OCR Page reader

• US 4,453,268 A
• Filed: 03/18/1981
• Issued: 06/05/1984
• Est. Priority Date: 03/18/1981
• Status: Expired due to Fees

• Current Assignee: Lundy Electronics & Systems Incorporated
• Original Assignee: Lundy Electronics & Systems Incorporated
• Inventors: Britt, Ronald H.
• Primary Examiner(s): Boudreau, Leo H.
• Application Number:
  US06/245,093
• Time in Patent Office: 1,175 Days
• Field of Search: 340/146.3 F, 340/146.3 B, 340/146.3 SY, 340/146.3 AG, 340/146.3 AC, 340/146.3 AQ, 340/146.3 J, 340/146.3 WD, 250/234, 250/235, 250/567, 250/568, 250/578, 350/6.2, 350/6.3, 358/285, 358/293, 358/282, 358/205, 358/206, 358/212, 358/213, 358/225, 235/436, 235/454, 235/470, 235/491, 382/37, 382/50, 382/51, 382/53, 382/65, 382/67
• US Class Current: 382/273
• CPC Class Codes: G06V 30/10 Character recognition
• CPC Class Codes: G06V 30/162 Quantising the image signal
• CPC Class Codes: G06V 30/196 using sequential comparisons of the image signals with a plurality of references

Abstract

An optical character recognition page reader includes a stationary paper guide for positioning documents illuminated by a stationary light source. An image of the documents is focused onto a stationary photosensitive device, e.g. a line of photodiodes, by a movable lens. Signals from the photodiodes are serially fed to a bit comparator which compares the amplitude of these signals to a threshold level that varies in accordance with a fraction of the previous maximum white level signal for each such photodiode, and produces digital bit outputs in response thereto. The digital bit outputs of the comparator for each horizontal scan of the document, i.e. each readout of the photodiode array, are stored for successive positions of the lens during its vertical scan of the document. The stored digital bits from a number of previous lens scan positions for a particular photodiode of the array are then used in a state machine to determine its next state. Bits from succeeding particular photodiodes are successively applied to that state machine to affect its state. The operation of the state machine is so conditioned that if it reaches its final state, it has uniquely identified a particular character from the stored bits.

Claims

1. An optical character recognition page reader for reading documents containing characters and for producing an output identifying the characters read, comprising:

means for receiving and illuminating at least one document to be read;

an array of light-sensitive elements for converting variations in light patterns on the document due to the characters into variations in an electrical output signal;

a lens positioned between the document and the array for focusing an image of a portion of a document onto the array;

lens moving means for moving the lens so that all portions of the document are sequentially focused on the array; and

an electronic control circuit for recognizing the variations in the outputs of the light sensitive elements as the characters being read on the document and for producing digital outputs in response thereto, said control circuit comprising;

means for transferring the present outputs of elements in parallel to a shift register;

means for storing previous maximum white reference signals for each element of the array;

reference comparator means for comparing the present output of each element of the array delivered in series from the shift register to the pertaining previously stored maximum white reference signal delivered in series from the means for storing, said comparator means producing an output whenever the present output of the element is larger than the pertaining previously stored maximum white reference signal; and

means for incrementally increasing the value of the previously stored maximum white reference signal whenever the reference comparator means has an output.

2. A reader as claimed in claim 1 further including a character bit comparator means for comparing the present output of each element of the array delivered from the shift register to a threshold level equivalent to a fraction of the pertaining previously stored maximum white reference signal, said character bit comparator producing an output indicative of a black character bit whenever the present output of the element is smaller than the threshold, the output of the character bit comparator inhibiting the output of the reference comparator, whereby the white reference signal is not incremented when a black character bit is detected.

3. A reader as claimed in claim 2, wherein the values of the stored maximum white reference signals are incrementally decreased on a periodic basis.

4. In an optical character recognition system in which portions of characters on a document are imaged onto a photodiode array, each photodiode of the array generating an electrical output related to the portion of the image it receives, the outputs of the photodiodes being serially presented to one input of a character bit comparator for determining whether the outputs represent black character bits or white background bits, the other input of the character bit comparator receiving a reference threshold signal such that the bit comparator generates a black character bit signal whenever the photodiode signal is less than the threshold, the improvement comprising means for generating the reference threshold signal as a plurality of individual levels, wherein one such level is provided for each photodiode of the array and wherein the value of said level is a fraction of the previous maximum signal representing background white generated by that particular photodiode, said means for generating the reference threshold signal comprising:

a white reference comparator receiving in series the present outputs of the photodiodes of the array on a first input;

a white reference storage means for storing a value related to the previous maximum white level signal produced by each particular photodiode;

means for sequentially applying the previous maximum white level signal for each particular photodiode to a second input of said reference comparator simultaneously with the presentation of the photodiode'"'"'s present output to the first input, said reference comparator producing an output whenever the present output is greater than the pertaining previously stored signal; and

adder means for adding one unit to the pertaining previously stored signal whenever the comparator has an output.

5. A system as claimed in claim 4 further including means for inhibiting the output of the reference comparator whenever the character bit comparator has an output.