KR100226564B1 - Apparatus for processing a video signal - Google Patents

Abstract

In an apparatus for processing an input video signal comprising a chroma signal and a luminance signal, the luminance signal is frequency modulated and the chroma signal is preferably subsampled by field-offset subsampling, while the subsampled chroma signal is frequency modulated. The frequency modulation is performed at a frequency band lower than the frequency band of the luminance signal. The frequency modulated luminance signal and the frequency modulated subsampled chromaticity signal are then combined, and the resulting combined signal is recorded on a recording medium such as a magnetic tape.

During reproduction of the recorded signal, interpolation in the frame is used to reconstruct the chroma signal. Recording of the frequency modulated subsampled chromaticity signal provides a reproduced chromaticity signal with a relatively wide bandwidth to allow for space-efficient recording of the video signal while at the same time having improved color reproduction.

Description

Input video signal playback device and video signal recording and playback system

1 is a block diagram of a conventional video tape recorder.

2 is a block diagram of a write circuit of a VTR according to an embodiment of the present invention.

3 is a block diagram of a regeneration circuit of a VTR according to an embodiment of the present invention.

4A-4D are schematic diagrams illustrating chroma signal subsampling in the embodiments of FIGS. 2 and 3;

5 is a schematic diagram illustrating interpolation of the reproduced chromaticity signals of the embodiments of FIGS. 2 and 3;

6 is a schematic diagram illustrating an effective bandwidth of a chroma signal recorded and reproduced according to the present invention.

7 is a graph illustrating a frequency response characteristic curve with cosine roll-off.

8 is a block diagram of a regeneration circuit according to another embodiment of the present invention.

9A and 9B are schematic diagrams illustrating chromatic signal western sampling used to record a signal reproduced by the embodiment of FIG.

10 is a block diagram of a video tape recorder according to another embodiment of the present invention.

11 is a graphical representation of a typical frequency band used for chroma signals.

12 is a graphical representation of a frequency response characteristic curve for a VTR electromagnetic conversion system.

13 is a graphical representation of a frequency response special curve for a high pass filter.

14 is a graphical representation of a frequency response curve for a low pass filter that is part of a recording circuit.

15 is a graphical representation of a frequency response characteristic curve for a low pass filter of a regeneration circuit.

16A and 16B are graphs of frequency response characteristic curves for explaining the configuration of the filter circuit according to the present invention.

17 is a graphical representation of frequency response characteristic curves for the entire recording system.

18 is a block diagram of a video tape recorder according to another embodiment of the present invention.

19 is a graphical representation of a frequency response characteristic curve for an electromagnetic conversion system of a VTR, which will be mentioned about describing a scatter in an electromagnetic conversion system.

20 is a diagram of a frequency response characteristic curve of a trap filter for trapping an audio signal.

21 is a graph of frequency response characteristic curves showing the output chromaticity signal of the trap circuit mentioned in FIG.

FIG. 22 is a graphical representation of a frequency response characteristic curve illustrating the scatter in the overall electromagnetic conversion system including the trap filter mentioned in connection with FIG. 20. FIG.

FIG. 23 is a block diagram of a low pass filter included in the VTR of FIG.

24 is a graphical representation of the magnitude characteristics of the chroma signal after correction by the lowpass filter of FIG.

Explanation of symbols for main parts of the drawings

32: luminance / chromatic separation circuit 33: luminance recording processing circuit

35: chromaticity decoder 36: offset subsample circuit

40: recording amplifier 41: rotary converter

59: comb filter

TECHNICAL FIELD The present invention relates to video signal recording and reproducing apparatus, and more particularly to such an apparatus in which down-converted chroma signals are recorded as frequency-modulated luminance signals.

In video tape recorders designed for consumer use, recording down-converted chroma signals with frequency-modulated (FM) luminance signals to minimize the tape area required for recording, thereby increasing the recording capacity of the tape cassette. It is known. According to this known approach, the chroma signal is converted, for example, into a frequency band having a center frequency of about 700 KHz and a bandwidth around 400 to 500 KHz.

This conventional type of VTR is generally indicated by reference numeral 1 in FIG. 1.

In the VTR 1, the input video signal SV is supplied to an automatic gain control (AGC) circuit 2 that corrects the signal level of the input video signal SV. The level correction signal output by the AGC circuit 2 is provided to the luminance / chromatic signal processing (Y / C) circuit 3 which separates this signal into the luminance signal Y and the chroma signal C. The separated luminance signal Y is frequency modulated by the luminance signal processing circuit 4 to generate the luminance recording signal YFM.

