U.S. patent application number 10/911209 was filed with the patent office on 2006-02-09 for method and apparatus for high resolution decoding of encoded symbols.
Invention is credited to William H. Equitz, Laurens Ninnink.
Application Number | 20060027657 10/911209 |
Document ID | / |
Family ID | 35756470 |
Filed Date | 2006-02-09 |
United States Patent
Application |
20060027657 |
Kind Code |
A1 |
Ninnink; Laurens ; et
al. |
February 9, 2006 |
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.
Inventors: |
Ninnink; Laurens; (US)
; Equitz; William H.; (Waban, MA) |
Correspondence
Address: |
ARTHUR J. O'DEA;LEGAL DEPARTMENT
COGNEX CORPORATION
ONE VISION DRIVE
NATICK
MA
01760-2077
US
|
Family ID: |
35756470 |
Appl. No.: |
10/911209 |
Filed: |
August 4, 2004 |
Current U.S.
Class: |
235/454 ;
235/462.11; 235/462.41 |
Current CPC
Class: |
G06K 7/14 20130101; G06K
7/1465 20130101 |
Class at
Publication: |
235/454 ;
235/462.41; 235/462.11 |
International
Class: |
G06K 7/10 20060101
G06K007/10 |
Claims
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.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to scanning devices for
decoding symbols, and more particularly to a method for decoding
symbols using a high resolution image sensor.
[0002] Encoded symbols such as ID bar codes, 2D bar codes and
symbols, such as data matrixes, are commonly found in retail,
industrial, and other applications for identifying labeled goods,
products, or components. Bar codes are symbols that comprise a
series of alternating white and black elongated bars or modules
which are aligned to define a code. Data matrixes comprise a
plurality of black and white cells which are arranged in a two
dimensional code. Both of these types of codes, as well as various
other symbols known in the art, can be found in applications for
identifying goods, applied either to a label or printed directly on
a part or component.
[0003] Devices for reading encoded symbols typically employ an
illumination device for shining light on the symbol and a camera
module for detecting the reflected light. The camera module
typically has a fixed focal distance and a fixed aperture,
providing a fixed field of view (FOV). The sensor in the camera
module is arranged as an array of pixels defined by a row and
column location in the sensor, and typically employs a low
resolution sensor having a VGA resolution of about 640.times.480
pixels. In operation, the scanning device illuminates the symbol,
and the camera module detects image data as reflected light from
the illuminated area in the field of view. A decoding algorithm is
employed to decode the symbol based on the acquired data.
[0004] The decoding algorithms used in these devices require a
certain number of pixels per symbology element bar or cell for
accurate decoding. When the FOV is fixed, as is typically found in
current devices, there is therefore a direct relationship between
the resolution of the sensor (in pixels per row/column) and the
smallest readable code (measured in mm/module for bar codes and
mm/cell for matrix codes). To provide the appropriate resolution,
and both fast and accurate decode times for different types of
symbols, readers are therefore typically specialized for a specific
application and include lenses and/or focal distances which are
fixed based on the expected application and the expected type of
symbol to be read.
[0005] These specialized devices are useful for work stations where
a single type of symbol is expected to be read under stable
environmental conditions. However, it is often desirable to read
different types of marks at a single station. To allow for reading
of different types of symbols under varying environmental
conditions, therefore, handheld readers are also available which
use autofocus or bifocal lenses. These devices extend the reading
range of the scanning device and therefore provide a variety of
magnifications, thereby providing more versatile scanning capable
at reading different types of symbols. Scanning devices including
autofocus and bifocal lenses, however, can also be expensive and
difficult to use. Autofocus and bifocal devices, for example, are
highly dependent on the skill of the operator, as the operator must
manually position the reader depending on the type of code being
read. Furthermore, as the reader is moved further away, proper
illumination of the symbol becomes problematic, rendering accurate
reading difficult. These devices, therefore, require frequent
re-positioning, are time-consuming to use, and can also be
inaccurate.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0006] FIG. 1 is a perspective view of a scanning system including
a scanning device and host computer.
[0007] FIG. 2 is an exploded view of the scanning device of FIG.
1.
[0008] FIG. 3 is a block diagram of a control system for the
scanning device of FIG. 2.
