Ozeki Camera Recorder Stat

How to implement rectangle detection in C#

In this chapter you will find detailed information on how to accomplish rectangle detection in C#. To implement this idea, OZEKI Camera SDK has to be installed and a reference to OzekiSDK.dll has to be added to your Visual Studio project.

Detected rectangles in C
Figure 1 - Detected rectangles

Important: you should study this article in order to find out how to setup your Windows Forms Application correctly.

Getting started

To get started it is recomended to Download and Install the latest version of Ozeki Camera SDK. After installation you can find the example code discussed in this page with full source code in the following location on your harddisk:

Download Ozeki Camera SDK: http://www.camera-sdk.com/p_13-download-camera-onvif.html
Windows forms version: C:\Users\user\Documents\Ozeki\Ozeki SDK\Examples\Camera\04_ComputerVision\11_RectangleDetection

To compile this example you will need Microsoft Visual Studio installed on your computer.

Corporate use of rectangle detection

The rectangle detection function of the Ozeki Camera SDK software can be an effective help in several situations and can be used in different Machine Vision applications.

You can use rectangle detection when you wish to detect rectangulars or detect discontinuities in shapes. Furthermore, you can benefit from this function in the field of counting since you can easily detect all rectangulars in a given area. In this way, this function can also help you in organizing. To mention another example, the rectangle detection can be useful when you wish to design different environments.

Implement rectangle detection in C#

Some computer vision possibilities which are supplied by the SDK require an extra ToolKit. This ToolKit is the OzekiComputerVision.dll to which a reference has to be added in the project, just like in the case of the OzekiSDK.dll. This dll is responsible for the algorithms and tools which are necessary for the CV (Computer Vision) actions.

Rectangle detection

For detecting faces we can use the IRectangleDetector object of the Ozeki Camera SDK. After an instance has been created with the help of the static ImageProcesserFactory class we can detect on frames and on video as well.

In the case of frames the output image can be created by the Process() method of the instance. In the case of videos we have to use the ImageProcesserHandler mediahandler.


This is a mediahandler from a VideoHandler class (so it is VideoReceiver and VideoSender at the same time) which means that the input can be a VideoSender (for example WebCamera) and the output can also be created for a VideoReceiver. These connections can be achieved with the help of an instance of the MediaConnector class in the SDK.

No actions are executed on the input frames they are simply forwarded by default. However, the object which implement the IImageProcesser interface (for example the IFaceDetector) can be added with the help of the AddProcesser() method. More instance can be added which implement IImageProcesser, they will run one after the other using the image which is before them in the list.

Global Variables

  • OzekiCamera _camera;
  • Webcamera instance, with the help of this we can get the images

  • MediaConnector _connector;
  • Using this we can connect the mediahandlers

  • CameraURLBuilderWF _myCameraUrlBuilder;
  • Make access to all avaiable cameras, which you can select from afterwards.

  • ImageProcesserHandler _imageProcesserHandler;
  • This is a Mediahandler, which runs the IImageProcesser interface (this processes the images) on the incoming video

  • IRectangleDetector _cornerDetector;
  • This is an image processer interface which can detect rectangles, this implements the IImageProcesser interface

  • VideoViewerWF instances
  • This is a GUI tool which is responsible for displaying the video for Windows Forms applications

  • DrawingImageProvider instances
  • Mediahandler which prepares the image which is sent by the mediahandlers from the VideoSender class for the VideoViewerWF instances.

C# code example for frame capture from an IP camera

Windows Form  


using System;
using System.Windows.Forms;
using Ozeki.Camera;
using Ozeki.Media;
using Ozeki.Vision;

namespace RectangleDetection_WF
    public partial class MainForm : Form
        private OzekiCamera _camera;
        private MediaConnector _connector;
        private CameraURLBuilderWF _myCameraUrlBuilder;
        private ImageProcesserHandler _imageProcesserHandler;
        private ILicensePlateRecognizer _licensePlateRecognizer;
        private IRectangleDetector _rectangleDetector;
        private ILineDetector _lineDetector;
        private DrawingImageProvider _originalImageProvider;
        private DrawingImageProvider _processedImageProvider;

        public MainForm()

        void MainForm_Load(object sender, EventArgs e)




        void Init()
            _myCameraUrlBuilder = new CameraURLBuilderWF();
            _connector = new MediaConnector();
            _originalImageProvider = new DrawingImageProvider();
            _processedImageProvider = new DrawingImageProvider();
            _rectangleDetector = ImageProcesserFactory.CreateRectangleDetector();
            _rectangleDetector.DetectionOccurred += _rectangleDetector_DetectionOccurred;
            _imageProcesserHandler = new ImageProcesserHandler();


