OSE 6938P. Flat Panel Displays

Transcription

1 OSE 6938P Flat Panel Displays Prof. Shin-Tson Wu College of Optics & Photonics University of Central Florida Office: CREOL 280 Phone:

2 OSE 6938P Lecture 1 Color Science & Engineering Outlines: 1. Introduction 2. The Eye 3. Colorimetry 4. Light sources 5. Photometry 1

3 2 Introduction

4 Introduction: What is color? Radiometry intensity, spectrum, polarization, phase Colorimetry red, blue, green Photometry brightness, reflectance, transmittance Psychometry warm, cold, harmonic 3

5 Historic Review of Color Definition (1) Famous Color Circles 4

6 Historic Review of Color Definition (2) Famous Color Circles 5

7 Formation of Color (1) 1. Light Source Illumination-- Visible Range, Natural or Man-Made 2. Objective Interaction-- Absorption, Transmission, Reflection, Scattering, and Fluorescence 3. Produce Stimulus-- Photons 4. Receive Stimulus-- The Eye, E-O Effect 6 5. Interpret Stimulus-- Brain

8 Formation of Color (2) Wavelength between 380nm to 780nm 7 Light source Reflectance Eye s Responsivity Color

9 8 Light Source (1)

10 Light Source (2) Color Rendering Index (CRI) and Color Temperature Y 5000K 6500K 10000K 9 X

11 Objective Interaction Reflection (1) 10

12 Objective Interaction Reflection (2) 11

13 Color Mixing Additive Subtractive 12

14 Produce and Reproduce a Color Printing System Display System 13

15 Homework #1: Color Mixing Questions: 1. Is color printing a kind of additive or subtractive mixing? Why? Due 1/18/07 14

16 15 The Eye

17 Human Eye Structure 16 Cones: Provide color sensitivity Rods: Color-insensitive Color perception depends on light level Scotopic vision regime: Low-light-level-vision regime Photopic vision regime: High-light-level-vision regime Ref:

18 Cone and Rod-- Spatial Distribution 17 Cone: +/- 10 o

19 Cone and Rod Spectral Sensitivity 1923 Gibson and Tyndall 1945 Crawford Cone: Bright (>1nit), color, 555 nm Rod: dark (<0.001 nit), gray, 510 nm CIE (Commission Internationale de l Eclairage) 1924, 300 people, 2-3 o 1951, <30 yrs, >5 o Relative Radiometric Intensity (log) Rod Cone Rod Cone 18 Wavelength (nm)

20 Spectral Sensitivity of Rods and RGB Cones 19 Ref:

21 CIE 1978 Eye Sensitivity Function and Luminous Efficacy Visible range: nm Definition of lumen: Green light (555 nm) with power 1 W of has luminous flux 683 lm Efficacy of radiation gives number of lumens per optical Watt 20 Ref: With same output power, green light are brightest

22 CIE Standards 21 Ref: There are several standards: Photopic: CIE 1931 CIE 1978 Scotopic: CIE 1951

23 22 Visual Signal Transmission

24 23 Video Compression

25 24 Which circle is bigger?

26 25 Parallel Lines?

27 26 How many colors in this figure?

28 Adaptation Spatial Domain Visual Experience 27 Ref. M. A. Webster, Opt. & Photon. News 16, 19 (2004).

29 28 Sharpness of the Eyesight

30 Sharpness of the Eyesight 0.1 cd/m cd/m 2 10 cd/m cd/m cd/m 2

31 30 Colorimetry

32 Colorimetry Hue (φ) that quality of color which we describe by the words red, yellow, green, blue, etc. Value (z) that quality of color which we describe by the words light, dark, etc., relating the color to a gray of similar lightness. Chroma (r) that quality which describes the extent to which a color differs from a gray of the same level. Greenish blue Bluish green Green Blue Greenish yellow Black White Value Purple Chroma Hue Yellow Red Orange 31

33 Color Matching White screen Red Green Blue Black shadow Eye Black shadow Light R Q -R Q 32

34 33 Color System

35 34 J. C. Maxwell System

36 J. Guild System nm, 542nm and 460nm; 7 people; 2 o 35

37 W. D. Wright System nm, 530nm and 460nm; 10 people; 2 o 36

38 CIE 1931 (R, G, B) System nm, 546.1nm and 435.8nm 37

39 38 CIE 1931 (X, Y, Z) System

40 Color Matching Functions and Chromaticity X Y Z = λ x( λ) P( λ) dλ = λ y( λ) P( λ) dλ = λ z( λ) P( λ) dλ X, Y, and Z are tristimulus values Chromaticity diagram and chromaticity coordinates x, y x = X X + Y + Z y = Y X + Y + Z z chromaticity coordinate not needed, since x + y + z = 1 Uniform chromaticity coordinates u, v and u, v 39 Ref:

41 40 CIE 1931 Chromaticity Diagram

42 Color Purity and Dominant Wavelength Ref: 41 Caution: Peak wavelength and dominant wavelength can be different. Peak wavelength is a quantity used in physics and optics. Dominant wavelength is used by in human vision.

