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hdace
11-07-2006, 02:20 AM
I need advice or pointing to a tutorial on what to do after the "beauty pass". I've been working for several years in LW, and I often do a render job split into background and character separate and put back in post (After Effects).

But I'm finding that increasingly is not adequate. And I've read that other people split things up a lot more, but I find LW's rednering controls quite confusing with regard to alpha, and camera not seeing objects, etc.

I want to do beauty, character, shadows, highlights and specular, and reflections separately. Is this possible? Not only can you adjust these effects more easily in post if they're still separate, but you can use very different degrees of anti-aliasing in each respective pass.

What happens when a character walks behind an object that's "camera off"? It looks like the object appears and disappears. Is it hard to place them in the right order in AE's timeline?

Thanks anyone helping out. Hal

jeremyhardin
11-07-2006, 03:29 AM
You can indeed split it up as much as you want. You can use any combination of the following LW native tools:

1. Render Buffer Export
2. PSD export
3. RLA export
4. RPF export
5. Splitting up different scenes by hand (such as an ambient occlusion pass).

Some 3rd party tools for this type of thing
1. exrTrader (http://exrtrader.com/) (commercial, very good, all your buffers, and hdr output. i use this one.)
2. asa_buffer_saver (http://lw-fin.org/plugins/asa/bs/plug_bs.html) (free, I think)

There's a pdf tutorial or two floating around somewhere about multi-pass rendering, quite useful.

here's an old example of mine (pardon the wrong refraction on the glass...it was an experiment).
render:
http://jeremy.lwidof.net/cgtalk/jeremyhardin_bottlecollecti.jpg
passes:
http://jeremy.lwidof.net/cgtalk/bottlecollection_passes.jpg

jeremyhardin
11-07-2006, 03:35 AM
What happens when a character walks behind an object that's "camera off"? It looks like the object appears and disappears. Is it hard to place them in the right order in AE's timeline?

Well, you only want to do this if you must. But if what's in front of what changes frequently, you'd want to use a holdout. I.e. a character is holding a can that blocks part of them from camera on some frames but on others the character blocks the can.
So you'd render the character normally with the can off, then on the can pass, turn the character on, but check "Matte Object" in the object properties. this makes the character render at completely black and with no alpha. So it effectively masks the can for you where it should be blocked by the character. Then in comp, you just put the can layer above the character layer. Does that make sense?

It's bad practice if you can avoid it, because you lose data. Such lost data can affect things like depth of field in post. But sometimes it's really just the most straightforward way to go about it. And if need be, you can render a can held out by the character and not held out by the character. so if you ever need the blocked can portions for something, you have them rendered and ready to use.

hdace
11-08-2006, 02:02 AM
Got delayed because of new beta installation.

Found pdf's with google that were written at Stanford. Way too abstract for me. Need specific tutorial for LW.

About your can example, shouldn't it have alpha? If I place the can layer in AE above the character's hand layer, won't the black parts of the image block the hand? Surely you need the alpha to see the hand.

Don't understand why I would lose data.

Tomorrow I will look at your other information as it is late. I tried to a little while ago, but was distracted by your outstanding plugins. Yours seem to be a lot more useful than those on other sites I've seen. I downloaded half a dozen and am looking forward to looking at them too, when I'm more awake.

Thanks, Hal

jeremyhardin
11-08-2006, 02:15 AM
Thanks for the kind words.

On the topic of the can in the hand, there are no black parts of the image. you see, with Matte object checked, the character's surface is black, as is it's alpha. So when the character's hand blocks the can, it blocks the can's alpha too.

As far as loosing data, if you were to try to rimlight your can in comp using the alpha, your rimlight's shape would be that of the cutout can and would change from frame to frame, looking wrong. but ignore this for now. revisit it once you get the hang of this stuff. it's tertiary to your goal of multipass rendering.

Here are a couple resources on mutlipass in LW that I found:
http://www.survivorsdiary.com/Passes/passes.html
http://www.survivorsdiary.com/Passes/advpasses.html
http://www.survivorsdiary.com/Passes/layers.html

hdace
11-09-2006, 02:30 AM
I've spent about an hour studying all your advice and links regarding multi-pass rendering. I feel like I've been watching too many blipverts. My head will explode any second, more from excitement than confusion, but there's still a bit of that too.

