Patent Publication Number: US-2019167085-A1

Title: In Vivo CAMERA WITH MULTIPLE SOURCES TO ILLUMINATE TISSUE AT DIFFERENT DISTANCES

Description:
CROSS-REFERENCE TO PRIORITY APPLICATIONS 
     This application is a continuation application of and claims priority from U.S. patent application Ser. No. 14/583,504 filed on Dec. 26, 2014 which is a continuation application of U.S. patent application Ser. No. 14/156,040 filed on Jan. 15, 2014 which in turn is a continuation application of U.S. patent application Ser. No. 12/475,435 filed on May 29, 2009, which in turn claims priority from U.S. Provisional Patent Application No. 61/060,068 filed on Jun. 9, 2008, with all the just-described applications having the title “In Vivo CAMERA WITH MULTIPLE SOURCES TO ILLUMINATE TISSUE AT DIFFERENT DISTANCES” and all these just-described applications having Gordon C. Wilson as inventor. U.S. patent application Ser. Nos. 14/583,504, 14/156,040 and 12/475,435 are all incorporated by reference herein, in their entireties. U.S. Provisional Patent Application No. 61/060,068 is also incorporated by reference herein, in its entirety. 
     RE-VISIT NOTICE 
     Applicant hereby rescinds any disclaimer of claim scope in the parent application namely U.S. application Ser. No. 14/583,504 and/or in the grandparent application namely U.S. application Ser. No. 14/156,040 (issued as U.S. Pat. No. 8,956,281) and/or in the great-grandparent application namely U.S. application Ser. No. 12/475,435 (issued as U.S. Pat. No. 8,636,653) and/or in the corresponding prosecution history thereof and advises the US Patent and Trademark Office (USPTO) that the claims in the current application may be broader than any claim in the parent and/or in the grandparent and/or in the great-grandparent. Applicant notifies the USPTO of a need to re-visit the disclaimer of claim scope in the parent, grandparent and great-grandparent applications, and to further re-visit all prior art cited in the parent, grandparent and great-grandparent applications, including but not limited to cited references over which any disclaimer of claim scope was made in the parent, grandparent and great-grandparent applications or in the corresponding prosecution histories thereof. See  Hakim  v.  Cannon Avent Group , PLC, 479 F.3d 1313 (Fed. Cir. 2007). Moreover, any disclaimer made in the current application should not be read into or against the parent or the grandparent or the great-grandparent. 
    
