One common type of flicker in video footage is rolling bands caused by lights being out of sync with the camera. This can be caused by shooting NTSC footage in Europe (for example) but most commonly it’s caused by LED lights, as the refresh rate of the lights conflicts with the camera shutter speed.
It’s the most common type of video flicker that we get asked about. So in this post I’ll discuss using Flicker Free to deflicker the rolling bands in a variety of footage..
You can download Flicker Free here
TL;DR
I’ll go into more detail below but for those that just want to try something quick:
With Rolling Bands, the flicker can be very fast or very slow. So deflickering may require different approaches.
- See if one of the presets fixes the flicker. Usually the default preset should work with fast flickering bands.
- If not, are the bands Slow? Use a higher Time Radius.
- If it still doesn’t work, try increasing Time Step.
- Once the flicker is gone, you may see blurring or ghosting if the camera is moving or there are fast moving objects.
- Use Detect Motion or Motion Compensation (or both) to deal with that problem.
- For very slow rolling bands, Flicker Free may not work.
When the rolling band flicker is slower, you may need to increase the Time Radius or Time Step to increase the time range Flicker Free is looking at. i.e. Time Radius of 7 will look at 7 frames before the frame being analyzed and 7 frames after for a total of 1/2 second of video (@ 30fps). If you increase Time Step to 2, that will double the time range to one second, as it will look at every other frame instead of every frame.
However, the more frames you’re looking at the slower it will render and the more chance for artifacts like blurring, which will require Detect Motion or Motion Compensation turned on (or both).
The above instructions will fix the flicker for a lot of footage but you may need to dive deeper into the settings.
The Flicking Details
Alright, let’s go more in depth.
* Rather watch a video than read? Here are video tutorials for some of the different host apps we support! (or scroll down to read) *
Davinci Resolve Premiere Pro
After Effects Final Cut Pro
Let’s check out Flicker Free.
When using Flicker Free it’s best to start off with the presets. These are great starting points or settings to try on your footage. Since Rolling Bands are the most common type of flicker we see Flicker Free get used for, the default preset is something that usually works. (It’s actually a great starting point for most types of flicker)
Fast Rolling Band Flicker
One thing that can complicate deflickering this type of footage is that the rolling bands can vary in speed. Faster bands are usually easier to deal with. They look worse but because they’re fast moving it’s easier for Flicker Free to figure out what the correct value of a given pixel is. Slower bands are harder and we’ll discuss those in a minute.
Generally the default preset should work pretty well for faster bands.
However if there’s a lot of camera movement or fast objects (dancers, sports, etc) in your scene, the flicker removal may result in blurriness. There are two ways to deal with this: Detect Motion and Motion Compensation. Detect Motion is faster and is the first thing you should try. If that doesn’t work try turning it off and using Motion Compensation. Sometimes you may need both!
For very fast bands you can also try setting Time Radius lower than the default of 8. This can also reduce blurring or ghosting. But it’s rare that a value of much less than 5 works for this type of flicker.
Slow Rolling Band Flicker
The bands can get REALLY slow and Flicker Free can’t really fix extremely slow bands. However for slow-medium speed bands, the default preset doesn’t usually work. What’s usually necessary to fix this type of rolling bands is to look at a larger range of time than normal. That means increasing Time Radius or Time Step or both.
Time Radius
The way Flicker Free works is by looking at a time range. Time Radius sets the number of frames that Flicker Free looks at before and after the current frame. So with a Time Radius of 8, the plugin is looking at 8 frames before, 8 frames after and the current frame. That’s a total of 17 frames… about half second of video.
Time Radius can go up to 19, which will give you about a second and a half of video being analyzed. However, the higher this is set, the more memory the plugin will use and the slower it’ll be. So only set this as high as necessary.
Time Step
However… sometimes even that isn’t enough for very slow rolling band flicker. The new Time Step parameter allows you to set an even wider time range. Time Step tells Flicker Free to skip every nth frame. So if it’s set to 2, it’ll look at every other frame. Set to 3, it’ll look at every third frame. Etc, etc.
If you set Time Radius to 15 and Time Step to 3, the plugin will look at 45 frames back (3 x 15), 45 frames ahead and the current frame… for about 3 seconds of video.
Why do we do this? Basically it saves memory. If we analyzed all 91 frames of video at once it’d probably crash your machine. By doing it this way we save memory, make Flicker Free faster and usually achieve the same result.
You can also play around with these settings! Setting Time Radius to 10 and Time Step to 4 can sometimes be just as effective as setting Time Radius to 19 and Time Step to 2. And it’ll be faster!
The videos above show how all this works on actual footage. They’re only about 5 minutes, so I recommend watching them.
If you’re still struggling, you’re welcome to send us a few seconds of the footage and we’ll recommend settings. Email us at cs@digitalanarchy.com
