I'm rendering a artist's studio that has sunlight coming in from the glass
roof.  Leaving that as the only light source and cranking up the ambiant on
the contents of the room doesn't look real at all.

Putting a fill light off to one side makes shapes look better (not "flat")
but adds shadows that are wrong.

Putting a large area light to one side looks great, for the major elements
of the scene.  Objects don't cast distinct shadows from this light source
but do show the vague darkening on the floor and close walls that we see in
a real room full of ambient light.  The =illumination= is still a point, not
a large surface, but it looks fine in this case.

However, I'm still getting stray shadows.  I got a sharp shadow from a small
object onto a nearby flat surface, which I presumed was because the
"adaptive" fails when the object is smaller than the light.  Hmm, on second
thought that's not right at all, as this would make =no= shadow (all four
corners of the light are unblocked when the object is in the middle), not a
sharp shadow with no prenumbra.

I tried turning off adaptive, and I still get a sharp shadow, even though
there are 25 sublights.  I'm trying a much larger number of sublights now,
but it's taking a long time to render.  If that shows no change, I don't
understand what's happening.

Anyway, I found that the "darkening" effect does a great deal toward making
a room look real.  If this isn't the best way to acheive that in an ambient
light situation, what is?  Would radiosity be the answer here, or does it
not help with this effect?

--John

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I've never encountered what you mention is wrong, and it sounds
peculiar. Did you use more than 'adaptive 1'?  I'm sure you must be
using 'jitter' in that too, aren't you? But what it almost sounds like
is a 'area_light' whose plane is aligned with the small object
somehow.

Bob

John M. Dlugosz <joh### [at] dlugoszcom> wrote in message
news:37cc8e2e@news.povray.org...
> I'm rendering a artist's studio that has sunlight coming in from the
glass
> roof.  Leaving that as the only light source and cranking up the
ambiant on
> the contents of the room doesn't look real at all.
>
> Putting a fill light off to one side makes shapes look better (not
"flat")
> but adds shadows that are wrong.
>
> Putting a large area light to one side looks great, for the major
elements
> of the scene.  Objects don't cast distinct shadows from this light
source
> but do show the vague darkening on the floor and close walls that we
see in
> a real room full of ambient light.  The =illumination= is still a
point, not
> a large surface, but it looks fine in this case.
>
> However, I'm still getting stray shadows.  I got a sharp shadow from
a small
> object onto a nearby flat surface, which I presumed was because the
> "adaptive" fails when the object is smaller than the light.  Hmm, on
second
> thought that's not right at all, as this would make =no= shadow (all
four
> corners of the light are unblocked when the object is in the
middle), not a
> sharp shadow with no prenumbra.
>
> I tried turning off adaptive, and I still get a sharp shadow, even
though
> there are 25 sublights.  I'm trying a much larger number of
sublights now,
> but it's taking a long time to render.  If that shows no change, I
don't
> understand what's happening.
>
> Anyway, I found that the "darkening" effect does a great deal toward
making
> a room look real.  If this isn't the best way to acheive that in an
ambient
> light situation, what is?  Would radiosity be the answer here, or
does it
> not help with this effect?
>
> --John
>
>
>

Post a reply to this message

Bob Hughes <inv### [at] aolcom> wrote in message
news:37cc9234@news.povray.org...
> I've never encountered what you mention is wrong, and it sounds
> peculiar. Did you use more than 'adaptive 1'?  I'm sure you must be
> using 'jitter' in that too, aren't you? But what it almost sounds like
> is a 'area_light' whose plane is aligned with the small object
> somehow.


It turns out that the shadow in question is correct, not generated by this
area light.  When I tested the image without the light to see if that shadow
went away, I must have used the wrong options, as the shadow went away <g>.

I'm still interested in general ideas for the "room edge" effect, or the
transition from ambiant to directional light.  I think my idea is OK for
some scenes, but because the illumination isn't an area (it only affects the
shadows) it can cause unwanted highlights too.

--John

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John M. Dlugosz wrote in message <37cc9f4f@news.povray.org>...
>
>Bob Hughes <inv### [at] aolcom> wrote in message
>news:37cc9234@news.povray.org...
>> I've never encountered what you mention is wrong, and it sounds
>> peculiar. Did you use more than 'adaptive 1'?  I'm sure you must be
>> using 'jitter' in that too, aren't you? But what it almost sounds like
>> is a 'area_light' whose plane is aligned with the small object
>> somehow.
>
>
>It turns out that the shadow in question is correct, not generated by this
>area light.  When I tested the image without the light to see if that
shadow
>went away, I must have used the wrong options, as the shadow went away <g>.
>
>I'm still interested in general ideas for the "room edge" effect, or the
>transition from ambiant to directional light.  I think my idea is OK for
>some scenes, but because the illumination isn't an area (it only affects
the
>shadows) it can cause unwanted highlights too.


Try using radiosity -- it has a much greater effect in this situation than
you'd expect.

