When and Why to Retopologize
This is always sort of a gray area for designers, and there is no definitive time to retopologize. Oftentimes you’ll want to make sure you retopologize before getting too far into details, as sometimes such details can get lost in the process when creating new topology and be difficult to get back.
Once you feel comfortable that large forms and masses in your design won’t be changing much, you’re probably safe to retopologize. If you think that the eye sockets, for example might need to move to the front of the head, rather than be on the sides of the head, you should wait. If your creature has horns and you might end up getting rid of them, you should also wait. If you think the cranial mass might need minor changes to the shape or volume, you can retopologize.
The goal is to have a nice clean mesh of evenly distributed polygons on your creature; that is why we retopologize. Having a clean mesh enables us to do things like sculpting, texturing, and posing details with more ease.
Prepping for Retopology
Before retopologizing your creature, there are a few things we can do to set ourselves up for success, including merging SubTools, DynaMeshing, duplicating, and decimating.
Merge SubTools
Merge any SubTools you want to be combined into the final mesh. For example, if you’ve inserted things like tentacles, horns, or other fun stuff and have not yet integrated them into your mesh, do that now. A good way to think of what to merge and what not to merge is to ask, “will this need a different material?” For example, tentacles share the same skin material as the body, so they would likely be merged, whereas things like gear, weapons, eyeballs, and teeth would use different materials (cloth or leather, metal, shiny and reflective surfaces, and so on) so they would likely be kept separate.,
- Make sure you’re at the highest subdivision level you want for each SubTool you’re going to merge. Delete all other subdivision levels by using Del Lower or Del Higher commands in the Tool > Geometry sub-palette.
- Merge SubTools using either Merge Down or Merge Visible commands in the Tool > SubTool > Merge sub-palette.
DynaMesh
With your SubTools merged into one, go to Tool > Geometry > Dynamesh to convert this merged SubTool into a DynaMesh.
- Make sure you give yourself enough resolution so that no detail is lost. A resolution setting of 128 or 256 would be a good place to start and you should increase that value only if needed. If you convert to DynaMesh and lose detail, undo the conversion before increasing the resolution, then increase and try again
- Be sure to save your ZTool before this conversion step because—depending on your computer’s hardware—this process might be very taxing and ZBrush could crash.
- Make sure Project (in the Dynamesh sub-palette) is turned on so that all details are projected onto the resulting DynaMesh.
Duplicate
You will want to duplicate the SubTool in order to save a copy of its current state. We'll later use that duplicate to reproject details that might get lost during the retopologizing process.
- Use Tool > SubTool > Duplicate to create the copy of your selected SubTool.
- For organization, you can rename the duplicate SubTool by going to Tool > SubTool > Rename. Call it something like “dummy” or “duplicate.”
- A useful way to cycle through SubTools is to use the Up/Down arrow keys. If you have three or more SubTools, press “N” to list all SubTools.
Decimate
Retopologizing a model can be a taxing process on your system’s memory. In order to help ZBrush execute that process without crashing, it can be a good practice to first decimate your model before attempting to retopologize it. See the next page for more on "Decimation Master."Decimation Master
Found in the Zplugin menu, Decimation Master is a plug-in that reduces the polycount of your mesh while keeping as much detail as possible.
Masking
- You can preserve more detail in areas that are masked. If you want to affect the decimation using masks, the masks must be applied before Pre-processing the SubTool.
Caption: “At the top, the ZTool has been masked in a couple areas: the mask on the head is painted at 100% opacity, whereas the mask on the nose is painted at about 50% opacity. The middle image represents the resulting decimated mesh using the masks. Notice how the head has more detail preserved because of the darker mask. The bottom image represents a decimated mesh with no masks applied."
Set Options
- Go to Zplugin > Decimation Master. The Pre-process Current and Pre-process All commands will allow you to decimate your current SubTool or all visible SubTools, respectively. If you choose Pre-process All, you will only be able to decimate them to the same resolution. Pre-processing must happen before decimating. When you click a Pre-process button, you’ll see a progress bar at the top of your interface. Wait for this to finish before doing anything else in ZBrush.
- Decimate
- Choose a decimation quality. The higher the percentage, the less decimation—you are decimating to a percentage of your current resolution. A 100% setting means no decimation. You can also specify a certain number of points (vertices) or polygons, settings are expressed in thousands of points or polygons. If you wanted 100,000 polygons, set the slider to a value of "100."
- When you've set the quality, press Decimate Current to decimate the selected SubTool, or select Decimate All to decimate all visible SubTools.
Decimation Master does not produce meshes that are production-ready from an animation standpoint. It will produce meshes, however, that are suitable for rendering. It is a common workflow to finish a design, decimate it as low as possible without sacrificing detail, export that decimated mesh, and render it in a third-party program. Reducing the polygon count through decimation can result in much faster rendering times.
ZRemesher
Process
- Set the Tool > Geometry > ZRemesher > Target Polygon Count to the number of polygons you want your retopologized model to have. This slider’s value is in thousands. A value of 10 would result in a mesh containing approximately 10,000 polygons.
- Go to Tool > Geometry > ZRemesher > ZRemesher. While ZRemesher is working its magic, you’ll see an orange progress bar at the top of your interface. If you need to, press the Esc key to cancel the process, otherwise just wait for it to finish.
Reprojection
Retopology oftentimes softens the surface of the new mesh, in which case you’ll want to reproject from your duplicated SubTool (source mesh) to your newly retopologized SubTool (destination mesh). It’s important that no sculpting happens between retopologizing your mesh and reprojecting the details. Reprojection relies on the two meshes sitting pretty much right on top of each other to capture the details. It will not reproject the opening of a mouth, rotations of limbs, or any large changes of that nature.
- Make sure the source and destination meshes are the only two SubTools visible.
- Select your destination mesh and step down to the lowest subdivision level.
- Store a Morph Target so that you can erase any imperfections from the projection process. It’s not uncommon to have points shooting off into space if source and destination meshes are not right on top of one another, there is a lot of overlapping or folding of forms, or there are openings or holes in your mesh.
- Select Tool > SubTool > Project > ProjectAll
- If you see any imperfections or artifacts from the projection, use the Morph brush to fix them.
- Sometimes there will be areas that you don’t want to project. If this is the case, mask any areas that you do not want to be projected. It’s common to mask any open edges as they can easily cause problems when projecting. By masking them first, you’re saving yourself from having to go back in and morphing them back into place.
- If you still don’t have all of the details from the source mesh, subdivide your destination mesh (Ctrl+D) - or step to the next higher resolution (D) - and project at this resolution. Repeat this process until you see all of your details.
- A good way to compare the source and destination SubTools is to turn on Solo and use the Up and Down arrow keys to switch back and forth between the two SubTools.
- Delete your source mesh, as you won’t need it anymore.
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