The MILA Scatter is the new way to handle subsurface scattering in Maya
and Mental Ray. This is good news because it's
much easier to use, and it's more flexible.
I have a character head here and right now
diffuse reflection assigned to my MILA material
material. It's just showing us what the diffuse texture map
looks like. Now if I look at the MILA material,
and check out the base component, I'll see that there is a 'scatter' parameter here,
a diffuse scatter, and if I turn that on,
I get a new scatter node that shows up. The thing is, if we look closely at all these
different attributes,
this is the same scatter node that has been in
Mental Ray forever. This is the Fast Skin node.
I don't want to use Fast Skin.
I want to use the new MILA Scatter material.
So I'm going to keep my base layer as a diffuse
and I'll start adding new layers on top of it.
I'll start by adding my scatter layer, and I'll do it as
a weighted layer. I'll just choose scatter from the
menu that pops up. And I'll see this
shows up here, and we see that the options are very different
than the scatter that we choose if we use it on the base diffuse layer.
This scatter works more easily to put
together than the previous version. Now that we've assigned this,
let's do a quick render, and see
what the new render looks like... and when the new
render pops up, we see, yes, subsurface scattering is working.
It's just working way too much. We've got something that
we can sort of make out the shadow of the nose and the mouth, but we're losing
all of our detail.
We still need to adjust its 'scale conversion factor'
that we used on the old Fast Skin, and we use it the exact same way.
Makes my object look less scattered with higher numbers.
Makes my object look more scattered the lower the number.
So I can turn this up to
a different value, and when I set that new value, that will render, and I'll get something
that should look
more solid. So the new render pops up and
I can see that it's very different. It's not as jelly-like
as my previous render. I can actually see
details on the surface of the object: we can make out the nose, make out the lips.
We're getting nice backscattering coming through the back of the ear.
ear. And what's really interesting about the MILA Scatter node,
is we can see that all the color swatches in my material are still
white. And yet, we're getting red bleed-through on the
ear, which is something we wouldn't think would happen. What's happening
is these radius numbers are controlling the way the light propagates through
our surface. And before, on the Fast Skin,
we has a single radius number that we typed in. All
light that penetrated the skin would travel a certain amount.
On the MILA Scatter, we've separated
light propagation into the three red green and blue channels.
This mimics the way actual skin behaves.
Red light wavelength is going to travel further through skin.
The blue wavelength is going to travel less through the skin.
So if we to turn these numbers up, we'll get an even more red
effect on the surface of our object and this makes using the MILA Scatter to tune
tune our subsurface scattering
much easier. We can see, comparing the new render to
the previous render, we get a lot more red in our shadowed areas
because I've adjusted the front and the back radius to have a higher red value.
This mimics the way skin actually
works, which is why we get such a red tone for skin and we
don't get a lot of blue. Right now I've got my perfectly white
with a little red subdermal material
and I do want to assign a texture to it.
I'll go into Photoshop so you can see the textures I'm using.
I created this subdermal texture, and the subdermal texture is going to give us
alot of the skin tone colors that we need. The subdermal
is going to be much more saturated than the top
layer - the surface or diffuse layer.
We see that there are some echoes of the color from the subdermal,
the diffuse color is going to be much more white.
This is to reflect the fact that the top layer
of our skin cells are actually very white.
So I'll plug that subdermal map in. I've got my MILA Scatter node
here, I've got my subdermal texture we just looked at over here,
I'm will middle mouse drag this onto the
'front tint'. That will change the look
of my material. I don't necessarily need to do it
for the 'back tint'. We won't notice a big difference if
we do. And when we rerender,
we'll see the new texture gives a lot of color to our object.
The render shows the updated subdermal texture,
now w're getting something that looks a lot more like regular skin.
When we do you apply this texture, we start to
see exactly how exaggerated the scatter looks right now.
I could go in and start playing around with my 'scale conversion' node.
But - we are not going to use the scatter
as our top layer. If we think about it, subsurface scattering -
we want the scattering to be happening under this surface.
And because the MILA Shader is a layered shader, we will put another layer on top of it.
I'm going to you add a layer to my MILA Material.
I'm going to use a Weighted Layer, and a
diffuse reflection. That will pop up on top,
and this diffuse reflection, if I render right now, would give me a pure grey material,
not very interesting. What I'm going to do with this diffuse materials is plug my
diffuse texture in there
and that is going to blend
between the scatter and the diffuse to give me more of
the skin tone I'm looking for. I'll take my diffuse texture and just
middle mouse drag
on to the color here.
Now my texture is plugged in, and if I rerender, it'll give me a
100 percent flat diffuse reflection. It'll look identical to this
initial render. So instead I want to combine it with my subsurface scattering.
To do that, because this is a weighted layer, all I need to do to adjust the
opacity of
the entire layer, is to just change the wight.
I'll lower the weight to 0.5 so it will
be HALF scatter, HALF diffuse reflection.
And then I'll rerender. And when it finishes rendering,
if I compare it to my previous one. I see the previous scatter node
is very very jelly-like. We can see through it very clearly.
With 50% of my diffuse laying on top of it,
suddenly I have something that feels more
solid. But if I compare it to the original diffuse,
this solid texture here, I get all sorts of gray shadows,
things look very hard. It looks very much like a Lambert material.
With the scatter applied, things look soft, and the shadows are warmed up.
There's more red in there. We're also getting backscatter
effects. This allows me to also plug in my bump map.
