JPH04179380A - Magnetic recorder for digital picture signal - Google Patents

Abstract

PURPOSE:To increase a recording density, and to enable a long time recording and reproduction by specifying the pitch of a truck, the diameter of a rotatry drum, and the rotational speed of the rotatry drum. CONSTITUTION:The pitch of the truck prepared on a magnetic tape 78 by magnetic heads 13A and 13B is less than 5.5mum, the diameter of a rotatry drum 76 is selected to be less than 25mm, and the rotational speed of the rotatry drum 76 is less than 150rps. As the result, the improvement of the linearity of the truck, and the decrease of a trucking error can be operated, and the truck can be prepared by a narrow truck pitch without interposed a guard band on the magnetic tape 78. Thus, the long time recording can be operated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for recording digital image signals such as digital video signals on a magnetic tape, and in particular, to a device for recording a digital image signal such as a digital video signal on a magnetic tape, and in particular, to a device for recording a digital image signal such as a digital video signal on a magnetic tape. According to
The present invention relates to a magnetic recording device for digital image signals that enables long-term recording.

[Summary of the invention]

This invention relates to a blocking circuit that converts an input digital image signal into block-by-block data consisting of a plurality of pixel data, an encoding circuit that compresses and encodes output data of the blocking circuit in block units, and A digital image signal having a channel encoding circuit for channel encoding the output encoded data of the circuit, and recording the output data of the channel encoding circuit on a magnetic tape by a magnetic head attached to a rotating drum. In the magnetic recording device, the pitch of the tracks formed on the magnetic tape by the magnetic head is 5.5 μm or less, the diameter of the rotating drum is 25 #lIl or less, and the rotation speed of the rotating drum is 150 rps or more. By setting the track length per unit time to a predetermined value, it is possible to record for a long time with a small mechanical part, and furthermore, it is possible to reduce errors related to the linearity of the track.

[Conventional technology]

In recent years, D1 format component type digital VTRs and D2 format composite type digital VTRs for broadcasting stations have been put into practical use as digital VTRs that digitize color video signals and record them on recording media such as magnetic tapes. .

The former D1 format digital VTR transmits the luminance signal and the first and second color difference signals at 13°5 MHz and 6 MHz, respectively.
．． After A/D conversion at a sampling frequency of 75 MHz, predetermined signal processing is performed and recorded on tape, and the ratio of the sampling frequencies of these component components is 4.
Since =2=2, it is also called the 4:2:2 system.

The latter D2 format digital VTR samples a composite color video signal with a signal whose frequency is four times the frequency fsc of the color subcarrier signal.
/D conversion, predetermined signal processing, and then recording on a magnetic tape.

Both of these digital VTRs are designed with the assumption that they will be used for broadcasting stations, so they are considered to have the highest image quality, and they can essentially process digital color video signals in which each sample is A/D converted to, for example, 8 bits. I try to record without compressing it.

As an example, the former D1 formant digital VT
The amount of data in R will be explained.

The amount of information of a color video signal is approximately 216 Mbps (megabits per second) when A/D conversion is performed at 8 bits per sample at the above-mentioned sampling frequency. Of these, if you exclude the data for the horizontal and vertical blanking periods, the number of effective pixels of the luminance signal in one horizontal period is 720,
The number of effective pixels of the color difference signal is 360, and the number of effective scanning lines for each field is 25 in the NTSC system (525/60).
0, the data amount Dv of the video signal for 1 second is D v = (720 + 360 + 360) x 8
250×60=172.8 Mbps.

Considering that even in the PAL system (625150), the number of effective scanning lines per field is 300 and the number of fields per second is 50, it can be seen that the amount of data is equal to that of the NTSC system. When redundant components for error correction and formatting are added to these data, the total bit rate of the video data is approximately 205.8 Mbps.

Also, the audio data Da is approximately 12.8 Mbps, and the additional data Do such as gaps for editing, preamble, postamble, etc. is approximately 6°6 Mbps, so the information amount Dt of the entire recorded data is as follows. Become.

Dt=Dv+Da+D.

=172.8 +12.8+6.6 =225.2 M
To record data with this amount of information, a D1 format digital VTR is used.
As a track pattern, a segment method is adopted in which 10 tracks are used in the first field in the NTSC system, and 12 tracks in the first field in the PAL system.

