Abstract:
An imaging device for imaging a document including an enclosed imaging-optical-chamber, a processor, a camera mounted inside the imaging-optical-chamber, at least two clusters of light sources disposed inside the imaging-optical-chamber, for directly illuminating of the document, and a glass-window. The clusters of light sources are operated, one at a time, in a preconfigured sequence, and the camera is preconfigured to acquire an image frame of the document, operatively coupled with the activation of each of the clusters. The direct illumination causes formation of hotspots in the acquired image frames at preconfigured locations, corresponding to the preconfigured positioning of the clusters. The processor is facilitated to cutout the preconfigured image frame portions containing the hot spots, forming clean portions of the acquired image frame, and to combine the clean portions of acquired image frame to form an output image frame of the document.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to illumination systems and methods for cameras, and more particularly to an illumination system and method facilitating a small-form camera-based imaging device for documents, wherein the imaged document is directly illuminated by alternating clusters of light sources. 
       BACKGROUND OF THE INVENTION 
       [0002]    There exist in today&#39;s market imaging devices capable of reading documents such as ID cards, drivers license, business cards, passports, medical cards and the like. In imaging devices that include an imaging sensor array, based on technologies such as a CCD or CMOS, it is required to illuminate the imaged document. It is desired that the illumination will be of high intensity and substantially uniform, in order to obtain a substantially true image of the imaged document. 
         [0003]    The document is typical place on the surface of a substantially flat and substantially transparent panel, typically, with no limitation, made of glass (herein, also referred to as “glass-window”). But the glass surface and the imaged document are also a reflective surface, returning a portion of the incident light rays striking the transparent glass surface. Thereby, the image frame acquired from the imaged document is distorted. An internal light source that directly illuminates the glass-window bring are reflected from the glass surface, thereby forming “hot spots” that distort the uniformity of the illumination of the imaged document, and thereby causing the image of the imaged document not to be a substantially true image of the imaged document. 
         [0004]    Reference is now made to  FIG. 1   a  (Prior art) and to  FIG. 1   b  (Prior art).  FIG. 1   b  depicts a pair of hot spots  40  caused by direct illumination of the imaged document disposed on the external surface of a glass-window  20 , as viewed from inside the camera housing.  FIG. 1   a  illustrates how hot spots  40  are formed by direct illumination of the imaged document  10  disposed on the external surface of a glass-window  20 . When imaging document  10  with a camera  50 , document  10  needs to be illuminated. In a conventional illumination method, as shown in  FIG. 1   a , illumination sources  30   a  and  30   b  are positions to directly illuminate glass-window  20 . Such configuration enables the return of the majority of light to the lens of camera  50 , but gives rise to a hot spot  40 , where the light source ( 30 ) itself is imaged by camera  50 . 
         [0005]    US patent application 20080285094, by Hatzav et al., provides a configuration method of the illumination system that reduces the hot spot problem, by disposing the light sources outside the field of view (FOV) of the camera. Reference is now made to  FIG. 2  (Prior art), illustrating a pair of light sources  30  that are disposed outside the conventionally preconfigured FOV  60  of camera  50 , which FOV  60  of camera  50  is denoted by virtual lines  62 . Furthermore, the inner walls  55  and  75  of inner space  70  of the prior art document imaging device are white to further enhance the uniformity of the illumination. However, back-light (indirect) illumination brings about loss of light intensity and requires a high intensity light source. Furthermore, hot spots of lower intensity, with respect to direct illumination, still appeared in the image formed. 
         [0006]    U.S. patent application Ser. No. 13/185,510, by Hatzav et al., provides a configuration method of the illumination system that reduces the hot spot problem, by disposing the light sources outside the field of view (FOV) of the camera. Reference is now made to  FIG. 3  (Prior art), a schematic side view illustration of an imaging device  80 , having light-occluding structures  88  disposed inside the housing  82  of imaging device  80  such that the imaginary light source  30 ′ of light sources  30  are situated outside the extended FOV  64  of camera  50 , combined with mirrors  84  and reflective glass-window  20 , which FOV  64  is denoted by virtual lines  66 . Imaging device  80  does provide a small form imaging device having a substantially uniform illumination, but imaging device  80  is complex to manufacture and substantial illumination intensity is still lost before reaching camera  50 . 
