Video camera

Abstract: In a video camera having three image pickup devices 1, 2, 3 in which a pixel G of one channel of channels forming three primary colours is spatially displaced from other pixels R, B of two channels by 1/2 pixel, when three primary colour signals output from the three image pickup devices are converted into digital three primary colour signals G, R, B, an aperture signal DTL is formed from the digital three primary colour signals, the aperture signal output is added to the digital three primary colour signals and a digital video signal Y₁. Y₂, R-Y, B-Y of a predetermined format is formed from the added signal, a clock frequency (36MHz) of an aperture signal forming circuit 30 is set to be twice the clock frequencies of the image pickup devices, an A/D converting circuit 7, 8, 9 and a video signal forming circuit.

Description: U.S. Patent US-A-4,855,829, for example, describes an aperture correction circuit that is applied to a video camera. As is well known, the aperture correction circuit is utilized in order to compensate for a deterioration of response of an image pickup device and to emphasize a sharpness in the video camera. Video cameras having a CCD (charge-coupled device) formed of 400,000 pixels are now commercially available on the market. The above 400,000-pixel CCD is driven at a horizontal drive frequency of 14.3 MHz. In the above video camera, an output signal from the 400,000-pixel CCD is converted into a digital signal serving as a main line signal by an A/D (analog-to-digital) converter. An aperture correction signal is formed from the digital signal thus converted by an aperture signal forming circuit. Then, the aperture signal thus formed and the digital signal serving as the main line signal are added to provide a corrected digital signal. The corrected digital signal is converted by a video signal forming circuit into a digital luminance signal and digital color difference signals or a digital composite video signal. In the conventional video camera thus constructed, the A/D converter, the aperture signal forming circuit and the video signal forming circuit are all driven by a clock frequency of 14.3 MHz that is the same frequency as a horizontal drive frequency of the 400,000-pixel CCD. In that case, there are obtained 560 television lines as a horizontal limit resolution. As a horizontal limit resolution for high-definition television receiver, there must be provided about 700 television lines or more. Therefore, in the conventional video camera, in order to increase a horizontal limit resolution, a pixel G is spatially displaced from pixels R and B by 1/2-pixel pitch, whereby the 4C0,000-pixel CCD and the A/D converter are driven by the clock frequency of 14.3 MHz and other aperture signal forming circuit, the video signal forming circuit, etc., are driven by a clock frequency of 28.6 MHz. According to this arrangement, a horizontal limit resolution can be increased to 900 television lines. However, if the video camera is arranged as described above, an electric power consumption of the circuits, in particular, an electric power consumption of the video signal forming circuit is increased considerably. European Published Patent Application EP-A-0,368,354 describes an image pickup device in which the CCD for green pixels is offset by half a pixel from the red and blue pixel CCDs. An aperture correction circuit is provided that operates at twice the frequency of the CCDs. According to the present invention, there is provided a video camera having three image pickup devices in which a pixel of one channel of channels forming three primary colors is spatially displaced from other pixels of two channels by 1/2 pixel, comprising: an analog-to-digital converting means for converting analog three primary colour signals output from said three image pickup devices into digital three primary color signals; aperture correction signal forming means supplied with output signals of said A/D converting means and forming an aperture correction signal from said digital three primary color signals; first adding means for adding said aperture correction signal output from said aperture correction signal forming means and said digital three primary color signals output from said A/D converting means; and forming means for forming color difference signals and a first luminance signal on the basis of an output signal of said first adding means; characterised by second adding means for adding said