请教个用GDI画图后保存为8位BMP文件时调色板的问题

#define BMP_SAVE_TPYE_24 24

#define BMP_SAVE_TPYE_8  8

BOOL SaveToFile(LPCTSTR lpFileName, DWORD dwSaveType/* = BMP_SAVE_TPYE_24*/)

{

	CFile file;

	BITMAPFILEHEADER bh;

	BITMAPINFOHEADER bi;

	DWORD dwSize = m_nHeight * m_nWidth * 4, dwNewSize, dwi;

	DWORD dwRowOffset = (m_nWidth * 3 + 3) / 4 * 4 - m_nWidth * 3;

	BYTE *pData = new BYTE[dwSize];



	if (pData == NULL)

	{

		goto Err;

	}



	DWORD	dwOffset = 0;

	dwNewSize = m_pBitmap->GetBitmapBits(dwSize, pData);

	if (dwNewSize == 0)

	{

		goto Err;

	}



	DWORD dwPixCount = 1;

	DWORD dwPaletteSize;

	RGBQUAD rgb[256];

	if (dwSaveType == BMP_SAVE_TPYE_8)

	{

		int  quadOffset = 50;

		int  x, y, z;

		BYTE B = 0, G = 0, R = 0;

		dwi = 0;

		for (x = 0; x < 6; x ++)

		{

			for (y = 0; y < 6; y ++)

			{

				for (z = 0; z < 6; z ++)

				{

					rgb[dwi].rgbRed = R;

					rgb[dwi].rgbGreen = G;

					rgb[dwi++].rgbBlue = B;

					B += quadOffset;

				}

				B = 0;

				G += quadOffset;

			}

			G = 0;

			R += quadOffset;

		}

		for (dwi = 0; dwi < dwNewSize; dwi ++)

		{

			BYTE B = (pData[dwi++] / quadOffset) * quadOffset;

			BYTE G = (pData[dwi++] / quadOffset) * quadOffset;

			BYTE R = (pData[dwi++] / quadOffset) * quadOffset;

			BOOL fFind = FALSE;

			for (x = 0; x < 256; x ++)

			{

				if (rgb[x].rgbRed == R &&

					rgb[x].rgbGreen == G &&

					rgb[x].rgbBlue == B)

				{

					fFind = TRUE;

					pData[dwOffset++] = x;

					break;

				}

			}

			if (fFind == FALSE)

			{

				pData[dwOffset++] = 255;

			}

			if (dwPixCount % m_nWidth == 0)

			{

				dwOffset += dwRowOffset;

			}

			dwPixCount ++;

		}

		dwPaletteSize = 1024;

	}

	else if (dwSaveType == BMP_SAVE_TPYE_24)

	{

		for (dwi = 0; dwi < dwNewSize; dwi ++)

		{

			pData[dwOffset++] = pData[dwi++];

			pData[dwOffset++] = pData[dwi++];

			pData[dwOffset++] = pData[dwi++];

			if (dwPixCount % m_nWidth == 0)

			{

				dwOffset += dwRowOffset;

			}

			dwPixCount ++;

		}

		dwPaletteSize = 0;

	}

	else

	{

		goto Err;

	}



	dwSize = dwOffset;



	bh.bfType = 0x4D42;

	bh.bfReserved1 = 0;

	bh.bfReserved2 = 0;

	bh.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + dwPaletteSize + dwSize;

	bh.bfOffBits = bh.bfSize - dwSize;



	bi.biSize = 40;

	bi.biWidth = m_nWidth;

	bi.biHeight = -m_nHeight;

	bi.biPlanes = 1;

	bi.biCompression = BI_RGB;

	bi.biClrImportant = 0;

	bi.biClrUsed = 0;

	bi.biXPelsPerMeter = 0;

	bi.biYPelsPerMeter = 0;

	bi.biSizeImage = dwSize;

	bi.biBitCount = dwSaveType;



	try

	{

		if (file.Open(lpFileName, CFile::modeCreate | CFile::modeReadWrite))

		{

			file.Write(&bh, sizeof(BITMAPFILEHEADER));

			file.Write(&bi, sizeof(BITMAPINFOHEADER));

			if (dwSaveType == BMP_SAVE_TPYE_8)

			{

				file.Write(&rgb[0], 1024);

			}

			file.Write(pData, dwSize);

			file.Close();

			delete [] pData;

			return TRUE;

		}

	}

	catch (CException* e)

	{

		e->Delete();

		file.Close();

	}

Err:

	if (pData != NULL)

	{

		delete [] pData;

	}



	return FALSE;

}