# Patent

## Title
Barcode reader configured for multi-lens ranging

## Abstract

A barcode reader comprising a plurality of illumination systems and first and second lens assemblies may also comprise fiducial offset data that is representative of fiducial offsets. The fiducial offsets may be offsets between locations of a plurality of fiducial points within a plurality of calibration image frames captured at different calibration distances. Each calibration image frame may comprise first and second calibration images. The barcode reader may (i) select a feature that is present in a first barcode image captured via the first lens assembly and a second barcode image captured via the second lens assembly, (ii) determine a feature offset that indicates an offset between a first location of the feature within the first barcode image and a second location of the feature within the second barcode image, and (iii) estimate a barcode distance based on the feature offset and the fiducial offset data.

## Background
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 and multiple sets of imaging optics.
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.
SUMMARY
According to one aspect of the invention, there is provided a barcode reader, comprising an illumination system, a first lens assembly, and a second lens assembly. The barcode reader also includes fiducial offset data determined from a plurality of calibration image frames captured at multiple different calibration distances. Each calibration image frame comprises a first calibration image of at least one fiducial feature captured via the first lens assembly, and a second calibration image of the at least one fiducial feature captured via the second lens assembly. The barcode reader also comprises instructions executable by a processor to (i) select at least one feature that is present in both a first barcode image captured via the first lens assembly and a second barcode image captured via the second lens assembly, (ii) determine at least one feature offset, each feature offset indicating an offset between a first location of a selected feature within the first barcode image and a second location of the selected feature within the second barcode image, (iii) determine an estimated barcode distance based on the at least one feature offset and the fiducial offset data, and (iv) use the estimated barcode distance to select at least one operating parameter of the barcode reader.
Alternatively or additionally, the illumination system comprises multiple illumination sub-systems. Each sub-system may be optimal for barcode reading within a different zone of a field of view of the barcode reader. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the illumination sub-system that is optimal for barcode reading within a zone that encompasses the estimated barcode distance.
Alternatively or additionally, the multiple illumination sub-systems comprise a dark field illumination system, a diffuse bright field illumination system, and a bright field illumination system. The dark field illumination system may direct dark field illumination into a field of view of the barcode reader. The dark field illumination may be optimal for barcode reading within a near zone of the field of view. The diffuse bright field illumination system may direct diffuse bright field illumination into the field of view. The diffuse bright field illumination may be optimal for barcode reading within a center zone of the field of view. The bright field illumination system directs bright field illumination into the field of view. The bright field illumination may be optimal for barcode reading within a far zone of the field of view. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the dark field illumination system if the estimated barcode distance is within the near zone of the field of view, the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view, and the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.
Alternatively or additionally, determining the estimated barcode distance comprises calculating, by interpolation, the barcode distance between at least two calibration distances using the at least one feature offset of the at least one selected feature to interpolate between a fiducial offset at each of the at least two calibration distances.
Alternatively or additionally, the barcode reader further comprises a look-up table storing, for each of the multiple different calibration distances, the fiducial offset data representative of at least one offset between locations of the at least one fiducial feature at that calibration distance. The barcode reader may also comprise instructions executable by the processor to capture the plurality of calibration images at the multiple different calibration distances, to determine the fiducial offset data, and to store the fiducial offset data in the look-up table.
Alternatively or additionally, the fiducial offset data comprises, for each of the multiple different calibration distances, data representative of the at least one offset between a first location of the at least one fiducial feature within the first calibration image captured at the calibration distance and a second location of the at least one fiducial feature within the second calibration image captured at the calibration distance.
Alternatively or additionally, the fiducial offset data comprises, for each calibration distance of the multiple different calibration distances, average fiducial offset data for multiple different fiducial features within the first calibration image captured at the calibration distance and the second calibration image captured at the calibration distance. The fiducial offset data for a particular fiducial feature may be data representative of an offset between a first location of the fiducial feature within the first calibration image captured at the calibration distance and a second location of the fiducial feature within the second calibration image captured at the calibration distance.
Alternatively or additionally, for each fiducial feature at each calibration distance, the data representative of the offset comprises the square of the offset along a first direction between the first location of the fiducial feature within the first calibration image and the second location of the fiducial feature within the second calibration image, and the square of the offset along a second direction, perpendicular to the first direction, between the first location of the fiducial feature within the first calibration image and the second location of the fiducial feature within the second calibration image.
Alternatively or additionally, determining a feature offset for a particular selected feature comprises determining the square of the offset along a first direction between the first location of the selected feature within the first barcode image and the second location of the selected feature within the second barcode image, and determining the square of the offset along a second direction, perpendicular to the first direction, between the first location of the selected feature within the first barcode image and the second location of the selected feature within the second barcode image.
Alternatively or additionally, determining the estimated barcode distance comprises calculating, by interpolation, the barcode distance between at least two calibration distances using the at least one feature offset of the at least one selected feature to interpolate between a fiducial offset at each of the at least two calibration distances.
According to another aspect of the invention, there is provided a barcode reader comprising a first lens assembly positioned within a first optical path to image a first field of view onto a first image sensor section and a second lens assembly positioned within a second optical path to image a second field of view onto a second image sensor section. The barcode reader may also comprise instructions executed by a processor to select a feature that is present in both a first barcode image captured on the first image sensor section by the first lens assembly positioned within the first optical path and a second barcode image captured on the second image sensor section by the second lens assembly positioned within the second optical path. The barcode reader may also comprise instructions executed by the processor to determine a feature offset that indicates an offset between a first location of the feature within the first barcode image and a second location of the feature within the second barcode image. The barcode reader may also comprise instructions executed by the processor to determine an estimated barcode distance based on the feature offset and to use the estimated barcode distance to select at least one operating parameter of the barcode reader.
Alternatively or additionally, the barcode reader further comprises offset data representing an offset between the first field of view and the second field of view. Determining the estimated barcode distance based on the feature offset may comprise calculating the estimated barcode distance as a function of the feature offset and the offset data representing the offset between the first field of view and the second field of view.
Alternatively or additionally, the offset data comprises, for each of multiple different calibration distances, an offset between a first location, within a first image on the first image sensor section, of a point within the first field of view, and a second location, within a second image on the second image sensor section, of the same point within the second field of view.
Alternatively or additionally, determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.
Alternatively or additionally, the offset data comprises, for each of the multiple different calibration distances: i) the square of an offset along a first direction between a first location of a point within a first image and a second location of the point within a second image; and ii) the square of an offset along a second direction, perpendicular to the first direction, between the first location of the point within the first image and the second location of the point within the second image.
Alternatively or additionally, determining the feature offset comprises determining the square of the offset along a first direction between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image, and the square of the offset along a second direction, perpendicular to the first direction, between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image.
Alternatively or additionally, determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.
Alternatively or additionally, the barcode reader further comprises a first illumination system and a second illumination system. The first illumination system may direct first illumination into a field of view of the barcode reader. The first illumination may be optimal for barcode reading within a first zone of the field of view. The second illumination system may direct second illumination into the field of view. The second illumination may be optimal for barcode reading within a second zone of the field of view. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the first illumination system if the estimated barcode distance is within the first zone, and the second illumination system if the estimated barcode distance is within the second zone.
Alternatively or additionally, the barcode reader further comprises a dark field illumination system, a diffuse bright field illumination system, and a bright field illumination system. The dark field illumination system may direct dark field illumination into a field of view of the barcode reader. The dark field illumination may be optimal for barcode reading within a near zone of the field of view. The diffuse bright field illumination system may direct diffuse bright field illumination into the field of view. The diffuse bright field illumination may be optimal for barcode reading within a center zone of the field of view. The bright field illumination system may direct bright field illumination into the field of view. The bright field illumination may be optimal for barcode reading within a far zone of the field of view. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the dark field illumination system if the estimated barcode distance is within the near zone of the field of view, the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view, and the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.
Alternatively or additionally, the barcode reader further comprises a look-up table stored in a non-transient memory. The barcode reader may also comprise instructions executable by the processor to capture a plurality of calibration image frames at each of multiple different calibration distances. Each calibration image frame may comprise a first image on the first image sensor section inclusive of an image of a point within the first field of view, and a second image on the second image sensor section inclusive of an image of the same point within the second field of view. The barcode reader may also comprise instructions executable by the processor to determine offset data comprising, for each of the multiple different calibration distances, an offset between the image of the point within the first field of view and the image of the same point within the second field of view. The barcode reader may also comprise instructions executable by the processor to record the offset data within the look-up table.
Alternatively or additionally, the offset data comprises, for each calibration distance of the multiple different calibration distances, data representative of an offset between a first location of the point within a first calibration image captured at the calibration distance and a second location of the point within a second calibration image captured at the calibration distance.
Alternatively or additionally, the offset data comprises, for each calibration distance of the multiple different calibration distances, average offset data for multiple different points within a first calibration image captured at the calibration distance and a second calibration image captured at the calibration distance. The offset data for the point may be data representative of an offset between a first location of the point within the first calibration image captured at the calibration distance and a second location of the point within the second calibration image captured at the calibration distance.
Alternatively or additionally, for each point at each calibration distance, the data representative of the offset comprises the square of the offset along a first direction between the first location of the point within the first calibration image and the second location of the point within the second calibration image, and the square of the offset along a second direction, perpendicular to the first direction, between the first location of the point within the first calibration image and the second location of the point within the second calibration image.
Alternatively or additionally, determining the feature offset comprises determining the square of the offset along a first direction between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image, and the square of the offset along a second direction, perpendicular to the first direction, between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image.
Alternatively or additionally, determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.
Alternatively or additionally, the offset data is a numerical value derived from a distance between the first lens assembly and the second lens assembly which, when divided by the feature offset yields the estimated barcode distance.
Alternatively or additionally, the offset data comprises a plurality of numerical values. The plurality of numerical values may comprise a separate numerical value for each of multiple different calibration distances. The numerical value corresponding to a particular calibration distance may be derived from: i) a distance between the first lens assembly and the second lens assembly; and ii) an offset between an image of a point at the calibration distance on the first image sensor section and an image of the point on the second image sensor section. Dividing each numerical value of the plurality of numerical values by the feature offset may yield a plurality of distance estimations. The estimated barcode distance may be a function of at least one of the plurality of distance estimations.
Alternatively or additionally, the barcode reader further comprises a first illumination system and a second illumination system. The first illumination system may direct first illumination into a field of view of the barcode reader. The first illumination may be optimal for barcode reading within a first zone of the field of view. The second illumination system may direct second illumination into the field of view. The second illumination may be optimal for barcode reading within a second zone of the field of view. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the first illumination system if the estimated barcode distance is within the first zone, and the second illumination system if the estimated barcode distance is within the second zone.
Alternatively or additionally, the barcode reader further comprises a dark field illumination system, a diffuse bright field illumination system, and a bright field illumination system. The dark field illumination system directs dark field illumination into a field of view of the barcode reader. The dark field illumination may be optimal for barcode reading within a near zone of the field of view. The diffuse bright field illumination system directs diffuse bright field illumination into the field of view. The diffuse bright field illumination may be optimal for barcode reading within a center zone of the field of view. The bright field illumination system directs bright field illumination into the field of view. The bright field illumination may be optimal for barcode reading within a far zone of the field of view. Use of the estimated barcode distance to select at least one operating parameter of the barcode reader may comprise selecting the dark field illumination system if the estimated barcode distance is within the near zone of the field of view, the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view, and the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.
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 a front view of a barcode reader in accordance with the present disclosure.
FIG. 10 illustrates a side view of the barcode reader shown in FIG. 9.
FIG. 11 illustrates a side view of an alternative embodiment of the barcode reader shown in FIG. 9.
FIG. 12 illustrates a method that may be performed by a barcode reader in order to implement multi-lens ranging.
FIG. 13 illustrates another method that may be performed by a barcode reader in order to implement multi-lens ranging.
FIG. 14 illustrates another method that may be performed by a barcode reader in order to implement multi-lens ranging.
FIG. 15 illustrates an example of a method that may be performed by a barcode reader in order to estimate the barcode distance based on the feature offset and the fiducial offset data.
FIG. 16 illustrates another example of a method that may be performed by a barcode reader in order to estimate the barcode distance based on the feature offset and the fiducial offset data.
FIG. 17 illustrates another example of a method that may be performed by a barcode reader in order to estimate the barcode distance based on the feature offset and the fiducial offset data.
FIG. 18A illustrates an example of a calibration target.
FIG. 18B illustrates another example of a calibration target.
FIGS. 19A-C illustrate examples of calibration image frames taken at different calibration distances.
FIG. 19D is a composite of the calibration image frames shown in FIGS. 19A-C.
FIGS. 20A-C are top-down views illustrating examples of different calibration distances.
FIGS. 21A-C illustrate different examples of fiducial offset data.
FIG. 22 illustrates an example of a barcode image frame.
FIG. 23 illustrates some of the components within a barcode reader that may be used to implement multi-lens ranging.



