A Real Poser

Some people have that great gift of being photogenic; that is to say that in whatever the circumstances, lighting, ambience,time of day or night, state of dress and personal demeanour there is always a perfect photograph enhancing all attributes and really catching the character and personality of the individual.

I am simply not one of that select group of the population.

I do not have a "good side" as is often claimed by those posing for a portrait or selfie snap.

I always look fat, even if in my minds eye I am not. My cheeks are always reddened, hair unkempt and I always seem to develop a double or triple chin. All of the above occurs even when I have paid meticulous attention to my personal hygiene, grooming and attire.

In group photographs, family or business, I am usually at the back, looking distracted or vague and often as not blinking or with eyes closed in the final click of the shutter.

It appears that the blinking individual or more than one person blinking is a regular phenomenon in any situation where a photograph is sought as a precious record or memento of that special occasion or function.

This problem caught the interest of a physicist , Dr Piers Barnes of The Commonwealth Scientific and Industrial Research Organisation (CSIRO)  in Australia who has dedicated time and effort to producing a formula and guide as to how many photographs it is necessary to take to get one where no-one is caught blinking.

In his study at a rudimentary level Dr Barnes  started counting  people, photos taken and what proportion of the photos were spoilt due to blinks.

Applying physical laws and mathematic theory it was clear that in order to be statistically significant, around two hundred photos would be the minimum for a workable sample.

As a starting point thought was given on the matter of why people blink.

In any situation and not just posing for a photograph a blink can be brought on by nervousness, dry air, shyness in a public setting, stress, fatigue, flatulence, not telling the truth , poorly fitting or irritating contact lenses , environmental pollution, pre-flash flashes (red-eye reduction) and even fancying the picture taker.

A photographer encouraging  people to avoid, if possible, blinking in photos can, naturally, have the opposite effect.

It appears that the average number of blinks made by someone getting their photo taken is ten per minute. The average blink lasts about 250 milliseconds and, in good indoor light, a camera shutter stays open for about eight milliseconds.

Because blinks are independent there is a completely random incidence of it. If a group of people are looking at a camera, one person blinking will not influence another.

There is, therefore, a very complex combination of variables at play to calculate the probability of a random blink occurring during the period of time during which the camera shutter is open.

Here is the maths.

The probability of one person spoiling a photo by blinking equals their expected number of blinks (x), multiplied by the time during which the photo could be spoilt (t).

This makes the probability of one person not blinking 1 - xt. For two people it's (1 - xt).(1 - xt) and for a group of people it's (1 - xt)n, n being the number of people. 

This means (1 - xt)n is also the probability of a good photo. Therefore, the number of photos should be 1/(1 - xt)n. 

Each shutter opening results in either a good photo or a spoilt one. A graph of these events and follows what statisticians call the normal distribution in a  bell curve

At one end of the curve the statistics represent  100% success, ie, the photographer got all good shots. In the middle, the number of good and bad photos is split 50:50. And, at the other end, are all dud trials or where the photographer captured a blink from the assembled group.

Dr Barnes then had to stress-test the theory in order to figure out how many shots would be needed to be 99% certain of getting a good one.

He found that photographing thirty people in bad light would need about thirty shots. A larger fifty person group, even in good light, gave very little prospect of a successful commission.

A rule of thumb for calculating the number of photos to take for groups of less than 20 was one product of the many hours of research and analysis  and that arrived at by dividing the number of people by three in good light and two in bad.

Of course, a clever photographer, pressed for time with another wedding party or function to attend on the other side of town may just opt for a clever reworking of the pictures using appropriate software or as Dr Barnes reverted to, propping people's eyelids open with cocktail sticks from the reception buffet.

Dr Barnes and co-author Nic Svenson were awarded an Ig Nobel Prize in 2006 for this staring, I mean sterling piece of research.