pigmented colorants: dependence on media and time - Cornell ...

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from the mirror is collimated (parallel). This light is dispersed into its various components upon striking the diffraction grating (D), as different wavelengths of light will reflect at different angles. The dispersed light is collected via another spherical mirror (E) and refocused on the exit slit (F). Figure 5.9: Diagram of a Czerny-Turner monochromator. The desired bandpass of light exiting the monochromator (G) is yielded via rotating the grating (D) to the proper position. Diffraction gratings consist of glass and a layer of deposited aluminum that has been pressure-ruled with a large number of fine equidistant grooves. They are designed to be maximally efficient at specific wavelengths (by varying grooves per distance), hence multiple gratings are required to cover wide wavelength ranges. Also, the range of wavelengths leaving the exit slit (G) is a function of the slit widths (B & F), which are user interchangeable. 161
Note that harmonics reflect at the same angle (a harmonic is a integer multiple of a frequency αf | α ∈ Z). Hence, to achieve the desired wavelength band, light exiting the monochromator is filtered. For example, light of 400nm reflects off the grating at the same angle as 800nm. If one desires the blue-violet band (400nm) and not light in the infrared (800nm), a filter must be in place to block the extraneous light. 5.2.2 Integrating sphere theory The desired wavelength band of light is then passed to an integrating sphere in order to calculate the diffuse reflectance of a material. In an integrating sphere, light enters from a small aperture in the sphere and strikes a sample on the opposing surface of the sphere. The light is reflected off the surface of the sample to the entire sphere. The surface of the sphere is covered in a highly reflective diffuse material (typically Polytetrafluoroethylene (PTFE) for measurements in the visible spectrum range). Hence, multiple scattering events occur and the light diffuses over the entire sphere. At another portion of the sphere is a detector to measure the response of light striking that portion. The basic theory for the integrating sphere has been evaluated analytically by Jacquez and Kuppenhiem [JK55]. In the comparison method, the integrating sphere reflectometer has a dual beam design. Incident light enters through an aperture in the sphere at one of two angles. Following these paths of light across the sphere, there are two apertures for samples–the test and comparison samples. A detector is placed at another location on the sphere. The method requires four separate scans: two calibration scans and two test 162 sample scans. During calibration, a standard reflectance sample of known re-
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PIGMENTED COLORANTS: DEPENDENCE ON
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ABSTRACT We present a physically ba
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Acknowledgements This work would no
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Table of Contents 1 Introduction 1
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List of Tables 2.1 Average pigment
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3.15 Photoreceptor absorption .....
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B.15 Variation of spectral reflecta
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corrode the surfaces of materials.
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Figure 1.1: Detail of the Azor-Sado
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However, since mural artwork is typ
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at a very high quality (albeit limi
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heterogeneous sum of very different
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which linseed oil derives (the most
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oration of a rigidly painted layer
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ing will hit the ground and reflect
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tion of paint tubes in 1841 and the
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Figure 2.8: Natural pigments of ant
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ecome more common recently. The Ame
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A V = O(r2 ) O(r3 ) = 1 O(r) 24 (2.
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Table 2.2: Pigment specific gravity
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provide the underlying color to a p
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though the speed of light in air is
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In general, when light travels from
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materials while lit from behind. Li
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Table 2.4: Index of refraction η f
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to completely congeal. Hence, these
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ond together to form proteins. Exam
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to its original state by any means.
