Disp map shows negative values when it shouldn't

[Nocturn]

I've tried all kinds of settings and ways to create the displacement map and I don't know why I also get darker values in the map, even though I only sculpted in the up direction.

For example in this map, I only used the default plane, sculpted a line, and I would expect to see only middle grey and white in the map, but I see darker values along the edges of the line, why? I tried saving in different 16b formats and same results.

http://img528.imageshack.us/img528/345/mudbox.jpg

[Darth Ziggy]

What's the poly count on the plane? I would imagine that the dark areas are where Mudbox is "bunching" up the polys in it's calculations. Just a thought. What does it look like in a render?

[Nocturn]

It's the default plane in Mudbox subdivided to level 7, about 1.6 million polys. In a render it renders what such a map would render like, I mean it renders the darker parts indented. If I do a Sculpt by displacement using this map in Mudbox, the plane is also indented. It's equally displaced both up and down.

Also when I create the map, it's telling me the min max height used and it goes to -7 to +7, so I'm wondering how this distance is calculated? It's not possible to have only positive displacement in the map? It looks like it's taking the search distance but always applies both a negative and a positive displacement when creating the map. There must be some combination of settings to use to get the proper map rendered, I hope :)

[Bryan Silva]

The reason this is happening is because when you add subdivision levels to a mesh and sculpt on the new level in mudbox, the information for that subdivision level is trickled down the the lower subdivision levels. This is why your level 0 mesh changes as you sculpt higher levels. Now when you take the plane up to level 7 and sculpt the "S" on it you are changing the lowest level. So when you extract your displacement map you are extracting a map that will work for the changed level 0 which is not a flat plane anymore. If you want your map to work for a flat plane then you need to import a flat plane and extract your displacement map with the flat plane as the target mesh. I have included an image to illustrate this.

[Nocturn]

Bryan, thank you so much for the reply, it makes perfect sense.