CRTs – A Review

1. 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

2. 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

3. Display Technology: LCDs • Liquid Crystal Displays (LCDs) • LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field • Crystalline state twists polarized light 90º.

4. Display Technology: LCDs • Liquid Crystal Displays (LCDs) • LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or E field • Crystalline state twists polarized light 90º

5. Display Technology: LCDs • Transmissive & reflective LCDs: • LCDs act as light valves, not light emitters, and thus rely on an external light source. • Laptop screen • backlit • transmissive display • Palm Pilot/Game Boy • reflective display

6. Display Technology: Plasma • Plasma display panels • Similar in principle to fluorescent light tubes • Small gas-filled capsules are excited by electric field,emits UV light • UV excites phosphor • Phosphor relaxes, emits some other color

7. Display Technology • Plasma Display Panel Pros • Large viewing angle • Good for large-format displays • Fairly bright • Cons • Expensive • Large pixels (~1 mm versus ~0.2 mm) • Phosphors gradually deplete • Less bright than CRTs, using more power

8. Display Technology: DMD / DLP • Digital Micromirror Devices (projectors) or Digital Light Processing • Microelectromechanical (MEM) devices, fabricated with VLSI techniques

9. Display Technology: DMD / DLP • DMDs are truly digital pixels • Vary grey levels by modulating pulse length • Color: multiple chips, or color-wheel • Great resolution • Very bright • Flicker problems

10. Display Technologies: Organic LED Arrays • Organic Light-Emitting Diode (OLED) Arrays • The display of the future? Many think so. • OLEDs function like regular semiconductor LEDs • But they emit light • Thin-film deposition of organic, light-emitting molecules through vapor sublimation in a vacuum. • Dope emissive layers with fluorescent molecules to create color. http://www.kodak.com/global/en/professional/products/specialProducts/OEL/creating.jhtml

11. Display Technologies: Organic LED Arrays • OLED pros: • Transparent • Flexible • Light-emitting, and quite bright (daylight visible) • Large viewing angle • Fast (< 1 microsecond off-on-off) • Can be made large or small • Available for cell phones and car stereos

12. Display Technologies: Organic LED Arrays • OLED cons: • Not very robust, display lifetime a key issue • Currently only passive matrix displays • Passive matrix: Pixels are illuminated in scanline order (like a raster display), but the lack of phospherescence causes flicker • Active matrix: A polysilicate layer provides thin film transistors at each pixel, allowing direct pixel access and constant illumination See http://www.howstuffworks.com/lcd4.htm for more info

13. Movie Theaters • U.S. film projectors play film at 24 fps • Projectors have a shutter to block light during frame advance • To reduce flicker, shutter opens twice for each frame – resulting in 48 fps flashing • 48 fps is perceptually acceptable • European film projectors play film at 25 fps • American films are played ‘as is’ in Europe, resulting in everything moving 4% faster • Faster movements and increased audio pitch are considered perceptually acceptable

14. Viewing Movies at Home • Film to DVD transfer • Problem: 24 film fps must be converted to • NTSC U.S. television interlaced 29.97 fps 768x494 • PAL Europe television 25 fps 752x582 • Use 3:2 Pulldown • First frame of movie is broken into first three fields (odd, even, odd) • Next frame of movie is broken into next two fields (even, odd) • Next frame of movie is broken into next three fields (even, odd, even)…

16. Additional Displays • Display Walls • Princeton • Stanford • UVa – Greg Humphreys

17. Display Wall Alignment

18. Additional Displays • Stereo

19. Visual System • We’ll discuss more fully later in semester but… • Our eyes don’t mind smoothing across time • Still pictures appear to animate • Our eyes don’t mind smoothing across space • Discrete pixels blend into continuous color sheets

20. Mathematical Foundations • Angel appendix B and C • I’ll give a brief, informal review of some of the mathematical tools we’ll employ • Geometry (2D, 3D) • Trigonometry • Vector spaces • Points, vectors, and coordinates • Dot and cross products

21. Scalar Spaces • Scalars: a, b, … • Addition and multiplication (+ and h) operations defined • Scalar operations are • Associative: a + (b + g) = (a + b) + g • Commutative: a + b = b + a a h b = b h a • Distributive: a h(b h g) = (a h b) h ga h(b + g) = (a h b) + (a h g)

22. Scalar Spaces • Additive Identity = 0 • a + 0 = 0 + a = a • Multiplicative Identity = 1 • ah1 = 1 h a = a • Additive Inverse = -a • a + (-a) = 0 • Multiplicative Inverse= a-1 • a h a-1 = 1

23. Vector Spaces • Two types of elements: • Scalars (real numbers): a, b, g, d, … • Vectors (n-tuples):u, v, w, … • Operations: • Addition • Subtraction

24. u+v Vector Addition/Subtraction • operation u + v, with: • Identity 0v + 0 = v • Inverse -v + (-v) = 0 • Addition uses the “parallelogram rule”: v u -v v -v u-v u

25. Affine Spaces • Vector spaces lack position and distance • They have magnitude and direction but no location • Add a new primitive, the point • Permits describing vectors relative to a common location • Point-point subtraction yields a vector • A point and three vectors define a 3-D coordinate system

