Thanks for the sample images.  From that, I see that it can indeed give
"shape" to objects not directly illuminated, like your yellow sphere.

Nieminen Juha <war### [at] cctutfi> wrote in message
news:37cce0a9@news.povray.org...
>   If you want real interreflection of light, you need to use radiosity.
>   See http://iki.fi/warp/pics/Radiosity_test2/

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John M. Dlugosz wrote:
> 
> Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
> 
> > but in some cases, a carefully-placed
> > spotlight will do the trick, similar to the way that photographers use
> > reflectors to subtly illuminate a model's face (if you've seen an
> > outdoor photo shoot, you know what I'm getting at).
> 
> That's basically what my 1m-square area "fill light" off-stage is doing to
> the main figure, in addition to providing edge-effect radiosity-like
> shadows.
> 
> > I have almost no idea what the scene's supposed to
> > look like or what's in it..
> 
> See http://www.dlugosz.com/POV/dryad_dreams.html for my notes.

Lemme see if I can say something useful.

Well, your notes call for a gleaming 50s sort of robot. Such a gleaming
robot would probably be chromed.. in which case you want more reflection
and a much tighter specular highlight. I should point out, however, that
the more reflective your robot is, the less "shape" it will have, since
it'll be more and more a warped copy of what's around it and less
affected by traditional shading.

The robot you have now has a pretty good "soft metallic" finish, but
that may or may not be what you intended.

If the robot is highly reflective, it would be an excellent idea to
finish the room by adding walls behind the camera to reflect off of the
robot's skin (if you've done this already, they must be really boring
walls). The walls themselves will never appear, but their effect on the
scene will. Also note that adding a couple of walls may change the
lighting in the room, especially if you're using a lot of radiosity.

As for the lighting itself, hmm...

Well, it's supposed to be an artist's studio, yes? AFAIK, those tend to
be pretty well lit, and not with point light either. You probably want
(a) several wide-beam spotlights, similar to track lighting, or a lot of
sunlight streaming in through windows. (I can't see it real well, but
you appear to have something like a skylight, which isn't going to do
the trick.. unless of course you WANTED that.) With that much light, it
would be safe to turn down ambient light for the whole scene to 0 and
crank up the radiosity, letting what lighting exists flood the room in a
more natural manner.

You're looking for an artificial appearance, so I'll stop here. Hope you
got some ideas.

-Xplo

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Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
news:37C### [at] unforgettablecom...

> Lemme see if I can say something useful.

Thanks for the comments.

> The robot you have now has a pretty good "soft metallic" finish, but
> that may or may not be what you intended.

Whatever I intended, I kind of like what I wound up with.  I want to run
with the idea of the robot being very simple in shape, like a post, but the
arms and the attentive posture makes it alive.  The more I can increase this
juxtaposition...

>
> If the robot is highly reflective, it would be an excellent idea to
> finish the room by adding walls behind the camera to reflect off of the
> robot's skin (if you've done this already, they must be really boring
> walls). The walls themselves will never appear, but their effect on the
> scene will. Also note that adding a couple of walls may change the
> lighting in the room, especially if you're using a lot of radiosity.

There are indeed walls on all four sides.  The walls are blank, and I know
it affects the appearance of metal.  That's why I started with an empty room
rather than a black stage.

> As for the lighting itself, hmm...
>
> Well, it's supposed to be an artist's studio, yes? AFAIK, those tend to
> be pretty well lit, and not with point light either. You probably want
> (a) several wide-beam spotlights, similar to track lighting, or a lot of
> sunlight streaming in through windows. (I can't see it real well, but
> you appear to have something like a skylight, which isn't going to do
> the trick.. unless of course you WANTED that.) With that much light, it
> would be safe to turn down ambient light for the whole scene to 0 and
> crank up the radiosity, letting what lighting exists flood the room in a
> more natural manner.

Hmm, the scene is indeed lit from a skylight.  Actually, there is no ceiling
at all in the model <g>.  I'd put in grids to cast shadows if it was
visible.

