Hey all,

I know what you're thinking: "Is this guy ever going to stop bothering us
with his petty little problems?"  The answer is NO!!!  Be prepared to be
tormented forever as I pick every nit I can find!!!

But seriously...  the attached image shows a ceiling with a bunch of
cylindrical cut-outs in it.  In every cut-out there are two light sources
(one at each end).  I'm using lights with fade_distance, but the far end of
the scene is as brightly lit as the near end (there is a fill-light
positioned at the camera position which also uses fade_distance, making the
nearest pillar slightly brighter than the others).  It seems as if light
quits fading when it hits an object.  Is this the case?  Should this be the
case??  Is this a bug???  I will re-render the scene making the more distant
lights progressively dimmer, but thought I'd ask anyway.  For reference, the
pillars are 8 units tall, 15 units apart, and there are 45 pairs of pillars
(making the farthest pillar 660 units from the nearest one).  The lights are
defined as:

#while (Looper < NumPillars)
  light_source {
    <0,8.5,(Looper*PillarGap)+CylGap+0.2>
    White*0.5
    fade_distance 8
    fade_power 3
  }
  light_source {
    <0,8.5,(Looper*PillarGap)-CylGap-0.2>
    White*LitePower
    fade_distance 8
    fade_power 3
  }
  #declare Looper = Looper+1;
#end

Eric
---------------
"A wise and frugal government, which shall restrain men from injuring one
another, which shall leave them otherwise free to regulate their own
pursuits of industry and improvement, and shall not take from the mouth of
labor the bread it has earned.  This is the sum of good government."
     - Thomas Jefferson
     - First inaugural address, 1801
---------------
http://www.ametro.net/~ericfree

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Attachments:
Download 'hallway.jpg' (18 KB)

Preview of image 'hallway.jpg'

Seems to me that you are thinking in terms of fade from the camera viewpoint.
It's only the lights that fade out and since they are also at the far end of the
hall they still emit their light the same way as the nearest ones do.
Is that it?  I think I see what you are saying though, the light reaching the
camera from far off should be faded as well.  Guess again.  The light on the
objects are what you are seeing and not the actual lights.  This is a good
premise about how it works and I agree that the light should still be faded out
with distance from the camera to be more accurate.
Maybe go with black fog instead of manipulating the light source intensities.

Bob

"Eric Freeman" <eri### [at] ametronet> wrote in message
news:388f4495@news.povray.org...
| Hey all,
|
| I know what you're thinking: "Is this guy ever going to stop bothering us
| with his petty little problems?"  The answer is NO!!!  Be prepared to be
| tormented forever as I pick every nit I can find!!!
|
| But seriously...  the attached image shows a ceiling with a bunch of
| cylindrical cut-outs in it.  In every cut-out there are two light sources
| (one at each end).  I'm using lights with fade_distance, but the far end of
| the scene is as brightly lit as the near end (there is a fill-light
| positioned at the camera position which also uses fade_distance, making the
| nearest pillar slightly brighter than the others).  It seems as if light
| quits fading when it hits an object.  Is this the case?  Should this be the
| case??  Is this a bug???  I will re-render the scene making the more distant
| lights progressively dimmer, but thought I'd ask anyway.  For reference, the
| pillars are 8 units tall, 15 units apart, and there are 45 pairs of pillars
| (making the farthest pillar 660 units from the nearest one).  The lights are
| defined as:
|
| #while (Looper < NumPillars)
|   light_source {
|     <0,8.5,(Looper*PillarGap)+CylGap+0.2>
|     White*0.5
|     fade_distance 8
|     fade_power 3
|   }
|   light_source {
|     <0,8.5,(Looper*PillarGap)-CylGap-0.2>
|     White*LitePower
|     fade_distance 8
|     fade_power 3
|   }
|   #declare Looper = Looper+1;
| #end
|
| Eric
| ---------------
| "A wise and frugal government, which shall restrain men from injuring one
| another, which shall leave them otherwise free to regulate their own
| pursuits of industry and improvement, and shall not take from the mouth of
| labor the bread it has earned.  This is the sum of good government."
|      - Thomas Jefferson
|      - First inaugural address, 1801
| ---------------
| http://www.ametro.net/~ericfree
|
|
|
|

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I remember reading in the manual that the light won't fade after it has
hit any kind of object. Made my life hard in the horror round entry :-)

Marc

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>I remember reading in the manual that the light won't fade after it has
>hit any kind of object. Made my life hard in the horror round entry :-)


That sucks! Can someone fix it?

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> I remember reading in the manual that the light won't fade after it has
> hit any kind of object. Made my life hard in the horror round entry :-)

You mean after bouncing off an object and then to the camera? If that's
what you mean then it by no means *should* fade.

