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C O L O R or Shade : Keys to Acceptance Presented by: CRABLE ENGINEERING LLC

C O L O R or Shade : Keys to Acceptance Presented by: CRABLE ENGINEERING LLC.

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C O L O R or Shade : Keys to Acceptance Presented by: CRABLE ENGINEERING LLC

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  1. COLOR or Shade: Keys to Acceptance Presented by: CRABLE ENGINEERING LLC CRABLE ENGINEERING LLC

  2. “Marketing psychologists state that a lasting impression is made within ninety seconds and that color accounts for 60% of the acceptance or rejection of an object, person, place, or circumstance. Because color impressions are both quick and long lasting, decisions about color are critical factors in the success of any visual experience.” - About Color The fields of shade (or color) and appearance are critical to the acceptance of paper and board products, yet these product attributes are often overlooked. Or, systems to support them are often an afterthought in the design and operation of a paper machine. CRABLE ENGINEERING LLC

  3. Now – What is Color (or Shade)? (Shade is a term used for color generally when discussing a white or near-white object.) CRABLE ENGINEERING LLC

  4. Color is a Perception • Color processing is done in the brain and is therefore subject to the interpretation of the viewer. CRABLE ENGINEERING LLC

  5. You know, I told those guys in Color & Appearance to give the sheet some "snap." Does that look "snappy" to you? ?... Communicating Color... CRABLE ENGINEERING LLC

  6. Three Red Samples: How would you describe their color differences? CRABLE ENGINEERING LLC

  7. The Three Attributes of Color • Hue: the attribute of color described as blue, green, yellow, orange, red, etc. • Saturation (also called chroma): the intensity or "vividness" of a color. • Lightness: the degree of black, gray, or white in a color. deep pastel CRABLE ENGINEERING LLC

  8. What Makes Color? Observer (Eye-Brain) Object Light Source CRABLE ENGINEERING LLC

  9. Color=(Light Source) x (Object) x (Observer) Common Light Sources for Color Viewing CRABLE ENGINEERING LLC

  10. Incandescent (most home lighting) Will they go away? • Cool White Fluorescent (most office lighting) • Daylight (outside lighting) • LEDs COMMON COLOR LIGHT SOURCES CRABLE ENGINEERING LLC

  11. The color of a light source influences the appearance of the objects it illuminates. • Lighting manufacturers often use terms like "warm," "cool" or "neutral" to indicate the color of a lamp. • The "Correlated Color Temperature" is a more specific term used to describe the color of a light source. Describing the Color of a Light Source CRABLE ENGINEERING LLC

  12. Assigning a correlated color temperature is an old practice that allows the color of a light source to be specified with a single number. • When a piece of metal is heated it changes color from red to yellow to white, to blue white. • The color at any point can be described in terms of the absolute temperature of the metal measured in degrees Kelvin (K): Correlated Color Temperature (or CCT) CRABLE ENGINEERING LLC

  13. A tungsten filament bulb (incandescent light) has a CCT of 3100K and is yellow in color. • Cool white fluorescent light has a CCT of 4150K and is greenish in color. • Daylight is blue-white; with the more common phases ranging between 5000K (D50) and 7500K (D75). CCTs of Common Light Sources CRABLE ENGINEERING LLC

  14. Ever-changing (must be specified). • The most common CCTs are 5000K (D50), 6500K (D65). • Rich in blue and UV energy. • Excellent color rendering properties. Daylight CRABLE ENGINEERING LLC

  15. Fluorescent Lamps • Efficient (high number of lumens per watt). • Most common form of office lighting (usually with some daylight present). • Color is generally described as "warm, neutral, or cool white." • Color rendering capabilities vary with manufacturer and bulb type. CRABLE ENGINEERING LLC

  16. Incandescent (tungsten filament bulbs) • Primarily used in the home. • Very yellow or "warm" in color. • Poor color rendering properties. CRABLE ENGINEERING LLC

  17. The Influence of The Light Source on Color • To fully understand how a light source contributes to the color of an object, we must know more than its Correlated Color Temperature. • The output of a light source is fully described by its Spectral Power Distribution. CRABLE ENGINEERING LLC

  18. Definitions... • The spectral power distribution of a light source describes how much energy is present at each wavelength across the visible spectrum. • The visible spectrum is a small range of wavelengths, within the larger electromagnetic spectrum, that the human eye can see. CRABLE ENGINEERING LLC