aperture correction signal to said first luminance signal output from said forming means to form a second luminance signal; a down sampling means for down sampling said aperture correction signal prior to supply of said aperture correction signal to said first adding means; and a rate converting means for rate converting said first luminance signal prior to supply of said first luminance signal to said second adding means; and characterised in that the clock frequency of said aperture correction signal forming means is set to be twice the clock frequency of said forming means and the clock frequency of said second adding means is set to be twice the clock frequencies of said image pickup devices, said A/D converting means and said forming means. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: FiG. 1 (formed of FIGS. 1A and 1B) is a block diagram showing a video camera which is not an embodiment of the invention as claimed; FIGS. 2A to 2F are frequency characteristic diagrams used to explain operation of the video camera shown in FIG. 1, respectively; FIGS. 3A to 3G are frequency characteristic diagrams used to explain operation of the video camera shown in FIG. 1, respectively; FIG. 4 (formed of FIGS. 4A and 4B) is a block diagram showing a video camera according to an embodiment of the present invention; and FIGS. 5A to 5D are frequency characteristic diagrams used to explain the video camera shown in FIG. 4, respectively. As shown in FIG. 1 (formed of FIGS. 1A, 1B drawn on two sheets of drawings so as permit the use of a suitably large scale) of the accompanying drawings, there are provided two-dimensional image pickup devices 1 to 3 that are CCDs correspondingly assigned to respective channels of three primary colors, respectively. In these CCDS 1 to 3, one pixel (in this case, pixel G) constructing three-primary color pixels is spatially (optically) displaced from remaining two pixels (pixels R and B) by a 1/2-pixel pitch. Each of these CCDs 1 to 3 includes 500,000 pixels and is driven by a horizonal drive frequency of 18 MHz. Analog three-primary color signals G 0 , R 0 , B 0 from the CCDs 1 to 3 are supplied through amplifiers 4 to 6 to A/D converters 7 to 9, each having a clock frequency of 18 MHz, respectively. The A/D converters 7 to 9 convert the electrical signals supplied thereto from the CCDs 1 to 3 into digital three-primary color signals G 1 , R 1 , B 1 , respectively. In FIG. 1, clock frequencies (MHz) of respective circuits are shown in a parenthesized fashion such as (18 MHz), (18) or the like in circuit blocks or near signal lines. FIG. 2A shows a frequency characteristic of the signal G 1 (abscissa represents a frequency f (MHz) and ordinate represents a standardized amplitude A). In FIG. 2A, a frequency characteristic 101 shown by a solid line from a direct current (hereinafter referred to as a DC, if necessary) to 18 MHz represents a base band component and a frequency characteristic 102 shown by a dashed line from DC to 18 MHz represents an alias component, respectively. In this embodiment, since the band of the analog video signal that is finally required is limited to 9 MHz, a frequency component of higher than 18 MHz need not be considered. The reason that the frequency band of the signals G 1 , R 1 and B 1 are considered up to 18 MHz is that a characteristic of an optical LPF (low pass filter), not shown, interposed between the CCDs 1 to 3 and a lens (not shown) has a band of from DC to 18 MHz. The above optical LPF has a gentle attenuation characteristic inherently so that, if an optical LPF having a band of DC to 9MHz is utilized, then a signal component up to 9 MHz is reduced too much and an S/N (signal-to-noise) is deteriorated. For this reason, the optical LPF having the band of from DC to 18 MHz is utilized. FIG. 2B shows frequency characteristics of the signals R 1 and B 1 . In FIG. 2B, a frequency characteristic 103 shown by a solid line from DC to 18 MHz represents a base band component and a frequency characteristic 104 shown by a dashed line represents an alias component, respectively. The alias components having the above frequency characteristics 102, 104 are produced by the sampling processing in the A/D converters 7 to 9. In FIGS. 2A and 2B, the frequency characteristics 102, 104 of the alias components are inverted about a frequency axis. The reason for this is considered as follows. since the CCDs 1 to 3 are spatially displaced by 1/2-pixel pitch, a sub-Nyquist sampling is