View Full Version : silly question: What are "passes"?

05-31-2017, 03:39 AM

Got a silly question... I keep on reading about "passes"... "render pass" "occlusion pass" "Shadow pass"...

What exactly is it? Why should I care?


05-31-2017, 04:12 AM
When you press F9/F10 normally there is rendered one RGBA image.
It's final image.
If you want to change something in it, you need to rerender.

Rendering in passes allows you to not have to rerender,
instead use compositing software.
f.e. you have some object too dark, too bright, wrong color.
Rerendering several minutes long animation can take long hours,
while fixing it in comp app, can take seconds.

Movie filmed in the real world, must be mixed with CG effects rendered in 3D app.
Merging them together is done in compositing software like Fusion.

stiff paper
05-31-2017, 06:43 AM
Search on YouTube for "Render passes."

The results won't be specific to LW but that doesn't matter. Passes are an industry standard technique for being able to adjust your render in every way imaginable once it's in post production (i.e in After Effects or some other compositing package).

Ryan Roye
05-31-2017, 07:23 AM
What exactly is it? Why should I care?

In layman's terms:

You need "passes" in order to use programs (compositors) that will enable you to easily modify any aspect of a render without re-rendering in addition to providing high control over specific areas of images. It can be very difficult at times to get exactly the kind of imagery desired by relying on just the rendered images.

I recommend Fusion if you want to explore this topic, as it is among the best out there and free to boot.

05-31-2017, 01:03 PM
Thank you guys!

So, since i'm basically re-learning Lightwave from scratch...

- I should dive completely into nodes
- Get used to a "pass" workflow

I've got Fusion and DaVinci and I'm startin to discover the power of it... mindblowing... I'm starting to look at LW render finals as "digital negatives"

In LW there's a plugin to save render buffers into PSD format, is that what "passes" are? What about other formats? I'm starting to like the OpenEXR format

05-31-2017, 04:19 PM
Yes the psd format does nest the passes. Though EXR is the best choice for that.

You can also just do the extra passes you need for your final render...like an AO pass, a depth pass (i use a fog instead) for depth of field and or fog.

It just all depends on what you want to have control in post.
You can also jusr make custom mask pass...like for example you want a mask for the main character or object in a render. You could just render the character object a solid color and the rest of the items a different color. Then use that a a mask to cut out the character from the final pretty render.

Those passes would / could require a different lws and objects so you can change the materials.

05-31-2017, 04:45 PM
From what I gather from the PSD plug-in....

LW internally renders an image at an insanly high bit depth, higher than RAW, but when saving it to a format it discards all information which is not used by this format, ergo doesn't it stand to reason that we would want to keep as much information as possible? ... or am I mistaken here with on how this "pass" thing works?

06-02-2017, 02:27 AM
Lernie Ang's Janus is great for this.

06-03-2017, 09:09 AM
There is another plugin for passes. I don't have LW installed here where I am. But this option lets you save in other formats.

There is no hard rule about passes. But simply they are a way of isolating a rendering aspect you want control of.

And on a job by job basis those things might be different.

You don't have to feel you should always be rendering passes. This is a very time consuming process for fine tuning.

And it is also borne out of a time when rendering was less capable. So you will also find some artists and teams happy to develop workflows with modern rendering that don' use them.

I am not saying it is outdated. Or not used. But I think you should be using it to save time.

So if you find you are having to spend a lot of time tweaking things that could be done in post then this is where passes come into good use.

A great example is depth of field. And very often dof needs to be animated.

This is very time consuming to render and to preview to get right.

You can render out a depth pass which is a grey scale image based on the depth in the scene.

This can be used in AE to post process and animate DOF.

Working it out from there. Just try passes one at a time until you get the hang of what each one can do in post.

Passes can also be used to create masks . And there are a lot of uses for that to.

Have fun exploring.