         [0007]    Thus there is a need for and it would be advantageous to have a simple direct illumination and thereby inexpensive, small-form camera-based imaging device that has an illumination system that provides uniform illumination with no hot spot effects, as well as avoiding substantial loss of illumination intensity. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of the limitations now presented in the prior art, the present invention provides a new, simple and useful imaging device for imaging documents that in effect, facilitates enhancement of the uniformity and intensity of the document illumination, utilizing an image sensor array and alternating clusters of light sources, disposed in preconfigured location inside the housing of the imaging device. 
         [0009]    The term “cluster of light sources”, as used herein, refers to a single light source, composed of one or more light emitting devices, such as, with no limitation a LED light source, are activated or deactivated as a single unit. When activated, the cluster of light sources directly illuminates at least a portion of the imaged document, at a preconfigured illuminating angle. 
         [0010]    The term “alternately operating” in relation to the operation of all clusters of light sources, as used herein, refers to the activation of all of the clusters of light sources, one at a time, in a preconfigured sequence. 
         [0011]    It is then a principle intention of the present invention to provide an imaging device for imaging documents that has a small form and that includes a direct illumination system that provides an output image frame of the imaged document that contains substantially no hot spots. 
         [0012]    The present invention is an improved imaging device for imaging documents, wherein the document is directly illuminated by at least two clusters of light sources, and wherein the output image frame does not contain hot spots formed as a result of the direct illumination of either of the at least two clusters of light sources. 
         [0013]    Preferably, the imaging device includes an enclosed housing that prevents internal light from escaping the optical chamber of the imaging device, and more importantly, prevents external light from entering the optical chamber of the imaging device and possibly distorting the uniformity of the illumination. 
         [0014]    According to the teachings of the present invention, there is provided an imaging device for imaging a document including an enclosed imaging-optical-chamber, a processor and at least one camera mounted inside the imaging-optical-chamber, wherein the camera is configured to acquire image frames of at least a portion of the document. The imaging device further includes a glass-window, wherein the document is operatively disposed on the external surface of the glass-window. 
         [0015]    The imaging device further includes a light source configuration, disposed inside said enclosed imaging-optical-chamber, facilitated to directly illuminate the document from at least two illuminating angles. That is, each point in the document is illuminated from at least two different angles. Preferably, the imaging device includes at least two static clusters of light sources, for directly illuminating the portion of the document being imaged. Optionally, the imaging device includes a single cluster of light sources, disposed inside the enclosed imaging-optical-chamber, operatively coupled with a deflection mechanism for deflecting the light beams may be emitted from the cluster of light sources. The mechanism for deflecting the light beams operatively deflects the light beams to at least two preconfigured illuminating angles, wherein the camera is preconfigured to acquire an image frame of the document at each of the at least two illuminating angles. 
         [0016]    The clusters of light sources are operated, one at a time, in a preconfigured sequence, and the camera is preconfigured to acquire an image frame of the portion of the document being imaged operatively coupled with the activation of each of the clusters of light sources. Since glass-window and the document are directly illuminated by the clusters of light sources, hotspots are formed in the acquired image frames at preconfigured locations, corresponding to the preconfigured positioning of the clusters of light sources. 
         [0017]    The processor is facilitated to cutout the preconfigured image frame portions containing the hot spots, forming clean portions of the acquired image frame. The processor is also facilitated to combine the clean portions of acquired image frame to form an output image frame of the portion of the document. Thereby, obtaining an output image frame of the imaged document that contains substantially no hot spots. 
         [0018]    Optionally, the document is an identity document. 
         [0019]    Optionally, each individual light source of the light source configuration is selected from the group of light sources type: Infra Red (IR), Ultra Violate (UV), Visible Light (VL) and fluorescence image. 
         [0020]    Optionally, each individual light source of the light source configuration is a LED light source. 
         [0021]    Optionally, each individual light source of the light source configuration is a halogen light source. 
         [0022]    Preferably, all walls of the optical chamber are opaque, except for the glass-window. 
         [0023]    Preferably, all internal walls of the imaging-optical-chambers, except for the glass-windows, are painted in black. 
         [0024]    An aspect of the present invention is to provide a method for imaging a document, including the steps of providing an imaging device as described hereabove, wherein the clusters of light sources are preconfigured to directly illuminating the portion of the document being imaged; wherein the clusters of light sources are preconfigured to alternately operate; and wherein the camera is preconfigured to acquire an image frame of the portion of the document being imaged operatively coupled with the activation of each of the clusters of light sources. 
