If you’ve ever tried to take video on your phone while walking, you know keeping the image still is tricky. There’s some neat technology designed to reduce that shaky-cam effect, and there are two different approaches to implementing it.

Optical image stabilization comes from the world of still photography, using complex hardware mechanisms inside a lens to keep the image still and enable a sharp capture. It’s been around for a long time, but has been adapted for video and recently miniaturized for smartphones. Digital image stabilization is more of a software trick, like a “digital zoom” but in reverse, actively selecting the correct part of an image on a sensor to make it seem like the subject and the camera are moving less. Let’s take a look at how both of them work, and how they’re being applied in the latest photography gadgets.

Optical Image Stabilization: A Stabilizer For Your Lens

How-To Geek already has an article explaining how optical image stabilization works. But for the sake of completeness, we’ll summarize: optical image stabilization, referred to as OIS for short and also called “IS” or “vibration reduction” (VR, no relation to virtual reality) depending on the brand of camera, is all about the hardware.

A camera lens with optical image stabilization has an internal motor that physically moves one or more of the glass elements inside the lens as the camera focuses and records the shot. This results in a stabilizing effect, countering the motion of the lens and the camera (from the shaking of the operator’s hands, for example) and allowing a sharper, less-blurry image to be recorded. This, in turn, allows photos to be taken in lower light or with a lower F-stop value while still being well-defined.

Canon image stabilization lens

The engineering that goes into this stuff is amazing. It’s a super-tiny version of external hardware like the multi-axis gimbals used on systems such as the Steadicam—those big shoulder-mounted camera braces you may have seen at sporting events or movie sets. The results from an in-lens or in-camera stabilization system aren’t as dramatic as those you get from exterior gyroscopic stabilizers, but they’re still pretty impressive. A camera with a lens featuring optical image stabilization can capture clearer still images at lower light levels than one without, and the same technology can be used to create a slight improvement in the blurry, shaky effect of recording video on a handheld camera. The big downside is that optical image stabilization requires a lot of extra components in a lens, and OIS-equipped cameras and lenses are much more expensive than less complex designs.

Optical image stabilization used to be limited to high-end still and video cameras. But the technology has been iterated enough that you can get it in consumer-level DSLR and mirrorless cameras now. It’s even been shrunken down so that an OIS lens can fit into a smartphone camera module. Yes, that means there’s a tiny, moving glass element in some smartphones that are under half an inch thick. If your phone has an OIS lens, you can hold the top end up to your ear, shake it a bit, and even hear the stabilizing element rattle around in the rear camera module. (Um, don’t do this too hard, though.)

Here’s an example of the tiny OIS element of a phone camera module. Note how the top portion of the lens assembly can move independently of the image sensor beneath.

With much smaller lenses and sensors, the OIS feature on phones isn’t as capable as it is on larger cameras. But it’s still helping you to take clearer photos and less-shaky video. Some notable phone designs featuring optical image stabilization include the iPhone 6+ and later, Samsung Galaxy S7 and later, the LG G-series, and Google’s Pixel 2.

Manual Image Stabilization: Cropping Video To Stabilize It

Digital image stabilization is all done in software. If you’re familiar with the difference between optical zoom and digital zoom (i.e., blowing up the pixels on an image without improving them), it’s similar. But digital stabilization has a much more immediate, measurable effect on video.

To stabilize a shaky pre-recorded video, you can crop out the sections on the borders that are “moving” around on each frame, resulting in a video that looks more stable. It’s an optical illusion: while the video is shaking around, the crop of each frame of the image is adjusted to compensate for the shaking, and you “see” a smooth track of video. This requires either zooming in on the image frame (and sacrificing image quality) or zooming out the frame itself (resulting in a smaller image with black borders that move around).

Patient video editors can do this manually with a finished recording, frame by frame. Here’s a dramatic example on a short shot from Star Wars Episode VII.

This is an exaggerated example of cropping for a stabilizing effect, but it shows how moving the image around the video frame relative to either the subject (the ship) or the background can result in smoother video. Here’s a collection of more typical examples with real-world subjects.

Digital Image Stabilization: Software Cropping Video For You

With the addition of advanced software, computers can apply this cropping-and-moving technique to video automatically. Video editing software like Adobe Premiere, Final Cut Pro, and Sony Vegas can do this, generally achieving the effect by cropping or zooming on a full-sized video a small amount and dynamically stabilizing it frame-by-frame. Here’s an example of an automatic stabilization effect on a video, performed in Final Cut Pro (skip to 3:34 if it isn’t set already).

Just like optical image stabilization, this post-processing software is becoming cheaper and more distributed. It’s even possible to use basic zoom-and-crop stabilization built into some free video services, like YouTube and Instagram. There’s a limit to how much this effect can be applied since it needs to zoom in to compensate for the shaking of the camera without showing black areas on the edge of the video frame. The more you zoom in, the lower the quality of the final video will be. Note that the following video the frame of the stabilized footage (top) is smaller than the full frame of the original non-stabilized video (bottom) due to the crop necessary for the stabilizing effect.

So that’s how image stabilization can be applied to an existing video. Now, combine that moving-and-cropping stabilization technique, a little extra room on a still camera sensor’s pixel grid when taking video, and super-advanced software that detects parts of the image and their motion, and you can do the stabilizing automatically, right as the video is being recorded! That software records the entire image on the camera’s sensor for every frame, automatically senses how the camera is shaking in relation to the primary subject and background and crops the video down to 4K or 1080p size while moving the image around to compensate for the movement of the camera itself.

That’s what “digital image stabilization” means: applying cropping tools to video, automatically and immediately in the camera, without the need for extra software after the video is recorded.

This technology doesn’t need any extra moving parts in the lens mechanism, making it cheaper to manufacture. It’s not as technically efficient as an optically-stabilized lens, because you need more advanced computerized processing to apply the cropping tools in real time. But with the right combination of hardware and software, the effects can be dramatic. Here’s a video of the latest digital image stabilization techniques in the new GoPro 7 series.

Note that the GoPro 7, like its predecessors, doesn’t have any moving stabilization parts in the camera itself, and the video above hasn’t been stabilized with extra software like Premiere or Final Cut. All of that video is taken directly from the camera, with cropping applied automatically to compensate for shaking and vibration. It’s not perfect—it’s not good enough to completely remove the shake from a bike going down a set of stairs, for example, and it puts about a 10% crop on the video frame. But it’s an impressive improvement over a non-stabilized camera, without the expense or time needed for OIS or software-only stabilization. GoPro has had in-camera digital image stabilization since the Hero 5 series, and it’s available on other action cameras as well.

Digital image stabilization can be applied to video on phones, too. Google used a software-only system on the original Pixel (referred to as “EIS” for “electronic image stabilization”), and now most high-end phones have at least some level of digital stabilization applied, explicitly or not. Samsung notes that on the Galaxy Note 8, Galaxy S9 and Galaxy S9+, both optical and digital image stabilization is used at the same time. But there is one big downside to digital image stabilization: unlike an optical stabilization system, it can’t be applied to still images. Since digital image stabilization relies on cropping a series of still video frames, it just doesn’t work on a single one at a time.

Image credit: Canon, GoPro