IL114650A - System and method for reading and decoding two dimensional codes of high density - Google Patents

Description

SYSTEM AND METHOD FOR READING AND DECODING TWO DIMENSIONAL CODES OF HIGH DENSITY A system for readinuitwo dimensional codes las well as regular bar codes. A laser scanner generates a narrow horizontal beam which is scanned by means of a scannjiig^mirror in the vertical direction which guides it on to its target : r le cojde The snir^ scanning mirror nr.cepfs the reflecting beam and passes it on to a lens array to yield high quality imaging characteristics all across a large field of view angle. The lens array and an auto focusing system produce images of the scanning lines in the sensor plane - a CCD linear array. The focusing beams pass from the lens array to the CCD rayj:hj_Quj>h optical wedges which deflect the image beams normal to sensor's plane). In the sensor's plane, sub aperture diaphragms generate partially overlapping fields of view from each of the elements of the lens array. The system Electronics, converts the CCD linear array is responsible for the autofocus adjustment algorithm , as well as for code classification and decoding. The processor module controls the operation of the system and its interface to the outside world.

Technical Field Back round of the invention Known two dimensional code readers are of two types: Th first type - Flying spot scanners7 , employing a focused laser spot , scanning two dimensional hnlh hn iV^n<1^ °ftH'^j<: ''<¾ftuy 'jfieliccond type - CCD based code readers" , where the scanning is obtained electronically , using an imaging lens and an area image sensor, or a"T7near CCD array , utilizing either a scanning mirror or a manual parameters of any bar code leader TTfcletermines the narrowest bar or space, that can be decoded. Resolution is typically measured in units of mil. (0.00 1 inch). As a rule , CCD-based Pi^e^eaders resolution than laser s^ajrngr^ , which can be explained as following: The spatial resolution of Hying spot laser scanners is determined by the-minimal effective spot ^iz^) of light , of the laser diode. This spot size is determined by the cross section of the focused laser beam in the working range , which is relatively large because of the diffraction limited beam waist in tlje_£gnter of the w o l i n jrange and nioreove.r_SP_.ai the ends of the working range . Ίη CCD based readers , the optical projection system creates the code's image on the surface of the CCD detector array1 . Optimal optical projection systems have Contrast Transfer Function(CTF), which allow to utilize effectively CCD sensors with a given pixel size so that the reader's spatial resolution at the surface of the code is determined solely by the size and number of the CCD array pixels.

Optical projection systems for reading two dimensional codes like PDF 4 1 7 need to have a wide field of view angle. Objectives of this kind have typically complicated optical schemes using 7-8 single optical elements , leading to a high component cost. Moreover so, the spatial resolution of such objectives is further limited at large field of view angles by off axis aberrations. Thus, the increase of spatial resolution of code readers, requires a new projection system design, that can yield high spatial resolution characteristics for a large area in the object's space, within the demanding working range.

Workin range (WR) is another significant parameter for bar code readers . It specifies the longitudinal distance range within which reading and decoding can be accomplished. Conventional CCD bar code scanners have a limited WR , determined by the limited depth of field of the optical system . Thus devices of that type are usable for reading bar codes at fixed distances only. This limitation of CCD bar code readers can be overcome by means of autofocus optics4'1 14.

Low reading sensitivity to the reader's holding position, is another significant parameter for code readers. The readers of two dimensional codes , available presently , are quite limited with this regard. Any small deviation from the optimal scanner position, prohibits code reading. The new type of reader , of the present invention , is capable of reading codes essentially at any rotational angle position. Furthermore , high speed processing techniques accelerate the code reading and decoding process .

Summary of the invention One goal of this invention is to increase the code reader's spatial resolution across the entire large field of view, or as known by the term: equipment resolution , used to print the code .

Another goal of this invention is to increase the light level intensity at the CCD linear array's surface , by employing imaging optics of a larger diameter to aperture ratio and by synchronizing the illumination with the image scanning .

