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How do pre-comps work?

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Dane Cannon
How do pre-comps work?
on Oct 22, 2010 at 4:16:28 pm

I mean, I understand how precomps work... but once they're put into another file -- is a render created and then any changes to that precomped comp will only access the render file? Or will they go back and do the math to the original? Additionally, if I have comps precomped and I turn on motion blur in the comp in which they're precomped (there must be some better word for this that I'm just not aware of--like "parent" and "child" but applied to comps), will it turn it on for the precomp as well? Or do I need to open that precomp and enable motion blur? My "how do precomps work" searches all seem to return basic kind of results, and while this is a basic question, I'm having trouble answering it.

Note: these question apply to a piece I'm doing that will accompany a yet to be recorded VO. I'm thinking I can get it close and bring all the pieces as precomps into a single comp, and then retime it a bit using time remapping, but I'm not sure if that will give the best visual results (ie, I need to not use pixel motion on some of the precomps for a frame skipping effect when time remap is applied, but I need the overall comp to use pixel motion).


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Dane Cannon
Edit...
on Oct 22, 2010 at 4:19:47 pm

The word I was looking for, ironically enough, was terminology. I feel like there's some terminology that I'm missing, and that's why I'm not getting the answers I'm looking for from my searches...


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Chris Wright
Re: How do pre-comps work?
on Oct 22, 2010 at 6:08:34 pm

"retime it a bit using time remapping"

some things you should know.

1. nesting a low fps precomp into a higher precomp makes the master comp not inherit the precomp's fps(it still stays smooth) unless you go to precomp's settings-advanced-retain nested fps.

2. if the comp has no effects on it, it won't have to do any math to re-render the precomp's timewarp features. it's instantenous.

3. timestretch affects the comp before timewarp does.

4. "is a render created and then any changes to that precomped comp will only access the render file?"

if you prerender out, it won't have to do math there again. it makes the computer faster and less prone to image buffer issues.

http://technicolorsoftware.hostzi.com/


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Dane Cannon
Re: How do pre-comps work?
on Oct 22, 2010 at 7:05:02 pm

Okay, this is making more sense. Good to know about the FPS not being inherited (its a fake projection of an old movie--which is supposedly run at a lower FPS, resulting in that sped up jerkiness). So it sounds like there are 2 ways to do this...

1 - Only do retiming on the most basic of levels, never do it to a precomp, and especially not a precomp that already has retiming going on in it.

OR

2 - Only do all retiming on the final level (but don't bring things in as precomps... bring them in as actual layers).

Is that right?

Is it still going to result in bad image quality if you retime a precomp that has no retiming within it?
I'm hoping not, because if so my life just got a bit harder.


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Chris Wright
Re: How do pre-comps work?
on Oct 22, 2010 at 7:22:50 pm

precomps and original layers act exactly the same when timestretched.

you can 50% timestretch(or timewarp's whole frames) a precomp, then 200% timestretch the comp to get exactly the same speed with zero loss in pixel quality. it's only not true if you use timewarp's frame blending or pixel because they are lossy functions.

http://technicolorsoftware.hostzi.com/


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Dane Cannon
Re: How do pre-comps work?
on Oct 22, 2010 at 7:30:12 pm

Okay, this is looking like good news then. I'm not using timewarp (no need), BUT doesn't time remapping use pixel motion too? I'm mainly speeding up footage, so it's not interframe interpolation, and it doesn't seem to be frame blending. Just it just skip frames and use others? Or does it use certain real frames and then try to interpolate between them for certain frames? I'm sorry that this is getting so convoluted... I appreciate the help.


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Chris Wright
Re: How do pre-comps work?
on Oct 22, 2010 at 7:41:58 pm

timewarp's whole frame and timestretch(with pixel motion off) are exactly the same thing. there's no loss in quality and it's fully reversible. it's simply a change of speed of the frames being played back.

http://technicolorsoftware.hostzi.com/


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Dave LaRonde
Re: How do pre-comps work?
on Oct 22, 2010 at 7:42:35 pm

You know what you ought to do? You ought to run some tests. Try some of the various methods you're contemplating. Render them out in simplified comps. Look at the results, and see what you think.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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