Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1999-11-24
2002-03-26
Lee, Michael G. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S375000, C235S385000, C235S462090, C235S462140, C235S462190, C235S462250
Reexamination Certificate
active
06360948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a method of reading information optically out of a two-dimensional code made up of a matrix of data cells in a decreased time and a storage medium storing a program used to implement such a method.
2. Background Art
U.S. Pat. No. 5,726,435 filed Mar. 10, 1998, assigned to the same assignee as that of this application teaches a two-dimensional code used in inputting coded information into a computer, for example.
Typical two-dimensional codes have a two-dimensional spread, as shown in FIG.
16
(
b
), which can carry a large amount of information in a narrow area as compared with a bar code, as shown in FIG.
16
(
a
), but the structure thereof is complex.
FIG. 17
shows one example of two-dimensional codes. The two-dimensional code
300
includes three location symbols
310
a
,
310
b
, and
310
c
and arrays of timing cells
320
a
and
320
b
. The location symbols
310
a
to
310
c
are used in locating the two-dimensional code
300
and each consist geometrically of a plurality of squares different in size. The arrays of timing cells
320
a
and
320
b
are each disposed between adjacent two of the location symbols
310
a
to
310
c
and consist of a plurality of white and black cells arranged in a reference pattern that are used as indices of data cells arranged in a data field
330
.
The two-dimensional code
300
is made up of a square matrix of n×n cells. Each of the location symbols
310
a
to
310
c
consists of a square frame
312
formed with four sides each consisting of 7 cells, a white square frame
314
formed with four sides each consisting of 5 cells, and a black square
316
consisting of 3×3 cells formed on the central portion of the white square frame
314
.
When each of the location symbols
310
a
to
310
c
is scanned through an optical reader along any line passing through the center thereof, an optical signal pattern which has a brightness component ratio of black:white:black:white:black=1:1:3:1:1 is detected. Thus, when an optical signal pattern having that brightness component ratio is detected during scanning of the two-dimensional code
300
, it may be determined as a candidate pattern for any one of the location symbols
310
a
to
310
c
. Specifically, when three optical signal patterns each having a brightness component ratio of 1:1:3:1:1 are detected, it may be determined that the two-dimensional code
300
lies on a square area defined by the three optical signal patterns.
The data filed
330
consists of data cells (not shown for the brevity of illustration) each formed with a black or white square indicating logical 0 or 1 of a binary-coded data. Two-dimensional coordinates of each data cell are geometrically calculated in a known algorithm by using the centers of the location symbols
310
a
to
310
c
and the timing cells
320
a
and
320
b
as indices of the coordinates.
When the two-dimensional code
300
is scanned optically from a slant direction undesirably or when the two-dimensional code
300
printed on a curved surface of an object is scanned optically, it will cause a deformed image of the two-dimensional code
300
, as shown in FIG.
18
(
a
), to be captured. Additionally, when the two-dimensional code
300
is printed on the surface of a round bottle, for example, it will cause, as shown in FIG.
18
(
b
), both sides of the two-dimensional code
300
to be deformed greatly. The deformation of the image of the two-dimensional code
300
will result in shift between the actual center and the center of each data cell geometrically calculated in the above manner. If the shift is greater than half a size of each data cell, it produces an error in reading the two-dimensional code
300
. The degree of the deformation producing such an error increases as the size of the two-dimensional code
300
is increased for carrying more information.
In order to avoid the above problem, Japanese Patent First Publication No. 10-208001 assigned to the same assignee as that of this application teaches a method of reading information out of a two-dimensional code correctly even if a captured image of the two-dimensional code is deformed. The two-dimensional code has location symbols used in locating a data field and alignment symbols (also called auxiliary symbols) each arranged in a predetermined positional relation to the location symbols. The position of each data cell in the data field in the image of the two-dimensional code is specified by determining the central positions, shapes, and arrangement of the location symbols and the alignment symbols. The central position of each of the alignment symbols is determined by mathematically estimating a central position based on the shape of cells of the location symbols and the central positions of the location symbols and scanning an image of the alignment symbol near the estimated central position to find an actual center of the alignment symbol. One example of such a method of determining the actual center of each alignment symbol is also taught in Japanese Patent First Publication No. 8-185429, however, it has the drawback in that many pixels should be scanned, thus taking a large amount of time to locate each alignment symbol, which will result in an increase in time required for reading information out of the two-dimensional code.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a method of reading information out of a two-dimensional code in a decreased time.
According to one aspect of the invention, there is provided a method of reading information out of a two-dimensional code made up of a matrix of cells having a given optical pattern. The two-dimensional code has at least one location symbol used to locate the two-dimensional code and at least one alignment symbol used to locate the cells. The method comprises steps of: (a) capturing an image around the two-dimensional code in a bit mapped pattern; (b) detecting a position of the location symbol to determine a position of the two-dimensional code in the captured image; (c) calculating a central position of the alignment symbol in the captured image mathematically using a predetermined positional relation of the alignment symbol to the location symbol; (d) selecting a dot in the captured image lying at the calculated central position of the alignment symbol as a reference brightness check dot and dots lying in some of the cells around one of the cells of the captured image in which the reference brightness check dot exists as surrounding brightness check dots to define an alignment symbol optical pattern with a combination of the reference brightness check dot and the surrounding brightness check dots; (e) comparing the alignment symbol optical pattern with a plurality of reference optical patterns each formed with one of possible combinations of one of the cells lying at an actual central position of the alignment symbol and as many cells arranged adjacent the one of the cells as the surrounding brightness check dots to select one of the reference optical patterns matching up with the alignment symbol optical pattern; (f) correcting the calculated central position of the alignment symbol based on a position of one of the surrounding brightness check dots in the captured image corresponding to the one of the cells of the matched reference optical pattern at the actual central position of the alignment symbol and a geometry of the alignment symbol to determine an actual central position of the alignment symbol in the captured image; (g) determining positions of the cells of the two-dimensional code in the captured image based on at least one of the position of the location symbol and the actual central position of the alignment symbol in the captured image; and (h) reading the cells of the two-dimensional code in the captured image optically to decode the information carried by the tw
Shigekusa Hisashi
Yang Xuhua
Denso Corporation
Lee Michael G.
Pillsbury & Winthrop LLP
Walsh Daniel I
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