In addition, the chroma signal C is supplied to the automatic chromaticity control (ACC) circuit 6 through a band pass filter (BPF) 5. The (ACC) circuit 6 outputs the level-corrected chromaticity signal C to the evphasis circuit 7, which embodies the chromaticity signal C to frequency the emphasized chromaticity signal. Output to the conversion circuit 8. The conversion circuit 8 down-converts the chroma signal C to the relatively narrow low frequency described above, and outputs the down-converted chroma signal to the adder circuit 10 through the low pass filter (LPF) 9. The adder 10 combines the down-converted chromaticity signal C with the luminance recording signal YFM and the tracking control pilot signal ATF, and outputs the combined signal to the magnetic head 12 through the amplifier 11. The magnetic head 12 records the processed video signal in a known format in a sequential oblique recording track on the magnetic tape T.

In the reproducing circuit of the VTR 1, the magnetic head 13 reproduces the signal recorded on the tape T, and the signal output by the magnetic head 13 is amplified by the amplifier 14.

The frequency modulated luminance signal YFM is provided so that the amplified signal output by the amplifier 14 is demodulated by the luminance signal processing circuit 15. In addition, the output signal of the amplifier 14 is supplied to the low pass filter 16, which draws the chromaticity signal component and corrects the phase. The signal output by the LPF 16 is provided to an automatic chromaticity control (ACC) circuit 17 for level calibration, and the resulting signal is provided to a frequency conversion circuit 18, which circuit 18 The chroma signal is converted back to the original frequency band, thereby inverting the effect of the frequency converter 8 of the recording circuit.

The frequency change chromaticity signal output by the change circuit 18 is passed through a band pass filter 19 and a comb filter 20 to a de-emphasis circuit 21, and the circuit 21. Inverts the processing affected by the emphasis circuit 7 to convert the synthesized de-emphasized chromaticity signal C into an adder 22 for combining with the demodulated luminance signal Y output by the processing circuit 15. to provide. The adder 22 outputs the combined signal as the reproduced video signal SV.

The down-inverted chroma signal is recorded for spatial efficiency recording, but down conversion causes the drawback of reducing the bandwidth of the chroma signal, causing the reproduced chroma signal component to degrade further than the reproduced luminance signal.

The luminance signal is generally more important than the chroma signal due to the reproduced image quality. Thus, the bandwidth of the luminance signal is increased to improve this image quality. However, other improvements in picture quality can be achieved by improving the reproduction of the chroma signal.

One possible approach to improving the reproducibility of chroma signal is to use a slightly higher recording carrier than typical 700 KHz. However, the change in carrier makes it incompatible with the conventional VTR. Moreover, the limit at which the carrier can be raised is limited to the need to avoid overlap of the recording band used for the frequency-modulated luminance signal. So, even if the compatibility problem is ignored, a significant improvement in the reproducibility of the chroma signal cannot be achieved using this approach.

Another possible approach in which the carrier does not change is with the regeneration circuit. According to this approach, the edge of the reproduced chroma signal is emphasized. However, this approach has the drawback of improving only part of the picture quality and not extending the recording band, while reducing the signal-to-noise ratio.

Accordingly, it is an object of the present invention to provide a video signal recording and reproducing apparatus having a wider chromaticity signal bandwidth while maintaining conventional VTR compatibility.

According to the present invention, an apparatus for processing an input video signal comprising a chroma signal and a luminance signal comprises means for subsampling a chroma signal, and an apparatus for processing a luminance signal means for subsampling a chroma signal, frequency modulating the luminance signal. Means for frequency converting the subsampled chromaticity signal into a lower frequency band than that of the frequency-modulated luminance signal, means for combining the frequency-modulated luminance signal and the frequency converted subsampled chroma signal to provide a combination signal And means for recording the combined signal on the recording medium.

According to another aspect of the invention, subsampling of the chroma signal is performed in a two-field or four-field cycle with an offset between successive fields. According to another aspect of the present invention, interpolation in the field is performed during signal reproduction to provide a reproduced color difference signal.

In the above-described apparatus according to the present invention, a wider color difference signal bandwidth improves color reproduction and picture quality than in a conventional VTR.

Hereinafter, with reference to the accompanying drawings will be described in more detail the present specification.

Embodiments in which the present invention is applied to the 8 mm video format are described with reference to FIGS. The recording circuit of this embodiment is shown in FIG. 2, and the reproducing circuit is shown in FIG.

In FIG. 2, a write circuit is described.

The composite input video signal to be recorded is provided at the input terminal 31. The signal received at the input terminal 31 is supplied to the luminance / chromatic separation (Y / C) circuit 32. The separated luminance signal Y output by the Y / C circuit 32 is supplied to the luminance recording processing circuit 33, which affects the recording processing such as frequency modulation, and the frequency-modulated luminance. Output the signal YFM to mixer 34.

