Hardware Reference
In-Depth Information
horizontal resolution
(also called the
x-direction sampling rate
). Some scanners also report
a
vertical dpi
, or
vertical resolution
, also called the
y-direction sampling rate
. This is the
number of separate lines per inch that are recorded as the light moves down the page.
Some scanners also have an
interpolated resolution
. Interpolation invents extra pixels
between the actual scanned ones and uses a math formula to determine their value. For
example, if one pixel has a value of 10 and the next one is 20, interpolation will insert a
pixel between them with the value of 15.
In a color scanner, there are three separate evaluations of each pixel in the image:
amount of red, amount of blue, and amount of green. The original scanners were 1-bit
systems; they were black-and-white only and transmitted a single bit of data for each
cell in the CCD. The number of bits is the number of binary digits required to represent
each pixel's value. In a 1-bit system, each pixel is either 0 or 1, off or on. Then came 4-bit
scanners (16 unique shades of gray) and 8-bit (256 shades of gray). Today, all scanners
support at least 24-bit scanning (8 bits each for red, green, and blue). This is known as
true
color
, and it uses a 24-digit binary code to represent each pixel.
Digital Cameras
A digital camera is like a scanner except that it works standing up. Rather than scan a fl at,
two-dimensional image, it projects its vision out into the 3D world and creates an image
based on what it sees.
How Digital Cameras Work
Technologically, a digital camera has a lot in common with a traditional camera. They both
have a lens that “sees” the image, and they both have focusing controls for that lens and
usually a built-in fl ash. The main difference is that a traditional camera's lens sends its data
to fi lm, whereas a digital camera sends its data to a digital storage medium such as fl ash
RAM, or directly to a computer if it's connected to one (as with a webcam).
The camera lens in a digital camera sends its data to a CCD like the one in a scanner, which
measures the amount of light received in each cell and conveys an electrical charge to the
camera's processor in proportion to the amount of light in a particular spot. As with a scanner,
a color fi lter is applied to the CCD to enable color photography. This data passes through an
analog-to-digital converter, which turns those electrical charges into binary computer data.
The data from the CCD passes through a digital signal processor that cleans it up and
makes some corrections that improve the image quality. Then the data is stored inside the
camera until it can be transferred to a computer.
Digital Camera Features
Some of the factors that differentiate one digital camera from another include the following:
Resolution
This is the number of pixels that form an image, measured in millions
(megapixels). The more pixels, the better an image will look when printed at a large size.
Multiply the camera's maximum picture height by the maximum picture width to determine
