US20170132441A1 - Hand held symbology reader illumination diffuser - Google Patents

Abstract

A hand held industrial identification symbol reader projects diffuse illumination onto a region of interest to produce high contrast images of symbols. The diffuse illumination is particularly well suited for producing images of symbols that are marked directly on objects. The diffuse illumination is created through the use of an optically translucent diffuser having a generally tapered shape that distributes diffuse illumination throughout the field of view of the reader. The diffuse illumination can be supplemented with dark field illumination using selectively actuated illumination sources.

Description

BACKGROUND OF THE INVENTION
• Field of the Invention
• This invention relates to illumination for image acquisition devices, and more particularly, to illumination for image acquisition devices used for reading industrial identification codes.
• Description of the Related Art
• Machine vision systems use image acquisition devices that include camera sensors to deliver information on a viewed subject. The system then interprets this information according to a variety of algorithms to perform a programmed decision-making and/or identification function. For an image to be most effectively acquired by a sensor in the visible, and near visible light range, the subject should be properly illuminated.
• In the example of identification symbol scanning using an image sensor, good lighting is highly desirable. Identification symbol scanning entails the aiming of an image acquisition sensor (CMOS camera, CCD, etc.) at a location on an object that contains a bar code, data matrix, or other identification symbol, and retrieval of an image of that symbol. The identification symbol contains a set of predetermined patterns that represent an ordered group of characters or symbols from which an attached data processor (for example a microcomputer) can derive useful information about the object (e.g. its serial number, type, model, price, etc.). Identification symbols are available in a variety of shapes and sizes. Two of the most commonly employed symbol types are the so-called one-dimensional barcode, consisting a line of vertical stripes of varying width and spacing, and the so-called two-dimensional barcode consisting of a two-dimensional array of dots or rectangles.
• In reading identification symbols or other subjects of interest the type of illumination employed is of particular concern. Where barcodes and other viewed subjects are printed on a flat surface with contrasting ink or paint, a diffuse, high-angle “bright field” illumination may best highlight these features for the sensor. By high-angle it is meant, generally, light that strikes the subject nearly perpendicularly (normal) or at an angle that is typically no less than about 45 degrees from perpendicular (normal) to the surface of the item being scanned. Such illumination is subject to substantial reflection back toward the sensor. By way of example, barcodes and other subjects requiring mainly bright field illumination may be present on a printed label adhered to an item or container, or on a printed field in a relatively smooth area of item or container.
• Conversely, where a barcode or other subject is formed on a more-irregular surface or is created by etching or peening a pattern directly on the surface, the use of highly reflective bright field illumination may be inappropriate. A peened/etched surface has two-dimensional properties that tend to scatter bright field illumination, thereby obscuring the acquired image. Where a viewed subject has such decidedly two-dimensional surface texture, it may be best illuminated with dark field illumination. This is an illumination with a characteristic low angle (approximately 45 degrees or less, for example) with respect to the surface of the subject (i.e. an angle of more than approximately 45 degrees with respect to normal). Using such low-angle, dark field illumination, two-dimensional surface texture is contrasted more effectively (with indents appearing as bright spots and the surroundings as shadow) for better image acquisition.
• To take full advantage of the versatility of a camera image sensor, it is desirable to provide both bright field and dark field illumination for selective or simultaneous illumination of a subject. However, dark field illumination must be presented close to a subject to attain the low incidence angle thereto. Conversely, bright field illumination is better produced at a relative distance to ensure full area illumination.
• In the situation where a barcode or other subject is formed on a specular surface, non-directional totally diffuse bright field illumination is preferred. This type of illumination, like that naturally produced on a cloudy day must surround the object upon which the barcode is placed. In typical machine vision applications, non-directional totally diffuse illumination is difficult and costly to provide, usually by way of surrounding a workpiece with a light tent.
BRIEF SUMMARY OF THE INVENTION
• In one aspect the present invention provides diffuse illumination in a hand held reader to produce high contrast images of symbols and barcodes. A tapered translucent diffuser is disposed between the imager and the region of interest with illumination behind the diffuser directed toward the region of interest. The tapered diffuser converts bright field illumination into totally diffused non-directional illumination. The narrow end of the tapered diffuser surrounds the lens at a position near to the lens of the reader. The wide end of the tapered diffuser surrounds the field of view near the region of interest. Accordingly, the field of view is flooded with diffuse illumination.
