Photo Finish Tech Explained

close-bike-race-sprint-finish

Special cameras capture sprints like the one above with perfect accuracy.

We all know that bike races can come down to thousandths of seconds, but how do officials catch such close sprints? We’ve compiled an explanation of the most common timing systems out there to give you a better idea of how your favorite races are being scored, behind the scenes, from your local crit to the Tour de France…

…everything you need to know about the tech side of scoring bike races. Before we get into the pro-level equipment, lets take a look at other systems you may have seen at your favorite races.

Consumer Video

While professional races have moved on to more advanced systems, we still see home camcorders sitting on tripods at finish lines at local events across the country. This can give us an idea of where everyone finishes, but when it comes to accuracy, this system is majorly lacking. Think of a piece of consumer video as a flipbook of still photos. Working together, our brain and eyes can process about 27 different images per second. But when you flash more than 27 sequential photos at someone, the sensation of video is created. Standard NTSC video records at 29.98 frames per second. Sprints are hard to call this way because when paused, the picture is often blurry, because the camera cannot focus and capture consistent clear photos. It may not be noticeable during playback, but when paused, fast moving subjects are often blurry and out of focus.

Chip Timing

Some races use chips like this one to track riders, but the system has some drawbacks.

Some races use chips like this one to track riders, but the system has some drawbacks.

Often times we see chips attached to the riders or bikes, which are read by a computer as the riders cross the line. Chip timing has made great strides in the past few years, but the modern transponder chip timing system has one major flaw; when riders cross the line, the clock stops when the chip physically crosses the line, instead of when the front tire “breaks the plane.” This means that riders are being scored based on when their chip first crosses the line, instead of when their bike first crosses the line. While it is instant and convenient, the margin of error is far too large for bike racing. Too much can happen in one one-hundredth of a second to risk it. Chip timing is mostly used for identification purposes in today’s major races.

High Speed Finish Line Camera

These are the cameras that capture those blindingly fast tour finishes. These high-speed cameras designed specifically to capture finishes tend to be the system of choice, in conjunction with chips, at most major races. But how does it work?

Instead of trying to capture a normal photograph frame, these cameras capture a frame that is only a few pixels wide, just as wide as the finish line. The camera is carefully measured and centered on the line; because of the narrow nature of the frame, perfect alignment is crucial. The high speed camera then shoots up to 2000 of these tiny pictures of the finish line each second, and sends them into a computer for processing and viewing.

Each of these tiny sequential slivers of photos are put into a composite image for the officials to view. Similar to pages in a book or slices of bread, each sliver contributes a small part to the final image, which can be closely examined. Notice the white background, which appears because of the white tape stuck on the ground to represent the line. Because the camera stays narrowly focused on the width of the line, each little photo contributing to the composite had a white background, and we don’t see any of the blacktop in the final picture. Here’s a great example of a finish that may have been missed without the camera.

cycling-timing-system-finish

Every pixel in the photos are captured on the line, then put together into a sequential scrollable image that represents exactly where each rider finishes. Here is a wider view of a finish (click for larger image.) The photo below represents a little under two seconds time.

wide-view-finish-camera-photo2

Because this image is composed of several thousand smaller, time stamped images , we can pinpoint the exact frame where each rider’s tire crossed the line, and score sprints with near perfect accuracy to the millisecond. Ideal setups have two cameras, one on each end of the line, in order to prevent missing any riders because of line of sight issues, and can combine with a chip system to identify riders instantly.

That’s it for today, class. Any questions?

Comments

voiceofreason - 02/09/10 - 4:57pm

Awesome, thanks for the description.
I kinda always wondered.

ryan - 02/09/10 - 5:03pm

Wow! Really cool.

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