Calibrate a camera

What calibration means

Calibration sets the difference between a camera's internal time and the actual time of day. You can think of a camera's internal clock as always starting at midnight - so when I start recording, my camera begins at its own "midnight" - and after recording for five minutes, my camera's internal time is 12:05 am.

We need to be able to match people's timing data (which marks the actual time of day that an athlete passes the timing point) to each camera's internal sense of time.

There are a two ways of doing this:

  • Identifying an athlete from the video at the moment that he / she is at the timing point, or
  • Having your camera operator load the website http://time.is on a cellphone and clearly displaying the phone to the camera right after starting recording

Identifying an athlete from the video

Using this approach you'll calibrate the camera by watching its video and pausing it when you can identify an athlete at the timing point. In the simplest case, for a finish line camera you'll know who your race winner was - so you can pause the video when the first athlete is at the finish line and enter his / her bib number in the calibration form.

Risks of relying on this approach include:

  • Your camera operator might not turn the camera on in time to catch the first athlete
  • A volunteer may be blocking the camera when your first athlete crosses the line
  • Your camera may be set up too far away to be sure who is crossing the line

For these reasons we strongly recommend that you use the other method of calibrating: having your camera operator load the website time.is on his / her cellphone and clearly displaying it to the camera right after starting to record.

Calibrating using a cellphone displaying the website time.is

A much more reliable method of calibrating a camera is to have your camera operator load the website time.is on his or her cellphone, then hold the phone up to the camera right after starting to record so that the camera can see what time is being displayed on the cellphone (see image.)

Using this method, when you calibrate the camera in our system you simply enter the hour, minutes and seconds shown on your operator's cellphone in the video and our system knows exactly what the time difference is between your camera and the actual time of day.

Screenshot from cellphone of website time.is

In either case, you'll need to confirm by identifying some athletes at the finish line

The way to know whether your camera is properly calibrated is to see if the timing data and calibration can be used to predict when an athlete will cross the timing point. So whichever method you choose, after setting the calibration our system will show you some screenshots from your video. If the timing data is accurate and your camera is properly calibrated, the screenshots will show athletes at the timing point. You'll need to be able to identify at least one of them; this will confirm that the video from your camera is ready.