Michael Mark Woolfson, a professor emeritus at the University of York in the UK, has had a long and distinguished career researching x-ray crystallography, the formation of stars and planets, and biophysics. He has also written more than 20 books on topics ranging from imaging to probability and statistics—an ambitious scope.
Woolfson clearly intends his latest book, Colour: How We See It and How We Use It, as a popularization. He hopes to cover his topic, he writes, in “a general broad-brush way without getting involved in the fine details that would only be of interest to professional engineers and scientists.” Although that is a worthy goal, the book contains serious factual errors. Furthermore, the wide-ranging material is disorganized and the topics seem haphazardly chosen, which leaves me wondering why some phenomena were included while others were left out.
Here are a few of the factual errors. In figure 4.1, Woolfson draws an International Commission on Illumination xy chromaticity diagram that includes a line from white (W) to 520-nm green (A). He then says, “The point M, midway between A and W, would roughly correspond to a mixture of spectral green and white with the same intensity.” In fact, a chromaticity diagram is a central projection from a three-dimensional color space, called tristimulus space, that is related to the sensitivity of the eye’s three types of cone cells. There is no physical significance to the distance ratio AM/AW.
In chapter 6, Woolfson discusses retinal photopigment bleaching, the process by which retinal pigment absorbs a photon and is rendered temporarily unable to absorb another one. In the discussion, he makes an incorrect connection between bleaching and the visual process. He appears to equate the eye’s visual response to the “proportion of active pigment”—that is, the remaining fraction of unbleached pigment. In fact, small light-induced fluctuations of intermediate and bleached photopigment are what initiate an electrical response in the eye. The unbleached pigment is like the charge in a battery—available for light stimulation but not itself part of the response.
The core of Woolfson’s error is in figure 6.10, which shows “curves of rhodopsin decay” after a light is turned on. Here, decay is the same as bleaching. However, if active photopigment decayed as quickly as Woolfson indicates, we would essentially be blind after less than a second in daylight. In reality, the photopigment in a normal eye is almost never appreciably bleached when exposed to common illumination. A secondary error in figure 6.10 is that, contrary to its caption, not all visual receptors have rhodopsin as a photopigment. Only the rods, responsible for vision at low light levels, use rhodopsin.
Other errors are simply matters of terminology. For example, Woolfson recounts the classic demonstration that a white object in a scene looks green through a small green filter, but it looks white if the filter is brought close enough to the eye to cover the whole scene. Then he says, “The light entering the eye in both cases has the same chromatic content.” He should have said “spectral content” because the chromatic (perceived color) content is not the same.
I was surprised that in a book on color, no mention is made of metamerism, a phenomenon in which two light spectra viewed under the same conditions can be perceived to have the same color. In particular, the trichromacy of vision implies that only three primary colors are required to make a match. For that reason, metamerism underlies color-reproduction systems from television to printed photographs, a fact that seems important to a popularization about color.
The style is also disappointing. Woolfson offers no overriding motif or question to launch his book and engage the reader. Color perception occupies several chapters, including chapters 6 and 10, but it is curiously absent from chapters 7–9, which present historical sketches of artistic uses of pigments, dyes, and pottery. At times, ideas jump around from sentence to sentence; for example, a discussion of nonvisual structures in the eye is interrupted by the out-of-context sentence, “The eye operates best at moderate light levels.” There are no references or photo credits to lead a reader to further information. That said, the author provides a good index and includes with each noted innovator that person’s dates of birth and death, nationality, and profession.
One high point in the book is figure 1.10. There, and in its associated discussion, Woolfson presents a retinal-processing model that captures three important visual effects. First, the light-gathering area for a retinal cell increases at low light intensities, which averages out noise. Second, the area decreases at high light intensities, thus increasing spatial resolution. Third, the contrast in neighboring bands of gray appears to be enhanced when the bands are touching, a phenomenon called the Mach band effect. I have seen such a model in technical papers but never in a popularization.
Although I don’t view the book as successful, I respect the author’s courage in writing about fields—from evolutionary teleology to cinematography—that are far from where he began.
Michael H. Brill is the director of research at Datacolor in Lawrenceville, New Jersey, and the corecipient of a Technology and Engineering Emmy Award for a vision model used in the telecommunications industry. He has written extensively about many aspects of color science and technology.
