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Author Topic: What is wrong with this video? (Red and White stripes)  (Read 2086 times)

Gordon Brinton

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What is wrong with this video? (Red and White stripes)
« on: May 27, 2016, 10:32:06 am »

The camcorder at stage right (guitar player) has red and white bands floating through the scene that don't belong there. All lighting was static/not flashing. I assume that it has something to do with LED light flicker and camera frame rate. However, I don't think that I can change either. I used a JVC Everio GZ‑V500. Lighting was run-of-the-mill cheap RGBW LED stage lights.

https://youtu.be/tU1fp4alJrQ

Any suggestions on how to prevent it next time?

EDIT: The camera was a few feet in front of a speaker, but I moved it around, (beside and behind the speaker,) but the color bands didn't change.
« Last Edit: May 27, 2016, 10:38:51 am by Gordon Brinton »
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Keith Broughton

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Re: What is wrong with this video? (Red and White stripes)
« Reply #1 on: May 27, 2016, 01:49:05 pm »

The camcorder at stage right (guitar player) has red and white bands floating through the scene that don't belong there. All lighting was static/not flashing. I assume that it has something to do with LED light flicker and camera frame rate. However, I don't think that I can change either. I used a JVC Everio GZ‑V500. Lighting was run-of-the-mill cheap RGBW LED stage lights.

https://youtu.be/tU1fp4alJrQ

Any suggestions on how to prevent it next time?

EDIT: The camera was a few feet in front of a speaker, but I moved it around, (beside and behind the speaker,) but the color bands didn't change.
What was the "good" camera with no flicker?
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Gordon Brinton

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Re: What is wrong with this video? (Red and White stripes)
« Reply #2 on: May 27, 2016, 02:56:12 pm »

What was the "good" camera with no flicker?

The other good camera was a JVC Everio GZ-E10. It's a cheaper camera and actually does a cleaner job most of the time.

So, I took out the bad camera, (the JVC V500) after the gig in question and shot some footage both indoors and outdoors here at home. Neither one has any sign of color bands like the music video above and it looks pretty good. The problem must have had something to do with the location (vibration or magnetic) or the lighting (flicker).

When I get time, I'll set up the same LED lights that were used at the band shoot and experiment some more.
« Last Edit: May 27, 2016, 02:59:43 pm by Gordon Brinton »
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Keith Broughton

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Re: What is wrong with this video? (Red and White stripes)
« Reply #3 on: May 27, 2016, 03:09:01 pm »



When I get time, I'll set up the same LED lights that were used at the band shoot and experiment some more.
Good plan.
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TJ (Tom) Cornish

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Re: What is wrong with this video? (Red and White stripes)
« Reply #4 on: May 27, 2016, 03:41:02 pm »

The camcorder at stage right (guitar player) has red and white bands floating through the scene that don't belong there. All lighting was static/not flashing. I assume that it has something to do with LED light flicker and camera frame rate. However, I don't think that I can change either. I used a JVC Everio GZ‑V500. Lighting was run-of-the-mill cheap RGBW LED stage lights.

https://youtu.be/tU1fp4alJrQ

Any suggestions on how to prevent it next time?

EDIT: The camera was a few feet in front of a speaker, but I moved it around, (beside and behind the speaker,) but the color bands didn't change.
That would be LED flicker.  The only real solution is to get better LED pars that are "flicker-free".
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Gordon Brinton

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Re: What is wrong with this video? (Red and White stripes)
« Reply #5 on: May 27, 2016, 04:00:00 pm »

That would be LED flicker.  The only real solution is to get better LED pars that are "flicker-free".

If so, I wonder why the stage left camera didn't have the same problem? Same lights on both sides of the stage. Both cameras were 1920 x 1080, 29 fps.
« Last Edit: May 27, 2016, 04:02:43 pm by Gordon Brinton »
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TJ (Tom) Cornish

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Re: What is wrong with this video? (Red and White stripes)
« Reply #6 on: May 27, 2016, 04:32:08 pm »

If so, I wonder why the stage left camera didn't have the same problem? Same lights on both sides of the stage. Both cameras were 1920 x 1080, 29 fps.
Difference in sensor capture rate under the hood.
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Dave Garoutte

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Re: What is wrong with this video? (Red and White stripes)
« Reply #7 on: May 31, 2016, 09:24:41 pm »

I've spent a fair amount of time experimenting with this issue.
What is important is the frame rate and exposure length of the camera and the PWM frequency of the LEDs.
LEDs dim by turning on and off quickly, not actually getting dimmer, like incandescents.  As you get to 50% dimmed, the square wave light is on half the time and off half the time.

With low frequency (as low as 60hz) each off section can coincide with a camera frame capture, and end up with NO LIGHT!  As the frequencies interact, you get beating, which shows up as flickering or the bands you describe.

The cheapo solution is turning the LEDs full on and using fewer of them, or taping over some of the elements.

The proper fix is to get fixtures that have a very high PWM frequency.  I've measured fixture with frequencies up to 2.5 khz.  These aren't actually flicker free as advertised, but interact with the video cameras as if they were.  Each frame capture has many on and off periods from the LED, so there is never a dark frame.

The true flicker free LEDs actually have a high, randomized PWM frequency, so a pattern never develops to cause the flicker.
« Last Edit: June 01, 2016, 04:06:31 pm by Dave Garoutte »
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Dave Garoutte

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Re: What is wrong with this video? (Red and White stripes)
« Reply #8 on: June 16, 2016, 04:30:33 pm »

I just looked at your video.
The flicker is from the LED interaction, but the waviness is a function of the chip in your camera.
There are two types: CMOS and CCD.
The CCD is more expensive, partly because it sample all the pixels at the same time, and doesn't have the wavy artifact you see in the video, or in other videos, where fast motion distorts straight things into curved things.
A CMOS chip does a progressive pixel scan which results in the curved and wavy artifacts.
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