Scan image target locator system for calibrating a printing system

• US 5,642,202 A
• Filed: 12/01/1994
• Issued: 06/24/1997
• Est. Priority Date: 12/01/1994
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Shiau, Jeng-nan, Williams, Leon C.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): JARDIEU, DEREK
• Application Number:
  US08/347,756
• Time in Patent Office: 936 Days
• Field of Search: 382/312, 382/319, 355/208, 355/52, 358/296, 358/298, 358/406, 358/448, 358/504, 358/474, 358/505, 358/530, 399/15
• US Class Current: 358/406
• 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 1/4076 dependent on references outside the picture
• CPC Class Codes: H04N 2201/02425 Self-adjusting arrangements, e.g. compensating for temperature fluctuations
• CPC Class Codes: H04N 2201/03162 Original guide plate
• CPC Class Codes: H04N 2201/0471 using dedicated detectors
• CPC Class Codes: H04N 2201/04717 on the scanned sheet, e.g. a reference sheet
• CPC Class Codes: H04N 2201/04729 in the main-scan direction
• CPC Class Codes: H04N 2201/04731 in the sub-scan direction
• 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 2201/04749 Detecting position relative to a gradient, e.g. using triangular-shaped masks, marks or gratings
• 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
• CPC Class Codes: H04N 2201/04789 in the main-scan direction
• CPC Class Codes: H04N 2201/04791 in the sub-scan direction
• CPC Class Codes: H04N 2201/04793 using stored control or compensation data, e.g. previously measured data

Abstract

A system and method for calibrating a printing system includes a printer and a master test image document printed by the printer. The master test image has three locator symbols and a plurality of test objects, each symbol having a distinct apex. The apexes are non-colinear. A memory prestores image data corresponding to the test objects printed on the master test image document and positional data corresponding to a desired coordinate value for each non-colinear apex. The system also includes a scanner for scanning the master test image document and detects the locator symbols printed on master test image document to generate transition data therefrom. The calibration process determines a coordinate value for each non-colinear apex based on the transition data and generates a transformation matrix based on a difference between the determined coordinate value for each non-colinear apex and the desired coordinate value for each non-colinear apex. A compensation process retrieves prestored image data corresponding to the scanned image data based on the transformation matrix. The calibration process then compares scanned image data with the retrieved prestored image data to generate compensation values based on a difference between the scanned image data and the prestored image data.

Claims

1. A system for calibrating a printing system, comprising:

a printer;

a master test image document printed by said printer, said master test image having three locator symbols and a plurality of test objects, each symbol having a distinct apex, the apexes being non-colinear;

scanning means for scanning said master test image document;

symbol means for detecting the locator symbols printed on said master test image document and for generating transition data therefrom;

coordinate means for determining a coordinate value for each non-colinear apex based on the transition data;

memory means for prestoring image data corresponding to the test objects printed on said master test image document and positional data corresponding to a desired coordinate value for each non-colinear apex;

transformation means for generating a transformation matrix based on a difference between the determined coordinate value for each non-colinear apex and the desired coordinate value for each non-colinear apex;

position compensation means for retrieving prestored image data corresponding to the scanned image data based on the transformation matrix; and

calibration means for comparing scanned image data with the retrieved prestored image data and for generating compensation values based on a difference between the scanned image data and the prestored image data.

2. The system as claimed in claim 1, wherein said position compensation means changes a coordinate value of the scanned image data based on the transformation matrix.

3. The system as claimed in claim 1, wherein said position compensation means changes a coordinate value of the prestored image data based on the transformation matrix.

4. The system as claimed in claim 1, wherein said symbol means detects the locator symbols when it is determined that a scanline contains a predetermined number of transitions between symbol image data and background image data.

5. The system as claimed in claim 1, wherein said symbol means detects the locator symbols when it is determined that a scanline contains six transitions between symbol image data and background image data.

6. The system as claimed in claim 4, wherein said symbol means generates transition data for each scanline having the predetermined number of transitions between symbol image data and background image data, the generated transition data being coordinate values representing points of transition along the scanline between symbol image data and background image data.

7. The system as claimed in claim 5, wherein said symbol means generates transition data for each scanline having six transitions between symbol image data and background image data, the generated transition data being coordinate values representing the six points of transition along the scanline between symbol image data and background image data.

8. The system as claimed in claim 6, wherein said symbol means forms a plurality of sets of coordinate values, each set having coordinate values which correspond to an edge of a locator symbol.

9. The system as claimed in claim 7, wherein said symbol means forms six sets of coordinate values, each set having coordinate values which correspond to an edge of a locator symbol.

10. The system as claimed in claim 8, wherein said coordinate means comprises:

line means for calculating an equation for each set of coordinate values, each equation corresponding to a line that passes through the coordinate values within a set; and

intersection means for determining a point of intersection for each locator symbol, each point of intersection being created by the intersection of two lines which represent two edges of a locator symbol, the point of intersection representing the apex of the locator symbol.

11. The system as claimed in claim 9, wherein said coordinate means comprises:

line means for calculating six equations, each equation corresponding to a line that passes through the coordinate values within a set; and

intersection means for determining three points of intersection, each point of intersection being created by the intersection of two lines which represent two edges of a locator symbol, the point of intersection representing the apex of the locator symbol.

12. A method for calibrating a printing system, comprising the steps of:

(a) printing a master test image document on a printer to be tested, the master test image having three locator symbols and a plurality of test objects, each symbol having a distinct apex, the apexes being non-colinear;

(b) scanning the master test image document;

(c) detecting the locator symbols printed on the master test image document and generating transition data therefrom;

(d) determining a coordinate value for each non-colinear apex based on the transition data;

(e) prestoring image data corresponding to the test objects printed on the master test image document and positional data corresponding to a desired coordinate value for each non-colinear apex;

(f) generating a transformation matrix based on a difference between the determined coordinate value for each non-colinear apex and the desired coordinate value for each non-colinear apex;

(g) retrieving a prestored image data corresponding to the scanned image image data based on the transformation matrix; and

(h) comparing scanned image data with the retrieved prestored image data and generating compensation values based on a difference between the scanned image data and the prestored image data.

13. The method as claimed in claim 12, wherein said step (g) changes a coordinate value of the scanned image data based on the transformation matrix.

14. The method as claimed in claim 12, wherein said step (g) changes a coordinate value of the prestored image data based on the transformation matrix.

15. The method as claimed in claim 12, wherein said step (c) detects the locator symbols when it is determined that a scanline contains six transitions between symbol image data and background image data and generates transition data for each scanline having six transitions between symbol image data and background image data, the generated transition data being coordinate values representing the six points of transition along the scanline between symbol image data and background image data.

16. The method as claimed in claim 15, wherein said step (c) forms a plurality of sets of coordinate values, each set having coordinate values which correspond to an edge of a locator symbol.

17. The method as claimed in claim 16, wherein said step (d) comprises the substeps of:

(d1) calculating an equation for each set of coordinate values, each equation corresponding to a line that passes through the coordinate values within a set; and

(d2) determining a point of intersection for each locator symbol, each point of intersection being created by the intersection of two lines which represent two edges of a locator symbol, the point of intersection representing the apex of the locator symbol.