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

[Lars O. Grobe]

Hi all,

I am wondering if this is still the effects from too many christmas 
cookies, but I am not able to solve the mismatch between (luminance) 
pixel values in two pictures rendered with and without (-aa 0) ambient 
cache.

The scene is as simple as possible, a window with a surface assigned a 
glass material (A1-A3 .7 .7 .7). Moderate two ambient bounces, a strong 
direct transmission. The same octree was used in two rendering runs, 
controlled by rad and distributed over several cores by rpiece (leading 
to some artefacts). I share the results as links:

To the compressed HDR images (hdr.bz2):
https://drive.switch.ch/index.php/s/m9l4gmWsoG995jO
https://drive.switch.ch/index.php/s/yifVqTxDOYWJ4dT

To the falsecolor illustrations (jpg):
https://drive.switch.ch/index.php/s/4JwoUBdgA7Ov4y1
https://drive.switch.ch/index.php/s/kGxCBVD8JcKGZhv

Values of a vertical row of pixels for varying -ad (and -lw = 1/ad) 
settings (pdf):
https://drive.switch.ch/index.php/s/UQq3Nh4g38rQ2Cs

The images were rendered with -ad 1024 -lw .0008 -aa .15 (with ambient 
cache) and -ad 4096 -lw .00024 -aa 0 (without cache). The plot indicates 
that for the given scene, even -ad 512 should give reasonable results. 
My expectation was that both images should be more or less equal, but 
obviously they are not. Can anyone explain this effect, or is there 
something I missed?

Cheers,
Lars.