ICS 415 Computer Graphics General Graphics Systems

1. ICS 415Computer GraphicsGeneral Graphics Systems Dr. Muhammed Al-Mulhem March 1, 2009 Dr. Muhammed Al-Mulhem

2. Display technologies • Cathode Ray Tubes (CRTs) • Most common display device today. • Evacuated glass bottle. • Extremely high voltage. • Components • Electron gun. • Focusing & deflection systems. • Phosphor coated screen. Dr. Muhammed Al-Mulhem

3. Electron gun • Contains a filament that, when heated, emits a stream of electrons. • Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube. • The picture tube is coated with small phosphor dots. • When the beam hits a phosphor dot it glows with a brightness proportional to the strength of the beam and how long it is hit. Dr. Muhammed Al-Mulhem

4. CRT characteristics • How might one measure CRT capabilities? • Size of tube • Brightness of phosphors • Speed of electron gun • Width of electron beam • Pixels Dr. Muhammed Al-Mulhem

5. Display technologies: CRTs • Vector Displays - Battlezone? Tempest? Dr. Muhammed Al-Mulhem

6. Display technologies: CRTs • Vector Displays • Early computer displays: basically an oscilloscope • Control X,Y with vertical/horizontal plate voltage • Often used intensity as Z (close things were brighter) • Disadvantages • Just does wireframe • Complex scenes cause visible flicker Dr. Muhammed Al-Mulhem

7. Display technologies: CRTs • Raster Displays • The most common CRT • The electron beam is swept across the screen, one row at a time. Dr. Muhammed Al-Mulhem

8. Display technologies: CRTs • Raster Displays • Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom • As beam sweeps across entire face of CRT, beam intensity changes to reflect brightness • Analog signal vs. digital display Dr. Muhammed Al-Mulhem

9. Display technologies: CRT • Can a computer display work like a black and white TV? • Solution: We need a special memory to buffer image. We call this the framebuffer. • Digital description to analog signal to digital display. Dr. Muhammed Al-Mulhem

10. Display Technologies: CRTs • Refresh • Frame must be “refreshed” to draw new images • As new pixels are struck by electron beam, others are decaying • Electron beam must hit all pixels frequently to eliminate flicker • Critical fusion frequency • Typically 60 times/sec • Varies with intensity, individuals, phosphor persistence, lighting... Dr. Muhammed Al-Mulhem

11. Display Technologies: CRTs • Interlaced Scanning • Assume we can only scan all pixels of entire screen 30 times / second • To reduce flicker, divide frame into two “fields” of odd and even lines Dr. Muhammed Al-Mulhem

12. Display Technology: Color CRTs • Color CRTs are much more complicated • Requires manufacturing very precise geometry • Uses a pattern of color phosphors on the screen: Delta electron gun arrangement In-line electron gun arrangement Dr. Muhammed Al-Mulhem

13. Display Technology: Color CRTs • Color CRTs have • Three electron guns • A metal shadow maskto differentiate the beams Dr. Muhammed Al-Mulhem

14. Display Technology: Raster • Raster CRT pros: • Allows solids, not just wireframes. • Leverages low-cost CRT technology • Bright! Display emits light • Cons: • Requires screen-size memory array • Discreet sampling (pixels) • Practical limit on size (call it 40 inches) • Bulky Dr. Muhammed Al-Mulhem

15. CRTs – A Review • CRT technology hasn’t changed much in 50 years • Early television technology • high resolution • requires synchronization between video signal and electron beam vertical sync pulse • Early computer displays • avoided synchronization using ‘vector’ algorithm • flicker and refresh were problematic Dr. Muhammed Al-Mulhem

16. CRTs – A Review • Raster Displays (early 70s) • like television, scan all pixels in regular pattern • use frame buffer (video RAM) to eliminate sync problems • RAM • ¼ MB (256 KB) cost $2 million in 1971 • Do some math… • 1280 x 1024 screen resolution = 1,310,720 pixels • Monochrome color (binary) requires 160 KB • High resolution color requires 5.2 MB Dr. Muhammed Al-Mulhem

17. Flat-panel display • Flat-panel refers to a class of video devices that have reduced Volume, Weight, and Power requirements compared to a CRT. • A significant feature of flat-panel displays is that they are thinner than CRTs, and we can hang them on walls or wear them on our wrists. Dr. Muhammed Al-Mulhem

18. Display Technology: LCDs • Liquid-crystal displays (LCDs) • Commonly used in small systems, such as laptop computers and calculators. • It produces a picture by passing polarized light from the surrounding or from an internal light source through a liquid-crystal material. Dr. Muhammed Al-Mulhem

19. Display Technology: LCDs • Organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field • Crystalline state twists polarized light 90º. Dr. Muhammed Al-Mulhem

20. Display Technology: Plasma • Plasma display panels • Also called gas-discharge displays. • Constructed by filling the region between two glass plates with a mixture of gases that usually include neon. • Similar in principle to fluorescent light tubes. Dr. Muhammed Al-Mulhem

21. Display Technology: Plasma • Plasma display panels • Firing voltages applied to an intersecting pair of horizontal and vertical conductors cause the gas at the intersection of the two conductors to break down into a glowing plasma of electron and ions. Dr. Muhammed Al-Mulhem

22. Display Technology: Plasma • Plasma display panels • Picture definition is stored in a refresh buffer. • Firing voltages are applied to refresh the pixel positions, at the intersection of the conductors, 60 times per second. Dr. Muhammed Al-Mulhem

23. Display Technology • Plasma Display Panel Pros • Large viewing angle • Good for large-format displays • Fairly bright • Cons • Expensive • Large pixels • Phosphors gradually deplete • Less bright than CRTs, using more power Dr. Muhammed Al-Mulhem

24. Review • Read Chapter 2 • Details about display devices Dr. Muhammed Al-Mulhem