Read QR Code from Image or Stream

Read QR Code from Image or Stream

Ever needed to find a QR code in an image or MemoryStream? With the snippet below you can. It uses the ZXing.Net Library to scan a MemoryStream for a QR Code and output the text.

The code below is for a WPF App. But the C# code itself can be used in other projects as well. The App can read a QR code from disk or take a screenshot of the desktop (even with multiple monitors) and search for the QR code.
Another example would be to create a tool that scans the feed from a webcam or IP camera every x seconds and do something when you hold a QR code in front of it.

Download VS Project

Code Snippets

The XAML of the MainWindow.

<Window x:Class="ReadQrCodeFromStream.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:ReadQrCodeFromStream"
        mc:Ignorable="d"
        Title="QR Code Reader" 
        Height="400" 
        Width="370"
        Background="#566895">
    <StackPanel>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="10" />
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="15" />
                <ColumnDefinition Width="*" />
                <ColumnDefinition Width="10" />
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="10" />
                <RowDefinition Height="30" />
                <RowDefinition Height="30" />
                <RowDefinition Height="70" />
            </Grid.RowDefinitions>

            <Button Name="ReadFromDesktop" Grid.Row="1" Grid.Column="1" Content="Read QR Code from Desktop" 
                    Click="ReadFromDesktop_Click" Background="#435175" BorderBrush="#2a385a" Foreground="White" />
            <Button Name="ReadFromDisk" Grid.Row="1" Grid.Column="3" Content="Read QR Code from Disk" 
                    Click="ReadFromDisk_Click" Background="#435175" BorderBrush="#2a385a" Foreground="White" />

            <TextBlock Name="TextBlock1" Grid.Row="3" Grid.Column="1" Grid.ColumnSpan="3" TextWrapping="Wrap" Foreground="White" />
        </Grid>
        
        <Image Name="Image1" Grid.Row="6" Grid.Column="0" Grid.ColumnSpan="3" Width="200" Height="200" Margin="0, 10, 0, 0" />
        
    </StackPanel>
</Window>

And the MainWindow C# code to make it all work.

using System;
using System.Windows;
using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Forms;
using System.IO;
using System.Windows.Media.Imaging;
using System.Threading.Tasks;
using ZXing;
using ZXing.Common;

namespace ReadQrCodeFromStream
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }


        private async void ReadFromDesktop_Click(object sender, RoutedEventArgs e)
        {
            //reset the ui
            ResetUI();

            //make sure the UI updates first before scanning the desktop otherwise it will find it's previously scanned qr code
            await Task.Run(() => Task.Delay(1));

            //get the size of the virtual screen (includes all monitors)
            int left = SystemInformation.VirtualScreen.Left;
            int top = SystemInformation.VirtualScreen.Top;
            int width = SystemInformation.VirtualScreen.Width;
            int height = SystemInformation.VirtualScreen.Height;

            //create a bitmap of the entire desktop
            using (var stream = new MemoryStream())
            using (var bmp = new Bitmap(width, height))
            using (var g = Graphics.FromImage(bmp))
            {
                g.CopyFromScreen(left, top, 0, 0, bmp.Size);

                //save to disk or a memorystream if you need the screenshot elsewhere
                //bmp.Save(stream, ImageFormat.Jpeg);
                //bmp.Save(@"c:\temp\test.jpg", ImageFormat.Jpeg);

                //try to find a qr code in the screenshot and display result
                TextBlock1.Text = FindQrCodeInImage(bmp);
            }
        }


        private void ReadFromDisk_Click(object sender, EventArgs e)
        {
            //reset the ui
            ResetUI();

            //open the file dialog with only images as the filter
            var dialog = new Microsoft.Win32.OpenFileDialog()
            {
                Filter = "QR Code | *.jpg; *.jpeg; *.gif; *.bmp; *.png"
            };

            //a file is selected
            if (dialog.ShowDialog() == true)
            {
                //read the selected file as a byte array
                var bin = File.ReadAllBytes(dialog.FileName);

                //try cath if the selected file is not an image or is corrupted
                try
                {
                    //make a bmp from the selected file
                    using (var stream = new MemoryStream(bin))
                    using (var bmp = new Bitmap(stream))
                    {
                        //read the qr code and show the result
                        TextBlock1.Text = FindQrCodeInImage(bmp);
                    }
                }
                catch
                {
                }
            }
        }


        private string FindQrCodeInImage(Bitmap bmp)
        {
            //decode the bitmap and try to find a qr code
            var source = new BitmapLuminanceSource(bmp);
            var bitmap = new BinaryBitmap(new HybridBinarizer(source));
            var result = new MultiFormatReader().decode(bitmap);

            //no qr code found in bitmap
            if (result == null)
            {
                System.Windows.MessageBox.Show("No QR Code found!");

                return null;
            }

            //create a new qr code image
            var writer = new BarcodeWriter
            {
                Format = BarcodeFormat.QR_CODE,
                Options = new EncodingOptions
                {
                    Height = 300,
                    Width = 300
                }
            };

            //write the result to the new qr code bmp image
            var qrcode = writer.Write(result.Text);

            //make the bmp transparent
            qrcode.MakeTransparent();

            //show the found qr code in the app
            var stream = new MemoryStream();
            qrcode.Save(stream, ImageFormat.Png);

            //display the new qr code in the ui
            Image1.Source = BitmapFrame.Create(stream);
            Image1.Visibility = Visibility.Visible;

            //and/or save the new qr code image to disk if needed
            try
            {
                //qrcode.Save($"qr_code_{DateTime.Now.ToString("yyyyMMddHHmmss")}.gif", ImageFormat.Gif);
            }
            catch
            {
                //handle disk write errors here
            }

            //return the found qr code text
            return result.Text;
        }


        private void ResetUI()
        {
            this.Dispatcher.Invoke(() =>
            {
                Image1.Visibility = Visibility.Hidden;
                TextBlock1.Text = "";
            });
        }
    }
}