Video signal processing

Abstract: In a VTR reproduction mode, since a signal of which a luminance signal and a chroma signal that have been band-limited are combined is supplied to a Y comb filter (3) and a C comb filter (4), processing can be performed with only one A/D converter (14). In addition, the A/D converter and 2H line delay circuits for processing camera signals can be commonly used in the VTR reproduction mode.

Description: This invention relates to video signal processing circuits. The reproduction system of a conventional video tape recorder (VTR) is provided with a Y (luminance) comb filter and a C (chrominance) comb filter for removing cross-talk. The Y comb filter and the C comb filter are conventionally composed of analog circuits. However, an attempt to construct the Y comb filter and the C comb filter from digital circuits has been made. However, when the conventional analog Y comb filter and C comb filter are composed of digital circuits, two A/D converters for use with a luminance signal and a chroma signal are required. In addition, a one-line delay circuit for the Y comb filter and another one-line delay circuit for the C comb filter are required. Thus, the circuit scale adversely increases. Particularly in the case of a small camcorder that digitally processes signals, it is important to reduce the circuit scale and the fabrication cost. The camcorder that digitally processes camera signals has an A/D converter that converts a photographed image signal into a digital signal. When the camcorder, which is small and digitally processes signals, has a digital Y comb filter and a C comb filter, A/D converters and one-line delay circuits for the comb filters are required. Thus, the circuit scale increases and the fabrication cost rises. US Patent Serial No. 5,142,375 discloses a video camera having an image pick-up device and a recording and reproducing device. The camera is provided with input selecting circuit for selectively inputting a photographed image signal photographed by the image pick up device, or a combined luminance and chrominance signal components of a video signal from the recording and reproducing mode. The output of the input selecting means is fed to an A/D converter, and the digital signal is fed to line delay circuits to reduce the cross-talk in the signals. The camera further includes a comb filter to process the luminance signal in order to encode the video signal or image pick up signal in a predetermined way, various aspects and features of the present invention are defined in the appended claims. Embodiments of the present invention can provide a video signal processing apparatus comprising an input selecting circuit for selectively inputting a video signal of which a component of a luminance signal and a component of a chroma signal are combined or a photographed image signal of an image photographed by an image pick-up device, an A/D converter for digitizing the selected signal selected by the input selecting circuit from the video signal of which the component of the luminance signal and the component of the chroma signal are combined or the image signal of an image photographed by the image pick-up device, a plurality of line delay circuits connected in series and adapted for delaying an output signal of the A/D converter, a luminance signal comb filter, a chroma signal comb filter, and a camera signal processing circuit for receiving output signals from connection portions of the line delay circuits connected in series, and an output selecting circuit for selecting an output signal of the luminance signal comb filter and the chroma signal comb filter or an output signal of the camera signal processing circuit. The invention is particularly (but not exclusively) applicable to VTR's, and especially (but not only) to camcorders. In such an application, in the VTR reproduction mode, since a signal of which a luminance signal and a chroma signal that have been band-limited are combined is supplied to a Y comb filter and a C comb filter, the process can be performed with only one A/D converter. In addition, since the A/D converter and the 2H line delay circuits that process the camera signals are used in common with those for the Y comb filter and the C comb filter, it is almost not necessary to add new circuits. That is, there is provided a video signal processing circuit having a digital Y comb filter and a digital C comb filter (for example, for removing crosstalk in a reproduction system of a VTR) that do not require an increase of circuit scale. The invention will now be further described, by way of illustrative and nonlimiting example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram showing an embodiment of the present invention; and Fig. 2 is a schematic diagram showing a frequency spectrum for explaining the embodiment of the present invention. Next, with reference to