CHARACTER RECOGNITION PHOTOSENSING APPARATUS HAVING A THRESHOLD COMPARATOR CIRCUIT

• US 3,599,151 A
• Filed: 12/29/1969
• Issued: 08/10/1971
• Est. Priority Date: 12/29/1969
• Status: Expired due to Term

• Current Assignee: Harr Jerome Danforth
• Original Assignee: Harr Jerome Danforth
• Inventors: HARR JEROME DANFORTH
• Application Number:
  US04/888,628
• Time in Patent Office: 589 Days
• US Class Current: 382/273
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/162 Quantising the image signal

Abstract

The recognition of human and machine readable characters of a family of type of which each character has one or more narrow line segments on a contrasting background and is enhanced by a positive and negative peaked level photosensing arrangement. The sensing apparatus comprises an optoelectronic circuitry for interpreting optomechanical gated scanning of short straight line segments in seriatim. It produces an electric representation in response to the presence and absence of a character line segment in the image. A photosensitive element is arranged to receive light from an area on a document. The highest and lowest light values are translated in a reference level clamping circuit followed by positive and negative peak storage circuits. A threshold comparator circuit is individually coupled to the positive and negative peak storage circuits for delivering potential levels of two values indicating marks or spaces (the absence of marks). Preferably, threshold adjusting circuitry is interposed between one of the peak storage circuits and the threshold comparator circuit. Dynamic adjusting thresholding circuitry is included. Analog control circuitry is coupled to the storage and thresholding circuitry for timing and controlling the overall system by timing pulses conventionally obtained.

Claims

1. Character recognition photosensing apparatus comprising a photosensitive element arranged to receive light from an area on a document to be scanned, a positive peak storage circuit having input terminals coupled to said photosensitive element and having output terminals, a negative peak storage circuit having input terminals coupled to said photosensitive element and having output terminals, a threshold comparator circuit having input terminals individually coupled to said positive and to said negative peak storage circuits and having output terminals at which appear potential levels of values indicating mark or space, threshold adjusting circuitry interposed between one of said peak storage circuits and said threshold comparator circuit, said threshold adjusting circuitry comprising a tapped potentiometer arrangement, a switch element for each tap on said potentiometer, and a detecting circuit coupled to said potentiometer arrangement and said switch elements for selecting the tap for the document being scanned.

2. Character recognition photosensing apparatus as defined in claim 1 and incorporating a counting circuit, and a gating circuit for each of said switch elements interposed between said detecting circuit and said switch elements.

3. Character recognition photosensing apparatus as defined in claim 1 and wherein said switch elements comprise field effect transistors.

4. Character recognition photosensing apparatus comprising a photosensitive element arranged to receive light from an area on a document to be scanned, a positive peak storage circuit having input terminals coupled to said photosensitive element and having output terminals, a negative peak storage circuit having input terminals coupled to said photosensitive element and having output terminals, a threshold comparator circuit having input terminals individually coupled to said positive and to said negative peak storage circuits and having output terminals at which appear potential levels of values indicating mark or space, threshold adjusting circuitry having input terminals connected to said positive and negative peak storage circuits and output terminals connected to said threshold comparator circuit, a differential amplifier circuit having one input terminal connected to said positive peak storage circuit, an output terminal connected to said threshold comparator circuit, and another input terminal, a differential voltage detector circuit having an input terminal coupled to the output terminal of said differential amplifying circuit and another input terminal connected to a point of potential intermediate to the output terminals of said peak storage circuits and having an output terminal, a voltage store, a potential charging source coupled to said voltage store and to said output terminal of said voltage detector circuit for storing a potential proportional to the contrast between the illumination levels on said mark and on the background of said document, and a variable impedance element connected to said voltage store and to the other input terminal of said differential amplifying circuit.

5. Character recognition photosensing apparatus as defined in claim 4 and wherein said voltage store is a capacitor, and said variable impedance element is a field effect transistor having a gate electrode connected to said capacitor and drain and source electrode connected in the input circuit of said differential amplifier.

6. Character recognition photosensing apparatus as defined in claim 4 and wherein said potential charging source is a constant current source.

7. Character recognition photosensing apparatus comprising a photosensitive element arranged to receive light from an area on a document to be scanned, a positive peak storage circuit having input terminals coupled to said photosensitive element and output terminals, a negative peak storage circuit having input terminals coupled to said photosensitive element and output terminals, a threshold comparator circuit having input terminals individually coupled to said positive and to said negative peak storage circuits and having output terminals at which appear potential levels of values indicating mark or space, at least one of said peak storage circuits comprising a differential amplifier having one input terminal connected for application of the electric wave for which the peak value is to be determined, another input terminal connected to an output terminal of said peak storage circuit for determining the difference between the input and the output voltage of said peak storage circuit and an output terminal, an emitter follower circuit having the output thereof connected to the output terminal of said peak storage circuit, a capacitor and a field effect transistor connected to maintain the output voltage proportional to that across the capacitor, and a transistor connected to the output terminal of said differential amplifier and to said capacitor for charging the latter to a value at which the output voltage of the peak storage circuit is equal to or greater than the input voltage.

8. Character recognition photosensing apparatus comprising a photosensitive element arranged to receive light from an area on a document to be scanned, a clamped circuit coupled to said photosensitive element and having output terminals at which appear potential levels of values referenced to reference black level, a positive peak storage circuit having input terminals coupled to said clamped level circuit output terminals and having output terminals, a negative peak storage circuit having input terminals coupled to said output terminals of said clamped level circuit and having output terminals, a threshold comparator circuit having input terminals individually coupled to said positive and to said negative peak storage circuits and having output terminals at which appear potential levels of values indicating mark or space, threshold adjusting circuitry having input terminals connected to said positive and negative peak storage circuits and output terminals connected to said threshold comparator circuit, a differential amplifier circuit having one input terminal connected to said positive peak storage circuit, an output terminal connected to said threshold comparator circuit, and another input terminal, a differential voltage detector circuit having an input terminal coupled to the output terminal of said differential amplifying circuit and another input terminal connected to a point of potential intermediate to the output terminals of said peak storage circuits and having an output terminal, a voltage store, a potential charging source coupled to said voltage store and to said output terminal of said voltage detector circuit for storing a potential proportional to the contrast between the illumination levels on said mark and on the background of said document, and a variable impedance element connected to said voltage store and to the other input terminal of said differential amplifying circuit, for varying the input impedance to said differential amplifier circuit.