Video signal format converting circuit

Abstract: A video signal format converting circuit is disclosed, comprising a signal converting matrix (6) circuit and a filter circuit (25,26) that is constructed of a time delaying device (62-71) for a video signal corresponding to a standard television format. When a digital video signal corresponding to a first video signal format is converted into a second video signal format that is different from the first video signal format and then output, the time delaying device (62-71) of the filter circuit (25,26) is used as a delaying circuit. The output signal of the delaying circuit or the video signal corresponding to the standard television signal format is selectively output. While or after the video signal corresponding to the first video signal format is converted into the video signal corresponding to the second signal format, the video signal is modified so as to protect it from being copied.

Description: The present invention relates to a video signal format converting circuit for generating a video signal of a video signal format other than a composite video signal from a digital video signal that is reproduced from a digital VCR, received by a digital satellite broadcasting television receiver or a digital cable television receiver, or the like and for modifying the video signal so as to protect it from being copied. In recent years, as digital signal processing technologies have advanced, digitization of video signals has been actively employed for digital VCRs and digital satellite broadcasting receivers. In addition to digital video apparatuses that handle composite video signals, other digital video apparatuses that handle so-called S terminal output signals, or a luminance signal and colour difference signals (YUV signals), or RGB signals have been placed in the market so as to improve image quality of programs. On the other hand, since apparatuses as represented by VCRs that record and reproduce video signals have been widely used, copy protecting methods such as video signal modifying method by Macrovision Corporation (as disclosed in US Patent Nos. 4631603, 4577216, 4819098, and 5315448) have been employed from a point of view of copyright protection for visual software packages. In a conventional analog VCR, a particular signal that causes the operation of the AGC circuit of a recording VCR that dubs video signals of a movie video tape to malfunction is placed in vertical blanking intervals of the video signals. The resultant video signals are output from the VCR. However, in the digital VCR and digital broadcasting television receiver, information in the vertical blanking intervals is not recorded and broadcast so as to reduce the data amount. In these apparatuses, when reproduced or received digital video signals are converted into standard television signals such as NTSC television signals, a synchronous signal or the like is added thereto. Thus, the signal that causes the operation of the AGC circuit of the above-descried recording VCR to malfunction is added along with the synchronous signal or the like. Thus, it is necessary to convert a received digital video signal into a signal format corresponding to other than the composite signal format so as to handle digital video apparatuses such as high image quality digital VCRs and digital broadcasting television receivers. In addition, when output signals other than the composite signals are not protected by a copyright law, it is improper from a view point of the protection of intellectual property rights. Consequently, it is necessary to modify video signals corresponding to other than the composite signals so as to protect them from being copied. An object of the present invention is to solve such a problem and provide a video signal converting circuit for converting a received digital video signal into a video signal corresponding to a composite video signal and a video signal corresponding to other than the composite video signal and modifying a video signal corresponding to any video signal output format so as to protect the signal from being copied. According to a first aspect of the present invention, there is provided a digital video apparatus for converting a digital video signal composed of a digital luminance signal, a first digital colour difference signal, and a second digital colour difference signal into an analog video signal and outputting the converted signal, characterised by comprising: signal modifying means for modifying at least the digital luminance signal by applying a pulse that exceeds the level of the video signal or that varies in the range equivalent to a pedestal level to the digital luminance signal so as to protect the video signal from being analogously copied when recording an analog video signal derived from the digital video signal, signal converting means for converting the modified luminance signal, the first digital colour difference signal, and the second digital colour difference signal into a first video output signal having an analog composite output format and a second video output signal of an analog output format which is not a composite output format; and signal outputting means for separately outputting the first video output signal and the second video output signal. According to a second aspect of the present invention, there is provided