JP2939959B2 - Video signal playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal which reproduces a recording medium recorded with pre-emphasis on the frequency of the video signal in the time axis direction and de-emphasizes the frequency of the reproduced video signal in the time axis direction. It relates to a playback device.

[0002]

2. Description of the Related Art When recording and reproducing a video signal on a recording medium such as a magnetic tape, the high frequency component of the video signal is enhanced (pre-emphasis) in comparison with the low frequency component in order to reduce the influence of noise in the recording and reproduction. Then, the high frequency component is attenuated (de-emphasis) at the time of reproduction to improve the SN ratio. 2. Description of the Related Art Conventionally, there is a device that performs pre-emphasis or de-emphasis of a video signal in the time axis direction, particularly as a device for improving the SN ratio improving effect. Here, the emphasis in the time axis direction of the video signal will be described as temporal emphasis, the pre-emphasis in the time axis direction will be referred to as temporal pre-emphasis, and the de-emphasis in the time axis direction will be described as temporal de-emphasis.

FIG. 3 is a schematic block diagram of a conventional video signal recording / reproducing apparatus. In FIG. 1, a video signal to be recorded, which is input to an input terminal 1, is supplied to a temporal pre-emphasis circuit 2, where a high frequency component in the time axis direction is relatively enhanced in level as compared with a low frequency component. After that, the signal is supplied to the recording signal processing circuit 3, where signal processing suitable for recording the video signal, for example, frequency modulation is performed. The video signal extracted from the recording system signal processing circuit 3 is supplied to a magnetic head (neither is shown) through a recording amplifier or the like, and is recorded on the magnetic tape 4.

On the other hand, at the time of reproduction, the video signal recorded on the magnetic tape 4 is reproduced by a magnetic head, and the reproduction signal processing circuit 5 passes through a reproduction amplifier (not shown) and the like, and performs the reverse of the signal processing at the time of recording. Is supplied to the temporal de-emphasis circuit 6. The temporal de-emphasis circuit 6 is provided for attenuating the high frequency component of the frequency in the time axis direction enhanced by the temporal pre-emphasis circuit 2 and returning it to its original state. The output reproduced video signal is taken out from the output terminal 7. .

FIG. 4 is a diagram showing a block configuration of the temporal pre-emphasis circuit 2 described above. In the figure, a video signal input to the input terminal 10 of the temporal pre-emphasis circuit 2 is supplied to subtraction circuits 17, 18 and an addition circuit 19, respectively. The video signal extracted from the subtraction circuit 17 is supplied to the delay circuit 13. The delay circuit 13 has a delay time of 2m fields or {(2m + 1) fields−0.5H} of the video signal (where m is 0, 1, 2,... (A positive integer), H indicates one horizontal period). The delayed video signal extracted from the delay circuit 13 is supplied to a subtraction circuit 18, where it is subtracted from the video signal from the input terminal 10. The output video signal of the subtraction circuit 18 is output to the coefficient circuit 15 and supplied to the subtraction circuit 17 via the coefficient circuit 14 for multiplying by the coefficient K1.
Returned to 3. The output video signal of the subtraction circuit 18 is also supplied to an addition circuit 19 through a coefficient circuit 15 for multiplying by a coefficient K2. The addition circuit 19 adds the output signal of the coefficient circuit 15 to the input video signal from the input terminal 10, and the output signal of the addition circuit 19 is output from the output terminal 16.

In the above configuration, the high frequency component of the video signal in the time axis direction is extracted by the feedback loop including the subtraction circuit 17, the delay circuit 13, the subtraction circuit 18, and the coefficient circuit 14. By adding the extracted high frequency component to the video signal from the input terminal 10 by the addition circuit 19 via the coefficient circuit 15, the output of the addition circuit 19 contains the high frequency component of the frequency in the time axis direction of the video signal. It is possible to obtain a video signal provided with a pre-emphasis characteristic (temporal pre-emphasis characteristic) whose level is relatively enhanced as compared with the low-frequency component.

