View Full Version : what is the purpose of rendering in multiple passes?

06 June 2003, 01:38 AM
Hello there,

I have a question.

What is(are) the advantage(s) of rendering in multiple passes? What does that even mean?

Thank you for your time in advance

06 June 2003, 01:59 AM
Imagine that you bought a car and found out the door handle was broken. You take it to the shop. What happens?

If the factory had built the car in one pass, you'd have to get a whole new car, at full price too.

But if the car was built in parts, as they actually are, all you need is a new door handle.

Similarly, if the car doesn't look quite right, you can change its look with just a new set of door handles instead of a whole new car.

Rendering is the same way. By rendering out multiple layers -- shadows, specularity, lights, volumetrics, atmospherics -- and then putting them together in post, many changes become extremely fast to implement. Darken those shadows, tweak the fog, fix the color. Fast, interactive, cheap. You also have considerable leeway in customizing the render, by enhancing contrast, or downplaying a specular highlight when the client complains about it, changing the color of something, and so on.

I am working on a shot right now that would be about 30 minutes a frame at 500 frames. With my current setup that's over ten days of rendering. I'd scream if I finished it and discovered a problem that necessitated a rerender, especially if it was something stoopid I forgot to turn on. But individual layers are faster to rerender than the whole shebang, and adjustable in post -- instead of every ten days.

Somewhere in here there's an old thread that was an excellent demonstration of the changes and variations that were possible from a single source render done in layers. I can remember the image, but not the author or title.:shrug:

06 June 2003, 02:01 AM
This was a good thread allllll about multipassing

06 June 2003, 02:03 AM
THAT's the one Shade01!:beer:

06 June 2003, 02:13 AM
How might I make use of multipass rendering if I do not own a compositing program? ( i do not currently own combustion, dfx, after effects or anything of that sort )

06 June 2003, 02:26 AM
You are not going to be able to multipass without at least some sort of image editor. Do a word search on FilmGimp or Cinepaint. It's a free film editing program and you can use that for compositing. There's also dogwaffle and a bunch of other free image/paint editing programs you can use.

Steve Warner
06 June 2003, 02:46 AM
The GIMP software is really fantastic if you're on a budget. And if you're looking for a Painter alternative, Dogwaffle is simply brilliant!

Brett H.
06 June 2003, 02:50 AM
Check this one out too, it's still in alpha but it does alot of things well:


06 June 2003, 03:06 AM
so how do i take advantage of this?
are there any clear and concise tutorials on it?

06 June 2003, 06:44 AM
an overview on jeremy birn's site (his book is killer as well):

there's also some video tutorials on DVgarage ( in the lab section i think.


06 June 2003, 02:12 PM
Hey, don't forget that LW itself allows a little bit of compositing in Layout. Granted its rather limited but sometimes its all you need. You can pre-render backgrounds/foregrounds and add them in under Scene/Compositing tabs. The book "Inside LightWave 6/7" has a good intro to LW compositing in chapter 18.

Let me add another reason for multi-pass rendering. There are times when I need filters and/or post production work but only on certain objects/surfaces. Rendering out just those items I can do what I need and then comp them back with the other images to get my final scene.

06 June 2003, 08:08 PM
Rendering in passes is also great for underwater scenery .

Render your scene without any fog or anything.
Render a depth pass.
Render a Volumetrics pass.
now take your basic pic in your compositing app and blur it
mix the blured pic with the basic pic by using the inverted depth pass as alpha ( you can adjust your depth pass with all color correction tools to change where and how soft it blends ).
now again take your basic pic/anim and color correct it to a nice underwater blue do as above with this pic and the first mix ( blur/basic mix ) . at last comose your volumetric lights over that all and adjust them to blend nicely with the rest. render time add for this depth fade + blur is only some seconds per frame :)


Heres an quickly thrown together example(which has no volumetrics and would need much more tweaking )

06 June 2003, 10:54 PM
Originally posted by aurora
Hey, don't forget that LW itself allows a little bit of compositing in Layout.

Here's a small tutorial (Edit: about compositing rendering passes in layout):

LW compositing, part2 (

06 June 2003, 11:13 PM
Oh, BTW, i just uploaded also part 3 of the tutorial series... creating bluescreen key in LW's image editor (Interesting, huh)?

My tutorials at LW-Fin (

06 June 2003, 11:16 PM
what is the purpose of rendering in multiple passes?

Because it rules :D

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