[Radiance-general] Different pixel values with/without ambient cache

[Lars O. Grobe]

Hi Greg,

thank you, that was in fact the reason for the mismatch. I had increased 
-ab without changing -lw.... In fact, this is also a problem with the 
"rules of thumb". I had initially set -ab 1 and -lw=1/ad (which often 
makes sense), and did not review this setting at a later point...

Cheers, Lars.

> Hi Lars,
>
> It's difficult to say for certain without your scene and knowing the rest of your options.  (Were they the defaults?)  I guess you aren't sharing your ambient cache file between rpiece processes as recommended.
>
> My first guess is that you are only computing a single bounce with -aa 0.  This would explain why the values are on the low side.  If you set -ad 4096 then use an -lw setting of 1/4096 as you have, the weight test fails after the first bounce because the weight used is the first surface reflection divided by 4096.  Without Russian roulette on (-lr negative), no interreflection rays will be traced past the first bounce.  In general, I like to make sure my -lw setting is maybe 1/10th of the 1/N value for -ad N.
>
> Cheers,
> -Greg
>
> P.S.  If this doesn't solve the problem, please send me your scene and commands off-list and I'll take a closer look.
>