Lecture data communication2_Gaurav Kumar.pptx

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1. Graphics Displays Session No.: 2 Course Name: Computer Graphics Course Code: R1UC408B Instructor Name: Mr. Shobhit Kumar Galgotias University 1

2. Pre session quiz on LMS Galgotias University 2 Galgotias University

3. Review of the key concepts of session no. 1 Galgotias University 3 Computer graphics covers a wide range of rendering, modelling, and visualization techniques. Almost every area utilizes computer graphics for better presentation, synthesis, and understanding of the data, processes, and operations. Broadly, computer graphics are classified into raster and vector graphics. Raster graphics are composed of pixels, whereas vector graphics are composed of drawings based on mathematical formulas.

4. What is the mechanism to display graphics on the screen? Galgotias University 4

5. Ask Questions How do you think printers print a beautiful drawing/image every time with same configuration as compared to humans? Galgotias University 5

6. At the end of this session students will be able to Learning Outcome 1: Recognize the graphics display technologies on monitors Learning Outcome 2: Recognize the graphics display mechanism on monitors Galgotias University 6

7. Session Outline 1 Video display devices 2 Raster Scan Displays 3 Random Scan Displays 4 Learning Activity 1 5 Flat Panel Displays 6 Color displays 7 Learning Activity 2 8 Summary Galgotias University 7

8. Display Devices depends on CRT (Cathode Ray Tubes) CRTs used for display purposes is same as used in black and white home TV sets. DESIGN OF CRT The electron gun emits a beam of electrons or cathode rays which passes through focusing system and magnetic deflection coils and finally hits the phosphor coated screen. Phosphor then emits small spots of light at point where electron beam strikes. The emitted light fades away very rapidly, so picture is not maintained for long on the screen. The solution to this problem is, repeatedly strike on the beam on the same point. Thus, phosphor keeps glowing and picture is visible on the screen for long time. This type of display is called Refresh CRT . 8 Display Devices Galgotias University

9. CRT (Cathode Ray Tube) 9 Galgotias University

10. Technical terms in CRT Dot Pitch : Represents the distance with two separate phosphor dots to the same color The lower value of the dot pitch picture provide better image quality Persistence : Time it takes the emitted light from the phosphor screen to decay to the 10% or 1/10th of the original light output. Lower-persistence phosphors require higher refresh rates to maintain a picture on the screen without flicker. A phosphor with low persistence can be useful for animation, while high-persistence phosphors are better suited for displaying highly complex, static pictures. Refresh Rate : Represents the number of image which are displayed per second or the number of times the image is reproduced each second Also called vertical scan rate, expressed in hertz(Hz) or Frames per sec Minimum refresh rate is 60 frames per sec Resolution: Represents the number of pixels per surface unit. Definition: Number of pixels that the screen can display. High resolution systems are referred to as high- definition systems. This number is between 640x 480 and 1600 x 1200, but higher resolutions are technically possible. 10 Galgotias University

11. Size Calculated by measuring the diagonal of the screen and is expressed in inches Aspect Ratio : Ratio of vertical points to the Horizontal points necessary to produce equal –length lines in both direction on the screen Types of CRT display devices Raster Scan Display System Random Scan Display 11 Galgotias University

12. Raster Scan Displays Raster: A rectangular array of points or dots Pixel: One dot or picture element of the raster Scan Line: A row of pixels 12 Galgotias University

13. In a raster scan system, the electron beam is swept across the screen, one row at a time from top to bottom. 13 Galgotias University

14. 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 . Refresh buffer or frame buffer: This memory area holds the set of intensity values for all the screen points. Stored intensity values then retrieved from refresh buffer and “ painted ” on the screen one row ( scan line ) at a time. Intensity range for pixel positions depends on the capability of the raster system. A black-and-white system: each screen point is either on or off, so only one bit per pixel is needed to control the intensity of screen positions. On a black-and-white system with one bit per pixel, the frame buffer is called bitmap . For system with multiple bits per pixel, the frame buffer is called pixmap . Sometimes, refresh rates are described in unit of cycles per second, or Hertz ( HZ ) Refreshing on raster scan displays is carried out at the rate 60 to 80 frame per second. 14 Galgotias University