the accompanying drawings, an embodiment of the present invention will be described. This embodiment is applied for an 8-mm standard camcorder. In Fig. 1, reference numeral 1 is an input terminal for a reproducing VTR signal. Reference numeral 11 is an input terminal for a camera signal. In a VTR reproduction mode, a reproduction video signal of which a luminance signal and a chroma signal including a cross-talk component are combined is supplied to the input terminal 1. In other words, as shown in Fig. 2, the luminance signal Y and the chroma signal C are band-limited and a component of the luminance signal Y and a component of the chroma signal C are combined in such a manner that they can be separated on frequencies. The resultant signal is supplied to the input terminal 1. A photographed image signal of an image photographed by a CCD image pick-up device is supplied to the input terminal 11. Reference numerals 21 to 25 are switch circuits switched over depending on whether the selected mode is the camera signal input mode or the VTR reproduction mode. In the camera signal input mode, the switch circuit 21 is placed in a terminal 21A position. On the other hand, in the VTR reproduction mode, the switch circuit 21 is placed in a terminal 21B position. In the camera signal input mode, the switch circuit 23 is placed in a terminal 23A position. Likewise, in the normal VTR reproduction mode, the switch circuit 23 is placed in the terminal 23A position. However, in the case that a drop-out takes place in the 8-mm standard mode (referred to as normal mode) in which the band of the luminance signal is limited to 3 MHz or less, the switch circuit 23 is placed in a terminal 23B position. In the camera signal input mode, the switch circuit 24 is placed in a terminal 24A position. On the other hand, in the normal VTR reproduction mode, the switch circuit 24 is placed in a terminal 24B position. However, in the case that a drop-out takes place in a mode of which the band of the luminance signal is 5 MHz or greater (referred to as Hi 8 mode), the switch circuit 24 is placed in a terminal 24C position. In the camera signal input mode, the switch circuit 25 is placed in a terminal 25A position. On the other hand, in the VTR reproduction mode, the switch circuit 25 is placed in a terminal 25B position. In the camera signal input mode, the operation of the VTR reproducing portion is not required. Thus, in this mode, the clock and signals are not supplied to the portions that perform the VTR reproducing operation. On the other hand, in the VTR reproduction mode, since the operation of the camera signal processing portion is not required, the clock and signals are not supplied to the portions that perform the camera signal processing operation. Thus, the power can be prevented from unnecessarily increasing. First, the camera signal input mode will be described. In the camera signal input mode, a photographed image signal is supplied from the CCD image pick-up device to the input terminal 11. The photographed image signal received from the input terminal 11 is supplied to the terminal 21A of the switch circuit 21 through an AGC circuit 12 and a sample hold circuit 13. In the camera signal input mode, the switch circuit 21 is placed in the terminal 21A position. Thus, an output signal of the sample hold circuit 13 is supplied to an A/D converter 14 through the switch circuit 21. The A/D converter 14 digitizes the photographed image signal. An output signal of the A/D converter 14 is supplied to a camera signal processing circuit 15 and the terminal 22B of the switch circuit 22. An output signal of the camera signal processing circuit 15 is supplied to the terminal 22A of the switch circuit 22. In the camera signal input mode, the switch circuit 22 is placed in the terminal 22A position. In addition, the switch circuit 23 is placed in the terminal 23A position. Thus, the output signal of the A/D converter 14 is pre-processed by the camera signal processing circuit 15 and supplied to the connection portion of a one-line delay circuit 16 and a one-line delay circuit 17 through the switch circuit 22 and the switch circuit 23. An output signal of the switch circuit 23, an output signal of the connection portion of the one-line delay circuit 16 and the one-line delay circuit 17, and an output signal of the one-line delay circuit 17 are supplied as signals of successive three lines to the camera signal processing circuit 15. The camera signal processing circuit 15 generates a luminance signal Y and a chroma signal C corresponding to the three successive lines of the photographed image signal. Camera signal processes such as a gamma compensating process and an aperture compensating process are performed for the generated luminance signal Y and chroma signal C. The resultant luminance signal Y is supplied to the terminal 24A of the switch circuit 24. The