{

            public short bfType;

            public int bfSize;

            public short bfReserved1;

            public short bfReserved2;

            public int bfOffBits;

        }

        public static System.Drawing.Image GetDwgImage(string FileName)

        {

            if (!(File.Exists(FileName)))

            {

                throw new FileNotFoundException("文件沒有被找到");

            }

            FileStream DwgF=null;   //文件流

            int PosSentinel;   //文件描述塊的位置

            BinaryReader br=null;   //讀取二進制文件

            int TypePreview;   //縮略圖格式

            int PosBMP;    //縮略圖位置 

            int LenBMP;    //縮略圖大小

            short biBitCount; //縮略圖比特深度 

            BITMAPFILEHEADER biH; //BMP文件頭，DWG文件中不包含位圖文件頭，要自行加上去

            byte[] BMPInfo;    //包含在DWG文件中的BMP文件體

            MemoryStream BMPF = new MemoryStream(); //保存位圖的內存文件流

            BinaryWriter bmpr = new BinaryWriter(BMPF); //寫二進制文件類

            System.Drawing.Image myImg = null;

            try

            {

                DwgF = new FileStream(FileName, FileMode.Open, FileAccess.Read); //文件流

                br = new BinaryReader(DwgF);

                DwgF.Seek(13, SeekOrigin.Begin); //從第十三字節開始讀取

                PosSentinel = br.ReadInt32();   //第13到17字節指示縮略圖描述塊的位置

                DwgF.Seek(PosSentinel + 30, SeekOrigin.Begin);   //將指針移到縮略圖描述塊的第31字節

                TypePreview = br.ReadByte();   //第31字節為縮略圖格式信息，2 為BMP格式，3為WMF格式

                if (TypePreview == 1)

                {

                }

                else if (TypePreview == 2 || TypePreview == 3)

                {

                    PosBMP = br.ReadInt32(); //DWG文件保存的位圖所在位置

                    LenBMP = br.ReadInt32(); //位圖的大小

                    DwgF.Seek(PosBMP + 14, SeekOrigin.Begin); //移動指針到位圖塊

                    biBitCount = br.ReadInt16(); //讀取比特深度

                    DwgF.Seek(PosBMP, SeekOrigin.Begin); //從位圖塊開始處讀取全部位圖內容備用

                    BMPInfo = br.ReadBytes(LenBMP); //不包含文件頭的位圖信息

                    br.Close();

                    DwgF.Close();

                    biH.bfType = 19778; //建立位圖文件頭

                    if (biBitCount < 9)

                    {

                        biH.bfSize = 54 + 4 * (int)(Math.Pow(2, biBitCount)) + LenBMP;

                    }

                    else

                    {

                        biH.bfSize = 54 + LenBMP;

                    }

                    biH.bfReserved1 = 0; //保留字節

                    biH.bfReserved2 = 0; //保留字節

                    biH.bfOffBits = 14 + 40 + 1024; //圖像數據偏移

                    //以下開始寫入位圖文件頭

                    bmpr.Write(biH.bfType); //文件類型

                    bmpr.Write(biH.bfSize);   //文件大小

                    bmpr.Write(biH.bfReserved1); //0

                    bmpr.Write(biH.bfReserved2); //0

                    bmpr.Write(biH.bfOffBits); //圖像數據偏移

                    bmpr.Write(BMPInfo); //寫入位圖

                    BMPF.Seek(0, SeekOrigin.Begin); //指針移到文件開始處 

                    myImg = System.Drawing.Image.FromStream(BMPF); //創建位圖文件對象

                    bmpr.Close();

                    BMPF.Close();

                }

                return myImg;

            }

            catch (EndOfStreamException)

            {

                throw new EndOfStreamException("文件不是標準的DWG格式文件，無法預覽！");

            }

            catch (IOException ex)

            {

                if (ex.Message == "試圖將文件指針移到文件開頭之前。/r/n")

                {

                    throw new IOException("文件不是標準的DWG格式文件，無法預覽！");

                }

                else if (ex.Message == "文件“" + FileName + "”正由另一進程使用，因此該進程無法訪問該文件。")

                {

                    //復制文件，繼續預覽

                    File.Copy(FileName, Application.StartupPath + @"/linshi.dwg", true);

                    Image image = GetDwgImage(Application.StartupPath + @"/linshi.dwg");

                    File.Delete(Application.StartupPath + @"/linshi.dwg");

                    return image;

                }

                else

                {

                    throw new Exception(ex.Message);

                }

            }

            catch (Exception ex)

            {

                throw new Exception(ex.Message);

            }

            finally

            {

                if (DwgF != null)

                {

                    DwgF.Close();

                }

                if (br != null)

                {

                    br.Close();

                }

                bmpr.Close();

                BMPF.Close();

            }

        }

讀取出來的背景色為白色，效果比較差，很多顏色顯示不出來，當時認為顯示DWG文件出錯誤了，問了些高手，（呵呵，別人告訴自己本身取出的就是白色背景，需要自己改變背景色，在此鄙視一下自己）所以繼續用C#操作返回的IMAGE對象，改變背景色

///<summary>

        ///顯示DWG文件

        ///</summary>

        ///<param name="Pwidth">要顯示的寬度</param>

        ///<param name="PHeight">要顯示的高度</param>

        ///<returns></returns>

        public static System.Drawing.Image ShowDWG(int Pwidth,int PHeight,string FilePath)

        {

            System.Drawing.Image image = GetDwgImage(FilePath);

            Bitmap bitmap = new Bitmap(image);

            int Height = bitmap.Height;

            int Width = bitmap.Width;

            Bitmap newbitmap = new Bitmap(Width, Height);

            Bitmap oldbitmap = (Bitmap)bitmap;

            Color pixel;

            for (int x = 1; x < Width; x++)

            {

                for (int y = 1; y < Height; y++)

                {

                    pixel = oldbitmap.GetPixel(x, y);

                    int r = pixel.R, g = pixel.G, b = pixel.B;

                    if (pixel.Name == "ffffffff" || pixel.Name == "ff000000")

                    {

                        r = 255 - pixel.R;

                        g = 255 - pixel.G;

                        b = 255 - pixel.B;

                    }

                    newbitmap.SetPixel(x, y, Color.FromArgb(r, g, b));

                }

            }

            Bitmap bt = new Bitmap(newbitmap, Pwidth, PHeight);

            return newbitmap;

        }