• In another aspect of the invention, diffuse illumination is produced in addition to low angle dark field illumination. In this aspect of the invention, a passive light pipe that produces low angle dark field illumination is positioned around the diffuser. Alternatively, an active light pipe surrounds the diffuser, with dark field illuminators directly projecting illumination at a low angle with respect to the region of interest. The reader can be configured to selectively actuate either the diffuse illumination from the tapered diffuser, or exclusive dark field illumination from the dark field light pipes, or a combination of both diffuse illumination and dark field illumination.
• In yet another aspect of the invention, in addition to the tapered diffuser that surrounds the lens at the narrow end of the diffuser, diffused illumination directed to a semi-transparent mirror positioned in front of the lens and aligned so that a portion of the light reflecting from the region of interest is projected into the lens, while a portion of the diffuse illumination is reflected onto the region of interest. In this aspect of the invention, uniform diffuse illumination can be projected onto the region of interest without producing a reflection of the lens in the image.
• Other objects and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• The present invention is further described in the detailed description which follows, by reference to the noted drawings by way of non-limiting illustrative embodiments, in which like reference numerals represent similar part throughout the several views of the drawings, and wherein:
• FIG. 1 is a perspective view of a handheld scanning system and an object having a symbol thereon;
• FIG. 2 is a schematic cross sectional view of an image formation system according to the prior art;
• FIG. 3 is a perspective view of a representative object having a two-dimensional symbol marked thereon, according to the background art;
• FIG. 4 is an image of a two dimensional symbol on a specular cylindrical object acquired using an image formation system according to the prior art;
• FIG. 5 is a schematic cross sectional view of an image formation system according an illustrative embodiment of the present invention;
• FIG. 6 is a perspective view of an illustrative embodiment of an image formation system according to the present invention;
• FIG. 7 is an image of a two dimensional symbol on a specular cylindrical object acquired using an image formation system according to the present invention;
• FIG. 8 is a schematic cross section of an illustrative embodiment of the present invention;
• FIG. 9 is a schematic cross section of an illustrative embodiment of the present invention;
• FIG. 10 is a schematic cross section of an illustrative embodiment of the present invention;
• FIG. 11 is an exploded perspective view of an image formation system according to an illustrative embodiment of the present invention;
• FIG. 12 is a schematic cross section of an illustrative embodiment of the present invention;
• FIG. 13 is a schematic cross section of an illustrative embodiment of the present invention;
• FIG. 14 is a perspective view of an illustrative embodiment of the present invention with the diffuser according to the invention adapted with a cylindrical shape; and
• FIG. 15 is a perspective view of an illustrative embodiment of the present invention with selective quadrant diffuse illumination.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 shows ascanning system101 adapted for handheld operation. An exemplary handheld scanning appliance orhandpiece102 is provided. It includes a grip section104 and abody section106. Animage formation system151, shown in phantom and described herein, can be controlled and can direct image data to an onboard embeddedprocessor109. This processor can include ascanning software application113 by which lighting is controlled, images are acquired and image data is interpreted into usable information (for example, alphanumeric strings derived from the barcode images). The decoded information can be directed via a cable111 to a PC or otherdata storage device112 having (for example) adisplay114,keyboard116 andmouse118, where it can be stored and further manipulated using anappropriate application121. Alternatively, the cable111 can be directly connected to an interface in the scanning appliance and an appropriate interface in thecomputer112. In this case the computer-basedapplication121 performs various image interpretation and lighting control functions as needed. The precise arrangement of the handheld scanning appliance with respect to an embedded processor, computer or other processor is highly variable. For example, a wireless interconnect can be provided in which no cable111 is present. Likewise, the depicted microcomputer can be substituted with another processing device, including an onboard processor or a miniaturized processing unit such as a personal digital assistant or other small-scale computing device.
• Thescanning application113 can be adapted to respond to inputs from thescanning appliance102. For example, when the operator toggles atrigger122 on the hand heldscanning appliance102, an internal camera image sensor (110, shown and described further below) acquires an image of a region ofinterest131 on anobject105. The exemplary region of interest includes a two-dimensional symbol195 that can be used to identify theobject105. Identification and other processing functions are carried out by thescanning application113, based upon image data transmitted from the hand heldscanning appliance102 to theprocessor109. Avisual indicator141 can be illuminated by signals from theprocessor109 to indicate a successful read and decode of thesymbol195.
