Abstract:
An imaging device includes: an optical system, for focusing light from subjects; color imaging element including a plurality of types of light receiving sections that detect light of different wavelength bands, for imaging focused images of the subjects; and an image processing section, for performing filtering processes to remove blur caused by the optical system from data output by the imaging element. The pitch among specified light receiving sections that contribute most to brightness signals is set smaller than that among other light receiving sections. The point spread diameter of the optical system on the specified light receiving sections is set to be greater than the pitch among the specified light receiving sections for wavelengths detected thereby, and less than the pitches among the other light receiving sections for wavelengths detected thereby. The image processing section performs the filtering process only on data output by the specified light receiving sections.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention is related to an imaging device. More particularly, the present invention is related to an imaging device that enables obtainment of color images in a focused state regardless of the distance to a subject. 
         [0003]    2. Description of the Related Art 
         [0004]    An imaging device has been proposed, in which the point spread properties of an imaging lens optical system are intentionally expanded to a size that includes a plurality of pixels of imaging elements, while image reconstruction processes, that is, processes in which image signals are passed through reconstructing filters having properties inverse the blur properties of the imaging lens optical systems, are administered to enable obtainment of images in a focused state regardless of the distances to subjects. Japanese Unexamined Patent Publication No. 2009-089082 and E. R. Dowski, Jr. and W. T. Cathey, “Extended depth of field through wave-front coding”, Appl. Opt., Vol. 34, No. 11, pp. 1859-1866, 1995 describe examples of such an imaging device. 
         [0005]    It is often the case that the aforementioned type of imaging device employs an imaging element constituted by a CCD or the like, similar to general imaging devices. In this case, a color imaging element, in which a color filter constituted by R (red), G (green), and B (blue) filters for each pixel arranged in a two dimensional matrix is provided on a photoelectric converting section, is often employed, to perform imaging of color images. 
         [0006]    Japanese Unexamined Patent Publication No. 2009-089082 proposes to generate a reconstruction filter for data of each of R, Gr, Gb, and B channels, and employing the generated reconstruction filters to independently perform reconstruction processes for each channel, in the case that such a color imaging element is employed. 
         [0007]    In the method described in Japanese Unexamined Patent Publication No. 2009-089082, convolution calculating processes, which have extremely high calculation costs, are administered for all pixels. Therefore, a problem is recognized that the calculation cost is high. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention has been developed in view of the foregoing circumstances. It is an object of the present invention to sufficiently reduce calculation costs (calculation time/amount of memory) when obtaining color images employing a color imaging element in an imaging device that enables obtainment of images in a focused state regardless of distances to subjects. 
         [0009]    An imaging device of the present invention comprises: 
         [0010]    a lens optical system, for focusing light from a subject; 
         [0011]    color imaging means, constituted by a plurality of types of regularly arranged fine light receiving sections that detect light of different wavelength bands, for imaging an image of the subject focused by the lens optical system; and 
         [0012]    an image processing section, for performing a filtering process in which data output by the imaging means is passed through an image reconstructing filter having properties inverse the blur properties of the lens optical system; 
         [0013]    the arrangement pitch of specified light receiving sections that contribute most to the generation of brightness signals from among the plurality of types of light receiving sections being set to be smaller than the arrangement pitches of other light receiving sections; 
         [0014]    the lens optical system being of a configuration that expands focal depth by stabilizing spatial frequency properties in the direction of the optical axis, the diameter of the point spread on the light receiving sections being greater than the arrangement pitch of the specified light receiving sections for wavelength bands to be detected by the specified light receiving sections, and less than the arrangement pitches of the other light receiving sections for wavelength bands to be detected by the other light receiving sections; and 
         [0015]    the image processing section being configured to perform the filtering process only with respect to data output by the specified light receiving sections. 
         [0016]    In an imaging device of the present invention in a more specific aspect, an imaging element having an R, G, B color filter in the Bayer pattern is employed as the imaging means; 
         [0017]    the lens optical system satisfies the following conditions with respect to point spreads: 
         [0000]        G min.&gt;√2·( Pb−Ab/ 2)
 
         [0000]        R max.&lt;2 Pb−Ab/ 2 
         [0000]        B max.&lt;2 Pb−Ab/ 2 
         [0018]    wherein 
         [0019]    Pb: pitch of the light receiving sections of the Bayer pattern color imaging element (in the horizontal and vertical directions) 
         [0020]    Ab: the aperture width of the light receiving sections of the Bayer pattern color imaging element 
         [0021]    Gmin.: the minimum radius of the point spread in the G wavelength 
         [0022]    Rmax.: the maximum radius of the point spread in the R wavelength 
         [0023]    Bmax.: the maximum radius of the point spread in the B wavelength; and 
         [0024]    the image processing section is configured to combine data obtained from Gr and Gb light receiving sections, which are designated as the specified light receiving sections, to generate a G channel, to perform the filtering process only onto data of the G channel, and thereafter, to perform a synchronizing process with respect to R, G, and B channels. 
