[Radiance-general] ambient light

[bei.xiao at gmail.com]

Thank you very much! I will try this and get back to you about the result.

Bei

On Tue, Nov 25, 2008 at 12:55 PM, Thomas Bleicher <tbleicher at arcor.de>wrote:

> Hello Bei.
>
> On 25 Nov 2008, at 16:49, bei.xiao at gmail.com wrote:
>
>  Hello,
>>
>> 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.
>>
>
> The ambient light setting in Radiance is different to other renderers
> - or maybe it's not if I think about it. Anyway, it's not supposed to
> replace
> a proper light source in your scene (a 'light' or 'source' material for
> example). It's just there to 'take over' when the proper ray tracing
> does not produce a light source in an acceptable time. That means
> it's only applied it the renderer has not found a light source after
> tracing a ray for '-ab' bounces through the scene.
>
> In your case with a box open to the dark void every ray that leaves
> the box adds nothing to the illuminance level of a point. The closer
> you are to the (front) edge the more rays escape the box and the
> darker this point will be in the image.
>
> The points at the back of the box are only 'bright' because the
> renderer assigns an artificial brightness to the ray after the first
> bounce (-ab 1). You can probably achieve a smoother gradient
> in your image by increasing the -ab value.
>
> If you enclose your open box and the camera with another
> closed box you will probably see that there is no directionality
> to the ambient light and everything will be uniformly grey (if
> there is only one material). Every ray not hits a surface and
> the brightness is only modified by the reflectance of the
> material.
>
> Regards,
> Thomas
>
>
>
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Bei Xiao
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Department of Neuroscience
University of Pennsylvania
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Web: www.psych.upenn.edu/~beixiao
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