gemelli david wrote:
> 
> hum... strange title but this scene is a WIP. I'm using it to test some
> radiosity parameters and technics, and it will be a comprative scene in
> POV and LightScape when the 3D Studio MAX model will be done.
> 
> Story:
> 
> I saw yesterday a photo in one of my brother's ebenist books of a studio
> like this. I decided to do it with POV.
> today, at work, while my computer was unused, I launched a render. A
> graphist wanted to test the same scene in LightScape (we are using it
> since a few days). So, he will do the model in MAX, and he will import
> it in LightScape, I will convert it to a POV scene and we will do
> tests...
> 
> My question:
> I used this parameters in megapov 0.6.
>     pretrace_start 0.04
>     pretrace_end 0.01
>     count 300
>     recursion_limit 2
>     nearest_count 3
>     error_bound 0.3
> I read the "Christoph's Page", I tried various values for radiosity but
> I still have this dark patches in the corner of the window.
> 
> and before, with megapov 0.5, I got dark circles even with a high count
> !

I need to write a tutorial on low-error radiosity one of these days so I
can stop typing this stuff out... >_<

One of the problems with using an error_bound of around .3 is that the
radiosity tends to be blotchy; the effect is almost as if you were
shining a light through a screen and getting a lot of holes, or
something like the multiple-shadow effect of area_lights, only more so.
I've found that increasing error_bound will make the blotches larger and
softer, and at the default error_bound of .6, they blend together well
enough as to all but disappear.. but of course, with your error_bound
this high, you won't get the neat shadows.

If you want to use these settings more or less as they are, it's crucial
that you set the pretrace_end low enough that you're getting 2-pixel
radiosity blocks (try something around .005). This will help smooth the
blotches. Also, your nearest_count is way too low; with an error of .3,
you should leave it at default. (You could even increase it to the max
of 20, but I don't think this will help.) Set low_error_factor to 1,
which should make the pretrace a little faster without hurting quality.

If you still get unacceptable dark artifacts or the smoothing still
isn't good enough, and you have a crapload of RAM, you can use a trick
to make the artifacts smaller than a pixel (which gives extremely smooth
results, if you follow me). Set your error_bound to .03, nearest_count
to 1, low_error_factor to 1, increase your count to, hmm, 500 or so for
this scene I think, and adc_bailout to 1. Pretrace_start and _end can be
set to anything you find convenient; with these settings, they have no
useful purpose other than giving you a mosaic preview and waste a lot of
time that could be used for rendering.

-Xplo

Post a reply to this message