static private Image GenerateNumberImage(
        Color backColor,
        Color foreColor,
        Color borderColor,
        int value,
        Size size,
        Font font = null)
    {
        //  Create a blank image of the specified size
        Bitmap bmp = new Bitmap(size.Width, size.Height, PixelFormat.Format32bppArgb);

        //  Create a Graphics object for the image
        using ( Graphics g = Graphics.FromImage(bmp) )
        {
            //  Use anti-aliasing to smooth curves
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;

            Rectangle rect = new Rectangle(Point.Empty, size);
            rect.Inflate(-2, -2);

            //  Background
            using ( Brush brush = new SolidBrush(backColor) )
            {
                g.FillEllipse(brush, rect);
            }

            //  Border
            using ( Pen pen = new Pen(borderColor, 2f) )
            {
                //rect.Inflate(-1, -1);
                g.DrawEllipse(pen, rect);
            }

            //  Number
            using ( Brush brush = new SolidBrush(foreColor) )
            {
                if ( font == null )
                    font = SystemFonts.DefaultFont;

                StringFormat sf = new StringFormat();
                sf.Alignment = StringAlignment.Center;
                sf.LineAlignment = StringAlignment.Center;

                g.DrawString(value.ToString(), font, brush, rect, sf );
            }
        }

        return bmp;
    }