问C#中的徒手图像裁剪

EN

int cropX, cropY, cropWidth, cropHeight;
        //here rectangle border pen color=red and size=2;
        Pen borderpen = new Pen(Color.Red, 2);
        System.Drawing.Image _orgImage;
        Bitmap crop;

        //fill the rectangle color =white
        SolidBrush rectbrush = new SolidBrush(Color.FromArgb(100, Color.White));

 private void pic_scan_MouseDown(object sender, MouseEventArgs e)
        {
            try
            {
                if (e.Button == MouseButtons.Left)//here i have use mouse click left button only
                {
                    pic_scan.Refresh();
                    cropX = e.X;
                    cropY = e.Y;
                    Cursor = Cursors.Cross;
                }
                pic_scan.Refresh();
            }
            catch { }
        }
 private void pic_scan_MouseMove(object sender, MouseEventArgs e)
        {
            try
            {
                if (pic_scan.Image == null)
                    return;

                if (e.Button == MouseButtons.Left)//here i have use mouse click left button only
                {
                    pic_scan.Refresh();
                    cropWidth = e.X - cropX;
                    cropHeight = e.Y - cropY;
                }
                pic_scan.Refresh();
            }
            catch { }
        }

        private void pic_scan_MouseUp(object sender, MouseEventArgs e)
        {
            try
            {
                Cursor = Cursors.Default;
                if (cropWidth < 1)
                {
                    return;
                }
                System.Drawing.Rectangle rect = new System.Drawing.Rectangle(cropX, cropY, cropWidth, cropHeight);
                Bitmap bit = new Bitmap(pic_scan.Image, pic_scan.Width, pic_scan.Height);
                crop = new Bitmap(cropWidth, cropHeight);
                Graphics gfx = Graphics.FromImage(crop);
                gfx.InterpolationMode = InterpolationMode.HighQualityBicubic;//here add  System.Drawing.Drawing2D namespace;
                gfx.PixelOffsetMode = PixelOffsetMode.HighQuality;//here add  System.Drawing.Drawing2D namespace;
                gfx.CompositingQuality = CompositingQuality.HighQuality;//here add  System.Drawing.Drawing2D namespace;
                gfx.DrawImage(bit, 0, 0, rect, GraphicsUnit.Pixel);

            }
            catch { }
        }

        private void pic_scan_Paint(object sender, PaintEventArgs e)
        {
            System.Drawing.Rectangle rect = new System.Drawing.Rectangle(cropX, cropY, cropWidth, cropHeight);
            Graphics gfx = e.Graphics;
            gfx.DrawRectangle(borderpen, rect);
            gfx.FillRectangle(rectbrush, rect);
        }