The screening technology was still under development by Creo Inc. at the time, and was being beta tested by Hemlock. It would eventually be launched as Staccato. In fact, the Keough's title would be the first art book in the world printed using Creo's breakthrough 10-micron stochastic process.
That's roughly equivalent to a 600 line screen, and three times greater resolution than high-end lithography commonly used for fine art books. To the naked eye, and under close inspection, there are virtually no visible dots making up the photographs.