Yet an additional goal of this invention is the increase of the light intensity uniformity of the illuminated images of the scanning lines on the CCD linear array, by employing similar angle magnitudes for the incident and reflecting light from the target at all scanning surface of code.

Yet an additional goal of this nvention is to minimize the sensitivity of the code reading capability to the rotational position of the reader , by employing electronic image rotation techniques.

Brief description of the drawings FIG. 1 is a simplified schematic illustration of the system provided by the present invention.

FIG. 2 is a simplified optical scheme of the optical projection system . A linear lens array, inclined relatively to each other yields a high quality Held of view angle, according to this invention.

FIG. 3 is the linear lens array with optical wedges placed between the lenses and the CCD linear array, according to this invention..

FIG. 4 is the linear lens array with optical wedges placed before the lenses, according to this invention.

FIG. 5 is the linear lens array with a cylindrical negative meniscus lens before the lens array, according to this invention.

FIG. 6 is the illuminating section with focusing cylindrical optics and beam-splitter, according to this invention.

FIG. 7 is the illumination section and the mirror scheme with a high reflectivity small central region, according to the present invention.

FIG. 8 is the illumination section and the mirror with a high reflectivity peripheral large area coating, according to this invention.

FIG. 9 is a How diagram of the electronics' main processing steps Detailed description of the invention FIG. 1 depicts an exploded view of system 1 00 of the present invention. The system 100 comprises a housing 1 10, having a base 1 12 and a cover 1 14. In the preferred embodiment , the housing parts are connected through an angle 1 16 , Since the geometry of the housing is selected to optimize ease to use by a human operator. Yet in another embodiment , where the code reader is not manually operated but rather mounted on a surface , the system can be combined of a different housing structure. The housing is used to place the inside parts of the system at fixed locations , as well as to protect them from any physical damage.

The inside of the reader consists of the following main parts: • Illumination unit • Receiver unit • Electronics A beam of monochromatic light , produced by a source 120 is focused by means of optical system 1 22 into a narrow line. The source 120 is preferably a laser diode in range of the visible light 635-670 nm. The choice of a laser diode has several advantages. It is a compact, low cost and energy efficient light source. A large number of laser diodes, generating radiation in this spectral range, are available from different sources. A specific example is the 3500 Series Diode Laser Systems from U N I PHASE. That series of laser diodes is low cost, compact and generates a high quality beam with adequate intensity.

The use of visible light in the spectral range of 635-670 nm has a following advantages: => User's ability to visually aim the raster pattern to the code . => The beam, reflected from the black and white printed code surface has a maximal contrast in this spectral range.

This spectral range coincides with the range of maximum sensitivity for the CCD detector array.

Very often laser diodes are fully integrated modules including beam correcting optics and diode driving electronics in one compact, cost-effective package. A cylindrical lens 122 generates a narrow line of laser light 124 with a fan angle sufficient to fully illuminate the code pattern within the working distance . The narrow focused line of light falls on the mirror 126 which is tilted by 45° to the output beam axis.

In the embodiment depicted in Fig. 6 the surface of the mirror 626 is coated with a 50% reflection coating so that the light beam 624 in this spectral range would be 50% reflected and 50% transmitted. Thus in this embodiment , the light beam generated by the laser diode , falls on the mi ror . 50 % of the light is deflected by 90° and 50 % of the light passes through the mirror without any change of direction. The light that passes through the mirror hits another mirror 128 at the same angle , which deflects the output beam by 90° again. This beam exits through the housing Avinclow 1 18 - a bandpass filter for the illumination's spectral range - and illuminates the code 130 in a way that the line of light 132 surpasses the edges of the code.

The mirror 1 28 has a scanning capability. Thus it can rotate using electromechanical means 160, by a predetermined reciprocal angle around an axis 1 27 located on its surface and parallel to the line of light 132 generated by the laser diode. In the process of scanning , the horizontal beam of light is moving consecutively across the object , covering the entire surface of the code while surpassing it at the edges.

