Patent EP0118905A2 successfully refreshed from Google Patents.
EP0118905A2
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Adaptive threshold circuit for image processing
Assignee: Wang Laboratories Inc
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Filing: 1984-03-09
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Granted: —
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Expires: 2004-03-09
Abstract
Abstract An adaptive threshold circuit is disclosed wherein reflectance values are measured in each of a number of scan lines on a document on which an image is scanned, digitized at a multiplicity of points and processed to create a processed digitized image signal that is stored or transmitted and then used to recreate the document accurately without objectional light and dark variations over the recreated documents and without being affected by the background color of the original document, variations in illuminating and the black/white makeup of the image. The unprocessed digitized data is first used to calculate a mean value of the digitized reflectance values for each of a number of columns on the document. The same data is then used to calculate a mean-above-mean value for the same columns. Each digitized reflectance value is compared to the mean value and only when it exceeds the mean value is the mean-above- - mean value updated. A threshold value is then calculated for each column using the updated mean-above-mean values for a particular column and for the two contiguous columns. At the same time the most recent threshold value for each column is compared to each unprocessed digitized reflectance value taken in the associated column and values above the threshold value are assigned a first binary value indicating the sample is white and values equal to or below are assigned the opposite binary value indicating the sample is black.
Inventors
- 👤 Alan Lee Moyer
- 👤 Vincent Joseph Messina
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 20:31
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/40; H04N1/403; G; G06; G06T; G06T5/00; G06T5/20; G06T7/00; G06T7/10; G06T7/12; G06T2207/00; G06T2207/10; G06T2207/10004; G06T2207/10008; G06T2207/20; G06T2207/20004; G06T2207/20012; G06T2207/30; G06T2207/30176
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
197 words
.l. A method for processing a digital signal representing indicia on a document to better represent said indicia for reproduction thereof, wherein the digital signal is derived by scanning the document to create an analog. signal which is then converted to a ditigal signal consisting of a string of binary numbers with each binary number representing a point on said document, characterized by: deriving a mean peak value for each group of said numbers using the binary numbers in the associated group, and each group of binary numbers represents an area on said document, deriving a threshold value for each portion of said document using the mean peak value for the associated portion of said document and using the mean peak value for other portions of said document contiguous to said associated portion, and comparing each of the binary numbers in each group of binary numbers with the threshold value for the corresponding group and assigning one binary number value when the threshold value exceeds the value of ones of the binary numbers, and assigning another binary number value when the threshold value is less than or equal to the value of ones of the binary numbers.
Claim 2
Dependent Claim
92 words
The method in accordance with claim 1 further characterized by: deriving a mean value for each group of said binary numbers using the binary numbers in each group and updating said mean values each time the associated portions of said document are scanned, comparing each of the binary numbers in each group of binary numbers with the mean value for the corresponding group, and updating said mean peak values by repeating the mean value deriving steps only when ones of said binary numbers has a value greater than the corresponding mean value.
Claim 3
Dependent Claim
97 words
3 . The method in accordance with claim 2 wherein said step of deriving said mean peak values characterized by: determining a present mean peak value for each portion of said document, updating said present mean peak values by algebraically adding a first percentage of the difference between each of said present mean peak values and the next one of said binary numbers representing a point in each of said last mentioned document portions to each of said present mean peak values, and changing said first percentage to a second percentage for predetermined parts of said document.
Claim 4
Dependent Claim
92 words
The method in accordance with claim 3 wherein said step of deriving said series of mean values characterized by: determining a present mean value for each portion of said document, updating said present mean values by algebraically adding a first percentage of the difference between each of said present mean values and the -next one of said binary numbers representing a point in each of said last mentioned document portions to each of said present mean values, and changing said first percentage to a second percentage for predetermined parts of said document.
Claim 5
Dependent Claim
65 words
The method in accordance with claim 4 wherein said step of deriving a threshold value for each portion of said document comprises the step of summing a first percentage of the present mean peak value for the portion of said document in which the most recent binary number represents a point with.a percentage of the present mean peak values for adjacent portions of said document.
Claim 6
Independent Claim
197 words
A method for processing a digital signal representing indicia on a document to more accurately represent said indicia for reproduction thereof, wherein the digital signal is derived by scanning the document to create an analog signal which is then converted to a ditigal signal consisting of a string of binary numbers with each binary number representing a point on said document, said method comprising the steps of: filtering said string of binary numbers with a one pole digital filter having unity gain and a given bandwidth to derive a mean peak value for each portion of said document, deriving a threshold value for each portion of said document using the mean peak value for the associated portion of said document and using the mean peak value for the portions of said document contiguous to said associated portion, and comparing each of the binary numbers in each group of binary numbers with the threshold value for the corresponding group and assigning one binary number when the threshold value exceeds the value of ones of the binary numbers, and assigning another binary number value when the threshold value is less than the value of ones of the binary numbers.
Claim 7
Dependent Claim
76 words
The method in accordance with claim 6 characterized by: filtering said string of binary numbers with a one pole digital filter having unity gain and a first bandwidth to derive a mean value for each portion of said document, comparing each binary number in each group of binary numbers with the mean value for the corresponding group, and updating said mean values by repeating said last mentioned filtering step using every binary number in the group.
Claim 8
Dependent Claim
43 words
The method in accordance with claim 7 characterized by: changing the bandwidth of said mean value digital filter to provide the best possible estimate of the mean value given the number of pixels available up to the point in scanning of the document.
Claim 9
Dependent Claim
68 words
9 . The method in accordance with claim 8 wherein said step of deriving a threshold value for each portion of said document comprises the step of: summing a first percentage of the present mean peak value for the portion of said document in which the most recent binary number represents a point with a percentage of the present mean peak values for adjacent portions of said document.
References Cited (Backward Citations)
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