To all the POVRay gurus,

I am a newbie, and I have found something that puzzles me.

Please look at the following POV-file:

- - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - -
- >8 - - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - - - >8 -
- - - - - - - - - >8

#include "colors.inc"
#include "stones.inc"    


camera {
    location <0, 9, -3>
    look_at  <0, -9,  1>
  }
                                           
light_source { <2.5, 45, 600> color Green}
light_source { <2.5, 39, 600> color Green}
light_source { <2.5, 35, 600> color Green}
light_source { <2.5, 31, 600> color Green}
light_source { <1.5, 21, 600> color Green}
light_source { <2.5, 11, 600> color Green}
light_source { <1.5, 1, 600> color Green}
light_source { <2.5, -11, 600> color Green}
light_source { <1.5, -21, 600> color Green}     
light_source { <2.5, -31, 600> color Green}
light_source { <1.5, -41, 600> color Green}
light_source { <2.5, -51, 600> color Green}
light_source { <1.5, -61, 600> color Green}
light_source { <2.5, -70, 600> color Green}
light_source { <2.5, -75, 600> color Green}
light_source { <2.5, -80, 600> color Green}
light_source { <2.5, -85, 600> color Green}                                           
light_source { <2.5, 39, 400> color Yellow}
light_source { <2.5, 35, 400> color Yellow}
light_source { <2.5, 31, 400> color Yellow}
light_source { <1.5, 21, 400> color Yellow}
light_source { <2.5, 11, 400> color Yellow}
light_source { <1.5, 1, 400> color Yellow}
light_source { <2.5, -11, 400> color Yellow}
light_source { <1.5, -21, 400> color Yellow}     
light_source { <2.5, -31, 400> color Yellow}
light_source { <1.5, -41, 400> color Yellow}
light_source { <2.5, -51, 400> color Yellow}
light_source { <1.5, -61, 400> color Yellow}
light_source { <2.5, -70, 400> color Yellow}
light_source { <2.5, -75, 400> color Yellow}
light_source { <2.5, -80, 400> color Yellow}   
light_source { <2.5, 35, 250> color Red}
light_source { <2.5, 31, 250> color Red}
light_source { <1.5, 21, 250> color Red}
light_source { <2.5, 11, 250> color Red}
light_source { <1.5, 1, 250> color Red}
light_source { <2.5, -11, 250> color Red}
light_source { <1.5, -21, 250> color Red}     
light_source { <2.5, -31, 250> color Red}
light_source { <1.5, -41, 250> color Red}
light_source { <2.5, -51, 250> color Red}
light_source { <1.5, -61, 250> color Red}
light_source { <2.5, -70, 250> color Red}
light_source { <2.5, -75, 250> color Red}
light_source { <2.5, 31, 100> color Red}
light_source { <2.5, 29, 100> color Red}
light_source { <2.5, 27, 100> color Red}
light_source { <1.5, 25, 100> color Red}
light_source { <2.5, 23, 100> color Red}     
light_source { <1.5, 21, 100> color Red}
light_source { <2.5, 19, 100> color Red}
light_source { <2.5, 17, 100> color Red}
light_source { <1.5, 15, 100> color Red}     
light_source { <2.5, 13, 100> color Red}
light_source { <2.5, 11, 100> color Red}
light_source { <2.5, 9, 100> color Red}
light_source { <2.5, 7, 100> color Red}
light_source { <1.5, 5, 100> color Red}
light_source { <2.5, 3, 100> color Red}     
light_source { <1.5, 1, 100> color Red}
light_source { <1.5, -1, 100> color Red}
light_source { <1.5, -3, 100> color Red}
light_source { <1.5, -5, 100> color Red}
light_source { <1.5, -7, 100> color Red}
light_source { <1.5, -9, 100> color Red}
light_source { <1.5, -11, 100> color Red}
light_source { <1.5, -13, 100> color Red}
light_source { <1.5, -15, 100> color Red}
light_source { <1.5, -17, 100> color Red}  
light_source { <1.5, -19, 100> color Red}
light_source { <1.5, -21, 100> color Red}     
light_source { <2.5, -23, 100> color Red}
light_source { <1.5, -25, 100> color Red}
light_source { <1.5, -27, 100> color Red}     
light_source { <1.5, -29, 100> color Red}     
light_source { <2.5, -31, 100> color Red}
light_source { <1.5, -33, 100> color Red}
light_source { <1.5, -35, 100> color Red}
light_source { <1.5, -37, 100> color Red}
light_source { <1.5, -39, 100> color Red}
light_source { <1.5, -41, 100> color Red}
light_source { <1.5, -43, 100> color Red}
light_source { <1.5, -45, 100> color Red}
light_source { <1.5, -47, 100> color Red}
light_source { <1.5, -49, 100> color Red}
light_source { <2.5, -51, 100> color Red}
light_source { <1.5, -53, 100> color Red}
light_source { <1.5, -55, 100> color Red}
light_source { <1.5, -57, 100> color Red}
light_source { <1.5, -59, 100> color Red}
light_source { <1.5, -61, 100> color Red}
light_source { <1.5, -63, 100> color Red}
light_source { <1.5, -65, 100> color Red}
light_source { <1.5, -67, 100> color Red}
light_source { <1.5, -69, 100> color Red}
light_source { <2.5, -70, 100> color Red}
light_source { <2.5, 31, 80> color Red}
light_source { <2.5, 29, 80> color Red}