         [0025]    The method further includes performing alternately, one at a time, for all of the clusters of light sources, the steps of: a) activating a first cluster of the clusters of light sources to directly illuminating the document being imaged; b) acquiring an image frame of at least a portion of the document; c) deactivating the first cluster of light sources; and d) discarding a preconfigured portion of the acquired image frame, thereby forming a clean portion of the acquired image frame. 
         [0026]    When the sequence of activated all clusters of light sources and obtaining a corresponding sequence of clean portion of the acquired image frame, the method further performs the step of combining the clean portions of the acquired image frame portions to form an output image frame of the portion of the document. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The present invention will become fully understood from the detailed description given herein below and the accompanying drawings, which are generally not drawn to scale and are given by way of illustration only and thus, not limitative of the present invention, and wherein: 
           [0028]      FIG. 1   a  (prior art) illustrates the hot spot problem caused by direct illumination of the imaged document or external light sources; 
           [0029]      FIG. 1   b  (prior art) depicts a hot spot caused by direct illumination of the imaged document and a substantially transparent window in front of the imaged document; 
           [0030]      FIG. 2  (prior art) illustrates an indirect illumination configuration, as provided by some prior art document imaging devices; 
           [0031]      FIG. 3  (prior art) is a schematic side view illustration of an imaging device, having light-occluding structures disposed inside the imaging device, such that the imaginary light sources are situated outside the extended FOV of camera, thereby providing a substantially uniform illumination. 
           [0032]      FIG. 4  is a side view illustration of an imaging device having alternating clusters of light sources, according to embodiments of the present invention, wherein a side wall has been removed for illustration purposes only; 
           [0033]      FIG. 5  is a perspective view illustration of the imaging device shown in  FIG. 4 , wherein a side wall has been removed for illustration purposes only; 
           [0034]      FIG. 6  depicts an example document; 
           [0035]      FIG. 7   a  depicts an image frame of the document shown in  FIG. 6 , acquired by the imaging device of the present invention, wherein  2  clusters of light sources were activated; 
           [0036]      FIG. 7   b  depicts an image frame of the document shown in  FIG. 6 , acquired by the imaging device of the present invention, wherein a first cluster of light sources is activated; 
           [0037]      FIG. 7   c  depicts an image frame of the document shown in  FIG. 6 , acquired by the imaging device of the present invention, wherein a second cluster of light sources is activated; 
           [0038]      FIG. 7   d  depicts the output image frame of the document shown in  FIG. 6 , composed from portions of the image frames shown in  FIGS. 7   b  and  7   c;    
           [0039]      FIG. 8  is a schematic flow chart showing an exemplary method of obtaining an output image frame that contains substantially no hot spot traces, according to embodiments of the present invention, utilizing a document imaging device as in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    Before explaining embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the host description or illustrated in the drawings. 
         [0041]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art of the invention belongs. The methods and examples provided herein are illustrative only and not intended to be limiting. 
         [0042]    Reference is now made to  FIG. 4 , a side view illustration of an imaging device  100 , according to embodiments of the present invention, wherein a side wall has been removed for illustration purposes only. Imaging device  100  includes a body  110  enclosing an imaging-optical-chamber  170 , a camera  150 , two or more clusters of light sources  130 , a glass-window  120  and a processor  190 . Reference is also made to  FIG. 5 , a perspective view illustration of imaging device  100 . It should be noted that in  FIGS. 4 and 5 , a side wall has been removed for illustration purposes only. 
         [0043]    Camera  150  is disposed on the internal surface of a camera wall  155  such that, preferably, the FOV  160  of lens  152  of camera  150  (also referred to as the FOV  160  of camera  150 ) views at least the whole of glass-window  120 . Typically, camera wall  155  is disposed opposite to glass-window  120 . Typically, clusters of light sources  130  are also disposed on the internal surface of camera wall  155  such that clusters of light sources  130  are not directly viewed by the FOV  160  of camera  150 . 
         [0044]    The operation of imaging device  100  is now explained through an example supported by  FIGS. 6 and 7   a - 7   d .  FIG. 6  depicts an example document  10   a , containing 9×9 rectangles arranged in a larger rectangle and separated by white gaps.  FIG. 7   a  depicts an example image frame  200  of document  10   a , acquired by imaging device  100 , wherein two clusters of light sources,  130   a  and  130   b , were activated, forming respective hot spots  230   a  and  230   b .  FIG. 7   b  depicts an example image frame  202  of document  10   a , acquired by imaging device  100 , wherein a first cluster of light sources  130   a  is activated, forming a respective hot spot  230   a .  FIG. 7   c  depicts an example image frame  204  of document  10   a , acquired by imaging device  100 , wherein a second cluster of light sources  130   b  is activated, forming a respective hot spot  230   b .  FIG. 7   d  depicts an example output image frame  206  of document  10   a , composed from portions of the image frames  202  and  204 . It should be noted that a cluster of light sources include one or more light source. 
