Private int CalculateWhitePixels( Bitmap image )
		{
			int count = 0;
 
			// lock difference image
			BitmapData data = Image.LockBits(New Rectangle(0, 0, width, height),
                ImageLockMode.ReadOnly, PixelFormat.Format8bppIndexed);
 
			int offset = data.Stride - width;
 
			unsafe
			{
				Byte * ptr = (Byte *) data.Scan0.ToPointer( );
 
				For (int y = 0; y < height; y++ )
				{
					For (int x = 0; x < width; x++, ptr++ )
					{
						count += ( (*ptr) >> 7 );
					}
					ptr += offset;
				}
			}
			// unlock image
			image.UnlockBits( data );
 
			Return count;
		}