Abstract:
A color shooting solid state image pickup apparatus is composed by using a solid state image pickup device having a number of color pixels disposed in a plurality of rows and columns in a pixel shift layout with distributing at least one color-type color pixels in a square lattice pattern aligned in row and column directions and by using a video signal proceeding unit being able to perform interpolation processes using color information obtained from pixel signals output from the solid state image pickup device excepting one piece of color information obtained from pixel signals of the color pixels distributed in a square lattice pattern. A moving image having a smooth motion can be reproduced on a monitor even if the process performance of the video signal proceeding unit is not improved so much.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application is based on Japanese Patent Application 2000-398244, filed on Dec. 27, 2000, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   A) Field of the Invention 
   The present invention relates to a solid state image pickup apparatus for color image pickup using a solid state image pickup device of a charge coupled device (CCD) type, a metal oxide semiconductor (MOS) type or another type as an area image sensor, and more particularly to a solid state image pickup apparatus using a simultaneous single-plate type color image pickup device. 
   B) Description of the Related Art 
   Solid state image pickup apparatuses for color image pickup using solid state image pickup devices as area image sensors are prevailing nowadays. Such solid state image pickup apparatuses are used, for example, in digital cameras, in digital cameras built in personal computers, personal digital assistants or the like. 
   Color shooting solid state image pickup apparatuses are roughly classified into a single-plate type and a three-plate type according to their image pickup methods. Single-plate type solid state image pickup apparatuses are further classified into a frame sequential type which time sequentially picks up color image information of each color, and a concurrent type which picks up color image information of all colors at the same time. A general purpose solid state image pickup apparatus generally uses a concurrent single plate type solid state image pickup device (hereinafter simply called a “solid state image pickup device”). 
   A solid state image pickup device has about several hundred thousand to several million color pixels. Each color pixel includes one photoelectric conversion element made of, e.g., a photodiode and one color filter disposed above the photoelectric conversion element (before the element in a light incidence course). 
   A solid state image pickup device has a predetermined number of color pixels including at least three color-types each of which detects color information different from each other. Color information detected by each color pixel is dependent upon a color of the color filter. For example, in the solid state image pickup device using primary color filters, the color pixels are classified into three color-types of red, green and blue. In the solid state image pickup device using complementary color filters, the color pixels are classified into three to four color-types. The complementary color filters often constitute one color filter array together with green color filters. Color pixels are disposed in a square matrix layout or in a pixel shift layout. The “square matrix layout” used in this specification is intended to include a matrix layout having different numbers of rows and columns. 
   The “pixel shift layout” used in this specification is intended to mean a number of color pixels disposed in the following manner. Each color pixel in an odd number column is shifted in the column direction from each pixel in an even number column by about a half of the pitch between color pixels in the column, whereas each color pixel in an odd number row is shifted in the row direction from each pixel in an even number row by about a half of the pitch between color pixels in the row, and each column contains only color pixels of either the odd rows or even rows. The “pixel shift layout” is one example of the layouts of a number of color pixels disposed in a plurality of rows and columns in a matrix shape. 
   The term “about a half of the pitch of color pixels in the column” is intended to include a precise half as well as a substantial half. Although the substantial half is not a precise half because of manufacture errors, rounding errors of pixel arrangement caused by design or mask manufacture, this value can be regarded as substantially the half from the viewpoint of the total performance of a solid state image pickup device and the image quality. The term “about a half of the pitch of color pixels in the row” is also intended to include a precise half as well as a substantial half. 
   As light becomes incident upon a color pixel, electric charge corresponding to the quantity of incidence light is accumulated in the photosensitive conversion element. A solid state image pickup device can sequentially output signals corresponding to the charges accumulated in color pixels. Each of these signals is called a “pixel signal” in this specification. Each pixel signal contains color information of substantially one color only. 
   A solid state image pickup apparatus generates a number of pixel signals for reproducing an image by using pixel signals sequentially output from a solid state image pickup device. In this specification, each of the pixel signals for reproducing an image is called an “output pixel signal”. 
   In accordance with output pixel signals from the solid state image pickup apparatus, an image constituted of a number of pixels is reproduced on a monitor or by a printer. In this specification, each of the pixels is called a “reproduction pixel”. 
   Spatial mixing is generally used for full-color printing by a printer and for full-color display by a monitor. Spatial mixing can be realized by additive mixing or subtractive mixing. In most cases, additive mixing of red, green and blue is performed. One pixel of a full-color image formed by additive mixing includes red, green and blue colors information. Each reproduction pixel includes therefore red, green and blue colors information. 
   A color shooting solid state image pickup apparatus generates three output pixel signals per one reproduction pixel, i.e., a red output pixel signal containing red color information, a green output pixel signal containing green color information, a blue output pixel signal containing blue color information. Three output pixel signals of red, green and blue per one reproduction pixel are called a “set of output pixel signals”. 
   If a solid state image pickup device uses complementary color filters, complementary color information is converted into primary color information, prior to executing an interpolation process to be later described. 
   As described earlier, a pixel signal of a color pixel of a solid state image pickup device contains color information of substantially one color only. Therefore, of color information to be contained in one set of output pixel signals, two pieces of color information not obtained from the pixel signal of one color pixel are generated through interpolation processes using signals based on pixel signals of other color pixels. 
   For example, of the color information to be contained in one set of output pixel signals for a reproduction pixel corresponding to one particular green pixel of the solid state image pickup device, green color information is obtained from a signal based on a pixel signal of one green pixel, red color information is generated by interpolation process using signals based on pixel signals of a plurality of red pixels disposed near the green pixel, and blue color information is generated by interpolation process using signals based on pixel signals of a plurality of blue pixels near the green pixel. 
   Most of solid state image pickup apparatuses have functions of generating output pixel signals at a relatively high resolution and at a relatively low resolution. 
   For example, output pixel signals generated at a relatively high resolution are stored in a recording medium and then printed out by a printer or the like to reproduce a fine still image. The number of output pixels is, for example, equal to the number of effective pixels of the solid state image pickup device, e.g., several hundred thousand to several million pixels. 