resultant chroma signal C is supplied to the terminal 25A of the switch circuit 25. In the camera signal input mode, the switch circuit 24 is placed in the terminal 24A position. Thus, the luminance signal received from the camera signal processing circuit 15 is supplied to a variable delay circuit 18 through the switch circuit 24. The variable delay circuit 18 is disposed in the camera signal processing circuit 15. An output signal of the variable delay circuit 18 is supplied to a D/A converter 19. The D/A converter 19 converts the digital luminance signal into an analog signal. An output signal of the D/A converter 19 is supplied to an output terminal 20. In the camera signal input mode, the switch circuit 25 is placed in the terminal 25A position. Thus, the chroma signal received from the camera signal processing circuit 15 is supplied to a variable delay circuit 40 through the switch circuit 25. The variable delay circuit 40 is disposed in the camera signal processing circuit 15. An output signal of the variable delay circuit 40 is supplied to a D/A converter 41. The D/A converter 41 converts the digital chroma signal into an analog signal. An output signal of the D/A converter 41 is supplied to an output terminal 42. Next, the VTR reproduction mode will be described. In the VTR reproduction mode, a reproduction video signal of which a luminance signal and a chroma signal including a cross-talk component are combined is supplied to the input terminal 1. The reproduction video signal is supplied to a sample hold circuit 2. In the VTR reproduction signal input mode (referred to as VTR input mode), the switch circuit 21 is placed in the terminal 21B position. Thus, an output signal of the sample hold circuit 2 is supplied to the A/D converter 14 through the switch circuit 21. The A/D converter 14 digitizes the signal received from the input terminal 1. An output signal of the A/D converter 14 is supplied to the terminal 22B of the switch circuit 22. In the normal VTR reproduction mode, the switch circuit 22 is placed in the terminal 22B position. The switch circuit 23 is placed in the terminal 23A position. Thus, the output signal of the A/D converter 14 is supplied to the connection portion of the one-line delay circuit 16 and the one-line delay circuit 17 through the switch circuit 23. An output signal of the switch circuit 23 and an output signal of the connection portion of the one-line delay circuit 16 and the one-line delay circuit 17 are supplied to a Y comb filter 3. An output signal of the switch circuit 23, an output signal of the connection portion of the one-line delay circuit 16 and the one-line delay circuit 17, and an output signal of the one-line delay circuit 17 are supplied to a C comb filter 4. An output signal of the Y comb filter 3 is supplied to the terminal 24B of the switch circuit 24. In the normal VTR reproduction mode, the switch circuit 24 is placed in the terminal 24B position. Thus, the output signal of the Y comb filter 3 is supplied to the D/A converter 19 through the variable delay circuit 18. The output signal of the D/A converter 19 is supplied to the output terminal 20. The output signal of the C comb filter 4 is supplied to the terminal 25B of the switch circuit 25. In the VTR reproduction mode, the switch circuit 25 is placed in the terminal 25B position. Thus, the output signal of the C comb filter 4 is supplied to the D/A converter 41 through the variable delay circuit 40. The output signal of the D/A converter 41 is supplied to the output terminal 42. The output signal of the connection portion of the one-line delay circuit 16 and the one-line delay circuit 17 is supplied to the terminal 23B of the switch circuit 23. In the case that a drop-out takes place in the normal mode, the switch circuit 23 is placed in the terminal 23B position. Thus, the input signal is substituted with a signal prior to one line. An output signal of a middle portion of the one-line delay circuit 16 (from a portion with a delay amount of 1 line - α) is supplied to the terminal 24C of the switch circuit 24. In the case that a drop-out takes place in the Hi 8 mode, the switch circuit 24 is placed in the terminal 24C position. Thus, the signal of the middle portion of the one-line delay circuit 16 is supplied to the D/A converter 19 through the switch circuit 24 and the variable delay circuit 18. The output signal of the D/A converter 19 is supplied to the output terminal 20. In the VTR reproduction mode, the variable delay circuits 18 and 40 cause the delay of the luminance signal Y to accord with the delay of the chroma signal C. Thus, since the variable delay circuits 18 and 40, which are composed of digital circuits, are disposed downstream of the Y comb filter 3 and the C comb filter 4, the delay of the luminance signal Y can be easily matched with the delay of the chroma signal C. Thus, according to the embodiment