A concept of graphics

Written BY k.das
And S.mishra
Dept of computer science

 Computer graphics is a field of computer
science that concerned with digitally
Synthesizing and manipulating visual contents.
 Computer graphics(cg) includes almost
everything on computer that is not text or
sound.
 The term cg refer to several different thing
1.The representation and manipulation of
pictorial data by a computer.
2.Various technologies used to create and
manipulate image.

 There are two kinds of computer graphics
:Raster(composed of pixel) and
Vector(composed of path).
 Raster image are called bitmap images.
 Bitmap image are mapped to a grid or an array
of pixels.
 In bitmap images, each pixel has assigned
color.
 Bitmap image are edited at the pixel level that
allows the color of any one pixel to change.

Bitmap image
 Bitmap images are not easily
scalable.
 Bitmap images are edited at
the pixel level that allows the
color of any one pixel to
change.
 Bitmap images are usually
created and edited in photo
or paint program such as
adobe Photoshop.

Vector image
 Vector image are not based on
picture patterns but instead
use mathematical formulas to
draw lines and curves that
can be combined to create
from geometric object such as
circle and polygons.
 Vector images are editing by
manipulating the lines and
curves that make up an image
using a program such as coral
draw.

Application of
Graphics
Paint program:
 It is a graphics program that
enables you to draw pictures
on the display screen which
is represented as bit maps
(bit-mapped graphics).
 Sophisticated paint
applications are often called
image editing programs.

Application of
Graphics
Animation
software:
 Enables you to chain and
sequence a series of images to
simulate movement. Each
image is like a frame in a
movie.
 . A cartoon on television is
one example of animation.
Animation on computers is
one of the chief ingredients of
multimedia presentations.

Graphics
Application
Card and
Desktop
publishing
 A CAD system is a combination
of hardware and software that
enables engineers and architects
to design everything from
furniture to airplanes.
 Provides a full set of word-
processing features as well as
fine control over placement of
text and graphics, so that you
can create newsletters,
advertisements, books, and
other types of documents. It
means by using a personal
computer or workstation high-
quality printed documents can
be produced.

Cathode ray
tube
 Cathode ray tube is a vacuum
tube containing one or more
electric gun and a
fluorescence screen used to
view images.
 It has a mean to accelerated
and deflect the electron beam
onto the screen to create the
images.

Working Principle of
cathode ray tube
 Heat is supplied to the
cathode by passing current
through a heater element.
 The cathode is a cylindrical
metallic structure that is rich
in electrons.
 On heating ,electron released
from cathode surface.
 Control grid is the next
element that follow the
cathode.

Working principle of
cathode ray tube
 Intensity of electron beam is
controlled by setting voltage
level on the control grid.
 A high negative voltage applied
to the control grid shuts off the
beam by repelling electrons and
stopping them from passing
through the small hole at the
end of the control grid
structure.
 Smaller negative voltage on the
control grid simply decrease
the number of electrons passing
through the cathode. Thus we
can control the brightness of
display by varying the voltage
on control grid.

Working principle
of CRT
 Positive charged anodes
accelerate the electrons towards
the phosphor screen.
 Focusing and deflection coil are
together needed to force the
electron beam to converge into
small spot , as it strike the
screen, otherwise the electron
would repel each other and
beam is spread out as it
approaches the screen.
 Finally when the accelerating
electron beam collide on
phosphor coating ,a part of
kinetic energy is converted into
light and heat.

 A raster scan display is most common method of
drawing images on a CRT screen.
 In this method horizontal and vertical deflection
signals are generated to move a beam all over the
screen in the pattern for displaying any image.
 The electron beam is swept across the screen one
row at a time from top to bottom.
 The electron beam swept back and forth from left
to right across the screen.
 Raster scan display resolution is poor because it in
contrast produces Zig-Zag lines that are plotted as
discrete point set.

HORIZONTAL RETRACE VERTICAL RETRACE
 The beam is on ,while it
moves from left to right.
The beam is off ,when it
moves back from right
to left. This
phenomenon is called
the horizontal retrace.
 As soon as the beam
reaches the bottom of
the screen ,it is turned
off and is rapidly
retraced back to top to
start again. This is
called vertical retrace.

 A raster scan display has an electron beam
directed only to the parts of the screen where a
picture is to be drawn .
 Random scan display draw a picture one line at a
time for this reason it is also known as vector
display picture.
 A picture definition is stored as a set of line
drawing command in the area of refresh buffer.
 Random scan display resolution is good than
random scan display as picture definition is stored
as a set of line-drawing instructions instead of a set
of intensity values for all screen point.

Working principle of
graphics display
 A graphics display consists of
three components: frame buffer,
display controller and a
monitor.
 Frame buffer: The frame buffer
stores an image as a matrix of
intensity values . In personal
computer, the frame buffer is
located on the graphics card
that manage the video
subsystem of the computer. It
have some memory stored
intensity values are then
retrieved from the refresh buffer
and displayed on the screen one
row at a time. Each intensity
value is represented by bit
zero(0) or one(1) in the frame
buffer.

Display controller
and display
device
Working
principle of
display
device(graphics)
 The video controller has
direct access to memory
locations in the frame buffer
and passing it to the display
device. It reads each
successive byte of data from
frame buffer and converts
this 0’s and 1’s in one line
into a corresponding video
signals and this line is called
scan line. If intensity is one(1)
then the controller sends a
signal to display a dot in
corresponding position on
the screen. if the intensity is
zero then no dot is displayed.

1 1 1 1 1 1 0 0
0 1 1 0 0 1 1 0
0 1 1 0 0 1 1 0
0 1 1 1 1 1 0 0
0 1 1 0 0 1 1 0
0 1 1 0 0 1 1 0
1 1 1 1 1 1 0 0
0 0 0 0 0 0 0 0

A concept of graphics

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