Image stabilization
iPhone cameras are surprisingly good at cutting out wobbles — but how?
When cine cameras became small enough to hold in one hand, they began to change the way we recorded family memories, as well as liberating movie directors from the pedestals on which bulky filming rigs were wheeled around. But there was a visible problem: while most could hold a still camera — well, still for long enough to take a photo — shooting moving pictures resulted in what became known as ‘shakycam’.
While the producers of gritty dramas shrugged it off as a style, audiences — including your in–laws — were inclined to grumble that they felt seasick and couldn’t see what was going on. In the mid–1970s, cameraman Garrett Brown invented a counterweighted, bodymounted gimbal system that used tensioned springs to transfer the operator’s movements to the camera without the jitter. Marketed as the Steadicam, it’s now become a Hollywood staple, but a rig costing tens of thousands of dollars and requiring weeks of training didn’t offer much hope for the quality of the average home movie.
Gyroscopic sensors
In the 1990s, SLR camera makers introduced stabilized lenses that used gyroscopic sensors to detect small movements, applying electromagnets to move a lens element to help compensate. Originally designed to prevent blur due to camera shake in still photos, the same technology — generally referred to as optical image stabilization (OIS) — can be used for video, although the results are less predictable. More recently, mirrorless camera makers have begun applying stabilization to the image sensor. Such practices can then work with unstabilized lenses, and allows larger movements to potentially be eliminated once and for all.
Stabilization is described as operating in two to six axes of movement; beyond the three dimensions (or X, Y and Z axes), this refers to handling translational motion — where the camera moves up, down, left, right, backwards or forwards — as well as angular motion, where it tilts, yaws, or rolls. Miniaturized systems like those in iPhones and small drones use servo motors, while bulkier gimbals use smoother, brushless motors.
Electronic stabilization
As digital sensors took over from film, electronic stabilization also became feasible. A camera’s software compares each frame to the last, finding shifts that represent small, unintentional movement or vibration, then shifting the pixels back.
Digital stabilization can’t quite match the results of its optical counterpart, though, unable to prevent motion blur affecting each frame, and larger amounts of movement still produce a rolling shutter effect. In this scenario, the sensor records each pixel in turn, and the time difference between the top left and bottom right of the frame distorts moving objects, creating a wobble ‘jelly’ effect.
Even so, because it doesn’t require any special camera hardware, only processing power, digital stabilization has become commonplace in phones, helped along by digital signal processor (DSP) chips. It’s the reason why clips from your iPhone look a lot steadier than those from old film reels or videotapes. But optical stabilization can do better if included.
First for phone cameras
Nokia’s Lumia 920, released in 2012, was the first phone camera with optical image stabilization, which helped both stills and video. But the 920 was criticized for being big and heavy, and as phones got slimmer and lighter, finding room for physical stabilizers got harder. It was only with the release of 2014’s oversized 6 Plus that the iPhone first offered OIS. Initially this was only optimized for still images, but with the folllowing year’s 6s Plus it was eventually applied to video as well.
Subsequent Plus models and the iPhone X use similar systems, with the iPhone X being the first to have dual OIS, whereas only the wide–angle lens in the 7 Plus and 8 Plus has optical stabilization. One catch is that the OIS system can’t be turned off. Users found that when used with external mounts that eliminate shake, such as a drone or handheld gimbal, Apple’s OIS makes the camera more susceptible to small vibrations rather than less. Some choose to lock the iPhone’s lens in place with a magnet. This could affect the hardware over time but the risk is small.
In 2016, Chinese manufacturer Oppo announced SmartSensor, a system for sensor stabilization in phones that claims to be more precise and energy efficient than lens–based OIS options. We haven’t seen it catch on as of yet, though.