# I don't understand time-of-flight cameras - without flash, that is

**URL:** <https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785>\
**Category:** Factual Questions\
**Created:** [August 4, 2017, 5:07pm UTC](https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785 "2017-08-04T17:07:49Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![komolono](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/komolono/32/532_2.png) [@komolono](https://boards.straightdope.com/u/komolono)\
**Post date:** [August 4, 2017, 5:07pm UTC](https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785/1 "2017-08-04T17:07:49Z")

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Well I didn’t read the corresponding Wikipedia either. But the basic problem is that object reflect light all the time. If the technology depended on flashing light, you could calculate the spent time, but I don’t see flashing while 3d-modelling. I don’t even see how a flash light could reach objects hundreds of meters away.

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**Author:** ![Ornery\_Bob](https://avatars.discourse-cdn.com/v4/letter/o/da6949/32.png) [@Ornery\_Bob](https://boards.straightdope.com/u/Ornery_Bob)\
**Post date:** [August 4, 2017, 5:34pm UTC](https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785/2 "2017-08-04T17:34:31Z")

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TOF cameras emit a pulse of _ **laser light** _ (not “flash” light) and measure the time for it to return.

Ambient light does not interfere because the sensor on the camera is tuned to the wavelength of the laser light only.

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**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\
**Post date:** [August 4, 2017, 8:12pm UTC](https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785/3 "2017-08-04T20:12:20Z")

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TOF cameras basically work like very high-precision radar, except using a laser instead of radio (so lidar.) They are literally measuring the _time_ that it takes for a laser pulse to _fly_ to the object and bounce back.

Because lasers are highly-focused, (think of the tiny dot of a laser pointer) you can point it at different parts of the object to get different readings, eventually getting a relatively good map of the whole surface.

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**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\
**Post date:** [August 4, 2017, 9:50pm UTC](https://boards.straightdope.com/t/i-dont-understand-time-of-flight-cameras-without-flash-that-is/792785/4 "2017-08-04T21:50:02Z")

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I know next to nothing about TOF cameras, but from reading the [Wikipedia article](https://en.wikipedia.org/wiki/Time-of-flight_camera), I gather that some cameras use lasers, while others use LEDs. These two technologies are used because they can be modulated at high speeds. They do not scan the target area point by point like a scanning LIDAR system, but illuminate the whole field of view (I guess there’s some kind of beam disperser for laser based cameras?). The illumination is often near infrared to make it less obtrusive but interference is avoided not by filtering the wavelength of the light, but by viewing the scene twice, once with the illumination turned off. Interference is possible if two TOF cameras are viewing the same scene at the same time.