Detect and Extract Barcodes Using Live Capture - WinForms C#

This tutorial shows how to use the LEADTOOLS Multimedia SDK to create a WinForms C# application that uses the CaptureCtrl with the LEAD Video Callback Filter to perform live capture of barcodes using a supported video device, like a webcam.

The LEAD Video Callback Filter is an in-place filter which calls a method or a user callback interface each time it receives a frame. It can be used to access image data for processing and recognition.

Overview  
Summary This tutorial covers how to implement live capture of barcodes from a supported video device (e.g., webcam) in a WinForms C# application.
Completion Time 30 minutes
Visual Studio Project Download tutorial project (11 KB)
Platform WinForms C# Application
IDE Visual Studio 2019
Development License Download LEADTOOLS

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 the Detect and Extract Barcodes Using Live Capture - WinForms C# tutorial.

Create the Project and Add LEADTOOLS References

In Visual Studio, create a new C# Windows Winforms project, and add the below necessary LEADTOOLS references.

The references needed depend upon the purpose of the project. References can be added by local DLL reference. This tutorial requires the following local DLLs, which are located at <INSTALL_DIR>\LEADTOOLS21\Bin\Dotnet4\x64:

The tutorial also requires adding a reference to the following COM Library:

Note

Different SDK features require different references. For a complete list, refer to Multimedia Files You Must Include With Your Application. For a complete list of which non-Multimedia DLLs are required for your application, refer to Files to be Included With 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:

Note

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

Create the Callback Filter Interface Implementation

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

In the Solution Explorer, right-click on the project and select Add -> New Item. Select the Class option and name the class LMVMyUserCallback.cs, then click Add.

The LMVMyUserCallback class will use the frame received by the callback filter to instantiate a RasterImage object with the image data and use a BarcodeReader instance to detect any barcode in the image. If found, the detected BarcodeData will be passed to an event handler in the form.

Add the following statements to the using block at the top of the LMVMyUserCallback class.

C#
using System; 
using Leadtools; 
using Leadtools.Barcode; 
using LMVCallbackLib; 

Add the following code to create the event arguments class which will be used to pass the detected BarcodeData to the form.

C#
public class BarcodeFoundEventArgs : EventArgs 
{ 
   public BarcodeData data { get; private set; } 
   public BarcodeFoundEventArgs(BarcodeData barcodeData) 
   { 
      data = barcodeData; 
   } 
} 

Use the code below for LMVMyUserCallback, which is a custom interface of the ILMVUserCallback filter interface.

C#
public class LMVMyUserCallback : ILMVUserCallback 
{ 
   // Event used in the form for when a barcode is found 
   public delegate void BarcodeFoundHandler(object sender, BarcodeFoundEventArgs e); 
   public event BarcodeFoundHandler OnBarcodeFound; 
 
   private BarcodeEngine engine = new BarcodeEngine(); 
   private RasterImage img = null; 
 
   public LMVMyUserCallback() 
   { 
      engine.Reader.ImageType = BarcodeImageType.Picture; 
   } 
 
   public void ReceiveProc(int pData, int lWidth, int lHeight, int lBitCount, int lSize, int bTopDown) 
   { 
      try 
      { 
         // Create new RasterImage object using frame properties 
         RasterViewPerspective viewPerspective; 
         if (bTopDown == 1) 
            viewPerspective = RasterViewPerspective.TopLeft; 
         else 
            viewPerspective = RasterViewPerspective.BottomLeft; 
 
         if (img == null || img.IsDisposed) 
         { 
            img = new RasterImage( 
               RasterMemoryFlags.User, 
               lWidth, 
               lHeight, 
               lBitCount, 
               RasterByteOrder.Bgr, 
               viewPerspective, 
               null, 
               IntPtr.Zero, 
               0); 
         } 
         // Copy image data from callback 
         img.SetUserData(new IntPtr(pData), lSize); 
 
         // Detect and read barcode in image 
         var data = engine.Reader.ReadBarcode(img, LeadRect.Empty, BarcodeSymbology.Unknown); 
 
         // When found, pass the data to the event handler 
         if (data != null) 
         { 
            var barcodeFoundEvent = new BarcodeFoundEventArgs(data); 
            OnBarcodeFound(this, barcodeFoundEvent); 
         } 
      } 
      catch (Exception ex) 
      { 
         Console.WriteLine(ex.Message); 
      } 
      finally 
      { 
         if (img != null) 
            img.Dispose(); 
      } 
   } 
} 

Create and Initialize the Capture Control

In the Solution Explorer, right-click on Form1.cs and select View Code to display the code-behind the form. Add the following statements to the using block at the top.

C#
using System; 
using System.IO; 
using System.Windows.Forms; 
using Leadtools; 
using Leadtools.Barcode; 
using Leadtools.Multimedia; 
using LMVCallbackLib; 

Add a CaptureCtrl control, a LMVCallback callback, and the LMVMyUserCallback custom interface as global variables.

C#
// Add these global variables 
private CaptureCtrl capture1; 
private LMVCallback lmvCallback; 
private LMVMyUserCallback lmvMyUserCallback; 
 
bool IsCapturing = false; 

Add the CaptureCtrl control to the form and call the InsertCallbackFilter() method to insert the lmvCallBack filter.

