video retouching – does it need to be de-interlaced?

[Steve Roberts]

Separate fields on the footage (file>interpret footage>main), then drop it into a 59.94 fps comp (twice normal) that’s the same frame size as the footage. Then you will see each field as a frame as you step through the comp. Do the roto in that comp.

Then you drag the 59.94 comp into a 29.97 comp and field render that.

Sorry, don’t know about animation in PS.

[Darby Edelen]

You MUST deinterlace if you are planning to do anything at all that will move the fields out of their proper position. This means ANY vertical movement, ANY blurring, ANY scaling, etc. As a general rule it’s best to consider deinterlacing even if you don’t think you’re going to be messing up the fields.

The workflow is as follows:

-Import footage into AE.
-Interpret footage with proper field order (lower or upper first?), optionally turn on Preserve Edges (can give better results, can give poorer results, depending on the footage content). Your footage is now deinterlaced in AE.
-Do as Steve says and place the footage in a 59.94 comp. I don’t normally do this, but only working on one field at a time should give you better results.

If you need to output interlaced footage then you need to turn on Field Render in the Render Settings, set it to the same field order as the original footage.

If you are working with still frames out of an image sequence in Photoshop for retouching they must be deinterlaced first, the healing/clone tools will not play nice with interlacing. You should do this step after you have deinterlaced your footage in AE, render out an image sequence from AE and make your changes in PS, bring the image sequence back in when you’re done and render out with fields.

Basically, the idea is to remove fields/interlacing before you do anything and then add them back only as the very final step.

Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA

[Paul Rijkaard]

thanks that is very helpful

but two further questions

1. the footage is pal what comp frame rate should i use for this?
2. by deinterlacing and then interlacing will the footage noticably degrade in quality? if so can this be curbed?

thanks

Paul Richards

[Steve Roberts]

1. twice the normal frame rate: in your case, 50 fps, no?
2. If all you do is roto, the footage should not degrade due to the deinterlacing, since you are not dropping fields and recreating them. Yes, you are doubling the lines (filling in the missing lines), but then you are removing them and reuniting the original lines back into an interlaced movie. You see?

(Note that AE always recompresses when it renders. So, depending on your codec, there may be some degradation due to recompression. Rendering to the Animation codec is one way to minimize this degradation due to recompression.)

At any rate, if you are concerned, you should do a test by separating fields, dragging into a 50fps comp, dragging that into a 25fps comp and rendering that interlaced. Then, to do the test, reimport the thing you just rendered, drag it into a new 25 fps comp along with the original footage (which has not had fields separated). Compare the two, either by masking off half of one, or by using Difference mode for the upper layer … if it’s completely black, the two are identical.

By the way, you can have a piece of footage interpreted two ways in a project. Duplicate the footage item in the Project window, then re-interpret it differently. Make sure you use the Comments panel in the project window to differentiate the two differently-interpreted footage items.

[Bret Williams]

Yes you most certainly will lower the quality. Once you deinterlace the footage, the fields are gone. There’s no bringing them back. You’ve now created progressive frames, and you can’t miraculously create fields from progressive. You’ve removed the field information, either by duplicating or most likely, interpolation. Sure, you can field render, but the video in the comp won’t have the extra info. Each field will be the same frame. Just half of it each field. But any added elements like moving type, would be correctly field rendered.

The better suggestion was the former. Drop it into a double frame rate comp, where each field becomes it’s very own frame. You’re now operating on a field level of roto. Then, (just like old 3d animation systems that couldn’t field render), drop that double rate comp into your 25fps comp. AE will utilize the extra info to create (in this case recreate) the field info.

[Bret Williams]

[Darby Edelen] “You MUST deinterlace if you are planning to do anything at all that will move the fields out of their proper position. This means ANY vertical movement, ANY blurring, ANY scaling, etc. As a general rule it’s best to consider deinterlacing even if you don’t think you’re going to be messing up the fields. “

Deinterlacing will mess up the fields. You’re second guessing AE and that’s generally a bad idea with bad results. Tell AE how to interpolate your footage. If your footage is field based, then tell AE that it is. AE will then know how to best scale and move the fields around within the comp you’re using. I’ve never had to deinterlace footage to move it or blur it. That’s just bizarre that you would even suggest that and I’ve never heard it suggested before. Once you’ve deinterlaced it the interlacing is gone. You can’t just “field render” and get it back.