        void SetVideoViewers()

        void InitDetectorFields()
            InvokeGuiThread(() =>

        void ConnectCam()
            _connector.Connect(_camera.VideoChannel, _originalImageProvider);
            _connector.Connect(_camera.VideoChannel, _imageProcesserHandler);
            _connector.Connect(_imageProcesserHandler, _processedImageProvider);


        void Start()

        void btn_HighlightSet_Click(object sender, EventArgs e)
            InvokeGuiThread(() =>
                if (tb_DrawThickness.Text.Length != 0)
                _rectangleDetector.DrawThickness = Int32.Parse(tb_DrawThickness.Text);

        void _rectangleDetector_DetectionOccurred(object sender, RectangleDetectedEventArgs e)
            InvokeGuiThread(() =>

                foreach (var info in e.Info)

        void InvokeGuiThread(Action action)

        private void button_Compose_Click(object sender, EventArgs e)
            var result = _myCameraUrlBuilder.ShowDialog();

            if (result != DialogResult.OK) return;

            tb_cameraUrl.Text = _myCameraUrlBuilder.CameraURL;

            button_Connect.Enabled = true;

        private void button_Connect_Click(object sender, EventArgs e)
            if (_camera != null)
                _camera.CameraStateChanged -= _camera_CameraStateChanged;
                _connector.Disconnect(_camera.VideoChannel, _processedImageProvider);
                _connector.Disconnect(_camera.VideoChannel, _originalImageProvider);
                _camera = null;

            _camera = new OzekiCamera(_myCameraUrlBuilder.CameraURL);
            _camera.CameraStateChanged += _camera_CameraStateChanged;

            button_Connect.Enabled = false;

        private void _camera_CameraStateChanged(object sender, CameraStateEventArgs e)
            InvokeGuiThread(() =>
                if (e.State == CameraState.Connecting)
                    button_Connect.Enabled = false;
                if (e.State == CameraState.Streaming)
                    button_Disconnect.Enabled = true;
                if (e.State == CameraState.Disconnected)
                    button_Disconnect.Enabled = false;
                    button_Connect.Enabled = true;

            InvokeGuiThread(() =>
                stateLabel.Text = e.State.ToString();

        private void button_Disconnect_Click(object sender, EventArgs e)
            if (_camera == null) return;

            _connector.Disconnect(_camera.VideoChannel, _processedImageProvider);
            _connector.Disconnect(_camera.VideoChannel, _originalImageProvider);
            _camera = null;

Code 1 - C# code example


Below you can find the code that belongs to the interface of the previously presented application. With the help of this section your Windows Forms Application will be able to work properly.

Detected rectangles in C
Figure 2 - Rectangle detection example GUI


namespace RectangleDetection_WF
    partial class MainForm
        private System.ComponentModel.IContainer components = null;

        protected override void Dispose(bool disposing)
            if (disposing && (components != null))

        #region Windows Form Designer generated code

        private void InitializeComponent()
            this.label1 = new System.Windows.Forms.Label();
            this.label2 = new System.Windows.Forms.Label();
            this.tb_DrawThickness = new System.Windows.Forms.TextBox();
            this.label5 = new System.Windows.Forms.Label();
            this.label4 = new System.Windows.Forms.Label();
            this.groupBox2 = new System.Windows.Forms.GroupBox();
            this.btn_HighlightSet = new System.Windows.Forms.Button();
            this.log_list = new System.Windows.Forms.ListBox();
            this.label12 = new System.Windows.Forms.Label();
            this.OriginalViewer = new Ozeki.Media.VideoViewerWF();
            this.ProcessedViewer = new Ozeki.Media.VideoViewerWF();
            this.groupBox5 = new System.Windows.Forms.GroupBox();
            this.stateLabel = new System.Windows.Forms.Label();
            this.label14 = new System.Windows.Forms.Label();
            this.button_Connect = new System.Windows.Forms.Button();
            this.button_Disconnect = new System.Windows.Forms.Button();
            this.tb_cameraUrl = new System.Windows.Forms.TextBox();
            this.label13 = new System.Windows.Forms.Label();
            this.button_Compose = new System.Windows.Forms.Button();

            this.label1.AutoSize = true;
            this.label1.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(238)));
            this.label1.Location = new System.Drawing.Point(7, 357);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(87, 13);
            this.label1.TabIndex = 0;
            this.label1.Text = "Original image";

