Apparatus and method of reproducing wide-band mode video signal

Abstract: A video signal recorded according to PAL (Phase-Alternation Line) system is reproduced. Luminance (300) and chrominance (400) signals of the video signal are separately processed. It is judged (70) whether the video signal has been recorded in a wide-band mode where a luminance carrier frequency is higher than a chrominance subcarrier. A pilot burst signal carried by the chrominance signal for each horizontal blanking period is canceled (240,250) when the video signal is judged as recorded in the wide-band mode. A reproduced composite video signal is output (160) on the basis of the processed luminance and chrominance signals. The luminance carrier frequency may be detected for judging whether the video signal has been recorded in the wide-band. The sub-deemphasis characteristics may be applied to the luminance signal where the sub-deemphasis characteristics is the inverse of sub-emphasis characteristics that has been applied to the luminance signal in recording of the video signal in the wide-band mode (50,60,80).

Description: BACKGROUND OF THE INVENTION The present invention relates to reproduction of video signals. Particularly, this invention relates to reproduction of video signals recorded in a narrow-band mode (standard mode, such as VHS format mode) and also video signals recorded in a wide-band mode (high definition mode, such as S-VHS format mode) according to the PAL (Phase-Alternation Line) system. There are two types of helical scanning-type magnetic recording and reproducing apparatus (called VTR hereinafter) using 1/2 inch-wide magnetic tapes. One is narrow-band mode VTR according to the VHS system (trademark). The other type is wide-band mode VTR according to the S-VHS system (trademark). In a narrow-band mode, the luminance carrier frequency is lower than the chrominance subcarrier. On the other hand, the luminance carrier frequency is higher than the chrominance subcarrier fsc in a wide-band mode. More detail, in a VTR of the standard VHS (standard mode), a video signal to be recorded is separated into luminance and chrominance (color) signals. The luminance signal is modulated into an FM (frequency modulated) luminance signal having a frequency deviation of 3.4 to 4.4 MHz. The chrominance signals are down-converted into a low frequency band around 629 kHz. The FM modulated luminance signal and the Frequency-down-converted chrominance signals are combined before being recorded on a magnetic tape. In a VTR of the S-VHS (high definition mode), a video signal to be recorded is separated into luminance and chrominance signals. The luminance signal is modulated into an FM (frequency modulated) luminance signal having a frequency deviation of 5.4 to 7.0 MHz. The chrominance signals are down-converted into a low frequency band around 629 kHz. The FM modulated luminance signal and the frequency-down-converted chrominance signals are combined before being recorded on a magnetic type. Recording PAL video signals by a wide-band mode VTR requires a pilot burst signal for each horizontal blanking period in the frequency-down-converted chrominance signal. The pilot burst signal indicates the status of a PAL video signal, such as, image quality, according to the S-VHS625 standards. In detail, in case of the S-VHS format PAL video signal recording, the pilot burst signal is used for recording PAL video signals with conversion of the luminance signal band into a band, such as, about 5 MHz, over the chrominance subcarrier signal fsc. The pilot burst signal is a burst signal of, for example, fsc = 4. 43 MHz, for PAL video signal recording according to Japanese Unexamined Patent Publication No. JP-A-1049395. Document EP-A-0669770 describes an apparatus for reproducing video signals recorded in VHS or S-VHS mode, comprising a judging section to judge whether the video signals have been recorded in VHS or S-VHS, based on the pilot burst availabilitates. On the other hand, recording PAL video signals in the narrow-band mode (standard mode, such as VHS format mode) does not require such a pilot burst signal. Narrow-band mode VTRs, such as VHS-ET (Expansion Technology) VTRs, for reproducing NTSC (National Television System Committee) video signals recorded in the wide-band mode (high definition mode, such as S-VHS format mode) have been developed. On the other hand, narrow-band mode VTRs for reproducing PAL video signals recorded in the wide-band mode have not been developed. This is because reproduction of PAL signals with pilot burst signals causes malfunction of a clump circuit on a TV set. This results in disturbance in reproduced video. The clump circuit of recording side VTR would also malfunction during dubbing. This results in unsatisfactory recording. SUMMARY OF THE INVENTION A purpose of the present invention is to provide an apparatus and a method, based on narrow-band mode, of reproduction of PAL video signals recorded