a digital video apparatus for converting a digital video signal into an analog video signal and outputting the converted signal, characterised by comprising: signal modifying means for modifying at least the digital luminance signal by applying a pulse that exceeds the level of the video signal or that varies in the range equivalent to a pedestal level to the digital luminance signal so as to protect the video signal from being analogously copied when recording an analog video signal derived from the digital video signal, signal generating means for generating a digital colour signal from the first digital colour difference signal and the second colour difference signal; mode selecting means for selecting a first mode for outputting the digital colour signal and a second mode for outputting the first digital colour difference signal and the second digital colour difference signal; and signal outputting means for converting the signal selected by said mode selecting means and the modified digital luminance signal into an analog signal and outputting the converted signal. Thus, a digital video signal is converted into a composite video signal and another video signal corresponding to a high image quality system. In addition, the resultant video signal can be modified so as to protect it from being copied. The invention will be further described by way of non-limitative example with reference to the accompanying drawings, in which:- Figs. 1A, 1B and 1C are block diagrams showing a signal format converting circuit according to a first embodiment of the present invention; Fig. 2 is a schematic diagram showing input signals of the apparatus according to first embodiment of the present invention; Fig. 3 is a block diagram showing an example of the construction of a filter circuit constructed of a plurality of time delaying devices according to the present invention; and Figs. 4A, 4B and 4C are block diagrams showing a signal format converting circuit according to a second embodiment of the present invention. Next with reference to the accompanying drawings, embodiments of the present invention will be described. In the following description, digital video signals for digital video apparatuses such as digital VCRs and digital broadcasting receivers are converted into a luminance signal (Y) and a colour signal (C), or a luminance signal (Y) and colour difference signals (U and V), or RGB signals that are different from composite video signals and then generated. As a method for protecting these video signals from being copied, the modification of video signals corresponding to the Macro Vision method is exemplified. More specifically, the present invention will be explained based on a digital video signal stream corresponding to CCIR-601 (ITU-R601). Figs. 1A, 1B and 1C are circuit diagrams showing the construction of a video signal converting circuit according to a first embodiment of the present invention. The video signal converting circuit has two selectable modes that are a first mode for outputting a composite signal, a luminance signal (Y), and a colour signal (C) and a second mode for outputting a luminance signal (Y) and colour difference signals (U and V). In Figs. 1A, 1B and 1C, reference numerals 1, 2, 3, 7, 8, 19, 20, 21, and 49 are signal input terminals. Reference numeral 4 is a clock generating circuit. Reference numeral 5 is a synchronous signal generating circuit. Reference numeral 6 is a matrix circuit. Reference numerals 9, 10, 11, and 27 are latch circuits. Reference numerals 13, 14, 38, 39, and 40 are signal interpolating circuits. Reference numerals 15, 16, and 17 are signal level converting circuits. Reference numeral 18 is a serial signal circuit that receives a command from a microcomputer (not shown). Reference numerals 22, 23, 24, 28, 31, 34, 36, 41, 42, 50, 51, and 52 are selectors. When the value of a selection signal S is "1", an input B is supplied to an output O. When the value of the selection signal S is "O", an input A is supplied to the output O. Reference numerals 25 and 26 are filter circuits that are constructed of a plurality of time delaying devices or the like. Reference numerals 29 and 30 are multiplier circuits. Reference numerals 32, 37, 43, and 44 are adder circuits. Reference numeral 33 is a copy protection signal generating circuit that generates a signal for modifying a video signal so as to protect it from being copied. Reference numeral 35 is a synchronous signal tilt generating circuit. Reference numerals 53, 54, and 55 are DA converting circuits. Reference numerals 56, 57, and 58 are output circuits. Reference numeral 60 is a burst signal generating circuit. Fig. 2 is a schematic diagram showing signal waveforms of a digital video signal stream (corresponding to the CCIR-601 (ITU-601) standard) that is supplied to the input terminal 1 or 7. Next, the operation of the first mode will be described. In Figs. 1A, 1B and 1C, a clock signal that is a reference signal of the system is supplied from the input terminal 2. A reset signal that initializes the system state is supplied from the input terminal 3. The clock signal generating circuit 4 supplies the clock signal and the reset signal to each portion (not shown) of the system. The microcomputer (not shown) outputs a mode designation signal and so forth to the serial signal circuit through the input terminals 