Photo Finish Tutorial
540►Get Photo Finish on Google Play: https://play.google.com/store/apps/details?id=com.ultrajuicy.photofinish
►Website: https://photofinish-app.com/
This Tutorial explains how to set up and connect phones to build a fully automatic timing system with our app photo finish.
FAQ:
►What is Photo Finish?
Photo Finish transforms android smartphones into a precise, fully automatic timing system optimized for track and field. Future updates for other sports (i.e. motorsports) are planned and will be announced.
►What is the advantage of a Photo Finish Pro subscription?
Measurements with a single smartphone can be performed for free with Photo Finish. If you want to connect several devices in Multi-Session mode to measure e.g. 30m flying sprints or sprints from the starting block, you need a Photo Finish Pro subscription. If you want to try it out, go ahead! The first 14 days are free! If you cancel within the trial period, there are no costs at all. Furthermore, in a Multi-Session, only the mobile phone that creates the session needs a Pro subscription. So you can connect as many devices as you like with just a single subscription!
►What are the technical prerequisites of Photo Finish?
For Single Session Mode, you just need your Android Smartphone. In Multi-Session Mode, all connected phones need an internet connection (since wifi is mostly not available at the track, you likely need mobile data). Photo Finish needs almost no data (way less than 1 Mb per training session), therefore a small volume flat rate or even prepaid is completely sufficient. If you are in Germany and need a SIM card exclusively for Photo Finish, we recommend the Smartmobil LTE prepaid tariff (https://www.smartmobil.de/prepaid-tarife) with 6 cents per MB, then you can use Photo Finish with 10 Euro credit even with regular training for years (as long as you do not use the credit for other purposes).
►How accurate is Photo Finish?
The accuracy depends on the accuracy of the camera clock of the smartphones used. It can either be medium or optimal. If all connected devices have an optimal camera clock accuracy, the accuracy is very high. With accurate alignment, the expected error is 0.01s or less. This makes Photo Finish more precise than a professional light barrier system. This is because Photo Finish uses image recognition to determine the chest position of the athlete. A light barrier can also be erroneously triggered by the hand or knee. If the accuracy is only "medium", there will likely be an error in the measured times. In our tests it was less than 0.05 seconds, so Photo Finish was still much more accurate than hand timing. A paper in which we explain the technical details of Photo Finish and compare the accuracy with a photocell system in a study is in planning and will be linked here as soon as it is published.
►What does the accuracy display mean when connecting?
Optimal accuracy ensures correct synchronization of the Smartphone clocks. If the accuracy is only high, it is possible that the clocks are not perfectly synchronized, resulting in a measurement error of at max 0.1 seconds. However, this is very unlikely. In most cases, the clocks are synchronized to less than 0.01 seconds even with high accuracy.
►Why does Photo Finish need access to the location?
Photo Finish uses Wi-Fi Direct technology to connect to other nearby devices. To use this technology, the app needs access to the device location.
►How does the detection work and why are there two images for each measurement?
Photo Finish takes 30 frames per second when the detection is active. This enables it to run in real-time on most modern smartphones, even on less powerful ones. An athlete crossing the finish line is thus captured 30 times per second and the chest position is calculated at the respective times. The exact moment at which the chest crosses the finish line is calculated using a cross-multiplication from the chest positions and the frame times directly before and after the crossing. This method allows to greatly increase the time resolution. Photo Finish displays the frame directly after the finish line by default. By tapping on the image you can switch between the two images and check the correct detection of the chest position.
►Do you have a proof for the accuracy of the timing?
We plan to conduct a study with a high-speed camera to measure the precision of Photo Finish and compare it to a commercial light barrier system. The results of the study will be linked here. Until then, everyone can convince themselves of the accuracy with a simple test: Place two smartphones connected in multi-session mode opposite to each other on the same target line and align them exactly vertically and to the respective other camera lens. Then run across the finish line a few times. If the alignment is precise, both smartphones capture the runner at the same time, typically the times differ by only 0.01 seconds or less.