Abstract:
An image pickup apparatus includes: a solid state image pickup device having pixels displaced by a 1/2 pixel pitch between two adjacent horizontal lines; a circuit for reading every second horizontal line and outputting read-out signals onto a plurality of channels; and a luminance signal generating circuit for generating switching pulses for dot-sequentializing the read-out signals onto the plurality of channels to obtain a luminance signal, the switching pulses having a phase shift of 180 degrees between first and second fields.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image pickup apparatus using a solid state image pickup device. 
     2. Related Background Art 
     A conventional MOS image pickup device used in a single CCD area array type camera is constructed as shown in FIG. 1. In FIG. 1, PE represents a photocell, PS a cell selection switch, VA a vertical shift register, HS a horizontal shift register, IL an interlace circuit, and CS a column switch which is turned on and off in response to outputs from the horizontal shift register. The resolution of such a solid state camera is determined primarily by the number of pixels. It is difficult to increase considerably the number of pixels because of restrictions by manufacturing processes, high aperture rate, driving speed and the like. 
     In order to improve the horizontal resolution without increasing the number of pixels, an image pickup device of a so-called &#34;pixel displacement type&#34; has been proposed, the construction of which is shown in FIG. 2. 
     In FIG. 2, three color filters Cy, W and Ye are used, one unit being composed of filters disposed over two lines in a triangular shape. A horizontal scan is effected in units of filters disposed in a triangular shape. Three color signals are outputted onto respective signal lines within the baseband. The misalignment between spacial positions and signal timings is corrected by delay lines provided outside of the device, in the manner as illustrated in FIG. 3. In the Figure, H clocks are shift clocks from the horizontal shift register HS. 
     Using the obtained signals, the color and luminance signals are calculated by the following equations at a matrix circuit. 
     