in wide-band mode with no disturbance in reproduced video. The present invention provides an apparatus for reproducing a video signal that has been recorded according to PAL (Phase-Alternation Line) system. The apparatus includes a luminance signal processor to process a luminance signal of the video signal; a chrominance signal processor to process a chrominance signal of the video signal; a judging section to judge whether the video signal has been recorded in a wide-band mode, a luminance carrier frequency being higher than a chrominance subcarrier in the wide-band mode; a canceller to cancel a pilot burst signal carried by the chrominance signal for each horizontal blanking period when the video signal is judged as recorded in the wide-band mode; and a reproducer to output a composite video signal on the basis of the processed luminance and chrominance signals. Furthermore, the present invention provides a method of reproducing a video signal that has been recorded according to PAL (Phase-Alternation Line) system, the method. A luminance signal of the video signal is processed. A chrominance signal of the video signal is processed. It is judged whether the video signal has been recorded in a wide-band mode, a luminance carrier frequency being higher than a chrominance subcarrier in the wide-band mode. A pilot burst signal carried by the chrominance signal for each horizontal blanking period is canceled when the video signal is judged as recorded in the wide-band mode. A composite video signal is output on the basis of the processed luminance and chrominance signals. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a block diagram of a wide-band mode recording apparatus; FIG. 2 shows a block diagram of a preferred embodiment of a reproducing apparatus according to the present invention; and FIG. 3 illustrates cancellation of pilot burst signals from a chrominance signal. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Before describing a preferred embodiment, recording a video signal which will then be reproduced according to the present invention is discussed with reference to FIG. 1. FIG. 1 shows a block diagram of a wide-band mode (high definition mode, such as S-VHS format mode) recording apparatus (S-VHS VTR, for example) that records a high definition PAL video signal on a magnetic tape. A composite PAL video signal supplied to the apparatus through an input terminal 10 is separated into a luminance signal Y and a chrominance signal C by a YC separator 12. The luminance signal Y is applied the sub-emphasis characteristics by a sub pre-emphasizer (SUB PRE-EMPH) 13 and further applied the emphasis characteristics by a main pre-emphasizer (MAIN PRE-EMPH) 14 for emphasizing high frequency components of the signal Y. The output of the main pre-emphasizer 14 is supplied to a clipper (CLIP) 15 for clipping signal components having the levels over a reference level. The clipped signal is supplied to a frequency modulator (FM) 16 for frequency modulation (the FM modulated luminance signal having a frequency deviation of 5.4 to 7.0 MHz) and then amplified by an amplifier (AMP) 17, to be a FM-luminance signal for recording. The chrominance signal C output by the YC separator 12 is added with a pilot burst signal by a pilot burst signal adder 18. The output of the adder 18 is converted into a low-band chrominance signal around 629 kHz by a low-band converter 19. Undesired signal components of the converted signal are removed by a low-pass filter (LPF) 20. The frequency-down-converted chrominance signal is then applied the burst emphasis characteristics by a burst-emphasizer (BE) 21. The FM-luminance signal and the low-band frequency-converted chrominance signal having the burst emphasis characteristics are mixed with each other and recorded on a magnetic tape 23 by a magnetic head 22. As described above, the luminance signal Y is applied the sub-emphasis characteristics in the wide-band mode recording; and hence, in wide-band mode reproduction, the luminance signal Y will be applied the sub-deemphasis characteristics. On the other hand, narrow-band VTRs (standard VTRs, such as standard VHS format VTRs) do not apply the sub-emphasis characteristics to luminance signal. Such VTRs thus do not have a sub-deemphasizer. The present invention then offers a reproducing apparatus having simply structured sub-deemphasis circuitry. Shown in FIG.2 is a block diagram of a preferred embodiment of a reproducing apparatus for both the narrow- and wide-band modes according to the present invention. One of the features of the present invention is that the sub-deemphasis circuitry consists of a linear deemphasizer (L DEMPH) 120 and a non-linear deemphasizer (NL DEMPH) 140. This circuitry is made on the basis of that fact that the sub-emphasis characteristics is composed of the linear and non-linear characteristics; and hence, the corresponding sub-deemphasis characteristics is also composed of the linear and