Giving Shape to Ideas

Transcription

1 Giving Shape to Ideas

2 Light and Color Educational Seminars and Workshops Light and color terminologies are difficult to understand and are not main stream education curriculum. At Konica Minolta, our education seminars and workshops are foundation to a successful color control and management program. Our Color Education Series, How to Measure Color?, Color Control and Management and Precise Color Communication has helped may engineers get started with their color challenges. Why Consider Color Education? There is no unified description of color. In-house color specifications are vague and misunderstood. Our quality control specialists are not visually graded for color inspection. The parts arriving at our plant has a wide color variance. My supplier does not understand color specifications. The color measurement data does not seem to agree with what we see. Color control is a complicated process. How do we measure metallic coating? We need to setup a color control workflow. Call Us Many manufacturers and their supply chain have benefited from our Color Education Series. Let us help you color your world. Visit our learning center for more information at Centasia Co.,Ltd Bangna Thani Tower-10 th Floor, suite A1-A2 1/20 Soi Bangna-Trad 34, Bangna-Trad Hwy Km.3, Bangna, Bangkok Tel: (662) or Write to us at teamiie@centasiathai.com

3 Color Perception Basic Elements Understanding COLOR Your Guide to Instrumentation A Light Source An Object An Observer Factors Affecting Perception Light Source Differences Factors Affecting Perception Observer Differences Daylight Tungsten Fluorescent 1

4 Factors Affecting Perception Size Differences Factors Affecting Perception Background Differences Less Vivid Lighter? Darker? More Vivid Factors Affecting Perception Surface Condition Differences Factors Affecting Perception Directional Differences Sandpaper Daylight Before Sanding (Glossy) After Sanding (Dull) Observer 2

5 Factors Affecting Perception Color Memory Color Matching Function The Human Eye Which sample is a darker red? Retina = BLUE 1 2 Observer Color Matching Function The Human Eye Color Vision Light is not a color in itself. It is the radiant energy from light that stimulates the retina in the eye. This produces a sense of sight where the concept of color is formed and the brain reacts to it. Among the colors of the spectrum, red, green and blue are described as the primary colors. Our eyes can perceived color because the eye has three types of cones which are sensitive to these 3 primary colors. Color Matching Function The Human Eye Retina - Rods and Cones. Cones - Respond to colors. There are three different types of cones. S 420 to 440 nm M 530 to 540 nm L 560 to 580 nm Rods - For vision in very dim light but do not impart color vision. Note : The colors that we see are the result of different x, y and z proportions (stimuli) in the light received from an object. 3

6 Color Matching Function The Human Eye Photopic Vision - Where the Cones are active and normal color vision is possible when the luminance level is above 3 cd/m2. Color Matching Function Sensitivity Curves Spectral Sensitivity Curves corresponding to the human eye Scotopic Vision - Where the Rods are active and no color vision is possible when the luminance level is below 0.05 cd/m2. Mesopic Vision - Vision at luminance level in between the scotopic and photopic. The ability to distinguish color decreases as the lighting level decreases. Rods Cones has a high sensitivity in the red wavelength region Y has a high sensitivity in the green wavelength region Z has a high sensitivity in the blue wavelength region Color Matching Function Sensitivity Curves The CIE YZ values are not the S,M,L responses of the human eye but rather a set of tristimulus values called YZ which are roughly red, greenand blue Note that YZ are not physically observed red, green and blue colors. Rather they may be thought of as derived parameters from the red, greenand bluecolors. The CIE YZ color space was derived from a series of experiments done in the late 1920s by W. David Wright and John Guild. Their experimental results were combined into the specification of the CIE RGB color space, from which the CIE YZ color space was derived Color Data The CIE tri-stimulus values, Y and Z of a color are obtained by multiplying together - the Spectral Power Distribution of a CIE standard illuminant - the Spectral Reflectance (or the transmittance) of the object and - the Color Matching Functions x(λ), y(λ) and z(λ). The products are summed up for all the wavelengths in the visible spectrum to give the tri-stimulus values. Spectral Power Distribution of illuminant x Spectral Reflectance of specimen x Color Matching Functions = Y Z 4

