compare images:best method..

[dave2k]

i have two images which are 4 bytes per pixel. i need to compare them to make sure that if the colour black, i.e. oxff,oxff,oxff occurs in either image, it occurs in the other image and the same coorindates. so far i am looping through using memcmp, and my code i below. But i have heard that because each pixel is a 32 bit value, i could use a simple int comparison. How could i change my code below to do this? And which method is quicker: mine or the nit comparison? Thanks.

bool IsBlack(BYTE* byt)
{
	BYTE black[] = {0x00,0x00,0x00};
	return memcmp(black, byt, 3) == 0;
}

    // 1st image
    HANDLE hBm1 = ::LoadImage(0, "C:\\Documents and Settings\\ftwyman.MARINEDATA\\Desktop\\1.bmp",
                                  IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE );
    BITMAP bm1;
    ::GetObject(hBm1, sizeof(BITMAP), &bm1);
    int size1 = bm1.bmHeight * bm1.bmWidth * bm1.bmBitsPixel / 8;
    BYTE *bytes1 = new BYTE[size1];
    ::GetBitmapBits((HBITMAP)hBm1, size1, bytes1);

    // 2nd image
    HANDLE hBm2 = ::LoadImage(0, "C:\\Documents and Settings\\ftwyman.MARINEDATA\\Desktop\\2.bmp",
                                  IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE );
    BITMAP bm2;
    ::GetObject(hBm2, sizeof(BITMAP), &bm2);
    int size2 = bm2.bmHeight * bm2.bmWidth * bm2.bmBitsPixel / 8;
    BYTE *bytes2 = new BYTE[size2];
    ::GetBitmapBits((HBITMAP)hBm2, size2, bytes2);

	for(int i=0; i < size1; i+=4)
	{
		if(IsBlack(&bytes1[i]) ^ IsBlack(&bytes2[i]))
		{
			break;
		}
	}

	if(i == size1) 
		std::cout << "matching!";