In order to attach the bump map,
I do you need to go to utilities and find a Bump 2D node,
and bring this in here. And I have my bump map texture here
and I'll connect that to the Bump 2D node.
Because it's a tangent space normal,
I switch this, and now I'm gonna this bump map
into the bump channel on the diffuse reflection.
Just middle mouse drag,
and now when I render, I'll get the bump node plugged into
the rest of the head. And when the render is finished, and the bump map
is applied, we're probably won't see a lot of effect from the bump map.
Some of this is because the way the scatter node works.
Because the scatter node is a SUBsurface scatter
node, a bump map is not going to affect it
because a bump map affects the surface.
And of course the scatters is SUB (or below) surface. So we can plug in
the bump map on our diffuse reflection, but generally it's not going to start
showing up until we start adding things like specular reflections.
Since the bump map won't work well without specular,
let's add a specular layer.
We can do either a weighted layer or
a fresnel layer. I'll do a weighted layer just keep things simple.
I'll use a glossy reflection.
So this is going to be applied over the top of
my object. And if I leave it at 100% opaque,
with a color of white, it's going to look pretty much like
chrome. So I will reduce
the opacity significantly, and I'm going to plug my bump map in
here. And when we render,
we get something that looks awfully shiny, but at the same time
it's going to show more surface detail of the skin.
So indeed the model looks extremely shiny,
as if coated in oil, so what we want to do here
is adjust the weight value down pretty significantly.
This will be an overall shininess layer, just a little bit
skin's natural oils. We definitely
want to raise the roughness on this reflection material
because we don't want this to actually reflect anything.
We want it to be shiny but not reflective.
We can compare it to before, it just adds a little bit to the
skin. When things start animating, the character starts moving around,
this is going to add to the surface a lot.
Let's add more specularity. Now I'll add a new fresnel layer,
another glossy reflection layer.
This one we want to be pretty shiny.
So I've got my new glossy reflection, and I'll plug my bump map in
and then I can do render
to see what it looks like, so I can see what starting material is going to be.
We see that we're getting a lot specularity around the
edges. We also get some really hot highlights where the bump
map is picking up some of the detail. One thing that we can do it up the
roughness of the new reflection layer, so we're not getting any really shiny stuff
and we can also up I O R (index of reflection)
and by raising the IOR, we make the reflection stronger,
but it also becomes more focused. We can lower the weight on that
channel. When we render we end up with something that
is a little bit more focused around the edges, but it's also going to
be much less
opaque. The end result: we get a more broad
specular and it's also less focused around the edges.
So it's not creating those really big bright white highlights.
Now - let's talk about adding a displacement map.
Generally, because of the way the subsurface scattering
works, it can be preferable to add a
displacement to our model, so that
even though the subsurface node won't show surface detail,
the entire model is going to be displaced so
we can't help but get more high-resolution detail.
I'll click on the shading group node that is the parent to the MILA Material
and I'll plug in a displacement into this displacement map
channel. I've got my displacement texture here, a black and white texture.
And when I'm using this black and white texture,
we want to turn on 'Alpha is Luminance', that usually give us a better result.
I plug that texture into the displacement node,
and now I can just middle mouse drag that onto the
displacement material. To view this,
it's a lot easier to view it if we're doing a before/after
on just a regular diffuse layer.
Now when we're using displacement in Mental Ray, there's
one more thing that we're usually want to check. We select our model
and go to the Windows Menu and then Rendering Editors, and then
Mental Ray. We're looking for this: the Approximation Editor.
The Approximation Editor allows us to adjust displacement
and subdivision tessellation on our object.
This tells Maya how you want it subdivided
for displacement when you render.
So I just create here and we can use whatever preset we want
Fine View High-Quality works fine. I could do the same thing
for subdivisions; and in this case I choose
Spatial. I'll rerender, this will generally make
the rendered take longer as well, because it's subdividing the
mesh more. It can give us a better quality result
however we will see that renders (anytime we're using displacement) are
taking much much longer than they otherwise would.
Now I render and we can see the displacements effect.
Comparing before and after, we see it has a pretty significant effect on the surface.
Now when using displacement in Mental Ray, there's one more thing that we're
usually want to check.
we want to select the model, go to the 'windows' menu
then 'rendering editors' and then 'mental ray'
we're looking for this: the 'approximation editor'.
The approximation editor allows us to adjust displacement
and the subdivision tessellation on the object
this basically tells Maya how you want it subdivided
for the displacement that is actually rendered.
I'll just create here and we can use whatever preset we want
'fine view high-quality' works fine. It is same thing
for subdivisions, and in this case
'spatial' is the one I usually want.
I'll rerender. This will generally make the render take
longer as well because it's subdividing the mesh
more. It's going to give us a better quality result.
However we will see that renders, anytime we're using displacement, are
going to take much much longer than they otherwise would.
So with those settings turned on, we should get a better result for the displacement/
Now I can re-enable all the other
layers: scatter layer, reflection layers etc.
The displacement now affects
all of those layers, so I should get
a much more accurate looking representation of my model.
Now we have displacement enabled on top of
the rest of the mesh. I'll go back
to this point here, where we can see, we're not seeing a lot of bump mapping
on this one because the subsurface hides it. And by turning on the displacement
we end up with a surface that works pretty well.
Compared to the original we have the displacement with
just a diffuse texture, we get something that looks a lot more
natural or interesting.