light_source { <2.5, 27, 80> color Red}
light_source { <1.5, 25, 80> color Red}
light_source { <2.5, 23, 80> color Red}     
light_source { <1.5, 21, 80> color Red}
light_source { <2.5, 19, 80> color Red}
light_source { <2.5, 17, 80> color Red}
light_source { <1.5, 15, 80> color Red}     
light_source { <2.5, 13, 80> color Red}
light_source { <2.5, 11, 80> color Red}
light_source { <2.5, 9, 80> color Red}
light_source { <2.5, 7, 80> color Red}
light_source { <1.5, 5, 80> color Red}
light_source { <2.5, 3, 80> color Red}     
light_source { <1.5, 1, 80> color Red}
light_source { <1.5, -1, 80> color Red}
light_source { <1.5, -3, 80> color Red}
light_source { <1.5, -5, 80> color Red}
light_source { <1.5, -7, 80> color Red}
light_source { <1.5, -9, 80> color Red}
light_source { <1.5, -11, 80> color Red}
light_source { <1.5, -13, 80> color Red}
light_source { <1.5, -15, 80> color Red}
light_source { <1.5, -17, 80> color Red}  
light_source { <1.5, -19, 80> color Red}
light_source { <1.5, -21, 80> color Red}     
light_source { <2.5, -23, 80> color Red}
light_source { <1.5, -25, 80> color Red}
light_source { <1.5, -27, 80> color Red}     
light_source { <1.5, -29, 80> color Red}     
light_source { <2.5, -31, 80> color Red}
light_source { <1.5, -33, 80> color Red}
light_source { <1.5, -35, 80> color Red}
light_source { <1.5, -37, 80> color Red}
light_source { <1.5, -39, 80> color Red}
light_source { <1.5, -41, 80> color Red}
light_source { <1.5, -43, 80> color Red}
light_source { <1.5, -45, 80> color Red}
light_source { <1.5, -47, 80> color Red}
light_source { <1.5, -49, 80> color Red}
light_source { <2.5, -51, 80> color Red}
light_source { <1.5, -53, 80> color Red}
light_source { <1.5, -55, 80> color Red}
light_source { <1.5, -57, 80> color Red}
light_source { <1.5, -59, 80> color Red}
light_source { <1.5, -61, 80> color Red}
light_source { <1.5, -63, 80> color Red}
light_source { <1.5, -65, 80> color Red}
light_source { <1.5, -67, 80> color Red}
light_source { <1.5, -69, 80> color Red}
light_source { <2.5, -70, 80> color Red}
light_source { <2.5, 31, 60> color Red}
light_source { <2.5, 29, 60> color Red}
light_source { <2.5, 27, 60> color Red}
light_source { <1.5, 25, 60> color Red}
light_source { <2.5, 23, 60> color Red}     
light_source { <1.5, 21, 60> color Red}
light_source { <2.5, 19, 60> color Red}
light_source { <2.5, 17, 60> color Red}
light_source { <1.5, 15, 60> color Red}     
light_source { <2.5, 13, 60> color Red}
light_source { <2.5, 11, 60> color Red}
light_source { <2.5, 9, 60> color Red}
light_source { <2.5, 7, 60> color Red}
light_source { <1.5, 5, 60> color Red}
light_source { <2.5, 3, 60> color Red}     
light_source { <1.5, 1, 60> color Red}
light_source { <1.5, -1, 60> color Red}
light_source { <1.5, -3, 60> color Red}
light_source { <1.5, -5, 60> color Red}
light_source { <1.5, -7, 60> color Red}
light_source { <1.5, -9, 60> color Red}
light_source { <1.5, -11, 60> color Red}
light_source { <1.5, -13, 60> color Red}
light_source { <1.5, -15, 60> color Red}
light_source { <1.5, -17, 60> color Red}  
light_source { <1.5, -19, 60> color Red}
light_source { <1.5, -21, 60> color Red}     
light_source { <2.5, -23, 60> color Red}
light_source { <1.5, -25, 60> color Red}
light_source { <1.5, -27, 60> color Red}     
light_source { <1.5, -29, 60> color Red}     
light_source { <2.5, -31, 60> color Red}
light_source { <1.5, -33, 60> color Red}
light_source { <1.5, -35, 60> color Red}
light_source { <1.5, -37, 60> color Red}
light_source { <1.5, -39, 60> color Red}
light_source { <1.5, -41, 60> color Red}
light_source { <1.5, -43, 60> color Red}
light_source { <1.5, -45, 60> color Red}
light_source { <1.5, -47, 60> color Red}
light_source { <1.5, -49, 60> color Red}
light_source { <2.5, -51, 60> color Red}
light_source { <1.5, -53, 60> color Red}
light_source { <1.5, -55, 60> color Red}
light_source { <1.5, -57, 60> color Red}
light_source { <1.5, -59, 60> color Red}
light_source { <1.5, -61, 60> color Red}
light_source { <1.5, -63, 60> color Red}
light_source { <1.5, -65, 60> color Red}
light_source { <1.5, -67, 60> color Red}
light_source { <1.5, -69, 60> color Red}
light_source { <2.5, -70, 60> color Red}
light_source { <2.5, 31, 40> color Blue}
light_source { <1.5, 21, 40> color Green}
light_source { <2.5, 11, 40> color Blue}
light_source { <1.5, 1, 40> color Red}
light_source { <2.5, -11, 40> color Blue}
light_source { <1.5, -21, 40> color Green}     
light_source { <2.5, -31, 40> color Blue}
light_source { <2.5, 31, 20> color Red}
light_source { <1.5, 21, 20> color Blue}
light_source { <2.5, 11, 20> color Red}
light_source { <1.5, 1, 20> color Green}
light_source { <2.5, -11, 20> color Red}    



