Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
2001-04-06
2003-08-12
St. Cyr, Daniel (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462100, C235S462250
Reexamination Certificate
active
06604682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a two-dimensional bar code reading method, a data storage medium carrying a computer program product embodying the method, and two-dimensional bar code reading apparatus. More particularly, the present invention relates to a two-dimensional bar code reading method, data storage medium, and two-dimensional bar code reading apparatus for locating the finder pattern in an image captured by scanning a two-dimensional code symbol, locating the direction module, locating the data module, and converting the data module to data characters.
2. Description of Related Art
Bar codes are a type of automated recognition technology that developed in the retail industry as a way to look up information in a database about an item quickly and accurately. Bar codes have since evolved and found application in such diverse industries as warehousing and distribution, government, medicine, research, and event management. As bar codes and their applications have become more varied, demand for bar codes has spread to industries and applications for which traditional bar codes are ill-suited, including bar code miniaturization for imprinting on very small items and high coding capacity. Two-dimensional bar codes addressing these needs have been developed in recent years.
There are two types of two-dimensional bar codes: stacked symbology (or multi-row codes), and matrix codes. Stacked symbologies comprise multiple rows of one-dimensional bar codes stacked in a vertical alignment. Stacked symbologies can be read using a laser scanner, CCD scanner, or other scanning method. Matrix codes encode data using black and white data cells arranged in a pattern determined by the particular code protocol. Matrix codes can be read using a CCD image reader or other image sensing method.
One type of matrix code is called MaxiCode. MaxiCode was designed for sorting and tracking package shipments. Package delivery services in the United States use MaxiCode in their collection and distribution centers for shorting shipments by destination and for ship loading. The two-dimensional (2D) symbol generated and displayed according to the MaxiCode standard is referred to below as the MaxiCode symbol.
A typical MaxiCode symbol is shown in FIG.
59
. FIG.
59
(
a
) shows a complete MaxiCode symbol, and FIG.
59
(
b
) shows the finder pattern and orientation module of the MaxiCode symbol.
As shown in FIG.
59
(
a
), a finder pattern
5901
is positioned at the center of every MaxiCode symbol
5900
. Every finder pattern
5901
comprises six concentric parts, including a white center circle, two white rings, and three black rings. The finder pattern
5901
is used to locate and isolate the MaxiCode symbol
5900
from the captured image. The center of the MaxiCode symbol is identified by locating the center of the finder pattern
5901
.
The space within the MaxiCode symbol around the finder pattern
5901
is populated by module groups consisting in total of 884 black or white interlocking modules
5902
. Each module
5902
is a regular hexagon. The module groups consist of six orientation module groups
5903
and a data module group. Each orientation module group consists of the 3 orientation modules indicating the orientation of the MaxiCode symbol
5900
. The data module group consists of the 864 data modules representing the encoded data; one data module corresponds to one data bit. Data modules are used for encoding data, and are used for error correction processing. Note that the two modules at the top right of the symbol are not used.
As shown in FIG.
59
(
b
), the regular hexagon module
5902
is sized so that it is internally tangent to the white center bullseye of the finder pattern
5901
. The orientation module groups
5903
define a virtual regular hexagon of which the center is the center point
0
of the finder pattern
5901
. Each orientation module group
5903
includes an inside orientation module
5904
, outside orientation module
5905
, and center orientation module
5906
. The six orientation module groups
5903
thus comprise a total 18 orientation modules. Finding these 18 orientation modules identifies the orientation of the MaxiCode symbol and enables the data to be read from the data modules.
It should be noted here that in each orientation module group
5903
the inside orientation module
5904
is the one located at the shortest distance from the center point
0
, the outside orientation module
5905
is the one located at the farthest distance from the center point
0
, and the center orientation module
5906
is the one located at a distance from the center point
0
that is between the distance from center point
0
to the inside orientation module
5904
and the distance from center point
0
to the outside orientation module
5905
.
An image sensing technique is used to read MaxiCode symbols, which as noted above are a type of two-dimensional code symbology. In other words, a MaxiCode symbol is captured as image data which is then interpreted (decoded). This operation is described more fully below.
The first step is to find the MaxiCode symbol finder pattern and orientation modules in the captured image, and then recognize the data modules. A bit pattern is then generated from the data modules, assigning a bit value of 1 to each dark (typically black) data module, and 0 to each light (typically white) data module. The resulting bit pattern is then converted to corresponding data characters to decode the data in the MaxiCode symbol. Various methods have been developed for decoding the scanned image of a MaxiCode symbol.
It is always necessary to find the center of the finder pattern to decode a MaxiCode to symbol. JP-A-10-21322 teaches one method for finding the center of the finder pattern.
This method first finds all Jordan curves having an angular distance between two points less than &Sgr;; then, finds all convex Jordan curves within the found Jordan curves; determines the equations of a pair of tangents from the end points of each convex Jordan curve; determines the equations of the center lines for each pair of tangents; determines the point of intersection of the center lines; and thus finds the center point of the finder pattern based on the intersection of the center lines. Decoding the MaxiCode symbol then proceeds.
A problem with the method taught in JP-A-10-21322 is that processing is time-consuming because of the steps needed to isolate all convex Jordan curves from among all Jordan curves found, then determine the equations of the tangents, and finally look for the center of the finder pattern of the symbol.
A method using templates to find the center of the finder pattern is taught in WO95/34043. However, WO95/34043 simply says that the six symbol axes, which are offset 60 degrees each, pass through the center of the bull's-eye, and that the center of the template is overlaid to the center of the bull's-eye. It says nothing specific about how to overlay the template with the center of the bull's-eye.
Finding the orientation modules is also important, and various methods of accomplishing this have been proposed. Finding the orientation modules is essentially finding the location and shape of the orientation modules. By finding the location and shape of the orientation modules it is not only possible to detect the location of each data module based on the dimensions of a MaxiCode symbol module, it is also possible to identify the color, that is, the bit value, of the detected data modules.
FIG. 60
shows module groups in a MaxiCode symbol. As shown in
FIG. 60
, module group
6000
comprises orientation module groups
6001
a
,
6001
b
,
6001
c
,
6001
d
,
6001
e
,
6001
f
, each containing plural orientation modules as noted above, and data module group
6002
comprising the individual data modules. Note, further, that the bit pattern (where black=1 and white=0) of the three orientation modules constituting each of the six orientation module groups
6001
a
,
6001
b
,
Arazaki Shinichi
Koyama Fumio
Ohori Haruyoshi
Wakamiya Hitomi
Yanagida Satoshi
Cyr Daniel St.
Hogan & Hartson LLP
Seiko Epson Corporation
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