Hi Kari,

I noticed you did not use any specular higlights in your glass textures. Are
you doing so because specular highlights do not exist in RL and you are
leaving the work to real reflections? I'm asking so since I know you are one
of the most *phisically correct* pov users... ;)
Are there any raytracing packages that do not fake highlights and make them
visible according to the phisical properties of the material?
I hope I was clear (today English does not seem to be my strong point...).

TIA,

--
Jonathan

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JRG <jrg### [at] hotmailcom> wrote:
: I noticed you did not use any specular higlights in your glass textures. Are
: you doing so because specular highlights do not exist in RL and you are
: leaving the work to real reflections?

  Specular highlights are a method to simulate a physical phenomenon which
happens in reality. It's very difficult to simulate this phenomenon by using
just reflection (you need *at least* blurred reflection and probably something
more).

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:3bc49ba9@news.povray.org...
> JRG <jrg### [at] hotmailcom> wrote:
> : I noticed you did not use any specular higlights in your glass textures.
Are
> : you doing so because specular highlights do not exist in RL and you are
> : leaving the work to real reflections?
>
>   Specular highlights are a method to simulate a physical phenomenon which
> happens in reality. It's very difficult to simulate this phenomenon by
using
> just reflection (you need *at least* blurred reflection and probably
something
> more).

Like wavelength scattering and polarization perhaps.

Bob H.

> #macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
> rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
> ],13),8)-3,10>#end blob{N(array[6]{11117333955,
> 7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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JRG wrote:
>
> I noticed you did not use any specular higlights in your glass textures. Are
> you doing so because specular highlights do not exist in RL and you are
> leaving the work to real reflections? 

I was just trying to copy how the highlights looked on
reference photos. I wasn't terribly concerned about the
realism of the simulation. The glass material is probably
ok but everything else is for the looks.

_____________
Kari Kivisalo

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"Warp" <war### [at] tagpovrayorg> wrote in message news:3bc49ba9@news.povray.org...
> JRG <jrg### [at] hotmailcom> wrote:
> : I noticed you did not use any specular higlights in your glass textures. Are
> : you doing so because specular highlights do not exist in RL and you are
> : leaving the work to real reflections?
>
>   Specular highlights are a method to simulate a physical phenomenon which
> happens in reality. It's very difficult to simulate this phenomenon by using
> just reflection (you need *at least* blurred reflection and probably something
> more).
>
Talking about specular highlights, I was considering removing them from my car
and simulate it with an area light and/or looks_like. Would this work?

- Nekar


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"Nekar Xenos" <j-p### [at] citywalkcoza> wrote in message
news:3bc53ac6@news.povray.org...
>
> Talking about specular highlights, I was considering removing them from my
car
> and simulate it with an area light and/or looks_like. Would this work?

area_light no, looks_like yes.  Since area lights still produce just one
point source it'll be the object acting as a light that will be seen in any
reflections.  If your looks like object has highlights on, it will also show
just the one source instead of a array of them.

Bob H.

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Nekar Xenos <j-p### [at] citywalkcoza> wrote:
: Talking about specular highlights, I was considering removing them from my car
: and simulate it with an area light and/or looks_like. Would this work?

  The problem with reflection is that it's linear. This means that if you
have a reflection 0.1, then *everything* which is reflected is multiplied
by 0.1. This means that a "light source" (with a looks_like object) of
color <1,1,1> will be multiplied by 0.1, so only <.1,.1,.1> is reflected.
  However, in realitity bright light sources are reflected in polished surfaces
more than dim light. This is exactly what the specular lighting model tries
to simulate (and succeeds a lot better than reflection alone).

  One idea: I haven't tested what happens if your looks_like object is
colored with <10,10,10> (while the reflecting surface has a reflection 0.1).

