[Radiance-general] Fwd: errors from hdrgen

[Greg Ward]

Hi Pillo,

Basically, I'm writing to agree with Santiago.  If you want repeatable 
measurements, you have to fix your camera's white balance to a 
particular setting.  Otherwise, the response curves for the three 
channels will change.  Technically, the camera merely applies a 
different multiplier to its three channels, but it does this in a color 
space other than RGB -- a space we cannot know after the image has been 
recorded in a JPEG or TIFF.  Because we cannot know when and how the 
camera's gamma/contrast curve is applied relative to its color 
transformation(s), it is not possible to back this out.  The best we 
can do is keep the color space transitions constant by fixing the white 
balance and contrast settings on the camera, and let hdrgen do its best 
to estimate the response function on the result.

-Greg

> From: Giulio Antonutto <Giulio.Antonutto at arup.com>
> Date: June 10, 2004 9:06:09 AM PDT
>
> My question arises from some experiments measuring the same paper 
> surface
> under different light conditions:
>
> Unfortunately it appears that if the source has a really narrow 
> spectrum
> this affects the results within a 40% with my camera (which I cannot 
> give
> the name... 001DNOKIN ;-) ).
>
> I am stressing the methodology to see if it is reliable enough to 
> substitute
> luminance readings for a wide range of conditions with consumer digital
> cameras (street lighting - interior lighting - day lighting ).
> I really underline the concept of 'wide use' (wide = cheap ;-) ).
>
> With this sort of equipment I would like to achieve an error within 
> +-10%
> and therefore a correction factor quite constant (within +-10%); is it
> feasible?
>
> ...