"UV mapping " by Ken Brilliant
ZBrush does a great job of protecting the artist from too many technical decisions during the creation process. For example, once you model an object, you can immediately start painting textures for it in a 3D fashion using Texture Master or 3D copy. You do not need to worry how that texture wraps onto the model. ZBrush objects inherently have the best mapping method associated with the models when they are first created, i.e. when a Sphere 3D is drawn on screen or an adaptive skin is made from Zspheres. Objects made from Zspheres, either through the adaptive or unified skinning method, are assigned the UVTiles mapping. This assigns a small rectangular area of texture to each polygon. Here is an example:
A model made from Zspheres The model painted by the adaptive skin method. using texture master.
The great thing about UVTiles is that there is no texture stretching. If you examine the texture image made during the process, you can get an idea of how it maps to the model.
The UV template
Each face on the model is represented by an equally sized square. The only downside to UV tiles is in the layout of the resulting image map. It is virtually impossible to work on this map unless it is applied to the model and in ZBrush. Most of the time, this isn?t an issue, but there are benefits to being able to work directly on the flat 2D image map:
1. It is easy to alter a map when it is clear what you are looking at. This can be done in ZBrush or any other traditional paint program.
2. When exporting models for use in other 3D programs, it is helpful to be able to adjust the UV maps (the layout of the polygons and how they relate to the image map.)
Luckily, in ZBrush, you do not have to leave everything in the default settings. This goes for UV mapping as well.
Under the Texture panel are the options for changing the UV mapping
A description and example of each follows:
Uvc: cylindrical mapping. This wraps the texture around the model as a cylinder.
Uvp: Planar mapping. This projects the texture straight through as if by a flat card.
Uvs: Spherical mapping: This wraps the texture around the model as a sphere.
The way these mapping methods are projected is determined by the orientation of the model in the Object Preview window.
It is important to determine which mapping method is best suited for your model. A good way to do that is to look at the general shape. For models such a heads, cylindrical or spherical are the best choices. The model in this example will use cylindrical mapping due to its shape.
Before you even take the time to paint any texture, you should see how the mapping works on your model. Attach a default texture to the model after you?ve assigned a mapping method. The checker texture works very well because it reveals potential problems such as texture distortion.
The cylindrical mapping with the checker texture on the example model.
Notice the large, stretched areas where the checker pattern is distorted. This is due to the poles (the top and bottom) that come with mapping methods such as cylindrical and spherical. Poles cannot be eliminated, but they can be moved to out of the way and less conspicuous places. To map this model better, it needs to be rotated 90 degrees on the X axis. Do this through the deformation panel. You should seethe model position change in the preview window.
Now, when the model is viewed with the checker texture, the distribution of the squares is much more uniform.
The nasty poles have been banished to the top and bottom of the head. It is easier to deal with the distortion here.
You can now rotate the model back.
When the checker board texture checks out, you can dive into the real painting. The model painted using texture master.
Now you also have the advantage of painting on the 2D texture as well. To do so, resize the document to the dimensions of the texture. This is usually determined when you start texture master, under the Texture size slider. If this was set to 1024, then set your document size to 1024 width, 1024 height. Use the Flip v button on the texture to get it to orient in a more familiar way, select the flat material, and fill the canvas (Ctrl+f). The texture will neatly fill the canvas, and you can continue to paint on it
in this fashion using any and all the tools at your disposal.
You can also paint difficult areas, such as the inside of the mouth, which would be hard to reach while working on the 3D model.
To get the new texture back onto the model, use the MRGBZ Grabber tool. Turn off Auto crop and Shaded RGB, and then select the whole canvas. The new texture will appear in the Texture panel.
Apply Flip V to it again, select your model and draw it on the canvas. The adjusted texture will fit right back into place on the model.
The UV coordinates of the model are also recognizable. This is helpful for working in outside 3D applications:
Texturing a full body model
Remapping an object is pretty straightforward when it is something simple when it?s a head, but what if the model is full body?
For a complex object such as a body, none of the 3 aforementioned mapping methods available will work well alone. They might work for some areas of the body, but not others.
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Most high-end traditional 3D applications have UV editing features. These allow the user to map sections of the model differently to get the best coverage for that particular body part.
The good news is that you don?t need a high end program to edit the UV coordinates. There is a readily available utility called UV Mapper. This comes in 2 versions: UV Mapper classic is free, and UV Mapper Pro, which has a few more features, is inexpensive. www.uvmapper.com This program can aid us in remapping the UV coordinates.
Once you have built your model, export it from ZBrush as an .obj file. Open UV Mapper, and load the model. You may or may not have UV coordinates already assigned to the model, but it doesn?t matter for we will be remapping the whole thing. To get started, assign a planar map to the whole model.
This will allow us to see and select the geometry. What we need to do is examine the figure, then break it down and determine which mapping method will work for which area of the body.
Starting from the top, the head is really very round, so the spherical method will work for that. Select the faces of the head and assign a spherical map to them along the Y axis.
For now, just move that geometry out of the way.
If we examine the body, it is pretty cylindrical. Select the faces from the neck to the waist, and give them a cylindrical map. Move those aside. We will arrange all the maps later.
The arms are much like tubes, so cylindrical mapping will work there. Select the faces down to the hands and apply a cylindrical map along the x axis.
A Planar map will work for the hands, but we can get some variety by splitting the top and bottom. (A feature that can be selected when assigning a planar map)
Since the legs are bent, a straight cylindrical map won?t work. A better plan is to break them up into planar maps; each representing the sides, front and back. The quickest way is to use the box mapping method. This will automatically assign a planar map to the geometry based on its orientation.
There still needs to be work done after this operation as some of the faces may overlap each other. Correct this, and even fit the pieces back together if you can determine where they go. The other option for the legs is to carefully select the faces and assign a planar map to them on the appropriate axis by hand. The feet were mapped with planar maps on the Y axis. If the geometry doesn?t map correctly, you can always select it differently and reapply the map.
Arrange the maps in a manner so that they make the best use of the space. You can make certain maps larger and therefore more detailed portion of the texture by sizing them bigger than the rest. The head is a good candidate for this. ZBrush does a seamless job of painting across maps of different proportions, but if you plan to paint in another program, be aware that a single brushstroke can vary when painted across maps that are not in proportion with each-other.
If you are using UV mapper pro, you can test the texture for stretching by assigning one of the pre-built checker texture maps and viewing the model (Tab key)
When the maps look decent, export the model out again, and import it into ZBrush. Now, you can paint happily in ZBrush with all its tools. You can even continue modeling the geometry.
A trick here is to assign the UV maps while a model is simpler in shape, and then continue sculpting to make it more complex. The only thing you shouldn?t do is add or remove geometry through divide or optimize, as this will mess up the UV coordinates.
Of course, the UV map can be painted on in the flat 2D mode.
Exploring UV mapping does take planning and thought, but the efforts will yield options for working with the textures. Don?t be afraid to get ?under the hood? of your model construction.
(c) Ken Brilliant, firstname.lastname@example.org