19, 20, and 21 so as to designate the mode of each portion of the system (only a part of the system is shown). Signals PD0-15 (in the case of the 16-bit mode) or signals PDO-7 (in the case of the eight-bit mode) shown in Fig. 2 are supplied from the input terminal 1 or 7. Fig. 2 shows both the cases of the eight-bit mode and the 16-bit mode of the digital video signal stream received from the preceding stages of the input terminals 1 and 7. The selected signal(s) is supplied to the matrix circuit 6. In the matrix circuit 6, the latch circuits 9, 10, and 11 separate signals Y, Cb, and Cr from the time series stream, respectively. The output signals of the latch circuits 10 and 11 are interpolated by the signal interpolating circuits 13 and 14 so that the number of pixels of the output signals of the latch circuits 10 and 11 accords with that of the luminance signal Y. The luminance signal Y is delayed by the delaying circuit 12 for a predetermined time period so as to compensate the signal delays in the signal interpolating circuits 13 and 14. The levels of the output signals of the delaying circuit 12 and the signal compensating circuits 13 and 14 are converted into levels suitable for signal processes by the signal level converting circuits 15, 16, and 17. In addition, the output signals of the delaying circuit 12 and the signal compensating circuits 13 and 14 are multiplied by predetermined coefficients and thereby these signals are converted into YUV signals (luminance signal and colour difference signals). The output signals U and V of the signal level converting circuits 16 and 17 are supplied to the filter circuits 25 and 26 so as to limit the frequency bands of the signals, respectively. In the copy protecting method of the video signal modifying method by Macrovision Corporation a pulse that exceeds the level of a video signal or that varies in the range equivalent to the pedestal level is applied to the luminance signal so as to cause the operation of the AGC circuit of the video signal recording/reproducing apparatus to malfunction. In addition, the phase of a chrominance subcarrier that is a reference of a colour signal process is inverted in a plurality of predetermined horizontal synchronous signal intervals so as to cause the colour signal processing circuit of the video signal recording/reproducing apparatus to malfunction. Corresponding to the video signal modifying method, the burst signal generating circuit 60 generates a burst signal having an inverted phase only in a plurality of predetermined horizontal synchronous signal intervals. In addition, the burst signal generating circuit 60 generates inverted phase burst signals and normal phase burst signals corresponding to the NTSC format and the PAL format. Corresponding to a control signal received from the copy protection signal generating circuit 33, the selectors 22, 23, 24, and 28 are controlled so as to supply the inverted burst signal to the selector 28. The selector 28 adds the inverted burst signal to the U signal so as to modify the U signal. The delay of the modified U signal is applied to the V signal by the latch circuit 27. The output signals of the latch circuit 27 and the selector 28 are multiplied by a cosine wave signal cos and a sine wave signal sin received from the chrominance subcarrier generating circuit (not shown) by the multiplier circuits 29 and 30, respectively. The resultant signals are added by the adder circuit 32 so that the luminance signal is converted into a colour signal (C). The resultant signal is output to the signal interpolating circuit 40 through the selector 34. The selectors 34, 41, and 42 are controlled corresponding to a control signal YUV received from the serial signal circuit 18. When the value of the control signal YUV is "O", the selectors 34, 41, and 42 output a signal on the side A. When the value of the control signal YUV is "1", the selectors 34, 41, and 42 output a signal on the side B. In the first mode, the value of the control signal YUV is "0". A synchronous signal is added to the luminance signal Y by the synchronous signal tilt generating circuit 35 and the selector 36. The synchronous signal tilt generating circuit 35 generates a synchronous signal with an analogous tilt to a digital synchronous signal (CSYNC) generated by the synchronous signal generating circuit 5. The copy protection signal generating circuit 33 generates a pulse that exceeds the level of the video signal or that vary in the range equivalent to a pedestal level corresponding to the video signal modifying method of Macrovision Corporation. The adder circuit 37 adds the pulse to the synchronous signal that is output from the selector 36. Thus, the video signal (luminance signal and colour signal) is modified with the copy protection signal corresponding to the video signal modifying method of Macrovision Corporation. The selector 31 and the copy protection signal generating circuit 33 are controlled corresponding to a control signal (anti taping) that is output from the serial signal circuit 18 that receives a command from the microcomputer (not shown). Thus, the addition of the copy protection signal can be enabled or disabled. In the case of the digital VCR, the copyright information recorded on the magnetic tape is reproduced and supplied to the microcomputer (not shown). The microcomputer