Method for reading barcodes in absence of location-indicating tags

Abstract

A method of recovering a waveform representing a linear bar code, the method including the steps of: moving a sensing device relative to the barcode, said sensing device having a two-dimensional image sensor; capturing, using the image sensor, a plurality of two-dimensional partial images of said bar code during said movement; determining, from at least one of the images, a direction substantially perpendicular to the bars of the bar code; determining, substantially along the direction, a waveform fragment corresponding to each captured image; determining an alignment between each pair of successive waveform fragments; and recovering, from the aligned waveform fragments, the waveform. The method is performed only in the absence of a location-indicating tag in a field of view of the image sensor.

1 . A method of recovering a waveform representing a linear bar code, the method including the steps of:
 moving a sensing device relative to the barcode, said sensing device having a two-dimensional image sensor;   capturing, using the image sensor, a plurality of two-dimensional partial images of said bar code during said movement;   determining, from at least one of the images, a direction substantially perpendicular to the bars of the bar code;   determining, substantially along the direction, a waveform fragment corresponding to each captured image;   determining an alignment between each pair of successive waveform fragments; and   recovering, from the aligned waveform fragments, the waveform,   
       wherein said method is performed only in the absence of a location-indicating tag in a field of view of the image sensor. 
     
     
         2 . The method of  claim 1 , wherein a field of view of the image sensor is smaller than the length of the bar code. 
     
     
         3 . The method of  claim 1 , wherein each partial two-dimensional image of said bar code contains a plurality of bars. 
     
     
         4 . The method of  claim 1 , further comprising the step of:
 determining a product code by decoding the waveform.   
     
     
         5 . The method  claim 1 , further comprising the step of:
 low-pass filtering the captured images in a direction substantially parallel to the bars.   
     
     
         6 . The method of  claim 1 , wherein the alignment between each pair of successive waveform fragments is determined by performing one or more normalized cross-correlations between each pair. 
     
     
         7 . The method of  claim 1 , wherein the waveform is recovered from the aligned waveform fragments by appending each fragment to a previous fragment, and skipping a region overlapping with said previous fragment. 
     
     
         8 . The method of  claim 1 , wherein the waveform is recovered from the aligned waveform fragments by:
 determining an average value for a plurality of sample values of the waveform, said sample values being contained in portions of the waveform contained in overlapping waveform fragments.   
     
     
         9 . The method of  claim 8 , wherein the average value is a weighted average, whereby sample values captured from a centre portion of each image have a higher weight than sample values captured from an edge portion of each image. 
     
     
         10 . The method of  claim 9 , wherein the sample values for each image are weighted in accordance with a Gaussian window for said image. 
     
     
         11 . The method of  claim 1 , wherein the waveform is recovered from the aligned waveform fragments by:
 aligning a current waveform fragment with a partially-constructed waveform constructed using all waveform fragments up to the current fragment.   
     
     
         12 . A sensing device for recovering a waveform representing a linear bar code, said sensing device comprising:
 a two-dimensional image sensor for capturing a plurality of partial two-dimensional images of said bar code during movement of said sensing device relative to said bar code; and   a processor configured for:
 determining, from at least one of the images, a direction substantially perpendicular to the bars of the bar code; 
 determining, substantially along the direction, a waveform fragment corresponding to each captured image; 
 determining an alignment between each pair of successive waveform fragments; and 
 recovering, from the aligned waveform fragments, the waveform, 
   
       wherein said method is configured to perform said steps only in the absence of a location-indicating tag in a field of view of the image sensor, 
     
     
         13 . The sensing device of  claim 12 , wherein a field of view of the image sensor is smaller than the length of the bar code. 
     
     
         14 . The sensing device of  claim 12 , wherein a field of view of the image sensor is sufficiently large for capturing an image of a plurality of bars. 
     
     
         15 . The sensing device of  claim 12 , wherein the processor is further configured for:
 determining the alignment between each pair of successive waveform fragments by performing one or more normalized cross-correlations between each pair.   
     
     
         16 . The sensing device of  claim 12 , wherein the processor is further configured for:
 determining an average value for a plurality of sample values of the waveform, said sample values being contained in portions of the waveform contained in overlapping waveform fragments.   
     
     
         15 . The sensing device of  claim 12  further comprising:
 communication means for communicating the waveform to a computer system. 
 
     
     
         20 . The sensing device of  claim 1 , wherein said image sensor has a field of view sufficiently large for capturing an image of a whole location-indicating tag disposed on a surface, and said processor is further configured for determining a position of the sensing device relative to the surface using the imaged tag when said location-indicating tag is contained in a field of view of the image sensor.