Abstract:
An optically-based and image processing-based scanner including a lens array, an imager, and an array of baffles to define paths of light between the lenses and the imager. Each of the lenses produces an inverted image of a portion of the object to be imaged. Components in the imager transpose and filter the individual images, or vice-versa, and assemble a composite image of the entire object. An array of plano-convex lenses is preferred.

Description:
FIELD OF INVENTION 
     The invention relates to a scanner that uses both optics and image processing to produce a scanned image, and more particularly to a scanner using an array of lenses that produce inverted sub-images for which the inverted data thereof is transposed and assembled into a complete image. 
     BACKGROUND OF THE INVENTION 
     Prior art scanners, such as might be used in a stand-alone manner or in a photocopier or facsimile machine, typically scan one line of pixels of the object document at a time. Such prior art which utilizes arrays of imaging lenses typically performs 1:1 imaging, i.e., neither reducing or enlarging, using non-inverted optical images. An example of a lens system that produces such 1:1 non-inverted images is an array of gradient-index (GRIN)lenses. An advantage of using the GRIN-lens array is that a 1:1 non-inverted imaged can be produced entirely with optics, i.e., without the need for image processing. 
     Currently, the highest resolution GRIN lens array-based scanner is 300-400 dots per inch (dpi), but a 600 dpi GRIN lens array-based scanner is anticipated to be commercially available soon. The technology for a 1200 dpi GRIN lens array-based scanner is not yet, and might not be for a long time, available. 
     A disadvantage of a GRIN lens array-based scanner is that it has a poor depth of field (DOF), i.e., a DOF less than 0.5 mm. A typical DOF for prior art GRIN lens array-based scanner is 0.2 mm or 0.3 mm. 
     It is desirable to have a DOF that is greater than 0.5 mm, and preferably 1.0 mm or better. A smaller DOF produces a scanner that is not robust. For example, if a piece of paper does not lie completely flat on the platen of the scanner because it has a crease in it, then the typical prior art DOF of 0.2 mm or 0.3 mm causes the image corresponding to the crease in the paper to be out of focus. 
     Having a depth of focus of 0.3 mm or less means that the mechanical positioning tolerances of the platen, lens array and optical-energy to electrical-energy converter must be less than 0.3 mm. This is difficult to manufacture with a low defect rate. 
     As resolutions increase, the problems of GRIN lens array-based scanners will increase. For a given GRIN lens array, changing the optical-energy to electrical-energy converter from 600 dpi to 1200 dpi will cut the DOF approximately in half. Thus, if the DOF was 0.3 mm at 600 dpi, it will be approximately 1.5 mm at 1200 dpi with the same GRIN lens array. 
     Prior art scanners that scan one line of a document at a time typically have an imager (for converting the optical image into electric signals) that is the width of the line to be scanned. For a document on 8.5 inch by 11 inch paper that is in the portrait (rather than the landmark) format, the imager needs to be 8.5 inches wide. Such a prior art imager is formed from a sequence of smaller, e.g., 1 inch, imagers, e.g., charge coupled devices (CCDs), connected end-to-end together. 
     The joint between two CCDs represents a non-imaging area on the order of one picture imaging element (pixel) wide. When used with a GRIN lens array, the non-imaging joints in the composite imager result in lost image data because the GRIN lens array produces a 1:1 image, a small portion of which impinges on the joints. Thus, either image information at the joints is lost or interpolation must be performed on the image data derived from the image formed by a GRIN lens array, which is a problem. 
     SUMMARY OF THE INVENTION 
     An objective of the invention is to improve upon the deficiencies of the prior art GRIN lens array-based scanners. In particular, an objective of the invention is to provide a scanner having a more robust depth of field (DOF) than the prior art GRIN lens array-based scanners. Also, an objective of an invention is to provide a scanner that is more economical to produce than the prior art GRIN lens array-based scanners. 
     These and other objectives of the invention are achieved by providing an imaging apparatus comprising: a lens array including a plurality of lenses, each lens in said lens array forming an inverted optical image of a portion of an object; an imager to convert the plurality of inverted optical images into image data; and a baffle array including a plurality of parallel light absorbing baffles, each baffle in said baffle array forming a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager. 
