Shooting slow motion footage, especially very high speed shots like 240fps or 480fps, results in flicker if you don’t have high quality lights. Stadiums often have low quality industrial lighting, LEDs, or both. Resulting in flicker during slow motion shots even on nationally broadcast, high profile sporting events.
I was particularly struck by this watching the NCAA Basketball Tournament this weekend. Seemed like I was seeing flicker on half of the slow motion shots. You can see a few in this video (along with Flicker Free plugin de-flickered versions of the same footage):
The LED lights are most often the problem. They circle the arena and depending on how bright they are, for example if it’s turned solid white, they can cast enough light on the players to cause flicker when played back in slow motion. Even if they don’t cast light on the players they’re visible in the background flickering. Here’s a photo of the lights I’m talking about in Oracle arena (white band of light going around the stadium):
While Flicker Free won’t work for live production, it works great for de-flickering this type of flicker if you can render it in a video editing app, as you can see in the original example.
It’s a common problem even for pro sports or high profile sporting events (once you start looking for it, you see it a lot). So if you run into with your footage, check out the Flicker Free plugin for most video editing applications!
One common problem you see a lot is flickering from stadium lights when football or other sports are played back in slow motion. You’ll even see it during the NFL football playoffs. Stadium lights tend to be low quality lights and the brightness fluctuates. You can’t see it normally, but play video back at 240fps… and flicker is everywhere.
Aaron at Griffin Wing Video Productions ran into this problem shooting video of the high school football championship at the North Carolina State stadium. It was a night game and he got some great slomo shots shooting with the Sony FS700, but a ton of flicker from the stadium lights.
Let’s take a look at a couple of his examples and break down how our Flicker Free plugin fixed the problem for him.
First example is just a player turning his head as he gazes down on the field. There’s not a lot of fast movement so this is relatively easy. Here are the Flicker Free plugin parameters from within After Effects (although it works the same if you’re using Premiere, FCP, Avid, etc.)
Notice that ‘Detect Motion’ is turned off and the settings for Sensitivity and Time Radius. Well discuss those in a moment.
Here’s a second example of a wide receiver catching the football. Here there’s a lot more action (even in slow motion), so the plugin needs different settings to compensate for that motion. Here’s the before/after video footage:
Here are the Flicker Free plugin settings:
So, what’s going on? You’ll notice that Detect Motion is off. Detect Motion tries to eliminate the ghosting (see below for an example) that can happen when removing flicker from a bunch of frames. (FF analyzes multiple frames to find the correct luminance for each pixel. But ghosts or trails can appear if the pixel is moving) Unfortunately it also reduces the flicker removal capabilities. The video footage we have of the football team has some pretty serious flicker so we need Detect Motion off.
With Detect Motion off we need to worry about ghosting. This means we need to reduce the Time Radius to a relatively low value.
Time Radius tells Flicker Free how many frames to look at before and after the current frame. So if it’s set to 5, it’ll analyze 11 frames: the current frame, 5 before it, and 5 after it. The more frames you analyze, the greater the chance objects will have moved in other frames… resulting in ghosting.
With the player looking our the window, there’s not a lot of motion. Just the turning of his head. So we can get away with a Time Radius of 5 and a Sensitivity of 3. (More about Sensitivity in a moment)
The video with the receiver catching the ball has a LOT more motion. Each frame is very different from the next. So there’s a good chance of ghosting. Here we’ve set Time Radius to 3, so it’s analyzing a total of 7 frames, and set Sensitivity to 10. A Time Radius of 3 is about as low as you can realistically go. In this case it works and the flicker is gone. (As you can see in the above video)
Here’s an example of the WRONG settings and what ‘ghosting’ looks like:
Sensitivity is, more or less, how large of an area the Flicker Free plugin analyzes. Usually I start with a low value like 3 and increase it to find a value that works best. Frequently a setting of 3 works as lower values reduce the flicker more. However, low values can result in more ghosting, so if you have a lot of motion sometimes 5 or 10 works better. For the player turning his head, three was fine. For the receiver we needed to increase it to 10.
Apple’s iPhone 6 and the Samsung Galaxy S5 both shoot 240fps (or so you might think… 1/8th speed at 30fps is 240fps). Since we make Flicker Free, a plugin that removes flicker that occurs when shooting at 240fps, I thought it’d be cool to do a comparison of the two phones and post the results.
However, there was a problem. The footage from the Galaxy S5 seemed to be faster than the iPhone. After looking into a number of possibilities, including user error, I noticed that all the S5 footage was playing back in Quicktime Player at 15fps. Could it be that the Samsung S5 was actually shooting in 120fps and playing it back at 15fps to fake 240fps? Say it’s not so! Yep, it’s so.
To confirm this I took a Stopwatch app and recorded it with the Galaxy S5 at 1/8th speed (which should be 240fps if you assume a 30fps play back like normal video cameras). You can see the result here:
If the S5 was truly shooting at 240fps, over one second the frame count should be 240. It’s not. It’s 120. If you don’t trust me and want to see for yourself, the original footage from the S5 can be downloaded HERE: www.digitalanarchy.com/downloads/samsung_120fps.zip
Overall, very disappointing. It’s a silly trick to fake super slow motion. It’s hardly shocking that Samsung would use a bit of sleight of hand on the specs of their device, but still. Cheesy.
You might ask why this makes a difference. It’s still playing really slow. If you’re trying to use it in a video editor and mixing it with footage that IS shot at 30fps (or 24fps), the 15fps video will appear to stutter. Also, from an image quality standpoint, where you really see the problem is in the detail and motion blur. As you can see in this example:
Also, the overall image quality of the iPhone was superior. But that’s something I’ll talk about when I actually compare them! That’s coming up next!
Wherein Jim Tierney rants and opines about After Effects, Premiere Pro, Final Cut Pro, and other nonsense