FIG. 5 is a diagram showing a block configuration of the temporal de-emphasis circuit 6 described above. In the figure, the input terminal 20 of the temporal de-emphasis circuit 6
, A reproduced video signal converted to the original signal form comes in. However, this reproduced video signal is given the temporal pre-emphasis characteristic. This reproduced video signal is supplied to the delay circuit 23 through the subtraction circuit 27,
It is also supplied to the subtraction circuits 28 and 29. The delay circuit 23 is set to the same delay time as the delay circuit 13 shown in FIG. 4, and the delayed reproduced video signal is supplied to a subtraction circuit 28, where it is subtracted from the reproduced video signal from the input terminal 20. . The output video signal of the subtraction circuit 28 is output to a coefficient circuit 25 and supplied to a subtraction circuit 27 through a coefficient circuit 24 for multiplying by a coefficient N1. Returned to 23. The output video signal of the subtraction circuit 28 is also supplied to a subtraction circuit 29 via a coefficient circuit 25 for multiplying the coefficient N2. The subtraction circuit 29 subtracts the output signal of the coefficient circuit 25 from the video signal from the input terminal 20, and the output signal of the subtraction circuit 29 is output to the output terminal 26.

In the above configuration, a high frequency component of the frequency of the video signal in the time axis direction is extracted by the feedback loop including the subtraction circuit 27, the delay circuit 23, the subtraction circuit 28, and the coefficient circuit 24. By subtracting the extracted high frequency component from the video signal from the input terminal 20 by the subtraction circuit 29 via the coefficient circuit 25, the output of the subtraction circuit 29 includes the high frequency component of the frequency of the video signal in the time axis direction. It is possible to obtain a video signal to which a de-emphasis characteristic (temporal de-emphasis characteristic) whose level is relatively attenuated compared to the low-frequency component is provided.

In FIGS. 4 and 5, for example, the coefficient K1 =
2.11, K2 = 0.422, N1 = 0.566, N2 =
When 0.679 is set, the temporal pre-emphasis characteristic and the temporal de-emphasis characteristic are inverse characteristics (that is, the product of the transfer function is 1), and are mutually complementary characteristics. That is, in FIG. 3, the temporal pre-emphasis circuit 2
Is equivalent to the transfer function when there is no temporal emphasis because the characteristics of the temporal pre-emphasis circuit 2 and the temporal de-emphasis circuit 6 cancel each other out. Therefore, the original waveform of the video signal recorded and reproduced by the video signal recording and reproducing apparatus such as a VTR is restored. Further, with the values of the coefficients N1 and N2, the temporal de-emphasis circuit 6 operates in the same manner as the cyclic noise reduction circuit, and thus has the effect of reducing the noise of the video signal reproduced from the magnetic recording medium. I have.

FIG. 6 shows the operation of temporal emphasis such as the above-mentioned temporal pre-emphasis circuit 2 and temporal de-emphasis circuit 6 and how it is recorded on a magnetic tape.

For example, when a video signal is recorded by a VTR, the video signal is recorded on the magnetic tape 4 in the order of frames as shown in FIG. In the processing of the temporal pre-emphasis circuit 2, the subtraction circuit 17, the delay circuit 13,
Due to the presence of the feedback loop formed by the subtraction circuit 18 and the coefficient circuit 14, a frame being processed input to the temporal pre-emphasis circuit 2 is circulated by multiplying a previous frame by a predetermined coefficient. For example, the frame Pn shown in FIG. 6 includes information of a plurality of frames before Pn-1.

When the magnetic tape recorded as described above is reproduced, it is reproduced in the order of elapse of the time of recording and subjected to temporal de-emphasis processing. For this reason, for example, when the frame Pn is subjected to temporal de-emphasis, information before the frame Pn-1 is already read into the delay circuit 23 of the temporal de-emphasis circuit 6, and the temporal de-emphasis circuit complements the characteristics of the temporal pre-emphasis circuit 2. An emphasis process can be performed.

