Radiance-general Digest, Vol g Issue 15ivcssynepjio



On Jul 15, 2015 9:00 PM, <[email protected]> wrote:

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Today's Topics:

   1. Re: accurate rendering of concavities (Chris Kallie)


Message: 1
Date: Tue, 14 Jul 2015 16:24:28 -0400
From: Chris Kallie <[email protected]>
To: Radiance general discussion <[email protected]>
Subject: Re: [Radiance-general] accurate rendering of concavities
Message-ID: <[email protected]>
Content-Type: text/plain; charset=windows-1252; format=flowed

Will try these two approaches.
Thanks for the suggestions!

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 <[email protected]>
>> 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