I’ve been remiss. A photographer asked me today how to prevent flicker and I realized I haven’t fully addressed this with a post in the five years I’ve been writing this blog. Flicker is one of the first headaches new time-lapse and stop-motion photographers encounter. It’s a difference in brightness between frames that causes a slight strobe effect throughout the finished video. The good news is flicker is largely preventable and often even fixable in post production. Flicker is caused by uneven light metering in camera, computer software, mechanical problems, changing light, and ghosts.
How to prevent flicker
The easiest way to prevent flicker is to use full manual settings on your camera. Even though light meters are good at detecting proper exposure, they can jump back and forth between exposure settings between shots during time-lapse. You’ll want to lock the lens’ aperture, shutter speed, and ISO. Any of these left unlocked will usually cause flicker. By using manual mode, you’ll prevent the camera from choosing settings that might be good for a photograph but won’t work for time-lapse.
Sometimes it’s just not possible to lock your camera and turn off light metering. In cases where I have to use active light metering, I find it’s important to set my spot metering point on a good subject. The spot metering point is often a rectangular box in the middle of the screen that you can move around to different subjects in the frame. I try to use a matte surface in the midtone range, such as the side of a building without windows or lights. The problem with using the sky is that clear sky will register much differently than clouds. If clouds are floating through your metering point, you’ll likely have strong flicker. Shadows from clouds can still cause flicker but it seems to be lessened by this method. Also remember to cover the eye piece with the little bit of rubber on your camera strap so your light meter gets an accurate reading through the lens. If you can’t move your spot meter, you might try experimenting with averaged metering.
Aperture also plays a strong role in flicker. The narrower the aperture, the more likely you’ll see flicker in the final time-lapse video. I’m not sure of the mechanical reasons but I assume it’s because a small movement of the aperture at f/22 would block out a much larger percentage of light striking the sensor than the same amount of movement at f/2.8. This is one of the reasons I prefer to shoot “wide open” by using the lowest f-stop number available.
HDR processing software is another main cause of flicker. The software blends together two or more photos into one final photo. Because every photo in a time-lapse is slightly different, the software processes the final photos a little different each time. These small changes in brightness between HDR photos have always caused flicker in my final videos.
“Ghosts” is the term I use for any flicker that persists despite my best efforts. There are plenty of times when I can’t shoot at low f-stops or have to use aperture priority mode. I shoot knowing I’ll definitely have flicker and will need to fix it in post production.
How to fix flicker (dealing with ghosts)
If you’re looking for a free solution that also works well, I already have a post about how to use MSU Deflicker with VirtualDub. After Effects also works with several deflicker filter plug-ins. I’ve never used Granite Bay but I know their software has been used by professionals for years.
The main problem with deflicker filters is they can minimize contrast and create a flat image. I find this is more common when I use higher settings to overcome strong time-lapse flicker, which is why capturing photos right the first time is so important. My suggestion is to play with the settings until you’ve found a good balance. You might also look at correcting dullness with contrast correction settings in your time-lapse compilation program.