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I'm trying to figure out what I should use to create diffusion on a spotlight,
similar to filters used in photography and theater.
I don't mean the diffusion function in povray itself, but an effect between the
light source and the target that spreads out the light to create soft edges on
everything. I already understand how to use the radius and falloff in a
spotlight source, but all my attempts so far in making a diffusion filter have
turned out badly.
I've experimented with using a thin glass-textured plate in the light beam and
using photon refraction effects, with varying the thickness of the object to
get more and less diffusion. I found that there seems to be a cutoff
thickness where it either doesn't change the light at all, or makes the light
so dull that there is no longer a circular beam even at 4 units away. That
is with changing the intensity of the light to compensate for fading loss.
Does anyone have an idea of how to do this?
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"cshake" <cshake+pov### [at] gmail com> wrote:
> I'm trying to figure out what I should use to create diffusion on a spotlight,
> similar to filters used in photography and theater.
>
> I don't mean the diffusion function in povray itself, but an effect between the
> light source and the target that spreads out the light to create soft edges on
> everything. I already understand how to use the radius and falloff in a
> spotlight source, but all my attempts so far in making a diffusion filter have
> turned out badly.
>
> I've experimented with using a thin glass-textured plate in the light beam and
> using photon refraction effects, with varying the thickness of the object to
> get more and less diffusion. I found that there seems to be a cutoff
> thickness where it either doesn't change the light at all, or makes the light
> so dull that there is no longer a circular beam even at 4 units away. That
> is with changing the intensity of the light to compensate for fading loss.
>
> Does anyone have an idea of how to do this?
By the sounds of it, you want to use area lights, not spotlights.
Spotlights in pov are treated as point lights, but have attenuated edges of the
lighted area, the shadows are still sharp.
Try using an area light but with an open cylinder around it to limit the light
to a spot. You can effect the amount of soft shadowing by the size of the
light/cylinder, etc. A while back I posted a method for making a square
spotlight using area lights. It would probably provide a good starting point.
I'll dig around and see if I can find it.
-tgq
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Here it is.
http://news.povray.org/povray.newusers/thread/%3Cweb.4668123c7fc265f0ff6e04e90@news.povray.org%3E/?ttop=282988&toff=200
-tgq
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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> By the sounds of it, you want to use area lights, not spotlights.
> Spotlights in pov are treated as point lights, but have attenuated edges of the
> lighted area, the shadows are still sharp.
Wouldn't a spotlight made into an area_light solve it? Or perhaps I'm not
reading his question correctly.
Ken W.
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Trevor G Quayle wrote:
> Here it is.
>
>
http://news.povray.org/povray.newusers/thread/%3Cweb.4668123c7fc265f0ff6e04e90@news.povray.org%3E/?ttop=282988&toff=200
>
>
> -tgq
>
>
Thanks, but I want to keep the spotlight a single source because I'm
trying to simulate a theatrical lighting instrument as closely as
possible. The type of fixture I'm modeling after has a ellipsoidal
reflector at the back of the instrument around a single lamp [bulb],
lenses in the body tube, and a frame at the front of the tube that
different colors and diffusion sheets can be placed in.
The whole body and lenses assembly basically focuses the light into
exactly what at spotlight in povray does (with cosine focus, field angle
and beam angle, etc), and placing a diffusion sheet in front of the
lenses makes the whole light spread out more. The only real difference
between what I'm doing with a 'diffusion sheet' in front of the
spotlight source and the real instrument is that the real instrument
isn't completely in focus at that point, while the spotlight source
always is.
More info:
Light I'm modeling: http://www.etcconnect.com/minisite/sourcefour/index.html
- Note the area at the front that holds a square frame for color or
diffusion.
Example of diffusion filters:
http://www.leefiltersusa.com/lighting/products/range/ref:I46C9C14F8BA5B/
I may try to use an area light, but I know the effect can be done with a
material in the beam itself because I use it in the theater where I work.
-cshake
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Trevor G Quayle wrote:
> Try using an area light but with an open cylinder around it to limit the light
> to a spot. You can effect the amount of soft shadowing by the size of the
> light/cylinder, etc. A while back I posted a method for making a square
> spotlight using area lights. It would probably provide a good starting point.
> I'll dig around and see if I can find it.
>
The area_light keyword can be used inside a spotlight. There's no
need to go to all this trouble with the cylinder to guide the light.
