How can an image be posterized in the compositor? I tried to split an image RGB values and re-combined it with rounded values in order to reproduce the results described in this BA Thread.

But instead of a posterized image all I get is an almost black image. Why is that?



The issue was that I loaded an HDR image, with standard images it works as 3pointedit pointed out the value should be reset (I just tried several values before the screenshot was made).
If you are replicating the setup on my BA thread http://blenderartists.org/forum/showthread.php?244118-Cool-nodes-I-didn-t-know-about

then the round value should be 0.1 not 1.0