The light reflected from the code's surface , is diffused and propagates in a spatial angle of 2π steradians. The intensity of the reflected light is the largest in the direction of the mi ror's specular reflection and decreases for larger angles between the direction of specular reflection and any other direction. A portion of the diffused reflected light 140 from the illuminated pattern passes through the housing window , hits the receiver part of the system , i.e. : hits the scanning mirror 128. The beam reflected from the scanning mirror in the direction of the mirror 126 , is divided into two equal intensity beams by means of the semi-reflection coating of this mirror . The first beam is deflected by an angle of 90° while the second beam is transmitted through without a change of direction.

The deflected beam , which is the input beam , is transmitted by means of this mirror to the optical projection system 150 , the axis of which coincides with the axis of the input beam. Thus the illumination and receiver parts are combined by means of the system of the two mirrors of the illumination section, which outputs a narrow divergent beam from the light source through the system housing window onto the code. Simultaneously these mirrors are mirrors of the receiver part , which capture the diffused light , reflected from the code and pass through the flller window housing.

Combining the illumination and receiver parts by common minors, in the present invention, enables to closely utilize the reflected beam in the direction of maximum intensity . Furthermore , it allows synchronizing the illumination and receiver beam scanning and illuminate simulaneously only one horizontal line and thus increase the illumination brightness.

The light intensity across the horizontal lines is uniform , while the intensity of the line decreases slightly as the distance from the central scanning line increases . The decrease of light intensity is symmetrical to the central line. This difference from prior art increases significantly the uniformity of light intensity across the code and allows for the system to read larger area codes at the same working range.

In this embodiment , passing the illumination beam through the mirror 126 with semi reflecting coating and reflecting the input beam from it , causes a 75% loss of input light intensity without considering any other losses in the optical system.

In the preferred embodiment , depicted in Fig. 7. , the loss of light on the mirror 726 can be negligible. To implement this feature , mirror 726 lias a central high renectivity small region 721 used to reflect the focused illuminating light 724 from the source 720, while the rest of the mirror 723 is transparent to transmit the input beam 740, coming from the scanning mirror to the optical projection system in the receiver part.

In another embodiment , depicted in Fig. 8 , mirror 826 has a transparent central small region 82 1 , used to pass the focused illuminating beam 824 from the source 820, while the rest of the mirror 823 has a high reflectivity coating for reflectin the input diffused beam 840, reflected from the code and coming from the scanning mirror to the optical projection system.

In the present invention , the optical projection system that receives the diffused reflected light from the code's surface, is a horizontal linear lens array 1 50 consisted of the individual lenses 152. As depicted in Fig. 2 , each element of the array 252, generates on the conjugate surface, a separate image 254 of the code illuminated line, at each angular position of the scanning mirror.

To increase the system field of view, in the working range , every lens 252 of the array is inclined in the horizontal surface relatively to the adjacent lens by twice the field of view angle of a single lens at the closest object plane in the working range. The optimal field of view angle for a single lens is the angle which generates an image with the optimal resolution for a given CCD array 256 pixel size. Each single lens of the array, forms its own image of code line 230. The central part of the line , located around the lens optical axis , has optimal image quality characteristics while the resolution decreases further away from it towards the edges of the image. The close edges of two adjacent line image sections represent an overlap part on the object line.

The system field of view equals 2n where a is the field of view angle for a single lens of the lens array and n is the number of lenses. The image surface is inclined similarly to the inclination of the lens array elements. This creates some defocusing effect at the inclined image edges of each lens, depending on the angle of inclination. The outcome is some degradation in image resolution at the edges. It is known that the permissible defocusing allowed is proportional the pixel size and inversely proportional to the lens aperture. Thus if a small aperture is used , the defocusing effect will be negligible.

In another embodiment , depicted in Fig. 3 , the focused beams from the single lens pass on the way from the lens 352 to the image plane through a corresponding array of optical wedges 358 , deviating the focused beam to the normal of the general image plane. Under these conditions , the image surface of each lens coincides with the general image plane .

