Storing an Image

Many applications store images permanently as files. For example, drawing applications store pictures, spreadsheet applications store charts, CAD applications store drawings, and so on.

If you are writing an application that will store a bitmapped image in a file, you should use the bitmap file format described in Bitmap Storage. To store a bitmap in this format, you must initialize a BITMAPINFO structure (consisting of a BITMAPINFOHEADER BITMAPV4HEADER, or BITMAPV5HEADER structure and an array of RGBQUAD structures), as well as an array of palette indexes.

The following example code defines a function that allocates memory for and initializes members within a BITMAPINFOHEADER structure.

PBITMAPINFO CreateBitmapInfoStruct(HWND hwnd, HBITMAP hBmp)
{ 
    BITMAP bmp; 
    PBITMAPINFO pbmi; 
    WORD    cClrBits; 

    // Retrieve the bitmap's color format, width, and height. 
    if (!GetObject(hBmp, sizeof(BITMAP), (LPSTR)&bmp)) 
        errhandler("GetObject", hwnd); 

    // Convert the color format to a count of bits. 
    cClrBits = (WORD)(bmp.bmPlanes * bmp.bmBitsPixel); 
    if (cClrBits == 1) 
        cClrBits = 1; 
    else if (cClrBits <= 4) 
        cClrBits = 4; 
    else if (cClrBits <= 8) 
        cClrBits = 8; 
    else if (cClrBits <= 16) 
        cClrBits = 16; 
    else if (cClrBits <= 24) 
        cClrBits = 24; 
    else cClrBits = 32; 

    // Allocate memory for the BITMAPINFO structure. (This structure 
    // contains a BITMAPINFOHEADER structure and an array of RGBQUAD 
    // data structures.) 

     if (cClrBits != 24) 
         pbmi = (PBITMAPINFO) LocalAlloc(LPTR, 
                    sizeof(BITMAPINFOHEADER) + 
                    sizeof(RGBQUAD) * (1<< cClrBits)); 

     // There is no RGBQUAD array for the 24-bit-per-pixel format. 

     else 
         pbmi = (PBITMAPINFO) LocalAlloc(LPTR, 
                    sizeof(BITMAPINFOHEADER)); 

    // Initialize the fields in the BITMAPINFO structure. 

    pbmi->bmiHeader.biSize = sizeof(BITMAPINFOHEADER); 
    pbmi->bmiHeader.biWidth = bmp.bmWidth; 
    pbmi->bmiHeader.biHeight = bmp.bmHeight; 
    pbmi->bmiHeader.biPlanes = bmp.bmPlanes; 
    pbmi->bmiHeader.biBitCount = bmp.bmBitsPixel; 
    if (cClrBits < 24) 
        pbmi->bmiHeader.biClrUsed = (1<<cClrBits); 

    // If the bitmap is not compressed, set the BI_RGB flag. 
    pbmi->bmiHeader.biCompression = BI_RGB; 

    // Compute the number of bytes in the array of color 
    // indices and store the result in biSizeImage. 
    pbmi->bmiHeader.biSizeImage = (pbmi->bmiHeader.biWidth + 7) /8 
                                  * pbmi->bmiHeader.biHeight 

• cClrBits;

// Set biClrImportant to 0, indicating that all of the 
    // device colors are important. 
     pbmi->bmiHeader.biClrImportant = 0; 
     return pbmi; 
 } 
 

The following example code defines a function that initializes the remaining structures, retrieves the array of palette indices, opens the file, copies the data, and closes the file.

void CreateBMPFile(HWND hwnd, LPTSTR pszFile, PBITMAPINFO pbi, 
                  HBITMAP hBMP, HDC hDC) 
 { 
     HANDLE hf;                 // file handle 
    BITMAPFILEHEADER hdr;       // bitmap file-header 
    PBITMAPINFOHEADER pbih;     // bitmap info-header 
    LPBYTE lpBits;              // memory pointer 
    DWORD dwTotal;              // total count of bytes 
    DWORD cb;                   // incremental count of bytes 
    BYTE *hp;                   // byte pointer 
    DWORD dwTmp; 

    pbih = (PBITMAPINFOHEADER) pbi; 
    lpBits = (LPBYTE) GlobalAlloc(GMEM_FIXED, pbih->biSizeImage);

    if (!lpBits) 
         errhandler("GlobalAlloc", hwnd); 

    // Retrieve the color table (RGBQUAD array) and the bits 
    // (array of palette indices) from the DIB. 
    if (!GetDIBits(hDC, hBMP, 0, (WORD) pbih->biHeight, lpBits, pbi, 
        DIB_RGB_COLORS)) 
    {
        errhandler("GetDIBits", hwnd); 
    }

    // Create the .BMP file. 
    hf = CreateFile(pszFile, 
                   GENERIC_READ | GENERIC_WRITE, 
                   (DWORD) 0, 
                    NULL, 
                   CREATE_ALWAYS, 
                   FILE_ATTRIBUTE_NORMAL, 
                   (HANDLE) NULL); 
    if (hf == INVALID_HANDLE_VALUE) 
        errhandler("CreateFile", hwnd); 
    hdr.bfType = 0x4d42;        // 0x42 = "B" 0x4d = "M" 
    // Compute the size of the entire file. 
    hdr.bfSize = (DWORD) (sizeof(BITMAPFILEHEADER) + 
                 pbih->biSize + pbih->biClrUsed 
                 * sizeof(RGBQUAD) + pbih->biSizeImage); 
    hdr.bfReserved1 = 0; 
    hdr.bfReserved2 = 0; 

    // Compute the offset to the array of color indices. 
    hdr.bfOffBits = (DWORD) sizeof(BITMAPFILEHEADER) + 
                    pbih->biSize + pbih->biClrUsed 
                    * sizeof (RGBQUAD); 

    // Copy the BITMAPFILEHEADER into the .BMP file. 
    if (!WriteFile(hf, (LPVOID) &hdr, sizeof(BITMAPFILEHEADER), 
        (LPDWORD) &dwTmp,  NULL)) 
    {
       errhandler("WriteFile", hwnd); 
    }

    // Copy the BITMAPINFOHEADER and RGBQUAD array into the file. 
    if (!WriteFile(hf, (LPVOID) pbih, sizeof(BITMAPINFOHEADER) 
                  + pbih->biClrUsed * sizeof (RGBQUAD), 
                  (LPDWORD) &dwTmp, ( NULL)) 
        errhandler("WriteFile", hwnd); 

    // Copy the array of color indices into the .BMP file. 
    dwTotal = cb = pbih->biSizeImage; 
    hp = lpBits; 
    if (!WriteFile(hf, (LPSTR) hp, (int) cb, (LPDWORD) &dwTmp,NULL)) 
           errhandler("WriteFile", hwnd); 

    // Close the .BMP file. 
     if (!CloseHandle(hf)) 
           errhandler("CloseHandle", hwnd); 

    // Free memory. 
    GlobalFree((HGLOBAL)lpBits);
}