vc++ mfc 里保存缩放的bmp图片 不失真

void CSaveView::OnFileSave() 
{
 BITMAP info;//原始图片
 m_bitmap.GetBitmap(&info);
 CDC DC1;
 DC1.CreateCompatibleDC(NULL);
 DC1.SelectObject(&m_bitmap);
 
 DC1.MoveTo(0,0);
 DC1.LineTo(info.bmWidth,info.bmHeight);
 
 CDC DC2;
 CBitmap bmp;//缩放后的图片
 bmp.CreateCompatibleBitmap(&DC1,200,200);
 DC2.CreateCompatibleDC(NULL);
 DC2.SelectObject(&bmp);
 int mode = SetStretchBltMode(DC2, COLORONCOLOR); //设置不失真缩放
 DC2.StretchBlt(0,0,200,200,&DC1,0,0,info.bmWidth,info.bmHeight,SRCCOPY);
 SetStretchBltMode(DC2, mode); 

 CFileDialog dlg(false,"bmp",NULL,OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT,NULL,this);
 if(IDOK == dlg.DoModal())
 {
  　　　 CString bmpfile = dlg.GetPathName();     
        CFile file(bmpfile,CFile::modeCreate|CFile::modeWrite);       
        BITMAP bInfo;     
　　　　 bmp.GetBitmap(&bInfo);
        //计算调色板大小      
        int panelsize = 0;     
        if (bInfo.bmBitsPixel<24) //非真彩色      
        {     
            panelsize = int(pow((double)2,bInfo.bmBitsPixel)*sizeof(RGBQUAD));
        }     
  
        //定义位图信息      
        BITMAPINFO*  bMapInfo = (BITMAPINFO*)LocalAlloc(LPTR,sizeof(BITMAPINFOHEADER)+panelsize);     
        bMapInfo->bmiHeader.biBitCount = bInfo.bmBitsPixel;     
        bMapInfo->bmiHeader.biClrImportant = 0;     
        bMapInfo->bmiHeader.biCompression = 0;     
        bMapInfo->bmiHeader.biHeight = bInfo.bmHeight;     
        bMapInfo->bmiHeader.biPlanes = bInfo.bmPlanes;     
        bMapInfo->bmiHeader.biSize = sizeof(BITMAPINFO);     
        bMapInfo->bmiHeader.biSizeImage = bInfo.bmHeight*bInfo.bmWidthBytes;     
        bMapInfo->bmiHeader.biWidth = bInfo.bmWidth;     
        bMapInfo->bmiHeader.biXPelsPerMeter = 0;     
        bMapInfo->bmiHeader.biYPelsPerMeter = 0;     
  
        //获取位图的实际数据      
        char* pData = new char[bMapInfo->bmiHeader.biSizeImage];     
 　　　　int len = GetDIBits(DC2.m_hDC,bmp,0,bInfo.bmHeight,pData,bMapInfo,DIB_RGB_COLORS); 
  
        BITMAPFILEHEADER bFileHeader;     
        bFileHeader.bfType = 0x4D42;     
        bFileHeader.bfReserved1 = 0;     
        bFileHeader.bfReserved2 = 0;     
        bFileHeader.bfSize = sizeof(BITMAPFILEHEADER);      
        bFileHeader.bfOffBits = sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+panelsize;   
  
        //向文件中写入位图数据      
        file.Write(&bFileHeader,sizeof(BITMAPFILEHEADER));     
        file.Write(&bMapInfo->bmiHeader,sizeof(BITMAPINFOHEADER));     
        file.Write(pData,bMapInfo->bmiHeader.biSizeImage+panelsize);     
        file.Close();     
        delete pData;     
        LocalFree(bMapInfo);     
　　} 
}