In another embodiment , depicted in Fig. 4 , the individual lenses of the lens array 452 are not inclined to each other and the optical wedges 458 are located symmetrically around the lens optical axis, between the mirrors of the receiver part and the lens array. Their size is defined by the full utilization diameter of each lens. The narrow ends of the optical wedges are directed towards the general optical axis of the system while the wedge angle is in the lens array axis plane. The magnitude of the wedges' angles , are determined as following : the light beams , in the space before the wedges, that pass through the wedges and are focused by the lenses, are inclined to each other at an angle which equals twice the field of view angle of a single lens. This yields, for the system, an overall field of view angle which equals 2an.

In the preferred embodiment, depicted in Fig. 5, a negative meniscus lens 559 is used , in front of the lens array.

The surfaces 555 of this lens is oriented perpendicular to the lens array and light gathering are optimized for cylindrical surfaces. The size of the meniscus along the lens array is determined by the number of the lenses in the array, while the perpendicular dimension is determined by the single lens diameter. The material and radii of curvature of the lens , are determined by the required image quality of the single lens and the field of view of the system. The overall aberrations are determined by the joint optical system combined of the meniscus lens and the lens array . The use of a lens array in this system , is enabled by utilizing the system electronics to omit the double overlap parts of the image line sections and synthesize them into a single continuous image line signal.

For every object plane in the working range of the system, there exists a equivalent conjugate image plane. Any change in the location of the code within the working range , changes the location of the image plane. In one embodiment of the system, the location of the image plane is adjusted automatically by translating the optical projection system along the optical axis of the system. The optical projection system is translated mechanically by electromechanical means 1 70, based on feedback from the system electronics. The feedback is determined by calculating the contrast of the digitized signal line across the code. Thus the optimum location of the optical projection system is determined at the position where the signal gains a maximum contrast (patent reference). The high contrast nature of the code's signal is a contributing factor to the autofocus implementation.

In this invention , a linear CCD array 1 56 , is located in the general image plane , where the sectional line images are formed. The linear CCD array coincides with the sectional image lines. The pixel size of the CCD array is determined by the required spatial resolution in the code plane; The number of pixels in the array is determined by the optical projection system parameters , in a way that all the individual sectional images are located on the CCD array . Some extra number of pixels are needed to account for imperfect alignment of the optical system.

Image field diaphragms 151 are located In the CCD array plane . This is to differentiate those fields and to prevent diffused beam passed through a lens to hit the image fields of the neighboring lenses. The sizes of the diaphragms along the horizontal axis are determined so that the sectional images 1 54 partially overlap image sections of neighboring lenses. The magnitude of overlap is determined by the requirement of the electronics to synthesize the sectional image into an integrated continuous image line.

The main algorithmic processing steps performed by the system electronics , are depicted in the flow diagram of Fig. 9. Those can be devided into the following three parts : • Pre-scanning processing • Code scanning • Post-scanning processing Prior to scanning the code, the scanning minor is fixed so that the system outputs a stationary illuminating line which can be aimed by the user to the center of the code. The pre-scanning processing algorithmic steps 960 performed during this time are those which require data from a single cross section of the code . The autofocus algorithm 962 provides the autofocus electromechanical means 170, the feedback required to determine the optimum lens array position. The cross-correlation calculation 964 provides the overlap data required during the image synthesis step 974.

During code scanning 970 , the scanning mirror rotates slightly so that the illuminating beam scans the entire code and the system performs the steps , required to store the digitized image into memory . Analog to digital conversion 972 , is the first step which yields digital data from the electrical signal output of the CCD array. Image synthesis 974 , prepare the data in real-time , during the scanning , to be stored in an integrated form. Image acquisition 976 , stores the integrated data into memory.

