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UV MAPPING
by Ken
Brilliant
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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.
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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:
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| A model made from ZSpheres using the
Adaptive skin method (left) and painted using TextureMaster
(right). |
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. In
version 1.55b, this method has been enhanced even further with the
creation of Adaptive UVTiles. Not only does the resulting UV map take up
as much of the texture space as possible, but this method also allows for
each square to be assigned a varying size based upon the relative sizes of
the polygons in the model. This allows even less texture distortion than
the already remarkable UVTiles. For more information regarding AUVTiles
and how to use it effectively, please see the Texturing and Materials page
of the Quick
Reference Guide.
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:
- 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.
- 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.
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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. |
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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.
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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.
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| 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. |
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| The UV coordinates of the model are also recognizable. This is
helpful for working in outside 3D applications: |
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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.
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. http://www.uvmapper.com/ This
program can aid us in remapping the UV coordinates. |
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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.
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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.
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For now, just move that geometry out of the way. |
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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. |
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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. |
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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)
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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. |
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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.
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