     These and other objects of the invention are also fulfilled by providing a method of calibrating an imaging apparatus (the imaging apparatus including a lens array, each lens in said lens array forming an inverted optical image of a portion of an object, an imager including an optical-energy to electrical-energy converter to convert the plurality of inverted optical images into a plurality of inverted image data sets corresponding thereto, respectively, each of said inverted data sets being a sequence of data having a beginning part, a middle part and an end part, and a controller to filter said sequence so as to discard said beginning and end parts and retain said middle part, and a baffle array, each baffle in said baffle array forming a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager), the method comprising: providing a calibration pattern of bars alternating between a first color and a contrasting second color, wherein widths of said bars of said calibration pattern are fixed such there is a first transition and a second transition in said calibration pattern from said first color to said second color approximately aligned with a first and second edge, respectively, of each lens in said array thereof; determining, at least indirectly based upon each of said inverted data sets, a first and second indicator of where said first transition and said second transition occur in each of said inverted data sets, respectively; and storing said first and second indicators for each of said inverted data sets. 
     These and other objects of the invention are also fulfilled by providing a method of forming an imaging apparatus, the method comprising: forming a lens array including a plurality of lenses, each lens in said lens array refracting an inverted optical image of a portion of an object; providing an imager to convert the plurality of inverted optical images into image data; forming a baffle array including a plurality of parallel light absorbing baffles separated by air gaps and one of a top baffle and a bottom baffle; aligning said lens array to a first end of said baffle array such that each baffle in said baffle array forms a light absorbing border between adjacent optical paths, said paths lying between said lens array and said imager; attaching said lens array to said baffle array; and attaching said imager to said baffle array. 
     The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus do not limit the present invention and wherein: 
     FIG. 1 is a block diagram of an optics-based and image-processing-based scanner according to the invention; 
     FIG. 2 is a diagram of the image inversion caused by the lens array of the embodiment of Figure 
     FIG. 3 is a diagram depicting the image of the calibration pattern formed by the lens array of the embodiment of FIG. 1; 
     FIG. 4 is a second embodiment of the invention that uses different optics than the embodiment of FIG. 1; 
     FIG. 5 is another embodiment that uses an arrangement of scanners that is different than the embodiment of FIG. 1; 
     FIG. 6A depicts a point in the construction process of the scanner according to the invention; 
     FIG. 6B depicts a later point in the construction process of the scanner according to the invention; 
     FIG. 7 depicts a cross section of the structure of FIG. 6A depicted along the line VII—VII prime; and 
     FIG. 8 is a diagram illustrating the relationship between the calibration pattern and the pixel locations in a CCD. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram of the optics-based and image-processing-based scanner  100  according to the invention. The scanner  100  includes an array of lenses  102 , which in this example is formed of plano-convex lenses  104 . The array of lenses  102  faces an object document  108  laying against an optional platen  106 . The array of lenses  102  is arranged with an array of baffles  110 . Each baffle includes a first part  112  and a second optional part  114 . The array of baffles  112  separates the array of lenses  102  from an imager  116 . 
     The lenses  104  in the array  102  thereof may be any type of refracting lenses such as, e.g., plano-convex lenses, bi-convex lenses, or lenses having one convex surface and one concave surface. The surface curvature of the lens  104  may be either spherical or aspherical. The lenses  104  are preferably spherical, plano-convex lenses. The planar surfaces of the lenses  104  face the imager  116  while the convex surfaces of the lenses  104  face the platen  106 . The figures depict 3 lenses  104  in the array  102  for simplicity, but any number of lenses can be used. 
     The imager  116  of FIG. 1 includes an optical-energy to electrical-energy converter  117 , such as one or more charge coupled devices (CCDs), one or more complimentary metal oxide semiconductor (CMOS) detectors, or one or more photonics-technology-based detectors. Each converter  117  has a plurality of pixel detectors. FIG. 1 depicts the converter  117  as a plurality of charge coupled devices (CCDs)  118  commensurate in number with the number of lenses  104  such that there is one CCD  118  for each lens  104 . The CCDs  118  are connected to an optional but preferred memory  120  via signal lines  122 . Note that it is not necessary that the number of CCDs  118  equals the number of lenses  104 . 
     The memory  120  is connected to a controller  124  via a bi-directional connection  126 . The controller  124  is preferably a microprocessor embodied on an integrated circuit. The controller is also directly connected to the CCDs  118  via control lines  128 . An output  130  of the controller  124  delivers the scanned image data. An optional but preferred non-volatile memory, such as a electrically erasable programmable read-only memory (EEPROM),  121  is connected via a bi-directional signal path  127  to the controller  124 . 
