PDA

View Full Version : compositing questions


stephen2002
11-25-2003, 04:01 PM
I have a few questions pertainting to compositing with Lightwave and Icarus. Icarus was a free motion tracking program that I downloaded a while ago. Unfortunatly it isn't avalable for free download anymore.

1. Is there any way to make a material that is invisible (not black, transparent) until it is hit by lights? What I am trying to do is match up some geometry in 3D with some objects in the 2D video so that things can go behind them and hopefully interact with lights.

2. Icarus made a whole bunch of tracking points in the Lightwave scene file. They are each individual objects. Is there any way to get all of these points into modeler so that I can build some masks out of them? If it is possible doing this will be a LOT easier than making geometry and trying to match it up. All of the tracking points are already matched up perfectly!

Steve Warner
11-25-2003, 05:17 PM
I'm not exactly sure what you're trying to do, but you can make 3D objects go behind real-world objects by using Front Projection mapping on some simple geometry in LightWave. Also, it's been awhile since I used ICARUS, but isn't there a masking function in it? That might be a quick solution.

I think the objects that are brought into LightWave from ICARUS are simple Nulls. You can use Cman's Nulls2Points plugin (http://www.m2estudios.com/plugins.html) to convert the nulls in Layout to Points in Modeler. From there you should be able to create your geometry.

Hope this helps!

Steve

stephen2002
11-25-2003, 06:19 PM
Yes, there is a masking function in Icarus. However that is only to hide portions of the video (like cars) that might confuse the motion tracking.

That script should do the trick.

Projection mapping is SO COOL! :applause: Thanks!

Now I just wish Lightwave used OpenGL more effectivly and didn't take so long to make the OGL textures. :rolleyes:

LittleFenris
11-25-2003, 06:47 PM
What is projection mapping? Can someone explain its uses and maybe an example of them at work? Thanks.

stephen2002
11-25-2003, 09:11 PM
I'll provide an example as soon as I get my particle effects working right :)

One example is that you can make really simple objects to use as masks to composite live action and CG elements together. The CG elements will be able to cast shadow and light onto the live action elements that you have turned into simple geometry. You would use projection mapping of your live action video onto the simple geometry so that it looks real. As long as you have the camera motions matched up with something like Icarus it all matches perfectly.

As for how it works it basically usues the camera as a projector for the texture.

stephen2002
11-25-2003, 11:07 PM
I've got another question. If I am using projection mapping as well as a background image for the composite is there any way to add noise to just the CG elements to match the background video or will I have to render in multiple passes somehow?

Steve Warner
11-26-2003, 12:15 AM
Matching grain is one of the biggest challenges in making CGI blend seamlessly with live action footage. If you're serious about getting it right, the best thing you can do is pick up Grain Surgery (http://www.visinf.com/gs/ae/). It is the best tool for what you're looking for.

You don't need to do multipass rendering, although it would probably be a good idea to save out your alpha channel as a separate sequence. That way you'll be able to isolate most of the CG elements from the live footage and have a better time at blending the two in your compositing application.

If you don't want to go with Grain Surgery, you could try to match the footage using Virtual Darkroom. It's not the easiest filter to master, but it should give you the control you'll need.

Hope this helps!

Steve

NanoGator
11-26-2003, 01:51 AM
Mulitple layers would be ideal, especially if you have After Effects. Why? Well the big reason is matching levels adjustments.

Boris B
11-26-2003, 05:35 AM
Originally posted by VWTornado
What is projection mapping? Can someone explain its uses and maybe an example of them at work? Thanks.

http://www.newtek.com/products/lightwave/tutorials/rendering/camera_mapping/camera_mapping.html

LittleFenris
11-26-2003, 02:20 PM
Thanks for the link. :wavey:

stephen2002
11-26-2003, 04:01 PM
Originally posted by Steve Warner
You don't need to do multipass rendering, although it would probably be a good idea to save out your alpha channel as a separate sequence. That way you'll be able to isolate most of the CG elements from the live footage and have a better time at blending the two in your compositing application.

Grain Surgery is nifty (the grain removal is probably what I would end up using) but overkill for this project. The only problem with saving out the alpha channel for the composit is that there are elements with projection mapped video that already have some grain on them. The source video actually isn't all that grainy so I think if I just throw a little bit more grain over the whole shot it will blend well enough.

Steve Warner
11-26-2003, 04:09 PM
If it's not critical, then adding a little grain to everything will probably work. If you find that it's making the live footage too grainy, render out all of your CGI elements in one pass, then do another pass with your front projection objects. It's more work, but you'll be able to use the alpha channels in your compositing app to back together again.

Good luck, and let us know how it turns out!

Cheers,

Steve

stephen2002
11-26-2003, 05:07 PM
As I came back from lunch that is exactly what I was thinking; render the front projection objects separetly.

Do you know if volumetric HyperVoxles generate a proper alpha layer?

I'll be sure to post the finished animation when it is done; probably in a week or so. In the mean time here is a test render:

http://www.solarflarestudios.com/temp/comptest3.jpg

I know it is rather dim but it is supposed to be a night-time shot and there are no lights in the windows for a reason. Everything but the color correction and tracking on the background video was done in Lightwave.

Wire:
http://www.solarflarestudios.com/temp/comptestwire.JPG

The building is using the front projection mapping. All of the nulls floating around are tracking points from Icarus.

Steve Warner
11-26-2003, 05:24 PM
Hypervoxels should show up in your alpha channel. If they don't, you can add the Post Alpha Plugin (http://www.ats-3d.com/#Image%20Filter%20Plugins) to help resolve the issues.

Your test render is looking good so far. But watch your lighting. The ship has so many lights on its underside that they'd be casting some sort of incendental light on the building.

Keep up the good work!

Steve

stephen2002
11-26-2003, 07:12 PM
Thanks for the lighting tip...I'll see if I can fix that.

CGTalk Moderation
01-16-2006, 07:00 PM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.