Defect identification with normalizing of gain function in optical-electrical inspection

Apparatus for defect identification with normalizing of the optical-electrical inspection system gain function of scans across a full width of a running product web comprising, in electrical circuit in the sequence recited, a source of electrical scan signals A, a memory storing a sufficient accumulation of a number of said signals A to permit the resolution of an acceptable average reference signal R, means computing said average signal R as the quotient of said accumulation of said number of said signals A divided by said number of said signals A accumulated, means computing the difference signal A-R for succeeding scan signals A, thereby effectively equalizing each successive scan signal A while preserving defect-related signals, and means identifying said defect-related signals by amplitude discrimination of said difference signal A-R.

The method of defect identification with normalizing of the optical-electrical system gain function of scans across a full width of a running product web comprising:

• (1) storing an accumulation of logarithmically processed characteristic individual electrical recurring scan signals A from said system and dividing by the number of said recurring scan signals A accumulated to obtain a reference signal R and (2) differencing each succeeding logarithmically processed scan signal A with said stored reference signal R to obtain the logarithmic ratio signal A/R, thereby equalizing each successive scan signal A while preserving defect-related signals in true perspective to the non-defect containing portions of said signal A/R, and then identifying said defect-related signals by amplitude discrimination of said logarithmic ratio signal A/R.

Apparatus for defect identification with normalizing of the optical-electrical inspection system gain function of scans across a full width of a running product web comprising, in electrical circuit in the sequence recited, an Analog/Digital converter to which logarithmically processed electrical scan signals A are input, a memory storing a sufficient accumulation of a number of said scan signals A to permit the resolution of an acceptable average reference signal R, means computing said average signal R as the quotient of said accumulation of said number of said scan signals A divided by said number of said scan signals A accumulated, means computing the logarithmic ratio signal A/R for each successive scan signal A, by subtraction of the logarithms of signals A and R, thereby effectively equalizing each successive scan signal A while preserving defect-related signals in true perspective to the non-defect containing portions of said signal A/R, and means identifying said defect-related signals by amplitude discrimination of said logarithmic ratio signal A/R.