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Tom Melly <tom### [at] tomandlu couk> wrote in message
news:3a5d7f8a$1@news.povray.org...
> "Hookflash" <hoo### [at] hotmailcom> wrote in message
> news:3A5### [at] hotmailcom...
>
> My intuition is that diffuse and reflection should add to 1.
Asuming the object does not absorb light. I recall reading in some
tutoial or book that diffuse should not be set to 1 as no object diffusely
reflects
all light falling on it.
I tend to work by the rule that ambient + diffuse + reflection < 1 unless
I'm trying
for some odd effect
Gail
********************************************************************
* gsh### [at] monotixcoza * System.dat not found. *
* http://www.rucus.ru.ac.za/~gail/ * Reformat hard drive Y)es O)k *
********************************************************************
* If at first you don't succeed, call it version 1.0 *
********************************************************************
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"Gail Shaw" <gsh### [at] monotixcoza> wrote in message
news:3a5d8947@news.povray.org...
>
>
> Asuming the object does not absorb light. I recall reading in some
> tutoial or book that diffuse should not be set to 1 as no object diffusely
> reflects
> all light falling on it.
>
> I tend to work by the rule that ambient + diffuse + reflection < 1 unless
> I'm trying
> for some odd effect
>
> Gail
I wondered about that, and consequently left it out. Aren't absorption and
pigment the same? i.e. the colour of an object is the colour of the light
that isn't absorped? Also, IMHO, ambient should be in a separate calc. Dunno
what though.
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In article <3a5d8947@news.povray.org>, "Gail Shaw"
<gsh### [at] monotixcoza> wrote:
> Asuming the object does not absorb light. I recall reading in some
> tutoial or book that diffuse should not be set to 1 as no object
> diffusely reflects all light falling on it.
Also, if you are using a pigment that is darker than pure white, that
will give a lower diffuse. The diffuse keyword just allows you to adjust
the whole thing...
--
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
<><
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On Thu, 11 Jan 2001 09:40:26 -0000, Tom Melly wrote:
>My intuition is that diffuse and reflection should add to 1. Light falling
>on an object that isn't reflected is diffused and visa versa. Ambient, on
>the other hand, is a "fake" effect to simulate radiosity in a scene.
Don't forget filter/transmit and specular. Those should be included in your
sum as well.
Ambient is equivalent to "diffuse reflection from unknown light sources" and
as such should probably also be included in the sum. I always include it in
the sum, at any rate.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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"Ron Parker" <ron### [at] povrayorg> wrote in message
news:slr### [at] fwicom...
>
> Ambient is equivalent to "diffuse reflection from unknown light sources"
and
> as such should probably also be included in the sum. I always include it
in
> the sum, at any rate.
>
Yes, it should be included - I'm just not sure how. After all, for an object
in deep space, ambient would be pretty much 0 for all objects. Which seems
to imply that ambient is a property of the scene rather than the object.
However, an object with reflection 1 always has, by implication, an ambient
of 0, which implies that it is an attribute of the object.
The trouble with ambient is that to make any real sense it should be
influenced by the overall strength of the light-sources available. Perhaps
one should code like this:
#declare light_strength = 0.75;
light_source{<0,0,0> color rgb<1,1,1>*light_strength translate <-300,
300, -300>}
object{foo finish{ambient 0.3*light_strength}}
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On Thu, 11 Jan 2001 13:45:07 -0000, Tom Melly wrote:
>The trouble with ambient is that to make any real sense it should be
>influenced by the overall strength of the light-sources available. Perhaps
>one should code like this:
>
>#declare light_strength = 0.75;
>light_source{<0,0,0> color rgb<1,1,1>*light_strength translate <-300,
>300, -300>}
>object{foo finish{ambient 0.3*light_strength}}
But one does code like that, if one knows about the all-important
global_settings { ambient_light COLOR } setting. Just look at it
as a big shadowless light source that casts light in all directions
from everywhere.
So, the ambient setting in a finish statement seems to me as though it
should be closely related to diffuse, particularly if brilliance is low.
As brilliance goes up, ambient should go down relative to diffuse. As
diffuse goes up, ambient should also go up.
If I were to propose a rule of thumb, I would say ambient and diffuse
should be roughly the same number, and that ambient shouldn't be included
in the requirement that filter+transmit+reflection+diffuse+specular <= 1.
The logic behind the first part is that ambient is just diffuse reflection
of light with an unspecified source, so if an object diffusely reflects
60% of any light falling on it, it should diffusely reflect 60% of the
ambient light. (If this makes your scene too bright, turn down the ambient
light in global_settings or consider using radiosity instead of ambient
light.)
