Judder demonstration

Judder demonstration

Cassidy Curtis
March 7, 2012

Click inside the box to get focus, then use the arrow keys to change the frame rates. Space bar toggles motion blur.

Processing source code: judder5.pde

What is this?

This is a demonstration of the "judder" or "strobing" effect, which is what you perceive when your eyes try to track a moving object across a movie or video screen. Video and film create the illusion of movement by rapidly displaying an object at different discrete locations, some number of times per second. However, your eyes track moving objects by moving smoothly. As a result, the object's position tends to gradually fall behind where your eyes are looking, and then suddenly catch up when the new frame appears. In film, this happens 24 times per second, which is slow enough to create a noticeable feeling of vibration or "judder".

For this demo, you can play with the frame rate using the arrow keys. Up and down control the actual frame rate of the moving background (within the limits of whatever display device you're using to look at this demo, of course.) Left and right control the frame rate at which the ball gets displayed on that background. Hit the space bar to turn the motion blur on or off.

Does it make you a little nauseous?

It should. That's the point of the demonstration. To see what actual smooth movement would look like, hit the left arrow until the "divider" goes down to 1. That's what looking at an actual moving ball in the real world is like. See how much nicer that is?

This is one of the main reasons why certain filmmakers are starting to shoot movies at higher frame rates. It's also why I like to sit near the back of the theater.

See also these blog posts for some context:
Frames per second
What would 120fps mean for animation?