Image by U. Richter, ca. 1925
Thomas Diedrich Robert Luther was born on January 2, 1868, in Moscow to German parents. His father Alexander was a lawyer. Among his direct ancestors was Hans Luther (1492–1558), a late cousin of the reformer Martin Luther. From 1885 to 1889, he studied chemistry at the University of Dorpat in Russia. Toward the end of 1889, he was named assistant to the chemist F. K. Beilstein at the University of St. Petersburg. A serious illness in 1891 forced him to recuperate during the next two years. In 1894, he resumed studying chemistry, this time at the University of Leipzig where he received his Ph.D. degree in 1895. His primary educator there was Wilhelm Ostwald (1853–1931). In 1896, Luther was named an assistant to Ostwald at the Physical Chemistry Institute of the University of Leipzig. In 1899, Luther submitted his habilitation thesis, titled “Equilibrium change between halogen compounds of silver and the free halogens caused by light,” and obtained lecturer status. In the same year, he published the monograph Chemical processes of photography, a record of six public lectures he gave on the subject. In these lectures, he demonstrated, among many other things, the chemical reaction kinetics in layers or volumes of substances, a subject that occupied him for the rest of his life. He also was the co-author of the second edition of Ostwald’s book on experimental methodology in physicochemical measurements in 1902. In the year 1900, he was named assistant director of the Ostwald Institute at the University of Leipzig. As colleagues, Ostwald and Luther were considerably different types. Ostwald did not like to have to lecture but published many papers and books. As a result, Luther was burdened with much of the lecturing activities at Ostwald’s institute. Despite important work in many fields, he rarely wrote articles. In 1904, Luther was named a regular professor of physical chemistry at the University of Leipzig. Ostwald, wanting to just manage the Institute, was found to be neglecting his lecturing duties and resigned from his position in 1906, retreating to his country estate in Grossbothen, where he launched into his color research. In the same year, Luther was named director of the newly formed photochemical department. In the fall-out of Ostwald’s departure, Luther found himself in a difficult position in Leipzig and in 1908 accepted an appointment at the Photographic Science Institute of the Technical University of Dresden, organized shortly before with the support of the local photographic industry (such as Zeiss). Luther remained there until his change to professor emeritus status in 1936, performing significant research in photographic and general physical chemistry and also concerning himself with the definition of color stimuli and color stimulus measurement. He was much admired by his students, among them Manfred Richter who later developed the DIN color order system. In 1909–1910, the well-known American photographer Imogen Cunningham (1883–1976) was a student of Luther, learning the technique of platinum prints. Luther remained in Dresden where he passed away on April 17, 1945, the last day of the Allied bombing runs on that city [1, 2].
54.1 Color and Spectrum
Luther’s interest in color phenomena was the natural outcome of his activities related to the chemistry of color photography. He clearly distinguished between what he considered to be an objective definition of color stimuli and perceptual color phenomena. Most of his seminal paper “Aus dem Gebiet der Farbreizmetrik” (on color stimulus metrics) [3] was ready for publication in 1923 under the title “color and spectrum,” as a contribution to a Festschrift for Ostwald in the Zeitschrift für angewandte Chemie (Journal of applied chemistry). However, the rabid inflation of the time prevented publication until 1927, as described in a footnote in the paper. His only other brief (2 pages) publication on the subject of color, from 1942, is concerned with practical application of the moment sum curve, developed in the 1927 paper.
- 1.
Colorimetry and optimal object color solid
The preliminary version of a trichromatic system of colorimetry had been worked on in Europe on basis of the visual sensitivity data, approximating cone responses, experimentally determined in Helmholtz’s laboratory by Arthur König in 1892. Luther used these data to develop a number of different systems of colorimetry based on different parameters. Using the König functions, he also developed secondary colorimetric functions in reasonable agreement with Hering’s four perceptually primary colors, yellow versus blue, and green versus red (purple), as shown in Fig. 54.1. Luther’s functions were supported some 30 years later by the experimentally determined unique hue functions of Hurvich and Jameson. The red–green function has two transition points, while the yellow–blue has one. Using these, he calculated the first optimal object color solids. The version based on the vertical axis representing lightness is shown in two views in Fig. 54.2. A version of the object color solid calculated in a tristimulus space was published in 1928 by the Russian researcher Nikolaus Nyberg. The general designation of such solids became known as Luther–Nyberg solid.
- 2.
Luther condition
In his paper, Luther also proposed what became known as the Luther condition: Spectral sensitivities of the color layers in color film or of color filters used in color photography should duplicate or closely match the color sensitivities of the human visual system.
- 3.
Sensitometry
Luther, together with his former student Emanuel Goldberg (1881–1970), with input from other researchers proposed a German standard for the determination of what became known as film speed, a definition of its sensitivity. It was published in 1934 as DIN4512. In 1998, it was replaced with the corresponding ISO standard.
Fig. 54.1Spectral functions calculated by Luther to represent a Hering-influenced colorimetric four-color system; on top the green–red, on bottom the blue–yellow function [3]
