In order to do this, the artist must picture an imaginary lighting algorithm in their head. Picture the imagined detail, and then choose a lighting model, then you would paint the surface as if it was being lit by that imaginary model. There are two primary lighting models used in painting color maps. The first is the GI (global illumination) also called occlusion lighting. It simulates lighting coming from all directions, and surfaces only shadowing when they come into close proximity of another object. Good examples of games that use this lighting model are the final fantasy games and lineage. The other lighting model is to imagine specific light sources, one point, two point, or more. The artist paints the planes of imagined geometry that face these imaginary lights lighter, and the edges that face away darker. Using colored imaginary lights can further help the illusion, as all faces that face imaginary light one are white, and those that face imaginary light two are red, etc. Games that use this model are Blood Rayne 2, and Dark Age of Camelot. Most games fall somewhere in between these two models.

If you are consistent with this fake lighting, the viewer will be fooled into believing that these pieces really exist. The downfall is that this lighting info will not change in real time, like the real modeled geometry will. It is a trade off however, as we do not have the poly counts to model everything, and even when we do (or have the normal maps to imply it) the lighting engines fail us in certain circumstances (those circumstances being any well lit area). So while this lighting will not change as the light and model move, it is better to have the implied detail, than to have a barren model that lights accurately.

One mistake that is commonly made is to paint color maps as if it was an elevation map. Any imagined geometry gets brighter as it gets further off the surface of the real model. This would be how you would paint a bump map or an elevation/topology map. What it results in is a model that looks “worn away” like anything sticking out has had its color rubbed off. The reason is that this is not how real object light. They receive light based on their facing ratio to the light source. When the face is perpendicular to the light source, it will be brightest, and as it angles away, it gets darker. In the occlusion model, the flatter the surface the brighter it is lit, and the closer the plane of the surface lays to another plane of the surface, the darker it gets. The more consistent the lighting model is, the more believable it will be. The ultimate way to do this, would be to actually model all of the geometry out, create all the advanced shaders to make each object look exactly like the material they are made out of, and then set up either a series of spot lights, or a global illumination scene, and render the high poly model to the color map of the low poly model. This is how normal mapping is done, however it only renders the difference information of the surface distance. Kaldera and 3ds max have built in abilities to render to the color channel.

This very process is what we as artists are trying to do in our heads. Because of the map size, many times it is more efficient (and rewarding) time wise, to do all of this in our heads, rather than model it all out, and figure out how to write these advance shader networks, to then render it to a lower poly model.

In addition to picturing how the light would fall, one must keep in mind how different surfaces react to being lit. Metal behaves completely differently that skin, even when lit in the exact same environment. Using photographs, or observing the real material, is the best way to learn how these materials behave. How much of the light do they reflect and how strong are the highlights? How fast do the highlights fall off? Do the objects reflect onto other objects around them? Do they change the color of the light? Does the object light differently depending on the amount of light they receive? (An example is skin, because of its translucency; it is a different color in the shadows than it is when well lit) If you use the same lighting treatment on all surfaces, it will make your models look as if they were made out of that single material as a maquette, and then painted with acrylics to appear like there are different materials. However it will not look as convincing as it would if you change the behavior per material.

A good process to use, that helps me, is that whenever I am painting a material, I try to find as many good images of that exact material as I can, and then I try to find an actual texture painted by an artist who did it well. I will look at the photos to learn the “rules” of the material, and I will look at the artist’s texture to see how they broke it down to work in a pixel environment. Sometimes I will follow their lead, sometimes I will elaborate, and sometimes I will go in a completely different direction.

All of these theories are well grounded in the traditional arts. Painting books, classes and techniques will aid you greatly. Knowledge of anatomy, product design, and composition all come into play. You have to know how this imaginary geometry works before you can imagine how it would be lit. If you do not know the structure of the human face, you will not be able to imagine it in your head.

The last bit of texturing theory I have to impart. Always remember the target platform. Is it going to be viewed on a monitor or a TV? What size will it be on screen? How will the player see it? When you are painting, constantly zoom out to the typical viewing distance and see how it works on that level. It might look awesome full screen zoomed in on a couple areas, but when viewed at 50 feet, it might all blur together into an unreadable mass. This will help you keep your mind focused on all three levels of detail, large, medium, and small. A great game model will have all three, and will look amazing at any viewing distance.

Download the word document of this.