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 FIGS. 2A, and the cross sectional views of the optical substrate 122 shown in 3A, and 3D to 3H 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 190a-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 121a-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 120a may be on a side edge lower than center while light source 120c may be on the opposing side higher than center. Light source 120d may be on the top edge to the right of center which light source 120b 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 120a-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 4C may be emitted at different angles relative to the optical axis compared to the illumination system 105 depicted in FIGS. 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 FIGS. 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 120a-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 120a-d may be positioned as shown in FIG. 3B or 3C. In FIGS. 3B and 3C, the light sources 120a-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 190a-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 190a-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 120a-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 120a-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 108a-b, which may be positioned behind refracting and/or diffusing optics 110a-b. The one or more secondary light sources 108a-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 108a-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 134a-b that permit the direct bright field illumination 112 (from the at least one secondary light source 108a-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 136a-b that permit targeting illumination from targeting light sources 109a-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 108a, 108b mounted within the housing 101. Secondary light sources 108a, 108b are the interior of the housing 101 and may be behind tertiary light sources 152a-b (discussed herein) which are behind diffusors 154a, 154b. The secondary light sources 108a, 108b may be in front of the tertiary light sources 152a, 152b. As will be discussed with respect to FIG. 6, the secondary light sources may also be positioned in front of the illumination sources 120a, 120b but behind the tertiary light sources 152a-b. 
The surfaces of the apertures 132, 134a-b, 136a-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 152a-b. Additional optics 154a-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 154a-b may utilize refraction, diffusion, prismatic effect, and/or total internal reflection to direct illumination 156a-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 156a-b. Light from the at least one tertiary light source may be emitted by the illumination system (i.e., the dark field illumination 156a-b) at an angle no more than 45° from a plane perpendicular to the optical axis 114.
The dark field illumination 156a-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 156a-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 152a-b is mounted on circuit boards at the sides of the reader housing 101. The optics 154a-b may comprise lenses, gratings, or diffusion material that diffuses the illumination 156a-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 152a-b is mounted on a circuit board 792 that is substantially perpendicular to the optical axis 114. Illumination 776a-b from the at least one tertiary light sources 152a-b is directed substantially parallel to the optical axis 114 toward prism optics 778a-b. More specifically, the at least one tertiary light source 152a-b may project illumination 776a-b into light pipes 788a-b, which use total internal reflection to propagate the illumination 776a-b toward the prism optics 778a-b. The prism optics 778a-b are used to re-direct the illumination 776a-b toward the field of view 106 at the desired angle.
The light pipes 788a-b may comprise chamfered ends 778a-b. These chamfered ends 778a-b may serve as the prism optics 778a-b that re-direct the illumination 776a-b toward the field of view 706. Each of the chamfered ends 778a-b may be angled such that total internal reflection redirects the illumination 776a-b at a non-zero angle (e.g., 45°) relative to the plane that is perpendicular to the optical axis 714. The illumination 776a-b may exit the light pipes 788a-b through the side facing the optical axis 714. It should be appreciated that the light pipes 778a-778b 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 110a-b, and 154a-b of FIG. 1. In this example, the at least one tertiary light source 152 comprise LEDs 152a-b positioned behind diffusion regions 884a-b of the optical substrate 880. The diffusion regions 884a-b direct dark field illumination 856a-b from the LEDs 152a-b into the field of view 806. The curved regions 882a-b provide structural support for the diffusion regions 884a-b as well as focusing the illumination projected from secondary illumination sources 108a, 108b —or secondary illumination sources 115a, 115b. 
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 110a-b of FIG. 1.
As shown in FIG. 8A, the illuminators 884 may include an optical substrate into which illumination 815a-b is projected by two side fire illuminators 813a-b. The illumination 815a-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, 3A-F, and 4A-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 825a-b is projected through the back major surface by two illuminators 819a-b. The illumination 825a-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, 3A-F, and 4A-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 884a-b direct dark field illumination 856a-b from the LEDs into the field of view 806. The curved regions 882a-b provide structural support for and focusing the illumination projected from secondary illumination sources 108a, 108b—or secondary illumination sources 115a, 115b. Posts 883a and 883b provide structural support for the dark field illumination systems 884a-b and prevent illumination from entering into the curved regions 882a-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).
Another embodiment of the barcode readers discussed previously will now be described in relation to FIGS. 9-11. In this embodiment the camera assembly 103 (FIGS. 1 and 5, 6 and 7) includes a first lens assembly 1904a and a second lens assembly 1904b in place of the single lens 104 in the camera assembly 103.
In the following discussion, unless otherwise indicated, the term “field of view” may refer to the field of view of the first lens assembly 1904a, the second lens assembly 1904b, the image sensor 1902, and/or the barcode reader 1900.
Reference is initially made to FIG. 9, which illustrates a front view of the barcode reader with this alternative embodiment camera assembly (referred to as barcode reader 1900). The barcode reader 1900 includes a dark field illumination system, a diffuse bright field illumination system and a bright field illumination system. (The bright field illumination system may alternatively be referred to as a direct bright field illumination system.) Each of these illumination systems directs illumination into the field of view. The illumination emitted by the dark field illumination system may be referred to herein as dark field illumination, and it may be similar to the dark field illumination systems described above in connection with FIGS. 1, 5, 6, 7, 8A, and 8B. The illumination emitted by the diffuse bright field illumination system may be referred to herein as diffuse bright field illumination, and it may be similar to the diffuse bright field illumination described above in connection with FIGS. 1, 2A, 2B, 2C, 2D, 2E, 3A, 3B, 3C, 3D, 3E, 3F, 4A, 4B, 4C, 5, 6, and 7. The illumination emitted by the bright field illumination system may be referred to herein as bright field illumination (and/or direct bright field illumination), and it may be similar to the bright field illumination 112 described above in connection FIGS. 1, 5, 6 and 7.
The dark field illumination system includes a first set of illumination sources 1952a positioned behind optics 1954a, and a second set of illumination sources 1952b positioned behind optics 1954b as described in FIG. 1, adjacent to the optics as described in FIG. 8A and/or behind the optics as described in FIG. 8B. The diffuse bright field illumination system includes an optical substrate 1922 and illumination sources 1920a-d in the manner described with respect to FIGS. 1 and 2A. Alternatively the diffuse bright field illumination system may be any of the embodiments described in FIGS. 1, 2A, 2B, 2C, 2D, 2E, 3A, 3B, 3C, 3D, 3E, 3F, 4A, 4B, 4C, 5, 6, and 7. The bright field illumination system includes illumination sources (not shown) positioned behind refracting diffusors 1910a-b in the manner described with respect to FIG. 1. Alternatively the bright field illumination system may be any of the embodiments described in FIGS. 1, 5, 6, and 7.
The optics 1954a-b may utilize refraction, diffusion, prismatic effect, and/or total internal reflection to direct the dark field illumination 156 into the field of view. If the optics 1954a-b utilize diffusion, and if the optics 1954a-b are positioned in front of the illumination sources 1952a-b (as shown in FIG. 9), then the optics 1954a-b may be referred to as back lit diffusors or back lit illumination diffusors. If the optics 1954a-b utilize both refraction and diffusion, then the optics 1954a-b may be referred to as refracting diffusors.
The dark field illumination 156 and the bright field illumination 112 may have a first illumination spectrum, and the diffuse bright field illumination 124 may have a second illumination spectrum that is different than the first illumination spectrum. More specifically, the illumination sources 1952a-b of the dark field illumination system and the illumination sources of the bright field illumination system may emit electromagnetic radiation within a first range of wavelengths, and the illumination sources 1920a-d of the diffuse bright field illumination system may emit electromagnetic radiation within a second range of wavelengths. Thus, the dark field illumination system and the bright field illumination system may each illuminate at least part of the field of view with a first illumination spectrum, and the diffuse bright field illumination system may illuminate at least part of the field of view with a second illumination spectrum. The second illumination spectrum may be broader than the first illumination spectrum. For example, the first illumination spectrum may include electromagnetic radiation primarily from 650 nm to 700 nm, and the second illumination spectrum may include electromagnetic radiation primarily from 400 nm to 700 nm.