[0009] FIG. 4 is a simplified view of the image sensor of FIG.
3.
[0010] FIG. 5 is a flow chart illustrating the steps for decoding a
symbol in accordance with one embodiment of the invention.
[0011] FIG. 6 is a view of the simplified image sensor of FIG. 4
illustrating a low resolution image acquisition of a partial read
of the full field of view.
[0012] FIG. 7 is a view of the simplified image sensor of FIG. 4
illustrating windowing based on a finder pattern.
[0013] FIG. 8 is a view of the sensor of FIG. 4 illustrating
windowing for a high resolution data set including all of the
pixels in a portion of the field of view.
[0014] FIG. 9 is a flow chart illustrating a second embodiment of
the invention.
[0015] FIG. 10 is a flow chart illustrating a third embodiment of
the invention.
BRIEF SUMMARY OF THE INVENTION
[0016] In one aspect, the present invention provides a method for
decoding an encoded digital symbol with a digital scanner which is
useful for decoding various types of symbols in various
environmental conditions. Initially, a low resolution image data
set of a field of view including the symbol is acquired, and
evaluated to attempt to decode the symbol. If the symbol is not
decoded in the first step, a high resolution image data set of at
least a portion of the field of view is acquired and, again,
evaluated to determine if it can be decoded. If the symbol is again
not decoded, additional high resolution image data sets of windowed
portions of the field of view are acquired until the symbol is
decoded.
[0017] In another aspect of the invention, a method for decoding an
encoded digital symbol with a digital scanner is provided. Here, a
high resolution image data set of a field of view of the scanner is
acquired and stored. The data set is then sub-sampled and the
resultant low resolution image data set is evaluated in an attempt
to decode the symbol. If the decode attempt does not succeed,
windowed portions of the high resolution image data set are
selected and evaluated, windowing as appropriate until the symbol
is decoded.
[0018] In yet another aspect of the invention, a digital scanner
device is provided for decoding an encoded digital symbol. The
scanner includes 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.
The controller is programmed to acquire a low resolution image data
set by reading a subset of the pixels in the sensor distributed
through the field of view, evaluate the low resolution image data
set to decode the symbol, and, when the evaluation does not decode
the symbol, to acquire a high resolution image data set by reading
a full set of the pixels in a selected portion of the field of
view. The high resolution image data set is then evaluated to
decode the symbol and, 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 acquiring and analyzing additional
data sets until the symbol is decoded.
[0019] In still another aspect of the invention, a method for
analyzing image data is provided. The method comprises the steps of
analyzing a sub-sampled image data set of the field of view for a
selected image parameter, and, if the image parameter is not found,
analyzing a fully sampled portion of a certain field of view for
the image parameter. If the image parameter is not found in the
fully sampled portion, windowing through the data and analyzing a
different fully sampled portion of the field of view for the image
parameter until the parameter is identified.
[0020] In yet another aspect of the invention, a digital scanner
for decoding symbols is provided including 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. 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, acquire low resolution image data and
switch to acquire high image resolution data when decoding of the
low resolution image data fails.
[0021] These and other aspects of the invention will become
apparent from the following description. In the description,
reference is made to the accompanying drawings which form a part
hereof, and in which there is shown a preferred embodiment of the
invention. Such embodiment does not necessarily represent the full
scope of the invention and reference is made therefore, to the
claims herein for interpreting the scope of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring now to the figures and more particularly to FIG.
1, a handheld digital scanning device 10 useful for performing the
present invention is shown. The digital scanning device 10 is
provided in a housing 12 having a body section 16 and a grip
section 14. The body section 16 provides illumination from a distal
end to illuminate a symbol such as a bar code or data matrix, as
described below. A moveable trigger 15 provided on the housing 12
is selectively activated by an operator to provide a start signal
to an internal processor to illuminate and decode the symbol. A
visual or audio indicator, such as an indicator light or buzzer,
can also be provided to alert the user when a symbol has been
decoded. Typically, the scanning device 10 is connected through a
cable 53 to a host computer 50 which receives decode data.