effected so that a sampling cycle in the A/D converters 8, 9 is displaced from that of the A/D converter by a phase π. The clock (sampling) frequency of 18 MHz is represented by a positive direction arrow 105 in FIG. 2A, and the clock (sampling) frequency of 18 MHz is represented by a negative direction arrow 106. The negative direction arrow 106 is used in order to express that the phase is displaced by π from the cycle of the clock frequency shown by the positive direction arrow 105. The signals G 1 , R 1 , B 1 having the above frequency characteristics are supplied to a pre-processing circuit 25. The pre-processing circuit 25 processes the signals G 1 , R 1 , B 1 in some suitable processing fashion such as an interpolation of defective pixel or the like and then outputs interpolated signals G 2 , R 2 , B 2 . In this embodiment, the frequency characteristics of the interpolated signals G 2 , R 2 and B 2 are equal to the characteristics 101, 103 of the signals G 1 , R 1 and B 1 . The signal G 2 is supplied to an LPF 26 and one input terminal of an adder 31 constructing an aperture signal forming circuit 30. The signal R 2 is supplied to an interpolation filter (IPF) 27 and the other input terminal of the adding circuit 31. The signal B 2 is supplied to an IPF 28. FIG. 2C shows a frequency characteristic 106 of the LPF 26 having a cut-off frequency of 9 MHz to which the signal G 2 is supplied. FIG. 2D shows frequency characteristics 107 of the IPFs 27 and 28 to which the signal R 2 is supplied. Each of the IPFs 27 and 28 comprises a 1/2-pixel group delay element for making the phase of the signal B 2 to that of the signal G 2 and a LPF having the same arrangement as that of the LPF 26. FIG. 2E shows a frequency characteristic of a signal G 3 which results from processing the signal G 2 having the frequency 101 by the LPF 26. Also in FIG. 2E, only a frequency characteristic 109 from DC to 9 MHz shown by a solid line must be considered. The frequency characteristic of the signal G 3 shown in FIG. 2E is obtained in response to a product of transfer functions of the signal G 1 shown in FIG. 2A and the LPF 26 shown in FIG. 2C. FIG. 2F shows frequency characteristics of signals R 3 , G 3 which result from processing the signals R 2 and B 2 having the frequency characteristic 103 by the LPFs 27, 28. In this case, only a frequency characteristic 115 from DC to 9 MHz shown by a solid line must be considered. The frequency characteristics of the signals R 3 , B 3 shown in FIG. 2F are obtained in response to a product of the transfer functions of the signals R 1 , B 1 shown in FIG. 2B and of the IPFs 27, 28 shown in FIG. 2D. Study of FIGS. 2E and 2F reveals that the frequency band is limited to DC to 9 MHz and the alias components within such frequency band are attenuated to frequency characteristics 115, 116 shown by dashed lines. The signals G 3 , R 3 , B 3 whose phase differences are canceled are corrected in color by a masking circuit 35 and provided as signals G 4 , R 4 , B 4 , respectively. The signals G 4 , R 4 , B 4 are respectively added to an aperture signal DTL 3 by adding circuits 36 to 38, thereby being produced as signals G 5 , R 5 , B 5 , respectively. The signals G 5 , R 5 , B 5 are corrected in gamma characteristic and knee characteristic by γ/knee correcting circuits 40 to 42, thereby being produced as signals G 6 , R 6 , B 6 , respectively. The signals G 6 , R 6 , B 6 are added to an aperture signal DTL 4 , respectively, by adding circuits 43 to 45, thereby being produced as signals G 7 , R 7 , B 7 thus aperture-corrected. When the aperture correction processing is not carried out, the aperture signals DTL 3 , DTL 4 supplied to the adding circuits 36 to 38 and the adding circuits 43 to 45 are both held at zero value because mixing ratio signals M 1 , M 2 supplied to the adding circuits 32, 33 through terminals 46, 47 from a system controller (not shown) are held at zero value. The signals G 7 , R 7 , B 7 are supplied to a matrix circuit 48 of a video signal forming circuit 50 that is formed of a matrix circuit 48 and an encoder 49. The matrix circuit 48 converts the signals G 7 , R 7 , B 7 into luminance signals Y 1 , Y 2 and color difference signals (R-Y), (B-Y) forming a digital video signal. FIG. 3A shows a frequency characteristic of the luminance signal Y 1 provided when the aperture correction processing is not carried out. In this case, the frequency characteristic 117 of the base band shown by a solid line