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5. How do digital cameras store photographs?
6. What feature allows mobile phone users to take pictures?
7. What kind of software is used to manipulate video clips on
the computer?
15. Read Text C:
Text C
Output Devices: Display Screens
A computer monitor is an output device that displays infor-
mation in pictorial form, it includes a screen, circuitry and the case
in which that circuitry is enclosed. It provides instant feedback by
showing you text and graphic images as you work or play. A
monitor is also known as a screen or a visual display unit (VDU).
Older computer monitors made use of cathode ray tubes
(CRT), which made them large, heavy and inefficient. Nowadays,
flat-screen LCD monitors are used in devices like laptops, PDAs
and desktop computers because they are lighter and more energy
efficient. LCD monitors are also called flat panel or flat screen dis-
plays.
A
CRT monitor is similar to a traditional TV set. It contains
millions of tiny red, green and blue phosphor dots that glow when
struck by an electron beam that travels across the screen and create
a visible image.
An LCD (Liquid Crystal Display) is made of two glass
plates with a liquid crystal material between them. The crystals
block the light in different quantities to create the image. Active-
matrix LCDs use TFT (thin film transistor) technology, in which
each pixel has its own switch. The amount of light the LCD moni-
tor produces is called brightness or luminance, measured in cd/mi
(candela per square metre).
Basic features and modern technologies
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Resolution – the clarity of the image depends on the number
of pixels (short for picture elements) contained on a display, hori-
zontally and vertically. A typical resolution is l024x768. The
sharpness of images is affected by dot pitch, the distance between
the pixels on the screen. The shorter the distance, the sharper and
clearer the images are, so a dot pitch of 0.28 mm or less will pro-
duce a sharp image.
Two measurements describe the size of your display: the as-
pect ratio and the screen size. Screen size – the viewing area is
measured diagonally; in other words, 17” screen measures l7 inch-
es from the top left corner to the bottom right. Aspect Ratio is the
relation of the vertical length to the horizontal length of the moni-
tor (e.g. 16:9 or 4:5). Historically, computer displays, like most
televisions, have had an aspect ratio of 4:3 – the width of the
screen to the height is four to three. For widescreen LCD displays,
the aspect ratio is 16:9, very useful for viewing DVD movies,
playing games and displaying multiple windows side by side.
High-definition TV also uses this format.
Inside the computer there is a video adapter, or graphics card,
which processes images and sends signals to the monitor. CRT
monitors use a VGA (video graphics adapter) cable, which con-
verts digital signals into analogue signals. LCD monitors use a
DVI (digital video interface) connection.
Colour depth refers to the number of colours a monitor can
display. This depends on the number of bits used to describe the
colour of a single pixel. For example, an old VGA monitor with an
8-bit depth can generate 256 colours and a Super VGA with a 24-
bit depth can generate 16.7 million colours. Monitors with a 32-bit
depth are used in digital video, animation and video games to get
certain effects.
Refresh rate is the number of times that the image is drawn
each second. If a monitor has a refresh rate of 75 Hertz (Hz), it
means that the screen is scanned 75 times per second. If this rate is
low, you will notice a flicker, which can cause eye fatigue.
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PCs can be connected to video projectors, which project the
image onto a large screen. They are used for presentations and
home theatre applications.
In a plasma screen, images are created by a plasma discharge
which contains noble (non-harmful) gases. Plasma TVs allow for
larger screens and wide viewing angles, making them ideal for
movies. Organic Light-Emitting Diodes (OLEDs) are thin-film
LED displays that don’t require a backlight to function. The mate-
rial emits light when stimulated by an electrical current, which is
known as electroluminescence. They consume less energy, pro-
duce brighter colours and are flexible – i.e. they can be bent and
rolled up when they’re not being used.
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