Whenever I create a scene that contains objects made of glass, I spend a lot of
time tweaking the various pigment, finish, and interior parameters of the
material to try and get something that looks realistic.  Sometimes I start with
what I can find in glass.inc, but it doesn't appear to have been updated since
v3.5.

Has anyone worked on something similar to RC3Metal for glass that takes
advantage of all of the new finish features in later versions?  It might be
something I'd be willing to explore, but I don't have a great grasp on how all
of combinations, including fresnel interact, so it's going to be hit and miss.

Thanks,

-- Chris R.

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Le 2022-08-02 à 11:29, Chris R a écrit :
> Whenever I create a scene that contains objects made of glass, I spend a lot of
> time tweaking the various pigment, finish, and interior parameters of the
> material to try and get something that looks realistic.  Sometimes I start with
> what I can find in glass.inc, but it doesn't appear to have been updated since
> v3.5.
> 
> Has anyone worked on something similar to RC3Metal for glass that takes
> advantage of all of the new finish features in later versions?  It might be
> something I'd be willing to explore, but I don't have a great grasp on how all
> of combinations, including fresnel interact, so it's going to be hit and miss.
> 
> Thanks,
> 
> -- Chris R.
> 
> 

Normally, for a transparent object having an IOR, you use reflection{1 
fresnel} to control the reflectivity. There is usually no need to use 
another value here.
Fresnel reflection depends entirely on the ratio between the ior on each 
sides of the surface and the angle of incidence. A ratio of 1 mean NO 
reflection. A standalone object without an interior defining an ior 
different from 1 will also show no fresnel reflection.

When the fresnel keyword is present, it always default to ON.
falloff and exponent should be left to their default values. Don't use 
those.
Do not use metallic.

Then, you should also use the fresnel option for the highlights. Need 
the latest version. IIRC, it was not implemented in version 3.7, but is 
supported in the latest V1.8 beta.
Examples : specular 0.7 fresnel roughness 0.001, phong 0.7 fresnel 
phong_size 500

Also, you should use transmit 1 or filter 1 as your pigment.
If you want the object to be coloured, use fading in the interior 
statement :
interior{ior 1.5 fade_color rgb<1, 0.6, 0.6> fade_distance 1 fade_power 
1001}// A pink object.
Adjust fade_distance for the dimension and scale of your object. It's 
easily the most important parameter when using fading colours in an 
interior.

ALWAYS use conserve_energy.

Sample glass :
texture{
	pigment{rgbt 1}
	finish{specular 1 roughness 0.001 fresnel
		ambient 0 diffuse 0
		reflection{ 1 fresnel }
		conserve_energy
	}
}
interior{ ior 1.5 //typical glass IOR
	fade_color rgb<0.9, 1, 0.9>//slightly greenish
	fade_distance 2 // Adjust to the size and scale of the object
	fade_power 1001}

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Alain Martel <kua### [at] videotronca> wrote:

> > Whenever I create a scene that contains objects made of glass, I spend a lot of
> > time tweaking the various pigment, finish, and interior parameters of the
> > material to try and get something that looks realistic.  Sometimes I start with
> > what I can find in glass.inc, but it doesn't appear to have been updated since
> > v3.5.
> >
> > Has anyone worked on something similar to RC3Metal for glass that takes
> > advantage of all of the new finish features in later versions?  It might be
> > something I'd be willing to explore, but I don't have a great grasp on how all
> > of combinations, including fresnel interact, so it's going to be hit and miss.
> >
> > Thanks,
> >
> > -- Chris R.
> >
> >
>
> Normally, for a transparent object having an IOR, you use reflection{1
> fresnel} to control the reflectivity. There is usually no need to use
> another value here.
> Fresnel reflection depends entirely on the ratio between the ior on each
> sides of the surface and the angle of incidence. A ratio of 1 mean NO
> reflection. A standalone object without an interior defining an ior
> different from 1 will also show no fresnel reflection.
>
> When the fresnel keyword is present, it always default to ON.
> falloff and exponent should be left to their default values. Don't use
> those.
> Do not use metallic.
>
> Then, you should also use the fresnel option for the highlights. Need
> the latest version. IIRC, it was not implemented in version 3.7, but is
> supported in the latest V1.8 beta.
> Examples : specular 0.7 fresnel roughness 0.001, phong 0.7 fresnel
> phong_size 500
>
> Also, you should use transmit 1 or filter 1 as your pigment.
> If you want the object to be coloured, use fading in the interior
> statement :
> interior{ior 1.5 fade_color rgb<1, 0.6, 0.6> fade_distance 1 fade_power
> 1001}// A pink object.
> Adjust fade_distance for the dimension and scale of your object. It's
> easily the most important parameter when using fading colours in an
> interior.
>
> ALWAYS use conserve_energy.
>
> Sample glass :
> texture{
>  pigment{rgbt 1}
>  finish{specular 1 roughness 0.001 fresnel
>   ambient 0 diffuse 0
>   reflection{ 1 fresnel }
>   conserve_energy
>  }
> }
> interior{ ior 1.5 //typical glass IOR
>  fade_color rgb<0.9, 1, 0.9>//slightly greenish
>  fade_distance 2 // Adjust to the size and scale of the object
>  fade_power 1001}

Thanks for the insights.  I am trying them out now.

