截图

Bitmap bm = new Bitmap(this.BackgroundImage, this.Width, this.Height);
            //绘制矩形，定义你需要截取的图像起始位置和宽高
            Rectangle r = new Rectangle(this.gdbSchem.Location.X, this.gdbSchem.Location.Y, this.gdbSchem.Width, this.gdbSchem.Height);

            //按矩形尺寸和起始位置截取bm的一部分
            bm = bm.Clone(r, System.Drawing.Imaging.PixelFormat.Undefined);

            gdbSchem.BackgroundImage = bm;