Registers – Coded record sensors – Particular sensor structure
Reexamination Certificate
1998-06-12
2001-12-11
Frech, Karl D. (Department: 2876)
Registers
Coded record sensors
Particular sensor structure
C235S462160, C235S462120
Reexamination Certificate
active
06328213
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to digitizing bar code symbol data.
Bar codes symbols are graphical objects that encode information as alternating dark and light portions, i.e., alternating regions of different light reflectivity, having specific relative widths. Bar code scanners have a wide range of applications, including reading bar code symbols provided on products. From analog electrical signals containing information representative of reflected light from the bar code symbols, the scanners produce digitized electrical signals that are typically fed to computing apparatus for decoding and providing an identification of the product to which the bar code symbol is applied. Examples of bar code symbols and scanners are found in almost every supermarket, convenience store, and department store, as well as in warehouses and factories that use bar code symbols and scanners for inventory and production control.
To decode the information, the bar code scanner must determine the relative widths of the dark and light portions to an effective degree of accuracy. Typically, if the scanner acquires a representation of the bar code symbol in which the symbol is blurred (e.g., due to optical or electrical filtering or being out-of-focus), decoding the information is difficult because the transitions between the dark and light portions (i.e., boundaries between the adjoining regions of different light reflectivity) become indistinct, which complicates the determination of the relative widths.
SUMMARY OF THE INVENTION
The invention provides a method and a system for use in digitizing blurred signals representative of bar code symbols by taking into account characteristics specific to bar code symbols, thereby improving the working range and effective resolving power of a bar code scanner by allowing the scanner to decode symbol images acquired at distances or under conditions that cause blurring of the analog signal representing the scanned symbol. Such blurring could result from out-of-focus optics, undersampling, poorly printed symbols, low pass filtering of the analog signal, or other causes. The invention also improves decoding accuracy in the presence of low and high frequency noise.
In a first aspect, the invention features processing an analog electrical signal containing information representative of reflected light from indicia including regions of different light reflectivity, wherein the analog electrical signal contains edge transitions corresponding to boundaries between adjoining regions of different light reflectivity of the indicia. Edge transitions of at least a part of the analog electrical signal are analyzed to determine a level of blur in that part of the electrical signal. Based on the determined level of blur, one of a plurality of different techniques is selected for producing the digitized signal (in which transitions in the digital level of the signal correspond to boundaries between adjoining regions of different light reflectivity of the indicia).
One or more of the following features may be incorporated in preferred implementations of the invention: The step of analyzing the edge transitions may be performed on a plurality of different parts of the analog electrical signal, and different digitizing techniques may be used on the different parts of the analog signal depending on the level of blur in the different parts of the analog signal. The edge transitions may be ranked by magnitude, and ranked edge transitions may be analyzed to detect the extent of blur represented in the part of the electrical signal. The ranking may be done by forming a histogram of the magnitudes of the edge transitions. A decision that significant blurring exists may be based on the analog electrical signal having edge transitions of substantially different magnitudes. Edge transitions having less than a threshold magnitude may be rejected. The edge transitions may be grouped into sets by magnitude, and whether the difference between a first magnitude associated with a first set and a second magnitude associated with a second set is substantially equal to the difference between the first magnitude and a third magnitude associated with a third set may be tested.
In a second aspect, the invention features determining whether an edge transition corresponds to a boundary between adjoining regions of substantially equal width; and based on the determination, producing the digitized electrical signal.
One or more of the following features may be incorporated in preferred implementations of the invention: Whether at least a part of the electrical signal is inconsistent with an alternating dark-and-light feature of a bar code symbol may be determined. If an inconsistency is found, at least that part of the analog electrical signal may be rejected. Whether a part of the analog electrical signal crosses a magnitude threshold more than once may be determined. If a part is found to cross the magnitude threshold more than once, at least that part of the analog electrical signal may be rejected. The extent to which an edge transition that corresponds to a boundary between two adjoining regions of different widths is affected by one of the regions may be determined.
In a third aspect, the invention features determining that the analog electrical signal contains edge transitions corresponding to less than all of the boundaries between the adjoining regions of different light reflectivity of the indicia; for at least part of the analog electrical signal, determining the number of boundaries that lack corresponding edges; and based on the determination about the number of boundaries that lack corresponding edges, producing the digitized electrical signal.
One or more of the following features may be incorporated in preferred implementations of the invention: Information about the relative positioning of the boundaries that lack corresponding edge transitions may be- determined. Information about the relative positioning of at least three boundaries that lack corresponding edge transitions may be determined. Information about the relative positioning of boundaries that lack corresponding edge transitions, between regions of dissimilar light reflectivity of the indicia may be determined. The relative positioning may be determined with respect to intermediate points in the regions. Information about the relative positioning of boundaries that lack corresponding edge transitions, between regions of similar light reflectivity of the indicia may be determined. Relative positioning may be determined with respect to intermediate points in the regions.
In a fourth aspect, the invention features determining the relative heights of edge transitions in the analog electrical signal; and depending on the relative heights, selecting one of a plurality of different techniques for processing the electrical signal to produce the digitized electrical signal.
In a fifth aspect, the invention features analyzing the edge transitions to classify at least a part of the analog electrical signal into one of three categories corresponding to slight, moderate, or severe levels of blur in that part of the analog electrical signal; if the part of the analog electrical signal is classified into the category corresponding a slight level of blur or into the category corresponding to a moderate level of blur, based on halfheight points in edge transitions in the analog electrical signal, determining information about the relative positions of boundaries between adjoining regions of different light reflectivity of the indicia; if the part of the analog electrical signal is classified into the category corresponding a severe level of blur, based on a determination about the number of regions disposed between regions about which relative positioning information is known, determining information about the relative positions of boundaries between adjoining regions of different light reflectivity of the indicia; and based on the information determined about the relative positions, producing the digitized electrical signal
He Duanfeng
Joseph Eugene
Frech Karl D.
Symbol Technologies Inc.
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