Linear imager rescaling method

• US 7,385,743 B2
• Filed: 10/16/2002
• Issued: 06/10/2008
• Est. Priority Date: 10/16/2001
• Status: Expired due to Term

• Current Assignee: Datalogic Automation Incorporated (Datalogic S.p.A.)
• Original Assignee: Accu-Sort Systems Incorporated (Datalogic S.p.A.)
• Inventors: Zhang, Han, Gagliano, Jeffrey A., Hecht, Kurt, Skokowski, Richard J. Jr.
• Primary Examiner(s): Cherry; Euncha P
• Application Number:
  US10/493,048
• Publication Number:
  US 20050036185A1
• Time in Patent Office: 2,064 Days
• Field of Search: 359196-226
• US Class Current: 359/196.1
• CPC Class Codes: G02B 27/0031 for scanning purposes
• CPC Class Codes: G06K 7/1404 Methods for optical code recognition
• CPC Class Codes: G06K 7/146 the method including quality enhancement steps
• CPC Class Codes: G06T 3/00 Geometric image transformations in the plane of the image
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: G06V 10/147 Details of sensors, e.g. sensor lenses fingerprint or palmprint sensors G06V40/13; vascular sensors G06V40/145; eye sensors G06V40/19
• CPC Class Codes: G06V 10/247 by affine transforms, e.g. correction due to perspective effects; Quadrilaterals, e.g. trapezoids
• CPC Class Codes: G06V 10/32 Normalisation of the pattern dimensions
• CPC Class Codes: H04N 1/387 Composing, repositioning or otherwise geometrically modifying originals

Abstract

A system and method for removing perspective distortion from an image of an object (112) moving along a transport device (114) having a top surface (124) is disclosed. A line scanner (110) to create a first image of an object. The first image is composed of a plurality of scan lines, each having a resolution. Each of the scan lines is then rescaled, so that the resolution of each scan line is equal to the resolution of every other scan line. Each of the scan lines is processed in two halves so that the center lines of the scan lines are co-linear after rescaling. The line scanner is optionally configured to vary its field of view as a function of the distance between the line scanner and the portion of the object being scanned.

Claims

1. A method of correcting an image of an object moving along a transport device having a top surface, the method comprising:

scanning at least a portion of the object using a line scanner to create a plurality of scan lines, each of the plurality of scan lines having a resolution; and

rescaling each of the plurality of scan lines, so that the resolution of each of the plurality of scan lines is equal to the resolution of every other of the plurality of scan lines.

2. The method of claim 1, wherein the resolution of each of the plurality of scan lines after the rescaling step is less than or equal to the lowest resolution of all of the plurality of scan lines before the rescaling step.

3. The method of claim 1, wherein each of the plurality of scan lines includes a first half, a second half and a center line and the rescaling step further comprises processing the first half of each of the plurality of scan lines separately from the second half of each of the plurality of scan lines.

4. The method of claim 3, further comprising processing the plurality of scan lines after the rescaling step to form a second image in which the center lines of all of the plurality of scan lines are co-linear.

5. The method of claim 1, wherein each of the plurality of scan lines includes a width, the method further comprising setting the width of each of the plurality of scan lines as a function of the resolution of each of the plurality of scan lines prior to the rescaling step, so that the widths of all of the plurality of scan lines are equal after the rescaling step.

6. The method of claim 1, in which the image is captured with an imaging device including a lens having a focal length and a field of view, the method further comprising the steps of:

(a) determining the distance between the lens and a first portion of the object at a first point in time;

(b) adjusting the focal length of the imaging device as a function of the distance between the lens and a first portion of the object at the first point in time;

(c) wherein the scanning of the first portion of the object at the first point in time creates a first scan line of the object or portion thereof comprising an array of pixels and a resolution; and

(d) the rescaling step further includes electronically rescaling the first scan line so that the resolution is equal to a target resolution.

7. The method of claim 6, wherein the target resolution is equal to the resolution of a scan line taken of the top surface of the transport device.

8. The method of claim 6, wherein the first scan line includes first and second halves, and the method further comprises processing the first half separately from the second half.

9. The method of claim 6, wherein the adjusting step further comprises adjusting the field of view of the lens as a function of the distance between the lens and the first portion of the object at the first point in time.

10. The method of claim 9, wherein the step of adjusting the field of view comprises varying a number of pixels in the array of pixels.

11. The method of claim 6, wherein the determining step further comprises determining a height of the first portion of the object above the top surface of the transport device.

12. The method of claim 11, wherein the determining step further comprises determining the speed at which the object is moving along the transport device.

13. A method for removing perspective distortion from an image of at least a portion of an object moving along a transport device, the image comprising a plurality of scan lines taken by an electronic imaging device, each of the plurality of scan lines having a resolution and the electronic imaging device including an optical sensor, a lens having a nodal plane, a focal length, and a pixel pitch, the method comprising:

determining a target resolution, wherein the target resolution is less than or equal to 1/((D1/LFL-1)*SPS) where;

D1=the distance between the nodal plane of the lens and the transport device LFL=the focal length of the optical sensor SPS=the pixel pitch of the optical sensor; and

rescaling each of the plurality of scan lines so that the resolution of each of the plurality of scan lines is equal to the target resolution.

14. A system for capturing perspective-corrected images of an object moving along a transport device comprising:

a line scanner having a focal length and a field of view, the line scanner being adapted to capture a plurality of scan lines, each of the plurality of scan lines having a resolution; and

a controller that determines a target resolution that is less than or equal to the lowest resolution of any of the plurality of scan lines and rescales each of the plurality of scan lines so that the resolution of each of the plurality of scan lines is equal to the target resolution.

15. The system of claim 14, further comprising a first device that determines the height of a portion of the object.

16. The system of claim 15, further comprising a second device that determines the speed at which the object is moving along the transport device.