Abstract:
A solid state imaging device comprises a semiconductor substrate defining a two-dimensional surface, a plurality of photoelectric conversion elements disposed in a light receiving area of said semiconductor substrate in a plurality of rows and columns, color filters in a plurality of colors, each color filter being arranged in correspondence with each photoelectric conversion element, wherein at least a color defining resolution corresponds to two photoelectric conversion elements adjacent to each other in a horizontal direction or in a vertical direction, a vertical electric charge transferring device that vertically transfers signal electric charges generated by the photoelectric conversion elements, a horizontal electric charge transfer device that horizontally transfers the signal electric charges transferred by the vertical electric charge transferring device, and an output device that outputs the signal electric charges transferred by the horizontal electric charge transferring device.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Japanese Patent Application 2004-038266, filed on Jul. 29, 2004, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     A) Field of the Invention 
     This invention relates to a solid state imaging device, especially to a structure of a solid state imaging device for a digital still camera. 
     B) Description of the Related Art 
     Recently the number of pixels in a digital still camera (hereinafter called DSC) follows a course of increase, and there is a DSC having over ten million pixels. It is obvious that an increase in the number of pixels leads to improvement of resolution; however, it also leads to various problems. For example, a quantity of output data will increase, a reading time for one frame (screen) becomes longer and a frame rate will be lowered. in order to prevent the lowering of the frame rate, it is necessary for the DSC to be driven faster (to have a high frame rate). Moreover, for example, increase in the number of pixels means that increase in a quantity of data to be stored; therefore, it causes increase in a size of a storage medium. Furthermore, a pixel size becomes smaller to increase the number of pixels without enlarging a size of a chip in the solid-state imaging device, and It lowers sensitivity of the solid-state imaging device, which is the most important feature of the solid state imaging device. Further, it will be difficult to generate a high quality motion picture (e.g., VGA quality) at a proper frame rate (e.g., 30 fps). 
     Generally an image taken by the DSC will be printed onto L-size (89×127 mm) photo paper, 4×6″ photo paper or a post card. The number of pixels sufficient for realizing necessary resolution to print the image onto such papers is two to three millions. Therefore, it is wasteful to take a picture for the papers in those sizes by using a solid-state imaging device having ten million pixels in its maximum performance, and it further causes decrease in resolution and in quality of a motion picture. 
       FIG. 9  is a schematic plan view of a conventional solid state imaging device  800 . 
     The solid state imaging device  800  is the most commonly used interlace-type CCD (ITCCD) as a conventional solid state imaging device, A large number of photoelectric conversion elements (pixels)  812  are arranged in a tetragonal matrix in a light receiving region  802 . A vertical electric charge transfer device (vertical charge coupled device: VCCD)  814  that reads out signal charges generated at the photoelectric conversion elements  812  and vertically transfers is formed including transfer electrodes and a vertical transfer channel for each column of the photoelectric conversion elements  812  and transfers the signal charges generated at photoelectric conversion elements  812  in a vertical direction. 
     In the drawing, a horizontal electric charge transfer device (horizontal charge coupled device: HCCD)  803  that transfers electric charges transferred by the VCCD  814  to a peripheral circuit  804  line by line is formed under the light receiving region  802 . Also, pixel lines on lines indicated with white arrows are first field lines in an interlace scanning method, and pixel lines on lines indicated with black arrows are second field lines. 
     A color filter arrangement corresponding to each pixel is presented with letters “R, G and B” in each pixel. Here in this specification, R, G and B respectively indicate red, green and blue. The color filter arrangement adopted in this solid state imaging device  800  is so-called Bayer arrangement and generally used for the solid state imaging device as an imaging device for a digital still camera (DSC). 
     In, the DSC, image information is extracted in the form of an electric signal; therefore, it is comparatively easy to generate a motion picture by reading out field images continuously. It is common to display the motion picture on a liquid crystal display monitor, which corresponds to a finder of a conventional camera, by using the above-described feature. 
