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3D DIRECT • November 13, 2000

The Artist's Canvas

"Marking Image": The poor man's custom texture work

by Eni Oken

By now it should be pretty obvious that the mark of good 3D work lies not only in the curvaceous, organic NURBS model, but also in the texture work that is applied on to the surface of the geometry. A good 3D artist strives to take care with the texture as much as with the modeling. This involves doing more than choosing a texture map from a commercial library and slapping it on to a model: it requires custom-made texture maps, carefully made to suit the final geometry.

Creating custom-made textures involves painting specific features that complement and suit the model, and in this way, enhancing the geometry. Figure 1 shows how a very specific map was created to be placed over a terrain. Certain features such as a path, stones, and dark edges improve the quality of the model by increasing natural and random feel.

Figure 1: Custom-made texture work allows for careful placement of certain features on to the model. Copyright 2000 Eni Oken, courtesy Eni Oken.

Figure 2: A seamless, tileable texture map applied to the same terrain geometry shows an artificial and computerized look. Copyright 2000 Eni Oken, courtesy Eni Oken.

Compared to the same model with an applied seamless, tileable texture map, it becomes clear that customization can greatly improve the quality of a 3D scene. It is common for poorly executed seamless textures to show a pattern of repetition over the model, which makes the final model look computerized and artificial. See figure 2.

While seamless texture work can be great to save memory when creating realtime projects such as 3D games or online communities, there is absolutely no excuse for not painting custom-made textures when working on pre-rendered projects such as film, broadcast, print, and cinematics.

However, carefully created custom-made texture work does not come without a price: besides taking longer to develop, other costly software such as 3D painting programs may be necessary to create precise customization. These programs can aid the artist tremendously, for they allow painting directly on to the 3D model, thus marking features precisely where the model requires (see Figure 3).

Figure 3: 3D painting programs allow artists to paint directly over the model, marking precisely where specific features should be placed. Copyright 2000 Eni Oken, courtesy Eni Oken.

But what about the starting artist who does not have a 3D painting program? For those artists, there are other alternatives that can become strong assets when entering the 3D market.

"Marking image" and UV mapping coordinates

One of those alternatives is to use a "marking image." A marking image is a grid image that is assigned as a temporary texture to the object (see Figure 4), helping the artist to have a clear understanding of how the final texture map is going to wrap around an object. The successful placement of a texture over the model depends exclusively on the type of UV mapping that is assigned to the geometry.

Figure 4: A grid-like image is assigned to the model as a temporary texture file.

UV mapping depends largely on the 3D software used and the type of geometry generated. For NURBS objects, the UV mapping is usually embedded in the geometry; with no need to assign UV mapping at all. The same goes for parametrically generated polygonal objects. Figure 5 shows how the marking image wraps neatly and uniformly around each object when generated parametrically or by using NURBS.

Figure 5: NURBS objects have embedded UV mapping, so the textures wrap around neatly. Copyright 2000 Eni Oken, courtesy Eni Oken.

On polygonal objects generated using other methods, such as the popular box modeling technique, lofts and lathes, sometimes the UV mapping needs to be assigned specifically to the object created. The UV mapping can then be assigned following certain geometric shapes such as cylindrical, planar, spherical, or box. This type of UV mapping is far from perfect, and the texture map usually stretches and distorts in places where the geometry does not conform exactly to the shape of the UV mapping icon (see Figure 6).

Figure 6: Examples of different UV mappings applied to the same geometry. Copyright 2000 Eni Oken, courtesy Eni Oken.

Understanding how the UV mapping behaves over specific geometry is fundamental for the artist to create an appropriate texture map.

Creating a marking image

Using Adobe Photoshop, you can easily create a marking image by doing the following:

  1. Create a new image, 100x100 pixels, keeping the ruler visible. Drag guide lines to the mid-point of the image, at 50 pixels (see Figure 7a).
  2. Using the rectangular selection marquee, create selections snapping to the guide lines, and fill them with alternating white and black (see Figure 7b).
  3. Select all and use Edit/Define pattern.
  4. Create a new image, this time with 500x500 pixels. Fill it up with the pattern by using Edit/Fill/Pattern (see Figure 7c).
  5. Select the upper row of the image using the rectangular marquee and pick a red color. Fill the selection by using Edit/Fill, with the Foreground color and Multiply composite chosen (see Figure 7d).
  6. Repeat the process filling the lower row with blue, the left row with green, and the right row with yellow (see Figure 7e).

Figure 7: Step-by-step construction of a marking image. Copyright 2000 Eni Oken, courtesy Eni Oken.

Figure 8: The marking image shows exactly how the final texture map will behave, including areas where it will distort and stretch. Copyright 2000 Eni Oken, courtesy Eni Oken.

The marking image is ready and can now be used as a temporary texture file–this allows the artist to visualize exactly how the final texture will behave, including areas that will distort and stretch. It is important to remember the exact location of each color (red on top, blue at the bottom, green on the left, and yellow to the right), so that you can understand how the image is wrapping around each object (see Figure 8). Once you observe the distortion suffered by the marking image, it is easy to compensated for those defects. You can also easily identify where specific features should be places, according to the colored lines and grid.


Applying a marking image as temporary texture before creating the final texture files can be useful for those entering the 3D field–not only as a practical tool, but also to understand how the complex art of UV mapping works. A good exercise for artists of all levels is to apply the marking image using different types of UV mapping (NURBS embedded, parametrically generated, UV mapping assigned) over various types of geometry and observe how each one behaves.

The marking image is particularly useful when detecting seams: the colored lines can clearly display where the image is going to wrap. Figure 9 shows an organic object with the marking image applied on to it. It is easy to identify where the yellow and green rows meet, showing where the seam of the texture will be placed.

Figure 9: The marking image helps detect the seams of a texture over organic objects. Copyright 2000 Eni Oken, courtesy Eni Oken.

Obviously using this technique is not as precise as having a 3D painting program, which allows for direct painting over specific locations. But using a marking image is surprisingly rewarding: understanding how the texture map distorts and bends under the whims of UV mapping can allow the artist to compensate for it when creating a final piece of texture.

Eni Oken is a Brazilian freelance 3D artist based in Los Angeles. As an architect with 13 years of experience in computer graphics, she has participated in the creation of 3D art for numerous interactive projects and has won several awards for her work. You can reach Eni at: http://www.oken3d.com