1. Gilman, P. B., Jr., International Congress of Photographic Science, Cambridge, England, 1982, Paper 3.3.
2. Weiss, G. and Helling, J., U.S. Patent 3,826,654 (1974).
3. Muenter, A. A., International Congress of Photographic Science, Cambridge, England, 1982, Paper 3.49 and references cited therein.