     At least 15 fps is necessary to smoothly express a motion of a target. Further to enjoy displaying the motion picture on a TV screen, 30 fps is necessary. However, as described in the above, it will be hard to read signals at a high frame rate when the number of pixels is increased for high resolution. Although a line curtailed operation in which a signal line is not read out at a predetermined interval to solve the problem, it may not be an efficient way because the line curtailed operation wastes the expressly taken signal electric charges. Therefore, it is efficient if the effective number of pixels can be reduced by adding the signals without curtailing the signal lines. That is, an adding operation reduces the number of signal pixels to increase quantity of signal for one pixel so that higher resolution can be realized. 
       FIG. 10A  to  FIG. 10D  are diagrams showing signal arrangements read by the conventional ITCCD solid state imaging device  800 . 
       FIG. 10A  is a diagram shoving a signal arrangement of the first field, and FIG. l 0 B is a diagram showing a signal arrangement of the second field. Both of the first field and the second field add same colored signals in every two lines. As a result, as shown in  FIG. 10C , a signal arrangement of a vertical two-pixel addition field synthesized frame generated by synthesizing each field after the vertical addition can be obtained. Moreover, the conventional reading method for the ITCCD cannot reproduce a colored motion picture. Because each field includes only two types of signals such as G and R color signals or G and B color signals, one field cannot generate color signals including all of R, G, and B color signals. Since the color signal including R, G and B can be naturally generated after the field synthesis, the color signal after the synthesis, for example, can be used for a still picture with decreased number of pixels. In this case, sensitivity will be about twice by the addition of the signals. 
       FIG. 10D  is a diagram showing spatial sampling centers after the vertical additions. The sampling points of G formed by the vertical addition of the first field with the Bayer Arrangement will be on lines indicated by white arrows, and the sampling points of G formed by the vertical addition of the second field with the Bayer Arrangement will be on lines indicated by black arrows. As obvious from the drawing, the sampling centers of the G signals after the vertical additions do not have regular intervals. Also, since the spatial sampling centers overlap with each another in wide areas, resolution obtained for the number of the sampling points will be lowered. 
       FIG. 11  is a schematic plan view of a conventional solid state imaging device  200 . 
     The solid state imaging device  200  is composed including a light receiving region  202  including a large number of photoelectric conversion elements  212  and vertical electric charge transfer devices (VCCD)  214  that vertically transfer signal charges generated at the photoelectric conversion elements  212 , a horizontal electric charge transfer device (HCCD)  203  that horizontally transfers the signal charges transferred by the VCCDs  214  and an output amplifier  204 . 
     The light-receiving region  202  in the imaging device adopting the pixel interleaved array CCD (PIACCD) as shown in the drawing consists of the plurality of photoelectric conversion elements configured in a pixel interleaved arrangement. Between each row of the photoelectric conversion elements, a vertical electric charge transfer device  214  which reads the signal electric charges generated by the photoelectric conversion elements  212  and transfers them to a vertical direction are arranged by traversing in the spaces among the photoelectric conversion elements  212  in the vertical direction. Transfer channels are positioned in the zigzag spaces formed by the pixel interleaved arrangement, and the adjacent transfer channels apart from each ether via the photoelectric conversion elements and come closer to each other via the channel stop region (not shown in the drawing). For example, the details of the pixel interleaved arrangement can be found in Japanese Laid-Open Patent Hei 10-136391 and Tetsuo Yamada, et al, February, 2000, “A Progressive Scan CCD Irnager for DSC Applications”, ISSCC Digest of Technical Papers, Page 110 to 111. 
     The vertical electric charge transfer device  214  is consisted of the vertical transfer channel (not shown in the drawing) and transfer electrodes which are formed over the vertical transfer channel via an insulating film (not shown in the drawing) and traversing between the photoelectric conversion elements  212  to the horizontal direction. 
     In the drawing, the color of the color filter (for example, green, blue or red) corresponding to each pixel is indicated by the letter G, B and R in each of the pixels  212 . Also, pixel lines on lines indicated with white arrows are first field lines in the interlace scanning method, and pixel lines on lines indicated with blacks arrow are second field lines. 
     In the PIACCD shown in the drawing, the improved addition disclosed in Japanese Patent Application No. 2004-38266, filed by the same inventor as the present invention can be carried out. When the signals for the first field lines are read, the first G-line and the second G-line, and the fifth G-line and the sixth G-line are read. When the signals for the second field lines are read, the third G-line and the fourth G-line, the seventh G-line and the eighth G-line are read. As shown in the drawing, each G-line is formed along a solid line repeatedly connecting a center of each pixel in a zigzag form. 