         [0025]    In recent Bayer pattern color filters, Pb is often approximately 1.4 μm, and Ab is often approximately 1.2 μm. In the case that these are the values of Pb and Ab, Gmin.&gt;1.13 μm, Rmax.&lt;2.2 μm, and Bmax&lt;2.2 μm. 
         [0026]    In another imaging device of the present invention according to a more specific aspect, an imaging element having an R, G, B color filter in a honeycomb pattern is employed as the imaging means; the lens optical system satisfies the following conditions with respect to point spreads: 
         [0000]        G min.&gt; Ph−Ah/ 2 
         [0000]        R max.&lt;√2·( Ph−Ah/ 2)
 
         [0000]        B max.&lt;√2·( Ph−Ah/ 2)
 
         [0027]    wherein 
         [0028]    Ph: pitch of the light receiving sections of the honeycomb pattern color imaging element (in the horizontal and vertical directions) 
         [0029]    Ah: the aperture width of the light receiving sections of the honeycomb pattern color imaging element 
         [0030]    Gmin.: the minimum radius of the point spread in the G wavelength 
         [0031]    Rmax.: the maximum radius of the point spread in the R wavelength 
         [0032]    Bmax.: the maximum radius of the point spread in the B wavelength; and 
         [0033]    the image processing section is configured to perform the filtering process only onto data obtained from G light receiving sections, which are designated as the specified light receiving sections, and thereafter, to perform a synchronizing process with respect to R, G, and B channels. 
         [0034]    In recent honeycomb pattern color filters, Ph is often approximately 2.5 μm, and Ah is often approximately 1.5 μm. In the case that these are the values of Ph and Ah, Gmin.&gt;1.75 μm, Rmax.&lt;2.47 μm, and Bmax&lt;2.47 μm. 
         [0035]    In still another imaging device of the present invention according to a more specific aspect, an imaging element having an R, G, B color filter in a clear bid pattern is employed as the imaging means; 
         [0036]    the lens optical system satisfies the following conditions with respect to point spreads: 
         [0000]        G min.&gt;( Pc/√ 2)− Ac/ 2
 
         [0000]        R max.&lt;2 Pc−Ac/ 2 
         [0000]        B max.&lt;2 Pc−Ac/ 2 
         [0037]    wherein 
         [0038]    Pc: pitch of the light receiving sections of the clear bid pattern color imaging element (in the horizontal and vertical directions) 
         [0039]    Ac: the aperture width of the light receiving sections of the clear bid pattern color imaging element 
         [0040]    Gmin.: the minimum radius of the point spread in the G wavelength 
         [0041]    Rmax.: the maximum radius of the point spread in the R wavelength 
         [0042]    Bmax.: the maximum radius of the point spread in the B wavelength; and 
         [0043]    the image processing section is configured to perform the filtering process only onto data obtained from G light receiving sections, which are designated as the specified light receiving sections, and thereafter, to perform a synchronizing process with respect to R, G, and B channels. 
         [0044]    In recent clear bid pattern color filters, Pc is often approximately 2.5 μm, and Ac is often approximately 1.5 μm. In the case that these are the values of Pb and Ab, Gmin.&gt;1.02 μm, Rmax.&lt;4.25 μm, and Bmax&lt;4.25 μm. 
         [0045]    Note that in the imaging device of the present invention, the imaging means is not limited to the single chip imaging elements having the R, G, B color filters in the patterns described above, but may be a three chip imaging means having an imaging element dedicated to each color. 
         [0046]    It is known that the perceived resolution of color images is affected by whether high frequency components having spatial frequencies, which are mainly included in brightness signals, are present. This is due to the visual perception properties of humans. These properties are widely used in color TV broadcasting, color image compression, and the like. In the imaging devices which are capable of obtaining images in a focused state regardless of distances to subjects described above as well, processes for reconstructing blur within brightness signals, that is, processes that increase gain for high frequency components, are particularly effective. 
