Patent Publication Number: US-10311271-B2

Title: Diffuse bright field illumination system for a barcode reader

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 15/230,380, titled “Diffuse Bright Field Illumination System For A Barcode Reader,” filed Aug. 6, 2016, with inventors Ming Lei and George Powell, which is a continuation of U.S. patent application Ser. No. 14/883,103, titled “Diffuse Bright Field Illumination System For A Barcode Reader,” filed Oct. 14, 2015, with inventors Ming Lei and George Powell, which is a continuation of U.S. patent application Ser. No. 14/510,341, titled “Diffuse Bright Field Illumination System For A Barcode Reader,” filed Oct. 9, 2014, with inventors Ming Lei and George Powell, which is a continuation of U.S. patent application Ser. No. 14/062,743, titled “Diffuse Bright Field Illumination System for a Barcode Reader,” filed Oct. 24, 2013, with inventors Ming Lei and George Powell. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to barcode readers. More specifically, the present disclosure relates to a barcode reader that includes multiple illumination systems, including a diffuse bright field illumination system. 
     BACKGROUND 
     A barcode is an optical machine-readable representation of information. Devices for identifying or extracting information from barcodes are generally referred to as barcode readers (or barcode scanners). An image-based barcode reader includes a camera for capturing an image of a barcode to be read. The camera includes a focusing lens that focuses light reflected from a target area onto a photo sensor array. Once an image of a barcode has been captured by the camera, a decoder processes the image and extracts the information contained in the barcode. 
     A barcode reader may include both a bright field illumination system and a dark field illumination system for illuminating a target area. A bright field illumination system typically includes multiple illumination elements (e.g., light-emitting diodes (LEDs)) with refracting and/or diffusing optics designed to direct illumination towards the target area essentially parallel to the optical axis (i.e., a line originating from the center of the focusing lens and extending outward into the center of the camera&#39;s field of view). A bright field illumination system may provide optimal illumination for a “far zone” of the camera&#39;s field of view, i.e., an area that is located relatively far away from the reader. 
     A dark field illumination system typically includes multiple LEDs with optics that project illumination from the sides of the reader towards the optical axis at an angle no more than 45 degrees from the plane that is perpendicular to the optical axis. A dark field illumination system may provide optimal illumination for a “close zone” of the field of view, i.e., an area that is nearly in contact with the reader. 
     SUMMARY 
     The present invention provides a barcode reader including an illumination system that illuminates the barcode using light that exits an optical substrate after traveling between a front major surface and a back major surface of the optical substrate in a direction transverse to an optical axis of a camera. 
     One aspect of the present disclosure is related to a barcode reader that includes a bright field illumination system, a dark field illumination system, and an additional illumination system that is better able to illuminate an area of the reader&#39;s field of view between the far zone (where bright field illumination is optimal) and the close zone (where dark field illumination is optimal). In this “center zone,” the dark field illumination may not be bright enough and the bright field illumination may not be diffuse enough for reading a barcode. 
     A diffuse bright field illumination system in accordance with the present disclosure may include an optic comprising light-diffusing characteristics and a plurality of illumination elements located on edges of the optic. The plurality of illumination elements may direct illumination into the optic. The light-diffusing characteristics of the optic may diffuse the illumination, and a majority of the diffused illumination may exit a front major surface of the optic. 
     According to one aspect of the invention, there is provided a barcode reader, comprising a bright field illumination system, a diffuse bright field illumination system, and a dark field illumination system. The bright field illumination system directs bright field illumination into a field of view of the barcode reader substantially parallel to an optical axis of the barcode reader. The bright field illumination is optimal for barcode reading within a far zone of the field of view. The diffuse bright field illumination system directs diffuse bright field illumination into the field of view substantially parallel to the optical axis. The diffuse bright field illumination is more diffuse than the bright field illumination. The diffuse bright field illumination is optimal for barcode reading within a center zone of the field of view. The dark field illumination system directs dark field illumination into the field of view at an angle no more than 45 degrees relative to a plane that is perpendicular to the optical axis. The dark field illumination is optimal for barcode reading within a close zone of the field of view. 
     Alternatively or additionally, the bright field illumination is not sufficiently diffuse and the dark field illumination is not sufficiently bright to provide optimal illumination for barcode reading within at least part of the center zone. 
     Alternatively or additionally, the center zone overlaps with the far zone and also with the close zone. 
     Alternatively or additionally, the diffuse bright field illumination system includes an optic comprising light-diffusing characteristics and a plurality of illumination elements located on corner edges of the optic. A front major surface and a back major surface of the optic are located in a plane that is substantially perpendicular to the optical axis. The back major surface and other edge surfaces of the optic are coated with an opaque reflective coating or covered with a reflective material. The back major surface may contain features that uniformly redirect the light coming from the edge to exit from the front major surface in directions substantially parallel to the optical axis. 
     Alternatively or additionally, the optic comprises a non-uniform index of refraction. 
     Alternatively or additionally, the bright field illumination system includes a first plurality of illumination elements positioned behind or before first optics. The diffuse bright field illumination system includes a second plurality of illumination elements and a second optic positioned between the second plurality of illumination elements. The dark field illumination system includes a third plurality of illumination elements positioned behind or before second optics. 
     Alternatively or additionally, the barcode reader includes a unitary optical component. The bright field illumination system includes a first plurality of illumination elements positioned behind curved regions of the unitary optical component. The diffuse bright field illumination system includes a second plurality of illumination elements and a second optic positioned between the second plurality of illumination elements. The dark field illumination system includes a third plurality of illumination elements positioned behind diffusion regions of the unitary optical component. 
     According to another aspect of the invention, a diffuse bright field illumination system for a barcode reader, includes an optic comprising light-diffusing characteristics and a plurality of illumination elements located on edges of the optic. The plurality of illumination elements direct illumination into the optic, the light-diffusing characteristics of the optic diffuse the illumination, and a majority of the diffused illumination exits a front major surface of the optic. 
     Alternatively or additionally, a back major surface and other external edge surfaces of the optic are coated with an opaque reflective coating. 
     Alternatively or additionally, the optic comprises a non-uniform index of refraction. 
     Alternatively or additionally, the optic includes a substrate having a first index of refraction and particles embedded within the substrate. The particles have a second index of refraction that is different than the first index of refraction. 
     Alternatively or additionally, the front major surface and a back major surface of the optic are smooth and planar. 
     Alternatively or additionally, the front major surface of the optic is smooth and planar and a back major surface of the optic is non-planar. 
     Alternatively or additionally, the optic includes a first material having a first index of refraction, the optic includes a second material having a second index of refraction that is different than the first index of refraction, and the first material is in contact with the second material along a non-planar surface. 
     Alternatively or additionally, the front major surface and a back major surface of the optic are non-planar. 
     Alternatively or additionally, the optic further comprises an aperture through which a field of view is visible to a camera of the barcode reader. 
     Alternatively or additionally, the optic further comprises a plurality of apertures that permit illumination from another illumination system within the barcode reader to be directed into a field of view without being affected by the optic. 
     Alternatively or additionally, the optic further includes a plurality of apertures that permit targeting illumination to be projected into a field of view without being affected by the optic. 
     Alternatively or additionally, aperture surfaces within the optic are coated with an opaque reflective coating. 
     According to a further aspect of the invention, there is provided a barcode reader, including a dark field illumination system and a diffuse bright field illumination system. The dark field illumination system including a first plurality of illumination elements and a plurality of prism optics. Each illumination element within the first plurality of illumination elements directs first illumination substantially parallel to an optical axis of the barcode reader toward a distinct one of the plurality of prism optics, which redirects the first illumination toward the field of view at a desired angle. The diffuse bright field illumination system including a second plurality of illumination elements and an optic including light-diffusing characteristics positioned between the second plurality of illumination elements. The second plurality of illumination elements direct second illumination into the optic. The light-diffusing characteristics of the optic diffuse the second illumination. 
     Alternatively or additionally, the plurality of prism optics include chamfered ends of a plurality of light pipes. 
     Alternatively or additionally, a front major surface and a back major surface of the optic are located in a plane that is substantially perpendicular to the optical axis and the second plurality of illumination elements are located on edges of the optic. 
     According to another aspect of the invention, there is provided a barcode reader, including a housing, a camera, and an illumination system. The camera is located within the housing and is configured to capture an image of a barcode within a field of view of the camera. The field of view is directed along an optical axis. The illumination system is configured to illuminate the barcode while the camera captures the image of the barcode. The illumination system includes at least one light source and an optical substrate. The optical substrate has front and back major surfaces arranged generally perpendicular to the optical axis, and between which light introduced from the at least one light source is transferred by total internal reflection primarily in a direction transverse to the optical axis. The optical substrate includes one or more extraction features configured to extract light from the optical substrate and into the field of view. 