must be considered. As will be clear from the frequency characteristic 117, alias components of the frequency characteristics 115, 116 (see FIGS. 2E and 2F) of the signals G 3 , R 3 , B 3 are canceled by the calculation within the matrix circuit 48 so that no alias component exists in the base band component of the luminance signal Y 1 . When a luminance signal Y 2 provided after the aperture correction processing is obtained, the signal G 2 and the signal R 2 are added at a twice drive clock frequency 36 MHz by the adding circuit 31 within the aperture signal forming circuit to thereby obtain an added signal (G 2 + R 2 ). The reason that the signals G 2 and R 2 are added at 36 MHz is that the signal component of the signal G 2 exists in the signal component of the signal R 2 due to the above 1/2-pixel displacement. FIG. 3B shows a frequency characteristic of the added signal (G 2 + R 2 ) A frequency characteristic 120 is a characteristic that results from synthesizing the frequency characteristic shown in FIG. 2A and the frequency characteristic shown in FIG. 2B. Thus, the alias components of DC to 18 MHz are canceled and do not exist in the frequency characteristic 120. FIG. 3C shows a synthesized frequency characteristic of a high-pass filter (HPF) 32 constructing the aperture correction circuit 30 and a LPF 33 connected to the output of the HPF 32, i.e., a BPF (bandpass filter) characteristic, or a differential characteristic. In the LPF 33, after the band of the aperture signal DTL 1 is limited to DC to 9MHz by a drive clock frequency of 36 MHz, a so-called down sampling is carried out by a drive clock frequency of 18 MHz to thereby select necessary data and throw away remaining data. The down sampling is carried out in order to add the aperture signal DTL 2 to the signals G 4 , R 4 , B 4 and the signals G 6 , R 6 , B 6 which are main line signals operable at 18 MHz. FIG. 3D shows a frequency characteristic of the aperture signal DTL 2 which is the output signal of the LPF 31. This frequency characteristic is obtained in response to a product of a transfer function corresponding to the frequency characteristic 120 shown in FIG. 3B and a transfer function corresponding to the frequency characteristic shown in FIG. 3C. In this case, the frequency characteristic from DC to 9 MHz must be considered. The aperture signal DTL 2 having such characteristic is multiplied at the mixing ratios M 1 , M 2 by the multiplying circuits 32, 33 and are thereby produced as the aperture signals DTL 3 and DTL 4 having predetermined amplitudes and then added to the signals G 4 , R 4 , B 4 and the signals G 6 , R 6 , B 6 , respectively. FIG. 3E shows a frequency characteristic 127 of the aperture-corrected luminance signal Y 2 that is the output signal of the matrix circuit 48. The frequency characteristic 127 shows a frequency characteristic of the luminance signal Y 2 which results from adding the luminance signal Y 1 having the frequency characteristic 117 shown in FIG. 3A and the aperture signal DTL 2 having the frequency characteristic 126 shown in FIG. 3D. The frequency characteristic 127 from DC to 9 MHz of this luminance signal Y 2 contains no alias component. Then, the luminance signal Y 1 and the color difference signals (R-Y), (B-Y) which are not aperture-corrected and the luminance signal Y 2 and the color difference signals (R-Y), (B-Y) which are aperture-corrected are converted by an encoder 49 into composite video signals CV 1 (monochrome), CV 2 (color) which are digital video signals, converted by D/A (digital-to-analog) converters 51,52 into analog composite video signals CV 3 , CV 4 and then supplied through an output terminal 53 to a viewfinder (not shown) and through an output terminal 54 to the outside. Since the thus converted analog composite video signals CV 3 , CV 4 are limited in band to 9 MHz by analog LPFs before they are used in actual practice, a signal component (noise component) exceeding 9 MHz need not be considered. Even when the aperture correction processing is carried out, the aperture correction signal DTL 3 having the same amplitude is added to the signals G 4 , R 4 , B 4 and the aperture correction signal DTL 4 having the same amplitude is added to the signals G 6 , R 6 , B 6 . Therefore, the color difference signals (R-Y), (B-Y) are not changed even when the luminance signal Y 1 that is not processed by the aperture correction is changed to the aperture-corrected luminance signal Y 2 . The luminance signals Y 1 , Y 2 and the color difference signals (R-Y), (B-Y) are temporarily converted by a rate converting circuits 56 into 54 MHz which is the lowest common multiple of 18 MHz and 13.5 MHz and then converted into digital video signals Y 3 , (R-Y) 3 , and (B-Y) 3 of a so-called D1 format formed of a luminance signal Y 3 having a clock frequency of 13.5 MHz and color difference signals (R-Y), (B-Y) having a clock frequency of 6. 