We’ve all been in a situation where the perfect shot is right in front of you, but to get the shot involves getting into a strange position and holding your camera handheld. When you start shooting, you realize that no matter what you do, the footage you capture is always shaky. So what happens now? That’s where Image stabilization (IS) comes in as it is designed to greatly reduce camera shake and vibration. There are two popular methods of image stabilization used by videographers – Electronic Image Stadilization (EIS) and Optical Image Stabilization (OIS) .
Optical Image Stabilization
The Optical Image Stabilization (OIS) system works before the image hits the Image sensor, meaning that no electronic adjustments are necessary and that the image is stable when it hits the chip, completely filling the chip’s entire surface area. This is done by placing a variable-angle prism near the front of the lens to bend the shifted image back center.
The prism is simply a pair of glass plates with a liquid-filled bellows system between them, where the bellows create the equivalent of a glass prism. As the image passes through the prism, the lens reduces or eliminates the image shake by detecting and matching the frequency and size or the amplitude of the shake and then rotating the plates of glass to change the angle of the prism. One glass plate rotates vertically, moving the image up and down. The other glass plate rotates horizontally, moving the image left and right. Similar to the EIS system, the idea is to move the image in the opposite direction from the shake, and if there is no movement detected, the prism mechanism simply centers itself.
Cameras with optical image stabilization typically also feature a gyro-sensor built into the camera to negate camera shake. The sensor measures any movement from the videographer and sends its measurements through a stabilization microchip to the Image sensor, which then shifts slightly to compensate for the movement. This type of correction is the most precise form of image stabilization, as it does not require increasing the ISO sensitivity, which can compromise the image quality. Best use of OIS is in low light Photography.
For best work of OIS check out, how Sony alpha cameras use OIS. Presently they are the best in class.
Pros And Cons Of Using OIS
As OIS systems utilize the full Image sensor area , it is slightly heavier and bulkier than the EIS systems. Also, in theory at least, OIS systems do not respond as quickly as EIS systems because the prism mechanisms have to be physically moved. However, these drawbacks are hardly noticeable when actually using the camera.
Electronic Image Stabilization
The Electronic Image Stabilization (EIS) system reduces image shake and controls image stability by manipulating the image electronically, using the light-sensing chip, the Image sensor of the camera. Once the image hits the chip, and if the system detects what it thinks is camera shake through its sensors, it responds by slightly moving the image so that it remains in the same place on the Image sensor. For example, if the camera shakes to the left, then the image moves to the right to compensate, thus eliminating the shake. Basically, when the image zigs, the EIS system zags, by precisely the same amount.
There are two ways the EIS system works to reduce the movement of the image. The first method is to increase the size of the image by digitally “zooming in on the image so that it is larger than the Image sensor. By making the image larger, the system can then scan within the image to counter the movement created by the shake. To test if your camera utilizes this system, simply turn it on and watch the image through the viewfinder. If the image zooms in slightly, then it is using this method of image stabilization. However, because this system zooms in on the image, the image resolution is somewhat decreased.
The second method of the EIS system uses of an oversized Image sensor. As a video image covers only about 90 percent of the chip’s area, there is system space available for which to move the image. For example, when the image is stable, the chip centers the image on the Image sensor. But if the camera shakes to the right, there is space for the image to roam back to the left to compensate for the shake, keeping it in exactly the same place on the Image sensor, thus eliminating the shake.
Pros And Cons Of Using EIS
EIS systems are compact because they do not add any bulk to the lens, and fast because there is no need for any physical movement, as all the heavy lifting occurs electronically at ultra high speeds. On the down side, as the video image occupies only 90 percent of the Image sensor, when the image is electronically magnified to fill the remaining 10 percent of the frame, there will be an inevitable loss of image quality and resolution.
What Makes EIS Better?
Because the lens doesn't move with EIS, the process of capturing each frame in your video is never slowed down by mechanical parts. EIS only need to adjust the image, resulting in a much smoother video.
Additionally, EIS systems have the ability to predict the shift of the next frame, making a huge difference in the quality of the video. While moving, the camera is determining the direction you are moving, and if it determines you're moving in a single direction (such as you panning the camera across an object), it can adjust the next shift accordingly. This allows for a much smoother video.
According to Google, when the Pixel's team had to decide between OIS versus EIS for the first Pixel, they agreed on EIS because of its video performance. According to Google's camera product lead, Isaac Reynolds:
"EIS and OIS have very different goals, so you can't compare them to ask which is better/worse. OIS primarily improves low light photography by physically compensating for hand shake within each single frame, and EIS improves shaky video by maintaining a consistent framing between multiple video frames. OIS is primarily for photo, and EIS is only for video."
While Google did add OIS in the Pixel 2, it was able to achieve fantastic stabilization with just EIS on the original Pixel thanks in part to their algorithms. This leads to another advantage of EIS, its ability to get better over time with software updates. Since algorithms are what determine how the system compensates for specific movements, as OEMs capture more data, they can improve the feature.
