convert bmp to grayscale

[flynny1st]

Hi,

all i basically want to do is convert an already existing bitmap to greyscale.

to do this i assume i will have to create a new bimapeaderinfo, fill in the needed details and then look at and convert each pixel in the exisiting image.

can anyone help me to do this? also am i calculating the width size of the destination bmp correctly?

BOOL CBitmapOCR::ConvertBitmap(LPTSTR path, LPTSTR dest, DWORD wBpp, int rVal, int gVal, int bVal)
{
	    // Make sure bits per pixel is valid
    if		(wBpp <= 1)	wBpp = 1;
    else if (wBpp <= 4)	wBpp = 4;
    else if (wBpp <= 8)	wBpp = 8;
    else if (wBpp <= 16)wBpp = 16;
    else if (wBpp <= 24)wBpp = 24;
    else				wBpp = 32;

	//load the bitmap
	CString szFilename(path);
	HBITMAP hBmp = (HBITMAP)::LoadImage(NULL,szFilename,
		           IMAGE_BITMAP,0,0,
			       LR_LOADFROMFILE|LR_CREATEDIBSECTION);
		
	BITMAP WorkBmp;
	GetObject(hBmp, sizeof(WorkBmp), &WorkBmp);

	//create the new bitmap
	BITMAPINFOHEADER head;

	// set the correct bpp value
    switch (wBpp)
	{
        case 1:
            head.biClrUsed = 2;
			break;
        case 4:
            head.biClrUsed = 16;
			break;
        case 8:
            head.biClrUsed = 256;
			break;
        default:
            head.biClrUsed = 0;
    }

	int dActualWidth = (WorkBmp.bmWidth * WorkBmp.bmBitsPixel + 3)&(~3);

	head.biSize = sizeof(BITMAPINFOHEADER); 
    head.biWidth = WorkBmp.bmWidth / WorkBmp.bmBitsPixel ;		
    head.biHeight = WorkBmp.bmHeight;
    head.biPlanes = 1;			
    head.biBitCount = (WORD)wBpp;		
    head.biCompression = BI_RGB;    
    head.biSizeImage = WorkBmp.bmHeight * WorkBmp.bmWidth;
    head.biXPelsPerMeter = 0;
    head.biYPelsPerMeter = 0;
    head.biClrImportant = 0;

	BITMAPINFO * pBmiSrc = ( BITMAPINFO * ) new BYTE[ WorkBmp.bmHeight * WorkBmp.bmWidth ];

	int x, y;
	int r,g,b;

	for(x=0;x<WorkBmp.bmWidth;x++)
	{
		for (y=0; y<WorkBmp.bmHeight;y++)
		{
			r = *((BYTE*)WorkBmp.bmBits + y * dActualWidth + x * WorkBmp.bmBitsPixel + 2);
			g = *((BYTE*)WorkBmp.bmBits + y * dActualWidth + x * WorkBmp.bmBitsPixel + 1);
			b = *((BYTE*)WorkBmp.bmBits + y * dActualWidth + x * WorkBmp.bmBitsPixel + 0);

			if(r==rVal && g==gVal && b==bVal)
			{
				//set pixel to be black
			}
			else
			{
				//set pixel to be white
			}	
		}
	}

	return true;
}

many thanks,

Matt.