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

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Visit my isosurface tutorial at http://members.aol.com/stbenge

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