Soulburn Studios Art Lessons

Converting A Mudbox Model To 3DSMax
By Neil Blevins
Created On: Sept 21st 2009
Updated On: Sept 28th 2013
Software: 3dsmax, Mudbox

Here's a tutorial on how to transfer a model from max to mudbox, export a mesh and a displacement map, and then render it in max using a bunch of different displacement methods (depending on what renderer you want to use). I'll be using 3dsmax 2009 and mudbox 2010, but the process is quite similar for any recent version of max and mudbox.

Making the Mesh in Max, and Exporting as Obj

Make Your Mesh in max. Just for testing purposes I created a simple sphere with a radius of 45 and 32 segments. A few notes on your mesh, ideally, your mesh should be mostly if not all quads, and the more square each individual face is, the better your mesh will displace. So try and avoid as much as possible long thin faces.
Make sure the "Generate Mapping Coords" is on. Or if you have a more complex object, create good uvs for the object using the UVW Map modifier and/or the Unwrap UVW modifier.
Export Selected, choose obj, use the mudbox preset...

Importing and Displacing in Mudbox

Open Mudbox
File -> Import, choose your obj file.
Subdivide Selection 4 times. (Shift-D)
Displace your mesh using various brushes

Save mudbox file

Creating A Displacement Map

Your next task is creating a displacement map, which serves as the difference between your Level 1 and Level 4 mesh. You may ask, why are we using a level 1 mesh, and not the original level 0 mesh? In general, I have found using the level 0 mesh doesn't give you enough mesh detail to allow the displacement map to do its job. The more detail in the actual mesh, the less detail your displacement map has to provide, and the better the final result. However, the more detail in the actual mesh means higher polygon counts in your 3d app's viewport, so there's a balance to be struck here. You don't want to export a level 6 mesh if your final mesh is a level 7, that will probably be way too many polygons to navigate properly in the 3d app, even though the final rendered result will look almost identical to the one in mudbox. So I generally export the low poly mesh at either a level 1 or 2, in an attempt to add more mesh detail without going too far.

Avoiding UV Smoothing Artifacts

While creating the displacement map CAN be done in mudbox, a word of warning. The way max and mudbox smooth their UVs is very different from each other by default. Mudbox defaults to linear UVs, and max's meshsmooth and turbosmooth modifiers default to partially smoothed uvs.

So if you have a lot of seams in your UVs or the UVs aren't lined up in a simple grid (like in the example below), you will see a lot of ugly artifacts in your displacement map unless you use max to extract the displacement map, or unless you modify max's uvs to use linear interpolation.

If your object doesn't have any UV seams and the UVs are nicely lined up (like in our example below), you will have no smoothing artifacts, no matter how you make your displacement map.

So I will show you two methods to make your displacement map, 1) Creating A Displacement Map in Mudbox, and 2) Creating A Displacement Map in Max. If you choose to make your disp map in mudbox, you either have to use the max linear uv trick I will show you below, or you have to have a simple uv case like the grid above. Or you can choose to make your displacement map inside max, and that works for all cases automatically, but it's a more complex process. Feel free to choose whichever technique you want to use on a case by case basis.

Creating A Displacement Map in Mudbox

Select the Object in Object List
Step Level Down three times (go to the Level 1 Subdivision Level)
Mesh -> Recreate Level UV's. This is a very important step, so don't miss it. Mudbox does not automatically generate uvs for every subdivision level to save on memory.
File -> Export Selection, save as obj, call it Level1.obj.
Maps -> Extract Texture Maps -> New Operation. See the dialog below.

Instructions:

Choose Displacement Map.
Select your model in the Object List, hit "Use Selected" in the Target Models section. Click on the text marked "level 0" and turn it into "level 1".
Turn "Smooth Target UV's" off.
Hit "Add Selected" in the Source Model section, make sure it's using level 4.
Search Distance. This should be the same as the highest value you've displaced your mesh (The "Best Guess" that mudbox picks is generally a good starting place). Setting this right mostly involves trial and error, you'll want this number to be as low as possible, but not so low that you miss the peaks of your displacement. Basically the highest and lowest points of your displacement get missed with a search distance that's too small, so you'll see neutral grey dots at your peaks and valleys (see the image below). I generally start small, render some test displacement maps, and I keep increasing it until the artifacts go away.

