JPH05176346A - Signal switching device - Google Patents

Abstract

PURPOSE:To improve picture quality at the time of specific reproducing based on a digital recording VTR by effectively utilizing data which are not convensionally effective at the time of specific reproducing. CONSTITUTION:Digital data respectively read out by a reproducing head 10 and a specific head 16 are respectively synchronized and supplied to a switch 23. On the other hand, the signal amplitude of the signals read out by the heads 10, 16 and respective synchronizing information are supplied to an effective data detecting circuit 22. At the time of specific reproducing such as a triple- speed reproducing mode, the circuit 22 finds out a switching point of the switch 23 and outputs a control signal to the switch 23. Data selected by the switch 23 are demodulated by a demodulating circuit 24 and header information is extracted by a header extracting circuit 25. Then an error correcting circuit 26 corrects an error and a demodulating circuit 27 demodulates the error- corrected data to a video signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal switching device for special reproduction in a video recording recorder (VTR) for digital recording, and more particularly to a signal switching device for reducing ineffective data during special reproduction.

[0002]

2. Description of the Related Art In an analog VTR such as a VHS or 8 mm, there is a device that employs a special reproduction head or a head for two modes to improve image quality during special reproduction, for example, triple speed reproduction. A conventional trick-play method will be described below with reference to the drawings.

FIG. 7 shows a simple structure of a drum having a special reproduction head built therein. In this figure, normal reproducing heads A and B are installed around the drum 1, and special heads C and D are installed next to them. When the azimuth angle of the reproducing head A is "+", the azimuth angle of the adjacent special head C is "-". On the contrary, when the reproducing head B has an azimuth angle of "-", the adjacent special head C has an azimuth angle of "+".

Using the special reproduction head described above with reference to FIG.
A reproduction signal processing method capable of special reproduction is shown. In this figure, the signal read by the reproducing head 10 is amplified by the amplifier 11 and supplied to the detection circuit 50 and the switch 23.
Similarly, the signal read by the special head 16 is sent to the amplifier 17
And is supplied to the detection circuit 51 and the switch 23. The envelope components of the supplied signals are detected by the detection circuits 50 and 51, and are output to the amplitude comparator 52.
The amplitude comparator 52 compares the amplitudes of the two input signals and supplies the comparison result to the switch 53.

A switching signal is also supplied to the switch 53, and one signal is selected by the mode selection signal and is supplied to the switch 23 as a control signal. The switch 23 selects one of the outputs of the amplifiers 11 and 17 based on the control signal, supplies it to the demodulation circuit 24, and demodulates it. The demodulated signal is returned to the original video signal by the reproduction processing circuit 54.

The above-mentioned switching signal is used to select a preset head output signal, and the switch 5
When this signal is selected in 3, the output of the amplifier 11 and the output of the amplifier 17 are alternately selected. On the other hand, the amplitude comparator 52 normally selects the one with the larger amplitude. Therefore, when the output of the amplitude comparator 52 is selected by the switch 53 by the mode selection signal, the amplifier 1 is switched by the switch 23.
Of the outputs of 1 and 17, the one with the larger amplitude is selected.

FIG. 9 shows a trace state during 3 × speed reproduction. In this figure, the tracks on the tape are slanted, but since the speed is triple, the head trace is perpendicular to the tape traveling direction. Therefore, the head trace is b,
It is straddling tracks c and d. However, since the azimuth angles are different on the tracks b and c or the tracks c and d, for example, in the trace 1, the reproduction heads from S to A, the special heads from A to B, and the reproduction heads from B to E are reproduced. The data on the trace 1 is reproduced by selecting the data.

When such reproduction processing is performed on an analog signal, an image without noise bars on the screen can be obtained. However, when performing digital processing, the data is recorded in blocks on the tape.
When the signals reproduced from the two heads are switched depending on the magnitude of the amplitude or a preset switching point, the switching may occur in the middle of the block. In this case, since the data of the block does not make sense, ineffective data is generated before and after the switching. This state is shown in FIG.

In FIG. 10, (α) is data reproduced by the reproducing head, and (β) is data reproduced by the special head. Further, "SY" is a synchronization signal, "ID" is an ID signal, "D" is data, and "PA" is a parity signal. Then, it is assumed that one block is formed from "SY" to "PA".

Here, if the switching points are A and B, both of them are switched in the middle of the data D. When the switching point is A, the "SY" positions coincide with each other, so that synchronization is achieved, but the data is invalid because of different tracks. Therefore, the part (b) of (α) and the part (b) of (β) are ineffective data. On the other hand, when the switching point is B, the position of "SY" is deviated and synchronization is not achieved. In this way, if the switching point is set in advance, or if it is set depending on the magnitude of the amplitude, ineffective data may be generated before and after the switching point, and synchronization may not be achieved.

[0011]

In the VTR, the head trace crosses three tracks on the magnetic tape at the time of reproducing at a triple speed. For this reason, in order to prevent a difference in azimuth angle and a noise bar from being generated on the screen, a special head is provided next to the normal head, and signals read by each head are switched and reproduced. However, when digital processing is performed, if the switching point is set in advance, or if the switching point is set depending on the magnitude of the amplitude, ineffective data may occur before and after the switching point, and synchronization may not be achieved.

