Advanced MFC Programming

Chapter 10. Bitmap
dwSize=
(
sizeof(BITMAPINFOHEADER)+
nSizeCT*sizeof(RGBQUAD)+
WIDTHBYTES(8*lpBi24->bmiHeader.biWidth)*lpBi24->bmiHeader.biHeight
);
hDIB=::GlobalAlloc(GHND, dwSize);
ASSERT(hDIB);
lpBi=(LPBITMAPINFO)::GlobalLock(hDIB);
ASSERT(lpBi);
*lpBi=*lpBi24;
lpBi->bmiHeader.biBitCount=8;
lpBi->bmiHeader.biSizeImage=WIDTHBYTES
(
8*lpBi->bmiHeader.biWidth
)*lpBi->bmiHeader.biHeight;
lpBi->bmiHeader.biClrUsed=0;
……
for(n=0; nbmiColors[n]=*(LPRGBQUAD)arRgbQuad[n];
}
The differences between the new and old bitmap information headers are member bitBitCount (8 for
256-color format), biSizeImage, and biClrUsed (Member biClrUsed can be used to indicate the color
usage. For simplicity, it is set to zero).
Next we need to convert explicit RGB values to color table indices. As mentioned before, there are two
situations. If the color table is extracted directly from the bitmap, we must compare each pixel with every
entry of the color table, find the index, and use it as the bitmap bit value. Otherwise the index can be
formed by omitting the lower 5 bits of red and green colors, the lower 6 bits of blue color then combining
them together. This eleminates the procedure of looking up the color table. It is possible for us to do so
because the color table is created in a way that if we implement the above operation on any color contained
in the table, the result will become the index of the corresponding entry.
For example, entry 1 contains color (32, 0, 0), which is (0x20, 0x00, 0x00). After bit omission, it
becomes (0x01, 0x00, 0x00). The followng calculation will result in the index of this entry:
red | (green bmiHeader.biWidth)*j
);
lpRowSrc=
(
(LPSTR)lpBi24+
sizeof(BITMAPINFOHEADER)+
WIDTHBYTES(lpBi24->bmiHeader.biBitCount*lpBi24->bmiHeader.biWidth)*j
);
for(i=0; ibmiHeader.biWidth; i++)
{
rgbQuad.rgbBlue=*lpRowSrc;
rgbQuad.rgbGreen=*(lpRowSrc+1);
rgbQuad.rgbRed=*(lpRowSrc+2);
rgbQuad.rgbReserved=0;
if(bStandardPal == TRUE)
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