Write down this Search Distance, you'll need it for your displacement in max. In this example, I used a Search Distance of 4.00.
The size of your bitmap. The higher the better, although the higher the more memory the map takes. 1 to 4k is a good value depending on how close you're getting to the mesh, and how much tiny detail you've added.
Click the folder icon, and choose a name and filetype for your displacement map. I use primarily 16-bit Tiffs. You can choose 8bit, but personally I advise against it, since it's likely 8bit displacement will produce artifacts in your disp map. A higher color depth means a smoother displacement map (since it has more values of grey), and hence a better representation of your displacement, which is why I chose 16bit. Note: If you choose a 32bit floating point image, export to a 32-Bit FP Tiff. Do not export to a 32-Bit FP Black and White Tiff, as this format is not supported by max.
Hit Extract

Creating A Displacement Map in Max

Select the Object in Object List
Step Level Down three times (go to the Level 1 Subdivision Level)
Mesh -> Recreate Level UV's. This is a very important step, so don't miss it. Mudbox does not automatically generate uvs for every subdivision level to save on memory.
File -> Export Selection, save as obj, call it Level1.obj.
Step Level Up three times (go to the Level 4 Subdivision Level)
File -> Export Selection, save as obj, call it Level4.obj.

Now lets go into max.

Open max. Make sure your default renderer is set to the scanline renderer (although feel free to experiment with mentalray if you'd like).
File -> Import, load the TWO obj files you created into max.
Select the Level 1 Mesh. Remember, this mesh needs to have uvs to do all the following steps.
Apply a Turbosmooth Modifier (Turbosmooth takes up way less memory than Meshsmooth, so for high subdivision models, using turbosmooth is a must to conserve memory), set to Render Iterations 3. 3 is the number of iterations between you level 1 mesh and your level 4 displacement map. So if you subdivided your mudbox object to level 6, and exported a level 2 obj file from mudbox, you'd want to set this value to 4.
Click On Rendering -> Render To Texture (Make sure your Level 1 mesh is still selected)

This dialog has many sections. I'll show you what to do for each section.

Under "General Settings", set your Output Path for your displacement map.

In "Objects To Bake", Under "Projection Mapping", choose Pick, and select your Level 4 mesh.
Click the Enabled checkbox beside the Projection.
Uncheck Sub-Object Levels.
Under Mapping Coordinates, choose Use Existing Channel, and set the channel to whatever map channel you want to use, usually Map channel 1, unless your object has more than 1 uv set (if the Channels dropdown has no numbers in it, that means you forgot to put uvs on your lowres mesh.)

Under "Projection Mapping", choose Options.
Method should be Raytrace.
Uncheck Use Cage, and start with a low Offset, say 2.0
Make sure Ray Miss Check is on.
Change Height Map, Min and Max Height to -2 and 2.
Close the Options Dialog

In "Output" hit the Add Button, add a HeightMap.
Under Filename and Type, save a tif file. I change the settings for the tif to 16-bit Color. But if you don't have too much detail, 8-bit may be ok. A higher color depth means a smoother displacement map (since it has more values of grey), and hence a better representation of your displacement, which is why I chose 16-bit. Note: I don't believe it's possible to save a 32bit floating point tif from max. If you want 32-bit, try an exr.
Choose the size of your bitmap. The higher the better, although the higher the more memory the map takes. 1 to 4k is a good value depending on how close you're getting to the mesh, and how much tiny detail you've added.
Hit Render

You should see a bitmap that looks sorta like this. Notice the red blotches. This is telling you that your offset and min and max heights are too low. Ideally the min and max values should be the same height as the highest value in your displaced mesh, but figuring out this value can take some trial and error. You could pick really high numbers, which will guarantee no red blotches, but doing so will produce less detail in your displacement map. So I usually start low, and keep raising it till the red blotches go away on my render.

Go back into "Projection Mapping", choose Options. Change the Offset to 4.0, the Min Height to -4.0 and the Max Height to 4.0.
Hit Render again. This time your red splotches are gone.

Make sure to write down your min and max height values. And thanks to Eric Craft for some help with this technique.

Importing Back into Max

Start a fresh scene of max.
Import the obj file of level 1 that you created in mudbox into max.

