C# 截取图像的一部分

        /// <summary>
        /// 截取图像的矩形区域
        /// </summary>
        /// <param name="source">源图像对应picturebox1</param>
        /// <param name="rect">矩形区域，如上初始化的rect</param>
        /// <returns>矩形区域的图像</returns>
        public static Image AcquireRectangleImage(Image source, Rectangle rect)
        {
            if (source == null || rect.IsEmpty) return null;
            Bitmap bmSmall = new Bitmap(rect.Width, rect.Height, System.Drawing.Imaging.PixelFormat.Format32bppRgb);
            //Bitmap bmSmall = new Bitmap(rect.Width, rect.Height, source.PixelFormat);
            using (Graphics grSmall = Graphics.FromImage(bmSmall))
            {

                grSmall.DrawImage(source, new System.Drawing.Rectangle(0, 0, bmSmall.Width, bmSmall.Height), rect, GraphicsUnit.Pixel);
                grSmall.Dispose();
            }
            return bmSmall;
        }