This tutorial will give you an overview
of what effects you can achieve with translucency.
Translucency simulates the effect of so-called
scattering. This basically means that light coming from behind the object
a) shines through to a certain amount (and with a certain color tint coming
from the object) and b) is reflected inside the object back to the light
source.
Fig. 1. Technical illustration of scattering.
Please note that in 3DSMax neither the Translucency material nor the translucency parameter from the raytrace material does “real” translucency. Both effects are for example not dependent on object thickness and only simulate forward scattering. So a lot of tweaking needs to be done to get realistic effects.
Effect no. 1: Shadows from behind
The first thing where we’ll work with
translucency are shadows from behind the translucent object. Examples are
leaves or sheets of paper illuminated from behind. For an extreme example
see fig. 2. Without translucency the image would loose the main part of
its information because the woman is only visible through her shadow.
Fig. 2. Backlit scene rendered without and with translucency.
Now, how to do the setup? I’ll show this on a very simple example instead of the scene above, but the workflow is exactly the same. Also I’ll work with a raytrace material, not with the Translucency shader from the standard material but the settings are not different at all.
All right, here we go:
Create a new scene and throw in a teapot
(yes, I really like teapots ;) ), and a plane. It doesn’t matter which
side your plane is facing to, we are going to make it two-sided anyways.
Now create a spotlight with shadow mapping
on behind the teapot shining on the plane and a second light in front of
the plane (just to make sure we see anything at all). Choose a viewpoint
like the one in the screenshots.
Fig. 3.
Open the material editor and assign a two-sided
raytrace material to the plane. If we render the scene now we see a nice
gray plane and perhaps a part of the teapot (depending on the point of
view you choose).
No matter what you are going to do now
with your plane material the scene won’t look realistic (well, as far as
a flying teapot in front of a flying plane can look realistic at all, but
that’s not the point here).
So we open up the material editor again
if it isn’t still open and expand the “Extended parameters” tab from the
raytrace material. Hit the colorfield behind “Translucency” and choose
a light gray.
Fig. 4.
Render again. You should see the shadow
from the teapot shining through (if you don’t see the shadow, go back and
make sure you have shadows turned on for the spotlight).
Fig. 5.
That’s it! The same technique was used for the picture with the woman above and can also be used for leaves, newspapers, etc.
But that’s not all what can be done with translucency. Think of a torch lit from inside, so here’s
Effect no. 2: Light from behind
Fig. 6. Example of a torch rendered without and with translucency.
This is what we called “forward scattering” at the start of this article. In real life it can be observed in materials like wax, milk, marble, etc. (essentially all non-metallic surfaces but in most cases the effect is to subtile to notice, for example wood).
What happens in case of forward scattering is light entering the material is scattered around and leaves the object at a nearly random position on the opposite side.
Let’s see an example. Create a new scene and throw in a teapot ( ;) ) and a point light behind it. As we just want to observe the translucency don’t create a second light this time. Also don’t enable shadows for the light (I’ll come to this later).
Fig. 7.
Now apply the material we created for the
plane in effect no. 1 and render.
Fig. 8.
Not impressed? There’s no reason to because
it looks like a flat, gray teapot (wow, two pages of tutorial to get a
flat, gray teapot, impressive, isn’t it? <irony off>).
Remember what I said about object thickness
and that 3DSMax won’t take it into account in respect to translucency?
That’s what we can observe here. But we can simulate it with the right
light setup.
So switch to the light properties and
enable “Far attenuation”. Choose “Start”- and “End”-settings like shown
in the screenshot below.
Fig. 9.
Render. Ahhhhh, that’s better.
Fig. 10.
One thing about lighting a whole scene
with a few translucent objects and shadows. As we use the light attenuation
to simulate object thickness the light is zero or near zero behind the
object ("behind" as seen from the light source). So if you’d like to light up the rest of the scene (which will
be true in most cases), you’ll need to create a second light at the same
position as the one for the translucency and “Exclude” the translucent
object from this second light. For the shadows: It needs a lot of effort
to get shadows on translucent objects. Tweak around with the shadow color
and density to get the effect you’re looking for.
[Grab the zipped tutorial here (205KB).]
If you have any questions or comments about this tutorial, don't hesitate to contact me: shawn.hempel@useddishes.com
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