7 Color Data Color Data CIE Illuminant D65 x Observer - CIE x Observer = CIE Tristimulus CIE Tristimulus L*a*b* Color Space (CIELAB) Lightness L* L* = 116 ( Y ) ⅓ - 16 Yn Reflectance = CIE y - Observer CIE Y Tristimulus CIE Y = 41.9 Chromaticity a* and b* a* = 500 [ ( ) ⅓ - ( Y ) ⅓ ] n Yn CIE z - Observer CIE z Observer = = CIE Z Tristimulus Y = 37.7 CIE Z Tristimulus Z = 8.6 b* = 200 [ ( Y ) ⅓ - ( Z ) ⅓ ] Yn Zn, Y, Z : Tristimulus values YZ for 2 deg standard observer n, Yn, Zn : Tristimulus values YZ for 2 deg standard observer of a perfect reflecting diffuser. = 41.9 Y = 37.7 Z = 8.6 Color Data Visible Spectrum Light ULTRAVIOLET VISIBLE SPECTRUM INFRARED Relative Energy Daylight Wavelength - Nanometers [nm] 5

8 Spectral Data Spectral Data The light given off by a light source (illuminant) as well as light reflected by an object (reflectance) can be measured with instruments in terms of its spectral characteristics (spectrophotometery). Wavelength (nm) Reflectance (%) Spectral Characteristics (% / nm) nm % White Grey Black Reflectance Reflectance Reflectance nm 400nm 400nm Wavelength Wavelength Wavelength 700nm 700nm 700nm Spectral Data Spectrophotometric Curve for Yellow 100 CIE COMMISSION INTERNATIONALE DE L ECLAIRAGE INTERNATIONAL COMMISSION ON ILLUMINATION INTERNATIONAL BELEUCHTUNGSKOMISSION % Relative Reflectance Wavelength [Nanometers] As its name implies, the International Commission on Illumination - abbreviated as CIE from its French title Commission Internationale de l Eclairage - is an organization devoted to international cooperation and exchange of information among its member countries on all matters relating to the science and art of lighting. The CIE is an autonomous organization. It is not appointed by any other organization political or otherwise but has grown out of the interests of individuals working in illumination. Since its inception, the CIE has been accepted as representing the best authority on the subject and as such is recognized by the ISO as an international standardization body. Central Bureau : Kegelgasse 27 A-1030 Wien Austria Phone : (43 1) /0 Fax : (43 1) /18 x0401daa@vm.univie.ac.at 6

9 CIE The International Commission on Illumination (CIE) is the international authority on light, illumination, color and color spaces. Established in 1913 is today based in Vienna, Austria. Seven divisions 1 - Vision & Color 2 - Measurement of Light and radiation 3 - Interior Environment and Lighting Design 4 - Lighting & Signaling for Transport 5 - Exterior Lighting & Other Applications 6 - Photobiology & Photochemistry 7 - Image Technology How To Quantify Color First we need to: Standardize the Light Source (Illuminant) Standardize the Observer Standardize the Measurement Method Standardize the Color System CIE Standard Illuminants Name Color Temp Description D K CIE Standard Illuminant D65 representing average daylight including ultraviolet radiation D K CIE Standard Illuminant D50 representing daylight including ultraviolet radiation C 6774 K CIE Standard Illuminant D65 representing average daylight including ultraviolet radiation A 2856 K CIE Standard Illuminant A representing an incandescent lamp F K CIE Fluorescent Illuminant F2 representing a cool white fluorescent lamp F K CIE Fluorescent Illuminant F6 representing a cool white fluorescent lamp CIE Standard Illuminants Name Color Temp Description F K CIE Fluorescent Illuminant F7 representing a daylight fluorescent lamp F K CIE Fluorescent Illuminant F8 representing a daylight white fluorescent lamp F K CIE Fluorescent Illuminant F10 representing a three band daylight white fluorescent lamp F K CIE Fluorescent Illuminant F11 (DIN TL-84) representing a three band white fluorescent lamp F K CIE Fluorescent Illuminant F12 representing a three band warm white fluorescent lamp (Ultralume 3000) 7