  Note that this only works for *perfect mirrors*. In reality surfaces are
seldom perfect mirrors, but they instead scatter light to all directions
(but not evenly: they reflect more light than they scatter to all directions,
and this is what causes highlights). That is, the reflection has a mirror
component and a scattering component.
  The result of this is that highlights are often fuzzy (except for very
polished/smooth surfaces, such as glass or polished metal). Objects do not
reflect the light source as a perfect mirror, but the light source is reflected
fuzzily/blurred.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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I have been trying to do scenes without specular highlighting for some time
now and take advantage of the fresnel type reflection.  I have been using a
white sphere with a high ambient value (say 100) with global ambient set to
1. All other textures have ambient set explicitly to 0.  This seems to work
as I want it to for shiny surfaces. I'm still working on a way to get a
blurred reflection.

-tgq

Try the following scene:

--start--
global_settings {
  assumed_gamma 1.0
  max_trace_level 25
  ambient_light 1
}

camera {
  up y
  right x*image_width/image_height
  location  <3,2,-3>
  look_at   <0,1,0>
}

#declare LB=sphere{0 .5 hollow pigment{rgb 1} finish{ambient 50}}

light_source{0
  rgb 1
  looks_like{LB}
  fade_power 2
  fade_distance 5
  translate <3,3,-3>
}

plane {y 0 pigment{checker rgb 1 rgb 0}}


#declare M1=
material{
  texture{
    pigment{red 1}
    finish{
      conserve_energy
      ambient 0
      diffuse 0
      reflection {
        0 1
        fresnel on
        metallic 1
      }
    }
  }
  interior{ior 25}
}

#declare M2=
material{
  texture{
    pigment{red 1}
    finish{
      conserve_energy
      ambient 0
      diffuse .25
      reflection {
        0 1
        fresnel on
        metallic 0
      }
    }
  }
  interior{ior 1.3}
}

sphere{<1,1,1> 1  material{M1}}
sphere{<-1,1,-1> 1  material{M2}}
--end--

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"Warp" <war### [at] tagpovrayorg> wrote in message
news:3bc5676c@news.povray.org...
>
>   The problem with reflection is that it's linear. This means that if you
> have a reflection 0.1, then *everything* which is reflected is multiplied
> by 0.1. This means that a "light source" (with a looks_like object) of
> color <1,1,1> will be multiplied by 0.1, so only <.1,.1,.1> is reflected.
>   However, in realitity bright light sources are reflected in polished
surfaces
> more than dim light. This is exactly what the specular lighting model
tries
> to simulate (and succeeds a lot better than reflection alone).

Keyword exponent in a reflection statement is the new way of saying
reflection_exponent as was used in v3.1, and it'll do a similar effect as
mentioned by Warp.  Value less than 1.0 will darken all but the brightest
scene objects.

Of course to use looks_like and have a reasonable highlight on the subject
object you'd want to use specular highlighting in the finish of a clear
object acting as the light source in order to get a softened fake highlight.
Else all you get is the directly reflected object outline instead.

That's what Warp was describing is different from the reality if you try
reflection alone.

>   One idea: I haven't tested what happens if your looks_like object is
> colored with <10,10,10> (while the reflecting surface has a reflection
0.1).

It does contribute more to the reflection.  Having checked, high diffuse
creates about the best faked highlighting, kind of figured it might.
Ambient and color are too solid to be useful.  Problem with that idea though
is how you need some non-transparent color for diffuse to do anything which
then can show up where not wanted.

Bob H.

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Bob H. <omn### [at] msncom> wrote:
:>   The problem with reflection is that it's linear.

: Keyword exponent in a reflection statement is the new way of saying
: reflection_exponent as was used in v3.1, and it'll do a similar effect as
: mentioned by Warp.

  Here we can see that even pros don't remember everything... :P

  Yes, the reflection exponent can help a lot here. Great point.

-- 
#macro N(D,I)#if(I<6)cylinder{M()#local D[I]=div(D[I],104);M().5,2pigment{
rgb M()}}N(D,(D[I]>99?I:I+1))#end#end#macro M()<mod(D[I],13)-6,mod(div(D[I
],13),8)-3,10>#end blob{N(array[6]{11117333955,
7382340,3358,3900569407,970,4254934330},0)}//                     - Warp -

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