[Radiance-general] rpict: color channel separation

[Stefan Schwarzer]

Dear list members:

While getting acquainted with radiance, I stumbled on a phenomenon
that I do not understand.

I keep the following scene description (of a red sphere lonely in vast Euclidean space) in a file called sphere_0.rad

void light SphereLight_0
0 0 3 0.000431188 0 0

SphereLight_0 sphere sphere_0
0 0 4 0 500 0 100

I use oconv and rpict to render the scene and check the output using pvalue.

oconv sphere_0.rad > o.conv
rpict -x 128 -y 128 o.conv | pvalue -o -h -u

The first few lines of output of these commands are

-Y 128 +X 128
     60      95       4.320e-04       9.537e-07       9.537e-07
     62      95       0.000e+00       0.000e+00       0.000e+00
     63      95       4.320e-04       9.537e-07       9.537e-07
     65      95       0.000e+00       0.000e+00       0.000e+00
     67      95       4.320e-04       9.537e-07       9.537e-07
     68      95       0.000e+00       0.000e+00       0.000e+00
     56      94       4.320e-04       9.537e-07       9.537e-07

They demonstrate that am picking up some small power contributions in
the g and b channel which seem suspicious to me. When I use rtrace in an
attempt to reproduce the phenomemon, I find 0 for g and b as I'd expect.

I'd be grateful if somebody could share her/his insight

ps - random observations:

- I have experimented with program options, but even though the defaults
of rtrace and rpict differ slightly, they seem to not be able to explain
rpict's behavior

- A colleague at Fraunhofer ISE checked the pic-file and mentioned to
me that the non-zero contributions are present in the rpict output and
are not created later by pvalue


-- 
Stefan Schwarzer
Fraunhofer-Institut für Physikalische Messtechnik IPM
Optische Fertigungsmesstechnik
Heidenhofstr. 8, 79110 Freiburg, Germany
Telefon: +49-(0)761-8857-366
stefan.schwarzer at ipm.fraunhofer.de
http://www.ipm.fraunhofer.de

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