Computer Graphics

in #computer2 years ago

Computer Graphics
 the interior parts of the vehicle during motion.
When object designs are complete, realistic lighting models and Computer graphics are pictures and movies created using computers - usually referring to image data created by a computer specifically with help from specialized graphical hardware and software.
 Computer Graphics: Computer Graphics is the use of computers to display and manipulate information in graphical or pictorial form, either on a visual-display unit or via a printer or plotter.

Computer graphics used in various areas that include science, engineering, medicine , business , industry , art , entertainment etc.

Interactive computer graphics involves two way communications between computer and user:

-> The computer, on the receiving signals from the input device can modify the displayed picture
approximately.
-> To the user, it appears that the picture is changing immediately in response to her commands.

Applications of Computer Graphics
 COMPUTER AIDED DESIGN
 Animations are often used in CAD applications.
 Real-time animations using wire frame displays are useful for testing performance of a vehicle.
 Wire frame models allow the designer to see surface rendering are applied.
 Manufacturing process of object can also be controlled through CAD.
 Interactive graphics methods are used to layout the buildings.
 Three-dimensional interior layouts and lighting also provided.
 With virtual-reality systems, the designers can go for a simulated walk inside the building

 PRESENTATION GRAPHICS
 It is used to produce illustrations for reports or to generate slide for with projections.
 Examples of presentation graphics are bar charts, line graphs, surface graphs, pie charts and displays showing relationships between parameters.
 3-D graphics can provide more attraction to the presentation.
 COMPUTER ART
 Computer graphics methods are widely used in both fine art and commercial art applications.
 The artist uses a combination of 3D modeling packages, texture mapping, drawing programs and CAD software.
 “Mathematical Art” can be produced using mathematical functions, fractal procedures.
 Photorealistic techniques are used to render images of a product.
 Animations are also used frequently in advertising, and television commercials are produced frame by frame.
 ENTERTAINMENT
 CG methods are now commonly used in making motion pictures, music videos and television shows.
 Many TV series regularly employ computer graphics method.
 Graphics objects can be combined with a live action.
 EDUCATION AND TRAINING
 Computer-generated models of physical, financial and economic systems are often used as educational aids.
 For some training applications, special systems are designed. Eg. Training of ship captains, aircraft pilots etc.,
 Some simulators have no video screens, but most simulators provide graphics screen for visual operation.
 VISUALIZATION
 The numerical and scientific data are converted to a visual form for analysis and to study the behavior called visualization.
 Producing graphical representation for scientific data sets are calls scientific visualization.
 And business visualization is used to represent the data sets related to commerce and industry.
 The visualization can be either 2D or 3D.
 IMAGE PROCESSING
 Computer graphics is used to create a picture.
 Image processing applies techniques to modify or interpret existing pictures.
 To apply image processing methods, the image must be digitized first.
 Medical applications also make extensive use of image processing techniques for picture enhancements, simulations of operations, etc.

GRAPHICAL USER INTERFACE
 Nowadays software packages provide graphics user interface (GUI) for the user to work easily.
 A major component in GUI is a window.
 Multiple windows can be opened at a time.
 To activate any one of the window, the user needs just to check on that window.
 Menus and icons are used for fast selection of processing operations.
 Icons are used as shortcut to perform functions. The advantages of icons are which takes less screen space.
 And some other interfaces like text box, buttons, and list are also used.

Video Display Devices:

  1. Refresh Cathode-Ray Tube
  2. Raster Scan Displays
  3. Random-Scan Displays
  4. Color CRT Monitors
    4.1 Beam-Penetration Method
    4.2 Shadow-Mask Method
  5. Direct-View Storage Tubes
  6. Flat-Panel Displays
    6.1 Plasma Panel
    6.2 Thin-Film Electroluminescent Display
    6.3 LED
    6.4 LCD

Refresh Cathode-Ray Tube:
Typically, the primary output device in a graphics system is a video monitor. The operation of most video monitors is based on the standard cathode-ray tube (CRT) design.
Fig 1 illustrates the basic operation of a CRT. A beam of electrons (cathode rays) emitted by an electron gun, passes through focusing and deflection systems that direct the beam toward specified positions on the phosphor-coated screen. The phosphor then emits a small spot of light at each position contacted by the electron beam. Because the light emitted by the phosphor fades very rapidly, some method is needed for maintaining the screen picture. One way to keep the
phosphor glowing is to redraw the picture repeatedly by quickly directing the electron beam back over the same points. This type of display is called a refresh CRT.

Fig 1: Basic design of a magnetic-deflection CRT.

Working Principle of CRT:
 The primary components of an electron gun in a CRT are the heated metal cathode and a control grid. Heat is supplied to the cathode by current through filament (coil of wire), which produces electrons.
 Intensity of the electron beam is controlled by setting voltage levels on the control grid. A high negative voltage shut off the beam, and a smaller negative voltage simply decreases the number of electrons in the beam.
 The focusing system in a CRT is needed to force the electron beam to converge into a small spot as it strikes the phosphor.
 The resolution is referred as the number of points per centimeter that can be plotted horizontally and vertically. Eg. 1280 × 1024.
 Aspect ratio: Ratio of vertical points to horizontal points necessary to produce equal-length lines in both directions on the screen.

