View Full Version : multipass rendering

02-22-2003, 11:18 PM
How am I able to do multipass rendering. I understand the alpha channels and such, but how do get the information for the specular, and lights, and all the other stuff as separate items. This is so confusing.

The reason why I'm asking is that I figured that I can have more creative control with an image in the post production environment.

All help is great!


Capt Lightwave
02-23-2003, 04:02 AM
Assuming you're using LW7.x theres a couple of ways to do this:
There's an Image Filter Plugin called "Buffer Saver", "Photoshop PSD Export", "Render Buffer Export" and a Pixel Filter plugin from ASA (do a search on Flay.com) called "ASA BufferSaver".

Seems like all of them are doing the same, but if you're asking which one is the best, I can't answer.

There's even "Extended RLA Export" and "Extended RPF Export", which I've heard a lot of opinions about....

02-23-2003, 12:04 PM
I was starting to think that LW couldn't do it. I am using 7.5 and I like it, but I'm finding that I need to fine tune my images after rendering and I really need more control over the whole image or in parts.

Thanks for you help. Do you know of any tutorials on the web that talk about this?


02-24-2003, 12:20 PM
They're pretty straightforward as far as use, for example, load your scene and the 'Photoshop PSD Export' as an Image Filter on the 'Processing' Tab. Double click it and select the individual layers you want tweakability for, select a base image name and location and F9 away. You'll get a PSD file with layers representing those you selected in the image filter properties. I typically start with Raw color, Diff, Spec and Refl. In Photoshop you'll get a layer stack with the bottom layer being the default RGB image, a black background layer above that and the others as clipping groups set to Screen mode above the background.

Render Buffer View and Render Buffer Export work similarly with the latter saving out the buffers you select as individual files. The former allows you to switch between the different buffers you've selected in the Image Viewer after F9, ie, make sure you have at least Image Viewer selected for Render Display under Rendering Options. The Image Viewer is essentially a multi-layered buffer viewer but you can't see the individual buffers unless you add the Render Buffer View image filter and select the buffers you'd like to see.

Keep in mind to you can stack multiples of these image filters on top of one another and they're processed one after another, so you can make a little change, save a file, make a change, save a file, etc.

02-25-2003, 04:13 PM
Okay I managed to render out an image with each of these items. So no what do I do with them? How can I manipulate each individual item? Say the specular. I can't seem to load the black and white layer. I noticed with Buffer view there is some colour screens that are viewable but not in the PSD file. I guess I opened a pandora's box here.

Soooo how am I to manipulate the image based on these settings in photoshop or another program like aftereffects? it interests me to be able to do you know where I can find any tutorials on this?

Thanks again.


02-25-2003, 05:21 PM
In Photoshop you can adjust the Opacity levels of the individual layers, for example. I'm not aware of any tutorials on the web covering this but I know Lee's been covering it a little on the Next Dimension Tour.

Here's another blurb about it from Flay.com:


02-25-2003, 05:51 PM
The link worked fine to Flay.com, but there was no other link other than that to register for a seminar (which I did of course). It's going to take a while and a lot of experimenting. I just wish that there was some sort of documentation available that discusses the how too...

Thanks again!

02-25-2003, 05:55 PM
Hopefully the documentation issue will be addressed and improved upon with 8.0.

02-25-2003, 06:00 PM
Ahhhh, wouldn't that be nice. Love the program, it's nice and versitile, but somethings are short on documentation. Yes somethings are artist exploration and trial and error, but others need documentation.


03-11-2003, 09:46 PM
I tried this once and when I opened the image in PS all the layers were "partially" locked! I really couldn't do s*%@, wtf! How do I unlock these layers so I can actually do some alterations to them.

03-12-2003, 04:14 AM
I never succeeded to unlock these layers... what I do is to duplicate the layer I need to manipulate. The copy comes unlocked. But hey, I'm not at all a PS guru...

Two additional questions/remarks on multipass rendering/PS export:

1. in the PhotoShop export I sometimes get "meshed" surfaces (colors) in the PS layers "Object ID" and "Surface ID" instead of nice flat colors. That makes it pretty useless to make selections using the color wand... It doesn't happen consistently but it seems to be linked to the resoltion of the render (high res enders messed up) and also seems to happen when using certain shaders (it seems to happen with procedurals). I didn't do a systematic "experience" to unravel the secrets of that export mystery...

2. Does anyone know a way to do AUTOMATIC multipass rendering in LightWave based on lights? I explain: in a scene lit by several lights, get separate renders with only one light source turned on for each render. This would allow to tweak the lighterning in PS. The only way I found is the manual way: change the settings and make a separate render with each light.


03-12-2003, 06:08 AM
Looks to me like the locked layers problem is a bug.

