Line-scan camera systems

A line-scan camera has a single row of pixel sensors, instead of a matrix of them. The frames are continuously fed to a computer that joins them to each other and makes an image. This makes possible sharp pictures of objects that have passed the camera at high speed. Sporting races commonly use this kind of camera to make photo finishes, i.e. determine the winner when multiple competitors cross the finishing line at nearly the same time. These cameras can also be used as industrial instruments for analyzing fast processes. A photo finish occurs in a sporting race when multiple competitors cross the finishing line at nearly the same time. As the naked eye may not be able to discriminate between which of the competitors crossed the line first, a photo or video taken at the finish line may be used for a more accurate check. Finish line photos are still used in nearly every modern racing sport. Although some sports use electronic equipment to track the racers during a race, a photo is considered the most important evidence in selecting the winner. They are especially important during close races, but they are also used to assign official times to each competitor during any race. Strip photography Photo finish cameras typically use strip photography, in which a camera is aimed at the finish line and captures a sequence of very narrow vertical images. These strips are arranged horizontally to show the state of the finish line over a period of time (including anything that crossed it)

In the final composite image, every part of each racer's body is shown as it appeared the moment it crossed the line. The horizontal position represents time, and time markings along the bottom of the photo can be used to find the exact crossing time of any racer. In a conventional photograph, the image shows a variety of locations at a fixed moment in time. Strip photography swaps the time and space dimensions, showing a variety of times at a fixed location. The final image often shows a solid white background, which is a continuous scan of the painted finish line. Racers may appear distorted based on the movement of their limbs and heads as they cross the line. [edit]Film Historically, this process was performed using a special slit camera, which used a single vertical slit instead of a shutter. Film was advanced continuously at a similar speed to the racers' images, creating a view of each racer as he or she passed across the slit. Originally, the film was cranked by hand, resulting in distortions of length but still preserving the order of finishers. [edit]Digital 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 10,000 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 or photovoltaic means.