MULTIMEDIA INPUT/OUTPUT TECHNOLOGIES
Multimedia Input and Output Devices
Wide ranges of Input and
output devices are available for multimedia.
Image Scanners: Image scanners are the scanners by which
documents or a manufactured part are scanned.
The scanner acts as the camera eye and take a photograph of the document,
creating an unaltered electronic pixel representation of the original.
Sound and Voice: When voice or music is captured by a
microphone, it generates an electrical signal. This electrical signal has analog sinusoidal waveforms. To
digitize, this signal is converted into digital voice using an
analog-to-digital converter.
Full-Motion Video: It is the most important and most complex
component of Multimedia System. Video
Cameras are the primary source of input for full-motion video.
. Pen Driver: It is a pen device driver that interacts with the
digitizer to receive all digitized information about the pen location and
builds pen packets for the recognition context manager. Recognition context
manager: It is the main part of the pen system. It is responsible for
co-ordinating windows pen applications with the pen. It works with Recognizer,
dictionary, and display driver to recognize and display pen drawn objects.
Recognizor: It recognizes hand written characters and converts them to ASCII.
Dictionary: A dictionary is a dynamic link library (DLL); The windows form
pen computing system uses this
dictionary to validate the recognition results.
Display Driver: It interacts with the graphics device interface' and display
hardware. When a user starts writing
or drawing, the display driver paints the ink trace on the screen.
Video and Image Display Systems Display System
Technologies
There are variety of display
system technologies employed for decoding compressed data for displaying.
Mixing and scaling technology: For VGA screen, these technologies are used.
VGA mixing: Images from multiple sources are mixed in the image acquisition
memory.
VGA mixing with scaling: Scalar ICs are used to sizing and positioning
of images in predefined windows.
Dual buffered VGA mixing/Scaling: If we provide dual buffering, the original
image is prevented from loss. In
this technology, a separate buffer is used to maintain the original image.
Visual Display Technology Standards
MDA: Monochrome Display Adapter.
It was introduced by IBM .
:.
It displays 80 x 25 rows and columns .
:.
It could not display bitmap graphics .
:.
It was introduced in 1981.
CGA: Color Graphics Adapter .
:.
It was introduced in 1981.
.:. It was designed to display both text and bitmap graphicsi
it
supported RGB color display,
.:. It could display text at a
resolution of 640 x 200 pixels .
:.
It displays both 40 x 25 and 80 x 25 row!' and columns of text
characters.
MGA: Monochrome Gr.aphics Adapter .
:.
It was introduced in 1982 .
:.
It could display both text and graphics .
:.
It could display at a resolution 720 x 350 for text and
720 x 338 for Graphics . MDA
is compatible mode for this standard.
EGA: Enhanced Graphics Adapter .
:.
It was introduced in 1984 .
:.
It emulated both MDt. and
CGA standards .
:.
It allowed the display of both text and graphics in 16 colors at a
resolution of 640 x· 350 pixels.
PGA: Professional Graphics Adapter.
.:. It was introduced in 1985 .
:.
It could display bit map graphics at 640 x 480 resolution and 256 colors
.
:.Compatible mode of this standard is CGA.
VGA: Video Graphics Array . :. It was introduced by IBM in 1988 .
:. It offers CGA and EGA
compatibility .
:. It display both text and
graphics .
:. It generates analog RGB
signals to display 256 colors .
:. It remains the basic standard
for most video display systems.
SVGA: Super Video Graphics Adapter. It is developed by VESA
(Video Electronics Standard Association)
. It's goal is to display with higher resolution than the VGA
with higher refresh rates
with minimize flicker.
XGA: Extended Graphics Array
It is developed by IBM . It
offers VGA compatible mode . Resolution of 1024 x 768 pixels in 256 colors is
offered by it. XGA utilizes an interlace scheme for refresh rates.
Flat Panel Display system
Flat panel displays use a
fluorescent tube for backlighting to give the display a sufficient level of
brightness. The four basic technologies used for flat panel display are:
1. Passive-matrix monochrome
2. Active-matrix monochrome
3.
