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reducing flicker for stop-motion animation and time-lapse photography

[Today's post is by Benjamin Markus, who is working with us as an intern this summer.]

If you’ve ever tried your hand at stop-motion animation or time-lapse photography, chances are you’ve run into the common problem of inconsistent lighting or luminance variation between consecutive pictures taken on the same camera, with the same lens and settings. This issue is usually referred to as flicker.

There are many causes of flicker, including–but not limited to–auto camera settings, the type of lens used, high aperture settings, fast shutter speeds, Av stepping, Tv stepping, natural lighting changes, incandescent and fluorescent lighting, fluctuating electricity, clothing worn while animating, and the materials that are being photographed.

This article provides solutions for reducing flicker, both during shooting and in After Effects.

manual fix in After Effects

Here’s a fix based on advice given by Dave LaRonde. It takes time, but it’s a sure-fire way of fixing every frame.

1. Go through the footage frame by frame. Find the first flicker frame.
2. Duplicate the layer, and on the duplicate, find an adjacent frame with no flicker.
3. Make the duplicate 1 frame long, put it above the original layer, and move it in time to cover the flicker frame.
4. On the first layer, create a feathered mask around the area(s) that received the flicker in the bad layer. If the shot moves, reposition as necessary.
5.Repeat the steps above until you’re done.

using Color Correction effects built into After Effects

Depending on the shot, you may be able to use Color Stabilizer effect, but if the camera is moving or there’s a bunch of movement in the scene, the Black Point and White Point will change and you’ll have to animate it using keyframes. The effect works by setting points on the screen that you wish to stabilize. Setting the sample area to sample more pixels will help. Then keyframe the positions of the sample points based on the movement in the scene. The idea is to pick the most stable regions in the shot.

Use a combination of Auto Color, Auto Levels, and/or Auto Contrast from the Color Correction effects category. Start off with Auto Levels. If that doesn’t work, try Auto Color and Auto Contrast.

third-party plug-ins for After Effects

camera settings

Make sure that all auto settings on the camera body and lens are turned off and set to manual. Any auto settings, such as auto-exposure, auto white balance, and light optimizer will usually cause luminance variations from shot to shot.

Use a slower shutter speed. Fast shutter speeds are also a common cause of flicker. For example, DSLRs cannot really be consistent from frame to frame when shooting at extremely fast shutter speeds. Instead, use an ND filter to compensate and keep the exposures to 1/30th of a second or greater.

For time-lapse photography, use a constant Av value and a bulb exposure if possible. This will help to prevent Av-stepping or Tv-stepping, which is a 1/3-stop jump in the iris or shutter speed that often happens while shooting from sunrise to sunset during an Auto Ramp time-lapse. Since bulb exposure times can be set with a precision of 1/1000 of a second, it’s possible to produce more gradual changes and reduce flicker.

Using auto-focus will not cause flicker, but it will most likely cause differences in the focal plane depending on the depth of field and movement within the shot, resulting in a different and potentially more severe problem. For stop-motion animation, it’s especially important to control the focus manually.

the lens

More often than not, the camera lens is what causes stop-motion flicker. Most modern lenses communicate with the camera body to assist the photographer in setting focus and exposure. Stop-motion flicker, often found in animation and time-lapse photography, usually occurs because the lens is wide open until the shutter or depth-of-field preview button is pressed. At this point, the lens stops down to take a picture or preview the depth of field. However, most modern digital cameras control the aperture of the lens from the camera body. And, since the camera controls the aperture mechanically, friction causes minute differences in the exact size of the aperture as the iris blades close each time a photograph is taken. Therefore, there’s a possibility for minor variations in luminance from shot to shot.

It’s very important to know each of your lenses. For instance, a Canon 16-35 II probably shouldn’t be stopped down past f/5.6. At f/16, most 16-35s will flicker. But, a Canon 50mm f/1.2 might start to flicker at f/4, if the iris is dodgy. There are general guidelines about not stopping down too far, but each copy of each lens has its own limits.

Any lens with a manual aperture ring should solve the problem, by keeping the iris blades in the same position for the entire duration of the stop-motion shot or time-lapse. Manual Nikon prime lenses (AKA fixed or hard lenses) with Canon EOS adapters have become the favorite of many stop-motion studios. However, the adapters vary in quality. In order to preserve the integrity of the lens and ensure its security on the camera body, it’s important to purchase a sturdy adapter that also focuses to infinity and allows manual aperture control.

Novoflex makes a very sturdy traditional adapter for Nikon G lenses to Canon EOS bodies, but they’re quite expensive.

Leitax is another company that makes custom adapters for all kinds of lenses at a slightly more affordable price. These adapters come in kits that you have to manually attach to the back of your lens using a custom set of screws, but the upside is they’re incredibly strong.

If you’re not in the market for a manual aperture lens and/or an expensive adapter, you can trick the camera body into cutting the communication with your lens by putting a piece of masking tape over the contacts on the rear element of the lens. However, this will just keep the iris permanently wide open. If you want to lock the aperture at a more closed down f-stop, follow these steps:

  1. Set the aperture on the camera body using the digital controls.
  2. Press the depth-of-field preview button (usually below the lens on the front of the camera body) and un-mount the lens while holding the button.
  3. Cover the lens contacts with tape (any kind that’s thin and won’t leave a residue or gum up the contacts).
  4. Reattach the lens without accidentally peeling off the tape.

