VRay material sub-surface effects
江西婺源简介
Many people speak today of things like absorption, translucency, sub-surface scattering. The topic of this tutorial is to give you an idea what are the effects and how to simulate them with VRay.
We will deal exclusively with the VRay material although a large part of the effects can be achieved with the VRay map as well.
This is the scene that we will work with for the most part of the tutorial (click the image for a larger view). Note that the teapot is not the standard MAX teapot. The standard teapot has holes, which is not a desirable property. This teapot is a completely clod mesh.
Click here to download the scene.
All of the above effects are sub-surface effects - they deal with light passing through the surface of objects into their interior.
Refraction
The most simple sub-surface light effect is refraction. In VRay all other effects are modifications of this simple one. To make our teapot refractive, t the Refraction color of the material to something other than black - for example to medium gray. The result should look something like this:
If we t the index of refraction (IOR) to 1.0 we will get a special ca of refraction - transparency, which looks like this:
A very important fact to notice about the above picture is that the shadow of the small sphere is not visible, although it falls on the teapot. This is becau the teapot's material is by default t to Double-sided. However, and this is important, for a large number of sub-surface effects we are actually interested in what happens on the outer side of surfaces, even if we are looking at them from the back. So, turn off Double-sided in the material. This time we get the following:
A modification of the simple refraction is glossy refraction (also called frosted or blurry refraction). It is caud by the refracted rays being scattered by an object's surface. In VRay's material the amount of scattering is controlled by the refraction Glossiness parameter. When it is t to 1.0, the surface produces perfect refraction. A value of 0.0 produces perfect scattering in all directions inside the object. For example tting refraction glossiness to 0.6 gives the result below. Notice how everything en through the teapot looks blurred. (Note that glossy refractions will try to produce caustics when ud with GI. If this is undesirable, simply turn on caustics in the VRay render parameters, without enabling casutics for any individual light).
Absorption (fog)
Absorption occurs when the inside of an object is not fully transparent, but absorbs light as it pass through. The effect is that the object looks foggy, and thin parts are more transparent than thick parts. In VRay this effect is controlled by the Fog and Fog multiplier parameters. Let us for a moment make the Refraction color completely white and t the glossiness back to 1.0 (so that the teapot is fully and ideally transparent). Set the fog color to light blue (RGB 200, 226, 247). You can control the strength of破风电影
the fog effect with the Fog multiplier. Note that the fog color and multiplier depend on the size of your object. Smaller objects will look more transparent, while bigger objects will look more opaque. Ideally, the fog should also affect the color of the shadow cast by the teapot. In this particular ca, you can make it do so by switching on Translucency:
Using only the effects mentioned so far, you can get quite interesting results. Here are some
combinations of glossy refraction, fog and different IORs.
石斛功能Fog transparency = 1.0
阿贵将军
Fog transparency = 0.1
Sub-surface scattering
Sub-surface scattering (SSS, 3S) occurs when light is not only absorbed by a medium, but is also
连续结晶器scattered (bounced) inside. Currently VRay simulates only a single bounce inside the medium. We will examine the effects of sub-surface scattering on the scene shown below. There is one omni light with
VRay shadows placed above the cube (note that we could also u shadow maps). Click here to download the start scene.
Here are the steps that will turn the cube's material into a light-scattering one.
First, uncheck Double-sided. Next we must enable refractions, so t the refraction color to RGB (85, 85, 85). The result so far looks like this:
Next, make the refractions glossy - for example glossiness 0.4:
Next, turn on Translucency:
让座看图写话二年级It's not very impressive (yet), but there are two things to notice - the cube appears a little brighter, and
also the shadow of the cube is transparent (becau the fog color is by default t to pure white). Next t the fog color to RGB (105, 150, 115) and fog multiplier to 0.3. At this point we get the following
result:
停止间转法
Notice how the shadows are darker (if the transparent shadows are bothering you, you can u shadow maps). We are almost done now. The sub-surface scattering effect is there, but is too subtle to be noticed (as it usually is in nature). To make the effect stronger, increa the Light multiplier parameter of the material (not the multiplier of the omni light!) to 15.0:
Notice how the top of the cube and its edges are brighter, becau the light goes a little way into the surface. The edges are brighter, becau I ud GI (with irradiance map), as I did on all previous images. Here is what the picture looks like without GI:
地王观光
You can control how deep into the object light reaches by adjusting the Thickness parameter. Here is what we get if we t it to 20.0:
Notice how the object looks softer and the light goes deeper inside. Our final image, with GI on, looks like below. Click here to download the final scene.
Below is a t of pictures showing the effect of Refraction glossiness on the translucency effect; GI is turned off and the fog and light multipliers are a bit changed so that the difference is more noticeable (Light multiplier is 30.0 and Fog multiplier is 0.1). Notice how the image is less noisy as the glossiness goes up.