Moreover, the chroma signal C separated by the Y / C circuit 32 is provided to the chroma decoder 35 which outputs the color difference signals R-Y and B-Y. The color difference signals R-Y and B-Y are supplied to an offset subsample circuit 36 that affects offset subsampling in the manner described below. The subsampled color difference signals R-Y 'and B-Y' are provided to the chromaticity signal recording processing signal 37 which affects the recording processing. In particular, the color difference signals R-Y 'and B-Y' are encoded to form a chromaticity signal, and are down-converted to a low frequency carrier at 743 KHz in this embodiment. The resulting down-converted chromaticity signal, denoted by the reference letter C ', is supplied to the mixer 34 through a band pass filter 38 that eliminates the folding noise contained in the chromaticity signal C'. The center frequency of the pass band of the BPF 38 is 743 KHz.

In addition to the down-converted chromaticity signal C ′ and the frequency-converted luminance signal YFM, the mixer 34 is also fed to the frequency-modulated audio signal AFM and tracking pilot signal ATF achieved at the input terminal 39. By frequency multiplexing, the luminance signal YFM, the chroma signal C ', the audio signal AFM ALC tracking pilot signal ATM SMS AHEN mixer 34 are mixed. As a result, the combined signal is supplied to the rotary head 42 by the recording amplifier 40 and the rotary converter 41 for recording on the video tape T in the predetermined recording format.

Offset subsampling of the chroma signal by the offset subsample circuit 36 is now described with reference to FIGS. 4A-4D. In the embodiment in Figures 2 and 3, four-field cycle sampling is performed with an offset between fields of 90 degrees. This sampling is performed using a sampling clock set to fsc / 4, where fsc is the color subcarrier, i.e., 3.58 MHz. Thus, fsc / 4 = 3.58 ÷ 4 = 895 KHz. The field portion sampled according to the offset sampling method is shown in Figs. 4A to 4D during four sequential fields. Since interlace scanning is used, the spatial position of the scan line differs between even and odd fields. As shown in FIG. 4A, in the first field, one of four samplings is performed at every fieldline. In adjacent lines, sampling is offset by 180 ° per line, in successive fields, sampling is offset by 90 ° per field, and in successive frames (each of two fields), the offset is 180 ° per frame.

Thus, in the next field, namely the second field shown in FIG. 4B, one of the four samplings is phase shifted by 90 ° relative to the first field. As shown in Fig. 4C, there is another 90 ° phase shift in the third field and another 90 ° phase shift in the fourth field (Fig. 4d). The next or fifth field is sampled in the same manner as the first field shown in FIG. 4A. The sampling pattern repeats in cycles of four fields. The signal thinned out by the subsample circuit 36 in accordance with the described offset subsampling process is mixed through the processing circuit 37 and the bandpass filter 38 to record as luminance, audio and tracking signals. 34 is provided.

A reproduction circuit for reproducing a video signal recorded in the manner described with respect to FIG. 2 is described with reference to FIG. In FIG. 3, the rotary head 43 reproduces the signal recorded on the tape T, and supplies the reproduced signal to the luminance reproduction processing circuit 46 by the rotary converter 44 and the reproduction amplifier 45. As shown in FIG. The processing circuit 46 detects and demodulates the frequency-modulated luminance signal YFM included in the reproduced signal and supplies the demodulated luminance signal Y to the mixer 47.

In addition, the reproduction signal output by the reproduction amplifier 45 is supplied to the band pass filters 48 and 49, and the filters 48 and 49 are respectively frequency-modulated audio signals AFM and tracking pilot signals. The AFM is provided to the output terminals 50 and 51 by passing through each pass band corresponding to these signals.

The output signal of the regenerative amplifier 45 is also supplied to the band pass filter 52, which has a pass band according to the center frequency at 743 KHz to derive the down-converted chromaticity signal C '. The output of the bandpass filter 52 is supplied to the chromaticity signal reproduction processing circuit 53 for conversion to the baseband color difference signals R-Y 'and B-Y'. The resulting frequency-converted color difference signals R-Y 'and B-Y' are fed to subsample 54 for sampling at a sampling rate of fsc / 4 = 895 KHz.

Then, the sampled color difference signal is supplied to an interpolation circuit 55 which interpolates the signal to provide a color difference signal having a transmission band of fsc / 2. Interpolation circuit 55 includes a frame memory and interpolates using four fields of the chrominance signal, the four fields being for example the most recent field of four or optionally including previous and subsequent fields.

The interpolated color difference signal is supplied to a chromatic noise reduction (CNR) circuit 56 from which noise is removed. The resulting signal is then provided to an encoder 57 which outputs a chroma signal modulated with a 3.58 MHz color subcarrier. These signals are provided to a mixer 47 that mixes into a luminance signal to achieve a composite video signal. This composite video signal is then provided at the output terminal 58.

A detailed description of the reproduction processing of the chroma signal is described with reference to FIGS. 5 and 6.

