Transcript CSC 150 UNGRADED QUIZ - Concordia University Wisconsin

HUMAN COMPUTER
INTERACTION 3:
OUTPUT
UNITS
Printers, monitors and
special purpose units.
Focus on character (and image)
formation and transfer.
1. Introduction.
 The purpose of any output unit is
 (1) to translate binary into useful
information,
 (2) display printing characters as characters,
 (3) execute non-printing control characters,
such as tab, line feed, form feed, scroll etc.
2. Printers.
 The purpose of printers is to produce
“hardcopy” of documents or graphics. So
much for the “paperless office”!
 There are three main printer concepts:
 (A) Printer speed,
 (B) Character formation method,
 (C) Character transfer method.
2A Printer speed.
 One measure of printer speed is how much
is printed at any one time.
 The early printers were character printers
printing one character after another e.g.
daisy wheel, dot matrix.
 Businesses used line printers, e.g. the chain
printer.
 The norm is now page printers e.g. laser
printers. Speed in pages per minute.
2B. Character formation method.
 How are the symbols on the page created?
 2 main methods:
 (1) Full form. Characters are fully formed
in the H/W e.g. daisy wheel / golf ball.
 (2) Simulation. There are no pre-formed
characters. They are created “on the fly”
e.g. as an arrangement of dots (dot matrix).
2B continued.
 See diagrams.
 How is a character created by a dot matrix
print head?
 A column at a time.
 How does the printer know which pins to
fire and not fire for each column?
 The S/W driving the printer maintains a
matrix of 0’s and 1’s.
2B continued.
 Comparison between full form e.g. daisy
wheel and simulation e.g. dot matrix.
 (1) Quality of printing.
 (2) Speed of printing.
 (3) Flexibility of fonts.
 (4) Graphic capability.
2C Character transfer method.
 How does the image get to the paper?
 Two methods:
 (1) Impact method: uses a physical
mechanism [e.g. a hammer to strike a
ribbon]. Includes typewriters, daisy wheels,
chain printers, impact dot matrixes.
 Note: not all dot matrix printers use impact.
2C Character transfer continued.
 (2) Non-impact. No mechanism strikes the
paper.
 Examples: (A) ink jet printers. Electric
current behind the nozzles heats ink until it
squirts onto the page,
 (B) laser printers. Each dot of a character is
converted into a light signal sent by a laser.
How do laser printers work?
 1. Each dot is a light signal.
 2. Light signals are directed at a photosensitive drum which rotates.
 3. Where light hits the drum it magnetizes a
spot. This attracts toner to that spot.
 4. The drum passes over paper.
 5. Heat and pressure transfer toner to
paper. See diagrams / CD.
Important Note:
 Laser printers still use a dot matrix to
represent characters, but:
 (a) It is a larger matrix (better resolution),
 (b) Impact is not used (no pins),
 (c) an entire page is prepared very rapidly
before transferring it to paper.
3. Monitors.
 Synonyms for monitors? CRTs, VDTs,
VDU’s, screens.
 3 main concepts for monitors.
 (A) Size,
 (B) Character formation method,
 (C) Character transfer method.
3A. Size.
 The size of the tube affects the viewable
area. A standard screen is 15” but for some
applications, 17”, 18” or 20” are needed
because of the amount that must be
displayed on one screen. E.g. for CAD /
CAM, art, weather systems.
3B. Character formation method.
 The character formation method is similar
to printers.
 CRT screens contain 100,000’s of dots
called “Pixels” = picture elements.
 E.g. SuperVGA 800 * 600 = 480,000 pixels.
3B. Character formation
continued.
 A pixel is really a positively charged
phosphor dot K+.
 It can be lit up when struck by electrons
from an electron gun in the back of the
CRT.
 How are shapes created?
 By selectively lighting up pixels.
3B. Character formation
continued.
 How does the gun know which pixels to
light up?
 S/W supplies a matrix of 0’s and 1’s.
 1 -- light up;
 0 -- don’t light up.
3C. Character transfer method.
 A non-impact method is used (nothing
mechanical strikes the screen, only
electrons).
 See diagram of monochrome screen.
 Problems: How do we maintain a whole
screen with only one gun? Since phosphor
only glows for a fraction of a second, how
do we keep an unchanged image constant?
3C. Character transfer continued.
 Answer:
 A very fast refresh rate. The entire screen is
“re-drawn” 60-80 times each second. Note
the cycle speed in Hz.
 Industry standard is 72Hz. The human eye
detects flicker even at 60Hz!
Color versus monochrome.
 Monochrome.
 (1) Actually get two colors: background and
foreground.
 (2) Each pixel glows one color but can
change intensity.
 (3) Simulate different colors by
grayscaling—also used for monochrome
printing.
Color versus monochrome.
 Color.
 (1) Pixel has three parts (Red, Green and
Blue), like a palette.
 (2) 3 electron guns needed to mix the
colors.
 (3) Why color?
4. Special purpose units.
 See your text book for more specific
information, photographs etc.
 (1) Plotters,
 (2) Voice synthesizers,
 (3) Music.
 Special sound cards and speakers needed
for good quality.