Dataform reader utilizing hand jittering compensation method

• US 6,006,990 A
• Filed: 01/24/1997
• Issued: 12/28/1999
• Est. Priority Date: 09/12/1995
• Status: Expired due to Term

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Telxon Corporation (Zebra Technologies Corporation)
• Inventors: Ye, Angi, Li, C. Jim
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): ST CYR, DANIEL
• Application Number:
  US08/788,178
• Time in Patent Office: 1,068 Days
• Field of Search: 235/454, 235/455, 235/466, 235/472, 235/469, 235/470, 235/462.01, 235/462.02, 235/462.1, 235/462.14, 235/462.26, 235/472.01
• US Class Current: 235/454
• CPC Class Codes: G06K 7/10722 Photodetector array or CCD scanning
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: G06K 7/10861 sensing of data fields affixed to objects or articles, e.g. coded labels postal sorting B07C3/14, conveying articles B65G47/48
• CPC Class Codes: G06K 7/1093 sensing, after transfer of the image of the data-field to an intermediate store, e.g. storage with cathode ray tube
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence
• CPC Class Codes: G06K 7/1491 the method including a reconstruction step, e.g. stitching two pieces of bar code together to derive the full bar code

Abstract

A imaging based dataform reader utilizes a method of compensating for image offset between consecutive image fields comprising an interlaced image frame. The method includes determination of a disparity vector corresponding to the direction and magnitude of the offset between portions of successive fields. The disparity vector is determined by trial matching feature recognition data for a template area of a second image field to feature recognition data for a reference area of a first image field. The second field feature recognition data is trial matched to first field data at a plurality of offsets typical of hand jittering. The offset position providing the best feature match between the first and second fields is used to derive a disparity vector. The disparity vector is then applied to provide enhanced decoding by use of first field image data and registration-corrected second field image data. Feature recognition is achieved by use of digital filter value sets which may be adapted for recognition of horizontal, vertical or curved feature transitions.

Claims

1. An imaging based dataform reader for reading a target dataform and adapted to compensate for lack of resolution between successive interlaced fields of an image frame, the dataform reader comprising:

a) a housing defining an interior region; and

b) an imaging assembly for imaging the target dataform including;

i) a camera assembly supported by the housing including a two dimensional photosensor array comprising a plurality of rows including a first set of rows including every other row in the plurality of rows and a second set of rows including rows not included in the first set of rows, the first set of rows being read out at a time t1 to generate a first image field including a first representation of the target dataform and the second set of rows being read out at a time t2 to generate a second image field including a second representation of the target dataform, the first and second image fields comprising an interlaced image frame; and

ii) a control and decoder board supported within the housing interior region and including;

1) signal processing circuitry for converting the first image field into a first set of gray scale values and the second image field into a second set of gray scale values; and

2) image processing circuitry including;

A) disparity vector generation circuitry for comparing the first and second sets of gray scale values, generating a disparity vector, and applying the disparity vector to one of the first and second sets of gray scale values to generate a modified set of gray scale values having improved resolution with the other of the first and second sets of gray scale values and further combining the modified set of gray scale values and the other of the first and second sets of gray scale values to generate a combined set of gray scale values;

B) cell extraction circuitry for processing the combined set of gray scale values and generating a set of binary values representative of light and dark areas of the target dataform; and

C) decoding circuitry to decode the set of binary values.

2. The dataform reader of claim 1 wherein the disparity vector generated by the disparity generation circuitry includes a horizontal disparity vector value and a vertical disparity vector value, the horizontal disparity vector value representative of a horizontal offset in pixel position on the photosensor array between the first representation of the target dataform of the first image field and the second representation of the target dataform of the second image field and the vertical disparity vector value representative of a vertical offset in pixel position on the photosensor array between the first representation of the target dataform of the first image field and the second representation of the target dataform of the second image field.

3. The dataform reader of claim 2 wherein the disparity generation circuitry applies the horizontal disparity vector value and the vertical disparity vector value to the second set of gray scale values by shifting horizontal and vertical pixel positions of the gray scale values of the second set of gray scale values relative to pixel positions of the first set of gray scale values.

4. The dataform reader of claim 2 wherein the disparity generation circuitry applies the horizontal disparity vector value and the vertical disparity vector value to the first set of gray scale values by shifting horizontal and vertical pixel positions of the gray scale values of the first set of gray scale values relative to pixel positions of the second set of gray scale values.