Abstract:
A workstation having low resolution and high resolution image capture apparatus such as is useful for tele-conferencing. Optical wedge apparatus is placed between an object and a focusing lens according to the invention to create multiple overlapping low resolution images of a whole object. Programmed or hardwired logic is then used to construction a high resolution image of the object by interleaving the picture elements of the low resolution images.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for enhancing the resolution of digital image capture devices such as CCD scanners and digital cameras. More particularly, the present invention relates to a method and apparatus which multiplexes picture elements. 
     2. Description of Related Art 
     There has been a continuing need in the art of image capture to increase the resolution of a captured image without significantly increasing the cost and complexity of the image capture apparatus. An example of an application where increased resolution is often desirable is in teleconferencing. A low resolution image of the face of a conference participant is usually adequate for effective communication. However, where a document or an article exhibit is to be shared in a tele-conference, much higher resolution of the text or article details are usually desired. Accordingly there is a need for an effective means and method of increasing resolution without significantly increasing cost and complexity at either end of the conference. 
     U.S. Pat. No. 4,103,109 relates to the multiplexing of image picture elements from a parallel CCD capture array onto a single output line in a more efficient way. This reference does not improve the resolution of the image captured by the CCD array. 
     U.S. Pat. No. 5,541,653 issued to Peters et al. relates to increasing resolution of digital color images using a beam splitter on the image side of the lens to create multiple offset images which are later combined electronically to create an image of “enhanced resolution”. A major disadvantage of the system of Peters is the need for high precision in the beam splitter and its placement. As a result of the requirement for high precision, commercial application of the technique of Peters is costly. 
     U.S. Pat. No. 5,502,578 issued to Smitt relates to an optical scanner having a variable apparent resolution. The varying resolution is obtained by varying the pixel and line sampling clock rates at differing amounts. The distances between CCD elements is fixed however and therefore actual sampling resolution must be fixed in this teaching. 
     U.S. Pat. No. 4,920,418 issued to Robinson relates to a scanning imaging system that includes an image shifting means between the lens and a CCD array. The image shifter which may be a rotatable glass plate driven by a piezoelectric bimorph, shifts an image of the object by less than the distance between adjacent PELS at the image plane. As a result of placement of the shifting device on the image side of the lens, expensive parts of close tolerances are required. Accordingly these systems have not achieved wide commercial success. 
     U.S. Pat. No. 5,449,898 issued to Dosmann relates to a test strip color and/or reflectance analyzer used in the field of clinical chemistry. The equipment of Dosmann is not increasing the resolution of an meaningful image but is detecting the existence of certain colors or reflectance with increased resolution. Accordingly, Dosmann is not concerned with the problem of how to combine or stitch together the partial fields  50   a  and  50   b  into a meaningful image. If Dosmann looks at a one half inch overlap field more than once to detect the presence of a color, it does not adversely affect the resultant analysis. On the other hand, when an overlap occurs while capturing a meaningful image, it is a complex task to eliminate the overlap and stitch the parts of the image back together. 
     U.S. Pat. No. 4,383,170 issued to Takagi et al. and U.S. Pat. No. 4,516,032 issued to Barr relate to similar image subarea capture methods. Here again it is a complex task to eliminate overlap or gaps between sub-areas and stitch the sub-areas of the image back together. 
     U.S. Pat. No. 5,771,123 issued to Hamano relates to a variable angle optical wedge in a zoom lens for compensating for hand tremors of a photographer. A variable angle optical wedge provides compensating displacement of the image to obtain a more stable image but does not yield a higher image resolution in terms of PEL density. 
     SUMMARY OF THE INVENTION 
     An advantage of the present invention is that an inexpensive low resolution camera can be externally fitted with the means of the invention to provide higher resolution image capture of text and exhibit details without complex image stitching or edge matching. 
     A further advantage of the invention is that object distances and magnifying lenses need not be altered in order to achieve higher resolution. 
     A still further advantage is that small easily controlled light ray deflections are used in the invention and therefore angular distortion is minimized. 
