Importance

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Abstract

A light source produces a light beam which is projected through a pattern to form a light beam incident on a surface of a continuous member. The pattern defines two transparent and opaque surfaces delimited by an angle. An opto-electronic device converts luminosity levels of elementary areas of a resultant image produced by the continuous member in a response to the incident light beam into respective electrical signal levels. A calculator calculates a bidimensional partial derivative for the electrical signal level corresponding to each elementary area of the resultant image as a function of the electrical signal levels produced by the opto-electronic device in response to respective luminosity levels of elementary areas contiguous to said each elementary area in order to produce the characteristic function. The optical member can be an optical instrument, a photographic film, a photoconductor or photoreceiver drum or, more generally, any optical image conversion device.

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First Claim