the same pile after making a few changes
Fig. 3. — Superposition of negative of Fig. 2 and positive of Fig. 1. The marked variations in shade indicate the changes.
(cropped from border and page)
ex M. H. Stillman. “Photographic Methods of Detecting Changes in a Complicated Group of Objects.”
Scientific Papers of the Bureau of Standards 16 (1921) : 437-448
University of Chicago copy, digitized May 24, 2012
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“When the photographs are properly made, those parts of the combination which correspond to the unchanged portion of the group of objects will appear as a field of practically uniform density, while a change in the group will be revealed by a considerable departure from this uniform density... Fig. 1 shows a pile of rocks before the change. Fig. 2 shows the same pile after making a few changes... Fig. 3 shows the appearance when the second negative is superposed upon the positive of the first.” p 438
tags:
change; pile of rocks
M. H. Stillman, “Photographic Methods of Detecting Changes in a Complicated Group of Objects” (1921)