5 shows the interpolation pattern used in the interpolation circuit 55. As shown in FIG. The numbers 1, 2, 3 and 4 shown in the cells of FIG. 5 correspond to the first, second, third and fourth fields subsampled by the subsampling method described in FIGS. 4A to 4D, respectively. Each portion of the fourth field is interpolated using the pattern shown in FIG. 5 to provide a reproduced chroma signal.

The resulting transmission rate of the reproduced chroma signal is fsc / 2 and the bandwidth is f'sc + (fsc / 4) as shown in FIG. 6, where f'sc is a 743 KHz low frequency converted carrier. In fact, the full chromaticity signal is reproduced.

A comparison between the bandwidth provided in the VTR according to the present invention and the bandwidth of a conventional system is provided in FIG. 6, where the curve shown by the solid line is determined by the chroma signal extraction filter and the filter characteristics, and the center frequency at 743 KHz is determined. It shows the frequency band of the prior art. In contrast, in the frequency band provided in accordance with the present invention, this band is flat up to 1.64 MHz (= f'sc + fsc / 4), indicated by the triangle shown in dashed lines in FIG.

A flat frequency band extending up to the subsampling clock frequency can be achieved when the overall transmission frequency response of the system from the tape recording according to subsimplying through reproduction and interpolation is in the form of symmetric cosine roll-off. Such total transmission frequency response is illustrated graphically in FIG. 7, where infinite attenuation occurs at f'sc ± 700 KHz.

The effective frequency band provided by the system of the present invention is more than twice as large as the prior art band, which is only 400 to 500 KHz. In other words, the system of the present invention provides a better frequency response to the chroma signal with a significant improvement in the reproduction power of the color signal. At the same time, the actual recorded chromaticity signal has the same bandwidth and carrier as that used in a typical 8 mm system, so that the system according to the present invention can easily reproduce the tape-recorded signal on a conventional VTR. Moreover, there is no need to improve the capacity of devices such as video tapes, recording and playback heads, etc. so that compatibility with conventional VTRs is achieved by the device. Moreover, the improvement of the frequency response of the chroma signal is completed so that the signal-noise ratio is not reduced.

Another embodiment of the invention is described with reference to FIGS. 8, 9a and 9b. Elements of FIG. 8 that correspond to those described with reference to FIG. 3 are identified by the same reference numerals and are not described in detail. In the described embodiment, different subsampling methods are used with the method used in the embodiments of FIGS. 2 and 3, and are described in FIGS. 4A-4B. Thus, in this embodiment, the subsample circuit 36 (FIG. 2) performs a two-field cycle with an offset between fields of 180 degrees as shown in FIGS. 9A and 9B. In other words, the subsampling phase is inverted between odd and even fields. In the odd field, as shown in FIG. 9A, one of the two samples is performed on each horizontal line and has no offset between lines of the same field. In the even field, as shown in FIG. 9B, the phase of the subsampling is inverted for the odd field, but there is no offset between the lines in the same field.

In this way, subsampling is performed with a 180 ° offset between the fields, making it possible to almost eliminate cross-talk between adjacent fields during playback as described below.

The regeneration circuit of FIG. 8 is described to a range different from that shown in FIG. In the circuit of FIG. 8, the reproduced subsample chromaticity signal output by the chroma signal reproduction processing circuit 53 is supplied to the line comb filter 59 from which noise is removed from the signal using the line correction. The reproduced chromaticity signal output from the filter 59 is then provided to the subsample circuit 54 and subsampled at fsc / 4. The subsampled chromaticity signal output by the subsample circuit 54 is interpolated in the interpolation circuit 55, the noise is reduced in the CNR circuit 56, and supplied to the mixer 47 in combination with the demodulated luminance signal. It is encoded at encoder 57 before. The interpolation performed by interpolation circuit 55 in this embodiment utilizes field memory where the previous field is stored and samples are taken selectively from the current field and the previous field.

In the embodiment shown in FIG. 8, the recorded cross-talk chromaticity signal is removed by the comb-shaped filter 59 so that the reproduced chromaticity signal is not affected by the cross-talk.

As is known to those skilled in the art, in a typical consumer VTR, a video signal is recorded on a video tape in an inclined track, and a signal for one field receives each track. Each track is affected by cross-talk from adjacent tracks. Even when so-called azimuth recording is used to minimize cross-talk by recording and reproducing adjacent tracks with each head having a different azimuth angle, the reduction of cross-talk is recorded at a relatively low frequency and thus is not efficient for chroma signal. Thus, it is known to provide a cross-talk chromaticity signal by adding a phase-inverted cross-talk signal.

In contrast, when a subsampled chromaticity signal is recorded according to the embodiment of the present invention described with reference to FIG. 8, since the chromaticity signal is not subsampled in a corresponding position in an adjacent track (ie, an adjacent field). There is no cross-talk in the chroma signal from adjacent tracks. Thus, conventional cross-talk removal cannot be performed properly. Thus, in the present embodiment, the cross-talk signal is provided by the comb filter 59 because the cross-talk provided at any field sampling position is the same, and line correlation is used.

