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Text of Computer Graphics display technologies(Computer graphics tutorials and tips)
Graphics display technologies They include: o cathode ray tube
o Plasma o LCD o Raster graphics
Cathode Ray Tube
Control grid determines the rate at which the electron will
pass thro. Electron beam- electrons travel without any hindrance
from the air/dust as the tube is a vacuum. Phosphor coated screen
It glows when struck by electrons. conductive coating - to soak up
the electrons that pile up at the screen-end of the tube. Focusing
anode It attracts scattered electron to a focal point. Accelerating
anode It gives the anode a high velocity so that we can use the
velocity/momentum to give the light we want.
A CRT monitor contains millions of tiny red, green, and blue
phosphor dots that glow when struck by an electron beam that
travels across the screen to create a visible image. In a cathode
ray tube, the "cathode" is a heated filament. The heated filament
is in a vacuum created inside a glass "tube." The "ray" is a stream
of electrons generated by an electron gun that naturally pour off a
heated cathode into the vacuum. Electrons are negative. The anode
is positive, so it attracts the electrons pouring off the cathode.
This screen is coated with phosphor, an organic material that glows
when struck by the electron beam. There is a conductive coating
inside the tube to soak up the electrons that pile up at the
screen- end of the tube.
There are three ways to filter the electron beam in order to
obtain the correct image on the monitor screen: shadow mask,
aperture grill and slot mask. These technologies also impact the
sharpness of the monitor's display. They are: 1. Shadow mask 2.
Aperture Grill 3. Slot mask
Advantages of phosphor electron r easily knocked off to give
light once electrons starts losing energy, phosphor stay glowing
for some time persistence
Persistence is defined as the time it takes for the emitted
light from the screen to decay to 1/10th of its origin in
intensity. Lower persistence phosphor require higher refresh rates
to maintain a picture on the screen w/o flicker. The phosphor with
low persistence is useful for animation. A high persistence
phosphor is useful for displaying high complex static pictures
Resolution. The max No. of points that can b displayed on the
screen on a CRT w/o overlap is called resolution. Typical
resolution of high definition system is 1280 by 1024. Screen size.
The physical size of a graphics monitor is given by the length on
the screen diagonally n normally quoted in inches. Aspect Ratio It
gives the ratio of vertical points to horizontal points necessary
to produce equal length lines in both direction of the screen.
In a raster scan display system the electron beam is swept
across the screen one row at a time from top to bottom and from
left to right. As the elec beam moves across each row, the beam
intensity is turned on or off to create a pattern of illuminated
spots. The spots to be turned on are dependent on the picture to be
drawn. The definition of this picture is stored in a memory area
called the refresh buffer or frame buffer.
Rasterization The term rasterization can in general be applied
to any process by which vector information can be converted into a
raster format. In normal usage, the term refers to the popular
rendering algorithm for displaying three- dimensional shapes on a
computer. Rasterization is currently the most popular technique for
producing real-time 3D computer graphics. Compared to other
rendering techniques such as ray tracing, rasterization is
extremely fast.
Interlacing Its a method of encoding a bitmap image such that a
person who has partially received it sees a degraded copy of the
entire image. When communicating over a slow communications link,
this is often preferable to seeing a perfectly clear copy of one
part of the image, as it helps the viewer decide more quickly
whether to abort or continue the transmission. Interlacing is
supported by the following formats: GIF PNG JPEG
FLAT PANEL DISPLAY PLASMA PANEL The basic idea of a plasma
display is to illuminate tiny, colored fluorescent lights to form
an image. Each pixel is made up of three fluorescent lights -- a
red light, a green light and a blue light. What is Plasma? The
central element in a fluorescent light is a plasma, a gas made up
of free-flowing ions (electrically charged atoms) and electrons
(negatively charged particles).
Under normal conditions, a gas is mainly made up of uncharged
particles. That is, the individual gas atoms include equal numbers
of protons (positively charged particles in the atom's nucleus) and
electrons. The negatively charged electrons perfectly balance the
positively charged protons, so the atom has a net charge of zero.
If you introduce many free electrons into the gas by establishing
an electrical voltage across it, negatively charged particles rush
toward the positively charged area of the plasma, and positively
charged particles rush toward the negatively charged area. In this
mad rush, particles are constantly bumping into each other. These
collisions excite the gas atoms in the plasma, causing them to
release photons of energy
How the system works Its composed of 2 glass plates. The 1st
plate is brought to the 2nd plate until the space btn them is
small. The edges are sealed off and space is left with air. The air
inside is then removed and replaced with the plasma gas (e.g neon).
Properties of the gas Must produce light when ionized Must be
easily ionized Produce the correct color of gas when ionized.
LIQUID CRYATAL DISPLAY. In a LCD display, there are 2
polarizers i.e vertical and horizontal polariszer. A polarizer is a
component that filters light. A vertical polarizer filters vertical
component of light and allow horizontal component of light thro. As
light strikes the first filter, it is polarized. The molecules in
each layer of the liquid crstal then guide the light they receive
to the next layer. As the light passes through the liquid crystal
layers, the molecules also change the light's plane of vibration to
match their own angle. When the light reaches the far side of the
liquid crystal substance, it vibrates at the same angle as the
final layer of molecules. If the final layer is matched up with the
second polarized glass filter, then the light will pass
through
For a particular voltage the liquid material at that
intersection of electrons changes the orientation of that liquid
crystal of that intersection. The horizontal component is converted
to a vertical component hence transmit light. If we apply an
electric charge to liquid crystal molecules, they untwist. When
they straighten out, they change the angle of the light passing
through them so that it no longer matches the angle of the top
polarizing filter. Consequently, no light can pass through that
area of the LCD, which makes that area darker than the surrounding
areas.
INTERACTIVE DEVICES They are devices that help in input of data
in the system and also help in giving out the processed
information. They include: Mouse Space balls right handed
co-ordinate system. The space ball doesnt move. It has a strain
gauge that measure the amount of pressure applied to the space ball
to provide input. Trackball its an upside down mouse Touch pad
Touch panel
LOGICAL INPUT DEVICES The need for interactive comp graphics
sys has resulted in the dev of diff kinds of physical interactive
devices which function differently from each other. Locator its a
device for specifying a co-rdinate position x,y, in world co-ord
input to the graphics package by the user selecting a point.
stroker a device for specifying a series of cor-ord positions
string a device for specifying input text valuater a device for
specifying scaler values. choice a device for selecting menu
options pic a device for