In addition, as a recording tape, one with a width of 19+gm (((accepted), there are two types of tape thickness, 13 μm and 16 μm, and 3 types of recording tape, large, medium, and small) to store this tape.
A variety of items are available. Because information data is recorded on these tapes in the format described above,
The data recording density is approximately 20°4 μ%/bit. Even if error correction encoding is performed, the above-mentioned numerical value is the limit for the recording density (if high, intersymbol interference or t magnetic density of the head/tape).

Combining the above parameters, the playback time of each size cassette of a DI format digital VTR is as follows.

[Problem to be solved by the invention]

In this way, the D1 format digital VTR is sufficient for use as a VTR for broadcasting stations that require top priority on image quality. Also, at most 1.
The playback time was only about 5 hours, making it extremely unsuitable for use as a home VTR. In order to improve recording density, it is effective to reduce the track pitch. However, in conventional VTRs, when the track pitch is small, there are many errors in the reproduced data due to the quality of track linearity, tracking errors, etc., and there is a limit in terms of minimizing track pinch. especially,
There has been a problem that compatibility between VTR devices is poor.

On the other hand, the β system, ■H3 system, 81B system, etc. are currently in practical use as home VTRs, but all record and playback in the form of analog signals, and the image quality of each has been considerably improved. However, for example, when you try to dub and copy something recorded by a camera, the image quality deteriorates considerably at the dubbing stage, and if this is repeated multiple times, it becomes difficult to watch. There was a drawback that it became something that could not be used.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a digital image signal recording apparatus that has good track linearity, is less likely to cause tracking errors, and can therefore have a small track pitch.

Another object of the present invention is to provide a digital image signal recording device that exhibits little deterioration in image quality even when dubbing is repeated a plurality of times.

[Means to solve the problem]

This invention consists of a blocking circuit (5, 6) that converts an input digital image signal into block-by-block data consisting of a plurality of pixel data, and a system that compresses and encodes the output data of the blocking circuit (5, 6) in block-by-block units. Encoding circuit (8)
and a channel encoding circuit (11) for channel encoding the output encoded data of the encoding circuit (8). In a magnetic recording device for digital image signals, the magnetic head (13A, 13B) records the digital image signal on the magnetic tape (78).
8) By setting the pitch of the tracks formed in 5.5 μm or less, selecting the diameter of the rotating drum (76) to be 25 mm or less, and setting the rotation speed of the rotating drum (76) to 150 rps or more, This is a magnetic recording device for digital image signals, characterized in that the track length is set to a predetermined value.

[Effect]

Since track linearity can be improved and tracking errors can be reduced, tracks can be formed with a narrow track pitch without interposing a guard band on the magnetic tape 78, and long-time recording can be performed.

〔Example〕

An embodiment of the present invention will be described below.

This description is given in the following order.

a. Signal processing section S. Block encoding C. Channel encoder and channel decoder d. Head/tape system e. Electromagnetic conversion system a. Signal processing section First, the signal processing section of the digital VTR in this embodiment will be explained. .

FIG. 1 shows the overall configuration of the recording side. I
For example, a digital luminance signal Y1 formed from three primary color signals R1G and B from a color video camera, and digital color difference signals U and 2 are supplied to input terminals indicated by Y, IU, 1 and 1, respectively. In this case, the clock rate of each signal is the same as the frequency of each component signal of the above-mentioned D1 format. That is, each sampling frequency is 13.
5 MHz and 6.75 MHz, and the number of bits per sample is 8 bits.

Therefore, as mentioned above, the data amount of the signals supplied to the input terminals IY, IU, and IV is approximately 216 Mbps.
becomes. The data amount is compressed to approximately 167 Mbps by a valid information extracting circuit 2 which removes data during the blanking period from this signal and extracts only valid head information.

Among the outputs of the effective information extraction circuit 2, the luminance signal Y is supplied to the frequency conversion circuit 3, and the sampling frequency is 13.5M.
It is converted from Hz to 3/4 of that. For example, a thinning filter is used as the frequency conversion circuit 3 to prevent aliasing distortion. The output signal of the frequency conversion circuit 3 is supplied to the blocking circuit 5, and the order of luminance data is converted into the order of blocks. The blocking circuit 5 is provided for the block encoding circuit 8 provided at the subsequent stage.

FIG. 3 shows the structure of a block of encoding units. This example is a three-dimensional block, and by dividing the screen over two frames, for example, as shown in FIG.
A large number of unit blocks (4 lines x 4 pixels x 2 frames) are formed. In FIG. 3, solid lines indicate odd field lines, and broken lines indicate even field lines.