  plane { <-1.5, -1.75, -1>, 1
    pigment {
      checker color White, color Black
    }
  }

- - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - -
- >8 - - - - - - - - - - >8 - - - - - - - - - - >8 - - - - - - - - - - >8 -
- - - - - - - - - >8

I was exploring the potential of the plane object, and toying with camera positions as
well as light_source functions.

What puzzles me about the above program is that my Yellow light_sources are all
located at the z-axis 400 location, as follows:

		light_source { <2.5, 39, 400> color Yellow}
		light_source { <2.5, 35, 400> color Yellow}
		light_source { <2.5, 31, 400> color Yellow}
		light_source { <1.5, 21, 400> color Yellow}
		light_source { <2.5, 11, 400> color Yellow}
		light_source { <1.5, 1, 400> color Yellow}
		light_source { <2.5, -11, 400> color Yellow}
		light_source { <1.5, -21, 400> color Yellow}
		light_source { <2.5, -31, 400> color Yellow}
		light_source { <1.5, -41, 400> color Yellow}
		light_source { <2.5, -51, 400> color Yellow}
		light_source { <1.5, -61, 400> color Yellow}
		light_source { <2.5, -70, 400> color Yellow}
		light_source { <2.5, -75, 400> color Yellow}
		light_source { <2.5, -80, 400> color Yellow}

But when I put the Red light_source at the 250 z-axis location, the Yellow lights
bleed from the 400 z-axis location and taking over the 250 z-axis location that
was assigned to the Red light_source.

	In other words, now the both 250 and 400 z-axis locations are lighted with Yellow
lights. 

And when I put put Red light_source at the 100 z-axis location, the Yellow lights had
taken over that location too !

The same happened when I put Red light_source at the 80, and then 60 z-axis locations.

In summary, if I put Yellow light_source at the 400 z-axis locations, and Red
light_source at 250, 100, 80, and 60 (all z-axis) locations, instead of the intented
lighting sequence, I got the equivalent of Yellow light_source at all the 400, 250,
100, 80 and 60 z-axis locations.

Why ?

Why the Yellow lights bleed into the Red lights territories ?

Since I am a newbie, I don't know what I have done. So if there's something really
stupid that I have done, please bare with me, and please point out my mistakes.

Is there a way to have a Red light_source and a Yellow light_source sitting
side-by-side, without one taking over the other's territory ?

English isn't my mother tongue, so please forgive me for any grammar mistake or
anything that might have been unclear.

Thanks for reading !

Specs: ---

OS: MS-Windows 98SE

RAM: 512 MB

POVRAY Version: Version 3.5 for Windows.


