![[General parameters]](vray_for_3ds_max_manual/vrayfastsss2_material/vrayfastsss2_general.png)
Preset
- allows you to choose one of several available preset materials. Most of
the presets are based on measured data provided by Jensen et al. in
[3].
Prepass rate -
VRayFastSSS2 accelerates the calculation of multiple scattering by
precomputing the lighting at different points on the surface of the object
and storing them in a structure called an illumination
map, which is similar to the irradiance map used to approximate
global illumination, and uses the same prepass mechanism built into V-Ray
that is also used for e.g. interpolated glossy reflections/refractions. This
parameter determines the resolution at which surface lighting is computed
during the prepass phase. A value of 0 means that
the prepass will be at the final image resolution; a value of
-1 means half the image resolution, and so on.
For high quality renders it is recommended to set this to
0 or higher, as lower values may cause artifacts
or flickering in animations. If the chosen prepass rate is not sufficient to
approximate the multiple scattering effect adequately,
VRayFastSSS2 will replace it with a simple diffuse term. This can
happen, for example, for objects that are very far away from the camera, or
if the subsurface scattering effect is very small. This simplification is
controlled by the Prepass blur parameter.
Scale - additionally scales the subsurface
scattering radius. Normally, VRayFastSSS2 will
take the scene units into account when calculating the subsurface scattering
effect. However, if the scene was not modelled to scale, this parameter can
be used to adjust the effect. It can also be used to modify the effect of
the presets, which reset the Scatter radius
parameter when loaded, but leave the Scale
parameter unchanged.
IOR - the index of refraction for the
material. Most water-based materials like skin have IOR of about
1.3.
Overall
color - controls the overall coloration for the material. This color
serves as a filter for both the diffuse and the sub-surface component.
Diffuse color - the color of the diffuse
portion of the material.
Diffuse amount - the amount for the
diffuse component of the material. Note that this value in fact blends
between the diffuse and sub-surface layers. When set to
0.0, the material does not have a diffuse component. When set to
1.0, the material has only a diffuse component,
without a sub-surface layer. The diffuse layer can be used to simulate dust
etc. on the surface.
Sub surface color - the general color for
the sub-surface portion of the material.
Scatter color - the internal scattering
color for the material. Brighter colors cause the material to scatter more
light and to appear more translucent; darker colors cause the material to
look more diffuse-like.
Scatter radius - controls the amount of
light scattering in the material. Smaller values cause the material to
scatter less light and to appear more diffuse-like; higher values make the
material more translucent. Note that this value is specified always in
centimeters (cm); the material will automatically take care to convert it
into scene units based on the currently selected system units.
Phase function - a value between
-1.0 and 1.0 that
determines the general way light scatters inside the material. Its effect
can be somewhat likened to the difference between diffuse and glossy
reflections from a surface, however the phase function controls the
reflection and transmittance of a volume. A value of 0.0
means that light scatters uniformly in all directions (isotropic
scattering); positive values mean that light scatters predominantly forward
in the same direction as it comes from; negative values mean that light
scatters mostly backward. Most water-based materials (e.g. skin, milk)
exhibit strong forward scattering, while hard materials like marble exhibit
backward scattering. This parameter affects most strongly the single
scattering component of the material. Positive values reduce the visible
effect of single scattering component, while negative values make the single
scattering component generally more prominent.
Specular
color - determines the specular color for the material.
Specular amount - determines the specular
amount for the material. Note that there is an automatic Fresnel falloff
applied to the specular component, based on the IOR
of the material.
Specular glossiness - determines the
glossiness (hightlights shape). A value of 1.0
produces sharp reflections, lower values produce more blurred reflections
and highlights.
Specular subdivs - determines the number
of samples that will be used to calculate glossy reflections. Lower values
render faster, but may produce noise in the glossy reflections. Higher
values reduce the noise, but may be slower to calculate.
Specular reflections - enables the
calculations of glossy reflections. When off,
only hilights will be calculated.
Specular trace depth - the number of
reflection bounces for the material.
Single
scatter - controls how the single scattering component is calculated:
None - no single scattering component is
calculated.
Simple - the single scattering component
is approximated from the surface lighting. This option is useful for
relatively opaque materials like skin, where light penetration is
normally limited.
Raytraced (solid) - the single scattering
component is accurately calculated by sampling the volume inside the
object. Only the volume is raytraced; no refraction rays on the other
side of the object are traced. This is useful for highly translucent
materials like marble or milk, which at the same time are relatively
opaque.
Raytraced (refractive) - similar to the
Raytraced (solid) mode, but in addition
refraction rays are traced. This option is useful for transparent
materials like water or glass. In this mode, the material will also
produce transparent shadows.
Single scatter subdivs - determines the
number of samples to make when evaluating the single scattering component
when the Single scatter mode is set to
Raytraced (solid) or
Raytraced (refractive).
Refraction depth - this determines the
depth of refraction rays when the Single scatter
parameter is set to Raytraced (refractive) mode.
Front lighting - enables the multiple
scattering component for light that falls on the same side of the object as
the camera.
Back lighting - enables the multiple
scattering component for light that falls on the opposite side of the object
as the camera. If the material is relatively opaque, turning this
off will speed up the rendering.
Scatter GI - controls whether the material
will accurately scatter global illumination. When off,
the global illumination is calculated using a simple diffuse approximation
on top of the sub-surface scattering. When on, the global illumination is
included as part of the surface illumination map for multiple scattering.
This is more accurate, especially for highly translucent materials, but may
slow down the rendering quite a bit.
Prepass blur - controls if the material
will use a simplified diffuse version of the multiple scattering when the
prepass rate for the direct lighting map is too low to adequately
approximate it. A value of 0.0 will cause the
material to always use the illumination map. However, for objects that are
far away from the camera, this may lead to artifacts or flickering in
animations. Larger values control the minimum required samples from the
illumination map in order to use it for approximating multiple scattering.
![[VRayFastSSS example]](vray_for_3ds_max_manual/vrayfastsss2_material/tn_vrayfastsss2.png)