75 MHz. FIG. 3F shows a frequency characteristic 134 of LPF within the rate converting circuit 56. In this rate converting circuit 56, the band is temporarily limited to 6.72 MHz by the above LPF and data are thinned at every four to provide an output of 13,5 MHz. The luminance signal Y 3 and the color difference signals (R-Y) 3 and (B-Y) 3 which are digital video signals thus converted to the D1 format are supplied through output terminals 57 to 59 to a video tape recorder (not shown). FIG. 3G shows a frequency characteristic 137 of the luminance signal Y 3 . As described above, according to this embodiment, the CCDs 1 to 3, each having 500,000 pixels disposed in a spatial pixel displacement fashion are utilized so that other circuit elements than the aperture signal forming circuit 59, the LPF portion of the LPF 33 and the rate converting circuit 56 are driven at the same clock frequency of 18 MHz as the horizontal drive frequency of the CCDs 1 to 3. The high band components of the signals G 2 , R 2 are added at 36 MHz which is twice the above clock frequency 18 MHz in the aperture signal forming circuit 30 and only the high band component is passed by the HPF 32 to thereby form the aperture signal DTL 1 . Thereafter, by the LPF 33 and the so-called down sampling processing within the LPF 33, the frequency is thinned to 18 MHz to form the aperture signal DTL 2 . Then, the aperture signals DTL 3 , DTL 4 corresponding to the aperture signal DTL 2 are added to the signals G 4 , R 4 , B 4 and the signals G 6 , R 6 , B 6 serving as the main line signals at the operation frequency of 18 MHz. Then, on the basis of the aperture-corrected signals G 7 , R 7 , B 7 , the luminance signal Y 2 and the color difference signals (R-Y), (B-Y) which are digital video signals and the composite video signals CV 1 , CV 2 which are digital video signals are formed by the video signal forming circuit 50. According to the above-mentioned processing, the high-definition property can be maintained by the aperture correction processing based on the aperture signal forming circuit 30 operated at the twice clock frequency, 36 MHz and the horizontal limit resolution of picture displayed on the composite video signals CV 1 , CV 2 becomes about 720 television lines, which can provide a sufficient resolution in actual practice. Further, since the clock frequencies of the circuits except the aperture signal circuit 30 are fundamentally selected to be 18 MHz which are half of the clock frequency 36 MHz for driving the aperture signal forming circuit 30, an electric power consumption of the circuit, in particular, the electric power consumption of the video signal forming circuit 50 can be reduced considerably. As described above, according to the video camera of the present invention, the drive clock frequency of the aperture signal forming circuit is selected to be twice the clock frequencies of the image pickup device, the A/D converter, the adding circuit and the video signal forming circuit. Therefore, the high-definition property can be maintained by the aperture correction processing based on the aperture signal forming circuit driven by the twice clock frequency and the horizontal resolution can be increased to the television lines sufficient for actual practice. Furthermore, the electric power consumption of the circuits other than the aperture signal forming circuit can be reduced comparatively and the electric power consumption of the whole of the circuits can be reduced. An embodiment of the video camera according to the present invention will be described next with reference to FIG. 4 (formed of FIGS. 4A and 4B drawn on two sheets of drawings so as to permit the use of a suitably large scale). In FIG. 4, like parts corresponding to those of FIG. 1 are marked with the same references and therefore need not be described in detail. In the second embodiment shown in FIG. 4, the band of the analog video signal required by the matrix circuit 48 is limited to 9 MHz and components of higher than 19 MHz in the frequency