TECHNOLOGY USED
Instead of film, digital cameras use electronic sensors that
are sensitive to light. There are currently two types of sensors in use: the
charge coupled device (CCD) and complementary metal oxide semiconductor (CMOS).
Each of these sensor types contains an array of light-sensitive sites, called
photosites. These photosites are usually square in shape and arranged in a
rectangular grid of rows and columns. Each photosite converts the light hitting
it into electrons (electrical charge). The more light that strikes the photosite,
the more electrons that are produced.
Most of the sensors currently in use are based on CCD technology. Although
this technology is quite advanced, and expensive. The production of CMOS sensors
is based on the same technology used to produce microprocessors and other
computer chips. As a result, their production cost is less. Also, additional
circuitry can be added on the same chip as the sensor, eliminating the need
for external processing chips required with CCD sensors. In time, CMOS sensors
will catch up and pass CCD sensors as the sensor of choice.
Did you know that the sensor photosites are color blind? Each photosite simply
collects the amount of light striking it and converts it to electrical charge.
There is no color data generated. So, how is color data generated? There are
several ways to do this. You could split the light coming through the camera
lens and route it to three different sensors, each of which could be adjusted
to react to a certain portion of the light spectrum. This is done by covering
each sensor with a filter colored to accept one of the three primary colors:
red, green, or blue. This technique is used in top-of-the-line cameras.
The table lists has some common sensor sizes.

As to which sensors are being used, the 1- and 2-Mpixel cameras use the type
1/2.7” or type 1/2”. Most of the 3- and 4-Mpixel cameras use the
1/1.8” sensors. The number of pixels captured by the image sensor is
commonly known as the resolution. For example, a camera may have a resolution
of 1024 x 768 pixels for a total of 786,432 pixels. Another camera may have
a resolution of 1600 x 1200 pixels for a total of 1,920,000 pixels, or approximately
two megapixels
The number of pictures that can be stored depend on their resolution, storage
format, and capacity of the storage medium. The typical image file size is
around 400 Kbytes. A 16-Mbyte storage card typically holds about 40 such images.
The pictures can then be uploaded to your computer via a serial or USB port.
The storage card can then be cleared and used for the next set of pictures.