by Chris Woodford. Last updated: November 1, 2020.
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
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 (based on compounds of silver)
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.
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
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: A typical image sensor. The green rectangle in the center (about the size of a fingernail) is the light-sensitive part; the gold wires coming off it connect it into the camera circuit.
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.
So far, it's just the same as a film camera.
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 one of two types, either a charge-coupled
device (CCD) or a CMOS image sensor.
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 image sensor chip, which breaks it up into millions
of pixels. The sensor 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 an image sensor produces a digital picture in our
article on webcams.
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've taken and load them into programs like PhotoShop
to edit them or jazz them up. 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.
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.
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
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
Imagine for a moment that you're a CCD or CMOS image sensing chip. 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
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.
What are "mirrorless" cameras?
There are effectively four different kinds of digital cameras. The simplest, known as point-and-shoot, have a lens
to capture light (which may or may not zoom), an image sensor to turn the pattern of light into digital form, and an LCD screen round the back for viewing your photos. At the opposite end of the spectrum, DSLR (Digital Single Lens Reflex) cameras look like traditional, professional film cameras and have a moving, hinged mirror inside that lets you view the exact picture you're going to shoot through the lens (for an explanation of how SLR works, see our article on film cameras). The most recent innovation, mirrorless digital cameras, are a sort of hybrid of these two designs: they abandon
the hinged mirror system in favor of a higher-resolution LCD viewfinder mounted nearer to the image sensor, which makes them smaller, lighter, faster, and quieter. Finally, there are smartphone cameras, which resemble point-and-shoot models but lack features like an optical zoom.
How do digital cameras compare with smartphone cameras?
From what I've said so far, you can see that digital cameras are great things—if you're
comparing them to old-style film cameras, that is. Thanks to their superb, cutting-edge image
sensors, there's really no good reason (other than a nostalgic preference for
analog technology) to use film.
You might be forgiven for thinking sales of digital cameras would be
rocketing as a result, but you'd be wrong. Over the last few years,
digital cameras have seen double-digit falls in sales in parallel
with the massive rise of smartphones and tablets (which now sell
than 1.5 billion each year). Check out a photo-sharing site like
Flickr and you'll find the most popular "cameras" are actually
phones: in September 2019, at the time I'm updating this article,
Flickr's top five cameras are all
iPhones. Is there a good reason to own a standalone digital
camera anymore or can you now do everything with a camera phone?
Photo: The pros and cons of digital cameras and smartphones summarized in three photos. Even point-and-shoot digital cameras like my old Canon Ixus have bigger, better, telescopic lenses (top) and sensors compared to the ones in the best smartphone cameras, like my new LG (middle). But smartphones undoubtedly score on connectivity and they have bigger, better, and clearer screens (bottom). Here you can see my smartphone's huge screen pictured in a preview photo on the Canon's tiny screen.
Sensors and screens
Step back a decade and there was no comparison at all between the
rough and clunky snapshot cameras on cellphones and even the most
mediocre compact digital cameras. While the digitals were boasting
ever-increasing numbers of megapixels, cellphones took crude snaps
little better than the ones you could get from a basic webcam (1
megapixel or less was common). Now all that's changed.
The 10-year-old Canon Ixus/Powershot digital camera I use routinely is rated at 7.1 megapixels, which is
perfectly fine for almost anything I ever want to
do. My new LG smartphone comes in at 13 megapixels, which
(theoretically, at least) sounds like it must be twice as good.
But wait! "Megapixels" are a misleading marketing ploy: what really matters is the size
and quality of the image sensors themselves. Generally, the bigger
the sensor, the better the pictures. Comparing the raw technical data, the Canon Ixus claims a 1/2.5" CCD
while the LG has a 1/3.06" CMOS (a newer, somewhat different type of sensor chip).
What do those numbers actually mean?
Sensor measurements are based on needlessly confusing math that I'm not going to explain here, and
you'll have take it on trust that both of these cameras have tiny sensors, about half the size of a pinkie nail (measuring less than 5mm in each direction), though the Canon sensor is significantly bigger.
The Digital Ixus, though eight years older than the LG smartphone, and with apparently half as many "megapixels,"
has a significantly bigger sensor chip and one that's likely to outperform the LG,
especially in lower light conditions.
The Canon also scores with a much better, telescopic lens
(technically rated 5.8–17.4 mm, which is equivalent to 35–105mm)—better quality and telescopic to boot—that can take everything from infinity-distance
landscapes to close-up macro shots of spiders and flies. But I have
to upload my photos to a computer to get a sense of how good or bad they
are because the Canon only has a tiny 6cm (2.5-inch) LCD screen.
The LG is over twice as good on the diagonal screen dimension, with a 14cm (5.5 inch) "monitor."
Where Canon estimates that the Ixus screen has 230,000 pixels, the LG
boasts quad HD (2560×1440 pixels), or roughly sixteen times more.
I might not be able to take better photos with the LG, but at least I can instantly assess and appreciate them on a screen as good as an HD TV (albeit still pocket-sized).
Bear in mind that my Canon is just a point-and-shoot compact, so this is not really a
fair comparison between what you can achieve with a really good digital camera and a really good smartphone.
