Digital cameras use simple principle to render complex images.
A few decades ago, digital cameras were the stuff of science fiction, gadgets whose image-capturing abilities bordered on magic. Now they're commonplace in our modern society, so cheap and effective that they threaten to make film cameras obsolete. How do these photographic marvels work?
Exposure
Digital cameras expose their sensors the same way conventional cameras expose film. Light is focused through a lens containing a variable iris, a circular curtain that controls the amount of light passing through the lens. A shutter opens to allow the focused light to shine onto the sensor for a precise amount of time.
The Bayer Array
Before the light can impact the sensor, it passes through a grid of colored filters called a Bayer array. The Bayer array is made up of red, green and blue filters arranged in a checkerboard-like pattern. Because our eyes are more sensitive to green light, there are more green filters than red or blue. These filters keep light that is not the appropriate color from hitting the sensor, allowing the light that does get through to be sorted into the three primary colors.
The Sensor
The sensor records how much light falls through each part of the Bayer array. The sensor has no concept of color; it simply sorts through the information it is given, the way a bank teller might separate coins without regard to their total value.
Bayer Demosaicing
The camera's computer compiles an image from the sensor's data through a process called Bayer demosaicing. This process records the intensity of each primary color for each pixel (meaning "picture element"), resulting in a mix that potentially includes more than 16 million possible colors.
Writing Files
Each pixel is written to the camera's memory card as a series of ones and zeros that correspond to its primary color values. If the camera delivers "RAW" images, this string of ones and zeros will be left uncompressed. However, if the camera delivers "JPEG" images, the camera's computer will compress the string of numbers and throw out redundant values, greatly reducing file size.
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