Dear Radiance community,

First of all, I would like to begin by congratulating the great team behind setting up the discourse pages. It is soooo much better than the old mailing lists !!

That being said, a while ago I was working quite intensively with Photon Mapping in radiance. I simulated a couple of test cases with pmap but when I compared the results with classic Radiance, I found some discrepancies which I could not fully explain. The luminance values from photon mapping were always lower compared to what I got from radiance classic. I am posting the two cases below:

I used Radiance 5.1 on a Linux machine with 30 processors for all simulations. These were my settings:

**[ Radiance Classic ]**

**rpict** -vf 05_31_18_Top_TS_0.vf -af ./05_31_18.amb -t 30 -ps 1 -pt 0.05 -pj 1 -dj 0 -ds 0.02 -dt 0 -dc 0.75 -dr 0 -dp 64 -st 0.85 -ab 8 -ad 8192 -as 4096 -ar 1200 -aa 0.100 -lr 18 -lw 0.050 ./05_31_18_IMG.oct > 05_31_18_0.unf

I then delete the .unf file from last step, and then run the following for Overture:

**rpict** -vf 05_31_18_Top_TS_0.vf -af ./05_31_18.amb -t 30 -ps 1 -pt 0.05 -pj 1 -dj 0 -ds 0.02 -dt 0 -dc 0.75 -dr 0 -dp 64 -st 0.85 -ab 8 -ad 8192 -as 4096 -ar 1200 -aa 0.100 -lr 18 -lw 0.050 ./05_31_18_IMG.oct > ./05_31_18_0.unf

**pfilt** -1 -r .6 -x/2 -y/2 ./05_31_18_0.unf > ./05_31_18_0.HDR

**[ PMAP Radiance with ooc ]**

I first create a global Pmap with 1000M global photons (it was a big project):

**mkpmap** -n 30 -apg 05_21_18_g1000M.gpm 1000M -apD 0.1 -dp 1000 -ds 0.02 -t 10 05_21_18_g1000M_RAD.oct

Then I run rpict with a global photon lookup radius of 600

**rpict** -vf Top_TS_Top_TS_0.vf -t 10 -ab -1 -ad 4096 -ar 0 -aa 0.1 -ps 1 -pt 0.05 -pj 1 -dj 0 -ds 0.02 -dt 0 -dc 0.75 -dr 0 -dp 64 -st 0.85 -lr 8 -lw 0.050 -ac 8 -aC 1M -ap ./05_21_18_g1000M.gpm 600 ./05_21_18_g1000M_RAD.oct > ./Top_TS_gBW600_0.unf

**pfilt** -1 -r .6 -x/2 -y/2 ./Top_TS_gBW600_0.unf > ./Top_TS_gBW600_0.HDR

I don’t understand why the luminance from the image in Pmap is less compared to the one from Radiance classic? I wonder what I am doing wrong… Any hints / explanations regarding this would be really helpful.