Negative & positive displacement?

[Zeddicus]

Hey all. Hoping someone can answer a question I have. Tonight while tinkering with Zbrush 2.0 and it's ability to generate displacement maps, I discovered (thanks to another Vray user) that Vray doesn't see middle grey as a zero displacement value with darker values being negative displacement and lighter ones being positive displacement. This is the type of displacement map that Zbrush outputs, and I'm curious if later versions of Vray will switch to this method, or at least add it as an option in the modifier to calculate displacement this way. The way Vray does it doesn't really make sense to me, limiting it to only positive or negative values but not both. Thanks in advance!

[dbuchhofer]

If for instance you displacement value is 2.. and you have a displacement map that runs from black to white.. the Shift value will allow you to 'place' where the ZeroPoint is on the displacement.. If you wanted it to work out that the middle grey would be the 0 point, you would only need to have your shift value set to -(displacement/2)

it gives you twice as much bitmap accuracy for the instances where you are only displacing in 1 direction.. (0 to 255, as opposed to 128 to 255), and still allows you to go both ways.

Now there are some issues with displacement, negative shift, and smoothing.. but haven't tracked them down enough to make a bugreport

[Zeddicus]

A most excellent explanation friend! Now I also understand what someone else said somewhere around here regarding a bug with positive displacment and negative shift. Many thanks!

[v_wrangler]

Re: Negative & positive displacement?

You can also do that via the map's Output Settings - if the map doesnt
have an output rollout built in, nest it into an Output Map. If you set the
RGB Offset spinner to -0.5, this will shift the whole displacement halfway...

[vlado]

Re: Negative & positive displacement?

You can also do that via the map's Output Settings - if the map doesnt
have an output rollout built in, nest it into an Output Map. If you set the
RGB Offset spinner to -0.5, this will shift the whole displacement halfway...

This will only work for the 2D displacement method. 3D displacement will clamp the map between black and white. You can still use a negative shift value though.

Best regards,
Vlado