In one embodiment, an illumination spectrum includes electromagnetic radiation primarily within a specified range if at least 90% of the electromagnetic radiation within the illumination spectrum is within the specified range. In another embodiment, an illumination spectrum includes electromagnetic radiation primarily within a specified range if at least 75% of the electromagnetic radiation within the illumination spectrum is within the specified range. In another embodiment, an illumination spectrum includes electromagnetic radiation primarily within a specified range if a majority (i.e., more than 50%) of the electromagnetic radiation within the illumination spectrum is within the specified range.
Reference is now made to FIG. 10, which illustrates a side view of the barcode reader 1900. As mentioned previously, the barcode reader 1900 includes a first lens assembly 1904a and a second lens assembly 1904b in place of the single lens 104 in the camera assembly 103. The lens assemblies 1904a-b may be focused to the same focal length.
In the depicted embodiment, the first and second lens assemblies 1904a-b each include a single optical lens. However, as used herein, the term “lens assembly” refers to a set of one or more optical lenses. Thus, in an alternative embodiment, the first lens assembly 1904a and/or the second lens assembly 1904b could include multiple optical lenses.
The barcode reader 1900 includes an image sensor 1902, which is configured to capture an image of an object (e.g., a barcode) that is positioned within the field of view. The lens assemblies 1904a-b each provide a corresponding image of the object (e.g., the barcode) on the image sensor 1902. There is a first optical path 1906a from the field of view through the first lens assembly 1904a to a first section (or portion) 1902a of the image sensor 1902. There is a second optical path 1906b (which is different from the first optical path 1906a) from the field of view through the second lens assembly 1904b to a second section (or portion) 1902b of the image sensor 1902. The first and second optical paths 1906a-b are substantially parallel to one another. The first lens assembly 1904a provides a first image of the object on the first section/portion 1902a of the image sensor 1902, and the second lens assembly 1904b provides a second image of the object on the second section/portion 1902b of the image sensor 1902.
Stated another way, the first lens assembly 1904a has a first field of view and a first optical path 1906a for illumination from the first field of view to project to a first section/portion 1902a of the image sensor 1902. The second lens assembly 1904b has a second field of view and a second optical path 1906b for illumination from the second field of view to project to a second section/portion 1902b of the image sensor 1902.
Alternatively, as shown in FIG. 11, the barcode reader 1900 may include a first image sensor 2102a and a second image sensor 2102b, which may collectively be referred to as an image sensor 2102. The first image sensor 2102a may be considered to be a first section (or portion) of the image sensor 2102, and the second image sensor 2102b may be considered to be a second section (or portion) of the image sensor 2102. The first optical path 1906a may extend from the field of view through the first lens assembly 1904a to the first image sensor 2102a. The second optical path 1906b may extend from the field of view through the second lens assembly 1904b to the second image sensor 2102b. 
Referring again to FIG. 9, the center of the optical substrate 1922 includes two openings 1912a-b through which an object (e.g., a barcode) within the field of view may be visible to the lens assemblies 1904a-b and the image sensor 1902. As shown in FIG. 9, the illumination sources 1952b are positioned to the right side (when facing the barcode reader 1900) of the lens assemblies 1906a-b. The illumination sources 1952a are positioned to the left side of the lens assemblies 1904a-b. 
The barcode reader 1900 includes control circuitry that may independently control the intensity of the illumination sources 1952a-b. More specifically, the control circuitry may be able to adjust the intensity of the illumination sources 1952a without affecting the intensity of the illumination sources 1952b, and vice versa.
Referring again to FIG. 10, the first optical path 1906a includes a filter 1910. The filter 1910 is configured to pass a spectrum of electromagnetic radiation that may be referred to herein as an acceptance spectrum of electromagnetic radiation. In addition, the filter 1910 is configured to attenuate a spectrum of electromagnetic radiation that may be referred to herein as an attenuated spectrum of electromagnetic radiation.
As indicated above, the dark field illumination 156 may have a first illumination spectrum. The first illumination spectrum may include the acceptance spectrum. In some embodiments, the first illumination spectrum may primarily be composed of the acceptance spectrum. In one embodiment, the first illumination spectrum may be identical or substantially identical (e.g., at least 90% identical) to the acceptance spectrum. In another embodiment, there may be at least a 80% overlap between the first illumination spectrum and the acceptance spectrum. In another embodiment, there may be at least a 60% overlap between the first illumination spectrum and the acceptance spectrum. The attenuated spectrum may include frequencies of visible light that are not included in the first illumination spectrum.
The first lens assembly 1904a and the filter 1910 may collectively be referred to as a first set of imaging optics. The second lens assembly 1904b may be referred to as a second set of imaging optics. The first set of imaging optics may provide a first image of an object (e.g., a barcode) on the image sensor 1902. The second set of imaging optics may provide a second image of the object on the image sensor 1902. Because the first set of imaging optics includes a filter 1910 and the second set of imaging optics does not, the first set of imaging optics and the second set of imaging optics respond differently to the different illumination spectrums of the dark field illumination system, the diffuse bright field illumination system and the bright field illumination system.
More specifically, the first set of imaging optics (including the first lens assembly 1904a and the filter 1910) may be configured so that it focuses an image of an object (e.g., a barcode) within the field of view with a superior contrast profile when the object is illuminated by the dark field illumination system and/or the bright field illumination system as compared to when the object is illuminated by the diffuse bright field illumination system.
Conversely, the second set of imaging optics (including the second lens assembly 1904b) may be configured so that it focuses an image of an object (e.g., a barcode) within the field of view with a superior contrast profile when the object is illuminated by the diffuse bright field illumination system as compared to when the object is illuminated by the dark field illumination system and/or the bright field illumination system.
As used herein, the phrase “superior contrast profile” means at least one of: (i) greater maximum amplitude between the portions of the image that are dark marks of the barcode and the portions of the image that are light marks of the barcode; and (ii) more distinct transitions between portions of the image that are dark marks of the barcode and the portions of the image that are light marks of the barcode.
Having different sets of imaging optics that respond differently to the different illumination spectrums of the dark field illumination system, the diffuse bright field illumination system and the bright field illumination system may enable the barcode reader 1900 to be used for reading barcodes that are printed (or otherwise created) using diverse technologies, including direct part marking.
The combination of the dark field illumination 156 and/or the bright field illumination 112 and the first set of imaging optics may be optimal (compared to other possible combinations of illumination and optics) for reading certain types of barcodes. For example, if the spectrum of the dark field illumination 156 and/or the bright field illumination 112 is substantially from 650-700 nm, and the acceptance spectrum of the filter 910 is primarily from 650-700 nm, the combination of the dark field illumination 156 and/or the bright field illumination 112 and the first set of imaging optics may be optimal for reading barcodes formed via copper marking on a red or green background. More specifically, in a captured image of a barcode formed via copper marking on a red background, this combination may cause the background to appear white and the barcode to appear dark. In a captured image of a barcode formed via copper marking on a green background, this combination may cause the background to appear dark and the barcode to appear white.
Conversely, the combination of the diffuse bright field illumination 124 and the second set of imaging optics may be optimal (compared to other possible combinations of illumination and optics) for reading other types of barcodes. For example, because the second set of imaging optics does not include a filter 1910, the second set of imaging optics may be preferable for reading barcodes of a certain color (e.g., red). As another example, the combination of the diffuse bright field illumination 124 and the second set of imaging optics may be optimal for reading barcodes that include dark ink on a green printed circuit board. In a captured image of such a barcode, this combination may cause the barcode to appear dark against a light background.
The filter 1910 in the first set of imaging optics may increase contrast between the portions of the image that are dark marks of the barcode and the portions of the image that are light marks of the barcode. The filter 1910 may also eliminate ambient noise. Therefore, the image that the first set of imaging optics projects onto the first section/portion 1902a of the image sensor 1902 may not have distortions caused by ambient illumination. Conversely, the image that the second set of imaging optics projects onto the second section/portion 1902b of the image sensor 1902 may include distortions caused by ambient illumination.
The barcode reader 1900 may include a housing that is similar to the housing 101 of the barcode reader 100 shown in FIG. 1. The first set of imaging optics and the second set of imaging optics may be positioned within the housing 101 such that the first optical path 1906a passes through the first set of imaging optics (including the first lens assembly 1904a and the filter 1910) to the first section (or portion) 1902a of the image sensor 1902, and the second optical path 1906b passes through the second set of imaging optics (including the second lens assembly 1904b) to the second section (or portion) 1902b of the image sensor 1902. The illumination sources 1952b of the dark field illumination system are positioned to the right side of the first and second sets of imaging optics, and the illumination sources 1952a of the dark field illumination system are positioned to the left side of the first and second sets of imaging optics.