Sincerely,
Marie
pen### [at] myrealboxcom

PS: Sorry for the cross-posting of this message. I don't know exactly which newsgroup
this message really belongs to.

Post a reply to this message

Do some reading into the subjects 'fade distance' and 'fade
power', should provide a solution.

Post a reply to this message

Your scene is way too complex to easily deduce what is the effect you
are trying to achieve and what is what you are not getting which you
expect to get.
  Making a minimal scene showing the problem would help a lot giving an
exact answer.

  Anyways, if you don't know how additive RGB works, you should find
info about it and experiment.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

Post a reply to this message

"Marie" <pen### [at] myrealboxcom> wrote in message
news:omlmqvk93bqkfmkrvg6umk9mhu3k1rm7iq@4ax.com...
> To all the POVRay gurus,

That's a hell of a lot of lights...

Are you sure you know which lights are having an effect on the scene, and which
are inside the plane? (which opens another can of worms since your camera is
inside the plane - check your warnings).

When I place the plane in a more conventional position and ensure that light
from all the lights hits it, I don't get the effect you're seeing with the
posted scene.

I would choose a more conventional vector for your plane which will allow you to
keep better track of the relationship between the various components of the
scene. At the moment, you're just making things unnecessarily complicated for
yourself.

Post a reply to this message

In article <omlmqvk93bqkfmkrvg6umk9mhu3k1rm7iq@4ax.com>,
 Marie <pen### [at] myrealboxcom> wrote:

> Since I am a newbie, I don't know what I have done. So if there's something 
> really stupid that I have done, please bare with me, and please point out my 
> mistakes.

You have a lot of lights, and they are all using full-brightness colors. 
Colors are composed of 3 float values, one for each of red, green, and 
blue. Although internally their range is practically unlimited, they are 
clipped to the range [0, 1] for output. A value of 1 is full brightness, 
and going higher will not have any effect. If you have 100 green lights 
and 2 red lights, it won't matter how much more brightly lit in green 
the surface is. A point lit with < 2, 100, 0> will appear to be < 1, 1, 
0> yellow. Basically, you just need to drastically reduce the brightness 
of your lights, and probably should use distance fading as well. And you 
should seriously look at whether all those lights are necessary...it 
looks like you may be trying to make area lights.


> PS: Sorry for the cross-posting of this message. I don't know exactly which 
> newsgroup this message really belongs to.

This group (povray.newusers) is the correct group for this kind of 
question.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

Post a reply to this message

Christopher James Huff <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> Colors are composed of 3 float values, one for each of red, green, and
> blue. Although internally their range is practically unlimited, they are
> clipped to the range [0, 1] for output. A value of 1 is full brightness,
> and going higher will not have any effect. If you have 100 green lights
> and 2 red lights, it won't matter how much more brightly lit in green
> the surface is. A point lit with < 2, 100, 0> will appear to be < 1, 1,
> 0> yellow.

That's the best explanation I've seen yet of light_ source output, thank
you.  My question is, what does fade_power do?

If I have a light_source with <7.5,5,1> it's output is white,  however using
a light_source of <.75,.5,.1> with a fade_power of 10 & fade_distance >
distance_to_camera, it's output still looks amber.

RG

Post a reply to this message

In article <3fac85b4@news.povray.org>, "gonzo" <rgo### [at] lansetcom> wrote:

> That's the best explanation I've seen yet of light_ source output, thank
> you.  My question is, what does fade_power do?
> 
> If I have a light_source with <7.5,5,1> it's output is white,  however using
> a light_source of <.75,.5,.1> with a fade_power of 10 & fade_distance >
> distance_to_camera, it's output still looks amber.

Your < 7.5, 5, 1> light source only *looks* white when shining on a 
surface where the reflected color is >= < 1, 1, 1>. Internally, it is 
really < 7.5, 5, 1>, and avery dark surface, thick media, or other 
circumstances can give visible effects from these high light 
intensities. Distance fading is pretty self-explanatory: it makes the 
light fade with distance.
http://povray.org/documentation/view/172/#s06_05_07_09

So with a fade_distance of 1 and fade_power 2, the light intensity from 
your < 7.5, 5, 1> light source at a distance of 5 units will be:
< 0.576923077, 0.384615385, 0.0769230769>

A fade_power of 2 is most realistic (approximating the inverse-square 
law), 10 doesn't correspond to any real-world effect. And fade_distance 
is just used to control the falloff rate, it has nothing to do with the 
camera position. It is really the same as adjusting the brightness of 
the light, though it is not implemented that way internally. The 
distance given to fade_distance is the distance where the light is at 
the specified brightness, it decreases with distance from there, and 
increases as the distance drops below fade_distance. (the documentation 
appears to be slightly incorrect about this: only the ratio of 
distance/fade_distance matters, not the size of fade_distance in 
relation to 1)

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

Post a reply to this message

Christopher James Huff <cja### [at] earthlinknet> wrote in message
news:cja### [at] netplexaussieorg...
> Your < 7.5, 5, 1> light source only *looks* white when shining on a
> surface where the reflected color is >= < 1, 1, 1>. Internally, it is
> really < 7.5, 5, 1>, and avery dark surface, thick media, or other
> circumstances can give visible effects from these high light
> intensities.

