Digital cameras
Last updated: September 18, 2008.
Digital cameras give a whole new
meaning to the idea of painting by numbers.
Unlike old-style film cameras, they capture and record images of the
world around us using digital technology. In other words, they store
photographs not as patterns of darkness and light but as long strings of numbers. This has many advantages: it
gives us instant photographs, allows us to edit our pictures, and
makes it easier for us to share photographs using cell phones (mobile
phones), e-mail, and web sites.
Photo: A typical low-cost digital camera. The circle is the lens;
the rectangle above it is a xenon flash lamp.
You can see what this camera looks like inside in the photo lower down this page.
How ordinary film cameras work
Photo: An old-style film camera from the late
1980s.
The film loads in a spool on the right and winds across to another
spool on the left, passing in front of the lens on the way. When you
take a photo, the shutter lets
light enter from the lens and expose the film.
It's all very 19th-century compared to digital photography!
If you have an old-style camera, you'll know that it's useless
without one vital piece of equipment: a film. A film is a long spool
of flexible plastic coated with special chemicals that are sensitive to light.
To stop light spoiling the film, it is wrapped up inside a tough,
light-proof plastic cylinder—the thing you put in your camera.
When you want to take a photograph with a film camera, you have to press a
button. This operates a mechanism called the shutter, which makes a
hole (the aperture) open briefly at the front of the camera, allowing
light to enter through the lens (a thick piece of
glass or plastic
mounted on the front). The light causes reactions to take place in
the chemicals on the film, thus storing the picture in front of you.
This isn't
quite the end of the process, however. When the film is full, you
have to take it to a drugstore (chemist's) to have it
developed. Usually, this involves placing the film into a huge
automated developing machine. The machine opens up the film
container, pulls out the film, and dips it in various other chemicals
to make your photos appear. This process turns the film into a series
of "negative" pictures—ghostly reverse versions of
what you actually saw. In a negative, the black areas look light and
vice-versa and all the colors look weird too because the negative
stores them as their opposites. Once the machine has made the
negatives, it uses them to make prints (finished versions) of your
photos.
If you want to take only one or two photographs, all of this can be a bit of
a nuisance. Most people have found themselves wasting photographs
simply to "finish off the film." Often, you have to wait
several days for your film to be developed and your prints (the
finished photographs) returned to you. It's no wonder that
digital photography has become very popular—because it solves
all these problems at a stroke.
(Incidentally, if you want to learn more about film cameras and traditional photography,
see our main article on how film cameras work.)
How digital cameras work
Photo: Digital cameras are much more convenient
than film
cameras. You can instantly see how the picture will look from the LCD
screen on the back.
If your picture doesn't turn out okay, you can simply delete it and try
again.
You can't do that with a film camera. Digital cameras mean
photographers can be more creative and experimental.
Photo by John L. Beeman courtesy of the US Navy.
Digital
cameras look very much like ordinary film cameras but they work in a
completely different way. When you press the button to take a
photograph with a digital camera, an aperture opens at the front of
the camera and light streams in through the lens. From this point on,
however, everything is different. There is no film in a digital
camera. Instead, there is a piece of
electronic equipment that
captures the incoming light rays and turns them into electrical
signals. This light detector is called a charge-coupled
device (CCD).
If you've
ever looked at a television screen close
up, you will have
noticed that the picture is made up of millions of tiny
colored dots or squares called pixels. Laptop LCD computer screens also make up their images using pixels, although they are
often much too small to see. In a television or computer screen,
electronic equipment switches all these colored pixels on and off
very quickly. Light from the screen travels out to your eyes and your
brain is fooled into see a large, moving picture.
In a digital camera, exactly the opposite happens. Light from the
thing you are photographing zooms into the camera lens. This incoming
"picture" hits the CCD, which breaks it up into millions
of pixels. The CCD measures the color and brightness of each pixel
and stores it as a number. Your digital photograph is effectively
an enormously long string of numbers describing the exact details
of each pixel it contains.
You can read more about how a CCD produces a digital photograph in our
separate article on how CCDs work.
Photo: What's inside?
Find out more in our article what's inside a digital camera?.
How digital cameras use digital technology
Once a picture is stored in numeric form, you can do all kinds of things
with it. Plug your digital camera into your computer, and you can
download the images you have taken and load them into your programs.
Or you can upload them onto websites, email them to friends, and so
on. This is possible because your photographs are stored in digital
format and all kinds of other digital gadgets—everything from
MP3-playing iPods to
cellphones and computers to photo printers—use digital
technology too. Digital is a kind of language that all electronic
gadgets "speak" today.
