Scale issue with displacements

#1

It seems like I need to scale objects up a lot in maya to be able to sculpt normally in mudbox. The only problem is when I bring them back into maya the displacement map is way too strong. Then I need to take the alpha gain down quite a bit.

Basically Im looking for a good workflow for going back and forth from maya. Is it ok to not scale objects up for mudbox. I saw a tutorial that said you should, also I notice the clipping planes are a problem unless you do scale up.

Thanks.

#2

im using the mudbox baseman as guide for maya…
units are set to meter…

#3

the exr file (if you use them) have the displacment scaled “baked” in them, thats why you if you dont change the scale they work as expected.

when you use non-floating point. then you need to take in accountthe alpha gain factor. whic is a multipler on the scale factor…kinda what you arelady done to fix it.
you can use the dispalcment slot in the SG node its elf if you want to have a “scale free” error…

I made a tutorial once for Autodesk class, I’ll see if they let me post it in public

#4

Ive been using floating point tiffs. Would these act differently than exrs? Id love to see that tutorial.

Thanks

#5

basically, (in most cases) when you import a model from mudbox/zbrush and you scale it inside maya either to pose it better, or to fit your scene, or scale in animation too…you need to adjust the alpha gain accordingly which is the intensity…or “distance” of the details pushing inwards/outwards because they dont scale along with your model and stay the same. now this depends on your displacement output workflow but the general idea is to use the same scale relationships all the time. say you exported from zbrush with disp exporter and u use alpha gain of 2 as a general rule. if you scale your model by 10 up you also have to scale the alpha gain by x10. meaning 2(alpha gain) x 10(your model scale) to get the right displacement intensity. for example in mudbox if you scaled your model in maya by x15 down to fit your scene then the alpha gain has to be divided by 15 as well.

#6

Cool thanks for the info. Is it a big problem if in mudbox if you decide to work on a much smaller scale than its default objects. For example if you make a sphere in maya and import that into mudbox without scaling up, will there be a problem when sculpting?

#7

2 things will happen…actually 4 might happen i’ve noticed.

  1. your brush size will be way too large and you would need to put like 0.005 in size which means you cant easily increase/decrease brush size but have to type it in, slow and annoying.
  2. there is a chance that if your model isnt PERFECTLY sitting(and even then) on the 0 axis your mirrored brush strokes on small details will not work(i’ve had that happen to me)
  3. the tablet pressure may not work well and you will lose range values(it’s my own estimate, but that’s the effect i feel is happening)
  4. might happen? your camera clip plane will cut off the model when you try to zoom in to small details and you wont be able to fix it up to a certain degree of “zoom”/closeness to the model.

what i do is take my models/cameras/everything in the scene and parent it/group it in maya and scale it by 30(usually that works just right) then export that to mudbox, bring it back scale the ground back to 1, works fine.
in zbrush there is a button to reset scale after import to “proper” dimensions/location of 0,0,0, not sure if there is one in mudbox.

#8

here is the vid
http://www.pixelcg.com/blog/?p=675

#9

thanks ash…!

#10

Awesome thanks I gotta try the lookup method

#11

I have founded the main problem that all of us have as general in mudbox to maya workflow:
As you can see:
http://forums.cgsociety.org/showthread.php?f=87&t=880878
and here:
http://forums.cgsociety.org/showthread.php?f=221&t=879051
I have had the same problem with my displacement maps in the past days and tried to
figured it out. so the MAIN PROBLEM IS, Mudbox has serious problems in working with small objects.

I have mentioned that my object was small in scale (0.5-2cm) and when I import/exporting it in and out of mudbox even without any modifications to the actual scale, I couldn’t get the result from the extracted displacement maps as I was sculpted in mudbox… so now that I toned down my alpha gain I can get the same amount of displacement out my extracted map…

Through my several tests I have founded that with the exact same workflow, when you start sculpting
on for example the mudbox’s own cube and applying the result as displacement map in maya or what ever application, you can get the same displacement effect even without adjusting alpha gain in maya.
So whether you use 32bit RGBA Float (like me) or not you must tone down your alpha gain, adjust it to get the same result as your actual sculpt in mudbox if you scaled the object in mud or maya or
if your object is small in scale…
AND (sorry for overuse of CAPS) the lesson in my opinion is… after modeling your objects or scene, if they are small in scale, group them all together and scale them up (from 2cm to 20cm for example) and then export them for sculpting…
This way you do not encounter the usual problems as “Gal” said in his posts, also there is more consistency between your sculpt and the extracted displacement maps (you don’t need to adjust the alpha gain).
Please Correct me if any of these thoughts was wrong :slight_smile:
Thanks

#12

I guess you had to learn it the hard way
I talked about this issue number of times in my videos, but I guess users don’t think it’s important
Scale is an important factor in your pipeline…not just Mudbox
it will also affect your render passes
you MUST have a reasonable scale compared to the unit space
anyways lesson learned , move on : )

#13

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