ZMapper QuickStart Guide
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Normal Map Generation Quick Start
This section is for readers who already possess a reasonable familiarity with ZBrush and the concepts of normal maps. It gives you the bare details you need to get going, without going into material you're likely already familiar with. If you do want to look at certain aspects in more details we've provided all of the appropriate cross-references.
Not included in this section is the process of projecting a previously generated normal map onto a new model with a different topology.
Normal Maps from Subdivision Models
ZBrush exploits its powerful multi-resolution subdivision modeling feature to allow easy creation of normal maps from a single model sculpted at both low and high resolutions. The process is simple:
- Install and load ZMapper.
- Create the low-resolution Polymesh3D model you want to start with, and make sure it conforms as closely as possible in shape to the high-resolution mesh that will be expressing all of the details.
- Using the ZBrush tools you are already familiar with, iteratively subdivide the model and sculpt finer and finer detail, until you have the desired final result.
- Create and select a texture that will hold the normal map. It must be square, and its side dimensions must be powers of two. (256, 512, 1024, and so on.) To capture all of the detail, the normal map area used (i.e. that portion not left blank by the UV mapping) should have about as many pixels as the high-resolution model has polygons. ZMapper will use whatever UV mapping you choose for the model.
- Set the model to its lowest subdivision setting. The selected level is the model level for which the normal map will be generated.
- Start ZMapper. Select Tangent Space N.Map or Object Space N.Map to choose between generating a tangent or object space normal map. Open the Normal &; Cavity Map tab, and press Create Normal Map.
- Once the normal map is complete, exit ZMapper. The finished texture map will be in the texture palette.
Normal Maps from Bump Maps
Another way to produce a normal map is to start with a bump map, and convert it to a normal map. This has the advantage that the resulting normal map no longer has the 'intensity adjustment' problems that can be encountered with bump maps, when transferring them between different programs. The process is straightforward.
- Choose a polymesh 3D model for which you wish to generate a normal map.
- The bump map will be a grayscale texture map that has a UV mapping to the model. Get it into the Alpha palette and select it as the current alpha map. The bump map dimensions should be between one to two times the dimensions of the final normal map. (So if your normal map is 1024x1024, choose a bump map from 1024x1024 to 2048x2048.) Less than this, and there's not a lot of point in using a bump map. More than this, and you risk putting a lot of work into the details of the bump map that will then be 'filtered out' because the normal map resolution is not high enough to support them. If you have enough memory, we recommend using a larger bump map than the normal map, and just keep in mind when editing that very fine details in the bump map will not come through. The higher resolution will still probably improve quality on the larger details.
- Create a texture that will hold the generated normal map. The restrictions outlined in the previous section as regards to normal map dimensions apply. (Square, power of two.)
- Set Tool:Displacement:Displacement Intensity to about 0.05. After a highly rigorous evaluation, this figure was chosen because it seems to work pretty well most of the time. Feel free to experiment. This is the setting that tells ZMapper the chosen alpha map is to be considered a bump map, and with what intensity to apply it.
- Go into ZMapper and, as in the previous section, choose the type of normal map to generate and then create it. When it has been created, exit ZMapper and your normal map will be in the texture palette and ready for use.
Creating Bump Maps In ZBrush
You've no doubt thought, "Aha, I can use ZBrush to create great bump maps as well, to use in the above process." You're right, of course. There is a plethora of ways to generate the requisite grayscale bump map from within ZBrush. You can paint directly to the 2.5D canvas and then grab an alpha off of there. Using Projection Master with the BumpViewerMaterial, you can paint a grayscale texture onto your model, and then create an alpha from that. The experienced ZBrush user will no doubt come up with many more ways to do this.
Normal Maps from Both Bump Maps and Subdivision Models
It's easy enough to combine the above two ways of generating normal maps. Just make sure you have an appropriate bump map alpha selected, and that you have a subdivision model set to its lowest level. Then go and create the map as usual. Both the geometry and the bump map will be incorporated.
Cavity Shading
Strictly speaking, cavity shading (a form of simulating ambient occlusion) has nothing to do in concept with normal mapping, but it turns out to be easy to incorporate a cavity shading effect into the normal map process, at no further end-use cost. ZMapper has the ability to produce and integrate cavity shading. The process is not difficult, but there are a number of settings that affect the final result, see the ZMapper reference and examples.
Caveats and Tips
- ZMapper will do its best, but no normal map generator can compensate for models whose large-scale structure varies significantly between the high-resolution and low-resolution models. In other words, don't turn a hillock in your low-resolution model into a tree in your high-resolution model, and expect to come up with anything intelligible.
- Another no-no is producing elements in the high-resolution model that 'fold over', where they did not do that in the low-resolution geometry. This produces a situation where one point in the normal map must represent two different normal directions (depending on viewing angle, no less!), and that simply isn't possible. You'll probably end up with a normal map, but not one you'd want to use.
- Creating normal maps between a very low-resolution model and a very high-resolution model can be problematic. For example, if your starting geometry is a single quad, and you then take that up to a million quads for the high-resolution model, ZMapper may have difficulties. The solution is to start with a higher-res low-resolution model (say 100 or 10,000 quads), and produce a normal map for it. Then, you can remap that normal map to a single quad to get the effect you want.
- There is a basic example in the "ZMapper Examples" section which nonetheless manages to touch on almost every issue discussed above.