So, given a "natural light" studio, how can it be well-lit other than a
single point source?  Lots of reflectors to make fill light?  If so, then
the large area light I already put in is the right idea -- models the large
white card or whatever he'll have set up.  Would I get the same effect by
using actual white reflectors and using a radiosity model?

> You're looking for an artificial appearance, so I'll stop here. Hope you
> got some ideas.

Yes, thanks.

--John

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Surely you must know by now that area lights have only a singular
point source for all purposes besides shadows.  Your statement seemed
to suggest otherwise.  But yes, I would think a white reflector
(ambient) should be very similar with the added plus of true
'area_light' appearance when used with 'radiosity'.  I'm thinking you
may have to go with both however in order to get good shadows too,
really not sure.

Bob

John M. Dlugosz <joh### [at] dlugoszcom> wrote in message
news:37cf302a@news.povray.org...
>
> So, given a "natural light" studio, how can it be well-lit other
than a
> single point source?  Lots of reflectors to make fill light?  If so,
then
> the large area light I already put in is the right idea -- models
the large
> white card or whatever he'll have set up.  Would I get the same
effect by
> using actual white reflectors and using a radiosity model?

Post a reply to this message

John M. Dlugosz wrote:
> 
> Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
> news:37C### [at] unforgettablecom...
> 
> > Well, it's supposed to be an artist's studio, yes? AFAIK, those tend to
> > be pretty well lit, and not with point light either. You probably want
> > (a) several wide-beam spotlights, similar to track lighting, or a lot of
> > sunlight streaming in through windows. (I can't see it real well, but
> > you appear to have something like a skylight, which isn't going to do
> > the trick.. unless of course you WANTED that.) With that much light, it
> > would be safe to turn down ambient light for the whole scene to 0 and
> > crank up the radiosity, letting what lighting exists flood the room in a
> > more natural manner.
> 
> Hmm, the scene is indeed lit from a skylight.  Actually, there is no ceiling
> at all in the model <g>.  I'd put in grids to cast shadows if it was
> visible.
> 
> So, given a "natural light" studio, how can it be well-lit other than a
> single point source?  Lots of reflectors to make fill light?  If so, then
> the large area light I already put in is the right idea -- models the large
> white card or whatever he'll have set up.  Would I get the same effect by
> using actual white reflectors and using a radiosity model?

If you're having light coming in through a large aperture, such as a
window or a skylight, using an area light roughly the size of the
aperture (preferably a fairly complex one, if you have the power to
render it) is probably the right way to go. Then, just render it with
the radiosity and see what happens.. it's entirely possible that the
objects in the room (most notably the walls.. real walls reflect a LOT
of light) will provide all the fill light you need/want. Then, if you
still need spot lighting, you can go and add that back in without
changing the overall lighting model very much.

If you wanted to play with white reflectors, you could do it that way as
well; the principle is basically the same, but the numbers won't be,
since your lighting will be different.

-Xplo

Post a reply to this message

Bob Hughes <inv### [at] aolcom> wrote in message
news:37cf3a85@news.povray.org...
> Surely you must know by now that area lights have only a singular
> point source for all purposes besides shadows.  Your statement seemed
> to suggest otherwise.

I know that.  soft shadows, but hard illumination.  In general, it can't
work because the lighting is still hard and a real array of lights will give
multiple phongs not soft illumination.  But for this scene, from this
viewing position, the fill light works OK.


> But yes, I would think a white reflector
> (ambient) should be very similar with the added plus of true
> 'area_light' appearance when used with 'radiosity'.  I'm thinking you
> may have to go with both however in order to get good shadows too,
> really not sure.

Post a reply to this message

Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
news:37D### [at] unforgettablecom...

> If you're having light coming in through a large aperture, such as a
> window or a skylight, using an area light roughly the size of the
> aperture (preferably a fairly complex one, if you have the power to
> render it) is probably the right way to go. Then, just render it with
> the radiosity and see what happens.. it's entirely possible that the
> objects in the room (most notably the walls.. real walls reflect a LOT
> of light) will provide all the fill light you need/want. Then, if you
> still need spot lighting, you can go and add that back in without
> changing the overall lighting model very much.


