When you look at a scene in 3D real-time, one wonders how a particular material is created. One of the main sources of questioning is probably the diffuse and its mix with the ambient and self illumination. Let's see how all these channels live together :
The diffuse and ambient. What is diffuse for a material? It is essentially the appearance of the object illuminated by a light. For example, for a yellow sphere, the diffuse is yellow. But then what is the ambient? It is the color of the object on the shaded side. The distinction is subtil and we'll develop a little. In the nature, a box that is yellow to light, is also yellow in its shaded side. Only the difference of light affects the color. In 3D, it's quite similar, since by default in 3ds Max, the value of diffuse is locked in the value of ambient by a small lock. However, for certain effects (such as Sub-Surface Scattering SSS -Sub Surface Scattering), for example, you can specify a particular value. But simply changing the color of the ambient is generally not sufficient, because another parameter is to be taken into account.
The ambient of the scene The ambient of the scene is an environment setting to simulate the light bounce. What is imperative to know, for 3DSMax as for
NOVA is that this value (usually color) multiplies the value of your ambient material. Let's take the example of the yellow ball. By default, the diffuse and ambient are set to yellow, but the shaded area of the ball remains black. If you increase the value of the ambiant of the scene to a medium gray (128/128/128 in RGB), the value of yellow reaches 50%. The shaded area is less black and more yellow. If you increase the value of ambient of the scene until a pure white, the ambient of the sphere is at its maximum value. The combinations are correspondingly: A diffuse yellow with a dark purpleambient and a pure green as scene ambient will produce surprising results.
But the self-illumination, then? Self-illumination is a misnomer; linked to the concept of lighting. A self-illuminated object does not light-up (in case suaf radiosity specific). By cons, we can translate the self-illumination of an object's ability to filter the value of ambient. The higher the value of self-illumination (called emissive in
NOVA and treated as a color) , the less the ambient is important, therefore more diffuse value is high. And, whatever the value of the ambient of the scene. In summary we can say that the value of self-illumination is the value of the diffuseversus the value of ambient. This becomes particularly important when you precalculate lighting into a texture. In that case, the texture is replacing the lighting. In other words, we no longer need the lighting of the scene. But if we take away the lights, the whole object is then subjected to the ambient of the scene. If it is black, it blacks out the material. That is why we use in conjunction with a texture of ambient the self-illumination channel. But another alternative is to let the Self-illumination at 0 and raise the ambient value to pure white.
What is this particularly relevant? Indeed, why use one method over another?In practice, it becomes obvious.Tthe ambient of the scene is more appropriate for varying ambient for all the materials with a single entry. For example, for day and night cycles, or if you treat all your objects texture baking lighting.By cons, playing with self-enlightenment would be coherent in the context of the evolution of one or more specific objects. By cons, playing with self-illumination is fine if you want to manage only one or two materials