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Microsoft LifeCam VX-1000 webcam on a table

Webcams

by Chris Woodford. Last updated: May 6, 2014.

Ever wanted to run your own TV station? A webcam lets you do just that. With one of these tiny, bug-eyed cameras hooked up to your computer, you can broadcast pictures of yourself or your home to the entire world! A webcam is a bit like a digital camera and works much the same way. But unlike a digital camera, it's designed to make relatively compact digital photos that are easy to upload onto Web pages or send across the Internet. It all sounds simple enough, but how do webcams actually work? Let's take a closer look!

Photo: This Microsoft LifeCam VX-1000 webcam can stand on a table or clip to the screen of a laptop. It has a built-in microphone and a long USB cable carries both picture and sound to your computer. Some laptops and netbooks have built-in webcams. That sounds like a good idea in theory but, again, it limits you to showing pictures of what is directly in front of the computer. Other popular cams are made by Logitech, Creative, Hue, and TeckNet.

How does a webcam work?

A webcam is a compact digital camera you can hook up to your computer to broadcast video images in real time (as they happen). Just like a digital camera, it captures light through a small lens at the front using a tiny grid of light-detectors, known as a charge-coupled device (CCD). As we'll see in a moment, the CCD converts the picture in front of the camera into digital format—a string of zeros and ones that a computer knows how to handle. Unlike a digital camera, a webcam has no built-in memory chip or flash memory card: it doesn't need to "remember" pictures because it's designed to capture and transmit them immediately to a computer. That's why webcams have USB cables coming out of the back. The USB cable supplies power to the webcam from the computer and takes the digital information captured by the webcam's CCD back to the computer—from where it travels on to the Internet.

While a good digital camera is designed to capture high-resolution (finely detailed) pictures, a webcam deliberately captures much lower resolution (more blurred, grainy, and "pixelated") images. A typical webcam makes image files that are about one tenth the size of a typical digital camera. That means webcam snapshots can be sent over the Internet much more quickly than large digital photos.

There are two main reasons why you'd want to send pictures in this way. You might want to publish a frequently updated still image of a particular place for others to view on the Internet. For example, a zoo might publish live pictures from its zebra or giraffe house. Or you might want to video chat with a friend using an instant messaging program, such as Skype or Live Messenger.

How does a CCD work?

Take the outer case off a webcam and you'll find it's little more than a plastic lens mounted directly onto a tiny electronic circuit board underneath. The lens screws in and out to increase its focal length, controlling the focus of your cam:

Parts inside a Logitech notebook webcam

Now take the lens off and you can see the light-sensitive CCD chip: it's the square thing in the middle of this circuit. Only the tiny, central part is light-sensitive: the rest of the CCD chip is concerned with connecting the light detector to the bigger circuit that surrounds it:

CCD inside a webcam

The CCD is the square chip in the middle of this circuit. Only the tiny, green-colored central part is light-sensitive: the rest of the CCD chip is concerned with connecting the light detector to the bigger circuit that surrounds it. Here's a closeup:

Webcam CCD or charge coupled device

Webcams versus digital cameras

So the CCD is the "electronic eye" of a webcam or a digital camera. It's a semiconductor chip made of millions of tiny, light-sensitive squares arranged in a grid pattern. These squares are called pixels. Basic webcams use relatively small CCDs with just a few hundred thousand pixels (typically a grid of 640 × 480. Good digital cameras use CCDs with many more pixels; that's why cameras are compared by how many megapixels (millions of pixels) they have. A basic webcam has about 0.3 megapixels (300,000, in other words), while a digital camera with 6 megapixels has over 20 times more—probably arranged in a rectangle with three thousand across and two thousand down (3000 x 2000 = 6 million). A better camera rated at 12 megapixels would have a 4000 x 3000 pixel CD. Take a photo the same size with those two cameras and the 12 megapixel one is going to give you 1000 more dots horizontally and 1000 more vertically—smaller dots giving more detail and higher resolution. A single pixel in a really good CCD is something like 10 micrometers (10μm) in diameter (5–10 times smaller than the diameter of a typical human hair)!

How does a CCD convert an image to digital form?

Artwork showing how digital camera CCD works

When you take a digital photo or stare into your webcam, light zooms into the lens. This incoming "picture" hits the CCD, which breaks it up into individual pixels. The CCD measures how much light is arriving at each pixel. This information is turned into a number that can be stored on a memory chip inside the camera. Thus, taking a digital photograph converts the picture you see into a very long string of numbers. Each number describes one pixel in the image—how bright or dark and what color it is.