commands the serial signal circuit 18 to generate the control signal (anti taping). When the copyright information recorded on the magnetic tape represents that the program has been protected by the copyright law, the control signal (anti taping) causes the selector 31 to output the signal on the side B. In addition, the control signal causes the copy protection signal generating circuit 33 to generate a pulse signal. The adder circuit 37 adds the pulse signal to the luminance signal (Y). On the other hand, when the copyright information recorded on the magnetic tape represents that the program has not been protected by the copyright law, the control signal (anti taping) causes the selector 31 to output the signal on the side A and prohibits the copy protection signal generating circuit 33 from generating the pulse signal. In the case of the digital satellite broadcasting television receiver, the copyright information is received along with the digital video signal. The copyright information is supplied to the microcomputer (not shown). The microcomputer commands the serial signal circuit 18 to generate the control signal (anti taping). The operation corresponding to the copyright information of the digital satellite broadcasting television receiver is the same as that of the digital VCR. After the pixels of the luminance signal (Y) and the colour signal (C) that have been processed in the above-described manner are interpolated by the signal interpolating circuits 38 and 40, the resultant luminance signal (Y) is converted into an analog signal by the DA converting circuit 53 through the selector 50 and then output from the output terminal 56. An offset value is added to the resultant colour signal (C) by the adder circuit 43. The resultant signal is converted into an analog signal by the DA converting circuit 55 through the selector 52 and then output from the output terminal 58. The resultant luminance signal (Y) and colour signal (C) are supplied to the adder circuit 44 through the selectors 41 and 42, respectively. The output signal of the adder circuit 44 is a composite signal. The composite signal is supplied to the DA converting circuit 54 through the selector 51. After the composite signal is converted into an analog signal by the DA converting circuit 54, the analog signal is output from the output terminal 57. The selectors 50, 51, and 52 select test signal inputs of the DA converting circuits 53, 54, and 55. Normally, the input A is selected. Thus, not only the composite signal that has been copy protected, but the luminance signal (Y) and the colour signal (C) that have been copy protected can be output. Next, the operation of the second mode for outputting the YUV signals (luminance signal and colour difference signals) will be described. In Figs. 1A, 1B and 1C, a clock signal that is a reference signal of the system is received from the input terminal 2. A reset signal that initializes the system state is received from the input terminal 3. The clock signal generating circuit 4 supplies the clock signal and the reset signal to each portion (not shown) of the system. The microcomputer (not shown) supplies a mode designation signal and so forth to the serial signal circuit through the input terminals 19, 20, and 21 so as to designate the mode of each portion of the system (only a part of the system is shown). Unlike with the first mode for outputting the composite signal, the luminance signal (Y), and the colour signal (C), in this operation, however, the value of a control signal YUV that is supplied to the filter circuit 25 and 26 and the selectors 34, 41, and 42 is set to "1" so as to output a YUV signal. The signals shown in Fig. 2 are received from the input terminal 1 or 7. The eight-bit mode or the 16-bit mode shown in Fig. 2 is selected corresponding to the signal that is received from the input terminal 8. The selected signal is supplied to the matrix circuit 6. In the matrix circuit 6, the latch circuits 9, 10, and 11 separate signals Y, Cb, and Cr from a time series signal. The output signals of the latch circuits 10 and 11 are interpolated by the signal interpolating circuits 13 and 14 so that the number of pixels of these signals accords with that of the luminance signal. The luminance signal Y is delayed by the delaying circuit 12 for a predetermined time period so as to compensate the time delays of the signals in the signal interpolating circuits 13 and 14. The levels of the output signals of the delaying circuit 12 and the signal interpolating circuits 13 and 14 are converted into levels of signals suitable for signal processes by the signal level converting circuit. In addition, the output signals of the delaying circuit 12 and the signal interpolating circuits 13 and 14 are multiplied by predetermined coefficients and thereby these signals are converted into YUV signals. When the YUV signals are output, the video signal cannot be modified corresponding to the copy protection signal. In addition, since the later signal process for the luminance signal is different from that for the colour difference signals, the time matching of the luminance signal and the colour difference signals is lost. To solve such a problem, according to the present invention, the Y signal and the U signal are modified so as to prevent the video signal from being copied. In addition, using the time