如何仅保存图片框中显示的图像

我正在试图找出如何保存从picturebox控件显示的视频快照。我已经可以保存一个图像文件,但是我的问题是我的相机“看到”的整个图像就是正在保存的图像。我想保存的是仅从我的picturebox控件显示的图像,这只是相机正在捕获的图像的一部分。顺便说一下,我使用的是Aforge框架的视频库。

我的图片框设置为 高度=400 和 宽度=400 .

下面是我的代码示例

private void Form1_Load(object sender, EventArgs e)
    {
        videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice);
        foreach (FilterInfo device in videoDevices)
        {
            drvrlist.Items.Add(device.Name);
        }
        drvrlist.SelectedIndex = 1;

        videosource = new VideoCaptureDevice();

        if (videosource.IsRunning)
        {
            videosource.Stop();
        }
        else
        {
            videosource = new VideoCaptureDevice(videoDevices[comboBox1.SelectedIndex].MonikerString);
            videosource.NewFrame += new NewFrameEventHandler(videosource_NewFrame);
            videosource.Start();
        }
    }

    private void startbtn_Click(object sender, EventArgs e)
    {
        if (videosource.IsRunning)
        {
            videosource.Stop();
        }
        else
        {
            videosource = new VideoCaptureDevice(videoDevices[drvrlist.SelectedIndex].MonikerString);
            videosource.NewFrame += new NewFrameEventHandler(videosource_NewFrame);
            videosource.Start();
        }
    }

    private void videosource_NewFrame(object sender, NewFrameEventArgs eventArgs)
    {
        pictureBox1.Image = (Bitmap)eventArgs.Frame.Clone();
        //throw new NotImplementedException();
    }

    private void save_btn_Click(object sender, EventArgs e)
    {
        SaveFileDialog savefilediag = new SaveFileDialog();
        savefilediag.Filter = "Portable Network Graphics|.png";
        if(savefilediag.ShowDialog()== System.Windows.Forms.DialogResult.OK)
        {
            if (pictureBox1.Image != null)
            {
                //Save First
                Bitmap varBmp = new Bitmap(pictureBox1.Image);
                Bitmap newBitmap = new Bitmap(varBmp);
                varBmp.Save(savefilediag.FileName, ImageFormat.Png);
                //Now Dispose to free the memory
                varBmp.Dispose();
                varBmp = null;
                pictureBox1.Image = null;
                pictureBox1.Invalidate();
            }
            else
            { MessageBox.Show("null exception"); }
        }
    }