The first section/portion 1902a of the image sensor 1902 may correspond to approximately a first half of the image sensor 1902, and the second section/portion 1902b of the image sensor 1902 may correspond to approximately a second half of the image sensor 1902. In one embodiment, the phrase “approximately . . . half of the image sensor 1902” refers to 45-55% of the image sensor 1902. In another embodiment, the phrase “approximately . . . half of the image sensor 1902” refers to 40-60% of the image sensor 1902.
The illumination sources 1952a-b and optics 1954a-b may be positioned similarly to the illumination sources 152a-b and optics 154a-b in the barcode reader 100 shown in FIG. 1. Thus, the angle and direction at which the dark field illumination system of the barcode reader 1900 emits the dark field illumination 156 may be similar to the angle and direction at which the dark field illumination system of the barcode reader 100 emits the dark field illumination 156. Accordingly, the dark field illumination system of the barcode reader 1900 may emit dark field illumination 156 towards the first optical path 1906a at an angle (which may be referred to herein as an emission angle) that is less than 45 degrees from a plane that is perpendicular to the first optical path 1906a. 
Stated another way, the dark field illumination system of the barcode reader 1900 may emit dark field illumination 156 into the field of view at an angle that is less than 45 degrees from a plane that is perpendicular to an optical path 1906a, where the optical path 1906a extends from the image sensor 1902 through the first set of imaging optics (including the first lens assembly 1904a and the filter 1910) into the center of the field of view of the first set of imaging optics.
In some embodiments, the optics 1954a-b may comprise back lit illumination diffusors that project dark field illumination 156 into the field of view at an angle that is less than 45 degrees from a plane that is perpendicular to the first optical path 1906a. 
The illumination sources 1920a-d and the optical substrate 1922 may be positioned similarly to the illumination sources 120a-d and the optical substrate 122 in the barcode reader 100 shown in FIG. 1. Thus, the angle and direction at which the diffuse bright field illumination system of the barcode reader 1900 emits the diffuse bright field illumination 124 may be similar to the angle and direction at which the diffuse bright field illumination system of the barcode reader 100 emits the diffuse bright field illumination 124. Accordingly, the diffuse bright field illumination system of the barcode reader 1900 may emit diffuse bright field illumination 124 substantially parallel to the optical paths 1906a-b. 
The illumination sources and diffusors 1910a-b of the bright field illumination system may be positioned similarly to the illumination sources 108a-b and diffusors 110a-b in the barcode reader 100 shown in FIG. 1. Thus, the angle and direction at which the bright field illumination system of the barcode reader 1900 emits the bright field illumination 112 may be similar to the angle and direction at which the bright field illumination system of the barcode reader 100 emits the bright field illumination 112. In one embodiment, the bright field illumination system of the barcode reader 1900 may emit bright field illumination 112 substantially parallel to the optical paths 1906a-b. In another embodiment, illumination from the illumination sources may enter the refracting diffusors 1910a-b at an entry angle that is substantially parallel to the second optical path 1906b. The bright field illumination 112 may exit the refracting diffusors 1910a-b toward the field of view at a converging angle (e.g., 30 degrees or less).
As shown in FIG. 10, the dark field illumination system of the barcode reader 1900 is positioned outside of the field of view. More specifically, FIG. 10 shows component 1913b, which is positioned behind illumination sources 1952b (as shown in FIG. 9). The diffuse bright field illumination system and the bright field illumination system are positioned between the lens assemblies 1904a-b and a point from which the dark field illumination system projects the dark field illumination 156 into the field of view. The diffuse bright field illumination system and the bright field illumination system are outside of the field of view.
The dark field illumination system projects the dark field illumination 156 into the field of view at a first angle from the first optical path 1906a. This first angle may be less than 45 degrees from a plane that is perpendicular to the first optical path 1906a. The diffuse bright field illumination system projects diffuse bright field illumination 124 and the bright field illumination system projects bright field illumination 112 into the field of view at a second angle from the second optical path 1906b. The second angle may be different than the first angle. For example, the second angle may be substantially parallel to the second optical path 1906b. 
In an alternative embodiment, the dark field illumination system of the barcode reader 1900 may be configured similarly to any of the other dark field illumination systems described previously. For example, in place of the optics 1954a-b, the dark field illumination system of the barcode reader 1900 may include refracting diffusors that take the form of light pipes 788a-b having chamfered ends 778a-b (as shown in FIG. 5). Illumination sources 1952a-b may project illumination 776a-b into the light pipes 788a-b at an angle (which may be referred to herein as an entry angle) that is substantially parallel to the first optical path 1906a. The chamfered ends 778a-b may re-direct the illumination 776a-b so that the dark field illumination 156 exits the light pipes 788a-b and is emitted toward the first optical path 1906a at an emission angle that is different than the entry angle. The emission angle may be less than 45 degrees from a plane that is perpendicular to the first optical path 1906a. 
In another embodiment, the dark field illumination system of the barcode reader 1900 may include an optical substrate 811 (as shown in FIG. 8A). Illumination sources 813a-b may project illumination 815a-b into the optical substrate 811 from the side, and this illumination 815a-b may be internally reflected within the substrate 811 and emitted as the dark field illumination 156. In this embodiment, the entry angle (i.e., the angle at which the illumination sources 813a-b project illumination 815a-b into the optical substrate 811) is substantially perpendicular to the emission angle (i.e., the angle at which the dark field illumination 156 is emitted toward the first optical path 1906a).
The optical substrate 1922 includes a front major surface 1940 and a back major surface 1938, which may be similar to the front major surface 140 and the back major surface 138 of the optical substrate 122. The front major surface 1940 and the back major surface 1938 are both substantially perpendicular to the optical paths 1906a, 1906b. The front major surface 1940 faces the field of view. The illumination sources 1920a-d propagate illumination between the front major surface 140 and the back major surface 138.
The optical substrate 1922 may include extraction features that are similar to any of the extraction features 142 described above in connection with the optical substrate 122. These extraction features 142 cause the diffuse bright field illumination 156 to exit the front major surface 1940 into the field of view.
As discussed above, the barcode reader 100 (shown in FIG. 1) may include a plurality of illumination systems. More specifically, the reader 100 may include a dark field illumination system that directs dark field illumination 156a-b into the field of view 106 of the reader 100, a diffuse bright field illumination system that directs diffuse bright field illumination 124 into the field of view 106, and a bright field illumination system that directs bright field illumination 112 into the field of view 106.
Each illumination system may be optimal for illuminating barcodes within a certain range of the field of view 106. For example, dark field illumination 156a-b may be optimal for illuminating barcodes located in a range that is close to the reader 100. The bright field illumination 112 may be optimal for illuminating barcodes located in a range that is far from the reader 100. The diffuse bright field illumination 124 may be optimal for illuminating barcodes located in an intermediate range that is between the close range of the dark field illumination system and the far range of the bright field illumination system.
Stated another way, different ones of the plurality of illumination systems may be optimal for barcode reading within different zones of the field of view 106. For example, the dark field illumination 156a-b of the dark field illumination system may be optimal for barcode reading within a near zone 158 of the field of view 106. The diffuse bright field illumination 124 of the diffuse bright field illumination system may be optimal for barcode reading within a center zone 126 of the field of view 106. The bright field illumination 112 of the bright field illumination system may be optimal for barcode reading within a far zone 116 of the field of view 106.
In this context, saying that the illumination provided by a particular illumination system is “optimal” within a certain zone means that the illumination is more favorable or desirable within that zone relative to illumination provided by other illumination systems within the reader 1900, which may include any of: i) the illumination having an even distribution of illumination intensity across the field(s) of view; ii) the illumination being directed to the field(s) of view at an angle which provides an even distribution of reflected illumination from an object within the field(s) of view; and iii) the illumination being at an optical wavelength or wavelength distribution.
For example, saying that the dark field illumination 156a-b of the dark field illumination system may be optimal for barcode reading within a near zone 158 of the field of view 106 means that the dark field illumination 156a-b may be more favorable or desirable within the near zone 158 relative to the bright field illumination 112 and/or the diffuse bright field illumination 124.
As also discussed above, the barcode reader 1900 (shown in FIGS. 9-11) may also include a plurality of illumination systems, like the reader 100 shown in FIG. 1. In addition, the reader 1900 may include a plurality of lens assemblies 1904 and optical paths 1906. More specifically, the reader 1900 may include a first lens assembly 1904a positioned within a first optical path 1906a from the field of view 106 to a first image sensor section 1902a, and a second lens assembly 1904b positioned within a second optical path 1906b from the field of view 106 to a second image sensor section 1902b. 