43 Statistical Data 1. Trichromatic Color Matching 2. Different Age and People 3. Convergent Points 42

44 MacAdam Ellipses 43 Color differences cannot be discerned with in the MacAdam ellipses Axes of MacAdam ellipses are shown 10 times longer than they are Humans can discern about different colors Ref:

45 CIE 1976 LUV System An UCS (Uniform Chromaticity- Scale) System 44 Ref:

46 45 3-D Color System

47 Chromaticity of D65 illuminant with different Y 46

48 47 Munsell Color System

49 48 Munsell Color System (with Constant Hue)

50 CIE 1976 LUV Color System Constant Lightness Constant Hue 49

51 CIE 1976 LUV Color System Constant Hue 50

52 System Transformation Colorimetry Formulas Nonlinear behavior of Y 51

53 52 Gamma Value

54 53 Light Sources

55 White Illuminant the Solar Spectra Note: There are many ways to create white light Sunlight is not an efficient way to create white light. Why? 54 Ref:

56 Color Temperature 55 Planckian spectrum or black-body radiation spectrum As temperature increases, objects sequentially glow in the red, orange, yellow, and white Ref:

57 Color Gamut Color gamut Gamut of Red-Green-Blue light source has triangular shape Area of gamut matters for displays, color printers, etc. 56 Ref:

58 Example of color mixing RGB color mixing Color gamut Gamut size increases with the number of light sources 57 Ref:

59 Color Rendering A light source has color rendering capability This is the capability to render the true colors of an object Example: False color rendering What is the color of a yellow banana when illuminated with a red LED? What is the color of a green banana when illuminated with a yellow LED? 58 Ref:

60 Example of Color Rendering 59 Clear differences in the color rendition can be seen in this August Renoir painting (left-hand side: high CRI; right-hand side: low CRI) Ref:

61 Color Rendering Index The color rendering capability of a test light source is measured in terms of the color rendering index Color rendering index of a high-quality reference light source is CRI = 100 An incandescent light source with the same color temperature serves as the reference light source Eight color sample objects serve as test objects Example: Color sample under reference source illumination Color sample under test source illumination slight difference in color! 60 Ref:

62 Calculation of Color Rendering Index CIE color definition: Color = Brightness, hue, and saturation Color rendering index: CRI = 100 Σ i = 1 8 E i * E i * represents color change CRI is a very good metric but not a perfect one! 61 Ref:

63 Reflectivity of Color Sample Objects Sample objects (Fruit, wood, etc.) 8 standard objects ( General CRI) 6 additional objects ( Special CRIs) 62Ref:

64 Discussions of Color rendering index (CRI) The reference objects are illuminated with reference light source. As a result, object will have a certain color. The reference objects are then illuminated with test light source. As a result, object will have a certain, but different, color. The CRI is a measure of the sum of the differences in color. If color difference is zero, then CRI = 100 If color difference is > zero, then CRI < 100 Some applications require high and very high CRI. Some applications do not require a high CRI. For some applications, CRI is irrelevant. Examples? Examples? Examples? Caution: CRI depends on the selection of the reference light source. Recommended for reference light source: Planckian radiator. 63 Ref:

65 CRI Examples Light source Color rendering index Sunlight 100 Quartz halogen W filament light 100 W filament incandescent light 100 Fluorescent light Phosphor-based white LEDs Trichromatic white light LEDs Hg vapor light coated with phosphor 50 Na vapor light 40 Hg vapor light 20 Dichromatic white light LEDs Green monochromatic light 50 Table: Color rendering indices (CRI) of different light sources. CRI > 85 suitable for most (even most demanding) applications 64 Ref:

66 65 Photometry

67 66 Photometry vs Radiometry

68 History of Photometric Units Photograph shows plumber s candle A plumber s candle emits a luminous intensity of 1 candela (cd). The cd is historical origin of all photometric units. First definition (now obsolete): The luminous intensity of a standardized candle is 1 cd. Second definition (now obsolete): 1 cm 2 of platinum (Pt) at 1042 K (temperature of solidification) has a luminous intensity of cd. Third definition (current): A monochromatic light source emitting an optical power of (1/683) Watt at 555 nm into the solid angle of 1 steradian (sr) has a luminous intensity of 1 cd. 67 Candlepower and candle are obsolete units. Candlepower and candle measure luminous intensity and are approximately equal to one cd. Ref:

69 Luminous Flux, Illuminance, and Luminance luminous flux: A light source with a luminous intensity of 1 cd emits a luminous flux of 1 lm into a solid angle of one steradian An isotropic light source with a luminous intensity of 1 cd emits a total luminous flux of 4π lm = lm Illuminance: If a 1 m 2 surface receives a luminous flux of 1 lm, then the illuminance of the surface is 1 lux Example: Moonlight 1 lux; reading light lux; surgery light 10 4 lux; direct sunlight 10 5 lux Luminance is the luminous intensity emitted per unit area of a light source. Luminance is a figure of merit for displays. Typical displays have a luminance of cd/m Ref:

70 Luminous Flux and Efficiency Φ lum Luminous flux lm = 683 W λ V ( λ) (Unit: lm) P( λ) dλ Luminous efficacy (Unit: lm / W) ( ) ( λ) λ lm Luminous efficacy = Φlum / P = 683 V ( λ) P( λ) dλ λ P d W λ 69 Luminous efficiency (Unit: lm / W) Luminous efficiency = Φlum / ( IV ) Caution: Some call luminous efficacy the luminous efficacy of radiation Caution: Some call luminous efficiency the luminous efficacy of the source Ref:

71 70 Conversion Factors of Different Units

72 Homework #2: Color Science 1. The CIE 1931 coordinate of the white light source E is (0.33, 0.33). Please find the R:G:B luminance ratio (in terms of photometry) for such a light source. (Hint: The wavelengths for the R, G, and B prime lights are 700nm, 546.1nm and 435.8nm) 2. Find the R:G:B luminance ratio in terms of radiometry R G B l 700nm 546.1nm 435.8nm x y z V(l) Due 1/18/07 71