Abstract:
A method for imaging includes focusing optical radiation so as to form respective first and second optical images of a scene on different, respective first and second regions of an array of detector elements. The focused optical radiation is filtered with different, respective first and second passbands for the first and second regions. A difference is taken between respective first and second input signals provided by the detector elements in the first and second regions so as to generate an output signal indicative of the difference.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application 61/419,891, filed Dec. 12, 2010. It is related to another U.S. patent application, filed on even date, entitled “Projection and Imaging Using Lens Arrays.” Both of these related applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to optical projection and imaging, and specifically to devices and methods that use arrays of lenses to enhance the performance and characteristics of projection and imaging systems. 
       BACKGROUND 
       [0003]    In most optical imaging and projection systems, the optical elements are arranged in series along a single optical axis. Some systems, however, use arrays of lenses arranged side by side. The best-known arrangement of this sort is the “fly&#39;s eye” lens array, which is generally used to achieve uniform irradiance in projection optics. 
         [0004]    Lens arrays are also used in some imaging devices. For example, U.S. Pat. No. 7,700,904, whose disclosure is incorporated herein by reference, describes a compound-eye imaging device, which comprises nine optical lenses arranged in a matrix array of three rows and three columns, and a solid-state imaging element for capturing unit images formed by the optical lenses. A stray light blocking member having a rectangular-shaped window is provided on the capture zone side of the optical lenses to block incident lights in a range outside each effective incident view angle range of each optical lens. 
         [0005]    In general, the optics used in an imaging device are designed to form a single image on an image sensor. In some applications, however, multiple images may be superimposed. Such a scheme is described, for example, by Marcia et al., in “Superimposed Video Disambiguation for Increased Field of View,”  Optics Express  16:21, pages 16352-16363 (2008), which is incorporated herein by reference. The authors propose a method for increasing field of view (FOV) without increasing the pixel resolution of the focal plane array (FPA) by superimposing multiple sub-images within a static scene and disambiguating the observed data to reconstruct the original scene. According to the authors, this technique, in effect, allows each sub-image of the scene to share a single FPA, thereby increasing the FOV without compromising resolution. 
         [0006]    Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing an optical image of the object. This sort of 3D map or profile is also referred to as a depth map or depth image, and 3D mapping is also referred to as depth mapping. 
         [0007]    Some methods of 3D mapping are based on projecting a laser speckle pattern onto the object, and then analyzing an image of the pattern on the object. For example, PCT International Publication WO 2007/043036, whose disclosure is incorporated herein by reference, describes a system and method for object reconstruction in which a coherent light source and a generator of a random speckle pattern project onto the object a coherent random speckle pattern. An imaging unit detects the light response of the illuminated region and generates image data. Shifts of the pattern in the image of the object relative to a reference image of the pattern are used in real-time reconstruction of a 3D map of the object. Further methods for 3D mapping using speckle patterns are described, for example, in PCT International Publication WO 2007/105205, whose disclosure is also incorporated herein by reference. 
         [0008]    Other methods of optical 3D mapping project different sorts of patterns onto the object to be mapped. For example, PCT International Publication WO 2008/120217, whose disclosure is incorporated herein by reference, describes an illumination assembly for 3D mapping that includes a single transparency containing a fixed pattern of spots. A light source transilluminates the transparency with optical radiation so as to project the pattern onto an object. An image capture assembly captures an image of the pattern on the object, and the image is processed so as to reconstruct a 3D map of the object. 
       SUMMARY 
       [0009]    Embodiments of the present invention that are described hereinbelow provide improved methods and apparatus for light projection and imaging using lens arrays. 
         [0010]    There is therefore provided, in accordance with an embodiment of the present invention, imaging apparatus, which includes an image sensor, including an array of detector elements, and objective optics, which are configured to focus optical radiation and are positioned so as to form respective first and second optical images of a scene on different, respective first and second regions of the array. First and second optical filters, having different respective first and second passbands, are positioned so as to filter the optical radiation focused by the first and second lenses onto the first and second regions, respectively. A subtracter is coupled to take a difference between respective first and second input signals provided by the detector elements in the first and second regions and to generate an output signal indicative of the difference. 
