id: 0x{0}, data length: {1}", tag.Id.ToString("X"), tag.GetData().Length); 
      } 
   } 
   else 
   { 
      writer.WriteLine("Not supported"); 
   } 
 
   writer.WriteLine(); 
} 

Run the Project

Run the project by pressing F5, or by selecting Debug -> Start Debugging.

If the steps were followed correctly, the application runs and initially writes an Exif user comment, reads the written user comment, then reads the Exif tags inside the given image and writes those tags to an external TXT file.

Wrap-up

This tutorial showed how to read and write Exif comments and tags. Also, we covered how to use the RasterCodecs and RasterTagMetadata classes.

See Also

• LEADTOOLS RasterCodecs Documentation
• LEADTOOLS RasterTagMetadata Documentation
• LEADTOOLS SDK Download