System and method for automatically detecting edges of scanned documents

• US 20020126330A1
• Filed: 02/01/2001
• Published: 09/12/2002
• Est. Priority Date: 02/01/2001
• Status: Active Grant

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Farrell, Barbara L.
• Granted Patent: US 6,930,804 B2
• Time in Patent Office: Days
• US Class Current: 358/538
• CPC Class Codes: H04N 1/00681 Detecting the presence, position or size of a sheet or correcting its position before scanning H04N1/047 takes precedence; mode signalling H04N1/333; skew detection or correction in image signals H04N1/3878
• CPC Class Codes: H04N 1/00702 Position
• CPC Class Codes: H04N 1/00708 Size or dimensions
• CPC Class Codes: H04N 1/00718 Skew
• CPC Class Codes: H04N 1/00737 using the scanning elements as detectors
• CPC Class Codes: H04N 1/00745 Detecting the leading or trailing ends of a moving sheet

Abstract

A method for identifying document edges collects a predetermined number scanlines of the document. Both first order and second order statistics are then calculated based on the scanned data. A first slope value being a function of the difference between a plurality of the first value and a second slope value being a function of the difference between a plurality of the second value are calculated. A document edge is detected using the first and second slope values.

Claims

1. A method for automatically detecting an edge of a document in a scanning system, comprising the steps of:

(a) scanning a portion of the document to obtain a set of image data;

(b) calculating a set of first values from the image data using a first function, the first function being a first-order function;

(c) calculating a set of second values from the image data using a second function, the second function being a second-order function;

(d) determining a first slope value, the first slope value being a function of the difference between a plurality of the first values;

(e) determining a second slope value, the second slope value being a function of the difference between a plurality of the second values; and

(f) determining a detected edge of the document from the first slope value and the second slope value.

2. The method according to claim 1, wherein step (f) comprises:

(f1) computing a product of the first slope value and the second slope value; and

(f2) generating a block sum value, the block sum value comprising the sum of a plurality of second values.

3. The method according to claim 1, further comprising:

(g) calculating a set of third values from the image data, each one of the third values being a fourth-order statistic;

(h) determining a second detected edge of the document from the set of third values; and

(i) reconciling the detected edge and the second detected edge to obtain the document edge.

4. The method according to claim 3, wherein step (h) comprises:

(h1) determining a third slope value, the third slope value being a function of the difference between a plurality of the third values;

wherein the second detected edge is identified from the third slope value.

5. The method according to claim 1, further comprising:

(g) calculating a plurality of block values, each block value comprising a mean of a plurality of first values; and

(h) verifying the detected edge using the plurality of neighbor block values.

6. The method according to claim 5, wherein step (g) comprises:

(g1) calculating a first block value, the first block value comprising a mean of a first plurality of first values;

(g2) calculating a second block value, the second block value comprising a mean of a second plurality of first values; and

(g3) computing a first block difference value, the first block difference value comprising an arithmetic difference between the first block value and the second block value;

wherein step (h) verifies the detected edge when the first block value is greater than a first block difference threshold.

8. The method according to claim 2, wherein step (f) comprises:

(f1) computing a product of the first slope value and the second slope value; and

(f2) generating a block sum value, the block sum value comprising the sum of a plurality of second values.

9. The method according to claim 1, further comprising:

(g) calculating a set of second values from the image data using a second, the second function being a fourth-order function;

(h) determining a second detected edge of the document from the set of second values; and

(i) reconciling the detected edge and the second detected edge to obtain the document edge.

10. The method according to claim 9, wherein step (h) comprises:

(h1) determining a second slope value, the second slope value being a function of the difference between a plurality of the second values;

wherein the second detected edge is identified from the third slope value.

7. A method for automatically detecting an edge of a document in a scanning system, comprising the steps of:

(a) scanning a portion of the document to obtain a set of image data;

(b) calculating a set of first values from the image data using a first function, the first function being a second-order function;

(c) determining a first slope value, the first slope value being a function of the difference between a plurality of the first values;

(d) generating a block sum value, the block sum value comprising the sum of a plurality of first values; and

(f) determining a detected edge of the document from the first slope value and the block sum value.