The downside is these steps must be followed each time you want to change the aperture. The upside is that shooting stop-motion or creating a time-lapse usually takes quite a long time so the aperture won’t need to be changed quickly or very often.

Another issue to be aware of is that once your lens ceases to communicate with the camera, it also ceases to communicate with any frame-grabbing or stop-motion software. If you use Dragon Frame or Dragon Stop Motion, you may have to adjust the “Exposure Preview Offset” setting in the Cinematography window to match the live view exposure to the final shot.

Conversely, many people play footage back in their frame-grabbing software using the live feed, which uses an auto exposure adjustment. The live feed usually flickers, so footage should be checked using the high-quality files captured from the camera. Both Dragon Frame and Dragon Stop Motion have the ability to play back the high-quality frames within the program. But, in order to be absolutely sure that there’s no flicker, it’s usually a good idea to render out those high-quality files using a lossless codec and inspect the video at the correct frame rate and highest quality.

electricity levels

If you have a fixed aperture lens or you’ve taped off the electronic connections between the camera and lens, and you’re still getting flicker, then it’s possible that electricity fluctuations are affecting your lighting set up over the course of the shot or throughout the day. In this case, a variac transformer will work wonders. They can range from very expensive to very cheap. It all depends on how big your set up is, how many lights your using and how much control you want.

lighting

Make sure that all of the bulbs in your lights are functioning properly. Bulbs often pop when the lights are turned on, so it’s a good idea to test all of them before shooting each day and watch for any dimming issues. This is an especially good idea if you plan on using more lights for another setup later on in the day. Hot light bulbs used in Mole Richardson lights tend to dim before they’re about to blow. Sometimes, the bulbs themselves darken, so you can visually see if they need replacing.

LED light panels are also great for both stop-motion and time-lapse photography. It’s true that LEDs flicker, but the rate at which they flicker is usually imperceptible to the human eye. Non-rectified LEDs, such as cheap Christmas lights, flicker at 60Hz, which is more likely to be noticeable, whereas rectified LEDs flicker at 120Hz, which should be virtually unnoticeable. The upside to using rectified LEDs is that they’re 30-40% brighter than non-rectified LEDs. The downside is that they’re less efficient. However, LEDs are still more efficient than most other light sources on the market.

If you’re using cheap fluorescents other than Kino Flos, or other non-flicker fluorescents, it’s a good idea to shoot at a very long exposure. Fluorescents constantly flicker, but usually a 1-2 second exposure should keep the images balanced.

Last, if you’re shooting in a studio, make sure that no light from outside–no matter how small–is polluting your shooting space. Also, make sure that all gels, screens, or other objects in front of the lights are tied down properly and not moving around due to airflow issues, such as a ceiling fan or a bouncing c-stand arm.

clothing

Wear dark clothing. Most stop-motion animators wear entirely black outfits while shooting to reduce the risk of light reflecting off their clothes. This may sound silly, but it’s actually a very common cause of stop-motion flicker. Also, black duvetyne is a highly opaque fabric commonly used in film studios for blocking and absorbing light.

sets, objects, and puppets

Know the limitations of the sets, objects, and puppets you’re shooting. Porous materials such as wood and foam are affected by moisture, and therefore they may expand or shrink depending on the weather and the time of day. This won’t necessarily cause flicker, but it can cause unwanted movement, which might be mistaken for flicker at first glance.

Also, watch out for highly specular materials that might be lying around or hanging on the walls of the shooting space. Mirrors, metallic objects, or pieces of Mylar left by a previous animator may be the ultimate cause of unwanted flicker.

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Thanks for those great tips!

Well written, excellent article.

You suggest using a variac transformer if the electricity fluctuations are the issue that may be causing flicker when you animate. But when I talk to people at electronic stores, they say that a variac transformer would not likely fix variations in luminosity of my bulbs. They say it only outputs the voltage you put in. In other words, if the power fluctuates going in, it will continue to fluctuate coming out. Do you have experience with a Variac Transformer for these purposes or is this something you have heard of second hand?

Thanks!

    if its a good enough transformer its output should remain the same regardless of the input voltage differences. The transformer should account for this in its electrical design with various electrical gismos that work the voodoo, but i would say transformers of this standard are pricey.

    By far the cheapest way to deal with flicker is to have longer exposures which essentially averages the luminescence variations, just get good white balances before shooting.

    Post flicker correction is a nightmare and time consuming.

Sorry for the confusion. You are right. A variac transformer will only output the same voltage you put in. Actually, the most common use of a variac transformer in stop-motion is specifically for animating the flickering of a light to achieve a specific lighting effect such as firelight, lightning or a flickering television.

Of course, if you’re starting a new take then a power fluctuation might not be a problem, but if you’re in the middle of a stop-motion shot and you go to lunch or leave the shot and come back the next day only to find a slight shift in the exposure or color temperature, you could use the variac to correct this rather than fiddling with the exposure and white balance settings in the middle of your shot.

However, there is a device called a voltage regulator that regulates all power that goes through it to match the exact voltage you dial into it. My understanding is that voltage regulators can be pretty pricey and they’re not really used even in the highest budget stop-motion productions.

I’ve heard that even at Laika all the camera operators just shoot Macbeth charts before each shot, and after taking all other necessary flicker precautions, any residual flicker caused by power fluctuation is simply fixed in the color correction and color timing stages of post production.

I hope this answers your question,

Ben

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