[Radiance-general] Re: Radiance-general Digest, Vol 17, Issue 20 (Out of Office Automated Response)

Mark de la Fuente MdelaFuente at wmtao.com
Fri Jul 22 12:02:09 CEST 2005


I will be out of the office and unavailable from July 21st through July 26th.

Mark de la Fuente
William Tao & Associates
Electrical Project Engineer
349 Marshall Avenue
Suite 200
Webster Groves, MO 63119
v. 314.961.5252 x 250
f.  314.961.5258

>>> radiance-general 07/22/05 05:01 >>>

Send Radiance-general mailing list submissions to
	radiance-general at radiance-online.org

To subscribe or unsubscribe via the World Wide Web, visit
	http://www.radiance-online.org/mailman/listinfo/radiance-general
or, via email, send a message with subject or body 'help' to
	radiance-general-request at radiance-online.org

You can reach the person managing the list at
	radiance-general-owner at radiance-online.org

When replying, please edit your Subject line so it is more specific
than "Re: Contents of Radiance-general digest..."


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)


----------------------------------------------------------------------

Message: 1
Date: Thu, 21 Jul 2005 19:29:42 +0200
From: Lars O. Grobe <grobe at gmx.net>
Subject: [Radiance-general] estimating -av values, color
To: Radiance general discussion <radiance-general at radiance-online.org>
Message-ID: <2d650bdc669b4373597cfcd9098128ce at gmx.net>
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.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 2134 bytes
Desc: not available
Url : http://radiance-online.org/pipermail/radiance-general/attachments/20050721/ee571035/smime-0001.bin

------------------------------

Message: 2
Date: Thu, 21 Jul 2005 13:55:36 -0400
From: Jack de Valpine <jedev at visarc.com>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <radiance-general at radiance-online.org>
Message-ID: <42DFE198.6010002 at visarc.com>
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.
>
>------------------------------------------------------------------------
>
>_______________________________________________
>Radiance-general mailing list
>Radiance-general at radiance-online.org
>http://www.radiance-online.org/mailman/listinfo/radiance-general
>  
>

-- 
#	John E. de Valpine
#	president
#
#	visarc incorporated
#	http://www.visarc.com
#
#	channeling technology for superior design and construction

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://radiance-online.org/pipermail/radiance-general/attachments/20050721/9c31c84e/attachment.html

------------------------------

Message: 3
Date: Fri, 22 Jul 2005 01:26:56 -0700
From: Carsten Bauer <cbauer- at t-online.de>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <radiance-general at radiance-online.org>
Message-ID: <42E0ADD0.3010709 at t-online.de>
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 <grobe at gmx.net>
Subject: Re: [Radiance-general] estimating -av values, color
To: Radiance general discussion <radiance-general at radiance-online.org>
Message-ID: <227fab3d7079cb70f772c7218959fc95 at gmx.net>
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.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 2134 bytes
Desc: not available
Url : http://radiance-online.org/pipermail/radiance-general/attachments/20050722/1b3f3e7f/smime-0001.bin

------------------------------

_______________________________________________
Radiance-general mailing list
Radiance-general at radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general


End of Radiance-general Digest, Vol 17, Issue 20
************************************************



More information about the Radiance-general mailing list