Digital Color
The computer monitor displays color using varying levels of RGB. (Generally 0-255 of each, but depending on the video card and monitor.)
This corresponds to 256 = 28 levels per color (8 bits) and 16,777,216 = 224 (24 bits) total number of colors.
Thus 24 bit color has become the standard for true color reproduction and storage.
Although 24 bits is standard, it doesnt mean that the human eye perceives 24 bit color.
The human responses to different parts of the color gamut are not uniform. We have greater sensitivity to neutral colors than to saturated colors, lighter than to darker and to certain hues over others.
The adaptive nature of perception makes us respond to relative differences in color rather than absolute ones.
To replicate the full range of intensities we would need millions of gray levels.
However it has been found that the number of discernible hues is about 200 and the number of gray levels is between 60 and 150, depending of level of background illumina
Thus, 24-bit color provides a sufficient number of colors but, because the perception is nonlinear, there is often too much or too little information.
Color Constancy - Human vision can recognize objects under enormous variations in lighting conditions.
Daylight varies from 1 lux (lumens/s) to over 100,000 in bright sunshine and in color from pink at dawn to orange at sunset, through the yellow of direct sunshine to the bluer light of the sky.
Indoors, artificial lighting is normally lacking in blue wavelengths, making objects appear more yellow.
Yet an object is always recognizable, we perceive the same flower indoors as outdoors. A rose is a rose is a rose.
Equally we recognize brightness under widely different levels of illumination.
Color Temperature - The exact color of white light is important, since if it tends towards one part of the spectrum, anything viewed in that light will have a color cast. The whiteness of a color is characterized in terms of its color temperature.
The color temperature is defined in terms of the corresponding black body radiation intensity versus wavelength plot (see figures below).
The color temperature of unfiltered sunlight is approximately 5900 oK. (see Fig 2-12 for other temperatures)
Standard color temperatures between 5000 oK and 7000 oK are used in the graphic arts. Your book mentions 5000 oK to define white light. 6500 oK is the default for Photoshop and is used in Europe.
Other concepts mentioned in your book are color rendering index and spectral power distribution. The color rendering index is a measure of how well a light source conforms to natural daylight on a scale from 0 to 100. The spectral power curve is a plot of light intensity versus wavelength.
A light source with a color temperature of 5000 oK and a spectral distribution similar to natural daylight is called a D50 illuminant. This combines color temperature and color rendering index.
Viewing conditions - The eye adapts to the ambient light source and sees it a neutral white. If the spectral power distribution of the source is uneven and weak in some wavelengths, it is impossible to judge colors accurately. Thus, it is important to standardize viewing conditions.
Standards defined by the American National Standards Institute (ANSI PH2.30-1989), BS 950 and ISO 3664 are in use and are functionally identical to one another. (See Table 2-1)
Standard D50 viewing stations are setup in the press room, the prepress room and the pilot plant.
Guidelines for setting up standard viewing stations are listed in the book.
Standard viewing conditions should always be used for comparisons between originals, proofs and prints.