[Radiance-general] Re: Average luminance or illuminance for a irregular shaped space

[Greg Ward]

Hi Karen,

No one ever responded to your query, so I thought I'd offer some 
general ideas, since I've never done this myself.

One thing you could try is creating a mask in Photoshop by drawing into 
a separate alpha layer over the area you want to average and saving the 
layer out as a grayscale TIFF.  (Start in Photoshop from the 
full-resolution original converted to TIFF using ra_tiff.)  Reverse 
this through ra_tiff to get a Radiance picture you can then feed to 
pcomb, like so:

% ra_tiff -r mask.tif mask.pic
% pcomb -e 'lo=li(1)*li(2)' -o orig.pic mask.pic | pvalue -d -b -h -H | 
total

Take this result, which will be a single number, and divide it by the 
sum over the mask:

% pvalue -d -b -h -H mask.pic | total

This is your area average.  I'm assuming that you have made the mask 
white where you want it to average, and black everywhere else.

I hope this makes sense.
-Greg

> From: "Karen Carrier" <karencarrier@cox.net>
> Date: November 27, 2003 9:26:40 AM PST
>
> Hi All,
>
> I recently used ximage for the first time to get average illuminance 
> values
> for a space by dragging a rectangle across the area of interest. This 
> worked
> well for a rectangular room. Does anybody know if there is a way to do 
> this
> for slanted or even completely irregular spaces with curves etc...
>
> Thanks,
> Karen
> _________________________
> Karen Carrier
> M. ARCH student
> UC Berkeley
> karencarrier@cox.net