     Alternatively or additionally, the at least one light source introduces light into an edge of the optical substrate between the front and back major surfaces. 
     Alternatively or additionally, the at least one light source introduces light into the optical substrate through the back major surface. 
     Alternatively or additionally, the optical substrate includes at least one aperture associated with at least one of the camera, the at least one light source, and at least one targeting light source. 
     Alternatively or additionally, the optical substrate includes a reflective backing adjacent the back major surface. 
     Alternatively or additionally, the reflective backing is attached to the back major surface. 
     Alternatively or additionally, the one or more extraction features introduce a variation in an index of refraction. 
     Alternatively or additionally, the variation in the index of refraction includes at least one of one or more particles, a planar surface within the optical substrate, a variation in the surface topography of the back major surface, and a variation in the surface topography of the front major surface. 
     Alternatively or additionally, the one or more extraction features are distributed non-uniformly throughout the optical substrate. 
     Alternatively or additionally, the one or more extraction features are distributed throughout the optical substrate such that light is uniformly emitted from the front major surface of the optical substrate. 
     Alternatively or additionally, the one or more extraction features are distributed throughout the optical substrate such that light is non-uniformly emitted from the front major surface of the optical substrate in a desired intensity pattern. 
     Alternatively or additionally, the illumination system additionally includes at least one secondary light source. The light from the at least one secondary light source emitted by the illumination system converges at a point along the optical axis different from the point along the optical axis that light emitted by the illumination system from the at least one light source converges. 
     Alternatively or additionally, the illumination system additionally includes at least one secondary light source. The light from the at least one secondary light source is emitted by the illumination system at an angle closer to parallel to the optical axis than the light from the at least one light source emitted by the illumination system. 
     Alternatively or additionally, the illumination system additionally includes at least one tertiary light source. The light from the at least one tertiary light source is emitted by the illumination system at an angle closer to perpendicular to the optical axis than the light from either the at least one light source or the at least one secondary light source that is emitted by the illumination system. 
     Alternatively or additionally, the light from the at least one tertiary light source is emitted by the illumination system at an angle no more than 45° from a plane perpendicular to the optical axis. 
     Alternatively or additionally, a shape of at least one of the front major surface and the back major surface is at least one of concave, convex, and parabolic. 
     Alternatively or additionally, the shape of at least one of the front major surface and the back major surface is not symmetrical about a plane perpendicular to the optical axis. 
     Alternatively or additionally, the optical substrate has an annular shape. 
     Alternatively or additionally, the camera is located near a center of the optical substrate. 
     Alternatively or additionally, the optical substrate includes an outer edge and an inner edge and the at least one light source introduces light into the outer edge of the optical substrate. 
     Alternatively or additionally, the optical substrate comprises an outer edge comprising a chamfered surface configured to reflect light onto a path relatively perpendicular to the optical axis. 
     Alternatively or additionally, the optical substrates further includes an inner edge including a surface relatively parallel to the optical axis such that a portion of the light exits the optical substrates through the inner edge at an angle no more than 45° from a plane perpendicular to the optical axis. 
     Alternatively or additionally, the at least one light source comprises a light emitting diode (LED). 
     Alternatively or additionally, the camera further comprises a lens located along the optical axis. 
     A number of features are described herein with respect to embodiments of the invention; it will be appreciated that features described with respect to a given embodiment also may be employed in connection with other embodiments. 
     The invention includes the features described herein, including the description, the annexed drawings, and, if appended, the claims, which set forth in detail certain illustrative embodiments. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top-down view of a barcode reader in accordance with the present disclosure. 
         FIGS. 2A-2E  are front views of different embodiments of an optical substrate within the barcode reader shown in  FIG. 1 . 
         FIGS. 3A-3F  illustrates cross-sectional views of different embodiments of the optic, taken along line A-A in  FIGS. 2A-2C . 
         FIGS. 4A-4C  are cross-sectional views of alternative embodiments of the optical substrate. 
         FIG. 5  is a top-down view of another embodiment of a barcode reader in accordance with the present disclosure. 
         FIG. 6  is a top-down view of another embodiment of a barcode reader in accordance with the present disclosure. 
         FIG. 7  is a top-down view of an additional embodiment of a barcode reader in accordance with the present disclosure. 
         FIGS. 8A-8B  are cross-sectional views of tertiary light sources illuminating the optical substrate in two embodiments of the barcode reader. 
         FIG. 9  illustrates one configuration of a barcode reader in accordance with the present disclosure. 
         FIG. 10  illustrates an example of a method that may be performed by the illumination selection circuitry of the barcode reader in accordance with the present disclosure. 
         FIG. 10A  illustrates an example showing the relative size of a test image compared with a subsequent image. 
         FIG. 11  illustrates another example of a method that may be performed by the illumination selection circuitry in accordance with the present disclosure. 
         FIG. 12  illustrates one example of a single test image comprising a plurality of window images. 
         FIG. 12A  illustrates another example of a single test image comprising a plurality of window images. 
         FIG. 13  illustrates another example of a method that may be performed by the illumination selection circuitry in accordance with the present disclosure. 
         FIGS. 14A and 14B  illustrate a plurality of test images comprising a plurality of window images. 
         FIG. 15  illustrates another example of a method that may be performed by the illumination selection circuitry in accordance with the present disclosure. 
         FIG. 16  illustrates another example of a method that may be performed by the illumination selection circuitry in accordance with the present disclosure. 
         FIG. 17  illustrates another example of a method that may be performed by the illumination selection circuitry in accordance with the present disclosure. 
         FIG. 18  illustrates various components that may be utilized in a barcode reader. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a barcode reader for imaging a barcode using diffuse light. The barcode reader illuminates a barcode using an illumination system including an optical substrate. Light introduced into the optical substrate by at least one light source propagates between a front major surface and a back major surface in a direction transverse to an optical axis of a camera. Light is mixed by total internal reflection as its travels within the optical substrate and one or more extraction features included in the optical substrate allow light to be removed from the optical substrate in a directed intensity pattern. By allowing the light to mix as it propagates within the optical substrates, the propagating light loses any structure imparted onto it by the one or more light sources. By illuminating the barcode with unstructured light, it is possible to more accurately and quickly read the information contained in the imaged barcode. 
       FIG. 1  is a top-down view of a barcode reader  100  in accordance with the present disclosure. The barcode reader  100  includes a housing  101 , a camera  103 , and an illumination system  105 . The barcode reader  100  illuminates a barcode with the illumination system  105  and captures an image of the barcode using the camera  103 . 
     The camera  103  is located within the housing  101  and is configured to capture an image of a barcode within a field of view  106  of the camera  103 . The field of view  106  of the camera  103  is directed along an optical axis  114  of the camera  103 . The camera may include a photo sensor array  102  and a lens  104  that focuses illumination reflected from objects (e.g., a barcode) within the field of view  106  onto the photo sensor array  102 . The optical axis of the camera  103  may be the optical axis of the lens  104 . The camera  103  may be located near a center of the optical substrate  122  in one or more of the vertical dimension and the horizontal dimension. 
     As will be understood by one of ordinary skill in the art, the camera  103  may comprise any device capable of capturing an image of a field of view. For example, the photo sensor array  102  may comprise any detector capable of measuring or quantifying light incident on the pixel array of the detector. The detector may comprise, for example, an image sensor, CCD sensor, CMOS sensor, or any device capable of measuring or quantifying light incident on the pixel array of the detector. Similarly, the lens may comprise a single lens or series of lenses capable of focusing light onto the photo sensor array  102 . Further details regarding specific embodiments of the camera  103  are discussed below. 
     The illumination system  105  is configured to illuminate the barcode while the camera  103  captures an image of the barcode. The illumination system  105  includes at least one light source  120  and an optical substrate  122  including one or more extraction features. The optical substrate  122  has a front major surface  140  and a back major surface  138  arranged generally perpendicular to the optical axis  114 . Light is introduced from the at least one light source  120  between the front major surface  140  and the back major surface  138  ( FIGS. 3A-3F and 4A-4C ). The introduced light is transferred by total internal reflection through the optical substrate  122  between the front major surface  140  and back major surface  138  in a direction transverse to the optical axis  114 . For example, in  FIG. 1 , light propagates through the optical substrate  122  in a directional generally perpendicular to the optical axis  114 . In an alternative embodiment depicted in the cross sectional views of the optical substrate  122  of  FIGS. 3B and 3C , the at least one light source  120  introduces light into the optical substrate  122  through the back major surface  138 . In this example, the optical substrate  122  has a chamfered surface  125  that reflects light  191  through total internal reflection towards the optical axis  114 . 
     As shown in  FIG. 1 , the front view of the optical substrate  122  shown in  FIG. 2A , and the cross sectional views of the optical substrate  122  shown in  3 A, and  3 D to  3 H the at least one light source  120  may be positioned adjacent an edge  186  of the optical substrate  122 . In this configuration, as shown in  FIG. 2A , light may exit the at least one light source  120  through a single light emitting surface (light leaving the light emitting surface is represented by arrows  190   a - d ). 