     An even further advantage of the invention is that partial images of-an object are avoided and therefore, there is no need for complex edge matching or stitching of partial images 
     These and other advantages which will become apparent from a study of the specification and drawings are obtained by the instant invention through the use of a unique combination of optical and electronic means. Optical wedge action is used in the invention to create multiple overlapping low resolution images of a whole object. Electronic means are then used to construction a high resolution image of the object by interleaving the picture elements of the low resolution images. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 . shows a tele-conferencing camera in which the instant invention finds utility. 
     FIG.  2 . is a more detailed block diagram of a camera according to the invention. 
     FIG.  3 . is a front view of an optical wedge. 
     FIG.  4 . is a side view of the optical wedge. 
     FIG.  5 . is a timing diagram. 
     FIG.  6 . shows a CCD array of CCD cells and sensitive areas. 
     FIG.  7 . is a diagram showing portions of an image with simple interleaving. 
     FIG.  8 . is a diagram of an eight by eight array of CCD cells and unshifted and shifted image location. 
     FIG.  9 . is a diagram of the array capturing the b picture elements of the image. 
     FIG.  10 . is a diagram of the array capturing the c picture elements of the image. 
     FIG.  11 . is a diagram of the array capturing the d picture elements of the image. 
     FIG.  12 . shows the interleaving of a, b, c and d picture elements captured with a larger angle optical wedge. 
     FIG.  13 . is a perspective view of optical wedges and shutters. 
     FIG.  14 . is a side view of the optical wedges. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG. 1, a teleconferencing application of the preferred embodiment of the invention will now be described. A workstation  100  has a display  103 , a keyboard  105  and a computer  107 . A stand  109  is placed under the computer  107  which helps to hold the stand  109  in place. Stand  109  includes a tubular upright member  111  into which a second tubular member  113  is inserted for rotatable support. The second tubular member  113  has an angled neck  115  and a joint  117  at it&#39;s upper extremity. A digital camera  200  is mounted to the joint  117  as shown for capturing an image of the workstation operator as part of a teleconference. The second tubular member  113 , being free to rotate within tubular member  111  allows the camera  211  to be rotated counter clockwise on it&#39;s stand  109  to a position placing camera  200  substantially over a document  119  which is to be transmitted as a digital image in a tele-conference. Joint  117  allows camera  200  to be rotated downward so as to be able to capture an image of document  119  in a horizontal plane of the table top or other support surface for the workstation  100 . When rotated counter clockwise and downward, the camera  200  is switched to it&#39;s high resolution mode for capturing the text of the document  119  in a most legible form for reading by other tele-conference participants. 
     FIG. 2 shows a more detailed diagram of digital camera  200  according to the invention. Camera  200  has a body  211 . Mounted within the body is a circuit board  213 . Circuit board  213  carries a charge coupled diode (CCD) array  215 , memory modules  217  and logic  219  which may be hardwired logic or a digital processor programmed by one of the memory modules in the form of a read only memory. It will be understood that the read only memory can also be embodied into the same integrated circuit substrate and the logic  219 . Mounted in front of CCD array  215  is a lens body  221  having a lens assembly  223  which focuses an image of an object in front of the lens onto CCD array  215 . 
     In front of the lens assembly  223 , lens body  221  also contains an optical wedge assembly  225 , including an optical wedge mounted in a ring gear having bearing surfaces engaging a ring track allowing the wedge  225  to be rotated continuously. 
     FIG. 3 shows a front view of the optical wedge  225  and FIG. 4 is a side view of optical wedge  225 . 
     A pinion gear  227  engages the ring gear. Pinion  227  is mounted on an elongated shaft of motor  229 . Motor  229  may be a stepping motor which, with it&#39;s control circuits  230  on board  213 , is part of an actuator assembly that can be controlled to rotate optical wedge  225  in ninety degree increments. In other embodiments, other means such as a geneva drive or other equivalent means may be employed to actuated the wedge in substantially ninety degree increments. 
     In another preferred embodiment, the wedge  225  is rotated continuously and the logic  219  resets and samples CCD array  215  in narrow time slots during which wedge  225  is substantially ninety degrees from its position during the previous sample. 
