Caustics render pass

Forums: Caustics render pass
Houdini Integrated Plugin

Moderator: juanjgon

Caustics render pass

Postby allenh » Sun Aug 01, 2021 2:53 am

allenh Sun Aug 01, 2021 2:53 am
I have a scene of a disco ball, and am using the PMC render kernel to try to render the reflected caustics. I can see a nice caustic pattern, and am wondering how I might isolate them for compositing purposes. I can't quite seem to figure out which render pass might be associated with this though. Could someone help me understand how I might do this?

Many thanks!
--a
allenh
Licensed Customer
Licensed Customer
 
Posts: 28
Joined: Tue Jan 03, 2017 2:19 am

Re: Caustics render pass

Postby allenh » Tue Aug 03, 2021 2:40 pm

allenh Tue Aug 03, 2021 2:40 pm
Anyone?
allenh
Licensed Customer
Licensed Customer
 
Posts: 28
Joined: Tue Jan 03, 2017 2:19 am

Re: Caustics render pass

Postby BK » Wed Aug 04, 2021 3:01 am

BK Wed Aug 04, 2021 3:01 am
allenh wrote:I have a scene of a disco ball, and am using the PMC render kernel to try to render the reflected caustics. I can see a nice caustic pattern, and am wondering how I might isolate them for compositing purposes. I can't quite seem to figure out which render pass might be associated with this though. Could someone help me understand how I might do this?

Many thanks!
--a


Hi Allenh,

Sorry for the late reply..
Please try using the Object Layer ID or if the scene has only Disco ball with HDRI then try enabling the "Alpha Channel" in the PMC Kernel tab.
https://docs.otoy.com/HoudiniH/HoudiniP ... ralOve.htm

cheers
Kind Regards

bk3d
BK
OctaneRender Team
OctaneRender Team
 
Posts: 1309
Joined: Mon Oct 31, 2016 7:54 pm

Re: Caustics render pass

Postby allenh » Wed Aug 04, 2021 7:24 pm

allenh Wed Aug 04, 2021 7:24 pm
Hi there, thanks for the response. Can I ask you to be more specific? I have a lot of trouble wrapping my head around "render passes".

To be specific, in my Houdini scene, at the top OBJ level, I have:

/obj/DiscoBall
/obj/FloorAndWalls
/obj/keyLight

The disco ball is pretty much what you might imagine: simply a piece of geometry covered with little mirrors (which is to say, using the Octane Metal shader using chrome-like settings). When I have all three objects participating together in a render, I see the disco ball and the floor/walls illuminated by the light. I see nice disco-y caustics (which is to say: lots of little square 'spots') on the floor and walls, which looks great. I would like to isolate ONLY the caustics into an image somehow - either as a standalone image or as a layer inside of an EXR file, whichever Octane allows.

The docs for render passes rather-inscrutably say they are used when "one part is meant to be visible, and the other parts capture the side effects of the visible geometry". In my case, I want the Floor/Walls to be visible, but not necessarily the Disco ball. And I would like to isolate caustics from any other "side effects" like indirect diffuse (which I see being cast between the walls and floor onto each other).

Can you explain how I might specifically attempt to set my scene up to do what I'm after?
allenh
Licensed Customer
Licensed Customer
 
Posts: 28
Joined: Tue Jan 03, 2017 2:19 am

Re: Caustics render pass

Postby joenyc » Thu Aug 05, 2021 2:58 am

joenyc Thu Aug 05, 2021 2:58 am
Under the settings for the light casting your caustics, you can assign a Light Pass ID. You can then select this ID as a pass in the Render Target node settings and render direct and indirect lighting for that specific light. These will appear as separate layers in your EXR file and the indirect pass will contain the caustics. This isn't a pure caustics-only render (I don't believe Octane offers that), but if you pick a light that is only targeted for caustics and only accept that light on the objects you want to have caustics, it should work. It isn't perfect, but it is OK.

However, since you are in Houdini, I'd recommend looking into rendering the caustics with the built-in Mantra renderer. Mantra is capable of rendering FAR more detailed and less noisy caustics, much more quickly. That way, you can avoid using the slow, noisy PCM Kernel and just comp in the Mantra caustics pass with an Octane PT Kernel render. Mantra is slower, but you can turn down the samples for the beauty pass and get a fairly quick caustics render which you can easily isolate by creating a pass specifically for the caustics light diffuse/reflect/refract channels. The diffuse caustics channel is pretty noise free, even with samples set very low (the reflect channel is another story). The caustics light gives you unrealistically bright caustics out of the box, but it gives you so much control in post, you can tweak to taste.

I'm including a hip file so you can see both setups. Also have some screenshots below in case you can't open the hip.

octane-caustics-setup.png


disco.png


mantra-caustics-setup.png


Hope that helps!
Joe
Attachments
disco.hiplc.zip
(118.9 KiB) Downloaded 101 times
Mac Pro (2019), 2.7 GHz 24-Core, 384GB RAM, AMD Radeon Pro W5700X | Houdini
joenyc
Licensed Customer
Licensed Customer
 
Posts: 30
Joined: Thu May 21, 2020 4:39 am

Re: Caustics render pass

Postby allenh » Thu Aug 05, 2021 1:18 pm

allenh Thu Aug 05, 2021 1:18 pm
What an incredibly helpful reply, thank you!

I think the main nugget here for me is that I shouldn't expect Octane to be able to do the thing I'm trying to do. That's fine, but knowing that helps me abort banging my head against all the inscrutable render pass/layer settings and just use a different renderer that does what I want. I also make heavy use of Redshift, and have a caustics pass working with it that I think works more or less similarly to Mantra's photon-mapping technique. But the elaboration you offer is very, very helpful, as are all the images you took the time to include. I'm really appreciative, thank you!
allenh
Licensed Customer
Licensed Customer
 
Posts: 28
Joined: Tue Jan 03, 2017 2:19 am

Re: Caustics render pass

Postby joenyc » Thu Aug 05, 2021 1:28 pm

joenyc Thu Aug 05, 2021 1:28 pm
You're welcome. And Redshift's caustics passes are definitely even more convenient than Mantra's if you have access to that software! They do use similar technology, Redshift is just faster as expected. Also worth noting that Octane announced a couple of years ago that they are working on a new kernel that does modern, fast caustics, but the timeline for launch isn't clear yet. Hopefully that includes a caustics pass, because I much prefer Octane for everything else!
Mac Pro (2019), 2.7 GHz 24-Core, 384GB RAM, AMD Radeon Pro W5700X | Houdini
joenyc
Licensed Customer
Licensed Customer
 
Posts: 30
Joined: Thu May 21, 2020 4:39 am

Return to Houdini


Who is online

Users browsing this forum: No registered users and 6 guests

Thu Mar 28, 2024 6:23 pm [ UTC ]