[0013]

FIG. 7 is a diagram showing a track pattern formed on the magnetic tape 4 by a helical scan type VTR. Arrow V in FIG.
Indicates the running direction of the magnetic tape 4, and the arrow S indicates the scanning direction of the magnetic head (not shown). In the case of a VTR in which the video signal recorded / reproduced for one scanning of the magnetic head is one field period, the track pattern formed on the magnetic tape 4 is, as shown in FIG. One inclined track is formed in the order of tracks 1A, 1B, 2A, 2B, 3A,... Per field period.
Therefore, the delay time of the delay circuit of the temporal pre-emphasis circuit and the temporal de-emphasis circuit is 1
In the processing of temporal emphasis such as a frame, the operation of temporal emphasis is performed in units of video signals recorded on two tracks on the magnetic tape 4.

FIG. 8 is a diagram showing the scanning trajectory of the magnetic head at the time of double speed reproduction in which the traveling speed of the magnetic tape 4 at the time of reproduction is twice that at the time of recording. In the figure, 1A, 1B, 2
A, 2B, 3A,... Are tracks formed on the magnetic tape 4 as described above. And 1C, 2
.., C, 3C, 4C,. At the time of double speed reproduction, the magnetic tape 4 runs at twice the speed of recording, but since the scanning speed of the magnetic head is the same, the tracks recorded on the magnetic tape 4 are reproduced every other track. become.
For example, as shown in FIG. 8, the tracks 1A, 2A, 3
A, 4A,... Are sequentially reproduced. Therefore, for example, the time interval between the reproduced video signals reproduced from the tracks 1A and 2A is one field period, and similarly between the tracks 2A and 3A, between the tracks 3A and 4A,. Are each one field period.

In such a 2 × speed reproduction state, when the reproduced video signal of the VTR is subjected to temporal deemphasis processing in units of frames by the conventional temporal deemphasis circuit 6 shown in FIG. 5, the deemphasis processing is performed in units of one frame. When the reproduced video signal of the track 3A is input to the subtraction circuit 27, the coefficient circuit 24
Is a reproduced video signal from the track 1A four tracks before on the magnetic tape 4. Similarly, the video signal to be processed from the reproduced video signal from the track 4A is the reproduced video signal from the track 2A four tracks before. Therefore, at the time of double speed reproduction, temporal de-emphasis processing complementary to temporal pre-emphasis processing at the time of recording, which is performed in units of a two-track recording video signal, is not performed. As a result, reproduction output from the temporal de-emphasis circuit is performed. There has been a problem that an afterimage and a blur occur in the video signal.

[0016]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention relates to a video signal reproducing apparatus for reproducing a recording medium on which a pre-emphasis is performed in units of frames with respect to a frequency of a video signal in a time axis direction. At the time of standard reproduction in which the running speed of the medium is equal to that at the time of recording, de-emphasis processing is performed for each frame with respect to the frequency in the time axis direction of the reproduced video signal, and at the time of double speed reproduction at which the running speed of the recording medium is twice that at the time of recording, It is an object of the present invention to provide a video signal reproducing apparatus characterized in that a de-emphasis process is performed on a frequency basis in a time axis direction of a reproduced video signal in field units.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of a video signal reproducing apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a block configuration of a first embodiment of a video signal reproducing apparatus according to the present invention. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, reference numerals 23a and 23b denote delay circuits each having a delay time of one field period, reference numeral 30 denotes a terminal to which a signal for instructing double-speed reproduction is supplied, and reference numeral 3 denotes a terminal.
2 is a system controller, and SW is a changeover switch. DB is a de-emphasis block. The output of the delay circuit 23a to which the output signal of the subtraction circuit 27 is supplied is connected to the fixed terminal a of the changeover switch SW and also to the delay circuit 23b. The output of the delay circuit 23b is connected to the fixed terminal b of the changeover switch SW. The movable terminal c of the changeover switch SW is configured to be connected to the negative input terminal of the subtraction circuit 28. The system controller 32 is supplied with a 2 × speed reproduction instruction signal from the terminal 30 and a DFF signal indicating the rotation phase of the magnetic head from a servo circuit (not shown). And this system controller 32
A reproduction mode signal is generated and output from the 2 × speed reproduction instruction signal and the DFF signal, and the changeover switch SW is controlled by the reproduction mode signal.

