Video display devices
- 2. The Primary Output devices in a graphics system is a video monitor. The operation of most video monitors is based on the standard Cathode-ray-tube(CRT) design.
- 3. Categories of video display devices Cathode ray tube Raster-Scan Display Random-Scan Display Color CRT Monitors Direct View Storage tubes Flat-panel Displays
- 4. Cathode Ray Tubes: CRT stands for Cathode ray tube. It is a technology which is used in traditional computer monitor and television. Cathode ray tube is a particular type of vacuum tube that displays images when an electron beam collides on the radiant surface.
- 7. Component of CRT: Electron Gun: The electron gun is made up of several elements, mainly a heating filament (heater) and a cathode. The electron gun is a source of electrons focused on a narrow beam facing the CRT. Focusing & Accelerating Anodes: These anodes are used to produce a narrow and sharply focused beam of electrons. Horizontal & Vertical Deflection Plates: These plates are used to guide the path of the electron the beam. The plates produce an electromagnetic field that bends the electron beam through the area as it travels. Phosphorus-coated Screen: The phosphorus coated screen is used to produce bright spots when the high- velocity electron beam hits it.
- 10. On a black-and-white system with one bit per pixel, the frame buffer is called a bitmap. For system with multiple bits per pixel ,the frame buffer is called pixmap.
- 12. Advantages: •Real image •Many colors to be produced •Dark scenes can be pictured Disadvantages: •Less resolution •Display picture line by line •More costly
- 15. Color CRT Monitors It is similar to a CRT monitor. The basic idea behind the color CRT monitor is to combine three basic colors- Red, Green, and Blue. By using these three colors, we can produce millions of different colors. The two basic color display producing techniques are: The beam – Penetration method for display color pictures has been used with random –scan monitors. Two layers of phosphor, usually red and green , are coated onto the inside of the CRT 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. A beam of very fast electrons penetrates through the red layer and excites the inner green layer. Beam Penetration Methods Beam penetration method has been an inexpensive way to produce color in random scan monitors, but only four colors are possible,and the quality of pictures is not as good as with other methods.
- 16. Shadow –mask methods: Shadow –mask methods are commonly used in raster scan systems(including color TV) because they produce a much wider range of colors that the beam penetration method. Shadow-mask CRT has three phosphor color dots at each pixel position. One phosphor dot emits a red light, another emits a green light, and the third emits a blue light.
- 17. Structure: It has three phosphorus color dots at each position of the pixel. First Dot: Red color Second Dot: Green color Third Dot: Blue color It has three different guns. Each for one color. It has a metal screen or plate just before the phosphorus screen, named “Shadow-Mask.” It also has a shadow grid just behind the phosphorus coated screen with tiny holes in a triangular shape. Working: A Shadow Mask is a metal plate with tiny holes present inside a color monitor.
- 19. Advantages: Display a wider range picture. Display realistic images. In-line arrangement of RGB color. Disadvantages: Difficult to cover all three beams on the same hole. Poor Resolution.
- 20. Direct View Storage Tube (DVST): It is used to store the picture information as a charge distribution behind the phosphor-coated screen. There are two guns used in DVST: 1.Primary Gun: It is used to store the picture information. 2.Flood / Secondary Gun: It is used to display a picture on the screen. Advantages: Less Time Consuming No Refreshing Required High-Resolution Less Cost Disadvantages: The specific part of the image cannot be erased. They do not display color.
- 21. Flat-Panel Displays: Flat Panel Display The term flat-panel display refers to a class of video devices that have reduced volume , weight , and power requirements compared to a CRT. We can separate flat panel display into two categories: Emissive displays Non emissive displays. •Emissive display (or emitters) are devices that convert electrical energy into light. Eg: Plasma display, LED’s •Non emissive display use optical effects to convert sunlight or light from some other source into graphics patterns. Eg: LCD’s