delaying devices of the filter circuits 25 and 26 that are not used when the YUV signals are output, the time matching of the luminance signal and the colour difference signals is maintained. Fig. 3 is a circuit diagram showing an example of the construction of the filter circuit 25 constructed of a plurality of time delaying devices. Likewise, the filter circuit 26 can be accomplished by a construction similar to that shown in Fig. 3. Since the filter circuit is a typical example of a digital filter, only the operation relating to the present invention will be described. Thus, the operation as the filter circuit will be omitted. In Fig. 3, reference numeral 59 and 60 are input terminals. Reference numeral 61 is an output terminal. Reference numerals 62, 63, 64, 65, 66, 67, 68, 69, 70, and 71 are time delaying devices. Reference numerals 72, 73, 74, 75, 76, 77, 78, 79, and 80 are adder circuits. Reference numerals 81, 82, 83, 84, 85, 86, 87, 88, and 89 are coefficient devices. Reference numerals 90 and 91 are selectors. Since a signal that is received from the input terminal passes through the time delaying device 62 and so forth, the signal is delayed. When the composite signal, the luminance signal (Y), and the colour signal (C) are output, the delayed signals are multiplied by a coefficient and they are added so as to accomplish a desired filter characteristic. However, when the YUV signals are output, these time delaying devices are used as a delaying circuit. Thus, a level signal with a value of "1" is supplied to the input terminal 59 and the selectors 90 and 91 are placed in the position B so as to connect the time delaying devices in series. This operation is clear from Fig. 3. In this embodiment, in the filter circuit using for example 10 time delaying devices, nine time delaying devices are connected in series. However, the present invention is not limited to such a construction. In other words, to accomplish the desired characteristic for the standard television signal, the number of the time delaying devices is not limited to ten. In addition, the number of the time delaying devices that are connected in series is not limited to nine. Instead, as long as the number of the time delaying devices does not exceed that for the standard television signal, the number of the time delaying devices is not limited. In the construction according to the present invention, the difference of time delay amounts in the later stages can be absorbed. Returning to Figs. 1A, 1B and 1C, the YUV signals obtained by the matrix circuit 6 are supplied to the filter circuits 25 and 26 that compensate the time delays. The filter circuits 25 and 26 delay the YUV signals so as to absorb time delay amounts in the later stages. The output signals of the filter circuits 26 are supplied to the signal interpolating circuit and the selector 31 that selects a signal that has been modified for protecting the video signal from being copied. When the video signal is not modified, the output signal of the filter circuit 26 is directly output to the selector 31. When the video signal is modified for protecting it from being copied, the output signal is obtained through the filter circuit 26 and the selector 28. The output signal of the selector 31 is supplied to the selector 34. The output signal of the selector 34 is supplied to the signal interpolating circuit 40. Since the process for the luminance signal is the same as that for the first mode for outputting the composite signal, the luminance signal (Y), and the colour signal (C), the description will be omitted. The signal that has been interpolated by the signal interpolating circuit 39 is selected by the selector 41. The offset value is selected by the selector 42. The output signal of the selector 41 and the output signal of the selector 42 are added by the adder circuit 44. The output signal of the adder circuit 44 is supplied to the DA converting circuit 54 through the selector 51. An analog signal that is the output signal of the DA converting circuit 54 is output as a V output from the output terminal 57. The output signal of the signal interpolating circuit 40 is added to the offset value by the adder circuit 43. The output signal of the adder circuit 43 is supplied as an analog signal to the DA converting circuit 55 through the selector 52. The analog signal is output from the output terminal 58. Next, the difference of time delay amounts of the luminance signal and the colour difference signals will be described in brief. As is clear from Figs. 1A, 1B and 1C, the difference of the processes for the luminance signal and the colour difference signals is whether or not the signals pass through selectors or adder circuits. The time delay amount of each constructional element is in the range from several clock pulses to twenty clock pulses. On the other hand, the characteristic of the filter circuit for the standard television signal directly affects the image quality. Thus, more time delaying devices than those for the difference of the time delay amounts of the luminance signal and the colour difference signals are required. As described above, according to the present invention, the YUV signals that are different from composite signals can be output from digital video signals without need to add any time delaying devices. In addition, any video signals can be modified