Next, the operation of the video signal reproducing apparatus shown in FIG. 1 will be described. The reproduced video signal reproduced from the magnetic tape 4 by the reproducing system signal processing circuit 5 has been subjected to temporal emphasis processing at the time of recording, and the temporally pre-emphasized reproduced video signal is supplied to a terminal 20. Since the delay times of the delay circuits 23a and 23b are each set to one field period, the output of the subtraction circuit 27 is delayed by one field period in the delay circuit 23a and supplied to the fixed terminal a of the changeover switch SW. Also, the delay circuit 23a, 23b connects the fixed terminal b of the changeover switch SW with a delay of one frame period by the series connection.

Accordingly, the movable terminal c of the changeover switch SW
The signal supplied to the subtraction circuit 28 through the switching between the one-field period and the one-frame period is switched by the reproduction mode signal supplied from the system controller 32.

When the video signal reproducing device is in the standard reproduction mode, the reproduction mode signal is at a low level, for example, whereby the changeover switch SW is connected to the movable terminal c to the fixed terminal b as shown in FIG. The output signal of the circuit 27 is delayed by one frame period and supplied to the negative input terminal of the subtraction circuit 28. Therefore, the de-emphasis block DB performs a temporal de-emphasis process on the reproduced video signal supplied to the terminal 20 in frame units. The operation of the de-emphasis block DB in the standard reproduction mode is the same as that of the conventional temporal de-emphasis circuit.

When the double speed reproduction instruction signal and the DFF signal are supplied and the double speed reproduction is instructed, the system controller 32 outputs a reproduction mode signal, for example, at a high level in synchronization with the DFF signal. When the reproduction mode signal changes from low level to high level, the changeover switch SW
Has a movable terminal c connected to a fixed terminal a, whereby
The output signal of the subtraction circuit 27 is delayed by one field period and supplied to the negative input terminal of the subtraction circuit 28. Therefore,
The de-emphasis block DB performs a temporal de-emphasis process on the reproduced video signal supplied to the terminal 20 in field units.

At the time of recording, for example, the recorded video signals of the tracks 1A and 2A are spaced by one frame period, and even at the time of standard reproduction, the reproduced video signals are spaced by one frame period. However, at the time of double speed reproduction, the reproduced video signals of the track 1A and the track 2A are separated by one field period, so that the movable terminal c of the switch SW is fixed according to the reproduction mode signal as described above. Connect to terminal a.
As a result, the de-emphasis block DB performs a temporal de-emphasis process on a field basis, thereby giving a temporal de-emphasis characteristic complementary to the temporal pre-emphasis characteristic at the time of recording to the double-speed reproduced video signal. So you can
Noise can be reduced without any afterimage or blurring.

Next, a second embodiment of the video signal reproducing apparatus of the present invention will be described with reference to FIG. FIG. 2 is a diagram showing a block configuration of a second embodiment of the video signal reproducing apparatus of the present invention. The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted.

The difference between the video signal reproducing device of the present invention shown in FIG. 2 and the configuration of FIG.
a, 23b and a changeover switch SW are replaced with a memory 23 and a memory control circuit 34. The video signal output from the subtraction circuit 27 is supplied to the memory 23c, and the output of the memory 23c is supplied to the negative input terminal of the subtraction circuit 28. The memory control circuit 34 is supplied with the reproduction mode signal and controls the delay time of the memory 23c. Other configurations are the same as those of the video signal reproducing apparatus shown in FIG.

Next, the operation of the video signal reproducing apparatus shown in FIG. 2 will be described. The address control of the memory 23c is as follows.
This is performed by the memory control circuit 34 in response to the reproduction mode signal from the system controller 32. At the time of standard reproduction, the reproduction mode signal is, for example, at a low level. At this time, the memory control circuit 34 For example, the read address of the memory 23c is controlled so that the difference between the read addresses corresponds to one frame period. Thereby, the de-emphasis block DB '
Means to give a temporal de-emphasis characteristic in frame units to the reproduced video signal.

Next, when the double speed reproduction is instructed and the reproduction mode signal from the system controller 32 becomes, for example, a high level to indicate the double speed reproduction, the memory control circuit 3
4 controls, for example, the read address of the memory 23c so that the difference between the write address and the read address for the memory 23c is equivalent to one field period. As a result, at the time of double speed reproduction, the de-emphasis block DB ′ gives a temporal de-emphasis characteristic to the reproduced video signal in units of one field.