Also, among the outputs of the effective information extraction circuit 2, two color difference signals U and ■ are supplied to the sub-sampling and supply-line circuit 4, and after the sampling frequency is converted from 6.75 MHz to half of that, two digital Color difference signals are alternately selected line by line and combined into one channel of data. Therefore, a line-sequential digital color difference signal is obtained from this sub-sampling and supply line circuit 4. FIG. 4 shows the pixel structure of the signal converted into sub-samples and main lines by this circuit 4.

In FIG. 4, ◯ indicates a sampling pixel of the first color difference signal U, Δ indicates a sampling pixel of the second color difference signal V, and × indicates the position of a pixel thinned out by subsamples.

The line sequential output signal of the subsampling and supply circuit 4 is supplied to a blocking circuit 6. Blocking circuit 6
As in the blocking circuit 5, color difference data in the scanning order of the television signal is converted into data in the block order. Like the blocking circuit 5, this blocking circuit 6 converts the color difference data into a block structure of (4 lines x 4 pixels x 2 frames). Blocking circuits 5 and 6
The output signal of is supplied to the combining circuit 7.

In the combining circuit 7, the luminance signal and color difference signal converted into the block order are converted into one channel data, and the output signal of the combining circuit 7 is supplied to the block encoding circuit 8. This block encoding circuit 8 includes an encoding circuit adapted to the dynamic range of each block (referred to as ADRC) and a DCT (Discr
ete Co51ne Transform) circuit, etc. can be applied. The output signal of the block encoding circuit 8 is supplied to the framing circuit 9 and converted into data having a frame structure. In this framing circuit 9, switching between the image system clock and the recording system clock is performed.

The output signal of the framing circuit 9 is supplied to an error correction code parity generation circuit 10, and a parity of the error correction code is generated. The output signal of the parity generation circuit 10 is supplied to a channel encoder 11, and channel coding is performed to reduce the low frequency portion of the recorded data. The output signal of the channel encoder 11 is supplied to magnetic heads 13A, 13B via recording amplifiers 12A, 12B and a rotary transformer (not shown), and is recorded on a magnetic tape.

Although not shown, the audio signal is compressed and encoded separately from the video signal and is supplied to the channel encoder.

Through the above signal processing, the input data amount is 216 Mbp.
s is approximately 16 by extracting only the effective scanning period.
7 Mbp s, and further frequency conversion, subsampling, and supplying reduce this to 84 Mbp s.
is reduced to s. This data is processed by the block encoding circuit 8.
By compressing and encoding it, it is compressed to about 25 Mbps, and when additional information such as parity and audio signals is added, the recorded data amount is 31.56 Mbps.
It will be about.

Next, the configuration on the playback side will be explained with reference to FIG.

In FIG. 2, the reproduced data from the magnetic heads 13A and 13B is transferred to a rotary transformer (not shown) and a reproduction amplifier 21A.
, 21B to the channel decoder 22. In the channel decoder 22, channel coding is demodulated, and the output signal of the channel decoder 22 is supplied to a TBC circuit (time base correction circuit) 23.

In this TBC circuit 23, time axis fluctuation components of the reproduced signal are removed. The reproduced data from the TBC circuit 23 is E
The signal is supplied to the CC circuit 24, where error correction and correction using an error correction code are performed. The output signal of the ECC circuit 24 is supplied to a frame decomposition circuit 25.

The frame decomposition circuit 25 separates each component of the block encoded data, and also switches the recording system clock to the image system clock. Each piece of data separated by the frame decomposition circuit 25 is supplied to a block decoding circuit 26, where restored data corresponding to the original data is decoded for each block, and the decoded data is supplied to a distribution circuit 27. This distribution circuit 27 separates the decoded data into a luminance signal and a color difference signal. The luminance signal and the color difference signal are supplied to block decomposition circuits 28 and 29, respectively. The block decomposition circuits 28 and 29 convert the decoded data in the order of blocks into the order of raster scanning, contrary to the blocking circuits 5 and 6 on the transmitting side.

The decoded luminance signal from block decomposition circuit 28 is supplied to interpolation filter 30 . In the interpolation filter 30, the sampling rate of the luminance signal is from 3fs to 4fs (4f
s = 13. 5MHz).

Digital luminance signal Y from interpolation filter 30 is taken out to output terminal 33Y.

