Image analysis – Applications
Reexamination Certificate
1998-11-16
2001-04-17
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Reexamination Certificate
active
06219434
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a maxicode locating method.
As is known, maxicodes (
FIG. 1
) are two-dimensional optical codes comprising a central target element (known as bull's-eye) by which to locate the code; and a number of dark/light (normally black/white) hexagonal-cell elements surrounding the central target element and containing the coded information associated with the code.
The central target element is defined by three concentric dark-coloured (normally black) rings of equal thickness separated by two light-coloured (normally white) annular spaces of the same thickness as the rings. The innermost ring surrounds a light-coloured (normally white) circular central space.
Known locating systems comprise an optoelectronic viewing system (normally comprising a focusing device and a television camera) for picking up a two-dimensional image (defined by a matrix comprising a number of pixels) of objects (in particular, moving objects, such as parcels traveling along a conveyor belt) to which maxicodes are applied and a processing device for locating the central space of the target element in the image and so locating the maxicode. The position of the central space of the target element in fact corresponds to the center of the maxicode.
The shape of the target element in the acquired image is affected by various factors, including:
Dimension scaling. The “apparent” dimension (measured, for example, in pixels) of the target element depends on the distance between the vision system and the maxicode. Since, in real applications, it must be possible for the maxicode to be located within a wide viewing range, the apparent dimension of the target element may vary within a fairly wide range of values.
Code ovaling. The target element of a maxicode is circular, but may be deformed, in particular, compressed along an axis into an ellipse (FIG.
2
), so that the target element differs considerably from the original circular shape and may assume any one of numerous variously compressed oval shapes.
Ovaling of the target element is caused by two main factors, which may occur simultaneously:
The plane of the viewing system lens is not parallel to the plane containing the maxicode (as in the case of a parcel which is not a parallelepipedon);
the traveling speed of the object is not synchronized correctly with the scanning speed of the vision system.
To eliminate the above drawbacks, the vision system is normally subjected to restrictions, which must be established highly accurately and/or maintained within a strictly predetermined range. Such restrictions may include:
the distance between the vision system lens and the maxicode is required, for the image to be re-scaled before searching for the target element;
the traveling speed of the maxicode is required, to calibrate the image scanning speed;
inclination of the objects with respect to the vision system.
Moreover, to permit scaling, known locating devices require a maxicode of predetermined size (1 square inch).
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a maxicode locating method for recognizing target elements with apparent dimensions and degrees of ovaling varying within a wide range of values and which involves no restrictions as regards the vision system.
It is a further object of the present invention to provide a method capable of also locating damaged target elements, e.g. target elements with missing ring portions.
According to the present invention, there is provided a method of locating an optical code of the maxicode type comprising a number of geometrically defined elements associated with coded information and a central target element defined by a number of concentric rings separated by annular spaces of a different colour from the rings; the innermost ring surrounding a circular central space defining the center of the target element; the method comprising the steps of: acquiring an image containing an image of said optical code; and binary-coding the acquired image to generate a binary-coded image defined by elementary representation units having a first binary value or a second binary value; the rings and spaces being represented by elementary representation units having first and second binary values respectively; characterized by comprising the steps of: examining oriented portions of said binary-coded image, each portion comprising a sequence of white and black elements, each black element being defined by at least one elementary representation unit having said first binary value, and each white element being defined by at least one elementary representation unit having said second binary value; performing a sequence control step to locate, in each examined portion of the image, at least one predetermined sequence of white and black elements; performing an assigning step in which the portions of said image containing a sequence of white and black elements corresponding to said predetermined sequence are recognized as portions intersecting the center of said target element.
More specifically, there is provided a pattern control step to determine whether the dimensions, in particular the widths, of the white and black elements in the examined sequence are relatable to a predetermined given sequence of a whole target element. Provision is also made for a further sequence control step, which is performed in the event of a negative outcome of said sequence control step; said further sequence control step comprising the step of locating, in each examined portion, at least one further predetermined sequence of white and black elements relating to a central portion of a modified, in particular damaged, target element.
REFERENCES:
patent: 4876732 (1989-10-01), Miyagawa et al.
patent: 5515447 (1996-05-01), Zheng et al.
patent: 5637849 (1997-06-01), Wang et al.
patent: 5655030 (1997-08-01), Suzuki
patent: WO95/34043 (1995-12-01), None
Amorosi Stefano
Saporetti Claudio
Datalogic S.p.A.
Hall Priddy Myers & Vande Sande
Johns Andrew W.
Nakhjavan Shervin
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