The multi-element lens arrangement of the system , can yield a combined large field of view angle with high performance image parameters all across the field. The outcome of combining n sectional views into a single large field of view, yields n- 1 small overlap areas between the sectional views . Those overlap areas ge erate double signal sections on the CCD array. A cross-correlate electronic unit finds the exact location of the pixels in the overlap areas to yield an integrated single continuous synthesized image . The image synthesis is implemented electronically by calculating the cross-correlation amount, between the signal end of one section and beginning of the signal of the following section. The point of maximum correlation would indicate the exact overlap area . The correlation can be expressed mathematically by the following function : ) · (/ + A- ) where /,, - Is the first pixel of the correlation function.

N - Is the number of pixels summed up for the correlation function. />· - Is the parameter that determines the exact distance of pixels between the signal of one section and the corresponding overlap signal in the subsequent section.

The purpose of the calculation is to find the value of A- , which determines the exact number of pixels between the two consecutive overlapping sections. This is performed by calculating repeatedly the crosscorelation function , until the maximum of this function is reached. Due to the high contrast nature of the signal, the crosscorrelation function would have a well defined maximum point and thus would allow finding A- quite easily. Since the distance in number of pixels between overlapping sections is invariable for a given working range, finding this number between every two consecutive sections, can be done as a calibration procedure and applied to the data acquisition during the scanning process.

Post-scanning processing 980 includes the algorithmic steps performed on the acquired image after the scanning , to yield tlie decoded data. Image rotation 982, measures the angle of rotation between the horizontal axes of the system and the code and restores the image data, correcting for that angle. Code discrimination 984 identifies automatically the type of code and determines whether the scanned code is two dimensional or a standard bar code. If a standard bar code is identified then it is decoded as a regular bar code. Decoding 986 decodes the code to yield the output data.

The horizontal scan lines of the scanner can be at any. arbitrary angle with respect to the orientation of the code. This requires a 'rotation' of the code image by an angular amount that would make the digital code stored in memory , aligned with the orientation of the code. Code rotation would be implemented in two steps: 1 . Rotational angle measurement - Two dimensional codes like PDF417 include several vertical parallel lines on both sides of the code. Those can be instrumental in measuring the rotational angle between the reader position and the two dimensional code. 2. Image rotatio - The calculation would be based on the following xy rotjkjkjkioh in ational equation : x(iww) = {x - x{.))}*cosO+{y - yifew ) = -{x-x{Q))*sinO+{y-y(Q \*cosO The actual code rotation would be implemented by a dedicated electronic module using lookup tables for the trigonometric functions and thus performing the image rotation in real-lime at the clock rate.

References: US patent documents 1. 4,900,907 Matiisima et al, February 1990 2. 4,935,609 Wike et al, June 1990 3. 5,155,343 Chandler et al,October 1992 4. 5,192,856 Schaham, March 1993 5. 5,192,857 Detwiler, March 1993 6. 5,210,398 Mellilsky, May 1993 7. 5,233, 170 Metlitsky et al, August 1993 8. 5,296,690 Chandler et al,March 1994 9. 5,304,786 Wang et al, March 1994 10.5,319,181 Shellhamnier el al, June 1994 11.5,319,185 Obata, June 1994 12.5,335,007 Choi,August 1994 13.5,378,881 Adachi, January 1995 14.5,387,786 Peng, February 1995

Claims (25)

Claims We claim:

1. A method for reading and decoding two dimensional data presentation at .hi a space bandwidth produc . in the far field, comprising: projecting and illuminating a narrow monochromatic line form light beam onto the two dimensional object , scanning it in the direction perpendicular to the illuminating line , relaying the diffused light reflected off the object's plane via the light projection system, to a dynamically focussing imaging means , imaging the illuminated object line as several sub- aperture separate images onto a linear detector array , electronically synthesizing the sub-aperture separate images into an integrated image line , digitizing and storing the scanned image , rotating the stored image to obtain proper image orientation and decoding the data.