On the other hand, the digital color difference signal from the block decomposition circuit 29 is supplied to the distribution circuit 31, and the line-sequential digital color difference signals U and 2 are separated into digital color difference signals U and V, respectively. digital color difference signal U from the distribution circuit 31;
(2) are supplied to the interpolation circuit 32 and interpolated respectively. The interpolation circuit 32 interpolates thinned line and pixel data using the restored pixel data.
, digital color difference signals U and V with a sampling rate of 4 fs are obtained and taken out to output terminals 33U and 33V, respectively.

b. Block encoding The block encoding circuit 8 in FIG. 1 described above is as follows:
ADR shown in Japanese Patent Application No. 59-266407 and Japanese Patent Application No. 59-269866 filed by the applicant earlier
C (Adaptive Dynamic Range
C.

ding) encoder is used. This ADRC encoder detects the maximum value MAX and minimum value MIN of a plurality of pixel data included in each block, and
The dynamic range DR of the block is detected from X and the minimum value MIN, encoding is performed in accordance with this dynamic range DR, and requantization is performed using a smaller number of bits than the number of bits of the original pixel data. As another example of the block encoding circuit 8, pixel data of each block is processed by DCT (Discrete Co51ne Trans).
form) After quantizing the coefficient data obtained by this DCT, the quantized data may be subjected to run-length Huffman encoding and compression encoding.

Here, an example of an encoder that uses an ADRC encoder and does not cause image quality deterioration even when multi-dubbing is performed will be described with reference to FIG.

In FIG. 5, a digital video signal (or digital color difference signal) in which one sample is quantized to 8 bits, for example, is inputted from the synthesis circuit 7 of FIG. 1 to an input terminal indicated by 41.

Blocked data from the input terminal 41 is supplied to a maximum value/minimum value detection circuit 43 and a delay circuit 44 . Maximum value,
The minimum value detection circuit 43 detects the minimum value MIN and maximum value MAX for each block. The input data from the delay circuit 44 is delayed by the time required for the maximum value and minimum value to be detected. The pixel data from the delay circuit 44 is sent to the comparison circuit 4.
5 and a comparison circuit 46.

The maximum value MAX from the maximum value/minimum value detection circuit 43 is supplied to a subtraction circuit 47, and the minimum value MIN is supplied to an addition circuit 48. These subtraction circuits 47 and addition circuits 48 are supplied with the value of one quantization step width (Δ=1/16DR) when performing non-edge matching quantization with a fixed length of 4 bits from a bit shift circuit 49. . The bit shift circuit 49 is configured to shift the dynamic range DR by 4 points so as to perform division by (1/16). The subtraction circuit 47 obtains a threshold value of (MAX-Δ), and the addition circuit 48 obtains a threshold value of (MIN+Δ). Threshold values from these subtraction circuit 47 and addition circuit 48 are supplied to comparison circuits 45 and 46, respectively.

Note that the value Δ that defines this threshold value is not limited to the quantization step width, and may be a fixed value corresponding to the noise level.

The output signal of comparison circuit 45 is supplied to AND gate 50, and the output signal of comparison circuit 46 is supplied to AND gate 51. AND gates 50 and 51 are supplied with input data from delay circuit 44 . The output signal of the comparison circuit 45 becomes high level when the input data is larger than the threshold value, and therefore, the output terminal of the AND gate 50 has (M
Pixel data of input data included in the maximum level range of AX-MAX-Δ) is extracted. The output signal of the comparison circuit 46 becomes high level when the input data is smaller than the threshold value, and therefore, the output terminal of the AND gate 5I has (
Pixel data of input data included in the minimum level range of MIN-MIN+Δ) is extracted.

The output signal of AND gate 50 is supplied to averaging circuit 52, and the output signal of AND gate 51 is supplied to averaging circuit 53. These averaging circuits 52 and 53 calculate an average value for each block, and a block period reset signal is supplied from a terminal 54 to the averaging circuits 52 and 53. From the averaging circuit 52, (MAX-MAX-
The average of pixel data belonging to the maximum level range of △) is 4aM
AX' is obtained, and from the averaging circuit 53, (MIN~M
The average value MIN' of the pixel data belonging to the minimum level range of IN18) is obtained. Average value MAX' to average value MI
N'' is subtracted by the subtraction circuit 55, and the dynamic range DR' is obtained from the subtraction circuit 55.