[0023] Referring now to FIG. 2, an exploded view of the digital
scanning device 10 of FIG. 1 is shown. A power supply board 20 is
provided in the grip section 14 and provides power to a CPU board
22, a camera or CAM board 24, and an illumination board 28 which
are mounted in the body section 16 of the scanning device 10. An
illumination pipe 26 is coupled between the CAM board 24 and the
distal end of the body portion 16 of the digital scanner 10, and
includes a recessed end 27 sized and dimensioned to receive the
illumination board 28 which, as described more fully below,
includes a plurality of lighting elements such as light emitting
diodes or LEDs 46 arranged in a ringed configuration to provide
dark field illumination. Although the illumination board 28 is
shown arranged at the end of the illumination pipe 26, a "passive"
illumination pipe 26, which receives light at a first end adjacent
the CAM board 24 and transmits the light through the illumination
pipe 26, can also be used, as described in co-pending application
Ser. No. 10/693,626 filed Oct. 24, 2003 which is incorporated
herein by reference for its description of such devices.
[0024] Referring now also to FIG. 3 the power supply board 20
includes a power supply 30 for providing logic level power to
components in the scanner 10 including the CPU board 22, the CAM
board 24, and the illumination PC board 28. As the power supply
board 20 is provided in the grip portion 14 of the scanning device
10, a switching element 40 activatable by the trigger 15 (FIG. 1)
is provided on the power supply board 20 for receiving a user-input
signal requesting a scan. The power supply board 20 further
includes a transmitter and receiver 32 for transmitting and
receiving information from the host system 50 which, as described
above, can be connected to the scanning device 10 to receive decode
information from the digital scanning device 10, and to transmit
data to the scanning device 10. The transmitter/receiver 32 can be
any of a number of different types of communication devices
including an RS 232 connection to the host system 50 or a PS2
connection which can be connected to a wedge between the keyboard
52 and the host system 50. Various other wired and wireless
communication systems, which will be apparent to those of skill in
the art, could also be used.
[0025] Referring still to FIG. 3, the central processing unit or
CPU board 22 includes a microprocessor or controller 38, and a
memory component 34 which can include both random access memory and
read only memory. The controller 38 is connected to the memory
component 34 for storing data to and retrieving data from memory,
to the power supply board 30 for transmitting signals to and
receiving signals from the host system 50 through the
transmitter/receiver 32 and the receiving a start scan signal fro
the switch 40, to the CAM board 24 to receive acquired image data
and to operate bright field illumination 44, as described below,
and to the illumination PC board 28 for driving the light elements
46 to provide dark field illumination to a symbol to be scanned,
also as described more fully below. Although direct connections are
shown between the controller 38 and various other elements, it will
be apparent that various I/O device, A/D converters, and other
elements can also be provided for implementing communication
between the various circuit boards.
[0026] Referring still to FIG. 3 and also to FIG. 4, the CAM board
24 includes an image acquisition sensor 42 which detects light
reflected from a symbol such as a barcode or a data matrix, along
with a lens 25 and other optical elements. The image acquisition
sensor 42 is a high resolution sensor, and preferably a CMOS sensor
having a resolution of at least a 1280.times.1024 provided in an
array of pixels 62 arranged in rows and columns. The sensor 42 can
be provided on a single chip including row select logic 64 and a
column readout device 66 which provides selective access to the
individual pixels 62 within the array, and can also include
acquisition hardware elements for selectively sub-sampling the
array and windowing portions of the array. Although a number of
suitable chips are commercially available, one image sensor
component suitable in this application is the megapixel sensor sold
as part number LM9638 from National Semiconductor of Santa Clara
Calif. A bright field illumination element 44, such as an LED, can
also be provided on the CAM board 24 and can be activated by the
controller 38 independently of or in conjunction with the dark
field illumination 46 provided on the illumination board 28.
[0027] Referring again to FIGS. 2 and 3, as described above, the
illumination PC board 28 includes a plurality of light emitting
diodes or LEDs 46 arranged in a ring configuration which, as shown,
is circular. The LEDs 46 are connected to the power supply 20 and
to the CPU board 22 such that the controller 38 can selectively
control the LEDs 46, either individually, as a group, or in
connected segments, to provide illumination from the scanning
device 10. Although a circular ring array is shown here, the light
elements provided in the illumination PC board 28 can be arranged
in various configurations, and the term ring is intended to include
various polygonal, rectangular, square, oval, and other
configurations.
