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 Windows file format described in Bitmap Storage. In order to store a bitmap in this format, you must initialize a BITMAPINFO structure (consisting of a BITMAPFILEHEADER structure and an array of RGBQUAD structures), as well as an array of palette indices.

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) * (2^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 = 2^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.

• oid 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,

(LPSECURITY_ATTRIBUTES) 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, (LPOVERLAPPED) 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, (LPOVERLAPPED) NULL))

errhandler("WriteFile", hwnd);

/* Copy the array of color indices into the .BMP file. */

dwTotal = cb = pbih->biSizeImage;

hp = lpBits;

while (cb > MAXWRITE) {

if (!WriteFile(hf, (LPSTR) hp, (int) MAXWRITE,

(LPDWORD) &dwTmp, (LPOVERLAPPED) NULL))

errhandler("WriteFile", hwnd);

cb-= MAXWRITE;

hp += MAXWRITE;

}

if (!WriteFile(hf, (LPSTR) hp, (int) cb,

(LPDWORD) &dwTmp, (LPOVERLAPPED) NULL))

errhandler("WriteFile", hwnd);

/* Close the .BMP file. */

if (!CloseHandle(hf))

errhandler("CloseHandle", hwnd);

/* Free memory. */

GlobalFree((HGLOBAL)lpBits);
}

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