         [0011]    Typically, the objective optics are arranged so that the first and second optical images contain a common field of view. In a disclosed embodiment, the objective optics include first and second lenses, which are configured to form the first and second optical images, respectively. 
         [0012]    In one embodiment, the subtracter is configured to take the difference by subtracting digital pixel values from the first and second regions. Alternatively or additionally, the image sensor includes an integrated circuit chip, and the subtracter includes an analog component on the chip. 
         [0013]    In some embodiments, the apparatus includes a projection module, which is configured to project a pattern onto the scene at a wavelength in the first passband, while the optical radiation focused by the objective optics includes ambient background radiation in both the first and second passbands, whereby the second input signal provides an indication of a level of the ambient background radiation for subtraction from the first input signal. The apparatus may include a processor, which is configured to process the output signal so as to generate a depth map of the scene responsively to the pattern appearing in the first optical image. 
         [0014]    There is also provided, in accordance with an embodiment of the present invention, imaging apparatus, which includes an image sensor, including an array of detector elements, and a plurality of lenses, which are configured to form respective optical images of respective portions of a scene on different, respective regions of the array along respective optical axes. Diverting elements are fixed to respective surfaces of at least two of the lenses and are configured to deflect the respective optical axes of the at least two of the lenses angularly outward relative to a center of the image sensor. 
         [0015]    In a disclosed embodiment, the diverting elements include diffractive patterns that are fabricated on the respective surfaces of the at least two of the lenses, wherein the diffractive patterns may define Fresnel prisms. 
         [0016]    In some embodiments, the lenses have respective individual fields of view, and the apparatus includes a processor, which is configured to process an output of the image sensor so as to generate an electronic image having a combined field of view encompassing the different, respective portions of the scene whose optical images are formed by the lenses. The apparatus may include a projection module, which is configured to project a pattern onto the scene, wherein the processor is configured to process the electronic image so as to generate a depth map of the scene responsively to the pattern appearing in the optical images of the respective portions of the scene. 
         [0017]    There is moreover provided, in accordance with an embodiment of the present invention, a method for imaging, which includes focusing optical radiation so as to form respective first and second optical images of a scene on different, respective first and second regions of an array of detector elements. The focused optical radiation is filtered with different, respective first and second passbands for the first and second regions. A difference is taken between respective first and second input signals provided by the detector elements in the first and second regions so as to generate an output signal indicative of the difference. 
         [0018]    There is furthermore provided, in accordance with an embodiment of the present invention, a method for imaging, which includes positioning a plurality of lenses to form respective optical images of respective portions of a scene on different, respective regions of an array of detector elements along respective optical axes of the lenses. Diverting elements are fixed to respective surfaces of at least two of the lenses so as to deflect the respective optical axes of the at least two of the lenses angularly outward relative to a center of the array. 
         [0019]    The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic, pictorial illustration of a system for three-dimensional (3D) mapping, in accordance with an embodiment of the present invention; 
           [0021]      FIG. 2A  is a schematic side view of an imaging module, in accordance with an embodiment of the present invention; 
           [0022]      FIG. 2B  is a schematic frontal view of the imaging module of  FIG. 2A ; 
           [0023]      FIG. 3A  is a schematic side view of an imaging module, in accordance with another embodiment of the present invention; 
           [0024]      FIG. 3B  is a schematic frontal view of the imaging module of  FIG. 3A ; 
           [0025]      FIG. 4  is a schematic side view of an imaging module, in accordance with yet another embodiment of the present invention; 
           [0026]      FIG. 5  is a schematic side view of a projection module, in accordance with an embodiment of the present invention; and 
           [0027]      FIG. 6  is a schematic side view of a projection module, in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview  
       [0028]    Embodiments of the present invention that are described hereinbelow use lens arrays in novel ways to enhance the performance of optical imaging systems and of pattern projectors. In the disclosed embodiments, the lenses in an array are typically used together to form respective images on the same image sensor, or to project different parts of a pattern. 
