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Browse Prior Art Database

Variable Threshold Control

IP.com Disclosure Number: IPCOM000095180D
Original Publication Date: 1965-Sep-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Kennedy, JJ: AUTHOR

Abstract

This is a variable threshold control which automatically sets the threshold of a video system in a character reader. Such occurs during a searching operation in accordance with the print contrast determined during the last preceding character recognition operation. The average amplitude of video signals occurring during the analyzing of a character is stored and used to modify a search threshold between characters. As the average video amplitude increases the searching threshold level is raised. As the average video amplitude decreases the level is lowered.

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Variable Threshold Control

This is a variable threshold control which automatically sets the threshold of a video system in a character reader. Such occurs during a searching operation in accordance with the print contrast determined during the last preceding character recognition operation. The average amplitude of video signals occurring during the analyzing of a character is stored and used to modify a search threshold between characters. As the average video amplitude increases the searching threshold level is raised. As the average video amplitude decreases the level is lowered.

Video signals are supplied to terminal VI and from here to a positive peak detector comprising transistor T1, capacitor C1, and resistor R1 for establishing a black level. Transistor T2, capacitor C2, and resistor R1 constitute a negative peak detector for establishing the current white level. The outputs from these are buffered by the emitter followers comprising T3 and R2, and T4 and R3 respectively. The signals are supplied from these to an operational amplifier A1 having associated with it four resistors R4A...R4D. These are connected and proportioned such that Al forms the sum equivalent to the current video amplitude, which is equal to the current black level minus the current white level.

This signal is supplied to storage capacitor C3 via resistor R5 only during the character following mode as determined by the closure of switch FSW. Thus, the voltage on C3 is proportional to...