It is an object of the present invention to effectively utilize data that has been ineffective in the past and improve the image quality during special reproduction.

[0013]

The means according to the present invention is provided with two or more normal video heads for normal reproduction provided on a rotating drum and adjacent to the normal video heads, and is used only during special reproduction. Two or more special video heads for special reproduction, first reproduction processing means for reproducing a compression-coded digital signal by reproducing the signal read from the magnetic tape by the normal video head, and the special reproduction head Second reproduction processing means for reproducing a compression-coded digital signal by reproducing the signal read from the magnetic tape by a video head, and outputs and switching signals of the first and second reproduction processing means. Of the outputs of the first and second reproduction processing means, the switching means calculates the switching point at which the ineffective data is least generated, and outputs the control signal. Selecting means for selecting one based on the control signal comprises a decoding means for decoding a video signal based on the output of the selection means.

[0014]

In the arithmetic means, switching is performed based on the synchronization of the digital signals output from the first and second reproduction processing means and the switching signal so that ineffective data is least generated in the output signal of the selecting means. By calculating the points and controlling the selecting means, a video signal that has high quality with almost no ineffective data is reproduced during special reproduction.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. The same components as those of the related art are designated by the same reference numerals. FIG. 1 is a diagram showing the configuration of a first embodiment according to the present invention. In this figure, the signal read by the reproducing head 10 is amplified by an amplifier 11, and then a waveform equalizing circuit 12
Then, the waveform equalization processing is performed and is supplied to the bit synchronization circuit 13.
The bit synchronization circuit 13 converts the supplied signal into digital data, and the synchronization circuit 14 detects the synchronization signal of each block, and then the TBC (time axis correction) circuit 15
Then, the time axis correction processing is performed and the result is supplied to the switch.

On the other hand, the signal read by the special head 16 is amplified by the amplifier 17 and then subjected to waveform equalization processing by the waveform equalization circuit 18 and supplied to the bit synchronization circuit 19. The bit synchronization circuit 19 converts the supplied signal into digital data, and the synchronization circuit 20 detects the synchronization signal of each block. Then, the TBC circuit 21 performs time-axis correction processing and supplies it to the switch 23.

The above-mentioned digital data is data that has been subjected to variable length compression coding processing and is composed of a synchronizing signal, an ID signal, data and a parity signal, and the synchronizing signal to the parity signal are one block. That is, it is effective data in block units.

The outputs of the synchronizing circuits 14 and 20 are also supplied to the valid data detecting circuit 22. Besides this, a switching signal is supplied to the valid data detection circuit 22. The valid data detection circuit 22 uses the switching signal and the synchronization circuit 14,
Based on the output data of 20, the switching point is set and the control signal for controlling the switch 23 is output during special reproduction such as the triple speed reproduction mode. Also, the TBC circuit 1
Time-axis correction signals are output to the circuits 5 and 21, and the TBC circuits 15 and 21 are synchronized based on these signals. The data selected by the switch 23 is the demodulation circuit 2
4 is demodulated, and header information is extracted by the header extraction circuit 25. After that, the error correction circuit 26 performs error correction, and the decoding circuit 27 decodes the video signal.

FIG. 2 is a timing chart for explaining the operation of the first embodiment. In this figure, the sync data (n1, n2, n3 ...) Of the signal read by the reproducing head 10 and the sync data (m0, of the signal read by the special head 16).
It is not synchronized with m1, m2 ...). When the switching signal is "HIGH", the synchronous data and data Dm on the special head side are selected, and when the switching signal is "LOW", the synchronous data and data Dn on the reproducing head side are selected.
In this state, the switching signal changes from "LOW" to "H" at point X.
IGH ”. The switching signal is a signal obtained from the comparison result of the signal amplitude, etc. as in the conventional case. In this case, the synchronization data on the reproducing head side is valid until the point X, and the special head side is synchronized. The sync data is validated from the data following the X point, so that the output sync data is n1,
n2, m2, m3 ... Similarly, the output data is Dn1,
Dn2, Dm2, Dm3, ...
n2 is valid.

Next, a second embodiment according to the present invention will be described.
FIG. 3 is a diagram showing the configuration of the second embodiment. In this figure, the reproducing head 10 to the TBC circuit 15 and the special head 16 to the TBC circuit 21 are the same as those in the first embodiment described above, and a description thereof will be omitted.

The output signal of the TBC circuit 15 is the demodulation circuit 30.
Are demodulated by and are supplied to the header extraction circuit 31. The header extraction circuit 31 extracts header information, which is information about data such as an address and a data length, and supplies the header information to the valid data detection circuit 22. Similarly, the TBC circuit 21
After being demodulated by the demodulation circuit 34, the output signal is supplied to the header extraction circuit 35, and the header information extracted by the header extraction circuit 35 is supplied to the valid data detection circuit 22. The output data of the header extraction circuits 31 and 35 are supplied to the buffers 33 and 37, respectively.