       FIG. 12A  to  FIG. 12D  are diagrams showing signal arrangements read by the conventional PIACCD solid state imaging device  200 . 
       FIG. 12A  is a diagram showing a signal arrangement of the first field, and  FIG. 12B  is a diagram showing a signal arrangement of the second field. G-lines adjoining each other to vertical direction exist in each field. These adjoining G-lines are added vertically. That is, the first G-lines and the second G-lines, the fifth G-lines and the sixth G-lines are respectively added in the first field, and the third G-lines and the fourth G-lines, and the seventh G-lines and the eighth G-lines are respectively added in the second field. As a result, as shown in  FIG. 12C , a signal arrangement of a vertical two-pixel addition field synthesized frame generated by synthesizing each field after the vertical additions can be obtained. 
       FIG. 12D  is a diagram showing spatial sampling centers after the vertical additions. In this embodiment, because the G-lines (the signals of the G-pixels) that are originally vertically adjoining are added, centers of the sampling points of G in a vertical direction after the field synthesis will be on a line indicated by white arrows after the vertical addition for the first field and on lines indicated by black arrows after the vertical addition for the second field. Therefore, as shown in  FIG. 12D , the centers of the sampling points are arranged with regular vertical intervals. 
     In this improved addition, the vertical resolution is reduced half. Further, regarding to the horizontal addition, the resolution of G will be less than half. The resolutions of R and B will be also less than half. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solid state imaging device that can execute signal addition with minimum decrease in horizontal and vertical resolution by adding pixel signals while original resolution is not sacrificed. 
     According to one aspect of the present invention, there is provided a solid state imaging device comprising: a semiconductor substrate defining a two-dimensional surface; a plurality of photoelectric conversion elements disposed in a light receiving area of said semiconductor substrate in a plurality of rows and columns; color filters in a plurality of colors, each color filter being arranged in correspondence with each photoelectric conversion element, wherein at least a color defining resolution corresponds to two photoelectric conversion elements adjacent to each other in a horizontal direction or in a vertical direction; a vertical electric charge transferring device that vertically transfers signal electric charges generated by the photoelectric conversion elements; a horizontal electric charge transfer device that horizontally transfers the signal electric charges transferred by the vertical electric charge transferring device; and an output device that outputs the signal electric charges transferred by the horizontal electric charge transferring device. 
     According to the present invention, there is provided a solid state imaging device that can execute signal addition with minimum decrease in horizontal and vertical resolution by adding pixel signals while original resolution is not sacrificed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view of a solid state imaging device  100  according to a first embodiment of the present invention. 
         FIG. 2A  to  FIG. 2C  are diagrams for explaining horizontal pixel addition according to the first embodiment of the present invention. 
         FIG. 3A  to  FIG. 3C  are diagrams for explaining horizontal pixel addition according to a second embodiment of the present invention. 
         FIG. 4A  to  FIG. 4C  are diagrams for explaining a first example of horizontal pixel addition according to a third embodiment of the present invention. 
         FIG. 5A  to  FIG. 5C  are diagrams for explaining a second example of horizontal pixel addition according to the third embodiment of the present invention. 
         FIG. 6  is a plan view showing the light reviving region  2  for explaining horizontal pixel addition according to a fourth embodiment of the present invention. 
         FIG. 7A  and  FIG. 7B  are diagrams for explaining 4-pixel addition according to a first modified example of the first embodiment of the present invention. 
         FIG. 8A  and  FIG. 8B  are diagrams for explaining 4-pixel addition according to a second modified example of the first embodiment of the present invention. 
         FIG. 9  is a schematic plan view of a conventional solid state imaging device  800 . 
         FIG. 10A  to  FIG. 10D  are diagrams showing signal arrangements read by the conventional ITCCD solid state imaging device  800 . 
         FIG. 11  is a schematic plan view of a conventional solid state imaging device  200 . 
         FIG. 12A  to  FIG. 12D  are diagrams showing signal arrangements read by the conventional PIACCD solid state imaging device  200 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a schematic plan view of a solid state imaging device  100  according to a first embodiment of the present invention. 