         [0047]    The present invention has been achieved based on the aforementioned knowledge. The property of “intentionally increasing the point spread of lenses to a size that includes a plurality of pixels of an imaging sensor, and increasing the range in which the pint spread is stabilized in the direction of the optical axis” is the essence of the mechanism for obtaining images in a focused state regardless of the distances to subjects. This property is utilized only to a specific color channel that contributes most to construct brightness signals, and the filtering process for resolving blur is only administered onto data from the specific color channel. Administration of the filtering process is eliminated for color channels that contribute little to brightness signals in this manner. Thereby, an advantageous effect, that the calculation processing costs are reduced as a whole, is obtained. 
         [0048]    Note that even in the configuration described above, data from color channels that contribute little to brightness signals do not greatly influence perceived resolution of color images, and point spread is suppressed in these color channels such that point images do not impinge on a plurality of light receiving sections. Therefore, the perceived resolution of ultimately obtained color images do not differ much at all from cases in which the filtering process is administered onto data from all color channels. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0049]      FIG. 1  is a schematic block diagram that illustrates the construction of an imaging device according to an embodiment of the present invention. 
           [0050]      FIG. 2  is a flow chart that illustrates the steps of image processes performed by the imaging device of  FIG. 1 . 
           [0051]      FIG. 3  is a schematic diagram that schematically illustrates the concept of the image process outlined in  FIG. 2 . 
           [0052]      FIG. 4  is a diagram that illustrates the relationships among light receiving sections and point spread in the imaging device of  FIG. 1 . 
           [0053]      FIG. 5  is a diagram that illustrates the relationships among light receiving sections and point spread in an imaging device according to a second embodiment of the present invention. 
           [0054]      FIG. 6  is a diagram that illustrates the relationships among light receiving sections and point spread in an imaging device according to a third embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0055]    Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. 
         [0056]      FIG. 1  is a schematic block diagram that illustrates the basic construction of a color imaging device according to an embodiment of the present invention. As illustrated in  FIG. 1 , the imaging device is equipped with: a lens optical system  12  constituted by a lens  10  and a phase plate  11 , for example, for focusing light from a subject; a color imaging element  13  constituted by a CCD, for example, for imaging an image of the subject focused by the lens optical system  12 ; an A/D converter  14  for digitizing analog output from the color imaging element  13 ; an image reconstruction processing section  15 , for administering an image reconstruction process to reduce image blur onto image data output from the A/D converter  14 ; a deconvolution filter  16  for performing the image reconstruction process; a memory  17  connected to the image reconstruction processing section  15  as a workspace; an interpolation processing section  18 , for administering an interpolation process with respect to data output from the image reconstruction processing section  15 ; a memory  19  connected to the interpolation processing section  18  as a workspace; and an image output section  20 , for outputting images based on R, G, and B image data output from the interpolation processing section  18 . 
         [0057]    Note that in the present embodiment, the aforementioned elements  15  through  19  are constituted by known computer systems. The elements  15  through  19  constitute an image processing section of the present invention. The image output section  20  may be a recording device that records images onto recording media, or display means that displays images employing a CRT, a liquid crystal display panel, etc. 
         [0058]    Hereinafter, the processes performed by the image reconstruction processing section  15  and the interpolation processing section  18  will be described with reference to  FIG. 2 , which illustrates the steps of the processes, as well as to  FIG. 3 , which schematically illustrates the processes. When the process starts, the image reconstruction processing section  15  first separates the digital color image data output from the A/D converter into three images, for each of an R, a G, and a B channel (step S 1  of  FIG. 2 ). This is illustrated in columns  1  and  2  (counted from the left edge) of  FIG. 3 . 
         [0059]    Note that a single chip color imaging element having a color filter in the Bayer pattern is employed as the color imaging element  13 . The images borne by the image data, which are the analog signals output from the color imaging element  13  and digitized by the A/D converter  14 , are Bayer pattern images, in which R images, G images (more specifically, Gr images which are alternately arranged with R images and constitute a single line, and Gb images which are alternately arranged with B images and constitute a single line), and B images are arranged, as illustrated in  FIG. 3 . 
         [0060]    Next, the image reconstruction processing section  15  administers an image reconstruction filtering process using the deconvolution filter  16  only onto data of the G channel, from among the data obtained for each of the R, G, and B channels (step S 2 ). The deconvolution filter  16  has properties inverse to the blur properties of the lens optical system, that is, the point spread function. By performing the filtering processing using the deconvolution filter  16  having such properties, image data that bear images in a focused state, in which blur has been resolved, are obtained. Note that this type of image reconstruction filter is described in detail in Japanese Unexamined Patent Publication No. 2009-089082 and E. R. Dowski, Jr. and W. T. Cathey, “Extended depth of field through wave-front coding”, Appl. Opt., Vol. 34, No. 11, pp. 1859-1866, 1995. Such a known image reconstruction filter may be employed in the present invention. 
