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Resolution & maintaining video quality

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Des LinleyResolution & maintaining video quality
by on Sep 30, 2010 at 10:50:27 pm

Ah, newish to AE and having to get to grips with some basics. I've have been searching around to get tutorials and info on this issue, but while I'm looking I'd thought I'd ask you helpful folks.
Hi. Nice to be here in non-lurker mode. I've learnt much from here already. Please bear with me :)

So I'm working on something, and I've seen my imported video looking soft, so I'm trying to work out how to maintain quality.

In simple terms, to demonstrate this simply:

- 1: Import a 1440x1080 25p video clip into AE.
- 2: Create two comps (V1 & V2) at the video size both containing this clip
- 3: In the V2 comp, scale the clip layer down to 25%
- 4: Create a new final comp (C1) at 1440x1080, and bring in V1 and V2 comps to it
- 5: Scale up the V2 comp layer by 400%, and position V1 and V2 side by side to see the differences

So - V1 contains the native video, and V2 has a comp with the video scaled down 4 times, and then is itself scaled up 4 times back to the video's original size.

Perhaps as expected, the video looks soft, so it clearly has been scaled down, and then scaled back up from the smaller version, losing quality.

At *first* I had thought that AE might well try to preserve the original video resolution by always using the full resolution of the source video clip in its calculations - in my simple example, the two clips would look more or less identical.

As it seems like this isn't happening, I went to the manual, which says that this is indeed what AE tries to to - use the original source resolution, unless "preserve resolution" is enabled in which case the comp resolutions are rippled through the nested comp (so if you throw away resolution, it stays thrown away.)

So I'm a little confused on this and am doing some tests and research to pin down the behaviour and work out the best practice - any advice/tips to clarify this would be appreciated.

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Todd KoprivaRe: Resolution & maintaining video quality
by on Oct 1, 2010 at 7:25:59 am

Read about collapsing transformations. Here's an excerpt:
"Collapsing transformations can, for example, preserve resolution when a layer is scaled down by half in a nested composition, and the nested composition is scaled up by a factor of two in the containing composition. In this case, rather than performing both transformations and losing image data in the process, one transformation can be performed—doing nothing, because the individual transformations cancel each other."

Please, if you're new to After Effects, start here and methodically work your way through the resources pointed to:

Todd Kopriva, Adobe Systems Incorporated
Technical Support for professional video software
After Effects Help & Support
Premiere Pro Help & Support

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Des LinleyRe: Resolution & maintaining video quality
by on Oct 1, 2010 at 9:36:02 am

THanks Todd.

Yes, I have read that bit about collapsing transformations (which added into my confusion about the behaviour) but need to investigate more. Thanks for the pointers!

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Des LinleyRe: Resolution & maintaining video quality
by on Oct 1, 2010 at 10:04:46 am

Ok, I had missed that switch - and yes, in my example project, that does indeed make the scaled video identical to the original. Great stuff.

It's not quite that simple in my actual project because of the way that collapse transform works - however, I may be able to structurally move things around to get round some of the unintended consequences of collapsing the transformations - but it wasn't the magic bullet in terms of quality that I might have hoped for, so I need to investigate a little further. But it's certainly helped, thank you.

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