film based counterparts. These are the sensor and
the storage system both of which are akin to a
‘‘digital film.’’
The Charge-Coupled Device (CCD) was in-
vented in 1969–1970 making it the first digital sen-
sor array. The array consists of a horizontal and
vertical grid of light sensitive elements that convert
light into electricity, and which can then be con-
verted into digital data by an analog-to-digital con-
verter (ADC). Each of the elements of an array is
called a pixel—a word corrupted from ‘‘picture ele-
ment.’’ During the 1970s it was common to have an
array of several hundred pixels across by several
hundred deep. By the 1980s an array was developed
by Kodak that was 1,500 pixels by 1,000. This
totals 1.5 million pixels marking the first step into
measuring the resolution of camera images in
megapixels (one million pixels is a megapixel).
Other forms of more recent sensor device include
the Complementary Metal Oxide Semiconductor
(CMOS) which, for example, Canon Inc., uses
and the Junction Field Effect Transistor (JFET)
which Nikon employs.
However, to say that the camera is collecting so
many megapixels of information can be mislead-
ing. In order for a sensor to capture color it has to
filter out the light so that it is reading only one
color at a time. Digital cameras function through
capturing red green and blue light independently
by placing a color filter in front of each element.
The most typical arrangement of these Color Fil-
ter Arrays (CFAs) is the Bayer grid developed by
Kodak. This consists of a 22 grid which con-
tains two green pixels and one each of red and
blue. Because only half of the green pixels are
really captured and a quarter of the blue and
red, a process called demosaicing was developed
to interpolate the missing color information. This
results in a slight blurring occurring in images that
use the CFA system. The Bayer grid is not the
only system; Sony Corporation has developed
another grid system not based upon red, green,
and blue (RGB) but upon cyan, yellow, magenta,
and green filters, and Fuji film corporation has
developed a CCD that uses a grid system at a
45 angle which, they claim, gives better data for
demosaicing. They have also developed a system
that captures at two different sensitivities in order
to increase dynamic range. Foveon Inc. makes a
CMOS chip that uses three layers of sensors to
capture full color data at every location. However,
this sensor has a lower sensitivity than CFA sys-
tems because the light has to pass through three
layers of sensors.
Another method of capturing full color data is to
capture the RGB data in three passes. This is how
most large format cameras with digital backs work.
They scan the subject line by line, three times over
in single color in order to create a full color com-
posite in the host computer to which the back is
tethered. The disadvantage of this is time: it can
take several minutes to ‘‘shoot’’ an image rendering
any moving subject unsuitable; the advantage is
that the quality is unparalleled as full color infor-
mation is captured for every pixel.
For digital backs the images are stored on the
host computer’s hard drive although for the major-
ity of cameras this is not the case. There are various
forms of storage that retain the information cre-
ated. Currently, the most common of these is a
Secure Digital card (SD) a card with a tiny form
factor (1" 11 = 3 ") and so is suitable for use in
compact digital cameras. Most commonly used in
digital single lens reflex (SLR) digital cameras is the
CompactFlash (CF) form factor, which is the size
of a matchbook. This comes in two differing forms
where the type II is slightly thicker than the type I.
CF Type I stores the information in flash mem-
ory—a nonvolatile form of memory where power is
not needed to maintain the information—and the
type II form factor is used most often with a
Microdrive, which is a small hard drive. Microd-
rives are slightly slower than flash media but are
available in larger capacities. There are several
other forms of memory; however, these two are
the principal types.
Although the memory and the sensor array are
the two distinguishing features of the digital cam-
era, probably the most significant feature is in its
connectivity to other digital systems: it sits much
more readily within the workflow of the digitized
publishing environment such as newspapers; be-
cause of specialized imaging needs, it is employed
in areas such as astronomy; and, with the rise of the
personal computer, a mass market for digital cam-
eras has become a reality.
Astronomy demonstrated the first benefits of
using digital technology in the mid-to late 1970s
where because of their sensitivity to individual
photons digital sensors provided images that con-
ventional film was unable to capture. In 1981
Sony introduced the first digital camera with the
Mavica (MAgnetic VIdeo CAmera), the original
still video camera. Still video cameras are video
cameras that capture single shots as photographs,
which is the system still used in the majority of
compact digital cameras but not in SLRs. Soon
after this, in 1984, photojournalism conspicuouslyCAMERA: DIGITAL