In the present disclosure, a reference to different image sensor sections (e.g., a first image sensor section and a second image sensor section) may be referring to (i) two different sections of the same image sensor (e.g., a first section 1902a and a second section 1902b of an image sensor 1902, as shown in FIG. 10 and described in connection therewith), or (ii) two different image sensors (e.g., a first image sensor 2102a and a second image sensor 2102b, as shown in FIG. 11 and described in connection therewith).
The first lens assembly 1904a may project an image of one or more objects (e.g., a barcode) within its field of view onto the first image sensor section 1902a. Similarly, the second lens assembly 1904b may project an image of one or more objects within its field of view onto the second image sensor section 1902b. The lens assemblies 1904a-b may be focused to the same focal length.
As used herein, the term “image frame” refers to a plurality of images that are captured by a barcode reader at substantially the same time via different lens assemblies and optical paths. For example, because the reader 1900 includes two lens assemblies 1904a-b and two optical paths 1906a-b, an image frame captured by the reader 1900 may include two images: (i) an image of the field of view of the first lens assembly 1904a, captured via the first lens assembly 1904a, the first optical path 1906a, and the first image sensor section 1902a, and (ii) an image of the field of view of the second lens assembly 1904b, captured via the second lens assembly 1904b, the second optical path 1906b, and the second image sensor section 1902b. 
The number of lens assemblies 1904a-b and optical paths 1906a-b within the reader 1900 should not be interpreted as limiting the scope of the present disclosure. A reader in accordance with the present disclosure may include more than two lens assemblies and optical paths. Generally speaking, if a barcode reader includes N lens assemblies and optical paths, then an image frame captured by the reader may include N images.
In accordance with the present disclosure, a reader 1900 that includes a plurality of lens assemblies 1904a-b that are positioned in different optical paths 1906a-b to different image sensor sections 1902a-b may utilize offsets between locations of features in different images within the same image frame to estimate the distance between the reader 1900 and a target object (e.g., a barcode). This estimated distance may then be used to adjust reader settings to optimize image capture at the estimated barcode distance. This process may be referred to herein as multi-lens ranging.
Reference is initially made to: i) the flow chart of FIG. 12, which illustrates a method 1200 that may be performed by the reader 1900 in order to implement multi-lens ranging; and ii) the calibration targets 1914a and 1914b of FIGS. 18A and 18B respectively.
The exemplary calibration target 1914a may include a plurality of fiducial features. In the depicted target 1914a, the fiducial features are fiducial points. There are five fiducial points in the calibration target 1914a shown in FIG. 18a, labeled P1, P2, P3, P4 P and P5, each spaced apart from the other fiducial points.
The exemplary calibration target 1914b may include a two-dimensional barcode, such as a MaxiCode®, such that distinct features of the barcode (e.g., the four corners and the center) form five fiducial points, which are shown in FIG. 18b labeled P1, P2, P3, P4 P and P5.
The calibration targets 1914a and 1914b are exemplary only and the quantity of fiducial points in each calibration target is exemplary only. Those skilled in the art will recognize that other graphic patterns with other quantities of fiducial points or other types of fiducial features are suitable. Preferably the fiducial points of the calibration target are spaced such that the area bounded by the fiducial points occupies most of the field of view when at the closest calibration distance.
In step 1202 of the flow chart of FIG. 12, the reader 1900 may capture a plurality of image frames while a calibration target 1914a or 1914b is within the field of view 106 of the reader 1900. The image frames 2002a-2002c of FIGS. 19A-C depict use of calibration target 1914a as an example. These image frames 2002a-c may be referred to herein as calibration image frames 2002a-c. Different calibration image frames 2002a-c may be captured at different distances D1, D2, D3 (FIGS. 20A-C) from the calibration target 1914. For example, a first calibration image frame 2002a (FIG. 19A) may be captured at a distance D1 (FIG. 20A) from the calibration target 1914, a second calibration image frame 2002b (FIG. 19B) may be captured at a distance D2 (FIG. 20B) from the calibration target 1914, and a third calibration image frame 2002c (FIG. 19C) may be captured at a distance D3 (FIG. 20C) from the calibration target 1914. The distances D1, D2, D3 may be referred to herein as calibration distances.
The number of calibration distances used should be at least three calibration distances and preferably would be a greater number of calibration distances. For purposes of depicting this invention, three calibration distances are depicted in the Figures.
The different calibration distances D1, D2, D3 (FIGS. 20A-C) preferably include a far distance D1 which extends into a far zone 116 of the field of view 106 and a close distance D3 which is within the near zone 158 of the field of view 106. Preferably there would be multiple calibration distances between D1 and D3 with at least one calibration distance D2 being within the center zone 126 of the field of view 106. These zones may correspond to zones 158, 126, and 116 discussed with respect to FIG. 1.
Because the reader 1900 includes two different lens assemblies 1904a-b and optical paths 1906a-b, each calibration image frame 2002 captured by the reader 1900 may include two different images: (i) a first image 2004 of the calibration target 1914a captured via the first lens assembly 1904a, the first optical path 1906a, and the first image sensor section 1902a, and (ii) a second image 2006 of the calibration target 1914a captured via the second lens assembly 1904b, the second optical path 1906b, and the second image sensor section 1902b. These images 2004, 2006 may be referred to herein as calibration images 2004, 2006.
Because the lens assemblies 1904a-b, and their two parallel optical paths 1906a and 1906b, are offset and have different fields of view, each image of the calibration target 1914a captured within the same image frame will have at least a portion of the fiducial points in different locations within the image. More specifically, each fiducial point Pi may be in different locations in the calibration images 2004, 2006 contained within a calibration image frame 2002. As used herein, the term “fiducial offsets” may refer generally to offsets between locations of each of a plurality of fiducial points Pi within the calibration images 2004, 2006 of a plurality of calibration image frames 2002. More specifically, a single “fiducial offset” may be the difference between the location of a particular fiducial point Pi within the calibration images 2004, 2006 of a particular calibration image frame 2002.
In FIGS. 19A-D, for the sake of clarity, the locations of the fiducial points Pi are indicated with different markings in different calibration image frames 2002. More specifically, the locations of the fiducial points Pi are indicated with “o” in the calibration image frame 2002a shown in FIG. 19A (taken at calibration distance D1), with “x” in the calibration image frame 2002b shown in FIG. 19B (taken at calibration distance D2), and with a solid circle in the calibration image frame 2002c shown in FIG. 19C (taken at calibration distance D3). These different markings are being used in order to more clearly illustrate how the fiducial points Pi are in different locations in the different calibration images 2004, 2006. The different locations are most clearly visible in the image frame 2002d shown in FIG. 19D, which is a composite of the image frames 2002a-c shown in FIGS. 19A-C. Of course, one skilled in the art would understand that in actual practice, fiducial points would not be indicated with different markings in different calibration image frames of the same calibration target.
Referring to FIGS. 19A-D generally, it can be seen that the distance between the fiducial points Pi becomes greater as the distance between the reader 1900 and the calibration target 1914 is decreased and the calibration target 1914 occupies more of the field of view. For example, the fiducial points Pi in the calibration image 2004a taken at calibration distance D1 are closer together than the fiducial points Pi in the calibration image 2004c taken at calibration distance D3. This is most clearly visible in the composite image frame 2002d shown in FIG. 19D.
Further, the offset between the location of a particular fiducial point Pi within the calibration images 2004, 2006 of a particular calibration image frame 2002 also increases as the distance between the reader 1900 and the calibration target 1914 is decreased. Stated differently, the offset of each fiducial point Pi within the calibration images 2004, 2006 of a particular calibration image frame 2002 is a function of the distance between the first optical path 1906a of the first lens assembly 1904a and the second optical path 1906b of the second lens assembly 1904b (the optical path offset) divided by the distance between the reader 1900 and the calibration target 1914. As such, the distance between the reader 1900 and the calibration target 1914 is a function of the optical path offset divided by the offset of each fiducial point Pi within the calibration images 2004, 2006.
Reference is once again made to FIG. 12. In step 1204, the reader 1900 may determine fiducial offset data 2208, which may be representative of fiducial offsets within a plurality of calibration images 2004, 2006 of a plurality of calibration image frames 2002a-c. The fiducial offset data 2208 may be determined via analysis of the calibration image frames 2002a-c and/or the composite calibration image frame 2002d. 
FIG. 21A illustrates a first example of fiducial offset data 2208a. In this example, the fiducial offset data 2208a includes a look-up table 2210a that includes, for each calibration distance Di, either or both of: i) a numerical value derived from the optical path offset which, when divided by the feature offset (which is defined below), yields the estimated distance; and ii) data representing the average offset of all fiducial points P1-5 at each calibration distance Di.
More specifically fiducial offset data 2208a may be, for each calibration distance Di of the plurality of calibration distances D1-3: the average of multiple numerical values, each being the numerical value derived from the optical path offset (which when divided by the feature offset yields the estimated distance), each calculated based on measured fiducial offset for one of the multiple fiducial points Pi within the calibration images 2004, 2006 at the calibration distance Di.