   If a solid state image pickup device having a number of color pixels disposed in the pixel shift layout is used, it is possible to generate output pixel signals, by interpolation, corresponding to virtual pixels each of which arranged between adjacent two color pixels in each color pixel column or each color pixel row of the solid state image pickup device. In this case, output pixel signals corresponding to about twice as many reproduction pixels as the total number of color pixels (effective pixels) of the solid state image pickup device can be obtained. 
   Output pixel signals generated at a relatively low resolution are output to a monitor of the solid state image pickup apparatus or another apparatus to reproduce a still image or moving image. The number of output pixels depends upon the number of pixels of the monitor. 
   The number of pixels of a monitor is determined by various standards. For example, 176×144 (about twenty five thousand) pixels according to the Quarter Common Intermediate Format (QCIF), 352×288 (about one hundred thousand) pixels according to the Common Intermediate Format (CIF), 640×480 (about three hundred thousand) according to the Video Graphics Array (VGA), and 1280×960 (about one million and two hundred thirty thousand pixels according to the Super Extended Video Graphics Array (SXVGA). Other standards are also known. 
   In order to reproduce a moving image having a smooth motion, it is necessary to output a number of output pixel signals in the predetermined order at a high frame frequency. A high process performance is therefore necessary for a signal processing circuit which generates output pixel signals. As a result, the productivity of a solid state image pickup apparatus becomes lower and the manufacture cost of the apparatus becomes higher. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a solid state image pickup apparatus capable of generating output pixel signals by relatively simple signal processing. 
   According to one aspect of the present invention, there is provided a solid state image pickup apparatus comprising: a solid state image pickup device having a number of color pixels disposed in a plurality of rows and columns in a pixel shift layout and generating and outputting pixel signals, said number of color pixels including at least three kinds of color pixels, color pixels of one of said at least three kind being distributed in a square lattice pattern aligned in row and column directions; and a first signal processing unit for generating output pixel signals by using signals based on said pixel signals, said first signal processing unit generating a part of output pixel signals directly from signals based on pixel signals of the color pixels of said one kind and generating another part of output pixel signals through interpolation process using signals based on pixel signals of color pixels of another of said at least three kinds. 
   In this solid state image pickup apparatus, signals based on pixel signals of color pixels of one color-type distributed in the square lattice pattern is not subjected to an interpolation process, in generation of the output pixel signals. Of the red, green and blue color information to be contained in each set of output pixel signal, each of the color information of only two colors is generated by interpolation process. 
   Of the color information of three colors to be contained in one set of output pixel signals, the color information of one color can be obtained without performing the interpolation process. It is possible to obtain output pixel signals by relatively simple signal processing. 
   An image reproduced by a printer or on a monitor has reproduction pixels distributed in the square matrix shape. Therefore, it is desired that the output pixel signals from the solid state image pickup apparatus are in correspondence with the reproduction pixels distributed in the square matrix shape. 
   Although the color pixels of the solid state image pickup device of the solid state image pickup apparatus are distributed in the pixel shift layout, it is possible to generate output pixel signals corresponding to color pixels of one color-type distributed in the square lattice pattern in the solid-state image pickup device. Output pixel signals suitable for reproducing an image whose pixels are distributed in the square matrix shape can be generated by relatively simple signal processing. 
   The number of output pixels of the solid state image pickup apparatus is smaller than the total number of color pixels (effective pixels) of the solid state image pickup device. However, for example, in a conventional solid state image pickup apparatus capable of taking both a still image and a moving image, the number of output pixels of a moving image is generally smaller than that of a still image. Therefore, a reduction in the number of output pixels does not pose a substantial problem. 
   The solid state image pickup apparatus can be structured in the following manner. For example, output pixel signals for an image which may be reproduced at a relatively low resolution, such as an image to be reproduced on a monitor, are generated by the first signal processing unit, and output pixel signals for an image which is required to be reproduced at a relatively high resolution, such as a high definition still image, are generated by another signal processing unit. 
   In this specification, “color pixels distributed in the square lattice pattern” are intended to include different numbers of color pixels in the row and column and different pitches of color pixels in the row and column directions. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram showing a solid state image pickup apparatus according to a first embodiment of the invention. 
       FIG. 2  is a schematic plan view showing a solid state image pickup device usable by the solid state image pickup apparatus shown in  FIG. 1 . 
       FIG. 3A  is a schematic diagram showing the layout of color pixels of the solid state image pickup device shown in  FIG. 2 . 
       FIG. 3B  is a conceptual diagram illustrating an interpolation process for generating color information of red to be executed by a first signal processing unit of a video signal proceeding unit shown in  FIG. 1 . 
       FIG. 3C  is a conceptual diagram illustrating an interpolation process for generating color information of blue to be executed by the first signal processing unit of the video signal proceeding unit shown in  FIG. 1 . 
       FIG. 4  is a conceptual diagram showing a distribution of reproduction pixels of an image reproduced on a monitor or by a printer in accordance with output pixel signals generated by the first signal processing unit. 
       FIG. 5  is a conceptual diagram showing a distribution of reproduction pixels of an image reproduced on a monitor or by a printer in accordance with output pixel signals generated by a second signal processing unit. 
       FIG. 6  is a schematic plan view of another solid state image pickup device usable as the solid state image pickup apparatus shown in  FIG. 1 . 
       FIG. 7  is a block diagram conceptually showing an example of the structure of the video signal proceeding unit shown in  FIG. 1 . 
       FIG. 8  is a block diagram conceptually showing a first interpolation circuit shown in  FIG. 7 . 
       FIG. 9  is a schematic diagram showing the cross sectional structure, as viewed along a predetermined direction, of color pixels of a CCD type solid state image pickup device usable as the solid state image pickup device shown in  FIG. 2 . 
       FIG. 10  is a schematic diagram showing the cross sectional structure, as viewed along another direction, of color pixels of the CCD type solid state image pickup device usable as the solid state image pickup device shown in  FIG. 2 . 