     Wedge  225  continues to rotate and therefore the mechanics are simpler and cheaper while the CCD reset and sample electronics are inexpensively embodied in read only memory and implemented by the processor in logic module  219 . 
     FIG. 5 shows the relationship between optical wedge angle and reset/sample times as the wedge is continuously rotated. The CCD array is reset for example when the position of the wedge reaches forty degrees and light is integrated in the CCD until the wedge reaches fifty degrees at which time, the charge accumulated in the CCD array is sampled out into a shift register, thereby allowing each sensor of the CCD array to capture a picture element (PEL) labeled a. Likewise, when the wedge has reached one hundred thirty degrees, the CCD array is again reset as indicated by the label R on the X axis of FIG.  5 . Upon reaching one hundred forty degrees, the CCD array is sampled as indicated by the label S, thereby allowing each sensor of the CCD array to capture a picture element (PEL) labeled b. These steps are repeated at two hundred twenty, three hundred ten, and at two hundred thirty, three hundred twenty respectively to capture PELs c and d of the image as it is shifted on the plane of the CCD array. 
     It is understood that the image is shifted around on the CCD array with the array held stationary. Further, it is understood that an optical wedge does not rotate the image itself but merely shifts it while the image itself remains in the same upright or inverted orientation in which it is formed by lens  223 . 
     We will now consider the various positions on the image that are sampled by an example sensor as the wedge is rotated. A portion  611  of a CCD array is shown in FIG.  6 . The-sensitive portion  615  of each CCD cell does not extend all the way to the CCD cell boundary  613  but only occupies the central twenty five percent of the total area within a CCD cell. Without the wedge of the invention being placed between the object and the lens, the sensor would sample only the central 25 percent of an image area since the image area would be stationary on the CCD array. However when the image of the object is shifted downward to the right by the wedge at approximately forty five degrees, as shown for one CCD: cell in FIG. 7, the sensitive portion  711  of each cell  713  samples a portion labeled a of the image  711  at an upper left corner of each cell. These samples labeled a are stored in a memory area for later interleaving with samples b, c and d. When the optical wedge is rotated to approximately one hundred thirty five degrees, as indicated by arrow  717 , each sensor samples the portions of the image labeled b, which are also captured. At approximately two hundred twenty five degrees, each sensor samples for capture, the portions of the image labeled c. Likewise, at approximately three hundred fifteen degrees, each sensor samples the portions of the image labeled d. In this way from FIG. 7, it can be seen that when they are later interleaved, the resolution of the combined four images captured by each CCD cell is four times as high as that which would be captured by the CCD cell without the rotating optical wedge. 
     In the example of FIG. 7, the image has been shifted by less that the spacing between CCD cells so the interleaving of the four captured images into one high resolution image is simple. The same cell generates a, b, c and d picture elements and therefore no cropping of the captured images a, b, c and d are required. However, there are implementation considerations wherein it is difficult to accurately fabricate an optical wedge of very small angle, while it is easier to accurately fabricate an optical wedge of a larger angle. In this case, the image on the plane of the CCD array would be deflected by more than the distance between adjacent CCD cells. Larger deflections require more complex interleaving logic but such incremental complexity in logic is nearly cost free and therefore is an alternate embodiment of the instant invention., and is shown in FIGS. 8,  9 ,  10 ,  11  and  12 . 
     FIG. 8 is a diagram of an eight by eight array of CCD cells which are numbered one through sixty four. Without being shifted, an image formed on the CCD array by lens  223  will be centered on the array as shown by broken line  811 . When the image is shifted by optical wedge  225 , the image takes the position shown by broken line  813 . In this embodiment, the image is shifted by three quarters of the diagonal spacing between adjacent CCD cells. This distance can be described as an integer multiple of the diagonal spacing between adjacent CCD cells minus a fraction of the diagonal spacing between adjacent CCD cells. It will be understood that this description of the amount of initial shift also describes the case where the total shift is only one quarter of the unshifted position as is the case in the embodiment of FIG.  7  and further accounts for the fact that in FIG. 7, the shift is down and to the right whereas in the embodiment of FIG. 8, the shift is upward and to the left. This is because in FIG. 7, the integer is zero and the distance becomes a negative number whereas in FIG. 8, the integer is one which leaves a positive distance of three quarters. 
