Method and apparatus for high resolution decoding of encoded symbols

Abstract

A method for scanning and decoding encoded symbols comprises processing low resolution image data from a full field of view and/or high resolution image data from one or more windowed segments of the field of view to provide imaging that is easily adaptable to different types of symbols and varying environmental conditions. The scanning method can be switched between the low resolution mode and the high resolution mode automatically based on whether the low resolution data is sufficiently accurate to decode the symbol.

1 . A method for decoding an encoded digital symbol with a digital scanner, the method comprising the following steps: 
 (a) acquiring a low resolution image data set of a field of view including the symbol;    (b) evaluating the low resolution image data set to decode the symbol;    (c) acquiring a high resolution image data set of at least a portion of the field of view if the symbol has not been decoded in step (b);    (d) evaluating the high resolution image data set to decode the symbol    (e) repeating steps (c) and (d) until the symbol is decoded.    
   
   
       2 . The method as defined in  claim 1 , wherein step (c) comprises selecting a windowed portion of the field of view.  
   
   
       3 . The method as defined in  claim 2 , wherein step (e) comprises selectively moving the windowed portion through the field of view as successive high resolution sets of image data are acquired.  
   
   
       4 . The method as defined in  claim 1 , wherein step (b) further comprises the step of evaluating the low resolution image data set to detect a location of the symbol in the low resolution image and using the location to determine the portion of the field of view for acquiring the high resolution image data set.  
   
   
       5 . The method as defined in  claim 1 , wherein step (e) includes selectively windowing through the field of view in a predetermined pattern.  
   
   
       6 . The method as defined in  claim 1 , wherein the low resolution image is acquired by sub-sampling the pixels in a sensor array.  
   
   
       7 . The method as defined in  claim 1 , wherein the high resolution image is acquired by sampling all of the pixels in the selected portion of the array.  
   
   
       8 . A method for decoding an encoded digital symbol with a digital scanner, the method comprising the following steps: 
 (a) acquiring a high resolution image data set of a field of view of the scanner;    (b) storing the high resolution image data set;    (c) sub-sampling the high resolution data set and evaluating the resultant low resolution image data set to decode the symbol;    (d) selecting windowed portions of the high resolution image data set if the symbol has not been decoded in step (c);    (e) evaluating the windowed portion of the high resolution image data set to decode the symbol; and    (f) repeating steps (d) and (e) until the symbol is decoded.    
   
   
       9 . The method as defined in  claim 8 , wherein step (c) further comprises the step of locating a finder pattern in the low resolution image.  
   
   
       10 . The method as defined in  claim 9 , wherein step (d) further comprises the step of using the finder pattern to define the portion of the high resolution image to evaluate.  
   
   
       11 . The method as defined in  claim 8 , wherein step (e) further comprises the step of locating a finder pattern in the high resolution image.  
   
   
       12 . The method as defined in  claim 8 , wherein step (c) comprises sub-sampling the image data set at a half resolution.  
   
   
       13 . A digital scanner device for decoding an encoded digital symbol, the digital scanner device comprising: 
 an illuminator for illuminating a field of view including the encoded digital symbol;    a sensor comprising a plurality of pixels for detecting reflected light from the encoded digital symbol and to provide an electrical signal when light is detected; and    a controller connected to the sensor to selectively read at least one of the pixels into an image data acquisition set;    wherein the controller is programmed to:    (a) acquire a low resolution image data set by reading a subset of the pixels in the sensor distributed through the field of view;    (b) evaluate the low resolution image data set to decode the symbol;    (c) when the evaluation does not decode the symbol, acquire a high resolution image data set by reading a set of the pixels in a selected portion of the field of view;    (d) evaluating the high resolution image data set to decode the symbol;    (e) when the evaluation of the high resolution image data set does not decode the symbol, reposition the selected portion of the field of view and repeating (c) and (d) until the symbol is decoded.    
   
   
       14 . The digital scanner device as recited in  claim 13 , wherein the controller is further programmed to evaluate the low resolution image date set to locate a finder pattern in the encoded symbol.  
   
   
       15 . The digital scanner device as recited in  claim 14 , wherein the finder pattern is used to select the portion of the field of view for the acquisition of the high resolution image data set.  
   
   
       16 . The digital scanner device as recited in  claim 13 , wherein the sensor comprises a switch for providing a signal to the controller to selectively enable the high resolution acquisition of image data.  
   
   
       17 . The digital scanner device as recited in  claim 13 , wherein the subset of pixels acquired in the low resolution image acquisition data set comprises one fourth of the pixels in the field of view.  
   
   
       18 . The digital scanner device as recited in  claim 13 , wherein the high resolution image data set comprises data from all of the pixels in half of the field of view.  
   
   
       19 . The digital scanner device as recited in  claim 13 , wherein the set of pixels in the high resolution image data set comprises all of the pixels in the selected portion.  
   
   
       20 . The digital scanner device as recited in  claim 13 , wherein the subset of pixels in the low resolution image data set are distributed through the field of view at a lower density than the set of pixels in the high resolution image data set.  
   
   
       21 . A digital scanner for decoding symbols, the scanner comprising: 
 an image sensor comprising an array of pixels for imaging the symbol; and    a controller connected to the sensor to analyze image data acquired by the sensor, wherein the controller is programmed to selectively:    acquire and decode low resolution image data comprising a sub-sampling of pixels in the field of view;    acquire and decode high resolution image data comprising a full sampling of pixels in at least a portion of the field of view; and    acquire low resolution image data and switch to high image resolution data when decoding of the low resolution image data fails.    
   
   
       22 . The digital scanner as recited in  claim 21 , wherein the sensor is a high resolution sensor having a resolution of at least 1280 by 1024 pixels.  
   
   
       23 . The digital scanner as recited in  claim 21 , wherein the controller is programmed to window through the field of view when acquiring high resolution image data.  
   
   
       24 . The digital scanner as recited in  claim 21 , wherein the controller is programmed to acquire image data for all of the pixels in the field of view when acquiring high resolution image data.  
   
   
       25 . The digital scanner as recited in  claim 21 , further comprising a switch for selecting between low resolution image acquisition, high resolution image acquisition, and switching between low and high resolution image acquisition.  
   
   
       26 . A method for analyzing image data of an encoded symbol, comprising the following steps: 
 (a) applying a decoding algorithm to analyze a sub-sampled image data set of the field of view;    (b) if the data set is not decoded in step (a), applying a decoding algorithm to analyze a fully sampled portion of the full field of view;    (c) if the imaging parameter is not found in step (b), applying a decoding algorithm to analyze a different fully sampled portion of the field of view; and    (f) repeating steps (d) and (e) until the encoded symbol is decoded.    
   
   
       27 . The method as defined in  claim 26 , wherein step (a) comprises analyzing a half sampled image data set of the field of view.  
   
   
       28 . The method as defined in  claim 26 , wherein step (a) comprises acquiring a high resolution image data set for the full field of view and storing the high resolution image data set for processing.  
   
   
       29 . The method as defined in  claim 26 , wherein step (a) comprises acquiring a sub-sampled low resolution data set.  
   
   
       30 . The method as defined in  claim 26 , wherein steps (b) and (c) comprise acquiring a windowed high resolution data set.  
   
   
       31 . The method as defined in  claim 26 , wherein steps (a), (b) and (c) comprise evaluating the image data set to find a finder pattern in the encoded symbol.  
   
   
       32 . The method as defined in  claim 26 , wherein step (a) comprises sub-sampling the image data set at successively increasing sampling levels.