Also, I've already used 3 of the plugins I found on your site. MGRecordPivotRotion is my favorite. I've got six characters with tons of skelegons to convert. I hate the way LW hands you rotation handles that are pointing the wrong way and are at times already in gimble-lock before you've even started. It's always taken me at least half an hour per character to fix in the past. You saved me several hours. Kickin'!

Okay, I don't completely get what an RPF is, but I'll experiment tomorrow and find out. I assume it's like a pdf saved with lots of layers per frame. Can AE import it? I didn't realize that rendering in passes doesn't actually involve rendering more than once. However, if I want my background to have PLD-15 pass, but my character only needs 3, surely I'll still have to render more than once, and select relevant buffers (passes) for appropriate layers.

I read all 3 tutorials. Learned a lot, but the biggest thing was the difference between passes and layers. New jargon always handy.

Loved your bottles on the window sill. I don't think I really need 14 passes to do my stuff, but very impressive nevertheless.

I think I'll be purchasing exTrader if it exports ambient occlusion in the same render.

It was also nice to find (in the tutorials) that LW does indeed premultiply edges when creating alpha channels. It's almost, "duh!" but I've never seen it in the manual and was never completely sure how to import in AE.

Thank you very much, Jeremy, for all your help.

Hal

jeremyhardin
11-09-2006, 02:42 AM
I've spent about an hour studying all your advice and links regarding multi-pass rendering. I feel like I've been watching too many blipverts. My head will explode any second, more from excitement than confusion, but there's still a bit of that too.

Also, I've already used 3 of the plugins I found on your site. MGRecordPivotRotion is my favorite. I've got six characters with tons of skelegons to convert. I hate the way LW hands you rotation handles that are pointing the wrong way and are at times already in gimble-lock before you've even started. It's always taken me at least half an hour per character to fix in the past. You saved me several hours. Kickin'!

Okay, I don't completely get what an RPF is, but I'll experiment tomorrow and find out. I assume it's like a pdf saved with lots of layers per frame. Can AE import it? I didn't realize that rendering in passes doesn't actually involve rendering more than once. However, if I want my background to have PLD-15 pass, but my character only needs 3, surely I'll still have to render more than once, and select relevant buffers (passes) for appropriate layers.

I read all 3 tutorials. Learned a lot, but the biggest thing was the difference between passes and layers. New jargon always handy.

Loved your bottles on the window sill. I don't think I really need 14 passes to do my stuff, but very impressive nevertheless.

I think I'll be purchasing exTrader if it exports ambient occlusion in the same render.

It was also nice to find (in the tutorials) that LW does indeed premultiply edges when creating alpha channels. It's almost, "duh!" but I've never seen it in the manual and was never completely sure how to import in AE.

Thank you very much, Jeremy, for all your help.

Hal

First off Hal, glad to help.

Secondly, I believe you've not found any plugins of mine, but those of Mike Green (who goes by Dodgy here). I'm sure he would appreciate your praise for those much more than I. :D

As to rendering more than once, I break down my scene into passes (characters, bg environment, fg environment, ambient occlusion, etc). So those are different scenes that are rendered separately. Then within those scenes, I use exrTrader as the render format and it saves all the spec/diffuse/shadow/reflection buffers into one image that I can access separately in compositing. So there's a healthy mix of rendering your buffers out and splitting up into different scenes.

And as of now, exrTrader doesn't generate an ambient occlusion pass for you. Mine are home-made. But that may change in future iterations, I believe. Though I'm not affiliated with them, so I may be incorrect there.

Lightwolf
11-10-2006, 01:07 AM
Then within those scenes, I use exrTrader as the render format and it saves all the spec/diffuse/shadow/reflection buffers into one image that I can access separately in compositing. So there's a healthy mix of rendering your buffers out and splitting up into different scenes.

Yup, in mose cases manually splitting the scene to different passes is the only option to get what you need.


And as of now, exrTrader doesn't generate an ambient occlusion pass for you. Mine are home-made. But that may change in future iterations, I believe.
I've got a couple of ideas here... :D

Cheers,
Mike