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clipka <ano### [at] anonymous org> wrote:
> At the default of "brilliance 1" the brightness of the diffuse component
> depends on the angle of the incoming light, following a cos(theta) law,
> where theta is the angle between the light ray and the surface normal
> (the vector perpendicular to the surface).
>
> Similarly, if we're talking about brightness as the total amount of
> light reaching the observer from any given patch of surface, the
> brightness of the diffuse component also depends on the angle of the
> /outgoing/ light (i.e. the angle at which the surface is seen by an
> observer), following the very same cos(theta) law. However, this is
> already modeled exactly by the patch of surface appearing to get smaller
> as theta increases, while the brightness of any individual pixel remains
> constant.
>
> Using "brilliance N" with any value other than 1 changes the dependency
> between the brightness of the diffuse component and the angle of
> incoming light: Rather than following a cos(theta) law, it now follows a
> cos(theta)^N law.
>
> Now there is some fundamental law known to the contemporary world of
> professional and academic rendering, that any physically realistic
> shading formula must be "bi-directional", i.e. if you exchange the
> incoming and outgoing light rays, the formula must still yield the same
> result.
>
> Thus, when you change the brightness' dependency on the incoming
> direction, you also need to change the dependency on the outgoing
> direction accordingly.
>
> Traditionally however, POV-Ray will fail to do this, always leaving the
> brightness of an individual pixel constant no matter what the
> orientation of the surface towards the observer, which - as mentioned
> before - happens to be a perfect match for "brilliance 1", but breaks
> bi-directionality at any other setting.
>
> Now fixing this behaviour of the "brilliance" keyword would be possible,
> but it would break each and every existing scene that makes use of
> brilliance. Therefore, I introduced an optional second parameter to
> "brilliance" which governs the dependency on the outgoing direction,
> allowing to restore bi-directionality by setting both parameters to the
> same value.
First of all, thank you very much for sharing this. This article is full of
information to me, and I'm interested in knowing such a thing. Now I get the
idea. You said that a bi-directionality is a law known to academic rendering, so
we believe it for now. And with many other new features I saw in your posts,
there is a marked gain with pov-ray. I'm impressed.
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clipka <ano### [at] anonymousorg> wrote:
> There's a caveat with the latter: When it comes to the brightness of
> light sources, POV-Ray's parameterization is off by some factor of pi or
> 2*pi (can't remember which, and whether you need to multiply or divide)
> from the parameterization commonly used in papers on image synthesis.
Thank you. I knew this. It must do. This is due to POV-Ray's light source
defines the color of a diffuse surface which is illuminate by the light source
at a distance of fade_distance.
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"And" <49341109@ntnu.edu.tw> wrote:
> Thank you. I knew this. It must do. This is due to POV-Ray's light source
> defines the color of a diffuse surface which is illuminate by the light source
> at a distance of fade_distance.
I'm very smart.!!
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On 26/06/2015 07:34, And wrote:
> "And" <49341109@ntnu.edu.tw> wrote:
>> Thank you. I knew this. It must do. This is due to POV-Ray's light source
>> defines the color of a diffuse surface which is illuminate by the light source
>> at a distance of fade_distance.
>
> I'm very smart.!!
>
LOL
You are too. :-)
--
Regards
Stephen
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On 26-6-2015 8:58, Stephen wrote:
> On 26/06/2015 07:34, And wrote:
>> "And" <49341109@ntnu.edu.tw> wrote:
>>> Thank you. I knew this. It must do. This is due to POV-Ray's light
>>> source
>>> defines the color of a diffuse surface which is illuminate by the
>>> light source
>>> at a distance of fade_distance.
>>
>> I'm very smart.!!
>>
>
> LOL
> You are too. :-)
>
Why do I feel depressed now? :-)
--
Thomas
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On 25-6-2015 20:00, And wrote:
> Just like the opinion clipka have answered you the other day, an emission sphere
> in the sky is too small to render. I always use the parallel light to
> simulate the sun light and it is very convenient. If you would like to place a
> white look-like object, the sun's color should like this: rgb<1,1,1>*10000.
> Is a very large quantity.
>
>
Depending on the scene, the multiplicator used can be less than that. In
my experiments shown in p.b.i I used a multiplicator of 2 which works
quite well. Much higher values overexpose the scene.
--
Thomas
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Am 26.06.2015 um 09:53 schrieb Thomas de Groot:
> On 25-6-2015 20:00, And wrote:
>> Just like the opinion clipka have answered you the other day, an
>> emission sphere
>> in the sky is too small to render. I always use the parallel light to
>> simulate the sun light and it is very convenient. If you would like to
>> place a
>> white look-like object, the sun's color should like this:
>> rgb<1,1,1>*10000.
>> Is a very large quantity.
