How to implement line detection in C#

In this lecture you will find all the needed information to satisfy your curiosity on how to implement line detection with your C# camera application using the Ozeki Camera SDK. First of all, Ozeki Camera SDK has to be installed and a reference to OzekiSDK.dll has to be added to your Visual Studio project.

line detection in C#
Figure 1 - Detected lines on the image

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:
Windows forms version: C:\Users\user\Documents\Ozeki\Ozeki SDK\Examples\Camera\04_ComputerVision\02_LineDetection\LineDetection

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

Corporate use of line detection

The line detection function indicates when an object in view crosses any (virtual) lines in any directions.

The line detection function of the Ozeki Camera SDK is an effective help in the different field of analytics, for istance designing physical environments or observing of customer traffic

Implement line 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.

Line detection

For detecting corners we can use the ILineDetector 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 objects which implement the IImageProcesser interface (for example the ILineDetector) 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

  • ILineDetector _lineDetector;
  • This is an image processer interface which can detect lines, 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.


  • Init()
  • The initialization of the global variables is the task of the Init() method. The instance of the FrameCapture mediahandler are set here and the ILineDetector instance is also created here with the help of the ImageProcesserFactory. This also can be added to the ImageProcesserHandler instance. The processing of all images is indicated by the DetectionOccured event of the ILineDetector instance. Here we can subscribe to this event.

  • SetVideoViewers()
  • The SetVideoViewer() creates and initialize the objects which are responsible for the displaying of the video. It defines the VideoViewerWF instances, configures their properties and assigns the appropiate DrawingImageProvider instances. Furthermore, the SetVideoViewers() adds these instances to the GUI.

  • InvokeGUIThread()
  • This method handles the GUI thread. It performs a specific method on the GUI thread in asynchronous mode

  • InitDetectorFields()
  • This method fills the TextBox-es which can be found on the GUI with the actual settings of the ILineDetector instance using the InvokeGUIThread() helper method

  • ConnectCam()
  • This method connects the appropiate mediahandler instances with the help of the MediaConnector instance. One of the ImageProvider object recives the original image of the webcamera and the other object receives the processed image

  • Start()
  • After the initializations the mediahandlers can start to operate which is the responsibility of the Start()method


  • AngleResolution:in the angle area this is responsible for adjusting the resolution
  • CannyThreshold: the value of thresholding can be determined here in order to find the strong edges' initial segments
  • CannyThresholdLinking: with the help of this peoperty we can get to know the amount of the pixels that can be found on the edges
  • DistanceResolution: provides the resolution between the pixel-related hosts
  • LineGap: this stands for the minimum size of the gap between the detectable lines
  • LineWidth: this stands for the minimum width of the detectable lines
  • Threshold: the detected line has to reach the value of this property in order to become truly detected

PostProcess configurations

After the detection we can configure the behavior of the output image and what changes are required. Examples for this kind of configurations:

  • ShowImage: declares whether the original image should be shown or only the detected shapes should be seen with black backround. It is important if there are more image processer algorithm are running after each other
  • DrawColor: the color of the selection of the detected object can be provided here
  • DrawThickness: the thickness of the selection of the detected object can be provided here


After all image/frame processing a DetectionOccurred event is popped up. In the arguments of this event you can find the list of detected lines where the centers/radius and area of the lines can be queried.

C# code example for line detection

Windows Form  

Windows forms version


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

namespace LineDetection_WF
    public partial class MainForm : Form
        private OzekiCamera _camera;
        private MediaConnector _connector;
        private CameraURLBuilderWF _myCameraUrlBuilder;
        private ImageProcesserHandler _imageProcesserHandler;
        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();
            _lineDetector = ImageProcesserFactory.CreateLineDetector();
            _lineDetector.DetectionOccurred += _lineDetector_DetectionOccurred;

            _imageProcesserHandler = new ImageProcesserHandler();


        void SetVideoViewers()

        void InitDetectorFields()
            InvokeGuiThread(() =>
                chk_horizontal.Checked = _lineDetector.LineAngle.IsHorizontal;
                chk_vertical.Checked = _lineDetector.LineAngle.IsVertical;
                tb_CannyThreshold.Text = _lineDetector.CannyThreshold.ToString();
                tb_CannyThresholdLinking.Text = _lineDetector.CannyThresholdLinking.ToString();

        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(() =>
                _lineDetector.CannyThreshold = Double.Parse(tb_CannyThreshold.Text);
                _lineDetector.CannyThresholdLinking = Double.Parse(tb_CannyThresholdLinking.Text);
                _lineDetector.LineAngle.IsHorizontal = chk_horizontal.Checked;
                _lineDetector.LineAngle.IsVertical = chk_vertical.Checked;

        void _lineDetector_DetectionOccurred(object sender, LineDetectedEventArgs 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;


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

Code 1 - Line detection example code in C#


After you have downloaded the Ozeki Camera SDK software you can find the GUI code in the Example folder.

