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CRT Advantages

CRT Advantages. CRTs use a simple & mature technology and can therefore be manufactured inexpensively in many industrialized countries. While the gap is getting smaller all the time, they remain significantly cheaper than alternative display technologies.

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CRT Advantages

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  1. CRT Advantages • CRTs use a simple & mature technology and can therefore be manufactured inexpensively in many industrialized countries. • While the gap is getting smaller all the time, they remain significantly cheaper than alternative display technologies. • The fact that phosphors emit light in all directions means that viewing angles of close to 180 degrees are possible. • Phosphors have been developed over a long period of time, to the point where they offer excellent color saturation at the very small particle size required by high-resolution displays.

  2. CRT Shortcomings • However, the CRT has obvious shortcomings • It sucks up too much electricity • It is simply too big and weighs too much • Its high-voltage electric circuits & strong magnetic fields create harmful electromagnetic radiation • The scanning technology employed makes flickering unavoidable, causing eye strain & fatigue • The surface is often either spherical or cylindrical, with the result that straight lines do not appear straight at the edges

  3. How does the LCD work? • The picture that you see on your laptop screen is again made up of many red, green and blue dots.

  4. Simplified version of the LCD • On a laptop screen each "dot" is actually a tiny device rather than a phosphor. • The “dot” is called a cell. • Light passes thru each cell. At the end of the cell, light goes through a red, green, or blue filter so the cell takes on that color. • A trio of RGB cells taken together is a pixel • Color of each pixel is determined by how bright its 3 cells are.

  5. LCD has Liquid Crystals • Liquid crystals first discovered in the late 19th century • Transparent substances, exhibiting the properties of both solid & liquid matter • Light passing thru liquid crystals follows the alignment of the molecules that make them up • In the 60s, it was discovered that charging liquid crystals with electricity changed their molecular alignment, and consequently the way light passed through them

  6. LCD Principles • The LCD is a non-emissive technology • Liquid Crystals are organic compounds consisting of long rod-like molecules • In their natural state, LC molecules arrange themselves with their long axes roughly parallel • The alignment of the molecules can be controlled by flowing the LC along a finely grooved surface. • The alignment follows the grooves, so if the grooves are parallel, then the alignment is parallel • First Principle of LCD: sandwich LCs between two grooved surfaces where the grooves of one surface are perpendicular to the grooves of the other. • Molecules at one surface align vertically & molecules at other end align horizontally. Those in-between twist.

  7. LCD Principles • Light follows the alignment of the molecules so it is twisted through 90o and light is blocked. • When a voltage is applied, the molecules rearrange themselves vertically • In the LCD screen: • Liquid crystal is sandwiched between two plates of glass • One plate has horizontal grooves • The other has vertical grooves • Molecules align themselves with the grooves so there is a layer of horizontal molecules & a layer of vertical ones. Ones in between do their best to align with their neighbors. • The results is called a “twisted cell” of liquid crystal. • http://www.colorado.edu/physics/2000/applets/dishsoap.html

  8. LCD Principles • Second Principle: • Natural light rays are oriented at random angles • A polarizing filter is a set of very fine parallel lines that act like a net, blocking all light rays except those parallel to the lines • A second polarizing filter with lines perpendicular to the first totally blocks this polarized light • http://www.colorado.edu/physics/2000/polarization/blocking_light.html

  9. Putting the two principles together

  10. Passive-matrix LCD • A picture is produced by passing polarized light through a liquid-crystal layer and a electric field that can be aligned to either block or transmit the light. • It consists of: vertical polarizer  vertical grid wires  liquid-crystal layer  horizontal grid wires  horizontal polarizer • When the crystals are in an electric field (voltage applied), the crystalline molecules line up in the same direction, the light is not twisted (no polarizing effect), thus the light is blocked. • Characteristics: low weight, low power consumption, small size

  11. How is Color achieved? • Red, blue, & green filters are used to filter the light in each cell. • http://www.colorado.edu/physics/2000/laptops/laptop_screen.html • The varying levels of brightness required to create a full color display is achieved by changing the voltage strength

  12. Active Matrix • Active-matrix LCD • An extra matrix of transistors is connected to the LCD panel • There is a transistor at each pixel. • The transistors are used to change the crystal state quickly • The transistors control the degree (voltage) to which the state has been changed • The transistors can serve as a memory of the state of each grid.

  13. Passive LCD screens Cycle through each element of the LCD matrix applying the voltage required for that element. Once aligned with the electric field, the molecules in the LCD will hold their alignment for a short time Active LCD screens Each element contains a small transistor that maintains the voltage until the next refresh cycle. Higher contrast and much faster response than passive LCD LCDs (cont.)

  14. Contrasting LCDs & CRTs • LCDs offer advantages in terms of bulk, power consumption, & flicker • They have a much higher price, a poorer viewing angle, & less accurate color performance • LCDs don’t support a range of resolutions well • The CRT has three electron beams that must converge faultlessly to create a sharp image. For an LCD, each cell is switched on and off individually. Text appears very crisp on the LCD. • LCD cells are either on or off so the flicker problem is not there. An image displayed at a refresh rate of 40-60 Hz should not produce any more flicker than one at a 75 Hz rate. • It is possible for one or more cells on the LCD panel to be flawed. • Viewing angle problems occur in LCDs because this is a transmissive system.

  15. Physical Devices • Pointing Devices • Joystick • Mouse • Trackball • Graphics Tablets

  16. 3D scanners

  17. Other Physical Devices

  18. Motion Capture

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