On Wed, 11 Dec 2002 18:54:41 +0100
"Philippe Debar" <phd### [at] wanadoobe> wrote:

> Okay. But if I read the formula right, it is still implicitly present,
> as lct/REF_WHITE is no more normalized. It should be more or less
> equivalent.

  Oops! I forget it, sorry:

(vnormalize((lct/REF_WHITE)+(<COLOR_FILTER.gray,COLOR_FILTER.gray,COLOR
_FILTER.gray>-COLOR_FILTER))*EXPOSURE) 

  Then no local intensity involved now... only the temperature
correction and color balancing, and of course the global exposure.

> BTW I have some colour theory ideas for lightsys, but I need to test
> them first. If I believe them to be of any interest, I'll mail them to
> you.

  Please! I only barely understand what I'm doing... any help, specially
on color theory, will be very welcomed.

> I just ignored the parts I did not understand ;-)

  Ah! This is an ancient technique... I use it so often that I even
honoured it with the name of my web site. :)
 
> Yes and no. I do not want the sky to be lighted by anything but
> itself. Moreover, I want the sky to act as a light_source for
> radiosity, hence the high ambient value and higher then <1,1,1>
> colours as you go near the sun.
> [...]
> Yes, POV says to use ambient 0 in radiosity for non-light-emitting
> objects. But I want the sky to be luminous, that is to light objects
> in the scene. It is no only a pretty / accurate (?) background, it
> also provides a realistic(? again) outdoor light setup.

  That's what I supposed. Anyhow, the SunColor returned isn't
supposed to have the sky color weighted in it? 

> What are the problems with the way it originally is? Tell me what
> isn't to your taste, I'll try to solve it.

  Perhaps I've not explained it very well: How I can use it on my
scenes, having this dirty (and perhaps stupid) habit of using global
ambient set to 0? 

> Decreasing the weight of the sun will probably increase the sky
> luminosity.

  Sorry, I wanted to write "decreasing overall luminosity and increasing
sun weight", of course... I must pay more attention to what I write. :(

> I hope you will not have to struggle too much with my file ;-)

  Not really... only with the fiLuminous declaration, really. 

  Well, going back to skylighting... 

-- 
Jaime Vives Piqueres
		
La Persistencia de la Ignorancia
http://www.ignorancia.org

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"Jaime Vives Piqueres" <jai### [at] ignoranciaorg> wrote in message
news:200### [at] ignoranciaorg...

> (vnormalize((lct/REF_WHITE)+(<COLOR_FILTER.gray,COLOR_FILTER.gray,COLOR
> _FILTER.gray>-COLOR_FILTER))*EXPOSURE)
>
>   Then no local intensity involved now... only the temperature
> correction and color balancing, and of course the global exposure.



I think that if I do that, Intensity_Mult will have no effects any more, so
you would be unable to set the sky luminosty relatively to the rest of the
scene.

I use Lct.gray, Lct beeing the color generated by the sky model, as lumen to
get an final light intensity related to the original intensity and allow
Intensity_Mult to affect it. With the formula you propose, all
lights/colours will be normalized, every point on the sky will be of equal
'brightness' (in the r+g+b sense, not in perceptual luminance).



<snip>

> > I just ignored the parts I did not understand ;-)
>
>   Ah! This is an ancient technique... I use it so often that I even
> honoured it with the name of my web site. :)



And a nice name it is, too. I  like it.





> > Yes and no. I do not want the sky to be lighted by anything but
> > itself. Moreover, I want the sky to act as a light_source for
> > radiosity, hence the high ambient value and higher then <1,1,1>
> > colours as you go near the sun.
> > [...]
> > Yes, POV says to use ambient 0 in radiosity for non-light-emitting
> > objects. But I want the sky to be luminous, that is to light objects
> > in the scene. It is no only a pretty / accurate (?) background, it
> > also provides a realistic(? again) outdoor light setup.
>
>   That's what I supposed. Anyhow, the SunColor returned isn't
> supposed to have the sky color weighted in it?



SunColor is the color of the sky (given by the model) at SolarPosition. I
found that using a light_source {SolarPosition SunColor} led to nicer
images.





> > What are the problems with the way it originally is? Tell me what
> > isn't to your taste, I'll try to solve it.
>
>   Perhaps I've not explained it very well: How I can use it on my
> scenes, having this dirty (and perhaps stupid) habit of using global
> ambient set to 0?



Sorry, I read too quickly and misunderstood. I set #default{finish{ambient
0}}, which has exactly the same effect, unless a texture specify an ambient.
This wont work if you use global ambient to override a non-zero ambient
specified in a texture. But it shouldn't be much work to replace any ambient
float to ambient 0 or comment it.



BTW, the complete #default I most usually use is #default{pigment{rgb
.66}finish{ambient (fRad?0:.2)}}, fRad being a flag I use for switching
radiosity. That way it look nice (er... kind of) with or without radiosity.
Alternatively I set ambient 0 and add a secondary light_source opposite to
the first and less intense in a #if(fRad)...#end structure.





>   Well, going back to skylighting...



:-D





Povingly,





Philippe

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Jaime Vives Piqueres wrote:
>  But, on the other hand, the POV docs encourage to use global ambient
> set to 0 for radiosity with light sources, wich is what I do usually, to
> use predefined and existant textures wich have ambient (rather than
> changing all the textures to set ambient to 0). What's the solution in
> that case? I can't think of anything right now... 

I think the solution is to stop making and using textures that have 
ambient in them but shouldn't.

-Xplo

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