Elimination of the cross-talk signal by the comb filter 59 does not affect the frequency response for the extended frequency band provided by the subsampling process. In other words, in the electronic embodiment (shown in FIGS. 2 and 3), the chroma signal band extends as shown by the dotted line in FIG.

Another advantage of the embodiment shown in FIG. 8 is that a single field memory is used for interpolation since the subsampling phase is inverted between consecutive fields. Therefore, less memory capacity is required to interpolate in this embodiment than in the embodiment of FIG. In addition, since interpolation is performed using the field memory, follow-up of a moving picture is improved. In particular, as shown in FIG. 4, with four-field cycle subsampling, as in the embodiment of FIG. 3, up to three fields of image affect the chroma signal. However, in the embodiment of FIG. 8, only the immediately preceding field affects the chroma signal. Since the change in color in the reproduced picture almost follows the movement in the picture, the so-called tailing effect is hindered.

In the embodiment as shown in FIG. 8, the cross-talk is removed by the comb filter 59 before interpolation, but optionally the comb filter can be arranged after the interpolation circuit.

Thus, in the above two embodiments of the present invention, the offset-subsampled chromaticity signal is recorded, and the chromaticity signal is restored by interpolation during reproduction. Thus, chromaticity signals having a frequency band several times wider than in the prior art can be recorded and reproduced when using a conventional recording frequency band.

In addition, the cross-talk signal can be almost eliminated by proper selection of the offset cycle used for subsampling during writing.

A third embodiment of the present invention is described with reference to FIG. 10, wherein elements corresponding to those of FIG. 1 are identified by the same reference numerals.

In FIG. 10, reference numeral 61 generally denotes a video tape recorder. In the VTR 61, the subsample circuit 62 and the nonlinear emphasis circuit 63 are disposed in place of the emphasis circuit 7 in FIG. 1, and the chroma signal C performs band suppression so that the subsample circuit 62 is performed. Is subsampled by At that time, the nonlinear emphasis circuit 63 performs a nonlinear emphasis process to prevent the deterioration of the quality of the reproduced image.

On the other hand, the regeneration circuit of the VTR 61 has a nonlinear de-emphasis circuit 64, a subsample circuit 65, and an interpolation circuit 66. The non-sampled de-emphasis circuit 64, the subsample circuit 65 and the interpolation circuit 66 instead of the de-emphasis circuit 21 of FIG. 1 together, the subsample circuit 62 and the non-linear emphasis circuit 63. Reverse the effect of e) and extend the frequency band of the reproduced chroma signal to provide the original signal.

As briefly described above, when the subsampled chromaticity signal is recorded and reproduced in the above-described manner, the frequency response characteristic of the entire recording and reproducing system needs to have a cosine roll-off form.

In particular, it has a cosine roll-off frequency response characteristic and exhibits almost infinite attenuation at the characteristic ± 700 KHz as shown in FIG. 7 in order to maintain compatibility with a typical 8 mm format.

However, in the conventional VTR 1 as shown in FIG. 1, the chroma signal band is limited to prevent interference with the pilot signal used for tracking control and the frequency modulated audio signal. Thus, as shown in FIG. 11, frequency bands extending beyond 500 KHz and below the carrier wave (3.58 MHz) are actually assigned to chroma signals. Thus, when a filter circuit such as that used in the conventional video tape recorder 1 is used in the VTR according to the present invention, it is difficult to achieve the required cosine roll-off.

Moreover, as shown by curve L1 in FIG. 12, the frequency response characteristic of the electromagnetic conversion system decreases at 6bB per octave on the low frequency side. Thus, there is a need to calibrate the frequency response of the electromagnetic conversion system to achieve the required cosine roll-off using conventional filter circuits.

For this reason, the VTR 61 of FIG. 10 does not include the low pass filter 9 of the VTR 1 of FIG. Instead, the high pass filter 67 and the low pass filter 68 are provided in FIG. 10 instead of the band pass filter (FIG. 1) of the VTR 1. Each frequency response characteristic of the HPF 67 and the LPF 68 is shown in FIGS. 13 and 14, and sets the frequency response characteristic of the recording circuit of the VTR 61 together.

In addition, in the recording circuit of the VTR 61, a low pass filter 69 having a characteristic as shown in FIG. 15 is provided instead of the low pass filter 16 (FIG. 1) of the VTR 1. In other words, in the conventional VTR 1, the chroma signal C is separated into the luminance signal Y by using a band pass filter, and the down-converted chroma signal is output through the low pass filter which limits the transmitted frequency band. Also, in the reproducing circuit of the VTR 1, the extraction of the chroma signal is performed by suppressing the signal in the band next to the chroma signal band.

On the other hand, in the VTR 61 of FIG. 10, the filter circuit is configured to provide desirable cosine roll-off characteristics in the complete recording and reproducing system.

