JPS58223977A - Video signal digital recorder and reproducer - Google Patents

Abstract

PURPOSE:To prevent an error of a decoding signal from being propagated, by inserting periodically a PCM signal without band compression, inserting this PCM signal to a part of each track, and reproducing this PCM signal part only at a high speed reproduction. CONSTITUTION:A digital video signal (x) being an output of an A/D converter 2 is applied to the 1st switching circuit 21 and a block memory 22. An output of the A/D converter 2 is connected to the input of a 1-frame memory 8 according to a switching signal s1 transmitted from a control circuit 20. The control circuit 20 generates an address signal (ad) representing to which block on a screen a block recorded with the PCM signal belongs and transmits it to an additional circuit 23, which adds the address signal (ad) to the PCM signal (p) read out from a block memory 22 and transmits it to the 2nd switching circuit 24. The switching circuit 24 switches a quantizing signal (q) and the PCM signal (p) according to a switching signal s2 and transmits it to a modulator 5. The output of the modulator 5 is amplified at an amplifier 25 and recorded via a head 26.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a recording and reproducing apparatus that converts video borrowing into a digital signal and records and reproduces the digital video signal with a reduced recording bit rate using a predictive coding method.

When a video signal is digitally recorded on a magnetic tape, if the digital signal obtained by converting the video signal is recorded as it is, the bit rate of the recording signal is high, so the amount of tape consumed increases. For example, when an NTSC Kafu TV signal is subjected to 8-bit/sample Φ conversion at a sampling frequency f=3fsc (8C color subcarrier frequency a58MH2), the bit rate is approximately 86 Mbps.

Therefore, encoding methods are used that utilize the correlation of video signals to reduce the deterioration of image quality and reduce the bit rate. This encoding method is also called a band compression method, and various methods have been proposed.

Next, as an example of a band compression method, interframe DPC
The M method will be explained. When the input signal is an NlSC color TV signal (hereinafter abbreviated as color TV signal), one frame of video signal is sent out every 1/30 seconds. In the inter-frame DPCM method, as shown in FIG.
) From the signals of several pixels in the frame, predict if!
(Xo is obtained, the prediction error (called a difference) between the current input pixel value x0 and its predicted value ■ is calculated, and the predicted error value is encoded. For example, as a method for calculating the predicted value, There is a method like this.

In FIG. 1, the pixel of the (K-1)th frame, which is one frame before the pixel X0 of the first frame, is xl.

The pixels before and after pixel x1 on the same line are x
1yX@, and the pixels just i′y in above and below the pixel x1 are respectively X4. Let it be X5. When the predicted value ■ is expressed as a linear combination of these five pixels, ■=α1x1+α
2x2+α3x3+α4x4+α5x5 (1) However, the 1-pixel XlO value may also be used as the predicted value. This is expressed by the formula α) where town=1. α, = α, :l: α, = α
.

This corresponds to when = 0.

FIG. 2 shows a block diagram of a transmission device using the interframe DPCM method. In FIG. 2, the Kafu W signal is supplied to the input terminal (1). A/D converter (smell is from Kawo TV)
The signal is sampled, quantized, and converted into a digital video signal X. For example, if the sampling frequency fs is 4f, c,
At 8 bits/sample, the bit rate is approximately 115
It becomes Mbp8. A subtracter (3) takes the difference between the digital video signal X and its predicted signal for each sample μ, and obtains a difference signal d. Digital μ video signal X and prediction signal
If it is bit/sample, the difference signal will be 9 bits/sample. When the predicted value is appropriate, the value of the difference signal d is 0
The probability of occurrence near is high, and the probability of occurrence of a value with a large absolute value is small. Therefore, by representing the 29 values of the difference signal d with, for example, 24 values, the bit rate can be reduced. The quantizer (4) thus converts the 9-bit/sample difference signal d into a 4-bit/sample quantized signal q.

The modulator (5) converts the quantized signal q into a transmission line code C suitable for the characteristics of the transmission line, and sends it to the transmission line +101.

