The headline is clearly, in some sense, silly. It’s silly because the usual notion people have of fps is something like video where you need to move your roll of film or read out from your sensor at that rate. The ‘frame rate’ for a photo finish is much more incidental to the way the image is made.
If you have an image from a typical digital camera that is 4000px high formed by a typical two-curtain shutter that shutters in 10ms, you expose 400 rows per ms or, in some silly sense, 400k FPS. If you wanted a 1-pixel high slit to be exposed then that’s an exposure of 1/400000s, which is faster than any camera I’m aware of. But I think the analogy is useful – instead of a shutter moving a slit over the focal plane, exposing different parts of the sensor at slightly different times, imagine the sensor being moved behind a fixed slit and then reading out the values from it. You can reasonably easily imagine doing this with film too – just move it past the slit at a steady rate – not dissimilarly from taking an old-school panorama camera and moving the body instead of the lens.
I think the thing happening here is not a moving sensor but rather a 1 pixel wide sensor (or perhaps a few pixels for colour reasons). This makes it thousands of times smaller than the resolution of the final image so even a fairly typical cmos sensor at 2e9 pixels per second could read 50000 pixel ‘frames’ at ‘40k FPS’. (In practice the number would probably be lower for synchronisation reasons). When your frame is very skinny, that still gives you plenty of resolution.
I don’t like the article because they did some silly arithmetic that produces a big number instead of digging into interesting details, e.g.
- talking about how the system works as a whole (when does it decide to start/stop the image, maybe something about buffering)
- talking about how much light you need and how you get enough
- talking about the optics, how you keep everyone sharp while still getting enough light, how you even focus such a thing
- talking how you make sure the camera is setup fairly (eg perpendicular to the lanes, able to get a good view of all the lanes)
- maybe something about reliability and how you avoid the bad scenario of the system failing when it matters most