         [0029]    The embodiments of the present invention that are described hereinbelow are useful particularly in pattern-based depth mapping. Therefore, for clarity and convenience of presentation, these embodiments are shown and described in the context of the components of a depth mapping system. The principles of these embodiments, however, may also be used in other electronic imaging and optical projection applications, all of which are considered to be within the scope of the present invention. 
         [0030]      FIG. 1  is a schematic, pictorial illustration of a system  20  for 3D mapping, in accordance with an embodiment of the present invention. In this example, an imaging device  22  is configured to capture images and generate 3D maps of a scene. The scene here includes a user  28  of the system (who is thus, in this case, the “object” of the imaging device, as well as its operator). The depth information in the 3D maps may be used by a host computer  24  as part of a 3D user interface, which enables the user to interact with games and other applications running on the computer and with elements shown on a display screen  26 . (This sort of functionality is described, for example, in U.S. Patent Application Publication 2009/0183125, whose disclosure is incorporated herein by reference.) This particular application of system  20  is shown here only by way of example, however, and the mapping capabilities of system  20  may be used for other purposes, as well, and applied to substantially any suitable type of scenes and 3D objects. 
         [0031]    In the example shown in  FIG. 1 , imaging device  22  comprises a projection module  23 , which projects a pattern of optical radiation onto the scene, and an imaging module  25 , which captures an image of the pattern that consequently appears on the body of user  28  and other objects in the scene (not shown in the figure). The optical radiation that is used for this purpose is typically, although not necessarily, in the infrared (IR) range, although visible or ultraviolet (UV) light may similarly be used. The terms “optical radiation,” “illumination,” and “light” are used synonymously in the present patent application and should be understood to include any or all of the IR, visible, and UV ranges. Module  23  may be designed to emit radiation in a narrow optical band, and a corresponding bandpass filter may be used in imaging module  25  in order to reduce the amount of ambient light detected by the imaging module. 
         [0032]    A processor, such as computer  24  or an embedded processor (not shown) in device  22 , processes the image of the pattern in order to generate a depth map of the body, i.e., an array of 3D coordinates, comprising a depth (Z) coordinate value of the body surface at each point (X,Y) within a predefined field of view. (In the context of an array of image-related data, these (X,Y) points are also referred to as pixels.) In the present embodiment, the processor computes the 3D coordinates of points on the surface of the user&#39;s body by triangulation, based on transverse shifts of the spots in the pattern, as described in the above-mentioned PCT publications WO 2007/043036, WO 2007/105205 and WO 2008/120217. This technique is referred to herein as “pattern-based depth mapping.” The functionality of a processor similar to that in system  20  is further described, for example, in U.S. Patent Application Publication 2010/0007717, whose disclosure is incorporated herein by reference. 
         [0033]    For many practical applications, it is advantageous that imaging module  25  have a wide field of view (FOV)—on the order of 90-120° or more in the horizontal direction and 60-90° or more in the vertical direction. The imaging module is also expected to provide a clear image of the pattern over a wide range of ambient light conditions, including scenes with a bright ambient background, which tends to reduce the contrast of the pattern in the captured images. On the other hand, power and safety considerations limit the output intensity of projection module  23 . The embodiments that are described hereinbelow address these issues. 
       Imaging Module wit On-Board Ambient Cancellation  
       [0034]      FIGS. 2A and 2B  schematically illustrate an ambient light cancellation arrangement in imaging module  25 , in accordance with an embodiment of the present invention.  FIG. 2A  is a side view showing an image sensor  30  and other elements of module  25 , while  FIG. 2B  is a frontal view. 
         [0035]    Image sensor  30  may be, for example, a CMOS device or CCD, comprising an array of detector elements  32 . (For convenience of illustration, only a small number of detector elements is shown in the figure, while in actuality the array typically contains a much larger number of elements, generally well in excess of one million.) The detector elements are typically uniform in size and functionality over the matrix, but in this embodiment they are divided into two regions  34  and  36 . The regions may be of the same size and shape, but for enhanced resolution of the specific image captured by region  34 , it may be advantageous that region  34  is wider and thus includes a larger number of columns of detector elements  32 , for example, twice as many columns as region  36 . Both regions, however, have the same number of rows. 