For example, in the case of magnetic recording, an electromagnetic conversion system is used as the transmission line 110).

The quantized signal q is also applied to a local requantizer (6).

The local requantizer (6) converts the 4-bit quantized signal q into a locally decoded difference signal d' expressed by 24 representative values among the 9-bit values. The local adder (7) sums the locally decoded difference signal d' and the predicted value X, and reproduces the locally decoded signal X'. The locally decoded signal X' corresponds to a value to be reproduced on the receiving side of the digital video signal X. This local decoded signal x' is stored in a one-frame memory (8) and used when obtaining the predicted signal X of the first frame. The prediction circuit (9) reads the first frame from the one frame memory (8).
A predicted value is obtained from the pixel X1 (1=1 to 5) k H'M extraction, 0) formula as shown in the figure, and sent to the subtracter (3) and local adder (7).

Demodulator (11) receives (or reproduces) transmission line code C
This is then decoded to reproduce the quantized signal q. The requantization i+H 21 has the same massaging characteristics as the local requantizer (6) on the transmitting side, and converts the 4-bit quantized signal q into a 9-bit decoded difference signal d'. Addition: 0 is the sum of the decoded difference signal d' and the prediction signal X, and the decoded signal
’ is played. The color value converter θQ converts the decoded signal X' into an analog signal and outputs it as a color TV signal at the output terminal (1η
Send from. 1fc, the decoded signal X' is stored in the one frame memory α0, and used when obtaining the predicted signal of the next frame. The prediction circuit o4 is the same circuit as the transmission side prediction circuit (9).

As described above, the locally decoded difference signal, locally decoded signal, and predicted signal on the transmitting side are the same signals as the decoded difference signal, decoded signal, and predicted signal on the receiving side. In this way, in order for the digital video signal to be played correctly on the receiving side,
The contents of one frame memory on each of the sending and receiving sides must match.

Next, a case will be described in which a digital video signal with a reduced bit rate is recorded on a magnetic tape. In Figure 3,
Helical scan type rotating head.

This shows the track T when recording was performed using the following. For example, it is assumed that one track is recorded with one band-compressed digital signal for one frame. When playing back by running the tape at the same speed as when it was recorded (hereinafter referred to as normal playback),
Color TV signals can be reproduced using the receiving device shown in FIG. However, when the tape is played back by running it at a faster speed than during recording (hereinafter referred to as high-speed playback), the recorded track Ti and the running trajectory S of the head are
, will no longer match, and only a portion of the signals of multiple frames can be reproduced during one scan of the head. FIG. 4(a) shows the case of 4x speed playback. Fourth
As shown in the figure, since only about 1/4 of each frame is reproduced in one scan, for example, the ! Because the signal before the frame is not being played back from track T1,
Correct decoding is impossible. Here) is the tape running direction.

Also, when the tape is played back by running it at a slower speed than during recording (hereinafter referred to as low-speed playback), the recorded track T
1 and the running trajectory SJ of the head do not match. In order to reproduce one track T, which is shown in the case of 1/2 speed reproduction as shown in FIG. For example, if normal playback is performed up to track T1 and low-speed playback is performed from track T, scan S1
Since the signal in track T is also reproduced, the same difference signal is used twice, and the value of the decoded signal contains an error.

In addition to the example shown in FIG. 4, there is a tracking method called AST. This head is equipped with a pedestal that deforms depending on voltage, such as a pymop, so that even during high-speed and low-speed playback,
This method controls the recorded tracks to be traced correctly. About the field using AST +: SS,
If this is clarified, the problems mentioned earlier will become clear. When performing 4-speed playback using ASTh, the first scan s1
And truck T11! :Trace correctly, and in the next scan S, trace T, Fr. In this case, since the digital signal of track T4, which is necessary to reproduce the video signal using the digital signal recorded on track T, is not reproduced, it is difficult to reproduce the video signal of track T. .

When performing 1/2 speed playback using AST, both the first scan S1 and the next scan S trace the track TI, so decoding using the same difference signal in the second scan will cause the difference in the decoded signal. The value changes.