Jerome
- --
mailto:jeb### [at] freefr
http://jeberger.free.fr
Jabber: jeb### [at] jabberfr
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iEYEARECAAYFAkmfrCcACgkQd0kWM4JG3k+FPACfTiu+NRUpOwws5hpP5RUaQbRs
0YkAoJSVehcFS87iYrYcSXK2i29v13n/
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Trevor G Quayle <Tin### [at] hotmailcom> wrote:
> Try using an area light but with an open cylinder around it to limit the light
> to a spot. You can effect the amount of soft shadowing by the size of the
> light/cylinder, etc. A while back I posted a method for making a square
> spotlight using area lights. It would probably provide a good starting point.
> I'll dig around and see if I can find it.
Out of curiosity: Didn't you even think of trying to define a light_source
as being a spotlight and an area light *at the same time*?
Because, as others noted, povray perfectly supports that.
--
- Warp
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Warp <war### [at] tagpovrayorg> wrote:
> Trevor G Quayle <Tin### [at] hotmailcom> wrote:
> > Try using an area light but with an open cylinder around it to limit the light
> > to a spot. You can effect the amount of soft shadowing by the size of the
> > light/cylinder, etc. A while back I posted a method for making a square
> > spotlight using area lights. It would probably provide a good starting point.
> > I'll dig around and see if I can find it.
>
> Out of curiosity: Didn't you even think of trying to define a light_source
> as being a spotlight and an area light *at the same time*?
>
> Because, as others noted, povray perfectly supports that.
>
> --
> - Warp
No I didn't. I guess I must've assumed that the user had maybe tried and it
didn't work.
This trick does work for recatngular spotlights though...
-tgq
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CShake <cshake+pov### [at] gmailcom> wrote:
ferent colors and diffusion sheets can be placed in.
>
> The whole body and lenses assembly basically focuses the light into
> exactly what at spotlight in povray does (with cosine focus, field angle
> and beam angle, etc), and placing a diffusion sheet in front of the
> lenses makes the whole light spread out more. The only real difference
> between what I'm doing with a 'diffusion sheet' in front of the
> spotlight source and the real instrument is that the real instrument
> isn't completely in focus at that point, while the spotlight source
> always is.
I see now what you mean. I have a good visual image of your problem, because I
do volunteer lighting at a local community theater. The 'beam spread' is spread
out and very fuzzy, almost non-distinct, when a diffusion gel or two is placed
in front of the light. It's almost as if there are *two* spotlights--one with a
fuzzy though not-too-spread out beam, the other with a much wider and fuzzier
beam. Yours is a good question (I wish I had an answer for you at present.)
I'll be curious to know what is suggested here, because I'd like to plug it
into my own POV-Ray 'theater lighting' scene, which I use from time to time.
Ken W.
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cshake nous illumina en ce 2009-02-20 21:08 -->
> I'm trying to figure out what I should use to create diffusion on a spotlight,
> similar to filters used in photography and theater.
>
> I don't mean the diffusion function in povray itself, but an effect between the
> light source and the target that spreads out the light to create soft edges on
> everything. I already understand how to use the radius and falloff in a
> spotlight source, but all my attempts so far in making a diffusion filter have
> turned out badly.
>
> I've experimented with using a thin glass-textured plate in the light beam and
> using photon refraction effects, with varying the thickness of the object to
> get more and less diffusion. I found that there seems to be a cutoff
> thickness where it either doesn't change the light at all, or makes the light
> so dull that there is no longer a circular beam even at 4 units away. That
> is with changing the intensity of the light to compensate for fading loss.
>
> Does anyone have an idea of how to do this?
>
>
>
You can...
- add area_light to your spot_light. This will make the shadows it cast blury.
- using photons and your filter, average a few normals. Keep the normals small.
Sample of the averaged normals:
cylinder{z, z+0.01, Radius pigment{rgbt 1}
#local Smpl = 5; #local R = seed(0);
normal{average normal_map{
#while(Smpl >0)
[1 bumps 0.1 scale 0.01 translate<rand(R),rand(R),rand(R)>*0.01]
#local Smpl = Smpl -1;
#end
}
}
interior{ior 1.5}
photons{target refraction on}
}
The value of "Smpl" controlls the smoothness of the bluring. Don't use a large
value, as it affect the rays on two surfaces, and squares the number of samples.
The value after bumps controlls the bluring's intensity.
--
Alain
-------------------------------------------------
You know you've been raytracing too long when your personal correspondence to
friends starts out with #Dear Linda =
Ken Tyler
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