         [0036]    Objective optics, comprising lenses  42  and  44  form images of the scene of interest on regions  34  and  36 , respectively, of sensor  30 . Typically, the lenses are designed and oriented so that regions  34  and  36  capture images containing a common field of view. The image formed by lens  44  may therefore be distorted in the horizontal direction in order to fit into the narrower shape of region  36 . Although, for the sake of simplicity, only a single lens is shown for each region, in practice arrays of multiple lenses may be used. Alternatively, a single lens (or group of lenses) with a suitable beamsplitting arrangement following the lens may be used to form the images on both of regions  34  and  36 . Although lenses  42  and  44  are pictured as simple lenses, in practice compound lenses may be used in this and all the other embodiments of imaging module  25 . 
         [0037]    Lens  42  forms its image through a bandpass filter  38 , which passes light of the wavelength (typically IR) that is emitted by projection module  23 . Thus, region  34  senses an image of the pattern that has been projected by module  23  onto the scene of interest, along with whatever ambient light is reflected from the scene in the passband of the filter. On the other hand, lens  44  forms its image through a bandpass filter  40 , whose passband does not include the wavelength of projection module  23 . Thus, region  36  senses only ambient background radiation from the scene. The passband of filter  40  may be selected to be near that of filter  38  and of similar bandwidth, so that the image received by region  36  will provide a faithful measure of the ambient light component in the image received by region  34 . 
         [0038]    The ambient input signal from the rows of detector elements  32  in region  36  is thus indicative of the level of the ambient component in the input image signal from the corresponding rows in region  34 . A subtracter takes a difference between this ambient component from region  36  and the input image signal generated by region  34  in order to generate an output signal representing to an electronic image of the pattern on the scene with improved signal/background ratio and hence improved contrast. Because the pixels in regions  34  and  36  are row-aligned, the image signals from the two regions are inherently synchronized. When a rolling shutter is used in image sensor  30  (as is common in CMOS-type sensors), the simultaneous capture and readout of the pixels in the two regions enables imaging module  25  to operate on non-static scenes without motion artifact. 
         [0039]    One way to subtract the ambient component is to digitize the respective raw images from regions  34  and  36  and then subtract the digital pixel values using a suitable digital processor, such as computer  24  or hardware logic (not shown) in device  22 . If region  36  is narrower than region  34 , as shown in the figures, the pixel values in region  36  may be interpolated before subtraction. 
         [0040]    Since the points of view of lenses  42  and  44  are slightly different, the images formed on regions  34  and also have slightly different perspectives (although typically, the disparity is less than ¾ of the sensor width). It is beneficial to register the pixels of the image in region  36  with those in region  34  prior to subtracting. Such registration can be achieved, for example, using optical flow techniques that are known in art. Prior to performing the subtraction, the image in region  36  is interpolated onto the image in region  34  so as to represent the same pixels, same point of view and same overall optical gain. (Gain correction can be important, since filters  38  and  40  are different.) 
         [0041]    Alternatively, as illustrated in  FIG. 2B , the subtraction may be carried out on the image sensor chip in the analog domain. For this purpose, regions  34  and  36  may have separate readout circuits, which are clocked so that each pixel in region  34  is read out at the same time as the corresponding pixel in region  36 . (The clock rates may be adjusted for the difference in widths of the regions.) An analog component, such as a differential amplifier  46  on the integrated circuit chip of the image sensor serves as the subtracter in this case, subtracting the signal level in region  36  from the signal level of the corresponding pixel in region  34 , so that the output from image sensor  30  is already corrected for ambient background. 
         [0042]    To improve accuracy of the results, image sensor  30  may also comprise circuitry for performing local operations of optical flow and gain modification, to ensure that the image signals from regions  34  and  36  have locally the same point of view and gain. 