of the present invention, in the VTR reproduction mode, since a signal of which the luminance signal and the chroma signal that have been band-limited are combined is supplied, the process can be performed with only one A/D converter. In addition, since the A/D converter 14 and the 2H delay circuits 16 and 17 that process the camera signals can be used also in the VTR reproduction mode, it is almost not necessary to add new circuits. The output signals of the Y comb filter 3 and the C comb filter 4 contain a component of the chroma signal and a component of the luminance signal, respectively. These residual components of the luminance signal and the chroma signal are removed by filters (not shown) disposed downstream of the filters 3 and 4. The filters that remove the residual components may be analog filters disposed downstream of the D/A converter or digital filters disposed upstream of the D/A converter. In the above-described embodiment, in the normal mode, the drop-out is compensated only with the digital circuits. In the Hi 8 mode, the drop-out is compensated with an external analog circuit along with the digital circuits. In other words, in the mode of which the band of the luminance signal is wide such as the Hi 8 mode of an 8-mm VTR, if a signal of which the luminance signal and the chroma signal are combined is supplied to a comb filter, since the luminance signal interferes with the chroma signal, the image quality deteriorates. To prevent the interference, the band of the luminance signal Y should be limited before it is combined with the chroma signal. Thus, in the Hi 8 mode, signals are processed with only the Y comb type filer, not the C comb filter. Since an output signal is obtained from the middle portion of the one-line delay circuit 16 (the portion with a delay amount of one line - α), the drop-out can be compensated with the digital circuits along with the external analog portion. The delay amount α is designated to a value of which the loop of the drop-out compensation has a delay of a total of one line due to the external analog portion other than the circuits between the sample hold circuit and the D/A converter. Since the component of the luminance signal corresponding to the band of the chroma signal is removed, the band of the drop-out signal becomes narrower than the band of the normal signal, no visual problem takes place. Having described a specific preferred embodiment of the present invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to that precise embodiment, and that various changes and modifications may 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 signal processing apparatus, comprising: an input selecting circuit (21) for selectively inputting a video signal (21B) of which a component of a luminance signal and a component of a chroma signal are combined or a photographed image signal (21A) of an image photographed by an image pick-up device; an A/D converter (14) for digitizing the selected signal selected by said input selecting circuit (21) from the video signal of which the component of the luminance signal and the component of the chroma signal are combined or the photographed image signal of an image photographed by the image pick-up device; a plurality of line delay circuits (16, 17) connected in series and adapted for delaying an output signal of said A/D converter; a luminance signal comb filter (3), a chroma signal comb filter (4), and a camera signal processing circuit (15) each receiving output signals from connection portions of said line delay circuits (16, 17) connected in series; an output selecting circuit (24, 25) for selecting an output signal (24B, 25B) of said luminance signal comb filter and said chroma signal comb filter or an output signal (24A, 25A) of said camera signal processing circuit, characterised by residual luminance and chroma signal filters arranged to remove residual chroma and luminance signal components respectively present in said output signals of said luminance signal comb filter and said chroma signal comb filter, and in that a drop-out compensating signal is obtained from a part of said line delay circuits connected in series, wherein the total loop delay amount produced by said part of said line delay circuits and said residual filters is a total amount of one line. The video signal processing circuit as set forth in claim 1, wherein a variable delay circuit (18, 40) is disposed downstream of said luminance signal comb filter (3) and said chroma signal comb filter (4).

Inventors: ENOMOTO TAKURO, KAGAWA TAKASHI, YOSHIKAWA TAKAO, ENOMOTO, TAKURO, KAGAWA, TAKASHI, YOSHIKAWA, TAKAO, Enomoto, Takuro, c/o Intellectual Prop. Divis., Kagawa, Takashi, c/o Intellectual Prop. Divis., Yoshikawa, Takao, c/o Intellectual Prop. Divis.
Applicants: SONY CORP, SONY CORPORATION
Application year: 1996
Main classification: H04N9
IPC codes: H04N5, H04N9