Convert To Editable Poly

Rendering using the Scanline and Displace Modifier

Apply a Material that has a diffuse color of 128,128,128 (mid gray)
Now if you used Mudbox to create your displacement map, you need to place a Unwrap UVW modifier on your object, then Edit the uvs, select all of them, and in the Uv Editor choose Tools -> "Break". That will ensure Linear UVs. If you used Max to create your displacement map, YOU DO NOT NEED TO DO THIS STEP.
Apply a Turbosmooth Modifier (Turbosmooth takes up way less memory than Meshsmooth, so for high subdivision models, using turbosmooth is a must to conserve memory), set Render Iters to 3. 3 is the number of iterations between you level 1 mesh and your level 4 displacement map. So if you subdivided your mudbox object to level 6, and exported a level 2 obj file from mudbox, you'd want to set this value to 4.
Apply Displace Modifier to the object.
When using an 8bit or 16bit image, in the Displace Modifier, set the Strength value. So if you extracted your disp map in mudbox, and your search distance was 4.0, then set the strength to twice that number, or 8.0. Or if you extracted in max, it's the difference between your Min and Max Height, in this case those were -4.0 to 4.0, so set the strength to 8.0. If you chose a 32-Bit floating point image, then leave this value at 1.
When using an 8bit or 16bit image, click on Luminance Center, make sure center is at 0.5. If you chose a 32-Bit floating point image, then leave this unchecked.
Click on "Use Existing Mapping".
In the Image area of the Displace Modifier, under Map, click the button that says "None" (Do not put anything in the Bitmap part of the Displace Modifier). In the Material/Map Browser that comes up, choose a Bitmap Map,then hit cancel without selecting your bitmap from the file dialog.

Open an instance of the map inside the material editor, and set the Filtering to None. When your displacement map was originally calculated, it goes through a filtering process to achieve the final result. Then when the geometry gets displaced in max, that geometry gets filtered as part of the standard renderer antialiasing process. If you turn on the image filtering as well, you're basically filtering the bitmap a 3rd time, which may make your final result blurrier than the result inside mudbox. But in some cases, especially if you have a lot of high contrast detail, you can play with turning this setting to "Pyramidal" or "Summed Area" and see if it helps remove any artifacts. But I've had more luck keeping it off. Note, if you chose a 32-bit floating point image, not turning Filtering to None will usually result in an out of memory error. So make sure to turn this to None before selecting your displacement map.
In the bitmap, select your Displacement Map that you created.
Render in Scanline

Rendering using Vray

Under Render, Assign Renderer, Production, choose Vray 2.40.
Now if you used Mudbox to create your displacement map, you need to place a Unwrap UVW modifier on your object, then Edit the uvs, select all of them, and in the Uv Editor choose Tools -> "Break". That will ensure Linear UVs. If you used Max to create your displacement map, YOU DO NOT NEED TO DO THIS STEP.
Optional Step: Apply a Turbosmooth Modifier and set Render Iters to 1. The higher this number, the more accurate your results with vray will be (ie, how close your vray disp will be exactly like your mudbox model). But also, the higher the polygon count. Do not set Render Iters above the difference between the iterations between you level 1 mesh and your level 4 displacement map, in this case, don't set it above 3. As another example, if you subdivided your mudbox object to level 6, and exported a level 2 obj file from mudbox, don't set the turbosmooth modifier any higher than iterations of 4.
Set Vray as your renderer.
Create a Vray Material, assign it to your object.
Add a VrayDisplacementMod modifier to your object.
Check 3D mapping.
Click the "None" button and choose your Bitmap.
When using an 8bit or 16bit image, set the modifier's Amount Value. So if you extracted your disp map in mudbox, and your search distance was 4.0, then set the strength to twice that number, or 8.0. Or if you extracted in max, it's the difference between your Min and Max Height, in this case those were -4.0 to 4.0, so set the strength to 8.0. If you chose a 32-Bit floating point image, then leave this value at 1.
When using an 8bit or 16bit image, set Shift to -4 (this sets a value of grey to be no displacement). If you chose a 32-Bit floating point image, then leave this value at 0.
Make sure Edge Length is set to a value of 4.0 and reduce if you need higher quality (but rendertimes will also go up).
Uncheck Smooth UVs and Smooth UVs At Borders.
Check Keep Continuity.
Set Texmap min and max to numbers that are larger than the pixel values in your displacement map. Start with values of 0 and 1, if you notice any clipping artifacts, try increasing the max and/or decreasing the min.

Open the Render Panel, go into the Vray Tab, and open the Global Switches rollout. Make sure that the checkbox next to Displacement is checked.
Render

Note: I found a really great tutorial similar to this one called Akin Bilgic's Accurate Displacement Workflow, which also contains info on vray for maya and zbrush, well worth checking out.