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Fun fact to know:
The realistic range for the "specular" and "phong" parameters is /not/
limited to 0..1.
Instead, for a polished material, a value of
specular 0.25 * ((1/ROUGHNESS)+1) * REFLECTION
or
phong 0.5 * (PHONG_SIZE + 1) * REFLECTION
is actually realistic, e.g.
finish {
reflection { 0.2 }
specular 50.05
roughness 0.001
}
or
finish {
reflection { 0.2 }
phong 100.1
phong_size 1000
}
BTW there's also a similar law goverining the "diffuse" parameter: If
you set "brilliance" to anything but 1, you should set "diffuse" to a
maximum of
diffuse 0.5 * (BRILLIANCE + 1)
which would correspond to a diffuse reflection of 100%.
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clipka <ano### [at] anonymous org> wrote:
> The realistic range for the "specular" and "phong" parameters is /not/
> limited to 0..1.
Using a very strong specular/phong highlight, but making the highlight
small, is a good trick to make a surface look like highly polished, such
as glass (which usually has very sharp highlights rather than smooth ones).
--
- Warp
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Thank you very much. Are these "Clipka's Laws", or is there another term for
these relations?
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clipka <ano### [at] anonymousorg> wrote:
> Instead, for a polished material, a value of
>
> specular 0.25 * ((1/ROUGHNESS)+1) * REFLECTION
>
> or
>
> phong 0.5 * (PHONG_SIZE + 1) * REFLECTION
>
> is actually realistic, [...]
How is this relationship affected if the material isn't "polished"?
How is this affected by variable or fresnel reflection?
Is there any relationship between reflection and roughness/phong_size?
> BTW there's also a similar law goverining the "diffuse" parameter: If
> you set "brilliance" to anything but 1, you should set "diffuse" to a
> maximum of
>
> diffuse 0.5 * (BRILLIANCE + 1)
>
> which would correspond to a diffuse reflection of 100%.
Does this mean that you can set diffuse > 1 if brilliance is > 1?
In metals.inc and golds.inc, brilliance is increased as reflection is increased.
Is there such a correlation in reality, or was that just the way it was decided
to define the textures?
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Am 04.07.2012 23:27, schrieb Cousin Ricky:
> clipka<ano### [at] anonymousorg> wrote:
>> Instead, for a polished material, a value of
>>
>> specular 0.25 * ((1/ROUGHNESS)+1) * REFLECTION
>>
>> or
>>
>> phong 0.5 * (PHONG_SIZE + 1) * REFLECTION
>>
>> is actually realistic, [...]
>
> How is this relationship affected if the material isn't "polished"?
Mu. POV-Ray's reflection is only realistic for polished surfaces.
> How is this affected by variable or fresnel reflection?
Phong and specular currently don't respect fresnel's law, so when using
fresnel reflection you should reduce the specular or phong parameter a
bit to compensate; it's not the real thing though.
> Is there any relationship between reflection and roughness/phong_size?
If we're talking about polished surfaces: Yes, obviously there is a
relationship - it's in the formulae given above.
If we're talking about dull surfaces, then mu - as stated above, POV-Ray
does not natively support dull (aka blurred) reflections.
>> BTW there's also a similar law goverining the "diffuse" parameter: If
>> you set "brilliance" to anything but 1, you should set "diffuse" to a
>> maximum of
>>
>> diffuse 0.5 * (BRILLIANCE + 1)
>>
>> which would correspond to a diffuse reflection of 100%.
>
> Does this mean that you can set diffuse> 1 if brilliance is> 1?
Well, you /can/ do that regardless of brilliance, except that it would
be unrealistic at brilliance = 1; but for a material with brilliance 2,
diffuse 1.2 isn't unrealistic.
> In metals.inc and golds.inc, brilliance is increased as reflection is increased.
> Is there such a correlation in reality, or was that just the way it was decided
> to define the textures?
That's just the way they did it. There's not much parameterization in
metals.inc or golds.inc that has any correlation to reality whatsoever -
the material parameters were chosen solely for artistic reasons.
BTW, by now POV-Ray has acquired some new syntax to automatically do the
above computations for you: Specifying
specular albedo SPECULAR_ALBEDO
roughness ROUGHNESS
phong albedo PHONG_ALBEDO
phong_size PHONG_SIZE
diffuse albedo DIFFUSE_ALBEDO
brilliance BRILLIANCE
is equivalent to:
specular 0.25 * ((1/ROUGHNESS)+1) * SPECULAR_ALBEDO
roughness ROUGHNESS
phong 0.5 * (PHONG_SIZE + 1) * PHONG_ALBEDO
phong_size PHONG_SIZE
diffuse 0.5 * (BRILLIANCE + 1) * DIFFUSE_ALBEDO
brilliance BRILLIANCE
Specular and phong albedo should be equal to reflection (for polished
materials), while the sum of reflection and diffuse albedo should be 1
or lower.
(Fresnel (or variable) reflection equivalent is still not supported for
highlights though, and significantly dull reflection is still not
available out of the box.)
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clipka <ano### [at] anonymousorg> wrote:
> Am 04.07.2012 23:27, schrieb Cousin Ricky:
> > How is this relationship affected if the material isn't "polished"?
>
> Mu. POV-Ray's reflection is only realistic for polished surfaces.
What is mu?
> > Is there any relationship between reflection and roughness/phong_size?
>
> If we're talking about polished surfaces: Yes, obviously there is a
> relationship - it's in the formulae given above.