Further, the average value MIN' is supplied to a subtraction circuit 56, and the average value MIN' is subtracted from the input data via the delay circuit 57 in the subtraction circuit 56, thereby forming data PDI after the minimum value has been removed. This data PDI and the modified dynamic range DR' are supplied to a quantization circuit 58. In this embodiment, the number of bits n allocated for quantization is 0 bit (no code signal is transmitted), 1 bit,
This ADRC has a variable length of 2 bits, 3 bits, or 4 bits, and performs edge matching quantization. The allocated bit number n is determined for each block by the bit number determination circuit 59, and data of the bit number n is supplied to the quantization circuit 58.

In variable-length ADRC, efficient encoding can be achieved by reducing the number of allocated bits n for blocks with a small dynamic range DR', and increasing the number of allocated bits n for blocks with a large dynamic range DR'. can. That is, if the threshold value for determining the number of bits n is T1 to T4 (TI<72<73<T4),
In the block of (DR'<T1), no code signal is transmitted, only the information of the dynamic range DR'' is transmitted,
The block for (TI≦DR'<T2) is (n=1), and the block for (T2≦DR'<73) is (n=2
), and the block with (T3≦DR′<74) is (n
=3), and the block with (DR”≧T4) is (n=
4).

In such variable length ADRC, the amount of generated information can be controlled (so-called buffering) by changing the threshold values T1 to T4. Therefore, variable length ADRC can also be applied to a transmission path such as the digital VTR of the present invention, which requires the amount of information generated per field or frame to be a predetermined value.

In FIG. 5, reference numeral 60 denotes a sofa ring circuit that determines threshold values T1 to T4 for setting the amount of generated information to a predetermined value. In the sofa ring circuit 60, a plurality of sets of threshold values (Tl, T2, T3, T4), for example, 32 sets, are prepared, and these sets of threshold values are set as the parameter code Pi (i=0.1 .2,...,31). It is set so that the amount of generated information decreases monotonically as the number i of the parameter code Pi increases.

However, as the amount of generated information decreases, the quality of the restored image deteriorates.

The threshold values T1 to T4 from the buffering circuit 60 are supplied to the comparator circuit 61, and the dynamic range DR' via the delay circuit 62 is supplied to the comparator circuit 61. Delay circuit 62 delays DR' by the time required for buffering 60 to determine the set of thresholds. In the comparison circuit 61, the dynamic range DR' of the block is compared with each threshold value, and the comparison output is supplied to the bit number determination circuit 59, which determines the number n of bits allocated to the block. In the quantization circuit 58, the minimum value removed data PDI passed through the delay circuit 63 is converted into a code signal DT by edge matching quantization using the dynamic range DR' and the allocated bit number n. The quantization circuit 58 is composed of, for example, a ROM.

The corrected dynamic range DR' and average directivity MIN' are outputted via delay circuits 62 and 64, respectively, and furthermore, a parameter code Pi indicating a set of code signal DT and threshold value is outputted. In this example, since the signal that has been previously non-edge match quantized is edge match quantized based on new dynamic range information, there is little image deterioration when dubbing.

C. Channel Encoder and Channel Decoder Next, the channel encoder 11 and channel decoder 22 shown in FIG. 1 will be explained. For details of these circuits, please refer to Japanese Patent Application No. 1-143491 filed by the applicant.
Although its specific structure is disclosed in the No. 1, its schematic structure will be explained with reference to FIGS. 6 and 7.

In FIG. 6, 71 is the parity generation circuit 1 of FIG.
This is an adaptive scrambling circuit that is supplied with an output of 0.Multiple M-sequence scrambling circuits are prepared, and the M-sequence that provides an output with the least high frequency components and DC components for the input signal is selected. It is configured to 72 is a precoder for the partial response class 4 detection method, which performs arithmetic processing of 1/1-D" (D is a circuit for unit delay). The output of this precoder is sent to the magnetic head 13A via recording amplifiers 12A and 12B. ,1
3B records and plays back, and the playback output is sent to the playback amplifier 21.
A and 21B are used for amplification.

In FIG. 7 showing the configuration of the channel decoder 22,
73 indicates the arithmetic processing circuit on the playback side of partial response class 4, and the calculation of 1+D is the playback amplifier 21A, 2
This is done for 1B output. Reference numeral 74 denotes a so-called Viterbi decoding circuit, which performs noise-resistant data decoding by performing calculations on the output of the calculation processing circuit 73 using data correlation, certainty, and the like. The output of this Viterbi decoding circuit 74 is supplied to a descrambling circuit 75, and the data rearranged by the scrambling process on the recording side is returned to the original sequence, and the original data is restored.