gui of an application for line detection in C#
Figure 2 - The graphical user interface of your application

Windows forms version


namespace LineDetection_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_CannyThreshold = new System.Windows.Forms.TextBox();
            this.tb_CannyThresholdLinking = 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.lb_Detection = 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.chk_horizontal = new System.Windows.Forms.CheckBox();
            this.chk_vertical = new System.Windows.Forms.CheckBox();

            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(348, 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_CannyThreshold.Location = new System.Drawing.Point(140, 16);
            this.tb_CannyThreshold.Name = "tb_CannyThreshold";
            this.tb_CannyThreshold.Size = new System.Drawing.Size(87, 20);
            this.tb_CannyThreshold.TabIndex = 4;

            this.tb_CannyThresholdLinking.Location = new System.Drawing.Point(140, 42);
            this.tb_CannyThresholdLinking.Name = "tb_CannyThresholdLinking";
            this.tb_CannyThresholdLinking.Size = new System.Drawing.Size(87, 20);
            this.tb_CannyThresholdLinking.TabIndex = 5;

            this.label5.AutoSize = true;
            this.label5.Location = new System.Drawing.Point(6, 44);
            this.label5.Name = "label5";
            this.label5.Size = new System.Drawing.Size(121, 13);
            this.label5.TabIndex = 12;
            this.label5.Text = "CannyThresholdLinking:";

            this.label4.AutoSize = true;
            this.label4.Location = new System.Drawing.Point(6, 19);
            this.label4.Name = "label4";
            this.label4.Size = new System.Drawing.Size(87, 13);
            this.label4.TabIndex = 11;
            this.label4.Text = "CannyThreshold:";

            this.groupBox2.Location = new System.Drawing.Point(358, 12);
            this.groupBox2.Name = "groupBox2";
            this.groupBox2.Size = new System.Drawing.Size(315, 89);
            this.groupBox2.TabIndex = 13;
            this.groupBox2.TabStop = false;
            this.groupBox2.Text = "Highlight";

            this.btn_HighlightSet.Location = new System.Drawing.Point(241, 60);
            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.lb_Detection.FormattingEnabled = true;
            this.lb_Detection.Location = new System.Drawing.Point(10, 390);
            this.lb_Detection.Name = "lb_Detection";
            this.lb_Detection.Size = new System.Drawing.Size(663, 173);
            this.lb_Detection.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(320, 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(351, 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(340, 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(80, 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(169, 39);
            this.button_Disconnect.Name = "button_Disconnect";
            this.button_Disconnect.Size = new System.Drawing.Size(80, 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, 11);
            this.button_Compose.Name = "button_Compose";
            this.button_Compose.Size = new System.Drawing.Size(80, 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.chk_horizontal.AutoSize = true;
            this.chk_horizontal.Location = new System.Drawing.Point(9, 65);
            this.chk_horizontal.Name = "chk_horizontal";
            this.chk_horizontal.Size = new System.Drawing.Size(73, 17);
            this.chk_horizontal.TabIndex = 20;
            this.chk_horizontal.Text = "Horizontal";
            this.chk_horizontal.UseVisualStyleBackColor = true;

            this.chk_vertical.AutoSize = true;
            this.chk_vertical.Location = new System.Drawing.Point(140, 65);
            this.chk_vertical.Name = "chk_vertical";
            this.chk_vertical.Size = new System.Drawing.Size(61, 17);
            this.chk_vertical.TabIndex = 21;
            this.chk_vertical.Text = "Vertical";
            this.chk_vertical.UseVisualStyleBackColor = true;

            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(690, 569);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
            this.MaximizeBox = false;
            this.Name = "MainForm";
            this.Text = "Line 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_CannyThreshold;
        private System.Windows.Forms.TextBox tb_CannyThresholdLinking;
        private System.Windows.Forms.Label label5;
        private System.Windows.Forms.Label label4;
        private System.Windows.Forms.GroupBox groupBox2;
        private System.Windows.Forms.ListBox lb_Detection;
        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;
        private System.Windows.Forms.CheckBox chk_vertical;
        private System.Windows.Forms.CheckBox chk_horizontal;

Code 2 - Line detection example GUI code in C#


With the help of this lecture you can successfully implement line detection with your C# camera application using the Ozeki Camera SDK. After examining this article you will have the needed information to be able to benefit from the line detection function on the fields of the different fields of analytics.

Related pages


Below you can find the answers for the most frequently asked questions related to this topic:

  1. Who can test the line detection function of the Ozeki Camera SDK?

    Anybody can test and use this function, it does not require expert skills. If you are interested in this topic all you have to do is to try our product and benefit from the advantages of line detection function.

  2. On what operating system can I use the line detection function of the Ozeki Camera SDK?

    You can use line detection on all Windows OS platforms.

  3. Can I use line detection in a "moving" environment, for example for examining items which are placed on a belt?

    Yes, the line detection function of the Ozeki Camera SDK enables you to examine tools and items which are placed on a belt, the lines will be detected successfully.

More information