I think that's not quite correct because you would lose the black value and you also don't get a maximum value 31!
maybe it looks better with this palette conversion!

0 -> 0 *
1 -> 2
2 -> 4
3 -> 6
4 -> 8
5 -> 10
6 -> 12
7 -> 14
8 -> 17 *
9 -> 19
10 -> 21
11 -> 23
12 -> 25
13 -> 27
14 -> 29
15 -> 31 *