The Viterbi decoding circuit 74 used in this embodiment provides an improvement of 3 dB in terms of reproduced C/N compared to the case where bit-by-bit decoding is performed.

d. Tape head system The above-mentioned magnetic heads 13A and 13B are attached to the rotating drum 76 at an opposing interval of 180°, as shown in FIG. 8A. Or as shown in Figure 8B,
Magnetic helads 13A and 13B are attached to drum 76 in a unitary structure. On the circumferential surface of the drum 76, 1
A magnetic tape (not shown) is wound diagonally at a corner where the winding is slightly larger or slightly smaller than 80°.

In the head arrangement shown in FIG. 8A, the magnetic heads 13A and 13B are approximately alternately in contact with the magnetic tape, and as shown in FIG.
In the head arrangement shown in , magnetic heads 13A and 13B simultaneously scan the magnetic tape.

The directions in which the gaps of the magnetic heads 13A and 13B extend (referred to as azimuth angles) are different. For example, as shown in FIG. 9, an azimuth angle of ±20° is set between magnetic heads 13A and 13B. Due to this difference in azimuth angle, a recording pattern as shown in FIG. 10 is formed on the magnetic tape. As can be seen from this Figure 1O, adjacent tracks T formed on the magnetic tape
A and TB are magnetic heads 13A with different azimuth angles.
and 13B, respectively.

Therefore, during reproduction, the amount of crosstalk between adjacent tracks can be reduced due to azimuth loss.

FIG. 11A and FIG. 11B show magnetic heads 13A and 13.
A more specific configuration is shown in which B has an integral structure (so-called double azimuth head). For example, 150rps (
Integrated magnetic heads 13A and 13B are attached to an upper drum 76 that rotates at a high speed (rotation speed common to the NTSC and PAL systems), and a lower drum 77 is fixed.

Therefore, in the case of the NTSC system, one field of data is recorded on the magnetic tape 78 by dividing it into five tracks. This segment method allows the length of the track to be shortened and errors in track linearity to be reduced. The winding of the magnetic tape 78 is such that the angle θ is 1, for example.
66°, and the drum system φ is 251IIIll or less, for example, 16.5a+m.

When realizing recording with a small track pitch such as 5.5 μm, mechanical errors in the head-drum mechanism related to device compatibility are caused by static track linearity errors,
Dynamic trunking error, pair of magnetic heads 13
Bearings A and 13B.

Static track linearity errors are caused by nonlinearity of the leads on the drum, maladjustment of the tape running system, and tilt of the axis of rotation of the drum 76. This nonlinearity of the lead and maladjustment of the tape running system are related to the track length, and the inclination of the rotation axis is related to the diameter of the drum 76. That is, the tracking function indicating static track linearity is proportional to the track pitch and inversely proportional to the product of the track length and the drum diameter.

In the above example, compared to the conventional 8+n+n VTR, the drum diameter is reduced from 40m1 to 16.5mn+, and the track length is reduced from 14mm to 26+mn, so even if the track pitch is as small as 5.5μm, 8II
A tracking function better than IIlVTR can be obtained. Therefore, errors in static track linearity do not increase as much as before.

It also uses a double azimuth head for simultaneous recording. Normally, due to eccentricity of the rotating part of the upper drum 76,
Vibration of the magnetic tape 78 causes dynamic tracking errors. As shown in FIG. 12A, the magnetic tape 78 is pressed downward, and as shown in FIG. 12B, the magnetic tape 78 is pulled upward, thereby causing the magnetic tape 78 to vibrate and change the track. Linearity deteriorates. However, compared to a case where a pair of magnetic heads are arranged facing each other at 180 degrees, by performing simultaneous recording with a double azimuth head, the amount of such tracking error can be reduced. Further, the double azimuth head has the advantage that the distance between the heads is small, so that bearing adjustment can be performed more accurately. Such a tape head system allows recording and reproduction of narrow tracks.

In this way, since errors occurring in the tape head mechanism can be reduced, recording can be achieved by recording at a small track pitch such as 5.5 μm.

e,! Magnetic Conversion System Next, the electromagnetic conversion system used in the present invention will be explained.

