rolling bands in image at night

K

kolbasz

Pulling my weight
Jul 27, 2020
205
103
America
so, when the weather was warm, my night images were normal. now that the weather cooled, I was reviewing footage and I see these rolling bands vertically in the image. they roll left to right. camera is a 5442

I have no idea if it is temperature related, but I wanted to make it known. looking at day time images, it does not seem visible. This is in blue iris and also directly on the dahua

Edit : perhaps I figured out the cause. I recently added some up lights at the front of the house and it seems this coupled with a shutter speed of 1/500, results in the banding.

When I disable the illuminator, switch to color and drop the shutter to 1/100, the bands go away.

So while I don't totally get it, seems my issue was self inflicted and perhaps it is resolved now.

1607661811509.png
 
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Does it only happen when you have the new lights on? Is it frequency matching that of the lights that you installed (LED?)? You'll see similar effects in that case. Can also try changing the cam to run from 60Hz to 50Hz (or vice versa) and see if that changes things. If so, then that's what it is.
 
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POE or DC (bad) input?
If DC, is it really stabilized ? not a old (heavy) transformer without stabilizing circuit.
 
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The light output from LED lights isn't totally constant - it fluctuates at twice mains frequency.
The human eye does not notice that.
So when you are sampling an LED-illuminated image with a camera that's using a framerate that 'beats' with that frequency, the result is illumination that varies across the frame, with what look like bands of varying brightness that will roll or be static depending on the relative frequencies.

You'll see the most variation of the interaction if you change the framerate as opposed to the exposure time.
 
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alastairstevenson said:
The light output from LED lights isn't totally constant - it fluctuates at twice mains frequency.
Click to expand...
Just out of curiosity I tested the LED lights in the room where I'm sitting.
The illumination doesn't vary a lot - just about 8% (0.5 of a division in 6.5, with zero light at the bottom of the screen) at a 100Hz frequency, 50Hz mains.
PC110302.JPG

But even that is enough to create noticeable banding that's visible on a uniform surface.
The framerate was set at a low 10fps to give multiple bands on the captured image.

Screenshot from 2020-12-11 17-02-42.png
 
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I see that effect with fluorescent, mercury vapor/high pressure sodium and LED. The cure is to adjust the shutter speed.
 
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Mike A. said:
Does it only happen when you have the new lights on? Is it frequency matching that of the lights that you installed (LED?)? You'll see similar effects in that case. Can also try changing the cam to run from 60Hz to 50Hz (or vice versa) and see if that changes things. If so, then that's what it is.
Click to expand...
seems to only happen when I have shutter priority at 1/500. As I played with it and the settings, when I got to 1/100 I no longer see them.

Also, I do not see them on the daytime image
 
alastairstevenson said:
The light output from LED lights isn't totally constant - it fluctuates at twice mains frequency.
The human eye does not notice that.
So when you are sampling an LED-illuminated image with a camera that's using a framerate that 'beats' with that frequency, the result is illumination that varies across the frame, with what look like bands of varying brightness that will roll or be static depending on the relative frequencies.

You'll see the most variation of the interaction if you change the framerate as opposed to the exposure time.
Click to expand...
that would explain why as I lower? (1/500 to 1/100) the bands seem to go away
 
It would appear that 1/500 is some multiple, beat frequency, of the light source. What is the source of the ambient light in the scene?
 
We know LEDs are actually switching at either 60 or 120 Hz. The same is true of street lights but I suspect they all switch at 60 Hz. That would mean any multiple, even a close multiple, would have that banding/flicker effect.
 
Need a 30 second video of the problem.

I have seen the banding problem when there are multiple light sources that are on difference phase of the power source.
 
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Its POE then its a "clean" powersource so its influenced of other things.
If you somehow increase your lightning and switch to longer exposure then you solve the problem as you already tested.

If you dont wan't to be seen of the illuminator, use 940nm IR light that is not visible to the human eye.
There is some redlight component of the 850nm, seen as a glow effect.
And be aware of that 940 is less efficient than 850, both by emission and sensisitivity of the sensor.

See the tests of IR illuminators that's in the forum of Accessories, very informative !
Never trust the sellers !
The only reliable could be Tendelux, I have none but the next one will be.

Brgd TheSwede
 
I get the same thing but my 'bars' are horizontal. This is 60Hz flicker (noise) from the street light when the shutter speed is not in sync with the AC. In this example I am running at 1/500. If I set the anti-flicker to 60Hz, the GUI sets the fastest speed to 1/120.



1607741156653.png
 
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Set the anti-flicker to whatever the power frequency is in you country (60 Hz in US). This tries to sync the shutter to the light flicker described above. It may help to set the camera to Even fraction of 60 Hz. I found the worst flicker was caused when I had wide dynamic range enabled.
 
I get the same issue with my LPR camera at night. There is a street lamp located near where my LPR is located. I chaulked those rolling bands up as some type of framerate/light flicker issue. I just ignore it. Mine are much slower however that what @samplenhold just showed.
 
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