         [0045]    Referring now to  FIG. 7   a , image frame  200  of document  10   a , the hot spot problem is illustrated. In this example, with no limitations, imaging device  100  includes two clusters of light sources  130   a  and  130   b , both of which clusters of light sources are activated, as often done in conventional imaging devices. Image frame  200  of document  10   a , acquired by imaging device  100 , includes two hot spots  230   a  and  230   b , formed respectively by the clusters of light sources  130   a  and  130   b.    
         [0046]    The method of the present invention is exemplified, with no limitations, in  FIGS. 7   b - 7   d . The two clusters of light sources  130   a  and  130   b  are alternately activated, at a preconfigured activation rate. When light source cluster  130   a  is ON, light source cluster  130   b  is OFF, and vice versa. Each image frame is subdivided, for example, into two sections, a top section and a bottom section, wherein “top” and “bottom” refer to the image frames ( 202 ,  204  and  206 ), as seen in  FIGS. 7   b - 7   c.    
         [0047]      FIG. 7   b  depicts image frame  202  of document  10   a , acquired when the first cluster of light sources  130   a  is ON (and the second cluster of light sources  130   b  is OFF), forming a respective cluster of hot spots  230   a  within the bottom section  202   b  of image frame  202 . It should be noted that typically, cluster of light sources  130   a  is disposed on the internal surface of camera wall  155  at a preconfigured location, such that the corresponding cluster of hot spots  230   a  is formed within the bottom section  202   b  of image frame  202 , with substantially no hot spot traces within the top section  202   t  of image frame  202 . 
         [0048]    Similarly,  FIG. 7   c  depicts image frame  204  of document  10   a , acquired when the second cluster of light sources  130   b  is ON (and the first cluster of light sources  130   a  is OFF), forming a respective cluster of hot spots  230   b  within the top section  204   t  of image frame  204 . It should be noted that typically, cluster of light sources  130   b  is disposed on the internal surface of camera wall  155  at a preconfigured location, such that the corresponding cluster of hot spots  230   b  is formed within the top section  204   t  of image frame  204 , with substantially no hot spot traces within the bottom section  204   b  of image frame  204 . 
         [0049]    The acquired image frames are stored in memory, operatively coupled with processor  190 . Each pair of the acquired image frame,  202  and  204 , includes an image frame section that is clean of hot spots formed by a cluster of light sources  130 . In image frame  202  the top section  202   t  is clean of hot spots formed by a cluster of light sources  130 , and in image frame  204  the bottom section  204   b  is clean of hot spots formed by a cluster of light sources  130 . Processor  190  discards of the bottom section  202   b  image frame  202  and the top section  204   t  of image frame  204 , and concatenates the top section  202   t  of image frame  202  onto the bottom section  204   b  image frame  204 , thereby forming a new image frame  206 . Image frame  206  contains substantially no hot spot traces that were originally formed image frames  202  and  204 . 
         [0050]    For the sake of clarity, light sources  130  may include any type of light source, preferably LED light sources, including IR, UV and visible light LED light sources or a combination thereof. Optionally, the light source is a halogen light source. 
         [0051]    Florescence image of the document may be acquired by illuminating the document with excitation light in UV, NUV or blue wavelength and acquiring data from the green and red sensitive pixels of a color sensitive sensor array. An optical filter designed to block the excitation wavelength may be used to protect the sensor. 
         [0052]    In variations of the present, the imaging device may include multiple clusters of light sources, each of which forms a hot spot cluster in the acquired image frame, when the cluster of light sources is activated. Any combination of clusters of light sources may be activated simultaneously, but not all of the clusters of light sources at once. Selected clusters of light sources are alternately activated, such that processor  190  forms a concatenated output image frame from a predetermined number of acquired image frames, such that the concatenated output image frame contains substantially no hot spot traces that were formed in the acquired image frames. 