--
Homepage: http://www.faricy.net/~davidf/
___     ______________________________
 | \     |_       <dav### [at] faricynet>
 |_/avid |ontaine      <ICQ 55354965>

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I'm confused; if you are saying that the light doesn't fade after reflecting
then that's exactly what's supposed to happen. Real-life objects appear the same
brightness no matter the distance from them (unless of course if there's
atmospheric effects--maybe that could solve your problem).
If you meant something else I'm not sure. Please clarify. ;-)

--
Homepage: http://www.faricy.net/~davidf/
___     ______________________________
 | \     |_       <dav### [at] faricynet>
 |_/avid |ontaine      <ICQ 55354965>

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Well there's always the inverse square with distance law (?) about light, which
should apply to any and all light despite it's origination, be it emitted
reflected or refracted light, it will diminish.  Am I right?
The thing is then that all objects should have a fading other than the
'interior' kind.  I think this brings up a good simulated reality question in
POV-Ray.  There's even a kind of perceived increase in brightness with distance
I think, maybe related to pupil size, surrounding light, etc.  Anyone have ideas
on the answer?  Because I'm just grasping at straws about it.

Bob

"David Fontaine" <dav### [at] faricynet> wrote in message
news:388FC9C9.B62DEB0F@faricy.net...
| I'm confused; if you are saying that the light doesn't fade after reflecting
| then that's exactly what's supposed to happen. Real-life objects appear the
same
| brightness no matter the distance from them (unless of course if there's
| atmospheric effects--maybe that could solve your problem).
| If you meant something else I'm not sure. Please clarify. ;-)
|
| --
| Homepage: http://www.faricy.net/~davidf/
| ___     ______________________________
|  | \     |_       <dav### [at] faricynet>
|  |_/avid |ontaine      <ICQ 55354965>
|
|

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> Well there's always the inverse square with distance law (?) about light, which
> should apply to any and all light despite it's origination, be it emitted
> reflected or refracted light, it will diminish.  Am I right?

You are exactly 100% correct! The thing is that an object twice as far away will
illuminate 1/4 the area on your retina at 1/4 the intensity and therefore appear the
exact same brightness. That is why distance shading is physically inaccurate.
<but_then_nothing_about_POV_light_is_physically_accurate_is_it?>
This does bring up a good point though. If the fade_power used is 3 like it is here
than it would be 1/9 the brightness for 1/4 the area and be approx. 1/2 as bright.
And normal non-fading lights should illimunate much brighter farther away. <g>
</but_then_nothing_about_POV_light_is_physically_accurate_is_it?>
I remember my brother asking me why planes got darker in the distance if light
didn't fade and I had to explain to him that the angle is increasing.

--
Homepage: http://www.faricy.net/~davidf/
___     ______________________________
 | \     |_       <dav### [at] faricynet>
 |_/avid |ontaine      <ICQ 55354965>

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"David Fontaine" <dav### [at] faricynet> wrote in message
news:388FC9C9.B62DEB0F@faricy.net...
>
> I'm confused; if you are saying that the light
> doesn't fade after reflecting then that's exactly
> what's supposed to happen. Real-life objects
> appear the same brightness no matter the
> distance from them (unless of course if there's
> atmospheric effects--maybe that could solve
> your problem).  If you meant something else
> I'm not sure. Please clarify. ;-)

That's what I meant and of course you are right.  I didn't think about it
before I posted (no surprise to people who know me)... the picture just
seemed wrong when I made it.  I recall my physics professor talking about
how we would all go blind if there was no dust in space... the entire sky
would be as bright as the sun from horizon to horizon because of the light
from all the stars.

Eric
---------------
"The whole problem with the world is that fools and fanatics are always so
certain of themselves, but wiser people so full of doubts."
--Bertrand Russel
---------------
http://www.ametro.net/~ericfree

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This looks perfectly accurate to me.

1) There is nothing to affect the amount of light returning from off in the
distance.

2) POV does things too perfectly, so you have an image of the perfect
hallway with the perfect lighting all the way down it.

3)  There is no variance in the lighting from each individual light... in
reality, some of the lights would be weaker casting lower levels of light.
In POV, and in this render, all the lights are equal.

4)  Dust and other things will add to the dim-ness of light seen way off in
the distance.

5) With regard to light cast by stars, if you were out in space with no
other bodies nearby, the light cast by all the stars combine would be
approximately equal.  Close to earth or within earth's atmosphere, you have
things affecting the "flavor" of light as well as a massive "star", the sun,
providing millions of candlepower more light than any star is providing.

6) With regard to the 1/4 rule, you have to look at the hallway... each
measure of distance down the hall reduces the size of the total number of
pixels each measure represents in 2D.  What light is available in each
measure is considerably less than that in the previous measure.  It is one
of those optical illusions played on our eyes that happens because we see in
2-D things that are 3-D.  Imagine if we had eyes on stalks sticking out from
our heads how much differently we would view the world we live in.

I believe to make this picture more realistic, you must program POV to use
random to vary the intensity and fade power of each light source.

Regards,
Robert J Becraft
aka cas### [at] aolcom

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