The Difference between Rolling Shutter and Global Shutter

In Understanding camera shutters and the shutter angle, we learnt there are two fundamental types of shutters relevant to the video industry:

  • Electronic Shutters
  • Rotating Discs

Rotating Discs are less common, and will probably be phased out completely, simply because their advantages can be incorporated into electronic shutters.

Global Shutter

Today, there are two fundamental types of electronic shutters:

  • Global Shutter
  • Rolling Shutter

Traditional film cameras have rotating discs, and each frame is exposed whole. Such a frame is called a progressive frame.

A global shutter captures a frame whole, exactly like a good film movie camera rotating disc shutter does. All the pixels are read at the same point of time, so we have a whole frame.

The ideal global shutter doesn’t exist, just as the ideal rotary disc shutter never existed. However, electronic global shutters have the potential for the greatest accuracy and uniformity across the frame.

For this reason, many people categorically proclaim every camera must have a global shutter. That’s baloney. It’s like saying all cameras should be black in color.

Rolling Shutter

A rolling shutter is an electronic system that scans lines (rows) of pixels, similar to how NTSC/PAL television scanning occurs.
Rolling Shutter Illustration

Look at the above image. Imagine each orange box is a pixel, and our image is made of only three pixels. As our hero climbs the stairs, the pixels are read one at a time, thereby causing a lag in the final frame.

Don’t let the simplicity of my example fool you. Rolling shutters are more complicated than this, and can be so designed to approximate global shutters.

The Rolling Shutter system follows television scanning systems in essence, and is quite useful if your camera is shooting interlaced broadcast television.

On the other hand, most people today prefer capturing in progressive frames, to emulate the film look, whether they know what that is or not. Therefore, it has become a general demand that electronic rolling shutters be confined to history. Here are some weird artifacts that might be caused by the rolling shutter:

  • Jello Effect
  • Skew
  • Smear
  • Exposure changes

 

Jello Effect, Author: Jonen
Skew Effect, Author: Axel1963

Which is better: Rolling Shutter or Global Shutter?

Usually CMOS sensors use rolling shutter systems while CCDs use global shutters. However, this is not universally true. There are CMOS sensors with global shutters and CCD sensors with rolling shutters.

Furthermore, there are different types of rolling shutters, and just because some technologies produce undesirable results doesn’t mean the system or methodology is bad.

E.g., a lot of people think the rolling shutter is bad. Most of this is due to misinformation from idiots who don’t understand the science and technology behind it. In fact, there are many situations where a rolling shutter will give a more filmic look than a global shutter!

Stay away from anyone who proclaims a technology is good or bad by itself. The simplest thing to do is forget about technology, and test for yourself. This is why I’ve included the video in this article. A painter won’t start creating a masterpiece with an untested brush recommended by an expert, so why would a filmmaker do the same?

After all, modern cameras are a lot more complicated. Soon we will reach a point where the technology is so beyond us (like computers, airplanes, medicine, etc.) that we will be forced to test. Get used to it.

3 replies on “The Difference between Rolling Shutter and Global Shutter”

  1. You say that in some situations rolling shutter can be better and more “filmic” than global shutter. What is an example of such a situation? Are you speaking of low light shooting where rolling shutters tend to do better?

Comments are closed.