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DORI distance for a 8MP (4K) camera with a 6 mm lens

Published standard EN 62676-4 pixel per metre thresholds and lens geometry
Quick answer

A 8MP (4K) camera with a 6 mm lens on a 1/2.8 inch sensor sees 46.2 degrees horizontally. Under the EN 62676-4 DORI standard it can identify a person out to about 59 ft (18 m), recognise someone already known to 118 ft (36 m), observe behaviour to 236 ft (72 m) and merely detect that a person is present to 591 ft (180 m).

How this is worked out

distance = horizontal pixels / (required pixels per metre x 2 x tan(horizontal field of view / 2))

The standard defines four thresholds in pixels per metre of the scene: 25 to detect, 62.5 to observe, 125 to recognise and 250 to identify. This camera puts 3840 pixels across whatever width the lens covers, so the further away the subject, the fewer pixels land on them.

DORI distances, 8MP (4K) sensor with a 6 mm lens
DORI levelPixels per metreMaximum distanceIn metresWhat this actually gets you
Detect 25591 ft180 mSomething is there, and it is a person rather than an animal or a shadow.
Observe 62.5236 ft72 mClothing and behaviour are visible. You can follow what someone is doing.
Recognise 125118 ft36 mYou can tell whether this is someone you already know.
Identify 25059 ft18 mA stranger can be identified from the footage to an evidential standard.
Identification is the expensive one. It needs ten times the pixel density of detection, which is why the identify distance is a tenth of the detect distance on the same camera.
Pixel density at a range of distances, 8MP (4K) with a 6 mm lens
DistanceScene width coveredPixels per metreBest DORI level reached
10 ft 9 ft1476Identify
15 ft 13 ft984Identify
20 ft 17 ft738Identify
30 ft 26 ft492Identify
40 ft 34 ft369Identify
60 ft 51 ft246Recognise
80 ft 68 ft185Recognise
100 ft 85 ft148Recognise
Pixel density falls off linearly with distance, not with the square of it, but it falls off fast enough that a camera which identifies at 59 ft is only detecting by 591 ft.

What a 6 mm lens is actually for

At 46.2 degrees, this lens is a middle distance lens, which is usually the right answer for a front door, a side return, or any approach where you want both context and a usable face.

The mistake this page exists to prevent is buying resolution to solve a lens problem. Going from 8MP (4K) to a higher resolution sensor increases identify distance in proportion to the horizontal pixel count, but going from 6 mm to a longer lens increases it in proportion to the focal length, and long lenses are far cheaper than large sensors.

Where these numbers stop being reliable

These figures come from lens geometry and the published sensor resolution. They assume the camera is looking at the scene square on and that there is enough light for the sensor to resolve what it is pointed at, so treat them as the ceiling rather than as a promise.

DORI is a daylight measure. At night an infrared illuminator lights the scene unevenly and the sensor is working much harder, so real identify distance after dark is materially shorter than the figure above. Where a camera publishes an infrared range, that is the distance its own lamp reaches, not the distance at which it can still identify anyone.

Cameras that change this answer

Ordered by sensor resolution, which is the term in the formula you can actually buy your way out of. A longer lens is the cheaper lever.

Common questions

Can a 8MP (4K) camera with a 6 mm lens identify someone at 50 feet?

Its identify distance is about 59 ft, so at 50 feet it is still within identification range under the DORI standard, assuming good light and a square on view.

What is the difference between recognise and identify in the DORI standard?

Recognise, at 125 pixels per metre, means you can tell whether the person on screen is somebody you already know. Identify, at 250 pixels per metre, means a stranger could be picked out from the footage to an evidential standard. It takes twice the pixel density to go from one to the other, which halves the working distance of any given camera.

Does digital zoom extend these distances?

No. Digital zoom crops the image and scales it up, so it adds no pixels to the scene and the pixels per metre figure does not change. Only optical zoom or a longer fixed lens increases pixel density on a distant subject, which is why an optical zoom camera reaches identification distances that no amount of software can match.

Is a wider lens always worse for identification?

Yes, for a fixed sensor. A wider lens spreads the same 3840 horizontal pixels across more scene, so pixel density at any distance drops in proportion. The usual resolution is to use a wide lens for coverage and awareness, and to place one narrower lens on the single approach where you genuinely need to identify a face.

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Keep going

Before you point a camera at anything. Aim cameras at your own property and your own boundary, never into a neighbour's windows or across their garden. Cameras in bedrooms, bathrooms, or anywhere else a person reasonably expects privacy are a serious legal problem, and that includes guests, lodgers and anyone who works in your home. Audio is legally different from video, many US states require the consent of every party to a recorded conversation, and several recorders capture audio by default, so check your own state before you enable it. Some places require visible notice that recording is taking place, and landlords and homeowner associations often impose their own rules on top. This is researched general information and not legal advice, and the law varies by state and by country.

And once it is installed. Change every default password, keep the firmware updated, and be clear with yourself about where the footage goes: a cloud camera means a third party holds recordings of your home, while a local recorder keeps them in your house. That is a genuine buying consideration, not a technicality.