Passive-matrix color
4.
Active-matrix color.
LCD (Liquid Crystal Display)
Construction: Two glass
plates each containing a light polarizer at right angles to the other plate,
sandwich the nematic (thread like) liquid crystal material.
Liquid crystal is the
compounds having a crystalline arrangement of molecules. But it flow like a
liquId. Nematic liquid crystal compounds are tend to keep the long axes of
rod-shaped molecules aligned. Rows of horizontal transparent conductors are
built into one glass plate, and columns of vertical conductors are put into the
other plate. The intersection of two conductors defines a pixel position.
Passive Matrix LCD
Working: Normally, the molecules are aligned in the 'ON' state.
Polarized light passing
through the materials is twisted so that it will pass through the opposite
polarizer. The light is then reflected back to the viewer. To turn off the
pixel, we have to apply a voltage to the two intersecting conductors to align
molecules so that the light is not twisted.
ACTIVE Matrix LCD
In this device, a transistor
is placed at each pixel position, using thin-film transisor technology.
The transistors are used to
control the voltage at pixel locations and to prevent charge from gradually
leaking out of the liquid crystal cells.
PRINT OUTPUT TECHNOLOGIES
There are various printing
technologies available namely Dot matrix, inkjet, laser print server and ink
jet color. But, laser printing technology is the most common for multimedia
systems.
To explain this technology,
let us take Hewlett Packard Laser jet-III laser printer as an example. The
basic components of the laser printer are
.:. Paper feed mechanism .:. Paper
guide .:. Laser assembly .:. Fuser .:. Toner cartridge.
Working: The paper feed mechanism moves the paper from a paper tray through
the paper path in the printer. The
paper passes over a set of corona wires that induce a change in the paper .
The charged paper passes over
a drum coated with fine-grain carbon (toner), and the toner attaches itself to the paper as a thin film of carbon .The paper
is then struck by a scanning laser beam that follows the pattern of the text on
graphics to be printed . The carbon particles attach themselves to the pixels
traced by the laser beam . The fuser assembly then binds the carbon particles
to the paper.
Role of Software in the printing mechanism:
The software package sends
information to the printer to select and control printing features . Printer
drivers (files) are controlling the actual operation of the printer and allow
the application
software to access the
features ofthe printer.
IMAGE SCANNERS
In a document imaging system,
documents are scanned using a scanner. \The document being scanned is placed on
the scanner bed or fed into the sheet feeder of the scanner .The scanner acts
as the camera eye and takes a photograph of the document, creating an image of
the original. The pixel representation (image) is recreated by the display
software to render the image of the original document on screen or to print a
copy of it.
Types of Scanners
A and B size Scanners, large
form factor scanners, flat bed scanners, Rotory drum scanners and hand held
scanners are the examples of scanners.
Charge-Coupled Devices All scanners use charge-coupled devices as
their photosensors. CCDs consists of
cells arranged in a fixed array on a small square or rectangular solid state
surface. Light source moves across a document. The intensity of the light
reflected by the mirror charges those cells. The amount of charge is depending
upon intensity of the reflected light, which depends on the pixel shade in the
document.
Image Enhancement Techniques
HalfTones In a half-tone process, patterns of dots used
to build .scanned or printed image create the illusion of continuous shades of gray or continuous shades of
color. Hence only limited number of shades are created. This process is
implemented in news paper printers.
But in black and white
photograph or color photograph, almost infinite levels of tones are used.
Dithering
Dithering is a process in
which group of pixels in different patterns are used to approximate halftone
patterns by the scanners. It is used in scanning original black and white
photographs.
Image enhancement techniques
includes controls of brightness, deskew (Automatically corrects page
alignment), contrast, sharpening, emphasis and cleaning up blacknoise dots by
software.
Image Manipulation
It includes scaling, cropping
and rotation.
Scaling: Scaling can be up or down, the scaling software is available to
reduce or enlarge. This software uses
algorithms.
Cropping: To remove some parts of the image and to put the rest of the image
as the subset of the old image.
Rotation: Image could be rotated at any degree for displaying it in different
angles.
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