Alternatively, fiducial offset data 2208a may be, for each calibration distance Di of the plurality of calibration distances D1-3: (i) a first location (x1, y1) of each fiducial point Pi within a first calibration image 2004 captured at a calibration distance Di, and (ii) a second location (x2, y2) of each of the same fiducial points Pi within a second calibration image 2006 captured at the calibration distance Di. These values may be used to calculate the average of the offset of the fiducial points P1-5 between the first calibration image 2004 and the second calibration image 2006. The offset of fiducial point Pi (i.e., ΔPi) at calibration distance Di equals the square root of Δx2 plus Δy2. Therefore the average offset at calibration distance Di equals the average of ΔP1-5. Further, those skilled in the art will recognize that for computational simplicity, the square root calculation can be omitted such that the average of Δx2 plus Δy2 for P1-5 is also representative of average offset and may be stored as the average offset value Oi in look up table 2210a. 
FIG. 21B illustrates an alternative example of fiducial offset data 2208b which, instead of storing numerical values or offset values Oi for each calibration distance Di stores data 2208b sufficient for calculating fiducial offsets. In this example, the fiducial offset data 2208b includes a look-up table 2210b that includes the following for each fiducial point Pi of the plurality of fiducial points P1-5 and for each calibration distance Di of the plurality of calibration distances D1-3: (i) a first location (x1, y1) of a fiducial point Pi within a first calibration image 2004 captured at a calibration distance Di, and (ii) a second location (x2, y2) of the fiducial point Pi within a second calibration image 2006 captured at the calibration distance Di.
In FIG. 21B (and FIG. 21D as well), the location data (x, y) for different fiducial points Pi and for different calibration distances Di are distinguished using the subscripts ij, where i denotes the fiducial point and j denotes the calibration distance. For example, (x1, y1)23 denotes the location of fiducial point P2 in the first calibration image 2004 at calibration distance D3, whereas (x2, y2)41 denotes the location of fiducial point P4 in the second calibration image 2006 at calibration distance D1.
FIG. 21C illustrates another example of fiducial offset data 2208c. In this example, the fiducial offset data 2208c includes a look-up table 2210c that includes the following for each fiducial point Pi of the plurality of fiducial points P1-5 and for each calibration distance Di of the plurality of calibration distances D1-3: an offset (Δx, Δy) between (i) a first location (x1, y1) of a fiducial point Pi within a first calibration image 2004 captured at a calibration distance Di and (ii) a second location (x2, y2) of the fiducial point Pi within a second calibration image 2006 captured at the calibration distance Di.
In FIG. 21C (and FIG. 21D as well), the offsets (Δx, Δy) for different fiducial points Pi and for different calibration distances Di are distinguished using the subscripts ij, which were discussed above.
FIG. 21D illustrates another example of fiducial offset data 2208d. In this example, the fiducial offset data 2208d includes a look-up table 2210d that includes the following for each fiducial point Pi of the plurality of fiducial points P1-5 and for each calibration distance Di of the plurality of calibration distances D1-3: (i) a first location (x1, y1) of a fiducial point Pi within a first calibration image 2004 captured at the calibration distance Di, (ii) a second location (x2, y2) of the fiducial point Pi within a second calibration image 2006 captured at the calibration distance Di, and (iii) an offset (Δx, Δy) between the first location (x1, y1) and the second location (x2, y2). The look-up table 2210d effectively is a combination of the look-up tables 2210b and 2210c of FIGS. 21B and 21C.
FIG. 13 illustrates another method 1300 that may be performed by the reader 1900 in order to implement multi-lens ranging. This method 1300 is a more detailed representation of the method 1200 shown in FIG. 12.
In step 1302, the reader 1900 may capture a calibration image frame 2002 at a calibration distance Di. The calibration image frame 2002 may include: (i) a first calibration image 2004 captured via the first lens assembly 1904a, the first optical path 1906a, and the first image sensor section 1902a, and (ii) a second calibration image 2006 captured via the second lens assembly 1904b, the second optical path 1906b, and the second image sensor section 1902b. 
In step 1304, the reader 1900 may determine the location of each fiducial point Pi within each of the calibration images 2004, 2006. In step 1306, the reader 1900 may calculate, for each fiducial point Pi, the offset between the location of the fiducial point Pi in the first calibration image 2004 and the location of the fiducial point Pi in the second calibration image 2006 which, as discussed may include calculating, for the fiducial point Pi, Δx and Δy, and the sum of Δx2 plus Δy2. Step 1306 is optional. If the fiducial offset data 2208b is as shown in FIG. 21B, then step 1306 is not necessary.
In step 1308, the reader 1900 may record, in association with the calibration distance Di between the reader 1900 and the calibration target 1914 at which the calibration image frame 2002 was captured, data representative of the fiducial offsets (i.e., fiducial offset data 2208).
As discussed with respect to FIG. 21A, step 1308 may include either or both of: i) calculating and recording each average numerical value in look up table 2210a; or ii) calculating and recording average offset data in look-up table 2210a. 
As discussed with respect to FIGS. 21B to 21D, step 1308 may include: i) recording location data in a look-up table 2210b as shown in FIG. 21B, ii) recording offset data in a look-up table 2210c as shown in FIG. 21C, and/or iii) recording both location data and offset data in a look-up table 2210d as shown in FIG. 21D.
In step 1310, a determination may be made about whether calibration image frames 2002 have been captured for all of the calibration distances. If not, then in step 1312 another calibration distance Di may be selected, and steps 1302 through 1310 may be repeated. In other words, steps 1302 through 1310 may be performed for each calibration distance Di in order to fully populate the look-up table 2210.
The methods 1200, 1300 shown in FIGS. 12 and 13 may be performed when the reader 1900 is being manufactured, as part of a calibration process. The fiducial offset data 2208 may be stored in the reader 1900 in nonvolatile memory. The fiducial offset data 2208 may be stored in the reader 1900 at least until the reader 1900 is recalibrated. There may not be a need to recalibrate the reader 1900 after it is manufactured.
FIG. 14 illustrates another method 1400 that may be performed by the reader 1900 in order to implement multi-lens ranging. Whereas the methods 1200, 1300 shown in FIGS. 12 and 13 may be performed when the reader 1900 is being manufactured, the method 1400 shown in FIG. 14 may be performed during typical operation of the reader 1900.
In step 1402, the reader 1900 may capture an image frame 2316 of a barcode 2318 (FIG. 22). The image frame 2316 may include: (i) a first image 2320 of the barcode 2318 captured via the first lens assembly 1904a, the first optical path 1906a, and the first image sensor section 1902a, and (ii) a second image 2322 of the barcode 2318 captured via the second lens assembly 1904b, the second optical path 1906b, and the second image sensor section 1902b. 
Alternatively, at step 1402 the reader 1900 may capture each of a first window section 2320a within the first image sensor section 1902a and a second window section 2320b within the second image sensor section 1902b, with each of the first window section 2320a and the second window section 2320b including the same portion of the barcode 2318. In an embodiment wherein the image sensor 1902 is rotated perpendicular to the optical path offset (i.e. image sensor columns in FIG. 22 are horizontal while image sensor rows are vertical) the two window sections 2320a and 2320b may be a single image sensor window section encompassing a group of rows within the sensor 1902.
Capturing one or more window sections of an image sensor is described in more detail in U.S. patent application Ser. No. 13/946,862 filed on Jul. 19, 2013, the entire contents of which are hereby incorporated by reference.
The image frame 2316 may be referred to herein as a barcode image frame 2316, and the images 2320, 2322 (or the first window section 2320a of image 2320 and the second window section 2320b of image 2322, each depicting the same portion of the barcode 2318) may be referred to herein as barcode images 2320, 2322.
In step 1404, the reader 1900 may select one or more features, such as features 2324a-c, that is/are present in both the first barcode image 2320 and the second barcode image 2322. The features 2324a-c may be distinct patterns, so that the location of the features 2324a-c can be accurately identified in both the first barcode image 2320 and the second barcode image 2322. Note, if windowing is used only features 2324a-b can be identified within the windows 2320a and 2320b. 
Exemplary features include distinct corner points, lines, and other patterns (for example barcode symbology identifying patterns present in both the first and second barcode images 2320, 2322). Various image processing algorithms, such as the Hough transform, may be used to extract robust distinct features present in both the first and second barcode images 2320, 2322.
In addition, the locations of the features 2324a-c may be close to the locations of one or more of the fiducial points Pi in the calibration images 2004, 2006 that were used to calibrate the reader 1900. Although not necessary, this can improve the accuracy of the barcode distance (i.e., the distance between the reader 1900 and the barcode 2318) that is estimated by the reader 1900 in step 1412 (discussed below).
In step 1406, the reader 1900 may determine the location of each feature 2324a-c within the first barcode image 2320. In step 1408, the reader 1900 may determine the location of each feature 2324a-c within the second barcode image 2322. In step 1410, the reader 1900 may, for each feature 2324a-c, determine an offset between the location of the feature 2324 within the first barcode image 2320 and the location of the feature 2324 within the second barcode image 2322. This offset may be an offset only in the same direction as the optical path offset (e.g., a vertical offset when the two lens assemblies are arranged vertically). Alternatively, as discussed, this offset may the sum of Δx2 plus Δy2. This offset may be referred to herein as a “feature offset.”
In step 1412, the reader 1900 may estimate the barcode distance based on the feature offset of at least one feature 2324a-c and the fiducial offset data 2208. Exemplary methods for performing this estimate are discussed with respect to FIGS. 15, 16, and 17.
