Browse Prior Art Database

Threshold Detector

IP.com Disclosure Number: IPCOM000053134D
Original Publication Date: 1981-Sep-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 92K

Publishing Venue

IBM

Related People

Schroeder, EN: AUTHOR

Abstract

In optical character recognition (OCR) systems, the document to be processed is exposed to incident light, and a scanner provides an electrical input signal proportional to the intensity of the reflected light provided by each scanned point on the document. A black or white (B/W) decision is then taken for each point by comparing the electrical signal value to a threshold reference value. Due to noise effects, the B/W decision needs rather complex detector systems to be reliable.

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Threshold Detector

In optical character recognition (OCR) systems, the document to be processed is exposed to incident light, and a scanner provides an electrical input signal proportional to the intensity of the reflected light provided by each scanned point on the document.

A black or white (B/W) decision is then taken for each point by comparing the electrical signal value to a threshold reference value.

Due to noise effects, the B/W decision needs rather complex detector systems to be reliable.

This is a sophisticated, reliable, programmable and low-cost digital threshold detector system, the basic operation of which is based on the following principles: 1. The system will track the signal and hold peak values as long as the variation between past and present signal values is below a given threshold. As soon as the signal variation reaches the threshold, then the system starts tracking the signal again. 2. The threshold values may be made different for different signal values.

As shown in Fig. 1, the video signal provided by the scanner is converted into digital form by a 4-bit analog-to-digital (A/D) converter. The converter output is then fed into the threshold detector system which is mainly comprised of two sections. Section A causes the "past" digital value to track the "current" value as long as the current value varies in the same direction by updating the contents of the register (REG). When the current value goes in the reverse direction, then the past value is retained unchanged in REG until the difference between "past" and...