Ah, so reflection (and probably specular or phong) will still see it
correctly as long it's <1. That's probably what I'm seeing.
>
> So with a fade_distance of 1 and fade_power 2, the light intensity from
> your < 7.5, 5, 1> light source at a distance of 5 units will be:
> < 0.576923077, 0.384615385, 0.0769230769>

It's distances less than fade_distance I'm most interested in.

> A fade_power of 2 is most realistic (approximating the inverse-square
> law), 10 doesn't correspond to any real-world effect.

That's the beauty of being utterly ignorant of real world mathmatics... I
can just do weird stuff without worrying about whether it's realistic or not
;-)

And fade_distance
> is just used to control the falloff rate, it has nothing to do with the
> camera position.

Oops, actually, I meant the distance between light_source & object, not
light_source & camera...

The
> distance given to fade_distance is the distance where the light is at
> the specified brightness, it decreases with distance from there, and
> increases as the distance drops below fade_distance. (the documentation
> appears to be slightly incorrect about this: only the ratio of
> distance/fade_distance matters, not the size of fade_distance in
> relation to 1)

Ok, that was confusing me too.

The main reason I use high fade_power is to simulate sunlight which is
waaaay bright, but seldom pure white. So I set the color I want the light to
be then boost fade_power way up.

An example is my Old Technology IRTC entry
(http://www.irtc.org/ftp/pub/stills/2003-02-28/async_rg.jpg) where I'm using
fade_power 7, fade_distance 1000 so everything in the scene is within the
fade_distance.  But I'm using scattering media atmosphere, and as you say
above, that can still use the higher intensity.  And looking at it now, the
color is most noticable where there is reflection or specular highlights.
And it does say in the docs that reflected or refracted light is not
attenuated, so I guess that explains it.

Thanks for the explanation.  So, ok, it doesn't work the way I thought it
did, but as long as it works...

RG

Post a reply to this message

3fadfd40@news.povray.org...
>
> The main reason I use high fade_power is to simulate sunlight which is
> waaaay bright, but seldom pure white. So I set the color I want the light
to
> be then boost fade_power way up.
>
you could mutliply your light color definition, say <1, 0.9, 0.8>*2, rather
using fade_power.
high fade_power is very unrealistic for the sun except if you translate it
far away because real sun is so far from earth that  scene distances are
very small relatively to sun distance.
We do not notice any sunlight fading due to distance on earth.

Marc

Post a reply to this message

In article <3fadfd40@news.povray.org>, "gonzo" <rgo### [at] lansetcom> wrote:

> Ah, so reflection (and probably specular or phong) will still see it
> correctly as long it's <1. That's probably what I'm seeing.

Reflection and other features will see it correctly no matter what the 
brightness is. Anything brighter than 1 will be clipped to 1 when the 
image is written to a file. If you make a very dark filter and put it in 
front of the camera, you will see the shading that you couldn't before.


> > So with a fade_distance of 1 and fade_power 2, the light intensity from
> > your < 7.5, 5, 1> light source at a distance of 5 units will be:
> > < 0.576923077, 0.384615385, 0.0769230769>
> 
> It's distances less than fade_distance I'm most interested in.

Those get brighter, up to 2x brighter than the specified light source 
brightness.


> The main reason I use high fade_power is to simulate sunlight which is
> waaaay bright, but seldom pure white.

This is highly inaccurate. At the distance of Earth's orbit, sunlight is 
essentially constant over any planetary distances. The sun is 
practically as bright on the moon as in near earth orbit, no matter what 
their relative positions are. You certainly aren't going to see any 
difference at smaller scales.
Light fading is only useful for situations where you are close to the 
source of the light or can see objects that have widely varying 
distances from the light.


> So I set the color I want the light to
> be then boost fade_power way up.

And this is the wrong way to adjust brightness...you should adjust 
fade_distance instead. BTW, I've done some more testing, and fade_power 
3 actually approximates inverse-square falloff more closely, at least as 
long as distance > fade_distance.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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