       FIG. 11  is a schematic plan view showing the layout of photoelectric conversion elements, vertical charge transfer elements, read gates, a horizontal charge transfer element and an output amplifier in the solid state image pickup device shown in  FIGS. 9 and 10 . 
       FIG. 12  is a schematic plan view showing the layout of photoelectric conversion elements, vertical charge transfer elements, read gates, a horizontal charge transfer element and an output amplifier in another CCD type solid state image pickup device usable as the solid state image pickup device shown in  FIG. 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a schematic block diagram showing a solid state image pickup apparatus according to a first embodiment. As shown in  FIG. 1 , the solid state image pickup apparatus  100  has an image pickup optical system  1 , a solid state image pickup device  10 , a driver circuit  60 , a video signal proceeding unit  65 , a control unit  80 , a first mode selector  82 , a second mode selector  84 , a pulse signal generator  86 , a display unit  90 , a recording unit  92 , a transmission unit  94 , and a television output terminal (hereinafter abbreviated to a “TV output terminal”)  96 . 
   The image pickup optical system  1  focuses an optical image upon the solid state image pickup device  10 . For example, the image pickup optical system  1  includes optical lenses, a diaphragm, an optical low-pass filter and the like. An arrow L in  FIG. 1  represents light. 
   The solid state image pickup device  10  converts an optical image focused by the image pickup optical system  1  into electric signals. The solid state image pickup device  10  has a number of color pixels necessary for color image pickup and an output unit. The output unit outputs electric signals (pixel signals) representing to electric charge accumulated in the color pixels. The specific structure of the solid state image pickup device  10  will be later described with reference to  FIGS. 9 to 11 . 
   The driver circuit  60  supplies drive signals to the solid state image pickup device  10  for image pickup operation. For example, the driver circuit  60  is constituted of a vertical driver, a horizontal driver, a DC power source and the like. 
   The video signal proceeding unit  65  receives pixel signals generated by the solid state image pickup device  10 , and executes various processes for the pixel signals to generate output pixel signals. The generated output pixel signals are supplied to the display unit  90 , recording unit  92 , transmission unit  94  or TV output terminal  96 . 
   The video signal proceeding unit  65  includes a first signal processing unit for generating output pixel signals at a relatively low resolution and a second signal processing unit for generating output pixel signals at a relatively high resolution. The specific configuration of the video signal proceeding unit  65  will be later described with reference to  FIG. 7 . 
   The control unit  80  controls the operations of the driver circuit  60  and video signal proceeding unit  65 . The control unit  60  is made of, for example, a central processing unit (CPU). 
   The first mode selector  82  is a selection switch for selecting an image pickup mode of the solid state image pickup apparatus  100 . For example, the solid state image pickup apparatus  100  has a first image pickup mode for generating output pixel signals at a relatively low resolution and a second image pickup mode for generating output pixel signals at a relatively high resolution. For example, the first image pickup mode is suitable for shooting a moving image, and the second image pickup mode is suitable for shooting a high definition still image. The first mode selector  82  is operated by a user of the solid state image pickup apparatus  100 . 
   The second mode selector  84  is a selection switch for designating the destination of image pickup data (output pixel signals) of the solid state image pickup apparatus  100 . The solid state image pickup apparatus  100  can output the image pickup data to the display unit  90 , recording unit  92 , transmission unit  94  or TV output terminal  96 . The second mode selector  84  is also operated by a user of the solid state image pickup apparatus  100 . 
   The pulse signal generator  86  generates pulse signals for synchronizing the whole operations of various circuits, and supplies they to the driver circuit  60 , video signal proceeding unit  65  and control unit  80 . For example, the pulse signal generator  86  is constituted of an oscillator for generating pulses at a constant period, a timing generator and the like. 
   In accordance with output pixel signals supplied from the video signal proceeding unit  65 , the display unit  90  displays a still image or moving image. The display unit  90  may be a liquid crystal display unit or other display units. 
   The recording unit  92  stores output pixel signals supplied from the video signal proceeding unit  65  in a recording medium such as a memory card. 
   The transmission unit  94  converts output pixel signals supplied from the video signal proceeding unit  65  into a predetermined format (e.g., MPEG) and transmits the converted output pixel signals to a communication channel. For example, if the transmission unit  94  performs wired transmission, it has a format conversion unit connected to a modulator-demodulator (modem). For example, if the transmission unit  94  performs wireless transmission, it is constituted of a format conversion unit for converting the output pixel signals to transmission signal format, an oscillator circuit for generating the radio carrier wave, an antenna and the like. 
   The TV output terminal  96  is used for interconnection between the solid state image pickup apparatus  100  and a television (not shown) via a cable or the like. 
   In the solid state image pickup apparatus  100  having these constituent elements, color pixels of the solid state image pickup device  10  have a special layout. 
     FIG. 2  is a schematic diagram showing an example of a solid state image pickup device usable as the solid state image pickup device  10 . In a solid state image pickup device  10   a  shown in  FIG. 2 , three color-types of color pixels including red pixels  20 R, green pixels  20 G and blue pixels  20 B are disposed in the pixel shift layout and special patterns. 
   More specifically, the green pixel  20 G is disposed at every second rows and columns along the pixel column direction and pixel row direction, respectively, and the green pixels are disposed as a whole in a square lattice pattern. On both sides along the column direction of each green pixel row, a pixel row (hereinafter called a “red/blue pixel row”) is disposed which has a red pixel  20 R and a blue pixel  20 B disposed at every second columns. Two juxtaposed red/blue pixel rows sandwiching green pixel row have the reversed orders of the red pixels  20 R and blue pixels  20 B from each other. 
   In the solid state image pickup device  10   a , a pixel signal from a green pixel  20 G of the green pixel row and a pixel signal from a red pixel  20 R or a blue pixel  20 B of the red/blue pixel row downstream of the green pixel row are alternately output one pixel signal after another. For example, from the most downstream pixel row and the second most downstream pixel row, a pixel signal from the blue pixel  20 B, a pixel signal from the green pixel  20 G, a pixel signal from the red pixel  20 R, and a pixel signal from the green pixel  20 G are sequentially output in this order. 
