[Radiance-general] Fwd: errors from hdrgen

[Rob Guglielmetti]

Hi Pillo,

Giulio Antonutto wrote:
> just a quick extra question about HDR and light sources:
> 
> supposing that with a camera we have got some images,
> 
> 1 we calculate the HDR image
> 2 we measure on the mac screen the luminance with ximage
> 3 we measure the luminance in the real scene.
> 4 we compare the numbers and find a factor ( k=lum(hdr):lum(real) ).

I think that there are a lot of reasons you will come up with a factor, 
and often they will vary (the factors, that is), making the factor an 
unreliable means of conversion.  In zones of extreme contrast, it's 
quite difficult to accurately sample a scene with a handheld luminance 
meter with the same precision that pextrem -o can find the peaks. The 
factor derived from peak values is different from the factor derived 
from other values, I've found. Which is right?  If the real scene and 
the HDR are within a certain precentage of each other, do you call them 
synonomous?  I'd love to hear others weigh in on this topic.

----

      Rob Guglielmetti

e. rpg at rumblestrip.org
w. www.rumblestrip.org