Steady on the Set: Inside Image Stabilization

Most new camcorders have some sort of image stabilization, either electronic or optical. Image stabilization, as its name implies, helps to stabilize the image and reduce shaky video. While all of us find this a useful tool, most video producers don’t understand how it works. Right beneath your nose, or at least right in front of it, there’s a small miracle going on. Read on and you’ll learn just how this miraculous technology works.

While MTV and The Blair Witch Project have made jerky shots popular, for the most part you’ll want to avoid them. After all, shaky shots tend to make videos look amateurish. But some shaky shots are hard to avoid. No matter how steady you hold your camera, you still might get some vibration into the camera body, which can add unwanted movement to your image.

Like a Rock

Imagine that you are shooting some footage of your family on vacation. The kids are having fun playing and you want to get some shots of them without being too obtrusive with the camcorder. So you’re forced to zoom in a bit to get more intimate with the moment. The only trouble is that the slightest movement of your camera is magnified proportionally with the act of zooming in on the image you’re trying to capture.

This is where an image stabilization system comes to the rescue. Armed with either an optical/mechanical system or a digital/electronic system, your camcorder smoothes out those jerky movements so you end up with smooth video of your loved ones.

Optical Systems

We’ve all seen how light bends, distorting the view of our legs when we’re standing in water. Well, optical image stabilization works using the same principle. Optical image stabilization (OIS) uses a system of servomotor-controlled lenses that physically alter the incident angle that light strikes the CCD (see Figure 1). Simply put, the servos bend the light to follow the movement of the CCD (the shake of the camera). Motion sensors detect camera movement and servomotors squeeze the perimeter of the lens system to keep the light entering the camera square to the CCD, which stabilizes the image by mimicking the movement of the camera. The optical system requires two motion sensors; one for pitch (tilting up and down) and the other for yaw (panning side to side). The motion sensors amplify and process the camera motion signals to determine where and how to move the image. OIS is a more complex and consequently more expensive stabilization system. The OIS option appears only on higher-end camcorders and many consider it to be the more accurate of the two stabilization systems available. Also, since it doesn’t manipulate the video signal itself, as does electronic image stabilization, it doesn’t degrade the picture or introduce artifacts into it.

Electronic Systems

The other more common and less expensive way of stabilizing images in video is through electronic image stabilization (EIS). With EIS, the goal is the same as in OIS-equipped camcorders to simulate a steady image by manipulation, but the means are different. Rather than adjusting the image by physically moving the lens and bending light before it reaches the CCD, EIS systems work by adjusting the image electronically, after it has reached the CCD, essentially reducing the pixels in the viewable area of the image.

Suppose a Mini DV camcorder has 460,000 pixels in its recorded image, for example. When EIS is engaged it will still be recording that original pixel count but the viewable area will be reduced. The pixels will be expanded in the view area to allow the remaining pixels to be used as a buffer zone. This buffer zone is what EIS uses to manipulate the sampled data to stabilize the recorded image. (see Figure 2).

EIS looks at key features in the image and measures the motion across the screen. It then calculates camera movement from that motion and electronically slides the key features of the image into a new position within the frame’s buffer zone.

Since this system does not actually sense the movement of the camera, it must assume and adjust for camera movement based on image information alone. The difficulty occurs when the system tries to differentiate between subject movement and camera movement. Imagine a still image that’s placed into the camcorder’s memory, divided into quadrants and compared with the current image that the camera is sampling. If all quadrants move in the same direction and at the same time then the EIS system assumes camera movement and compensates accordingly. If only a portion of the image moves compared to the rest of the quadrants, then the EIS system deduces subject movement (see Figure 3). Since the viewable pixels have been reduced to allow for the buffer zone there is a loss of image quality.

Wrapping it up

With the proliferation of digital cameras, image stabilization has become a staple among camcorder options. OIS has a significant advantage over EIS in that it does not lose any image data to perform its image stabilization process.

Image stabilization systems have forever changed how most of us shoot video. Although image stabilization systems aren’t meant as substitutes for tripods, lugging around heavy tripods every time you want to shoot video is no longer as necessary as before. Smooth video has become much more attainable, eliminating hurky-jerky video and that awful motion sickness. So the next time you’re shooting, turn on your image stabilizer, your audience will thank you for it.

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