   In this specification, assuming that transfer of a signal from a color pixel to the video signal proceeding unit is regarded as one flow, the relative position of each component is defined as “upstream of something” or “downstream of something”, when necessary. 
   As described earlier, the video signal proceeding unit  65  shown in  FIG. 1  generates output pixel signals in accordance with pixel signals supplied from the solid state image pickup device  10   a . While the first image pickup mode is selected by the first mode selector  82 , pixel signals supplied to the video signal proceeding unit  65  are converted to the output pixel signals through the first signal processing unit which generates the output pixel signals at the relatively low resolution. 
   The first signal processing unit does not subject color information (signals) obtained from pixel signals of the green pixels  20 G to an interpolation process for generating output pixel signals for reproduction pixels of a reproduction image. While each of the color information (signals) obtained from pixel signals of the blue and red pixels  20 B and  20 R is subjected to interpolation process in the first signal processing unit for generating the output pixel signals. The reproduction pixels are at the relatively corresponding position of the green pixels  20 G. 
   The concept of the interpolation processes by the first signal processing unit will be described with reference to  FIGS. 3A ,  3 B and  3 C. 
     FIG. 3A  is a schematic diagram showing the layout of color pixels of the solid state image pickup device  10   a . In  FIGS. 3A to 3C , a character G represents a green pixel, a character R represents a red pixel, and a character B represents a blue pixel. In order to simplify the identification of each pixel, the pixel rows and columns are numbered. 
   In the following description, each pixel is identified by using one of the characters R, G and B, one row number and one column number. For example, a “red pixel R 57 ” is a red pixel R at the fifth row and seventh column. 
     FIG. 3B  illustrates the concept of the interpolation process for generating color information of the red to be executed by the first signal processing unit. The circled character R in  FIG. 3B  represents red color information generated by interpolation process. 
   As shown in  FIG. 3B , red color information of a reproduction pixel to be contained in one set of output pixel signals corresponding to the position of the green pixel G (refer to  FIG. 3A ) is generated by interpolation process using color information obtained from pixel signals of two red pixels R on the upper left upstream side and lower right downstream side, or on the upper right upstream side and lower left downstream side. For example, red color information to be contained in one set of output pixel signals for a reproduction pixel corresponding to the position of the green pixel G 44  is generated by interpolation process using color information obtained from pixel signals of two red pixels R 53  and R 35 . Red color information to be contained in one set of output pixel signals for a reproduction pixel corresponding to the position of the green pixel G 64  is generated by interpolation process using color information obtained from pixel signals of two red pixels R 75  and R 53 . 
     FIG. 3C  illustrates the concept of the interpolation process for generating color information of the blue to be executed by the first signal processing unit. The circled character B in  FIG. 3C  represents blue color information generated by interpolation process. 
   As shown in  FIG. 3C , blue color information of a reproduction pixel to be contained in one set of output pixel signals corresponding to the position of the green pixel G (refer to  FIG. 3A ) is generated by interpolation process using color information obtained from pixel signals of two blue pixels B on the upper right upstream side and lower left downstream side, or on the upper left upstream side and lower right downstream side. For example, blue color information to be contained in one set of output pixel signals for a reproduction pixel corresponding to the position of the green pixel G 44  is generated by interpolation process using color information obtained from pixel signals of two blue pixels B 55  and B 33 . Blue color information to be contained in one set of output pixel signals for a reproduction pixel corresponding to the position of the green pixel G 64  is generated by interpolation process using color information obtained from pixel signals of two blue pixels B 73  and B 55 . 
   One set of output pixel signals corresponding to one reproduction pixel contains green color information obtained from a pixel signal of a green pixel G, and blue and red color information generated by the interpolation processes described above. 
     FIG. 4  is a conceptual diagram showing the relative distribution of reproduction pixels in an image reproduced on a monitor or by a printer in accordance with output pixel signals generated by the first signal processing unit. The row number and the column number shown in  FIG. 4  do not correspond to those in the reproduced image but to those in the solid state image pickup device  10   a.    
   As shown in  FIG. 4 , in an image reproduced from output pixel signals, reproduction pixels P are distributed in a square lattice pattern with corresponding to the positions of the green pixels G (refer to  FIG. 3A ) of the solid state image pickup device  10   a.    
   Of the red, green and blue color information to be contained in each reproduction pixel, the first signal processing unit generates only the blue and red color information by the interpolation processes. Green color information is not necessary to be obtained through interpolation process. Green color information is obtained directly from green information (signals) obtained from the pixel signals of green pixels. 
   Although a number of color pixels are disposed in the pixel shift layout in the solid state image pickup device  10   a , output pixel signals corresponding to the layout of reproduction pixels in the square matrix shape can be generated without performing a particular conversion process. 
   It is therefore possible to obtain predetermined output pixel signals by relatively simple signal processing. 
   Since the green color information is obtained without performing interpolation process, a time taken to obtain green color information to be contained in one set of output pixel signals is different from a time taken to obtain blue or red color information to be contained in the set of output pixel signals. If necessary, the green, blue and red color information to be contained in the set of output pixel signals is adjusted so as to be output from the video signal proceeding unit  65  at approximately the same timing. 
   This adjustment is possible, for example, by forming a delay circuit at a proper position in the transmission path of the pixel signals of the green pixels or in the transmission path of the green color information, or by disposing a storage unit such as a frame memory for storing the pixel signals of green, blue and red or color information of green, blue and red at a proper position in the first signal processing unit or outside the first signal processing unit. 
   The number of output pixels in the first image pickup mode is about a half of the number of effective pixels (color pixels) of the solid state image pickup device  10   a.    
   If the first mode selector  82  shown in  FIG. 1  selects the second image pickup mode, the video signal proceeding unit  65  can generate output pixel signals for reproduction pixels about twice as many as the total number of effective pixels (color pixels) of the solid state image pickup device  10   a.    