     A solid state imaging device  100  at least includes a receiving region  2  having a large number of photoelectric conversion elements  12  and a vertical electric charge transfer device (vertical charge coupled device: VCCD)  14  that vertically transfers signal charge generated by the photoelectric conversion elements  12 , a horizontal adding line memory  20 , a horizontal addition circuit  23  including an eight-phase driven horizontal electric charge transfer device (horizontal charge coupled device: HCCD) that horizontally transfers the signal charge transferred by the VCCD)  14  and an output amplifier  4 . Further, the contents of “DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS” in the specification of Japanese Patent Application No. 2000-295896 (Japanese Laid-Open Patent NO. 2002-112119) are herein incorporated by reference for structural details of the horizontal adding line memory  20  and the horizontal addition circuit  23 . 
     In every embodiment of the present invention, horizontal addition is carried out by using horizontal adding device consisted of the horizontal adding line memory  20  and the horizontal addition circuit  23 . 
     The light-receiving region  2  is consisted of the plurality of the photoelectric conversion elements  12  by configuring them in the so-called pixel interleaved arrangement or the honeycomb arrangement. The pixel interleaved arrangement used in this specification indicates an arrangement combining the first lattice of a two-dimensional tetragonal matrix and the second lattice of the two-dimensional matrix of which each lattice point is positioned at the center of the first lattice. For example, the photoelectric conversion elements  12  in the even numbered rows (lines) or columns and in the odd numbered rows (lines) or columns are shifted in the horizontal direction by about a half pitch of the photoelectric conversion elements  12 , and the photoelectric conversion elements  12  in the even numbered lines (rows or columns) and in the odd numbered lines (rows or columns) are shifted in the vertical direction by about a half pitch of photoelectric conversion elements  12 . Each row of the photoelectric conversion elements  12  includes the photoelectric conversion elements  12  in either one of the even numbered row and in the odd numbered row. Similarly, Each line of the photoelectric conversion elements  12  includes the photoelectric conversion elements  12  in either one of the even numbered line and in the odd numbered line. The pixel interleaved arrangement is one of the arrangement styles for arranging a multiplicity of the photoelectric conversion elements in a matrix having a plurality of rows and lines. 
     The phrase “about a half” represents a pitch including an exact half pitch and also a pitch regarded as substantially equal to the half pitch from the performance and image quality although this pitch is different from the exact half pitch because of manufacture tolerances, rounding errors of pixel positions caused from design or manufacturing of a mask or the like. 
     The vertical electric charge transferring device  14  that reads out the signal electric charges generated by the photoelectric conversion elements  12  and vertically transfers them are formed between columns of the photoelectric conversion elements  12  by vertically traversing between spaces of the photoelectric conversion elements  12 . Transfer channels are positioned in the zigzag spaces formed by the pixel interleaved arrangement, and the adjacent transfer channels apart from each other via the photoelectric conversion elements  12  and come closer to each other via the channel stop region. 
     The vertical electric charge transfer device  14  is consisted of the vertical transfer channel and transfer electrodes which are formed over the vertical transfer channel via an insulating film and traversing between the photoelectric conversion elements  12  to the horizontal direction. 
     A color filter is formed above each photoelectric conversion element  12 . In the drawing, G, B and R respectively indicate the color filter of green, blue and red. 
     In a first and second embodiments of the present invention, the color filters are arranged differently from the color filter arrangement of the solid-state imaging device  200  in  FIG. 11  but a unit of two R pixels adjacent to each other in the horizontal direction and a unit of two B pixels adjacent to each other in the horizontal direction are arranged alternatively in the horizontal and the vertical directions. Moreover, in a third embodiment of the present invention, a group of an R line and a B line binding a G line therebetween is arranged in a stripe in the horizontal direction (refer to  FIG. 4A ). Further, in a fourth embodiment of the present invention, the same color filter arrangement as in the solid-state imaging device  200  in  FIG. 11  is adopted as shown in  FIG. 5 . 
       FIG. 2A  to  FIG. 2C  are diagrams for explaining horizontal pixel addition according to the first embodiment of the present invention.  FIG. 2A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the horizontal addition according to the first embodiment of the present invention.  FIG. 2B  shows graphs for Nyquist&#39;s limits of colors without the horizontal addition, and  FIG. 2C  shows graphs for Nyquist&#39;s limits of colors with the horizontal addition. 
