How Do Pictures and Videos Work? Pixels, Colours and Moving Frames
Every photo on every screen is a grid of tiny coloured squares. Every video is just a lot of those pictures, shown fast enough to fool your eyes.
The whole idea, in one diagram
A picture is a grid of pixels, and each pixel is one colour.
Every colour on a screen is mixed from just three lights: red, green and blue.
Video shows around 24 to 60 separate pictures every second, and your brain joins them up.
What problem did it solve?
To keep a picture of something you had to draw or paint it, which took skill and hours. To show something moving you had to be there. Most people went their whole lives with no image of their own family.
First chemistry captured light onto a plate. Then electronics turned light into numbers, so a picture could be copied, sent and edited without ever losing quality.
Almost everyone now carries a camera. Memories, news, science and school all changed, and so did the fact that a picture can no longer be trusted just because it exists.
How it started
- 1826
The first photograph that lasted
👤 Nicéphore Niépce, France
He pointed a box at the view from his window and left it there. The exposure took hours, and the result is a blurry rooftop scene that still exists.
Why it mattered: It was the first time light drew a picture by itself, with no artist. Everything since is a faster version of the same idea.
- 1878
Proving a horse flies
👤 Eadweard Muybridge, England and USA
People argued about whether a galloping horse ever has all four hooves off the ground. He set up a row of cameras triggered as the horse ran past, and settled it. It does.
Why it mattered: A row of still pictures played in order looked like movement. That accidental discovery is the beginning of film.
- 1895
The first paying cinema audience
👤 The Lumière brothers, France
They showed short films to an audience who had paid to get in, projected onto a wall.
Why it mattered: Moving pictures became something you watched together. The pattern of an audience in a dark room lasted more than a century.
- 1975
The first digital camera
👤 Steven Sasson at Kodak, USA
A camera the size of a toaster that captured 0.01 megapixels in black and white, took 23 seconds to record one picture onto a cassette tape, and needed a television to view it.
Why it mattered: It was the first picture made of numbers rather than chemistry. His employer, who sold film, was not enthusiastic.
- 1992
Squeezing pictures down
👤 The JPEG group, international
A shared method for making picture files far smaller by throwing away detail human eyes barely notice.
Why it mattered: Without squeezing, a single photo would take minutes to load. Almost every photo you have ever seen online was shrunk this way.
- 2000s
A camera in every pocket
👤 Phone makers
Cameras were added to phones. The pictures were poor at first, and people took them anyway, everywhere, constantly.
Why it mattered: News, families and memory all changed. Events are now recorded by whoever happened to be standing there.
- 2010s onwards
Video that arrives as you watch
👤 Streaming services
Instead of downloading a whole film first, video arrives in small chunks, and the quality is lowered automatically when your connection struggles.
Why it mattered: It is why a video suddenly goes blurry rather than stopping. The player chose a smaller version to keep going.
Who made it happen
Nicéphore Niépce
1765 to 1833 · France
Made the first photograph that survived, around 1826, using an exposure that lasted hours.
Eadweard Muybridge
1830 to 1904 · England and USA
Used a row of cameras to prove a galloping horse leaves the ground, and accidentally invented the idea of film.
Steven Sasson
born 1950 · USA
Built the first digital camera in 1975 for Kodak, a company that made its money selling film.
The Lumière brothers
1895 · France
Held the first film shows for a paying audience, projected on a wall.
Edwin Land
1909 to 1991 · USA
Invented instant photography after his daughter asked why she could not see the picture straight away.
Willard Boyle and George Smith
1969 · USA
Invented the light-sensing chip that made digital cameras possible. They shared a Nobel Prize in 2009.
From light hitting a lens to a picture on your screen
- 1
Light lands on a sensor
A lens focuses light onto a chip covered in millions of tiny light detectors. The brighter the light hitting one, the bigger the number it produces.
- 2
Colour is measured three times
Each detector sits behind a red, green or blue filter, so it only measures one colour. Mixing those three amounts can make almost any colour a human can see.
- 3
The picture becomes a list of numbers
The result is a grid of pixels, each one recorded as an amount of red, green and blue. That grid of numbers IS the photo now.
- 4
It gets squeezed
The raw grid would be enormous, so the file is compressed by removing detail your eyes barely notice. Squeeze too hard and you can see it: blocky patches and fuzzy edges.
- 5
A screen rebuilds it with light
A screen has its own tiny red, green and blue lights. It reads the numbers and lights each pixel to match. Put your eye very close and you can sometimes see the three colours.
- 6
For video, do it all again, very fast
A video is 24 to 60 of these pictures every second. Because each one is so similar to the last, video files only store what changed, which is why a still scene needs far less data than a busy one.
Nothing on a screen is really a picture. It is a grid of numbers that a screen turns back into light, which is exactly why a photo can be copied perfectly and also changed without leaving a mark.
Find a magnifying glass and hold it very close to a switched-on screen, or take a photo of a screen and zoom right in. You should be able to see the separate red, green and blue lights that are pretending, from a distance, to be white.
Quiz: how much did you remember?
Quiz time!
10 questions, picked at random from 30. No sign-in and no score is kept. Play as many times as you like, the questions change every time.
Questions about pixels and video
What is a pixel?
A pixel is one tiny square of a picture, and it holds one colour. The word is short for picture element. A phone photo is usually several million of them arranged in a grid.
Why are screens red, green and blue?
Human eyes have three kinds of colour detector, roughly matching red, green and blue light. Mixing just those three in different amounts can fool your eye into seeing almost any colour.
What does megapixel mean?
One megapixel is a million pixels. A 12 megapixel camera captures about twelve million tiny squares per photo. More is not automatically better, because the size and quality of the sensor and lens matter just as much.
How does video work?
A video is a fast sequence of still pictures, usually 24 to 60 every second. Your eyes and brain cannot separate them that quickly, so you see smooth movement instead of a flicker book.
Why do videos go blurry sometimes?
The player is watching your connection. If data is arriving too slowly it switches to a smaller, lower quality version so the video keeps playing rather than stopping to load.
Why do some photos look blocky?
Because they were compressed too hard. Squeezing a file throws away detail to make it smaller, and if you take away too much you start to see square patches and fuzzy edges.
What was the first photograph?
A view from a window in France, taken by Nicéphore Niépce around 1826. The exposure took hours, which is why nothing in it is moving, and the picture still exists today.
Can you trust a photo?
Less than people used to. Because a photo is only numbers, it can be changed without leaving any obvious trace, and computers can now create pictures of things that never happened. Where a picture came from matters as much as what it shows.
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