non-linear characteristics. The PAL video signal that has been recorded on the magnetic tape 24 in the wide-band mode as discussed with reference to FIG. 1 is reproduced as described below. The reproduced RF PAL video signal is supplied to a preamplifier (PREAMP) 30 through a reproducing head 25, to be a RF (Radio Frequency) signal having a predetermined amplitude level. The RF signal is processed by luminance signal circuitry 300 and also chrominance signal circuitry 400. The signal components processed by each of the circuitry 300 and 400 are added to each other by an adder 160, to be a composite reproduced PAL video signal. The composite video signal is then amplified by an amplifier (AMP) 270 and output from the reproducing apparatus. Firstly, the luminance signal circuitry 300 is described. The RF signal output by the preamplifier 30 is supplied to an automatic gain controller (AGC) 40 for giving a constant level to the envelope of the RF signal; and then supplied to an equalizer (EQ) 50, an S-equalizer (SEQ) 60 and a judging unit 70. The judging unit 70 determines whether the RF signal has been recorded in the wide-band mode. In detail, the unit 70 detects the luminance carrier frequency that is 3.8 MHz for PAL VHS and 5.4 MHz for PAL S-VHS. When recording in the wide-band mode is detected, the unit 70 sends a switching signal to switches 80, 130 so that they are turned on to the "S" side. The switching signal is also sent to a switch 240 so that it is turned on. The RF signal output by the automatic gain controller 40 is then supplied to a frequency demodulator (FDM) 90 through the S-equalizer 60. The S-equalizer 60 removes the lower-band converted chrominance signal components from the RF signal and adjusts the frequency characteristics of both the side-band signal components. The RF signal processed by the S-equalizer 60 is supplied to the frequency demodulator 90 and demodulated into a video (luminance) signal. The demodulated signal is supplied to a deemphasizer (DEMPH) 100. The deemphasizer 100 applies the deemphasis characteristics to the demodulated signal. The deemphasis characteristics is the inverse of the emphasis characteristics applied by the main pre-emphasiser 14 in recording for emphasizing high frequency components in FIG. 1. The application of deemphasis characteristics reduces triangle wave noise components of the demodulated signal. The noise-reduced signal is supplied to a low-pass filter (LPF) 110 for removing undesired signal components. As disclosed above, in reproduction of a PAL video signal recorded in the wide-band mode, the mode is detected by the judging unit 70 to turn on the switch 130 to the "S" side, so that the output of the low-pass filter 110 is supplied to the linear deemphasizer (L DEMPH) 120. The linear deemphasizer 120 applies the linear characteristics, that is the inverse of the linear characteristics of the sub-emphasis characteristics applied by the sub pre-emphasizer 13 (FIG. 1) in recording, to the output of the low-pass filter 110. The output of the linear deemphasizer 120 is supplied to the non-linear deemphasizer 140 via switch 130 and applied the non-linear characteristics that is the inverse of the nonlinear characteristics of the sub-emphasis characteristics applied in recording. As disclosed, according to the present invention, the sub-emphasis circuitry consists of the linear deemphasizer 120 and the non-linear deemphasizer 140 to apply the sub-deemphasis characteristics that is the inverse of the sub-emphasis characteristics applied in recording to the input PAL signal. The luminance signal having the sub-emphasis characteristics is supplied to a noise canceller (NC) 150. After high frequency noise components are eliminated, the luminance signal is supplied to the adder 160. Next, the chrominance signal circuitry 400 is described. The RF signal output by the preamlifier 30 is supplied to a low-pass filter (LPF) 170, a trap 180 and another low-pass filter (LPF) 190, and undesired signal components of frequency-down-converted chrominance signals are eliminated. The low-band converted chrominance signal is supplied to a converter (CONV) 200 and converted into a high-band (chrominance subcarrier signal frequency) converted chrominance signal which is then supplied to a band-pass filter (BPF) 210. The high-band converted chrominance signal (subcarrier frequency chrominance signal) is supplied to an adder 250 after undesired signal components are eliminated by the band-pass filter (BPF) 210. The luminance signal output by the nonlinear deemphasizer 140 of the luminance signal circuitry 300 is supplied to a synchronizing signal separator (SYNC SEP) 220 of the chrominance signal circuitry 400. The reproduced luminance signal to be supplied to the separator 220 is a luminance signal without the sub-emphasis characteristics that have been applied in recording, or having the sub-deemphasis characteristics. This is a must, otherwise, a synchronizing signal