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

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Presentation on theme: "COLOR or Shade: Keys to Acceptance Presented by: CRABLE ENGINEERING LLC 1."— Presentation transcript:

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

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. 2CRABLE 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.) (Shade is a term used for color generally when discussing a white or near-white object.) 3CRABLE ENGINEERING LLC

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

19 The Electromagnetic Spectrum 19 CRABLE ENGINEERING LLC

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

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

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

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

24 The Object 24CRABLE ENGINEERING LLC

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

26 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. Specular Reflection Diffuse Reflection 26CRABLE ENGINEERING LLC

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

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

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

30 Spectral Curves 300 UV IR 800 % Reflectance Yellow Object Curve Blue Object Curve % Reflectance 30CRABLE ENGINEERING LLC

31 Blue Object Curve % Reflectance = 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. Color Mixing % Reflectance Yellow Object Curve % Reflectance Green Object Curve % Reflectance 31CRABLE ENGINEERING LLC

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

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

34 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. Three Numbers Required to Describe Color: Tristimulus Values 34 CRABLE ENGINEERING LLC

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

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

37 * * 37CRABLE 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 The color difference between any two samples is expressed in terms of "deltas": 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 Color Differences 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. L* a* b* dL*=1.0, da*=0.5, db*=0.5 39CRABLE ENGINEERING LLC

40 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). - Add red for +dL*; cut yellow and blue for -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*. Control Strategies 40 CRABLE ENGINEERING LLC

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

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

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

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

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

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

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

48 SUMMARY 1 Color=(Light Source) x (Object) x (Observer) Light Source Object Observer (Eye-Brain) 48 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 49 CRABLE ENGINEERING LLC

50 SUMMARY 3 Color = X, Y, Z tristimulus units for the Red, Green, and Blue cones (receptors) in our eyes. X, Y, Z tristimulus 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 50 CRABLE ENGINEERING LLC

51 SUMMARY 4 dE* = SQRT(dL* **2 + da* **2 + db* **2) dE* is the total (summed) color error, and putting a limit on it prevents all 3 of dL*, da*, and db* from being at specifications limits at the same time. (See Slide 39.) It takes all four of dL*, da*, db*, and dE* being within specification for good color reproduction. Beware of metamerism! 51 CRABLE ENGINEERING LLC


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