Stop motion flicker: why it happens and how to fix it

What flicker is

Flicker is brightness or colour changing from one frame to the next when it shouldn't. In real time you'd never notice a 2% change. In stop motion, each pose sits on screen for two frames at a time and the eye reads every change, so a tiny shift in exposure turns into a shimmer across the whole clip.

Almost all flicker has one of five causes. Find yours first, then fix that one.

A two-minute flicker test

Lock your set down, record ten seconds without touching anything, and play it back. Then do it again while reaching in and out.

• Flickers with nothing happening: the light or the camera is changing. See causes 1 to 4.
• Flickers only when you reach in: your hands, arms and shadow are changing the light or the camera's metering. See causes 1, 2 and 5.

The five causes

1. Auto exposure

The camera meters the scene and adjusts brightness all the time. When your hand, a dark sleeve or a bright prop enters the frame, the metering changes and the camera brightens or darkens the whole picture. When your hand leaves, it drifts back. This is the most common cause of stop motion flicker. Fix: lock exposure before you start and don't let it re-meter.

2. Auto white balance

Same idea, but with colour. A warm hand or a coloured sleeve can push the camera's white balance, so your white backdrop goes slightly pink then slightly blue. Fix: lock white balance as well as exposure.

3. Window light

Daylight changes constantly. A passing cloud, the sun moving across the sky and even a person walking past the window change your scene over a few minutes. A lock in the camera can't fight that, because the light itself is changing. Fix: close the curtains or blinds, block the window, and light the set with lamps instead.

4. Mains-powered lamps

Cheap LED and fluorescent lamps and dimmers pulse at twice the mains frequency. Your eye doesn't see it, but a camera sometimes does, as slow-rolling bands or a pulse in brightness. Fix: use decent steady lamps, avoid dimmers, don't mix different lamp types, and avoid lights that are running low on battery.

5. You

Your body is between the lamp and the set more often than you think. Your arm throws a shadow, your bright shirt bounces extra light onto the scene and a lamp you bump moves the pool of light. Fix: wear dark, plain clothes, keep your body out of the light's path and make sure the lamps are well away from where you stand.

Bonus: autofocus hunting

It isn't flicker strictly, but it looks like it. If the lens re-focuses between poses, the picture breathes. Lock focus too.

How Unhanded helps

• Locked capture. Focus, exposure and white balance lock when you start recording, which covers causes 1 and 2 and the focus problem. Frame your shot and let the scene settle before you hit record.
• Frames with shadows and arms are dropped. Unhanded's motion check doesn't only look for hands. It also catches arms, shadows and things still settling, so frames where you are casting a shadow over the set don't become poses.
• The sharpest frame of each pose. Rather than taking whichever frame happens to be there, Unhanded takes the one with the most fine detail from the middle of the hold, which avoids soft frames from the end of a movement.

If you searched "Stop Motion Studio flickering"

Users of that app often report exposure drifting even with the lock turned on. We can't tell you why in each case, and we won't promise that Unhanded is immune. Our approach is to lock at capture, then be picky about which frames become poses. We're testing it on real footage before launch, and we'll publish what we find.

Related: how hold detection works and how Unhanded compares with Stop Motion Studio.