• FIG. 2 depicts animage formation system151 typically used in a hand heldscanning appliance102.FIG. 2 shows a cross sectional view of a priorart imaging system100 for reading marks or symbols on anobject105. Theimaging system100 has animager110 that is one of a variety of types of photosensitive imaging sensors, such as a CMOS or CCD device. Alens130 disposed in front of theimager110 is configured to direct illumination onto theimager110. Theimager110 andlens130 together form anoptical axis140 that defines the center of a field of view, which is bound by the polyhedral volume defined aslines150 inFIG. 2.
• At a given focus setting, a sharply focused image of the surface of anobject105 will be projected by thelens130 onto theimager110 when the object is positioned at an appropriate distance from theimaging system100. Optical properties of the system will affect the range of distance from which theobject105 can be positioned in front of thesystem100 while projecting an image of theobject105 onto theimager110 that exhibits features of sufficient sharpness and contrast so as to be perceived as a focused image. The range upon which a focused image can be formed on theimager110 is a called the depth offield125.
• Illuminators120 are shown in thesystem100 for directing illumination towards theobject105. Typically, adiffuser180 is disposed in front of theilluminators120 to diffuse the illumination so that a uniform distribution of illumination can be spread over the surface of the object. Without thediffuser180, the illumination from theilluminators120 will appear as areas of high intensity illumination surrounded by areas of low intensity illumination. As shown inFIG. 2, the field of view of an image of acylindrical object105 is the portion of the surface of the object frompoint B135 topoint A145.
• Although the entire field of view is illuminated, only a portion of the reflective surface (frompoint P175 to point Q165) will reflect light into theimaging system100. This results from the maximum angle of illumination, depicted aslines155 inFIG. 2, that can be reflected into theimaging system100, depicted aslines160 inFIG. 2, being significantly less than the field of view. The image of a cylindrical object using the priorart imaging system100 will depict a brightly illuminated band over the area defined by lines through points P and Q.
• FIG. 3 depicts a two-dimensionaldata matrix symbol195 etched on the surface of a cylindrical object, e.g., adrill bit190. Presenting theexemplary drill bit190 to theimaging system100 will produce an image of thesymbol195 as shown inFIG. 4. A brightly illuminated band can be observed between the regions defined aslines P175 andQ165. The illumination that strikes the remaining portion of the object does not reflect into the optics of theimaging system100, and therefore, the image is too dark to produce a clear representation of the data matrix symbol so that decoding algorithms can be applied to decode the symbol.
• FIG. 5 depicts animproved imaging system200 according to the present invention that can be used as animage formation system151 in a hand heldscanning appliance102. Theimproved system200 has animager110 that is one of a variety of types of photosensitive imaging sensors, such as a CMOS or CCD device. Alens130 disposed in front of theimager110 is configured to direct illumination onto theimager110. Theimager110 andlens130 together form anoptical axis140 that defines the center of a field of view, which is bound by the polyhedral area defined aslines150 inFIG. 4
• At a given focus setting, a sharply focused image of the surface of theobject105 will be projected by thelens130 onto theimager110 when the object is positioned at an appropriate distance from theimproved system200. Optical properties of the system will affect the range of distance from which theobject105 can be positioned in front of theimproved system200 while projecting an image of theobject105 onto theimager110 that exhibits features of sufficient sharpness and contrast so as to be perceived as a focused image. The range upon which a focused image can be formed on theimager110 is a called the depth offield125.
• Illuminators120 are shown in theimproved system200 for directing illumination towards theobject105. Optionally, adiffuser180 can be used to diffuse the bright field illumination. In an illustrative embodiment of the present invention, aconical diffuser300 is disposed between thelens130 and theobject105. One skilled in the art will appreciate that while the illustrative embodiment describes a conical shapeddiffuser300, other embodiments can be employed with alternative shapes without departing from the scope of the invention. For example, parabolic, cylindrical, and hemispherical shaped diffusers can be used as adiffuser300.
• FIG. 6 depicts a perspective view of the basic elements of the illustrative embodiment of the present invention. Theconical diffuser300 is constructed from an translucent plastic material, such as polymethyl methacrylate (PMMA) with a roughened surface to achieve the optical property of translucency. In an embodiment of the invention, the optical properties of thediffuser300 has translucency like that of ordinary white paper, in that illumination will cause the surface of the diffuser to appear bright. Theconical diffuser300 can be molded with a rough mold surface, or sandblasted to roughen the normally clear material to be translucent. Thediffuser300 is configured so that a first distal end, the narrow opening, of the diffuser surrounds the opening of thelens130 and aligned with the imager110 (shown in phantom). Theilluminators120 are distributed around thelens130 so that an even distribution of illumination can be projected.
• Referring back toFIG. 5, the entire field of view is illuminated with diffuse illumination since the second distal end of thediffuser300 surrounds the field of view near theobject105. The maximum angle of illumination from thediffuser300, shown asline310 strikes theobject105 within the region defined as the field of view betweenpoint A145 andpoint B135, reflecting toward thelens130 and theimager110 aslines150. Illumination from the diffuser that strikes the object outside of that region is outside the field of view, and therefore, not captured by theimager110.