In step 1414, the reader 1900 may use the estimated barcode distance (determined in step 1412) to select at least one operating parameter of the reader 1900. For example, the reader 1900 may adjust its settings to optimize image capture at the estimated barcode distance. Step 1414 may include selecting, based on the estimated barcode distance, the best illumination system (i.e., the illumination system that best illuminates a barcode 2318 at the estimated barcode distance) for capturing a subsequent image frame. Alternatively or additionally, step 1414 may include setting gain and/or exposure time for best capturing a subsequent image frame of a barcode 2318 at the estimated barcode distance when the barcode 2318 is illuminated by the selected illumination system.
The barcode image frame 2316, or windows 2320a, 2320b within the image frame 2316 captured in step 1402 may be a test frame that is captured specifically for the purpose of estimating the barcode distance. In other words, the reader 1900 may perform the method 1400 shown in FIG. 14 in order to estimate the barcode distance, without attempting to decode the barcode 2318 within the barcode images 2320, 2322. Alternatively, the reader 1900 may attempt to decode at least one of the barcode images 2320, 2322 in the barcode image frame 2316 captured in step 1402, and then perform steps 1404 through 1414 only if neither barcode image 2320, 2322 is successfully decoded.
FIG. 15 illustrates an example of a method 1500 that may be performed by the reader 1900 in order to estimate the barcode distance based on the feature offset and the fiducial offset data 2208. In other words, the method 1500 shown in FIG. 15 represents one possible implementation of step 1412 in the method 1400 shown in FIG. 14.
In step 1502, the reader 1900 may determine the average offset of a plurality of the features 2324a-c present within both the first and second barcode images 2320, 2322. The plurality of features 2324a-c may be all features identified at step 1404 (FIG. 14), the features 2324a-b within the windows 2320a-b, or only a portion of the features 2324a-c identified which the reader 1900 determines to be the most robust—meaning the location(s) of the feature(s) 2324 within each of the first and second barcode images 2320, 2322 may be accurately identified and precisely located with minimal uncertainty as to the location(s). As discussed, in one embodiment the average offset may be the average offset in the dimension parallel to the optical path offset for the plurality of features 2324a-c as depicted by step 1502a. In another embodiment the average feature offset may be the average of Δx2 plus Δy2 for each of the plurality of features 2324a-c as depicted in step 1502b. 
In step 1504, the reader 1900 may determine the estimated barcode distance.
In one embodiment determining the estimated barcode distance may include, for each numerical value of the offset data 2208a, dividing the numerical value by the feature offset to yield a distance estimation as depicted in step 1504a. The estimated distance is a function of the distance estimations which may be: i) the average of the distance estimations or ii) the distance estimation based on the numerical value that was associated with (was determined based on) a calibration distance that is closest to the distance estimation.
In another embodiment the estimated barcode distance may be determined via interpolating between the average offset O1-5 (FIG. 21A) at each calibration distance D1-5 as depicted in step 1504b. For example, if the magnitude of the average feature offset determined at step 1502 is halfway between O2 and O3, then the estimated barcode distance may be determined to be halfway between the calibration distance D2 and the calibration distance D3.
FIG. 16 illustrates another example of a method 1600 that may be performed by the reader 1900 in order to estimate the barcode distance based on the feature offset and the fiducial offset data 2208. In other words, the method 1600 shown in FIG. 16 represents another possible implementation of step 1412 in the method 1400 shown in FIG. 14.
In step 1602, the reader 1900 may determine the closest fiducial point Pi to one or more selected features 2324a-c. In step 1604, the reader 1900 may identify corresponding fiducial offsets.
More specifically, for each feature 2324a-c, the closest fiducial point may be the fiducial point Pi (from among the plurality of fiducial points P1-5) that is located closest to the feature 2324. The reader 1900 may compare the location of the feature 2324 within the barcode images 2320, 2322 with the locations of the plurality of fiducial points P1-5 in the corresponding calibration images 2004, 2006. For example, the location of the feature 2324a within the barcode image 2320 captured via the first lens assembly 1904a and first optical path 1906a may be compared with the locations of the fiducial points P1-5 in the calibration images 2004 captured via the first lens assembly 1904a and first optical path 1906a. Similarly, the location of the feature 2324a within the barcode image 2322 captured via the second lens assembly 1904b and second optical path 1906b may be compared with the locations of the fiducial points P1-5 in the calibration images 2006 captured via the second lens assembly 1904b and second optical path 1906b. In the barcode images 2320, 2322 shown in FIG. 22 and the calibration images 2004, 2006 shown in FIGS. 19A-D, it appears that fiducial point P1 is the closest fiducial point to feature 2324a. 
In step 1604, the reader 1900 may, for each feature 2324a-c, identify corresponding fiducial offsets, i.e., the fiducial offsets that correspond to the closest fiducial point Pi to the feature 2324 identified in step 1502. In this context, the phrase “corresponding fiducial offsets” refers to the fiducial offsets that are associated with the closest fiducial point Pi. In other words, the corresponding fiducial offsets are the fiducial offsets to which the feature offset is to be compared for estimating the distance of the barcode 2318 from the reader 1900.
If the fiducial offset data 2208b is as shown in FIG. 21B, then identifying the corresponding fiducial offsets may involve calculating the corresponding fiducial offsets based on the fiducial offset data 2208b. For example, if P1 is the closest fiducial point (closest meaning the average offset between the feature and the fiducial point in both images), then the reader 1900 may perform the following calculations: Offset at D1=(x2−x1)112+(y2−y1)112; Offset at D2=(x2−x1)122+(y2−y1)122; and Offset at D3=(x2−x1)132+(y2−y1)132.
If the fiducial offset data 2208c is as shown in FIG. 21C or 2208d as shown in FIG. 21D, then identifying the corresponding fiducial offsets may involve looking up the corresponding fiducial offsets in a look-up table 2210c, 2210d within the fiducial offset data 2208c, 2208d. For example, if P1 is the closest fiducial point, then Δx2+Δy2 may be calculated for each of (Δx, Δy)11, (Δx, Δy)12, and (Δx, Δy)13.
In step 1606, the reader 1900 may determine the estimated barcode distance via: (i) for each feature, interpolating between the calibration distances D1-3, using the feature offset and the corresponding fiducial offsets at the calibration distances, and then (ii) averaging such estimated barcode distances.
FIG. 17 illustrates another example of a method 1700 that may be performed by the reader 1900 in order to estimate the barcode distance based on the feature offset and the fiducial offset data 2208. In other words, the method 1700 shown in FIG. 17 represents another possible implementation of step 1412 in the method 1400 shown in FIG. 14.
In step 1702, the reader 1900 may calculate interpolated fiducial offsets Δx2+Δy2 for each calibration distance Di at an imaginary fiducial location that corresponds to the feature location. More specifically, the imaginary fiducial location is used to interpolate each of Δx and Δy of at least two fiducial points to determine an imaginary Δx and an imaginary Δy of the imaginary fiducial point at the feature location.
In step 1704, the reader 1900 may determine the estimated barcode distance using the methods discussed with respect to step 1604 and step 1606 of FIG. 16.
FIG. 23 illustrates some additional components within the reader 1900 that may be used to implement multi-lens ranging. The reader 1900 may include a processor 2426. The processor 2426 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 2426 may be referred to as a central processing unit (CPU). Although just a single processor 2426 is shown, in an alternative configuration, a combination of processors (e.g., an ARM and DSP) could be used.
The reader 1900 may also include memory 2428 in electronic communication with the processor 2426. That is, the processor 2426 may be able to read information from and/or write information to the memory 2428. The memory 2428 may be any electronic component capable of storing electronic information. The memory 2428 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 2426, 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 2428. 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 2426 to implement one or more of the methods 1200, 1300, 1400, 1500, 1600, 1700, 1800, operations, functions and/or procedures described herein. Executing the instructions may involve the use of the data that is stored in the memory 2428. The data may include fiducial offset data 2208 and other types of data described herein.
The methods 1200, 1300, 1400, 1500, 1600, 1700, 1800 and other functionality described herein may be distributed across multiple applications, programs, routines, sub-routines, functions, procedures, etc. For example, a calibration application 2430 may be configured to perform the methods 1200, 1300 that were described above in connection with FIGS. 12 and 13. A distance estimating application 2432 may be configured to perform the methods 1400, 1500, 1600, 1700, 1800 that were described above in connection with FIGS. 14-18.
FIGS. 19-21 show the first optical path 1906a of the reader 1900 with a filter 1910. A reader that is configured for multi-lens ranging as described herein may (i) include a filter in just one of the optical paths 1906a-b, as shown in FIGS. 19-21, (ii) include a filter in both optical paths 1906a-b, or (iii) be configured without a filter in either of the optical paths 1906a-b. 
As used herein, the phrase “substantially parallel” means within five degrees of parallel. In another embodiment, substantially parallel means within 15 degrees of parallel. In another embodiment, substantially parallel means within 20 degrees of parallel.
As used herein, the phrase “substantially perpendicular” means within five degrees of perpendicular. In another embodiment, substantially perpendicular means within 15 degrees of perpendicular. In another embodiment, substantially perpendicular means within 20 degrees of perpendicular.
As used herein, the term “determining” (and grammatical variants thereof) 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.