    
     BACKGROUND 
     Various prior art devices have been developed that are configured to capture an image from within in vivo passages and cavities within an organism&#39;s body, such as cavities, ducts, and tubular organs within the gastrointestinal (GI) tract. Several prior art devices are formed as a capsule dimensioned small enough to be swallowed. The capsule typically holds a camera and one or more light sources for illuminating an object outside the capsule whose image is recorded by the camera. The electronics in the capsule may be powered by batteries or by inductive power transfer from outside the body. The capsule may also contain memory for storing captured images and/or a radio transmitter for transmitting data to an ex vivo receiver outside the body. A common diagnostic procedure involves a living organism (such as a human or animal) swallowing the capsule, followed by the camera in the capsule capturing images at various intervals as the capsule moves passively through the organism&#39;s cavities formed by inside tissue walls of the GI tract under the action of peristalsis. 
     Two general image-capture scenarios may be envisioned, depending on the size of the organ imaged. In relatively constricted passages, such as the esophagus and the small intestine, a capsule which is oblong and of length less than the diameter of the passage, will naturally align itself longitudinally within the passage. In several prior art capsules, the camera is situated under a transparent dome at one (or both) ends of the capsule. The camera faces down the passage so that the center of the image is formed by a dark hole. The field of interest is the intestinal wall at the periphery of the image. 
       FIG. 1A  illustrates an in vivo camera capsule  100  of the prior art. Capsule  100  includes a housing that can travel in vivo inside an organ  102 , such as an esophagus or a small intestine, within an interior cavity  104  of the organ. In the image-capture scenario shown in  FIG. 1A , capsule  100  is in contact with an inner surface  106  of the organ, and the camera lens opening  110  captures images within its field of view  128 . The capsule  100  may include an output port  114  for outputting image data, a power supply  116  for powering components of the camera, a memory  118  for storing images, compression circuitry  120  for compressing images to be stored in memory, an image processor  122  for processing image data, and LEDs  126  for illuminating surface  106  of the organ so that images can be captured from the light that is scattered off of the surface. 
     A second scenario occurs when a capsule is in a cavity, such as the colon, whose diameter is larger than any dimension of the capsule. In this scenario the capsule orientation is much less predictable, unless some mechanism stabilizes it. Assuming that the organ is empty of food, feces, and fluids, the primary forces acting on the capsule are gravity, surface tension, friction, and the force of the cavity wall pressing against the capsule. The cavity applies pressure to the capsule, both as a passive reaction to other forces such as gravity pushing the capsule against it and as the periodic active pressure of peristalsis. These forces determine the dynamics of the capsule&#39;s movement and its orientation during periods of stasis. The magnitude and direction of each of these forces is influenced by the physical characteristics of the capsule and the cavity. For example, the greater the mass of the capsule, the greater the force of gravity will be, and the smoother the capsule, the less the force of friction. Undulations in the wall of the colon tend to tip the capsule such that a longitudinal axis  118  of the capsule is not parallel to the longitudinal axis of the colon. 
       FIG. 1B  shows an example of a passage  134 , such as a human colon, with capsule  100  in contact with surface  132  on the left side of the figure. In this case, an optical axis (not shown) of the camera is parallel to the longitudinal axis of passage  134  (both axes are oriented vertically in the figure). Capsule  100  also has a longitudinal axis  118  that is coincident with its camera&#39;s optical axis. A ridge  136  in passage  134  has a front surface  138  which is visible and thus imaged by capsule  100  as it approaches the ridge (assuming capsule  100  moves upwards in the figure). Backside  140  of ridge  136 , however, is not visible to the lens opening  110 , and hence does not form an image of backside  140 . Specifically, capsule  100  misses part of surface  140  and note that it misses an irregularity in passage  134 , illustrated as polyp  142 . 
     In  FIG. 1B , three points within the field of view of lens opening  110  are labeled A, B and C. The distance of lens opening  110  is different for these three points, where the range of the view  112  is broader on one side of the capsule than the other, so that a large depth of field is required to produce adequate focus for all three simultaneously. Also, if the LED (light emitting diode) illuminators provide uniform flux across the angular FOV, then point A will be more brightly illuminated than points B and C. Thus, an optimal exposure for point B results in over exposure at point A and under exposure at point C. An optimal exposure for point A results in under exposure at points B and C. For each image, only a relatively small percentage of the FOV will have proper focus and exposure, making the system inefficient. Power is expended on every portion of the image by the flash and by the imager, which might be an array of CMOS or CCD pixels. Moreover, without image compression, further system resources are expended to store or transmit portions of images with low information content. In order to maximize the likelihood that all surfaces within the colon are adequately imaged, a significant redundancy, that is, multiple overlapping images, is required in using this prior art capsule. 
     U.S. Pat. Nos. 6,836,377 and 6,918,872 disclose two prior art geometries for non-panoramic capsule cameras. In U.S. Pat. No. 6,836,377, the capsule dome is ellipsoidal with the pupil at its center and LEDs lying on the focal curve. In U.S. Pat. No. 6,918,872, the dome is spherical with the pupil centered on the center of curvature and LEDs in the same plane further toward the edge of the sphere. The just-described two patents are incorporated by reference herein in their entirety, as background. Various illumination geometries for capsule endoscopes with panoramic imaging systems are disclosed in U.S. patent application Ser. No. 11/642,285 filed on Dec. 19, 2006 by Kang-Huai Wang and Gordon Wilson entitled “In Vivo Sensor with Panoramic Camera” and assigned to CapsoVision, Inc. The just-described patent application is incorporated by reference herein in its entirety. 
     US Patent Publication 2006/0178557 by Mintchev et al. entitled “Self-Stabilizing Encapsulated Imaging System” is incorporated by reference herein in its entirety as background. This publication describes a capsule endoscope illustrated in  FIG. 10  attached hereto, wherein a light emitting diode (LED)  154  and an imager  152  (e.g. a CMOS imager) are mounted in a central region of a capsule, between ends  156   a  and  156   b . The capsule includes an RF transmitter  158  that transmits images acquired by imager  152  to an external receiver. The capsule also includes batteries  160   a  and  160   b , and a controller  162 . 
     The inventor believes that improvements in illumination for imaging in vivo passages by endoscopes are desired. 
     SUMMARY 
     In accordance with the invention, an endoscope provides illumination inside a body cavity using multiple sources of light, and captures images of tissue in the body cavity using a camera enclosed therein. In certain embodiments of the invention, one of the sources (also called “long-range source”) is used to image tissue located in a predetermined distance range from the endoscope. In the just-described embodiments, tissue located in contact with or close to (e.g. within 5 mm of) the endoscope is illuminated by another of the sources (also called “short-range source”). 
     The just-described two light sources may be positioned relative to the camera as described next, based on (1) a point of intersection of an optical axis of the camera with an inner surface of a housing of the endoscope, hereinafter “optical-axis intersection point” or simply “intersection point”; (2) one region (hereinafter “long-range illumination region”) of the housing through which light (also called “long-range light”) from the long-range source exits the housing; and (3) another region (hereinafter “short-range illumination region”) of the housing through which light (also called “short-range light”) from the short-range source exits the housing. Specifically, the short-range light source and the long-range light source are positioned such that the optical-axis intersection point is contained within (and is a portion of) the short-range illumination region, but the optical-axis intersection point is located outside the long-range illumination region. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIGS. 1A and 1B  illustrate, in cross-sectional diagrams, a prior art capsule endoscope in a small intestine and a large intestine respectively. 
         FIG. 10  illustrates, in a perspective cut-away view, a prior art endoscope described in US Patent Publication 2006/0178557 by Mintchev et al. 
         FIG. 2A  illustrates, in a perspective view, a capsule endoscope  200  in one embodiment of the invention, having a tubular wall  201 M with an imaging region  212  overlapping an illumination region  210  through which light is transmitted for short-range illumination and another illumination region  211  through which light is transmitted for long-range illumination. 
         FIGS. 2B and 2C  illustrate, in perspective views, the capsule endoscope of  FIG. 2A , when viewed from the left of  FIG. 2A , showing overlapping beams of illumination ( FIG. 2B ) and a coalesced region formed thereby ( FIG. 2C ). 
         FIG. 2D  illustrates, in a perspective view, an arrangement of light sources within the capsule endoscope of  FIG. 2A . 
         FIG. 2E  illustrates, a cross-sectional view of the capsule endoscope  200 , taken in the direction  2 E- 2 E in  FIG. 2C . 
         FIG. 2F  illustrates, a cross-sectional view of the another capsule endoscope in accordance with the invention. 
         FIG. 2G  illustrates an endoscope in still another embodiment of the invention, wherein the tubular wall has a central region of a diameter larger than the two ends. 
         FIG. 2H  illustrates an endoscope in another embodiment of the invention, wherein the tubular wall has an aspect ratio less than 1. 
         FIG. 2I  illustrates, in a graph, the radiant energy generated by a lower LED  217  and an upper LED  205  illustrated in  FIG. 2E , depending on distance of tissue from the endoscope. 
         FIGS. 2J and 2K  illustrate distribution of intensity of light beams and spot sizes, at different distances, in response to current applied to LEDs  217  and  205  to generate radiant energy as illustrated in  FIG. 2I . 
         FIGS. 2L and 2M  illustrate the endoscope of  FIG. 2A  with multiple short-range sources enclosed in the housing, positioned at a common latitude relative to the optical axis but located at different longitudes (i.e. radial directions). 
         FIG. 2N  illustrates use of the endoscope of  FIGS. 2L and 2M  in normal operation, wherein the multiple short-range sources create successively overlapping regions spanning 360°. 
         FIG. 2O  illustrates lenses L 1 -L 4  and sensors Q 1 -Q 4  that are also enclosed in an endoscope of the type illustrated in  FIGS. 2L, 2M and 2N . 
         FIG. 2P  illustrates an endoscope that includes a distal tip of the type illustrated in  FIG. 2A , mounted at an end of an insertion tube in accordance with the invention. 
         FIG. 2Q  illustrates, in an enlarged cross-sectional view, the distal tip of  FIG. 2P . 
         FIGS. 3, 4 and 5  illustrate, in cross-sectional views taken in direction  2 E- 2 E of  FIG. 2C , positioning of light source(s) in three embodiments of an endoscope, at locations outside of a field of view of a camera. 
         FIG. 6  illustrates, in an enlarged view of an endoscope of the type shown in  FIG. 3 , an angular relationship implemented in some embodiments, between a light source, an objective lens of a camera, and surface of the tubular wall. 
         FIGS. 7, 8 and 9  illustrate, in an enlarged view of an endoscope of the type shown in  FIG. 3 , an optical element used in some embodiments, to reduce angular dispersion of a light emitter. 
         FIG. 10  illustrates an embodiment wherein the optical element is implemented by an angular concentrator which is positioned so that its axis “Z” passes through a location of the light emitter. 
         FIG. 11  illustrates, in a perspective view, an annular angular concentrator that is used in some embodiments of an endoscope. 
         FIG. 12A  illustrates, in a side view an annular angular concentrator shown in  FIG. 11 . 
         FIG. 12B  illustrates, in a cross-sectional view in the direction A-A, in  FIG. 12C , a portion of the annular angular concentrator of  FIG. 12A . 
         FIG. 12C  illustrates, in a top elevation view, one half portion of the annular angular concentrator of  FIG. 11 . 
         FIG. 12D  illustrates, in a side view in the direction D-D, in  FIG. 12C , the half portion of the annular angular concentrator. 
         FIG. 12E  illustrates, in a bottom elevation view, a half portion of the annular angular concentrator of  FIG. 11 . 
         FIG. 13  illustrates, in a cross-sectional view, relative positions of a light emitter and a compound parabolic concentrator in some embodiments of an endoscope in accordance with the invention. 
         FIGS. 14A and 14B  illustrate, in a top view and a side view respectively, an assembly of multiple light emitters and an annular concentrator in some embodiments of an endoscope 
         FIGS. 15 and 16  illustrate, in cross-sectional views, two alternative embodiments of combination of a light emitter and a concentrator, in accordance with the invention. 
         FIG. 17  illustrates use of an endoscope having two light emitters, for illumination and imaging over short distances, in accordance with the invention. 
         FIG. 18  illustrates use of the endoscope of  FIG. 17  for long range illumination and imaging, also in accordance with the invention. 
         FIG. 19  illustrates use of an endoscope having two light emitters, for axial illumination and imaging, in an alternative embodiment of the invention. 
         FIG. 20  illustrates, in a block diagram, the numbering of LEDs and the numbering of sectors of a sensor for use in an illumination control method of the type shown in  FIG. 21 . 
         FIG. 21  illustrates, in a flow chart, a method used in some embodiments, to operate light emitters for panoramic illumination and imaging. 
         FIG. 22  illustrates, in a graph, timing relationships between signals between a controller, LEDs and sensors in an endoscope in accordance with the invention. 
         FIG. 23  illustrates, in a block diagram, electronic circuitry including controller, LEDs and sensors in an endoscope in accordance with the invention. 
         FIG. 24  illustrates a monolithic sensor chip wherein four regions Q 1 -Q 4  are used to capture four portions of a panoramic 360° image. 
         FIG. 25  illustrates dimensions of an exemplary annular mirror  218  having a convex reflecting surface in some embodiments of the invention. 
         FIG. 26  illustrates dimensions of an endoscope shaped as a capsule in some embodiments of the invention. 
         FIG. 27  illustrates, in a partial cross-sectional view, formation of three virtual sources by a two-layer window in some embodiments of a capsule endoscope in accordance with the invention. 
         FIG. 28A-28D  illustrate in a front view, relative positions of a long-range illumination region  211 , a short-range illumination region  210  and an imaging region  212  on a window of a capsule endoscope in some embodiments of the invention. 
         FIGS. 28E and 28G  illustrate overlap of a pair of adjacent imaging regions  282 A and  282 B with one another, and additionally another overlap of another pair of adjacent imaging regions  282 Z and  282 A with one another, in a capsule endoscope of the type illustrated in  FIGS. 28A and 28C  respectively. 
         FIGS. 28F and 28H  illustrates a union  282  of adjacent imaging regions in a capsule endoscope of the type illustrated in  FIGS. 28E and 28G  respectively. 
         FIGS. 28I and 28J  illustrate, on an unrolled tubular wall of a capsule endoscope of the type illustrated in  FIGS. 28E-28F and 28G-28H  respectively, the position of a union  282  of imaging regions relative to the position of another union  281  of adjacent short-range illumination regions. 
         FIGS. 28K and 28L  illustrate overlap of imaging region  282 A with a corresponding short-range illumination region  283 A, in a capsule endoscope of the type illustrated in  FIGS. 28A and 28C  respectively. 
         FIGS. 29A, 29B and 29C  illustrate, in partial cross-sectional views, geometry for positioning a light source S relative to a pupil P of a camera to eliminate or minimize capture of virtual sources in an image. 
         FIG. 30  illustrates, in a cross-sectional plan view, relative positions of long-range and short-range illumination sources in a capsule endoscope in some embodiments of the invention. 
         FIGS. 31 and 32  illustrate, in cross-sectional side views, two embodiments of a capsule endoscope in accordance with the invention, housing a radially-symmetric optical element in a camera. 
         FIG. 33  illustrates changes in energy emitted in accordance with this invention relative to changes in distance of two illumination regions of an endoscope from a gastrointestinal tract. 
         FIG. 34  illustrates an endoscope having two cameras at two ends of a capsule in an alternative embodiment of the invention 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with the invention, an endoscope  200  ( FIG. 2A ) provides illumination inside a body cavity  241  of a diameter D, using multiple light sources  205 ,  206 , and captures images of tissue using a camera enclosed therein. In some embodiments, endoscope  200  has an aspect ratio greater than one, with a longitudinal axis  222 . The orientation of endoscope  200  is determined by the dimension and orientation of body cavity  241  that itself is typically elongated. Examples of body cavity  241  are various portions of the gastrointestinal tract, such as the small intestine and the colon (large intestine). Note that in  FIG. 2A , a number of lines  299  are used as shading on a smoothly curved surface of housing  201 , specifically to convey a visual sense of depth in the perspective view. Similar shading lines are also used in  FIGS. 2B-2D ,  FIGS. 2G-K , and  FIGS. 2M-2P . 
     Referring to  FIG. 2A , source  205  of endoscope  200  is a “long-range source” that is used to image tissue located in cavity  241  within a predetermined distance range from the endoscope, e.g. between 10 mm and 35 mm. Long-range source  205  is not used when tissue of the body cavity  241  is in contact with the endoscope. Instead, in-contact tissue is imaged using illumination primarily from a short-range source  206 . Tissue which is close to (e.g. within 5 mm of) the endoscope, but not in contact with the endoscope, is illuminated by both sources  205  and  206  in some embodiments of the invention. 
     Regardless of how implemented, in many embodiments multiple light sources  205  and  206  are positioned relative to a pupil  202  ( FIG. 2A ) of a camera as described next. Pupil  202  has an optical axis  203  that intersects with an internal surface of housing  201  of endoscope  200  at a point  204 . Note that housing  201  in  FIG. 2A  is illustratively shown to have no thickness, although as will be readily apparent to the skilled artisan the housing has a finite thickness (e.g. 4 mm). Point  204  is also referred to herein as an “optical-axis intersection point” or simply “intersection point”. Long-range source  205  is positioned relative to lens  202  such that optical-axis intersection point  204  is located outside of a region (also called “long-range illumination region”)  211  through which light (also called “long-range light”)  209  transmitted by long-range source  205  exits housing  201 . Moreover, short-range source  206  is positioned relative to lens  202  such that optical-axis intersection point  204  is located inside of another region (also called “short-range illumination region”)  210  through which light (also called “short-range light”)  208  transmitted by short-range source  206  exits housing  201 . Note that short-range illumination region  210  is larger than the long-range illumination region  211 , by design so as to ensure adequate uniformity in illumination of tissue when the tissue is close to or touching the endoscope. 
     To summarize the arrangement described in the preceding paragraph, light sources  205  and  206  are positioned such that optical-axis intersection point  204  is contained within (and is a portion of) short-range illumination region  210 , but is located outside of long-range illumination region  211 . In the embodiment illustrated in  FIG. 2A , long-range illumination region  211  not only does not enclose intersection point  204 , this region  211  also does not overlap a region (also called “imaging region”)  212  of housing  201  through which light (also called “reflected light”) reflected by tissue is transmitted through housing  201  and is captured by the camera. In some embodiments, the specific position and orientation of light sources  205  and  206  relative to pupil  202  of the camera is determined empirically, with a goal to improve uniformity in illumination of tissue, located in multiple ranges of distances from the endoscope. 
     Note that stray reflected light may enter endoscope  200  through other regions, but it is a boundary of region  212  which demarcates the light used in forming a diagnosable image within endoscope  200 . The boundary of region  212  excludes any light which is not sensed by a sensor within endoscope  200 . Moreover, the boundary of region  212  also excludes any light which may be sensed but is not eventually used in a diagnosable image, e.g. light which generates a portion of an image that is “cropped” (i.e. not used) prior to diagnosis. 
     Imaging region  212  is typically determined by a field of view (“FOV”)  214 . Field of view  214  is defined by a range of angles in a plane passing through optical-axis intersection point  204  and optical axis  203  over which tissue  241  located outside housing  201  forms an image captured by the camera for diagnosis. Note that the field of view is sometimes called the angle of coverage or angle of view. The field of view depends on the focal length of an objective lens adjacent to pupil  202 , and the physical size of the film or sensor used to record the image. An intersection of field of view  214  with housing  201  forms imaging region  212  of endoscope  200 . In endoscope  200 , each of light sources  205  and  206  are located outside the field of view  214  so as to avoid imaging light from these sources. The aforementioned FOV refers to the longitudinal direction; an angular field of view exists for the lateral direction as well. However, the lateral FOV is not germane to the present discussion. 
     Moreover, the above-described lack of overlap between long-range illumination region  211  and imaging region  212  eliminates any possibility that a virtual image (also called “ghost”), due to long-range light  209  reflected by housing  201 , is present in an image that is captured by the camera and used for diagnosis. In certain alternative embodiments, a ghost from reflection of long-range light by the housing, is present in an image that is formed in the camera, and a sensor is operated to exclude the ghost e.g. by cropping the image. During cropping, a part of an image in a central region thereof is transmitted by endoscope  200  to a computer for use in diagnosis, and the rest of the image containing the ghost is not processed. Depending on the embodiment, cropping is performed either by a computer located outside the body, in which case the entire image is transmitted, or alternatively performed within housing  201 . In the just-described alternative embodiments, cropping is performed in electronic circuitry, e.g. by a sensor and/or by a processor (see  FIG. 18 ). 