• Presenting the exemplary drill bit190 (FIG. 3) to theimproved imaging system200, an image of thedata matrix symbol195 will be formed like that shown inFIG. 7. The entiredata matrix symbol195 is visible, since the region defined as the field of view betweenpoint A145 andpoint B135 receive diffuse illumination, and therefore, decoding algorithms operating on the image can readily extract the encoded information.
• FIG. 8 shows another implementation of thediffuser300 with a passivelight pipe800, shown in cross section relative to thelens130, to provide diffuse illumination in combination with, or in the alternative to dark field illumination.Dark field illumination810 is directed into thelight pipe800 that is internally reflected at a chamferedportion815 to be directed at theobject105 at a low angle. Further information regarding the design and implementation of passive light pipes with selectively actuated illumination to provide dark field illumination can be found in commonly assigned U.S. patent application Ser. No. 10/693,626, incorporated herein by reference.Bright field illumination820 is converted into totally diffuse illumination by thediffuser300, to project diffuse illumination on theobject105 within the field of view, depicted as the region defined bylines150. Optionally, thediffuser300 can be removably attached to the hand heldscanning appliance102 so that a user can operate the hand held scanning appliance using non-diffuse bright field illumination. The removability of thediffuser300 can be achieved by incorporating snap-fit clearances and/or features in the diffuser and light pipe that permit removable assembly (not shown).
• When dark field illumination is exclusively applied to theobject105 in the embodiment of the invention according toFIG. 8, scattered illumination may reflect from theobject105 and then from thediffuser300 to unintentionally cause diffuse illumination on theobject105. This condition may be undesirable for reading certain parts that are best imaged with low angle dark field illumination, such as peened data matrix marks on a highly specular surface.
• FIG. 9 shows an alternate embodiment of the implementation of thediffuser300 with a passivelight pipe800, shown in cross section relative to thelens130, to provide selectively exclusive dark field illumination or diffuse illumination. In this embodiment, a color specificdark field illumination835 is projected into thelight pipe800. Thediffuser300 is fabricated with amaterial840 having a color characteristic different from the color of the color specificdark field illumination835, and illuminated with color specificbright field illumination825 that matches the color characteristic of thematerial840. In this embodiment, when the color specific dark field illumination is exclusively actuated, the low angle dark field illumination is projected onto theobject105, and any scattered illumination reflecting from theobject105 and then thediffuser300 will not be converted into totally diffuse illumination.
• In an illustrative embodiment according toFIG. 9, the color specificdark field illumination835 is red, and the color specific bright field illumination is blue, with thematerial840 having a blue color. In this embodiment, if only low angle dark field illumination is desired, the reddark field illumination835 is turned on, with the blue bright field illumination turned off. The low angle red illumination striking the object, if scattered to reflect off the bluecolored material840 of thediffuser300, will not appear bright in an image, and therefore not contribute to the illumination of the object with totally diffuse illumination. Conversely, if the bluebright field illumination825 is turned on, the bluecolored material840 of the diffuser will transmit and diffuse the illumination to provide totally diffuse illumination of theobject105 within the field of view, depicted as the region defined bylines150. One skilled in the art will appreciate that alternative color characteristics, such as red/infrared can be employed according to the illustrative embodiment ofFIG. 9.
• FIG. 10 shows another illustrative embodiment of the implementation of thediffuser300 with a passivelight pipe800, shown in cross section relative to thelens130, to provide selectively exclusive dark field illumination or diffuse illumination. In this illustrative embodiment,dark field illumination810 is projected into thelight pipe800 to produce low angle dark field illumination while thebright field illumination820 is turned off. Alight absorbing foil860, such as a neutral density filter material is applied to the interior surface of thediffuser300. Low angle dark field illumination that reflects off theobject105 is absorbed by thefoil filter860 so that totally diffuse illumination is not reflected back onto the object. If diffuse illumination is desired, either instead of dark field illumination, or in combination with dark field illumination, thebright field illumination820 is turned on. The intensity of thebright field illumination820 would need to be increased to compensate for the absorption of such illumination by thefoil filter820. With the bright field illumination actuated, totally diffuse illumination will transmit from thediffuser300, through thefoil filter860, and onto the object within the field of view, depicted as the region defined bylines150.