If you open up a digital photograph in a paint (image editing) program,
you
can change it in all kinds of ways. A program like this works
by adjusting the numbers that represent each pixel of the image. So,
if you click on a control that makes the image 20 percent brighter,
the program goes through all the numbers for each pixel in turn and
increases them by 20 percent. If you mirror an image (flip it
horizontally), the program reverses the sequence of the numbers it
stores so they run in the opposite direction. What you see on the
screen is the image changing as you edit or manipulate it. But what
you don't see is the paint program changing all the numbers in
the background.
Photo: A 4.0 megapixel digital camera with zoom
lens.
The lens moves in and out at the touch of a button: it's powered by
a compact electric motor.
Some of
these image-editing techniques are built into more sophisticated
digital cameras. You might have a camera that has an optical zoom and
a digital zoom. An optical zoom means that the lens moves in and out
to make the incoming image bigger or smaller when it hits the CCD. A
digital zoom means that the microchip inside the camera blows up the
incoming image without actually moving the lens.
So, just like moving closer to a TV set, the image degrades in quality.
In short, optical zooms make images bigger and just as clear, but
digital zooms
make images bigger and more blurred.
Why digital cameras compress images
Image for a moment that you're a CCD. Look out of a window and try to
figure out how you would store details of the view you can see.
First, you'd have to divide the image into a grid of squares.
So you'd need to draw an imaginary grid on top of the window.
Next, you'd have to measure the color and brightness of each
pixel in the grid. Finally, you'd have to write all these
measurements down as numbers. If you measured the color and
brightness for six million pixels and wrote both down both things as
numbers,
you'd end up with a string of millions of numbers—just to
store one photograph! This is why high-quality digital images often
make enormous files on your computer. Each one can be several
megabytes (millions of characters) in size.
To get
around this, digital cameras, computers, and other digital gadgets
use a technique called compression. Compression is a mathematical trick
that involves squeezing digital photos
so they can be stored with fewer numbers and less memory.
One popular form of compression is called JPG (pronounced J-PEG, which
stands for Joint
Photographic Experts Group, after the scientists and mathematicians
who thought up the idea). JPG is known as a "lossy"
compression because, when photographs are squeezed this way, some
information is lost and can never be restored. High-resolution JPGs
use lots of memory space and look very clear; low resolution JPGs use
much less space and look more blurred. You can find out more about
compression in our article on MP3
players.
Most digital cameras have settings that let you take pictures at higher or
lower resolutions. If you select high-resolution, the camera can
store fewer images on its memory card—but
they are much better quality. Opt for low-resolution and you will get more images, but the
quality won't be as good. Low-resolution images are stored with greater compression.
Turning
ordinary photos into digital photos
There is a
way to turn photos from an ordinary film camera into digital
photos—by scanning them. A scanner is a piece of computer
equipment that looks like a small photocopier
but works like a
digital camera. When you put your photos in a scanner, a light scans
across them, turning them into strings of pixels and thus into
digital images you can see on your computer.
A brief history of photography
- 4th century BCE: Chinese invented the camera obscura (a darkened
room
with
a hole in the drapes that projects an image of the outside world onto
a distant wall).
- Late
1700s: Thomas Wedgwood (1771-1805) and Sir Humphry Davy
(1778–1829),
two English scientists, carried out early experiments trying to
record images on light-sensitive paper. Their photos were not
permanent: they turned black unless permanently stored in a dark
place.
- 1827:
French Joseph Nicéphore Niépce
(1765-1833) made the world's
first
photographs. His method was no good for taking portraits of people
because the camera shutter had to be left open for eight hours.
- 1839: French opera-house scene painter Louis
Daguerre (1787–1851)
announced the invention of photos on silver plates called
daguerreotypes.
- 1839: William Henry Fox Talbot
(1800–1877)
invented the photographic
negative process.
- 1851:
British artist and photographer Frederick Scott
Archer
(1813-1857)
invented a way of taking pin-sharp photos onto wet glass plates.
- 1870s:
British physician Dr Richard Maddox
(1816-1902) developed a way
of
taking photos using dry plates and gelatin.
- 1883:
American inventor George Eastman (1854-1932)
invented the
modern
photographic film.
- 1888:
George Eastman launched his easy-to-use Kodak camera. His slogan was:
"You push the button and we do the rest."
- 1947: Edwin Land (1909-1991) invented
the
instant polaroid camera.
- 1963:
Edwin Land invented the color polaroid camera.
- 1990s: Digital cameras start to become popular.
Further reading
Books you can read
Web pages
