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Old February 11th, 2016, 03:57 AM   #1
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What is this Banding caused by?

This was shot last weekend in an arena with prolly MH lighting over the ice and floressents nearby
Used a Sony AX100 4K mode f4 and 1/250 of a second shutter (so I can extract sharp stills)
When the 4k file is encoded for blu-ray delivery I noticed those large bands on the ice. What is the cause of those things?
tks
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What is this Banding caused by?-banding.jpg  
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Old February 11th, 2016, 04:03 AM   #2
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Re: What is this Banding caused by?

I would say a "wrong" shutter caused it caused by the lights, this kind of banding should be visible while you shoot and you should adjust the shutter until they disappear.
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Old February 11th, 2016, 04:21 AM   #3
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Re: What is this Banding caused by?

Yes They are present as well in the footage right out of the camera
I wonder if they can be filtered out after the fact?
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Old February 11th, 2016, 07:48 AM   #4
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Re: What is this Banding caused by?

With UHD 30P and that shutter speed the video will surely stutter too. The different lighting banks may be out of sync but all at 60hz so may have this effect with such a high shutter speed.

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Old February 11th, 2016, 08:17 AM   #5
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Re: What is this Banding caused by?

I was expecting some apparent stutter but it's pretty smooth to my eyes. It did look a bit stuutery in the camera panel while recording but playback is not stuttery.
Those ugly rolling bands however only show up under 4k and that fast shutter.

the stills are nice and sharp (all 5000 of them from a 3 minute skate)
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Old February 11th, 2016, 09:23 AM   #6
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Re: What is this Banding caused by?

When changing to shutter speeds other than 1/60, I don't het option of 1/180 or 1/ 240, which i would expect in ntsc camera rather the 1/250 shutter speed is offered. Is that the case with everyone?

the 1/180 is available and I should have selected that rather than 1/250 perhaps
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Old February 11th, 2016, 09:28 AM   #7
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Re: What is this Banding caused by?

Fluorescents not synced to the camera shutter speed. You're trying to shoot above the refresh rate for the fluorescent lighting in the rink and that will always be a problem at higher shutter speeds.

This is why pro cameras have a "clear scan" mode to sync the camera to the refresh rate of lighting or similar.
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I wait for the day cost-efficient global shutter 60fps capable CMOS sensors emerge for use on major manufacturers' cameras. (Sony, Canon, etc.) Rolling Shutters are a plague.
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Old February 11th, 2016, 09:51 AM   #8
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Re: What is this Banding caused by?

ah I wondered what clear scan was about tks
going to try 4k 1/180 nest time and hope for no banding and a few sharp stills
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Old February 11th, 2016, 03:30 PM   #9
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Re: What is this Banding caused by?

1/120 or 1/60 are your best options.

Power cycles at 60 times a second, but there is a positive and a negative swing to the sine wave. Lamps generate light regardless of voltage polarity, so the lighting cycle lasts for 1/120th of a second.

I even had this problem with stills at an event in a fluorescent lit venue a month or so ago. I was shooting with a 1/250s shutter for crisp results. I noticed that the exposure was inconsistent for some shots. Finally, there was a group of shots across banks of lights and sure enough, they had the same ripple that your screen captures show. Then it hit me: a fast shutter isn't just bad for video under fluorescent lights; it can affect photos too. It's just that we see the affect more clearly in video as it ripples across the screen.

One reason that photos show is more clearly than video is rolling shutter. With a mechanical shutter for photos, you expose everything at roughly the same time. With rolling shutter for video, the frame gets exposed at different times in the lighting cycle. The issue for photos is that the exposure will be higher or lower, depending where you catch the cycle. You only see the wave thing when different banks of lights have different delays. This can happen when you have a mix of newer and older lights, each with different ballasts which can change the lead or lag time depending on the power factor.

So yeah, 1/120 is right not just for video but for photos too. If you look back at your stills, do you see some unexpected inconsistency in the exposures? If so, the fast shutter under fluorescent lights is the reason.
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Old February 12th, 2016, 01:25 AM   #10
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Re: What is this Banding caused by?

It's not just fluorescent tubes but sodium lighting does it too, as do all the discharge lights as they don't have filaments to stay hot and balance it it out. LED lighting doesn't do it, but only when on 100%. As many fixtures consist of red, blue, green white and amber LEDs, it's common to tweak the colour with the faders on the desk, especially when video people want the blue or orange tinge removed, but this leaves some very flickery results when high shutter speeds are used. I suspect the problem gets worse from here on as older continuous lights get rarer.
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Old February 12th, 2016, 07:28 AM   #11
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Re: What is this Banding caused by?

Quote:
Originally Posted by Bruce Dempsey View Post
the 1/180 is available and I should have selected that rather than 1/250 perhaps
No, it'll still give a problem. You need 1/60 though 1/120 may be OK (giving exactly half a cycle).

The problem can come when you're only capturing less than half a mains cycle, as the colour of one part of the cycle can be different from anotherwith something like a fluorescent source. Over an entire half cycle it will integrate out so isn't usually something we're aware of, but start to use only part of the cycle and strange colours can result.

Your example shows that and also the problem of not being a sub multiple of 1/60. So 1/180 may be better, but you really need to try 1/120. Try a variety, including some very short speeds.
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Old February 12th, 2016, 03:51 PM   #12
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Re: What is this Banding caused by?

ok
i will try 1/120
the goal is to shoot 4k video from which sharp stills can be captured and even 1/60th will produce a few sharp photos of these figureskaters. No doubt 1/120 will produce twice as many and 1/180 even more usable stills.
The 1/250 I used on the weekend was fast enough so that most of the 5000 frames in each 3 minute routine were sharp enough but I only need a half dozen really good ones and of course the video needs to be as good as it can be so 1/120 it is then,
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