characteristic of the signal G 1 shown in FIG. 2A therefore need not be considered. Further, in the second embodiment shown in FIG. 4, the video signal forming circuit 50 comprises the matrix circuit 48, a rate converting circuit 60, an adding circuit 61 and the encoder 49. In the second embodiment shown in FIG. 4, the luminance signals Y 1 , Y 2 output from the matrix circuit 48 are converted by the rate converting circuit 60 into a luminance signal Y 4 having a twice clock frequency 36 MHz. FIG. 5A shows a frequency characteristic (LPF characteristic of 9 MHz) of the rate converting circuit 60. FIG. 5B shows a frequency characteristic 139 of the luminance signal Y 4 that is the output signal of the rate converting circuit 60. The luminance signal Y 4 is supplied to one input terminal of the adding circuit 61. FIG. 5C shows a frequency characteristic 140 of an aperture signal DTL 5 supplied to the other input terminal of the adding circuit 61. The aperture signal DTL 5 is an attenuated signal which results from multiplying the aperture signal DTL 1 , formed by the aperture signal forming circuit 30 on the basis of the signals G 2 , R 2 with a value of a mixing ratio signal M3 supplied to a multiplying circuit 63 through a terminal from a system controller (not shown). This aperture signal DTL 5 is added to the luminance signal Y 4 serving as the main line signal by the adding circuit 61 to provide a luminance signal Y 5 having a frequency characteristic 141 (see FIG. 5D) in which a high band component is compensated for. An operation frequency of the luminance signal Y 5 is 36 MHz. The luminance signal Y 5 and the color difference signals (R-Y) and (B-Y) are supplied to the encoder 49. In the encoder 49, the color difference signals (R-Y) and (B-Y) are mixed with carrier signals (not shown) by two balancing modulators (not shown) to provide a carrier chrominance signal (not shown). This carrier chrominance signal is converted by a rate converting circuit (not shown) into a carrier chrominance signal having a clock frequency of 18 MHz to 36 MHz. Then, the carrier chrominance signal of 36 MHz and the luminance signal of 36 MHz are added by an adding circuit (not shown) having a clock frequency of 36 MHz to provide a signal in which the luminance signal Y 5 and the carrier chrominance signal are superimposed upon each other. The signal thus superimposed is added with a synchronizing signal and is thereby converted into the composite video signal CV 2 which is the digital video signal. Further, the synchronizing signal is added to the luminance signal Y 5 to provide the composite signal CV 1 (monochrome) which is the digital video signal. The composite video signals CV 1 , CV 2 are converted by the D/A converters 51, 52 into analog composite video signals CV 3 , CV 4 and then supplied through the output terminal 53 to the viewfinder (not shown) and also supplied through the output terminal 54 to the outside. The analog composite video signals CV 3 , CV 4 thus converted are limited in band to about 18 MHz by an analog LPF before being used. As described above, according to the second embodiment, the CCDs 1 to 3, each having 500,000 pixels disposed in a spatial pixel displacement fashion are utilized so that other circuit elements than the aperture signal forming circuit 30, one portion of the LPF 33, the rate converting circuits 56, 60, the adding circuit 61 and the encoder 49 are driven at the same clock frequency of 18 MHz as the horizontal drive frequency of the CCDs 1 to 3. The high band components of the signals G 2 , R 2 are added at 36 MHz which is twice the above clock frequency 18 MHz in the aperture signal forming circuit 30 and only the high band component is passed by the HPF 32 to thereby form the aperture signal DTL 1 . Thereafter, by the LPF 33 and the so-called down sampling processing within the LPF 33, the frequency is thinned to 18 MHz to form the aperture signal DTL 2 . Then, the aperture signals DTL 3 , DTL 4 corresponding to the aperture signal DTL 2 are added to the signals G 4 , R 4 , B 4 and the signals G 6 , R 6 , B 6 serving as the main line signals at the operation frequency of 18 MHz. Then, on the basis of the aperture-corrected signals G 7 , R 7 , B 7 , the luminance signal Y 2 and the color difference signals (R-Y), (B-Y) which are digital video signals are formed by the matrix circuit 48 forming the video signal forming circuit 50. Further, the luminance signal Y 5 whose high band component is