01-dispcolor

01-dispcolor - Lecture 1 Display and Color Reading •...

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Unformatted text preview: Lecture 1 Display and Color Reading • Foley van Dam. 4.1-3, 13.3-4. • Hearn Baker (3/E). 2.1-2, 12-2.7 Further reading: • I.E. Sutherland. Sketchpad: a man-machine graphics communication system. Proceedings of the Spring Joint Computer Conference , p. 329-346, 1963. • T.H. Myer & I.E. Sutherland. On the design of display processors. Communications of the ACM 11(6): 410-414, 1968. • B r i a n W a n d e l l . Foundations of Vision. Chapter 4. Sinauer Associates, Sunderland, MA, 1995. • Gerald S. Wasserman. Color Vision: An Historical Introduction. John Wiley & Sons, New York, 1978 Lecture outline: 1. Display devices (CRT, LCD, and FED) 2. Frame Buffer (Memory to Display) 3. Color Lookup Table 4. Gamma Correction 5. Color Spaces: RGB, CMY, HSV, YIQ, CIE XYZ 6. Alpha Channel and Double Buffering DISPLAY DEVICES (1) CRT-CATHODE RAY TUBE Mechanism: Shoot electrons with varying energy through vertical & horizontal deflectors to hit spot on screen Phosphors on screen jump to excited state when hit by electrons, emit monochromatic light when they drop to rest state. Random Scan / Vector Scan Raster Scan • Electron beam traces over screen in raster scan order . – Each left-to-right trace is called a scan line . – Each spot on the screen is a pixel . – When the beam is turned off to sweep back, that is a retrace , or a blanking interval. How do you make a picture? Raster scan: Sweep screen with electron beam. start end Vertical Retrace (large delay) Intensity on one line is like a graph x distance Intensity Refresh rate – number of pictures drawable in one second How do you see a whole image ? Phosphor light emission decays with time. So screen is only partially lit at any time Photo of screen will show partial picture time Beam .. hit I bright at spot, fading trail You see whole picture because your eyes see all light flashes within ~ 1/45 sec of each other as simultaneous Look like t=1/45 sec t=0 steady image Matching Phosphors & scan rate to human eye Fast-Decay Phosphor (short persistence) Slow Refresh 1/30sec flicker in single lines, OK in bury TV images if interlaced Fast Refresh ~1/60-1/70 sec No flicker Slow Decay Phosphor (long Persistence) Slow refresh No flicker, interlace or non-interlaced Fast refresh MOTION GHOSTS - after images Problems: - no good long-persistence blue - need a solution when we need to use short-persistence phosphor (see next slide) 1 2 3 4 INTERLACING: trick to get less flicker out of fixed signal bandwidth similar trick in movies: 24 frames/sec doubled to 48 by repeating each frame! RS170 Video - 30Hz interlaced 1 3 483 1/60 sec 2 482 1/60 sec + row# Reference: www.taudio.com/tripod_pages/tech_DTV.html Video Terminology Summary 1. Refresh Rate : 30Hz, 60Hz = # times full image is redrawn each second 2. Interlaced, Non-Interlaced : Image drawn twice (even lines then odd lines) in one, refresh time OR, Image drawn once in one refresh time 3. Persistence : Short phosphor : disappears quickly allows quick moving images Long phosphor : disappears slowly prevents flicker on 30 Hz refresh systems (2) LCD ( Liquid Crystal Display )...
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This note was uploaded on 10/19/2009 for the course COMP 341 taught by Professor Qu,huamin during the Spring '09 term at HKUST.

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01-dispcolor - Lecture 1 Display and Color Reading •...

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