     Alternatively, as shown in  FIG. 2B  the front view of the optical substrate  122  shown in  FIG. 2B , and the cross sectional views of the optical substrate  122  shown in  FIGS. 3B and 3C , the at least one light source  120  may be positioned on the back major surface  138  at locations  121   a - d . In this configuration light may exit the at least one light source  120  through a single light emitting surface (light leaving the light emitting surface) and be reflected from the chamfered edge  125  and directed towards the optical axis in direction  191 . 
     Alternatively, as shown in  FIG. 2C , the at least one light source  120  may be positioned within a recess  121  in the optical substrate  122 . In this example, the at least one light source  120  may emit light from multiple light emitting surfaces and the light from all of the light emitting surfaces may enter the optical substrate  122 . 
     Referring briefly to  FIG. 2D , the at least one light source  120  may be reduced to four (4) light sources, each of which is arranged on one exterior edge of the substrate  122  at a location that is not centered on the edge. For example, light source  120   a  may be on a side edge lower than center while light source  120   c  may be on the opposing side higher than center. Light source  120   d  may be on the top edge to the right of center which light source  120   b  may be on the bottom edge to the left of center. 
     Referring to  FIGS. 1 and 2A , the one or more light sources  120  may comprise multiple LEDs  120   a - d . As will be understood by one of ordinary skill in the art, the one or more light sources  120  may comprise any suitable light emitting device. Further, the multiple light sources  120  may emit illumination with different characteristics. For example, a portion of the light sources  120  may be white LEDs while another portion may be red LEDs, or LEDs of another color. 
     As shown in  FIG. 1 , the optical substrate  122  may comprise a substantially flat plate. For example, the optical substrate  122  may comprise a clear and colorless acrylic substrate which may be made from any other material suitable for transferring light by total internal reflection. The optical substrate  122  may be positioned within the reader  100  so that a front major surface  140  and a back major surface  138  of the optical substrate  122  are located in a plane that is substantially perpendicular to the optical axis  114 . In one embodiment, “substantially perpendicular” means within five degrees of perpendicular while in an alternative embodiment substantially perpendicular means within 15 or 20 degrees of perpendicular. 
     The light emitted from the optical substrate  122  may have different characteristics depending on the characteristics of the optical substrate  122 . For example, the optical substrate  122  may utilize refraction, diffusion, prismatic effect, and/or total internal reflection to direct more diffuse illumination  124  into the field of view  106 . Depending on the properties of the optical substrate  122  and the at least one light source  120 , the illumination system may be referred to as a diffuse bright field illumination system. The diffuse bright field imaging system may also be called a midfield illumination system or a medium field illumination system. 
     In one embodiment, the light emitted from the optical substrate  122  may be emitted substantially parallel to the optical axis  114 . For example, light may be emitted within 10 degrees of parallel to the optical axis  114 . Illumination having a smaller angle spread around the optical axis  114  may be referred to herein as diffuse bright field illumination  124 . 
     Alternatively, referring to  FIGS. 4A to 4C , the optical substrate  122  may be shaped such that the shape of the front major surface  140  and/or the back major surface  138  is concave, convex, parabolic, or some combination thereof. For example, as shown in  FIG. 4A , the optical substrate  122  has a generally concave shape front major surface  140  and a convex shaped back major surface  138 , while in  FIG. 4B , the optical substrate  122  has a generally convex shape front major surface  140  and a concave shaped back major surface  138 . The shape of at least one of the front major surface and the back major surface need not be symmetrical, but may be asymmetrical about a plane perpendicular to the optical axis  114 . In  FIG. 4C , the front major surface  140  may include three generally planar sections with the central section being generally perpendicular to the optic axis  114  and two generally planar sections adjacent to, and on opposing sides, of the central section being at an angle relative to the optic axis. In one embodiment the angle may be no greater than 45 degrees. In this embodiment the back major surface  138  may also include corresponding sections with the central section being generally perpendicular to the optic axis  114  and two generally planar sections adjacent to, and on opposing sides, of the central section being at an angle relative to the optic axis. In one embodiment, the angle of the two opposing sides of the back major surface  138  may be the same angle as the two opposing sides of the front major surface  140 . In another embodiment the angle may be different. 
     The light emitted by the configurations shown  FIGS. 4A   4 C may be emitted at different angles relative to the optical axis compared to the illumination system  105  depicted in  FIG. 1 . the illumination system  105  with these configurations is a diffuse bright field illumination system providing uniform illumination for barcodes applied to a concave/convex surface. 
     In embodiments in which the illumination system  105  emits diffuse light, the illumination may be optimal for reading a barcode that has a reflective surface that is located in a near zone  158  and/or a center zone  126  of the field of view  106 . The center zone  126  may begin at a center zone starting boundary  128  and end at a center zone ending boundary  130 . The center zone starting boundary  128  is closer to the reader  100  than a far zone starting boundary  118 . For example, the center zone starting boundary  128  may be located approximately 25 mm away from the reader  100 . The center zone ending boundary  130  may be located within the far zone  116 . Thus, the center zone  126  and the far zone  116  may overlap. 
     As discussed, the optical substrate  122  may be positioned between the one or more light sources  120 . For example, as shown in  FIG. 1, and 2A  the one or more light sources  120  may be located along an edge  186  of the optical substrate  122  that is located between the front major surface  140  and the back major surface  138 . The one or more light sources  120  introduce light into the edge  186  of the optical substrate. In  FIG. 1 , light is introduced from the one or more light sources  120  into the optical substrate  122  in a direction generally perpendicular to the optical axis  114  and generally towards the optical axis  114 . 
     For example, as shown in  FIG. 3B  the one or more light sources  120  may be located along an edge of the back major surface  138  of the optical substrate  122  with the chamfered edge  125  reflecting illumination in a direction between the front major surface  140  and the back major surface  138  in a direction generally perpendicular to the optical axis  114  and generally towards the optical axis  114 . 
     The center of the optical substrate  122  may include an opening  133  or an aperture  132  through which objects (such as a barcode) within the field of view  106  may be visible to the lens  104  and the photo sensor array  102 . As shown in  FIGS. 2A, 2B, and 2C , the aperture may be rectangular and of sufficient size such that the optical substrate  122  is not within the field of view  106  of the camera  103 . As shown in  FIG. 2E , the optical substrate  122  may have an approximately annular shape where the center opening  133  of the annular optical substrate  122  is circular and of sufficient size such that the optical substrate  122  is not within the field of view  106  of the camera  103 . 
     With continued reference to  FIG. 2C , the optical substrate  122  may have an annular shape that includes an outer edge  186  and an inner edge  187 . In the depicted embodiment multiple light sources  120   a - d  are positioned on the back major surface  140  of the optical substrate  122  and input light into the optical substrate  122  through the back major surface  140 . For example, the light sources  120   a - d  may be positioned as shown in  FIG. 3B or 3C . In  FIGS. 3B and 3C , the light sources  120   a - d  input light through the back major surface  140  in a direction approximately parallel to the optical axis  114 . After entering the optical substrate  122 , the light is reflected by a chamfered surface  125  of the outer edge  186 . The chamfered surface  125  is configured to reflect light onto a path relatively perpendicular to the optical axis  114 . In another embodiment (not shown) in which the optical substrate has an annular shape, light enters the optical substrate  122  through the outside edge  186  in a direction approximately perpendicular to the optical axis  114 . 
     To prevent the optical substrate  122  from functioning simply as a light pipe or light guide, the optical substrate  122  includes one or more extraction features  142  configured to extract light from the optical substrate  122  and into the field of view  106 . The extraction features  142  may introduce a variation in the index of refraction (i.e., a location of non-uniform index of refraction) of the optical substrate  122 . Each extraction feature  142  functions to disrupt the total internal reflection of the propagating light that is incident on the extraction feature. 
     As described above with respect to  FIGS. 2A and 2D , the illumination  190   a - d  directed into the edge  186  of the optical substrate  122  generally propagates through the optical substrate  122  due to total internal reflection. Any illumination  190   a - d  that is incident on the one or more extraction features  142  may be diffused with a first portion being diffused at an angle such that the illumination continues propagating within the optical substrate  122  (based on total internal reflection) and a second portion may be diffused at an angle (i.e., an escape angle) that overcomes total internal reflection, “escapes” the surface, and is directed into the field of view  106 . 
     The extraction of illumination through the front major surface introduced by the extraction features  142  may comprise at least one of: i) one or more particles within the substrate  122 , ii) a planar surface within the optical substrate  122 , iii) a variation in the surface topography of the back major surface  138 , and iv) a variation in the surface topography of the front major surface  138 . For example, in  FIGS. 3A and 3B , the optical substrate  122  is embedded with particles  142  having an index of refraction greater or less than the optical substrate  122 . As light travels from the edge  186  of the optical substrate  122  through total internal reflection towards a center of the optical substrate  122 , the particles  142  disrupt the total internal reflection of the light, causing a portion of the propagating light to exit through the front major surface  140 . 
