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

[Gregory J. Ward]

Hi Chris,

This is more of a Radiance question, I suppose, but the problem is  
that you have an EXPOSURE= value in your header that ximage is smart  
about, but the renderer ignores.  To get absolute values out of rvu,  
either set a factor in your glow to 1/EXPOSURE (in all three  
channels) or "undo" the exposure by passing your picture through  
pfilt with -e set to the reciprocal of the exposure getinfo tells you.

Cheers,
-Greg

P.S.  Having the renderers ignore the EXPOSURE line was a design  
decision to facilitate texture normalization under the more typical  
circumstance when it is being used to modify reflectance.

> From: "chris at christianhumann.com" <chris at christianhumann.com>
> Date: January 23, 2008 2:18:27 PM PST

> 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