The present invention aims to prevent errors in decoded signals that occur when a digital video signal with a reduced recording bit rate is recorded in V'rRK using the DPCM method and is played back at high or low speed. .

In order to prevent the propagation of errors in decoded signals in the DPCM system, the present invention periodically inserts a PCM signal that does not compress the band, and also inserts a PCM signal in a part of each track. This attempts to achieve high-speed reproduction by reproducing only the PCM signal portion.

In addition, during low-speed playback, for differential signals that are played multiple times, by stopping the decoding operation after the 24th stanza,
This is an attempt to realize low-speed playback.

An embodiment of the present invention will be described below based on the drawings. Before explaining the present invention in detail, a method for inserting a PCM signal will be explained. In methods such as the DPCM method, which uses the previous signal to decode the next signal, if an error occurs in the decoded signal due to dropouts in magnetic recording or noise in transmission, the decoded signal is used to decode the next signal. An error will also occur in the next signal to be predicted, and the error will propagate. In order to prevent this, a PCM signal is inserted in the middle of the DPCM signal, and a signal used for prediction (in FIG. 2, data stored in one frame SV) is set with this signal. In the present invention, this PCM signal is inserted into each track little by little. For example, when resetting the entire screen in one second, one frame of PCM signal will be inserted into the 30 frame signal.6 One frame consists of 525 fins, so each frame has approximately 18 fins of t-PCM. It can be transmitted as a signal.

Which part of each frame is transmitted as a PCM signal is determined by
Various methods are possible. An example is shown in FIG. 6th
Figure (1) In ω, the V-frame screen is divided into 30 blocks of 18 fins each, and one block of P is created for each frame.
This shows the case of transmission using a CM signal. Also, Figure 6■
In this example, the screen is divided into approximately square blocks. Also.

Another possible method is to divide each pixel on the screen into 30 groups in pixel units and transmit data for each group.

Next, the recording format of the PCM signal on the track will be explained. - Various recording formats are possible, but in the embodiment of the present invention, the PCM signal portion t- is recorded collectively at the leading end of each track, as shown by the hatched area in FIG.

Next, an example of a magnetic recording/reproducing apparatus implementing the present invention will be described. Here, by the method explained above, P
This is an example in which an interframe DPCM method is used to insert a CM signal. FIG. 7 shows a block diagram of the recording side.

In FIG. 7, an input terminal (1), an A/D converter (2),
Subtractor (3), quantizer (4), modulator (5) 1 local requantizer (6), local adder (71i frame memory (
8) and the prediction circuit (9) are the same as those with the same numbers in FIG. 2, and the operation for performing interframe DPCM is also the same, so a detailed explanation will be omitted, and the operation for inserting the PCM signal will be explained. .

The digital μ video signal X, which is the output of the converter
The first I71 switch is applied to I) and the block memory shift. A first switching circuit (1) normally connects the output of one local adder (7) to the input of one frame memory (8). According to the switching signal s1 sent from the control circuit (3), the output of the converter (2) is stored in one frame memory (
Connect to the input of 8). The control circuit (transfer) sends out a switching signal s1 so as to write the digital video signal X belonging to the block to be recorded in the PCM signal into the one frame memory (8) as shown in the second diagram. The block memory (2) stores the digital video signal X belonging to the block as a PCM signal p according to the switching signal s1.The control circuit S0 stores which block on the screen is the block to be recorded with the PCM signal. It generates an address signal ad indicating and sends it to the additional circuit (?3).The additional circuit (a) sends the address signal a to the PCM @no.p read from the block memory +22.
d is added, and the second switching circuit (sent to 24J, mag ζ, control circuit Shiro) generates a switching signal S2 so that the recording format shown in FIG. The switching circuit 4 switches between the quantized signal q and the PCM signal p and sends it to the modulator (5) according to the switching signal S2.The modulator (5) modulates the recording code C and sends it to the recording amplifier. (
The signal is amplified by a magnetic head and recorded on a magnetic tape. At this time, the format of the recording track is as shown in FIG. That is, at the leading end of the track, a PCM signal p for one block and an address signal ad indicating the address of the block are recorded, followed by an interframe DPCM signal.