   In the second image pickup mode, in accordance with the concept same as that illustrated in  FIG. 3B  or  3 C, interpolation processes are executed for color information obtained from pixel signals of the green, blue and red pixels. In addition, output pixel signals for reproduction pixels corresponding to virtual color pixels are generated by the interpolation processes. Each of the virtual color pixels is arranged between two color pixels in each of the pixel columns and rows in the solid state image pickup device  10   a.    
     FIG. 5  is a conceptual diagram showing the distribution of reproduction pixels in an image reproduced on a monitor or by a printer in accordance with output pixel signals generated by the second signal processing unit. Since the output pixel signals for reproduction pixels corresponding to virtual color pixels are generated by the interpolation processes, an image reproduced from the output pixel signals generated by the second signal processing unit has reproduction pixels P about twice as many as the total number of effective pixels (color pixels) of the solid state image pickup device  10   a  (refer to  FIG. 2 ). 
   The solid state image pickup device  10  shown in  FIG. 1  is not limited only to a device using primary color filters, but it may be a device using complementary color filters. 
     FIG. 6  is a schematic diagram showing another example of a solid state image pickup device usable as the solid state image pickup device  10 . A solid state image pickup device  10   b  shown in  FIG. 6  uses complementary color filters and has three color-types of color pixels including cyan pixels  20 Cy, yellow pixels  20 Ye and green pixels  20 G disposed in the pixel shift layout and special patterns. 
   More specifically, the green pixel  20 G is disposed at every second rows and columns along the pixel column direction and pixel row direction, respectively, and the green pixels are disposed as a whole in a square lattice pattern. On both sides along the column direction of each green pixel row, a pixel row (hereinafter called a “cyan/yellow pixel row”) is disposed which has a cyan pixel  20 Cy and a yellow pixel  20 Ye disposed at every second columns. Two juxtaposed cyan/yellow pixel rows sandwiching the green pixel row have the reversed orders of the cyan pixels  20 Cy and yellow pixels  20 Ye from each other. 
   In the solid state image pickup device  10   b , a pixel signal from a green pixel  20 G of the green pixel row and a pixel signal from a cyan pixel  20 Cy or a yellow pixel  20 Ye of the cyan/yellow pixel row downstream of the green pixel row are alternately output one pixel signal after another. For example, from the most downstream pixel row and the second most downstream pixel row, a pixel signal from the yellow pixel  20 Ye, a pixel signal from the green pixel  20 G, a pixel signal from the cyan pixel  20 Cy, and a pixel signal from the green pixel  20 G are sequentially output in this order. 
   In use of the solid state image pickup device  10   b , prior to executing the interpolation processes already described with reference to  FIGS. 3A to 3C  and  FIGS. 4 and 5 , complementary color information is converted into primary color information. Without changing the structures of the first and second signal processing units, it is possible to generate output pixel signals similar to those of the solid state image pickup apparatus using the solid state image pickup device  10   a  shown in  FIG. 2 . 
   The video signal proceeding unit  65  having the first and second signal processing units may have the configuration such as shown in  FIG. 7 .  FIG. 7  is a conceptual block diagram showing an example of the configuration of the video signal proceeding unit  65 . The video signal proceeding unit  65  shown in  FIG. 7  has a correlation double sampling (CDS) circuit  66 , an automatic gain control (AGC) circuit  67 , a first switching circuit  68 , a first signal processing unit  70 , a second signal processing unit  77 , and a memory unit M such as a dynamic random access memory (DRAM). 
   Pixel signals sequentially output from the solid state image pickup device  10  are input to the CDS circuit  66  which eliminates noises of the pixel signals and then supplied via the AGC circuit  67  to the first switching circuit  68 . 
   If the solid state image pickup device  10  uses primary color filters, each of red, green and blue color information obtained from pixel signals is sequentially supplied to the first switching circuit  68 . All or a part of the color information is also supplied to the memory unit M to be stored and managed therein. 
   If the solid state image pickup device  10  uses complementary color filters, a complementary/primary color conversion circuit  69  is provided, for example, between the AGC circuit  67  and first switching circuit  68 . The complementary/primary color conversion circuit  69  temporarily stores complementary color information obtained from pixel signals of at least three color pixel rows in the memory unit M. Necessary complementary color information is read from the memory unit M to perform color separation and generate red, green and blue color information. The operation of the complementary/primary color conversion circuit  69  is controlled, for example, by the control unit  80  shown in  FIG. 1 . 
   The red, green and blue color information generated by the complementary/primary color conversion circuit  69  is sequentially supplied to the first switching circuit  68 . All or a part of the color information is supplied to the memory unit M to be stored and managed therein. 
   While the first mode selector  82  shown in  FIG. 1  selects the first image pickup mode, the red, green and blue color information sequentially supplied to the first switching circuit  68  is supplied to the first signal processing circuit  70 . The operation of the first switching circuit  68  is controlled, for example, by the control unit  80  shown in  FIG. 1 . 
   In the first signal processing unit  70 , the red color information R is supplied to a first interpolation circuit  71   a , the blue color information B is supplied to a second interpolation circuit  71   b , and the green color information G is supplied via a delay circuit  75  or directly to a second switching circuit  72 . The delay circuit  75  adjusts the arrival timing of the green color information G to the second switching circuit  72  so that the red, green and blue color information to be contained in one set of output pixel signals is supplied to the second switching circuit  72  at substantially the same timing. 
   As shown in  FIG. 8 , the first interpolation circuit  71   a  has an address signal generator AG and an interpolation operating circuit IP. The address signal generator AG is controlled by the control unit  80  and generates a predetermined address signal. In accordance with this address signal, red color information necessary for the interpolation process is read from the memory unit M, and supplied to the interpolation operating circuit IP. 
   By using red color information newly input from the first switching circuit  68  and red color information already stored in the memory unit M, the interpolation operating circuit IP performs an interpolation process such as described with  FIG. 3B  to generate red color information to be contained in a set of output pixel signals. 
