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Question

I want to make an application which activates the webcam and detects movement. So far I can turn ON and OFF the application. Now I'm trying to implement motion detector. The problem is - 'bitmap' does not exist in the current context. The method from which it originates is private. I tried with public, but still. And somehow Form1 is able to use it.

    using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

using AForge.Video;
using AForge.Video.DirectShow;
using AForge.Vision.Motion;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        // create motion detector
        MotionDetector detector = new MotionDetector(new SimpleBackgroundModelingDetector(), new MotionAreaHighlighting());

        public VideoCaptureDevice videoSource = null;
        public FilterInfoCollection videoDevices;


        public Form1()
        {
            InitializeComponent();
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // enumerate video devices
            videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice);

            // create video source
            videoSource = new VideoCaptureDevice(videoDevices[0].MonikerString);

            // set NewFrame event handler
            videoSource.NewFrame += new NewFrameEventHandler(video_NewFrame);

            // continuously feed video frames to motion detector
            while (true)
            {
                // process new video frame and check motion level
                if (detector.ProcessFrame(bitmap) > 0.02) << // PROBLEM
                {
                    // ring alarm or do something else
                }
            }

            // start the video source
            videoSource.Start();
        }

        private void button2_Click(object sender, EventArgs e)
        {
            videoSource.Stop();
            pictureBox1.Image = null;
        }

        // Method:
        private void video_NewFrame(object sender, NewFrameEventArgs eventArgs)
        {
            // get new frame
            Bitmap bitmap = eventArgs.Frame;
            // process the frame

            // Put image in picture box
            pictureBox1.Image = (Bitmap)bitmap.Clone();

        }
    }

}

Answer 1

Delete this code:

while (true)
{
    // process new video frame and check motion level
    if (detector.ProcessFrame(bitmap) > 0.02) << // PROBLEM
    {
        // ring alarm or do something else
    }
}

And change the event code to this:

// Method:
private void video_NewFrame(object sender, NewFrameEventArgs eventArgs)
{
    // get new frame
    Bitmap bitmap = eventArgs.Frame;
    // process the frame

    // Put image in picture box
    pictureBox1.Image = (Bitmap)bitmap.Clone();

    if (detector.ProcessFrame(bitmap) > 0.02) << // PROBLEM
    {
        // ring alarm or do something else
    }
}

It looks like you reused some code but put it in the wrong place.

Don't take me wrong but putting a while loop inside button1_Click is an indication that you are just starting with c#. Aforge.net is quite advanced stuff, I recommend you keep your programs simple as much as possible for now - motion detector may be too big of a chunk.