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My empirical studies with MegaPOV radiosity have shown that it
works as advertised. There are some other factors that are more
important for realism than the radiosity settings.
1. assumed_gamma & Display_Gamma
These parametrs relate only to the CRT and have nothing to do
with simulating light transport and should be taken out of
the simulation by using assumed_gamma 1.0. Display_Gamma should
be set to a value correct for the particular monitor.
2. Light source intensity distribution
In real life there are no omnidirectional light sources. By this I mean
that all ligh sources have some charachteristic intensity distribution.
In this scene the light source is a flat square panel. It's projected
area decreases by cos(angle) and so does it's brightness. For this reason
just using area_light isn't enough because it still radiates in all
directions with equal intensity (see fig.3). I used spotlight to simulate
this cosine falloff. (tightness 0 produces cos(angle*2)/2+0.5 intensity)
3. fade_power
In real life light source's apparent brightness follows 1/r^2 equation.
The correct value for fade_distance seems to be 1.4*light_source_diameter.
All three factors must be taken into account if relism is the goal.
As proof I present 3 images (gamma 2.2):
1) The Cornell reference image.
2) MegaPOV 0.5 image rendered with with:
assumed_gamma 1.0, Display_Gamma=2.2
spotlight modifier
fade_power 2
This is a nice match with basically the default MegaPOV radiosity settings.
All texture and radiosity parameters within nominal range.
3) The same scene with same settings without:
assumed_gamma
spotlight modifier
fade_power
(Texture and light colors gamma corrected)
This is a typical 1st attempt at radiosity. Too much color bleed,
not enough diffuse light, flat shading.
Once again, the difference between images 2 and 3 is caused by
assumed_gamma, spotlight and fade_power. Source to binaries.scene-files
by Monday.
_______________________________________________________________________
Kari Kivisalo www.kivisalo.net
Post a reply to this message
Attachments:
Download 'realistic.jpg' (26 KB)
Preview of image 'realistic.jpg'
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I commend you for your work. Very well done. You should make a tutorial, I
think.
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Good job of looking into other factors for squeezing more realism out of radiosity.
Kari Kivisalo wrote:
> My empirical studies with MegaPOV radiosity have shown that it
> works as advertised. There are some other factors that are more
> important for realism than the radiosity settings.
>
> 1. assumed_gamma & Display_Gamma
>
> These parametrs relate only to the CRT and have nothing to do
> with simulating light transport and should be taken out of
> the simulation by using assumed_gamma 1.0. Display_Gamma should
> be set to a value correct for the particular monitor.
>
> 2. Light source intensity distribution
>
> In real life there are no omnidirectional light sources. By this I mean
> that all ligh sources have some charachteristic intensity distribution.
> In this scene the light source is a flat square panel. It's projected
> area decreases by cos(angle) and so does it's brightness. For this reason
> just using area_light isn't enough because it still radiates in all
> directions with equal intensity (see fig.3). I used spotlight to simulate
> this cosine falloff. (tightness 0 produces cos(angle*2)/2+0.5 intensity)
>
> 3. fade_power
>
> In real life light source's apparent brightness follows 1/r^2 equation.
> The correct value for fade_distance seems to be 1.4*light_source_diameter.
>
> All three factors must be taken into account if relism is the goal.
>
>
> As proof I present 3 images (gamma 2.2):
>
> 1) The Cornell reference image.
>
> 2) MegaPOV 0.5 image rendered with with:
> assumed_gamma 1.0, Display_Gamma=2.2
> spotlight modifier
> fade_power 2
>
> This is a nice match with basically the default MegaPOV radiosity settings.
> All texture and radiosity parameters within nominal range.
>
> 3) The same scene with same settings without:
> assumed_gamma
> spotlight modifier
> fade_power
>
> (Texture and light colors gamma corrected)
>
> This is a typical 1st attempt at radiosity. Too much color bleed,
> not enough diffuse light, flat shading.
>
> Once again, the difference between images 2 and 3 is caused by
> assumed_gamma, spotlight and fade_power. Source to binaries.scene-files
> by Monday.
>
> _______________________________________________________________________
> Kari Kivisalo www.kivisalo.net
>
> ------------------------------------------------------------------------
> [Image]
--
Samuel Benge
E-Mail: STB### [at] aol com
Visit my isosurface tutorial at http://members.aol.com/stbenge
Post a reply to this message
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On Sat, 10 Jun 2000 16:05:02 +0300, Kari Kivisalo <kar### [at] kivisalonet>
wrote:
>My empirical studies with MegaPOV radiosity have shown that it
>works as advertised. There are some other factors that are more
>important for realism than the radiosity settings.
>
>1. assumed_gamma & Display_Gamma
...
>2. Light source intensity distribution
...
>3. fade_power
And your images prove your words. Impressive work!
My only concern is fade_power, shouldn't you use 1000?
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
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Peter Popov wrote:
> My only concern is fade_power, shouldn't you use 1000?
I'm pretty sure that every physics book I have red says 1/r^2.
You must be thinking about interior fade_power :)
_______________________________________________________________________
Kari Kivisalo www.kivisalo.net
Post a reply to this message
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On Sat, 10 Jun 2000 23:47:06 +0300, Kari Kivisalo <kar### [at] kivisalonet>
wrote:
>> My only concern is fade_power, shouldn't you use 1000?
>
>I'm pretty sure that every physics book I have red says 1/r^2.
>You must be thinking about interior fade_power :)
I wouldn't question your physics books because mine read the same
<grin>. It escaped me that realistic attenuation is only suppoted for
object interior. But then, isn't light fading unrealistic in this
case? Can you try placing the whole scene in a transparent object and
using realistic attenuation?
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] usanet
TAG e-mail : pet### [at] tagpovrayorg
Post a reply to this message
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good work - its noce to see the megapov defaults with minpr tweaking are
right on the nail for my money - maybe you should make a tutorial on how to
do the req'd tweaks!
Rick
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Rick wrote:
> right on the nail for my money - maybe you should make a tutorial on how to
I posted realistic.pov with some comments to binaries.scene-files.
Tweaking the radiosity block has only minor effect to the overall scene.
To Popov:
This 1/r^2 attenuation is purely geometric and has nothing to do
with media interaction.
_______________________________________________________________________
Kari Kivisalo www.kivisalo.net
Post a reply to this message
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Peter Popov <pet### [at] usanet> wrote...
> I wouldn't question your physics books because mine read the same
> <grin>. It escaped me that realistic attenuation is only suppoted for
> object interior. But then, isn't light fading unrealistic in this
> case? Can you try placing the whole scene in a transparent object and
> using realistic attenuation?
Actually, the equation that POV uses for light attenuation is a good
approximation. Interior attenuation, however, is simulating a totally
different phenomenon, and therefore _should_ be using a totally different
equation. However, in the official POV-Ray, it uses the same equation. The
fade_power 1000 "hack" just tells POV to use a different equation to produce
more realistic results. That equation, though, would not work for simulating
light attenuation caused by the energy spreading out over a larger area as
distance increases.
-Nathan
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Kari Kivisalo <kar### [at] kivisalonet> wrote...
>
> My empirical studies with MegaPOV radiosity have shown that it
> works as advertised. There are some other factors that are more
> important for realism than the radiosity settings.
>
> 1. assumed_gamma & Display_Gamma
> 2. Light source intensity distribution
> 3. fade_power
Great detective work! I'm glad to hear that things are working correctly.
:-)
-Nathan
Post a reply to this message
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