  19. The Electromagnetic Spectrum CRABLE ENGINEERING LLC

  20. Relative Spectral Power Distribution of a Tungsten Filament Bulb (Illuminant A; CCT = 3100K) CRABLE ENGINEERING LLC

  21. IR UV Relative Spectral Power Distributions of Two Cool White Fluorescent Sources (CCT = 4150K) CRABLE ENGINEERING LLC

  22. IR UV Relative Spectral Power Distributions for Two Phases of Daylight (D50 with a CCT of 5000K and D65 with a CCT of 6500K) CRABLE ENGINEERING LLC

  23. Selecting the "Right" Light Source for Color Viewing and Measurement • Should approximate the color viewing condition(s) our customers use, if we know what those are. • The "right" light source should have sufficient energy across the entire spectrum for optimal color discrimination. CRABLE ENGINEERING LLC

  24. The Object CRABLE ENGINEERING LLC

  25. The Interaction of Light with Paper Incident white Light Transmitted Light Surface Reflected and Scattered Light Red Light Reflectedby Dyed Fiber & Fillers CRABLE ENGINEERING LLC

  26. Specular Reflection Diffuse Reflection The Scattering Properties of Glossy and Matt Samples GLOSSY SURFACE MATT SURFACE The surface properties of a sample influence the quality and quantity of light that reaches our eye; influencing the way an object appears. In fact, we sometimes calender samples to get “the right look.” CRABLE ENGINEERING LLC

  27. The Observer • Different people see color differently due to: • Age • Macular Pigment • Number and ratio of rods and cones • Some average or "standard" observer of color must therefore be established for consistent color measurements to be determined for any object. CRABLE ENGINEERING LLC

  28. The Standard Observer Development CRABLE ENGINEERING LLC Source: Principles of Color Technology, 2nd Edition Fred Billmeyer, Jr. and Max Saltzman

  29. The Standard Observer 2° (1931) and 10° (1964) At 18 inches ~ dime & baseball. IR UV CRABLE ENGINEERING LLC

  30. 300 UV 400 500 600 700 IR 800 Yellow Object Curve Blue Object Curve Spectral Curves % Reflectance % Reflectance 400 500 600 700 400 500 600 700 CRABLE ENGINEERING LLC

  31. 400 500 600 700 Color Mixing Blue Object Curve Green Object Curve Yellow Object Curve = + % Reflectance % Reflectance % Reflectance % Reflectance 400 500 600 700 400 500 600 700 Colorants like paint, dye, and ink reflect only certain wavelengths of light and absorb all others. Mixing two different colors will produce an entirely new color by combining their light absorbance. CRABLE ENGINEERING LLC

  32. IR UV IR UV IR UV Light Source Output X Sample Reflectance = The Light That Enters The Eye CRABLE ENGINEERING LLC

  33. Light that Reaches Our Eye... "Green" Sensitivity "Blue" Sensitivity "Red" Sensitivity "Blue" Response "Green" Response "Red" Response CRABLE ENGINEERING LLC Z Y X

  34. Tristimulus Values Three Numbers Required to Describe Color: X = k * x(l) * R(l) Y = k * y(l) * R(l) Z = k * z(l) * R(l) A spectrophotometer measures only R(l) or % Reflectance across the spectrum. All else is math, done in a computer. CRABLE ENGINEERING LLC

  35. Tristimulus values are not perceptually uniform; (equal distances in tristimulus space will not appear visually equal). • Tristimulus values describe color but are not intuitive. • Tristimulus values are therefore transformed into L*, a*, b* space. Color is Three Dimensional CRABLE ENGINEERING LLC

  36. Equations for TransformingTristimulus Values to Hunter L, a, b (1942)[This original unit system, Hunter admitted, had flaws.] Equations for Transforming Tristimulus Values to CIE L*, a*, b* (1976) [An improved version – more linear.] L = 100 x (Y/Yn)1/2 a = 175 x {0.0102*Xn/(Y/Yn)}1/2 x {(X/Xn) - (Y/Yn)} b = 70 x {0.00847*Zn/(Y/Yn)}1/2 x {(X/Xn) - (Y/Yn)} L* = 116 x (Y/Yn)1/3 - 16 a* = 500 x {(X/Xn)1/3 - (Y/Yn)1/3} b* = 200 x {(Y/Yn)1/3 - (Z/Zn)1/3} CRABLE ENGINEERING LLC

  37. * * CRABLE ENGINEERING LLC

  38. MacAdam Ellipses Note that there are larger tolerances for green and deep shades than there are for blue and white shades – that means that our eyes are more sensitive to small differences in white, blue, gray and tan colors.

