ZBrush To Softimage XSI 16-Bit Displacement Guide · PDF file 2 1. introduction 3 2. model...

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Transcript of ZBrush To Softimage XSI 16-Bit Displacement Guide · PDF file 2 1. introduction 3 2. model...

  • ZBrush To Softimage XSI 16-Bit Displacement Guide

    Greg Punchatz

    Senior Creative Director, Janimation

    November 10, 2005

    © 2005 Pixologic, Inc. All rights reserved.

    Pixologic and the Pixologic logo, and ZBrush and the ZBrush logo, are registered trademarks of Pixologic, Inc.

    Photoshop is a registered trademark of Adobe Systems, Inc.

    Softimage and Softimage XSI are registered trademarks of Softimage, Inc.

    All other trademarks are the property of their respective owners.

    Please mail comments or suggestions about this document to doc@pixologic.com.

  • 2

    1. INTRODUCTION 3

    2. MODEL SETUP IN XSI 3

    3. WORKING IN ZBRUSH 3

    3.1. OPENING THE MODEL IN ZBRUSH 3 3.2. CHECKING THE MODEL 4 3.2.1. FIXING OVERLAP PROBLEMS IN MODELS YOU’VE ALREADY MODIFIED 6 3.3. DETAILING THE MODEL 7 3.4. CREATING A DISPLACEMENT MAP 7 3.4.1. MORE ABOUT DISPLACEMENT OPTIONS 9

    4. BACK INTO XSI 10

    4.1. IMPORTING THE OBJ AND DISPLACEMENT MAP 10 4.1.1. SETTING UP THE DISPLACEMENT MAP OPTIONS 10 4.1.2. CHECKING THE DISPLACEMENT GEOMETRY 12

    5. WORKING WITH MULTIPLE MODELS 14

    5.1. USING XSI TO SET UP THE UVS FOR MODEL MERGING 14 5.2. DETAILING THE MERGED MODEL IN ZBRUSH 18 5.2.1. SETTING UP ZBRUSH GROUPS TO EASE YOUR WORK 18 5.2.2. EXPORTING 16-BIT DISPLACEMENT MAPS 19 5.2.3. EXPORTING 32-BIT DISPLACEMENT MAPS FROM MULTI DISPLACEMENT 2 20

    6. ALL DONE! 21

  • 1. Introduction This guide covers transferring models and displacement maps between Softimage XSI® and ZBrush. It will cover most of the dos and don’ts in both programs, but you will need a basic knowledge of both packages to understand some of the concepts.

    These workflows makes use of a freely available ZBrush plugin called the Alpha Displacement Exporter, available for download at www.zbrushcentral.com. Please make sure you have it installed before going further.

    2. Model Setup in XSI We’ll need to start with a model in XSI with a single set of UVs and then export it as an OBJ file, as ZBrush can only read one set of UVs. We need to make sure the model has certain properties for everything to work correctly:

    • The model must have just a single set of UV coordinates, as ZBrush works with only one set of UVs at a time.

    • The model cannot have any overlapping UVs. Overlapping UVs will (of course) cause undesired visual artifacts, and may also cause ZBrush to have difficulties as it creates a displacement map. Tip: There is an option in XSI’s UV editor that will show you polygon overlaps highlighted in pink.

    • The mesh should consist of only quads and tris. In addition, there should be as few tris as possible, and they should be in the less visible areas of the model. Tip: You can use the Select n sided polygon tool in the MCP>select>n- sided polygons of XSI to find out if your mesh is has any five sided polygons.

    3. Working in ZBrush

    3.1. Opening the Model in ZBrush Now we need to import the model’s OBJ file into ZBrush. In ZBrush, models are called tools. This is different from traditional 3-D packages. So, to get your model into ZBrush you need to use the Tool:Import button under Tool menu at the top of your ZBrush interface, as shown in the figures below.

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    Fig. 1. THE TOOL PALETTE

    Fig. 2. THE TOOL:IMPORT BUTTON

    Tool:Import will bring up a standard dialog allowing you to select and open the model.

    And we should mention this right now, too:

    To save your model you must save it as a tool. This is done with the Tool:Save As button. Saving a document (Document:Save or Document:Save As) will not save a model.

    3.2. Checking the Model After we import our model/tool, in this case a chimp I'm working on, there are several things we should do before we begin modeling.

    First off, ZBrush provides a UV check tool that will show in red areas where problems are that we need to eliminate before we continue. Even after checking for this in XSI, I will still find from time to time I have missed the few very small overlapping UV's. Press Tool:Texture:Uv Check (the Uv Check button in the Texture subpalette of the Tool palette) to perform the UV check.

