EP0052187A2 Expired / Lapsed EP ⏱️ 0.0 years remaining

Optical density representing input signal thresholder

Assignee: International Business Machines Corp

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Filing: 1981-08-28

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Granted: —

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Expires: 2001-08-28

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Abstract

Abstract A scanner converts light reflected from a narrow band of a page bearing an image into a series of analog signals representing the optical density of elements of the image. The analog signals are input on a line (18) to a thresholder to determine whether to treat the element as black or white and to output a digital signal in accordance with the determination. The input signal is complemented (21) and added (22) to a first reference amount from a buffer (23). A non-linear bias derived from a table look-up ROM (24) is given to the difference which is then combined (25) with the first reference amount and produces an updated first reference amount in the buffer (23). This amount is complemented (32) and added to a second reference amount selected from a shift register (30). A non-linear bias derived from a table look-up ROM (34) is given to the difference which is combined with the selected second reference amount and produces an updated selected second reference amount in a buffer (36). This amount replaces the selected second reference amount in the shift register (30) and is applied to a comparator (40). The input signal is also applied to a multi-stage shift register (20) to introduce a delay and a non-linear bias is applied by a table look-up ROM (40) prior to its application to the comparator (40) whose output on line (42) is a digital signal representing black or white.

Inventors

👤 Robert Lory Melamud
👤 James Darwin Nihart
👤 James Merrill White

Bibliographic Details

Application Number —

Jurisdiction EP

Data Source google_patents

Last Synchronized 2026-11-02 16:22

CPC Classifications

H; H04; H04N; H04N1/00; H04N1/40; H04N1/403

Claims Analysis

Total Claims: 9

Claim 1

Independent Claim 200 words

1 A thresholder for input signals representing the optical density of elements of a two-dimensional density varying image, wherein transducer means (15) produces series of such input signals, each series corresponding to density variations along a first dimension (14) of the image, characterised by information storage means (23,30) for storing a first reference amount and a plurality of second reference amounts, first means (25) for combining an amount representing one of the input signals with the first reference amount in accordance with a function of the difference therebetween to produce an updated first reference amount and for operatively replacing in the storage means (23) the first reference amount with the updated first reference amount, second means (35) for combining the updated first reference amount with a selected one of the second reference amounts to produce an updated second reference amount as a function of the difference therebetween and for operatively replacing in the storage means (30) the selected one of the second reference amounts with the updated second reference amount, and comparison means (40) for producing a binary output as a function of the relative magnitude of one of the input signal representing amounts and an updated second reference amount.

Claim 2

Dependent Claim 200 words

Claim 3

Dependent Claim 59 words

2 A thresholder according to claim 1, wherein the information storage means includes means for storing a second reference amount corresponding to each elemental position along the first dimension of the image, and wherein the selected one of the second reference amounts is selected as a function of its adjacency to a second one of the input signal-representing amounts.

Claim 4

Dependent Claim 66 words

3 A thresholder according to claim 1 or 2, wherein the first combining means comprises means (22) for calculating the difference between the one input signal-representing amount and the first reference amount, table look-u p means (24) responsive to the difference for producing an update factor, and means (25) for combining the update factor with the first reference amount to produce the updated first reference amount.

Claim 5

Dependent Claim 24 words

4 A thresholder according to claim 3, wherein the table look-up means (24) has a calibration bias to be non-linearly responsive to the difference.

Claim 6

Dependent Claim 74 words

5 A thresholder according to any preceding claim, wherein the second combining means comprises means (33) for determining the difference between the updated first reference amount and the selected one of the second reference amounts, table look-up means (34) responsive to the last mentioned difference for producing an update factor and means (35) for combining the update factor with the selected one of the second reference amounts to produce the updated second reference amount.

Claim 7

Dependent Claim 24 words

6 A thresholder according to claim 5, wherein the table look-up means (34) has a calibration bias to be non-linearly responsive to the difference.

Claim 8

Dependent Claim 34 words

7 A thresholder according to any preceding claim, including delay means (20) for causing the second input signal-representing amount to be delayed in time with respect to the updated second reference amount computed thereform.

Claim 9

Dependent Claim 32 words

8 A thresholder according to any preceding claim, including calibration bias table look-up means (41) for applying a non-linear modification to the signal-representing amounts, prior to their application to the comparison means.

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