     The extraction features  142  may be configured to extract light in a defined intensity profile over the front major surface  140 , such as a uniform intensity profile, and/or a defined light ray angle distribution. In  FIG. 3A , the one or more extraction features  142  are distributed non-uniformly throughout the optical substrate  122 . In this example, the one or more extraction features  142  are distributed throughout the optical substrate such that light is uniformly emitted from the front major surface  140  of the optical substrate  122 . For example, the extraction features  142  may be spread throughout the optical substrate  122  in concentrations that increase with distance from the at least one light source  120 . 
     Alternatively, in  FIG. 3B , the one or more extraction features  142  may be distributed uniformly or non-uniformly throughout the optical substrate. In this example, the one or more extraction features are distributed throughout the optical substrate such that light is not uniformly emitted from the front major surface  140  of the optical substrate  122 . Instead the light is emitted from the front major surface  140  in a desired intensity pattern. While not shown, the one or more extraction features  142  may be distributed in alternative patterns that result in the light being emitted from the front major surface  140  of the optical substrate  122  having a more structured appearance (i.e., a non-uniform intensity pattern). 
     As shown in  FIGS. 3C and 3E , the extraction features  142  may also comprise a surface variation in the topography of at least one of the front major surface  140  and the back major surface  138 . In the depicted embodiment of  FIG. 3C , the one or more extraction features  142  comprise variations in the back major surface  138  of the optical substrate  122 . In this example, the front major surface  140  of the optical substrate  122  is smooth and planar, while the back major surface  138  includes a topography of convex and concave indentations and protrusions. In the depicted embodiment of  FIG. 3E , both the back major surface  138  and the front major surface  140  include extraction features  142  comprising convex and concave indentations and protrusions. 
     These embodiments are configured to result in a homogenous output of light from the front major surface  140 . 
     The convex and concave indentations and protrusions may be: i) features  142  with specific optical properties, such as micro lenses formed by, for example, molding or laser cutting; or ii) features  142  with no specific optic properties (i.e. random) such as a roughened surface formed by any of a textured tool or sanding of the surface after molding. Further, the shape, density, or other optical properties of the extraction features  142  may increases with distance from the light source  120   a - d  in order to produce uniform illumination from the optical substrate. 
     Turning to  FIGS. 3D and 3F , the one or more extraction features  142  comprise a surface within the optical substrate  122 . In this embodiment, the optical substrate  122  may be made of two different materials  546 ,  548 . These materials  546 ,  548  may have different indices of refraction, and they may be in contact with one another. In  FIG. 3E , the contact is along a surface forming the one or more extraction features  142 . In  FIG. 3F  the contact is along a surface of convex and concave shapes, either patterned or random. Refraction at the one or more extraction features  142  directs illumination towards the front major surface  140  of the optical substrate  122  at an angle where the illumination exits the front major surface  140  towards the field of view  106 . As a variation to these embodiments, the materials  546 ,  548  may have the same index of refraction, but a material with a different index of refraction may be sandwiched between the materials  546 ,  548  at the non-planar contact surface  550 . 
     As will be understood by one of ordinary skill in the art, the optical substrate  122  and the extraction features  142  are not limited to these described embodiments. Other embodiments of the optical substrate  122  including extraction features  142  are also within the scope of the present disclosure. 
     In all of these embodiments, to further increase the quantity of illumination exiting through the front major surface  140 , a reflective backing  144  may be applied to the back major surface  138 . The reflective backing  144  may be applied uniformly such that it covers the entire back major surface  138 . The reflective backing  144  reduces the amount of light that escapes through the back major surface  138  by reflecting light back inward into the optical substrate  122 . In another embodiment, a cladding film (not shown) having an index of refraction less than the index of refraction of the optical substrate  122  is adjacent the back major surface  138 . The cladding film reduces the amount of light that escapes by reflecting light inward through total internal reflection. Similarly, all edges and surfaces of the optical substrate  122  (except for the edges  186  where the one or more light sources  120   a - d  project illumination into the optical substrate  122 ) may also be coated with a reflective backing  144 . 
     Depending on the properties of the illumination system  105 , the light emitted by the illumination system  105  from the one or more light sources  120  may not be sufficiently bright to provide optimal illumination for reading a barcode that is located farther away from the reader  100  than the center zone ending boundary  130 . For this reason, as shown in  FIG. 1 , the illumination system may comprise at least one secondary light source  108 . The at least one secondary light source  108  may be referred to as a direct bright field illumination system or a far field illumination system. Light from the at least one secondary light source  108  that is emitted by the illumination system  105  may converge at a point on the optical axis  114  that is different from the point along the optical axis  114  that light from the at least one light source  120  converges. For example, the light may be emitted by the illumination system  105  at an angle closer to parallel to the optical axis  114 , for example at a convergence angle of approximately 70 degrees) than the light from the at least one light source  120  that is emitted by the illumination system  105 . 
     The at least one secondary light source may comprise one or more LEDs  108   a - b , which may be positioned behind refracting and/or diffusing optics  110   a - b . The one or more secondary light sources  108   a - b  may direct illumination  112  into the field of view  106  substantially parallel to the optical axis  114  but with a slight convergence angle. For example, the one or more secondary light sources  108   a - d  may direct illumination into the field of view  106  at an angle from 0-30 degrees from the optical axis  114 . This illumination  112  may be referred to herein as direct bright field illumination  112  or far field illumination. As indicated above, the optical axis  114  is a line originating from the center of the focusing lens  104  and extending outward into the center of the field of view  106 . 
     Light emitted by the illumination system from the at least one secondary light source may be better suited for reading a barcode with a diffuse surface such as a paper label. Light emitted by the illumination system from the at least one secondary light source may also be optimal for reading a barcode that is located in a far zone  116  of the field of view  106 , i.e., an area of the field of view  106  that is relatively far away from the reader  100 . In other words, light from the at least one secondary light source may have sufficient intensity to illuminate a barcode that is located within the far zone  116 . The far zone  116  may begin at a far zone starting boundary  118  and end at a far zone ending boundary  119 . In one implementation, the far zone starting boundary  118  may be located about 75 mm away from the reader  100 . The bright field illumination  112  may not be sufficiently diffuse to provide optimal illumination for reading a barcode that has a reflective surface. For longer range reading, the illumination system may additionally comprise a focus lens associated with the at least one secondary light source in order to provide illumination for reading a barcode that is located farther away from the reader  100  than the far zone ending boundary  119 . 
     The optical substrate  122  may further include apertures  134   a - b  that permit the direct bright field illumination  112  (from the at least one secondary light source  108   a - b ) to be directed into the field of view  106  without being affected by the optical substrate  122 . Further yet, the optical substrate  122  may include apertures  136   a - b  that permit targeting illumination from targeting light sources  109   a - b  ( FIG. 1 ) mounted behind the optical substrate  122  to be projected into the field of view  106  without being affected by the optical substrate  122 . 
     The secondary light source may include secondary light sources  108   a ,  108   b  mounted within the housing  101 . Secondary light sources  108   a ,  108   b  are the interior of the housing  101  and may be behind tertiary light sources  152   a - b  (discussed herein) which are behind diffusors  154   a ,  154   b . The secondary light sources  108   a ,  108   b  may be in front of the tertiary light sources  152   a ,  152   b . As will be discussed with respect to  FIG. 6 , the secondary light sources may also be positioned in front of the illumination sources  120   a ,  120   b  but behind the tertiary light sources  152   a - b.    
     The surfaces of the apertures  132 ,  134   a - b ,  136   a - b  within the optical substrate  122  may be coated with an opaque reflective material (not shown). This material may cause illumination within the optical substrate  122  that is incident on the surface of a particular aperture to be reflected back into the optical substrate  122  regardless of its angle of incidence. Reflecting illumination back into the optical substrate  122  prevents illumination from exiting the optical substrate  122  through the surface of any aperture at an angle where it would illuminate the region behind the optical substrate  122 , such as directly illuminating the lens  104  and degrading the quality of the image of an object within the field of view  106 . 
     Referring again to  FIG. 1 , the illumination system  105  may also include at least one tertiary light source  152 . Light from the at least one tertiary light source  152  may be emitted by the illumination system  105  at an angle closer to perpendicular to the optical axis  114  than the light from either of the at least one light source  120  or the at least one secondary light source  108  that is emitted by the illumination system  105 . The at least one tertiary light source  152  may comprise multiple LEDs  152   a - b . Additional optics  154   a - b  may also be associated with the at least one tertiary light source  152  to direct illumination to the field of view  106 . The additional optics  154   a - b  may utilize refraction, diffusion, prismatic effect, and/or total internal reflection to direct illumination  156   a - b  into the field of view  106 . 
