Hardware Reference
In-Depth Information
In the post-capture phase, the camera's software applies the white-balance
color correction to compensate for reddish or bluish light (e.g., from a subject in
shadow or the use of a flash). Then it applies an algorithm to do noise reduction
and another one to compensate for defective CCDs. After that, it attempts to
sharpen the image (unless this feature has been disabled) by looking for edges and
increasing the intensity gradient around them.
Finally, the image may be compressed to reduce the amount of storage re-
quired. A common format is
JPEG
(
Joint Photographic Experts Group
), in
which a two-dimensional spatial Fourier transform is applied and some of the
high-frequency components omitted. The result of this transformation is that the
image requires fewer bits to store but fine detail is lost.
When all the in-camera processing is completed, the image is written to the
storage medium, usually a flash memory or
microdrive
. The postprocessing and
writing can take several seconds per image.
When the user gets home, the camera can be connected to a computer, usually
using a USB or proprietary cable. The images are then transferred from the cam-
era to the computer's hard disk. Using special software, such as Adobe Photoshop,
the user can then crop the image, adjust brightness, contrast, and color balance,
sharpen, blur, or remove portions of the image, and apply numerous filters. When
the user is content with the result, the image files can be printed on a color printer,
uploaded over the Internet to a photo-sharing Website or photofinisher, or written
to CD-ROM or DVD for archival storage.
The amount of computing power, RAM, disk space, and software in a digital
SLR camera is mind boggling. Not only does the computer have to do all the
things mentioned above, but it also has to communicate with the CPU in the lens
and the CPU in the flash, refresh the image on the LCD screen, and manage all the
buttons, wheels, lights, displays, and gizmos on the camera in real time. This is an
extremely powerful embedded system, often rivaling a desktop computer of only a
few years earlier.
Each computer has a set of characters that it uses. As a bare minimum, this set
includes the 26 uppercase letters, the 26 lowercase letters, the digits 0 through 9,
and a set of special symbols, such as space, period, minus sign, comma, and car-
riage return.
In order to transfer these characters into the computer, each one is assigned a
number: for example, a = 1, b = 2, ..., z = 26, + = 27,
= 28. The mapping of
characters onto integers is called a
character code
. It is essential that communi-
cating computers use the same code or they will not be able to understand one an-
other. For this reason, standards have been developed. Below we will examine
three of the most important ones.
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