       Imaging Module with Wide Field of View  
       [0043]      FIGS. 3A and 3B  schematically illustrate an optical arrangement of imaging module  25  that provides a wide field of view (FOV) in a compact, low-cost optical design, in accordance with an embodiment of the present invention.  FIG. 3A  is a side view showing an image sensor  50  and other elements of module  25 , while  FIG. 3B  is a frontal view. The principles of this embodiment may be combined with those of the embodiments of  FIGS. 2A and 2B  to give both wide FOV and ambient light rejection. 
         [0044]    Image sensor  50  in this embodiment is divided into three regions  52 ,  54  and  56 , each with its own lens  62 ,  64 ,  66 . Image sensor  50  may be a standard CMOS device or CCD. The lenses in this case are assumed to be refractive, although diffractive or combinations of refractive and diffractive elements may alternatively be used for the same purpose. Furthermore, although the pictured embodiment divides the image sensor into only three regions with respective lenses, a smaller or larger number of regions and lenses may be used. In the embodiment shown in  FIGS. 3A and 3B , lenses  62 ,  64  and  66  are arranged in a single row, thus expanding the FOV of module  25  in one direction only (the horizontal direction relative to the pages of these figures), but a two-dimensional array of lenses may likewise be used to expand the FOV in both horizontal and vertical directions. 
         [0045]    Each of lenses  62 ,  64  and  66  has a respective FOV  72 ,  74 ,  76 , as shown in  FIG. 3A . At least two of the lenses, such as lenses  62  and  66 , also have a diverting element, such as Fresnel prisms  68  and  70 , fixed to one of their surfaces, such as the front surface in the pictured embodiment. These diverting elements deflect the respective optical axes of the lenses on the front side of module  25  (i.e., the side facing toward the scene and away from image sensor  50 ) angularly outward relative to the center of image sensor  50 . The angle of deflection of prisms  68  and  70  is chosen so that fields of view  72  and  76  look outward and overlap only slightly at their inner borders with FOV  74 . 
         [0046]    As a result, module  25  has an overall FOV that is three times the width of the individual FOV of each of the lenses. Each of regions  52 ,  54  and  56  thus receives an image of a different part of the overall FOV, although it is possible that the images may overlap or that there may be gaps between the images. An image processor, such as computer  24  or a processor embedded in device  22 , may process the electronic image output from sensor  50 , if necessary, for proper blending and avoidance of artifacts at the borders between the regions. In order to prevent stray light from passing between the lenses, separator walls  78  may be interposed between the channels. Similar sorts of separators may be used in the other embodiments described herein (but they are omitted from the figures for the sake of simplicity). 
         [0047]    Module  25  as shown in  FIGS. 3A and 3B  may achieve an overall FOV of 90-120° with good image quality throughout (at least sufficient for the purposes of system  20 ). Normally, good image quality over a FOV this wide requires a large, costly lens, extending a large distance forward from the image sensor. By using an array of lenses, on the other hand, the present embodiment achieves the same FOV with a much more compact, less costly design, and improved performance, since the FOV of each of lenses  62 ,  64 ,  66  is only one-third of the overall FOV. The use of diffractive technology for this purpose enables Fresnel prisms  68  and  70  to be fabricated as part of the lenses themselves and avoids the need for bulky refractive prisms or reflective elements. 
         [0048]      FIG. 4  is a schematic side view of an optical arrangement of imaging module  25  that provides a wide field of view (FOV) in a compact, low-cost optical design, in accordance with another embodiment of the present invention. In this embodiment, too, an array of lenses  82  images the scene of interest onto an image sensor  80 , wherein each lens captures the image in a respective FOV  86 ,  88 ,  90 , . . . . In this case, there are nine lenses  82  in a 3×3 array (although only three of the lenses are seen in the side view of  FIG. 4 ), but again, larger or smaller numbers of lenses may be used in either a one- or two-dimensional array. Alternatively, a single imaging lens may be used, with a suitable arrangement of beam combiners to multiplex and superimpose all of FOVs  86 ,  88 ,  90 , . . . , through this same lens. 
