[Radiance-general] Difference between .pic colours and traced ray colours

[Greg Ward]

Hi Tarik,

The difference could be due to the change in pixel center between 
vwrays and rpict.  Rpict normally "jitters" pixel centers as an 
anti-aliasing measure.  If you rerender your image, turning jitterinig 
off with -pj 0, you will get the exact pixel centers produced by 
vwrays.  Being off by even a fraction of a pixel can make a difference 
in the result, especially near the object's visible boundaries.

-Greg

> From: Tarik Rahman <tarik.rahman at ed.ac.uk>
> Date: March 16, 2005 3:22:14 AM PST
>
> Sorry I meant that I have created the .pic and then I view it in 
> HDRShop. Say
> the first pixel of the green surface rendered, ( Aren't .pics rendered 
>  from
> top down, left to right?) pixel 216, 238 has the luminance (sorry, not
> reflectance) value of
> (0.307, 0.541, 0.291)
> Well, in the rays.txt file from
>
>  ./vwrays.exe -fd greenbox.pic | rtrace -fda `vwrays -d greenbox.pic` 
> -ovm
> testroom.oct  | grep "green_plastic" > rays.txt
>
> I get (0.239, 0.443, 0.219) which are similar but not exactly the same 
> values.