     The baffles  112  and optionally but preferably  114  of the array thereof  110  form light absorbing borders alongside optical paths between the lenses  104  and the CCDs  118 , respectively. The baffles  112  and  114  are made to be light absorbing to reduce the amount of light reaching the CCD  118  which did not reflect off the corresponding portion of the object. The material for the baffles should be inherently light absorbing and/or coated with a light absorbing substance. 
     FIG. 2 is a diagram illustrating how each lens  104  in the array thereof  102  refracts light from the corresponding portion of an object  200  as denoted by only two, for simplicity, rays of light  202  and  204 . The image on the corresponding CCD  118  in the converter  117  is inverted. The ray  202  from the area A (which is above the area B) of the object  200  is imaged on the CCD  118  below the image for the area B. Also, it is noted that the area AB of the image sensed by the CCD  118  is smaller than, i.e., reduced relative to, the area AB of the object  200  that corresponds to the lens  104  through which the rays  202  and  204  travel. 
     FIG. 3 is a diagram illustrating the relationship between the array  102  of lenses  104  and a calibration pattern  300 , resulting in the patterned images on the CCDs  118 . The pattern  300  has black portions  302  and white portions  304 , each of which is equal in width to the width of the lenses  104 . However, any repeating pattern of alternating, contrasting colors will suffice so long as transitions between colors in the repeating pattern approximately coincide or align with the edges of each lens. Knowing the number of transitions that should be completely imaged by each CCD  118  makes it possible to calibrate the converter  117 , as will be discussed further below. 
     In FIG. 3, the top lens  104   1  is aligned with a white portion  304   1  of the calibration pattern  300 . A black portion  302   2  of the calibration pattern  300  is aligned with the second lens  104   2  while a white portion  304   2  is aligned with the third lens  104   3 . 
     Because the array  102  of lenses  104  produce a corresponding plurality of reduced images, the charge distribution in the CCDs  118  represent a complete image of the portion of the calibration pattern to which the corresponding lens  104  is aligned, plus partial images of the portions of the calibration pattern immediately above and below the calibration pattern  300  to which the lens is aligned. More particularly, the CCD  118   1  has a beginning part  314  of the charge distribution that represents the black portion  302   2  of the calibration pattern  300 , a middle part  316  that represents the white portion  304   1  of the calibration pattern  300  and an end part  318  representing the black portion  302   1  of the calibration pattern  300 . Similarly, the charge distribution in the CCD  118   2  has a beginning part  320  corresponding to the white portion  304   2 , a middle part  322  corresponding to the black portion  302   2 , and an end part  324  corresponding to the white portion  304   1 . The charges in the beginning portion  314 , the end portion  318  and the middle portion  322  represent the color black, while the charges in the middle part  316 , the beginning part  320  and the end part  324  represent the color white. 
     The end part  318  of the charge distribution in the first CCD  118   1  represents light such as the ray  306  coming from the black portion  302   1  of the calibration pattern. The beginning part  320  of the charge distribution in the CCD  118   2  represents light from the white portion  304   2 . Thus, the end part  318  and the beginning part  320  represent noncontiguous areas of the calibration pattern  300 . 
     If a person were to concatenate the image data provided by the CCDs  118 , the result would be a distorted representation of the calibration pattern  300 . However, if one can concatenate the middle parts  316 ,  322 ,  328  etc., then the resultant image would be an accurate representation of the calibration pattern  300 . A technique for such filtration is described below. 
     FIG. 4 is a diagram of an alternative embodiment of the scanner according to the invention that differs from the embodiment of FIG. 1 by including a second array  400  of lenses  402 . In the example of FIG. 4, the lenses  402  are plano-convex lenses. The convex surfaces of the lenses  402  face the convex surfaces of the lenses  104 . 
     The extra array of lenses  400  of FIG. 4 contribute to images in the CCDs  118  that have fewer aberrations. However, it is more preferred to use only the array  102  of lenses  104  because the reduced cost and complexity of manufacture outweighs the relative increase in accuracy contributed by the additional array  400 . 
