34 Color Management in Practice Setting up the equipment and environment needed for color management has never been easier. Most promising is the release of the EIZO ColorEdge series of Adobe RGB-compatible LCD monitors, designed for superb color management. Ideally, monitors offering high-precision color reproduction allow users to match the colors displayed and printed. In fact, the creation of color reproduction standards, a major development in recent years, has benefited both the printing and advertising industries. Print workflows rely on color proofing; now, Japan Color, JMPA colors, and other standards can serve as guidelines in establishing workflows. JMPA colors in particular make it possible to replace conventional proofing with DDCP or to use inkjet printers instead of presses for proofing. No extra work; simply specify JMPA profiles before output. Those involved know what to expect right from the start, when the original ad has been completed on-screen. Comparing images on ColorEdge monitors to documents printed with JMPA profiles brings you closer to a perfect match between monitor and proof colors. This requires expert knowledge of software and hardware, and this book can shed some light on the subject. The first step is to try it and see. W.W. Abney. A TREATISE ON PHOTOGRAPHY, 1918 ©iStockphoto.com/wsfurlan © DWH Co., LTD. Color Management Basics 35 Color Management Color 02Basics ©iStockphoto.com/Hello Vector! ©iStockphoto.com/wsfurlan 36 Maxwell also established the visible to us. Newton’s original Light radiation, Wavelengths fundamental principle that light classifications of red, orange, yellow, reflection, absorption, travels in waves, and his research green, blue, indigo, and violet are too and color in light on electricity and magnetism led general for work in this context. and transmission to the development of the unified As for wavelengths we cannot Light can be described by its Combining red, green, and blue light to model of electromagnetism. Today, see (shorter than 380 nm or longer than 780 wavelength, which determines its produce white was a famous feat by James both phenomena are identified as nm), scientists knew that these waves color in the spectrum. Two factors Clerk Maxwell (1831–1879) in lectures at manifestations of electromagnetic existed even before Maxwell's time. affect the wavelength of light: King's College in London in 1861, where he force. Maxwell showed that light is Sir Frederick William Herschel radiation and absorption. demonstrated the world's first color photo. a form of energy we can describe as discovered infrared radiation, with Maxwell also explored how we perceive visible an electromagnetic wave and that wavelengths longer than 780 nm, in Radiation of light: light in the electromagnetic spectrum. wavelengths of visible light lie in the 1800. This was followed in 1801 by When another form of energy In the 20th century, as we began to range of 380–780 nm (with one million a discovery at the opposite end of the is converted to light energy, light understand how insects and many other nanometers in a millimeter). spectrum by Johann Wilhelm Ritter, radiates from the energy source. This creatures are physically equipped to perceive One consequence is that shorter who identified ultraviolet radiation radiation is generated by chemical phenomena, researchers in animal behavior wavelengths of light are refracted with wavelengths shorter than 380 nm. or physical processes, such as the found that various creatures perceive various more sharply. Research on the Maxwell correctly concluded that burning or heating or cooling of wavelengths of light. What we perceive as spectrum since Newton has made the electromagnetic waves exist at atoms or molecules. It is worth color, for example, is the specific range of it possible to assign values to these wavelengths, but that our eyes noting here that the definition of the spectrum that the particular RGB-sensing the spectral wavelengths that are simply cannot perceive them. “white” light varies. system of our eyes reveals to us. icEne edicin ision adar dcast ic Gene m rg M e V R oa in tr ra to y r g c t le o A r B E wavelength（1nm=10-4m） ultraviolet rays infrared rays human being butterfly deep-sea fish Each animal species perceives color differently. monkey Animals are equipped with what we may regard birds / fowl as unique optical instruments. The particular biological hardware of one species lets it perceive fish different wavelengths of light than another snake species. In each case, perception results from long-term evolutionary changes to promote 300 340 survival in various environments. ultraviolet rays infrared rays Color Management Basics 37 Light absorption and reflection: Spectral data and For objects that radiate light, For transmissive objects as well, Absorption is the opposite of spectral curves radiance can be measured and transmissivity can be measured and radiation, occurring when light charted. Radiance is the relative charted. Transmissivity is the ratio energy is converted into another Objects can be broadly