[Radiance-general] Obtaining RGB output data

[alira at gsd.harvard.edu]

Hi Alexa!

Thanks for responding my email. I've been `playing´ with the "pvalue"
command and I assume I obtain the x-y position of the pixel of any picture
and the R, G, and B value of that pixle. You told me in your e-mail that
is up to me how I interpret this RGB data. When I use the pvalue I obtain
data like this (for example):


   xposition     y position      R            G              B

      345            240       7.495e-02    7.495e-02     3.495e-02

However, which type of units are this? Are there no units at all? Is this
illuminance? Also, in most of my pixels, the R,G, and B data is the same,
i.e, 7.495e-02 in the three (RGB). Does this means that that pixel has a
neutral color?

Thanks for your help,

Adriana












> Hi Adriana,
>
> if I'm not mistaken you want to look into the use of 'pvalue'.
> Note, that RGB values will give you some idea about the colorimetric
> properties of any point in the scene, but if you are remotely interested
> in accurate data - your comparison with the spectroradiometer suggests
> this - then you might want to look into spectral rendering. You can also
> do that with RADIANCE. see e.g. Yang & Maloney, 2001, Vision Research,
> 41:2581-2600 (the appendix).
> As far as I remember RADIANCE will return RGB values < 0 and > 1, and
> it's up to you how you interpret this data, i.e. outside of the
> RGB-gamut of the default phosphors (also somewhere defined in RADIANCE),
> which will definitely become an issue with day-light scenes.
>
> Good luck!
>
> alexa
>
>
> alira at gsd.harvard.edu wrote:
>>    hi all,
>>
>>    I'm starting to use Radiance and I want to work with it in order to
>> simulate both daylight and artificial light. I want to change both the
>> RGB propeties of the light source and the materials. After Radiance
>> analizes the scene one can obtain as the output data, the luminance of
>> any point I select in my scene. Besides knowing what is the luminance
>> in any desired point, I'm very interested in knowing what is the RGB
>> component also of any point of the scene (such as if I were measuring
>> the RGB spectral component in several points of a room with a
>> spectometer). Is that possible? And if yes, what do you recommend me to
>> do in order to obtain this as an output data?
>>
>>    I would appreciate any help.
>>
>> Than you,
>> -adriana
>>
>>
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>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Dr. Alexa I. Ruppertsberg
> Department of Optometry
> University of Bradford
> Bradford
> BD7 1DP
> UK
>
> email: 	a.i.ruppertsberg at bradford.ac.uk
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
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