My LG is right up at the better end of smartphone cameras, but the Ixus isn't anywhere near as good
as the best digital cameras. A professional DSLR would have a much bigger sensor than a smartphone—up to 3.6cm × 2.4cm—so it would be able to capture really fine detail in even the lowest of light levels.
It would also have a bigger and better screen and better (interchangeable) lenses.
Photo: This is a closeup of the camera inside the LG (with its cover popped off). What you're looking
at here is the lens: the image sensor chip is directly underneath it. (In case it's not clear, the red thing is a pen I'm pointing with.)
Of course, where smartphone cameras really score is in the "smartphone"
department: they're computers, in essence, that are pop-in-the-pocket
portable and always online. So not only are you more likely to
capture chance photos (because you're always carrying a camera), but
you can instantly upload your snaps to the aptly-named Instagram,
Facebook, or Twitter. And that's the real reason why smartphone
cameras have surpassed old-school digitals: photography itself has
changed from the digital-equivalent of the 19th-century Daguerreotype
(itself a throwback to the portrait paintings of old) to something
more off-the-cuff, immediate, and, of course, social. For the
purposes of Facebook or Twitter, often viewed on small-screen mobile
devices, you don't need more than a couple of megapixels, at most.
(Prove it yourself by downloading a hi-res image from Instagram or
Flickr, and you'll find it's seldom more than a couple of hundred
kilobytes in size and 1000 megapixels or less in each dimension,
making less than one megapixel in total.) Even on better
photo-sharing websites like Instagram and Flickr, most people will
never be browsing your photos in multi-megapixel dimensions:
they simply wouldn't fit on the screen. So even if your smartphone doesn't have masses of megapixels, it
doesn't really matter: most people flicking through your photos on their
smartphones won't notice—or care. Social media means never having
to say you're sorry you forgot your DSLR and only had your iPhone!
Now it's absolutely the case that photos taken with a top-notch
Canon or Nikon DSLR will beat, hands down, snapshots from even the
best smartphones—but that's often because it's not a
like-for-like comparison. Often, we're comparing good amateur photos
taken with smartphones to brilliant professional photos taken with
DSLRs. How much of what we're seeing is the camera... and how much
the eye of the photographer? Sometimes it's hard to separate the two
Professionals can achieve amazing results with smartphones—but so can amateurs,
with a bit of extra help. One of the drawbacks of smartphone cameras is the lack of
manual control (generally even less than with a basic compact
digital camera). You can get around that, to a certain extent, by
using add-on apps that give you much more control over
fiddly, old-school settings like ISO, aperture, shutter speed, and white balance.
(Search your favorite app store for keywords like "professional photography"
or "manual photography".) You can also add snap-on lenses to smartphones to get around the drawbacks of
a fixed-focal-length lens (though there's nothing you can do
about the tiny, poorer-quality image sensor). Once your photos are
safely snapped, there are plenty of photo-editing apps for smartphones as well, including a slimmed-down,
free version of PhotoShop, which can help you retouch your amateur
"sow's ears" into professional "silk purses."
So why still buy digital?
Since many people now own a smartphone, the real question is
whether you need a digital camera as well. It's very hard to see an
argument for point-and-shoot compacts anymore: for social-media
snaps, most of us can get by with our phones. For this website, I take a lot of macro
photos—close-ups of circuits and mechanical parts—with my Ixus that I couldn't possibly
capture with the LG, so I won't be jumping ship anytime soon.
If you want to take professional quality photos, there's really no comparison between
smartphones and DSLRs. A top-notch DSLR has a better-quality image
sensor (up to 50 times bigger in area than the one in a
smartphone) and a much better lens:
these two fundamentally important things make the "raw" image
from a DSLR far better. Add in all those fiddly manual
controls you have on a DSLR and you'll be able to capture a far
greater range of photos across a far wider range of lighting
conditions. If you really care about the quality of your photos,
instant-uploading to sharing sites might be a less important
consideration: you'll want to view your photos on a big monitor,
retouch them, and only share them when you're happy. Having said
that, you can now buy hybrid digital cameras with built-in Wi-Fi that
offer similar instant-sharing convenience to smartphones. And, of
course, there's nothing to stop you carrying a smartphone and a DSLR
if you really want the best of both worlds!
A brief history of photography
Artwork: The original digital camera, invented in the 1970s by Steven Sasson, worked a bit like an old-style
camcorder and needed a separate playback monitor. First (top), you took your photos with the camera (blue), which used a CCD to record them onto a magnetic tape (red). Later (bottom), when you got back home, you took out the tape, inserted it into a computer (orange), and viewed the pictures you'd taken on a computer monitor or TV (green). Artwork from US Patent 4,131,919: Electronic still camera by Gareth A. Lloyd, Steven J. Sasson courtesy of US Patent & Trademark Office.
- 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 that became known as 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.
- 1975: US electrical engineer Steven Sasson invented the first CCD-based electronic camera with Gareth Lloyd at Eastman Kodak.
- 1990s: Digital cameras started to become popular, gradually making film cameras obsolete.
- 2000s: Advanced cellphones with built-in digital cameras began to make standalone digital cameras redundant for everyday snapshot photography.