Techniques for reading postal code

Details Techniques for reading postal code Techniques for reading postal code

1999-04-07

2001-01-23

Pitts, Harold I. (Department: 2876)

Registers

Coded record sensors

Particular sensor structure

C235S462020

Reexamination Certificate

active

06176428

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to techniques for reading various types of postal codes using optical code reading devices. Aspects of the invention are particularly useful in imaging optical code readers which are designed to read a wide variety of optical codes in addition to postal code.
BACKGROUND OF THE INVENTION AND OBJECTS
Optical codes are patterns made up of image areas having different light reflective or light emissive properties, which are typically assembled in accordance with a priori rules. The term “bar code” is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Devices for identifying or extracting data from optical codes are sometimes referred to as “optical code readers” of which bar code scanners are one type. Optical code readers are used in both fixed or portable installations in many diverse environments such as in stores for checkout services, in manufacturing locations for work flow and inventory control and in transport vehicles for tracking package handling. Optical code readers have been widely adopted in the routing and sorting of mail.
Most conventional optical scanning systems are designed to read one-dimensional bar code symbols. The bar code is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light reflecting characteristics. One example of a one dimensional bar code is the UPC/EAN code used to identify, for example, product inventory.
The present disclosure relates to techniques especially adapted for reading postal codes. Typically postal codes are characterized by a sequence of bars of uniform width and uniformly spaced along a principal axis of the code. The symbology typically includes a region of regular parallel bars called a clock track. Certain of the bars may extend above and/or below the clock track. These elongated bars are sometimes called ascenders and descenders, and contain coded information.
An example of a postal code is the Postal Numeric Encoding Technique (POSTNET). POSTNET was developed by the U.S. Postal Service to provide an optimized code system for encoding address information on mail. Referring to
FIG. 1
, the basic elements of the POSTNET code
12
are tall bars or ascenders such as bar
1
and short bars such as bar
2
. These bars represent two states, i.e., binary ones and zeros, respectively. Both types of bars are aligned at one edge represented by the line
18
(line
18
is not part of the code symbol). Five bars of code represent one character, for example, one digit of a zip code. The left and right margins of the code are marked by tall bars
3
. The postal code called PLANET has a similar structure, but different encoding. In POSTNET code the five bars representing one character include two long and three short bars. In PLANET code the five bars representing one character include three long and two short bars.
Another type of postal code is Canadian Post Office Code. An example of a Canadian Post Office Code is shown in FIG.
1
(
a
). The code is a modified form of the POSTNET code. It is a four-state code with increased alphabetic coding capacity over the POSTNET code described above. The four-states are each exemplified by the ascender bar
4
, descender bar
5
, full bar
6
(i.e. a bar having both ascending and descending portions) and short, clock bar
7
. The clock track lies between lines
8
and
9
. (Lines
8
and
9
are not part of the code symbol). Another type of postal code is UK postal code. UK postal code is similar to a two-layer U.S. code with the bottom symbol flipped and the two clock tracks merged. UK code uses 4 bars per character, as compared to 5 bars per character in U.S. POSTNET code. Other four state codes include Australian, Japanese and Belgian Postal Codes.
Postal codes can be read employing imaging devices. For example an image sensor may be employed which has a two dimensional array of cells or photo sensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor may be a two dimensional or area solid state sensor and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view. An imaging module useable in reading postal codes is disclosed in U.S. patent application Ser. No. 09/096,578, filed Jun. 12, 1998, entitled
IMAGING ENGINE AND METHOD FOR CODE READERS
to Correa et al., which is hereby incorporated by reference. Alternatively, the post processing part of the following algorithm is applicable to systems which use laser scanning imaging, such as the ones disclosed in U.S. patent application Ser. No. 08/275,515 filed Jul. 15, 1994 entitled “
Method And Apparatus For Raster Scanning Of Images
” to Dvorkis et al., which is incorporated herein by reference.
It is an object of the present invention to provide efficient and accurate techniques for reading postal codes.
It is another object of the present invention to provide techniques for reading postal codes employing an optical imaging system.
It is another object of the present invention to provide techniques for employing an optical imager capable of reading various types of one and two dimensional codes and for identifying and reading various types of postal codes.
It is another object of the present invention to provide techniques for reading postal codes of initially unknown type and orientation with respect to the optical code reader.
These and other objects and features of the invention will be apparent from this written description and drawings.
SUMMARY OF THE INVENTION
The present invention relates to techniques for reading postal codes useful in optical code readers, especially imaging optical code readers.
More specifically, there is disclosed methods for identifying and reading various types of postal code contained in image data arrays obtained by an optical code reader. The postal codes are assumed to include a clock track of regularly arranged, parallel bars. The system defines a subimage which contains a characteristic indicative of the presence of postal code. A candidate baseline is located within the subimages which extends across the clock track of the postal code from the left to right of the symbol. If the correct baseline has been chosen, every bar in the symbol will intersect the baseline. Each bar is then tracked above and below the baseline to obtain a string of states based on bar length. The type of code is determined and the string of states is translated to obtain the information contained in the postal code.
In preferred embodiments, the baseline which crosses the clock track from one margin of the postal code to the other is located by selecting a first point on a left margin bar; selecting a second point on a right margin bar and line walking from the first to second point. The selection of end points is verified by testing the uniformity of bar widths and spaces along the baseline to determine whether the baseline is located entirely within the clock track. In a more preferred embodiment a look-up table is used to select said first and second points. Various alternate points, corresponding to new candidate baselines, are selected until the clock track is found.
Preferred embodiments of the present invention employ processing techniques for identifying the type of postal code and applying the appropriate translating algorithm, such as for POSTNET, Canadian Postal Code, PLANET Code or UK Postal Code. In these methods there is first obtained pixel data identified as potentially containing all or a portion of an image of postal code. The entire clock track of the postal code is first located, advantageously in the manner described above. Each bar in the located clock track is examined to determine whether each such bar extends above or below the clock track and to obtain a string of states for the code. The regularity of bar

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