Color Seminar


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An overview of the science of color concepts

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  • Color Seminar

    1. 1. 2
    2. 2. Contents• 1. Introductions• 2. Light and Color Science (Light• Source, Object and Observer)• 3. Light and Color Measurement• 4. Visual and Instrumental Color• Management 3
    3. 3. Light and Color• What is Color? ASTM E284 • color, n—(1) of an object, aspect of object appearance distinct from form, shape, size, position, or gloss that depends upon the spectral composition of the incident light, the spectral reflectance or transmittance of the object, and the spectral response of the observer, as well as the illuminating and viewing geometry. • (2) perceived, attribute of visual perception that can be described by color names such as white, gray, black, yellow, brown, vivid red, deep reddish purple, or by combinations of such names. 4
    4. 4. Light SourceVisible Spectrum 5
    5. 5. Thank you! 6
    6. 6. LIGHT AND COLOR 7
    7. 7. Light and Color• Color Perception • 3 parts that can influence our perception of color: Light Source Observer 1. Light source 2. Object being viewed 3. Observer (person) Object Observer Situation 8
    8. 8. Light Source• Light • Light is a form of energy also known as visible light. Light is a small portion of the electromagnetic spectrum which covers an extremely broad range, from electrical and radio waves to microwaves and gamma rays. • Visible light represents a very small portion of the electromagnetic spectrum. The relative insensitivity of the human eye limits the visible portion of the spectrum to a very narrow band of wavelengths between approximately 380nm to 760nm. 9
    9. 9. Light Source• Electromagnetic Spectrum • Velocity of Light = (Wavelength) x (frequency in meters) x (cycles per second or Hertz) » (3 x 108 m/sec) 10
    10. 10. LIGHT SOURCE 11
    11. 11. Light Source• Light Energy • White light is dispersed into its component colors by refraction. • The angle of deviation varies with wavelength. 12
    12. 12. Light Source• Chromaticity and Color Temperature • Color temperature is the absolute temperature T (K) which a blackbody or perfect radiator would emit light of a certain color. The color of the emitted light changes from red to yellow to white as the temperature increases. 13
    13. 13. Light Source• Color Temperature 20000K Blue Northwest Sky Blue Sky with Thin White Clouds Blue Sky 10000K 7500K high CRI 7000K North Sky fluorescents 6000K Overcast North Sky Short-arc Xenon 5000K 5000K high CRI fluorescents Noon Sun 4000K CW & CWX 3000K Deluxe Mercury WW & WWX Incandescent 2000K HPS Candle Flame 14
    14. 14. Light Source• CIE – Standard Illuminants Illuminant Description Color Temperature A Incandescent 2856K B Noon Daylight 4874K C Average Daylight 6770K D50 Noon Sky Daylight 5003K D65 Average North Sky Daylight 6504K D75 North Sky Daylight 7504K F2 Cool White Fluorescent 4230K F11/TL84 Narrow Band Fluorescent 4000K F12/U30 Narrow Band Fluorescent 3000K 15
    15. 15. Visual Color Management• Light Source Selection • Use established industry procedures or standards that specify specific light sources and viewing practices. • Choose light sources that fit your specific application. • Specify color temperature, SPD, CRI, CIE Assessment and lamp technology. • Everyone must agree to use the same light sources and procedures. 16
    16. 16. Visual Color Management• Common Light Sources Daylight Incandescent Horizon Daylight Fluorescent 17
    17. 17. Visual Color Management• Metamerism • Samples appear to match under daylight viewing conditions but do not match under other lighting conditions. 18
    18. 18. Instrumental Color Management• Reflectance Curves of a Metameric Pair 19
