Average luminance or illuminance for a irregular shaped space

radiance-general
1

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
[email protected]

2

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" <[email protected]>
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
[email protected]