[HDRI] surface characterisation with hdr

[Gregory J. Ward]

Hi Guilio,

I haven't done this myself, but I see no reason why it wouldn't work,  
at least for Lambertian (or nearly Lambertian) surfaces.  You just  
need a suitable reflectance standard to set in the plane of the  
surface -- any of the commercially available gray cards would do.  To  
avoid issues with variability in the incident light, you should  
probably average surface values all around the gray card, rather than  
to one side of it, or cut a hole in the gray card and do the  
reverse.  People have also used polarizing filters to separate out  
the specular component if there is one.

If you can get a sample of your material, a scanner combined with  
macbethcal works even better.

-Greg

> From: giulio antonutto <geotrupes at mac.com>
> Date: December 9, 2006 3:09:10 AM PST
>
> does anybody know of anyone having measured surface reflectance (r  
> table, illuminance / luminance coefficients) trough HDR imaging?
>
> we are trying to set up such a system but  just wanted to double  
> check before inventing the wheel, again :-)
>
> thanks a lot
> G.