     The at least one tertiary light source  152  may be referred to as a dark field illumination system or a near field illumination system. Light emitted by the illumination system from the at least one tertiary light source may be referred to herein as dark field illumination  156   a - b . Light from the at least one tertiary light source may be emitted by the illumination system (i.e., the dark field illumination  156   a - b ) at an angle no more than 45° from a plane perpendicular to the optical axis  114 . 
     The dark field illumination  156   a - b  may be optimal for reading a barcode that is located within a close zone  158  of the field of view  106 . The close zone  158  may begin at a close zone starting boundary  160  and may end at a close zone ending boundary  162 . The close zone starting boundary  160  may be closer to the reader  100  than the center zone starting boundary  128 . The close zone starting boundary  160  may correspond to the face of the reader  100 . The close zone ending boundary  162  may be within the center zone  126 . Thus, the close zone  158  and the center zone  126  may overlap. However, the dark field illumination  156   a - b  may not be sufficiently bright to provide optimal illumination for reading a barcode that is located farther away from the reader  100  than the close zone ending boundary  162 . 
     In the embodiment shown in  FIG. 1 , the at least one tertiary light source  152   a - b  is mounted on circuit boards at the sides of the reader housing  101 . The optics  154   a - b  may comprise lenses, gratings, or diffusion material that diffuses the illumination  156   a - b  from the at least one tertiary light source  152 . 
     With reference to  FIG. 5 , an alternative embodiment of the barcode reader  100  is depicted. In this embodiment, the at least one tertiary light source  152   a - b  is mounted on a circuit board  792  that is substantially perpendicular to the optical axis  114 . Illumination  776   a - b  from the at least one tertiary light sources  152   a - b  is directed substantially parallel to the optical axis  114  toward prism optics  778   a - b . More specifically, the at least one tertiary light source  152   a - b  may project illumination  776   a - b  into light pipes  788   a - b , which use total internal reflection to propagate the illumination  776   a - b  toward the prism optics  778   a - b . The prism optics  778   a - b  are used to re-direct the illumination  776   a - b  toward the field of view  106  at the desired angle. 
     The light pipes  788   a - b  may comprise chamfered ends  778   a - b . These chamfered ends  778   a - b  may serve as the prism optics  778   a - b  that re-direct the illumination  776   a - b  toward the field of view  706 . Each of the chamfered ends  778   a - b  may be angled such that total internal reflection redirects the illumination  776   a - b  at a non-zero angle (e.g., 45°) relative to the plane that is perpendicular to the optical axis  714 . The illumination  776   a - b  may exit the light pipes  788   a - b  through the side facing the optical axis  714 . It should be appreciated that the light pipes  778   a - 778   b  are shown in cross section and may be on each side of the camera (all four sides, left, right, top, bottom) or may even form an annular ring around the field of view of the camera. 
     Turning to  FIG. 6 , another embodiment of the barcode reader  100  is shown. In this embodiment, the optical substrate  880  forms a protective window over optical substrate  122  and replaces the optics  110   a - b , and  154   a - b  of  FIG. 1 . In this example, the at least one tertiary light source  152  comprise LEDs  152   a - b  positioned behind diffusion regions  884   a - b  of the optical substrate  880 . The diffusion regions  884   a - b  direct dark field illumination  856   a - b  from the LEDs  152   a - b  into the field of view  806 . The curved regions  882   a - b  provide structural support for the diffusion regions  884   a - b  as well as focusing the illumination projected from secondary illumination sources  108   a ,  108   b —or secondary illumination sources  115   a ,  115   b.    
     Turning to  FIG. 7 , another embodiment of the barcode reader  100  is shown. In this embodiment, the optical substrate  881  forms a protective window over optical substrate  122  and replaces the optics  110   a - b  of  FIG. 1 . 
     As shown in  FIG. 8A , the illuminators  884  may include an optical substrate into which illumination  815   a - b  is projected by two side fire illuminators  813   a - b . The illumination  815   a - b  is internally reflected within the substrate  811  and extracted as diffuse illumination  156  from the optical substrate  811 . The optical substrate  811  may have any of the characteristics, and extraction features, as the optical substrate  122  as described with respect to  FIGS. 1, 2A -D,  3 A-F, and  4 A-C, as well as reflective coatings such that illumination propagates between a front major surface and aback major surface of optic  811  and it extracted through the front major surface as illumination  156 . 
     As shown in  FIG. 8B , the illuminators  884  may include an optical substrate  821  into which illumination  825   a - b  is projected through the back major surface by two illuminators  819   a - b . The illumination  825   a - b  is reflected from chamfered surfaces such that it propagates between the front major surface and the back major surface and is extracted as diffuse illumination  156  from the optical substrate  821 . As with optical substrate  811 , the optical substrate  821  may have any of the characteristics, and extraction features, as the optical substrate  122  as described with respect to  FIGS. 1, 2A -D,  3 A-F, and  4 A-C, as well as reflective coatings such that illumination propagates between a front major surface and aback major surface of optic  811  and it extracted through the front major surface as illumination  156 . 
     The diffusion regions  884   a - b  direct dark field illumination  856   a - b  from the LEDs into the field of view  806 . The curved regions  882   a - b  provide structural support for and focusing the illumination projected from secondary illumination sources  108   a ,  108   b —or secondary illumination sources  115   a ,  115   b . Posts  883   a  and  883   b  provide structural support for the dark field illumination systems  884   a - b  and prevent illumination from entering into the curved regions  882   a - b.    
     The previous discussion has been directed to a barcode reader that includes three different light sources: at least one secondary light source (a bright field illumination system—positioned at any of: i) closer to the field of view (i.e. in front of) than the tertiary light sources, ii) behind the tertiary light sources but in front of the diffuse bright field illumination sources; or iii) behind the diffuse bright field illumination sources and optical substrate  122 ), at least one light source (a diffuse bright field illumination system), and at least one tertiary light source (a dark field illumination system). 
     It should also be appreciated that each of these illumination sources may generate illumination with different characteristics. For example, the diffuse bright field illumination may be white LEDs (illumination with intensity across a wide spectrum of wave lengths) while the tertiary light source and the secondary light source may be red LEDs (i.e. intensity at 660 nm). 
     These three illumination systems can be independently operated such that a barcode can be read with the illumination system that provides the best illumination for reading the barcode. The discussion that follows includes some examples of how this may be accomplished. Although some of these examples involve only two different illumination systems, those examples may be extended to barcode readers that include three (or more) different illumination systems. 
     Photo sensor arrays can be operated in two modes: a rolling shutter mode of operation and a global shutter mode of operation. In the global shutter mode of operation, all photo sensors within the array (i.e., all rows of the array) may be exposed at the same time for the duration of an exposure period. During the exposure period charge may accumulate on each photo sensor based on the incident illumination. At the end of the exposure period the charge may be read out row by row. 
     In the rolling shutter mode of operation, two different signals may be utilized: a reset signal and a read signal. The reset signal may affect all of the photo sensors in a row and may put the photo sensors in a state to convert light intensity into an electrical signal. The read signal may similarly be applied to all of the photo sensors in a row, and may cause the electrical signals from each photo sensor in the row to be read electronically. 
     To capture an image, the reset signal may be applied sequentially to each row in the photo sensor array, starting at the top of the photo sensor array and proceeding row-by-row to the bottom of the photo sensor array. At some fixed time interval after this reset process has started, the readout process may begin, i.e., the read signal may be applied sequentially to each row in the photo sensor array. The “exposure” of a row of photo sensors refers to the period of time between the row of photo sensors being reset and the row of photo sensors being read. 
     The exposure time may be expressed as an integer value. The actual exposure time may be the integer value multiplied by the duration of time required to read out a single row. As such, the size of the rolling “exposure zone” may be the quantity of lines represented by the integer value. For example, if the exposure value is 10, when exposure of row  1  is complete and read out of row  1  starts, row  11  would start exposure and be exposed for the duration of read out of rows  1  to  10 . 
     In both the global shutter mode of operation and the rolling shutter mode of operation, windowing may be utilized. When windowing is utilized, only a portion of the photo sensor array (typically a horizontal window) is used for exposure and read out. Because only a portion of the photo sensor array is used for exposure, imaging a barcode using windowing is faster than using the entire photo sensor array. For example, for the global shutter mode a window of 128 rows between rows 128 and 256 may be simultaneously exposed for an exposure duration, and the accumulated charge may be read out row by row. In this example, there is no read out of rows below 128 or above 256. In the rolling shutter mode, a window of 128 rows between rows 128 and 256 may be exposed and read out using a rolling exposure zone as discussed above. Again there would not be any read out of rows below 128 or above 256. 
