Hi folks,

I'm sorry if this has been addressed elsewhere; if so please point me
in the correct direction.

I am trying to render some translucent objects (plastic pipette tips, to be
specific).  I tried using the standard transparency, but the background was
transmitted too cleanly and sharply; instead of plastic, the pipette tips
ended up looking as if they were made of glass.  The problem is that these
items aren't transparent per se, but they are not opaque, either (so
some kind of subsurface shading that uses internal opaque objects
doesn't seem like a viable option either - I need some elements
of the background visible through the plastic objects... Or a way of
faking it).  They transmit a certain amount of light and even some detail,
but not clear detail.  I'm hunting for a way to model this.
I've become sort of caught up in the idea of rendering translucent
objects.  What about frosted glass, for example?  Or shoji screens?  Anyone
have any advice?

Thanks much!

-Brook

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> I am trying to render some translucent objects

If you're material consists of only one color and density, you can use 
attenuation:

http://povray.org/documentation/view/3.6.1/416/

Otherwise, for more control over the effect, use media, especially 
absorbing and scattering media:

http://povray.org/documentation/view/3.6.1/419/


HTH, just ask if you got further questions!
Florian

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Wasn't it Brook who wrote:

>I am trying to render some translucent objects

You might try using mirconormals. If you're not using specular
highlights, you can just use something like 
        normal {granite 0.4 scale 0.000001}

For shiny objects, however, that also breaks up the highlights and makes
it obvious that the effect is happening on the surface, rather than in
the interior of the object. To fix that, you can add a second, slightly
scaled, copy of the shape that is entirely invisible apart from a smooth
specular highlight. (I couldn't manage to get the effect to work using
layered textures.)

Antialiassing is required for the effect to look anything like
convincing.

global_settings {assumed_gamma 1.0}
camera {location  <0,10,-10> look_at <0,0,0> angle 20}
light_source {<-30, 100, -30> color rgb 1}

plane {y, -1 pigment {checker}}

sphere {0,1
  pigment {rgbt <1,1,1,0.8>}
  interior {ior 1.1}
  normal {granite 0.4 scale 0.000001}
}

sphere {0,1.00001
  pigment {rgbt <1,1,1,1>}
  finish {phong 1}
}



-- 
Mike Williams
Gentleman of Leisure

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Thank-you very much Mike!  This is in the direction I am aiming, although
the backgrounds end up looking sort of speckled when viewed through
objects.  Not perfect, but closer.  I was thinking the next step might be
to iteratively average a bunch of textures on the "inner" sphere (same
technique for making blurred reflections) with different normals.

Again, thanks!

-Brook




Mike Williams <nos### [at] econymdemoncouk> wrote:

> Wasn't it Brook who wrote:
>
> >I am trying to render some translucent objects
>
> You might try using mirconormals. If you're not using specular
> highlights, you can just use something like
>         normal {granite 0.4 scale 0.000001}
>
> For shiny objects, however, that also breaks up the highlights and makes
> it obvious that the effect is happening on the surface, rather than in
> the interior of the object. To fix that, you can add a second, slightly
> scaled, copy of the shape that is entirely invisible apart from a smooth
> specular highlight. (I couldn't manage to get the effect to work using
> layered textures.)
>
> Antialiassing is required for the effect to look anything like
> convincing.

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FYI, this produced pretty much what I am looking for, although it
predictably shoots my rendering time through the roof.  No complaints here
though!  I'm going to fiddle with it some more and then I'll upload some
results.  While poking around I somewhat sheepishly discovered this:

http://tag.povray.org/povQandT/languageQandT.html#blurredreflection

Which describes more or less what I want; should have read this before
pestering you guys =)

Thanks for your help!

-Brook

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