By the way, a switching signal is also supplied to the valid data detection circuit 22, and a decision logic for setting a switching point is performed based on the supplied signal, and the switch 2
A control signal for controlling 3 and a control signal for controlling the buffers 33 and 37 are output.

The buffers 33 and 37 are controlled to read data by a control signal, and the read data are both supplied to the switch 23. One of the data is selected by the switch 23 by the above-mentioned control signal and is supplied to the error correction circuit 32. Then, the error-corrected data is supplied to the decoding circuit 28, the variable-length data is decoded, and the original image data is reproduced.

FIG. 4 is a timing chart for explaining the operation of the second embodiment. In this embodiment, the data is delimited in units of encoded data length, not in the sync signal.
In FIG. 4, the data on the reproducing head side supplied to the buffer 33 is Dai (i is an integer), and the data on the special head side supplied to the buffer 37 is Dbi. If the switching signal switches at the Y point, the output data will be the data Da2 and Db2 at the Y point. That is, the output data becomes Da1, Da2, Db2, Db3 ... This avoids having to invalidate the data at the switching point.

Next, a third embodiment according to the present invention will be described.
FIG. 5 shows the configuration of the third embodiment. In this figure, the header extractors 31 and 35 are the same as those in the second embodiment shown in FIG.

The outputs of the header extraction circuits 31 and 35 are supplied to the error correction circuits 32 and 36, respectively. If the errors can be corrected, the errors are corrected. If the errors cannot be corrected, an error detection flag is added to the buffer. 33, 37. The error detection flag is also supplied to the valid data detection circuit 22. The buffers 33 and 37 are controlled by the control signal which is the output of the valid data detection circuit 22, and their outputs are both supplied to the switch 23.
In the switch 23, one of the two supplied signals is selected by the control signal output from the valid data detection circuit 22, and is supplied to the decoding circuit 28. Then, the variable length data is decoded and the original image data is obtained.

FIG. 6 is a timing chart for explaining the operation of the third embodiment. In this embodiment, data switching is performed depending on the presence / absence of an error in the unit of encoded data length, and the switching signal and the synchronization signal are not particularly relevant.

In FIG. 6, among the reproducing head side data Da, Da5 and Da6 have a portion where an error cannot be corrected.
In this case, since the error detection flag is added, the error detection signal becomes "HIGH". Similarly, among the special head side data Db, there are portions where Db1 and Db2 could not be error-corrected. Therefore, the output data is a combination of the data excluding those portions where the error cannot be corrected.
Specifically, Da1, Da2, Da3, Da4, Db3, Db4, Db5
… Will be. As a result, all valid data is reproduced.

As described above, when the drum provided with the reproducing head and the special head is used and the signal read from the reproducing head and the signal read from the special head are switched at the time of triple speed reproduction, the synchronization data other than the switching signal is used. The invalid data can be eliminated by switching the signal based on the unit, the encoded data length unit, the error detection signal, or delaying one and connecting it to the other.

[0030]

As described above, in addition to the switching signal, the signal is switched based on the sync data unit, the coded data length unit and the error detection signal, or the invalid data is eliminated by delaying one and connecting it to the other. be able to.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of a first embodiment according to the present invention.

FIG. 2 is a timing chart explaining the operation of the first embodiment according to the present invention.

FIG. 3 is a configuration diagram showing a configuration of a second embodiment according to the present invention.

FIG. 4 is a timing chart illustrating the operation of the second embodiment according to the present invention.

FIG. 5 is a configuration diagram showing a configuration of a third embodiment according to the present invention.

FIG. 6 is a timing chart explaining the operation of the third embodiment according to the present invention.

FIG. 7 is a configuration diagram showing a configuration of a drum.

FIG. 8 is a configuration diagram showing a conventional configuration.

FIG. 9 is an explanatory diagram illustrating a relationship between a track and a head trace.

FIG. 10 is an explanatory diagram illustrating a configuration of compressed code image data.

[Explanation of symbols]

10 ... Playback head, 15, 21 ... TBC circuit, 16 ... Special head, 22 ... Effective data detection circuit, 23 ... Switch, 24 ... Demodulation circuit, 26 ... Error correction circuit, 27 ... Decoding circuit.

Claims (1)

[Claims] 1. Two or more normal video heads for normal reproduction provided on a rotating drum, and two or more special video heads for special reproduction adjacent to the normal video head and used only during special reproduction. A first reproduction processing means for reproducing a compression-coded digital signal by reproducing the signal read from the magnetic tape by the normal video head; and a signal read from the magnetic tape by the special video head. Second reproduction processing means for reproducing a compression-coded digital signal by performing reproduction processing, and based on the outputs of the first and second reproduction processing means and the switching signal, ineffective data is least generated. One of the outputs of the calculation means for calculating the switching point and outputting the control signal and the output of the first and second reproduction processing means is selected based on the control signal. Selecting means, signal switching apparatus characterized by comprising a decoding means for decoding a video signal based on the output of the selection means.