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DPC

Eliminating moiré on LED screens?

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Last year I filmed a corporate event where people spoke for two days in front of an 30m long wall made up of joined LED screens. This looked great to the audience but I had terrible problems with moiré. Some angles were simply impossible and the camera needed to be locked off on a tripod to minimise the problem. Spontaneous shooting was almost impossible. It was very stressful, especially because I'd been flown half way around the world to do it and didn't want to let my client down.

I'm going to cover the same event this year and, apparently, the same screen technology will be used.

So my questions are : (1) Is there any solution to this problem or do I have to live with it? (2) Does the choice of camera / sensor technology play a role? (3) Is there any on lens filtration that might help? (4) Am I right in thinking that the only real solution would be to cover the screens with an anti-moiré diffusion screen?

My research suggests that the real problem is that the screen used wasn't really appropriate for being filmed.

Thanks in advance!

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jonpais, thanks but the first "here" suggests using film or rotating the camera, the second concerns screen scan flicker which is not my problem and the third, defocus your smartphone's camera, isn't really applicable either.

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8 hours ago, jonpais said:

There are many responses to this question around the internet: here, here, and here are just a few. Hopefully, one of them solves your problem.

 hi, at third link say to soften the image but doesn't seem to explain how. may you give us some advice plase?

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To OP, could you share a clip? One of the links does mention throwing the screen out of focus. Is this possible for you to do, or must the screen be sharp?

34 minutes ago, Dan Wake said:

 hi, at third link say to soften the image but doesn't seem to explain how. may you give us some advice plase?

They say there are apps available to soften the image. Another option is to use a wider aperture. These tips are all mentioned in the links. But the OP doesn't say whether the entire screen must be shown, whether it must be sharp or not, and what equipment he is using. 

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19 hours ago, DPC said:

I wasn't clear enough. I would like to eliminate the moiré that appears on footage of LED screens when filmed.

Like I said, you can try using a circular polariser to fade out the LED screens. Attached image - left is an LED screen, right is an LCD screen. I don't know if it will eliminate moire but fading them out will make them less distracting.

DSC_6704.JPG

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???

Actually, since it didn't bother your client the first time around, I wouldn't even worry about it. You said you shot the event once already, and they're hiring you to shoot it again, so they must have been happy. Personally, though, moire and aliasing drive me absolutely nuts, but it seems most people aren't even aware of it.

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Moire will arise when you try and project one grid of pixels onto another grid the doesn't quite match up. Gaps between the photo sites on the camera sensor will make this worse, and if you use a DSLR or similar that bins pixels from a high res sensor to create an HD image, then the moire will go crazy. 
Some of the more "gap-less" options are A7S series - where the readout is 1 to 1 with very little gap between photo sites, or a camera which oversamples a 6K image down to 4K - such as the A6300 (which will probably not be suitable for long takes with overheating issues) or A7Rii in crop mode which does a similar 6k to 4k trick.

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Thanks for all you replies.

Jonpais, your pragmatic reply about a happy client is more sensible than I am. I suppose it's just that I don't like technical issues forcing me into a particular way of working.

BasiliskFilm, I'm going to have to think about all that.  I know moiré comes because of clash between the frequencies of the subject and the sensor pixels but I've never really bothered to go much further than that. Last year I had GH4s and G7s. This year it will probably be A7Rii / RX10ii / GX80. I'm sorry I can't share footage of the problem publicly but I can find any that doesn't clearly show people who haven't given me permission or brand names. 

I had a long conversation about this with the technicians in a big rental house today. Conclusion : it's a problem and there's no real solution other than to warn the client in advance and try to shoot angles that attenuate the moiré.

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21 hours ago, DPC said:

Thanks for all you replies.

Jonpais, your pragmatic reply about a happy client is more sensible than I am. I suppose it's just that I don't like technical issues forcing me into a particular way of working.

BasiliskFilm, I'm going to have to think about all that.  I know moiré comes because of clash between the frequencies of the subject and the sensor pixels but I've never really bothered to go much further than that. Last year I had GH4s and G7s. This year it will probably be A7Rii / RX10ii / GX80. I'm sorry I can't share footage of the problem publicly but I can find any that doesn't clearly show people who haven't given me permission or brand names. 

I had a long conversation about this with the technicians in a big rental house today. Conclusion : it's a problem and there's no real solution other than to warn the client in advance and try to shoot angles that attenuate the moiré.

or, as someone else has pointed out, defocus. The A7S (or A7Sii)  would give you the best result, with gapless 4K full frame. Stick a long f2.8 lens on that and focus on the people and the screens should be out of focus. The A7Rii would probably be cleaner in S35 crop, as FF mode involves line skipping of some sort. S35 will increase your DOF, but stick a speed-booster and f2.8 lens on and your backgrounds will again be thrown out of focus. The smaller sensors on the other cams will make defocusing more difficult.

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On September 1, 2016 at 3:54 AM, DPC said:

Is there any solution to this problem

You could always exploit the benefit of shallow depth of field. Position full frame cameras with fast lenses at a distance ( if possible ) that allows for focus on foreground subjects but knocks out background into a good bit of that 'ol "circle of confusion."

If you never focus on the screens, you'll never have to worry about the Moire. 

Of course, this kind of prohibits wide shots...

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