As described above, when reproducing a magnetic tape on which a video signal subjected to temporal pre-emphasis processing in a frame unit is recorded at the time of recording, the delay time of the memory 23c is set to one frame period at the time of standard reproduction.
Temporal de-emphasis processing is performed in units of frames, and during double-speed playback, temporal de-emphasis processing is performed in units of fields with the delay time of the memory 23c as one field period, thereby allowing temporal reproduction during recording of double-speed playback video signals. Temporal de-emphasis processing complementary to the pre-emphasis characteristic can be performed, and afterimages and blurring do not occur, and noise can be reduced.

The de-emphasis block D of the first and second embodiments of the video signal reproducing apparatus of the present invention described so far.
B and DB ′ have a configuration in which the video signal delayed by one frame or one field is fed back from the output of the subtraction circuit 28 via the coefficient circuit 24 in order to feed back to the input side, that is, the negative input terminal of the subtraction circuit 27. Alternatively, the output of the coefficient circuit 25, not the output of the subtraction circuit 28, may be fed back to the negative input terminal of the subtraction circuit 27 via the coefficient circuit 24. In this case, the coefficient circuit 24 can be omitted by appropriately setting the coefficient of the coefficient circuit 25.
Further, between the output of the subtraction circuit 28 and the negative input of the subtraction circuit 29 and in a path forming a feedback loop, for example, the output of the coefficient circuit 25 In the case of a configuration in which feedback is made to the negative input terminal, a limiter for limiting the level of the input signal is provided on the input side or the output side of the coefficient circuit 25, so that the de-emphasis blocks DB and DB 'are input to the reproduced video signal. A non-linear de-emphasis circuit whose temporal de-emphasis characteristic changes according to the level of the non-linear de-emphasis circuit.

[0030]

As described above, according to the video signal reproducing apparatus of the present invention, at the time of the standard reproduction in which the running speed of the recording medium is equal to that at the time of recording, the de-emphasis is performed on the frequency in the time axis direction of the reproduced video signal in frame units. In the case of the double speed reproduction in which the running speed of the recording medium is twice that of the recording, the de-emphasis processing is performed on the frequency of the reproduced video signal in the time axis direction in field units. When reproducing a recording medium recorded with pre-emphasis in units of frames with respect to the frequency in the direction, in any of standard reproduction and double-speed reproduction, afterimages and blurring do not occur and reproduction with reduced noise is performed. This has the effect that a video signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a block configuration of a first embodiment of a video signal reproducing apparatus according to the present invention.

FIG. 2 is a diagram showing a block configuration of a second embodiment of the video signal reproducing device of the present invention.

FIG. 3 is a diagram showing a schematic block system of a conventional video signal recording / reproducing apparatus.

FIG. 4 is a diagram showing a block configuration of a conventional temporal pre-emphasis circuit.

FIG. 5 is a diagram showing a block configuration of a conventional temporal de-emphasis circuit.

FIG. 6 is a diagram for explaining a state of recording on a magnetic tape.

FIG. 7 is a diagram showing a track pattern.

FIG. 8 is a diagram showing a scanning trajectory of a magnetic head during 2 × speed reproduction.

[Explanation of symbols]

 Reference Signs List 4 magnetic tape (recording medium) 5 reproduction system signal processing circuit 23a, 23b delay circuit 23c memory 24, 25 coefficient circuit 27, 28, 29 subtraction circuit 32 system controller 34 memory control circuit DB, DB 'de-emphasis block SW changeover switch

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/91-5/956 H04N 9/79-9/898

Claims (1)

(57) [Claims] 1. A video signal reproducing apparatus for reproducing a recording medium recorded with pre-emphasis on a frame basis with respect to a frequency of a video signal in a time axis direction. De-emphasis processing is performed on a frame basis with respect to the frequency of the reproduced video signal in the time axis direction, and at the time of double-speed reproduction in which the running speed of the recording medium is twice as high as during recording, the frequency of the reproduced video signal in the time axis direction is divided into fields. A video signal reproducing device configured to perform de-emphasis processing.