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Compositing keyed 4k footage with 2k footage

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jim bachalo
Compositing keyed 4k footage with 2k footage
on May 19, 2013 at 6:29:46 pm

In order to achieve the best results, which of the following options should I use in compositing keyed or roto'd 4k footage with 2k footage if my end result is 2k?

1 Key or roto the 4k footage in a 4k comp then render out as 2k RGB+alpha, reload and composite with the 2k footage.

2 create a 2k composition, scale the 4k footage down, key or roto then composite with the 2k in the same comp

3 create a 4k comp, do my key or roto, nest this comp and bring in on top of my 2k footage in a 2k comp.

Local is the new global

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Stephen Norrington
Re: Compositing keyed 4k footage with 2k footage
on May 19, 2013 at 9:29:50 pm

Hi there,

I'm not an expert with keying by any means but I've had good results rotoing 4K for downsizing as follows:

- Create a 4K comp with the element to be rotoed.

- Bring the 2K BG into the 4K comp and scale it up to the 4K frame.

- Do the roto on the 4K, paying attention to how the edge looks over the scaled-up 2K.

- When you're happy, render out the rotoed 4K with an alpha, bring it into the 2K comp and scale it down to fit.

Doing it this way has given me some very nice clean comps that take account of the interplay between BG and FG. However, when the rotoed 4K render gets scaled down the edges get sharper so that might not be what you want - in that case, scaling the 4K down in a 2K comp might be your best bet - either way, I've always found rotoing over a relevant BG plate (so you can see what's going on with the edge feathers and moblur etc.) is the way to go.

Stephen Norrington

Artproject Independent Production

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