     As indicated above, the present disclosure relates generally to techniques for selecting the type of illumination that will be most suitable for reading a barcode in a particular situation.  FIG. 9  illustrates one configuration of a barcode reader  902  in accordance with the present disclosure. 
     The barcode reader  902  includes a photo sensor array  904 . The photo sensor array  904  may be capable of operating in accordance with a global shutter mode of operation and/or a rolling shutter mode of operation, as discussed above. The photo sensor array  904  may also be capable of utilizing windowing, as discussed above. 
     The barcode reader  902  also includes a plurality of illumination systems  906   a - b  having different illumination characteristics. Some examples of different illumination characteristics include the angle of illumination with respect to an optical axis, the intensity of illumination, the wavelength of illumination, diffusion characteristics of the illumination, etc. 
     The plurality of illumination systems  906  may include a bright field illumination system  906   a  and a dark field illumination system  906   b . The bright field illumination system  906   a  may provide illumination having characteristics designed to illuminate a target area that is located relatively far away from the reader  902 . Conversely, the dark field illumination system  906   b  may provide illumination having characteristics designed to illuminate a target area that is located relatively close to the reader  902 . 
     Of course, the number of illumination systems  906   a - b  shown in  FIG. 9  is for purposes of example only. In an alternative configuration, a barcode reader may include more than two different illumination systems. Alternatively still, a barcode reader in accordance with the present disclosure may include a single illumination system that is configured to provide illumination having different illumination characteristics (e.g., by changing the intensity, wavelength, angle, and/or diffusion characteristics of the illumination). 
     The barcode reader  902  also includes illumination selection circuitry  908 . The illumination selection circuitry  908  may be configured to perform operations that are related to selecting the type of illumination that will be most suitable for reading a barcode in a particular situation. 
       FIG. 10  illustrates an example of a method  1000  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The circuitry  908  may be configured to cause the photo sensor array  904  to capture  1002  at least one test image. For example, the photo sensor array  904  may capture  1002  a single test image  1210  (see, e.g.,  FIGS. 11 and 12 ). Alternatively, the photo sensor array  904  may capture  1002  a plurality of test images  1210   a - b  (see, e.g.,  FIGS. 13, 14A and 14B ). 
     The photo sensor array  904  may utilize windowing when the test image(s) are captured  1002 , so that the test image(s) may each be smaller than a full photo sensor array image. As used herein, the term “full photo sensor array image” refers to an image that is captured when an entire photo sensor array  904  is exposed and read out. Thus, a full photo sensor array image may include pixels corresponding to all of the photo sensors in the photo sensor array  904 . In contrast, the test image(s) may each include pixels corresponding to only a subset (i.e., less than all) of the photo sensors in the photo sensor array  904 . Capturing a test image that includes pixels corresponding to only a subset of the photo sensors in the photo sensor array  904  takes less time than capturing a full photo sensor array image. 
     The test image(s) may include at least a portion of a barcode. That is, only a portion of a barcode (i.e., less than an entire barcode) may be visible in the test image(s). Alternatively, an entire barcode may be visible in the test image(s). 
     The test image(s) may include a plurality of window images. As used herein, the term “window image” refers to an image that is smaller than a full photo sensor array image. In one possible configuration, a single test image  1210  may be captured, and the single test image  1210  may comprise a plurality of window images  1212   a - b . (See, e.g.,  FIG. 12 .) In another possible configuration, a plurality of test images  1410   a - b  may be captured, and each test image  1410  may comprise a window image  1412 . (See, e.g.,  FIGS. 14A-14B .) 
     Returning to  FIG. 10 , the circuitry  908  may be configured to provide  1004  illumination for each window image from a distinct configuration of the plurality of illumination systems  906   a - b . For example, if the barcode reader  902  includes a bright field illumination system  906   a  and a dark field illumination system  906   b , the test image(s) may include at least two different window images. The illumination for capturing a first window image may be provided solely by the bright field illumination system  906   a , and the illumination for capturing a second window image may be provided solely by the dark field illumination system  906   b.    
     Alternatively, multiple illumination systems  906   a - b  may be activated at the same time with various permutations of balanced intensity. For example, the illumination for capturing the first window image may be provided by the bright field illumination system  906   a  at 60% power and the dark field illumination system  906   b  at 40% power. The illumination for capturing the second window image may be provided by the bright field illumination system  906   a  at 40% power and the dark field illumination system  906   b  at 60% power. 
     The circuitry  908  may also be configured to determine  1006  a selected illumination system configuration. The selected illumination system configuration may be a configuration of the plurality of illumination systems  906   a - b  that yielded a window image having highest quality among the plurality of window images. 
     Generally speaking, the quality of an image of a barcode may be measured in terms of the contrast between the light cells and the dark cells within the barcode. A barcode image having relatively high contrast between dark cells and light cells may be considered to have higher quality than another barcode image having relatively low contrast between dark cells and light cells. 
     The terms “dark cells” and “light cells” are used herein because barcodes have traditionally been printed with ink. This gives barcodes the appearance of having dark cells (the portion that is printed with ink) and light cells (the unprinted substrate background, typically white). However, with direct part mark technology, ink is not always used and other techniques (e.g., laser/chemical etching and/or dot peening) may be used instead. Such techniques may be utilized to create a barcode by causing different portions of a substrate to have different reflective characteristics. When these different portions of the substrate are imaged, the resulting barcode image may have the appearance of including dark cells and light cells. Therefore, as used herein, the terms “dark cells” and “light cells” should be interpreted as applying to barcodes that are printed with ink as well as barcodes that are created using other technologies. 
     The contrast between the dark cells and the light cells in a barcode may be a function of illumination. Ideally, it is desirable to provide illumination that is consistent across the barcode and of an intensity such that the exposure of the image yields both dark cells and light cells that are within the dynamic range of the photo sensor array  904 . This yields better contrast than any of the following: (i) a dimly lit barcode; (ii) a brightly lit barcode wherein the image is washed out beyond the dynamic range of the photo sensor array  904 ; (iii) an unevenly lit barcode with bright washed out spots; or (iv) a barcode illuminated with illumination that is not compatible with the reflectivity characteristic(s) of the cells of the barcode. An example of (iv) is that illumination directed from the sides of the field of view yields a higher contrast image of a barcode formed by etching technology than does illumination parallel to the optical axis. 
     If the quality of a window image is measured in terms of contrast, determining  1006  the selected illumination system configuration may include determining which window image of the plurality of window images has highest contrast between light and dark cells of the barcode, and determining which configuration of the plurality of illumination systems  906   a - b  was activated when the window image having the highest contrast was captured. 
     Alternatively, the quality of the window images may be measured in terms of the presence of desired barcode features and/or patterns. A score or metric may be calculated for each window image. A particular window image&#39;s score/metric may indicate the number of desired barcode features and/or patterns that are detected in the window image. For example, a higher score/metric may indicate a greater number of desired barcode features and/or patterns (or vice versa). If the quality of the window images is measured in this way, then determining  1006  the selected illumination system configuration may include determining which window image of the plurality of window images has the most favorable score/metric based on features or patterns of the barcode, and determining which configuration of the plurality of illumination systems  906   a - b  was activated when the window image having the most favorable score/metric was captured. 
     The circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1008  a subsequent image using the selected illumination system configuration. The subsequent image may be captured using a global shutter or a rolling shutter mode of operation. As indicated above, the test image(s) may include only a portion of a barcode (i.e., only part of the barcode may be visible within the test image(s)). However, the subsequent image may include an entire barcode (i.e., the entire barcode may be visible within the subsequent image). 
     The subsequent image may be a full photo sensor array image. That is, the subsequent image may include pixels corresponding to all of the photo sensors in the photo sensor array  904 . Alternatively, the subsequent image may include pixels corresponding to substantially all of the photo sensors in the photo sensor array  904 . In this context, the phrase “substantially all” of the photo sensors in the photo sensor array  904  may mean at least 95% of the photo sensors in the photo sensor array  904 . 
     Alternatively still, the size of the subsequent image may be larger than the test image(s), but less than a full photo sensor array image. For example, referring to  FIG. 10A , a test image  1010  may include pixels corresponding to a first subset  1018  of the photo sensors in the photo sensor array  904 , and the subsequent image  1016  may include pixels corresponding to a second subset  1020  of the photo sensors in the photo sensor array  904 . The second subset  1020  may be larger than the first subset  1018 . However, the second subset  1020  may not include all of the photo sensors in the photo sensor array  904 . 
     The size and location of the second subset  1020  may be determined based on defined rules. For example, the size and location of the second subset  1020  may correspond to the size and location of a previously read barcode. Alternatively, the size and location of the second subset  1020  may be determined by estimating the border of the barcode  1022  in the test image  1010  based on characteristics of the barcode  1022  visible in the test image  1010 , and then setting the size and location of the second subset  1020  to include the estimated border. 