Fig 2: Operation of an electron gun with an accelerating anode.

Fig 3: Operation of an electron gun with an accelerating anode.

The classification of CRT depends upon three factors. They are
->Persistence: Different types of phosphors are available and are made use in the construction of the CRT. The difference in phosphors is based on their color and the duration of time they continue to emit light, after the CRT beam is removed. This factor is called persistence.
->Resolution: The resolution of a CRT is the highest number of points that can be displayed without overlap on the CRT. A more precise definition is the number of points per centimeter that can be plotted horizontally and vertically.
->Aspect Ratio: Aspect ratio gives the ratio of vertical points to horizontal points necessary produce equal length lines in both directions on the screen. An aspect ratio of 2/3 means that a vertical line plotted with two points has the same length as a horizontal line with 3 points.

Raster Scan Displays:

In a raster-scan system, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. Picture definition is stored in a memory area called the refresh buffer or frame buffer used for redrawn. Each screen point is referred to as a pixel or pel (picture element). Refreshing on raster-scan displays is carried out at the rate of 60 to 80 frames per second. The unit for refreshing rate is Hertz (Hz).

Random-Scan Displays:

The CRT has the electron beam directed only to the parts of the screen where a picture is to be
drawn. Random-scan monitors draw a picture one line at a time, called as vector display.
Refresh rates on a ransom-scan system depends on the number of lines to be displayed. Picture
definition is stored as a set of line-drawing commands in the refresh display file or refresh
buffer.
These systems are designed for the line-drawing applications and can’t display realistic shaded
scenes.

Color CRT Monitors:

 Two basic methods are used for producing color displays
 Beam penetration and
 shadow-mask method.
Beam-Penetration Method:

 The beam penetration method for displaying color pictures has been used with random scan monitors.
 Two layers of phosphor, usually red and green are coated onto the screen and the displayed color depends on how far the electron beam penetrates into the phosphor layers.
 A beam of slow electrons excites only the outer red layer, fast electrons penetrates through red layer and excites the inner green layer. The electrons with intermediate speed produce the combinations of red and green color are emitted to show two additional colors, orange and yellow.
 The speed of electrons is controlled by the beam-acceleration voltage. But the quality of the pictures is not good here.
Shadow-Mask Method:
 It can produce a much wider range of color than the beam-penetration method. A shadow-mask CRT has three phosphor color dots at each pixel position with red, green and blue. This type of CRT has three electron guns, one for each color. The three electron beams are deflected and focused as a group onto the shadow mask, which contains corresponding holes for each pixel position.
 The color variation is obtained by varying the intensity levels of the three electron beams. For example, turning off the green and red beam, we will get only blue color.

Direct-View Storage Tubes:
 An alternative method for maintaining a screen image is to store the picture information inside the CRT instead of refreshing the screen.
 A direct-view storage device stores the picture information as a charge distribution just behind the phosphor coated screen. Two electron guns are used, the primary gun is used to store the picture pattern, the second, the floor gun, maintains the picture display.

 Advantage:
Because of no refreshing is needed very complex pictures can be displayed at very high resolutions without flicker.
 Disadvantage:
It cannot display colors, and selected parts of a picture can’t be erased. To eliminate the selected part of a picture, the entire screen must be erased and redrawn. It is a time consuming process.

Flat-Panel Displays:

 It refers to a class or video devices that have reduced volume, weight and power requirements composed to CRT. A main advantage of flat-panel displays is that they are thinner than CRTs and we can hang them on walls or wear on our wrists. The two categories of flat-panel displays are
 Emissive displays: the device which convert electrical energy into light. (Plasma panel), Thin-Film Electroluminescent Display, LED.
 Non-Emissive displays: used optical effects to convert sunlight or light from some other source into graphic patterns. (LCD)
Plasma Panel:
How plasma displays works?

 A plasma display panel is an array of hundreds of thousands of small, luminous cells positioned between two plates of glass. Each cell is essentially a tiny neon lamp filled with rarefied neon, xenon, and other inert gases; the cells are luminous when they are electrified through "electrodes".

 The long electrodes are stripes of electrically conducting material that also lie between the glass plates, in front of and behind the cells. The "address electrodes" sit behind the cells, along the rear glass plate, and can be opaque. The transparent display electrodes are mounted in front of the cell, along the front glass plate. As can be seen in the illustration, the electrodes are covered by an insulating protective layer. Control circuitry charges the electrodes that cross paths at a cell, creating a voltage difference between front and back. Some of the atoms in the gas of a cell then lose electrons and become ionized, which creates an electrically conducting plasma of atoms, free electrons, and ions. The collisions of the flowing electrons in the plasma with the inert gas atoms leads to light emission; such light-emitting plasmas are known as glow discharges.

