Webcams
Last updated: April 15, 2008.
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—so
let's
take a closer look at webcams and the technology behind them.
Photo: A typical webcam fixed to the screen of a
laptop.
How webcams work
A webcam is a compact camera you can hook up to your computer. 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). 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. (You can find out exactly
how this happens in our article on digital
cameras.) Unlike a digital
camera, a webcam has no built-in memory or flash
memory
card. It's designed to capture pictures 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.
Inside a webcam
Oh you know me, I just can't help taking things to pieces.
So when I found a broken Logitech webcam, I couldn't resist!
Getting the plastic case off proved almost impossible.
But once I'd succeeded, here's what I found inside.
You can see that the webcam is 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.
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.
Here's a close-up of the CCD. If you tilt it slightly in the light, you can get a sense that there are lots of light-sensitive squares lurking inside, ready and waiting to generate your pixels!
Webcam stills
Photo: A 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 every 5 minutes or so. 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 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:
- Marwell Zoo: "There are currently four webcams for
you to view. Visit the Giraffe house, or see if you can spot a Tiger,
Meerkat or a Penguin!"
- Lamb Cam:
Watch Farmer Bob and his lambs live.
- Panda Cam:
Check out the Wolong Panda cam in China.
- Cruise
cams: Watch the view from a Princess ocean liner at sea.
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 P2P
(peer-to-peer) networking. You can read more about it in our
article on how the Internet works.
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Some webcams you might like...
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