FIG. 8 shows a block diagram of the playback side. In Figure 8,
M adjuster (11), re-hf stopper (1), addition delay OL prediction circuit (1 unit, 1 frame memory 0), D/A converter 0 ring and output terminal (lη is the same number in Fig. 2) Since the decoding operation of interframe DPCM is also the same as that of
The operation of reproducing a PCM signal will be explained.

The signal reproduced from the magnetic tape Qη through the head (2 hinoki) is amplified by the reproduction amplifier (8I), and the demodulator (11) demodulates the recording code C into the %PCM signal p signal and the quantized signal q. The decoded signal q is sent to the interframe DPCM decoding unit (requantizer θ, adder H1 prediction circuit 04), 1 frame V-memo!J (151), and reproduces the decoded signal X'. ' is applied to the terminal ←) of the third switching circuit (c). The third switching circuit selects one of the three terminals (A) and (RIG) according to the mode switching signal m. For DPCM playback mode, select the terminal ←),
Decoded signal xr: l frame memo! Write to JQ51 and playback buffer memory (36).

The identification circuit (34) detects the address signal ad, sends out the address signal ad to the reproduction control circuit (voice), and also adds the detection signal k to the PCM separation circuit (34). PCM signal signal separation,
It is sent to the terminal (c) of the third switching circuit 061. When the reproduction control circuit (Incorporated) receives the address signal ad, it sets the mode switching signal m to the PCM reproduction mode. Also, PCM
Signal Signal - In order to reproduce to the block position at the time of recording, a frame memory control signal f and a reproduction buffer memory control signal S are generated according to the address signal ad and sent to the respective memories (15) and 06.

The third switching circuit (for the 3rd generation, the mode switching signal m is PCM1
When the mode is entered, the terminal (c) is selected and the PCM signal signal is sent to the one-frame memory θX and the playback buffer memory (g). Each memory receives a frame memory control signal f,
According to the reproduction buffer memory control signal S, data is written in correspondence with the block position at the time of recording the PCM signal signal.

When the above PCM signal writing is completed, the reproduction control circuit (g) returns the mode switching signal m to the DPCM mode.

In normal playback, the PCM signal recorded for each track is played back in this way, and the signal used for prediction and the stored 1-frame memory (151) and playback buffer memory (3 moments are reset, so the error Propagation can be prevented.

Next, the case of performing high-speed reproduction will be explained.

In the case of high-speed playback, as mentioned above, the signal of the previous frame is not necessarily played back, so if DPCM is decoded, a significant error will occur. In the present invention, PC
High-speed reproduction is achieved by reproducing only the M signal portion.

In Figure 8, when performing high-speed playback,
↑Apply playback mode designation signal β to mode input terminal -. When the reproduction control circuit (2) receives the high-speed reproduction mode designation signal β, it always sets the mode switching signal m to the PCM mode. The operation after the mode switching signal m changes to the PCM mode is similar to the operation of reproducing the PCM signal during normal reproduction described above. However, the V% mode does not work unless the hoop l playback mode designation signal α and low speed playback mode designation signal γ are added to the mode nesting (from the decoy).

Also; in this way, by rewriting the 1-frame memory (15) used for DPCM decoding with the PCM signal, υ
, then when the mode is changed to hoop I and playback, the effect of the predicted signal can be reduced.

Next, a case of performing low-speed playback will be explained.

In the case of low-speed playback, the difference signal of the same frame may be played back multiple times, so even though there is no transmission error (error during recording, 11th raw), the decoding input The revised name may contain errors. In the present invention, low-speed playback is realized by stopping the second and subsequent productions.

In FIG. 8, when performing low-speed reproduction, a low-speed reproduction mode designation signal r is applied to the mode input terminal. When the reproduction control circuit (2) receives the low-speed reproduction mode designation signal γ, it starts checking the address signal ad sent out by the identification circuit (incorporated). If the same address signal ad is detected successively, the mode switching signal m is set to the prohibited mode. The third switching circuit 0 [il selects the terminal when the mode switching signal m reaches the prohibition mode]. Nothing is connected to terminal (A).

