Channels

Materials can have different channels (usually, textures are loaded to affect each one of those channels) and each one of them controls different properties of the material (color, reflectivity, transparency, and so forth) A lot of people find it hard to understand what channels are, so here is a brief description of the function of some of the most commonly used channels:

Diffuse Color: This channel defines a surface’s color.

Transparency: This channel defines the parts of a surface that should be either transparent or opaque. A black-and-white image or an image with alpha (transparency) is usually used for this channel. Black areas of the image would be transparent and white areas would be opaque.

Emission: Usually, this channel is a black/transparent image with some areas of color. Where the image used for this channel has color, the software will take that color as the light emission color and the alpha value of the image as the emission intensity. Emission works by adding light to the surface in those parts in which the image used has color.

Specular: This channel defines the parts of a surface that are more or less shiny. Black has no shine at all, while white has full specularity. If you use colors, this channel will tell the software on which specific colors a shine should be placed.

Reflection: This channel’s texture would make some parts of a surface reflective. Again, black has no reflection, any other color defines the color of the reflection, and the lighter the color is, the more reflection you’ll get.

Roughness: When used together with specularity and reflection, a black-and-white texture tells the software where a surface is more or less rough; this channel diffuses and blurs the shine and reflections in those areas with a rough surface.

Bump: A black-and-white image gives the appearance of relief to the surface. The software uses this channel to determine how light reflects off a surface. It’s very useful for small details that are not big enough to be modeled, such as scars or scratches.

Normal: This channel is like an advanced bump. It’s an RGB texture in which each color tells the software in which direction light should be reflected off a surface. This effect is widely used in video games to make the objects appear to have much more detail than provided by the model’s geometry. Normal maps (also called normal bumps) are rarely hand painted. They’re usually created by having two versions of your model: one with high resolution and one with low resolution. Normal maps are then generated by “baking” the details of the high-resolution model into a texture for the low-resolution model.

Occlusion: With a very minimal effort from the artist, this channel can significantly improve the lighting realism of the model. It’s basically like a soft shadows pass in which holes and cavities of the model are marked. This channel is also used to create realistic contact shadows between objects—the type of soft shadows that you’d see on a cloudy day. The occlusion channel is usually generated automatically by baking from the model into a texture.

Basically, in most of the channels, black and white in the textures define the values, and colors define the colors. This can apply to specularity, reflection, emission, and so on.