L. A. Jones, "Photographic Reproduction of Tone," Journal of the Optical Society of America, May 1921

SCHEMATIC DIAGRAM OF THE CYCLE OF TONE REPRODUCTION

In Fig. 2 [right] is given a schematic diagram somewhat analogous in structure to the graphic diagram in Fig. 1, but expanded so as to include not only a statement of the nature of each phase of the problem but also the particular data necessary for the specification of each phase and the factors required for the transformation of the data relative to one phase into that relating to each of the contiguous phases.