[Radiance-general] Obtaining RGB output data

[Greg Ward]

Hi Adriana,

Unless you use the -o option of pvalue, the output is not in any  
particular units.  With the -o option, the reported RGB values are in  
radiance units, i.e., watts/sr/meter^2.  However, it is probably  
better for you to work directly in photometric units, which you can  
easily do with the ra_xyze command,  like so:

% ra_xyze rendered.pic | pvalue -o [other options]

The "RGB" values reported will then be in calibrated CIE XYZ  
coordinates (i.e., the Y channel will be luminance in cd/meter^2).

The only caveat to the above is if the pictures are rendered using  
the -i option of rpict, then the output will be in units of  
irradiance (watts/meter^2) in the first case, and illuminance (lux)  
in the case where you apply ra_xyze.

Best of luck,
-Greg

> From: alira at gsd.harvard.edu
> Date: September 8, 2005 3:19:48 PM PDT
>
> 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
>