     The Green (G) pixels are arranged in a tetragonal matrix with an arrangement pitch p in the horizontal and the vertical directions; therefore, two-dimensional Nyquist&#39;s limits by outputting signals individually without addition are ½p in the horizontal and the vertical directions as shown in  FIG. 2B , and the Nyquist&#39;s limits in the horizontal and the vertical directions are same. The two-dimensional Nyquist&#39;s limit of each of the colors R, G and B is the reciprocal of twice a pitch (the arrangement pitch) p between adjacent pixels in the same color. Although a phase in the vertical direction is different from that in the horizontal direction, line pitches (vertical pitches) of the blue (B) pixels and the red (R) pixels are the arrangement pitch p as same as the horizontal pitches. Therefore, two-dimensional Nyquist&#39;s limits by outputting signals individually without addition are ½p in the horizontal and the vertical directions as shown in  FIG. 2B , and the Nyquist&#39;s limits in the horizontal and the vertical directions are same. As described above, the color filter arrangement according to the first embodiment can obtain the same resolution as in the conventional color filter arrangement shown in  FIG. 11  when the horizontal addition is not carried out. 
     Next, it will be explained that two pixels horizontally adjacent each other and enclosed in a rectangle in  FIG. 2A  are horizontally added. In the drawing, a black circle represents an added center of gravity of the G pixels, and a white circle represents an added center of gravity of the R pixels or B pixels. 
     In the first embodiment, phases of the added centers of gravity of the G pixels in an odd-numbered line and an even-numbered line are shifted by 180 degree; therefore, the horizontal pixel pitch (sampling pitch) of G after the addition will be p, and the Nyquist&#39;s limit in the horizontal direction will be ½p as similar to that without the addition. Since the addition is not carried out in the vertical direction, the two-dimensional Nyquist&#39;s limits are ½p in both of the horizontal and the vertical directions as shown in  FIG. 2C , and the Nyquist&#39;s limits in the horizontal and the vertical directions are same. Regarding to R and B, the horizontal pixel pitch (sampling pitch) after the addition will be 2p, and the two-dimensional Nyquist&#39;s limits will be ¼p in the horizontal direction and ½p in the vertical direction. That is, resolutions of R and B will be a half by the horizontal addition according to the first embodiment. 
     As described in the above, according to the first embodiment, although the resolutions of R and B become a half by the horizontal addition, the resolution of G, which substantially defines resolution of an output image, remains the similar resolution as in the resolution without the addition. Moreover, quantities of signals are doubled by the two-pixel addition; therefore, an effective sensitivity will be doubled. 
       FIG. 3A  to  FIG. 3C  are diagrams for explaining horizontal pixel addition according to a second embodiment of the present invention.  FIG. 3A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the horizontal addition according to the second embodiment of the present invention.  FIG. 3B  shows graphs for Nyquist&#39;s limits of colors without the horizontal addition, and  FIG. 3C  shows graphs for Nyquist&#39;s limits of colors with the horizontal addition according to the second embodiment. 
     In this second embodiment, the color filters are arranged in the same arrangement as in the first embodiment; therefore, the two-dimensional Nyquist&#39;s limits are similar to those in the first embodiment. 
     Next, it will be explained that two pixels horizontally adjacent each other and enclosed in a rectangle in  FIG. 3A  are horizontally added. In the drawing, a black circle represents an added center of gravity of the G pixels, and a white circle represents an added center of gravity of the R pixels or B pixels. 
     A difference between the first embodiment and the second embodiment is that spatial phases of the pixel arrangements of R and B at the time of the horizontal addition in a group of the first and the second R/B lines and a group of the third and the fourth R/B lines are shifted by 180 degrees. Since the phases are shifted by the pitch p, the horizontal pixel pitches (sampling pitches) of R and B after the addition will be p, and the two-dimensional Nyquist&#39;s limits in the horizontal and the vertical directions will be ½p as shown in  FIG. 3C , which are the similar to those without the addition. Therefore, by the horizontal addition according to the second embodiment, the resolutions of all the colors R, G and B remain similar to those without the addition. 
