Anti-flicker not working

[porina]

I take 60fps video in a 50 Hz power grid country. I use auto exposure. The camera has a setting for flicker reduction, and I set it to 50 Hz. How this should work is the shutter is kept open a little longer than standard for 60fps, to capture a half cycle of 50 Hz instead therefore there shouldn't be any flicker. But there is. Quite often lighted signs or other lights in day time show flickering.

 

My guess at this point is that it can't set the shutter long enough in bright light. Maybe I could use a ND filter to drop it into a range it can use. I'd need to research further what the camera limits are, therefore how strong a filter I need. Does this sound about right? I can't be 100% sure, but I don't recall seeing any flicker at night for example.

 

Edit:

Camera is a pocket 3, with fixed f/2 lens and min ISO of 50. Apply Sunny 16 rule that implies a daylight exposure time around 1/3200. There's my problem! I'd need a 5 stop ND to bring that to 1/100. Anyone confirm my maths?

[Jeppes]

Are those lights even ac? At least here almost everything is led:s these days and its pwm controlled if it flickers.

[porina]

5 minutes ago, Jeppes said:

Are those lights even ac? At least here almost everything is led:s these days and its pwm controlled if it flickers.

Shop signs and window decorations, so almost certainly. Some LEDs might boost to a higher frequency, which shouldn't be a problem, but I can't make that assumption for all lights.

 

 

I looked up the official ND filter kit for the camera I have. It comes with 4, 6 and 8 stop filters. I guess 4 could be for cloudy days, 6 for sunny and 8 if... you're looking directly at the sun? [don't do that!] Or just want a bit more creative control.

 

I did try looking for a GND in the past but they don't exist for my specific camera, and it wouldn't be easy to adapt anything for it.

[Electronics Wizardy]

Can you show an example of this flickering? What lighting is in the room that is being used?

 

1 hour ago, porina said:

I take 60fps video in a 50 Hz power grid country. I use auto exposure. The camera has a setting for flicker reduction, and I set it to 50 Hz. How this should work is the shutter is kept open a little longer than standard for 60fps, to capture a half cycle of 50 Hz instead therefore there shouldn't be any flicker. But there is. Quite often lighted signs or other lights in day time show flickering.

 

Does the flickering go away if your shooting at 50/25 fps? What about with a long shutter speed?

 

25 minutes ago, porina said:

I looked up the official ND filter kit for the camera I have. It comes with 4, 6 and 8 stop filters. I guess 4 could be for cloudy days, 6 for sunny and 8 if... you're looking directly at the sun? [don't do that!] Or just want a bit more creative control.

 

Probably get that ND kit here. 

 

[porina]

1 hour ago, Electronics Wizardy said:

Can you show an example of this flickering? What lighting is in the room that is being used?

Outdoors only.

 

https://youtu.be/sUM6pdFsG8s?si=UbLwwhkr2-GAY4DT&t=570 - ice cream shop sign on left

https://youtu.be/9jb6ryAdmpQ?si=lxrLNhIZ2H0kUGlp&t=773 - window "open" sign on food place to right, same on cafe slightly later

https://youtu.be/cCE0ozwaDMo?si=Kt5lwovJh6jDjdVi&t=386 - shop lights on right

 

Lots of instances like this. I also see it in other people's videos doing similar style content.

 

1 hour ago, Electronics Wizardy said:

Does the flickering go away if your shooting at 50/25 fps? What about with a long shutter speed?

Don't think I ever tried 25/50, as archaic TV standards don't really have a place online. As mentioned before I let the camera adjust settings so I have no idea what it chooses. Based on calculations earlier, in daylight I couldn't set longer exposures without massive overexposure. Thinking more about it, the shutter time must be very short as there is practically no motion blur in individual frames. However, if I go to night videos, I can make out a little motion blur and no flickering. This does tend towards confirming my theory I need a ND filter for daytime usage.

 

1 hour ago, Electronics Wizardy said:

Probably get that ND kit here. 

I'll have to research if I should get the first party option or gamble with a cheaper 3rd party one. A possible new problem for me is that I usually use a wide angle adapter which is effectively a filter in itself, so I'd have to worry about problems with stacked filters. I have seen 3rd party "slim" filters previously.

[Electronics Wizardy]

1 hour ago, porina said:

Outdoors only.

 

https://youtu.be/sUM6pdFsG8s?si=UbLwwhkr2-GAY4DT&t=570 - ice cream shop sign on left

https://youtu.be/9jb6ryAdmpQ?si=lxrLNhIZ2H0kUGlp&t=773 - window "open" sign on food place to right, same on cafe slightly later

https://youtu.be/cCE0ozwaDMo?si=Kt5lwovJh6jDjdVi&t=386 - shop lights on right

 

Lots of instances like this. I also see it in other people's videos doing similar style content.

 

That really feels like the pwm on leds. 

 

Get the ND filters will probably fix this issue and you can set a lower shutter speed then, which should help here.

 

[jimm_eh]

First thing to do is to get your shutter angle at 360 degrees.  This means that the shutter is "open" for the entire frame time.  E.g. 1/60 shutter for 60fps video.  So, switch to shutter priority, set the shutter to match your frame rate, and then use aperture, ISO and ND filters to get your exposure.

That way, any PWM flicker that is *higher* frequency, will get averaged out over each frame and will disappear, since the shutter is basically open at all times, and where the "dark spots" land in each frame won't matter.