[0028] Referring again to FIG. 4, a simplified schematic
illustration of an image acquisition sensor 42 is shown. As
described above, the image acquisition sensor 42 comprises an array
of pixels 62 which are arranged in a row and column configuration
and which are selectively accessible by controller 38 (FIG. 3)
through row select logic 64 and a column readout 66. A full field
of view (FOV) typically includes all of the pixels 62 in the array
of the image sensor 42. As described below, various portions of the
image acquisition sensor 42 array can be accessed and individually
read out thereby providing the ability to select various portions
of the array for imaging.
[0029] Referring again to FIGS. 2, 3, and 4, in operation, the
trigger 15 on the scanning device 10 is activated by a user,
activating the switch 40 on the power supply board 20, and
providing a control signal to the controller 38 to activate at
least a portion of the LEDs 46 on the illumination board 28 and/or
the bright field illumination 44 to illuminate a symbol to be
decoded. Reflected light from the symbol is detected by the image
acquisition sensor 42 on the CAM board 24, which has a fixed lens
to provide a fixed focal distance. Image data acquired by the
sensor 42 is read out by the controller 38, and can be processed or
stored in the memory component 34 as a series of pixels 62. In
accordance with the present invention image data from the high
resolution sensor 42 is acquired or processed using subsets of
pixels to provide improved processing speeds. These subsets can be,
as described below, sub-sampled portions of the FOV in which a
portion of the available pixels across the FOV are sampled, or
windowed higher resolution data sets including all of the pixels
acquired in a segment or portion of the FOV. By selectively
processing reduced sets of data, high speed acquisition and
decoding of image data can be achieved, and the scanning device can
automatically adjust for varying symbology and environmental
condition.
[0030] To provide a full range of capabilities, the digital
scanning device 10 can, in some applications, be selectively
operated in each of a low resolution mode, in which acquired data
is sub-sampled over the entire FOV as described above, in a high
resolution mode, in which acquired data is fully sampled over a
portion of the field of view and subsequent acquisitions "window"
through the field of view, and an automatic switching mode, as
described with reference to FIGS. 5 and 8, below. Switching between
the various modes can be provided, for example, by activating the
trigger 15 repeatedly within a predetermined period of time, by
adding an additional single position or multi-position switch to
the scanning device 10, by selecting a mode from the keyboard 52 of
the host computer 50, or in various other ways which will be
apparent to those of skill in the art. Although a high resolution
mode is described as employing a windowing process, a high
resolution image could also be acquired for all of the pixels in
the FOV.
[0031] Referring now to FIG. 5, one embodiment of a method for
decoding the symbol in accordance with the present invention using
automatic switching between low resolution and high resolution
modes is shown. Here, after the trigger 15 is activated the initial
set of image data acquired is a low resolution image data set in
which the pixels 62 are sub-sampled such that data is acquired from
a subset of the available pixels. The subset can include, for
example, image data acquired from reading every other row and
column of the array, as shown in FIG. 6 where the dark pixels 67
represent sampled pixels (step 68). The first low image resolution
data set therefore includes image data for the full field of view
(FOV) but sampled at partial, typically half resolution, providing
a large but lower resolution image than would be available if data
were acquired from all the pixels 62 in the image sensor 42. The
half resolution image data set comprises each pixel that is read, a
scan of both in every other row and every other column, resulting
in a set of pixels which is one fourth cut the total number of
pixels in the image.
[0032] In step 70, the controller 38 in CPU board 24 attempts to
decode the low resolution image data set by applying a decode
algorithm. In step 72 a determination is made as to whether the
decode of the low resolution image data set has been successful. If
the decode is successful, the process is complete, the CPU board 24
activates an indicator 36 indicating that a decode has been
completed, and can also transmit decode data to the host system 50
(step 74). If the decode is not successful, the low resolution
image data set is evaluated to determine whether a finder pattern
or code, which provides symbol location information to the scanner
can be located within the symbol being analyzed (step 76). If so,
the finder pattern is used to set windowing parameters (step 78)
for acquiring additional high resolution image data sets of the
symbol which are smaller in size than the FOV, but which include
most and preferably all, of the pixels 62 in at least a portion of
the sensor 42, as shown schematically in FIG. 7. Here, the symbol
is a data matrix having a finder pattern of a solid line along the
left side and bottom of the symbol and the window 91 is positioned
around the symbol.
