Adjustable read level threshold for optical mark scanning

Details Adjustable read level threshold for optical mark scanning Adjustable read level threshold for optical mark scanning

1993-09-17

1995-05-30

Shepperd, John

Registers

Coded record sensors

Particular sensor structure

235456, 434358, G06K 710

Patent

active

054204070

ABSTRACT:
To determine a read level threshold for discriminating those response bubbles on a scannable answer sheet intended to be marked from those response bubbles not intended to be marked, an adjustable read level threshold is dynamically determined based on the read levels of a designated pool of response bubbles. In an optical scanner the darkness (read level) of each response mark entered for a particular question is determined to make a profile. From this profile showing the various read levels present for the response marks, the system determines read level "gaps," i.e., read levels in the profile for which there are no marks present, and adjusts the threshold for discriminating intended marks based on the read level(s) comprising the gaps.

REFERENCES:
patent: 4153895 (1979-05-01), Weisbrod et al.
patent: 4217487 (1980-08-01), Kjeer
patent: 4300123 (1981-11-01), McMillin et al.
patent: 5073700 (1991-12-01), D'Onofrio

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