     As another example, if the dark field illumination system  906   b  yields a higher quality window image than the bright field illumination system  906   a , then the entire photo sensor array  904  may be utilized to capture the subsequent image  1016  (because the “up close” barcode  1022  will be larger). Conversely, if the bright field illumination system  906   a  yields a higher quality window image than the dark field illumination system  906   b , then a subset  1020  (e.g., a central portion) of the photo sensors within the photo sensor array  904  may be utilized to capture the subsequent image  1016  (because the “far away” barcode  1022  will be smaller). 
       FIG. 11  illustrates another example of a method  1100  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The circuitry  908  may be configured to cause the photo sensor array  904  to capture  1102  a single test image  1210  (shown in  FIG. 12 ) of at least a portion of a barcode using a rolling shutter mode of operation. Windowing may be utilized, so that the test image  1210  may be smaller than a full photo sensor array image. 
     The circuitry  908  may be configured to cycle through  1104  a plurality of configurations of the plurality of illumination systems  906   a - b  while the test image  1210  is being captured, so that each illumination system configuration is activated for a distinct time period while the test image  1210  is being captured and is not otherwise activated while the test image  1210  is being captured. Consequently, the test image  1210  may include a plurality of window images  1212   a - b . Each window image  1212  may correspond to a distinct band (e.g., a horizontal band) within the test image  1210 , and each window image  1212  may correspond to a distinct illumination system configuration. 
     For example, during exposure of a first section  1214   a  of the photo sensor array  904 , the bright field illumination system  906   a  may be activated, while the dark field illumination system  906   b  may be deactivated. During exposure of a second section  1214   b  of the photo sensor array  904 , the dark field illumination system  906   b  may be activated, while the bright field illumination system  906   a  may be deactivated. (Both the bright field illumination system  906   a  and the dark field illumination system  906   b  may be activated during exposure of the section of the photo sensor array  904  between the first section  1214   a  and the second section  1214   b , as the transition is made from one system to the other.) 
     In this example, the test image  1210  that is captured includes two distinct bands. The band corresponding to the first section  1214   a  of the photo sensor array  904  is captured using illumination solely from the bright field illumination system  906   a . Thus, this window image  1212   a  may indicate the suitability of the bright field illumination system  906   a  for capturing an image of a barcode. The band corresponding to the second section  1214   b  of the photo sensor array  904  is captured using illumination solely from the dark field illumination system  906   b . Thus, this window image  1212   b  may indicate the suitability of the dark field illumination system  906   b  for capturing a barcode. 
     In the example just described, there is one window image  1212  for each illumination system  906 . However, under some circumstances multiple window images may be captured for one or more of the illumination systems  906 . For example, during exposure of a first section of the photo sensor array  904 , the bright field illumination system  906   a  may be activated, while the dark field illumination system  906   b  may be deactivated. During exposure of a second section of the photo sensor array  904 , the dark field illumination system  906   b  may be activated, while the bright field illumination system  906   a  may be deactivated. During exposure of a third section of the photo sensor array  904 , the bright field illumination system  906   a  may be activated at reduced power (e.g., 50%), while the dark field illumination system  906   b  may be deactivated. The test image in this example may include three window images corresponding to three distinct bands within the test image. The first window image may indicate the suitability of the bright field illumination system  906   a  for capturing an image of a barcode. The second window image may indicate the suitability of the dark field illumination system  906   b  for capturing an image of a barcode. The third window image may indicate the suitability of the bright field illumination system  906   a , operating at reduced power, for capturing an image of a barcode. 
     Alternatively, both illumination systems  906   a - b  may be activated at the same time with various permutations of balanced intensity. For example, the band corresponding to the first section  1214   a  of the photo sensor array  904  may be captured using illumination from the bright field illumination system  906   a  powered at 60% and the dark field illumination system  906   b  powered at 40%. The band corresponding to the second section  1214   b  of the photo sensor array  904  may be captured using illumination from the bright field illumination system  906   a  powered at 40% and the dark field illumination system  906   b  powered at 60%. 
     In  FIG. 12 , the width of the test image  1210  and the width of the window images  1212   a ,  1212   b  within the test image  1210  are shown as being equal to the width of the photo sensor array  904 . As shown in  FIG. 12A , however, the width of the test image  1210 ′ and the width of the window images  1212   a ′,  1212   b ′ within the test image  1210 ′ may alternatively be less than the width of the photo sensor array  904 . 
     Returning to  FIG. 11 , the circuitry  908  may also be configured to determine  1106  a selected configuration of the plurality of illumination systems  906   a - b . The selected illumination system configuration may be the configuration of the plurality of illumination systems  906   a - b  that yielded a window image  1212  having highest quality among the plurality of window images  1212   a - b . The circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1108  a subsequent image using the selected illumination system configuration. 
       FIG. 13  illustrates another example of a method  1300  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The circuitry  908  may be configured to cause the photo sensor array  904  to capture  1302  a plurality of test images  1410   a - b  (shown in  FIGS. 14A-6B ) of at least a portion of a barcode. The plurality of test images  1410   a - b  may be captured  1302  using a rolling shutter mode of operation or using a global shutter mode of operation. As shown in  FIG. 14A , the plurality of test images  1410   a - b  may correspond to different sections of the photo sensor array  904 . In other words, a first section of the photo sensor array  904  may be exposed and read out in order to capture the first test image  1410   a , and a second section of the photo sensor array  904  may be exposed and read out in order to capture the second test image  1410   b . Alternatively, as shown in  FIG. 14B , the plurality of test images  1410   a - b  may correspond to the same section of the photo sensor array  904 . In other words, the same section of the photo sensor array  904  may be exposed and read out in order to capture both test images  1410   a - b.    
     The circuitry  908  may be configured to cycle through  1304  a plurality of configurations of the plurality of illumination systems  906   a - b  while the plurality of test images  1410   a - b  are being captured, so that each illumination system configuration is used as the sole source of illumination for at least one test image  1410 . Each test image  1410  may therefore be considered to be a window image  1412  corresponding to a particular illumination system configuration. In other words, the plurality of test images  1410   a - b  may comprise a plurality of window images  1412   a - b . Each window image  1412  may correspond to a different one of the plurality of test images  1410   a - b . Each window image  1412  may also correspond to a different one of the plurality of illumination system configurations. 
     For example, a first test image  1410   a  and a second test image  1410   b  may be captured. The bright field illumination system  906   a  may be activated and the dark field illumination system  906   b  may be deactivated while the first test image  1410   a  is being captured. Conversely, the dark field illumination system  906   b  may be activated and the bright field illumination system  906   a  may be deactivated while the second test image  1410   b  is being captured. The first test image  1410   a  may be considered to be a window image  1412   a  corresponding to the bright field illumination system  906   a . The second test image  1410   b  may be considered to be a window image  1412   b  corresponding to the dark field illumination system  906   b.    
     Alternatively, the bright field illumination system  906   a  may be activated at 60% power and the dark field illumination system  906   b  may be activated at 40% power while the first test image  1410   a  is being captured. The bright field illumination system  906   a  may be activated at 40% power and the dark field illumination system  906   b  may be activated at 60% power while the second test image  1410   b  is being captured. 
     Returning to  FIG. 13 , the circuitry  908  may also be configured to determine  1306  a selected illumination system configuration. The selected illumination system configuration may be the configuration of the plurality of illumination systems  906   a - b  that yielded a window image  1412  having highest quality among the plurality of window images  1412   a - b . The circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1308  a subsequent image using the selected illumination system configuration. 
     In the examples that are shown in  FIGS. 14A and 14B , the width of the test images  1410   a - b  and window images  1412   a - b  are equal to the width of the photo sensor array  904 . Alternatively, however, the width of the test images and window images may be less than the width of the photo sensor array  904 . 
       FIG. 15  illustrates another example of a method  1500  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The illumination selection circuitry  908  may be configured to cause the photo sensor array  904  to capture  1502 , using one or more test images, a plurality of window images of at least a portion of a barcode. 
     The plurality of window images may include a first window image and a second window image. The illumination selection circuitry  908  may be configured to provide  1504  illumination having a first set of illumination characteristics for capturing the first window image and illumination having a second set of illumination characteristics (different than the first set of illumination characteristics) for capturing the second window image. In this context, a “set of illumination characteristics” may include multiple illumination characteristics, or only a single illumination characteristic. Some examples of different illumination characteristics were described above. 
     Different illumination systems  906   a - b  may be utilized to provide illumination having different illumination characteristics. Alternatively, a single illumination system  906  may be utilized, but the illumination system may be capable of providing illumination having different illumination characteristics. 
     The illumination selection circuitry  908  may also be configured to determine  1606  a selected set of illumination characteristics. The selected set of illumination characteristics may be the set of illumination characteristics that yielded a window image having highest quality among the plurality of window images. 