Step by step

  1. Light from the object (in this case, a bicycle) enters the camera lens.
  2. The CCD inside the camera splits the image up into millions of pixels (squares). An LCD display on the back of the camera shows you the image that the CCD is capturing—not an image of the object seen through a series of lenses (as with a conventional camera), but a redrawn, computerized version of the original object displayed on a screen.
  3. The CCD measures the color and brightness of each pixel.
  4. The color and brightness are stored as binary numbers (patterns of zeros and ones) in the camera's memory card. When you connect your camera to a computer, these numbers are transmitted instantly down the wire.

Who invented CCDs?

The CCD was invented in fall 1969 by Canadian-born Willard S. Boyle (1924–) and American George E. Smith (1930–), two colleagues working at Bell Laboratories (a famous American research center in New Jersey responsible for all kinds of amazing inventions, most famous of which is the transistor). Boyle and Smith were trying to develop a new kind of computer memory—in their notes, originally called a charge "bubble" device—but what they actually invented proved far more useful for capturing and storing images in digital form.

The science behind the CCD (turning light energy into electrical energy) dates back much further—to 1905. Known as the photoelectric effect, it was the first major scientific discovery by Albert Einstein (1879–1955). Einstein showed how a light beam could give up its energy when it hit the surface of a material, knocking out electrons that would then form an electric current—and a quantity of electrons that could be related directly to the intensity of the incoming light. It was for this early piece of work (and not his much more famous later work on relativity) that Einstein was awarded the Nobel Prize in Physics 1921. Boyle and Smith earned their own place in history almost 90 years later when they won the Nobel Prize in Physics 2009 (shared with fiber-optic pioneer Charles Kao).

Webcam stills

A Logitech notebook webcam

Photo: A Logitech Quickcam laptop webcam. The USB cable curling out of the camera has two jobs: it takes power to the cam from the computer and then carries the pictures from the cam back the opposite way.

Suppose you want to broadcast images of your garden on a website and update them at regular intervals. You can do that with a webcam. You simply point the cam at your garden, hook it up to your computer, and install a special piece of software. The software captures an image from the cam every five minutes (or at some preset interval) and copies it onto your website using a simple process called FTP (file-transfer protocol). Every time a new image is uploaded, it replaces the previous one on your website. When people look at your site, they see the latest image that your cam has uploaded. Most people design their cam pages so they "refresh" (automatically reload) every few minutes. That ensures they're always showing the latest images.

Here are some examples of webcams that work this way:

Video chat

Now many more people have broadband Internet connections, webcam videoconferencing (or video chat) has become very popular. Using webcams and computers, you can talk to your family and friends anytime, anywhere in the world. To chat to someone like this, you both need a webcam and you both need to be running a video chat program on your computer. Examples include the MSN, Yahoo, and AIM instant messaging programs, and Skype.

Video chat programs work just like still webcams—only they're uploading photos constantly. Suppose I am video chatting with you. My camera captures a picture of me, turns it into digital format, and sends it my computer. The chat program on my machine "streams" the image information across the Internet to your computer. The chat program on your machine receives the image information and converts it back into a picture, which it displays on your screen. Meanwhile, your camera is doing exactly the same thing with a picture of you and sending it in the opposite direction. This two-way process happens constantly, so each of us gets a constantly updated picture of the other. To speed things up, video chat programs like Skype make a direct connection between your machine and mine, bypassing centralized servers. This very efficient way of using the Net is called (VOIP) Voice Over Internet Protocol and is an example of what's known as P2P (peer-to-peer) networking. You can read more about it in our article on how VOIP works.

Can I use my digital camera as a webcam?

If you've got a digital camera already and a webcam is essentially the same thing, it might occur to you to use your ordinary cam as a webcam. Some digital cameras even have a built-in webcam button or mode making it very easy. For others, you'll need to find out if there's a driver available (that's a small file that tells your computer how to use a plug-in device in a certain way). Sometimes people write their own programs and drivers and make them available online for others, so Googling something like "use canon ixus as webcam" will often bring up helpful results.

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However, there's one thing you do need to be very wary of. A USB connection contains a 5-volt power supply as well as a data connection to and from your computer. Plug a digital camera into a USB socket on your PC and it will draw power the whole time it's connected. Digital cameras are not normally meant to be plugged into computers for more than a minute or two at a time (while you're uploading your photos). Leave a camera plugged in for a long time (half an hour or a couple of hours) while you're using it as a webcam and it can heat up considerably, either damaging the camera or overcharging the batteries. Consider that a good digital camera costs perhaps 10–50 times more than a basic webcam and you'll see what a risk you're taking. The message is simple: if you plan on using a webcam regularly, or for any length of time, buy a proper USB webcam. They're not expensive (you can get one for less than $20/£10)—and you'll save damage to your digital camera, which probably was expensive!

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Text copyright © Chris Woodford 2007, 2014. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2007) Webcams. Retrieved from http://www.explainthatstuff.com/webcams.html. [Accessed (Insert date here)]

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