     FIG. 5 is a diagram of another example embodiment  500  of the scanner according to the invention. It is noted that while FIGS. 1-4 are top cross-sectional views, FIG. 5 is a side cross-sectional view. As such, the array of baffles  110  is not depicted in FIG.  5 . Rather, a top baffle  502  and a bottom baffle  504  are depicted. Again, the baffles  502  and  504  are formed of light absorbent material such that they form a light absorbing border alongside an optical path between the lens  104  and imagers  506 ,  508  and  510 . Also again, the baffles  502  and  504  help reduce the amount of unwanted light that reaches the imagers  506 ,  508  and  510 . 
     In FIG. 5, the irradiating light is assumed to be white light. There are three filters  512 ,  514  and  516  situated between the lens  104  and the imagers  506 ,  508  and  510 . Each of the imagers  506 ,  508  and  510  is identical to the imager  116  of FIG.  1 . The filter  512  is a red filter. The filter  514  is a green filter. The filter  516  is a blue filter. The imagers  506 ,  508  and  510  image negligibly different areas of the object  108 . The choice of the filter colors is variable depending upon the particular application requirements. 
     The embodiment  500  of the color scanner of FIG. 5 can alternatively be implemented by the embodiment of FIG. 1 where the object  108  is illuminated by three different colors of light, rather than the monochrome or white light assumed for FIG.  1 . Light of a first color, e.g., from a red light emitting diode (LED), would be impinged upon the object  108  and the reflection thereof imaged by the imager  116 . After the brief illumination with red light, the object  108  would be illuminated with a second color of light, e.g., from a green LED, for an equally brief interval and the reflection thereof imaged by the imager  116 . After the green illumination, the object  108  would be illuminated by a third color light, e.g., from a blue LED for the same brief interval and the reflection thereof imaged by the imager  116 . 
     For a color scanner, the embodiment using three colored LEDs is preferred to the embodiment using three imagers because the multiple imagers in the latter embodiment result in a more expensive implementation. 
     FIG. 6 is a top plan view of the array  110  of baffles  112  and optionally  114 . The array  110  has a space  600  into which will be fitted at least one array of lenses such as the array  102 . The ends of the space or gap  600  can be formed, e.g., by extending the outermost baffles  112  so that they join the outermost baffles  114 . 
     FIG. 6B is a top plan view of the embodiment  100  of the scanner according to the invention after the array  102  of lenses  104  has been inserted into the array  110  of baffles  112  and optionally  114 , and after the imager  116  has been positioned against the end of the array  110  of baffles  112  and optionally  114 . 
     FIG. 7 is a cross-section taken along the line VII—VII′ in FIG.  6 A. Note that either the top baffle  502  or the bottom baffle  504  may be integrally formed with the baffle array  110 . 
     FIG. 8 shows a portion of FIG. 3 in more detail, for the purposes of explaining the filtration process. It is noted that the proportions in FIG. 8 have been distorted for the purposes of simplifying the depiction of the pixel locations P O , P 1 , P 2 , . . . P J−1 , P J  . . . P K , P K+1 , . . . P N−1 , P N , within the CCD  118   1 . 
     Again, the charge distribution in the CCD  118   1  has a beginning part  314 , a middle part  316  and an end part  318 . The beginning part  314  stores charge representative of the black color in pixel locations P K+1  through P N . The middle part  316  stores charge representative of the white color in pixel locations P J+1  through P K . The end part  318  stores charge representative of the color black in the pixel locations P 0  through P J−1 . An image  800  is impinged upon the CCD  118   1 . The regions A-I of the calibration pattern  300  are also noted in the image  800  so as to emphasize the inversion caused by the lens  104 . 
     As discussed previously, the reduction in image size by the lens  104  makes it necessary to discard the pixels P 0  through P J−1  and the pixels P K+1  through P N  while retaining the pixels P J  through P K . The charge distribution changes or transitions from being representative of the color black to being representative of the color white from pixels P J−1  to P J . Similarly, the charge distribution transitions from being representative of the color white to being representative of the color black from pixel P K  to pixel P K+1 . 
     During calibration, the controller  124  can shift out the charges in the pixel locations P 0  through P N , i.e., the image data for the pixels P 0  to P N . The controller  124  will sort the image data P 0  through P N  to determine the two transition points. These transition points are stored in a EEPROM  121  for the CCD  118 . This process is repeated for each of the CCDs  118  such that the two transitions for each of the CCDs  118  is stored in the EEPROM  121 . Once the transitions are known, the controller  124  can determine the starting pixel P J  and the ending pixel P K  of the image data to be saved. The image data from pixels P 0  to P J−1  and P K+1  to P N  will be discarded. Again, the values for J and K will have been uniquely determined for each CCD  118 . 