15. Horizontal retrace : The return to the left of the screen, after refreshing each scan line Vertical retrace : At the end of each frame (displayed in 1/80 th to 1/60 th of a second) the electron beam returns to the top left corner of the screen to begin the next frame. 15 Galgotias University

16. Random scan display system Electron beam directly strikes those parts of the screen where a picture has to be drawn Also known as Vector Displays or Stroke - writing Displays or Calligraphic Displays As it draws one line at a time The lines can be drawn in any Arbitrary order of the display commands, hence called Random Scan System. The display commands or the display list (or programs) is stored in refresh buffer to draw the picture. Every time we refresh the screen, we have to cycle through this refresh buffer, one line at a time. The number of lines in the buffer decides the refresh rate. In general, refresh rate is 60 frames per sec. 16 Galgotias University

17. Advantages: This minimal amount of information translates to a much smaller file size. (file size compared to large raster images). On zooming in, and it remains smooth The parameters of objects are stored and can be later modified (transformation). High resolution since picture definition is stored as line drawing commands, easy animation, and requires little memory (just display program). Disadvantages : Limited colour capability and flicker occurs as complexity of image increases. 17 Galgotias University

18. Learning Activity 1 Make a single-answer question as per the following statement through wooclap What is the total count of pixels being illuminated/traversed in one minute in a raster scan display over a screen of size 1200*900 pixels with the refresh rate of 60 frames per second. Galgotias University 18

19. Reflection- Learning Activity 1 Galgotias University 19 Answer is: 1200*900*60*60 = 3,888,000,000

20. Advantages of CRT The cathode rayed tube can easily increase the monitor’s brightness by reflecting the light. They produce more colours The Cathode Ray Tube monitors have lower price rate than the LCD display or Plasma display. The quality of the image displayed on a Cathode Ray Tube is superior to the LCD and Plasma monitors. The contrast features of the cathode ray tube monitor are considered highly excellent. 20 Galgotias University

21. Disadvantages of CRT They have a big back and take up space on desk. The electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning of living cells. CRTs emit a small amount of X-ray band radiation which can result in a health hazard. Constant refreshing of CRT monitors can result in headache. CRTs operate at very high voltage which can overheat system or result in an implosion Within a CRT a strong vacuum exists in it and can also result in a implosion They are heavy to pick up and carry around 21 Galgotias University

22. Flat Panel Displays A class of video devices that have reduce volume ,weight and power requirement compared to a CRT. A significant feature of flat panel displays is that they are thinner than CRTs. Two main categories: Emissive Displays Non-emissive Displays Emissive or Emitters Displays Emissive displays convert electrical energy into light energy. Examples: Plasma panel, thin-film electroluminescent displays, Light-Emitting Diodes (LED) and flat CRT. Non-emissive or Non-emitters Displays Use optical effects to convert sunlight or light from some other source into graphics pattern. Example: Liquid-Crystal Device (LCD) 22 Galgotias University

23. Current uses for flat panel displays: Small TV monitors Calculators Pocket video games Laptop computers Advertisement boards in elevators Flat CRT : Electron beams are accelerated parallel to the screen, then deflected 90 º to the screen. Flat-panel displays are commonly of three types: Plasma displays LED displays LCD displays 23 Galgotias University

24. Plasma displays (gas-discharge display) A layer of gas (usually neon) is sandwiched between two glass plates. By applying high voltage to a pair of horizontal and vertical conductors, a small section of the gas (tiny neon bulb) at the intersection of the conductors break down into glowing plasma of electrons and ions. Refresh buffer used to store picture information Firing voltages applied to refresh the pixel positions Electroluminescent displays (phosphor illuminating display) In the below figure if there is a gas in place of phosphor then it is called plasma display and in case of phosphor it is called electroluminescent display. LED display (Light-emitting diode display) 24 Galgotias University A matrix of diodes is arranged to form pixel positions in the display, and picture definition is stored in a refresh buffer. 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. Flat Panel Emissive Displays

25. LCD Display Used in small systems, such as calculators, laptop computers. Produce a picture by passing polarized light (from the surrounding or from an internal light source) through a liquid-crystal material that can be aligned to either block to transmit the light. Uses small amount of power, so is good for battery-operated devices Liquid crystal: These compounds have a crystalline arrangement of molecules, yet they flow like a liquid. Two glass plates, each containing a light polarizer at right angles to the other plate, sandwich the liquid crystal materials. Rows of horizontal transparent conductor & columns of vertical conductors (put into glass plates) 25 Flat Panel Non-Emissive Displays Galgotias University