What I'm asking is for a given reflection value, can we predict what the
roughness value will be?
> If we're talking about dull surfaces, then mu - as stated above, POV-Ray
> does not natively support dull (aka blurred) reflections.
This is probably not a good idea (yet?) anyway. Best to let the users weigh the
various methods and tradeoffs.
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Am 06.07.2012 02:22, schrieb Cousin Ricky:
> clipka<ano### [at] anonymousorg> wrote:
>> Am 04.07.2012 23:27, schrieb Cousin Ricky:
>>> How is this relationship affected if the material isn't "polished"?
>>
>> Mu. POV-Ray's reflection is only realistic for polished surfaces.
>
> What is mu?
A concept from (AFAIK) Zen Buddhism: A reply given to questions for
which there is no meaningful answer.
>>> Is there any relationship between reflection and roughness/phong_size?
>>
>> If we're talking about polished surfaces: Yes, obviously there is a
>> relationship - it's in the formulae given above.
>
> What I'm asking is for a given reflection value, can we predict what the
> roughness value will be?
No; the reflection value describes how /much/ of the incoming light is
reflected (for light coming from other objects); the roughness value
describes how /focused/ the reflection of incoming light will be (from
light sources).
>> If we're talking about dull surfaces, then mu - as stated above, POV-Ray
>> does not natively support dull (aka blurred) reflections.
>
> This is probably not a good idea (yet?) anyway. Best to let the users weigh the
> various methods and tradeoffs.
Well, I personally think blurred reflections are a /great/ thing to
have. They can really make or (in case of their absence) break a scene
(especially if they're in tune with the highlights parameters).
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clipka <ano### [at] anonymousorg> wrote:
> Am 06.07.2012 02:22, schrieb Cousin Ricky:
> > clipka<ano### [at] anonymousorg> wrote:
> >> If we're talking about dull surfaces, then mu - as stated above, POV-Ray
> >> does not natively support dull (aka blurred) reflections.
> >
> > This is probably not a good idea (yet?) anyway. Best to let the users weigh the
> > various methods and tradeoffs.
>
> Well, I personally think blurred reflections are a /great/ thing to
> have. They can really make or (in case of their absence) break a scene
> (especially if they're in tune with the highlights parameters).
I agree; I just don't know that we've agreed upon the best way to implement it.
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Am 06.07.2012 16:47, schrieb Cousin Ricky:
> clipka<ano### [at] anonymousorg> wrote:
>> Am 06.07.2012 02:22, schrieb Cousin Ricky:
>>> clipka<ano### [at] anonymousorg> wrote:
>>>> If we're talking about dull surfaces, then mu - as stated above, POV-Ray
>>>> does not natively support dull (aka blurred) reflections.
>>>
>>> This is probably not a good idea (yet?) anyway. Best to let the users weigh the
>>> various methods and tradeoffs.
>>
>> Well, I personally think blurred reflections are a /great/ thing to
>> have. They can really make or (in case of their absence) break a scene
>> (especially if they're in tune with the highlights parameters).
>
> I agree; I just don't know that we've agreed upon the best way to implement it.
It seems plain as hell to me that the only reasonable way to implement
it is some kind of oversampling with jitter added to the reflected ray.
And it seems also plain as hell to me that the only reasonable way to
handle the resulting heavy blow on render performance is to integrate
all oversampling-based mechanisms into one bigger picture, encompassing
anti-aliasing, focal blur, media, fog, area lights, subsurface light
transport, and blurred reflections/refractions. As it is now, all of
these features do their own full-blown oversampling, thus having a fully
multiplicative effect on render time each, even though oversampling
could be much more "lazy" whenever additional oversampling is performed
somewhere "closer" to the camera anyway.
That, in my opinion, is the only reasonable way to implement it.
As for syntax, parameterization should obviously make it easy to
properly "synchronize" reflection and highlight parameters, ideally in
such a way that the very same values used in both the reflection
"blurriness parameter" and specular roughness produces the most
realistic match (not the phong_size BTW, as specular highlights are the
better choice when it comes to realism); adding fresnel support for
highlights would be highly desirable as well.
Some additional parameters might be added to control the oversampling,
though I think they can just as well be deduced from the blurriness and
strength of reflection.
All in all, aside from the choice of keywords and other syntax details,
I think that after giving it thorough thought, there are no notable
things to disagree about.
(Speaking of Syntax, copying the MCPov one for the sake of scene
portability is definitely a no-go; not only is it far away from all
traditional POV-Ray syntax patterns - it also uses a totally
intransparent "blurriness" parameterization, and the oversampling
parameterization is rather poor as well.)
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Le 06/07/2012 19:34, clipka a écrit :
> Am 06.07.2012 16:47, schrieb Cousin Ricky:
>> clipka<ano### [at] anonymousorg> wrote:
>>> Am 06.07.2012 02:22, schrieb Cousin Ricky:
>>>> clipka<ano### [at] anonymousorg> wrote:
>>>>> If we're talking about dull surfaces, then mu - as stated above,
>>>>> POV-Ray
>>>>> does not natively support dull (aka blurred) reflections.
A bit late, but have a look at "crand".
It's not a blurred reflection, but the noise added to the usual
reflection is often enough to move away from the perfectly smooth surface.
Crand has not been re-implemented in povray 3.7RC6, but the next RC
should have it.
(so, look at it in 3.6 in the meantime)
--
Real software engineers work from 9 to 5, because that is
the way the job is described in the formal spec. Working
late would feel like using an undocumented external procedure.
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