Detect Image Format and Extension - Windows C DLL

This tutorial shows how to read a given image file and detect the proper format, along with the appropriate file extension, using the LEADTOOLS SDK in a Windows C/C++ API application. This is useful if the filename's extension is incorrect or missing, or if the image is being read from a memory buffer.

Summary This tutorial covers how to use LEADTOOLS to detect a file's format and file extension in a Windows CDLL application.
Completion Time 30 minutes
Visual Studio Project Download tutorial project (18 KB)
Platform Windows C DLL Application
IDE Visual Studio 2017, 2019
Development License Download LEADTOOLS
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Required Knowledge

Get familiar with the basic steps of creating a project and loading/displaying an image by reviewing the Add References and Set a License and Load, Display, and Save Images tutorials, before working on the Detect Image Format and Extension - Windows C DLL tutorial.

Create the Project and Add LEADTOOLS References

Start with a copy of the project created in the Load, Display, and Save Images tutorial. If the project is not available, create it by following the steps in that tutorial.

Open the pre-compiled header file (either pch.h or stdafx.h, depending on the version of Visual Studio used) and ensure the below lines are added.

#define LTV22_CONFIG  
#include "C:\LEADTOOLS22\Include\L_Bitmap.h" // use the actual path where LEADTOOLS is installed  
#pragma comment (lib, "C:\\LEADTOOLS22\\Lib\\CDLL\\x64\\Ltkrn_x.lib")  
#pragma comment (lib, "C:\\LEADTOOLS22\\Lib\\CDLL\\x64\\Ltfil_x.lib") // file loading and saving  


For a complete list of DLLs that are required for specific application features, refer to Files to be Included with your Application - C API.

Set the License File

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

There are two types of runtime licenses:


Adding LEADTOOLS references and setting a license are covered in more detail in the Add References and Set a License tutorial.

Add the Detect Image Format Code

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

In the Solution Explorer, double-click the resources file (.rc).

Add a new &Image Format menu item to the File drop-down menu, between the Open and Save items. Leave the new menu item's ID as ID_FILE_IMAGEFORMAT.

Open the project's CPP file and navigate to the WndProc function. Under the switch (wmId) statement that is below the WM_COMMAND case, add a new case and the code below.

switch (wmId) 
   TCHAR szFileName[260] = TEXT(""); // File name 
   if (SUCCESS != GetBitmapLoadingName(hWnd, szFileName, ARRAYSIZE(szFileName))) 
   FILEINFO info = { 0 }; // Make sure to fill the struct with zeros before using it 
   if (SUCCESS != L_FileInfo(szFileName, &info, sizeof FILEINFO, FILEINFO_TOTALPAGES, NULL)) 
      MessageBox(hWnd, TEXT("Error getting file information"), TEXT("LEADTOOLS Demo"), MB_ICONERROR); 
   L_TCHAR szExtension[100] = TEXT(""); 
   L_GetFormatFileExtension(info.Format, szExtension, sizeof szExtension); 
   L_TCHAR szMimeType[100] = TEXT(""); 
   L_GetFormatMimeType(info.Format, szMimeType, sizeof szMimeType); 
   L_TCHAR CONST szFormatMessage[] = L_TEXT( 
      "Image Format: %d\n" 
      "Information for: %s\n" 
      "Extension: %s\n" 
      "Mime Type: %s"); 
   L_TCHAR szMessage[1024] = TEXT(""); 
   wsprintf(szMessage, szFormatMessage, 
   MessageBox(hWnd, szMessage, TEXT("File Information"), MB_ICONINFORMATION); 
// Keep rest of the code as is 

The code for the GetBitmapLoadingName() function, called inside the code above, is listed in the Load, Display, and Save Images tutorial.


The FILEINFO structure must be filled with zeros before using it with L_FileInfo().

Run the Project

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

If the steps are followed correctly, the application starts. To test, follow the instructions below.

  1. Select File -> Image Format.

  2. Select the image you would like to detect extension information for and press OK.

The image below shows the result for a PNG image file that was incorrectly named with ".txt" extension.

The application runs and a message displays the extension information from the selected image file.


This tutorial showed how to use the L_FileInfo, L_GetFormatFileExtension and L_GetFormatMimeType functions to retrieve extension and type information from a selected image.

See Also

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Products | Support | Contact Us | Intellectual Property Notices
© 1991-2022 LEAD Technologies, Inc. All Rights Reserved.