32 Bit displacement map vs 16 bit

Jonathan85

Hello, i have read quite a lot about this issue on net, but i have few questions i didnt find the answer to.
The main advantages for using 32 bit displacement maps over 16 bit is:

1) The absence of "terrace" effects (artifacts) in 32 bit
2) And the ability to push the mesh even down, not just up (as 16 bit displacement map does).

I understand and saw the advantage of the 1st one, but i have questions about the 2nd one.

Is it really true that you cannot "push" the mesh below/under/down with the 16 bit displacement map? (only up)

Is there any workaround how can i push the mesh down using just the 16 bit map? for example in vray for 3ds max theres a vray displace modifier with "shift" option, but that pushes the whole mesh below, not just the parts "painted" in the displacement map.

Isnt there any workaround for this?

(i use zbrush for generating displacement maps, and 3ds max and vray for rendering)?

artquest

You can indeed push a mesh down with a 16 bit displacement map. You just need to use an expression in maya(not sure how to set this up in 3ds max) to keep your scale properly set and offset the depth settings so that your lowest value pushes into the surface instead of being right on the surface.

The issue is that 16 bit displacements I believe can't contain negative values so what you are essentially doing is forcing everything below 50% grey to be negative.

you can read more about it here:

http://www.zbrushcentral.com/showthread.php?4571-How-to-calculate-alpha-gain-and-alpha-offset-in-maya-when-using-disp-maps-from-Zbrush

EarthQuake

Most shaders have some sort of way to set the grey point or zero point, the texture value in your map at which zero displacement occurs. Once you calibrate that value, values brighter in your texture should push out while values darker should push in.

Jonathan85

Well im using 3ds max and vray, does anybody has experience with that? (3ds max 2009 and vray 1.5) which are quite old, but i dont see any menu there for this...

artquest

Jonathan85 wrote: »

Well im using 3ds max and vray, does anybody has experience with that? (3ds max 2009 and vray 1.5) which are quite old, but i dont see any menu there for this...

I don't have any experience with rendering displacement maps in 3ds max but here is some info:

http://www.3dbuzz.com/forum/threads/126009-Tip-for-Zbrush-displacements-in-other-apps

ysalex

Zbrush uses grey as a midpoint, so a 16bit map is definitely capable of pushing down. Both maps use a higher range of value to express "positive" values, so the expression needed is setting the shift value to -1/2 whatever the positive value is. So for instance if you set your displacement to 1, then the proper shift value is -0.5 (value of .5 shift would be -0.25, etc.)

The biggest pro of a 32 bit displacement is accuracy.

The biggest pro of a 16 bit displacement is that you can use the layered texture nodes to layer displacement. For example I could make my characters displacement, then create a seperate tiling displacement map for skin detail, and add that new tiling map over the top of my original 16bit displacement. Not possible with 32bit.

This is a huge plus, for a lot of reasons. Just depends what you're trying to get done. For example I have a character with 8192 map for displacement, but I have a micro tiling displacement that is 1024, tiles 120 tiles, which is equivilant to more than a 100,000 pixel widextall map. Could never actually bake a map that size.