Choosing “Custom…” from the menu brings up the texture application dialog box where you can select the parameters that a texture map will change. There are a lot of options on this screen, but most of them are very straightforward to use and understand. Beyond changing the color of the object, there are options for every other surface parameter and a few esoteric functions. The default setting for texture mapping is to use the color in the image for the object color.
Every surface has five properties used for shading: ambience, diffuse, specular, reflectivity, and transparency. A texture (PICT) can be applied to any or all of these attributes, either complete replacing the color (i.e. selecting Diffuse Color, Specular Color, etc.), or combining the “brightness” (or “V”) of the image with the object color. This can produce especially striking results when one texture map is used for the object color, and other texture maps are used to add detail to the ambient, diffuse, specular, reflectivity or transparency parameters.
In addition to using the color, or brightness level, of a picture, the texture mapping controls can take advantage of the fourth overlay layer (or Alpha channel). The most powerful use is as an application stencil, so that the color of the picture is only applied in certain areas. While the rectangular shape of picture files is useful for some textures, the real world is filled with circular and odd shaped images and emblems. By painting a white field in the alpha layer using a paint package, and selecting the Stencil check box next to the desired property; the colors, or brightness, of the picture will only be applied to the material inside the stencil.
(If the Invert Alpha box is checked, the stencil is reversed, and the texture will be applied outside the original painted area of the Alpha).
The alpha can also be used for a bump map so that the color and bump of an object can be created together in a paint package, and will align on the object without additional effort.
Esoterica:
Beyond the basic controls, Presenter 3D offers advanced texturing controls originally custom designed with productions companies producing special effects for film and broadcast television. These controls can aid in producing models and images that rival the best work of master model-makers and model-painters.
Alpha Channel: Forget reality now, we’re talking about production hacks designed to foil reality because reality is not flexible enough. This control allows you to create holdout areas in the image where the background will show through. Essentially this opens a hole in hyperspace to let “space” show through. The resulting image will not cover over a background image during post-matting operations. This is not an alternative for transparency, but a tool to achieve custom layering effects in a compositing program.
Spectral: This control varies the glossyness (or highlight size) of the surface dependent on the brightness (V) (or alpha level, if A is checked). This mimics the high-end practice of painting miniatures with varying layered coats of paint to give the surface an aged patchwork look. As the model rotates and the highlight moves across the object, the highlight changes in size; Hollywood’s best producers will be thinking you’ve just filmed a $50,000 miniature.
Refraction: Ray tracers are great at rendering glass, but it's too perfect. Even applying a bump map doesn’t solve the problem because the thickness still seems perfect; or so much bump is applied that you can’t see through the surface. In the real world, glass is a liquid, and it is constantly flowing (very slowly), and is almost never a perfectly consistant thickness. Texture mapping the refraction index will change the way that light bends, simulating varied thickness and impurities, giving the glass a real-world look.
Invert Alpha: This control allows you to reverse the values in the alpha channel, just in case the alpha channel values are opposite of what you actually want.
Invert Transparency: This control is usefull if you are using the alpha channel to apply a color, and create a holdout around the same area. Because Presenter uses transparency and not opacity mapping, the object will be transparent where the applied map is white.
