On Tue, 19 Nov 2002 12:27:13 -0000, "Andrew Cocker"
<mai### [at] andrewcockercouk> wrote:

>How did you implement the subsurface scattering?

It's quite easy, actually.

First of all, you obviously need, well, subsurface scattering :), or,
in POV terms, scattering media filling a hollow object. Make it white,
so that it scatters all light equally. Make it realistic, i.e.
extinction 1

Then you need to ensure that light actually penetrates the surface.
Give all your colors a filter 1 (easy in my case, as these are all
image maps). With enough scattering on the inside, the white light
from inside filters through the colored surface and it looks like the
object is opaque.

As you might have seen in my original post, this approach causes some
problems at shallow angles, as the media does not scatter enough light
to extinguish all of it and the background can be seen through. To
avoid it, add an opaque interior_texture. For most realism, make it
the same as the external one, though you may wish to remove reflection
from it as it will only contribute to the render times and not to the
image.

Last, you need to avoid self-shadowing as it really kills the effect.
Simply putting no_shadow won't do it because then the object will not
cast a shadow on anything, and we don't want that. Light groups may be
an option, but it's easier to separate the surface from the interior.
Simply make two copies of the object, one being the "shell" - with
texture and interior texture, and the other being the "interior",
slightly smaller, with a clear pigment and object scattering media.
Give the "shell" no_shadow and you're in business.

To push things really on the cool side, give the "shell" some ior.
This bends the image inside so that you get a distorted terminator
line characteristic of subsurface scattering (see some MAX/Brazil
images implementing a s. sc. shader).

That's it, quite simple, really, but the result is good.

>How noticeable an effect is it giving to the scene?

See for yourself. First attachment is without, second is with.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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