compensated for is formed by the rate converting circuit and the adding circuit 61. Thereafter, the digital video signals CV 1 , CV 2 which are the digital video signals are formed by the encoder 49. According the above processing, a high-definition property can be maintained by the aperture correction processing based on the aperture signal forming circuit 30 that is driven at the twice clock frequency 36 MHz and a horizontal limit resolution of picture displayed on the basis of the composite video signals CV 1 , CV 2 becomes substantially about 1000 television lines, which can provide a relatively high resolution. Further, since the circuits that can operate at the clock frequency 36 MHz are limited to the aperture signal forming circuit 30, the rate converting circuit 60, the encoder 49 or the like, the electric power consumption of the whole of the circuits can be reduced relatively. As described above, the clock frequencies of the aperture signal forming circuit and the second adding circuit are set to be twice the clock frequencies of the image pickup device, the A/D converter and the matrix circuit. Therefore, the high-definition property can be maintained by the aperture correction processing based on the aperture signal forming circuit and the second adding circuit that can be driven by the above twice clock frequency. Hence, the horizontal resolution can be increased. Furthermore, since the electric power consumption of other circuits than the aperture signal forming circuit and the second adding circuit can be reduced relatively, the electric power consumption of the whole of the circuits can be reduced comparatively. At least preferred embodiments of the invention provide: a video camera in which electric power consumption of a signal processing circuit can be reduced; and a video camera which can provide a horizontal resolution of television lines sufficient for actual practice. Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims: A video camera having three image pickup devices (1,2,3) in which a pixel (G) of one channel of channels forming three primary colors is spatially displaced from other pixels of two channels (R,B) by 1/2 pixel, comprising: an analog-to-digital (A/D) converting means (7,8,9) for converting three analog primary colour signals (G 0 ,R 0 ,B 0 ) output from said three image pickup devices into three digital primary color signals (G 1 ,R 1 ,B 1 ); aperture correction signal forming means (30) supplied with output signals of said A/D converting means and forming an aperture correction signal (DTL 1 ) from said three digital primary color signals; first adding means (36,37,38) for adding said aperture correction signal output from said aperture correction signal forming means and said three digital primary color signals output from said A/D converting means; and forming means (48) for forming color difference signals (R-Y,B-Y) and a first luminance signal (Y 1 ,Y 2 ) on the basis of an output signal of said first adding means; characterised by second adding means (61) for adding said aperture correction signal to said first luminance signal output from said forming means to form a second luminance signal (Y 5 ); a down sampling means (33) for down sampling said aperture correction signal (DTL 1 ) prior to supply of said aperture correction signal (DTL 2 ) to said first adding means; and a rate converting means (60) for rate converting said first luminance signal (Y 1 ,Y 2 ) prior to supply of said first luminance signal (Y 4 ) to said second adding means; and characterised in that the clock frequency of said aperture correction signal forming means is set to be twice the clock frequency of said forming means and the clock frequency of said second adding means is set to be twice the clock frequencies of said image pickup devices, said A/D converting means and said forming means. The video camera according to claim 1, further comprising second forming means (49) supplied with an output signal of said second adding means and said color difference signals output from said forming means to form a digital composite video signal.

Inventors: ASAIDA TAKASHI, KIHARA TAKU, MURAYAMA HIDEAKI, SUDO FUMIHIKO, ASAIDA, TAKASHI, KIHARA, TAKU, MURAYAMA, HIDEAKI, SUDO, FUMIHIKO, ASAIDA, TAKASHI, C/O SONY CORPORATION, Kihara, Taku, c/o Sony Corporation, Murayama, Hideaki, c/o Sony Corporation, SUDO, FUMIHIKO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1993
Main classification: H04N9
IPC codes: H04N9