Converted floating point to integer math

Difference in result from FP math is on average less than 1 level. Decent performance boost =)
Massaged the fixed point code a little bit. It turns out that shifting up the alpha range by 1 and then subtracting 1 to force rounding down was doing more harm than good.
Also, saturating the result to 255 avoids overflows that eventually happen due to some of the liberties taken.
All in all the absolute difference in result from fixed point and floating point deviate, on average, by less than 0.03.
The fixed point code can detect a couple more images than the previous code; however it also detects a couple less. Zero sum I suppose? However it's much faster, so still a win ;)