    19. 19. Visual Color Management• Visual Color Evaluation Limitations The reason for the use of instruments • Visual color evaluation is subjective. • Observers have differing color vision and color opinions. • Color differences are difficult to quantify and communicate. • Many variables need to be controlled including light intensity, angle of view, surround color, light source quality etc. 20
    20. 20. Visual Color Management• Viewing Geometry 21
    21. 21. Visual Color Management• Proper Visual Color Evaluation Requires; • Selection of the correct light source(s). • Viewing booth must be kept clear of extra samples. • Samples should be placed inside the light booth. • Orient Standard and Sample in same direction, side by side, touching. • Depending upon gloss of the samples, determine a standard viewing geometry. • Limit the amount of ambient light flooding the viewing booth. • If assessor is wearing brightly colored clothing, a neutral lab coat should be worn during assessment. • If assessor wears glasses with tinted lenses, they should be removed for the assessment. 22
    22. 22. Visual Color Management• What’s Wrong With This Picture? 23
    23. 23. Light Source• Color Models • Additive Principals (Light) blue green red 24
    24. 24. Object• Color Models • Subtractive Principals (Dyes and Pigments) Magenta Yellow Cyan 25
    25. 25. Object• Object – Primary Types of Light Distribution 26
    26. 26. Object• Red Object = Red Object Spectral Reflectance Curve 27
    27. 27. Object• Object – Spectral Reflectance Curves 28
    28. 28. ObjectGlossmeter Design and Use • ASTM D523 29
    29. 29. OBSERVER 30
    30. 30. Light Source• CIE Standard Observer Experiment red sample 31
    31. 31. Color Measurement• Field of View 2o 1.7cm 50cm 10o 8.8cm • At normal viewing distance of 50 cm (20 in.), the circle on the top represents the 2° field on which the CIE 1931 standard observer is based. The figure at the bottom is the 10° field on which the 1964 CIE supplementary standard observer is based. 32
    32. 32. Observer• Facts About Color Vision • 1 in every 12 males or 8% is color defective as a function of their single x chromosome. • 1 in every 250 females is color defective. • The most common color deficiency is a partial green defective. • Being color blind is rare, only 1 in 33,000, you would be missing all three receptors known as Acromatopsia and the individual is called an “Achromat”. 33
    34. 34. Color Measurement• Instrumentation Colorimeter: Spectrophotometer: Filter Based (3 or 4) Fixed Grating & Array Fixed Illuminant (C/D65) Multiple Illuminant Fixed Observer (2° or 10°) Choice of Observer Tungsten Halogen Light Source Pulsed Xenon Light Source No Metamerism Testing Metamerism Detection Colorimetric Data (XYZ, L*a*b*) Spectral & Color Data Quality Control Q.C., R&D, Formulation, etc. 35
    35. 35. Light Measurement• 3-Filter Colorimeter Receptor section Microprocessor Numerical Values x(l )sensor X = 21.21 The tristimulus values X, Y, Z are calculated y(l )sensor Y = 13.37 by the microprocessor z(l )sensor Z = 9.32 and can be converted to other colour space Three sensors corresponding toLight sourceunder test three types of cones in human eye 36
    36. 36. Color Measurement• Spectrophotometers • Analyzes spectral distribution of reflected or transmitted light wavelength by wavelength, across the visible spectrum. • Measures the ratio of reflection or transmission by a specimen relative to a reference standard. CM-3700d CM-3500d CM-2600d 37
    37. 37. Color Measurement• Integrating Sphere Geometry D8 Geometry 38
    38. 38. Color Measurement• Specular Included vs Specular Excluded Geometry 39
    39. 39. Color Measurement• SCI vs SCE UsesSCI: SCE: • Includes all angles of illumination • Good correlation with visual • Measurement independent of sample assessment surface (gloss or texture) • Characterizes effects of sample • Measurement of true color surface • Sample must touch the sphere • Non-contact possible, for on-line • Widely used for color matching applications • Values similar to 0/45, depending on gloss level 40