  39. Color Differences L* a* 1.0 0.5 b* 0.5 dL*=1.0, da*=0.5, db*=0.5 delta L* or dL* = L*SAMPLE - L*STANDARD delta a* or da* = a*SAMPLE - a*STANDARD delta b* or db* = b*SAMPLE - b*STANDARD delta E* or dE* = [(dL*)2 + (da*)2+ (db*)2]1/2 The color difference between any two samples is expressed in terms of "deltas": dE* is a measure of overall color difference. Establishing a reject limit for dE* constrains the three dimensions of color so that they can't simultaneously be at their outer limits. (Our eyes perceive acceptable color differences as ellipsoids, not rectangles.) Saturated and deep colors can have broader tolerances, while whites and neutral shades (grays) may need tighter tolerances. CRABLE ENGINEERING LLC

  40. Control Strategies If dL* is positive (+): sample is too light. Add dye. If dL* is negative (-): sample is too dark. Cut dye. If da* is positive (+): sample is too red (or not green enough). NOW CHECK dL*! [Is the sheet light or dark?] • - Add yellow and blue for +dL*; cut red for -dL*. If da* is negative (-): Sample is too green (or not red enough). • - Addredfor +dL*; cutyellowandbluefor -dL*. If db* is positive (+): sample is too yellow (or not blue enough). NOW CHECK dL*! [Is the sheet light or dark?] • - Add blue for +dL*; cut yellow for -dL*. If db* is negative (-): Sample is too blue (or not yellow enough). • - Add yellow for +dL*; cut blue for -dL*. CRABLE ENGINEERING LLC

  41. Standard Measures:L* = 74.5, a* = 40.4, b* = 27.8What color is this? • Sample Measures:L* = 75.1, a* = 41.0, b* = 28.7What are the deltas?What adjustment should we make? Color Control Exercises: Case 1 (Using Red, Blue, and Yellow Dyes.) CRABLE ENGINEERING LLC

  42. Standard Measures:L* = 81.9, a* = -22.7, b* = 13.4What color is this? • Sample Measures:L* = 81.2, a* = -21.9, b* = 13.1What are the deltas?What adjustment should we make? Color Control Exercises: Case 2 (Using Red, Blue, and Yellow Dyes.) CRABLE ENGINEERING LLC

  43. Standard Measures:L* = 78.9, a* = -13.0, b* = -10.5What color is this? • Sample Measures:L* = 79.5, a* = -12.2, b* = -10.4What are the deltas?What adjustment should we make? Color Control Exercises: Case 3 (Using Red, Blue, and Yellow Dyes.) CRABLE ENGINEERING LLC

  44. Standard Measures:L* = 80.7, a* = 0.1, b* = 2.2 What color is this? • Sample Measures:L* = 81.4, a* = 0.0, b* = 2.0What are the deltas?What adjustment should we make? Color Control Exercises: Case 4 (Using Red, Blue, and Yellow Dyes.) CRABLE ENGINEERING LLC

  45. Metamerism When two samples appear to be the same color but havedifferentspectral reflectance curves, they may match under one light source but not another. CRABLE ENGINEERING LLC

  46. Common Sources of Metamerism • Different dyes • Different levels of fluorescence • Different pulps • Different fillersThe potential for metamerism between a color standard and production is almost always present. CRABLE ENGINEERING LLC

  47. Metamerism is the 2nd major cause of color complaints. • Colors can match in one set of lighting conditions and still be rejected by the customer if viewed under a different light source. • The better we control the variables that contribute to metamerism the more consistent our products will be. Important things to know about metamerism... CRABLE ENGINEERING LLC

  48. SUMMARY 1 Color=(Light Source) x (Object) x (Observer) Observer (Eye-Brain) Light Source Object CRABLE ENGINEERING LLC

  49. SUMMARY 2 Color = (Light Source), an Array of Known (shade) Values for Each Defined Light Source X (Observer), a 3-Column Table of Known x, y, z Values for The Two Defined Observer Functions: (2 degree and 10 degree) X (Object), a Measured Array of % Reflectance Numbers CRABLE ENGINEERING LLC

  50. SUMMARY 3 Color = X, Y, Ztristimulus units for the Red, Green, and Blue cones (receptors) in our eyes. X, Y, Ztristimulus units are converted to L*, a*, b* units for ease of use and discussion where L* = 0 to 100 for dark to light; a* = -100 green to +100 red; b* = -100 blue to +100 yellow (in this ‘opponent color system) dL*, da*, db* are color differences: Sample – Standard values for each CRABLE ENGINEERING LLC

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