     As described in the above, according to the second embodiment, the resolutions of R, G and B remain the similar resolution as in the resolution without the addition. Moreover, quantities of signals are doubled by the two-pixel addition; therefore, an effective sensitivity will be doubled. 
       FIG. 4A  to  FIG. 4C  are diagrams for explaining a first example of horizontal pixel addition according to a third embodiment of the present invention.  FIG. 4A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the first example of the horizontal addition according to the third embodiment of the present invention.  FIG. 3B  shows graphs for Nyquist&#39;s limits of colors without the horizontal addition, and  FIG. 3C  shows graphs for Nyquist&#39;s limits of colors with the horizontal addition according to the first example of the third embodiment. 
     In the third embodiment of the present invention, a group of an R line and a B line binding a G line therebetween is arranged in a stripe in the horizontal direction. In this case, the two-dimensional Nyquist&#39;s limits without the addition are ½p in the horizontal direction and ¼p in the vertical direction that is the horizontal resolution is twice the vertical resolution. Regarding to this point, the conventional PIACCD solid state imaging device is superior to a balance of the horizontal and the vertical resolutions; however, it is very difficult to recognize the inferiority of the image by the third embodiment in the sizes of the paper such as the L-size, 4×6 or the post card when the solid state imaging device has ten millions pixels. Moreover, the difference is difficult to be recognized even in a A4 sized paper except a special imaging target. 
     Next, it will be explained that two pixels horizontally adjacent each other and enclosed in a rectangle in  FIG. 4A  are horizontally added. In the drawing, a black circle represents an added center of gravity of the G pixels, and a white circle represents an added center of gravity of the R pixels or B pixels. 
     In the third embodiment as similar to the first and the second embodiment, phases of the added centers of gravity of the G pixels in an odd-numbered line and an even-numbered line are shifted by 180 degree; therefore, the horizontal pixel pitch (sampling pitch) of G after the addition will be p, and the Nyquist&#39;s limit in the horizontal direction will be ½p as similar to that without the addition. 
     Regarding to R and B, the horizontal pixel pitch (sampling pitch) after the addition will be 2p by adding adjacent two pixels because it is the same situation as reducing the number of the pixels in the horizontal direction a half. Therefore, the two-dimensional Nyquist&#39;s limits will be ¼p in both of the horizontal and the vertical directions as shown in  FIG. 4C , and the horizontal resolution and the vertical resolution become similar to each other. These Nyquist&#39;s limits are similar to those obtained by so-called Bayer arrangement. 
     That is, by the first example of the horizontal addition according to the third embodiment, the similar resolutions as in the solid state imaging apparatus having the Bayer arranged half number of the pixels in the PIACCD solid state imaging apparatus. 
       FIG. 5A  to  FIG. 5C  are diagrams for explaining a second example of horizontal pixel addition according to the third embodiment of the present invention.  FIG. 5A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the second example of the horizontal addition according to the third embodiment of the present invention.  FIG. 3B  shows graphs for Nyquist&#39;s limits of colors without the horizontal addition, and  FIG. 3C  shows graphs for Nyquist&#39;s limits of colors with the horizontal addition according to the second example of the third embodiment. 
     In this second example, the color filters are arranged in the same arrangement as in the first example shown in  FIG. 4A ; therefore, the two-dimensional Nyquist&#39;s limits are similar to those in the first example shown in  FIG. 4B . 
     In this second example of the third embodiment, it is different from the first example that the spatial phases of each of horizontal adding combinations of R and B is shifted by 180 degrees. That is, the spatial phases of the sampling centers of the first R line and the second R line are shifted by 180 degrees. Moreover, the spatial phases of the sampling centers of the first B line and the second B line are shifted by 180 degrees. By horizontally adding under the combinations, the horizontal pixel pitches (sampling pitches) of R and B after the addition will be p, and the two-dimensional Nyquist&#39;s limits in the horizontal direction will be ½p. Therefore, decrease in the resolution by the horizontal addition can be restrained comparing to the first example of the third embodiment. 
     Moreover, quantities of signals are doubled by the two-pixel addition; therefore, an effective sensitivity will be doubled according to both of the first and second example of the third embodiment of the present invention. 
       FIG. 6  is a plan view showing the light reviving region  2  for explaining horizontal pixel addition according to a fourth embodiment of the present invention. 
