CaptchaRecogition.ImageProcess.RemoveBg C# (CSharp) Метод

        public static Image RemoveBg(Bitmap img, int dgGrayValue)
        {

            int width = img.Width;
            int height = img.Height;
            BitmapData bdata = img.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite,
                PixelFormat.Format32bppRgb); //红绿蓝个八位，其余8位没使用
            unsafe
            {
                byte* ptr = (byte*)bdata.Scan0.ToPointer();
                for (int i = 0; i < height; i++)
                {
                    for (int j = 0; j < width; j++)
                    {
                        if (ptr[1] > dgGrayValue)//背景点
                        {
                            ptr[0] = ptr[1] = ptr[2] = 255;
                        }
                        ptr += 4;
                    }
                    ptr += bdata.Stride - width * 4;
                }
            }
            #region 内存法
            //获取位图中第一个像素数据的地址

            //int byteNum = width * height * 4;
            ////byte[] four = new byte[width *height ];
            //byte[] rgbValue = new byte[byteNum];
            ////把内存中的图像copy到数组
            //Marshal.Copy(ptr, rgbValue, 0, byteNum);
            //for (int i = 0; i < rgbValue.Length; i += 4)
            //{
            //    if (rgbValue[i] >= dgGrayValue) //是背景点
            //    {
            //        rgbValue[i] = rgbValue[i + 1] = rgbValue[i + 2] = 255;
            //        //  four[i/4] = rgbValue[4];
            //    }
            //    else
            //    {
            //        //不是背景点的做标记，下一阶段处理噪点用**第四个字节默认值都是255**我们标记为 111
            //        rgbValue[i + 3] = 111;
            //    }
            //}
            ////将修改好的数据复制到内存
            //Marshal.Copy(rgbValue, 0, ptr, byteNum); 
            #endregion
            //从内存中解锁
            img.UnlockBits(bdata);
            return img;
        }

        /// <summary>
        /// 去背景
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btn_bg_Click(object sender, EventArgs e)
        {
            Image img_noise = (Image)pb_grey.Image.Clone();
            //得到灰度图像前景色临界值

            // img_noise = ccccccmd.ImageHelper.RemoveBlock(img_noise,2);//报错
            //int v = ImageProcess.GetDgGrayValue(img_noise);
            int v = ImageProcess.ComputeThresholdValue((Bitmap)img_noise);
            //Image test = ImageProcess.RemoveBg((Bitmap)img_noise ,v );
            // int v2 = Test.ImageProcess.GetDgGrayValue(img_noise);
            Image img_bg = ImageProcess.RemoveBg((Bitmap)img_noise, v); //-----------去背景，内存法

            imgBged = Image2Num((Bitmap)img_bg);
            WriteToFile(imgBged, "experiment\\" + Path.GetFileNameWithoutExtension(imgurl) + "_bged.txt");
            pb_bg.Image = img_bg;
        }