Optimized technique for decoding a bar code from an image of an

Details Optimized technique for decoding a bar code from an image of an Optimized technique for decoding a bar code from an image of an

1997-08-27

1999-09-07

Hajec, Donald

Registers

Coded record sensors

Particular sensor structure

23546201, G06K 710

Patent

active

059490535

DESCRIPTION:

BRIEF SUMMARY
FILED OF THE INVENTION

The invention relates to improvements in barcode decoding, and more particularly, to the decoding of barcodes from pixel-based images.


DESCRIPTION OF RELATED ART

Barcodes are very widely used nowadays to associate coded information with a wide variety of objects, such as items for sale in shops, letters and parcels during the postal sorting process and manufactured goods both during the manufacturing process itself and in distribution. The advantage of barcodes is that they lend themselves particularly well to automated optical reading.
The decoding of optically-sensed barcodes is a mature technology and performance near 100% can be achieved using high quality barcode labels and laser scanning technology.
However, in practice many barcode labels are poorly printed, or physically damaged in the course of handling, which leads to a degradation in the decoding process.
Furthermore, many modern applications of barcode technology require barcodes to be identified from pixel-based images generated by, for instance, CCD (Charge Coupled Device) cameras. Such cameras have a lower resolution than the laser scanners conventionally used for barcode sensing. This, coupled with the fact that the spatial resolution of a captured image decreases as the speed of objects passing an image capture station increases, leads to the continued need for improvements to the decoding of barcodes from low resolution and possibly corrupted pixel-based images.
The problem of decoding barcodes from pixel-based images has generally been addressed in two ways in the prior art. Some prior art techniques concentrate on the repeated attempts to decode single reference lines through such images, relying on checksum data or inherent self-checking properties of the barcode definitions to highlight errors, when one line fails, another is tried. An example of such a technique is described in U.S. Pat. No. 5,343,028. These techniques have the drawback that in many cases there may not be a single line in the image which is correct and therefore in these cases it is not possible to decode the barcode.
Other prior art techniques sum or average the pixel values in a number of columns of the image and process the result as if it were a single grey scale scan line. Examples of these techniques can be found in EP-A-315515 in which a recursive technique is used to determine a threshold in order to identify the edges of the bars and in U.S. Pat. No. 5,276,315 in which the image is divided horizontally into a plurality of two-dimensional sections and an intensity value is assigned to each section by calculating the average intensity of all the pixels in that section, thereby forming a vertical projection of the image.
The major drawback with these known techniques is that some of the information in individual lines is lost in the summing or averaging process. These techniques are also very sensitive to spatial distortions in the source images.


SUMMARY OF THE INVENTION

This invention is directed to providing an improved technique for decoding a low-resolution pixel-based barcode image.
To achieve this, the invention provides apparatus for producing a coded representation of a barcode, for use in barcode recognition, from an image of the barcode in the form of an array comprising rows and columns of pixels stored in digital form by determining a series of bar start and bar end locations from the image, characterized by: means for determining for each column of pixels in said image the number of rows of pixels in the image in which runs of black or white pixels start or end at said column; and optimization logic for selecting the bar start and bar end locations for the series by finding an extremum in a predefined target function, the target function being a function of said number of rows of pixels in the image in which runs of black or white pixels start or end at each column, thereby optimizing the agreement on the location of the bar starts and ends between all of the rows in the image.
The use of a target function which takes

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patent: 5635699 (1997-06-01), Cherry et al.

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