[HDRI] Fisheye Lense + IBL with HDR image question.

[chris at christianhumann.com]

Hi Magali,

Sigma just released a 4.5 mm 180 degree fisheye for APS-C size (the 
smaller sensors) digital SLR cameras.
http://www.sigmaphoto.com/news/news.asp?nID=3377

I just received one yesterday from B+H photo in New York and so far it 
seems to deliver as promised. I'm using it with a Nikon D50.

Question (sorry if this is back to basics but despite many archive 
searches I'm still at a loss):
When viewing an HDR image with "ximage" and taking spot measurements 
with the "L" command I get reasonably accurate luminance values.  When I 
map the HDR image as an emissive glow on to a "source" geometry and view 
the scene with "rvu" I get much lower luminance values than at the same 
spots measured in ximage.  Below is the scene description:
########
void colorpict skypict
11 red green blue sky.hdr fisheye.cal fish_u fish_v -rz 180 -rx -90
0
0

skypict glow skyglow
0
0
4 1 1 1 0


skyglow source sky
0
0
4 0 0 1 180
#########

My end goal is to document various sky conditions to be used for IBL 
scenes.

Happy New Year and thanks in advance.
Chris