Light travels through the Universe as a wave, but it is rather different than the ripples we see moving across the surface of a lake. Light waves are made up of electric and magnetic fields. So another name for light is electromagnetic radiation. And the entire spectrum of light is similarly called the electromagnetic spectrum.

The camera can be used on a drone or a car to help it avoid obstacles, for instance. But the uses that ToF can be used can also be used for identifying a subject, or for gesture recognition. ToF can be used for security applications – helping to identify the user – or simply, perhaps, telling the difference between the neighbor's cat and a human intruder.

His first serious camera was the iconic Olympus OM10, with which he won the title of Young Photographer of the Year - long before the advent of autofocus and memory cards. Today he uses a Nikon D800, a Fujifilm X-T1, a Sony A7, and his iPhone 15 Pro Max.

Infrared wavelength

Current ToF cameras tend to rather low resolution. The time-of-flight camera in the  Samsung's S10 5G recently-announced is just 240x160 pixels.

The real connection is that everything in the Universe that is warm also gives off light. This is true of stars, planets, people, and even the Universe itself! Physicists call this light blackbody radiation. Every object in the Universe, even one that is as black as a lump of charcoal, will give off this light. Where this light falls in the spectrum, however, depends on the temperature of the object.

Chris George has worked on Digital Camera World since its launch in 2017. He has been writing about photography, mobile phones, video making and technology for over 30 years – and has edited numerous magazines including PhotoPlus, N-Photo, Digital Camera, Video Camera, and Professional Photography.

As we are talking about the speed of light, the measurement takes place in far less of a blink of an eye. As every geekly schoolkid will tell you, the light travels at 300,000km per second. So for a subject that is 5m away, for instance, the time difference between the light leaving the camera and returning is just 33 nanoseconds. Or 0.000000033sec, if you prefer.

A time-of-flight camera has an imaging sensor in much the same way as a normal digital camera. But the job of each photosite on the CCD sensor is to measure the time it takes for a beam of infrared light fired from the camera to return to the camera – after it it reflects off the objects in the scene in front of it. The whole scene is captured and measured with a single pulse of light – so there are no moving parts.

Midinfrared

With drones, a ToF is a great way of seeing and avoiding obstacles – but are particulary useful navigating through buildings.

The technology has been around for a while - but the processing speed needed has meant that this depth sensing tech has taken a little while to make it onto everyday gadgets.

Infrared light falls just outside the visible spectrum, beyond the edge of what we can see as red. Sir William Herschel first discovered infrared light in 1800. He split light into a rainbow (called a spectrum) by passing sunlight through a prism, and then placed a thermometer in different colors in that spectrum. Unexpectedly, he found the thermometer showed a rise in temperature, even when placed in the dark area beyond the edge of the red light. He hypothesized that there must be more light beyond the color red that we simply could not see with our own eyes. You can recreate Herschel's experiment yourself with a box, a prism, three thermometers, and a few other common supplies.

Astronomers who want to study the most frigid things in the Universe turn to infrared telescopes to reveal their faint glow. Clouds of dust that range from hundreds to tens of degrees above absolute zero appear as black soot in visible light, but glow brightly at infrared wavelengths out to several hundred microns.

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Since we think of infrared light as something that makes us feel warm, is there a connection between heat and light? Are they the same thing?

These time differences are measured at every single pixel across the image – and it is this 'picture' that gives creates the three-dimensional map of the scene. And it can do this continuously – with a typical maximum frame rate of 60fps.

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In the workplace, ToF sensors and cameras are sold as components. So they can, for instance, be used on production lines by robots to pick the right component, or to spot faulty goods.

Similarly, the depth information can help the AI software on the phone to defocus the background of an image – giving the bokeh blur loved by professional portrait photographers.

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The ToF sensor can be used to give a additional features - and the depth information registered by it can be used in different ways by different apps on the phone.

The easiest way of thinking about time-of-flight is that is like a sonar system – except it uses light rather than sound to detect things.

Our eyes detect differences in the wavelength of visible light as differences in color. Essentially, color is your brain's way of converting the different wavelengths of light that your eyes see into something that you can quickly understand. Red light has a longer wavelength than green light, which in turn has a longer wavelength than blue light. The wavelength of infrared light is longer than red light, in some cases many hundreds of times longer. These longer wavelengths carry less energy than red light and do not activate the photoreceptors in our eyes, so we cannot see them.

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Infrared light

Time-of-flight cameras are starting appear on a number of gadgets. These ToF cameras measure depth in a scene – and are used to help map the surroundings, and to navigate around obstacles, and much more. Let's take a closer look at what a time-of-flight camera does, what it is used for, and which bits of tech are featuring them…

Infrared is a form of light... light that we can not see with our eyes, but that we can sometimes feel on our skin as heat.

When we think of light, we may imagine the glare of the Sun on a summer day, or the soft glow of a light bulb at night. But visible light, the only light our eyes can see, makes up just a tiny sliver of all the light in the world around us.

Time-of-flight is being used in a wide range of applications... and it is not always easy to predict how they will be used. Mobile phones are in some part incorporating the technology so that it can be integrated with software and apps that have yet to be written.

He has written about technology for countless publications and websites including The Sunday Times Magazine, The Daily Telegraph, Dorling Kindersley, What Cellphone, T3 and Techradar.

Near-infraredwavelength

The ToF camera could be used for gesture recognition for instance - so you it can recognise that you want the camera to take a picture when you raise your hand.

Infrared wavelength range

The latest generation of mobile phones don't just have one camera. For a long while they have had two - one for photos of what is in front of them, and the other for selfies. But the newest phones have now have several front cameras - with between two and six different lenses each with their own sensors. Some of these are used to give a choice of different focal lengths – so that you get a truly wide-angle view should you want to, or a decent telephoto without the need to crop the image.

Cooler objects glow faintly at longer wavelengths of light, while hotter objects glow more brightly at shorter wavelengths. Our Sun's temperature is a blistering 5,778 K (9,940° F), which is so hot that it glows brightest at visible wavelengths of light (around 0.4 - 0.7 microns). People, who are much cooler (310 K, 98° F), actually glow as well, but in infrared light with a wavelength of around 10 microns. A micron is a millionth of a meter.

Light does not stop at just the visible and infrared. Other types of light that you may have heard of include gamma rays, X-rays, ultraviolet, microwave, and radio. Everything in this spectrum travels at the ultimate speed limit of the Universe which is, of course, the speed of light.

One of the basic properties of any wave is its wavelength, which is just the distance between the peaks of one ripple, or wave, and the next. For light, it is the length of one full cycle, or pulse, of the electric and magnetic fields. A related property is the frequency, or the number of waves that pass a fixed point every second.

Scientists measure temperature using the Kelvin temperature scale. 0 K - absolute zero 273 K - water freezes 373 K - water boils

Infrared light that falls on your skin will cause it to warm up, and you will feel the heat. In a way, this means that your skin lets you "see" light that your eye can not!

Time-of-flight cameras, or ToF cameras,  are becoming an increasing common feature on mobile phones, drones and on industrial robots. Also known as depth cameras, they map out the surroundings creating a basic three-dimensional representation of what is in front of them.

They also have an important role to play in VR and augmented reality applications – allowing games, for instance, to overlay a virtual world on the real world.