In particular, in the VTR 61, the preferred cosine roll-off on the high frequency side is achieved to take advantage of the characteristics of the LPF 69 of the reproduction circuit and the HPF 67 of the recording circuit as shown in FIG. 16A. The LPF 69 serves to attenuate or trap a frequency modulated audio signal recorded as a chroma signal.

On the low frequency side, the preferred cosine roll-off is achieved by the response characteristics of the LPF 68 and the electromagnetic conversion system in the recording system (FIG. 16B). Cosine roll-off on the high frequency side is not affected by the electromagnetic conversion system.

The frequency response characteristic of the recording system is described in FIG. 17 and reflects the characteristic of the filter included in the recording circuit as described above. The functionality of the conventional BPF 5 of FIG. 1 in the VTR 61 is provided through the combined characteristics of the HPF 67 and the LPF 68. At the same time, the HPF 67 provides trapping of the frequency-modulated audio signal performed by the LPF 9 of the VTR 1.

Moreover, in the reproduction circuit of the VTR 61, the LPF 69 performs trapping of the frequency-modulated audio signal provided by the conventional LPF 16 of the VTR 1. Thus, compatibility with the frequency band of the conventional VTR format can be maintained.

By the way, in the embodiment of FIG. 10, the trap for the tracking pilot signal ATF is omitted. However, testing is performed by omitting the trap filter so that omitting such a trap filter makes this embodiment impractical.

The BPF 19 of FIG. 10 is the same as the BPF 19 of FIG. 1 and has a broad passband that generally does not affect the frequency characteristics of the system. The BPF 19 is arranged such that the group delay characteristic is flat in the pass band as in the case of the filters 67, 68 and 69.

With the recording and reproducing circuit as enumerated for FIG. 10, the Filton is arranged to compensate for the frequency characteristics of the electromagnetic conversion system so that the required cosine roll-off is achieved. Thus, the subsampled chromaticity signal can be recorded and reproduced to improve the image quality.

Another embodiment of the present invention is described with reference to FIG. 18, wherein elements corresponding to those of FIG. 1 are identified with the same reference numerals. Therefore, in FIG. 18, the VTR, generally indicated by the reference numeral 71, converts the chroma signal C into the color difference signals U and V. FIG. In particular, in the VTR 71, the color difference signal conversion circuit 72 converts the chroma signal C into the color difference signals U and V, and supplies this signal to the subsample circuit 73. Band suppression is achieved in circuit 73 by offset subsampling as described above. The subsampled signal output by the subsample circuit 73 is provided to the chromaticity signal write processing circuit 75 through the bandpass filter 74. The processing circuit 75 downconverts this signal and provides the mixer 10 with the downconverted signal through the low pass filter 76. In this regard, the chroma signal is band-suppressed to record down the frequency bands used in conventional formats as well.

In the regeneration circuit of the VTR 71, the reproduced signal S1 provided by the magnetic head 13 is amplified by the amplifier 14. The automatic following (ATF) circuit 77 detects the tracking control pilot signal provided to the amplified signal provided by the amplifier 14, and the reproduced chromaticity signal provided to the amplified signal provided by the amplifier 14 is The retracted chromaticity signal processing circuit 79 receives the signal from the amplifier 14 through the low pass filter 78. The extracted signal is converted into chrominance signals U and V and output to the subsample circuit 81 through the band pass filter 80. In the subsample circuit 81, the color difference signals U and V are subsampled, and the subsampled signal is then interpolated by an interpolation circuit 82 using the preceding or trailing line color difference signals U and V, thereby causing the subsample circuit 81 to be subsampled. The image information thinned is restored. The comb filter 83 receives the signals output by the interpolation circuit 82, corrects the frequency characteristics of these signals and suppresses noise components resulting from the use of the field memory in the interpolation circuit 82. The signal output by the comb filter 83 is then up-converted to a custom carrier by the frequency conversion circuit 84.

In summary, in the VTR 71, subsampling is performed after converting the chroma signal C into the color difference signals U and V, and the frequency response characteristic of the system from the subsample circuit 73 to the subsample circuit 81 is cosine. It is arranged to roll off. Thus, the frequency response characteristic of the overall recording and reproducing system for the chroma signal C is cosine roll-off.

In particular, the pass bands of the low pass filters 76 and 78 are largely arranged so as not to affect the frequency response of the recording and reproducing system generally for the chroma signal band.

Furthermore, band pass filters 74 and 78 are interpolated between subsampling circuits 73 and chromaticity signal processing circuits 75, and reproduced chromaticity signal processing circuits 79 and subsampling circuits 81, respectively, It is arranged to calibrate the frequency response characteristics of the conversion system and generally provides the cosine roll-off characteristics required for the recording and playback system.

