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radiance-general 07/22/05 05:01 >>>
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Today's Topics:
1. estimating -av values, color (Lars O. Grobe)
2. Re: estimating -av values, color (Jack de Valpine)
3. Re: estimating -av values, color (Carsten Bauer)
4. Re: estimating -av values, color (Lars O. Grobe)
···
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Message: 1
Date: Thu, 21 Jul 2005 19:29:42 +0200
From: Lars O. Grobe <[email protected]>
Subject: [Radiance-general] estimating -av values, color
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Hi list,
I have a question regarding the so-often given advice to use a neutral
-av setting. Why? Is it assumed that in general, the light conditions
in a building are like that? I have used a -av of .5 .5 .5 here,
together with -ae excluded objects (I wrote enough questions on that
topic ;-). This results in a strange image, as the calculated ambient
is redish, and the ambient-excluded objects appear very strange (like
blueish) because they are the only objects illuminated by this neutral
color. I can understand that if using -ab 0, setting a colored -av
would not make sense as ALL indirect illumination would be neutral
than.
So, am I right that in the case here (I use the -av settings only for
the -ae excluded objects in a scene that is rendered with -ab 2), using
a neutral value would be simply wrong and I have to use the "measured"
(from rview) radiance?
TIA+CU Lars.
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Message: 2
Date: Thu, 21 Jul 2005 13:55:36 -0400
From: Jack de Valpine <[email protected]>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Hi Lars,
Estimating ambient values is part science and part art as far as I have
learned over the years. I don't think that I know of a situation where
we have ever used a non neutral ambient value. I suppose if one were
trying to more accurately account for certain kind of atmospheric shifts
this might be a case to do this....?
Without knowing what your scene looks like (pictures help) it is
difficult to help diagnose what is going on. My suscpicion though is
that an ambient value of .5 .5 .5 may be too high for the given scene,
thus the odd looking ("glowing") results. A very good option would be to
use the "compamb" script that Greg wrote. This runs a pass on a small
image using fairly high parameters and then does some calculations to
come up with a good ambient value for the scene. This is pretty easy to
use and does not take that long to return the results.
Note the av value affects the whole simulation not just the excluded
objects.
-Jack
Lars O. Grobe wrote:
Hi list,
I have a question regarding the so-often given advice to use a neutral
-av setting. Why? Is it assumed that in general, the light conditions
in a building are like that? I have used a -av of .5 .5 .5 here,
together with -ae excluded objects (I wrote enough questions on that
topic ;-). This results in a strange image, as the calculated ambient
is redish, and the ambient-excluded objects appear very strange (like
blueish) because they are the only objects illuminated by this neutral
color. I can understand that if using -ab 0, setting a colored -av
would not make sense as ALL indirect illumination would be neutral than.So, am I right that in the case here (I use the -av settings only for
the -ae excluded objects in a scene that is rendered with -ab 2),
using a neutral value would be simply wrong and I have to use the
"measured" (from rview) radiance?TIA+CU Lars.
------------------------------------------------------------------------
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--
# John E. de Valpine
# president
#
# visarc incorporated
# http://www.visarc.com
#
# channeling technology for superior design and construction
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Message: 3
Date: Fri, 22 Jul 2005 01:26:56 -0700
From: Carsten Bauer <[email protected]>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi Lars,
you can think of the av value being a substitution for the rest amount
of light hovering in the room which gets ommitted in your calculations
when you follow
ambient rays only a certain number of bounces deep, instead of following
them infinitely deep. And if you have a neutral source, but red walls,
the diffuse indirect light will be red, and so should also be the av
setting, to be a correct compensation...
So generally your're right in considering the color bias of the scene
also for the constant ambient approximation. But definitely also keep in
mind Jacks remark on -av affecting all objects...
-cb
------------------------------
Message: 4
Date: Fri, 22 Jul 2005 11:47:07 +0200
From: Lars O. Grobe <[email protected]>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
So generally your're right in considering the color bias of the scene
also for the constant ambient approximation. But definitely also keep
in mind Jacks remark on -av affecting all objects...
Hi,
thanks to Jack and Carsten for the responses, this list is always of
great help. I didn't really use -av in previous projects, but need it
now because the complexity of the scene forces me to exclude modifiers
from the ambient calculation.
As far as I understood, the influence of the -av setting (on objects
not excluded from the ambient calculation) can be dimmed by the -aw
setting, and as I start my renderings with an "ouverture calculation"
the computed ambient distribution should be stable enough. Am I wrong
here?
CU Lars.
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