     In some embodiments of the type described above, light source  206  is deliberately positioned so that short-range illumination region  210  overlaps imaging region  212 . The just-described overlap is chosen to ensure that short-range light  208  illuminates tissue adequately enough to obtain a diagnosable image in the camera, even when the tissue is in contact with an external surface of housing  201 . 
     In embodiments of the type shown in  FIG. 2A , regions  210 ,  211  and  212  are oriented transversely e.g. on a tubular wall  201 M ( FIG. 2B ) which is a portion of housing  201 . Moreover, in  FIG. 2A , tubular wall  201 M forms a portion of a housing  201  that is shaped as a capsule with two domes  201 T and  201 B located on each of the two sides of wall  201 M. In the embodiment shown in  FIG. 2A , tubular wall  201 M is capped with a dome-shaped end (or simply “dome”)  201 T on one side and another dome-shaped end  201 B on the other side, to implement a capsule endoscope. Domes  201 T and  201 B constitute portions of a housing that also includes tubular wall  201 M. 
     In endoscope  200  ( FIG. 2A ) domes  201 T and  201 B are not used to pass any light to a region outside of endoscope  200 . Domes  201 T and  201 B are also not used to receive any light that forms an image to be diagnosed. Instead, light exits endoscope  200  and enters endoscope  200  through tubular wall  201 M, and the just-described orientation of light relative to the endoscope is referred to herein as “radial”. Domes  201 T and  201 B are used (with tubular wall  201 M) to form a water-tight housing for optical and electronic components enclosed within endoscope  200 . Note that other embodiments of an endoscope in accordance with the invention may have different shapes, e.g. endoscope  290  illustrated in  FIGS. 2P and 2Q  has a distal tip  291  at an end of insertion tube  292 . Distal tip  291  also illuminates a body cavity radially, through a tubular wall similar to endoscope  200 . Note that in alternative embodiments, regions  210 ,  211  and  212  are oriented axially e.g. on dome  201 T or dome  201 B as illustrated in  FIG. 19 . 
     As discussed above, a radially-illuminating endoscope (regardless of whether shaped as a capsule as in  FIG. 2A  or as a distal tip  291  at the end of an insertion tube  292  as shown in  FIGS. 2P and 2Q ) provides illumination through tubular wall  201 M. Tubular wall  201 M may have a circular cross section, such as a cylinder or a frustum of a prolate or oblate spheroid. The endoscope&#39;s tubular wall  201 M can alternatively have a non-circular cross section, such as an elliptical cross-section. Regardless of the cross-section, a majority of light (e.g. greater than 50% of the energy) exits from endoscope  200  radially, side-ways through tubular wall  201 M ( FIG. 2B ) of the endoscope. Moreover, tissue-reflected light passes back through tubular wall  220  also laterally, to form within endoscope  200  an image to be diagnosed (not shown in  FIG. 2B ). 
     In several embodiments, short-range light  208  exiting an endoscope is initially generated by a light emitter (such as an LED) within the housing, and short-range light  208  is then split by an optical element (also within the housing) into at least two fractions that respectively form at least two overlapping spots on the housing. For example,  FIG. 2B  illustrates two spots  210 A and  210 B formed by two fractions of short-range light  208  resulting from splitting. Splitting of short-range light  208  into two or more fractions enables a larger area of tissue to be illuminated by overlapping spots which provide greater uniformity in energy distribution across the illumination region, relative to a single spot which has a single peak in its center. 
     In the example shown in  FIG. 2B , the two spots  210 A and  210 B overlap one another on housing  201 , to form at least a majority of (i.e. greater than 50% of area of) short-range illumination region  210  as illustrated in  FIG. 2C . In  FIGS. 2B and 2C , a third spot  210 C is also formed, by a third fraction of short-range light  208  and included in short-range illumination region  210 . In one illustrative embodiment, two roughly equal fractions (approximately 25% of energy) of short-range light  208  form spots  210 A and  210 B. In the illustrative embodiment, another fraction (approximately 50% of energy) of short-range light  208  forms a third spot  210 C. 
     As will be readily apparent to the skilled artisan, the examples of percentages that form the various fractions of short-range light  208  are different in different embodiments. Moreover, other embodiments (not shown) split short-range light  208  into only two fractions, i.e. do not form a third spot  210 C. Still other embodiments (also not shown) split short-range light  208  into four or more fractions, i.e. form four or more spots of short-range illumination region  210 . Moreover, also depending on the embodiment, the spots of short-range light  208  may or may not coalesce together, to form a single continuous region. 
     In endoscope  200 , the long-range illumination region  211  and the short-range illumination region  210  may or may not overlap one another, depending on the embodiment. Also depending on the embodiment, imaging region  212  may or may not overlap the long-range illumination region  211 . 
     In many embodiments, two spots  210 A and  210 B are formed by two beams  208 A and  208 B ( FIG. 2D ) that are two fractions of short-range light  208  ( FIG. 2A ). Beams  208 A and  208 B are transmitted towards the interior surface of housing  201  by two light sources  206  and  218  respectively that are located on opposite sides of optical axis  203 . Optical axis  203  is shown in  FIGS. 2A and 2D  as a horizontal line and for convenience, the two sides of optical axis  203  are referred to herein as “above” and “below” the axis, although it is to be understood that the two sides orient differently depending on the orientation of axis  203  relative to the observer (e.g. “left” and “right” if axis  203  is oriented vertically). 
     Referring to  FIG. 2D , light source  206  is located below optical axis  203  and transmits a majority of (i.e. greater than 50% of energy in) beam  208 A below optical axis  203 . Accordingly, optical-axis intersection point  204  is located in a top portion of spot  210 A. In some embodiments, a light emitter is located below optical axis  203 , and this light emitter is included in light source  206  which additionally includes an optical element that splits short-range light  208  received from the light emitter. Light source  206  is located below optical axis  203  and located sufficiently close to (e.g. in contact with) housing  201  such that the angles of incidence of beam  208 A on housing  201  are sufficiently large, within region  212 , to minimize or eliminate capture by the camera of any portion of beam  208 A directly reflected by housing  201 . 
     The above-described optical element in some embodiments forms beam  208 B from light  208  received from the light emitter in addition to the above-described beam  208 A. Beam  208 B is initially transmitted by the optical element across optical axis  203  to mirror  218 . As shown in  FIG. 2D , mirror  218  is located above optical axis  203 , and includes a reflective surface that re-transmits a majority of beam  208 B received from the light emitter to form spot  210 B on an inner surface of the housing. Optical-axis intersection point  204  is located in a bottom portion of spot  210 B. Note that in the embodiment illustrated in  FIGS. 2B-2D , bottom portion of spot  210 B overlaps the top portion of spot  210 A and intersection point  204  is located within the overlap. Moreover, in the embodiment illustrated in  FIG. 2B , spots  210 A and  210 B are aligned relative to one another, along a direction that is aligned with longitudinal axis  222  (e.g. within 5°). Note that here as well, mirror  218  is located sufficiently close to housing  201  such that the angles of incidence of beam  208 B are sufficiently large to minimize or eliminate capture by the camera of any portion of beam  208 B directly reflected by housing  201 . 
     In the illustrative embodiment shown in  FIG. 2D , a third beam  208 C is also formed by the optical element in splitting short-range light  208 , and beam  208 C is directly incident on housing  201  to form spot  210 C a majority of which is located below spot  210 B (with a small overlap therebetween). Note that spot  210 C is located in illumination region  210  outside of imaging region  212 . Accordingly, a majority of the third fraction which is incident on spot  210 C does not reach the camera when the tissue is in contact with the housing. However, beam  208 C provides illumination through short-range illumination region  210  that does reach the camera when tissue is located a short distance away from the housing (e.g. 5 mm away). 
       FIG. 2E  illustrates an exemplary implementation of one embodiment of an endoscope  200  of the type described above in reference to  FIGS. 2A-2D . Specifically, as illustrated in  FIG. 2E , a light emitter  217  supplies short-range light to an optical element  216  that splits the short-range light into three beams as follows. One beam  208 C ( FIG. 2D ) is directly incident on the housing with intensity distribution  219 C ( FIG. 2E ). Another beam  208 A ( FIG. 2D ) is mostly below optical axis  203  and is incident on the housing with intensity distribution  219 A ( FIG. 2E ). A third beam  208 B ( FIG. 2D ) crosses optical axis  203  and is reflected by a mirror  218  and then is incident on the housing with intensity distribution  219 B ( FIG. 2E ). An example of optical element  216  is a compound parabolic concentrator (CPC) as discussed below. Lens L is an objective for the camera, and light received therethrough is reflected by a mirror M to sensor  232  for sensing and storage of the image. 
     Note that the implementation illustrated in  FIG. 2E  is symmetric about longitudinal axis  222 , and endoscope  200  holds four copies of a light emitter in long-range source  205 , another light emitter  217  and optical element  216  (together forming a short range light source), an optical element e.g. mirror  218  (wherein mirror  218  together with light emitter  217  and optical element  216  forms another short range light source), lens L and mirror M. Note also that sensor  232  and light emitter  217  are both supported by a board  249 . In another embodiment, there are a pair of light emitters in each of eight radial directions (for a total of sixteen emitters) that are used to generate a 360° panoramic image of a body cavity. 
     Although an endoscope  200  illustrated in  FIG. 2E , has two light emitters in a given radial direction, alternative embodiments may use four light emitters in a single radial direction, as shown in the cross-sectional view illustrated in  FIG. 2F . In  FIG. 2F , endoscope  250  includes two light emitters  221 A and  224 A that are used as two long-range light sources. Moreover, endoscope  250  also has two additional light emitters  222 A and  223 A that are used as short-range light sources. Moreover, in some embodiments, light emitters are positioned in the endoscope to illuminate along each of four radial directions (e.g. north, south, east and west around a circular boundary of the housing, when viewed from the top). Three sets of light sources in corresponding three radial directions are illustrated in  FIG. 2F  as sources  221 A,  222 A,  223 A and  224 A in the west direction, sources  221 B,  222 B,  223 B and  224 B in the north direction, and sources  221 C,  222 C,  223 C and  224 C in the east direction (with sources in the south direction being not shown in  FIG. 2F  because it is a cross-sectional view). In certain embodiments, light emitters are positioned in the endoscope to illuminate along each of eight radial directions (e.g. north, north-east, east, south-east, south, south-west, west, and north-west, again, when viewed from the top). 
     The embodiment shown in  FIG. 2A  has an aspect ratio greater than 1, whereby endoscope  200  has a larger dimension along axis  222  than any other dimension located within a cross-section that is transverse to axis  222 . For example, endoscope  200  has a length along tubular wall  201 M that is larger than the outer diameter of tubular wall  210 M (in case of a circular cross-section). Accordingly, tubular wall  202  has a cylindrical shape, in the just-described embodiment. 
     In several alternative embodiments of the invention, an endoscope has a tubular wall of varying cross-section along the length of the endoscope. For example,  FIG. 2G  illustrates an endoscope  223  wherein a tubular wall  224  has an outer diameter  225  (in case of a circular cross-section) in the middle which is larger than an outer diameter  226  at the ends, i.e. tubular wall  224  has a bulge at its center. In another example (not shown), the tubular wall of an endoscope in accordance with the invention has narrower central portion with wide ends, i.e. an hourglass shape. Regardless of the shape of the tubular wall, illumination and imaging are performed through various overlapping and non-overlapping regions of the tubular wall, as described above in certain embodiments of the invention. 
     Furthermore, in another alternative embodiment illustrated in  FIG. 2H , an endoscope  227  has an aspect ratio less than 1, whereby a dimension along axis  222  is smaller than at least one dimension in a cross-section transverse to axis  222 , e.g. thickness  229  is smaller than diameter  228  (in case of a circular cross-section). Even though aspect ratio less than 1, in this embodiment as well, overlapping and non-overlapping regions for illumination and imaging are formed on the tubular wall  229  as described above. 
     In one illustrative embodiment, endoscope  200  ( FIG. 2B ) has a diameter  231  of 1.1 cm and a length  232  of 2.6 cm. Note that in this illustrative embodiment, tubular wall  201 M has a transparent window of height 5.0 mm. Moreover, imaging region  212  ( FIG. 2A ) has a width expressed as an arc length, of 0.9 cm and a height of 0.5 cm. Furthermore, illumination region  210  ( FIG. 2C ) does not have an exact boundary. Hence, the contour shown in  FIG. 2C  is for a specific intensity level, such as 10% of maximum intensity. In the illustrative embodiment, contour  210  has a height of 0.7 cm and a maximum arc width of 0.7 cm. Additionally, note that tubular wall  201 M ( FIG. 2B ) has a length of 2.0 cm. Also, each of domes  201 T and  201 B has a height of 0.3 cm (see  FIG. 2C ) and a diameter of 1.1 cm (which diameter is same as the diameter of tubular wall). Note that the dimensions identified herein are merely for illustration, and other dimensions are used in other embodiments. 
     In some embodiments, imaging region  212  ( FIG. 2A ) and illumination regions  210  and  211  are located closer to top dome  201 T (also called “near end”), and farther removed from bottom dome  201 B (also called “far end”). Space adjacent within the endoscope which is enclosed within or adjacent to either or both of domes  201 T and  201 B is used in certain embodiments to house various electronic components, such as a battery and a wireless transmitter (not shown) of the type normally used in a capsule endoscope. 
     In other embodiments, illumination and imaging regions  210  and  212  overlap a half-way line (e.g. an “equator”) that is located equidistant from each of two farthest points on two domes  201 T and  201 B of a capsule endoscope. In still other embodiments (also not shown), illumination and imaging regions  210  and  212  are centered at the half-way line and in these embodiments the half-way line passes through optical-axis intersection point  204  ( FIG. 2A ; half-way line not shown). In some embodiments imaging region  212  and illumination region  210  (as shown in  FIG. 2A ) have their respective centers offset from one another, although in other embodiments the two centers are coincident. 
     Referring to  FIG. 2A , illumination region  210  is formed by light originating at short-range light source  206  that is located towards the far end  201 B. Short-range source  206  is offset in a longitudinal direction along axis  222  from optical axis  203  by a distance  233 . Long-range light source  205  is also offset from optical axis  203  in the longitudinal direction along axis  222  similar to light source  206 , but the direction is opposite. In  FIG. 2A , light source  205  is located towards near end  201 T at an offset distance  234  from optical axis  203 . Furthermore, as shown in  FIGS. 2A and 2D , another light source includes a mirror  218  that is also offset in the longitudinal direction along axis  222  towards near end  201 T, at an offset distance  235  from optical axis  203 . 
     Sources  206  and  205  and a source that includes mirror  218  are positioned at locations and oriented at angles that are selected to ensure that any reflection of light from these sources by tubular wall  201 M does not enter pupil  202 . In one illustrative embodiment, short-range offset distance  233  is 0.2 cm, long-range offset distance  234  is 0.4 cm, and the mirror&#39;s offset distance  235  is 0.4 cm. Note that offset distances can be smaller if the angular distribution of light from the source is narrowed. Accordingly, a projection onto a longitudinal plane, of mirror-reflected rays, is in a narrow range of angles relative to rays from the other two sources, and for this reason the mirror&#39;s offset distance is also smaller relative to the other two sources&#39; offset distances. 
     In some embodiments, light sources  205  and  206  are operated to generate different amounts of radiant energy relative to each other depending on distance of tissue  241  from endoscope  200 . The distance of tissue is determined by a controller (mounted on a printed circuit board  249 ) in endoscope  200  based on intensity of light reflected by the tissue and sensed by a sensor  232  of the camera. Using the sensed intensity, current applied to sources  205  and  206  are automatically changed by the controller (see  FIG. 23 ), using an empirically-determined relationship between radiant energy and distance. In the example illustrated in  FIG. 2E , the intensity distribution of light from source  205  is not shown. 
     Source  205  may be operated to generate a minimal amount of radiant energy (or even switched off depending on the embodiment) if the tissue to be imaged is in contact with the endoscope  200 . As noted above, in-contact tissue is illuminated by light from short-range source  206 . When tissue is far away from the endoscope, multiple light sources  205  and  206  and a source that includes mirror  218  may all be used simultaneously, concurrently or contemporaneously (depending on the embodiment) to provide the illumination needed to generate a diagnosable image. Accordingly, the number of sources used for imaging is varied depending on distance, to ensure that the tissue&#39;s image is formed within the camera within a predetermined intensity range. 
     In some embodiments, the predetermined intensity range is selected ahead of time empirically, based on adequacy of images to enable resolution of the detail necessary for diagnosis by a doctor. The specific manner in which tissue&#39;s distance and/or light emitter energy emission are determined for an endoscope is different in various embodiments. Accordingly, numerous methods to determine tissue&#39;s distance and/or light emitter energy emission will be readily apparent to the skilled artisan, in view of this disclosure. 
     Inclusion of multiple light sources in an endoscope in accordance with the invention enables the endoscope to image tissue located at different distances from the endoscope by using illumination of different amounts and/or distributions depending on the distance of the tissue. In a first example, when tissue is located in contact with or at a very short distance D 1  from an external surface of the endoscope (e.g. less than a 1/10 the diameter D of the body cavity of interest), tissue  241  is illuminated (and imaged) by supplying LED  217  with current to generate radiant energy E 2  ( FIG. 2I ). The resulting illumination includes intensity distributions  219 A- 219 C ( FIG. 2J  and  FIG. 2K ) generated by respective beams  208 A- 208 C via imaging region  212 . At this time, long-range source LED  205  is operated to generate a negligible amount of energy E 1  which results in a distribution  215 , and a majority of its energy is outside of field of view  214 , i.e. not used in imaging. Hence source  205  may be turned off at this stage, if appropriate. 
     In a second example, tissue is located at an intermediate distance D 2  from the endoscope (e.g. on the order of ⅕ of body cavity diameter) and as illustrated in  FIG. 2I  both LEDs  217  and  205  in endoscope  200  are driven to generate the same amount of radiant energy E 3 . The resulting illumination now includes intensity distribution  215  ( FIG. 2J  and  FIG. 2K ), a portion of which now overlaps optical axis  203 , although a majority of energy is above axis  203 . Note that the peak of (and hence the center of) distribution  219 B also has moved (in the longitudinal direction) to a location above the peak of distribution  215 . Furthermore, a peak of distribution  219 A has moved from a location above axis  203  to a location below the peak  219 C. Accordingly, within the camera&#39;s field of view  214  at intermediate distance D 2 , long-range source LED  205  provides approximately the same amount of illumination as the illumination provided by short-range source LED  217 . 
     In a third example, tissue is located at another intermediate distance D 3  (e.g. on the order of ⅓ of body cavity diameter) and long-range source LED  205  is operated to generate energy E 5  ( FIG. 2I ) that is almost double the energy E 4  of short-range source LED  217 . The intensity distribution  215  ( FIG. 2J  and FIG.  2 K) at distance D 3  constitutes a majority of illumination (e.g. provides &gt;50% of energy). Hence, long-range source LED  205  provides a majority of illumination. Note that at distance D 3 , the peaks of distributions  219 A and  2198  are located outside of the camera&#39;s field of view  214 . While the peak of distribution  219 C is within the field of view  214 , this distribution&#39;s contribution to the total illumination is small (e.g. less than 20%). 
     Finally, in a fourth example, tissue is located at a large distance D 4  (e.g. on the order of ½ of body cavity diameter), long-range source LED  205  is supplied power P 6  ( FIG. 2I ) that is an order of magnitude greater than power P 4  of short-range source LED  217  (whose power P 4  remains same as at distance D 3 ). As shown in  FIG. 2K , intensity distribution  215  from long-range source LED  205  provides the primary illumination. Contributions, from short-range source LED  217  are minimal at distance D 4  (e.g. 5% or less). 
     Note that in some embodiments of the type shown in  FIG. 2I , the integration time of each pixel is shifted relative to another pixel, although the pixels have a common integration time during which time each of the LEDs within the endoscope is turned on, e.g. sequentially one after another, or all on simultaneously. Note further that the amount of radiant energy emitted by an LED (and consequently captured by a pixel) depends on the duration of time for which the LED is turned on and the power output by the LED during the time it is on. A summary of distances and radiant energy discussed above is provided in the following table, for one specific illustrative embodiment, with numbers in the following table being examples which have different values in other embodiments. In the following table, p is the distance from the longitudinal axis of endoscope to a plane in which tissue is located, R is the radius of the endoscope, Utop is proportional to the luminous energy of the top long-range LED, and Ubottom is proportional to the luminous energy of the short-range source LED  217   
     
