win32位图错误地转换为单色

Question

我试图获取窗口图标的位，以便通过套接字发送它们。为了测试我是否能够获得与HICON相对应的BITMAP，我将其保存在文件中。

问题是，打开我保存位图的文件，它显示为单色（黑白，不是灰度）。

这是BITMAPINFO结构：

info.biSize = sizeof(BITMAPINFOHEADER);
info.biWidth = bitmap.bmWidth;
info.biHeight = bitmap.bmHeight;
info.biPlanes = 1;  
info.biBitCount = 32;
info.biCompression = BI_RGB;    
info.biSizeImage = 0;
info.biXPelsPerMeter = 0;  
info.biYPelsPerMeter = 0;     
info.biClrUsed = 0; 
info.biClrImportant = 0;

我计算位图的大小为：

DWORD dwBmpSize2 = ((bitmap.bmWidth * bi.biBitCount + 31) / 32) * 4 * bitmap.bmHeight;

然后：

// Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper functions that 
    // call HeapAlloc using a handle to the process's default heap. Therefore, GlobalAlloc and LocalAlloc 
    // have greater overhead than HeapAlloc.
    HANDLE hDIB = GlobalAlloc(GHND, dwBmpSize);
    char *lpbitmap = (char *)GlobalLock(hDIB);

    //Prendo i bit dell'icona
    HDC hdc = GetDC(hwnd);
    GetDIBits(hdc, hbit, 0, (UINT)bitmap.bmHeight, lpbitmap, (BITMAPINFO*)&bi,DIB_RGB_COLORS);
    wcout « "lpbitmap buffer: "« lpbitmap « endl;

    // A file is created, this is where we will save the screen capture.
    HANDLE hFile = CreateFile(L"captureqwsx.bmp",
      GENERIC_WRITE,
      0,
      NULL,
      CREATE_ALWAYS,
      FILE_ATTRIBUTE_NORMAL, NULL);

    // Add the size of the headers to the size of the bitmap to get the total file size
    DWORD dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    //Offset to where the actual bitmap bits start.
    bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);

    //Size of the file
    bmfHeader.bfSize = dwSizeofDIB;

    //bfType must always be BM for Bitmaps
    bmfHeader.bfType = 0x4D42; //BM   

    DWORD dwBytesWritten = 0;
    WriteFile(hFile, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);
    WriteFile(hFile, (LPSTR)&bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);
    WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);