Hey all, first poster here, please excuse if I am posting in the wrong area. I am a high school student trying to learn Houdini on the side, and had a question about Pyro FX. In all the VFX breakdowns I have seen online, it seems like they render out a turbulence/velocity pass, smoke pass, and fire pass separately. I have rendered to .exr files, but upon splitting the exr, there is no smoke pass. How do they get these separate smoke/fire passes? Thanks!

Hi, to get sperate render passes , just add “extra image planes” on a mantra Rop node. You will find it in “Images/Extra Image Planes” tab (on houdini 14).
-> click on “+” button at the bottom, then you can add any vex variable name.

-> for pyro shader you can find a list of build in variables : smoke_color , smoke_mask, fire_color, fire_mask. Enter on of these in the “vex variable” field. Be careful to set the “vex type” to something suitable.

->Then you can render your image, and mantra will output a separate image plane for each vex variable you want to export ( you can render any pass you can imagine.)

Hope it helps.

Thanks gui, I tried that and the smoke_color variable is yielding what looks like more fire, not smoke, when separated out. Where can I find this list of vex variables you were speaking of?

in the pyro shader node, go in “Utils” tab, and then “Exports” tab.

The smoke color pass is different than is shown in the color pass. I am attaching the file for everyone and anyone, let me know if anything stands out at you. Thanks so much for all of your help, gui!

I figured it out, the error was in the rendering method I was using. PBS, for some reason, made the smoke grey in the color pass. When I switch to ray tracing, the smoke matches the smoke_color plane. Hope this helps anyone with similar problems!