       
         
           
               
               
               
               
             
               
                   
                   
               
               
                   
                 ρ/R 
                 Utop 
                 Ubottom 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 D1 
                 1.0 
                 0.004 
                 0.02 
               
               
                   
                 D2 
                 1.8 
                 0.03 
                 0.03 
               
               
                   
                 D3 
                 3.2 
                 0.1 
                 0.05 
               
               
                   
                 D4 
                 7.0 
                 1.0 
                 0.05 
               
               
                   
                   
               
            
           
         
       
     
     The intensity distributions shown in  FIGS. 2J and 2K  are based on annular mirror  218  having a convex reflective surface. The intensity distributions are roughly the same for a flat mirror  218 , although the exact distribution shape becomes a bit narrower. Note that the peak in distribution  215  from light transmitted by long-range LED  205  roughly follows a line inclined at an angle of the LED (e.g. 20 degrees relative to optical axis  203 ). So, if the tilt of LED  205  changes, the horizontal distance at which the center of distribution  215  intersects the optical axis  203  also changes. This distance is given by (distance of LED from axis)/tan (inclination angle). In the absence of significant illumination from the short-range LED, this is the distance at which the long-range illumination&#39;s intensity distribution is symmetrical relative to the camera. For greater distances the distribution is less symmetrical but uniformity actually improves because the distribution spreads faster than the field of view expands. 
     As noted above,  FIG. 2A  illustrates radial illumination by endoscope  200  in one direction (namely towards the west or left in  FIG. 2A ) although endoscope  200  has similar structure in other radial directions (e.g.  3  additional directions), to enable generation of a 360° panoramic image of tissue  241  all around within a body cavity of diameter D ( FIG. 2A ). Specifically, as illustrated in  FIG. 2L , endoscope  200  includes, in addition to a short-range light source LED  217 , three additional short-range light source LEDs  242 ,  243  and  244  that are mounted within a common lateral plane  251  in which LED  217  is mounted. While LED  217  forms illumination region  210 , other sources form other illumination regions around the tubular wall of endoscope  200 . Specifically, as illustrated in  FIG. 2M , source  242  forms illumination region  252  that is at a different longitude from region  210 . Note that regions  252  and  210  are adjacent to one another and have an overlap such that when both sources  217  and  242  are simultaneously turned on these two regions merge to form a continuous region  253  as shown in  FIG. 2N . 
     Note that endoscope  240  also includes various optical and/or electronic components required to form images that may be combined by a computer (not shown) to form a continuous 360° panoramic image. For example, some embodiments use as the objective a wide-angle lens that has an extremely wide field of view (e.g. 160°). One or more additional optical elements, such as a mirror, a lens and/or a prism are included in an optical path within endoscope  200  from the lens, e.g. to create an appropriate image for capture by a sensor. Note that in some embodiments, the additional optical elements include a mirror followed by three lenses that are selected to ensure low aberration and distortion and to provide an appropriate field of view as will be apparent to the skilled artisan in view of this disclosure. Certain illustrative embodiments, include additional optical elements as described in U.S. application Ser. No. 12/463,488 entitled “Folded Imager” filed by Gordon Wilson et al on May 11, 2009 which is incorporated by reference herein in its entirety. 
     Endoscope  200  may enclose several lenses (e.g. 4 lenses) used as objectives in each of several longitudinal planes, and light from the objectives passes to corresponding sensors via additional optical elements (as necessary).  FIG. 2O  illustrates lenses L 1 -L 4  that are used as objectives for reflected light that enters the endoscope. Light from lenses L 1 -L 4  is reflected by mirrors (not shown in  FIG. 2O ; see mirror M in  FIG. 2E ), and passes through additional lenses to sensors Q 1 -Q 4  for imaging therein. 
     Although a capsule shaped endoscope has been illustrated in  FIGS. 2A-2F , in an alternative embodiment illustrated in  FIG. 2P , an endoscope  290  includes a distal tip  291  at an end of an insertion tube  292 . Tube  292  is connected to a control section  293  that in turn is connected to a universal cord  294 . As shown in  FIG. 2Q , distal tip  291  includes a tubular wall  291 M and a top dome  291 T at its near end but does not have another dome at the bottom. Instead, the bottom of distal tip  291  is connected to the insertion tube  292 . Note that distal tip  291  illuminates a body cavity radially, through tubular wall  291 M. 
     A capsule endoscope  300  ( FIG. 3 ) in accordance with the invention images in vivo objects that are close to or touching the capsule housing by use of a lens  301  as an objective of a camera  304 . Lens  301  has an associated input pupil P ( FIG. 3 ). Note that  FIG. 3  schematically illustrates capsule endoscope  300  with a single objective lens  301 , a pupil P, and image plane I on which image  305  forms. For simplicity, camera  304  is shown in  FIG. 3  modeled as a pinhole with the input and output pupils collocated and an angular magnification of one. 
     In  FIG. 3 , lens  301  has a field of view (FOV) directed, sideways through a window  303  in a tubular wall  351  of capsule endoscope  300 . The term FOV denotes a field of view of the overall imaging system in all directions, and is defined by the range of field angles about the optical axis  306  that produces an image  305  on a target region R of the image plane I. The objective lens  301  may have a larger FOV that produces an image that overfills the target region R on the image plane I. For example, the target region R may be defined by all the active pixels on an image sensor I or by a subset of these pixels. 
     A projection of the FOV in a longitudinal plane of capsule endoscope  300  ( FIG. 3 ) is referred to as longitudinal FOV. An example of longitudinal FOV is the field of view  214  in  FIG. 2A . Another projection of the FOV in a lateral plane (perpendicular to the longitudinal plane) is referred to as lateral FOV. If the capsule endoscope is oriented vertically as shown in  FIG. 3 , the longitudinal FOV is located within a vertical plane (which is the same as the plane of the paper in  FIG. 3 ), and the lateral FOV is in a horizontal plane (perpendicular to the plane of the paper). The longitudinal FOV spans angles on either side of optical axis  306  and is delineated by lines of perspective A and B as shown in  FIG. 3 . Accordingly, the lateral FOV is located in a plane that passes through an optical axis  306  of capsule endoscope  300  ( FIG. 3 ). The lateral FOVs of multiple objective lenses, included in capsule endoscope  300  and located at different longitudes, overlap at their boundaries such that a 360° panorama is imaged by camera  304  as described above in reference to  FIG. 2O . 
     A short-range light source  302  is located within the capsule endoscope  300  but outside of a body of camera  304 . Thus, a portion of the illuminating light from source  302  passes out through tubular wall  351  via an optical window  303 . Reflected image-forming light returns into the capsule endoscope  300  through the same optical window  303  and is collected by camera  304  to form an image  305  of the exterior object (not shown in  FIG. 3 ). Camera  304  may also capture illumination light reflected by the exterior surface  303 E and interior surface  3031  of the window  303 . These reflections appear as light spots in image  305 , degrading the image&#39;s quality and its diagnostic value. 
     For color imaging by capsule endoscope  300 , short-range light source  302  is implemented as a white light source. In some embodiments, the white light source is formed by use of a blue or violet LED encapsulated with phosphors that emit at longer visible wavelengths when excited by the blue or violet LED. In order to minimize the size of the cavity, an LED with conductive substrate is used in several embodiments, so that only one bond wire and associated bond pad is required. Alternatively, multiple LEDs emitting at different wavelengths, such as red, green, and blue, are combined in certain embodiments. Still other embodiments of capsule endoscope  300  use light sources which include organic LEDs (OLEDs), electroluminescent devices, and fluorescent sources. 
     In some embodiments of capsule endoscope  300 , antireflection (“AR”) coatings on interior surface  3031  and/or exterior surface  303 E are used to reduce these reflections. Specifically, using standard processes such as sputtering and evaporation, AR coatings are applied to surfaces that are roughly normal to the line-of-sight flow of material from its source. Accordingly, antireflection coating of a tubular wall of cylindrical shape in a capsule endoscope on its exterior surface  303 E is performed in some embodiments. Conformal coatings of materials such as polymers or the imprintation or etching of microstructures onto the tubular wall are various techniques that are used in such embodiments to achieve an AR coating. 
     AR coatings, which are used on some embodiments of a capsule endoscope  300 , are designed to resist scratching at least as well as the polymer material used to form endoscope  300 &#39;s tubular wall, and satisfy its other requirements such as hydrophobia and biocompatibility. Even with AR coating, some level of reflection is imaged in some embodiments. Moreover, in embodiments of a capsule endoscope wherein AR coatings are either not available or difficult to apply, no AR coatings are used. Instead, certain illuminator and/or camera geometries are used in some embodiments of a capsule endoscope  300 , to ensure that internal reflections do not overlap with the image  305  on the image sensor I. 
     Specifically, as shown in  FIG. 3 , inner wall  3031  and outer wall  303 E both reflect light from short-range light source  302  back into capsule endoscope  300 . The reflections appear to have come from mirror images of source  302 , namely virtual sources VS 1  and VS 2 . The mirror images are distorted in the horizontal direction in  FIG. 3  by the cylindrical shape of window  303  which is a portion of tubular wall  351  of endoscope  300 . In the vertical direction in  FIG. 3 , the mirror images VS 1  and VS 2  are not distorted unless the tubular wall of capsule  300  is not exactly cylindrical. For example, capsule endoscope  300  may be a prolate spheroid. 
     Tertiary reflections, e.g. optical paths with two reflections off the outer wall  303 E and one off the inner wall  3031  produce tertiary virtual images that are at a farther distance from capsule endoscope  300  than the virtual sources VS 1  and VS 2 . The tertiary virtual images are much fainter than images VS 1  and VS 2  for the following reason. The energy in a reflected ray is reduced by 1/R n  after n reflections. For normal incidence, the reflectivity is typically 3-5% for polymers in air. The reflectivity of unpolarized light increases with incident angle at a single dielectric interface. Accordingly, the geometry of short-range light source position and objective lens position in some embodiments of a capsule endoscope  300  are independent of whether or not tertiary virtual images are captured by camera  304 . 
     Other reflective surfaces within capsule endoscope  300  may combine with surfaces  3031  and/or  303 E to produce a significant secondary reflection. For example, if the body of camera  304  is reflective, then two additional virtual sources are produced further outside capsule endoscope  300 , than VS 1  and VS 2 . Therefore the body of camera  304  in some embodiments of the invention has a low-reflectivity surface. 
     If virtual sources VS 1  and VS 2  lie within the FOV and the source  302  emits into a wide range of angles, then the mirror images VS 1  and VS 2  are captured in the image  305 . If the virtual sources VS 1  and VS 2  lie outside the FOV, as shown in  FIG. 3 , they are not imaged. Two exemplary rays are shown in  FIG. 3 . One ray  307  reflects from the inner wall  3031  towards the pupil. The other ray  308  reflects from the outer wall  303 E toward the pupil P. VS 1  and VS 2  thus have a direct line of sight with the pupil P in object space. However, these lines of sight are outside the FOV so the reflections VS 1  and VS 2  do not appear in the target image  305 . 
     In certain embodiments of endoscope  300 , short-range source  302  is kept a certain distance (e.g. 4 mm) from the optical axis  306 . The closer to a longitudinal axis  309  of capsule endoscope  300  that a source  302  is, the greater its distance from optical axis  306 . Likewise, the greater the longitudinal FOV (shown in  FIG. 3 ) the further that source  302  is placed from optical axis  306 . However, source positioning to keep reflections out of the image as shown in  FIG. 3  has certain drawbacks. For example, the volume of the optical system of capsule endoscope  300  increases as source  302  is forced farther from optical axis  306 . The height of capsule endoscope  300  is reduced in some embodiments by using small sources  302  (i.e. they occupy an annulus of small width) placed close to window  303  of tubular wall  351 . Small sources near the housing of endoscope  300  produce non-uniform illumination and “harsh” shadows. Accordingly, in some embodiments of capsule endoscope  300 , large diffuse light sources with incident angles &lt;60° relative to the illuminated object are used as short-range sources  302 , to produce better illumination of tissue. 
     Moreover, white sources with dimensions smaller than a few millimeters are used in some embodiments of capsule endoscope  300 . Other embodiments of capsule endoscope  300  use white LEDs that are formed by a blue or violet LED encapsulated in an epoxy with phosphors. Also in certain embodiments of capsule endoscope  300 , a die of the LED is located in a reflective cavity along with an encapsulant, a positive electrode and a negative electrode. The reflective cavity is designed to efficiently scatter light from the LED and phosphors, which both emit omnidirectionally, out from the encapsulant into a hemispheric distribution. The die-attach and wirebond processes limit how small the cavity can be made relative to the die. 
     In some embodiments of capsule endoscope  300 , the LED substrate is insulating and two sets of wirebonds are included in the endoscope, to connect the die to each electrode. In other embodiments of capsule endoscope  300 , the LED substrate is conductive, and the LED is bonded with conductive epoxy or solder to one electrode and wirebonded to the other electrode. The last-described embodiments have a single wire bond, and result in a capsule endoscope  300  that is more compact than using two sets of wirebonds. One illustrative embodiment uses as source  302 , the following: EZBright290 available from Cree, Inc., 4600 Silicon Drive, Durham, N.C. 28703, USA Tel: +1.919.313.5300, www.cree.com. 
     In some embodiments, an endoscope  400  ( FIG. 4 ) has a short-range light source  409  that includes a reflective cavity  401  and light emitting diode (LED)  402 . Cavity  401  directs light from LED  402  through an aperture  403 , and out of endoscope  400  through a window  404  of the tubular wall. In these embodiments, the light source is positioned at a predetermined distance  405  (measured along a longitudinal axis which is not shown in  FIG. 4 ) from the optical axis  406  such that an aperture  407  of a virtual source VS 3  is outside the FOV. 
     In certain embodiments, a short-range light source is placed such that one or more of its mirror images would be within the FOV, but for the presence of internal walls (i.e. baffles) which are deliberately positioned between the light source and the window in the tubular wall to ensure that no line-of-sight exists from the pupil to the virtual images. For example, in one such embodiment illustrated in  FIG. 5 , a light source S is higher than (i.e. closer to the optical axis than) the light source  302  in  FIG. 3  such that in  FIG. 5  a portion of virtual image VS 4  is located within the FOV. The endoscope of  FIG. 5  also includes a baffle that is perpendicular to the tubular wall of the endoscope and located above the light source S. In the example illustrated in  FIG. 5 , the endoscope&#39;s tubular wall is oriented vertically, and a baffle  501  is oriented horizontally, mounted peripherally, and located in a plane between the objective and the light source S. Baffle  501  is formed as an annular wall in one illustrative embodiment. 
     Baffle  501  reflects or absorbs incident rays, such as rays from source S or rays reflected by window  503 . In the embodiment of  FIG. 5 , a virtual image  502  of the baffle blocks the line-of-sight between virtual image VS 4  and P within the FOV. Note that the baffle  501  creates a shadow on an object (e.g. tissue) which is illuminated outside the endoscope, which can be a disadvantage if captured in a diagnosable image. Note that mirror  218  in  FIG. 2E  is a baffle because it blocks rays originating at source  205  from forming a virtual image that can be captured by the camera. 
     In some embodiments, an aperture through which a source emits lies partially or fully within the FOV although the range of ray angles emitted from the aperture is restricted as illustrated in  FIG. 6 . Specifically, in  FIG. 6  a ray emitted from an aperture of source S is reflected from the window  601  at a point U. The projection of the ray onto a vertical plane containing U and the center of curvature C of the arc AUB (defined by the intersection of window  601  with a plane containing U and parallel to optical axis PQ) at U makes an angle θ i  with the normal N to window  601 . For a window  601  of a cylindrical shape, C is on the longitudinal axis (not shown in  FIG. 6 ) of the endoscope  600 . Let a be the angle between the normal and optical axis PQ. The reflected ray  607  ( FIG. 6 ) does not enter pupil P if θ i &gt;θ FOV +α and this condition is satisfied in some embodiments of endoscope  600 , in accordance with the invention. 
       FIG. 7  illustrates an endoscope  700  of some embodiments including a short-range source  709  formed by a LED  701  located within a cavity  702  and mounted on a printed circuit board (PCB)  703 . On the same PCB  703  is mounted an image sensor  704 . A mirror  705  folds the optical axis and directs image forming light onto sensor  705 . Short-range source  709  emits light into an input aperture A 1  of an optical element  710  that reduces the light&#39;s angular dispersion, i.e. an angular concentrator  710 . Light exits concentrator  710  through an output aperture A 2 . 
     In certain embodiments of endoscope  700 , angular concentrator  710  limits the angular divergence in all directions to a half-angle of θ 2 , and β is the angle between the optical axis  706  of camera  711  and optical axis  707  of the concentrator  710  and a is the angle (see  FIG. 6 ) between a housing surface normal N and the camera&#39;s optical axis  706 . Such embodiments ensure that internal reflections are outside the FOV by satisfying the following relationship θ 2 &lt;β−θ FOV −2α. Note that for several of these embodiments, β is in the range 45° to 135°. In some embodiments, window  712  is of cylindrical (or conical) shape, the pupil P is located on the longitudinal axis of the cylinder (or cone), and concentrator  710  only limits the divergence in the radial direction (with respect to the window) to θ 2 . These conditions are not met in other embodiments which limit the divergence in the tangential direction as well, although not necessarily to an angle as small as θ 2 . In general, the divergence is limited such that θ i &gt;θ FOV +α where θ i  is as defined above for all rays emitted from A 2 . 
     In a number of embodiments of an endoscope  700 , the maximum angular concentration in one dimension is defined from the radiance theorem as 
     
       
         
           
             
               C 
               max 
             
             = 
             
               
                 
                   sin 
                    
                   
                       
                   
                    
                   
                     θ 
                     1 
                   
                 
                 
                   sin 
                    
                   
                       
                   
                    
                   
                     θ 
                     2 
                   
                 
               
               = 
               
                 
                   a 
                   2 
                 
                 
                   a 
                   1 
                 
               
             
           
         
       
     
     Where θ 1  and θ 2  are the incident and exit angles, a 1  and a 2  are the input and exit aperture diameters. The definition of C max  assumes that the input and exit media are air. If the input aperture A 1  of concentrator  710  is positioned directly on the encapsulant in cavity  702  wherein LED  701  is mounted, only those rays that do not suffer total internal reflection enter the concentrator  710 , and the input is considered to be these rays after refraction into free space. C max  quantifies the maximum possible reduction in angle with concentrator  710 , relative to without the concentrator. If θ 1 =π/2 then 
     
       
         
           
             
               sin 
                
               
                   
               
                
               
                 θ 
                 2 
               
             
             ≥ 
             
               
                 
                   a 
                   1 
                 
                 
                   a 
                   2 
                 
               
               . 
             
           
         
       
     
