c#裁剪图片后使用zxing生成二维码

private void button1_Click(object sender, EventArgs e)
        {
            if (string.IsNullOrEmpty(this.textBox1.Text.Trim()))
            {
                MessageBox.Show("请输入需要转换的信息！");
                return;
            }
            string content = textBox1.Text;
            Hashtable hints= new Hashtable();   
            hints.Add(EncodeHintType.ERROR_CORRECTION, ErrorCorrectionLevel.L);//纠错级别
            hints.Add(EncodeHintType.CHARACTER_SET, "UTF-8");//编码格式
            ByteMatrix byteMatrix = new MultiFormatWriter().encode(content, BarcodeFormat.QR_CODE, 300, 300, hints);
            Bitmap bitmap = toBitmap(byteMatrix);
            pictureBox1.Image = bitmap;

            SaveFileDialog sFD = new SaveFileDialog();
            sFD.Filter = "*.png|*.png";
            sFD.AddExtension = true;
            try
            {
                if (sFD.ShowDialog() == DialogResult.OK)
                {
                    writeToFile(byteMatrix, System.Drawing.Imaging.ImageFormat.Png, sFD.FileName);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        public static void writeToFile(ByteMatrix matrix, System.Drawing.Imaging.ImageFormat format, string file)
        {
            System.Drawing.Imaging.EncoderParameters eps = new System.Drawing.Imaging.EncoderParameters();
            eps.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L);
            Bitmap bmap = toBitmap(matrix);
            bmap.Save(file, format);
        }
        public static Bitmap toBitmap(ByteMatrix matrix)
        {
            int width = matrix.Width;
            int height = matrix.Height;
            Bitmap bmap = new Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
            for (int x = 0; x < width; x++)
            {
                for (int y = 0; y < height; y++)
                {
                    bmap.SetPixel(x, y, matrix.get_Renamed(x, y) != -1 ? ColorTranslator.FromHtml("Purple") : ColorTranslator.FromHtml("0xFFFFFFFF"));//可以自定义颜色和背景色
                }
            }
            return bmap;     
        }