so as to protect them from being copied. The above-described first mode or second mode can be selected corresponding to the type of the digital video apparatus (for example, a digital VCR, a digital satellite broadcasting television receiver, and so forth). Thus, in the same system, these modes cannot be manually selected. This applies to the second embodiment of the present invention. Next, with reference to Figs. 4A, 4B and 4C, a second embodiment of the present invention will be described. In the second embodiment, as with the first embodiment, the first mode for outputting the composite signal, the luminance signal (Y), and the colour difference signal (C) or the second mode for outputting the YUV signals can be selected from the digital video signal stream corresponding to the CCIR-601 (ITU-R601) standard. In addition, a third mode for outputting the RGB signals can be also selected. In the third mode unlike with the first embodiment, a second matrix circuit 45 generates the RGB signals. The RGB signals are modified so as to protect them from being copied. Since the method for generating the RGB signals from the YUV signals is known, the description thereof will be omitted. In the third mode, selectors 46, 47, and 48 are placed in a position B corresponding to a selection control signal RGB that is output from a microcomputer 18. Signals B, R, and G are output to output terminals 56, 57, and 58 through selectors 50, 51, and 52 and DA converting circuits 53, 54, and 55, respectively. As described above, according to the present invention, the RGB signals as output signals can be output from the digital video signals without need to add any time delaying devices. In addition, the video signals can be modified so as to protect them from being copied. In the above-described embodiments, the digital video signals are converted into the NTSC analog signals. As the method for protecting signals from being copied, the Macrovision Corporation method is used. However, it should be noted that the present invention is not limited to such a system. Instead, the video signal formats of the above-described embodiments can be changed. Moreover, in the above-described embodiments, the Macrovision Corporation method was exemplified as a video signal modifying method for protecting signals from being copied. However, the present invention is not limited to such a method. Thus, even if another video signal modifying method is used, the effects of the present invention are not deteriorated. According to the present invention, digital video signals are converted into video signals other than composite video signals. Video signals other than the composite video signals can be modified so as to protect them from being copied. Having described specific preferred embodiments of the present 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 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 digital video apparatus for converting a digital video signal composed of a digital luminance signal, a first digital colour difference signal, and a second digital colour difference signal into an analog video signal and outputting the converted signal, characterised by comprising: signal modifying means (33, 37, 60, 28) for modifying at least the digital luminance signal (Y) by applying a pulse that exceeds the level of the video signal or that varies in the range equivalent to a pedestal level to the digital luminance signal (Y) so as to protect the video signal from being analogously copied when recording an analog video signal derived from the digital video signal, signal converting means (29, 30, 32, 34, 41, 42, 44, 53-55) for converting the modified luminance signal (Y), the first digital colour difference signal (U), and the second digital colour difference signal (V) into a first video output signal having an analog composite output format and a second video output signal of an analog output format which is not a composite output format; and signal outputting means (56-58) for separately outputting the first video output signal and the second video output signal. The digital video apparatus as set forth in claim 1, wherein said signal modifying means (33, 37) is arranged to be enabled or disabled depending on copyright information transmitted along with the digital video signal. The digital video apparatus as set forth in claim 1 or 2, wherein said signal converting means includes means (29, 30, 32) for generating a digital colour signal (C) from the first digital colour difference signal (U) and the second digital colour difference signal (V) and means (44) for mixing the digital colour signal (C) and the digital luminance signal (Y) so as to generate a digital composite signal (COMP), and wherein said signal outputting means includes a first digital-analog converting circuit (53, 55) for converting the digital colour signal and the digital luminance signal into an analog signal and outputting the converted signal and a second digital-analog converting circuit (54) for converting the digital composite signal into an analog signal and outputting the converted signal. The digital video apparatus as set forth in any one of the preceding claims, wherein said signal modifying means includes means (60, 28) for modifying the first digital colour difference signal (U) and means (27) for delaying the second digital colour