    40. 40. Color Measurement• 0/45 and 45/0 Geometries 41
    41. 41. Color Measurement• Specialty Instruments – Multi Angle Goniospectrophotometers Face CM-512m3 42
    42. 42. Color Measurement• Developing a new color space based on what we have learned 1931 CIE Chromaticity Diagram 1976 CIE UCS Diagram = X = X/(X+Y+Z) u’ = 4X/(X+15Y+3Z) y = Y/(X+Y+Z) V’ = 9Y/(X+15Y+3Z) 43
    43. 43. Color Measurement• Opponent Color Theory black-white code blue-yellow code red or green code 44
    44. 44. Color Measurement• CIE L*a*b* 45
    45. 45. Color Measurement• CIE L*a*b* Values for a Red Object • 10° Observer, Illuminant D65 L*=39.90 a*=48.04 b*=17.18 46
    46. 46. Color Measurement• CIE L*a*b* Color Difference Trial Standard Lighter - = Redder Less Yellow• L* = 40.40 L* = 39.90 DL* = 0.50• a* = 49.49 a* = 48.04 Da* = 1.45• b* = 13.83 b* = 17.18 Db* = -3.35 47
    47. 47. Color Measurement• CIEL*a*b* DE*Total Color Difference Calculation: ΔE* = [ΔL*2 + Δa*2 + Δb*2]1/2 From previous example: ΔE* = [(0.50)2 + (1.45)2 + (-3.35)2]1/2 ΔE* = 3.68 48
    48. 48. Color Measurement• Color Difference • Color difference is the numerical comparison of trials to the standard. • It indicates the difference in absolute color coordinates between a trial and a standard. • Differences are called Deltas (L*, a* b*). • Deltas for L*, a* or b* may be positive or negative. • Delta E must always be positive. • Delta E only indicates the magnitude of a total color difference but does not indicate how to correct it. 49
    49. 49. Color Measurement• Creating a Color Tolerance in CIEL*a*b* 50
    50. 50. Color Measurement• Creating a Color Tolerance in CIEL*a*b* • Tolerances typically should be established for each component, DL* , Da* and Db*. • DE* can be used for tolerances, provided the user evaluates individual attributes. • These tolerances do not have to be symmetrical. 51
    51. 51. Color Measurement• CIE LCh 52
    52. 52. Color Measurement• CMC Provides for Elliptical Tolerances 53
    53. 53. Color Measurement• Creating a Color Tolerance in CMC • CMC is based on visual acceptability. • Key to success is the acceptability ellipsoids vary in shape and size depending upon the color of the standard. • CMC enables the same tolerance value (DECMC) to be used for all colors. 54
    55. 55. Visual Color Management• Visual Assessments • Establish a numeric and visual tolerance that everyone can achieve • Remember your eyes see color non-uniformly. • Avoid global color tolerances • Acceptable not perceptible • Avoid submitting a “Perfect” Sample • Avoid “Concession Color” 56
    56. 56. Visual Color Management• Color Communication • Develop guidelines internally for consistent communication of color assessments and directions. • No % should be used in descriptions. Example: Hue descriptions - Red, Green,Yellow or Blue Chroma descriptions - Bright or Dull Value descriptions - Light or Dark Adjectives - Very, Moderately or Slightly 57
    57. 57. Instrumental Color Management• Physical Standards • Represents the target color (Ideally, in the same medium on the same substrate) Advantages Disadvantages • Allows for visual comparison • May change over time • Decreases dependency on (deterioration, handling) absolute agreement between color • May be difficult to produce or obtain measuring systems several pieces that match 58
    58. 58. Visual and Instrumental Color Management• Phases of a Color Quality Program • Design & Color Specifications • Color Matching & Formulation • Visual & Instrumental (Hardware/Software) Analysis • Quality Control of the Color Manufacturing Process • Applications Procedures & Methods • Training & Education • Understanding the Customers Preferences Education and Training must be an integral part of each step within the program. 59
    59. 59. Instrumental Color ManagementQuestions? 60