‘Why does the road look white?’ and other Photo finish mysteries

If you’ve been watching they Olympic track cycling, you’ll have become familiar with two things: one, the fact that the chief commissaire is a bastard (unfortunately despite much searching, I am unable to bring you the name of the man who decided that China shouldn’t have a Gold in the team sprint, that eliminating people from the omnium late and thus affecting who got silver and bronze wasn’t a big deal or that the sprint between Pendleton and Meares had something wrong with it, but I have found plenty sprints the UCI will have to go back and reclassify if any sort of consistency is to be maintained), and two, that photo finishes are fantastic. Those pesky try-athletes (not a spelling mistakes) were oh so pleased when they got a dead heat to show how close their race had been. Unfortunately the photo was rather clear. There’s none of that nonsense in cycling – we have proper dead heats. But how do they manage to claim such close races and decide medal destinations by but a pixel? And why does the road always look white? Read on…

Anna Meares and Victoria Pendleton complete a thrilling race with a 1/1000th time gap…until, that is, the commissaires decided they wanted some attention

The photo finish has been a staple of sporting competition for some time, since January 16th 1936 in fact, when a camera was installed at Hialeah Race track in Hialeah Fla, which is for horses of course. It was unfortunate that the technology had not been innovated by cycling in the same year – the 1936 Paris-Roubaix was wracked with controversy when the men who literally stood on the line to judge the finish in those days (you can watch them get the decision wrong at http://www.youtube.com/watch?v=BjOkn1xTBZU) somehow managed to award the victory to Frenchman Georges Speicher over Belgian Romain Maes, despite everyone in the stadium and everyone who has eyes to watch the video seeing that Maes was clearly ahead (indeed, fighting almost broke out over the result, which stood).

Despite crossing the line in this position, victory went to rider on the right, rather than Maes, the ‘true’ winner/

Since then though, the photo finish has been used to ensure that no one, no matter if they tried to celebrate before hand, could claim a victory that wasn’t rightfully there own.

Erik Zabel must be fed up of the usual front on view of him celebrating too soon to let Freire win the 2004 Milan San Remo, so here’s the side view, which is still probably annoying.

The photo finish essentially works as a high speed camera that is only a few pixels wide – specifically, the width of the finish line. It does this at a rate that has increased somewhat over the years. The first photo finish at an Olympics was at London in 1948, but it could still only time athletes to a tenth of a second, whilst by Atlanta, the camera was shooting a thousand frames a second, and these days the cameras are capable of over 10,000 frames a second – well over the thousand of a second required by the regulations. Cycling is of course somewhat unique in that even dead heats can be separated by tiny margins, especially when the cameras now have such huge pixel densities and all that is required is a pixel width to separate the riders. Visibility is helped by the fact that the finish line is usually white, in order to stand out from the road. As the final photo finish image you see is essentially a composite of all the very thing images of the finish line stitched together, the only road underneath a rider at any time is the white line – thus, the road looks white. It is a common misconception that the image is a still image of the moment the riders crossed the line. In reality, it is an image of the point when every rider crossed the line…

All these riders are on the finish line when this picture was taken. Your mind is blown.

This time distortion is also the reason that the wheel spokes are often deformed, due to their changing position as the camera fires itself – not because they are whurring too fast to be captured in a still motion.

Time dilation demonstrated by someone crashing over the line

Another question sometimes posed is whether or not one rider has an advantage over the other, as surely the camera scans in a certain direction? After all, if the camera took, say 1/100th of a second to scan the image from top to bottom, the rider at the bottom would have advanced by whatever distance is achievable in a 100th of a second, and could possibly take the result because of this. Luckily, there are too solutions – firstly, the camera is ridiculously quick anyway, but more importantly, it scans in a direction perpendicular to the finish line so that it fires as the riders pass the line exactly.

Unfortunately Matt Goss can’t claim the camera was to blame for his loss to Mark Renshaw at the 2012 Tour of Turkey.

Dead heats are however still possible to come by despite the cameras. They are not, as some seem to think, impossible, even though it is arguable you can always split things down to smaller and smaller parts etc etc. There are thus two types of dead heats that can occur in cycling: a true dead heat and an obscured dead heat. A true dead heat is as it suggest on the tin – the two riders and their tyres simply cannot be separated, no matter how closely the officials analyse the image the camera produces.

In this example of a true dead heat, Guillaume Boivin (Canada, top) and Taylor Phinney (USA, bottom) tied for the bronze at the U23 Worlds in 2010, with the camera unable to seperate them at the line.

Alternatively, you can have what happened at the Olympics, where the riders obscure each others wheel giving no opportunity to separate them.

With the New Zealander’s wheel unseen, the officials had no option but to award two bronze medals.

Hopefully this somewhat ill informed and no doubt inaccurate piece has been of some value, and you forever have the fact the whole road is white burnt into your brain whenever you see another finish! Oh, and if you see this bloke, you know what to do…

But in the mean time, here’s some other photo finishes to enjoy:

Tyler Hamilton gets in on the action

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