Motion blur

Motion blur is the streaky smear that appears when an object or the camera moves while the image is being exposed. A real camera’s shutter stays open for a short but measurable moment, so a passing car, a walking person or a spinning fan is recorded along its path rather than frozen in one sharp position.

Why it matters in animation

If every frame of a computer animation is rendered perfectly sharp, movement looks choppy and mechanical. Our eyes expect the slight blur we are used to from film. Motion blur smooths the step from one frame to the next and conveys speed. In architectural animations the camera usually moves slowly, so the effect is subtle, but it makes a clear difference on passing traffic, people and trees moving in the wind.

How it is produced

Motion blur can be calculated physically during rendering, or added later in post-production from a velocity pass. The physical route is more accurate but takes longer; the post route is fast but can break down where moving objects cross in front of each other. In still images it is sometimes used on purpose, for instance on a car driving past a facade, to bring a bit of life into an otherwise static scene. For more on producing animated work, read about architectural CGI and animation.