Ken Burns effect

The technique is older than the name. Filming a photograph and moving the camera slowly across it, closing in on a face or drifting from one edge of a crowd to the other, is how archival material has been cut into documentaries for as long as there have been documentaries. It carries the name of the American filmmaker Ken Burns because his series leaned on it so heavily that the move became his signature, and Apple then shipped a feature called after him in iMovie, which is how a director’s habit became a checkbox.

On the web it is one CSS transform. A picture is cropped by a container with the overflow hidden, and the picture itself is slightly larger than the crop and animates between two transforms, so the visible region drifts and tightens. Because it is transform and nothing else, it is one of the few decorative effects that costs almost nothing to run: the compositor can carry it while the rest of the page gets on with its work. Hero sections, slideshow slides, and the still frames between video segments are where it turns up.

The craft is entirely in restraint. One direction, not two. A zoom of ten or fifteen percent over eight to twelve seconds, not a march across the frame. Linear timing, because a drift that eases is a drift the eye can see starting and stopping, and the whole point is that the motion should be noticed only in the sense that the image feels alive. The crop has to be chosen around the focal point of the picture, so that the tightest moment lands on the face or the horizon rather than on somebody’s elbow, and the source image has to have the pixels to spare, or the ending is a soft one.

It is also an effect with no information in it, which makes the accessible answer simple. Under a stated preference for reduced motion the picture holds still, at a crop that was composed to be looked at rather than at whichever frame the animation happened to reach. Not slower, not shorter: static. Nothing was being said by the movement, so nothing is lost by removing it, which is a rarer and more comfortable position than most motion decisions get to be in.