绘制图像边缘点

Question

我正在尝试使用Aforge.Net框架处理图像。我想在二进制图像上计算圆度量。这是我的c＃代码;

        List<IntPoint> edgePoints; //Global variables
        List<IntPoint> corners; //Global variables
        Bitmap _imageInvert; //Global varibles


        // Here is something code
        // For instance, applying some filters and some processing
        // pictureBox2 has a _imageInvert and running below lines 

        AForge.Imaging.Blob[] blobs = blobCounter.GetObjectsInformation();

        double[] blobAdjustedSize = new double[blobs.Length];
        for ( int i = 0, n = blobs.Length; i < n; i++ )
        {
            edgePoints = blobCounter.GetBlobsEdgePoints( blobs[i] );
            corners = PointsCloud.FindQuadrilateralCorners( edgePoints );

        }


        Graphics grafik = Graphics.FromImage( _imageInvert ); //GIVING ERROR
        Pen myPen = new Pen( System.Drawing.Color.Red, 15 );
        DrawEdge( grafik, myPen, edgePoints );



    private static System.Drawing.Point[] PointsListToArray( List<IntPoint> list )
    {
        System.Drawing.Point[] array = new System.Drawing.Point[list.Count];

        for ( int i = 0, n = list.Count; i < n; i++ )
        {
            array[i] = new System.Drawing.Point( list[i].X, list[i].Y );
        }

        return array;
    }

    // Draw object's edge
    private static void DrawEdge( Graphics g, Pen pen, List<IntPoint> edge )
    {
        System.Drawing.Point[] points = PointsListToArray( edge );

        if ( points.Length > 1 )
        {
            g.DrawLines( pen, points );
        }
        else
        {
            g.DrawLine( pen, points[0], points[0] );
        }
    }

当我点击运行时，我收到错误。

错误： System.Drawing.dll中出现未处理的“System.Exception”类型异常

附加信息：无法从具有索引像素格式的图像创建Graphics对象。

如何在_BoxI2上绘制egdepoints，以便在pictureBox2上绘制。提前致谢。 （对不起我的语言。）

类似的屏幕截图是here。