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    Fig. 3. THE UV CHECK BUTTON

    Overlapping UVs show up in red. (Remember to rotate your model to check all of it). In this case I've missed a spot on the chimp’s forehead and also a few inside the mouth.

    Fig. 4. OVERLAPPING UVS SHOWN BY UV CHECK

    If you do find a problem, you need to return to XSI to fix it. As you can see in XSI, I missed these polygon overlaps.

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    Fig. 5. OVERLAPS IN THE ORIGINAL XSI LAYOUT

    Fix the problems and bring the model back into ZBrush.

    3.2.1. Fixing Overlap Problems in Models You’ve Already Modified If you don’t become aware of an overlap problem until you detail the model in ZBrush, you can still fix the overlaps easily. Here’s what to do:

    1. Make sure your ZBrush model is at its lowest subdivision level. 2. Export the tool to its OBJ file, and then open that file from Softimage. 3. Fix the problems, and then save that file again from Softimage. 4. Import the file into ZBrush again, making sure that the corresponding tool is

    selected and still at its lowest subdivision setting. This works because importing your OBJ file, while you still have your tool selected and at its lowest subdivision level, simply updates the UVs of the tool. This changes the UVs and any modifications to the lowest resolution of model you made while in XSI, yet it keeps all the detail work on the higher subdivision levels that were created in ZBrush. In fact, I’ve often completely redone my UV layout after detailing in ZBrush, using this technique. Of course, never change the polygon topology while editing in XSI. In other words, don’t add or remove any points, polygons or edges; moving points around is fine.

    When moving a model to XSI and back, vertices are occasionally put in a different order. The problem won’t show itself until you raise the subdivision level on your ZBrush tool. If the polygons were reordered, you will know immediately as you will have a giant mess on your screen1. If this happens, and you must still fix your UVs outside of ZBrush, try exporting a dotXSI file from Softimage and using a program like Deep Exploration® to convert your dotXSI to OBJ.

    1 This does not appear to occur when using ZBrush with XSI 5.

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    3.3. Detailing the Model Now that we have cleaned up our UVs, it’s time to detail the model. ZBrush has a million and one tools for detailing and sculpting your model and I can’t possibly cover that in this tutorial. But, I do recommend purchasing some DVD training material to get you up to speed quickly. Gnomon and Digital Tutors both have very good DVDs on learning ZBrush. Below is the chimp model after detailing in ZBrush.

    Fig. 6. CHIMP MODEL WITH DETAILS DONE IN ZBRUSH

    3.4. Creating a Displacement Map When your model is detailed, it’s time to create a displacement map and export it and the model to XSI. Here’s how to do it:

    1. If your system resources permit, subdivide your model an additional level (or more) beyond the highest level you used for detailing. This can improve the final result. I subdivide as many times as my system allows.

    2. Now, set the model’s subdivision level (using the Tool:Geometry:SDiv slider) to display that model’s target geometry, i.e. the geometry the displacement map will be applied to. This is usually level 1. See figure Fig. 7`.

  • 8

    Fig. 7. SETTING THE SUBDIVISION LEVEL

    3. Export the model to an OBJ file.

    4. Set appropriate values for generating a displacement map, in the Tool:Displacement subpalette. Those shown in the figure below generally work well. We’ll talk about some of these settings in more detail in a moment.

    Fig. 8. DISPLACEMENT SETTINGS

    5. Press Tool:Displacement:Create DispMap to make a displacement map. It will appear as an alpha texture in the Alpha palette.

    6. In the Alpha palette, select the newly created displacement map.

    7. Look up and record the value of the Alpha:Alpha Depth Factor slider. This is a scaling value you’ll enter into XSI, to tell it how much to scale values in the displacement map while actually generating displacements. A convenient way to remember this value is to include it as part of the file name when you export the alpha.

    8. Use the Alpha:DE Options button to bring up the Alpha Displacement Exporter, shown below. Choose the R16 setting, make sure Status is On, and set Vertical Flip to Yes. Make sure the other settings are as shown.

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    Fig. 9. ALPHA DISPLACEMENT EXPORTER

    9. Click the Export Current button and save as a .TIF file. Remember, the file name is a good place to record your Alpha Depth Factor.

    3.4.1. More About Displacement Options I tend to use the same settings for everything (as was shown in Fig. 8), but you can try other things. Here are brief descriptions of some of the displacement map options you might want to alter or play with:

    • DPRes: Controls how big your displacement map will be! • DSubPix: Causes ZBrush to do additional levels of subdivision while creating

    displacement maps. Setting it higher will give better results, but cause map generation to take more time.

    I