classified intensity of light energy radiated at of incident light to transmitted light form of energy, when the atoms or into three categories based on how various wavelengths, based on the at each wavelength. In the chart, green molecules of an object or medium they interact with light. In each case, total amount of light energy. In the indicates the transmissivity of cyan ink. struck by light absorb the light. spectral curves show how objects chart, yellow indicates the spectral A colorimeter can be used to How much light of the various affect light of various wavelengths. curve for daylight, with the diagonal measure the spectral data of any wavelengths is absorbed depends on The following chart shows examples line indicating values for an ordinary object and derive spectral curves. the chemical structure of the object of several spectral curves. incandescent (tungsten) bulb. Thus, spectral data provides a or medium. Interactions between Similarly, reflectivity can be detailed record of the amount of wavelengths and the structure of ① Radiant objects (such as daylight measured and charted for objects light reflected at each wavelength, the object cause light to be reflected or monitors) that reflect light. Reflectivity is the something that cannot be confirmed from or absorbed into the surface. ② Reflective objects or objects that ratio of incident light to reflected by sight alone. Measurements of this Thus, reflections can also be viewed absorb light light at each wavelength. In the chart, kind require an instrument called a as radiation occurring after light is ③ Transmissive objects magenta indicates the reflectivity of spectrophotometer. partly absorbed. red objects. Transmission of light: 100 Ancient scholars puzzled over Daylight spectra the nature of clear materials and the （%） light passing through such materials. Reflectivity of a red object Their confusion arose from a 80 misunderstanding—that color was Transmissivity of cyan ink inherent in the surface of things. ower ① Radiant objects Light passing through clear or al P Incandescent (tungsten) bulb semitransparent substances such as 60 water, air, film, or ink is transmitted through the substance. This occurs ② Reflective objects/ light-absorbing objects when more of some wavelengths Relative Spectr 40 of light are absorbed than others as they strike molecules and particles in a substance. The thickness of a particular object determines the 20 Monitor (red phosphor) extent to which various wavelengths are absorbed or passed. Only a vacuum fully transmits light of all ③ Transmissive objects 0 wavelengths. 400 500 600 700 wavelengths（nm） 38 Color rendering defined The suitcoat and pants that appeared The following figure shows Metamerism to match at the store somehow clash colors affected by metamerism and Publications that discuss at a party. Or the bouquet of flowers colors that maintain a consistent and color rendering color often address favorable that looked beautiful at the florist appearance. These three products or unfavorable color rendering looks dull and lifeless under your appear identical under natural properties, but the underlying lighting at home. There are countless sunlight, but incandescent lighting concept of color rendering is rarely examples. brings out a reddish tinge in two defined. It is worthy of initial We can reverse the underlying of them. Of course, we can also consideration, since this is a key issue principle applying in all these cases imagine the opposite effect. in the context of metamerism. to create color with a consistent As for ensuring consistent Color rendering is the effect of appearance by combining multiple colors through the data used in the color of the light source on the color components. For example, photographic prints or printing, appearance of color in objects. This instead of creating gray from newer inkjet printers can reduce the characteristic is known as the light black and white as usual, we can effects of metamerism, but a D50 or source’s color rendering property. create the same color by mixing D65 light source is recommended The color rendering index is one way complementary hues such as red and for post-printing proofing. Use the to compare relative performance in blue-green, yellow and bluish purple, isochromatic samples at the end of this regard. or blue and orange. this book. Metamerism Three requirements are essential in perceiving color: light, objects, and our eyes. Metamerism occurs when these elements are out of sync from their normal relationship. The phenomenon can make two colors that appeared identical under one With metamerism light source look different under another. Our eyes are susceptible to metamerism, but in fact, the phenomenon also affects other instruments that operate on principles of RGB light mixing, such as scanners and digital cameras. Realistic examples are often cited in explanations of metamerism. Buy fresh fish that looks delicious at the deli, and you may lose your appetite when you see the colors With metamerism Without metamerism under fluorescent lighting at home.