ROLLING SHUTTER, WHAT IT IS AND HOW TO AVOID IT
The ability to capture video with our digital cameras is nothing new, but does bring along a unique set of problems that affect your video, commonly known as the “Rolling Shutter” effect. We look at these problems and how to minimize their effects. When we think of cameras and shutters, we generally think of the traditional DSLR shutter that closes quickly to prevent excess light from hitting the film, thus giving you a properly exposed image.
With the advent of digital though, imaging sensors have replaced film, and this brings with it a different set of advantages and disadvantages - some of which are more obvious when we start to take video.
CMOS OR CCD?
There are two main types of sensors used: CMOS and CCD, each with a different approach to the way they collect light.
CMOS sensors generally use what is called a Rolling Shutter method that reads the exposure information line by line. This means information is read line-by-line down the sensor through the duration of exposure. When the entire sensor has gathered enough light, the pixel-rows again terminate in succession, hence giving the appearance of “rolling”.
CCD sensors on the other hand, tend to use a Global Shutter method, in which the entire sensor is activated and deactivated together. There’s no physical shutter that covers and uncovers the sensors, and the entire process is driven by timing.
Both sensor types suffer from their own types of artifacts. CCD sensors tend to suffer from vertical smearing from bright light sources, while CMOS sensors are prone to skew, wobble, and partial exposure because of the way the sensor collects data.