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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old August 12th, 2007, 05:54 PM   #1
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Flicker Help

Hi, I shot a wedding yesterday and It was flickering while capturing. Another cameraman beside me had the same issue while he was recording. Now I have the tape and its full of the flicker, I think it was because of the LED lighting from above. I tried every mode on my camcorder and even changed the shutter speeds but it would not go. I have uploaded a clip of the movie so you can see what I am talking about, can anybody tell me why this happened and any ideas on how to remove it using something like FCP.

Thank you so much guys.

http://www.shaadihall.co.uk/fcp/help.mov
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Old August 12th, 2007, 07:35 PM   #2
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What shutter speed were you using.
What type of lighting was it?

Looks a bit like the flicker you can sometimes get with fluorescent or other types of discharge lighting, especially with faster shutter speeds
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Old August 12th, 2007, 08:37 PM   #3
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You weren't shooting on auto, were you. I've seen something like this from a DSR250 when the shutter was on auto.
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Old August 12th, 2007, 10:42 PM   #4
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Hi Tariq.........

I'd guess from the style of wedding, and the very even spread of the lighting, in what was, probably, an extremely large venue, that they were using some type of gas discharge lighting.

The only way I know to beat that is to be shooting much, much slower than the flicker rate of the lights, probably 100 Hz. Ergo 1/50 max and even slower if possible.

There is a possibilty that they were using electronic control units which means the flicker rate would be a lot higher, whether it would be high enough to get into range of the ClearScan feature on the camera is debateable, but certainly worth trying.

As for getting rid of it on shot footage, blimey, haven't got the foggiest.

CS
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Old August 13th, 2007, 12:56 AM   #5
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I guess you can get rid of it by using the clear scan function. See page 69 in your manual.

I did not know LED flickers.
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Old August 13th, 2007, 02:45 AM   #6
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Flicker

I had it on auto mode, I also changed the shutter speed to the slowest and it was still flickering. I will try the clear scan. Does anybody know how to fix what I already have?
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Old August 13th, 2007, 07:55 AM   #7
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What was the slowest shutter you used?
Which auto modes did you use?
That shutter data should be in the footage data code perhaps.

With discharge lighting adfn main frequency of 50 Hz, the color variations usually happen is the exposure is shorter than half a cycle of the line (mains) frequency, or not an even multiple of half the line frequency. Thus you may see it in the UK with shutter speed faster than 1/100, but 1/25, 1/50 and 1/100 should be OK. A shutter of 1/120 could present a problem.

How to clean it up in post - good question.
Are there any automatic white balance plug-ins that work at the individual field level? That is, they can be set to individually correct each field or frame by varying amounts to achieve the same end white balance, without having to manually correct each frame?

I've not tried it so I do nto know it if would work, but an alternative might be to go back to the venue and shoot a white card and try use it as a color mask to adjust the overall cast of the image. Might help if the beat between the camcorder and the lighting remains the same frequency as your originl shoot (but that is not too likely).
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Old August 13th, 2007, 09:53 AM   #8
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When I went through it frame by frame, I could see that the flicker caused every other frame to be more reddish, so it might be possible to eliminate the flicker by doing an every-other-frame color balance. That would definitely be time consuming.

Usually if the shutter speed is matched to the frame rate, ie., 1/48 if you're shooting 24fps or 1/60 for 30fps (and the 1/50 rate for PAL's 1/25) there's no noticeable fluorescent light flicker. Were the lights fluorescent or something else?

I wonder if auto iris could have anything to do with it, if the camera was not on auto shutter? Or maybe auto gain? The fact that anything auto was on makes me think that might have been a factor.
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Old August 13th, 2007, 08:39 PM   #9
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One of the things mentioned by Bill was the auto gain.

I shot a little this weekend in a dark environment (with the lighting changing a lot) with auto gain on and saw flickering on the LCD. So I switched off the auto gain, went to manual and my flickering went away.
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Old August 13th, 2007, 08:51 PM   #10
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I had this problem once with the Sony DSR-300 shooting in a supermarket under florescent lighting...unfortunately, I couldn't see anything amiss in the b/w viewfinder (a color monitor would have help; lesson learned). At the time, I couldn't do anything to get rid of it...but with current tools, there might be a way.
Try rendering a deinterlaced version, or doing a time-remapping function (as its called on Premiere Pro). Some sort of frame-blending function might work. You might also try exporting to another format (QT, Flash, etc), then re-importing. Try small chunks as a test first.
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Old August 13th, 2007, 10:12 PM   #11
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In FCP you could copy the track and use the blink filter on the top one, then filter the two tracks to match. Maybe.
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Old September 20th, 2007, 05:11 PM   #12
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Perfect!

Quote:
Originally Posted by Glenn French View Post
In FCP you could copy the track and use the blink filter on the top one, then filter the two tracks to match. Maybe.
You my friend have saved my life! Thank u!
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Old September 20th, 2007, 10:54 PM   #13
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Glad you got it fixed. My guess is that it was caused by shooting on auto. Auto shutter and auto gain can do that, and auto iris and auto white balance can also cause similar problems, but auto shutter is usually the cause. First thing to do when you unpack a new camera like the XH A1 is turn off all the auto stuff.
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Old September 21st, 2007, 04:38 AM   #14
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I'm new to video, so I'm just asking ... would de-interlacing
in post production effectively merge neighboring frames and
hide the flicker (assuming the flicker is in every other frame)?
Is that what de-interlacing does (merge neighboring frames)?

Last edited by Eric Muehling; September 21st, 2007 at 04:40 AM. Reason: Clarification of the question
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