         [0053]    In variations of the present, the imaging device may include a single cluster of light sources, wherein the emitted light beams may be shifted or deflected by a deflection mechanism. The mechanism for deflecting the light beams operatively deflects the light beams to at least two preconfigured illuminating angles, wherein camera  150  is preconfigured to acquire an image frame of the document at each of the at least two illuminating angles. 
         [0054]    The deflection mechanism can be, for example, a rotating prism may be placed in the path of the light beams. In another example, mirrors may be disposed on the inner side of side walls  112  of body  110  and the light cluster is rotatable to alternately illuminate one mirror, wherein the light beams deflect from the mirror the illuminate document  10 . Image frames are acquired when illuminating either mirror, wherein the hotspots are respectively imaged at different location of the image frame. 
         [0055]    An exemplary method  300  of obtaining an output image frame that contains substantially no hot spot traces, in a document imaging device  100  having an imaging-optical-chamber  170 , a camera  150 , two or more clusters of light sources  130 , a glass-window  120  and a processor  190 , wherein the document is directly illuminate by clusters of light sources  130 , through glass-window  120 , is outlined in  FIG. 8  and includes the following steps: 
         [0000]    Step  310 : activating imaging device  100  with alternating clusters of light sources  130  preconfigured to acquire sequences of image frames.
       Imaging device  100  with alternating clusters of light sources  130  is preconfigured to acquire sequences of image frames, when a cluster of light sources  130  is turned ON (activated), while other clusters of light sources  130  are turned OFF (deactivated).   Typically, the length of a sequence of image frames corresponds to the number of different alternating clusters of light sources  130 . In the example shown in  FIGS. 7   a - 7   d , the length of the sequence is typically 2.
 
Step  320 : activating a first cluster of light sources  130  and acquiring an image frame.
   A first cluster of light sources  130  is turned ON and camera  150  acquires an image frame of document  10 , while the other clusters of light sources  130  are kept OFF. For example,  FIG. 7   b  depicts image frame  202  of document  10   a , acquired when the first cluster of light sources  130   a  is turned ON, while the second cluster of light sources  130   b  is kept OFF. The acquired image frame  202  contains a cluster of hot spots  230   a  within the bottom section  202   b  of image frame  202 , respective to the disposition of first cluster of light sources  130   a  inside imaging-optical-chamber  170 .
 
Step  330 : discarding a preconfigured portion of the acquired image frame.
   A preconfigured portion of the acquired image frame, containing the hot spots caused by the direct illumination of the cluster of light sources  130 , is discarded.   In the example shown in  FIGS. 7   a - 7   d , after image frame  202  is acquired, the bottom section  202   b  of image frame  202  is discarded. After image frame  204  is acquired, the top section  204   t  of image frame  204  is discarded.
 
Step  335 : check if this is the last image frame in the sequence of image frames.
   If last image frame in the current sequence has been acquired, go to step  350 .
 
Step  340 : activating the next cluster of light sources  130  and acquiring an image frame.
   The next cluster of light sources  130  is turned ON and camera  150  acquiring an image frame of document  10 , while the other clusters of light sources  130  are kept OFF. For example,  FIG. 7   c  depicts image frame  204  of document  10   a , acquired when the second cluster of light sources  130   b  is turned ON, while the second cluster of light sources  130   a  is kept OFF. The acquired image frame  204  contains a cluster of hot spots  230   b  within the top section  202   t  of image frame  204 , respective to the disposition of first cluster of light sources  130   b  inside imaging-optical-chamber  170 .   Go step  330 .
 
Step  350 : concatenating the preconfigured portions of the acquired image frames into an output image frames, having substantially no hot spot traces that were formed in the acquired image frames.
   The preconfigured portions of the acquired image frames in a sequence, having substantially no hot spot traces that were formed in the acquired image frames, are concatenated in a preconfigured pattern, to thereby form an output image frame.   In the example shown in  FIGS. 7   a - 7   d , Processor  190  concatenates top section  202   t  of image frame  202  onto bottom section  204   b  image frame  204 , thereby forming a new image frame  206 . Image frame  206  contains substantially no hot spot traces that were originally formed image frames  202  and  204 .
 
Step  355 : optionally, check if this is the last sequence of image frames.
   Optionally, if this is not the last sequence of image frames, go to step  320 .       
 
         [0067]    In variations of the present, the imaging device may include two or more image sensors, such that the combined FOV of all image sensors covers a continuity of the glass-window ( 20 ) area. 
         [0068]    Although the present invention has been described with reference to the preferred embodiment and examples thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the following claims.