Traditional cameras capture images onto film while digital cameras use an electronic chip known as a Charged Coupling Device (CCD). The CCD is actually a grid of miniature light-sensitive diodes. These diodes convert photons (light) that strikes them into electrons (electrical impulses). The technical name for these diodes is ‘photosite’. The brighter the light is that hits the photosite the stronger the electrical charge is that’s produced.
After converting the photons into electrons, a mini-computer, located inside of the camera, reads the stored electrical value in each photograph. Then a built-in analog-to-digital converter turns the stored electrical value into a digital value. These digital values are then stored on the cameras memory storage device. When these digital values are recalled by software, and displayed on a screen, they reproduce the image that was originally captured by the camera or digital input device.
The digital image that is created by the CCD is huge. It’s far too big to be easily stored in the relatively little amount of storage space that’s available to a digital camera. Accordingly, the camera’s computer compresses the image to make it smaller.
There are two basic methods for achieving this compression. The first method takes advantage of repetitive patterns in the image. For example, if you are taking a picture of an airplane that is flying in the sky, a lot of the picture will be a chunk of blue sky. The camera recognizes that there are multiple parts of the image containing the same digital information, so it only records a small piece of the sky. Then it simply creates a map to tell it where the rest of the sky belongs. When the picture is ultimately displayed the sky appears exactly the same as it did in the original image when it was first captured. The only difference is that the overall storage requirements were reduced thanks to the camera’s clever mapping techniques.
The other method uses a procedure called irrelevancy. This methodology automatically removes digital information that is not visible to the human eye such an infra red light.