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Hi, I'm a newbie, and my english is very poor.
Sorry...
Exist a method (or macro, or tutorial, etc...)
to use Povray for a "technic" simulation of artificial light?
I mean the simulation with the radiometry (or photometric) value of
a lamp (power, light intensity, or Photometric Solid, etc...).
Thanks,
Manuel
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On Wed, 14 May 2003 00:57:06 +0200, "Manuel" <mba### [at] tiscalinet it>
wrote:
>Exist a method (or macro, or tutorial, etc...)
>to use Povray for a "technic" simulation of artificial light?
>I mean the simulation with the radiometry (or photometric) value of
>a lamp (power, light intensity, or Photometric Solid, etc...).
Try Jaime's realistic light simulation macros (lightsys3)at
http://www.ignorancia.org/t_lightsys.php
Hope it helps.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG e-mail : pet### [at] tagpovrayorg
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> Hope it helps.
Great!!
Thanks!!!!
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>I mean the simulation with the radiometry (or photometric) value of
>a lamp (power, light intensity, or Photometric Solid, etc...).
Best way to use POV-Ray light simulation is to multiply light source color
with real light luminance (cm/m^2). Then set fade_distance using following
formula:
sqrt(pi * A) / pi
Real world fade_power is 2. Because POV-Ray doesn't have dynamic range
compression, this isn't enough. I recommend you to define two adjusting
variables "Gamma" and "Max_Luminance" to make dynamic range compression.
Gamma is the gamma used to compress image dynamic range and Max_Luminance
is the luminance (cd/m^2) where pixel luminance at range 0..1 is "1".
Max_Luminance controls image brightness. When using these variables you can
calculate light source color multiplier using formula:
pow(light_source_luminance / Max_Luminance, Gamma)
And global Fade_Power to *all* light sources by using formula:
(ln(-exp(-ln(2) * Gamma) + 2) + ln(2) * Gamma) * 2 / ln(3)
To simulate photograph dynamic range compression I think that Gamma should
be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
half bright.
Light source color luminance (without multiplier) must be one. Good starting
value for Max_Luminance is 50. Light source colours luminances without
multiplier must be one. Example for white light, light color is <1, 1, 1>.
Because you probably want to make other light sources than omnidircetional,
you need to simulate light distribution using spotlights. If light source
is flat, use spotlight radius -90 falloff 90 tightness 1 for cosine
falloff.
I don't recommend to use Jaime's lightsys because it doesn't use physically
accurate lightning. (Sorry Jaime).
Matti
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On Wed, 14 May 2003 09:47:33 EDT
"Matti Karnaattu" <nomail@nomail> wrote:
> I don't recommend to use Jaime's lightsys because it doesn't use
> physically accurate lightning. (Sorry Jaime).
Of course! Lightsys doesn't simulates lightning... :)
--
Jaime Vives Piqueres
La Persistencia de la Ignorancia
http://www.ignorancia.org
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From: fff
Subject: Re: Radiometry, photometry, candela, lux, etc...
Date: 15 May 2003 16:05:26
Message: <3ec3f306@news.povray.org>
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Thanks again.
And (excuse my ignorance) about the radiosity?
I must include it for a good simulation?
Ehm...have you a sample scene that I can study?
I'm new to pov 3.5, and I only know roughly the old version...
thx,
Manuel
"Matti Karnaattu" <nomail@nomail> ha scritto nel messaggio
news:web.3ec248f5a14066c9bef0bd7d0@news.povray.org...
> >I mean the simulation with the radiometry (or photometric) value of
> >a lamp (power, light intensity, or Photometric Solid, etc...).
>
>
> Best way to use POV-Ray light simulation is to multiply light source color
> with real light luminance (cm/m^2). Then set fade_distance using following
> formula:
>
> sqrt(pi * A) / pi
>
> Real world fade_power is 2. Because POV-Ray doesn't have dynamic range
> compression, this isn't enough. I recommend you to define two adjusting
> variables "Gamma" and "Max_Luminance" to make dynamic range compression.
> Gamma is the gamma used to compress image dynamic range and Max_Luminance
> is the luminance (cd/m^2) where pixel luminance at range 0..1 is "1".
> Max_Luminance controls image brightness. When using these variables you
can
> calculate light source color multiplier using formula:
>
> pow(light_source_luminance / Max_Luminance, Gamma)
>
> And global Fade_Power to *all* light sources by using formula:
>
> (ln(-exp(-ln(2) * Gamma) + 2) + ln(2) * Gamma) * 2 / ln(3)
>
> To simulate photograph dynamic range compression I think that Gamma should
> be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
> half bright.
> Light source color luminance (without multiplier) must be one. Good
starting
> value for Max_Luminance is 50. Light source colours luminances without
> multiplier must be one. Example for white light, light color is <1, 1, 1>.
>
> Because you probably want to make other light sources than
omnidircetional,
> you need to simulate light distribution using spotlights. If light source
> is flat, use spotlight radius -90 falloff 90 tightness 1 for cosine
> falloff.
>
> I don't recommend to use Jaime's lightsys because it doesn't use
physically
> accurate lightning. (Sorry Jaime).
>
> Matti
>
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>And (excuse my ignorance) about the radiosity?
>I must include it for a good simulation?
Absolutely. Use it with #default { finish { ambient 0 } }
>Ehm...have you a sample scene that I can study?
I use these newsgroups from netcafe now, but I can put scene to net some
day.
Matti
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> >Ehm...have you a sample scene that I can study?
>
> I use these newsgroups from netcafe now, but I can put scene to net some
> day.
Thx,
I'm waiting... :-)
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From: Manuel
Subject: Re: Radiometry, photometry, candela, lux, etc...
Date: 22 May 2003 17:03:30
Message: <3ecd3b22@news.povray.org>
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> sqrt(pi * A) / pi
A is the emitter area, right?
Can you tell me about the origin of this formula?
> To simulate photograph dynamic range compression I think that Gamma should
> be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
> half bright.
Ehmm... can you explain more about this?
thx, sorry for boring questions.
Manuel
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>> sqrt(pi * A) / pi
>A is the emitter area, right?
Correct.
>Can you tell me about the origin of this formula?
I solve it myself and it is based on basic geometry formulas. I also create
Cornell box scene to test it. Instrutions to Cornell Box scene are here:
http://www.graphics.cornell.edu/online/box/data.html
It works. I can't explain better because my notes and files are home and I
have to use net from cafe until I get own Internet connection.
>> To simulate photograph dynamic range compression I think that Gamma should
>> be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
>> half bright.
>Ehmm... can you explain more about this?
Photographers use gray surface which reflects 18% light back to make
adjustments because it looks half bright.
0.18^x = 0.5
x = ln(0.5)/ln(0.18)
I'm not sure about this gamma. I'm still looking more information about
simulating camera and human eye dynamic range.
Matti
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