[0033] If a finder pattern is not available, in step 80 default
windowing parameters for selecting an initial the location for
acquiring "windowed" high resolution image data is instituted.
Referring now to FIG. 8, using these default parameters, for
example, windowing will typically begin in the center 90 of the
sensor 42 and continue to a second location 92 based on data
acquired from the first window 90, which can include, as described
above, a finder pattern for locating successive windows, a default
set of windowing parameters, or identifying a portion of the symbol
which allows repositioning of the window to the second location 92.
Using any of these methods, the controller 38 attempts to zoom in
on the symbol, and to decode the symbol using the acquired high
resolution images, windowing through the FOV as appropriate in step
82, attempting to decode the symbol in step 83, changing the
windowing parameters in step 85 until the image is decoded in step
84. When the symbol is decoded, the controller 38 again activates a
user indicator to provide an indication to the operator that the
symbol has been decoded, and/or downloads decode data to the host
system 50.
[0034] Referring now to FIG. 9, a flow chart illustrating a second
embodiment of the invention is shown, in which identical steps to
those described above with reference to FIG. 5 are given like
numbers. Here, a high resolution data set is initially acquired for
the entire FOV in step 94. This high resolution image data set is
stored in memory. The controller 38 initially retrieves a low
resolution subset of the acquired data (step 96) which can be, for
example, every other pixel 67 or alternate rows and columns of
pixel data, as described above with respect to steps 72-80. If
decode is not successful, processing continues by retrieving and
windowing through high resolution sets of data (steps 85, 96 and
98), and processing of the data then continues as described above.
Here, rather than acquiring successive sets of image data through
hardware, as described above, sampling and windowing of the data is
a software function.
[0035] The present invention therefore provides a scanning device
which is capable of consistently reading a variety of symbols in a
variety of environmental conditions without the need for the
operator to adjust to either the symbol being scanned or the
surrounding conditions. By employing a higher resolution sensor and
processing smaller or lower resolution portions of the available
pixels, the invention also provides fast processing of the data,
particularly when the reduced image contains all the information
needed to decode the symbol.
[0036] Referring now to FIG. 10, although the invention is
described specifically above for use in decoding symbols, similar
methods can be used for any type of image data for which imaging
parameters can be defined and evaluated. Here, for example, a first
low resolution image set comprising sub-sampled data over the FOV
is acquired in step 100, and then analyzed for a selected parameter
in step 102. If the parameter is found, the process is complete,
and an indication of success can be provided (step 106). If the
parameter cannot be found in the image data acquired, high
resolutions images of windowed portions of the FOV re acquired
(step 108), evaluated for the parameter (step 110), changing the
window field of view (step 114) until the process is successful
(step 112) or, in the alternative, until all of the data has been
imaged at a high resolution. In alternate embodiments, successive
sub-sampled, full FOV images could be acquired at varying levels of
sampling, including, for example, a first step at a resolution of
one quarter of the pixels, a second step at a resolution of one
third of the pixels, and a third step at a resolution of half of
the pixels. Similarly, windowing could be provided for successively
larger or smaller portions of the FOV, or at successively increased
sampling levels.
[0037] Therefore, although specific embodiments have been shown and
described, it will be apparent that a number of variations could be
made within the scope of the invention. For example, although a
handheld scanner with specific hardware configuration has been
described above, it will be apparent to those of ordinary skill in
the art that many variations could be provided in the hardware and
software described. Additionally, a fixed mount scanning device
could also be used. Furthermore, although specific lighting
conditions and symbols have been described, these are not
considered to be limitations of the invention, as the methods
described herein could be employed in various applications, as will
be apparent from the description above. Additionally, although the
method has been described above for use in decoding symbols, it
will be apparent that similar methods can also be used in several
imaging applications. It should be understood therefore that the
methods and apparatuses described above are only exemplary and do
not limit the scope of the invention, and that various
modifications could be made by those skilled in the art that would
fall under the scope of the invention. To apprise the public of the
scope of this invention, the following claims are made:
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