which will be separated from the luminance signal would be an inaccurate signal. Signal processing conducted by the synchronizing signal separator 220, a canceling pulse generator 230 and the adder 250 is described with reference to FIG. 3. A synchronizing signal SYNC is separated from the luminance signal by the synchronizing signal separator 220 and supplied to the canceling pulse generator 230. The generator 230 generates a canceling pulse CP on the basis of the synchronizing signal. As already described, the switch 240 has been turned on by the switching signal from the judging unit 70 that has judged that the RF signal had been recorded in the wide-band mode. The canceling pulse CP is then supplied to the adder 250 via switch 240, to which the high-band converted chrominance signal has been supplied from the band-pass filter 210. The chrominance signal supplied to the adder 250 is shown in FIG. 3 as a chrominance signal A that includes a chrominance signal component C, a pilot burst signal PB and a color burst signal CB. The pilot burst signal PB is canceled by addition of a zero-level DC signal while the canceling pulse CP is "HIGH". A chrominance signal B that includes the chrominance signal component C and the color burst signal CB without the pilot burst signal PB is then output by the adder 250. The chrominance signal B is supplied to a burst deempahsizer (BD) 260 and applied the burst deemphasis characteristics which is the inverse of the burst emphasis characteristics applied by the burst emphasizer 21 (FIG. 1) in recording. The adder 160 mixes the luminance signal from the noise canceller 150 and the chrominance signal from the burst deempahsizer 260. The output of the adder 160 is supplied to an amplifier (AMP) 270 and amplified at a predetermined level, to be an output reproduced composite video signal. As described above, a PAL video signal that has been recorded in the wide-band mode can be reproduced by using the reproduction circuitry for narrow-band mode. Described next is reproduction of a PAL video signal that has been recorded in the narrow-band mode (standard mode, such as VHS format mode). For simplicity, the functions of the circuit components the same as for the PAL video signal recorded in the wide-band mode and described above is not descried in detail. A reproduced RF PAL video signal recorded in the narrow-band mode is supplied to the judging unit 70 through the preamplifier 30 and automatic gain controller 40. When recording in the narrow-band mode is detected, the judging unit 70 sends a switching signal to the switches 80 and 130 so that they are turned on to the "V" side. The switching signal is also supplied to the switch 240 so that it is turned off. A RF signal output by the automatic gain controller 40 is supplied to the frequency demodulator 90 through the equalizer 50. The equalizer 50 removes the lower-band converted chrominance signal components from the RF signal and adjusts the frequency characteristics of both the side-band signal components. The RF signal processed by the equalizer 50 is further processed by the frequency demodulator 90, deemphasizer 100 and low-pass filter 110 and then supplied to the non-linear deemphasizer 140 via switch 130 with no processing by the linear deemphasizer 120. The RF signal processed by the non-linear deemphasizer 140 is supplied to the adder 160 through the noise canceller 150. The reproduced RF PAL video signal recorded in the narrow-band mode is also supplied to the low-pass filter 170 through the preamplifier 30 and the automatic gain controller 40. The output of the low-pass filter 170 is supplied to the adder 250 through the trap 180, low-pass filter 190, converter 200 and band-pass filter 210. The output of the band-pass filter 210 passes through the adder 250 as it is because the switch 240 is turned off for the PAL video signal which has been recorded with no pilot burst signal in the narrow-band mode. The output of the adder 250 is processed by the burst de-emphasizer 260 and supplied to the adder 160. The luminance signal from the noise canceller 150 and the chrominance signal from the burst deemphasizer 260 are added by the adder 160, to be a reproduced composite video signal. The composite video signal is output from the reproducing apparatus through the amplifier 270. As disclosed above, the present invention achieves reproduction of PAL video signals recorded in the narrow-band mode by means of a non-linear deemphasizer and also reproduction of PAL video signals recorded in the wide-band mode by the combination of the non-linear deemphasizer and a linear deemphasizer. Pilot burst signals carried by PAL video signals in the wide-band mode can be canceled by means of the result of processing by the judging unit, the canceling pulse generator and the adder. Cancellation of pilot burst signals achieves avoidance of disturbance in reproduced PAL video signals that have been recorded in the wide-band mode.