         [0061]    Next, the image reconstruction processing section  15  performs a process to return the data, which have undergone the filtering process, to the Bayer pattern (step S 3 ). Data which have been returned to the Bayer pattern are illustrated in the third column of  FIG. 3 . The data, which have been returned to the Bayer pattern, are sent to the interpolation processing section  18  of  FIG. 1 . The interpolation processing section  18  administers an interpolation process onto the data in the Bayer pattern (step S 4 ). This process is generally referred to as a synchronizing process, and is a process that interpolates spatial shifts among color signals that occur due to color filter arrangement, to calculate color data for each point. Thereby, a three color image signal that represents data for each of three colors R, G, and B is obtained, as illustrated in the fourth column of  FIG. 3 . 
         [0062]    The three color image signal is sent to the image output section  20  of  FIG. 1 . A color image in which blur has been resolved can be obtained, by outputting an image based on the signal. Hereinafter, this point will be described in greater detail.  FIG. 4  is a diagram that schematically illustrates the relationships among light receiving sections of the color imaging element  13  and point spread of the lens optical system  12 . Note that here, R light receiving sections at which the R filters are arranged are denoted by the hatched squares, G light receiving sections (both Gr and Gb) at which the G filters are arranged are denoted by the white squares, and B light receiving sections at which the B filters are arranged are denoted by the dotted squares. 
         [0063]    The lens optical system  12  is that of which the point spreads satisfy the following conditions: 
         [0000]        G min.&gt;√2·( Pb−Ab/ 2)
 
         [0000]        R max.&lt;2 Pb−Ab/ 2 
         [0000]        B max.&lt;2 Pb−Ab/ 2 
         [0064]    wherein 
         [0065]    Pb: pitch of the light receiving sections of the Bayer pattern color imaging element (in the horizontal and vertical directions); 
         [0066]    Ab: the aperture width of the light receiving sections of the Bayer pattern color imaging element; 
         [0067]    Gmin.: the minimum radius of the point spread in the G wavelength; 
         [0068]    Rmax.: the maximum radius of the point spread in the R wavelength; and 
         [0069]    Bmax.: the maximum radius of the point spread in the B wavelength. 
         [0070]    That is, the point spread of the lens optical system  12  is of a size between the large diameter circle and the small diameter circle illustrated in  FIG. 4 . As described previously, in the case that Pb=1.4 μm and Ab=1.2 μm, Gmin.&gt;1.13 μm, Rmax.&lt;2.2 μm, and Bmax&lt;2.2 μm. 
         [0071]    By employing the lens optical system  12  having the properties as described above, the point spread expands across a plurality of light receiving sections for the G light receiving sections, which particularly contribute to the generation of brightness signals. The image reconstruction filtering process is administered onto data from the G light receiving sections, that is, data of the G channel. Thereby, image data that represent images in which blur has been resolved, and which are in a focused state regardless of distances to subjects, are obtained. 
         [0072]    In contrast, as can be understood from  FIG. 4 , the point spread does not expand across a plurality of light receiving sections for the R light receiving sections and the B light receiving sections, which contribute little to the generation of brightness signals. In addition, data from the R and B channels that contribute little to brightness signals do not greatly influence perceived resolution of color images. Therefore, blur does not particularly stand out in ultimately obtained color images compared to cases in which the filtering process is administered onto data from all color channels, even if the image reconstruction filtering process is not administered onto data from the R and B channels. By omitting administration of the filtering process for data of the R and B channels, the calculation processing costs are reduced as a whole. 
         [0073]    The embodiment described above employs the single chip color imaging element  13  equipped with the Bayer pattern color filter. The present invention may be applied to imaging means equipped with color filters of other arrangements as well. Hereinafter, a case in which a color imaging element equipped with R, G, and B color filters in a honeycomb pattern is employed will be described with reference to  FIG. 5 . 
         [0074]      FIG. 5  is a diagram that schematically illustrates the relationships among light receiving sections of the color imaging element having R, G, and B filters in a honeycomb pattern and point spread of a lens optical system. Note that here, R light receiving sections at which the R filters are arranged are denoted by the hatched octagons, G light receiving sections (both Gr and Gb) at which the G filters are arranged are denoted by the white octagons, and B light receiving sections at which the B filters are arranged are denoted by the dotted octagons. 