However, if anything in your scene is flickering **below** your FPS, particularly something like cheap halfwave LED lights or old-style fluorescent lights running directly off 50Hz mains, there's no way to avoid seeing it, because the 50Hz changes in that light source over time are too "big".  Imagine someone just turning a light on and off by hand - that's a frequency of something like 5Hz, and there's no way to hide that from a 60fps sample rate.

The only way to beat that is to "sample" at a lower frequency, also with 360 degree shutter angle - 1/30 shutter at 30fps, or 1/24 at 24.

[porina]

8 hours ago, jimm_eh said:

First thing to do is to get your shutter angle at 360 degrees.  This means that the shutter is "open" for the entire frame time.  E.g. 1/60 shutter for 60fps video.  So, switch to shutter priority, set the shutter to match your frame rate, and then use aperture, ISO and ND filters to get your exposure.

I only figured out yesterday how to see what settings it auto selects. In low light, it does seem to go to 360 degrees. I'll have to do more testing in brighter light.

 

I did buy a ND filter set, but haven't really tried it out yet. A disadvantage of the camera I'm using is I physically can't stack filters, and I often want to use the wide angle adapter which counts as one. I'd have to choose between that and the ND, unless I find other options.

 

Unfortunately no aperture adjustment whatsoever as fixed lens.

 

Quote

The only way to beat that is to "sample" at a lower frequency, also with 360 degree shutter angle - 1/30 shutter at 30fps, or 1/24 at 24.

If I were to go to lower rates, then in theory I only need to use 1/50 shutter to match a single cycle of the power frequency. Alternatively I could shoot at 50fps but it does seem a bit of a mess how computers handle displaying that as most cheap displays may be fixed at 60 Hz, and it could end up a stutter mess.

[AbydosOne]

On 9/15/2024 at 3:59 AM, porina said:

Unfortunately no aperture adjustment whatsoever as fixed lens.

Aperture is f-stop. I think you're thinking of focal length. Unless you're running some really quirky lenses, you almost certainly have adjustable aperture.

[porina]

1 hour ago, AbydosOne said:

Aperture is f-stop. I think you're thinking of focal length. Unless you're running some really quirky lenses, you almost certainly have adjustable aperture.

Look up the Pocket 3 as mentioned earlier. It has a fixed f/2 lens at 20mm equivalent focal length. The only adjustment it has is focus.

 

Getting the ND filters was to try out the below since I can't set the shutter long enough without it:

https://www.red.com/tools#flicker-free-video

 

[jimm_eh]

On 9/15/2024 at 1:59 AM, porina said:

 

If I were to go to lower rates, then in theory I only need to use 1/50 shutter to match a single cycle of the power frequency. Alternatively I could shoot at 50fps but it does seem a bit of a mess how computers handle displaying that as most cheap displays may be fixed at 60 Hz, and it could end up a stutter mess.

If you set 1/50 shutter while recording to a 60fps format, the camera will simply duplicate frames to get the required time for the shutter exposure - so while the file will show as 60fps, the apparent frame rate at playback will be 30fps.  But now that you are fitting a 1/50 second into what is now a 1/30 container, it pushes your effective shutter angle below 360 to around 205 degrees or so, which will likely bring visible moving flicker artifacts back since it's now sampling at 30fps which doesn't divide cleanly into the 50Hz flicker.

If you have the option to drop down to a 50fps format, then you'll get your full 50fps visual look as intended, and you'll have 360 shutter, so no flicker.

Not sure about playing 50fps on a 60Hz display - I run a 60Hz-only display, and back in 2012 when I was into camcorders, some of the sample videos I downloaded were 50fps from European versions of the cameras.  There was a bit of judder on playback, but I barely noticed any issues on my display - it was less noticeable than the "shimmering" you'd see in North America when watching Fawlty Towers or Blackadder back in the pre-HD days;).

[porina]

8 hours ago, jimm_eh said:

If you set 1/50 shutter while recording to a 60fps format

That was a typo, I meant 1/100. It doesn't make sense to have a shutter time longer than the frame rate. As I separately said multiple times otherwise, I need to use 1/100 in 50 Hz power region. If you rectify a 50 Hz sine wave, you get a pattern repeating at 1/100s intervals hence that is the target exposure to eliminate flicker. Or multiples thereof at lower frame rates.

 

8 hours ago, jimm_eh said:

If you have the option to drop down to a 50fps format, then you'll get your full 50fps visual look as intended, and you'll have 360 shutter, so no flicker.

180 degree shutter is the general target. 1/100 at 60 results in 216 degrees which is close enough. Even if I shot in 50, I'd be targeting 1/100.

 

 

Anyway, as a minor follow up, I have been trying out the ND filters. Yesterday was a dull overcast day, I tried the weakest one I have at 3 stops, which was enough to allow 1/100s exposure within the auto-ISO limits. If it was a sunny day I'd have to go to 5 stops according to my earlier calculation. If I pause the video there is now visible motion blur on subjects which wasn't really there without filter. Like with gaming, I don't "see" lack of motion blur, but I strongly dislike excessive motion blur. Video looks fine. I'll have to try and find a spot that has visible light flicker and test more with the filters to verify that it is resolved.

[jimm_eh]

@Porina  I'm glad you got good results with your initial tests. Good luck!

180 degrees is definitely the cinematic look, so I hope you can arrive at something workable.