Digital cameras use a 1-dimensional array sensor to take 1-pixel-wide sequential images of the finish line. Since only a single line of the CCD is read out at a time, the frame rates can be very high (up to 20,000 frames per second). Unlike a film based photo finish, there is no delay from developing the film, and the photo finish is available immediately. They may be triggered by a laser, photovoltaic means, or even motion sensing done within the photo finish camera.