C100: C100 Moire!

C

Conan Coatsworth

Member
Hey chaps, I didn't notice until i got it into FCP the mega moire issues with the actress jacket. This seemed to calm down when I uploaded the film but woah! the tie at 02:55! Is this something i can do something about?. Is it my fault?.

http://vimeo.com/80859022

The sharpness was at -10. I was using the 17-55.

Please don't destroy me for all of the other stuff I did wrong in the film as I may run away crying.
 
I've been generally pleased with the lack of moire in my C100 (but I'm coming from 7D Moire Hell). You can beat it with a very slight (and virtually unnoticeable) gaussian blur sometimes. You might could cut a matt that covers the tie and only blur that but I'm a Premiere guy and know nothing of FCP.
 
I usually tell my actors or on camera people no tight herringbone patterns, this coat and tie would've been red flags to me before even shooting. Those tight lines would be trouble with just about any camera. Now that it's shot, you could try the blur mentioned above. Check out SLICEX if you havent already. Can track a matte and blur just those areas.
 
Conan Coatsworth said:
but woah! the tie at 02:55! Is this something i can do something about?. Is it my fault?.
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The tie is really bad, yes. The jacket, after vimeo compression, is very very mild, there's only one section (about 2:30) where it draws any attention to itself, but even then it's so mild that I would think 99.98% of your intended audience will never notice.

As to whether it's your fault or not, the only way to know is to play the original source footage on a 1080p TV and see if the tie looks like that direct from the camera. If it does, then ... yeah, you didn't do anything to cause it. But if the tie looks pristine in the original footage, then yes, it'd be something you did in post. Re-sizing/scaling is the most likely candidate for introducing moire into an image after the fact.

If this was a for-pay job then yes, you'd need to get a handle on it to keep it from happening again. If it's your own project for your own channel, then -- don't sweat it, nobody but us camera geeks is likely to even notice.
 
Paul Frederick said:
I usually tell my actors or on camera people no tight herringbone patterns, this coat and tie would've been red flags to me before even shooting.
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That is, of course, the proper way to go about it, I should have mentioned that, so thanks Paul for spelling it out. Stripes, herringbone, checkers, corduroy, any fine repeating pattern can cause moire at the right frequency. If you have a good 1080p monitor you can check for it while shooting; if it appears, usually just zooming in or zooming out a little can be enough to minimize or eliminate it.
 
I was filming someone playing a piano and the keys were going ballistic with moire. I had sharpness @ -8 recording to ProRes.

This moire is a concern - I will be shooting a doco for broadcast in the coming weeks, I'm hoping as the deliverable is to standard definition digibeta it will help....hmmm some tests need to be done.
 
BeeHop said:
This moire is a concern - I will be shooting a doco for broadcast in the coming weeks, I'm hoping as the deliverable is to standard definition digibeta it will help....hmmm some tests need to be done.
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Doesn't reducing the resolution actually increase moire, similar to how a DSLR with a 21.1 megapixel sensor reducing the image down to 1080p creates moire? Often in Premiere I'll see moire on the small Program Monitor, but then when I switch it to full screen the moire goes away.
 
Cheers guys, great responses, made me feel much better about it.

Regarding resizing and or scaling. Is that something FCP does automatically? I have made sure that 'progressive' is selected as I am shooting in 25p mode. I was a little shocked when I saw what the footage looked like before that!

Would it be a better option to shoot in 24p for things like this (outdoor, no UK light frequencies to deal with)?

It does sound like the best course is to restrict fine patterned clothing etc.

The zooming trick sounds simple. Is it just a case of keep a deep DOF and pulling focus within that range? (So as not to lose focus but just move the sweet spot)
 
BeeHop said:
I was filming someone playing a piano and the keys were going ballistic with moire. I had sharpness @ -8 recording to ProRes.

This moire is a concern - I will be shooting a doco for broadcast in the coming weeks, I'm hoping as the deliverable is to standard definition digibeta it will help....hmmm some tests need to be done.
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Moire is result of the high analogue frequences from the chip (fine details) and "low" frequence of AD converter. Sharpness has nothing to do with this (you can only blur the whole image). If you see this fine patterns then you can only gently defocus (or you can use less sharp lens, no canon macro for example). Hope this help.

And yes, every camera can sometime show moire because it is about compromise, there is no ideal lens, no ideal OLPF, e.t.c.
 
Eric Coughlin said:
Doesn't reducing the resolution actually increase moire, similar to how a DSLR with a 21.1 megapixel sensor reducing the image down to 1080p creates moire? Often in Premiere I'll see moire on the small Program Monitor, but then when I switch it to full screen the moire goes away.
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No. Oversampling and downscaling properly helps. Consider the nyquist sampling theorem.

It's possible to make a camera with an overaggressive OLPF that will not have moire at all, but it will have unnecessarily poor resolution, too. The C100 has pretty serious moire for a "cinema" camera but it's sharp as hell. This is worse than I've seen other than one weird instance with a red fabric. There is an easy way to fix this in post to a very acceptable level (neat video with temporal window set to 5, mask out the area you want to affect, put a top layer over it of the footage with a 5-pixel blur and superimpose it using color transfer mode and mask that out too) but I think you just had bad luck and should avoid that frequency of detail in clothing in the future if possible.
 
Eric Coughlin said:
Doesn't reducing the resolution actually increase moire, similar to how a DSLR with a 21.1 megapixel sensor reducing the image down to 1080p creates moire? Often in Premiere I'll see moire on the small Program Monitor, but then when I switch it to full screen the moire goes away.
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Yes, when two patterns are involved, the subject pattern and the video format pattern, the lower the resolution, the lower the spatial frequency at which moire can occur and the more noticeable it is. Even with analog TV's and cameras back when, moire on patterns was an issue.

But that is an entirely separate essentially camera independent issue, it is a product of the spatial resolution pattern of the video format itself.

Chroma moire and aliasing on single chip Bayer based cameras is related to optical filtering, the quality of the deBayer process applied, downscaling or sub sampling techniques for oversampled images, and compression encoding. All can cause problems at some point or another.
 
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