1. Many of the figures from this book may be reproduced free of charge in scholarly articles, proceedings, and presentations, provided only that the following citation is clearly indicated: “Reproduced with the permission of the publisher from Computer Graphics: Principles and Practice, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley. Copyright 2014 by Pearson Education, Inc.” Reproduction for any use other than as stated above requires the written permission of Pearson Education, Inc. Reproduction of any figure that bears a copyright notice other than that of Pearson Education, Inc., requires the permission of that copyright holder.

2. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.1 The spectral power distribution of a fluorescent lamp. The power emitted at each wavelength varies fairly smoothly across the spectrum, with a few high peaks. Figure provided courtesy of Osram Sylvania, Inc.

3. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.2 The spectral power distributions of several LEDs. The light is concentrated at or near a single wavelength for each kind of LED; an ideal monospectral source would have all energy at a single wavelength.

4. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.3 A contrived spectral power distribution with 500 nm as its dominant wavelength.

5. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.4 The approximate spectral response functions of the three types of cones in the human retina; the labels R, G, and B are misleading, because the peaks of the R and G curves both correspond to monospectral lights that most people describe as in the “yellow” range.

6. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.5 Light, described by its spectral power distribution, enters the eye; the three types of cones each respond and their individual responses are conducted by the optic nerves to the brain, resulting in a perception of color. These correspond to three distinct areas of study: physics, physiology, and perceptual psychology.

7. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.6 The luminous efficiency at each wavelength tells how much less bright light of that wavelength appears than light at the standard wavelength of 555 nm.

8. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.7 The luminous efficiency in photopic vision has a peak at 555 nm; the peak for scotopic vision is closer to 520 nm.

9. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.8 The percent output of rods and cones. The rods’ output flattens out at modest luminance levels, and no change in output occurs even in very bright scenes; the cones’ response also flattens out, but the absolute position of the curve may vary along the log luminance axis substantially as the cones adapt to the light present.

10. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.9 Tints, tones, and shades, as commonly used to describe colors.

11. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.10 The response curve for monospectral visible light. Note that the short-wavelength-response axis has a different scale. We show the curve from two different views.

12. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.11 The response of the three cone types to a monospectral light can be read from the plot of their sensitivities. Light at 450 nm, for instance, generates about equal short- and medium-wavelength responses (shown in blue and green and labeled “S” and “M”), but a slightly smaller long-wavelength response (shown in red and labeled “L”). Light at 640 nm generates a large red response, a small green response, and almost no blue response.

13. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.12 The set of all possible responses from combinations of monospectral lights (i.e., all possible spectral power distributions) forms a generalized cone in the space of response triples. The cone’s intersection with the S + M + L = 1000 plane (tan) is the area bounded by the aqua curve.

14. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.13 The set of responses associated to monospectral lights of equal brightnesses. These form a curve in a plane of constant brightness. Three points, corresponding to percepts of “red,” “green,” and “blue,” are marked on the curve.

15. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.14 One color painted atop another. Light can be reflected from the top, from the bottom after passing through the top, or from the substrate on which the bottom is painted. Assuming some attenuation for each time the light passes through a paint layer, we get a model of the reflected light.

16. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.15 The squares labeled A and B have identical gray values, but we perceive them as very different shades of gray; indeed, we’re inclined to call one a “white square” and the other a “black square.” One may regard this as a failure of the visual system to “recognize the same color,” but it’s more appropriate to regard it as the success of the visual system in detecting color constancy in the presence of varying illumination: We perceive all the black squares to be black even though the actual gray values in the image vary substantially. (Courtesy of Edward H. Adelson.)

17. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.16 The color-matching functions, which indicate, for each wavelength, how much of a standard red, green, and blue light must be mixed to produce the same sensor responses as a monospectral light of wavelength λ. At least one mixing coefficient is negative for many monospectral lights, indicating the impossibility of making those colors as mixes of red, green, and blue.

18. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.17 The color-matching functions x¯, y¯, and z¯ for the 1931 CIE primaries.

19. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.18 The CIE chromaticity diagram. The boundary consists of chromaticities corresponding to monospectral lights of the given wavelengths, shown in nanometers. The dot in the center is a standard “white” light called “illuminant C.”

20. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.19 Colors on the chromaticity diagram. D and E are complementary.

21. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.20 Mixing of colors in the chromaticity diagram. Colors on the line IJ can be created by mixing the colors I and J; all colors in the triangle IJK can be created by mixing the colors I, J, and K.

22. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.21 Two metameric light spectra (top) are each multiplied (wavelength by wavelength) by the reflectance spectrum (middle). The resultant spectra are no longer metameric. (Next to the spectrum for each light are its corresponding RGB response values.)

23. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.22 Surrounding context can vary our perception of tones. (Figure concept from Poynton [Poyb].)

24. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.23 The color gamut for a typical display within the CIE XYZ color space. Note that white can be displayed very brightly, while red, green, and blue have much less intensity. Note, too, that many colors are not within the display gamut at all, particularly bright and dim ones.

25. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.24 The RGB cube. Grays lie along the main diagonal.

26. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.25 Converting from XYZ values to Y′C B C R values. XYZ is converted to RGB by multiplication by a matrix M 1 ; the RGB values are then nonlinearly encoded by a 0.45 power function; the resultant values are then transformed by another matrix, M 2, and shifted slightly, to form Y′, C B, and C R, where Y′ approximately represents intensity and the other two encode chrominance information. Finally, the resultant values are digitized by a step called the subsampling filter. Conversion to analog component video is similar, except that the subsampling filter is replaced by band-limiting.

27. From Computer Graphics, Third Edition, by John F. Hughes, Andries van Dam, Morgan McGuire, David F. Sklar, James D. Foley, Steven K. Feiner, and Kurt Akeley (ISBN-13: 978-0-321-39952-6). Copyright © 2014 by Pearson Education, Inc. All rights reserved. Figure 28.26 The simultaneous contrast effect. The two gray squares at the top appear to be different colors, but are in fact identical. The gray stripe on the bottom is a single color across its whole length.