Color

An Introduction to Practice and Principles

Rolf G. Kuehni

• Publisher: Wiley
• Year: 2015
• ISBN:
  9781118533550
• Edition: 3
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie civile

The one-stop reference to the essentials of color science and technology—now fully updated and revised

The fully updated Third Edition of Color: An Introduction to Practice and Principles continues to provide a truly comprehensive, non-mathematical introduction to color science, complete with historical, philosophical, and art-related topics.

Geared to non-specialists and experts alike, Color clearly explains key technical concepts concerning light, human vision, and color perception phenomena. It covers color order systems in depth, examines color reproduction technologies, and reviews the history of color science as well as its relationship to art and color harmony. Revised throughout to reflect the latest developments in the field, the Third Edition:

• Features many new color illustrations, now fully incorporated into the text
• Offers new perspectives on what color is all about, diverging from conventional thinking
• Includes new information on perception phenomena, color order, and technological advances
• Updates material on such topics as the CIE colorimetric system and optimal object colors
• Extends coverage of color reproduction to display systems, photography, and color management
• Contains a unique timetable of color in science and art, plus a glossary of important terms

Praise for the previous editions:

"A nice bridge to areas usually not covered in academic visual science programs... outstanding."
—Joel Pokorny, visual scientist at The University of Chicago

"A good addition to any library, this should be useful for the color interests of artists, designers, craftsmen, philosophers, psychologists, color technologies, and students in related fields."
—CHOICE

1
Sources of Color

For the normally sighted person, color is everywhere. In the interior of a dwelling are natural and stained woods, wallpapers, upholstery fabrics, pottery, paintings, plants and flowers, a color television set, and many more things seen as colored. Outdoors, and depending on the time of the year, there is a riot of colors such as those on an alpine summer meadow, or they are spare in a desert, with olives, browns, garnets, and grays. Colors can be pleasantly subdued, enhancing relaxation, or loud and calling to us from advertising billboards or magazines. Color entices us to eat, consume, or at least to buy.

Color likely has helped us to survive as a species. Our (known) contacts with the world and the universe are by way of our five senses. Persons with a normally functioning visual system obtain what is probably the largest amount of information about the world surrounding them from vision, and color experiences are an important outcome of this flow of information. In the past several thousand years, color has blossomed into much more than just a survival and communications tool. We have learned to derive aesthetic pleasure from it by way of crafts, design, and art.

The question of the nature of color experiences has puzzled humans since antiquity and has resulted in many and varied answers. The number of different color phenomena in the natural world, from colored sunsets and rainbows and the color of a rose to those of an opal and the glow of phosphors, has made understanding the phenomenon of color rather difficult. The popular view is shaped strongly by our everyday experiences. Bananas are yellow, a ruby-throated hummingbird has a dazzling red patch below his beak, clear water and the sky are blue, and so on. A fabric is dyed with red dye; when painting, we use variously colored pigments or draw with variously colored crayons or ink pens. The rainbow has four colors, or is it six or seven? In a mirror, we see colors of objects appearing slightly duller and deeper than in the original. On a winter day toward evening, shadows look deeply blue. We are told that color illustrations in an art book are printed just with four pigments and that all colors on a display screen are “made” from red, blue, and green light-emitting phosphor compounds.

To cope with these confusingly varied sources of color, we just disregard them in our everyday languages. An apple is red, the traffic light is red, the rose as seen reflected in a mirror is red, the bar in the bar graph on a tablet display is red, and paint on the brush is red. All of these varied experiences have something in common: redness. We simply attach the perceived phenomenon to the object without bothering about the source or much thinking about the nature of color.

We normally experience color as a result of the interaction between light, materials, and our visual apparatus, eye and brain. However, there are also means of having color experiences in the dark, with eyes closed:

• Under the influence of migraine headaches
• Under the influence of certain drugs
• By direct electrical stimulation of certain cells in the brain
• By pressing against the eyeballs or hitting the temples moderately hard
• By dreaming

In some manner, these situations or actions trigger responses in our visual system that have the same result as conventional color stimuli. Such phenomena are not unlike an electronic burglar alarm somehow triggered by an overflying aircraft rather than by a burglar.