2. A system for reading and decoding information which is encoded as an array of consecutive rows of black and white squares, i.e. a two dimensional code , the system comprises of means to illuminate the code , to detect the diffused light reflected off the code surface , to convert the detected diffused light into electrical digital signals and decode the data carried by the code , said system comprising: • a housing containing an illuminating unit , comprising: a filter window; a source of directed monochromatic radiation; optics for focusing the radiation from said source onto a narrow dispersed light beam; a system of two mi rors, placed following each other on the direction of the beam from the light source , placed at an angle to the beam axis, the two mirrors direct the said light beam through the said window , so that the beam illuminate the said two dimensional code along the horizontal axis; • a receiving unit comprising: a filler window; an input system of two mirrors , placed following each other on the direction of the light reflected off the code's surface and entering the system through the said window; an optical projection system which receives the diffused reflected light off the code's surface through window and the receiving mirrors and focuses the beams to create the image of the code in the conjugate image plane; sub-aperture diaphragms; a linear CCD array , placed in the image plane , which is the conjugate to the code's surface; autolOcus electromechanical means , translating said projection optics to yield a focused image at the stationary plane of said CCD array at varying ranges of said system from said code's surface; • an electronics system comprising: an image synthesizer module to generate a single continuous image line from the original partially overlapping sub-images obtained by the system optics; an image rotatio module , which includes means to rotate the code image acquired at any angular position of the said system; an autofocusing module , including a method to provide focusing feedback data to said autofocus mechanism.; a general processing module including a code classifying and decoding means.

3. A system according to claim 2 where the mirrors of said illuminating unit which output the illuminating beam are the same mirrors, used by the receiving unit to input the beam reflected off the object's surface , in a manner where the output beam and the input beam are scanning the object synchroneously.

4. A system according to claim 3 where the second mirror on the output beam axis of the said illuminating unit, which is the first mirror on the input beam axis in the receiver unit, is made to scan the vertical axis of the said two dimensional code , by changing the angular position of said mirror , turning this mirror moves the horizontal output light beam vertically , as well as directs the corresponding line of the code onto the said projection optics of the receiving unit.

5. A system accordin to claim 2,3 or 4 where the first mirror on the output beam axis, of the said illuminating unit has a small reflective coated central region which is used to reflect the focused beam coming from the source, the rest of the mirror , which is transparent , is used to pass the diffused reflected beam from the code surface on its way from the said scanning mirror to the said optical projection system.

6. A system according to claim 2,3 or 4 where the first mirror on the output beam axis, of the said illuminating unit has a small transparent central region, used to pass the focused light beam coming from the source to the scanning mirror, the rest of the min or , coated with a high reflectivity coating , is used to direct the diffuse reflected light from the code's surface , on its way from the said scanning mirror to the said optical projection system.

7. A system according to claim 2,3 or 4 where the first mirror on the output beam axis, of said illuminating part has a semi-transparent coaling , where half of the focused light beam coming from the source to the said scanning mirror, passes through, while half of the diffused light reflected from the code's surface on it way through the scanning mirror , is reflected by this mirror to the said optical projection system.

8. A system according to claim 2 where said optical projection system , that receives the diffused light , reflected by the code's surface is made of a linear lens array mounted on a common horizontal base line. The parameters of said lenses are optimized to yield the highest image quality for the said spectrum and the given working range . The sub- aperture horizontal code images are generated by said lenses in the plane of said CCD linear detector array so that each sub-aperture image the edges slightly overlaps with the sub-aperture image of the neighboring lenses.

9. A system according to claim 2 where the said optical projection system is made of a linear lens array where the individual lenses are inclined to each oilier in the horizontal plane. The angle of inclination equals twice the field of view angle of the individual lens so that each lens creates a high quality image of the corresponding horizontal line section on the code's surface, each lens creates a high quality sectional image of part of a horizontal line on the code's surface so that the overall field of view angle of the system equals 2 Ν , where a equals the field of view of the individual lens , N equals the number of individual lenses in the said lens array.

