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Bedeviled by Deinterlace

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Tom DonnellyBedeviled by Deinterlace
by on Feb 14, 2012 at 2:23:32 pm

I've not come across this scenario before, rendered many tests and cannot get a satisfactory result...

Footage originated from FCP, XDCam 1080i. Was slo-moed a bit in FCP, then outputted self contained from FCP to AE. Interpreted upper field first in AE. The footage is nested in another comp and corner pinned in main comp (to fit in a slowly horizontally panning TV screen) from mocha data. The main comp is then rendered ProResHQ, upper field first.

The resulting movie looks great in all respects EXCEPT the precomped, corner pinned TV screen composite - a diagonal line is VERY jagged/aliased, and the rest of the shot also looks like its missing half the field info.

I am indicating "upper field" in the AE render settings and also checking "Interlaced/upperfield" within the ProRes HQ options in the Output Module settings - is it correct to check both of these? If I ONLY select upper field in the output module setting (and not in the main render settings tab), then the corner pinned shot looks fine - but then am I really re-interlacing the full shot properly?

Thanks for help getting rid of these jaggies...

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Dave LaRondeRe: Bedeviled by Deinterlace
by on Feb 14, 2012 at 3:52:15 pm

Don't do the slo-mo in FCP. Do it as you're compositing the entire shot in AE. To preserve image quality on the slo-mo, I would stick with changing the footage speed by dividing by intergers: 1/2, 1/3, 1/4, etc. If you have Twixtor available to you, I recommend using it.

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

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Kevin CampRe: Bedeviled by Deinterlace
by on Feb 14, 2012 at 4:38:22 pm

it can be hard to trouble shoot this issue remotely, but the typical workflow within ae when you have interlaced footage coming in and want interlaced going out, is make sure all imported footage is correctly identified within ae -- select a footage item in the prject window and choose file>interpret footage>main (or click the little interpret footage icon in the project window). in the case of 1080i, make sure that ae is set to separate fields (upper), also make sure that ae sees the frame rate as 29.97.

when creating comps, make sure that they have the same frame rate as the footage (29.97).

then when you render, click the render settings and set ae to field render (upper).

one other tip, if you know that you will be manipulating scale or rotation, making the footage layer 3d, or using a plugin that distorts the footage (like corner pin, or turbulent displace,, etc) then in the interpret footage settings you should also select the option for preserve edges. this can help maintain image quality when the frame is distorted. i would not choose this option if the footage was going to be full frame in the comp.

so where did things go bad...? well things can go bad before footage gets to ae -- wrong field order, pulldowns not being correctly handled, scaling without proper deinterlacing that happened in the nle or at export...

things can also go bad in ae, often wrong footage interpretation, like footageis 24p but has a pulldown so it appears as 29.97, but without removing the pulldown, the scaled/manipulated footage looks awful in ae. mixing 24p and 29.97i can also be problematic.

i would start by looking at the bad footage by double clicking it in the project window and using the arrow keys to go through frame by frame and make sure the footage shows interlacing.

Kevin Camp
Senior Designer

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