• FIG. 11 depicts another illustrative embodiment of the implementation of thediffuser300 as animage formation system151 in a hand heldscanning appliance102. In the illustrative embodiment according toFIG. 11, thediffuser300 is inserted into an activelight pipe870. The activelight pipe870 provides low angle dark field illumination from a ring ofdark field illuminators875, as disclosed in the commonly assigned International Patent Application WO02/075637, incorporated herein by reference. Thedark field illuminators875 are held in place with a threadedcollar880, andflexible sleeve890.Bright field illuminators120 project bright field illumination that is diffused by anoptional diffuser180, that is diffused over the entire field of view by thediffuser300. Atransparent window895 protects thelens130 and other internal components from the operating environment.
• In the illustrative embodiment according toFIG. 11, theconical diffuser300 can be positioned to diffuse the dark field illumination from thedark field illuminators875, or optionally constructed to permit illumination from thedark field illuminators875 to project onto the object at low angle without being diffused. This optional configuration can be achieved by inserting theconical diffuser300 further into the activelight pipe870 toward thelens130 to expose thedark field illuminators875, or by constructing theconical diffuser300 to have a transparent optical property at the distal end where it is disposed in front of thedark field illuminators875. When the hand held scanning appliance having animage formation system151 according to the illustrative embodiment according toFIG. 11 is operated, the user can configure or select exclusive dark field illumination or exclusive diffuse illumination, or a combination of both modes of illumination thereof.
• In the illustrative embodiment according toFIG. 11, theconical diffuser300 can be optionally removed from theimage formation system151 so that the hand heldscanning appliance102 can be operated without diffuse illumination. This condition may be desired if high intensity non-diffuse bright field illumination, or if exclusive dark field illumination is required. The removable aspect of thediffuser300 can be achieved by unscrewing the threadedcollar880 to remove thediffuser300, and re-threading thecollar880 without the diffuser in place.
• FIG. 12 shows a schematic representation of the effect of illuminating anobject105 having a highlyspecular surface910 according to the present invention. The resultingimage920 will exhibitfeatures925 associated with a reflection of thelens130. Though the field ofview930, as defined as the region bound bylines150, will be illuminated with totally diffuse illumination from thediffuser300, theimage920 will exhibit a darkened region offeatures925 that is a reflection of light not emanating from thediffuser300.
• FIG. 13 shows an illustrative embodiment of the invention that further improves the uniform distribution of diffuse illumination over the field of view according to the present invention.Bright field illumination820 is converted into totally diffuse illumination by thediffuser300, to project diffuse illumination on theobject105 within the field of view, depicted as the region defined bylines150. Asemi-reflecting mirror950 is disposed in front of thelens130, and behind the diffuser at an appropriate angle so that the image of the field of view is projected into thelens130. A second brightfield illumination source935 is directed toward thesemi-reflecting mirror950, with asecond diffuser940 disposed between thesecond illumination source935 and thesemi-reflecting mirror950. Thesecond diffuser940 is composed of the same material as thediffuser300, with the same translucent optical properties. One skilled in the art will appreciate that a single diffuser can be fabricated or molded that can provide the functionality of both thediffuser300 and thesecond diffuser940. The intensity of thesecond illumination source935 may require an increased level during operation since a portion of theillumination935 will not be reflected onto theobject105, but rather through the semi-reflecting mirror into the body of the hand heldscanning appliance102. By adjusting the intensity level of thesecond illumination935, an even distribution of diffuse illumination can be achieved over the entire field ofview930.
• FIG. 14 shows an illustrative embodiment of the invention that provides acylindrical shape990 in thediffuser300 so that anobject105 having an extended length can be presented to theimproved imaging system200. Thecylindrical shape990 of the diffuser provides relief so that thediffuser300 can increase an area of diffuse illumination pattern on a reflective cylindrical object. Further, thecylindrical shape990 provides an aiming assistance to the user.
• FIG. 15 shows a plurality of selectively actuatedilluminators985 that can provide selective illumination of thediffuser300. In this illustrative embodiment, the North illuminator996 can be actuated with theSouth illuminator998 while theEast illuminator994 and theWest illuminator992 are not actuated. Conversely, theEast illuminator994 and theWest illuminator992 can be actuated while the North illuminator996 and theSouth illuminator998 are not actuated. Selective quadrant illumination according to this illustrative embodiment permits an adjustment, or compensation, of the uniformity of the illumination that is converted into totally diffuse illumination by thediffuser300, on an axis parallel with the axis of aspecular object105.
• While the invention has been described with reference to certain illustrated embodiments, the words which have been used herein are words of description rather than words of limitation. Changes may be made, within the purview of the appended claims, without departing from the scope and sprit of the invention and its aspects. Although the invention has been described herein with reference to particular structures, acts and materials, the invention is not to be limited to the particulars disclosed, but rather extends to all equivalent structures, acts, and materials, such as are within the scope of the appended claims.

