ZBrush Connection
3D modeling software these days are becoming increasingly easier to use. The ability to work in a perspective view and magnet tools are just a couple features that add to a more intuitive modeling experience. In fact, users can pretty much jump into modeling with very little or no preliminary work.
But there’s still a fair amount of technical knowledge that needs to be kept in mind when modeling, whether it be polygonal or NURB based. And thinking about these requirements as you work can slow down the creative processes. Wouldn’t it be great to work 3D data as quickly as one would sketch on paper?
The good news is that you can. There are a few software packages that specialize in "virtual sculpting". You generally work with an airbrush like tool, but instead of spraying color, they push and pull geometry. This method is by far the easiest and most intuitive way of digital sculpting. No needn’t worry about anything technical as you shape the geometry. Just go with what suits your eye.
Unfortunately, this freedom does come at another sacrifice; the 3d data usually needs to be fairly dense to get the desired effect and sufficient detail. If your intent is to have a model suitable for animation, this data doesn’t lend itself to editing or making morph targets. The usual procedure for polygonal animation models is to create a low resolution "cage" object that is subdivided and drives a higher resolution version upon rendering. The density and layout of the 3d sculpted models just won’t work for this. But there are ways to get the best of both worlds.
MODELING
ZBrush by Pixologic, is an interesting 2D/3D hybrid painting and illustration software. It doesn’t have any animation features or standard quad view orthographic modeling windows. Instead, you create images by virtual sculpting 3D data and a combination of its unique 2.5D brushes, which give the illusion of 3D. There is some stunning imagery done with this package. Check out their web site at www.
The focus of this article concerns ZBrush’s sculpting and 3D painting features and incorporating them into a modeling and texturing workflow for producing models that work for animation purposes. The standard sculpting procedure in ZBrush is to start with a primitive such as a sphere or imported objects, and then used the brushes to shape it. See
Figure 1.
Figure 1. Sculpting has begun on a default sphere.
This is both fast and fun and allows for some nice 3D sketching sessions. If you see a shape or form you like, then develop it further. Divide the mesh in masked off areas to add detail and work it until you are happy. See Figure 2.
Figure 2. The finished ZBrush sculpture
You can export this model out as an .obj or .dxf file format. Here’s where the technical process comes into play. You will load this model into your favorite modeling package and use it as a base to rebuild a lighter, animation friendly model.
This can be done is several ways. The model in this example was rebuilt in a face by face fashion. The points were used as a basis for creating new faces. Attention was paid to keeping a good "flow" of polygon configuration to allow for natural bending and wrinkling. This sometimes means rebuilding it different fashion than the dense grid-like layout of the original. It’s important to add just enough faces to recreate the original shapes. See Figure 3.
Figure 3. A lighter polygonal model is rebuilt over the dense ZBrush model
To make the process a little less visually confusing, cut the original model in half and hide geometry you aren’t working on at the moment, Some areas might need to be created from scratch, such as the inside of the mouth.
Figure 4 shows the comparison of 1: the original ZBrush model and 2: its wire frame data. 3: the reconstructed cage model and 4: the subdivided finished model
Figure 4. The comparison of original model and reconstructed model
This is just one technique. Another method can be to build spline patches or NURBS over the original model. Or, the original model can be used as just a background guide similar to a drawing.
The reverse technique of the one described above is to rough out a fairly low resolution form in ZBrush, export it and then add, rearrange and cut new faces to form details such as the eyes and mouth See Figure 5.
Figure 5. A low resolution, low detail form was created in ZBrush and reworked
TEXTURING
Once you are happy with the reconstruction, you can bring it back into ZBrush for additional sculpturing and texturing. Although not an official 3D paint software, ZBrush has some formidable features that make it quite usable for this stage.
Your model will need UV map coordinates. These can be created in another software or in ZBrush, although most other UV mapping features in other software have more control for how individual faces can be mapped. ZBrush has the standard cylindrical, spherical and planar mapping methods which can be picked from the Modifiers/Texture menu once the file is imported. One very nice feature is ZBrush will adjust your image maps to compensate for the stretching and pinching that appear on the tops or poles of cylindrical and spherical maps.
Import your reconstructed model back in as an .obj and draw it on the screen. ZBrush has the 3D copy feature which allows you to "pick up" color data from the screen background and map it onto the model, but there is a Zscript (the ZBrush native scripting language) called Texture Master that greatly simplifies the process. This script is free for download off the ZBrush site, so there’s very little reason to do it the "old" way.
Once your model is on screen, load the Texture Master Script. A very clean interface appears on the bottom of the screen. See Figure 6.
Figure 6. The Texture Master interface
Creating textures here is a process of dropping the model to the canvas, painting, then picking it back up to view the results in the round, rotating it and dropping again. This is just a matter of pressing "G". While the model is dropped, it cannot be rotated. You can utilize all of Zbrush’s brushes and alphas at this stage, so experiment! You can copy the color information on both sides of the model by pressing the B+F button in the texture master window. This saves a good deal of time. See Figure 7.
Figure 7. Texture information can be picked up on two sides of the model by pressing the B+F button in the Texture Master interface
One of the best features of 3D painting software is the ability to see your bump map information on your model as you work. This can be accomplished in ZBrush as well. Assign a material such as the Basic Material and adjust the color bump slider. You will see changes in the depth information on the model. (FIG) Many times, though, your color map won’t necessarily reflect the bump information, that is, you may not want to have a darker color in every wrinkle or light one on every raised bump, which is how ZBrush and other 3D packages interpret bump maps. In this case, you’ll need to make a new map to use just as the bump, and paint in shades of gray to determine bump depth. Create a new texture map for the model and begin the Texture Master process again with shades of gray. This is not as visually clean as you do see the color on the model, but you can get a good idea of how the actual bump map will look when rendered in your 3D package. Be sure to save out the texture map or model with a different name so you don’t overwrite you color version. See Figure 8
Figure 8 The bump map is painted on the model using shades of gray.
Don’t forget to save often. You can export out the textures alone, or export the whole model again, which will also save out an image file as long as you have the "TXR" button depressed under export menu.
You can also work on the image alone on the canvas. Clear the layer (Ctrl+N) and resize the document to be the same size as the image map. If you don’t the texture will fill the canvas at it’s current size. Select the image map under the Texture menu, and press "Fill" under the Layers panel. See Figure 9.
Figure 9. The texture map can be worked on in a traditional flat manner
Here you can continue to paint with ZBrush’s myriad of brushes and tools. You can then export out the document as the image map, or assign it back to your model for continued editing with the MRGBZGrabber tool.
If you want to continue to sculpt the model, you can as well. Export the revised model when done.
This is just one Texture Master example. You can view several tutorials its usage by pressing the "Show and Tell" button.
Back in your preferred rendering package, you assign the texture images to the model with either the UV coordinates you set up beforehand or the one created in ZBrush. Do test renderings, and go back into ZBrush if necessary. See Figure 10.
Figure 10. The finished model.
Incorporating alternative software such as ZBrush into your tool set can open new channels of creation. By sculpting your models in the fashion illustrated here, you can free your mind in the most crucial stages of the creative process, and concern yourself with the technical side later.