       FIG. 8  illustrates an endoscope  800  using a collimating lens  801  to form an angular concentrator  802  to reduce the angular divergence of light from the short-range source  803 . In  FIG. 8 , the concentration ratio is limited by the numerical aperture (NA) of lens  801 . Since θ 1 =π/2 much of the light from source  803  entering input A 1  does not pass through lens  801 . In general, imaging systems, even complicated ones with multiple lenses, are not efficient angle concentrators (i.e. collimators) if the numerical aperture (NA) required approaches one. 
     The concentration ratio of non-imaging concentrators, on the other hand, can approach C max .  FIG. 9  illustrates an endoscope  900  using a compound parabolic concentrator (CPC)  902  as the angular concentrator. The sides of concentrator  902  have reflective surfaces  903  and  904 . Depending on the embodiment, the body of concentrator  902  may be hollow as shown with mirrored surfaces  903  and  904  of sidewalls, or alternatively the body of the concentrator  902  is a dielectric with side walls whose surfaces  903  and  904  face each other and reflect light from each to the other, using total internal reflection (TIR). Hence some embodiments of endoscope  900  use two-dimensional CPCs, which are trough shaped, to approximate or even reach the maximum theoretical optical concentration. Variations of endoscope  900  in such embodiments include truncated CPCs for which the height is reduced with only a small loss of concentration ratio. Certain embodiments of endoscope  900  use other forms of concentrators, with planar sloped walls for example, achieve a lower concentration ratio than the CPC but may still be useful. 
     The geometry of a cross section of a CPC  902  that is used in some embodiments of endoscope  900  is illustrated in  FIG. 10 . The input aperture of CPC  902  is QQ′. The profile P′Q′ of one surface  903  of concentrator  902  is a portion of a parabola with focus at Q and axis at an angle γ to the axis Z of concentrator  902 . Note that the LED  701  is located on the axis Z directly facing input aperture QQ′. The length L of concentrator  902  is chosen in some embodiments of endoscope  900  such that a skew ray from Q intersects the parabola at P. The emission half-angle is θ 2 =γ. A truncated CPC reduces L and θ 2 &gt;γ. Details may be found in  Nonimaging Optics,  R. Winston, J. C. Minano, P. Benitez, Elsevier Academic Press, 2005, pp. 43-97 and 467-479 which is incorporated by reference herein in its entirety. 
     Some embodiments of an endoscope  900  include a cylindrical capsule enclosing a panoramic imaging system with an annular CPC  1100  of the type shown in  FIG. 11 . The cross-section of CPC  1100  in a plane containing a radius is a two-dimensional CPC as illustrated in  FIG. 10 . CPC  1100  includes two halves, namely a first half  1101  and a second half  1102  that are each glued to a ring (called “LED ring”). Each half includes two sidewalls that are physically attached to one another by radial spokes for structural support. For example, in  FIG. 11 , the first half  1101  has an outer sidewall  1105  and an inner sidewall  1106  that face each other, with spokes  1107 - 1109  providing support therebetween. Note that the two halves  1101  and  1102  of CPC  1100  are mirror images of each other, and for this reason when only the first half  1101  is described below it is to be understood that second half  1102  has similar dimensions, properties etc. 
     Note that in  FIG. 11 , outer sidewall  1105  surrounds inner sidewall  1106 . Surface  1106 R of inner sidewall  1106  faces surface  1105 R of outer sidewall  1105 , and these two surfaces  1106 R and  1105 R reflect light such that it is deflected upwards. Sectioning sidewalls  1105  and  1106  along a radius of CPC  1100  results in a cross-section which forms a two dimensional CPC as illustrated in  FIG. 9 . Edges  1106 E and  1105 E of respective sidewalls  1106  and  1105  are adjacent to one another in a bottom lateral plane. Accordingly, edges  1106 E and  1105 E together with edges of two adjacent spokes define a boundary of an input aperture of CPC  1100  at its bottom surface (not shown in  FIG. 11 ; see  FIG. 12E ). 
     In some embodiments, short-range sources in the form of LEDs are positioned beneath each input aperture of CPC  1100  in a lead frame or package (not shown in  FIG. 11 ; see  FIG. 13 ). Specifically CPC  1100  has, on a bottom surface  1201  ( FIG. 12A ), several outward projections or bosses, such as bosses  1202  and  1203 . The bosses are button shaped and are dimensioned and positioned to fit into and mate with corresponding depressions or pockets in a lead frame wherein the LEDs are mounted. Moreover, an outer surface  1111  (which is a surface of outer sidewall  1105 ) is made diffusing so that light from the input aperture diffuses laterally out of surface  1111 . 
       FIG. 12C  illustrates, in a top elevation view, first half  1101  of CPC  1100  of  FIG. 11 .  FIG. 12B  illustrates, in a cross-sectional view in the direction A-A, in  FIG. 12C , first half  1101  of annular CPC  1100  of  FIG. 11 .  FIG. 12D  illustrates, in a side view in the direction D-D, in  FIG. 12C , the first half  1101  of  FIG. 11 .  FIG. 12E  illustrates, in a bottom elevation view, in the direction E-E, in  FIG. 12C , first half  1101  of  FIG. 11 . Note that portions  1208  of the bottom surface of CPC  1101  are made diffusing so that light incident thereon is transmitted through CPC  1101  and exits laterally through outer surface  1111  ( FIG. 12A ). The height of side walls  1105  and  1106  are 1.0 mm. 
     In some embodiments of an endoscope, CPC  1100  is formed as a molded polymer with a metal coating on the inside surfaces  1106 R and  1105 R to form mirrors. The walls of spokes  1107 - 1109  are sloped mirror-like planes that help to direct light upwardly. For example, spoke  1108  in  FIG. 11  has spoke walls  1108 A and  1108 B that provide a degree of concentration in the tangential direction. Spokes  1107 - 1109  block rays from LEDs located underneath the input apertures of CPC  1100  with a large tangential component that would otherwise lead to ghost images of the LEDs when internally reflected from the endoscope&#39;s housing, if the camera pupils are not located on the longitudinal axis of the endoscope. Depending on the embodiment, spokes  1107 - 1109  may be absorbing instead of reflecting although this reduces the efficiency in energy usage by the endoscope. 
       FIG. 13  illustrates certain embodiments of an endoscope that includes CPC  1100  of the type described above in reference to  FIGS. 11 and 12A-12E , mounted on a lead frame  1300  such that LEDs supported therein face input apertures in CPC  1100 . In some embodiments, length L is on the order of 1 mm. LED lead frame  1300  of the embodiments shown in  FIG. 13  is also ring shaped as illustrated in  FIGS. 14A and 14B . Lead frame  1300  contains multiple cavities  1401 - 1408  ( FIG. 14A ). Each of cavities  1401 - 1408  holds an LED encapsulated therein with a phosphor in epoxy. For example, in  FIG. 14A , cavity  1403  holds an LED  1409  that is connected by a single bondwire  1410  to cathode lead  1411 . Cavity  1403  also holds an anode lead  1412 . In some embodiments, the walls of each cavity of lead frame  1300  are white diffuse reflectors. 
     LED lead frame  1300  also has a number of pockets, such as pocket  1415  ( FIG. 14A ) that mates with and holds button shaped bosses of CPC  1100  when they are press-fit or otherwise inserted. Note that in some embodiments the just-described bosses and pockets are reversed in position, i.e. the CPC has pockets and the LED lead frame has bosses. Also depending on the embodiment, other structures may or may not be used to physically join LED lead frame  1300  and CPC  1100  to one another. 
     In the embodiment shown in  FIG. 13 , the LED lead frame  1300  has cavity  1403  with an aperture A 3  that is located only partially under input aperture A 1  of the CPC  1100 . Specifically, a portion of aperture A 3  of cavity  1403  is covered by a surface  1208  of outer sidewall  1105  of CPC  1100 . In one illustrative example, A 3  is 0.9 mm and A 1  is 0.5 mm. Hence, light from LED  1409  enters sidewall  1105  through surface  1208 . Surface  1208  of some embodiments is diffusive as shown in  FIG. 12E . Any such light which has entered sidewall  1105  then passes laterally through outer surface  1111  to a scene outside the endoscope, if the CPC&#39;s outer sidewall is transparent. A portion of this light which exits surface  1111  is reflected by the reflective cavity surface of CPC  1100 . 
     Surface  1111  at the outer rim of CPC  1100  has a rough surface so that light exiting the endoscope from surface  1111  is scattered and diffused, which is used to illuminate objects at a short to intermediate distance from the endoscope (see  FIGS. 2I, 2J and 2K ). In the endoscope structure illustrated in  FIG. 13 , the same LED provides short-range light to illuminate objects at a short or intermediate distance from the endoscope by diffuse illumination through surface  1111 , and also provides additional short-range light via aperture A 2  for use in radially illuminating objects touching or a short distance from the endoscope. For example, an annular mirror (see mirror  218  in  FIG. 2E  or mirror  231  in  FIG. 17 ) reflects a portion of light that exits aperture A 2 , out of a window of a tubular wall of the endoscope, and simultaneously another portion of the light exits out of the window directly from aperture A 2 . 
     In some embodiments, a CPC of an endoscope has an input aperture A 1  that coincides with the aperture A 3  of a short-range source, wherein there is no overlap (or negligible overlap) of the CPC&#39;s outer sidewall with the lead frame&#39;s cavity as shown in  FIG. 15 . Also, in certain embodiments, a CPC  1600  in an endoscope is made of a dielectric material as shown in  FIG. 16 , although the concentration ratio is reduced for a given length L of CPC due to refraction at the output aperture. 
     Some embodiments of an endoscope of the type described herein provide multi-modal illumination in accordance with the invention, by using different amounts of energy to illuminate tissue, depending on the distance of the tissue. Specifically as illustrated in  FIG. 17  on the right side, mucosa surface  1701  at points F and G which is close to (e.g. &lt;5 mm) or touching endoscope  1700 , is illuminated by light emerging from CPC  1100 , both directly and after reflection from annular mirror  231 . In the illustrative embodiment shown in  FIG. 17 , mirror  231  enables light from an emitter in short-range source  1703  to reach an illumination region of the endoscope from both sides of the field of view, thereby to illuminate tissue surface  1701  more uniformly in an image to be diagnosed, as compared to short-range illumination from only one side of the field of view. 
     Additionally, a tissue surface  1701  located at point H which is in contact with endoscope  1700  is also illuminated by light emerging from surface  1111  which light entered CPC  1100  through a bottom surface as described above, and is reflected by a convex surface in CPC  1100 . As tissue surface  1701  is in contact with endoscope  1700 , point H is outside the FOV of the camera. However, as the distance increases, point H falls within the FOV. Accordingly, endoscope  1700  uses a minimum amount of energy, e.g. by using primarily just a single LED within short-range source  1703  in the direction towards the right of  FIG. 17 . 
     Note that endoscope  1700  of these embodiments includes an additional LED used for long-range source  1704  that, when turned on, also provides light in the same radial direction, i.e. towards the right of  FIG. 17 . Long-range source  1704  is positioned longitudinally offset from the objective&#39;s optical axis, e.g. positioned behind mirror  231  which acts as a baffle. Note that there is little or no overlap between the long-range illumination region on the endoscope&#39;s tubular wall (close to point E in  FIG. 17 ) lit up by light source  1704 , and the above-described short-range illumination region lit up by light source  1703 . The area of long-range illumination region lit up by light source  1704  is several times and in some cases an order of magnitude, smaller than the corresponding area of short-range illumination region lit up by light source  1703 . 
     Endoscope  1700  increases the radiant energy generated by the long-range light source  1704  as the distance of the tissue to be imaged increases. Using long-range light source  1704  simultaneously with short-range light source  1701  provides sufficient illumination to image mucosa  1701  that is located far away (e.g. ˜20 mm away). For example, points A-D shown on the left side of  FIG. 17  are illuminated by turning on both light sources  1706  and  1707 . 
     Use of both light sources  1706  and  1707  does use up a maximum amount of energy (relative to use of just one source  1706 ), although such use provides better images which enable a more thorough diagnosis of a body cavity, such as a gastrointestinal tract. The energy generated by multiple light sources  1703  and  1704  to illuminate radially in a given direction may be scaled appropriately, to illuminate tissue located at intermediate distance(s) as described above in reference to  FIG. 2I . Accordingly, endoscope  1700  in some embodiments of the invention operates multi-modally, specifically in a minimum energy mode, a maximum energy mode and one or more intermediate energy modes. For certain body cavities, such as a small intestine, endoscope  1700  of these embodiments operates continuously in a minimal mode, by turning on only the short-range source, e.g. source  1703  (i.e. the long-range source is kept turned off). 
     Note that endoscope  1700  of  FIG. 17  incorporates four objectives with optical axes spaced 90° apart, although only two lenses  1711  and  1712  that are oppositely directed are shown in  FIG. 17 . In this embodiment, eight LEDs are arrayed in a ring under an annular truncated CPC  1100 . The eight LEDs emit out the outer surface  1111  of CPC  1100  and also through the top of the CPC apertures A 2  (not labeled in  FIG. 17 ). Some of the light from aperture A 2  is reflected down and out of the endoscope  1700  by annular mirror  231  located above the imaging region. In  FIG. 17 , the angle of the mirror  231  relative to the optical axis is chosen such that the reflected light satisfies the relationship θ r &lt;θ 2  where θ 2  is the maximum angle of light exiting the CPC cavity in the radial direction and θ r  is the angle of a ray reflected from the annular mirror relative to an inner or outer surface of the tubular wall. 
     Note that the embodiment illustrated in  FIG. 18  is similar or identical to the embodiment described above in reference to  FIG. 17  except that in  FIG. 18  the annular mirror has a convex cross section. The convex cross-section mirror is used because the relationship θ r &lt;θ 2  need not be satisfied for all reflected rays. The shape of the mirror&#39;s reflective surface is empirically chosen, to optimize uniformity of illumination. In one illustrative embodiment, a convex section of the reflective surface has a radius of curvature close to 10 mm. 
     In the embodiments of  FIGS. 17 and 18 , the outer rim of the CPC is sufficiently below the optical axis so that virtual images of it are outside the FOV. Thus, no single-reflection ghost images of it will be visible. The light emitted from the cavity of the CPC is restricted in angle so that reflections will miss the camera pupil. Additionally, as noted above, in order to illuminate distant objects, set of LEDs is arrayed around the endoscope, above the mirror. The output apertures of these LEDs are sufficiently above the optical axis so that single-reflection ghost images are outside the FOV. If the mucosa is close, these LEDs primarily illuminate region E which is outside the FOV, and for this reason the LEDs need not be turned on. If the mucosa is at an intermediate distance, the top LED illuminates primarily the top half (D) of the mucosa while light emitted from the side of the CPC primarily illuminates the bottom half (C). If the mucosa is farther away, the top LED effectively illuminates the entire FOV (I, J, K). 
     In some embodiments, the lower LEDs  217  ( FIG. 2E ) do shine light on objects within the capsule, such as parts of the camera, whose mirror images are within the FOV. To minimize ghost images, these objects have low reflectivity. Also, the angle of reflection from these objects is controlled by making the surfaces specular and choosing their angles relative to incident light appropriately. In several embodiments, these strategies reduce but not eliminate ghosting. Thus, certain embodiments limit the intensity of the lower (also called “bottom”) LEDs  217 . As the mucosa moves further from the endoscope, more illumination light is provided. However, the additional light is provided from the top LEDs  205  which direct all of their light outside the capsule  200 . The illumination, and hence image exposure, is controlled by varying the intensity of the LEDs  205  and  217  in an attempt to make illumination uniform as described below. The flux from the bottom LEDs  217  is limited in some embodiments to a maximum value that provides sufficient illumination when the mucosa is close but not so high as to produce objectionable ghosting. 
     Numerous modifications and adaptations of the embodiments described herein will become apparent to the skilled artisan in view of this disclosure. 
     For example, although some embodiments of the invention use radial illumination, other embodiments use longitudinal illumination with two light sources that are mounted adjacent to a dome-shaped end to provide illumination in a longitudinal direction. Specifically, an endoscope  1900  has a dome-shaped end  1903  through which illumination is provided by a first set of LEDs (e.g. four LEDs) mounted in a common plane (perpendicular to a longitudinal axis) and labeled as “LED A” in  FIG. 19 . The first set of LEDs A are used to provide short-range illumination when tissue is close to or in contact with endoscope  1900 . In the embodiment of  FIG. 19 , endoscope  1900  has a second set of LEDs (e.g. four LEDs) which are labeled as “LED B” in  FIG. 19 . The second set of LEDs B are used to provide long-range illumination when tissue is at an intermediate distance or even far away, at a predefined outer limit of the endoscope. Hence, depending on the distance between tissue to be imaged and endoscope  1900 , the first set of LEDs A is used by itself or in combination with the second set of LEDs B (as illustrated in  FIGS. 2I, 2J and 2K ) to provide illumination necessary to generate diagnosable images in endoscope  1900 . 
     In the embodiment illustrated in  FIG. 19 , light from the first set of LEDs A exits dome-shaped end  1903  longitudinally (rather than laterally as noted above for other embodiments) via an aperture  1905  defined by a cylindrical wall  1901 . Wall  1901  surrounds LEDs A so that light from the first set is directed out of aperture  1905 . Moreover, LEDs B are mounted farther away (in radial distance from a longitudinal axis of endoscope  1900 ) than LEDs A. In the embodiment illustrated in  FIG. 19 , LEDs B surround the wall  1901  and are mounted facing a diffuser  1902 . Diffuser  1902  may be, for example, a Fresnel optic, hologram or other optical element that diffuses the light from LED B. Accordingly, endoscope  1900  uses LEDs A primarily to illuminate close and distant objects and uses LEDs B primarily to illuminate distant objects. 
     Moreover, instead of light other embodiments use electromagnetic radiation that is invisible to the human eye, e.g. ultra-violet or infra-red ranges. Hence, numerous modifications and adaptations of the embodiments described herein are encompassed by the scope of the invention. 
       FIG. 25  illustrates dimensions, in millimeters, of an exemplary annular mirror  218  having a convex reflecting surface in some embodiments of the invention. Moreover,  FIG. 26  also illustrates dimensions, in millimeters, of an endoscope shaped as a capsule in some embodiments of the invention, which contain the annular mirror  218  of  FIG. 25 . 
     Referring to  FIG. 13 , an aperture A 3  of lead frame  1300  is located only partially under input aperture A 1  of the CPC  1100 . CPC  1100  has an additional input aperture A 5  (“second input aperture”), which is in addition to the above-discussed input aperture A 1  (“first input aperture”). Apertures A 1  and A 5  together form an input aperture A 4  through which all light is received by CPC  1100  from LED  1409 . Specifically, rays  1301  and  1302  from LED  1409  enter CPC  1100  via the second input aperture A 5  through surface  1208  of CPC  1100 . Ray  1301  is refracted within sidewall  1105  of CPC  1100  on entry at surface  1208  and then reflected by a layer  1309  formed on sidewall  1105 . The layer  1309  has two surfaces, namely a convex surface  1309 X which is formed on sidewall  1105  located opposite to outer surface  1111 , and a concave surface which forms an inside surface  1105 R of CPC  1100 . 
     More specifically, as shown in  FIG. 13 , surfaces  1309 X and  1105 R are two sides of a layer  1309  that constitutes a portion of CPC  1100 , in addition to sidewall  1105 . In one illustrative example, surfaces  1309 X and  1105 R of layer  1309  are within 100 microns of each other, i.e. the layer  1309  is 100 microns thick. Surface  1309 X of layer  1309  (shown as a heavy black line in  FIG. 13 ) reflects at least some of the incident illumination towards outer surface  1111 , as illustrated by reflection of ray  1301  at point  1321 . Note that CPC  1100  additionally includes another layer  1399  (shown in  FIG. 13  as another heavy black line) whose concave surface forms another inside surface  1106 R. Depending on the embodiment, either or both of layers  1309  and  1399  may be formed as either (a) a single metal layer (e.g. aluminum or silver) or (b) a multi-layered stack of dielectric layer(s) and/or metal layer(s). 
     Illumination from LED  1409  which is incident from within sidewall  1105 , on outer surface  1111  ( FIG. 13 ) diffuses out from CPC  1100  through an output aperture A 6  as light portions  1311  and  1312 , e.g. respectively resulting from rays  1301  and  1302 . Specifically, as shown in  FIG. 13 , a ray  1302  also enters sidewall  1105  via the second input aperture A 5 , although its angle of incidence and its angle of refraction, are of such values that this ray  1302  is not reflected by surface  1105 R of reflective layer  1309 . Instead, ray  1302  is refracted at surface  1208  and is transmitted to and directly incident on surface  1111  at output aperture A 6  without reflection, and thereafter diffuses out of sidewall  1105  as shown in  FIG. 13  as light portion  1312 . Accordingly, two light portions  1311  and  1312  are redirected towards aperture A 6  by refraction and either direct transmission or transmission and reflection by CPC  1100 , so as to be incident on bottom spot  210 C in  FIG. 2B  (see intensity distribution  219 C in  FIG. 2E ) which constitutes one fraction formed by beam  208 C ( FIG. 2D ). As noted above, bottom spot  210 C has area less than 50% of the total area of short-range illumination region  210  of a capsule endoscope  200 . 
     As noted above, one light portion  1311  ( FIG. 13 ) is included in a portion of the light fraction (“first fraction”) emitted by LED  1409  that is reflected by surface  1309 X of the layer  1309 . Another surface  1105 R of layer  1309  receives a portion of another fraction (“second fraction”) of light emitted by LED  1409  which enters first input aperture A 1  (illustrated by ray  1303 ). Surface  1105 R reflects most of this portion through output aperture A 2 , towards another optical element, namely mirror  218  as illustrated by ray  1313  (see  FIG. 13 ). Accordingly, CPC  1100  of  FIG. 13  has two output apertures namely apertures A 2  and A 6 , and these two output apertures are oriented laterally relative to one another (e.g. oriented at 90 degrees). 
     Note that in the embodiment illustrated in  FIG. 13 , another portion of a second light fraction from LED  1409  which enters the CPC  1100  at first input aperture A 1 , is illustrated by a ray  1304  that reaches another inside surface  1106 R of another reflective layer  1399  of CPC  1100 . Light reflected by inside surface  1106 R also exits the CPC  1100  through output aperture A 2 , e.g. as shown by ray  1314 . Depending on the angle of incidence, ray  1314  may be reflected by surface  1106 R at such a small angle relative to a longitudinal axis of the endoscope that this ray  1314  also reaches mirror  218 . Mirror  218  may also receive another portion of the second light fraction that is transmitted through CPC  1100  without reflection, as illustrated by ray  1316 . As noted above, rays reaching mirror  218  from aperture A 2  constitute a beam  208 B which is reflected by mirror  218  toward a top spot  210 B as shown in  FIG. 2B  (see intensity distribution  219 A in  FIG. 2E ). 
     Depending on an offset distance  1398  between LED  1409  and CPC  1100  (e.g. measured from a center of the CPC cross-section), a third light fraction as illustrated by ray  1319  is reflected by surface  1106 R at an angle sufficient large relative to the longitudinal axis such that the ray directly exits the endoscope without reflection, e.g. via a middle spot  210 A of illumination region  210  in  FIG. 2C  (see intensity distribution  219 B in  FIG. 2E ). Also included in the third light fraction is another ray  1315  which is also directly transmitted through CPC  1100  without reflection therein. As noted above, the third light fraction forms a beam  208 A which exits the endoscope housing at a middle spot  210 A. 
     Note that the offset distance  1398  shown in  FIG. 13  determines the relative proportion of light transmitted through the two input apertures of the CPC, specifically A 1  and A 5 . If offset distance  1398  is increased then the amount of light through input aperture A 5  increase relative to input aperture A 1 . Depending on the embodiment, offset distance  1398  can be a predetermined fraction (e.g. two-thirds, half, one-third, or even one-fifth) of the width of input aperture A 1 . In one illustrative embodiment, offset distance  1398  is one half of width of input aperture A 1  which results in about one half of light from the LED  1409  entering aperture A 5  and exiting sidewall  1105  through a non-imaging region of the housing, e.g. region  210 C and another half of the light entering aperture A 1  and exiting through an imaging region  212  of the housing (see  FIG. 2A ). 
     In embodiments of the type illustrated in  FIG. 13 , LED  1409  and a phosphor in epoxy within cavity  1403  together form a source of light, wherein all light from this source is emitted on one side (e.g. bottom side) of a plane  1397 . Note that CPC  1100  (which is an optical element) is located on the other side (e.g. top side) of the plane  1397 . Additionally, as illustrated in  FIG. 14 , this source includes a pair of terminals represented by cathode lead  1411  and anode lead  1412  and a current passing therebetween causes the light emitting diode to generate light. As a portion of the generated light directly emerges from aperture A 3  ( FIG. 13 ), LED  1409  is an emitter for this portion. Another portion of the generated light is incident on the phosphor which absorbs the incident light and uses the energy therefrom to generate light in a different wavelength, and hence the phosphor is another emitter. Note that although a short-range illumination source is illustrated in  FIGS. 13 and 14 , in some embodiments both types of sources (long-range and short-range)  205  and  206  that are enclosed within a housing of an endoscope are identical to one another. Specifically, multiple copies of the same LED are used as a long-range source  205  and also as a short-range source  206 . 
     Referring to  FIGS. 4 and 5  as described above, only one virtual source is illustrated in each figure to aid in conceptual understanding. In capsule endoscopes of most embodiments, there are at least two virtual sources as shown in  FIG. 3 . Specifically, reflections from an inner surface (not labeled in  FIG. 4 ) and from an external surface (also not labeled) of window  404  result in two virtual sources, of which only a virtual source formed by reflection from the external surface of the endoscope&#39;s window is shown in  FIG. 4 . Similarly, there are two reflections from the two surfaces of window  503 , of which only a reflection by the external surface is shown in  FIG. 5 . 