[Steve Roberts]

We probably all agree, but there may be a semantic thing going on, I think.

1. Most of us should avoid the term “deinterlacing” with regard to AE. When we need to move/blur/rotate/scale/distort interlaced footage, we need to SEPARATE FIELDS. (please excuse the caps, I have no bolding options with the COW on Mac) I think Darby was talking about “separating fields” when he said “deinterlace”.

2. Deinterlacing is often destructive, while separating fields is not.
When you let AE separate fields, the fields are not gone. They are effectively held, but not shown. In draft mode, the first field is duplicated for display. In high-quality mode, the fields are interpolated for display.

3. Deinterlacing with Fieldskit is a different manner, as you interpret (not “interpolate”) the footage as “no fields” for that plugin to work. I only use it when I know I wan’t to get rid of a field altogether, and never want to see it again.

4. When we render field-separated footage as an interlaced movie, two things happen: 1) any animation done in AE becomes field-rendered and 2) the same operations performed on the visible field are done to the held field. So if we fly an interlaced movie around the screen, we do not lose the second field — AE renders the first field (interlaced) then it moves one field forward and renders the second field interlaced with the first. This is easy to test:step 1) make an interlaced 10-frame movie of an ellipse crossing the screen and import it. 2) Let AE separate fields, or make sure AE separates fields. Drag that movie onto the new comp button to make a comp. Render that comp and reimport, but don’t separate fields — you want to see interlacing. You should see both fields. Now … if that second-field data was lost when the first movie had its fields separated, where did it come from?

Here’s a doc on the subject:
https://livedocs.adobe.com/en_US/AfterEffects/8.0/help.html?content=WS3878526689cb91655866c1103906c6dea-7f37.html

5. In case anyone (outside this thread) ever uses the term “field dominance”, we’re not talking about separating fields and field order. Dominance refers to the field chosen by an editing system when making a cut: cut on the upper or lower field. Field order refers to the location of the first (in time) field in the frame: does field 1 occur before field 2, or vice-versa? (Apple uses “field dominance”, but they really mean “field order”.)

Anyway, separating fields is done all the time. Deinterlacing is not — I’d prefer we only use that term when specifically referring to Fieldskit Deinterlacer. But that’s just me … 🙂

[Darby Edelen]

[Bret Williams] “Tell AE how to interpolate your footage. If your footage is field based, then tell AE that it is. AE will then know how to best scale and move the fields around within the comp you’re using. I’ve never had to deinterlace footage to move it or blur it. That’s just bizarre that you would even suggest that and I’ve never heard it suggested before. Once you’ve deinterlaced it the interlacing is gone. You can’t just “field render” and get it back.”

I believe the confusion here is one of semantics. When I said deinterlace, I meant interpret with the correct field order to separate the fields. I probably should have used a different term, like “separate the fields.”

If you drop the footage into a double frame rate (field rate) comp at that point you will have exactly what I believe you are talking about. As I said before, that is the proper way to treat your footage after separating the fields to maintain the fields…

What I was saying about blurs refers to the case in which you do not separate the fields (deinterlace was the word I used) in your interlaced footage.

Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA

[Paul Rijkaard]

Ok thanks for the help

just one final question,

I am being handed the footage as 50fps 1080i Avid DNX120 codec

it has already been edited and graded on an avid system and im just doing some cover up work (although I would prefer to work on the pre-graded footage.

can you simply explain to me:

will footage shot/supplied on 50i already have fields separated?

nothing is broadcast at 50 fps, right?

thanks

Paul Richards

[Steve Roberts]

Ugh. They might have to grade it again, if the footage is YUV, and AE works in RGB. I can’t help much on that, since I haven’t delved into CS3’s color space features. If the colour changes when going through AE, try searching the COW for “YUV”, and check the Help on that soprt of thing. Can anybody else help on that?

1. Maybe, maybe not. Import the footage, and make sure it is interpreted “no fields”, or “field separation off”. Double-click on it. If you see interlacing, it’s interlaced. If you see no interlacing, it’s progressive, or already separated, and this whole thread has been unnecessary. 🙂

2. Hmm . Maybe this will help:
https://www.burnyourbonus.info/hdtv-faq/faq2.html