I don't think so -- the sun casts sharp shadows.  Ah! at least that's what
it looks like in Dallas, with a clear sky and no clouds at all.  On an
overcast day, you get even illumination from the sky.

As for using radiosity, I'll have to play with the numbers to see if I can
get it to "work".  I suppose varying the distance_maximum is enough to get
it working, or will I have to explore more degrees of freedom?  My earlier
try basically didn't work.

--John

Post a reply to this message

"John M. Dlugosz" wrote:

> As for using radiosity, I'll have to play with the numbers to see if I can
> get it to "work".  I suppose varying the distance_maximum is enough to get
> it working, or will I have to explore more degrees of freedom?  My earlier
> try basically didn't work.
> 
> --John

I am far from any kind of expert on the subject but as I understand it when
you use radiosity be sure to keep the distance of your objects from each
other down to a minimum. If your room is hundreds of units wide and it that
far from objects to walls the feature does not work very well. Small rooms
and scales are almost mandatory for radosity to work right. This I have heard
but have spent little time with the feature to date.

-- 
Ken Tyler

See my 850+ Povray and 3D Rendering and Raytracing Links at:
http://home.pacbell.net/tylereng/index.html

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John M. Dlugosz wrote:
> 
> Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
> news:37D### [at] unforgettablecom...
> 
> > If you're having light coming in through a large aperture, such as a
> > window or a skylight, using an area light roughly the size of the
> > aperture (preferably a fairly complex one, if you have the power to
> > render it) is probably the right way to go. Then, just render it with
> > the radiosity and see what happens.. it's entirely possible that the
> > objects in the room (most notably the walls.. real walls reflect a LOT
> > of light) will provide all the fill light you need/want. Then, if you
> > still need spot lighting, you can go and add that back in without
> > changing the overall lighting model very much.
> 
> I don't think so -- the sun casts sharp shadows.  Ah! at least that's what
> it looks like in Dallas, with a clear sky and no clouds at all.  On an
> overcast day, you get even illumination from the sky.

Oh, hmm. What on earth was I thinking? Oh right.. I was trying to
duplicate a "square" of light. Silly me. ^_^;;;

Yes, you WOULD be better off with a single light set back some distance
from the window.

-Xplo

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Lowering 'gray_threshold' nearer to zero helps to blend more color
from objects than the default of 0.5, that can sometimes help to show
more radiosity than would otherwise be seen (doesn't brighten it
though).  Also reducing 'distance_maximum' will tighten the blending
closer and thus seems to make it brighter if a lower 'count' is used.

Bob

John M. Dlugosz <joh### [at] dlugoszcom> wrote in message
news:37d091a5@news.povray.org...
>
> Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
> news:37D### [at] unforgettablecom...
>
> > If you're having light coming in through a large aperture, such as
a
> > window or a skylight, using an area light roughly the size of the
> > aperture (preferably a fairly complex one, if you have the power
to
> > render it) is probably the right way to go. Then, just render it
with
> > the radiosity and see what happens.. it's entirely possible that
the
> > objects in the room (most notably the walls.. real walls reflect a
LOT
> > of light) will provide all the fill light you need/want. Then, if
you
> > still need spot lighting, you can go and add that back in without
> > changing the overall lighting model very much.
>
>
> I don't think so -- the sun casts sharp shadows.  Ah! at least
that's what
> it looks like in Dallas, with a clear sky and no clouds at all.  On
an
> overcast day, you get even illumination from the sky.
>
> As for using radiosity, I'll have to play with the numbers to see if
I can
> get it to "work".  I suppose varying the distance_maximum is enough
to get
> it working, or will I have to explore more degrees of freedom?  My
earlier
> try basically didn't work.
>
> --John
>
>

Post a reply to this message