     Hence, the number of virtual sources formed by a corresponding number of reflections from a capsule endoscope&#39;s window in turn corresponds to the number of surfaces in the window. Specifically, in several embodiments a window in fact includes multiple interfaces (e.g.  3  interfaces as illustrated in  FIG. 27 ), in which case orientation of the multiple interfaces and materials used to form layers in the endoscope&#39;s window determine the actual paths of transmitted and reflected rays resulting from an illumination ray. In the illustration of  FIG. 27 , a ray originating from source  302  is reflected at each of surfaces  3031 ,  303 E and  303 N, and such reflections form three virtual sources VS 1 , VS 2  and VS 3 . 
     Accordingly, in several embodiments, illumination regions  210  and  211  and imaging region  212  (illustrated in  FIGS. 2A and 28A ) are all formed on an inner surface of the housing of endoscope  200 . In other embodiments all these regions  210 - 212  are formed on an outer surface of the housing of endoscope  200 . And in still other embodiments all these regions  210 - 212  are formed on an intermediate surface (i.e. an interface) within the housing of endoscope  200 . 
     Regardless of the number of surfaces of a window in a capsule endoscope of some embodiments, imaging of the corresponding virtual sources in the camera is avoided by one or more of the above-described methods, e.g. by positioning the source sufficiently spaced apart (in the longitudinal direction) from the optical axis of the camera as illustrated in  FIG. 3  or by shielding as illustrated in  FIGS. 4 and 5 . Furthermore, note that although only a single light source is illustrated in each of  FIGS. 3-5 and 28 , several embodiments use multiple light sources and imaging of their respective virtual sources is also avoided or minimized as described above. 
     Moreover, similar to  FIG. 2C  discussed above,  FIG. 28A  illustrates wall  201 M of capsule-shaped endoscope  200  of some embodiments having an imaging region  212  overlapping a short-range illumination region  210  through which light is emitted from endoscope  200  for short-range illumination. Wall  201 M in  FIG. 28A  also has a long-range illumination region  211  through which light is emitted from endoscope  200  for long-range illumination. Note that in  FIG. 28A , imaging region  212  does not overlap the long-range illumination region  211 . The just-described absence of overlap between imaging region  212  and long-range illumination region  211  enables operation of a long-range illumination source at a significantly higher intensity (e.g. an order of magnitude higher) relative to the intensity of a short-range illumination source, without resulting in an unduly bright region within the image formed within a camera of endoscope  200 , which is in contrast to capture of point  2805  shown in  FIGS. 28B and 28D  (discussed below). 
     In certain alternative embodiments, imaging region  212  overlaps long-range illumination region  211 , as illustrated by point  2805  in  FIGS. 28B and 28D . In several such embodiments, there is no overlap between the short-range illumination region  210  and the long-range illumination region  211  ( FIG. 2B ). In these embodiments, imaging region  212  ( FIG. 2B ) also contains a point  2804  that lies in short-range illumination region  210  but does not lie in the long-range illumination region  211 . Point  2804  can be any point in the imaging region  212 , e.g. an intersection of an optical axis of the camera with an outer surface of the housing. In some embodiments, all three regions  210 ,  211  and  212  overlap one another as illustrated by point  2805  in  FIG. 28D . Note that overlap of the type illustrated in  FIGS. 28B and 28D  typically results in an exceptionally bright region in an image, and the bright region is cropped as discussed above, and in the next paragraph. Note that embodiments that use other types of cameras (such as a panoramic camera) also satisfy one or more of the above-described relationship, e.g. see point  2804  in  FIGS. 31 and 32 . 
     In several embodiments of the type shown in  FIG. 28B , an image formed within the camera includes an unduly bright region, caused by reflection of that fraction of light exiting the endoscope which originates in a long-range illumination source. Hence, in some embodiments of the type shown in  FIG. 28B , image data representing a diagnosable image at a specific location in a gastrointestinal tract is obtained by excluding (i.e. discarding) certain data (“additional data”) which represents the unduly bright region. Specifically, depending on the embodiment, a diagnosable image can be generated in different ways, such as (a) inherent cropping by appropriate design of hardware within the endoscope&#39;s camera e.g. by including therein a sensor sized and positioned appropriately to not sense the additional data and/or (b) cropping performed by appropriately programming firmware and/or software executed by a processor included within endoscope  200 , and/or (c) cropping performed by imaging application software executed by an external computer that receives a combination of image data and additional data from the transmitter (such as Microsoft® Office Picture Manager available from Microsoft Corporation), to generate image data (by excluding the additional data), store the image data in the computer&#39;s memory, and display a diagnosable image to a physician (e.g. a gastroenterologist) for use in diagnosing diseases. 
     The just-described cropping is not required if positions of the two sources relative to the camera are such that imaging region  212  does not overlap the long-range illumination region  211  as noted above in reference to  FIG. 28A . Note that the just-described lack of overlap is further illustrated in other embodiments of the type shown in  FIG. 28C  wherein short-range illumination region  210  overlaps the long-range illumination region  211 . In the embodiments of  FIG. 28C , imaging region  212  contains point  2804  that lies in short-range illumination region  210  but does not lie in long-range illumination region  211 . Moreover, certain embodiments that perform cropping as described above have the two illumination regions and the imaging region, i.e. all three regions overlap one another as shown in  FIG. 28D . As noted above, in embodiments of the type illustrated in  FIG. 28D , point  2805  is located within each of the three regions  210 ,  211  and  212 . Note that in the embodiments of  FIGS. 28D and 28A , imaging region  212  contains point  2804  that lies in short-range illumination region  210  but does not lie in long-range illumination region  211 . Note that the just-described condition is satisfied in each of the four types of embodiments illustrated in  FIGS. 28A-28D . 
     In some embodiments, a number of imaging regions that are adjacent, overlap each other, as illustrated by overlap regions  285 A and  285 B in  FIG. 28E . Specifically, overlap region  285 A results from overlap of the two adjacent imaging regions  282 A and  282 Z, and overlap region  285 B results from overlap of the two adjacent imaging regions  282 A and  282 B. As noted elsewhere herein, a set of sensors (e.g. two sensors  3401  and  3402  illustrated in  FIG. 34 ) are located within a central region of endoscope  200 , and each sensor in the set receives and forms a portion of an image of light reflected by tissue and reaching a corresponding one of the respective imaging regions  282 A- 282 Z shown in  FIG. 28E . Hence, in several embodiments, data generated by a set of sensors is supplied in whole or in part (after optional cropping by a processor) to a transmitter that in turn transmits image data representing a diagnosable image to an external device. 
     Note that although a set of two sensors is illustrated in  FIG. 34  for some embodiments of an endoscope, other embodiments use fewer or more sensors in a set coupled to the transmitter (e.g. one embodiment uses a set of one sensor). In an illustrative embodiment, a sensor chip in an endoscope has a pixel array to record four portions of an image from four objectives in four regions thereof, as illustrated by Q 1 -Q 4  in  FIG. 2O  and  FIG. 20 , and the sensor chip supplies the image data captured therein to a transmitter. As will be readily apparent to the skilled artisan in view of this disclosure, other embodiments do not use four regions of a single monolithic sensor chip as shown in  FIG. 2O  and  FIG. 20  and instead use a set of four sensors, and image data resulting from operation of the set of four sensors at a single location is supplied to the transmitter for generation of a diagnosable image by an external computer. 
     In embodiments of the type illustrated in  FIG. 28E , the light reaching overlap region  285 A is sensed by two sensors for imaging regions  282 Z and  282 A respectively. Similarly, there are two sensors within endoscope  200  which receive light that has been reflected by tissue of the gastrointestinal tract and reaches overlap region  285 B. Due to overlaps, a region  282  ( FIG. 28F ) formed by a union of all imaging regions  282 A- 282 Z of an endoscope is a continuous band (i.e. union region  282 ) around the endoscope&#39;s tubular wall as illustrated in  FIG. 28I . Accordingly, imaging region  282  of endoscope  200  is defined by an intersection of a surface (e.g. outer surface) of the housing with electromagnetic radiation (“imaging illumination”) entering the housing and being captured in image data supplied by the set of sensors to a transmitter. As noted elsewhere herein, a computer that eventually receives the image data is appropriately programmed to generate therefrom a panoramic 360° image that is displayed to a physician. 
     In embodiments of the type illustrated in  FIG. 28E , ghosting is prevented by positioning a long-range illumination source within the endoscope housing such that a majority of light exiting the housing which originates from the long-range illumination source passes through a region  281 A of the housing (“long-range illumination region”). Long-range illumination region  281 A of such embodiments ( FIG. 28E ) does not overlap any of imaging regions  282 A- 282 Z (and therefore does not overlap union region  282  of  FIG. 28F ). Specifically, in some embodiments, long-range illumination region  281 A is separated (in the direction of the longitudinal axis of endoscope  200 ) from a corresponding imaging region  282 A. Hence, in the embodiment of  FIG. 28E , there is no overlap between regions  281 A and  282 A due to a vertical separation distance  200 V therebetween, which has a positive value. Furthermore, note that regions  281 A and  282 A may be also offset in the circumferential direction. Specifically, in the embodiment shown in  FIG. 28E , a center  282 C of region  282 A is separated by circumferential distance  200 H from a center  281 C of region  281 . 
     However, as illustrated in  FIG. 28G , in many embodiments, due to constraints on the size of a capsule that is small enough to be swallowable, the vertical separation distance  200 V has a negative value, which results in an overlap region  286 A ( FIG. 28H ) between regions  281 A and  282 A. Due to a positive value for circumferential distance  200 H (not labeled in  FIG. 28G , see  FIG. 28E ), the long-range illumination region  281 A also overlaps an adjacent imaging region  282 B, as shown in  FIG. 28H  by the overlap region  286 B. However, in other embodiments, circumferential distance  200 H ( FIG. 28E ) is sufficiently small to eliminate any overlap between long-range illumination region  281 A and adjacent imaging region  282 B. 
       FIG. 28H  shows a non-overlapping illumination region  286 C which is a remainder of region  281 A left by disregarding overlap regions  286 A and  286 B. Specifically, regions  286 A,  286 B and  286 C together form long-range illumination region  281 A. Overlap regions  286 A and  286 B (if any) are kept small, within conformance with space constraints of a swallowable capsule, to minimize ghosting resulting from light originating at the source, being reflected by an inner surface and reaching the camera(s) without ever exiting the capsule endoscope  200 . Hence, several capsule endoscopes of the type described herein have at least 50% of (e.g. a majority of, or most of) light, which is emitted by a single long-range light source and which exits through long-range illumination region  281 A actually exit capsule endoscope  200  through non-overlapping region  286 C. Specifically, in several embodiments, non-overlapping region  286 C is several times larger than overlap regions  286 A and  286 B. 
     In many embodiments, a majority of light, which exits endoscope  200  and originates in a long-range light source, does not exit through union region  282 . To re-iterate, in some embodiments, the light, which exits through overlapping regions  286 A and  286 B, is less than 50% of light from any long-range light source that exits the housing to reach outside the endoscope  200 . At least a portion of the just-described majority is incident on the gastrointestinal tract, gets reflected therefrom, and enters endoscope  200  through union region  282 . 
     Note that in certain specific embodiments of capsule endoscope  200 , wherein each long-range illumination region  281 A is sufficiently aligned with a corresponding imaging region  282 A, almost all of the light (e.g. 90% or more) which exits capsule endoscope  200  through long-range illumination region  281 A is emitted by a single long-range light source corresponding thereto. Hence, in the just-described embodiments, only a negligible amount of stray light from other light sources (e.g. adjacent sources) within the capsule endoscope exits through each long-range illumination region. 
     As noted above in reference to  FIG. 2C , many embodiments of a capsule endoscope also have one or more short-range light illumination region(s)  210 , which may correspond to (but are not necessarily aligned with) either or both of imaging region  212  and/or long-range illumination region  211 , depending on the embodiment. Specifically, as shown in  FIGS. 28K and 28L  for embodiments that correspond to  FIGS. 28E and 28G  respectively described above, a short-range illumination region  283 A overlaps imaging region  282 A in overlap region  289 A. Overlap region  289 A has an area which constitutes more than 50% of the area of imaging region  282 A. 
     Hence, more than 50% of light which exits some embodiments of a capsule endoscope through imaging region  282 A, actually exits through overlap region  289 A. Accordingly, in certain embodiments, at least 50% of light (e.g. a majority or most of light) emitted by a short-range light source and exiting the housing of a capsule endoscope, actually exits through union region  282 . In several such embodiments, multiple short-range illumination regions also overlap one another, to form a continuous band  283  around the circumference of a tubular wall (which is shown unrolled for illustration purposes in  FIGS. 28I and 28J , as noted above). 
     Furthermore, as shown in  FIGS. 28A-28D , the area of a short-range illumination region  210  is typically several times e.g. 2 times, 3 times, 4 times or even 5 times larger than the area of a long-range illumination region  211 . Also as illustrated in  FIGS. 28K and 28L , the area of illumination region  283 A is 3 or 4 times larger than the area of illumination region  281 A, In several such embodiments, the two types of light sources included in a capsule endoscope, namely a short-range light source and a long-range light source, each include emitters that are identical to one another, i.e. the emitters are implemented using multiple copies of a single product (e.g. LED), and accordingly have the same ratings as one another. However, as noted above, the short-range light sources of a capsule endoscope in accordance with the invention include one or more optical devices to split light from the emitter therein, into multiple fractions and/or portions and/or parts that are initially redirected by the optical device(s) along different paths but finally brought together at the housing, to form an illumination region  210  which is several times larger than illumination region  211  formed by light incident directly on the housing from an emitter in a long-range light source. 
     Several embodiments differ from the above-described embodiments illustrated in  FIGS. 6 and 7 , wherein several differences are illustrated in  FIGS. 29A and 29B  and/or described below. In embodiments of the type illustrated in  FIGS. 29A and 29B , an illumination ray  2901  emitted from source aperture S is reflected from an inner surface  2902  of window  2903  in a tubular wall of the housing of the endoscope. Specifically, point U is at the intersection of the incident ray  2901  and the reflected ray  2904 . In  FIG. 29A , the ray  2901  is collinear with a line  2907  and reflects from inner surface  2902  at point U on inner surface  2902  to form reflected ray  2904  along a line  2908 . Note that in  FIG. 29A , V is a plane formed by the three points S, U and P where P is within the pupil of the camera. In some embodiments, plane V in  FIGS. 29A and 29B  is vertical, i.e. coincident with the plane of the paper in  FIG. 29A , and therefore points U, P, S lie in plane V as do ray  2904  and normal line N. 
     Accordingly, in the just-described embodiments, plane V is a longitudinal plane coincident with the plane of the paper on which  FIG. 29A  is drawn. This longitudinal plane V passes through the above-described point U and through a point C, wherein C is the center of curvature of an arc AUB ( FIG. 6 ). The just described lateral plane is parallel to the optical axis PQ ( FIGS. 6 and 29A ) and passes through the intersection point U. The lateral plane and the longitudinal plane are perpendicular to one another in embodiments of the type illustrated in  FIG. 29A . In other embodiments, plane V is not vertical and instead points P and S in  FIG. 29A  are projections in a vertical plane that is coincident with the plane of the paper in which normal line N lies. Accordingly, the geometry shown in  FIG. 29A  is similar to the geometry shown in  FIG. 6  except that in  FIG. 29A , the angle of incidence of ray  2901  is θ i  whereas in  FIG. 6  θ i  is the projection of the angle of incidence on to a vertical plane containing C and U, i.e. the vertical plane projection of ray SU in  FIG. 6 . 
     Referring to  FIG. 29B , incident illumination ray  2901  is first refracted at the inner surface  2902  into window  2903 , reflects from outer surface  2905  as ray  2906 , and then refracts at inner surface  2902  to become reflected ray  2904 . In  FIG. 29B , point U is within the window  2903 , and N is a line that bisects an angle formed by incident ray  2901  and reflected ray  2902 . If inner surface  2902  and outer surface  2905  are parallel to one another, then line N is normal to both surfaces  2902  and  2905 , at point U. 
     Referring to both  FIGS. 29A and 29B , an angle of incidence of ray  2901  at inner surface  2902  is θ i  as discussed above. Also in both  FIGS. 29A and 29B , illumination ray  2901  and line N together define the above-described plane V. In several embodiments, there exists a set of image forming rays entering the pupil P of an endoscope&#39;s camera within the field of view (FOV) which lie in plane V and which either pass through point U ( FIG. 29A ) or appear to pass through point U when viewed from inside the endoscope ( FIG. 29B ). Specifically, consider a ray UP going from point U to point P, with P within the pupil, that makes an angle σ with line N. The reflection of incident illumination ray  2901  intersects point P if θ i =σ. 
     Hence in several embodiments, the illumination rays from source S are restricted in angle such that θ i &gt;σ for a majority of pairs of rays (such as one pair  2901  and  2904 , and another pair  2911  and  2914 ) in all planes V of  FIGS. 29A and 29B , to reduce or eliminate a ghost of the source S (i.e. a virtual source) from an image captured by the camera. For example, in several embodiments source S is positioned, by experiment, at a location that is chosen to be at an angle θ i  relative to the optical axis of the camera, selected to be sufficiently larger than angle σ (e.g. 1° larger), so as to avoid ghosting in the geometry illustrated in  FIGS. 25 and 26 . 
     As described above, image data representing a diagnosable image is supplied to a transmitter of the endoscope. A transmitter as used herein includes a wireless transmitter (e.g. a device for sending electromagnetic waves that generates and modulates current, and conveys it to an antenna included therein for radio-frequency transmission or conveys it to a LED, laser, or other light source included therein for optical transmission) or a wireline transmitter (e.g. that includes output terminal(s) coupled to transistor(s) included therein to generate electrical signal(s) for transmission across one or more wires). 
     Hence a field of view  212  ( FIGS. 2A and 29C ) of the endoscope is a range of angles through which an image of the gastrointestinal tract is captured by at least one camera, optionally cropped and supplied to the transmitter. Therefore, in several embodiments of the invention, an endoscope&#39;s field of view  214  is effectively (an “effective field of view”) smaller than a typical camera&#39;s field of view traditionally defined by lens  202 &#39;s field of view  2993  ( FIG. 29C ) and also limited by sensor  232 &#39;s size (thereby defining its own field of view  2992 ). As illustrated in  FIG. 29C , a region  2994  of an image formed in a plane  2991  inside the camera is inherently cropped by the position and dimensions of sensor  232 . Additionally, in embodiments of the type illustrated in  FIG. 29C , a processor within the endoscope further discards another region  2995  in plane  2991  even though additional data representing region  2995  is captured by sensor  232 . Accordingly, the endoscope&#39;s field of view  214  is defined by a region  2999  of the sensor wherein image data of a diagnosable image is generated. 
     In several embodiments illustrated in  FIG. 30 , short-range source  206  (described above and shown in  FIGS. 2A, 2D and 2E ) is centered in a radial plane  3002  while long-range source  205  is centered in a different radial plane  3001 . Planes  3001  and  3002  are radial relative to housing  201 , i.e. each of these planes passes through the longitudinal axis  222  which is at the center of the cross-section of housing  201 . Radial planes  3001  and  3002  make are at angles O 1  and O 2  respectively, relative to a plane  3000 . Plane  3000  passes through seams  1103  and  1104  at which the two halves  1101  and  1102  of the optical element  1100  are glued to one another. Angles O 2  and O 1  may be same as or different from one another depending on the embodiment. In an illustrative embodiment, angle O 2  is 25° and angle O 1  is 22.5°. However, as will be apparent to the skilled artisan, different values of angles O 2  and O 1  are used in other embodiments, depending on the relative position of the compound parabolic concentrators formed within optical element  1100 . The precise values of angles O 2  and O 1  in a specific embodiment may be determined by experiment and/or trial and error. 
     Some embodiments of an endoscope of the type described above use a radially-symmetric optical element within a camera, as illustrated in  FIGS. 31 and 32 . Specifically, a capsule endoscope of certain embodiments houses a panoramic camera which includes a single objective lens  3100  ( FIG. 31 ) whose optical axis  3101  is substantially parallel to (e.g. within 20° of) the longitudinal axis  222  of the capsule endoscope.  FIG. 32  shows another embodiment wherein the capsule endoscope houses a mirror  3200  with its optical axis  3202  being also substantially parallel to the longitudinal axis  222 . 
     Panoramic cameras of the type shown in  FIG. 31  provide a Field of View (FOV) that exceeds 180° but with an obscuration at the center of the FOV. For example, the FOV in one embodiment is a full 360° in latitude (i.e. in all radial directions in the cross-sectional view shown in  FIG. 30 ). In this example, the longitudinal range of angles for the FOV span only 40° relative to a lateral plane perpendicular to the longitudinal axis and passing through the center of lens  3100 , i.e. the longitudinal FOV  3102  ( FIG. 31 ) of this example spans 200° less 160° (angle of obscuration). Note that half of the angles 200° and 160° are illustrated in  FIG. 31  as  3103  and  3104  respectively. 
     Panoramic annular lens  3100  of  FIG. 31  is similar or identical to panoramic annular lenses (PALs) described in, for example, U.S. Pat. Nos. 4,566,763 and 5,473,474 both of which are incorporated by reference herein in their entirety. A capsule endoscope with a PAL imaging system is also described in US Patent Publication 20080143822 entitled “In vivo sensor with panoramic camera” filed by Kang-Huai Wang and Gordon Wilson on Dec. 19, 2006 which is incorporated by reference herein in its entirety. 
     In the embodiments illustrated in  FIG. 32  surface  3201  of mirror  3200  is formed as a conicoid surface of revolution, such as a spheroid, paraboloid, hyperbaloid, or any aspheroidal shape depending on the embodiment. Note that in certain embodiments of  FIG. 32 , the objective optical system  3250  is similar or identical to a corresponding objective optical system of the type described in US Patent Publication 20050049462 entitled “Capsule Endoscope” filed by Masafumi Kanazawa on Aug. 31, 2004 which is incorporated by reference herein in its entirety. Several embodiments as shown in  FIGS. 31 and 32  have a camera with a central axis coincident with a longitudinal axis  222  of a housing of the capsule endoscope, in other embodiments these two axes are not aligned, and may even be oriented at a predetermined angle relative to one another depending on the embodiment. 
     The image exposure in certain illustrative embodiments of the invention is determined by averaging pixel levels sensed in pre-defined sectors of sensor regions Q 1 -Q 4  illustrated in  FIG. 2O . The sector positions are adjusted to account for possible decenter of images on the sensors, but, roughly speaking, each of the four sensor regions Q 1 -Q 4  illustrated in  FIG. 2O  is subdivided into 4 sectors. The 16 sectors of a sensor  232  ( FIG. 24 ) are labeled as shown in  FIG. 20  relative to labels of the corresponding LEDs. Sensor regions Q 1 -Q 4  map to a cylindrical field of view, and therefore sensor regions Q 1  and Q 4  are adjacent to one another. 
     Note that in some embodiments, each of sensor regions Q 1 -Q 4  is one quadrant in a single monolithic sensor chip  232  as shown in  FIG. 24 . The illuminated scene is imaged by the camera onto the single monolithic sensor chip that captures four images in four sensor regions, labeled Q 1 -Q 4 . Each sensor region is itself divided into four sectors by two perpendicular lines and the sectors are labeled with sector numbers (as shown in  FIG. 24 ). As noted above, each sector is labeled relative to the corresponding LED as shown in  FIG. 20 . 
     Several embodiments of an endoscope use sixteen LEDs, including eight LEDs located above an annular mirror  218  ( FIG. 2E ) that are labeled with odd numbers, and eight LEDs located in a lower portion of the endoscope that are labeled with even numbers. The sixteen LEDs are all turned on sequentially, one after another, in rapid succession, to generate a panoramic image on sensor  232 . 
     The luminous energy recorded by each pixel in the sensor chip is proportional to the illuminating luminous energy incident upon that portion of the scene imaged onto the pixel. The constant of proportionality depends, or efficiency with which scattered light is collected by the sensor, depends on many factors including the reflectance of the objects in the scene, the f# of the camera. Note that f# is the light-collection ability of a lens, the smaller the f# the more light is collected. For example, the f# of a lens is related as an inverse square of the amount of light collected. 
     The location and orientation of the LEDs is such that each LED principally affects the illumination of one corresponding sensor sector, although “cross talk”, i.e. illumination of a sector by a non-corresponding LED, also is significant. For the ith sector, the exposure is given by averaging the signal levels σ of the N pixels in the sector 
     
