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View Full Version : problem in compositing (key colour) with motion blur


FabioMSilva
05-18-2003, 07:09 PM
ok what i´m trying to do is to render an helicopter in a separate layer from the background. i make the heli´s blades have motion blur when spining but that becomes a pain in the ass in keying(doesnt look any good at all). Any ideas on how to outcome this? I use 3dsmax 5 to render the cg-heli, and i think i can solve my problem if i render another separete file of alpha channels...the problem is that the only way i know to do that is to create a material of flat 100% brightness and then apply it to the objects(which is a really pain in the ass to render anyway)
does anyone knows of a way to render the alpha channels(in a separate movie file) during the actual 3d-normal-render? and if so, how can i then tell AE5.5 that i want this movie to be the footage and this one to be the alpha channel?

Help is welcome!

:beer: cheers

dmeyer
05-18-2003, 10:13 PM
I'm not a Max user I would assume that it renders an alpha during the default render, just like every other 3d app, just make sure you are rendering to a format that supports alpha.

FabioMSilva
05-18-2003, 10:14 PM
hum...which format? now that u tell it, AE5.5 does ask if i want to use the alpha map on my mov files...but since i didnt thought they were included i never gave it a try...i shall give a look into it

thanx

Chris
05-18-2003, 10:33 PM
some of the codecs within quicktime support alpha channels. 'Animation' codec is one of them, set the quality on 'best' & the colour depth to 'millions of colours+' (not millions of colours)

dmeyer
05-18-2003, 11:20 PM
Also, depending on the scene and how well Max handles alphas on blurred elements...it can be helpful to do all your motion blur in post. AE's motion blur is pretty weak though so it might be a bad idea in this instance.

jussing
05-20-2003, 11:28 AM
Dmeyer, how would you motion blur helicopter blades in post? There's no way AE can "guess" the motion of the various parts of the helicopter....?

I'd say, render with motion blur ON in 3DS Max, render on a BLACK background, and like Chris says, use Quicktime, Animation, "Best" and "Millions of colors+". Dat's da way to go.

Then, when importing in AE, chose to interpret the Alpha as "Premultiplied", and be sure to choose BLACK as background color.

The "Premultiplied" bit is essential, or you'll get black edges around your chopper, particularly in the motion blurred areas.

Cheers to y'all,
- Jonas

dmeyer
05-20-2003, 01:02 PM
Originally posted by jussing
Dmeyer, how would you motion blur helicopter blades in post? There's no way AE can "guess" the motion of the various parts of the helicopter....?


I have Maya write out vector data to channel in an IFF file, then you can have Shake use this to apply blur. Don't think you can do this with AE though.

jussing
05-20-2003, 03:23 PM
Originally posted by dmeyer
I have Maya write out vector data to channel in an IFF file, then you can have Shake use this to apply blur. Don't think you can do this with AE though.

:eek: Wow.... I didn't even know there was technology/formats/compatibility for that kind of thing... very clever, though. Thanks for the enlightenment. :thumbsup:

- Jonas

dmeyer
05-20-2003, 07:03 PM
Originally posted by jussing
:eek: Wow.... I didn't even know there was technology/formats/compatibility for that kind of thing... very clever, though. Thanks for the enlightenment. :thumbsup:

- Jonas

Saves tremendously on render time too - your average comp package will compute blur much faster than your average 3d package, plus it looks better! :buttrock:

policarpo
05-20-2003, 11:37 PM
Solid Snake...be sure to render out your scene as a 32bit .TGA sequence.

If you know what your background plate is going to look like in the final composite, try rendering the max scene with a similar background plate. This should hide any weird alpha artifacts which might be coming over in your comp. I'm not sure how max computes the alpha with Motion Blur files.

Also, try to never render to an animation file if you are going to composite at a later date if you can help it. Render to 32bit .TGA. You do this because you can render out later frames and just replace the original ones if something changes in your shot sequence. Plus it's a hell of a lot easier to manage in your workflow. You get more predictable results as well.

Rendering to an animation codec is only a smart idea once everything is completed and it's being edited.

Just anf FYI, hope it helps. :beer:

dmeyer
05-20-2003, 11:54 PM
It can also ease color correction and make your alphas cleaner if your renderer has the ability to render unpremultiplied images, and render the alpha as a separate file. Makes for cleaner edges.

FabioMSilva
05-20-2003, 11:59 PM
i´ve been playing around a bit with Combustion2 and i´ve got some pretty good results. The Animation codec for quick-time works quite good even with motion blur(later on i added more "motion blur" effect on my Chopper Layer and it got pretty good.

thank u all ppl

Now i´m just having a little problems in Combustion2 Particle effects. Cant control them like i wanted to(it gets the pc too danm slow) also i´ll give u an example of why i think of it being so damn hard:

-I got the background plate(rolling sea and sky at high speed in camera´s direction)(1st layer)
-Helicopter flying towards camera(2º layer, with motion blur&glow)

So in order to make a Waterjet trail(cause the chpper is flying close the water) i need to put the heli-layer in the back of the particle systems to track more closely its motion, then i put it again in front of it. Isnt there an easier way? anyway i got some pretty good results for an 1st aproach...the movie is starting to look really cool. Any1 knows how to achieve the Displacement effect on airplane/choppers/aircraft? Ive tryied i few from AE5.5 and C2 but didnt got what i expected. I wanted something more like "Air Blaster" effect(if u see the anime´s NAruto episode 33 u´ll understand what i mean). Or also present in Final Fantasy TSW or in other movies that displacement effects from big engines.

Here i go again with my big mouth, always interested in learning more ;)

thanx ppl. good job :thumbsup:

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