10 CIE Standard Illuminants Spectral Power Distribution Graph is a plot of the relative power of the light source against the wavelength. This can be measured using a Spectroradiometer CS Co-related Color Temperature of a light source is the temperature of the blackbody when heated to a certain temperature to give the color of the light source. White Lamp Green Lamp Red Lamp CIE Standard Illuminants Blackbody is an idealized physical body that absorbs all incident electromagnetic. Because of this perfect absorption at all wavelengths, it is also the best emitter of thermal radiation. All matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a body's thermal energy into electromagnetic energy, and is therefore called thermal radiation. An object that absorbs all radiation falling on it, at all wavelengths, is called a black body. Heat Source Tungsten Fluorescent Daylight Black Body 2856 K 4230 K 6504 K CIE Standard Illuminants As the temperature increases past a few hundred degrees Celsius, black bodies start to emit visible wavelengths, appearing red, orange, yellow, white, and blue with increasing temperature. The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of comparable hue to that of the light source. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K. CIE Standard Illuminants Typical Daylight Tungsten Filament Lamp Daylight D65 The spectral power distribution or relative power at each wavelength for typical daylight (Judd 1964, CIE1971) Tungsten A The spectral power distribution of blackbodies with color temperature of 2854K (Source A) and 6500K (Pivovonski 1961). (The curves are adjusted to a relative power of 100 at 560 nm. 8

11 CIE Standard Illuminants CIE Standard Illuminants Mercury Arc Lamp The spectral power distribution of a typical line source, a mercury arc lamp (IES 1981). Standard Illuminant A ( 2856 K ) Standard Illuminant C ( 6774 K ) Standard Illuminant D65 ( 6504 K ) Cool White Fluorescent Lamp The spectral power distribution of a cool white fluorescent lamp (IES 1981). CIE Standard Observer 2 Degree Standard Observer The average human chromatic response views through a 2 angle, due to the belief that the color-sensitive cones resided within a 2 arc of the fovea. The fovea is responsible for sharp central vision (foveal vision), which is necessary in humans for: CIE Standard Observer 10 Degree Standard Observer A more modern alternative is the CIE Standard Observer, which is derived from the work of Stiles and Burch and Speranskaya. For the 10 experiments, the observers were instructed to ignore the central 2 spot. The 1964 Supplementary Standard Observer is recommended for more than about a 4 field of view. Reading Watching TV or movies Driving Any activity where visual detail is of primary importance. 9

12 CIE Standard Observer At normal viewing distance of 50cm, the circle on the top represents the 2 field on which the CIE 1931 standard observer is based. The figure on the bottom is the 10 field on which the 1964 CIE supplementary standard observer is based. CIE Standard Observer The color matching functions x, y, z of the 1931 CIE standard observer and x10, y10, z10 of the 1964 CIE supplementary standard observer are compared here (data from CIE 1974). These sets of tristimulus values of the spectrum color, defining the 1931 CIE standard observer and the 1964 CIE supplementary standard observer, respectively, in terms of the same, Y and Z primaries are a little different. Most significantly, y10 is not the same as y or V(). Measurement Methods Measurement Methods Instrumentation Visual Method: BLUE Colorimetric Method: = Y = Z = 9.32 Spectrophotometric Method: BRAIN MICRO- COMPUTER RED GREEN BLUE RED GREEN BLUE CONES THREE SENSORS EYE x() y() z() Reflectance Measurement Color measurement of a sample based on the light reflection from the surface of the sample. Light source and sensor are on the same side. Transmittance Measurement Color measurement of a sample based on the light transmitted through the sample. Light source and sensor are on the opposite side. Trans-Reflectance Measurement Color measurement of a sample based on the light transmitted through the sample. Light source and sensor are on the opposite side. = Y = Z = Y Z MICRO- COMPUTER SPECTRAL SENSORS + Y Z 10