         [0075]    Here, the lens optical system satisfies the following conditions with respect to point spreads: 
         [0000]        G min.&gt; Ph−Ah/ 2 
         [0000]        R max.&lt;√2·( Ph−Ah/ 2)
 
         [0000]        B max.&lt;√2·( Ph−Ah/ 2)
 
         [0076]    wherein 
         [0077]    Ph: pitch of the light receiving sections of the honeycomb pattern color imaging element (in the horizontal and vertical directions); 
         [0078]    Ah: the aperture width of the light receiving sections of the honeycomb pattern color imaging element; 
         [0079]    Gmin.: the minimum radius of the point spread in the G wavelength; 
         [0080]    Rmax.: the maximum radius of the point spread in the R wavelength; and 
         [0081]    Bmax.: the maximum radius of the point spread in the B wavelength. 
         [0082]    That is, the point spread in this case is of a size between the large diameter circle and the small diameter circle illustrated in  FIG. 5 . As described previously, in the case that Ph=2.5 μm and Ah=1.5 μm, Gmin.&gt;1.75 μm, Rmax.&lt;2.47 μm, and Bmax&lt;2.47 μm. 
         [0083]    By employing the lens optical system having the properties as described above, the point spread expands across a plurality of light receiving sections for the G light receiving sections, which particularly contribute to the generation of brightness signals in this case as well. The image reconstruction filtering process is administered onto data from the G light receiving sections, that is, data of the G channel. Thereby, image data that represent images in which blur has been resolved, and which are in a focused state regardless of distances to subjects, are obtained. 
         [0084]    In contrast, as can be understood from  FIG. 5 , the point spread does not expand across a plurality of light receiving sections for the R light receiving sections and the B light receiving sections, which contribute little to the generation of brightness signals. In addition, data from the R and B channels that contribute little to brightness signals do not greatly influence perceived resolution of color images, as described previously. Therefore, in this case as well, blur does not particularly stand out in ultimately obtained color images compared to cases in which the filtering process is administered onto data from all color channels, even if the image reconstruction filtering process is not administered onto data from the R and B channels. By omitting administration of the filtering process for data of the R and B channels, the calculation processing costs are reduced as a whole. 
         [0085]    Next, a case in which a color imaging element equipped with R, G, and B color filters in a clear bid pattern is employed will be described with reference to  FIG. 6 .  FIG. 6  is a diagram that schematically illustrates the relationships among light receiving sections of the color imaging element having R, G, and B filters in a clear bid pattern and point spread of a lens optical system. Note that here, R light receiving sections at which the R filters are arranged are denoted by the hatched octagons, G light receiving sections (both Gr and Gb) at which the G filters are arranged are denoted by the white octagons, and B light receiving sections at which the B filters are arranged are denoted by the dotted octagons. 
         [0086]    Here, the lens optical system satisfies the following conditions with respect to point spreads: 
         [0000]        G min.&gt;( Pc/√ 2)− Ac/ 2
 
         [0000]        R max.&lt;2 Pc−Ac/ 2 
         [0000]        B max.&lt;2 Pc−Ac/ 2 
         [0087]    wherein 
         [0088]    Pc: pitch of the light receiving sections of the clear bid pattern color imaging element (in the horizontal and vertical directions); 
         [0089]    Ac: the aperture width of the light receiving sections of the clear bid pattern color imaging element; 
         [0090]    Gmin.: the minimum radius of the point spread in the G wavelength; 
         [0091]    Rmax.: the maximum radius of the point spread in the R wavelength; and 
         [0092]    Bmax.: the maximum radius of the point spread in the B wavelength. 
         [0093]    That is, the point spread in this case is of a size between the large diameter circle and the small diameter circle illustrated in  FIG. 6 . As described previously, in the case that Pc=2.5 μm and Ac=1.5 μm, Gmin.&gt;Rmax.&lt;4.25 μm, and Bmax&lt;4.25 μm. 
         [0094]    By employing the lens optical system having the properties as described above, the point spread expands across a plurality of light receiving sections for the G light receiving sections, which particularly contribute to the generation of brightness signals in this case as well. The image reconstruction filtering process is administered onto data from the G light receiving sections, that is, data of the G channel. Thereby, image data that represent images in which blur has been resolved, and which are in a focused state regardless of distances to subjects, are obtained. 
         [0095]    In contrast, as can be understood from  FIG. 6 , the point spread does not expand across a plurality of light receiving sections for the R light receiving sections and the B light receiving sections, which contribute little to the generation of brightness signals. In addition, data from the R and B channels that contribute little to brightness signals do not greatly influence perceived resolution of color images, as described previously. Therefore, in this case as well, blur does not particularly stand out in ultimately obtained color images compared to cases in which the filtering process is administered onto data from all color channels, even if the image reconstruction filtering process is not administered onto data from the R and B channels. By omitting administration of the filtering process for data of the R and B channels, the calculation processing costs are reduced as a whole.