Rendering ZBrush Displacement-Maps In External Renderers (May 9th: 2nd file added)

[Thomas_Helzle]

Rendered with messiah:studio 2.0 (http://www.projectmessiah.com/). Since messiah supports 16 bit greyscale images natively and has an easy to use MinMax node to "center" the values around zero (with settings of -1.0 for min and 1.0 for max), ZBrush displacements are very easy to import (it even has U/V-flipping buttons so you don't have to do that externally).
The rendering in 1024x1024 took 4.20 minutes on a P4 3.2 Ghz with 2pass "Enhanced" Antialiasing, Subpolydisplacement, MonteCarlo GI and a slight raytraced reflection of the environment.
The only problem are the errors in the displacementmap that are also visible when the file is reimported in ZBrush itself and used for displacement there... messiah is a bit more "unvorgiving" in this regard

Cheers,

Thomas Helzle

[Gregory Glezakos]

Hello....
Here's a Messiah Studio 2.0 quick test.
6 min render with three soft ray trace shadow spots and maximum antialiasing settings.



Cheers,
______________________
Gregg "T.Rex" Glezakos
3D Artist

[aL3891]

well maybe this thread is dead.. but iäll post my little mental ray for maya 6 render anyways results look quite nice i think

heres what i did:
flipped map in ps
converted to rgb
saved to 16bit tif

loaded up the model ni maya and applyed the map
set the alpha gain to 8,34 (ie the zbrush disp. gain * 10)
set the alpha ofset to -4.5. this value was worked out by trying to set the alpha ofset as low as possible starting at -5 in this case and working upwards

disp. aprox set to finest hi qual. preset and the distance setting set to 0.025

subdiv aprox set to spratial min 4 and max 9 subdivisions and distance to 0.50

rendertime at production quality 56 secounds
on a 2700xp athlon w/ 512 drr333 ram

[wigal]

Finally!!!! Dont know if it's the complete resetup of the system or aL3891's setup...
but this time the displacemt worked...

additionally i tried to add a bone driven expression to see how the map would look alike... except the lazy skinning inside the mouth, and the fact the head wasn't modelled for such things in this region i find the result promising...

[bisenberger]

Max 5.1 and VRay beta 1.45.70

[Nekro3D]

Good Displace Vray Beta!!
What settings??!!

[bisenberger]

Hi Nekro3D,
Here is a screen capture of the displacement settings. Shift by average has the same affect as the -.25 shift with this displacement map. I also used global illumination and one target direct light.

[Junk]

bisenberger could you post your scene?

I don't have the same result, I think it a scale issue wth the mesh and the units set up of Max

I test several times with this objet or personnal work and my result in Vray are far from perfect

[Gregory Glezakos]

Hello...
Here's another test, this time using Lightwave 8.



Cheers,
_____________________
Gregg "T.Rex" Glezkos
3D Artist

[Gregory Glezakos]

And another one with Messiah Studio 2 again, but this time with some more surfacing on and a biger render...



Cheers,
______________________
Gregg "T.Rex" Glezakos
3D Artist

[Przemek]

Hi all I took me like 3 hours to read all the treads but I made it Still I cant get the head model to render right in my 3D MAX6
There was 2 replys with the instructions and I did it although it didnt work here is my screen as you can see I checked "Use exsisting mapping" although when I rotate the displacment gizmo I se the changes on the Head. What am I doing wrong how do I set up the UV's? also when i change the strenght of the displacment it eather inflates or colapses.

[devilbunny]

Don't you need to set V Tile to -1? And have you Meshsmoothed or otherwise subdivided the mesh?

[Gryphon]

With respect to Poser 5, EXACTLY how did you manipulate the TIF file to get it to work properly? Saying "invert" alone is not enough to tell me whether you inverted the alpha channel or the vert/horiz position.

Same question for LW 8.

Thanks!!!

--Scot

[Nekro3D]

Thanks! bisenberger...
Testing Now configs in vray beta, LoL!

[aL3891]

Ok no more guessing.. Here’s a way to calculate alpha gain and alpha offset at least for mental ray for Maya.. It should work with most packages though at least the way to calc alpha offset

Quick fix:
If you don’t need to understand what the problem is and how the solution works here’s the values in short

Alpha gain: (Alpha Depth Factor from zbrush * 10) * 2

Alpha offset: the negative (the inverse?) of half the alpha gain.

Example:
Zbrush Alpha Depth Factor = 0.834
Maya alpha gain = 16.68
Maya alpha offset = -8.34

An alternative to using this method is using the set range node and the multiply divide node.

Don’t change anything on the file node.
Connect the out alpha from the file node to the value x in the set range node
Use these settings for the set range node

Min: -1
Max: 1
Old min: 0
Old max: 1

Connect the outvalue.X from the set range to input1.x on the multiply divide node
Connect the outvalue.x from the multiply divide node to your displacement.

Now instead of changing the alpha gain when we want to scale the displacement, change input2.x value on the multiply divide node.

These methods will give you the exact same result but the one using set range is a bit less math.

Now for the ppl who just need to know (like me)

The reason ppl have been getting "bloated" result is because the midpoint or the "no displacement" color of maps made by zbrush is 0,5 or gray instead of 0 or black

THIS HOWEVER IS NOT A BAD THING

Why? Because when modeling in zbrush you are quite likely to push your model inwards, creating negative displacement. If we wanted to get these negative displacements into a map while at the same time having the no displacement color at 0 (black) we would have to have negative color values. This is not supported by any image format I know of. This is why the makers of zbrush have decided to set the zero displacement color to 0.5 or gray.

So what to do? Well you could split the map in one negative and one positive displacement map by using Photoshop to save out al the values above 0.5 to one map and the ones below 0.5 to another.

How ever this poses a new problem and that’s how to get to displacement maps onto a single object. I didn’t find any way to do this in Maya so another way had to be found.

Something that is less that obvious in Maya (and mental ray) is that the displacement node actually can displace negatively. If you want to see for your self add a displacement material without any texture and set the displacement to a negative value. The whole object will shrink.

So what we need to do is subtract half of the values that we got from the map, simple enough just set the alpha offset to -0.5 and you’re done right? Well kinda.

The way alpha gain and alpha offset works is the value from the map is multiplied by the alpha gain and then added to the alpha offset.

Example:
If the value from the map is 0.5,
The AG is 1
And AO is -0.5
The out value would be 0.

This is what we want. Gray in the map is now zero displacement. But what happens if we change the alpha gain?

0.5 from the map
AG is 2
AO is -0.5

(0.5 * 2) - 0.5 = 0.5

Woops.. Now gray in the map means a displacement of 0.5. When using AG of 2 we must subtract another 0.5 using the Alpha offset. So for gray to be zero displacement we have to set the alpha offset to -1

This means that the relationship between AO and AG should be
Alpha offset = -(alpha gain/2)

Now we have one more problem. Let’s say we have these settings
Value from map: 1
AG: 1
AO: -0.5

The out value will be 0.5 not 1. To fix this we double the AG and change the AO accordingly.
So:

AG: 2
AO: -1

Now we'll get an out value of 1 when the value from the map is 1, we'll get an out value of 0 when the map says 0.5 and we'll get an out value of -1 when the map says 0.

And that’s all folks