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Group Photo Blink Probability

From the number of people and each person's blink probability, calculate the chance everyone has their eyes open in a group photo, plus how many shots to take to avoid a blink.

Input

A probability model assuming each person blinks independently. Real photos depend on timing and verbal cues, so treat the result as a rough guide.

People

people
%

About 4% is typical in bright settings. It rises in dim light or with longer exposures.

sec

Enter seconds to see an estimated blink probability, assuming roughly 10 blinks per minute.

Result

Chance everyone's eyes are open in one shot

29.4%

= (1 − 4.0%) to the power of 30

Chance someone blinks

70.6 %

Average shots to succeed

3 shots

Shots needed for 95% success

9 shots

Shots needed for 99% success

14 shots

Suggested number of shots to get everyone with eyes open

Target success rateShots needed
Success rate per shot29.4 %
50%3 shots
95%9 shots
99%14 shots

How it works

  • The chance everyone has their eyes open is '(1 − blink probability) to the power of the number of people'. The probability drops sharply as the group grows, and the chance someone blinks is '1 − the all-eyes-open probability'.
  • A typical blink probability per person, per shot is about 4% in bright conditions. It rises when the room is dark or the exposure time is long.
  • The shots needed for a target success rate are computed as 'shots ≥ log(1 − target) ÷ log(1 − all-eyes-open probability)', rounded up to a whole number. This tells you the count to aim for 95% or 99% success.
  • The 'average shots to succeed' is the reciprocal (expected value) of the per-shot success rate. On average, taking this many shots yields one frame with everyone's eyes open.
  • This is a simplified model where each person's blink is independent and equally likely. In reality, verbal cues, burst shooting, and timing change the outcome a lot, so use it as a reference value.
  • From the optional exposure time, the blink probability is estimated assuming about 10 blinks per minute and roughly 0.25 seconds per blink.