First, a magnetic tape as a recording medium is manufactured by the following method.

That is, polyethylene phthalate (PE) with a thickness of 7 μm
T) After applying a liquid containing an emulsion containing an acrylate latex as a main component onto a base made of film, it is dried to form microprotrusions made of the emulsion fine particles on the entire surface of the base. The surface roughness of the base treated in this way is 0.0015 μm in center line average roughness R, and the density of microprotrusions is approximately 50 μm.
00,000 pieces/W12.

Thereafter, using the vacuum evaporation apparatus shown in FIG. 13, a magnetic layer containing CO as a main component is formed on the base by oblique evaporation in an oxygen atmosphere as follows.

In FIG. 13, symbols 81a and 81b are vacuum chambers, 82
83 is a partition plate, and 83 is a vacuum exhaust valve.

84 is a supply roll of base B, 85 is a take-up roll,
86 is a guide roll, and 87a and 87b are cylindrical cooling cans that guide the base B. Also, 88a
, 88b are CO evaporation sources, and 89a and 89b are electron beams that heat the evaporators 88a and 88b, respectively. 90
A and 90b are shielding plates for regulating the incident angle of the evaporation beam with respect to the base B, and 91a and 91b are oxygen gas introduction pipes.

In the vacuum evaporation apparatus configured in this way, the base B
is transferred from the supply roll 84 to the cooling can 87a1, the guide roll 86, the cooling can 87b, and the take-up roll 85 in this order. At this time, cooling can 8
7a and 87b, a magnetic layer consisting of two OCO layers is formed by oblique vapor deposition in an oxygen atmosphere.

In this vacuum deposition, the vacuum chambers 81a and 81b are heated to a vacuum degree of I
These vacuum chambers 81 are maintained at 10-' Torr.
Oxygen gas is introduced into the chambers 81a and 81b at a rate of 250 cc/win using introduction vibrators 91a and 91b.

In this case, the angle of incidence of the evaporation beam with respect to base B is 45
-90° range. Further, the Co layer is deposited to a thickness of 1,000 layers in each of the cooling cans 87a and 87b, so that the thickness of the entire magnetic layer is 2,000 layers.

After applying a back coat made of carbon and an epoxy binder and a top coat on the lubricating side made of perfluoropolyether to the base B on which the magnetic layer made of two OCO layers was formed in this way, this was coated with a thickness of 8 mm. Cut to width to make magnetic tape.

The characteristics of the finally obtained magnetic tape are the residual magnetic flux density B
, = 4150G, coercive force H, = 16900e, R, = 7
It was 9%. Also, the surface roughness of this magnetic tape is 0 at the center line average roughness R, reflecting the surface roughness of the base B.
．． It was extremely small at 0.015 μm.

Note that the surface roughness is normally measured according to JIS BO601, but this time the measurement was performed under the following conditions.

Measuring device: Talystep (manufactured by Rank Taylor) Needle diameter: Q
, 2×0.2 μm, square needle stylus pressure: 2 tng Bypass filter: 0.33 Hz FIG. 14 shows a recording magnetic head used in the present invention.

As shown in FIG. 14, this magnetic head consists of single crystal Mn
A gap 104 is provided between Fe-Ga-3i-Ru soft magnetic layers 102 and 103 formed by sputtering on the -Zn ferrite cores 101A and 101B. Glass 1 is provided on both sides of this gap 104 in the track width direction.
05.106, thereby regulating the track width to approximately 4 μm. 107 is a winding hole, into which a recording coil (not shown) is wound. The effective gap length of this magnetic head is 0°20 μm.

Since this magnetic head uses Fe-Ga-3i-Ru soft magnetic layers 102 and 103 with a saturation magnetic flux density BS of 14.5 kG near the gap 104, the head Recording can be performed without incurring magnetic saturation.

By using the ME tape and magnetic head as described above, a recording density of 1.25 μm''/bit or less can be achieved.

That is, as mentioned above, by recording a signal with a shortest wavelength of 0.5 μm for a track width of 5 μm,
5 μm”/bit is achieved.

However, it is known that the C/N of the reproduced output deteriorates as the recording wavelength and track width decrease, and in order to suppress this deterioration, the tape and head having the above-described configuration are used.

