CMOS sensor: how a camera turns light into a photo

A CMOS sensor is a chip with millions of light-sensitive pixels that turns the light coming through the lens into an electrical signal. Almost all modern phone cameras, cameras and webcams use CMOS sensors.

Sensor pixels catch light like buckets catch rain

In plain words

Imagine a field of millions of little buckets out in the rain. Each bucket is a pixel and the rain is light. After the "shot", you count how much water each bucket collected and draw the picture from that. A colour filter over the buckets lets through only its own colour: red, green or blue.

How it works

The lens focuses light onto the sensor.
Each photodiode pixel turns light into an electric charge.
Colour filters (a Bayer pattern) let different colours through.
Circuitry reads the charge from the pixels and turns it into numbers.
The ISP processes this data and creates the photo.

A CMOS sensor turns light into a signal

Where you'll see it

Well-known makers of phone sensors are Sony (the LYTIA and IMX series), Samsung (ISOCELL) and OmniVision. Camera specs sometimes give the sensor model and size: "Sony LYT-900, 1-inch".

Does it matter when buying

The sensor model and size are useful clues when choosing a camera phone. Large modern Sony and Samsung sensors usually give better night shots. But without good processing, even a top sensor will not save the day.

Myths

Myth: CMOS is worse than old CCD sensors. Reality: Modern CMOS overtook CCD on most counts long ago.
Myth: Megapixels are a sensor's main spec. Reality: Sensor and pixel size often matter more.

FAQ

What is a BSI sensor?

A back-side illuminated sensor where the wiring does not block the light - it is more sensitive.

What is a stacked sensor?

A multi-layer sensor with fast memory - faster readout and less distortion with motion.

Can I find out the sensor model?

Sometimes from specs or reviews, or with camera analysis apps.