I've also been struggling with this. We oftentimes want to render shadows completely separate (separate EXR), with a shadow catcher on relevant geometry to give comp the ability to mix the shadows / adjust them to their liking. Using Geometry properties and background plate I was able to create all of the necessary mattes / holdouts needed to individual objects & render layers - the one hang-up seems to be getting shadows alone on alpha.

A noob question: I saw an LPE holdouts;shadow;CDL in the tutorial "Houdini Karma | Render Matte-Phantom-Shadow", and there are similar-looking LPEs in this thread (post of Feb. 2, 2023 6:57 P.M.)

I understand CDL is an LPE, but what about this holdouts;shadow; prefix? I haven't found any documentation mentioning these names, and I'm not sure where to look---is this an aspect of Karma only, or... ?

Thanks in advance for your help.

gladstein
I understand CDL is an LPE, but what about this holdouts;shadow; prefix? I haven't found any documentation mentioning these names, and I'm not sure where to look---is this an aspect of Karma only, or... ?

Yes, something like that. I think it's Karma specific. As interoperable as LPE's were meant to be, every renderer has their own syntax for renderer-specific stuff.

Excellent information, thanks so much!

Now, my final question on the subject: is there any documentation on what LPE prefixes Karma supports? unoccluded is mentioned in the Karma Standard Render Vars documentation, and houdouts;shadow; was mentioned in a tutorial, but what about the others? I found a good explanation in the renderman documentation (https://rmanwiki.pixar.com/display/REN22/Using+LPE) but I'm not clear on which ones Karma supports.

Bump this thread as I'm also lost about these LPEs "unoccluded", "shadow", are they documented?

Best
/Timo

Any updates or solutions on this?

Mirko Jankovic
Any updates or solutions on this?

Nope. It's hard to believe that the feature is still not supported in Houdini's Karma renderer in 2024. It‘s been in use since around 2003. It’s a pretty simple, straightforward methodology, and essential for any renderer. Renderers like Vray, Redshift, Renderman, and Arnold have it.(even Metntal Ray)

Neohan

Mirko Jankovic
Any updates or solutions on this?

Nope. It's hard to believe that the feature is still not supported in Houdini's Karma renderer in 2024. It‘s been in use since around 2003. It’s a pretty simple, straightforward methodology, and essential for any renderer. Renderers like Vray, Redshift, Renderman, and Arnold have it.(even Metntal Ray)

Also IRay and Unreal...
Wonder if 20.5 can manipulate the new Cop system to send it back to the Karma XPU.

I'm actually trying to ditch Redshift completely and move to Karma XPU , but with 2 currently running projects I rely heavy rely on shadow mate. Now can that be changed in workflow and add that as separate pass in comp? sure.. but having actually shadow mate makes my life sooo much easier and faster to work in this example of mine that it is hard to move...

i think this should help

Looks like getting somewhere but need to test more if it works as planed without actual back plate image, only using objects in the scene to catch shadows.

Background Plate LOP did not work as expected last time I looked into. Was expecting it to work similar to how Redshift does it, Regarding getting a shadow in the alpha channel. It's also slow to update when using Karma XPU, try to just move a light and you will notice it.

But it does seems to get usable shadow pass to comp it later so... it is not like arnold or redshift shadow catcher that is for sure which is shame as it makes life a bit easier but should be able to use it after all.

Mirko Jankovic
But it does seems to get usable shadow pass to comp it later so... it is not like arnold or redshift shadow catcher that is for sure which is shame as it makes life a bit easier but should be able to use it after all.

Yes, the result looks good. But the reduction in interactivity was a shame, it was only a problem with XPU not CPU. I will have to test again with the new slap comp feature.

And back on this subject. Is there any progress on sorting out shadow catcher in the scene?
Plain and simple to have an object catching and rendering shadow only as explained multiple times and showed examples?

Just been playing around with Arnold and its Shadow Matte in Solaris (Houdini 20.5), it seems to work well, as it's supposed to, I tried to setup the same in Karma, to do the same but without any luck, so frustrating...

I am on a project where we rely heavily on the backgroundplate lop - and it works for us. It is important to notice that this just started working correctly recently (I belive between the 2nd and 3rd 20.5 production build). and it was broken with the most recent production build again and is fixed now since end of last week in the nightlies. So If you pick up the latest nighty build you should be fine. If you dive into the lop, there should be a mtlx network inside (not a vex shader network). All that said, this all does only concern Karma XPU.

Cheers Ronald, thanks for that, do you have an example scene handy which I can run a test on?

Sure. The scene attached is not pretty, but it should show you everything you need.

Thanks for that Ronald, but it's not the same as using an environment (Dome light) image in the background plate, the image in the background plate is a static image on a plate, what is needed is an environment hdr image instead of a plate with a static image or video sequence on it, so when you pan around the scene the background environment image is also panned. Also this is very slow at updating the render. If you have a video or a still image, then your technique is o.k. but if you want to pan around with an environmental background hdri then this doesn't work.
T.