26. Q v P Points • Points support these operations • Point-point subtraction: Q - P = v • Result is a vector pointing fromPtoQ • Vector-point addition: P + v = Q • Result is a new point • Note that the addition of two points is not defined

27. Y Y Z X Right-handed coordinate Left-handed system coordinate system Z X Coordinate Systems • Grasp z-axis with hand • Thumb points in direction of z-axis • Roll fingers from positive x-axis towards positive y-axis

28. Euclidean Spaces • Euclidean spaces permit the definition of distance • Dot product - distance between two vectors • Projection of one vector onto another

29. Euclidean Spaces • We commonly use vectors to represent: • Points in space (i.e., location) • Displacements from point to point • Direction (i.e., orientation) • We frequently use these operations • Dot Product • Cross Product • Norm

30. Scalar Multiplication • Scalar multiplication: • Distributive rule: a(u + v) = a(u) + a(v) (a + b)u = au + bu • Scalar multiplication “streches” a vector, changing its length (magnitude) but not its direction

31. v θ u Dot Product • The dot product or, more generally, inner product of two vectors is a scalar: v1 • v2 = x1x2 + y1y2 + z1z2 (in 3D) • Useful for many purposes • Computing the length (Euclidean Norm) of a vector: length(v) = ||v|| = sqrt(v • v) • Normalizing a vector, making it unit-length: v = v / ||v|| • Computing the angle between two vectors: u • v = |u| |v| cos(θ) • Checking two vectors for orthogonality • u • v = 0.0

32. w v u Dot Product • Projecting one vector onto another • If v is a unit vector and we have another vector, w • We can project w perpendicularly onto v • And the result, u, has length w • v

33. Dot Product • Is commutative • u • v = v • u • Is distributive with respect to addition • u • (v + w) = u • v + u • w

34. Cross Product • The cross product or vector product of two vectors is a vector: • The cross product of two vectors is orthogonal to both • Right-hand rule dictates direction of cross product

35. Cross Product Right Hand Rule • See: http://www.phy.syr.edu/courses/video/RightHandRule/index2.html • Orient your right hand such that your palm is at the beginning of A and your fingers point in the direction of A • Twist your hand about the A-axis such that B extends perpendicularly from your palm • As you curl your fingers to make a fist, your thumb will point in the direction of the cross product

36. Cross Product Right Hand Rule • See: http://www.phy.syr.edu/courses/video/RightHandRule/index2.html • Orient your right hand such that your palm is at the beginning of A and your fingers point in the direction of A • Twist your hand about the A-axis such that B extends perpendicularly from your palm • As you curl your fingers to make a fist, your thumb will point in the direction of the cross product

37. Cross Product Right Hand Rule • See: http://www.phy.syr.edu/courses/video/RightHandRule/index2.html • Orient your right hand such that your palm is at the beginning of A and your fingers point in the direction of A • Twist your hand about the A-axis such that B extends perpendicularly from your palm • As you curl your fingers to make a fist, your thumb will point in the direction of the cross product

38. Cross Product Right Hand Rule • See: http://www.phy.syr.edu/courses/video/RightHandRule/index2.html • Orient your right hand such that your palm is at the beginning of A and your fingers point in the direction of A • Twist your hand about the A-axis such that B extends perpendicularly from your palm • As you curl your fingers to make a fist, your thumb will point in the direction of the cross product

39. Cross Product Right Hand Rule • See: http://www.phy.syr.edu/courses/video/RightHandRule/index2.html • Orient your right hand such that your palm is at the beginning of A and your fingers point in the direction of A • Twist your hand about the A-axis such that B extends perpendicularly from your palm • As you curl your fingers to make a fist, your thumb will point in the direction of the cross product

40. 2D Geometry • Know your high school geometry: • Total angle around a circle is 360° or 2π radians • When two lines cross: • Opposite angles are equivalent • Angles along line sum to 180° • Similar triangles: • All corresponding angles are equivalent

41. Trigonometry • Sine: “opposite over hypotenuse” • Cosine: “adjacent over hypotenuse” • Tangent: “opposite over adjacent” • Unit circle definitions: • sin () = x • cos () = y • tan () = x/y • etc… (x, y)

42. P = (x, y) y P2 = (x2, y2) P1 = (x1, y1) x Slope-intercept Line Equation • Slope =m • = rise / run • Slope = (y - y1) / (x - x1) = (y2 - y1) / (x2 - x1) • Solve for y: • y = [(y2 - y1)/(x2 - x1)]x + [-(y2-y1)/(x2 - x1)]x1 + y1 • or: y = mx + b

43. Parametric Line Equation • Given points P1 = (x1, y1) and P2 = (x2, y2) x = x1 + t(x2 - x1) y = y1 + t(y2 - y1) • When: • t=0, we get (x1, y1) • t=1, we get (x2, y2) • (0<t<1), we get pointson the segment between(x1, y1) and (x2, y2) y P2 = (x2, y2) P1 = (x1, y1) x

44. Other helpful formulas • Length = sqrt (x2 - x1)2 + (y2 - y1)2 • Midpoint, p2, between p1 and p3 • p2 = ((x1 + x3) / 2, (y1 + y3) / 2)) • Two lines are perpendicular if: • M1 = -1/M2 • cosine of the angle between them is 0

45. Reading • Chapters 1 and Appendix B of Angel