Apparatus for correcting skew, distortion and luminance when imaging books and the like

• US 5,940,544 A
• Filed: 08/21/1997
• Issued: 08/17/1999
• Est. Priority Date: 08/23/1996
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Nako, Kazuyuki
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): SHERALI, ISHRAT I
• Application Number:
  US08/915,978
• Time in Patent Office: 726 Days
• Field of Search: 358/490-497, 358/486-488, 358/474, 358/429, 358/456, 358/458, 382/275, 382/270, 382/293, 382/242, 382/298-299, 382/289, 382/295-297
• US Class Current: 382/293
• 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 1/00718 Skew
• CPC Class Codes: H04N 1/00748 Detecting edges, e.g. of a stationary sheet
• CPC Class Codes: H04N 1/047 Detection, control or error compensation of scanning velocity or position H04N1/0402 and H04N1/17 take precedence
• CPC Class Codes: H04N 1/401 Compensating positionally unequal response of the pick-up or reproducing head H04N1/403 takes precedence
• CPC Class Codes: H04N 2201/0434 specially adapted for scanning pages of a book
• CPC Class Codes: H04N 2201/04703 using the scanning elements as detectors, e.g. by performing a prescan
• CPC Class Codes: H04N 2201/04732 Detecting at infrequent intervals, e.g. once or twice per line for main-scan control
• CPC Class Codes: H04N 2201/04737 by detecting the scanned medium directly, e.g. a leading edge
• CPC Class Codes: H04N 2201/04787 by changing or controlling the addresses or values of pixels, e.g. in an array, in a memory, by interpolation

Abstract

An object of the invention is to correct a distortion due to inclination of a document and to correct a luminance.

First, an edge detection section detects an edge of a document image from a picture obtained by imaging the document. Then, a skew detection section detects a skew of the document from the edge. A rotation correction section causes the picture to rotate on the basis of the skew detected by the skew detection section. Subsequently, the edge detection section again extracts a document image edge from the picture rotated by the rotation correction section. Further, a height calculation section calculates from the edge a height of the document. Simultaneously, a magnification calculation section calculates from the edge a magnification of the picture. Next, a distortion correction section corrects a distortion by magnification/reduction of the picture rotated by the rotation correction section on the basis of the document height and the magnification. Lastly, a luminance correction section corrects the luminance of pixels of the distortion-corrected picture. Whereby, even when the document suffers from skew added thereto, distortion correction and luminance correction can be performed.

Claims

1. A picture processing apparatus comprising:

first edge detection means for detecting an edge of a document image from a picture obtained by imaging the document;

skew detection means for detecting a skew of the document from the edge detected by the first edge detection means;

rotation correction means for rotating the picture on the basis of the skew;

second edge detection means for detecting an edge of the document image from the picture rotated by the rotation correction means;

magnification calculation means for calculating a magnification of the picture from the edge detected by the second edge detection means;

height calculation means for calculating a height of the document from a reference plane on the basis of the edge detected by the second edge detection means; and

distortion correction means for correcting a distortion of the picture through magnification/reduction of the picture rotated by the rotation correction means on the basis of the magnification and the height of the document.

4. The picture processing apparatus of claim 1, further comprising luminance correction means for correcting a luminance of the picture whose distortion has been corrected by the distortion correction means, in such a manner that the higher the luminance the closer the luminance comes to a predetermined upper limit.

6. The picture processing apparatus of claim 1, wherein the edge detection means subdivides the picture into a plurality of detection blocks, to detect an edge position of each detection block at a predetermined location, to connect lines each defined by two of the plurality of detected edge positions, thereby designating an edge.

7. The picture processing apparatus of claim 6, wherein the edge detection means reduces the detection block in response to increases in variation amount of the edge within the picture.

10. The picture processing apparatus of claim 1, wherein the skew detection means determines a maximal point and a minimal point from among the edges, and detects as a skew an angle between a straight line penetrating such maximal and minimal points and a predetermined reference axis line in the picture.

2. A picture processing apparatus comprising:

first edge detection means for detecting an edge of a document image from a picture obtained by imaging the document;

skew detection means for detecting a skew of the document from the edge detected by the first edge detection means;

picture reshaping means for reshaping a predetermined region of the picture on the basis of the skew;

second edge detection means for detecting an edge of the document image from the picture reshaped by the picture reshaping means;

magnification calculation means for calculating a magnification of the picture from the edge detected by the second edge detection means;

height calculation means for calculating a height of the document from a reference plane on the basis of the edge detected by the second edge detection means; and

distortion correction means for correcting a distortion of the picture through a magnification/reduction of the picture reshaped by the picture reshaping means on the basis of the magnification and the height of the document.

8. The picture processing apparatus of claim 2, wherein the picture reshaping means enlarges the predetermined region as the skew becomes larger.

3. A picture processing apparatus comprising:

edge detection means for detecting an edge of a document image from a picture obtained by imaging the document;

skew detection means for detecting a skew of the document from the edge;

magnification calculation means for calculating a magnification of the picture from the edge;

height calculation means for calculating a height of the document from a reference plane on the basis of the edge;

distortion correction means for correcting a distortion of the picture by subdividing a predetermined region of the picture into a plurality of trapezoidal segments on the basis of the skew to individually perform magnification/reduction for each trapezoidal segment on the basis of the skew, magnification, and height of the document.

5. The picture processing apparatus of claim 3, further comprising luminance correction means for correcting a luminance of each trapezoidal segment of the picture whose distortion has been corrected by the distortion correction means, in such a manner that the higher the luminance the closer the luminance comes to a predetermined upper limit.

9. The picture processing apparatus of claim 3, wherein the distortion correction means enlarges the predetermined region as the skew becomes larger.