Help processing a 16 bit bitmap

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C++

bitwise

Hello, I could really use a little help from one of you bitwise gurus. I trying to add 16 bit capabilities to a function to greyscale an image inplace that I use for generating a disabled toolbar imagelist.

I found and tried tried 2 different methods;
The first one returns me a RGB value of (248, 248, 248) for a pixel that should be (255, 255, 255).
The second method does as well when I use the code for RGB 555 (so I take it that Windows uses RGB 555 for 16 bit memory bitmaps).

here is the function:

 inline void GreyScaleImage(CBitmap* pbmpTarget, COLORREF crMask)
{
	// Various greyscale algorithms
	//int iGrey = (((bRed)+(bGreen)+(bBlue)) / 3);
	//int iGrey = (bBlue * 11 + bGreen * 59 + bRed * 30) / 100;
	//int iGrey = ceil(0.3 * bRed + 0.59 * bGreen + 0.11 * bBlue);
	//int iGrey = (bBlue + bGreen * 6 + bRed * 3) / 10;

	// Get bitmap information
	BITMAP bm = {0};
	pbmpTarget->GetBitmap(&bm);
	// Allocate memory for bitmap data
	DWORD dwSize = (bm.bmHeight * bm.bmWidthBytes);
	BYTE* pData = new BYTE[dwSize];
	memset(pData, 0, dwSize);
	// Get bitmap data
	pbmpTarget->GetBitmapBits(dwSize, pData);
	
	if(bm.bmBitsPixel == 16) 
	{ 
		BYTE* pPixel = pData;
		WORD* p = (WORD*)pData;

		for(int x = 0; x < (bm.bmHeight * bm.bmWidth); x++)
		{ 
			// Method from here:
			// https://social.msdn.microsoft.com/Forums/vstudio/en-US/eea4b207-4f3c-4dd8-9420-afbb9a05783b/how-to-develop-a-code-to-find-lowest-rgb-on-bitmap-image-in-certain-area-in-mfc?forum=vcgeneral
			BYTE blue = pPixel[0] & 0x1F;
			BYTE green = pPixel[0] >> 5;
			green |= (pPixel[1] & 0x03) << 3; 
			BYTE red = pPixel[1] & 0x1F;
			WORD wRed = red*8; 
			WORD wBlue = blue*8; 
			WORD wGreen = green*8; 

			// Method from here:
			//  http://msdn.microsoft.com/en-us/library/windows/desktop/dd390989%28v=vs.85%29.aspx
			WORD pixel = p[0];

			// RGB 565 
			BYTE red_value		= (pixel & 0xF800) >> 11;
			BYTE green_value	= (pixel & 0x7E0) >> 5;
			BYTE blue_value		= (pixel & 0x1F);
			BYTE bRed   = red_value << 3;
			BYTE bGreen = green_value << 2;
			BYTE bBlue  = blue_value << 3;

			// RGB 555 
			//BYTE red_value		= (pixel & 0x7C00) >> 10;
			//BYTE green_value	= (pixel & 0x3E0) >> 5;
			//BYTE blue_value		= (pixel & 0x1F);
			//BYTE bRed   = red_value << 3;
			//BYTE bGreen = green_value << 3;
			//BYTE bBlue  = blue_value << 3;

			// Check for mask color
			if(RGB(bRed,bGreen,bBlue) != crMask)
			{
				int iGrey = (((bRed)+(bGreen)+(bBlue)) / 3);
				//pCurrPixel[0] = iGrey;
			}

			p++;
			pPixel += 2;
		} 
	} 
	else if(bm.bmBitsPixel == 32) 
	{ 
		BYTE* pPixel = pData;
		for(int x = 0; x < (bm.bmHeight * bm.bmWidth); x++)
		{
			BYTE bRed	= pPixel[0];
			BYTE bGreen = pPixel[1];
			BYTE bBlue	= pPixel[2];
			if(RGB(bRed,bGreen,bBlue) != crMask)
			{
				int iGrey = (((bRed)+(bGreen)+(bBlue)) / 3);
				pPixel[0] = iGrey;
				pPixel[1] = iGrey;
				pPixel[2] = iGrey;
			}
			pPixel += 4;
		} 
	}
	// Set bitmap data
	pbmpTarget->SetBitmapBits(dwSize, pData);
	// Clean up
	delete pData;
}

Any insight would be greatly appreciated, bitwise stuff is not my cup of tea.