C#
public Form1() 
{ 
   InitializeComponent(); 
   SetLicense(); 
 
   // Add Capture Control 
   capture1 = new CaptureCtrl { Dock = DockStyle.Fill }; 
   capture1.VideoDevices.Selection = -1; 
   Controls.Add(capture1); 
          
   InsertCallbackFilter(); 
} 

Create a new method named InsertCallbackFilter(), which will be called inside Form1() as shown above. Add the code below to insert the lmvCallBack filter and assign an OnBarcodeFound event handler that will trigger when a barcode is detected.

C#
private void InsertCallbackFilter() 
{ 
   try 
   { 
      Processor videoCallback = capture1.VideoProcessors.Callback; 
      capture1.SelectedVideoProcessors.Add(videoCallback); 
      lmvCallback = (LMVCallback)capture1.GetSubObject(CaptureObject.SelVideoProcessor); 
      lmvMyUserCallback = new LMVMyUserCallback(); 
      lmvCallback.ReceiveProcObj = lmvMyUserCallback; 
      lmvMyUserCallback.OnBarcodeFound += LmvMyUserCallback_OnBarcodeFound; 
   } 
   catch (Exception ex) 
   { 
      MessageBox.Show(ex.Message); 
   } 
} 

Add the code below to the OnBarcodeFound event to display the barcode information to the user.

C#
private void LmvMyUserCallback_OnBarcodeFound(object sender, BarcodeFoundEventArgs e) 
{ 
   MessageBox.Show(e.data.Symbology.ToString() + " Barcode Found. Value: " + e.data.Value); 
   StopCapture(); 
} 

In the Solution Explorer, double-click Form1.cs to display it in the Designer. Click the Events icon in the Properties Windows. Then, double-click the Load event to create an event handler, if one does not already exist.

Creating a Load event for the Form.

Add the following code inside the Form1_Load event handler. This will add the names of all available capture devices to a menu in the user interface. Clicking on the device's name will set it as a capture device for the CaptureCtrl control.

C#
private void Form1_Load(object sender, EventArgs e) 
{ 
   // Setup Capture Devices Menu 
   foreach (Device dev in capture1.VideoDevices) 
   { 
      ToolStripItem mi = new ToolStripMenuItem(); 
      mi.Text = dev.FriendlyName; 
      mi.Click += videoDevices_click; 
      videoDeviceToolStripMenuItem.DropDownItems.Add(mi); 
   } 
} 

Add the code below to the videoDevices_click event to set the selected capture device for the CaptureCtrl control.

C#
private void videoDevices_click(object sender, EventArgs e) 
{ 
   ToolStripItem ti = (ToolStripItem)sender; 
   capture1.EnterEdit(); 
 
   try 
   { 
      capture1.VideoDevices.Selection = (ti.OwnerItem as ToolStripMenuItem).DropDownItems.IndexOf(ti); 
   } 
   catch (Exception) 
   { 
      MessageBox.Show("This video capture device is not available. Make sure no other program is using the device or try changing the display resolution", "Error"); 
   } 
} 

Create the User Interface

Open Form1.cs in the Designer. Inside the Toolbox, double-click MenuStrip, which will add a menu to the form.

Adding a MenuStrip to the Form.

Add two menu items with the text Video &Device and &Start. Leave the new items' names as videoDeviceToolStripMenuItem and startCaptureToolStripMenuItem.

Double-click the Start menu item to create its event handler. Add the following code in it:

C#
private void startToolStripMenuItem_Click(object sender, EventArgs e) 
{ 
   if (!IsCapturing) 
   { 
      startCaptureToolStripMenuItem.Text = "Stop"; 
 
      capture1.PreviewSource = CapturePreview.Video; 
      capture1.PreviewTap = CapturePreviewTap.Processors; 
      capture1.Preview = true; 
 
      capture1.ReadyCapture(CaptureMode.Video); 
 
      IsCapturing = true; 
   } 
   else 
      StopCapture(); 
} 

Clicking Start will configure the CaptureCtrl control so that a preview is generated from the video device. This will allow image frames to be passed to the lmvCallBack filter for barcode detection.

Create a new method inside the Form1 class named StopCapture(). This method will be called inside the startToolStripMenuItem_Click event handler as shown above. Add the code below inside the StopCapture() method to stop the CaptureCtrl.

C#
private void StopCapture() 
{ 
   startCaptureToolStripMenuItem.Text = "Start"; 
   capture1.StopCapture(); 
   IsCapturing = false; 
} 

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 the form should appear. To test, follow the steps below:

  1. Click on the Video Device dropdown menu and select your preferred device for capture.

  2. Click Start to bring up the CaptureCtrl preview. At this time the application will start gathering the frames from the device as RasterImages, and running barcode detection.

  3. Place the barcode you want to recognize in front of the camera.

  4. When you are done, select Stop to stop capturing.

    Detect and Extract Barcode using Live Capture

Wrap-up

This tutorial showed how to detect barcodes in the frames of a live capture video device using the CaptureCtrl and BarcodeReader classes.

See Also

Help Version 21.0.2021.6.17
Products | Support | Contact Us | Intellectual Property Notices
© 1991-2021 LEAD Technologies, Inc. All Rights Reserved.