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Aliasing

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Keith Pratt
Aliasing
on Mar 25, 2010 at 6:56:26 pm

What are you all doing to combat aliasing in DSLR video?

I've seen recommendations for Caprock Anti-moire filters, and whilst there seems to be certain lens and filter combos that almost entirely eliminate aliasing, Caprock's product range is somewhat patchy, meaning there isn't a solution for every lens you may wish to use. Are there any alternative brands of anti-moire filter you've had success with?

In your experience, how does scaling (in Compressor or via a Kona card) from 1080 to 720 affect aliasing? Is the resampling enough to eliminate the jitter that can occasionally arise, or go some way to making a slated roof look acceptable?

Or are you just accepting this aliasing as a fact of these cameras and living your lives?


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Noah Kadner
Re: Aliasing
on Mar 25, 2010 at 9:09:33 pm

You can accept a certain amount of aliasing as pretty much a way of life. But yes filtering either on the lens (not recommeded) or in post can help to minimize it. I would do my scaling on the fly with a Kona card, I'd really crunch on it with MPEG Streamclip or Compressor- make sure you're not adding any additional artifacting with less than full quality down converts.

Noah

Check out my book: RED: The Ultimate Guide to Using the Revolutionary Camera!
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Uli Plank
Re: Aliasing
on Mar 26, 2010 at 6:57:42 am

You'll have to accept this until DSLRs get way faster to downscale the whole image at full quality. An OLPF can't be optimized for hi-res photography and lo-res vdeo (yes, HD is lo-res on a DSLR) at the same time.
That said, the problem is often exaggerated. The very shallow DOF helps, since only regular patterns which are in full focus can produce moiré. Any blur is like an OLPF.
Plus, reduce sharpening quite a bit, it only enhances false detail anyway.

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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Noah Kadner
Re: Aliasing
on Mar 26, 2010 at 3:39:41 pm

Personally I think that things like aliasing and even severe skew are artifacts most average viewers- i.e. non-DPs don't even notice most of the time. If they like what the video is about they don't care. :)

Noah

Check out my book: RED: The Ultimate Guide to Using the Revolutionary Camera!
Unlock the secrets of 24p, HD and Final Cut Studio with Call Box Training. Featuring the Sony EX1 Guidebook, Panasonic HVX200, Canon EOS 5D Mark II and Canon 7D.
Watch Formosa- My indie movie shot with the SDX900 and finished with Final Cut Studio.


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Keith Pratt
Re: Aliasing
on Mar 27, 2010 at 9:19:47 pm

I agree that most people wouldn't notice it, but it'd bug the hell out of me. I'm sure I'll fight it for a while and then admit defeat.

Has anyone tried Boris DV Fixer on VDSLR footage? I'm thinking the following might yield results I can live with: try to keep focus on the soft side when shooting, ingest at 1080, run DV Fixer, then downscale to 720p.


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Uli Plank
Re: Aliasing
on Mar 28, 2010 at 12:48:30 pm

Aliasing is not that much connected with color subsampling here, which only shows with very saturated, contrasting colors to the naked eye (where DV fixer may help).

It's system inherent (OLPF way beyond the Shannon/Nyquist limit) in DSLRs of today.

Director of the Institute of Media Research (IMF) at Braunschweig University of Arts


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Keith Pratt
Re: Aliasing
on Apr 4, 2010 at 6:32:00 pm

Without having the slightest clue how DV Fixer achieves what it does, I wondered if it might work (even a little bit), despite the differing reasons for the aliasing. I sent Boris an quick e-mail about it a week ago but haven't had a response.


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Matthew Mullen
Re: Aliasing
on Apr 5, 2010 at 6:13:16 pm

Keith,

What e-mail address did you send to?

what specific questions do you have on the filter?

You can always send inquiries to support@borisfx.com


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Keith Pratt
Re: Aliasing
on Apr 10, 2010 at 11:02:35 pm

I e-mailed info@borisfx.com.

My question was whether the way DVFixer worked meant it would only be useful for smoothing blockiness that comes as a result of chroma subsampling or if it would also work (to some extent) for footage that had aliasing as an artifact of bad scaling.


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Matthew Mullen
Re: Aliasing
on Apr 12, 2010 at 3:52:21 pm

The point of the filter is to remove or smooth stair-casing. I think what you are describing it should work for you but you should really test out the trial or send us the clip to look at.



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