Claims: An apparatus for reproducing a video signal that has been recorded according to PAL "Phase-Alternation Line" system, the apparatus comprising: a luminance signal processor to process a luminance signal of the video signal; a chrominance signal processor to process a chrominance signal of the video signal; a judging section to judge whether the video signal has been recorded in a wide-band mode, a luminance carrier frequency being higher than a chrominance subcarrier in the wide-band mode; a canceller to cancel a pilot burst signal carried by the chrominance signal for each horizontal blanking period when the video signal is judged as recorded in the wide-band mode; and a reproducer to output a composite video signal on the basis of the processed luminance and chrominance signals. The apparatus according to claim 1 wherein the judging section detects the luminance carrier frequency for judging whether the video signal has been recorded in the wide-band. The apparatus according to claim 1 wherein the luminance signal processor includes a sub-deemphasis section that applies sub-deemphasis characteristics to the luminance signal, the sub-deemphasis characteristics being the inverse of sub-emphasis characteristics that has been applied to the luminance signal during recording of the video signal in the wide-band mode. The apparatus according to claim 3 wherein the sub-deemphasis section includes a linear deemphasizer and a non-linear deemphasizer. The apparatus according to claim 3, the canceller including: a separator to separate a synchronizing signal from an output signal of the sub-deemphasis section; and a generator to generate a canceling pulse on the basis of the synchronizing signal, the pilot burst signal being canceled by means of the canceling pulse. A method of reproducing a video signal that has been recorded according to PAL "Phase-Alternation Line" system, the method comprising the steps of: processing a luminance signal of the video signal; processing a chrominance signal of the video signal; judging whether the video signal has been recorded in a wide-band mode, a luminance carrier frequency being higher than a chrominance subcarrier in the wide-band mode; canceling a pilot burst signal carried by the chrominance signal for each horizontal blanking period when the video signal is judged as recorded in the wide-band mode; and outputting a composite video signal on the basis of the processed luminance and chrominance signals. The method according to claim 6 wherein the judging step includes the step of detecting the luminance carrier frequency for judging whether the video signal has been recorded in the wide-band. The method according to claim 6 wherein the luminance signal processing step includes the step of applying sub-deemphasis characteristics to the luminance signal, the sub-deemphasis characteristics being the inverse of sub-emphasis characteristics that has been applied to the luminance signal during recording of the video signal in the wide-band mode. The method according to claim 8 wherein the sub-deemphasis characteristics applying step includes the step of applying linear and non-linear deemphasis characteristics to the luminance signal. The method according to claim 8, the canceling step including the steps of: separating a synchronizing signal from a result of application of the sub-deemphasis characteristics; and generating a canceling pulse on the basis of the synchronizing signal, the pilot burst signal being canceled by means of the canceling pulse.

Inventors: ISHII KANJU, MUROYA TSUYOSHI, ISHII, KANJU, MUROYA, TSUYOSHI
Applicants: VICTOR COMPANY OF JAPAN, VICTOR COMPANY OF JAPAN LIMITED
Application year: 2000
Main classification: H04N9
IPC codes: H04N9, H04N5