         [0049]    In contrast to the preceding embodiment, in the present embodiment all of lenses  82  cast their respective images of different areas of the scene onto a common area (typically the entire area) of the array of detector elements  32  in sensor  80 . Thus, each of FOVs  86 ,  88 ,  90 ,  . . . is imaged with the full resolution of sensor  80 . The signal output by the sensor, however, becomes a superposition of the images of all the individual fields of view. An image processor, such as computer  24  or a processor embedded in device  22 , separates out the individual images by a process of matched filtering of the output signal from sensor  80 , in order to reconstruct the specific images of the individual fields of view. These specific images may be stitched together or otherwise processed over the entire, combined FOV in order to provide an image with both wide FOV and high resolution. 
         [0050]    The matched filtering performed by the image processor is based on optical encoding of the images formed by lenses  82  with different, respective coding patterns. Various means may be used to perform this encoding. For example, the individual image formed by each lens  82  may be optically encoded, using means such as a respective coded aperture  84  associated with the optical aperture of each lens  82 . A coded aperture, as is known in the art, applies a predetermined spatial modulation to the incoming light, which may be either an amplitude modulation or a phase modulation or a combination of the two. The resulting individual image formed at the focus of the lens on image sensor  80  is then a convolution of the result of geometrical optical imaging with the Fourier transform of the aperture modulation function (representing the diffraction effects). Appropriate defocusing will thus cause a geometrical image of the aperture to appear as the image of a point source, and the modulated image will be a convolution of the aperture with the original unmodulated image. 
         [0051]    A set of mutually-orthogonal modulation functions may be chosen, with a different one of the functions applied by each of the different apertures  84 . The modulation functions are “mutually orthogonal” in the sense that the spatial correlation between any pair of the functions is insignificant by comparison to the autocorrelation of each function with itself. Each function will then have a different, respective deconvolution kernel, which serves as a matched filter for the image formed through the corresponding aperture  84 . To extract the individual image formed by each of lenses  82 , the image processor performs a succession of deconvolution operations using the respective kernels or alternatively solves simultaneously for all the individual images. The deconvolution of the individual images and reconstruction of the combined FOV can be performed frame by frame, without reliance on previous image frames or other temporal information. 
         [0052]    As another alternative, projection module  23  may serve as the means for encoding the images by projecting a pattern chosen so that the respective partial patterns projected onto the scene in the different fields of view  86 ,  88 ,  90 , . . . are mutually orthogonal. In this case, these partial patterns themselves can serve as the matched filters. The image processor may perform a correlation computation between the image output from sensor  80  and each of these partial patterns in order to extract the individual images of the partial patterns and find local pattern shifts as a function of position in each of the fields of view. The processor uses these pattern shifts in computing a depth map (with wide FOV), as described above. 
         [0053]    As in the preceding embodiment, the use of the array of lenses  82 , each with a moderate individual FOV, enables the system to achieve a wide overall FOV at low cost, while maintaining a compact optical configuration. 
         [0054]    In an alternative embodiment, the optical arrangement shown in  FIG. 4  can be used to provide a sort of “zoom” functionality in pattern detection and depth mapping. In this embodiment, projection module  23  initially projects a given pattern over the entire combined FOV of the array of lenses  82 . The image processor processes all of the individual images, as described above, to give a wide-angle, low-resolution depth map. The image processor may identify an object of interest in a certain sector of this depth map, within one or more of fields of view  86 ,  88 ,  90 , . . . . The image processor may then instruct projection module  23  to adjust its optical configuration so that the pattern is projected, possibly with higher resolution, only into the limited sector in which the object is located. 
         [0055]    The dimensions of the projected pattern in this “zoom” mode are less than or equal to the dimensions of the FOV of a single lens  82 , while the pattern itself may be contained within the FOV of a single lens or may overlap the fields of view of two or more of the lenses. As a result, imaging module  25  will receive a single image of the pattern, via one or more of lenses  82 , without other superimposed images of the pattern as in the wide-angle mode. The image processor may process this individual image in order to create an enhanced-resolution depth map of the object of interest. Thus, system  20  has simultaneously large FOV and high resolution and is able to choose a high-resolution sub-image from within the large FOV. 