     When the image has been shifted by the wedge, it overlays the CCD cells labeled a 1  through a 46 . These CCD cells are sampled and stored as described above and the image is again shifted, this time by rotation of the wedge approximately ninety degrees. After rotation of wedge  225  to approximately one hundred thirty five degrees, the image has been shifted as shown in FIG.  9 . The amount of shift between FIG.  8  and FIG. 9 is one and one half times the lateral spacing between adjacent CCD cells. This distance can be described as an integer multiple of the lateral spacing between adjacent CCD cells minus a fraction of the lateral spacing between adjacent CCD cells. In this case, the integer is two and the fraction is one half. When the image has been shifted by the wedge, it overlays the array of CCD cells labeled b 3  through b 48 . These CCD cells are sampled and stored in another memory area as described above. 
     After further rotation of wedge  225  to approximately two hundred twenty five degrees, the image has been shifted as shown in FIG. 10 by the broken line  1013 . The amount of shift between FIG.  9  and FIG. 10 is one and one half times the lateral spacing between adjacent CCD cells. This distance can again be described as an integer multiple of the lateral spacing between adjacent CCD cells minus a fraction of the lateral spacing between adjacent CCD cells. Again, the integer is two and the fraction is one half. When the image has been shifted by the wedge, it overlays the array of CCD cells labeled c 19  through b 64 . These CCD cells are sampled and stored in a third memory area as described above. 
     After another rotation of wedge  225  to approximately three hundred fifteen degrees, the image has been shifted as shown in FIG. 11 by the broken line  1113 . The amount of shift between FIG.  10  and FIG. 11 is again one and one half times the lateral spacing between adjacent CCD cells. This distance can again be described as an integer multiple of the lateral spacing between adjacent CCD cells minus a fraction of the lateral spacing between adjacent CCD cells. Again, the integer is two and the fraction is one half. When the image has been shifted by the wedge, it overlays the array of CCD cells labeled d 17  through d 62 . These CCD cells are sampled and stored in a fourth memory area as described above. 
     Having captured four complete low resolution and overlapping images, these low resolution images are now interleaved by logic  219  as shown in the diagram of FIG.  12 . Interleaving when images are shifted according to FIG. 7 is simple in that picture elements a 1 , b 1 , c 1  and d 1  are merely grouped together as shown in FIG. 7 to capture a high resolution image. When a larger wedge angle is employed as in FIGS. 8 through 11, the picture elements b 1 , b 2  and a 7 , a 8  are not available due to cropping. If they are not cropped, as they were in FIGS. 8 and 9, but allowed to capture picture elements, they may be retained as part of the final image. However, since a 7 , a 8  and b 1 , b 2  have no corresponding c and d picture elements they must remain part of low resolution image areas. 
     Referring now to FIG. 12, and recalling FIGS. 8,  9 ,  10  and  11 , it is seen that a 1 , b 3 , d 17  and c 19  picture elements combine to increase the resolution at this portion of the image by four fold. This form of interleaving is more complex but still yields a cost effective way to achieve high resolution of document capture for use in such applications as teleconferencing and other similar applications. 
     In the above described embodiment, separate memory areas have been shown to aid in understanding the invention. It will be understood that the interleaving logic can be active with the capture logic to store each low resolution image as it is captured directly into appropriate memory locations such as are shown in FIG.  12 . Of course each of the memory areas indicated in FIGS. 8 through 11 can be considered as overlapping memory areas. Further, the interleaving logic may operate directly to a display and/or communication network and the high resolution image may not need to be combined in memory at all. 
     Of course, many additional modifications and adaptations to the present invention can be made in both embodiment and application without departing from the spirit of this invention. For example, although optical wedge rotation is shown as clockwise, opposite rotation works as well. Further, the image may be shifted by a shuttered four facet wedge between the object and the lens. In such an embodiment, four adjacent fixed optical wedges and four optical shutters respectively achieve the actuation for shifting the image by opening only one shutter at a time. Accordingly, this description should be considered as merely illustrative of the principles of the present invention and not in limitation thereof.