Blink-free Photo Calculator

Calculate the odds that a group photo comes out with everyone's eyes open, and how many shots to take to hit a target confidence level.

Quick Facts

Formula
P(blink-free photo) = (1 − p)^n
Each person's blink is treated as an independent event, so the group's success chance shrinks fast as headcount grows.
Shots needed
k = ln(1−C) / ln(1−(1−p)^n)
Derived from the geometric distribution for the number of independent trials to reach confidence C.

Your Results

Calculated
Single-photo success chance
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P(nobody blinks) = (1−p)^n
Photos needed
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To reach your target confidence
Burst time required
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Shots needed ÷ burst rate
Average shots to first success
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Expected value, 1 ÷ success chance

Ready

Set group size, blink probability, and target confidence, then press Calculate.

Understanding the Blink-free Photo Calculator

This tool estimates the odds of capturing a group photo where nobody's eyes are closed, and tells you how many shots to take to reach a chosen confidence level. It treats each person's blink as an independent random event — a fair assumption for casual photos where a flash, fatigue, or lighting hasn't synchronized everyone's blinking.

The formula

If a single person blinks in a given photo with probability p, the chance that person's eyes are open is (1 − p). For a group of n people, assuming their blinks are independent of one another, the probability that everyone's eyes are open at once is the product of each person's chance:

  • P(blink-free photo) = (1 − p)n — the chance a single shot has zero blinks.
  • P(at least one blink) = 1 − (1 − p)n — the complement, and the "failure" chance for one shot.

Because each shot is an independent trial, taking multiple photos follows a geometric distribution. To reach a target confidence level C (say, 95%) of getting at least one blink-free shot, solve for the smallest whole number of photos k satisfying:

k ≥ ln(1 − C) / ln(1 − (1 − p)n)

The calculator also reports the average (expected) number of shots until the first blink-free photo, which is 1 / (1 − p)n, and converts the required shot count into real time using your camera's burst rate (photos per second).

Why group size matters so much

Because the per-person probabilities multiply, adding people to a photo shrinks the success chance exponentially. At a 10% individual blink rate, a solo portrait succeeds about 90% of the time, but a group of 10 succeeds only about 35% of the time (0.910) — which is why large group photos so often need several attempts.

Choosing a blink probability

There's no universal value for p — it depends on lighting, whether a flash fires, how tired the subjects are, and their age (young children tend to blink less predictably than adults). A commonly used starting point is around 10% per person per photo; raise it for bright flash or tired subjects, and lower it for calm, well-lit conditions without a flash.

Frequently Asked Questions

How is the probability of a blink-free photo calculated?
If each person in the frame has an independent probability p of blinking in a given photo, the chance that a specific person has their eyes open is (1 − p). For n people to all have their eyes open at once, multiply that chance across everyone: (1 − p)^n. With a 10% blink chance and 5 people, that's 0.9^5, about 59%.
How many photos should I take to get one blink-free shot?
Treat each photo as an independent trial with success probability (1 − p)^n. To reach a target confidence level C, the number of photos needed is the smallest whole number k satisfying k ≥ ln(1−C) / ln(1−(1−p)^n). Larger groups or higher blink probabilities push k up quickly.
Why does adding people to the photo hurt the odds so much?
Because the per-person probabilities multiply. Each extra person is another independent chance for a blink, so the probability of a fully open-eyed shot shrinks exponentially with group size even if each individual rarely blinks.
What blink probability should I use?
There is no single correct value — it depends on lighting, camera flash, fatigue, and age. A commonly used starting estimate is around 10% per person per photo; raise it for young children, bright flash, or tired subjects, and lower it for calm, well-lit conditions.

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