       
         
           
             
               v 
               i 
             
             = 
             
               
                 1 
                 N 
               
                
               
                 
                   ∑ 
                   k 
                   N 
                 
                  
                 
                   
                     σ 
                     k 
                     
                       1 
                       / 
                       Γ 
                     
                   
                   . 
                 
               
             
           
         
       
     
     In the above equation, v denotes the radiant energy (also called luminous energy) received by the sensor and integrated over an area.
 
If the averaging is done before gamma correction, Γ=1. Otherwise, Γ is the gamma factor, e.g.  2 . 2 . Averaging after gamma correction may produce better results with high contrast images, but that is an open question.
 
Let u i   (n)  be the luminous energy of the ith LED for exposure n. Assuming that the LEDs have linear L-I curves, u i   (n)  is proportional to the integrated LED drive current integrated over exposure time τ
 
     
       
         
           
             
               
                 u 
                 i 
                 
                   ( 
                   n 
                   ) 
                 
               
               ∝ 
               
                 
                   ∫ 
                   0 
                   τ 
                 
                  
                 
                   
                     
                       I 
                       i 
                       
                         ( 
                         n 
                         ) 
                       
                     
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                    
                   dt 
                 
               
             
             , 
           
         
       
     
     Note that in the above equation, u denotes the energy output by an LED. Since illuminance adds linearly, 
     
       
      
       v=Au.  
      
     
     For a design of an endoscope as illustrated in  FIGS. 17 and 18 , A is a square matrix with the diagonal elements dominating. A is not constant but depends on the shape of the body cavity and the endoscope&#39;s orientation within it. Typically, we desire the illumination to be the same in all sectors. Let the target exposure be {tilde over (v)} i =v 0 . In principle the needed LED energies can be determined as 
         u=A   −1   {tilde over (v)} . 
     However, A is not known exactly.
 
The LED energies for the next frame u (n+1)  may be estimated based on u (n)  and v (n)  for the current frame n
 
         u   (n+1)   =u   (n)   +B ( {tilde over (v)}−v   (n) ).  (0.1)
 
     If B=A −1  then we expect exact convergence to the desired exposure in the next frame. In order to make the illumination control method more stable, we estimate B such that |B i,j &lt;|A i,j   −1 | for all i and j. Also, we include off-diagonal elements to account for cross talk from neighboring LEDs. The optimal matrix B depends on the endoscope and/or tissue geometry. For example, the cross talk increases as the lumen wall (i.e. wall of the body cavity, or tissue) recedes from the endoscope. Thus, the magnitude of current to off-diagonal elements increases with increasing endoscope-lumen distance. The lumen distance is not known. However, u i  is correlated to the endoscope-lumen distance so B i,j =ƒ(u i , j). This relationship will be determined through raytrace modeling and experimentation. 
     Given these relationships, u (n+1)  may be estimated straightforwardly. 
     