   The second interpolation circuit  71   b  is configured in the manner similar to the first interpolation circuit  71   a  shown in  FIG. 8 . In accordance with a predetermined address signal generated by the address generator, the second interpolation circuit  71   b  reads blue color information necessary for the interpolation process from the memory unit M. The blue color information is supplied to the interpolation operating circuit. 
   By using blue color information newly input from the first switching circuit  68  and blue color information already stored in the memory unit M, the interpolation operating circuit performs an interpolation process such as described with  FIG. 3C  to generate blue color information to be contained in the output pixel signals. 
   In this manner, each of the first and second interpolation circuits  71   a  and  71   b  may be configured to read only one of two pieces of the color information necessary for the interpolation process, i.e., only the color information obtained from a pixel signal generated faster in the time axis, from the memory unit M and is supplied with the other color information from the first switching circuit  68 . 
   Each of the first and second interpolation circuits  71   a  and  71   b  may be configured so that two pieces of color information necessary for the interpolation process are read from the memory unit M. In this case, the first switching circuit  68  is not necessary to be wired to the first and second interpolation circuits  71   a  and  71   b.    
   The red color information generated by the first interpolation circuit  71   a  and blue color information generated by the second interpolation circuit  71   b  are supplied to the second switching circuit  72  (refer to  FIG. 7 ). 
   The second switching circuit  72  supplies the color information to an output destination selected by the second mode selector  84  shown in  FIG. 1 . 
   If the output destination of the color information is the display unit  90  (refer to  FIG. 1 ), the color information is supplied, for example, directly to the display unit  90 . If the output destination is the recording unit  92  or transmission unit  94 , the color information is supplied, for example, to a first compression circuit  73   a  whereat the information is compressed and then supplied to the recording unit  92  or transmission unit  94 . If the output destination is the TV output terminal  96 , the color information is supplied to a Y/C conversion circuit  74  whereat the color information is converted into luminance signals Y and color difference signals C which are then supplied to the TV output terminal  96 . 
   While the first mode selector  82  shown in  FIG. 1  selects the second image pickup mode, red, green and blue color information sequentially supplied to the first switching circuit  68  is supplied to the second signal processing unit  77 . 
   In the second signal processing unit  77 , the red color information R is supplied to a third interpolation circuit  71   c , the blue color information B is supplied to a fourth interpolation circuit  71   d , and the green color information G is supplied to a fifth interpolation circuit  71   e.    
   Each of the third to fifth interpolation circuits  71   c  to  71   e  can be configured in the similar manner to the first interpolation circuit  71   a , and the operation thereof is similar to that of the first interpolation circuits  71   a.  The operation of each of the third to fifth interpolation circuits  71   c  to  71   e  will be described briefly. 
   The third interpolation circuit  71   c  performs an interpolation process by using two to four pieces of red color information obtained from two to four pixel signals of red color pixels per one reproduction pixel to generate red color information to be contained in the output pixel signals. Reproduction pixels are disposed in the square matrix shape such as shown in  FIG. 5 . 
   Similarly, the fourth interpolation circuit  71   d  generates blue color information to be contained in the output pixel signals by the interpolation process, and the fifth interpolation circuit  71   e  generates green color information to be contained in the output pixel signals by the interpolation process. 
   The color information generated by the third to fifth interpolation circuits  71   c  to  71   e  is supplied to a second compression circuit  73   b  whereat the information is compressed and supplied to one of the display unit  90 , recording unit  92  and transmission unit  94  in accordance with the output destination selected by the second mode selector  84 . The solid state image pickup apparatus  100  may be structured in such a manner that the output from the second compression circuit  73   b  can be supplied to the TV output terminal  96 . 
   The solid state image pickup device  10  for generating pixel signals which are supplied to the image signal proceeding unit  65  is, for example, a CCD type or MOS type solid state image pickup device. 
     FIGS. 9 and 10  are schematic diagrams showing the structure of a color pixel of a CCD type solid state image pickup device  10   c  usable as the solid state image pickup device  10   a  shown in  FIG. 2 .  FIG. 9  is a schematic cross sectional view taken along line IX—IX shown in  FIG. 2 , and  FIG. 10  is a schematic cross sectional view taken along line X—X shown in  FIG. 2 . In  FIGS. 9 and 10 , the scales in the direction perpendicular to the thickness direction of the solid state image pickup device  10   c  are made different for convenience. 
   As shown in  FIGS. 9 and 10 , each of the color pixels  20 R,  20 G and  20 B has a photoelectric conversion element (photodiode)  22  formed in one surface of a semiconductor substrate  15  and a corresponding one of color filters  34 R,  34 G and  34 B disposed above the photoelectric conversion element  22  (before the element  22  in the light incidence course). By disposing a micro lens  38  for each  25  photoelectric conversion element  22  thereabove, the light use efficiency of the photoelectric conversion element  22  can be improved. 
   In the example shown in  FIGS. 9 and 10 , the semiconductor substrate  15  is constituted of an n-type semiconductor substrate  15   a  and a p-type impurity doped region  15   b  formed in the surface of the substrate  15   a.    
   Each photoelectric conversion element  22  has an n-type impurity doped region  22   a  and a p + -type impurity doped region  22   b  disposed on the region  22   a . A p-type impurity concentration in the p + -type impurity doped region  22   b  is higher than that of the p-type impurity doped region  15   b.    
   A channel stopper region  24  is formed surrounding the outer periphery of each photoelectric conversion element  22  as viewed in plan, excepting the regions where read gate regions  48   a  are formed as shown in  FIG. 10 . For example, the channel stopper region  24  is made of a p+-type impurity doped region. 
   As will be later described, one read gate region  48   a  is disposed for each photoelectric conversion element  22 . The read gate region  48   a  is formed in the lower right area of associated photoelectric conversion element  22  as viewed in plan and adjoined to the element  22 . 