10. A system according to claim 9 where the beams focused by the said lenses, pass to the said CCD linear detector array , through horizontally arranged optical wedges , which deflect the beam in a direction normal to the plane of the CCD detector array.

11. I I . A system according to claim 8 where the diffused beams reflected off the code's surface and pass through the said two receiver mirror system pass through an array of optical wedges , the optical wedges , centered on the optical axis of each of the lenses , deflect the input beams so that the sub-images created by the lenses of the said lens array, are placed on the general image plane of the said linear lens array, the top angles of the wedges are directed to the central optical axis of the system the wedges being inclined to each other in an angle so that the overall field of view angle of the system equals 2αΝ , where a equals the field of view of the individual lens , N equals the number of individual lenses in the said lens array.

12. 1 2. A system according to claim 8 where the diffused beams reflected off the code's surface and pass through the said two receiver mirror system, pass through a negative meniscus lens, the outer diameter of the lens along the horizontal axis is determined by the overall dimension of the linear lens array while its width in the. perpendicular axis is determined by the single lens diameter, the parameters of the meniscus lens such as material and radii of curvature, of the its optical surfaces, are designed to optimize the image quality at the plane of the CCD linear array and in the field of view of the system.

13. A system according to claim 8 where a series of diaphragms are placed in the plane of the said CCD linear detector array, the dimension of each diaphragm along the horizontal axis , are determined by the field of view of the individual lens of the said lens array , the field of view of each lens is designed to partially overlap with the field of view of the neighboring lenses, the size of the overlapping section being optimized for the said synthesizing electronics module , used to generate an integrated continuous line from the sectional line images.

14. A system according to claim 2 where the means of electronics image synthesis generates an integrated continuous image line from the sub- image line sections , generated by the said optical projection system and converted to an electrical signal by the said CCD linear array, the image synthesis is implemented by omitting the pixels at the edges of the partial image sections which include the overlap image areas, the overlap area is determined by a cross-correlation function and applied to the said electronics synthesizer module to synthesize the digital image signal in real-time.

15. 1 5. A system according to claim 2 where means of image rotation rotates the image in real-lime by an angle equal and opposite in direction to the angle between the horizontal axis of the code to the horizontal axis of the said system, to lower reading sensitivity to the angular position of the said system, angle of rotation being measured by using vertical reference code lines on its surface and applying the angle of rotation to a dedicated angle rotation electronics module, which rotates the image in real-time.

16. 1 6. A system according to claim 2 without an autofocusing mechanism is not present , or where it is not operated since a fixed working range of the system does not require it.

17. 1 7. A system according to claim 2 where a means is used to classify the type of code automatically , if a regular bar-code is being detected, the class of code is detected automatically the bar-code is decoded, if a two dimensional code is being detected , it is classified and decoded as a two dimensional code, the type of code can be predetermined manually by the operator, prior to operating the system to save processing time.

18. 1 8. A system according to claim 2 where it is operated manually by an operator holding it in his hand.

19. A system according to claim 2 where it is operated automatically while being mounted at a fixed location.

20. A system according to claim 2 where it is connected electrically to a computer via a computer interface and uses the computer memory to store the decoded output data.

21. . A system according to claim 2 where it operates independently by using a rechargable battery option to power the system and additional nonvolatile memory to save temporarily the said decoded output data.

22. A system according to claim 2 1 where an optional infrared transmitter is used in conjunction with an infrared receiver to transmit the decoded output data to a computer located further away from the said system.

23. An system according to claim 22 where an optional radio transmitter is used in conjunction with a radio receiver to transmit the decoded output data to a computer located further away from the said system.

24. Method for reading and decoding two dimensional data presentation, and especially two dimensional bar codes, substantially as hereinbefore described and with reference to the Figures.

25. A system tor reading information and decoding it, and especially for reading and decoding two-dimensional bar codes, substantially as herein described and with reference to the enclosed Figures.