Realism is hard to attain. Perhaps you have struggled as I have with making things look realistic. You try your best, but it still ends up looking more like a lego commercial than a picture which inspires reverence and awe. It's hard to feel like an artist exploring deep philosophical themes when you keep getting e-mail orders for these plastic lego sets.

To help keep the lego orders down, I'll share with you the basics of the more complex mapping techniques. But, before I can tell you the specifics on the techniques, I must explain the key element in them all.

The Key Element

The most important thing to grasp when working with these more complex mapping techniques is what I call "Altitude map concept." To grasp this concept, I must first have you close one eye, (keep one open to read) and imagine you have just opened a large Rand-McNally atlas of South America. Got it? Find the specific map in your mind called "landforms." It should have the different altitudes shown by different colors. Ok, now look closely at the mountains of Peru. In this case, the high altitudes are colored purple, with green being the plains. You'll notice on your map that across most of Peru, there's a thick line of purple, right next to some green. You can even imagine a 3d model of Peru, where the purple areas would be tall mountains and the green areas would be sea-level plains.

That's what the "Altitude map concept" is all about. Except that white is high and black is low. In general the lighter the area, (higher RGB value) the higher the bump map is, and the darker (lower RGB value) the color the lower the bumps are. With bump mapping, this can be adjusted oppositely by entering a negative number, but white=high is the norm. Once you have this concept down, it's easily applied to other map types. Knowing this, now we'll get down to the actual map types.

BUMP MAP

This type of mapping generates surface pseudo-shadows from the texture colors to add the illusion of bumps, plates, dents, scratches, etc. I generally use RGB mapping, and average heights of 25%-50%. Though it varies by situation, I commonly use Bump mapping for everything from hatches, vents, and plating on vehicles to make more realistic textures.

TRANSPARENCY MAP

In this kind of mapping, the darker the texture color, the more transparent the object will be; and the lighter the color, the more opaque (not letting light pass through; not transparent or translucent). Transparency mapping can be used to create glowing spheres. (See TOPAS User's Guide 5.1 pp.299-300 under Materials>Images>Edit Procedurals). It can also be used for such things as glass effects, for making parts of an object invisible or see-through (like a lattice texture), and exotic uses like simulating trees (see bottom of article -- procedure of making a picture of tree textures and a rendered tree.)

SHININESS MAP

Shininess follows the same principle. In this case, the lighter areas make that part of the object reflect light. If you mapped the alpha channel (black and white map used for altitude mapping) of the tree onto a plain polygon, parts of it would "shine" more when lit. This would be useful for instance, if you had a gold veined marble, and you wanted the veins to shine more than the rock around it. You would then create an identical map that it is all black except for white veins.

LUMINESCENCE MAP

Luminance also follows the concept of lightness and darkness. The lighter the color of the texture, the brighter it will be self lit. Pure black leaves the surface of the object unchanged. Setting luminesce only creates the appearance. It does not actually cast light. Luminance mapping is useful for many things, such as adding lighted windows to distant objects such as skyscrapers and space stations, for making complex switchboards covered with lights, and sometimes when you don't want a texture shaded or darkened, but want it to be shown exactly, you might luminescent map the object with a solid white texture. Also remember that the luminance maps only makes the object's surface brighter -- it doesn't give it any color.

Think about using several different maps on the same object that enhance each other. For example, in the tree texture sequence below, a transparency map is applied onto the same object as a color map. They complement each other: the transparency map makes certain parts of the polygon invisible, while the color map adds color to the section that IS visible. All of the maps can be mixed. For a space station I usually draw a luminance map, a bump map, and a color map. The luminescent map makes certain parts of the white color map shine out without lights, the bump map adds the plates, hatches, etc. that make it look much more detailed, and the color map of course gives it the colors and painted areas. All of this needs a lot of practice, but it is well worth it when you're able to start creating models that inspire, as opposed to lego forms.

Here's a few sites with some good -free- textures:
http://www.3dcafe.com (The tree textures came from this site)
http://www.3d-design.com (You have to search for their texture section)
http://www.corbis.com
http://www.3dpix.com