The logic behind the second part is that what an object does with light
from unspecified sources shouldn't have any effect on what it does with
light from a specific source. That is, you wouldn't keep everything
below .5 just because you have two light sources, so there's no reason
to do so because you have ambient light.
Actually, now that I think about it, I'm not so sure both specular and
reflection should be in the sum either, since the purpose of specular is
to simulate reflection for light sources. By the same logic, specular and
reflection should probably be fairly closely related unless you're using
blurred reflection in MegaPOV.
--
Ron Parker http://www2.fwi.com/~parkerr/traces.html
My opinions. Mine. Not anyone else's.
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"Ron Parker" <ron### [at] povrayorg> wrote in message
news:slr### [at] fwicom...
>
> But one does code like that, if one knows about the all-important
> global_settings { ambient_light COLOR } setting. Just look at it
> as a big shadowless light source that casts light in all directions
> from everywhere.
>
Well, yes, but even using global ambient, the ambient of objects won't
change as you adjust the strength of the light-sources in the image.
> So, the ambient setting in a finish statement seems to me as though it
> should be closely related to diffuse, particularly if brilliance is low.
Yes.
> As brilliance goes up, ambient should go down relative to diffuse. As
> diffuse goes up, ambient should also go up.
>
> If I were to propose a rule of thumb, I would say ambient and diffuse
> should be roughly the same number, and that ambient shouldn't be included
> in the requirement that filter+transmit+reflection+diffuse+specular <= 1.
>
I'm sure you're right - however, understanding this would require me to
think of more than two things at the same time, so I cannot verify ;)
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Ron Parker wrote:
>
> If I were to propose a rule of thumb, I would say ambient and diffuse
> should be roughly the same number, and that ambient shouldn't be included
> in the requirement that filter+transmit+reflection+diffuse+specular <= 1.
Even though, you hint on it in the next paragraph, you should point out
that this formula is only valid if you are not using radiosity.
>
> The logic behind the first part is that ambient is just diffuse reflection
> of light with an unspecified source, so if an object diffusely reflects
> 60% of any light falling on it, it should diffusely reflect 60% of the
> ambient light. (If this makes your scene too bright, turn down the ambient
> light in global_settings or consider using radiosity instead of ambient
> light.)
>
> The logic behind the second part is that what an object does with light
> from unspecified sources shouldn't have any effect on what it does with
> light from a specific source. That is, you wouldn't keep everything
> below .5 just because you have two light sources, so there's no reason
> to do so because you have ambient light.
>
> Actually, now that I think about it, I'm not so sure both specular and
> reflection should be in the sum either, since the purpose of specular is
> to simulate reflection for light sources. By the same logic, specular and
> reflection should probably be fairly closely related unless you're using
> blurred reflection in MegaPOV.
>
> --
> Ron Parker http://www2.fwi.com/~parkerr/traces.html
> My opinions. Mine. Not anyone else's.
--
Francois Labreque | Unfortunately, there's no such thing as a snooze
flabreque | button on a cat who wants breakfast.
@ | - Unattributed quote from rec.humor.funny
videotron.ca
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Tom Melly wrote:
>
> "Ron Parker" <ron### [at] povrayorg> wrote in message
> news:slr### [at] fwicom...
> >
> > But one does code like that, if one knows about the all-important
> > global_settings { ambient_light COLOR } setting. Just look at it
> > as a big shadowless light source that casts light in all directions
> > from everywhere.
> >
>
> Well, yes, but even using global ambient, the ambient of objects won't
> change as you adjust the strength of the light-sources in the image.
If global ambient is linked to the strength of your light sources (or
number thereof) via something similar to the "ambient
0.3*Light_Strength*light_num", then the induvidual ambient of objects
doesn't need to be played with as long as you also take into account the
proximity of the light sources to the object (as someone mentioned
earlier: in space, there is very little ambient) when giving these
objects ambient values in the first place.
I personally prefer setting ambient to 0 and let radiosity take care of
all this stuff. But then again, I have the horsepower necessary for it,
so ymmv.
--
Francois Labreque | Unfortunately, there's no such thing as a snooze
flabreque | button on a cat who wants breakfast.
@ | - Unattributed quote from rec.humor.funny
videotron.ca
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"Francois Labreque" <fla### [at] videotronca> wrote in message
news:3A5DCD94.E1942106@videotron.ca...
>
> If global ambient is linked to the strength of your light sources (or
> number thereof) via something similar to the "ambient
> 0.3*Light_Strength*light_num", then the induvidual ambient of objects
Pretty much what I suggested earlier.
>
> I personally prefer setting ambient to 0 and let radiosity take care of
> all this stuff. But then again, I have the horsepower necessary for it,
> so ymmv.
>
I personally prefer it if people don't rub my nose in the fact that a P90 is
not the ideal rendering platform - particularily if they're french ;)
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