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

CRABLE ENGINEERING LLC “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

CRABLE ENGINEERING LLC 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

CRABLE ENGINEERING LLC Color is a Perception The eyes of humans have two sets of light receptors in their retinas (the neuronal layers at the back of the eyes). These are called rods and cones. Color processing is done in the brain and is therefore subject to the interpretation of the viewer. CRABLE ENGINEERING LLC

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

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

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. pastel deep CRABLE ENGINEERING LLC

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

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

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

Describing the Color of a Light Source 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. CRABLE ENGINEERING LLC

Correlated Color Temperature (or CCT) 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): CRABLE ENGINEERING LLC

CCTs of Common Light Sources 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). CRABLE ENGINEERING LLC

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

CRABLE ENGINEERING LLC 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

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

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

CRABLE ENGINEERING LLC 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

CRABLE ENGINEERING LLC The Electromagnetic Spectrum CRABLE ENGINEERING LLC

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

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

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

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

CRABLE ENGINEERING LLC The Object CRABLE ENGINEERING LLC

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

The Scattering Properties of Glossy and Matt Samples Specular Reflection Diffuse Reflection 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

CRABLE ENGINEERING LLC 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

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

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

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

CRABLE ENGINEERING LLC Color Mixing Yellow Object Curve Blue Object Curve Green Object Curve 400 500 600 700 % 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

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

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

CRABLE ENGINEERING LLC 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

Color is Three Dimensional 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. CRABLE ENGINEERING LLC

Equations for Transforming Tristimulus Values to CIE L*, a*, b* (1976) Equations for Transforming Tristimulus Values to Hunter L, a, b (1942) [This original unit system, Hunter admitted, had flaws.] 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)} Equations for Transforming Tristimulus Values to CIE L*, a*, b* (1976) [An improved version – more linear.] 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

CRABLE ENGINEERING LLC * * CRABLE ENGINEERING LLC

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.

CRABLE ENGINEERING LLC Color Differences The color difference between any two samples is expressed in terms of "deltas": L* a* b* 0.5 1.0 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 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

CRABLE ENGINEERING LLC 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). - 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*. CRABLE ENGINEERING LLC

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

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

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

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

CRABLE ENGINEERING LLC 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. CRABLE ENGINEERING LLC

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

Important things to know about metamerism... 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. CRABLE ENGINEERING LLC

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

CRABLE ENGINEERING LLC 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) (Object), a Measured Array of % Reflectance Numbers CRABLE ENGINEERING LLC

CRABLE ENGINEERING LLC 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 CRABLE ENGINEERING LLC

CRABLE ENGINEERING LLC 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! CRABLE ENGINEERING LLC