System and method for automatically detecting edges of scanned documents

• US 6,741,741 B2
• Filed: 02/01/2001
• Issued: 05/25/2004
• Est. Priority Date: 02/01/2001
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Farrell, Barbara L.
• Primary Examiner(s): Johns, Andrew W.
• Assistant Examiner(s): Alavi, Amir
• Application Number:
  US09/775,334
• Publication Number:
  US 20020126899A1
• Time in Patent Office: 1,209 Days
• Field of Search: 382/173, 382/190, 382/172, 382/194, 382/199, 382/219, 382/221, 382/203, 382/228, 382/266, 382/272, 358/446, 358/449, 358/486, 358/487, 358/488, 358/504, 358/505, 250/559.42
• US Class Current: 382/199
• 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 against a light backing and a dark backing. A first set of first-order statistics are calculated from the image data obtained by scanning the document against the light backing. A second set of first-order statistics are calculated from the image data obtained by scanning the document against the dark backing. A document edge is detected using the first and second sets of first-order statistics.

Claims

1. A method for detecting an edge of a document being scanned, comprising:

(a) scanning a portion of the document against a substantially light reflecting backing to obtain a first set of image data;

(b) scanning a portion of the document against a substantially light absorbing backing to obtain a second set of image data;

(c) calculating a set of first values from the first set of image data, each one of the first values being a first-order statistic;

(d) calculating a set of second values from the second set of image data, each one of the second values being a first-order statistic; and

(e) determining a detected edge of the document from the set of first values and the set of second values.

2. The method of claim 1, wherein step (e) comprises:

(e1) determining a set of first difference values, each one of the first difference values being the difference between one of the first values and one of the second values;

(e2) determining a second difference value, the second difference value being the difference between two of the first difference values; and

(e3) identifying the detected edge when the second difference value is greater than a threshold value.

3. The method according to claim 2, wherein:

step (c) calculates a first mean value for each one of selected columns of pixels within the first set of image data; and

step (d) calculates a second mean value for each for each one of selected columns of pixels within the second set of image data.

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

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

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

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

5. The method according to claim 4, wherein step (g) comprises:

(g1) determining a first slope value, the first slope value being a function of the difference between a plurality of the third values;

(g2) generating a block sum value, the block sum value comprising the sum of a plurality of third values; and

wherein the second detected edge is identified from the first slope value and the block sum.

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

(g3) determining a second slope value, the second slope value being a function of the difference between a plurality of the second values; and

(g4) computing a product of the first slope value and the second slope value;

wherein the second detected edge is identified from the product, the first slope value and the block sum.

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

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

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

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

8. The method according to claim 7, wherein step (g) comprises:

(g1) determining a first slope value, the first slope value being a function of the difference between a plurality of the third values;

(g2) determining a set of first difference values, each one of the first difference values being the difference between one of the first values and one of the second values; and

(g3) determining a second difference value, the second difference value being the difference between two of the first difference values;

wherein the second detected edge is identified from the first slope value and the second difference value.

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

(f) calculating a plurality of block values, each block value comprising a mean of a plurality of second values; and

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

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

(f1) calculating a first block value, the first block value comprising a mean of a first plurality of second values;

(f2) calculating a second block value, the second block value comprising a mean of a second plurality of second values; and

(f3) 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 (g) verifies the detected edge when the first block value is greater than a first block difference threshold.

11. The method according to claim 10, wherein step (f) further comprises:

(f4) calculating a third block value, the third block value comprising a mean of a third plurality of second values;

(f5) calculating a fourth block value, the fourth block value comprising a mean of a fourth plurality of second values; and

(f6) computing a second first block difference value, the second block difference value comprising an arithmetic difference between the third block value and the fourth block value;

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

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

(f) calculating a plurality of first block values, each of the first block values comprising a mean of a plurality of first values;

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

(h) verifying the detected edge using the first plurality of block values and second plurality of block values.

13. The method according to claim 12, wherein step (h) comprises:

(h1) calculating a plurality of first difference values, each of the first difference values comprising an arithmetic difference between one of the first block values and a selected pixel column;

(h2) calculating a plurality of second difference values, each of the second difference values comprising an arithmetic difference between one of the second block values and the selected pixel column;

(h3) confirming the detected edge when each of the first and second difference values are greater than a threshold value.

14. A method for detecting an edge of a document being scanned, comprising:

(a) scanning a portion of the document against a substantially light reflecting backing to obtain a first set of image data;

(b) scanning a portion of the document against a substantially light absorbing backing to obtain a second set of image data;

(c) calculating a set of first values from the first set of image data, each one of the first values being a first-order statistic;

(d) calculating a set of second values from the second set of image data, each one of the second values being a first-order statistic;

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

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

(g) determining a first edge detection from the set of first values and the set of second values;

(h) determining a second edge detection from the set of first values and the set of second values;

(i) determining a third edge detection from the set of first values, the set of second values and the set of fourth values; and

(k) reconciling the first edge detection, the second edge detection and the third edge detection to obtain a document edge.

15. The method according to claim 14, wherein step (g) comprises:

(g1) determining a set of first difference values, each one of the first difference values being the difference between one of the first values and one of the second values;

(g2) determining a second difference value, the second difference value being the difference between two of the first difference values; and

(g3) identifying the first edge detection when the second difference value is greater than a threshold value.

16. The method according to claim 14, wherein step (h) comprises:

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

(h2) generating a block sum value, the block sum value comprising the sum of a plurality of third values;

(h3) determining a second slope value, the second slope value being a function of the difference between a plurality of the second values; and

(h4) computing a product of the first slope value and the second slope value;

wherein the second edge detection is identified from the product, the first slope value and the block sum.

17. The method according to claim 14, wherein step (i) comprises:

(i1) determining a first slope value, the first slope value being a function of the difference between a plurality of the fourth values;

(i2) determining a set of first difference values, each one of the first difference values being the difference between one of the first values and one of the second values; and

(i3) determining a second difference value, the second difference value being the difference between two of the first difference values;

wherein the third edge detection is identified from the first slope value and the second difference value.