   An electrically insulating layer  26  made of silicon oxide or the like is formed on the surface (surfaces of the impurity doped regions) of the semiconductor substrate  15 , and a passivation (protection) layer  28  is formed on the insulating layer  26 . For example, the passivation layer  28  is made of silicon nitride, silicon oxide, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), polyimide or the like. This passivation layer also covers each vertical charge transfer element  40  to be described later. 
   A light shielding layer  30  covers each vertical charge transfer element  40  and the inner peripheral area, as viewed in plan, of the photoelectric conversion element  22  near the vertical charge transfer element  40 . The light shielding layer  30  has an opening  30   a  disposed for each photoelectric conversion element  22  thereabove. The surface of each photoelectric conversion element  22  in the opening  30   a , as viewed in plan, is a light incidence plane. 
   The light shielding layer  30  is made of: a metal thin layer of aluminum, chromium, tungsten, titanium, molybdenum or the like; an alloy thin layer of two or more of these metals; a multi-layer of metal thin layers; a multi-layer of two or more selected from a group consisting of the metal thin layers and alloy thin layers. 
   A first planarizing layer  32  covers the light shielding layer  30  and the passivation layer  28  exposed in the openings  30   a . The first planarizing layer  32  may be also used as a focus adjusting layer for the micro lenses  38 . If necessary, inner lenses are formed in the first planarizing layer  32 . 
   For example, the first planarizing layer  32  is formed by spin-coating transparent resin such as photoresist to a desired thickness. 
   Color filters  34 R,  34 G and  34 B are formed on the first planarizing layer  32 . For example, each of the color filters  34 R,  34 G and  34 B is formed by forming resin (color resin) layer containing pigment or dye of desired color on the first planarizing layer  32  in predetermined areas by photolithography. 
   A second planarizing layer  36  covers the color filters  34 R,  34 G and  34 B. For example, the second planarizing layer  46  is formed by spin-coating transparent resin such as photoresist to a desired thickness. 
   Each micro lens  38  is formed on the second planarizing layer  36 . For example, these micro lenses  38  are formed by patterning a layer of transparent resin (including photoresist) having a refractive index of about 1.3 to 2.0 into sections having a predetermined shape by photolithography, melting each section of the transparent resin by heat treatment, rounding the sides by the surface tension, and then cooling them. One section corresponds to one micro lens. 
   As light becomes incident upon each of the color pixels  20 R,  20 G and  20 B, electric charge corresponding to the quantity of the incident light is accumulated in the n-type impurity doped region  22   a . Each column of color pixels disposed in the pixel shift layout is provided with the vertical charge transfer element  40  made of CCD in order to read the charges from corresponding ones of the color pixels  20 R,  20 G and  20 B and transfer them to a horizontal charge transfer element. 
   The vertical charge transfer element  40  has a charge transfer channel  41  formed in the p + -type impurity doped region  15   b  and a number of vertical transfer electrodes  45  and  46  traversing over the charge transfer channel  41  as viewed in plan. 
   The charge transfer channel  41  is made of, for example, an n-type impurity doped region, and extends along the color pixel column in a zigzag way. Channel stopper regions  43  (refer to  FIG. 9 ) are formed in regions wherein two charge transfer channels  41  juxtapose with no photoelectric conversion element  22  intervening therebetween. For example, the channel stopper region  43  is made of a p + -type impurity doped region formed in the p-type impurity doped region  15   b.    
   Each vertical transfer electrode  45  (refer to  FIG. 10 ) is made of, for example, a first polysilicon layer formed on the electrically insulating layer  26 . The vertical transfer electrode  45  is provided for each color pixel row and extends in a zigzag way along the corresponding color pixel row on the downstream side thereof. Each of the vertical transfer electrodes  45  extends to the color pixel row direction as a whole. 
   The vertical transfer electrode  45  covers, as viewed in plan, the read gate regions  48   a  adjoining to the photoelectric conversion elements  22  constituting the corresponding color pixel row. One read gate  48  (refer to  FIG. 10 ) is constituted of one read gate region  48   a  and a partial region of the vertical transfer electrode  45  covering, as viewed in plan, the read gate region  48   a.    
   Each vertical transfer electrode  46  is made of, for example, a second polysilicon layer formed on the electrically insulating layer  26 . The vertical transfer electrode  46  is provided for each color pixel row and extends in a zigzag way along the corresponding color pixel row on the upstream side thereof. Each of the vertical transfer electrodes  46  extends to the color pixel row direction as a whole. 
   The vertical transfer electrode  46  and the nearby vertical transfer electrode  45  have an overlap structure. The side area of the vertical transfer electrode  46  overlaps the side area of the vertical transfer electrode  45 . 
   An electrically insulating layer IF made of, for example, a silicon oxide layer is disposed for each vertical transfer electrode  45  thereon and for each vertical transfer electrode  46  thereon. The electrically insulating layer IF electrically isolate the vertical transfer electrode  45  and the nearby vertical transfer electrode  46  from each other. 
     FIG. 11  is a schematic diagram showing the plan layout of the photoelectric conversion elements  22 , vertical charge transfer elements  40  and read gates  48 , respectively of the solid state image pickup device  10   c  shown in  FIGS. 9 and 10 .  FIG. 11  also shows the layout of a horizontal charge transfer element and an output amplifier omitted in  FIGS. 9 and 10 . 
   In  FIG. 11 , each of the photoelectric conversion elements  22  is given a character R, G or B in order to identify the color-type of the color pixel of which the photoelectric conversion element  22  is a constituent member. The photoelectric conversion element  22 R is a constituent member of the red color pixel  20 R (refer to  FIG. 2 ), the photoelectric conversion element  22 G is a constituent member of the green color pixel  20 G (refer to  FIG. 2 ), and the photoelectric conversion element  22 B is a constituent member of the blue color pixel  20 B (refer to  FIG. 2 ). 
   In order to clearly show the position of the read gate  48  as viewed in plan, the read gate  48  is shown hatched. 
     FIG. 11  also shows an example of wiring for driving the vertical charge transfer elements  40  by four-phase drive signals φV 1  to φV 4  and driving the horizontal charge transfer element  50  by two-phase drive signals φH 1  and φH 2 . 