     As indicated above, the quality of a window image may be measured in terms of image contrast. Therefore, determining  1506  the selected set of illumination characteristics may include determining which window image of the plurality of window images has highest contrast between light and dark cells of the barcode, and determining which set of illumination characteristics was utilized when the window image having the highest contrast was captured. 
     Alternatively, as indicated above, the quality of a window image may be measured in terms of the presence of desired barcode features and/or patterns. Therefore, determining  1506  the selected set of illumination characteristics may include determining which window image of the plurality of window images has the most favorable score/metric based on features or patterns of the barcode, and determining which set of illumination characteristics was utilized when the window image having the most favorable score/metric was captured. 
     The illumination selection circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1508  a subsequent image using the selected set of illumination characteristics. The subsequent image may be captured using a global shutter or a rolling shutter mode of operation. As indicated above, the test image(s) may include only a portion of a barcode. However, the subsequent image may include an entire barcode. 
       FIG. 16  illustrates another example of a method  1600  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The illumination selection circuitry  908  may be configured to cause the photo sensor array  904  to capture  1602  a single test image  1210  of at least a portion of a barcode using a rolling shutter mode of operation. Windowing may be utilized, so that the test image  1210  may be smaller than a full photo sensor array image. 
     The circuitry  908  may be configured to cycle  1604  through a plurality of sets of illumination characteristics while the test image  1210  is being captured, so that each set of illumination characteristics is utilized for a distinct time period while the single test image  1210  is being captured and is not otherwise utilized while the single test image  1210  is being captured. Consequently, the test image  1210  may include a plurality of window images  1212   a - b , where each window image  1212  corresponds to a distinct band within the test image  1210 , and where each window image  1212  corresponds to a distinct one of the plurality of sets of illumination characteristics. 
     For example, during exposure of a first section  1214   a  of the photo sensor array  904 , a first set of illumination characteristics (e.g., direct, high intensity illumination) may be utilized. The window image  1212   a  may correspond to this first set of illumination characteristics. During exposure of a second section  1214   b  of the photo sensor array  904 , a second set of illumination characteristics (e.g., angled, low intensity, diffuse illumination) may be utilized. The window image  1212   b  may correspond to this second set of illumination characteristics. 
     Alternatively, during exposure of the first section  1214   a  of the photo sensor array  904 , both the bright field illumination system  906   a  and the dark field illumination system  906   b  may be activated, with the bright field illumination system  906   a  powered at 60% and the dark field illumination system  906   b  powered at 40%. During exposure of the second section  1214   b  of the photo sensor array  904 , both the bright field illumination system  906   a  and the dark field illumination system  906   b  may be activated, with the bright field illumination system  906   a  powered at 40% and the dark field illumination system  906   b  powered at 60%. 
     The circuitry  908  may also be configured to determine  1606  a selected set of illumination characteristics. The selected set of illumination characteristics may be the set of illumination characteristics that yielded a window image  1212  having highest quality among the plurality of window images  1212   a - b . The circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1608  a subsequent image using the selected set of illumination characteristics. 
       FIG. 17  illustrates another example of a method  1700  that may be performed by the illumination selection circuitry  908  in accordance with the present disclosure. The circuitry  908  may be configured to cause the photo sensor array  904  to capture  1702  a plurality of test images  1410   a - b  of at least a portion of a barcode. The plurality of test images  1410   a - b  may be captured using a rolling shutter mode of operation or using a global shutter mode of operation. The plurality of test images may correspond to different sections of the photo sensor array  904  (as shown in  FIG. 14A ), or to the same section of the photo sensor array  904  (as shown in  FIG. 14B ). 
     The circuitry  908  may be configured to cycle  1704  through a plurality of sets of illumination characteristics while the plurality of test images  1410   a - b  are being captured, so that each set of illumination characteristics is used as the sole source of illumination for at least one test image  1410 . Each test image  1410  may therefore be considered to be a window image  1412  corresponding to a particular set of illumination characteristics. In other words, the plurality of test images  1410   a - b  may include a plurality of window images  1412   a - b , where each window image  1412  may correspond to a different one of the plurality of test images  1410   a - b , and where each window image  1412  may correspond to a different one of the plurality of sets of illumination characteristics. 
     The circuitry  908  may also be configured to determine  1706  a selected set of illumination characteristics. The selected set of illumination characteristics may be the set of illumination characteristics that yielded a window image having highest quality among the plurality of window images. The circuitry  908  may also be configured to cause the photo sensor array  904  to capture  1708  a subsequent image using the selected set of illumination characteristics. 
       FIG. 18  illustrates various components that may be utilized in a barcode reader  1802 . Any of the barcode readers  100 ,  700 ,  800 ,  902  described previously may include some or all of the components of the barcode reader  1802 . 
     The barcode reader  1802  includes a processor  1804 . The processor  1804  may be a general purpose single- or multi-chip microprocessor (e.g., an ARM), a special purpose microprocessor (e.g., a digital signal processor (DSP)), a microcontroller, a programmable gate array, etc. The processor  1804  may be referred to as a central processing unit (CPU). Although just a single processor  1804  is shown in the barcode reader  1802  of  FIG. 18 , in an alternative configuration, a combination of processors (e.g., an ARM and DSP) could be used. 
     The barcode reader  1802  also includes memory  1806  in electronic communication with the processor  1804 . That is, the processor  1804  can read information from and/or write information to the memory  1806 . The memory  1806  may be any electronic component capable of storing electronic information. The memory  1806  may be random access memory (RAM), read-only memory (ROM), magnetic disk storage media, optical storage media, flash memory devices in RAM, on-board memory included with the processor  1804 , programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable PROM (EEPROM), registers, and so forth, including combinations thereof. 
     Data and instructions may be stored in the memory  1806 . The instructions may include one or more programs, routines, sub-routines, functions, procedures, etc. The instructions may include a single computer-readable statement or many computer-readable statements. The instructions may be executable by the processor  1804  to implement one or more of the methods, operations, functions and/or procedures described above. Executing the instructions may involve the use of the data that is stored in the memory  1806 . 
     The barcode reader  1802  may include several components that may collectively be referred to as a camera  1808 . Illumination components  1810  within the camera  1808  may be activated so as to illuminate a target area. The illumination components  1810  may be configured to provide illumination having different illumination characteristics (e.g., by changing the intensity, wavelength, angle, and/or diffusion characteristics of the illumination), as described previously. The illumination components  1810  may be included in a plurality of different illumination systems having different illumination characteristics (e.g., a bright field illumination system, a diffuse bright field illumination system, and a dark field illumination system). Alternatively, the illumination components  1810  may be included within a single illumination system that is configured to provide illumination having different illumination characteristics. The illumination components  1810  may include light-emitting diodes (LEDs) and appropriate control circuitry. One or more lenses  1812  within the camera  1808  may focus light reflected from item(s) within the target area (e.g., a barcode) onto a photo sensor array  1814 . The photo sensor array  1814  may be a solid-state photo-detecting device containing a relatively large number of light-sensitive pixels that are arranged in horizontal rows and vertical columns. Read-out circuitry  1816  may electronically read the pixels within the photo sensor array  1814  in order to obtain a digital image. 
     The barcode reader  1802  may include one or more user controls  1818  that may be used to provide user input. Examples of different kinds of user controls  1818  include one or more buttons, a touchscreen, a keyboard (actual and/or virtual), a microphone, a trackball, a lightpen, etc. 
     The barcode reader  1802  may include a display  1820 . The display  1820  may utilize any suitable image projection technology, such as a liquid crystal display (LCD), light-emitting diode (LED), gas plasma, electroluminescence, etc. The display  1820  may be a touchscreen. A display controller may also be provided, for converting data stored in the memory  1806  into text, graphics, and/or moving images (as appropriate) shown on the display  1820 . 
     The barcode reader  1802  may include one or more communication interfaces for communicating with other electronic devices. For example, the barcode reader  1802  may include a wireless modem  1822  that allows the barcode reader  1802  to be connected to a wireless network. Alternatively, or in addition, the barcode reader  1802  may include a wired communication interface  1824  (e.g., a USB interface). 
     As used herein, the term “determining” encompasses a wide variety of actions and, therefore, “determining” can include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” can include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” can include resolving, selecting, choosing, establishing and the like. 
     As used herein, the phrase “based on” does not mean “based only on,” unless expressly specified otherwise. In other words, the phrase “based on” describes both “based only on” and “based at least on.” 
     One or more of the features, functions, procedures, operations, components, elements, structures, etc., described in connection with any one of the configurations described herein may be combined with one or more of the functions, procedures, operations, components, elements, structures, etc., described in connection with any of the other configurations described herein, where compatible. 
     The steps and/or actions of the methods described herein may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     The claims are not limited to the specific implementations described above. Various modifications, changes and variations may be made in the arrangement, operation and details of the implementations described herein without departing from the scope of the claims.