         R=W-Cy 
    
     
         B=W-Ye 
    
     
         G=Cy+Ye-W 
    
     
         Y=Cy+W+Ye 
    
     As described above, in order to correct the misalignment between spatial positions and output signal timings, it is necessary to provide delay lines outside the image pickup device. However, if there is a difference in phase and amplification factor of the delay lines, interference signals within the bandwidth of the luminance signal appear on the displayed image. Thus, it is required to use delay lines having high precision phase and amplification factor. 
     In addition, there arises a problem that it is difficult to use delay lines having the same characteristic because the characteristic varies with each delay line. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an image pickup apparatus capable of obtaining an image of high horizontal resolution without using high precision delay lines. 
     In order to achieve the above object, the image pickup apparatus of the first embodiment of this invention comprises: a solid state image pickup device having pixels displaced by 1/2 pixel pitch between two adjacent horizontal lines; means for reading every second horizontal line and outputting read-out signals onto a plurality of channels; and luminance signal generating means for generating switching pulses for dot-sequentializing said read-out signals onto said plurality of channels to obtain a luminance signal, said switching pulses having a phase shift of 180 degrees between first and second fields. 
     According to the first embodiment, in producing a luminance signal by selectively switching output signals from a solid state image pickup device of a so-called &#34;1/2 pixel displacement type&#34;, the phase of switching pulses is shifted by 180 degrees between the first and second fields in the case of interlaced scanning with one line reading from frame storage, to thereby obtain an image of high horizontal resolution without using high precision delay lines as conventional. 
     Further, in order to achieve the above object, the image pickup apparatus of the second embodiment of this invention comprises: a solid state image pickup device having pixels displaced by a 1/2 pixel pitch between two adjacent horizontal lines; means for reading two horizontal lines at the same time and outputting read-out signals onto three output channels; and means for generating switching pulses for dot-sequentializing said read-out signals onto said three output channels to obtain a luminance signal, the frequency of said switching pulse being set 1.5 times as high as that for one line reading. 
     According to the second embodiment, in producing the luminance signal by selectively switching output signals from a solid state image pickup device of a so-called &#34;1/2 pixel displacement type&#34;, the two line simultaneous reading is performed using switching pulses whose frequency is set 1.5 times as high as, for example, that for interlaced scanning with one line reading from frame storage, to thereby obtain an image of high horizontal resolution without using high precision delay lines as in conventional system. 
     The above and other objects, and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 show the structure of conventional MOS type image pickup devices; 
     FIG. 3 is a timing chart illustrating the operation of reading signals from the image pickup device shown in FIG. 2; 
     FIG. 4 is a block diagram showing a first embodiment of the image pickup apparatus according to this invention; 
     FIG. 5 shows the structure of the MOS type image pickup device of the first embodiment; 
     FIG. 6 is a timing chart illustrating the operation of reading signals from the image pickup device shown in FIG. 5; 
     FIG. 7 shows the pixel arrangement of an image pickup device according to another embodiment of this invention; 
     FIG. 8 shows the structure of an X-Y address type image pickup device according to a second embodiment of this invention; and 
     FIGS. 9(A) and 9(B) are timing charts illustrating the operation of reading signals from the image pickup device shown in FIG. 8. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4 is a block diagram showing a single CCD area array type color image pickup apparatus using a solid state image pickup device according to this invention. In the Figure, a solid state image pickup device 1 may use an X-Y address type image pickup device as shown in FIG. 5. As particularly shown in FIG. 5, R, G and B color filters are attached to the image pickup device 1 while displacing them by a 1/2 pixel pitch between two adjacent lines. In the present invention, if only an X-Y address type image pickup device is used wherein each pixel signal is read upon designation of horizontal and vertical addresses, it is apparent that any type of image pickup devices may be used including MOS type, SIT type, CMD type, BASIS type, with or without uni-junction transistors, and other types. The solid state image pickup device 1 is driven by drive pulses generated by a timing generation circuit 2 to obtain R, G and B three output signals. 
     R, G and B signals are applied to respective pre-amplifiers 3 to remove spike current therefrom, sampled and held at sample-hold circuits 4, and then applied to clamp circuits 5 to fix the black level potential. 
     Using the three primary color signals, a luminance signal is calculated. For example, the luminance signal for a three CCD areas array type image pickup apparatus is calculated through addition in the equation of Y=0.3 R+0.59 G+0.11 B. For a single CCD area array type image pickup apparatus, if the same additional signal is used for calculating the luminance signal, the horizontal resolution is degraded. In consideration of this, as shown in FIG. 5, the signals read out in synchronism with the horizontal selection pulses (H clocks) outputted from the horizontal shift register are supplied to the pre-amplifiers 3. The output signals from the pre-amplifiers 3 are sampled and held in synchronism with sample-hold pulses (S/H pulses). The sampled and held signals are selectively switched at a switching circuit 6 in synchronism with switch pulses (SW pulses) generated by the timing generation circuit 2. Specifically, the signals are sequentially gated by switch pulses of high level, to generate a luminance signal. In such a manner the resolution can be improved. 
     The luminance signal thus obtained, as well as the R, G and B primary color signals, are subjected to band-elimination at low-pass filters LPF 7, and to white balance, gamma correction and matrix calculation at a color process circuit 8, to thereby obtain luminance signal Y and color difference signals R-Y and B-Y. The luminance signal Y is directly supplied to an FM modulator F2, whereas the (R-Y) and (B-Y) signals are first line-sequentialized and thereafter supplied to an FM modulator F1. After modulation, they are added together at an adder 9, and the addition result is recorded in a recording device 10. 
     The frequency of switch pulses (SW pulses) shown in FIG. 5 is 1.5 times as high as that for interlaced scanning, with one line reading from frame storage, of a solid state image pickup device with pixel disposal as shown in FIG. 5. The image pickup device shown in FIG. 4 may use the image pickup device with pixel disposal as shown in FIG. 7. In this case, the same frequency as high as 1.5 times is used. 
     With the image pickup apparatus constructed as above, there is no need for high precision delay lines conventionally used for correcting a misalignment between image pickup device output signal timings and spatial positions, thus readily obtaining an image of high horizontal resolution. 
     FIG. 8 shows the second embodiment of this invention. In obtaining a frame image by using the solid state image pickup device shown in FIG. 8, if interlaced scanning with one line reading from frame storage is performed in a moving image taking mode, then frame residual images appear. Therefore, in this embodiment, a frame image is obtained through two line simultaneous reading. In a still image taking mode, the shutter is opened only during light exposure and closed after the exposure, and interlaced scanning with one line reading is performed to obtain a frame image. Therefore, a frame image can be obtained through two line simultaneous reading. 
     FIGS. 9(A) and 9(B) illustrate how a frame image is obtained through one line reading in the still image taking mode. As shown in FIG. 9(A), signals in the first field read in synchronism with horizontal selection pulses are sampled and held, and thereafter selectively switched in synchronism with switch pulses same in phase with horizontal selection pulses, to thereby obtain a luminance signal. 
     Pixels in the second field are displayed by a 1/2 pixel pitch relative to pixels in the first field as shown in FIG. 9(B). The misalignment is corrected not by shifting horizontal selection pulses, but by shifting the phase of switch pulses (SM pulses) so as to match pixel spatial positions, as seen from FIG. 9(B). Therefore, the phases of switch pulses in the first and second fields are shifted by 180 degrees. This arrangement can also enjoy the same effects as the first embodiment. 
     In the first and second embodiments, R, G and B pure color filters have been used. However, it is apparent that complimentary color filters such as W, Ye and Cy may be used with the same advantageous effects. 
     As described so far, according to the solid state image pickup device of this invention, in producing a luminance signal by selectively switching color output signals, the phase of switching pulses is shifted by 180 degrees between the first and second fields in the case of interlaced scanning with one line reading from frame storage. In the case of two line simultaneous reading, the frequency of switching pulses is made 1.5 times as high as that for interlaced scanning with one line reading from frame storage. Therefore, the present invention can readily obtain an image of high horizontal resolution without using conventional high precision delay lines.