1969

Digital Imaging

Bruce E. Bayer (1929–2012), Willard S. Boyle (1924–2011), George E. Smith (b. 1930)

The first photograph was sent by wire in 1907, and the first photograph was digitized with a scanner in 1957. But capturing an image directly from light to digital form required the invention of light-sensitive semiconductors that could be packed into a rectangular array.

That invention was the charge-coupled device (CCD), developed by Willard S. Boyle and George E. Smith at Bell Laboratories in New Jersey. The device makes use of the photoelectric effect, by which certain kinds of materials eject electrons when stimulated by light. The CCD collects these electrons in an array of capacitors, with each capacitor receiving an electric charge proportional to the amount of light to which it is exposed. The electrons then cascade across the CCD to its edge, where their voltage is measured and digitized.

In a digital camera, the light-sensing capacitors are arranged in a two-dimensional array, so that the entire image is captured at once. But in satellites and fax machines, the CCD is arranged as a one-dimensional strip, and the image (the Earth below, or a piece of paper) sweeps by the sensor.

The first CCDs captured only black-and-white photos; color requires capturing three separate images through three colored filters—red, green, and blue—and electronically combining them by overlaying the image sensor with an array of tiny red, green, and blue filters. In practice, the filters are arranged in an R, G, B, G pattern, called a Bayer color mask after its inventor, Bruce Bayer at Kodak. This RGBG pattern produces twice as many green pixels as red or blue, which works out well, because people are most sensitive to green light. As a result, the sensor provides greater spatial resolution and dynamic range, without sacrificing too much color resolution and accuracy.

For their work on the CCD, Boyle and Smith shared the 2009 Nobel Prize in Physics.

SEE ALSO Fax Machine Patented (1843), First Digital Image (1957)

The technology inside smartphones’ cameras can be traced back to the invention of the charge-coupled device (CCD).