Advantages
Picture quality
Capable of producing deeper blacks allowing for superior contrast ratio.
 Wider viewing angles than those of LCD; images do not suffer from degradation at high angles like LCDs
 Less visible motion blur, very high refresh rates and a faster response time, contributing to superior performance when displaying content with significant amounts of rapid.
Disadvantages
Earlier generation displays were more susceptible to screen burn-in and image retention, recent models which reduces the effect of burn-in but does not prevent it.
 Use more electricity, on average, than an LCD TV.
 Do not work as well at high altitudes due to pressure differential between the gases inside the screen and the air pressure at altitude. It may cause a buzzing noise. Manufacturers rate their screens to indicate the altitude parameters.
 For those who wish to listen to AM radio, or are Amateur Radio operators (Hams) or Shortwave Listeners (SWL), the Radio Frequency Interference (RFI) from these devices can be irritating or disabling.
Due to the strong infrared emissions inherent with the technology, standard IR repeater systems cannot be used in the viewing room. A more expensive "plasma compatible" sensor must be used.
Thin-Film Electroluminescent Display:

The thin film EL glass panel consists of a luminescent phosphor layer sandwiched between transparent dielectric layers and a matrix of row and column electrodes. A circuit board containing the drive and control electronics is connected to the back of the glass panel. Voltage is applied to row and column electrodes causing the area of intersection (a pixel) to emit light.
The result of this solid-state design is a flat, compact, reliable, and inherently rugged display with exceptionally fast response times (< 1 ms).

 LED:
A matrix of diodes is arranged to form the pixel positions in the display, and the picture definition is stored in a refresh buffer. As in scan-line refreshing of a CRT, information is read from the refresh buffer and converted to voltage levels that are applied to the diodes to produce the light patterns in the display.
Lasts much longer than traditional lighting. It has been known to last up to 50,000 hours. That's way more than any other available lighting type.
Can easily resist thermal shocks and vibrations. Normal light bulbs are useless when you drop or bump them. Not LED lights.
Great for spotlighting due to a directional distribution. All of the light molecules can easily be sent in one direction without losing energy.
 There is no infrared lighting from LED lights. And there is no UV radiation, which is better for you and the environment.
 Contains no mercury making it safer.
 They make great colored lights from anywhere on the light spectrum
 Disadvantages:
 A very limited variety and selection for your home compared to other types of lighting.
 Hard to find in smaller towns where consumers may have a smaller interest in this lighting alternative.
 Significantly more expensive than regular lighting and not budget conscious.
 Not good for residential flood lighting. You will need extra equipment to make this work
 Although they are available in many colors, the quality of the colors is not quite as good as with regular lighting.
LCD:
 LCD is commonly used in small systems, such as calculators, and portable, laptop computers. These non-emissive devices produce a picture by passing polarized light from the surroundings or from an internal light source through a liquid-crystal material that can be aligned either block or transmit the light.
 Advantages:

  1. Sharpness
    Image is perfectly sharp at the native resolution of the panel. LCDs using an analog input require careful adjustment of pixel tracking/phase.
  2. Geometric Distortion
    Zero geometric distortion at the native resolution of the panel. Minor distortion for other resolutions because the images must be rescaled.
  3. Brightness
    High peak intensity produces very bright images. Best for brightly lit environments.
  4. Screen Shape
    Screens are perfectly flat.
  5. Physical
    Thin, with a small footprint. Consume little electricity and produce little heat.
     Disadvantages:
  6. Resolution
    Each panel has a fixed pixel resolution format determined at the time of manufacture that can not be changed. If you need fine text and graphics at more than one resolution do not get an LCD display.
  7. Interference
    LCDs using an analog input require careful adjustment of pixel tracking/phase in order to reduce or eliminate digital noise in the image. Automatic pixel tracking/phase controls seldom produce the optimum setting. Timing drift and jitter may require frequent readjustments during the day. For some displays and video boards you may not be able to entirely eliminate the digital noise.
  8. Viewing Angle
    Limited viewing angle. Brightness, contrast, gamma and color mixtures vary with the viewing angle.
  9. Black-Level, Contrast and Color Saturation
    LCDs have difficulty producing black and very dark grays. As a result they generally have lower contrast than CRTs and the color saturation for low intensity colors is also reduced. Not suitable for use in dimly lit and dark environments.
  10. Color and Gray-Scale Accuracy
    The internal Gamma and gray-scale of an LCD is very irregular. LCDs typically produce fewer than 256 discrete intensity levels. Generally not suitable for professional image color balancing.
  11. Bad Pixels and Screen Uniformity
    LCDs can have many weak or stuck pixels, which are permanently on or off. Some pixels may be improperly connected to adjoining pixels, rows or columns. Also, the panel may not be uniformly illuminated by the backlight resulting in uneven intensity and shading over the screen.
  12. Motion Artifacts
    Slow response times and scan rate conversion result in severe motion artifacts and image degradation for moving or rapidly changing images.
  13. Aspect Ratio
    LCDs have a fixed resolution and aspect ratio. For panels with a resolution of 1280x1024 the aspect ratio is 5:4=1.25, which is noticeably smaller than the 4:3=1.33 aspect ratio for almost all other standard display modes.
  14. Cost
    Considerably more expensive than comparable CRTs.

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