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-   -   heavy strobing (https://www.dvinfo.net/forum/photon-management/511110-heavy-strobing.html)

Noa Put October 2nd, 2012 04:22 AM

heavy strobing
Last weekend I was filming a wedding with a Canon 550d, at the evening reception they had a lot of small spots build in that where LED and each spot had 4 leds. There spots however created a heavy strobing effect in my dslr image.

The only option I had with the dslr was to lower the shutter to 1/40 (I"m in pal country so normally use 1/50 shutter) and my camera was set to 1080p 25p, everything above and below 1/40 shutter made the strobing worse. When viewing my footage the strobing is clearly visible and all throughout my footage. I also had a small handicam with me which displayed the same problem, though a little less. This is the first time in 8 years I have encountered that bad strobing, with my xh-a1 I had a clear scan function which I think should be able to eliminate the strobing effect but my current camera's don't have that option.

Does anyone know of a way to get rid of this effect with a dslr?

Chris Medico October 2nd, 2012 05:23 AM

Re: heavy strobing
I've not seen such a feature on a Canon dSLR. I know my 7d doesn't have anything that would solve that kind of problem.

Warren Kawamoto October 2nd, 2012 09:05 AM

Re: heavy strobing
We've had similar situations with both DSLR and video. The problem is the led light itself. The good ones are a little more expensive, and don't flicker at all. The cheaper ones strobe. The worst are the ones that can change color and dim. Some colors are ok, but as the color changes or dims, it will strobe like crazy. The problem is that there's no way to get rid of it in post, unless you apply a heavy motion blur, but that looks awful!

Zoran Vincic October 3rd, 2012 06:52 AM

Re: heavy strobing
The cause of this behavior is badly designed PWM dimmers in cheap led lights, there's no remedy for that.

Marius Tatarasanu October 3rd, 2012 07:11 AM

Re: heavy strobing
LEDs aren't continuous light. It intermitent. It has a frequency. And if that doesnt fit with your camera settings it will show flickering.

Noa Put October 3rd, 2012 05:10 PM

Re: heavy strobing
Thx for the replies, those type of lights got me a quite worried, there was an area where the lights where not dimmed but the main part of the reception was very dark and the lights where almost completely dimmed.

In the bright area my image was just unusable, big grey stripes running from top to bottom, really ugly, in the dimmed area you could still clearly see the lines but they where much less visible, just imagine if they would not have dimmed the lights, not sure how I would explain that to my client.

I think I will keep my xh-a1 (which has been collecting dust the past months) in my car at all times just in case, that old timer might just save my day when the LED horror strikes hard again. I have not tested it but the clearscan function on the xh-a1 should eliminate the problem.

Warren Kawamoto October 3rd, 2012 07:12 PM

Re: heavy strobing
The problem for me was that the flickering didn't show up on my camera's lcd monitor (EX1), so I didn't realize the problem until I was in post. From what I've heard from other videographers, clear scan doesn't work too well, because it's hit or miss. It definitely won't work at all if the lights keep changing colors, or if there are changes in dimming. Some designers set their lights to automatically cycle colors. If so, some colors will come out clean, and others will strobe like crazy. Today, I warn couples that if cheap LED uplights or DJ lights are used, their video will flicker and there is nothing I can do about it. I already shot a wedding after warning the couple, and their reception was strobing but they accepted it because they were warned ahead of time.

Chris Medico October 3rd, 2012 07:28 PM

Re: heavy strobing
If you have footage you must try to save one of the BCC plugins may help.

Repair Video with BCC Flicker Fixer

Warren Kawamoto October 4th, 2012 12:12 AM

Re: heavy strobing
1 Attachment(s)
I don't know if that BCC plugin would work for LED lights. If you slow down the strobing footage, you'll see that the effect occurs as a "wave" that travels down or up the screen.

Noa Put October 4th, 2012 01:21 AM

Re: heavy strobing
Thx for the link Chris but the the bcc plugin solves flickers which is actually just adjusting exposure, the problem with the strobing is like Warren showed with grey waves traveling down your screen, in my case they where more small dark grey lines (will post a expample later on)
Strange that you did not see it on your ex1, in my case it was on both my dslr and handicam clearly visible, I think I have to include that into my contract so that in the worst case I won't get sued, something like this can totally ruin your footage unless your camera can deal with it. I might go back to that reception where I encountered the problem and ask if I can test with my xh-a1.

Noa Put October 4th, 2012 02:38 AM

Re: heavy strobing
Here an example:

Chris Medico October 4th, 2012 05:47 AM

Re: heavy strobing

Originally Posted by Warren Kawamoto (Post 1756615)
I don't know if that BCC plugin would work for LED lights. If you slow down the strobing footage, you'll see that the effect occurs as a "wave" that travels down or up the screen.

I played around with the plugin some and that is some severe flicker. I got a lot of it out but to keep it looking good it would require some composting of the speaker. It would be a LOT of work to get it looking reasonable.

Noa Put October 7th, 2012 02:06 AM

Re: heavy strobing
ughh... yesterday another wedding where the DJ had a set of LED lights in blue and red with him, luckily I managed to find a workable shutter that reduced the strobing effect to a minimum but I must say this isn't making me happy and I guess these LED's lights will become more common in the future.

Warren Kawamoto October 7th, 2012 08:02 AM

Re: heavy strobing
Noa, what shutter speed did you end up using? With which camera? As for me, I shot my wedding with an EX1 and didn't even see the flicker on the LCD. I went all night without noticing anything wrong. In the sample I posted, the flicker got worse later, when the DJ started cycling different colors. Some colors would flicker fast, others slowly, and some not at all. I also shot many other weddings where LED lights didn't flicker.

If you think about it, LEDs for video, such as Litepanels, don't flicker. I was also told that theatrical stage LEDs don't flicker. My guess is that cheap power supplies in the DJ lights are the cause of the problem. Maybe every videographer here could help each other by noting the brand of DJ and/or uplight LED lights they encounter, and posting results of whether they flicker or not.

Noa Put October 7th, 2012 10:42 AM

Re: heavy strobing
I had a canon 550d and a sony cx730 with me, with the canon I had to select 1/40 shutter for best results, I still could see the strobing in the image while filming and like you said depending on the colour the strobing became a bit worse or was better. I also saw the strobing on the small sony, it was a very dark reception and at 21db or 24db gain the strobing was equal, only I noticed when the gain was wide open and when I turned the wheel on the camera just a little bit (which has exposure set to it) I almost could remove the strobe effect. I will have to view at the footage in camera to see what setting I was at exactly.

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