In 1988, the applicant prototyped a digital VTR using 8+nm ME tape with a track pitch of 15 μm and a shortest wavelength of 065 μm. At this time, a rotating drum with a diameter of 40 mm was used and the drum was rotated at 60 rpm to perform recording and reproduction. With this system, a C/N of 51 dB was obtained for a recording wavelength of 1 μm. The bit error rate of the system was 4.times.10-'.

If a track with a width of 5 μm is used as in the embodiment of the present invention, a C/N of only about 44 dB can be obtained with the same specifications, resulting in deterioration of image quality. In order to compensate for this 7 d B C/N deterioration, the configuration of the present invention described above will be used.

That is, - It is known that the signal output level decreases when the spacing between the tape and the head during recording and replaying on a boat increases, and the amount of spacing depends on the flatness of the tape. It is also known that Furthermore, in the case of coated tapes, the flatness of the tape depends on the coating agent, but in the case of vapor-deposited tapes, it is known that it depends on the flatness of the base itself. In the above embodiment, the C/N can be reduced by selecting the surface roughness of the base film to be as small as possible.
An experimental result was obtained that showed a dB increase.

Furthermore, by using the vapor deposition material and vapor deposition method of the above-described embodiment, an experimental result showed that a C/N improvement of 3 dB was obtained compared to the tape used in the prototype in 1988. From the above, by using the head and tape of the present invention, a C/N increase of 4 dB was obtained compared to the previous prototype.

Furthermore, in this invention, since Viterbi decoding is used for channel decoding, it has been confirmed that an increase of 3 dB can be obtained compared to the bit-by-bit decoding used in the previous prototype.

Therefore, it is possible to compensate for the C/N deterioration of 7 d,B as a whole, and at a recording density of 1.25 μm''/bit, the C/N deterioration of 198
This will result in an error rate equivalent to that of the 80-year prototype. Regarding playback output, it is necessary that the error rate at the stage before the error correction code correction process is 10-4 or less, which is the amount that can be corrected when using an error correction code with a redundancy of about 20%. This is to reduce errors.

〔Effect of the invention〕

This invention can record digital image signals with a small track pitch, so recording density can be increased.
Long-term recording and playback is possible using a small cassette. Furthermore, since the diameter of the rotating drum is small, the size of the mechanism can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the recording side of the signal processing section in an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the forwarding side of the signal processing section, and FIG. Figure 4 is a route map used to explain subsampling and purine, Figure 5 is a block diagram of an example of a block encoding circuit, and Figure 6 is a schematic diagram of an example of a channel encoder. 7 is a block diagram schematically showing an example of a channel decoder, FIG. 8 is a route map used to explain the head arrangement, FIG. 9 is a route map used to explain the azimuth of the head, and FIG. 10 is a block diagram showing the outline of an example of a channel decoder. is a route map used to explain the recording pattern, Figure 11 is a top view and side view showing an example of a tape head system, and Figure 12 is a route diagram used to explain that vibrations of the tape are applied due to eccentricity of the drum. Figures 13 and 13 are route diagrams used to explain the magnetic tape manufacturing method, and Figure 14 is a perspective view showing an example of the structure of a magnetic head. Explanation of main symbols in the drawings IY, IU, IV: Input terminals for component signals 5.6: Blocking circuit 8 Niblock encoding circuit 11: Channel encoders 13A, 13B = Magnetic head 22: Channel decoder 26: Block decoding circuit 28.29 Niblock Disassembly Circuit Agent Patent Attorney Tadashi Sugiura Tomo A B Fig. 11 Fig. 12 Naya Sonel ENC Fig. 6 Mutual Naya Soful DEC Fig. 7 Hep@Otsu 1 Fig. 8 Mouth Hole Hev V Fig. 9 2σ Blind Shayoshi Nogutano Figure 10

Claims (1)

[Scope of Claims] Blocking means for converting an input digital image signal into block-by-block data consisting of a plurality of image data; encoding means for compressing and encoding the output data of the blocking means in block-by-block units; and channel encoding means for channel encoding output encoded data of the encoding means, and the output data of the channel encoding means is recorded on a magnetic tape by a magnetic head mounted on a rotating drum. In the magnetic recording device for digital image signals, the pitch of the tracks formed on the magnetic tape by the magnetic head is set to 5.5 μm or less, the diameter of the rotary drum is selected to be 25 mm or less, and the rotation speed of the rotary drum is set to be 5.5 μm or less. 1. A magnetic recording device for digital image signals, characterized in that the track length per unit time is set to a predetermined value by recording a speed of 150 rps or more.