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While it has been used since the 19
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organic binder found in more conven
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3.1.1 Visible Light Spectrum Light
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Figure 3.2: Hue, brightness and sat
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measures how much light is reflecte
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Figure 3.6: Additive color mixing o
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Figure 3.9: The physical amount of
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The vascular tunic lies on the wall
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Figure 3.11: Cross section of the r
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Not all areas have the same sensiti
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identify and distinguish between va
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that range between zero and full in
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spectrum. This insures that the res
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Figure 3.19: Graphical representati
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X x = (X + Y + Z) Y y = (X + Y + Z)
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color into the appropriate RGB colo
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components in the image (the smalle
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haviors of subtractive mixing and i
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of perceptually equal sizes. Unfort
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enabling one to transform between t
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andwidth as converted signals are s
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Figure 3.28: Retinal ganglion recep
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example shown in Figure 3.28. Under
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Figure 3.31: The work of Josef Albe
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sensations for each trial and picke
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Chapter 4 Previous Work There is no
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different location. Subsurface scat
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describes the scattering and absorp
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only accounts for a small percentag
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σ ′ t = σa + σ ′ s and α
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104 Figure 4.4: A model of an alaba
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effects or are too computationally
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108 Figure 4.6: Results using Kubel
Page 123 and 124: specifying pigments works adequatel
Page 125 and 126: color representation, it is not fea
Page 127 and 128: time. A metallic surface patina is
Page 129 and 130: the system consisted of wetness and
Page 131 and 132: or darkening enables the museum per
Page 133 and 134: in front of a displayed work. Felle
Page 135 and 136: light exposure. This effect is espe
Page 137 and 138: over time. Perceptually, these hues
Page 139 and 140: The rate of change of the concentra
Page 141 and 142: over white grounds) suffer the grea
Page 143 and 144: protects the deeper remaining color
Page 145 and 146: light source. This method is used w
Page 147 and 148: chemical smog and have been identif
Page 149 and 150: Chapter 5 Preparation & Measurement
Page 151 and 152: tending transparent pigments used i
Page 153 and 154: 140 Figure 5.1: Spectral reflectanc
Page 155 and 156: the requirements of the work at han
Page 157 and 158: 144 Figure 5.2: Left: Magnified vie
Page 159 and 160: Table 5.2: Relevant data regarding
Page 161 and 162: historically one of the best grades
Page 163 and 164: created far too strong of a binder,
Page 165 and 166: too brittle and cracking. While wor
Page 167 and 168: 154 Figure 5.4: Reflectance values
Page 169 and 170: 5.1.5 Painting After the layers of
Page 171 and 172: The gray card reflected 18% of the
Page 173: 160 Figure 5.8: The optical setup f
Page 177 and 178: Note that the calibration factors f
Page 179 and 180: Chapter 6 Experimental Results 6.1
Page 181 and 182: 168 Figure 6.1: Lapis Lazuli in dif
Page 183 and 184: (such as CIE standards C, D50, orD6
Page 185 and 186: 172 Table 6.2: Perceptual differenc
Page 187 and 188: 174 Figure 6.3: Munsell plots of La
Page 189 and 190: and j has a saturation of red rsat,
Page 191 and 192: 178 Figure 6.4: Variation of spectr
Page 193 and 194: visible spectrum are increasing at
Page 195 and 196: 182 Figure 6.5: Munsell plots of La
Page 197 and 198: trying to match color ca from the p
Page 199 and 200: as it ages. This is in direct contr
Page 201 and 202: teractive viewer. In our applicatio
Page 203 and 204: 190 Figure 7.1: Our simulated canva
Page 205 and 206: where n is the normal at the curren
Page 207 and 208: In summary, our implementation prov
Page 209 and 210: Chapter 8 Conclusion We have studie
Page 211 and 212: inks are beginning to find their wa
Page 213 and 214: Appendix A Derivation of K-M theory
Page 215 and 216: ∆i − =(K + S) idx 202 ∆j −
Page 217 and 218: Equation A.8 is now: Rearranging yi
Page 219 and 220: and if the paint is infinitely thic
Page 221 and 222: One concatenates the layers into a
Page 223 and 224: 210 Figure B.1: Cold Glauconite in
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Table B.1: Color conversions from t
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214 Figure B.4: Munsell plots of Co
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216 Figure B.5: Burnt Sienna in dif
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220 Figure B.8: Munsell plots of La
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222 Figure B.9: Red Ochre Tint in d
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226 Figure B.12: Munsell plots of C
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228 Figure B.13: Variation of spect
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230 Figure B.15: Variation of spect
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Table B.13: Color conversions of Bu
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234 Figure B.18: Munsell plots of C
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236 Figure B.20: Munsell plots of R
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References [Alb71] Josef Albers. In
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240 [GLL + 04] Michael Goesele, Hen
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242 [KM31] Paul Kubelka and Franz M
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[Rat72] Floyd Ratliff. Contour and
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