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SchoolTrack 5 · Digital

LESSON · THE SENSOR

How a digital camera sees

A sensor is a grid of millions of light-sensitive sites. Each turns light into a small electric signal; the camera turns the signals into numbers, and the numbers into a picture.

  1. 01

    Light

    Through the lens onto the sensor.

  2. 02

    Photosites

    Each one converts light into a signal in proportion to its brightness.

  3. 03

    Colour filter

    Most sensors put a red, green or blue filter over each site.

  4. 04

    Processor

    Fills in the missing colours and makes the image.

  5. 05

    File

    RAW keeps the data; JPEG keeps a finished picture.

THE BAYER PATTERN

HALF GREEN · A QUARTER RED · A QUARTER BLUE

Why so much green

The pattern is named after Bryce Bayer of Eastman Kodak, who patented it in 1976. Each site sees only one colour; the camera estimates the other two from its neighbours. He used twice as many green sites as red or blue to copy the human eye, which in daylight is most sensitive to green.

RAW

What the sensor recorded. More room to fix exposure and colour later; larger files.

JPEG

A finished, compressed picture. Ready to share; less room to change it.

SENSOR SIZES · SAME SCALE

Bigger sensor, more light

A larger sensor gathers more light at the same framing, which means less noise and a softer background at the same f-number.

  • Full frame36 × 24 mm
  • APS-Cabout 23.5 × 15.6 mm
  • Micro Four Thirds17.3 × 13 mm
  • 1-inch type13.2 × 8.8 mm
1975

Steven Sasson, an engineer at Eastman Kodak, built a self-contained electronic camera on a monochrome CCD sensor.