       
         
           
             
               B 
               
                 i 
                 , 
                 j 
               
             
             = 
             
               { 
               
                 
                   
                     
                       
                         
                           
                             f 
                             1 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           i 
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           odd 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             2 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           i 
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           even 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             3 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           
                             i 
                             + 
                             1 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           odd 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             4 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           
                             i 
                             - 
                             1 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           even 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             5 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           
                             i 
                             ± 
                             2 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           odd 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             6 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           j 
                           = 
                           
                             i 
                             ± 
                             2 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           even 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             7 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             j 
                             = 
                             
                               i 
                               - 
                               1 
                             
                           
                           , 
                           
                             i 
                             + 
                             3 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           odd 
                         
                       
                     
                     
                       
                         
                           
                             f 
                             8 
                           
                            
                           
                             ( 
                             
                               u 
                               i 
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             j 
                             = 
                             
                               i 
                               + 
                               1 
                             
                           
                           , 
                           
                             i 
                             - 
                             3 
                           
                         
                       
                       
                         
                           i 
                            
                           
                               
                           
                            
                           even 
                         
                       
                     
                     
                       
                         0 
                       
                       
                         otherwise 
                       
                       
                         
                             
                         
                       
                     
                   
                    
                   
                       
                   
                    
                   and 
                    
                   
                     
 
                   
                    
                   j 
                 
                 -&gt; 
                 
                   { 
                   
                     
                       
                         
                           j 
                           + 
                           16 
                         
                       
                       
                         
                           j 
                           &lt; 
                           1 
                         
                       
                     
                     
                       
                         
                           j 
                           - 
                           16 
                         
                       
                       
                         
                           j 
                           &gt; 
                           16 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     The functions ƒ m (u i ), m=1, 2, . . . , 6, are tabulated. 
     
       
         
           
             
               
                 f 
                 m 
               
                
               
                 ( 
                 
                   u 
                   i 
                 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       ρΓ 
                        
                       
                           
                       
                        
                       
                         a 
                         
                           1 
                            
                           m 
                         
                       
                     
                   
                   
                     
                       0 
                       &lt; 
                       
                         u 
                         i 
                       
                       &lt; 
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           u 
                           1 
                         
                       
                     
                   
                 
                 
                   
                     
                       ρΓ 
                        
                       
                           
                       
                        
                       
                         a 
                         
                           2 
                            
                           m 
                         
                       
                     
                   
                   
                     
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           u 
                           1 
                         
                       
                       &lt; 
                       
                         u 
                         i 
                       
                       &lt; 
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           u 
                           2 
                         
                       
                     
                   
                 
                 
                   
                     ⋮ 
                   
                   
                     
                         
                     
                   
                 
                 
                   
                     
                       ρΓ 
                        
                       
                           
                       
                        
                       
                         a 
                         
                           n 
                            
                           
                               
                           
                            
                           m 
                         
                       
                     
                   
                   
                     
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           u 
                           
                             n 
                             - 
                             1 
                           
                         
                       
                       &lt; 
                       
                         u 
                         i 
                       
                       &lt; 
                       
                         ρ 
                          
                         
                             
                         
                          
                         
                           u 
                           n 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     where n is a reasonably small number ˜4. Γ is a feedback gain. If Γ is too high, the convergence will be unstable. If Γ is too low, the convergence will be slow. ρ is adjusted to account for differences in the average reflectivity of the object (test cylinder or colon). For the white test cylinder ρ≈0.95. For the colon ρ≈0.3. 
     The bottom LEDs (which are used for short range illumination) most strongly affect the exposure when the lumen is close and the top LEDs are more effective when the lumen is farther away. Accordingly, to conserve energy in the endoscope, the value of u i  is capped at a maximum value u max upper  for i odd. After initially calculating u (n+1) , any upper LED values of the vector that exceed u max upper  would be reduced to that value. Depending on the embodiment, upper LED values may be limited differently, e.g. by using a different matrix B. 
     If the lumen is touching the endoscope, the top LEDs (which are used for long-range illumination) have very little impact on the exposure. Thus, it could happen that the amount of current to these LEDs is increased to a high value, which would waste power. When this condition occurs, the energy of the upper LED (in the long-range light source) is limited to maximum value u max upper . The best indicator of this condition is the LED level for a neighboring lower LED. If u i+1   n &lt;b 1 , then we require u i   n &lt;b 2 . 
     If an LED drive u k  is capped and {tilde over (v)} k −v k   (n) &gt;0 the u k  does not change in the next iteration. However, the matrix elements are based on the assumption that it will increase and other LEDs may not converge properly. Similarly, if u k =u min , where u min  is the minimum LED drive (typically zero or one) and {tilde over (v)} k −v k   (n) &gt;0, a similar problem occurs. To remedy the problem with either set of conditions, we temporarily set some matrix elements to zero 
     
       
         
           
             
               B 
               
                 i 
                 , 
                 j 
               
               ′ 
             
             = 
             
               { 
               
                 
                   
                     0 
                   
                   
                     
                       
                         j 
                         = 
                         k 
                       
                       , 
                       
                         j 
                         ≠ 
                         i 
                       
                     
                   
                 
                 
                   
                     
                       B 
                       
                         i 
                         , 
                         j 
                       
                     
                   
                   
                     otherwise 
                   
                 
               
             
           
         
       
     
     Determining LED drive levels: u i  is the luminous energy. Due to variations among LED efficiencies, the electrical charge required to achieve that energy will vary somewhat. Let u i =α i q i , where q i  is the LED drive value and α i  is the efficiency of the ith LED. It may be convenient to choose the nominal efficiencies to be approximately one q i  and u i  fall between 0 and 255. 
     The efficiencies can be determined by calibration. In the current final-test plan, the illumination control method is run with the endoscope in a uniform white cylinder for a number of iterations. The resulting image is examined for uniformity. Also, the LED drive levels q i  are recorded. If the test conditions are symmetric, then all the luminous energies should be equivalent for all upper and lower LEDs respectively. 
         u   i   =u   old =α i   q   i  for all  i  odd
 
         u   i   =u   even =α i   q   i  for all  i  even
 
     Thus, the efficiencies α i  are deduced. 
     During calibration, α is not known. A constant is chosen as an initial guess. A typical value might be 0.2 mA−1, if the maximum value of u is 255. The initial guess value may be 1. 
     The above-described principles are implemented by appropriately programming a processor in an endoscope to perform a method illustrated in  FIG. 21 . Specifically, the processor starts in act  2101  (see  FIG. 21 ), by setting the frame number to zero. Then in act  2102 , the processor looks up initial values of LED drives namely the vector u(n) and LED drive cap values u(cap). The initial values in vector u(n) at the beginning when the endoscope is first turned on are all 0, in one example. Note that u(cap) is determined by experiment and is set to as low as possible to minimize ghosts while still achieving good uniformity at a variety of distances D 1 -D 4  as described above in reference to  FIGS. 2I and 2K . Note that the energy of the lower LED (in the short-range light source) is limited to the maximum value u(cap). 
     Referring to  FIG. 21 , the processor enters a loop starting with act  2103 . Note that act  2103  itself is repeatedly performed for each element u i   (n) , wherein the processor checks if u i   (n)  is greater than ui(cap) and if so saves the value of ui(cap) as u i   (n) . After performing act  2103  for each element u i   (n) , the processor then proceeds to act  2104 . In act  2104 , the processor sets the LED drives to generate the current in vector u(n) and then proceeds to act  2106  to capture the image. In act  2104 , the processor also performs an act  2105  to determine the matrix B(n)(u(n)) based on the LED drives, simultaneously or contemporaneously with acts  2106 - 2109 . 
     Note that the values of the LED drives are proportional to u i   (n)  depending on the efficiency of the LED. After act  2106 , the processor goes to act  2107  and calculates an average (or other such function) of luminance value, for each sector of image sensor—vector v(n). 
     In some embodiments, the pixel values (e.g. 50,000 pixels in a sector) are simply summed up and divided by their number so as to obtain a simple average, although other embodiments may use a weighted average. Some embodiments exclude outliers (e.g. all saturated pixels or some maximum percentage of saturated pixels). Yet another embodiment uses a median instead of an average. 
     Note that in act  2107 , a more complicated function than a simple average is computed in several embodiments. For example, in some embodiments, pixels with luminance values above or below a preset threshold are rejected, i.e. not used in computing the result. In one illustrative embodiment, the pixel value of 255 in an 8 bit number is rejected as being above a preset upper threshold, because this number may represent any over-exposed value, even a value resulting from specular reflection. In the just-described illustrative embodiment, the pixel values of 2, 1 and 0 are also rejected as being below a preset lower threshold, because these values may represent noise. 
     After act  2107 , the processor goes to act  2108 , and calculates a difference between target luminance vt and measured luminance for each sector—vector (v(t)−v(n)). Typically, target luminance vt is a scalar constant, e.g. 60 out of a maximum of 255. 
     Next, the processor goes to act  2109 , and computes new LED drives, as u(n)=u(n)+B(n)(v(t)−v(n)). Note that in act  2109 , the processor receives the result of act  2105 , i.e. the matrix B(n)(u(n)). 
     After act  2109 , the processor goes to act  2110  to increment n, and then iterates back to the beginning of the loop, specifically to act  2103 . A graph of timing relationships between signals between a controller, LEDs and sensors in an endoscope is illustrated in  FIG. 22 . Note that the LEDs are turned on during an integration time for pixels in the sensors, thereby to capture an image formed by light that is emitted by the LEDs and reflected by tissue. 
     As noted above, energy emitted in short-range electromagnetic radiation is capped or limited to use energy efficiently in some embodiments. Referring to  FIG. 33 , endoscope  200  moves from a current location  3301  to a new location  3302  at which an increase Δd 1  (e.g. 3 mm) in a distance d 1  (e.g. 13 mm) of the short-range illumination region from the gastrointestinal tract is greater than an increase Δd 2  (e.g. 6 mm) in distance d 2  (e.g. 14 mm) of the long-range illumination region from the gastrointestinal tract (when measured in a common direction). In response to such movement, some embodiments of an endoscope in accordance with the invention automatically increase radiant energy E 2  (e.g. 5 micro Joules) emitted in the long-range electromagnetic radiation from the long-range illumination region by an amount ΔE 2  (e.g. 1 micro Joule) which is larger than an increase ΔE 1  (e.g. 0.1 micro Joule) in radiant energy E 1  (e.g. 5 micro Joules) emitted in the short-range electromagnetic radiation. After these increases, endoscope  200  stores in its memory another portion of another image of the tract from the new location. The current inventor submits that it is non-obvious to make ΔE 1 &lt;ΔE 2  in response to a movement which makes Δd 1 &gt;Δd 2 . As noted above, in some embodiments E 1  is capped to a maximum value u max upper . Hence, in some situations wherein such a preset limit is reached, ΔE 1  is kept at zero in order to conserve energy even if Δd 1 &gt;Δd 2 . 
     Numerous modifications and adaptations of the embodiments described herein will be apparent to the skilled artisan in view of the disclosure. 
     For example, some embodiments of a device include a housing sufficiently small to be insertable into a gastrointestinal tract of a human, a camera enclosed within said housing, wherein an optical axis of the camera intersects the housing at an intersection point, a first source of electromagnetic radiation enclosed within said housing, with first electromagnetic radiation from the first source exiting through a first region of the housing on operation of the first source, wherein the first source is positioned within the housing such that the first region contains the intersection point of the optical axis with the housing, a second source of electromagnetic radiation enclosed within said housing, with second electromagnetic radiation from the second source exiting through a second region of the housing on operation of the second source, wherein the second source is positioned within the housing such that the intersection point of the optical axis with the housing is located outside the second region. 
     As another example, certain embodiments of a device include a housing sufficiently small to be swallowed, a camera enclosed by the housing, the endoscope having a field of view defined by a largest image effectively transmitted by the endoscope to an external computer, a plurality of sources of light enclosed within the housing, wherein each source in the plurality of sources has an aperture positioned within the housing to emit rays reflected by the housing and forming a mirror image of said aperture outside of the field of view of the endoscope. 
     Also, instead of using a CPC as optical element  216 , alternative embodiments of endoscope  200  in accordance with the invention use annular angular concentrators having other types of cross-sections that may less effectively reduce angular divergence, such as a cone or a paraboloid. In two illustrative embodiments, a concentrator cross-section that is used in an annular angular concentrator has the same shape as a handheld flashlight&#39;s concentrator or an automobile headlight&#39;s concentrator. 
     Some embodiments of an endoscope of the type described herein minimize the amount of light received by a sensor after reflection from the housing of the endoscope by one or more techniques, such as (a) employing optical elements (such as the CPC) to reduce a range of angles through which light is emitted by a source (such as a short-range source) and (b) providing one or more sources (such as a long-range source) that emit a majority (or most) of the light through a region of the housing through which image forming rays (to the sensor) do not pass. 
     In some illustrative embodiments, a device in accordance with the invention comprises: a housing sufficiently small to travel through a gastrointestinal tract of a human, a first source of electromagnetic radiation enclosed within the housing, with first electromagnetic radiation from the first source exiting through a first region of said housing, a second source of electromagnetic radiation enclosed within said housing, with second electromagnetic radiation from the second source exiting through a second region of said housing, a camera enclosed within the housing; wherein the endoscope has a field of view defined by a range of angles through which a cropped image of the gastrointestinal tract is captured by a sensor in the camera, on operation of the camera, wherein the cropped image is formed by reflection of at least a portion of said first electromagnetic radiation and a portion of said second electromagnetic radiation from the gastrointestinal tract, wherein the field of view intersects the housing at a third region overlapping at least a portion of the first region; and wherein the camera has an optical axis intersecting the housing at a point in said portion of the first region overlapped by the third region, the point being outside the second region. 
     In several illustrative embodiments, a device in accordance with the invention includes a housing sufficiently small to be enclosed within an organ of a human; at least one upper source of electromagnetic radiation enclosed within the housing; wherein, on operation of the at least one upper source, electromagnetic radiation, of a first intensity that is at least a first predetermined percentage (e.g. almost all or over 90%) of maximum intensity from the at least one upper source, exits through an upper illumination region of a surface of the housing; at least one lower source of electromagnetic radiation enclosed within the housing; wherein, on operation of the at least one lower source, electromagnetic radiation, of a second intensity that is at least a second predetermined percentage (e.g. 37%) of maximum intensity from the at least one lower source, exits through a lower illumination region of the surface of the housing; wherein the lower illumination region is larger than (e.g. 1.2 times larger or 1.5 times larger or even 5 times larger) the upper illumination region; at least one camera enclosed within the housing; wherein the at least one camera forms an image of light emitted from at least one of the lower illumination region and the upper illumination region and entering the housing after reflection from a surface of the organ through the lower illumination region. 
     Δdditionally, note that a “majority of electromagnetic radiation” as used herein refers to a majority of power. 
     Furthermore, note that as region  212  ( FIGS. 2J, 28A-28D ) demarcates reflected light entering endoscope  200  which is used in forming a diagnosable image, any region outside of the boundary of region  212  is referred to herein as a non-imaging region. Hence, region  211  is a non-imaging region in  FIG. 28A . Accordingly, a majority of electromagnetic radiation emitted by a long-range light source of some embodiments exits the housing of endoscope  200  through a non-imaging region (i.e. any region outside of boundary  212 ). Moreover, in such embodiments, a majority of electromagnetic radiation emitted by a short-range light source exits the housing of endoscope  200  outside of the non-imaging region, i.e. exits through the region  212 . 
     Note that an organ as used herein can be a uterus or any part of a gastrointestinal tract (such as a colon, small bowel (small intestine), esophegous, stomach, rectum). Accordingly, an apparatus as described herein can be used to obtain images of any organ of a human or other such mammal. 
     In certain embodiments, short-range illumination region  210  is significantly larger (e.g. several times larger, such as 2 times larger, 3 times larger, or even 5 times larger) than long-range illumination region  211 . This relationship between the two types of illumination regions is illustrated in  FIGS. 2B and 2C  wherein each of overlapping regions  210 A,  210 B and  210 C for short-range illumination are individually larger than long-range illumination region  211 , and hence their combination into region  210  is significantly larger than region  211 . 
     Finally, although endoscope  1900  has been illustrated in  FIG. 19  as enclosing a single camera located in one dome at one end of a capsule, a similar endoscope  3400  illustrated in  FIG. 34  encloses two cameras at the two ends of such a capsule. Specifically, endoscope  3400  has two apertures  3405  and  3406  and two pupils P 1  and P 2  respectively through which reflected light from a gastrointestinal tract is received by two sensors  3401  and  3402  respectively. Sensors  3401  and  3402  together constitute a set of sensors that generate image data at different positions of endoscope  3400  relative to the tract. Image data obtained by the set of sensors (i.e. sensors  3401  and  3402  in  FIG. 34 ) is supplied to a transmitter  3403  that in turn supplies the image data to an external computer (after optional cropping), for use in generation and display of a diagnosable image.