I don't have a good understanding of when to use the albedo keywork for specular
and diffuse reflection.  I note that you do not use it above.

-- Chris R.

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On 8/4/22 14:12, Chris R wrote:
> I don't have a good understanding of when to use the albedo keywork for specular
> and diffuse reflection.  I note that you do not use it above.
> 
> -- Chris R.

I'm attaching a text file which amounts to my current notes related to 
finish concerns with POV-Ray - and to some degree what I've been playing 
with in povr to address them(a).

Near the top are my general finish recommendations related to albedo use.

(a) - The file is packaged with my povr tarballs. The version attached 
being my most current - with updates last done in February of this year.


---
I started investigating and writing the file with a hope of creating 
better albedo documentation. I too find the albedo keyword use and 
behavior confusing. Today, despite the file name, it's grown to be my 
'notes / current thinking' related to all finish block concerns.

Bill P.

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Attachments:
Download 'albedofresnelstory.txt' (31 KB)

Le 2022-08-04 à 14:12, Chris R a écrit :
> Alain Martel <kua### [at] videotronca> wrote:
>> Le 2022-08-02 à 11:29, Chris R a écrit :
>>> Whenever I create a scene that contains objects made of glass, I spend a lot of
>>> time tweaking the various pigment, finish, and interior parameters of the
>>> material to try and get something that looks realistic.  Sometimes I start with
>>> what I can find in glass.inc, but it doesn't appear to have been updated since
>>> v3.5.
>>>
>>> Has anyone worked on something similar to RC3Metal for glass that takes
>>> advantage of all of the new finish features in later versions?  It might be
>>> something I'd be willing to explore, but I don't have a great grasp on how all
>>> of combinations, including fresnel interact, so it's going to be hit and miss.
>>>
>>> Thanks,
>>>
>>> -- Chris R.
>>>
>>>
>>
>> Normally, for a transparent object having an IOR, you use reflection{1
>> fresnel} to control the reflectivity. There is usually no need to use
>> another value here.
>> Fresnel reflection depends entirely on the ratio between the ior on each
>> sides of the surface and the angle of incidence. A ratio of 1 mean NO
>> reflection. A standalone object without an interior defining an ior
>> different from 1 will also show no fresnel reflection.
>>
>> When the fresnel keyword is present, it always default to ON.
>> falloff and exponent should be left to their default values. Don't use
>> those.
>> Do not use metallic.
>>
>> Then, you should also use the fresnel option for the highlights. Need
>> the latest version. IIRC, it was not implemented in version 3.7, but is
>> supported in the latest V1.8 beta.
>> Examples : specular 0.7 fresnel roughness 0.001, phong 0.7 fresnel
>> phong_size 500
>>
>> Also, you should use transmit 1 or filter 1 as your pigment.
>> If you want the object to be coloured, use fading in the interior
>> statement :
>> interior{ior 1.5 fade_color rgb<1, 0.6, 0.6> fade_distance 1 fade_power
>> 1001}// A pink object.
>> Adjust fade_distance for the dimension and scale of your object. It's
>> easily the most important parameter when using fading colours in an
>> interior.
>>
>> ALWAYS use conserve_energy.
>>
>> Sample glass :
>> texture{
>>   pigment{rgbt 1}
>>   finish{specular 1 roughness 0.001 fresnel
>>    ambient 0 diffuse 0
>>    reflection{ 1 fresnel }
>>    conserve_energy
>>   }
>> }
>> interior{ ior 1.5 //typical glass IOR
>>   fade_color rgb<0.9, 1, 0.9>//slightly greenish
>>   fade_distance 2 // Adjust to the size and scale of the object
>>   fade_power 1001}
> 
> Thanks for the insights.  I am trying them out now.
> 
> I don't have a good understanding of when to use the albedo keywork for specular
> and diffuse reflection.  I note that you do not use it above.
> 
> -- Chris R.
> 
> 

You use albedo when you also use a brilliance that differs from the 
default of 1.

As I did not use brilliance in my example, it was not useful to use albedo.

Example of the use of albedo and fresnel with an opaque pigment :

pigment{rgb< 0.7, 1, 0.2>}
finish{
	brilliance 10 //high brilliance for a very highly polished surface
	diffuse albedo 0.7 // albedo needed to have correct illumination
	specular albedo 1 roughness 0.01// albedo also needed due to the high 
brilliance
// I like to put the roughness on the same line as specular as they work 
together
// Same thing for phong and phong_size.
	fresnel // have the IOR also affect the highlights

	reflection{1 fresnel}
	}
interior{ior 1.7}

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On 8/5/22 13:29, Alain Martel wrote:
> You use albedo when you also use a brilliance that differs from the 
> default of 1.
> 
> As I did not use brilliance in my example, it was not useful to use albedo.

FWIW. In the latest v3.8/v4.0 code only the diffuse component of finish 
changes on the brilliance value. Further, the diffuse value as used by 
radiosity changes on brilliance of other than 1.0 only 'without' the use 
of albedo. With albedo only the non-radiosity diffuse value is adjusted.

Bill P.

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