light path expressions

[s_gru]

my goal was to see if i could create an LPE such that, i could change the color of a wall or box in post. the idea is that i could render out all the light for a wall - the wall itself and then the bounced light off the wall that affects nearby objects etc... then in post i could simply add an HSL adjustment layer. everything else would be black.

using a box in a simple room with simple lights and colors on the walls floor etc... i think i have figured out 2 good LPE's

CR.'box'.*L <---- appears to give me all the light reflected off the box (bounced light)

CR'box'.*L <---- appears to give me the box itself.

in coming up with the 2nd LPE, it's very similar to the first in fact it's identical except for the . after the CR why is that?

my other question is: can i combine the 2 LPEs?

thanks,

[hermit.crab]

Bear in mind that the R and the dot are separate events, so the LPE label affects them differently. R.'box' means: Reflections from any object, followed by any event from the box. While R'box' means: Reflections from the box.

You can combine them like so:

C((R'box')|(R.'box')).*L

You can read more about LPE here.

EDIT: Clarified explanation.

[s_gru]

oh i see. the R or R. goes with the 'box' and not the C. it's grouped with the box so to speak. thanks for the link.

[s_gru]

here's my result. i used the following LPEs: ^C.*<..'white'>.*L and C.*<..'white'>.*L the only difference being the ^ character at the beginning which means "not this". i will post those two images next.

i'm noticing some noise when i crank up the HSL layer in PS to colorize the white wall to yellow. i used denoiser, and this is from the VFB with IPR rendering just about full screen.

i saved each element as 32 bit .exr file and layered in photoshop with a HSL layer clipped to the wall layer which sat on top of the not-wall layer. the colorized wall layer was set to Add blend mode.

[s_gru]

and the two separate LPE results...