     The operation of FIG. 1 will be now be described. For simplicity, only two example light rays  132  and  134  have been depicted in FIG.  1 . The rays  132  and  134  are reflections off the object  108  which pass through the platen  106  and are refracted by the lens  104  to produce data in the CCD  118  representing a reduced image. Similar processes occur in the other lenses  104  and CCDs  118 . The controller sends control signals to the CCDs  118  over the control lines  128  which cause the CCDs  118  to shift their data into the memory  120 . The data from each CCD  118  must be transposed. This can be done by storing the data from the CCD  118  in the memory  120  according to the order in which it is output and then transposing that array. Alternatively, the controller can perform a transposition by simply reading the data for each CCD  118  from the memory  120  in the opposite order in which it was stored from the CCD  118 . The transposition technique that will be preferred depends upon the details of the particular application. 
     If needed, the controller can control the CCDs  118  to output their data  120  at the same time. This would, e.g., permit the next row of pixels to be irradiated and the CCDs  118  to be correspondingly energized while the controller transposed the data from the previous line of pixels in the memory  120 . 
     The scanner  116  has been depicted with a memory  120  and a EEPROM  121  that are separate from the controller  124 . Alternatively, a controller could be chosen with sufficient memory on the integrated circuit to make it possible to eliminate the separate structures  120  and  121 . 
     The filtration process (to remove the unwanted parts of each sub-image) has been described as taking place after the transposition process. However, the filtration could be performed before the transposition; this is a matter of design choice that depends upon the details of the particular application. The advantage of performing the filtration before the transposition is that it results in less data that must be transposed, i.e., a lesser computational load upon the controller  124 . 
     The formation of the embodiment of the scanner according to the invention will now be described in terms of FIGS. 6A and 6B. First, the array  110  of baffles  112  and optionally baffles  114  and the bottom  504  are formed by a machining or a molding process, e.g., by an injection molding process, as depicted in FIG.  6 A. Next, the array  102  of lenses  104  is inserted into the corresponding gap  600  in the array  110  of baffles  112  and optionally  114 , as depicted in FIG.  6 B. Also, the imager  116  is attached to the end of the array  110  of baffles such that the CCDs  118  (not shown in FIG. 6B) in the imager  116  align with the lenses  104 . It is noted that either the array  102  of lenses  104  can be inserted into the array  110  of baffles before the imager  116  is attached, or vice-versa. 
     After the imager  116  and the array  102  of lenses  104  have been put together with the array  110  of baffles  112  and optionally  114 , the top baffle  502  is attached. The order of attachment of the top and bottom baffles  502  and  504  might vary depending upon the particular application. 
     A non-limiting example of dimensions for the embodiment  100  of the scanner according to the invention are a distance of 20 mm between the convex surfaces of the lenses  104  and the object  108 , a 1.6 mm thickness of lenses  104  and a 10 mm distance between the planar surfaces of the lenses  104  and the CCDs  118 . A corresponding width of the lenses  104  is 2 mm, so that a 2 mm wide portion of an object results in a 1 mm wide corresponding image of that portion on the CCDs  118  in addition to partial images from adjacent portions of the object. A corresponding width of the black portions  302  and white portions  304  of the calibration pattern  300  is 2 mm. 
     The calibration process preferably takes place once, preferably at the time that the scanner is manufactured. However, it may be necessary to recalibrate the scanner, depending upon the effects of aging. 
     A scanner should have a Modulation Transfer Function (MTF) of 50% or greater for a given line pattern at an appropriate distance from the lens array  102  to the object  108  (20 mm in the above example). As used herein, MTF is typically measured for the captured image of an industry standard line pattern of equal width black and white bars with a periodicity denoted by the number of line pairs per inch (LPI). A typical line density for a 300 dpi scanner is 70 LPI, for a 600 dpi scanner is 105 LPI and for a 1200 dpi scanner is 140 LPI. The line pattern produces a modulation in the output of the converter  117  with a greater signal corresponding to the image of a white bar (max) and a lesser signal corresponding to the image of a black bar (min). The modulation transfer function (MTF) is defined as MTF=(max−min)/ (max+min), and is expressed as a percentage. The invention is expected to have an MTF of 50% or greater for 600 dpi and 1200 dpi resolutions. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.