Thin fibers react to light in a complex way to give fur and hair their unique looks. Lit fibers have a much more complex appearance than "normal" surfaces like wood or chrome. Sasquatch's lighting model reproduces these effects to make photoreal results, even in the preview mode which is invaluable for perfecting your shading settings interactively.

Diffuse and Specularity

The most basic shading adjustment is Diffuse which, like LightWave's own Diffuse control, changes the sensitivity of an object to light. Black hair has a low Diffuse setting, white hair has a high value. Diffuse is tweaked more often than any other shading control, since it is the easiest way to brighten or dim the fur's appearance.

Fur and hair specular highlights are very important and behave very differently than normal surface highlights. This is because the fibers are actually narrow tubes, and the highlights become stretched along the tube's long direction. When you look at fur or hair, you can see this stretched, aligned, highlight easily, even if you're very far away and can't see individual fibers. Normal specular surfaces (like a glass ball or something) show a very simple bright specular spot when you shine a light on them, but fur fibers will create intricate patterns which depend on the combing, length, and styling of the fur.

Complex specular highlight patterns in real hair

The Specular value controls the strength of specular highlights. Glossiness is the width of the highlight, with high values creating small, bright highlights, and low values making broader, dimmer ones. These behave similarly to LightWave's own Specular and Glossiness controls.

Specular Tinting allows you to change the color of the highlight by adding the fiber color to the specularity. When Specular Tinting is 0%, highlights are the same color as the lights that make them. As you increase Specular Tinting, the base fiber color of the highlight will be mixed into the specularity.

Dark Hair Highlights

Dark (or black) hair is interesting since the only effect you're really seeing is specularity. You can obviously make dark hair by selecting dark (or black) colors for the hair color, but a more effective alternative is simply to lower the Diffuse value. This darkens the hair (all the way to black if you wish) regardless of what colors you've set. If you use low Diffuse and high strong Specular Tinting, you can completely determine the highlight color of the black hair. Some real dark hair has light blue highlights, some has reddish, and some has simple white highlights. In Sasquatch, you can choose the highlight color freely with the Color controls since the low Diffuse hides the base color. In summary, make dark and black hair with low Diffuse values, not with dark hair colors, so you can control the highlight tints easily.

Translucency and Sensitivity

Most fibers are so thin that light passes through them. In real life, this translucency depends on the coarseness, color, and type of fibers. Many, many real fibers, including human hair, react even when they are lit directly from behind. This "backlighting" effect can be very strong, for example when loose blonde hair is backlit by sunlight.

Backlit blonde hair

Sasquatch lets you control backlighting with the Translucent Lighting setting. Large values will make hair react to lights that are behind the hair (backlighting.) Small values will reduce backlighting, giving the impression that the fiber is thick, opaque, or both. An interesting side effect of this property is that high values of Translucent Lighting will make your fibers less sensitive to light direction. This is usually useful, since it's easy to set up lights for your hair or fur, but have your beautiful appearance change quickly when you move the light or object. Low Translucent Lighting settings are useful for the coarsest, darkest fibers, perhaps porcupine quills or animal whiskers.

Real fur and hair has an interesting property that causes it to be brightest when the light comes from an angle, not when it's directly aligned with the fiber itself. This can make surprising patterns; you may shine a light onto a furry surface, but see a dark spot where the light is pointed, surrounded by a ring of brighter fur! This is because the center fibers are aligned with the light direction. You can see this clearly in real life by shining a flashlight onto the head of a friend with a crewcut. It's surprising to see since we're used to seeing a bright spot where we point a light.

Sasquatch's Direct Lighting controls how sensitive the fiber lighting is to this effect. High values will make Sasquatch less sensitive, which usually makes lighting easier, but a little less realistic.

Final Shading Options

Sasquatch fibers will react to LightWave's ambient light and radiosity. However, often fur looks better with less ambient lighting than other surfaces. The Ambient/Radiosity Sensitivity value lets you reduce the amount of ambient lighting that's applied to the fur. Sasquatch still uses LightWave's global ambient light setting, but simply reduces (or boosts) the value by this sensitivity multiplier.

The final shading control, Self Shadow, is often crucial for photorealism. This attribute is discussed in detail in the Shadowing chapter.

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