The square or rectangular shaped diode(s), used to collect the light striking
the image during the exposure, is referred to as the image sensor. The CCD (Charged
Coupled Device) is one of the most popular types of digital image sensors (imaging
chip) used in digital cameras. Another type is the CMOS (Complementary Metal
Oxide Semiconductor) which is a newer technology than CCDs and is also becoming
very popular.
CCD (Charged Coupled Device)
The square or rectangular shaped diodes are the current or most often used
CCD types. Newer types use octagonal-shaped diodes, which can be configured
into more diodes per inch resulting in a more detailed image. The image sensor
changes the light it senses into numbers or data that represent different
levels of brightness. The sensor measures the level of red, green, and blue
and makes a color interpolation, assigning values to each image pixel. The
CCD may produce 4 MB of color data which, when interpolated (pixels are added)
increases to 12 MB of data, becoming a 12 MB image file.
To capture an image, digital cameras use the CCD technologies single-pass
(one shot), 3-pass, or 4-pass, and scanning processes, several of which may
be selectable options on one camera.
- Single pass captures an image with one exposure and is best used for action
shots or any images in which movement occurs. The resolution is most often
low.
- 3 and 4-shot exposure provide higher resolution and are best used for
product shots.
- A standard 3 or 4-pass exposure scans the image for red, green, and blue
colors (RGB processing). The 4-pass process will scan green twice in order
to separate the component colors correctly. Since the images are shot 3
or 4 times (one each for red, and blue, and one or two for green) there
must be no movement or the image will be blurred.
- Scanning exposure, most often found on camera backs, creates the largest
file size with the highest resolution. Images of products or any non-moving
subjects that will be enlarged are best produced with scanning technology.
- Cameras using scanning technology do not interpolate color information,
since they contain rows of sensors (one red, one green, an one blue) which
collect the color information on the entire image as it is scanned line
by line.
CMOS (Complementary Metal Oxide Semiconductor)
The CMOS is a widely used type of semiconductor which is used as an imaging
sensor in digital cameras. It uses both negative and positive polarity circuits,
with only one of the circuit types on at any time. This configuration allows
the CMOS to use less power than CCD technology. The chips are well suited
for devices that are battery powered such as digital cameras and portable
computers because the lower power consumption provides more operational time.
Battery powered CMOS memory is also used in personal computers to maintain
the date and the time and the system setup commands after the main power source
has been switched off.
The CMOS chip is known as a "camera on a chip" because of the advantages
it has over CCD technology. CCDs require several support chips to function,
are more expensive to produce, and require more power than CMOS. CCDs are
still the best choice for applications requiring the highest level of quality
because of the high resolution and high definition that they provide, but
CMOS technology is improving and are becoming much more common in lower cost
digital cameras.