Mark

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John M. Dlugosz <joh### [at] dlugoszcom> wrote:
: I'm rendering a artist's studio that has sunlight coming in from the glass
: roof.  Leaving that as the only light source and cranking up the ambiant on
: the contents of the room doesn't look real at all.

  If you want real interreflection of light, you need to use radiosity.
  See http://iki.fi/warp/pics/Radiosity_test2/

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

Post a reply to this message

Mark Wagner <mar### [at] gtenet> wrote in message
news:37ccb22d@news.povray.org...
> Try using radiosity -- it has a much greater effect in this situation than
> you'd expect.


I did try it, briefly.  I'm sure I could twiddle the parameters a LOT, but
off hand I saw that it didn't illuminate metal the way I wanted.  When
backlit by the key light, it looked just like a high ambiant -- no curves or
shape visible.

Physically, the other end of the room is a light source, and lambert shading
applies.  And in the case of metal, more spectral highlights are noticable
as well.  Turning up ambiant light levels didn't give the objects any
=shape=, and my try at using radiosity was no different.  Would adjusting
the parameters help with that specific effect?

Also, I may be on the "painting" rather than "photo" side of things, making
it look like the way I see it in my mind, which is not necessarily the way a
camera sees it.  So I need some kind of "modeling light" in localized areas,
as well as the room-edge effect.

More than once I've wished that it was possible to declare that specific
light sources interact only with specific objects.

--John

Post a reply to this message

John M. Dlugosz wrote:
> 
> Mark Wagner <mar### [at] gtenet> wrote in message
> news:37ccb22d@news.povray.org...
> > Try using radiosity -- it has a much greater effect in this situation than
> > you'd expect.
> 
> I did try it, briefly.  I'm sure I could twiddle the parameters a LOT, but
> off hand I saw that it didn't illuminate metal the way I wanted.  When
> backlit by the key light, it looked just like a high ambiant -- no curves or
> shape visible.

Some 3D effects look best when animated (though you wouldn't necessarily
think so offhand); your brain uses the movement to see how an object's
appearance reacts to the objects around it. Metal and glass are probably
the best examples of this, as movement helps you perceive reflection and
refraction. (The ability to see different sides of an object, or to
judge its distance relative to other objects, also require movement, but
are based on perspective rather than interactivity.)

Of course, you don't sound like you're planning to animate this.

The next thing, then, would be to take a careful look at exactly what
you're illuminating, and how. With some thought and tweaking, you can
probably get it to look how you want. (I can't offer any more specific
suggestions, since I have almost no idea what the scene's supposed to
look like or what's in it.. I must have missed the first post.)

> Physically, the other end of the room is a light source, and lambert shading
> applies.  And in the case of metal, more spectral highlights are noticable
> as well.  Turning up ambiant light levels didn't give the objects any
> =shape=, and my try at using radiosity was no different.  Would adjusting
> the parameters help with that specific effect?

Ambient lighting (effectively) hits an object from every angle, so no,
obviously it wouldn't produce shadows that would help define the shape
of the object. In fact, it would do the opposite, by fading or
eliminating those shadows.

> More than once I've wished that it was possible to declare that specific
> light sources interact only with specific objects.

I don't think you can do this.. 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).

-Xplo

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"John M. Dlugosz" wrote:

> Mark Wagner <mar### [at] gtenet> wrote in message
> news:37ccb22d@news.povray.org...

<snip>

>
> More than once I've wished that it was possible to declare that specific
> light sources interact only with specific objects.
>
> --John

If you don't mind using a patch, the SuperPatch will allow light sources that
only interact with specific objects. It might be worth a try.
Mr.Art

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Xplo Eristotle <inq### [at] unforgettablecom> wrote in message
news:37C### [at] unforgettablecom...
> Of course, you don't sound like you're planning to animate this.


> 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.

--John

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Am am indeed using the SuperPatch!  Thanks for the tip.

... reading txt file ...

So, are the lights nominated by the light_group for a specific object the
only lights to contribute to the illumination of that object?

I suppose I can make a modeling light by excluding it from every other
object (looks rather intrusive, since I can't change the meaning of "all"
... maybe can change the defaults) and also making it have no_shadow for
that object.

I'll have to experiment with that feature, or find a better
description/tutorial somewhere.  Any pointers?

--John


Mr. Art <mr.### [at] gcinet> wrote in message news:37CDF0EC.8CEA2118@gci.net...
>
>
> "John M. Dlugosz" wrote:
>
> > Mark Wagner <mar### [at] gtenet> wrote in message
> > news:37ccb22d@news.povray.org...
>
> <snip>
>
> >
> > More than once I've wished that it was possible to declare that specific
> > light sources interact only with specific objects.
> >
> > --John
>
> If you don't mind using a patch, the SuperPatch will allow light sources
that
> only interact with specific objects. It might be worth a try.
> Mr.Art
>

Post a reply to this message