       Compact Pattern Projectors  
       [0056]    When projection module  23  is required to project a pattern over a wide FOV, the projection lens may suffer from similar problems of size and cost as are encountered by the imaging lenses in the wide FOV imaging configurations described above. Furthermore, when coherent illumination is used, large, wide-angle projection lenses can exacerbate eye safety concerns. The embodiments described below address these issues. 
         [0057]      FIG. 5  is a schematic side view of projection module  23 , in accordance with an embodiment of the present invention. The module comprises a light source  91 , such as a laser diode or LED. A condenser, such as a lens  93 , collimates or gathers, shapes, and directs the beam of light emitted by the light source toward a transparency  95 , which is interposed in the beam and typically creates a pattern of light and dark spots. Light source  91 , lens and transparency  95  together serve as a patterned illumination source. 
         [0058]    Transparency  95  may comprise any of a wide range of optical components. The transparency may comprise, for example, a gray-level or otherwise patterned optical element or a patterned microlens array (MLA), as described in the above-mentioned PCT International Publication WO 2008/120217, or any other suitable sort of patterned refractive of diffractive optical element (DOE). 
         [0059]    The pattern created by this illumination source is projected onto the scene of interest by an array  100  of projection lenses  92 ,  94 ,  96 ,  98 . These lenses each project a part of the overall pattern onto a respective FOV  102 ,  104 ,  106 ,  108 , although there may be small overlaps or gaps between the respective parts of the pattern projected by the individual lenses. Thus, the lenses of array  100  together project the pattern onto a wide overall FOV, typically 120° wide or more, with each lens projecting its part of the pattern onto a different, respective area of the scene. The use of an array of small lenses of this sort makes module  23  smaller and, typically, less costly to manufacture, while improving the performance of the individual lenses and thus of the whole array. Although only one dimension of array  100  is shown in this figure, the projection lenses may be arrayed in two dimensions, i.e., into the page as well as vertically in the view presented here. Furthermore, although the lenses in  FIGS. 5 and 6  are shown in the figures as simple lenses, in practice compound lenses may be used in all embodiments of projection module  23 . 
         [0060]      FIG. 6  is a schematic side view of projection module  23  in accordance with another embodiment of the present invention. This embodiment shares the benefits of compactness, low cost, and improved performance with the preceding embodiment, while adding the benefit of enhanced eye safety. In this case, projection lenses  112 ,  114 ,  116 ,  118 , . . . in an array  110  are all configured to project respective parts of the pattern generated by an illumination source including a transparency  97  onto the same FOV  120 . (Transparency  97  may comprise any of the types of transparencies mentioned above in reference to transparency  95 .) Each of the projection lenses, in other words, projects its own pattern, generated by the corresponding part of transparency  97  (or equivalently, each of the lenses may be associated with its own pattern generating element) onto an area of the scene that is common to all of the lenses. The resulting pattern in FOV  120  is a superposition of all the individual patterns cast by the lenses. Intricate patterns can be created in this manner. 
         [0061]    The eye safety is enhanced in this embodiment due to the following consideration: The light power that a projector can safely emit is defined by the AEL (Accessible Emission Limit). For an extended source, the AEL is proportional to the angular subtense of the source, referred to as α, as well as by the f# of the projections lens, the FOV, and the area of the source (in this case the area of transparency  97 ). Maintaining the same area of transparency  97 , the same f# for the projection lenses, and the same FOV, but dividing the projection lens into an array of n×n lenses, for example, will provide a factor of n increase in the AEL for the whole system. The reason for this increase is that the aperture of each lens has an angular subtense that is 1/n of the original angular subtense, but there are n×n such apertures, so that overall the system can project n times more power while maintaining the same level of eye-safety. 
         [0062]    It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.