In the circuit of FIG. 18, the chroma signal C is converted into chrominances U and V, so that band suppression is performed, and the whole system has a cosine roll-off frequency response characteristic which is achieved by correcting the frequency characteristic of the electromagnetic conversion system. Thus, the chroma signal C can be recorded with subsampling and reproduced with improved picture quality.

As is well known, according to the present invention, the recording and reproducing of the band-suppressed down-converted chromaticity signal is performed with the correction of the system frequency characteristic to compensate for the frequency characteristic of the magnetic head and the magnetic recording medium.

The frequency characteristic of the entire system is arranged to be a cosine roll-off characteristic such that the band suppressed chromaticity signal is properly recorded and reproduced by subsampling, resulting in an improved color image. However, the frequency characteristics of the electromagnetic conversion system convert according to different tape transport rates and different types of magnetic tapes. In particular, as shown in FIG. 19, the frequency response of the electromagnetic conversion system is generally inclined at 6bB per octave on the low frequency side, but this characteristic is in the low frequency band (i.e. around 743 Hz) where the chroma signal is recorded. Easy to change

In the conventional VTR 1 shown in FIG. 1, the chroma signal is drawn out through a trap filter, which suppresses the frequency modulated audio signal and has the response characteristic shown in FIG. The combination of the electromagnetic conversion system shown in FIG. 19 and the trap filter characteristic shown in FIG. 20 results in the combined frequency characteristic shown in FIG. However, since the characteristics shown in FIG. 19 are changed in accordance with a change in tape conveyance speed and tape type, the overall characteristics shown in FIG. 21 are likely to change.

As can be seen from the test measurements, the change in the electromagnetic conversion system is shown in FIG. 22, where curve L11 represents the system characteristic when the signal on the metal magnetic tape is reproduced after recording at the standard tape transport speed, curve L12 Shows the system characteristics when the signal on the metal tape is reproduced after recording at the transport rate for extended recording, and curve L13 is the signal when the signal on the standard (i.e. non-metal) tape is reproduced after recording at the standard transport speed. Characteristics. Different characteristics are found when the signal on the standard tape is reproduced after recording at the transport speed for extended recording (not shown in FIG. 22). From FIG. 22, the frequency characteristic of the electromagnetic conversion system changes depending on the tape transport recording speed and the tape type. In addition, there are different properties when evacuated metal tapes to coated metal tapes are used. Moreover, frequency characteristics are also affected by factors related to the magnetic head, such as head wear.

If the change in the frequency characteristic is as large as about 1bB, the Nyquist theory is not satisfied during subsampling, which significantly degrades the reproduced picture quality.

For this reason, the VTR 71 according to the embodiment shown in FIG. 18 includes a low pass filter 78 capable of correcting scatter or variations in frequency response characteristics of the electromagnetic conversion system. The LPF 78 is described in detail with reference to FIG. 23, and the amplified signals S1 output by the reproduction amplifier 14 are band pass filters (BPF) 91 and 92 and finite impulse response (FIR) filters 93. As shown in FIG. Are provided at the same time.

The BPF 91 draws out the predetermined pilot signal PI which is one of four kinds of the tracking control pilot signal ATF provided to the reproduced signal S1. The BPF 92 separates the 743 kHz carrier signal SC from the reproduced signal S1. These signals PI and SC are provided to the signal level detection circuit 94 by the BPF 91 and the BPF 92, respectively, which detect these signal levels and change over the circuit ( 95) outputs a detection result reflection signal.

By the output signal from the detection circuit 94, the coefficient switching circuit 95 changes the amplitude of the gain provided by the variable gain amplifier which is the LPF 78 section. Thus, the frequency characteristics of the signal output by the filter circuit 93 are maintained to match the desired frequency characteristics despite variations in the characteristics of the electromagnetic conversion system.

In particular, the FIR filter circuit 93 comprises five delay circuits D1 to D5 connected in series. The output signals of the delay circuits D1 and D5 are provided to respective input terminals of the adder circuit 96 which outputs the sum of these signals to the variable amplifier 98. Output signals from delay circuits D2 and D4 are provided to each input of adder 97 which outputs the resulting sum of these signals to variable amplifier 99. The output of delay circuit D3 is provided directly to variable amplifier 100. The signals received by the amplifiers 98, 99 and 100, respectively, are weighted by the amplifier in accordance with the signals output by the coefficient switching circuit 95. The signals output by the amplifiers 98, 99 and 100 are provided to each input of the adder 101 which outputs the sum of these signals as the output signal SO. Each weight provided by the amplifiers 98, 99 and 100 is adjusted by the signal output by the coefficient switching circuit 95 so that a predetermined ratio of the levels of the carrier signal SC and the pilot signal PI is maintained. In this regard, the frequency characteristic of the VTR 71 for the chroma signal is corrected to the characteristic shown in FIG.

