Use OpenCVDotNet object to Capture image

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// I want to capture image from USB camera but my application show error:

C#

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using OpenCVDotNet;

namespace WindowsApplication6
{
    public partial class Form1 : Form
    {
        private CVCapture capture;
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            capture = new CVCapture(0);
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
                using (CVImage nextFrame = capture.QueryFrame())
                {
                    selectPictureBox1.Image = nextFrame.ToBitmap(); // THIS LINE ERROR
	            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            timer1.Enabled = !(timer1.Enabled);
        }
    }
}

Error show : "Object reference not set to an instance of an object"

Please help me fix this error. Thanks !

Posted 1-Nov-11 22:15pm

hien123

Updated 1-Nov-11 22:20pm

RaisKazi

v2

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lukeer · Answer 1 · 2011-11-01T23:06:00

Solution 1

Either selectPictureBox1 or nextFrame, or both, is/are not initialized at the moment the marked line is executed.

Maybe QueryFrame() failed and left nextFrame set to null?

Posted 1-Nov-11 23:06pm

lukeer

Comments

hien123 2-Nov-11 5:32am

Thanh you lukeer !

QueryFrame() failed.That why nextFrame == null.

my problem is how nextFrame!=null.

please help me again

lukeer 2-Nov-11 6:40am

I'm sorry. I have no idea of how CVCapture.QueryFrame() should work. I guess you'll have to read the documentation.

Pandya Anil · Answer 2 · 2011-11-01T23:12:00

the error message is very generic..
check null condition for all your objects before use.
like, it will give you an idea that which object is null.

C#

if(nextFrame != null)
{
   if(selectPictureBox1 != null)
   { 
      selectPictureBox1.Image = nextFrame.ToBitmap(); 
   }
}

if selectPictureBox1 object is null, check for that. if nextFrame object is null check for the solution regarding that, means your 'using (CVImage nextFrame = capture.QueryFrame())' is not working.
-> check camera connection, if possible click photos before using with your app for varification.
-> check for help in CVCapture API