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

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small amount to our perception of a color. Changes in the amount of light in the middle spectral wavelengths have a much larger affect on the resulting color since they are heavily weighted by ¯y(λ). Therefore, in our example with Lapis lazuli the hue moves slightly closer to green instead of purple. For the sample of Lapis Lazuli, this behavior is typical of the first stage of fading (a perceived increase in both value and chroma, as well as hue shifts due to changes in the spectra away from the reflectance maxima), which was discussed in the previous chapter. More examples of time-dependent behavior for different pigment-media combinations can be seen in Appendix B. 6.1.3 Applications None of the research discussed in the previous chapter addresses material changes from the artist’s point of view–from the initial fresh mark of paint. As a painter, one only has control over the initial conditions of a color in a painting–one has full control over the combination of pigments, media and other materials. An artist’s vision is expressed through the mixing and application of fresh paints on a canvas support. Yet, once defined, the appearance of the paint is a function of time. Then, for what time should the artist create a painting for? Is the artist’s creative vision only fulfilled upon the immediate completion of a work or is the artwork the living and evolving material object? A second intrinsic problem in working with paint is color matching. Most creative works are far too complex to be created in a single day. As such, an artist must return to a work for subsequent treatment after some period of time. However, as previously described, many changes (which are often perceptually 183 evident) occur to a paint sample after it has been applied. Assume a painter is
trying to match color ca from the previous day. If the same exact paint is applied on the second day of work, the color cb will be one day removed from fading. As seen in Figure 6.6, the colors will not exactly match (as there is some perceptual difference ∆E). The longer the artist waits to match evolving color ca with wet color cb on his/her palette, the more dissimilar the colors will be. As a result, a color match will be more difficult, as the fresh color will not have been subjected to the same conditions as the dry color. Figure 6.6: Left: Visual comparison of Lapis Lazuli in Gouache changing at each time interval. Right: the overall change. Hence, in order to match a previously painted brushmark, the artist must alter the pigment mixture of the fresh paint. The logical method would be to save the paint from the previous session and alter the mixture slightly to account for the change. While this may work for some paints (such as oil), many paints have to be made fresh daily (the working properties of different binding media are discussed in previous chapters). This presents a difficult problem, as not only does an artist have to mix a color from scratch to match the previous one, the paint has to be modified (via changes in the concentrations of pigments) in order to account for the color changes that have already taken place. Even if the artist has no idea that the color is changing over time, he/she attempts to match what is seen (and since what is seen changes, the match changes). 184 For artists, this skill is typically learned based on one’s familiarity with the
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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
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over white grounds) suffer the grea
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protects the deeper remaining color
Page 145 and 146: light source. This method is used w
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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,
Page 191 and 192: 178 Figure 6.4: Variation of spectr
Page 193 and 194: visible spectrum are increasing at
Page 195: 182 Figure 6.5: Munsell plots of La
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
Page 243 and 244: 230 Figure B.15: Variation of spect
Page 245 and 246: 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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