difference signal for the time period necessary to modify the first digital colour difference signal (U). The digital video apparatus as set forth in claim 4, wherein said signal modifying means includes means (60) for generating a colour burst signal with an inverted phase only in a plurality of predetermined horizontal synchronous signal intervals and means (28) for adding the colour burst signal to the first digital colour difference signal (U). A digital video apparatus for converting a digital video signal into an analog video signal and outputting the converted signal, characterised by comprising: signal modifying means (33, 37, 60, 28) for modifying at least the digital luminance signal (Y) by applying a pulse that exceeds the level of the video signal or that varies in the range equivalent to a pedestal level to the digital luminance signal (Y) so as to protect the video signal from being analogously copied when recording an analog video signal derived from the digital video signal, signal generating means (29, 30, 32) for generating a digital colour signal (C) from the first digital colour difference signal (U) and the second colour difference signal (V) ; mode selecting means (18) for selecting a first mode for outputting the digital colour signal (C) and a second mode for outputting the first digital colour difference signal (U) and the second digital colour difference signal (V); and signal outputting means (53-58) for converting the signal selected by said mode selecting means (18) and the modified digital luminance signal (Y) into an analog signal and outputting the converted signal. The digital video apparatus as set forth in claim 6, further comprising digital low pass filter means (25, 26) for restricting a frequency band of the first digital colour difference signal (U) and the second digital colour difference signal (V) in the first mode and for delaying the first digital colour difference signal (U) and the second colour difference signal (V) for the time period necessary to modify the digital luminance signal (Y). The digital video apparatus as set forth in claim 6 or 7, wherein said signal modifying means is arranged to be enabled or disabled depending on at least the digital luminance signal corresponding to copyright information transmitted along with the digital video signal. The digital video apparatus as set forth in any one of claims 6 to 8, wherein said signal modifying means includes means (28) for modifying the first digital colour difference signal (U) and means (27) for delaying the second digital colour difference signal (V) for the time period necessary to modify the first digital colour difference signal (U). The digital video apparatus as set forth in claim 9, wherein said signal modifying means includes means (60) for generating a colour burst signal with an inverted phase only in a plurality of predetermined horizontal synchronous signal intervals and means (28) for adding the colour burst signal to the first digital colour difference signal. The digital video apparatus as set forth in any one of claims 6 to 10, further comprising a matrix circuit (45) for generating digital RGB signals from the digital luminance signal (Y), the first digital colour difference signal (U), and the second digital colour difference signal (V), wherein said mode selecting means (18) includes means (46-48) for selecting a third mode for outputting the digital RGB signals. A method for protecting an analog video signal converted from a digital video signal composed of a digital luminance signal, a first digital colour difference signal, and a second digital colour difference signal from being copied, characterised by comprising the steps of: modifying at least the digital luminance signal by applying a pulse that exceeds the level of the video signal or that varies in the range equivalent to a pedestal level so as to protect the video signal from being analogously copied when recording an analog video signal derived from the digital video signal generating a digital colour signal from the first digital colour difference signal and the second digital colour difference signal; generating a digital composite signal from the modified digital luminance signal and the digital colour signal; converting the digital colour signal and the modified digital luminance signal into analog signals and outputting the converted signals; and converting the digital composite signal to an analog signal and outputting the converted signal. The method as set forth in claim 12, further comprising modifying the first digital colour difference signal and delaying the second digital colour difference signal for the time period necessary to modify the first digital colour difference signal. The method as set forth in claim 12 or 13, wherein said signal modifying step is performed by generating a colour burst signal with an inverted phase only in a plurality of predetermined horizontal synchronous signal intervals and adding the colour burst signal to the first digital colour difference signal.

Inventors: MOGI YASUHIDE, NARITA ATSUSHI, YAMAUCHI ETSURO, MOGI, YASUHIDE, NARITA, ATSUSHI, YAMAUCHI, ETSURO, Mogi, Yasuhide, c/o Sony Corporation, Narita, Atsushi, c/o Sony Corporation, YAMAUCHI, ETSURO, C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1995
Main classification: H04N5
IPC codes: H04N9, H04N5, H04N7