In calibration of the characteristics of the electromagnetic conversion system, band pass filters 91 and 92 provide the frequency characteristics of the recording and reproducing system to be the desired cosine roll-off for the chromaticity signal.

At the same time, the BPF 74 (FIG. 18) is arranged to float the frequency characteristic of the electromagnetic conversion system on the low frequency side, and is arranged in combination with the BPF 80 so that the group delay characteristic is flat.

Further, in the VTR 71, the LPF 78 corrects the characteristic change of the electromagnetic conversion system by the pilot signal PI and the carrier signal SC. In this regard, the frequency characteristic for the chromaticity signal band can be maintained as a desirable cosine roll-off even when there is a variation in the electromagnetic conversion system characteristics due to magnetic head wear or other factors. Thus, improved picture quality can be achieved while maintaining compatibility with conventional VTR formats.

Although the embodiment described above utilizes a magnetic tape for recording and reproducing, the present invention is not limited thereto and can be applied to recording and reproducing using other magnetic recording media.

Moreover, in the above-described embodiment, the scatter of the frequency characteristic of the electromagnetic conversion system is corrected by the ATF tracking control pilot signal and the subcarrier signal, but the present invention is not limited to this, for example, the scattering of the scatter in the electromagnetic conversion system. The calibration is performed in particular by each recorded reference signal which is provided for the scattering's calibration.

While preferred embodiments of the invention have been described with reference to the accompanying drawings, the invention is not limited to such embodiments, and various modifications are possible to those skilled in the art within the spirit or scope of the invention as defined in the appended claims. Can be modified.

Claims (11)

An input video signal processing apparatus comprising a chroma signal and a luminance signal, comprising: sub sampling means for sub sampling the chroma signal; Frequency modulating means for frequency modulating the luminance signal; Frequency converting means for frequency converting the subsampled chromaticity signal into a low frequency band lower than a frequency band of the frequency-modulated luminance signal; Combining means for combining the frequency-modulated luminance signal and the frequency-modulated subsampling chromaticity signal to provide a combined signal; And recording means for recording the combined signal on a recording medium. 2. An input video signal processing apparatus according to claim 1, wherein said subsampling means comprises means for performing two-field cycle offset-subsampling on said chroma signal. 2. An input video signal processing apparatus according to claim 1, wherein said subsampling means comprises means for performing four-field cycle offset-subsampling on said chroma signal. The apparatus of claim 1, wherein the subsampling means comprises means for sampling the chroma signal according to an fsc / 4 sampling clock, wherein fsc is a color subcarrier frequency. 2. The apparatus of claim 1, further comprising: means for reproducing the recorded combined signal from the recording medium; Means for separating the frequency-converted chromaticity signal from the reproduced combined signal; Means for converting the separated chroma signal into a color difference signal; And means for interpolating the chrominance signal. A video signal recording and reproducing system, comprising: a subsampling means for subsampling the chromaticity signal; Modulation means for frequency modulating the luminance signal; Frequency converting means for converting a frequency of the subsampled chromaticity signal into a low frequency band lower than a frequency band of the frequency-modulated luminance signal; Combining means for combining the frequency-modulated luminance signal and the frequency-modulated subsampling chromaticity signal to provide a combined signal; Recording means for recording the combined signal on a recording medium; And means for reproducing the recorded frequency modulated chromaticity signal from the recording medium. 7. The video signal recording and reproducing system of claim 6, wherein the video signal recording and reproducing system comprises means for equalizing the chroma signal so that the overall chromatic frequency response characteristic is a cosine roll-off frequency response characteristic. 8. The video signal recording and recording apparatus as claimed in claim 7, wherein the equalizing means comprises means for detecting a reference signal level reproduced from the recording medium and means for equalizing a chroma signal reproduced by the detected reference signal level. Playback system. 7. The apparatus according to claim 6, wherein the reproducing means comprises: reproducing means for reproducing the recorded combined signal from the recording medium; Separating means for separating the frequency-converted chromaticity signal from the reproduced combined signal; Conversion means for converting the separated chroma signal into a color difference signal; And interpolation means for interpolating the chrominance signal. 10. The apparatus of claim 9, wherein the separating means comprises: variable low pass filter means for low pass filtering the regenerated combined signal according to a variable amplitude characteristic to provide the separated chroma signal; Separating means for separating at least one reference signal from the reproduced combined signal; Detecting means for detecting the separated reference signal and outputting a detection signal according to the detected level of the separated reference signal; And means for changing said variable amplitude characteristic by said detection signal such that the overall chromaticity frequency response characteristic of said recording and reproducing system is a cosine roll-off response characteristic. 11. The apparatus of claim 10, wherein said separating means for separating at least one reference signal comprises means for separating a tracking control pilot signal and a carrier signal from said reproduced combined signal, and said detecting means comprises said separated tracking control pilot signal. And means for detecting each level of the carrier signal.