- speed:
	scanning a 238x420 grayscale image at 6 dpmm takes:

		13.07 seconds at speed 0
		12.94 seconds at speed 1
		21.35 seconds at speed 2
		21.18 seconds at speed 3
		21.23 seconds at speed 4
		12.95 seconds at speed 15

	color:
		1dpmm:	19.5 seconds (234 bytes/line, 79 lines)
		2dpmm:	26.6 seconds (480 bytes/line, 161 lines), 1 backtrack

- brightness:	no noticeable difference
- contrast:	no noticeable difference
- grain: controls size of averaging filter (0==8x8, 5==2x2)
