[Radiance-general] Radiance-general Digest, Vol g Issue 15ivcssynepjio

[Josep Barberillo]

L
On Jul 15, 2015 9:00 PM, <radiance-general-request at radiance-online.org>
wrote:

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>    1. Re: accurate rendering of concavities (Chris Kallie)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Tue, 14 Jul 2015 16:24:28 -0400
> From: Chris Kallie <kallie at umn.edu>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] accurate rendering of concavities
> Message-ID: <55A56FFC.9060307 at umn.edu>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> Will try these two approaches.
> Thanks for the suggestions!
> -Chris
>
> On 7/13/15 11:47 PM, Greg Ward wrote:
> > Did you try rendering first with an "overture" calculation -- create and
> discard a lower-resolution version of the same image in order to fill the
> ambient cache?  This sometimes helps.  Also, reducing the -aa value down as
> low as 0.01 should improve the subtle shading in the indirect regions.
> >
> > -Greg
> >
> >> From: Chris Kallie <kallie at umn.edu>
> >> Subject: [Radiance-general] accurate rendering of concavities
> >> Date: July 13, 2015 7:56:55 PM PDT
> >>
> >> Dear fellow Radiance users,
> >>
> >> Recently, I did an experiment that involved the study of subtly-shaded,
> locally-concave surface patches, including contours that were indirectly
> illuminated in some areas. The problem was, in these deeper regions of the
> object, the ambient lighting term dominated the rendered patch.
> >>
> >> In the physical world, there is probabilistically only one darkest
> region (i.e., a single darkest pixel in HDRI) in any particular image of a
> scene. However, with Radiance, I find large patches that share the same
> darkest luminance value, and the subtle shading information is lost. In my
> last experiment, I was able to overcome this problem with a hack: I added a
> large, dim area light for fill. This, in effect, caused the cosine
> reflectance function to dominate the shading values, which is not the same
> as indirect lighting effects caused by inter-reflections and contour
> changes. Unfortunately, although that hack worked for my purposes at the
> time, it would not be the right approach for my current project. How does
> one eliminate this problem in his/her renderings using Radiance?
> >>
> >> In general, is there a way to recreate an environment using Radiance
> that ensures photometric accuracy in subtly-shaded concave regions of
> convoluted objects (e.g., caused by gradual orientation changes, umbras,
> self-occlusions, and inter-reflections)?
> >>
> >> Thank you for your thoughtful considerations.
> >>
> >> Sincerely,
> >> Chris Kallie
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> End of Radiance-general Digest, Vol 137, Issue 15
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