            this.label2.AutoSize = true;
            this.label2.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(238)));
            this.label2.Location = new System.Drawing.Point(357, 357);
            this.label2.Name = "label2";
            this.label2.Size = new System.Drawing.Size(103, 13);
            this.label2.TabIndex = 1;
            this.label2.Text = "Processed image";
            this.tb_DrawThickness.Location = new System.Drawing.Point(140, 23);
            this.tb_DrawThickness.Name = "tb_DrawThickness";
            this.tb_DrawThickness.Size = new System.Drawing.Size(87, 20);
            this.tb_DrawThickness.TabIndex = 4;

            this.label5.AutoSize = true;
            this.label5.Location = new System.Drawing.Point(248, 26);
            this.label5.Name = "label5";
            this.label5.Size = new System.Drawing.Size(48, 13);
            this.label5.TabIndex = 12;
            this.label5.Text = "Max:255";
            this.label4.AutoSize = true;
            this.label4.Location = new System.Drawing.Point(6, 26);
            this.label4.Name = "label4";
            this.label4.Size = new System.Drawing.Size(87, 13);
            this.label4.TabIndex = 11;
            this.label4.Text = "Draw Thickness:";
            this.groupBox2.Location = new System.Drawing.Point(360, 12);
            this.groupBox2.Name = "groupBox2";
            this.groupBox2.Size = new System.Drawing.Size(322, 89);
            this.groupBox2.TabIndex = 13;
            this.groupBox2.TabStop = false;
            this.groupBox2.Text = "Setting";

            this.btn_HighlightSet.Location = new System.Drawing.Point(251, 55);
            this.btn_HighlightSet.Name = "btn_HighlightSet";
            this.btn_HighlightSet.Size = new System.Drawing.Size(58, 23);
            this.btn_HighlightSet.TabIndex = 19;
            this.btn_HighlightSet.Text = "Set";
            this.btn_HighlightSet.UseVisualStyleBackColor = true;
            this.btn_HighlightSet.Click += new System.EventHandler(this.btn_HighlightSet_Click);

            this.log_list.FormattingEnabled = true;
            this.log_list.Location = new System.Drawing.Point(10, 390);
            this.log_list.Name = "log_list";
            this.log_list.Size = new System.Drawing.Size(670, 121);
            this.log_list.TabIndex = 14;
            this.label12.AutoSize = true;
            this.label12.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(238)));
            this.label12.Location = new System.Drawing.Point(7, 374);
            this.label12.Name = "label12";
            this.label12.Size = new System.Drawing.Size(91, 13);
            this.label12.TabIndex = 15;
            this.label12.Text = "Detection info:";

            this.OriginalViewer.BackColor = System.Drawing.Color.Black;
            this.OriginalViewer.FlipMode = Ozeki.Media.FlipMode.None;
            this.OriginalViewer.FrameStretch = Ozeki.Media.FrameStretch.Uniform;
            this.OriginalViewer.FullScreenEnabled = true;
            this.OriginalViewer.Location = new System.Drawing.Point(10, 110);
            this.OriginalViewer.Name = "OriginalViewer";
            this.OriginalViewer.RotateAngle = 0;
            this.OriginalViewer.Size = new System.Drawing.Size(335, 240);
            this.OriginalViewer.TabIndex = 17;
            this.OriginalViewer.Text = "videoViewerWF1";

            this.ProcessedViewer.BackColor = System.Drawing.Color.Black;
            this.ProcessedViewer.FlipMode = Ozeki.Media.FlipMode.None;
            this.ProcessedViewer.FrameStretch = Ozeki.Media.FrameStretch.Uniform;
            this.ProcessedViewer.FullScreenEnabled = true;
            this.ProcessedViewer.Location = new System.Drawing.Point(360, 110);
            this.ProcessedViewer.Name = "ProcessedViewer";
            this.ProcessedViewer.RotateAngle = 0;
            this.ProcessedViewer.Size = new System.Drawing.Size(320, 240);
            this.ProcessedViewer.TabIndex = 18;
            this.ProcessedViewer.Text = "videoViewerWF1";

            this.groupBox5.Location = new System.Drawing.Point(12, 12);
            this.groupBox5.Name = "groupBox5";
            this.groupBox5.Size = new System.Drawing.Size(333, 89);
            this.groupBox5.TabIndex = 21;
            this.groupBox5.TabStop = false;
            this.groupBox5.Text = "Connect";