   As seen from  FIG. 11 , in the solid state image pickup device  10   c , the vertical transfer electrodes  45  and  46  are provided for each photoelectric conversion element row (each color pixel row). Three auxiliary transfer electrodes  47   a ,  47   b  and  47   c  are provided downstream of the most downstream vertical transfer electrode  45 . 
   The vertical transfer electrodes  45 ,  46 , and three auxiliary transfer electrodes  47   a  to  47   c  are classified into four groups to which different vertical drive signals φV 1  to φV 4  are applied. One group is constituted of the transfer electrodes  45 ,  46 ,  47   a ,  47   b  or  47   c  selected at every third positions. Each vertical charge transfer element  40  is made of a four-phase drive type CCD. 
   Each vertical charge transfer element  40  has four transfer electrodes per each photoelectric conversion element  22  (each color pixel) so that pixel signals of all pixels of the solid state image pickup device  10   c  can be read at a time. The read pulses are superposed upon the vertical drive signals φV 1  and φV 3 . 
   Charges read from the photoelectric conversion elements  22 R,  22 G and  22 B to the associated vertical charge transfer element  40  are transferred by this element  40  to the horizontal charge transfer element  50 . In this case, charges read from a photoelectric conversion element row (color pixel row) of the odd row as counted from the downstream side and charges read from another row upstream of the first-mentioned row by just one row are transferred to the horizontal charge transfer element  50  at the same timing. 
   The horizontal charge transfer element  50  is made of a two-phase drive type CCD driven by the horizontal drive signals φH 1  and φH 2 . This horizontal charge transfer element  50  has a horizontal charge transfer channel  52  and a number of horizontal transfer electrodes (not shown) traversing the channel  52  as viewed in plan. 
   The horizontal charge transfer channel  52  is made, for example, of an n-type impurity doped region formed in the p-type impurity doped region  15   b  (refer to  FIG. 9  or  10 ) of the semiconductor substrate  15 , and extends to the photoelectric conversion element row (color pixel row) direction. 
   Each horizontal transfer electrode is made of, for example, the first or second polysilicon layer formed on the electrically insulating layer  26  (refer to  FIG. 9  or  10 ). For example, four horizontal transfer electrodes are provided for each vertical charge transfer element  40 , and the horizontal transfer electrode made of the first polysilicon layer and the horizontal transfer electrode made of the second polysilicon layer are alternately and repetitively disposed. An electrically insulating layer made of, for example, a silicon oxide layer (thermally oxidized layer), is disposed for each horizontal transfer electrode thereon. 
   The horizontal charge transfer element  50  sequentially transfers the charges supplied from the vertical charge transfer elements  40  to an output amplifier  55 . 
   The output amplifier  55  sequentially receives the charges from the horizontal charge transfer element  50 , converts the received charges into signal voltages, for example, by using a floating capacitor (not shown), and amplifies these signal voltages by using a source follower circuit (not shown) or the like to generate pixel signals. The charge in the floating capacitor after the detection (conversion) is absorbed in a power source (not shown) via a reset transistor (not shown). 
   The pixel signals generated by the output amplifier  55  are supplied to the video signal proceeding unit  65  shown in  FIG. 1  or  7 . 
     FIG. 12  is a schematic diagram showing the plan layout of the photoelectric conversion elements  22 , vertical charge transfer elements  40 , read gates  48 , horizontal charge transfer element  50  and output amplifier  55 , respectively of another solid state image pickup device  10   d  usable as the solid state image pickup device  10   a  shown in  FIG. 2 . 
   The solid state image pickup device  10   d  shown in  FIG. 12  includes (n+1) vertical transfer electrodes  145  and  146  for n (n is an integer of 1 or larger) photoelectric conversion element rows (n color pixel rows). The vertical transfer electrodes  146  and  145  are alternately and repetitively disposed in this order from the downstream side. Three auxiliary transfer electrodes  147   a ,  147   b  and  147   c  are provided downstream of the most downstream vertical transfer electrode  146 . Therefore, each vertical charge transfer element  40  has two transfer electrodes per one photoelectric conversion element  22  (one color pixel). Excepting these points, the solid state image pickup device  10   d  has same structure as that of the solid state image pickup device  10   c  shown in  FIG. 11 . 
   Constituent elements shown in  FIG. 12  having the functions similar to those of the constituent elements shown in  FIG. 11  are represented by the identical reference symbols to those shown in  FIG. 11 , excepting the vertical transfer electrodes and auxiliary transfer electrodes, and the description thereof is omitted. 
   The solid state image pickup device  10   d  having the above-described structure is driven, for example, under the half thinning drive mode. In the half thinning drive mode, one frame is divided into two fields in the unit of a photoelectric conversion element row (color pixel row). Charges are read from the photoelectric conversion elements (color pixels) of each field to the associated vertical charge transfer element  40 . For example, one field is constituted of photoelectric conversion element rows (color pixel rows) selected at every third positions, and the photoelectric conversion element rows (color pixel rows) upstream of the first-mentioned rows by just one row. 
   In using the solid state image pickup device  10   d  as the solid state image pickup device  10  shown in  FIG. 1 , it is preferable that the memory unit M of the video signal proceeding circuit  65  has a capacity capable of storing color information corresponding to the pixel signals of one frame. In this case, the interpolation processes are performed by using the color information stored in the memory unit M. 
   The solid state image pickup device of the embodiments has been described above. The present 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. 
   Especially, the operation excepting the interpolation processes for generating output pixel signals at a relatively low resolution could be modified in various ways. 
   The image signal proceeding unit may be realized by using various circuits such as a clamp circuit, a gamma correction circuit, a white clip circuit, a contour correction circuit, a vertical false signal suppressing circuit, a tracking correction circuit, a high luminance coloring preventing circuit and a low chroma compression circuit in addition to the constituent elements shown in  FIG. 7 . 
   As described so far, according to the present invention, output pixel signals can be obtained by relatively simple signal processing. A solid state image pickup apparatus can be provided with a lower cost.