>>
>>
>
> Depending on the scene, the multiplicator used can be less than that. In
> my experiments shown in p.b.i I used a multiplicator of 2 which works
> quite well. Much higher values overexpose the scene.
Maybe there's a misundertanding here:
The multiplicator is needed on the looks_like object; the light_source
brightness should stay the same if you don't use fade_power.
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On 26-6-2015 14:55, clipka wrote:
> Am 26.06.2015 um 09:53 schrieb Thomas de Groot:
>> On 25-6-2015 20:00, And wrote:
>>> Just like the opinion clipka have answered you the other day, an
>>> emission sphere
>>> in the sky is too small to render. I always use the parallel light to
>>> simulate the sun light and it is very convenient. If you would like to
>>> place a
>>> white look-like object, the sun's color should like this:
>>> rgb<1,1,1>*10000.
>>> Is a very large quantity.
>>>
>>>
>>
>> Depending on the scene, the multiplicator used can be less than that. In
>> my experiments shown in p.b.i I used a multiplicator of 2 which works
>> quite well. Much higher values overexpose the scene.
>
> Maybe there's a misundertanding here:
>
> The multiplicator is needed on the looks_like object; the light_source
> brightness should stay the same if you don't use fade_power.
>
True enough. THere was a misunderstanding though from my side (of
course) as I had also added an emission to the looks_like object which
it doesn't need in fact with And's suggestion.
--
Thomas
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Am 26.06.2015 um 16:52 schrieb Thomas de Groot:
> On 26-6-2015 14:55, clipka wrote:
>> Am 26.06.2015 um 09:53 schrieb Thomas de Groot:
>>> On 25-6-2015 20:00, And wrote:
>>>> Just like the opinion clipka have answered you the other day, an
>>>> emission sphere
>>>> in the sky is too small to render. I always use the parallel light to
>>>> simulate the sun light and it is very convenient. If you would like to
>>>> place a
>>>> white look-like object, the sun's color should like this:
>>>> rgb<1,1,1>*10000.
>>>> Is a very large quantity.
>>>>
>>>>
>>>
>>> Depending on the scene, the multiplicator used can be less than that. In
>>> my experiments shown in p.b.i I used a multiplicator of 2 which works
>>> quite well. Much higher values overexpose the scene.
>>
>> Maybe there's a misundertanding here:
>>
>> The multiplicator is needed on the looks_like object; the light_source
>> brightness should stay the same if you don't use fade_power.
>>
>
> True enough. THere was a misunderstanding though from my side (of
> course) as I had also added an emission to the looks_like object which
> it doesn't need in fact with And's suggestion.
Um... a looks_like object should _always_ have a emission! Otherwise it
won't look like what a light source would look like.
However, And has correctly hinted someplace else at conflict between
different ways of simulating the same thing when using a "looks_like"
object. A light source should only show up in one of the two ways of
each of the following pairs:
- Classic diffuse illumination vs. radiosity: A "looks_like" object
should always have "no_radiosity on" set, which unfortunately isn't the
default. (Theoretically, an alternative would be to make the light
source invisible for the sake of the "diffuse" component, but in
practice that doesn't make any sense due to the vast differences in
computational effort; if you want to go that far, just leave out the
light source entirely and go with the "looks_like" object alone.)
- Specular highlights vs. reflections: A "looks_like" object should have
"no_reflection on" set. An alternative would be to make the light source
invisible for the sake of specular highlights, but POV-Ray doesn't
support this at the moment (which puts me to shame, as I must admit).
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Thomas de Groot <tho### [at] degrootorg> wrote:
> On 26-6-2015 14:55, clipka wrote:
> > Am 26.06.2015 um 09:53 schrieb Thomas de Groot:
> >> On 25-6-2015 20:00, And wrote:
> >>> Just like the opinion clipka have answered you the other day, an
> >>> emission sphere
> >>> in the sky is too small to render. I always use the parallel light to
> >>> simulate the sun light and it is very convenient. If you would like to
> >>> place a
> >>> white look-like object, the sun's color should like this:
> >>> rgb<1,1,1>*10000.
> >>> Is a very large quantity.
> >>>
> >>>
> >>
> >> Depending on the scene, the multiplicator used can be less than that. In
> >> my experiments shown in p.b.i I used a multiplicator of 2 which works
> >> quite well. Much higher values overexpose the scene.
> >
> > Maybe there's a misundertanding here:
> >
> > The multiplicator is needed on the looks_like object; the light_source
> > brightness should stay the same if you don't use fade_power.
> >
>
> True enough. THere was a misunderstanding though from my side (of
> course) as I had also added an emission to the looks_like object which
> it doesn't need in fact with And's suggestion.
>
> --
> Thomas
I saw the third one 'rsocp_uber_metallic.png' is just what my skill. I like it.
The color of sky is realism, too.
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