            this.stateLabel.AutoSize = true;
            this.stateLabel.Location = new System.Drawing.Point(80, 72);
            this.stateLabel.Name = "stateLabel";
            this.stateLabel.Size = new System.Drawing.Size(0, 13);
            this.stateLabel.TabIndex = 24;

            this.label14.AutoSize = true;
            this.label14.Location = new System.Drawing.Point(39, 72);
            this.label14.Name = "label14";
            this.label14.Size = new System.Drawing.Size(35, 13);
            this.label14.TabIndex = 23;
            this.label14.Text = "State:";

            this.button_Connect.Enabled = false;
            this.button_Connect.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.5F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(238)));
            this.button_Connect.ForeColor = System.Drawing.Color.Black;
            this.button_Connect.Location = new System.Drawing.Point(83, 39);
            this.button_Connect.Name = "button_Connect";
            this.button_Connect.Size = new System.Drawing.Size(71, 23);
            this.button_Connect.TabIndex = 18;
            this.button_Connect.Text = "Connect";
            this.button_Connect.UseVisualStyleBackColor = true;
            this.button_Connect.Click += new System.EventHandler(this.button_Connect_Click);

            this.button_Disconnect.Enabled = false;
            this.button_Disconnect.Location = new System.Drawing.Point(180, 39);
            this.button_Disconnect.Name = "button_Disconnect";
            this.button_Disconnect.Size = new System.Drawing.Size(69, 23);
            this.button_Disconnect.TabIndex = 22;
            this.button_Disconnect.Text = "Disconnect";
            this.button_Disconnect.UseVisualStyleBackColor = true;
            this.button_Disconnect.Click += new System.EventHandler(this.button_Disconnect_Click);
            this.tb_cameraUrl.Location = new System.Drawing.Point(83, 13);
            this.tb_cameraUrl.Name = "tb_cameraUrl";
            this.tb_cameraUrl.ReadOnly = true;
            this.tb_cameraUrl.Size = new System.Drawing.Size(166, 20);
            this.tb_cameraUrl.TabIndex = 21;
            this.label13.AutoSize = true;
            this.label13.Location = new System.Drawing.Point(6, 16);
            this.label13.Name = "label13";
            this.label13.Size = new System.Drawing.Size(71, 13);
            this.label13.TabIndex = 20;
            this.label13.Text = "Camera URL:";

            this.button_Compose.Location = new System.Drawing.Point(255, 13);
            this.button_Compose.Name = "button_Compose";
            this.button_Compose.Size = new System.Drawing.Size(69, 23);
            this.button_Compose.TabIndex = 19;
            this.button_Compose.Text = "Compose";
            this.button_Compose.UseVisualStyleBackColor = true;
            this.button_Compose.Click += new System.EventHandler(this.button_Compose_Click);

            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(694, 525);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
            this.MaximizeBox = false;
            this.Name = "MainForm";
            this.Text = "Rectangle Detection";
            this.Load += new System.EventHandler(this.MainForm_Load);


        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.TextBox tb_DrawThickness;
        private System.Windows.Forms.Label label5;
        private System.Windows.Forms.Label label4;
        private System.Windows.Forms.GroupBox groupBox2;
        private System.Windows.Forms.ListBox log_list;
        private System.Windows.Forms.Button btn_HighlightSet;
        private System.Windows.Forms.Label label12;
        private Ozeki.Media.VideoViewerWF OriginalViewer;
        private Ozeki.Media.VideoViewerWF ProcessedViewer;
        private System.Windows.Forms.GroupBox groupBox5;
        private System.Windows.Forms.Button button_Connect;
        private System.Windows.Forms.Button button_Disconnect;
        private System.Windows.Forms.TextBox tb_cameraUrl;
        private System.Windows.Forms.Label label13;
        private System.Windows.Forms.Button button_Compose;
        private System.Windows.Forms.Label stateLabel;
        private System.Windows.Forms.Label label14;

Code 2 - GUI example in C#


This guide demonstrated how you can implement rectangle detection with your C# camera application. On this page you can find detailed information and documentation about the operating and about the corporate use of this function. Furthermore, you can get a free code example to implement your idea.

Related pages


  1. What kind of developer environment is needed?

    • Microsoft Visual Studio 2010
    • Microsoft .Net Framework 4.0
    • Internet connection
  2. How can I get the URL of the camera?

    You can get the URL from the producer of the camera.

  3. I have not managed to build the solution. How to solve it?

    • Please set the Target framework property of the project to .NET 4.0.
    • You should add the OzekiSDK.dll to the references of the solution.
    • Please import the missing classes.