## Claims

1. A barcode reader, comprising:
an illumination system;
a first lens assembly;
a second lens assembly;
fiducial offset data determined from a plurality of calibration image frames captured at multiple different calibration distances, each calibration image frame comprising:
a first calibration image of at least one fiducial feature captured via the first lens assembly; and
a second calibration image of the at least one fiducial feature captured via the second lens assembly; and

instructions executable by a processor to (i) select at least one feature that is present in both a first barcode image captured via the first lens assembly and a second barcode image captured via the second lens assembly, (ii) determine at least one feature offset, each feature offset indicating an offset between a first location of a selected feature within the first barcode image and a second location of the selected feature within the second barcode image, (iii) determine an estimated barcode distance based on the at least one feature offset and the fiducial offset data, and (iv) use the estimated barcode distance to select at least one operating parameter of the barcode reader.

2. The barcode reader of claim 1, wherein:
the illumination system comprises multiple illumination sub-systems, each sub-system being optimal for barcode reading within a different zone of a field of view of the barcode reader; and
use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting the illumination sub-system that is optimal for barcode reading within a zone that encompasses the estimated barcode distance.

3. The barcode reader of claim 2:
wherein the multiple illumination sub-systems comprise:
a dark field illumination system that directs dark field illumination into a field of view of the barcode reader, the dark field illumination being optimal for barcode reading within a near zone of the field of view;
a diffuse bright field illumination system that directs diffuse bright field illumination into the field of view, the diffuse bright field illumination being optimal for barcode reading within a center zone of the field of view;
a bright field illumination system that directs bright field illumination into the field of view, the bright field illumination being optimal for barcode reading within a far zone of the field of view;

wherein use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting:
the dark field illumination system if the estimated barcode distance is within the near zone of the field of view; and
the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view; and
the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.

4. The barcode reader of claim 1, wherein determining the estimated barcode distance comprises calculating, by interpolation, the barcode distance between at least two calibration distances using the at least one feature offset of the at least one selected feature to interpolate between a fiducial offset at each of the at least two calibration distances.

5. The barcode reader of claim 1, further comprising:
a look-up table storing, for each of the multiple different calibration distances, the fiducial offset data representative of at least one offset between locations of the at least one fiducial feature at that calibration distance; and
instructions executable by the processor to capture the plurality of calibration images at the multiple different calibration distances, to determine the fiducial offset data, and to store the fiducial offset data in the look-up table.

6. The barcode reader of claim 5, wherein the fiducial offset data comprises, for each of the multiple different calibration distances, data representative of the at least one offset between:
a first location of the at least one fiducial feature within the first calibration image captured at the calibration distance; and
a second location of the at least one fiducial feature within the second calibration image captured at the calibration distance.

7. The barcode reader of claim 5, wherein the fiducial offset data comprises, for each calibration distance of the multiple different calibration distances, average fiducial offset data for multiple different fiducial features within the first calibration image captured at the calibration distance and the second calibration image captured at the calibration distance, the fiducial offset data for a particular fiducial feature being data representative of an offset between:
a first location of the fiducial feature within the first calibration image captured at the calibration distance; and
a second location of the fiducial feature within the second calibration image captured at the calibration distance.

8. The barcode reader of claim 7, wherein, for each fiducial feature at each calibration distance, the data representative of the offset comprises:
the square of the offset along a first direction between the first location of the fiducial feature within the first calibration image and the second location of the fiducial feature within the second calibration image; and
the square of the offset along a second direction, perpendicular to the first direction, between the first location of the fiducial feature within the first calibration image and the second location of the fiducial feature within the second calibration image.

9. The barcode reader of claim 8, wherein determining a feature offset for a particular selected feature comprises:
determining the square of the offset along a first direction between the first location of the selected feature within the first barcode image and the second location of the selected feature within the second barcode image; and
determining the square of the offset along a second direction, perpendicular to the first direction, between the first location of the selected feature within the first barcode image and the second location of the selected feature within the second barcode image.

10. The barcode reader of claim 9, wherein determining the estimated barcode distance comprises calculating, by interpolation, the barcode distance between at least two calibration distances using the at least one feature offset of the at least one selected feature to interpolate between a fiducial offset at each of the at least two calibration distances.

11. A barcode reader, comprising:
a first lens assembly positioned within a first optical path to image a first field of view onto a first image sensor section;
a second lens assembly positioned within a second optical path to image a second field of view onto a second image sensor section;
instructions executed by a processor to:
select a feature that is present in both:
a) a first barcode image captured on the first image sensor section by the first lens assembly positioned within the first optical path; and
b) a second barcode image captured on the second image sensor section by the second lens assembly positioned within the second optical path;
determine a feature offset that indicates an offset between a first location of the feature within the first barcode image and a second location of the feature within the second barcode image;
determine an estimated barcode distance based on the feature offset; and
use the estimated barcode distance to select at least one operating parameter of the barcode reader.

12. The barcode reader of claim 11, further comprising offset data representing an offset between the first field of view and the second field of view, wherein determining the estimated barcode distance based on the feature offset comprises calculating the estimated barcode distance as a function of the feature offset and the offset data representing the offset between the first field of view and the second field of view.

13. The barcode reader of claim 12, wherein the offset data comprises, for each of multiple different calibration distances, an offset between:
a first location, within a first image on the first image sensor section, of a point within the first field of view; and
a second location, within a second image on the second image sensor section, of the same point within the second field of view.

14. The barcode reader of claim 13, wherein determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.

15. The barcode reader of claim 12, wherein the offset data comprises, for each of the multiple different calibration distances: i) the square of an offset along a first direction between a first location of a point within a first image and a second location of the point within a second image; and ii) the square of an offset along a second direction, perpendicular to the first direction, between the first location of the point within the first image and the second location of the point within the second image.

16. The barcode reader of claim 15, wherein determining the feature offset comprises determining:
the square of the offset along a first direction between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image; and
the square of the offset along a second direction, perpendicular to the first direction, between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image.

17. The barcode reader of claim 16, wherein determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.

18. The barcode reader of claim 17:
further comprising:
a first illumination system that directs first illumination into a field of view of the barcode reader, the first illumination being optimal for barcode reading within a first zone of the field of view; and
a second illumination system that directs second illumination into the field of view, the second illumination being optimal for barcode reading within a second zone of the field of view; and

wherein use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting:
the first illumination system if the estimated barcode distance is within the first zone; and
the second illumination system if the estimated barcode distance is within the second zone.

19. The barcode reader of claim 17:
further comprising:
a dark field illumination system that directs dark field illumination into a field of view of the barcode reader, the dark field illumination being optimal for barcode reading within a near zone of the field of view;
a diffuse bright field illumination system that directs diffuse bright field illumination into the field of view, the diffuse bright field illumination being optimal for barcode reading within a center zone of the field of view; and
a bright field illumination system that directs bright field illumination into the field of view, the bright field illumination being optimal for barcode reading within a far zone of the field of view;

wherein use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting:
the dark field illumination system if the estimated barcode distance is within the near zone of the field of view;
the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view; and
the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.

20. The barcode reader of claim 11, further comprising:
a look-up table stored in a non-transient memory; and
instructions executable by the processor to:
capture a plurality of calibration image frames at each of multiple different calibration distances, each calibration image frame comprising:
a first image on the first image sensor section inclusive of an image of a point within the first field of view; and
a second image on the second image sensor section inclusive of an image of the same point within the second field of view;

determine offset data comprising, for each of the multiple different calibration distances, an offset between:
i) the image of the point within the first field of view; and
ii) the image of the same point within the second field of view; and

record the offset data within the look-up table.

21. The barcode reader of claim 20, wherein the offset data comprises, for each calibration distance of the multiple different calibration distances, data representative of an offset between:
a first location of the point within a first calibration image captured at the calibration distance; and
a second location of the point within a second calibration image captured at the calibration distance.

22. The barcode reader of claim 20, wherein the offset data comprises, for each calibration distance of the multiple different calibration distances, average offset data for multiple different points within a first calibration image captured at the calibration distance and a second calibration image captured at the calibration distance, the offset data for the point being data representative of an offset between:
a first location of the point within the first calibration image captured at the calibration distance; and
a second location of the point within the second calibration image captured at the calibration distance.

23. The barcode reader of claim 22, wherein, for each point at each calibration distance, the data representative of the offset comprises:
the square of the offset along a first direction between the first location of the point within the first calibration image and the second location of the point within the second calibration image; and
the square of the offset along a second direction, perpendicular to the first direction, between the first location of the point within the first calibration image and the second location of the point within the second calibration image.

24. The barcode reader of claim 23, wherein determining the feature offset comprises determining:
the square of the offset along a first direction between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image; and
the square of the offset along a second direction, perpendicular to the first direction, between the first location of the feature within the first barcode image and the second location of the feature within the second barcode image.

25. The barcode reader of claim 24, wherein determining the estimated barcode distance comprises using the feature offset to interpolate between the offset data corresponding to at least two calibration distances of the multiple different calibration distances.

26. The barcode reader of claim 12, wherein the offset data is a numerical value derived from a distance between the first lens assembly and the second lens assembly which, when divided by the feature offset yields the estimated barcode distance.

27. The barcode reader of claim 12, wherein:
the offset data comprises a plurality of numerical values, the plurality of numerical values comprising a separate numerical value for each of multiple different calibration distances;
the numerical value corresponding to a particular calibration distance is derived from: i) a distance between the first lens assembly and the second lens assembly; and ii) an offset between an image of a point at the calibration distance on the first image sensor section and an image of the point on the second image sensor section;
dividing each numerical value of the plurality of numerical values by the feature offset yields a plurality of distance estimations; and
the estimated barcode distance is a function of at least one of the plurality of distance estimations.

28. The barcode reader of claim 27:
further comprising:
a first illumination system that directs first illumination into a field of view of the barcode reader, the first illumination being optimal for barcode reading within a first zone of the field of view; and
a second illumination system that directs second illumination into the field of view, the second illumination being optimal for barcode reading within a second zone of the field of view; and

wherein use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting:
the first illumination system if the estimated barcode distance is within the first zone; and
the second illumination system if the estimated barcode distance is within the second zone.

29. The barcode reader of claim 27:
further comprising:
a dark field illumination system that directs dark field illumination into a field of view of the barcode reader, the dark field illumination being optimal for barcode reading within a near zone of the field of view;
a diffuse bright field illumination system that directs diffuse bright field illumination into the field of view, the diffuse bright field illumination being optimal for barcode reading within a center zone of the field of view; and
a bright field illumination system that directs bright field illumination into the field of view, the bright field illumination being optimal for barcode reading within a far zone of the field of view;

wherein use of the estimated barcode distance to select at least one operating parameter of the barcode reader comprises selecting:
the dark field illumination system if the estimated barcode distance is within the near zone of the field of view;
the diffuse bright field illumination system if the estimated barcode distance is within the center zone of the field of view; and
the bright field illumination system if the estimated barcode distance is within the far zone of the field of view.