Help Key: Why 120Hz Video Looks “Weird”

I’ve been testing an HD projector here at the house and, in its initial, out-of-the-box setting we found that the picture was ridiculously “sharp.” The picture, I suppose, looked like an old Dr. Who episode where the action on screen is smoother than the background, creating a jarring disparity when watching movies with lots of movement. It’s sometimes called the “Soap Opera Effect.” We decided to do a little digging to figure out why.

Most film is recorded at 24 frames per second, but your LCD TV probably either displays at 60 fps or 120 hz (hertz is just a measurement of frequency per second). There are three main ways to cope with this.

First is to simply display each frame longer, this is the oldest technique in LCD tech. However, its undesirable side effects include the possibility of motion blur, or of judder. Judder is an artifact of adjusting the framerate and it looks like a sort of stutter in movement that would otherwise be smooth (a slow pan, for instance).

The second technique is one used on Plasmas and CRT TVs. Instead of showing a bright image the whole time, they display the frame, then a short frame of either darkness or a very dimmed picture. This alleviates much of the issue with judder and motion blur as it allows your brain to fill in the gap faster than you can consciously notice. It is also an old technique, and is used in theaters. It provides the traditional cinema feel.