Posted by: George Hall
Video image stabilization is an important feature of contemporary still and video camera lenses. Image stabilization or “IS” for short is accomplished in the lens of the camera. It works by reducing the effective area of exposure of the imaging sensor(s) in the camera by 10-15%. If the camera shakes while recording, the camera uses that 10-15% border area to smooth the image. IS is popular for handheld work. We use IS for tripod mounted shots that require a medium to long focal lengths. IS is perfect for eliminating jitter commonly found with tripod mounted shots where the floor the tripod sits on is not solid or in live environments where the press shows up and knocks your gear around. There are a couple of drawbacks to IS however. The first is that IS stretches the usable pixels in the reduced image size to create the impression that you are using 100% of the available surface area of the image sensor. This reduces the image quality by a small and usually imperceptible amount.
This is fine as long as there is not too much shake. In reality IS will correct minor vibrations. It will not correct long movements such as pan or tilt. If your particular shot has pan or tilt requirements in it you should turn IS off. If you do not turn off IS and you try to pan in a video, bad things happen. When you first start to pan with IS turned on, the lens senses this motion and shifts the image to the unused border area on the right or left side of the image sensor. Once you run out of border area on the image sensor to move to, and as the pan continues, IS runs out of border area and “jumps” ahead to try to re-establish IS. This jump is noticeable in the resulting video clip. The same rules apply to up and down tilt. So those are the basics of how image stabilization works. The only rule you really need to remember is that IS is good for eliminating image jitter. If your shot requires any pan or tilt of the camera then turn off Image Stabilization for that shot.
About the Author:
George Hall Founder/President of VideoSSC. He has over 30 years’ experience as a high technology engineering executive. With significant experience in high performance computing, Military electronics, IP networks and Video Broadcasting. Board member Public Television. An author and frequent guest on technology programs and panels. He holds a BA in mathematics from Hillsdale College.