View Full Version : Having trouble with Multipass Rendering using nodes

10-26-2012, 11:32 AM

OK, I'll admit, I probably don't know what I'm doing (with nodes), but here is what I'm trying to do.

I'm wanting to light a scene with Global Illumination via HDRI Probe and then capture out the shadows and reflections into separate files to composite in After Effects.

According to this lightwiki post, it should be possible: http://lightwiki.net/wiki/Multipass_Rendering_with_Filter_Node_Editors
I've tried it, but when I render using F9, nothing shows up, only a black screen.

If I don't use the nodes, my scene renders fine with all lights out and global illumination. I just have a simple ground plane and a cube just for testing purposes.


Also, my other question would be, how do I save these out to separate files when I press F10 to render the scene?

Any help would be much appreciated.



10-26-2012, 12:26 PM
DP Filter a rough documentation but at least it describes
basic functionnality, like,
if you output a buffer from Render Buffer node,
the appropriate buffer (here Radiosity Color) must
be enabled in the panel of the node editor (right on your image).

If you want to save separate passes you should use
one of the Global Buffers and leave the main Color and Alpha
for the beauty passes, for that it may be more interesting
to use the Pixel Filter node editor, with AA option,
for setting up output image file, use the Get Global Buffer node.


10-26-2012, 03:09 PM
Indeed. The article also points out the procedure when describing the first pass:

"To make a buffer active, double-click the Image Filter output and check the buffers you want to activate."

Several other procedures are described in the first pass.

As for saving buffers, there' a whole section about it too:

http://lightwiki.net/wiki/Multipass_Rendering_with_Filter_Node_Editors#Savin g_Buffers

Common passes like Reflections or Shadows can be got also through LW's Compositing Buffer Export.
Consider DP Filter Node Editors are far more useful when we need to built our own custom / non-conventional passes, add post FX, compose passes, perform color gradings, etc.


10-28-2012, 05:05 PM

Does LW Compositing Buffer Export allow you to actually get a shadow pass from GI/HDRI?
I can get a shaded reflection just fine, but the shadow pass comes out solid black and the alpha doesn't have any shadow in it either.

That's why I was trying to use the DP Filter.
I'm doing some external compositing in After Effects with live action footage where I need to have the control AE gives me with layers, etc.
I'm wanting to add reflections and shadows of the objects interacting with my ground plane (which needs to be unseen by the camera) and only have the shadows/reflections show up in separate image sequences.
Then I can composite the final objects into AE and have it look like the pieces are actually in the live action scene.
Anyway, sorry for the long post. I'm still fairly new at all this and for me, it seems like I just need to click a few options and it should work for me.

But maybe not.

Thanks for any insight you can give.

10-28-2012, 11:18 PM
I show how to export a buffer made with nodes using the Compositing Buffer Export in the video I posted last week :)


10-28-2012, 11:51 PM
Wow, great tutorial.
Could you do one on getting the stuff I need :)
I'll experiment with that.

Or maybe I could just drive up to where you're located. From your web site, you're about an hour north of where I'm at.


10-29-2012, 12:47 AM
Well, I haven't done what you're trying to do, but in looking at your screen grab I can see that you have 'Shadow' checked on your Image Filter node and you need to have 'Radiosity Color' checked instead. You may have been thinking that by checking Shadow, you were rerouting the radiosity color buffer to the shadow buffer. Those check boxes are just to tell the Image (or Pixel) Filter node which Render Buffers to watch out for. Think of it like a transmitter/receiver. If your receiver is on the wrong channel (Shadow), it won't pick up what you're transmitting (Radiosity Color). They have to match.

We could possibly meet up in Lacey or Olympia some time. I might be up against a deadline this week, though.

10-29-2012, 01:35 AM
Yeah, I'm up against a deadline this week too.

I'll try that Radiosity Color checkbox and see what I get.


10-29-2012, 05:54 AM

Does LW Compositing Buffer Export allow you to actually get a shadow pass from GI/HDRI?
A 'shadow' provided by GI is not a shadow properly, is a shade, or better said a shadowing. LW Compositing Buffer Export can help you to get GI shadowing (through the Radiosity buffer), but you won't get it (this is known as Radiance Occlusion pass) directly from it. If you want/need export a Radiance Occlusion pass directly from LW, you could use DP Filter Node Editors as described here (http://lightwiki.net/wiki/Multipass_Rendering_with_Filter_Node_Editors#Radia nce_Occlusion_.28RO.29_Pass) (updated section). Understand you are against a deadline but I already commented this in this thread (http://forums.newtek.com/showthread.php?131280-Rendering-only-Shadows-%28shadow-pass%29-using-Shadow-Catcher-HDR&p=1277900&viewfull=1#post1277900) where you asked about Shadow Catcher.