26. Colour CRT Monitors A CRT monitor displays color pictures by using a combination of phosphors that emit different color lights. An electron gun for each colour – red, green and blue Color CRTs are much more complicated Requires manufacturing very precise geometry Uses a pattern of color phosphors on the screen Methods Of Color CRT Monitor Beam Penetration Shadow Mask 26 Galgotias University

27. Beam Penetration Method Two layers of phosphor ( red and green ) are coated onto the inside of the CRT screen. The display color depends on haw far (length) the electron beam penetrates into the phosphor layers. The speed of the electrons, and the screen color at any point, is controlled by the beam acceleration voltage In the beam penetration method: Only four colors are possible ( red , green , orange , and yellow ). Quality of pictures is not as good as with other methods. 27 Galgotias University

28. Shadow Mask Method Three color phosphor dots ( red , green and blue ) at each point on the screen Three electron guns , each controlling the display of red, green and blue light Used in raster-scan systems Produce wide range of color with RGB color model The delta -delta method: 28 Galgotias University

29. Create an activity on wooclap for the following questions. How many colors can be generated by a shadow mask color monitor (Red, green, blue) display system with the pixel specification of 8 bits. Galgotias University 29 Learning Activity 2

30. Reflection- Learning Activity 2 Galgotias University 30 Answer: 2^8*2^8*2^8 = 256*256*256 = 16,777,216

31. Summary CRT displays the graphics using the boiled electrons accelerated and deflected towards the phosphor screen. Phosphor screen glows as a result of excitation of the phosphor electrons by the cathode electrons, which decays as soon as the phosphor electrons sit back in their previous unexcited state. To excite the phosphor electrons again and again, CRT has to be refreshed to perform the same operation again and again. The intensity of the pixels on the screen to be illuminated through refresh CRT is stored in the frame buffer. Raster scan display refreshes all pixels of the screen whereas random scan display refreshes only the pixels of the drawing to be displayed. Flat panel displays are advancements in the video displays with reduction in size and less power supply as compared to the CRT. Plasma, electroluminescent, and LED are emissive displays whereas LCD is an example of non-emissive display. Beam penetration method of color CRT uses only two phosphor layers of red and green color, whereas shadow masking method uses three layers of red, green, and blue with three respective cathode guns. Galgotias University 31

32. Ensure attainment of LOs in alignment to the learning activities: outcomes (1-2) Outcome 1: Recognized the graphics display technologies on monitors Outcome 2: Recognized the graphics display mechanism on monitors Galgotias University 32

33. Discussion on the post session activities Galgotias University 33 Can you relate the raster graphics and vector graphics with the raster scan display and random scan display. In today's display devices, the dominant technology is raster scan display; almost all modern monitors, TVs, and mobile screens use this method to display images, as it allows for high-quality, realistic visuals with the ability to show complex details and color gradients. Examples of random scan display devices are oscilloscope, Radar displays, early CAD systems, etc.

34. Information to next topic of the course Galgotias University 34 The next topic of the subject will cover the architecture of a raster scan system mainly focusing on frame buffer and video controller. How the frame buffer and video controller together facilitates the generation of graphics on the screen

35. Galgotias University 35 1. In a raster scan display, the electron beam moves: a) Directly to draw images b) Line by line from top to bottom c) Randomly across the screen d) In a circular motion Answer: b) Line by line from top to bottom 2. Which of the following is a disadvantage of raster scan displays? a) High memory requirement b) Cannot display complex images c) Used only in oscilloscopes d) Cannot handle colors Answer: a) High memory requirement 3. Raster scan displays store images in a: a) Frame buffer b) Register c) CPU cache d) Magnetic tape Answer: a) Frame buffer 4. Which of the following devices commonly use raster scan technology? a) Radar systems b) CRT monitors and modern LCDs c) Oscilloscopes d) CAD systems Answer: b) CRT monitors and modern LCDs 5. Which of the following applications is best suited for random scan displays? a) Video games b) Television broadcasting c) Engineering and CAD software d) Movie projectors Answer: c) Engineering and CAD software Assignment Quiz on LMS

36. Review and Reflection from students Galgotias University 36

37. Thank You Galgotias University 37