Claims (20)

What is claimed is:

1. An apparatus for imaging a symbol on an object, the apparatus comprising:

a hand held portable imaging system having an imager;

a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;

an illuminator adjacent to the lens, directing illumination towards the region of interest; and

a tapered translucent diffuser concentrically aligned with the optical axis, having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the region of interest.

2. The apparatus according toclaim 1 wherein the tapered translucent diffuser is composed of polymethyl methacrylate.

3. The apparatus according toclaim 2 wherein the tapered translucent diffuser is fabricated in an injection molding process.

4. The apparatus according toclaim 1 wherein the tapered translucent diffuser has a conical shape.

5. The apparatus according toclaim 1 wherein the tapered translucent diffuser has a cylindrical shape.

6. The apparatus according toclaim 1 further comprising:

a dark field illuminating light pipe concentrically aligned with the optical axis and surrounding the tapered translucent diffuser; and

a dark field illuminator directing illumination into the dark field illuminating light pipe.

7. The apparatus according toclaim 6 wherein the tapered translucent diffuser is removably attached.

8. The apparatus according toclaim 6 wherein the tapered translucent diffuser has a first color characteristic, the illuminator emits illumination having a color characteristic similar to the first color characteristic, and the dark field illuminator emits illumination having a second color characteristic.

9. The apparatus according toclaim 8 wherein the first color characteristic is blue, and the second color characteristic is red.

10. The apparatus according toclaim 8 wherein at least one color characteristic is infrared.

11. The apparatus according toclaim 6 further comprising:

a light absorbing filter applied to the diffuser and disposed between the diffuser and the region of interest.

12. The apparatus according toclaim 1 wherein the illuminator further comprises a plurality of selectively actuated illuminators.

13. The apparatus according toclaim 12 wherein the plurality of selectively actuated illuminators have a north-south and east-west selective actuation.

14. An apparatus for imaging a symbol on an object, the apparatus comprising:

a hand held portable imaging system having an imager;

a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;

an illuminator adjacent to the lens, directing illumination towards the region of interest;

a dark field illuminating light pipe having a first distal end surrounding the lens and the illuminator, and a second distal end surrounding the field of view proximate to the region of interest, the second distal end configured to emit a dark field illumination toward the object at a low angle; and

a tapered translucent diffuser concentrically aligned with the optical axis and disposed within the dark field illuminating light pipe, the diffuser having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the object.

15. The apparatus according toclaim 14 wherein the tapered translucent diffuser does not diffuse the dark field illumination.

16. The apparatus according toclaim 15 wherein the tapered translucent diffuser has a transparent optical property where it is disposed before the dark field illumination.

17. The apparatus according toclaim 14 wherein the tapered diffuser is removable.

18. The apparatus according toclaim 14 and further comprising a plurality of dark field illuminators at the second distal end of the dark field illuminating light pipe configured to provide the dark field illumination.

19. An apparatus for imaging a symbol on an object, the apparatus comprising:

a hand-held portable imaging system having an imager;

a lens disposed between the imager and a region of interest, the region of interest being the intended position of the symbol on the object, the lens and imager defining a field of view and an optical axis;

a first illuminator adjacent to the lens, directing illumination towards the region of interest;

a semi-reflecting mirror disposed in front of the lens aligned with the optical axis configured to direct at least a portion of illumination reflected from the region of interest into the lens;

a second illuminator directing illumination at the semi-reflecting mirror so that at least a portion of the illumination from the second illuminator is directed towards the region of interest;

a first diffuser disposed between the second illuminator and the semi-reflecting mirror; and

a tapered translucent diffuser concentrically aligned with the optical axis, having a first distal end surrounding the field of view proximate to the lens, and a second distal end surrounding the field of view proximate to the region of interest.

20. The apparatus according toclaim 19 wherein the first illuminator has a first intensity, and the second illuminator has a second intensity, so as to configure the apparatus to produce a uniform distribution of illumination over the field of view at the region of interest.

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