There are two sets of facts that complicate understanding of the phenomenon of color: (1) many different stimuli can result in an essentially identical color experience and (2) a particular stimulus can result in many different color experiences, usually as the result of changes in illumination and/or surrounding stimuli. The same situation applies to vision in general. These facts can be seen as indicating that colors are subjective phenomena rather than components of objects. On the other hand, the facts that blood is red, that bananas when ripe are yellow, and that we can make some object look blue by painting it with blue pigments, and countless other results of observation, have produced the common point of view that colors are located in objects. In support of the former position, Newton already said with respect to color perceived in light: “For the rays, to speak properly, are not coloured. In them there is nothing else than a certain power and disposition to stir up a sensation of this or that Colour” (Newton 1704). The “objective” position is represented by a comment in a recent book: “The pessimistic notion that colors are ‘mere mental paint’ and have no relation to the physical and chemical constitution of things at all is popular in science and (especially) in philosophy, but it has no basis in fact” (Koenderink 2010). This matter is a subject of argumentation ranging back to the early Greek philosophers and has as yet not found a factually supported convincing answer, as will be discussed in slightly more detail in Chapter 2.

Color is the result of the activity of one of our five senses, vision. So far, we have not succeeded in defining the essence of the results of sensory activities, emotions, or feelings: what is sweet, what is happy, or blue? Dictionary definitions of color are, therefore, of necessity vague:

a: a phenomenon of light (as red, brown, pink, or gray) [?] or visual perception that enables one to differentiate otherwise identical objects; b (1): the aspect of the appearance of objects and light sources that may be described in terms of hue, lightness, and saturation for objects and hue, brightness, and saturation for light sources <the changing color of the sky>; also: a specific combination of hue, saturation, and lightness or brightness <comes in six colors>; (2): a color other than and as contrasted with black, white, or gray. (Merriam-Webster 2011)

Scientists have not been able to do better and have resorted to a circular definition: “Color: Attribute of visual perception consisting of any combination of chromatic and achromatic content. This attribute can be described by chromatic color names such as yellow or brown, red, pink, green, blue, purple, etc., or by achromatic color names such as white, gray, black, etc., and qualified by bright, dim, light, dark, etc., or by combinations of such names.” (CIE 1987). Before considering the difficult subject of the nature of color further, it is useful to gain a fuller understanding of the causes of color.

One of the most impressive displays of color occurs when, in an otherwise dark room, a narrow beam of sunlight passes through a glass prism, as described by Newton (Fig. 1.1). What leaves the prism is the same light entering it. But on leaving the prism, the beam has been transformed into a band of light that, when viewed as reflected from a white surface, produces in the observer’s vision system a multitude of color experiences: the colors known as those of the spectrum. A less elaborate method for viewing these colors is by looking at a compact disk at different angles in daylight or the light of a lamp.

A considerable number of processes and materials can result in color experiences. Many have been discovered by artisans and craftsmen over the course of millennia, but until recently, the underlying causes remained mostly hidden. Colored materials (many used as colorants) are commonly thought to interact in similar ways with light, but their apparent color is in fact caused by a variety of specific physical phenomena. Nassau has identified and described a total of 15 causes of color, with four dealing with geometrical and physical optics, and those remaining dealing with various effects involving electrons in atoms or molecules of materials and causing absorption or emission of light at selected wavebands (Nassau 2003). With the exceptions listed earlier, color phenomena have one common factor: light. Aristotle wrote that the potential of color in materials is activated by light. German poet and natural scientist Goethe called colors “the actions and sufferings of light.” The most common source of light is the process of incandescence. Our first step is to gain understanding of the nature of light and incandescence.

FIGURE 1.1 Schematic representation of a narrow beam of daylight light passing through a prism and being separated according to wavelength by refraction. The individual wavelength rays do not appear colored unless directly viewed front-on or after reflection from a white surface.

LIGHT

Light consists of a certain range of electromagnetic radiation, which is a convenient name for the as yet not fully explained phenomenon of energy transport through space. Electromagnetic radiation, depending on its energy content, has different names: X-rays capable of passing through our bodies and, on prolonged exposure, causing serious harm, ultraviolet (UV) radiation that can tan or burn our skin, light that we employ to gain visual information about the world around us, infrared radiation that we experience on our skin as warmth or heat, information transmission waves for radio and television, or electricity transmitted and used as a convenient source of energy (Fig. 1.2). Electromagnetic radiation travels at high speed (the speed of light, about 300,000 km/s). T...