     In the fourth embodiment, the color filters are arranged similarly to the conventional solid state imaging apparatus shown in  FIG. 11 , the spatial phases of the added centers of gravity of the G pixels, which substantially defines resolution of an output image, in an odd-numbered line and an even-numbered line are shifted by 180 degree as shown in  FIG. 6 . By adopting this type of combination, decrease in the resolution after the horizontal addition can be restrained even if the color filter arrangement of the conventional technique is adopted. 
       FIG. 7A  and  FIG. 7B  are diagrams for explaining 4-pixel addition according to a first modified example of the first embodiment of the present invention.  FIG. 7A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the horizontal addition according to the first modified example of the first embodiment of the present invention.  FIG. 7B  shows graphs for Nyquist&#39;s limits of colors with the 4-pixel addition according to the first modified example of the first embodiment. 
     In this modified example, the spatial phases of the added centers of gravity of the G pixels are agreed with each other horizontal lines. Therefore, the horizontal pixel pitch (sampling pitch) of G after the horizontal addition will be 2p, and the Nyquist&#39;s limit in the horizontal direction will be ¼p. In addition to that, the vertical pixel pitch (sampling pitch) of G after the vertical addition will also be 2p, and the Nyquist&#39;s limit in the vertical direction will be ¼p. Therefore, the two-dimensional Nyquist&#39;s limits will be ¼p in both of the horizontal and the vertical directions as shown in  FIG. 7B , and the horizontal resolution and the vertical resolution become similar to each other. 
     Regarding to R and B, the horizontal pixel pitch (sampling pitch) after the additions will be 2p in the horizontal direction and p and 3p alternatively in the vertical direction, which can be considered as about 2p by the average in terms of macro view. Therefore, the two-dimensional Nyquist&#39;s limits as shown in  FIG. 7B  can be obtained approximately. By this 4-pixel addition, the resolutions of R, G and B will be a half of those without the additions. Moreover, quantities of signals are multiplied by four by the four-pixel addition; therefore, an effective sensitivity will be four times that without the additions. 
       FIG. 8A  and  FIG. 8B  are diagrams for explaining horizontal pixel addition according to a second modified example of the first embodiment of the present invention.  FIG. 8A  is a schematic plan view of the light receiving region  2  showing combinations of the pixels in the horizontal addition according to the second modified example of the first embodiment of the present invention.  FIG. 8B  shows graphs for Nyquist&#39;s limits of colors with the horizontal addition according to the second modified example of the first embodiment embodiment. 
     In this second modified example, unlikely to the first modified example, phases of the added centers of gravity of the G pixels in an odd-numbered line and an even-numbered line are shifted by 180 degree; therefore, the horizontal pixel pitch (sampling pitch) of G after the addition will be p, and the Nyquist&#39;s limit in the horizontal direction will be ½p as similar to that without the addition. Other combinations are the same as in the first modified example. By doing that, an effective sensitivity can be four times that without the additions, and the resolution of G, which substantially defines resolution of an output image, remains the similar resolution as in the resolution without the additions. 
     As described in the above, according to the embodiments of the present invention, the horizontal two-pixel addition is carried out between two pixels adjacent to each other in the horizontal direction, and the addition of the pixels that substantially defines resolution of an output image (e.g., G pixels) are added by shifting the spatial phases of adjacent horizontal lines by 180 degrees. Therefore, decrease in the resolutions is restrained in the minimum degree and the image signal having the doubled sensitivity can be obtained. 
     Furthermore, signals of all the pixels can be output independently without the adding operations when higher resolution is needed whereas an image with improved sensitivity by adding pixels may be needed during normal shooting and when shooting in dark place. 
     Furthermore, signals of all the pixels can be output independently without the adding operations when higher resolution is needed whereas an image with improved sensitivity by adding pixels at the normal shooting and a shooting in a dark place. 
     Moreover, an image having much higher sensitivity can be output by increasing number of adding times. 
     Moreover, the embodiments have been explained by using the CCD-type solid state imaging device as examples, it is not limited to the CCD-type solid state imaging device. For example, a CMOS-type solid state imaging device can be adapted for the present invention. 
     The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It is apparent that various modifications, improvements, combinations, and the like can be made by those skilled in the art.