Thank you very much! I will try this and get back to you about the result. <br><br>Bei <br><br><div class="gmail_quote">On Tue, Nov 25, 2008 at 12:55 PM, Thomas Bleicher <span dir="ltr"><<a href="mailto:tbleicher@arcor.de">tbleicher@arcor.de</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">Hello Bei.<div class="Ih2E3d"><br>
<br>
On 25 Nov 2008, at 16:49, <a href="mailto:bei.xiao@gmail.com" target="_blank">bei.xiao@gmail.com</a> wrote:<br>
<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hello,<br>
<br>
I am trying to render an image using only ambient light. I noticed that the reflected light appears to be non-uniform across the objects in the scene. The scene is a open box with the open part facing the viewer and only surfaces inside the box are lit (outside of the box is dark). It appears that the light has some directionality to it.<br>
</blockquote>
<br></div>
The ambient light setting in Radiance is different to other renderers<br>
- or maybe it's not if I think about it. Anyway, it's not supposed to replace<br>
a proper light source in your scene (a 'light' or 'source' material for<br>
example). It's just there to 'take over' when the proper ray tracing<br>
does not produce a light source in an acceptable time. That means<br>
it's only applied it the renderer has not found a light source after<br>
tracing a ray for '-ab' bounces through the scene.<br>
<br>
In your case with a box open to the dark void every ray that leaves<br>
the box adds nothing to the illuminance level of a point. The closer<br>
you are to the (front) edge the more rays escape the box and the<br>
darker this point will be in the image.<br>
<br>
The points at the back of the box are only 'bright' because the<br>
renderer assigns an artificial brightness to the ray after the first<br>
bounce (-ab 1). You can probably achieve a smoother gradient<br>
in your image by increasing the -ab value.<br>
<br>
If you enclose your open box and the camera with another<br>
closed box you will probably see that there is no directionality<br>
to the ambient light and everything will be uniformly grey (if<br>
there is only one material). Every ray not hits a surface and<br>
the brightness is only modified by the reflectance of the<br>
material.<br>
<br>
Regards,<br><font color="#888888">
Thomas</font><div><div></div><div class="Wj3C7c"><br>
<br>
<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Quote of the Day<br><br>Writing your PHD thesis is one chance that you can be bold at your arguments because it will receive no reviews!<br><br>-David Brainard (my advisor) <br>
<br>Bei Xiao<br>Room 330 C<br>3401 Walnut Street C Wing<br>Department of Neuroscience<br>University of Pennsylvania<br>Philadelphia, PA 19104, USA<br>Web: <a href="http://www.psych.upenn.edu/~beixiao">www.psych.upenn.edu/~beixiao</a><br>
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