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

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Table 6.3: Color conversions of Lapis Lazuli in Gouache over time. ∆E is the distance from the previous to current L ∗ a ∗ b ∗ color. X Y Z H V C L ∗ a ∗ b ∗ ∆E wet 8.42 8.63 23.53 3.13PB 3.43 6.56 35.27 2.10 -32.21 1day 9.03 9.46 26.48 2.43PB 3.58 7.13 36.85 0.53 -34.33 3.08 1 week 13.23 14.28 36.17 1.61PB 4.33 7.52 44.63 -1.96 -34.66 8.18 1month 14.78 16.00 38.51 1.48PB 4.55 7.30 46.97 -2.34 -33.55 2.62 3months 14.86 16.11 39.23 1.46PB 4.57 7.46 47.11 -2.48 -34.20 0.68 6months 14.67 16.03 38.84 1.16PB 4.56 7.41 47.01 -3.20 -33.88 0.30 wavelengths, an equal additional amount of every wavelength is the perceptual equivalent of the color shifting closer to white. Similarly, if the overall reflectance curve shift is downwards, the material is perceived as getting darker. In both instances, this is not exactly the case, since the spectra must be integrated against the eye’s response matching functions (which are wavelength-dependent). Hence, luminance changes are wavelength-dependent to some extent. In Figure 6.4, the spectral curves of Lapis lazuli in Gouache are increasing substantially over time. This is occurring at relatively a uniform rate and one is safe to presume that the overall luminance is increasing (the corresponding images also support this behavior). In the same manner in the previous section, the spectral reflectance data has been converted into the various color systems to aide in further analysis. Viewing any of the luminance indicators (Y , V ,orL ∗ )also supports the behavior that was observed–all of these indicators increase with time. However, the spectral reflectance curves are not changing entirely uniformly with this material. Reexamining the diffuse reflectance at the six time intervals, 179 it is evident that the reflectance values of the lower and higher regions of the
visible spectrum are increasing at different rates. Yet, understanding the effect on perception of nonuniform changes in the spectral distribution is more complicated than with uniform changes. Hue shifts occur when spectral distribution reflectance curves change unequally with respect to wavelength. The color of a material depends on both the light that is reflected and light that is absorbed. First, a nonlinear increase in a material’s reflectance affects the appearance. For instance, increasing a material’s reflectance between 565 − 590nm will in turn reflect more yellow light back into the environ- ment. As a result, the viewer will see the material as being yellower. The second case is slightly less intuitive. For instance, oil paints typically experience a slight yellowing of the binding material due to oxidation. This equates to a drop in the lower regions of the spectral reflectance curve. Then, the material is absorbing more blue light than previously. In other words, the material is thus reflecting less blue light back toward the viewer. Therefore, the material is reflecting relatively more yellow light and hence appears to have yellowed. In both cases, a hue change is dependent on the relative balance between light reflected and absorbed. A nonuniform change in either can affect the overall perception of a hue. It is worth mentioning that in paint, what we perceive as hue shifts typically occur when a nonlinear change occurs away from the central tendency of the material’s reflectance. For instance, we typically state that a blue has yellowed, or a purple shifted toward red, etc. However, when these changes occur near the central tendency of the reflectance, the perceptual change is not that of hue, but of chroma. 180 Consider the previous case of Lapis Lazuli in gouache. As the paint evolves,
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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
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specifying pigments works adequatel
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color representation, it is not fea
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time. A metallic surface patina is
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the system consisted of wetness and
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or darkening enables the museum per
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in front of a displayed work. Felle
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light exposure. This effect is espe
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over time. Perceptually, these hues
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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 and 174: 160 Figure 5.8: The optical setup f
Page 175 and 176: Note that harmonics reflect at the
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
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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,
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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
Page 225 and 226: Table B.1: Color conversions from t
Page 227 and 228: 214 Figure B.4: Munsell plots of Co
Page 229 and 230: 216 Figure B.5: Burnt Sienna in dif
Page 233 and 234: 220 Figure B.8: Munsell plots of La
Page 235 and 236: 222 Figure B.9: Red Ochre Tint in d
Page 239 and 240: 226 Figure B.12: Munsell plots of C
Page 241 and 242: 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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