Slow LED Light Flickering / Banding / Scrolling - Any fix in HFX?

GreenAcre
GreenAcre Posts: 3 Just Starting Out*

I just installed some new LED lights in my workshop and discovered (in post, after all shots have been done) that there is a slow scrolling discolored band of light in all my footage. This is extremely apparent while playing the clips back at fast speeds (i.e. 500%). Is there a way to fix this flickering / banding / scrolling from my lights in HFX (HitFilm Express)? I've been searching for hours online and not come across anything -- from plugins, comp. settings, handbrake settings with the video files, etc. Here is a link to some raw footage. The first part is at 500%, the second is at 1,000%. You can see the discoloration bands very easily at 1,000%. 

Going forward, I've got to adjust my camera settings to fix the issue, but I'm trying to salvage this project if at all possible.

Thanks!
Sam

Comments

  • triforcefx
    triforcefx United StatesPosts: 1,425 Moderator

    The simple answer? You can’t. Not easily anyways.

    The long answer: This is an in-camera artifact. LED lights flicker at a specific frequency, similar to an LED screen. Just like with older CRTs, you’ll have to adjust your shutter speed (and possibly your framerate) to match the frequency of the LEDs. 

    AFAIK, fixing it would be a monumental task... even Hollywood studios would throw it out and reshoot it, even though they have the budget to fix it in post. In this instance (if I'm remembering the video correctly, it's not THAT bad) I would just post it and leave a note explaining to your subscribers that you know about the banding and will fix it for future videos.

    I'll let other people detail how to fix it if they want, but IMO, it's just a case of learning from experience and doing better next time.

  • Stargazer54
    Stargazer54 Posts: 3,740 Ambassador

    What @triforcefx said.  But matching frame rate with the LEDs might be an impossible task as they may oscillate at a frequency you can't match.  Will just  have to experiment.  First step is to find some data from the manufacturer of the LEDs.

    But as stated it is hardly noticeable.  To get rid of it completely you might consider changing to a different light source.

  • tddavis
    tddavis Posts: 5,171 Expert

    @GreenAcre To add further thought on the issue (and it's probably not an issue) but I wondered if the motor on the lathe wasn't causing some interference with either the LED lights or possibly even the camera as it is electronic most likely.  If you feel froggy and want to experiment, you might try setting up the same set up and start recording without the lathe running and then switch it on just to rule it out.  But I wouldn't make a special effort to try it based on my half-baked theory. :)  It's more than likely the cycles of the lights which I am guessing here in the US anyway are probably at 60 cycles per sec.  It's kind of like when I used a film camera to film the TV screen.  To keep the scan bar away you had to be at 1/60th sec.  Just a thought I had on the matter...

     

  • [Deleted User]
    [Deleted User] Posts: 1,995 Just Starting Out
    edited March 2020

    Hello,

    This is caused by the pulse width modulation of the LED. If it still happens at full brightness it is time to invest in new LED and theyll be very easy to find. Commonly marketed as PWM-free or flicker free (you want full range, 0-100 brightness). 

  • GreenAcre
    GreenAcre Posts: 3 Just Starting Out*

    Thank you all for the helpful information and suggestions! My fix was to adjust my GoPro Hero 8 Black settings from auto-shutter to 1/120th speed. Thank you all for the help!

  • [Deleted User]
    [Deleted User] Posts: 1,995 Just Starting Out
    edited March 2020

    While the pulse width is twice the mains, itll not be usable footage if youre actually using the led to shoot with when and if theres motion. Note that there is a rule for shutter speed which is called the 180 degree rule, in short it means that you want the shutter speed to double the framerate. So if you intend to shoot at 24 FPS, the shutter speed should be 1/48. The 180 degree rule was worked out to work and became the standard for all video because it is the closest you can get to the perceived blur of the human eye, anything else will be noticable, good or bad for the viewer. Now I say good because if youre shooting in slowmo, you want the shutter speed as high it can go, realistically, 120 FPS footage meaning well over 400 shutter speed, because in those scenarios youll want as little blur as possible. 

    Food for thought.

  • Stargazer54
    Stargazer54 Posts: 3,740 Ambassador

    @ArdelleTrulove You are responding to an old thread and your comment seems unrelated to the content. Please respond that you are a real person. And if you have a legit question, please start a new thread.

  • assensy
    assensy Posts: 42 Enthusiast

    The video is duplicated as a new layer and shifted 1 frame back, setting 50% opacity. Another copy is then made at the top and shifted forward one or two frames, setting the opacity to 30%. Sometimes you get it without a third layer.


  • DataDesign
    DataDesign Posts: 638 Enthusiast

    @ArdelleTrulove You are responding to an old thread and your comment seems unrelated to the content. Please respond that you are a real person. And if you have a legit question, please start a new thread.

  • Stargazer54
    Stargazer54 Posts: 3,740 Ambassador
    edited May 11

    @DataDesign Thanks for the assist. This has been dealt with.

    Closing thread.

This discussion has been closed.