13 Measurement Methods Reflectance Application Opaque Solid s Plastic Metal Fabric Paper Opaque Granular s Resin Powder Granules Opaque Paste s Cream Sauce + Y Z Measurement Methods Reflectance Requirement Portable or Benchtop Chroma Meter Spectrophotometer Different Target Mask Size Small : 3 or 4 mm Medium : 8 mm Large : 25.4 or 30 mm White Calibration Plate Standard accessory with instrument Petri Dish & Cells Measurement Methods Transmittance Application Transparent Solid s Plastic Film / Plate Glass Transparent Semi-Solid s Jelly Gel Transparent Liquid s Chemicals Beverages + Measurement Methods Transmittance Requirement Benchtop Spectrophotometer With transmittance chamber CM-5, CM-3600A, CM-3700A Large Target Mask 30mm 25.4mm White Calibration Plate Standard accessory Zero Calibration Plate Optional accessory 11

14 Measurement Methods Transmittance Requirement Transmittance Specimen Holder Optional accessory Measurement Methods Transmittance Requirement 10mm Cell Transmittance Holder Optional accessory Cell Type Cell Size Quartz Glass Acrylic Plastic 20mm 10mm 2mm Cell Type Cell Size Quartz Glass 10 x 10mm 10 x 20mm 10 x 50mm Measurement Methods Trans-Reflectance Application Translucent s Hazy Plastic Hazy Glass Measurement Methods Trans-Reflectance Requirement Portable or Benchtop Chroma Meter Spectrophotometer Various Target Mask 3mm or 4mm (Small) 8mm (Medium) 25.4mm or 30mm (Large) White Calibration Plate Standard accessory + Y Z White Tile Backing 12

15 Metamerism Fluorescent Lamp (F2) A B Tungsten Lamp (A) Spectral reflectance of metameric objects are different Tristimulus values are the same under one light but different under another Problem is due to the use of different pigments and materials Color Instruments will display metamerism index (MI) to indicate the extent of the changes A B Color Notations Whiteness Index (ASTM E 313), Whiteness Index (CIE) Yellowness Index (ASTM E 313), Yellowness Index (ASTM D 1925) Blue Reflectance (ASTM E 313) Dominant Wavelength, Excitation Purity CMC FMC2 ANALab Chromatic Strength Tappi Brightness Opacity Apparent Strength E at Equal Apparent Strength Metamerism Index ISO Crock and Gray Scale Color Measuring Instrument How to Make Selection Color Meter or Spectrophotometer Reflectance or Transmittance Benchtops or Portables Geometry: d/8, d/0, 45/0, 0/45 Measuring Area: 3mm, 8mm, 30mm Specular Component: SCI or SCE Standard Illuminant: D65, A, F2, etc Standard Observer: 2 or 10 Instrument Geometry Reflectance Measurement D/8 Geometry Diffused illumination / 8 Viewing 8 Integrating Sphere Integrating Sphere D/0 Geometry Diffused illumination / 0 Viewing 0 eon Lamp eon Lamp 13

16 Instrument Geometry Reflectance Measurement Instrument Geometry Transmittance Measurement 0/45 Geometry 0 illumination / 45 Viewing 45/0 Geometry 45 illumination / 0 Viewing 0/0 Geometry 0 illumination / 0 Viewing d/0 Geometry Diffused illumination / 0 Viewing Lamp eon Lamp eon Lamp eon Lamp Lamp Transparent Transparent Specular Component Specular Light - Light reflected directly opposite the incident light Diffuse Light - Light that are scattered in many directions Total Reflectance - Specular Reflectance + Diffuse Reflectance Specular Component Excluded (SCE) Light Trap Opened Incident Light Specular Light eon Lamp Integrating Sphere Diffuse Light Specular component escapes through the light trap. captures only the diffuse component. Correlates to the way an observer sees the color of a sample. This is known as SCE condition. 14

17 Specular Component Included (SCI) Light Trap Closed eon Lamp Integrating Sphere Specular component is trapped within the integrating sphere. captures both the diffuse and specular component. Measures the total color appearance independent of the surface conditions. This is known SCI condition. 15