Furthermore, the reproduction control circuit ((4) prohibits write operations in each memory using the frame memory control signal f and the reproduction buffer memory control signal S.

When a different address signal ad is detected, the reproduction control circuit (clock) returns the mode switching signal m from the inhibit mode to repeating the PCM mode and DPCM mode, which is the same as during normal reproduction.

The playback pap memory (A) writes the decoded signal in each mode as described above, and depending on the rate of the output signal,
The decoded signals are read out sequentially. A D/A converter (10) converts the decoded signal into an analog signal and sends it out as a color TV signal through the output terminal 0η.

In this embodiment, in order to simplify the explanation, the i-frame memory (15) used for DPCM decoding and the pinned buffer memory (
36), but one frame memory can also be used for both.

As explained above, according to the present invention, the interframe DP
Even in a digital/l/recording/reproducing apparatus using a predictive coding method such as a CM, it is possible to provide a video signal digital recording/reproducing apparatus that can perform high-speed and low-speed reproduction with little deterioration in image quality.

Note that in this embodiment, the interframe DPCM method was used as the predictive encoding method, and the recording format was 1) a method of recording one frame of digital signal on a rack. This method is intended to simplify the method and is not limited to this method. Generally speaking, if the method requires digital signals contained in other tracks in order to reproduce a video signal from a digital signal contained in one track, it is not possible to implement the ``undiscovered method''. can.

In addition, in this example, helicopter power! Although the explanation has been given using a rescan type VTR as an example, the present invention is not limited to this, but can be easily applied to a magnetic or optical disc, for example.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the correspondence of pixels between frames, FIG. 2 is a block diagram of a digital μ transmission device using the inter-frame DPCM method, and FIG. 3 is a schematic diagram showing recording tracks of helical scan type YrH. Fig. 4 is a schematic diagram showing the relative relationship between the head scan locus and the track when performing low-speed playback and low-speed playback at high C, and Fig. 5 is a schematic diagram showing an example of the recording format when inserting a PCM signal. FIG. 6 is a schematic diagram showing a method of dividing the screen. FIG. 7 is a block diagram showing the configuration of the recording side of the digital VTR according to the present invention. FIG. 8n: A block diagram showing the configuration of the playback side of the digital TV VTR. It is. (2)...N's converter, (3)...Subtractor, (4)
...Quantizer, (61...Modulator, (Ill...
Demodulator, (121... Requantizer, (L4... Adder, ;9) α4... Prediction... Circuit, +8101fl.
...1 frame memory, (field...D/A converter, (3
)...recording control circuit, f2+1 Hml...switching circuit, wire...block memory, -...playback control circuit,
(To)...A: 1 addition circuit, Iz...PCM separation circuit, (Incorporated)...Identification circuit, (3 members...Reproduction buffer memory agent Yoshihiro Moriki Figure 1, Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] L A digital μ recording and reproducing device that digitally converts a video signal, performs band compression using a predictive coding method, and records and plays back a digital signal with a reduced recording bit rate. means for recording a second digital signal without band compression on the same track together with the first digital signal subjected to band compression; a switching circuit for selecting one of the signals and a second digital video signal reproduced; a memory for sequentially storing the output signals of the switching circuit; and a switching circuit for reading out the digital video signal from the memory, converting it into an analog signal, and converting the digital video signal into an analog signal. A video signal digital/L' recording and reproducing device equipped with a converting means for reproducing. The digital video signal according to claim 1, characterized in that the λ switching circuit is controlled to select only the second digital video signal when reproducing the video signal at a higher speed than during recording. Recording and playback device. & When the video signal is played back at a slower speed than when it was recorded, the switching circuit and memory are prohibited from outputting from the switching circuit and writing to the memory for signals that have been played back repeatedly from the same track. 2. The video signal digital μ recording and reproducing device according to claim 1, wherein the video signal digital μ recording and reproducing device is controlled to repeatedly read out the written digital signal.