What about the Render Buffer Export Image filter?

For each render pass needed add another Buffer Export Filter.
Useable in aftereffects as well..

03-12-2003, 06:11 AM
Ooo just remembered this might help with understanding the renderpasses theory..


Hope that helps some more...

03-12-2003, 10:47 AM
Well, I'm back, and still haven't managed to figure any of this out. Now Lord, you mentioned the document that uses AfterEffects (which seems straight forward enough), but I'm not sure how that works with Photoshop. I'm still trying to figure out how to unlock and manipulate the individual layers.

I love this stuff, confusing and time wasting right now, but love it.


03-12-2003, 11:02 AM
..to unlock just delete the black "Backround" layer.

03-12-2003, 05:53 PM
Open your Exported Render Buffer images in photoshop, I suggest using the Targa format as the export option from Lightwave, copy each one as a new layer to a master photoshop file and change the blending mode on the Layers palette as appropriate, the link above should give you an idea as to what type of blending mode is most appropriate for each pass, these are the same in After Effect and Photoshop, you can then tweak each layer as needed.

03-14-2003, 02:45 AM
In my quest to find this out for myself, the solution I came across (and can't remember where or how :rolleyes: ) was when you load the image into photoshop with the layers all locked, go to Layer (top menu) and go down to Ungroup or just hit Shft-Ctrl-G. That should do it.:D Using PS5.5 btw

03-14-2003, 08:04 AM
should be able to double clcik a locked layer, click YES on the popup and it will unlock

03-14-2003, 10:50 AM
so by unlocking the layers then you would be able to adjust the colours, levels, etc. right? So with MPR should you create an image for each light and how much information is too much information?


03-14-2003, 01:49 PM
Originally posted by fabmedia
so by unlocking the layers then you would be able to adjust the colours, levels, etc. right? So with MPR should you create an image for each light and how much information is too much information?


on the 1st part.....if we are talking about the layer in the layer pallet of PS (to be clear), especially on the background layer in new compositions. the layer will have a little pad lock looking thing on the right side.

yep, just double click and click yes to the dialog, that says something about new layer. this will unlock to adjust as you need.

BTW i have PS 7 should be same for other versions.


Arnie Cachelin
03-18-2003, 09:37 AM
When some of the buffers appear to have the wireframe drawn in, it is due to adaptive sampling, which skips the rendering of some pixels. Turn this off when exporting extra buffers.

03-18-2003, 10:41 AM
the layers seemed locked because they are grouped and have
preserve transparency on.

you can still edit the layer opacity with the slider.

what I find confusing is that I though the way the PSD saver
worked was so that when all the layers were active you got the
image, but it doesn't seemed to work that way.

03-18-2003, 10:46 AM
I find it weird that Arnie has "newbie member" next to his name!!!


03-18-2003, 11:36 AM
so by unlocking these layers I can adjust the colour and saturation of each layer. So another question is Should you multipass render an item with each individual light or not? And I guess it would be in my best interest to make sure that the scene is what I want by doing a couple of test renders to see if the scene and the feeling is right. Right?


03-18-2003, 01:01 PM
you can still play with the opacity slider despite this, preserve
transparency stops you drawing on the layer, but doesn't stop
you playing with the opacity slider.

multipass rendering using the photoshop layers saver takes
all lights into account by the looks of it.

so if you want to use multipass rendering to render the scene
in full but with each layer as a different light (while the others are turned
off) I don't think the photoshop layers plugin is for you.

am I right in thinking you want to use multipass rendering to
play around with the lighting?

if so the way to do this is to render the scene with each light in
turn (at 100% intensity) save the image and layer them up in photoshop.

set all the layer mode to 'screen' apart from the bottom one,
so in photoshop it looks like:

etc . . .
light05 - layer mode screen
light04 - layer mode screen
light03 - layer mode screen
light02 - layer mode screen
light01 - layer mode normal

now you can play with the opacity of the lights to see what
changes you need to make eg:

etc . . .
light05 - layer mode screen opacity 50%
light04 - layer mode screen opacity 20%
light03 - layer mode screen opacity 100%
light02 - layer mode screen opacity 10%
light01 - layer mode normal

03-18-2003, 07:58 PM
Originally posted by roguenroll

yep, just double click and click yes to the dialog, that says something about new layer. this will unlock to adjust as you need.

BTW i have PS 7 should be same for other versions.


Maybe this is true for PS 7 but PS 6 comes up with errors when these locked layers from PS export file are double clicked, meaning that you can't unlock them. The work around has been to duplicate the layer first and then delete the original.

03-25-2003, 03:00 PM
Do you know if Final Cut Pro can handle the multipass rendering files? I'm wondering if I should make an investment.