Allied Guppy, Technical Manual, Page: 227 / 238

Glossary
GUPPY Technical Manual V4.0.1
227
PxGA P i x el G ain A mplifier
Pixel Pixels are generally thought of as the smallest complete sample of an
image. The definition is highly context sensitive. For example, we can
speak of pixels in a visible image (e.g. a printed page) or pixels carried by
one or more electronic signal(s), or represented by one or more digital
value(s), or pixels on a display device, or pixels in a digital camera (pho-
tosensor elements). This list is not exhaustive and depending on context
there are several synonyms which are accurate in particular contexts, e.g.
pel, sample, bytes, bits, dots, spots, superset, triad, stripe set, window,
etc. We can also speak of pixels in the abstract, in particular when using
pixels as a measure of resolution, e.g. 2400 pixels per inch or 640 pixels
per line. Dots is often used to mean pixels, especially by computer sales
and marketing people, and gives rise to the abbreviation DPI or dots per
inch.
The more pixels used to represent an image, the closer the result can
resemble the original. The number of pixels in an image is sometimes
called the resolution, though resolution has a more specific definition. Pix-
els can be expressed as a single number, as in a
three-megapixel digital
camera, which has a nominal three million pixels, or as a pair of numbers,
as in a
640 by 480 display , which has 640 pixels from side to side and 480
from top to bottom (as in a VGA display), and therefore has a total number
of 640 × 480 = 307,200 pixels.
The color samples that form a digitized image (such as a JPG file used on
a web page) are also called pixels. Depending on how a computer displays
an image, these may not be in one-to-one correspondence with screen pix-
els. In areas where the distinction is important, the dots in the image file
may be called texels.
In computer programming, an image composed of pixels is known as a bit-
mapped image or a raster image. The word raster originates from analogue
television technology. Bitmapped images are used to encode digital video
and to produce computer-generated art.
Pulse-width
modulation Pulse-width modulation of a signal or power source involves the modula-
tion of its duty cycle, to either convey information over a communications
channel or control the amount of power sent to a load.
PWM PWM = p ulse- w idth m odulation
QE QE = q uantum e fficiency
Quadlet Four bytes of data