Instead of exposing a photosensitive chemical known as film to a scene to create an imprinted image, most digital cameras use a charge-coupled device (CCD), an electronics instrument that creates a pixel map based on the electric charge generated when photons slam into a sensitive material. This phenomenon is called the photoelectric effect, and was elucidated by Albert Einstein in a famous 1905 paper. Less frequently used than a CCD is a complementary-metal-oxide-semiconductor (CMOS).
The term CCD-based camera is sometimes used interchangeably with digital camera, because by its very nature the CCD-based camera takes pictures — photos with a certain pixel-by-pixel resolution that can be encoded digitally. These files can easily be transferred from a camera to many devices, including computers, screens, phones, and printers.
A charge-coupled device is an integrated circuit, meaning it uses multiple semiconductor elements on a unified platform to achieve its goals. The active components of a CCD-based camera are the capacitors. These are linked in a circuit, which is why they're called charge-coupled. A capacitor is a basic electronics device that stores a potential difference, or voltage, in the variance between two plates with equal but opposite electrical charges.
A lens projects the image onto the CCDs, and each capacitor acquires a charge proportional to the brightness of incoming light. CCDs are not inherently color-sensitive, and to take color photos, a Bayer mask must be used to selectively filter light into designated pixels based on color. Upon acquiring the charge, the capacitors begin passing their charge to adjacent capacitors in a charge-coupled, daisy-chain fashion. A register at the end of the array makes the appropriate measurements, and a 2D pixel map is created.
Because their sensitivity to light is about 35 times that of a conventional camera, approaching the quantum limit, digital cameras are often favored by event photographers and astrophotographers alike. Because of the lack of active chemical components, images do not need to be “developed” and are stored directly in the camera shortly after exposure.
