JP3203005B2 - Magnetic recording method of digital image signal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording method of a digital image signal suitable for recording a digital image signal such as a digital video signal on a magnetic tape.

[0002]

2. Description of the Related Art In recent years, a digital VT for digitizing a color video signal and recording it on a recording medium such as a magnetic tape.
As R, a D1 format component digital VTR for broadcast stations and a D2 format composite digital VTR have been put to practical use. The former D1 format digital VTR converts a luminance signal and first and second color difference signals into 13.5 MHz signals, respectively.
After performing A / D conversion at a sampling frequency of 6.75 MHz, predetermined signal processing is performed and recorded on a magnetic tape. Since the sampling frequency ratio of these component components is 4: 2: 2, the ratio is changed to 4: 1. : 2: 2 system. The latter D2 format digital VTR performs A / D conversion by sampling a composite color video signal with a signal having a frequency four times the frequency fsc of the color subcarrier signal, performs predetermined signal processing, and then performs magnetic tape recording. To be recorded.

[0003] Since these digital VTRs are both designed to be used for broadcasting stations,
Priority is given to image quality, and one sample is converted to A /
The D-converted digital color video signal is recorded without being substantially compressed. As an example, the data amount of the former D1 format digital VTR will be described. The information amount of the color video signal is
When the A / D conversion is performed at 8 bits per sample at the sampling frequency described above, the information amount is about 216 Mbps (megabits / second). Excluding the data in the horizontal and vertical blanking periods, the number of effective pixels of the luminance signal in one horizontal period is 720, and the number of effective pixels of the color difference signal is 3 in one horizontal period.
60, and the number of effective scanning lines in each field is 250 in the NTSC system (525/60). Therefore, the data amount Dv of the video signal per second is Dv = (720 + 360 + 360) × 8 × 250 × 60 = 172.8 Mbps. Become.

[0004] Even in the PAL system (625/50), considering that the number of effective scanning lines per field is 300 and the number of fields per second is 50, the data amount is NT.
It turns out that it becomes equal to SC system. When a redundant component for error correction and formatting is added to these data, the bit rate of the video data is about 205.
8 Mbps. The audio data Da is about 12.8 Mbps, and the additional data Do such as the gap, preamble, and postamble for editing is about 6.6 Mbps. Therefore, the information amount Dt of the entire recording data in the case of the NTSC system is It is as follows. Dt = Dv + Da + Do = 172.8 + 12.8 + 6.6 = 192.2 Mbps

[0005] In order to record data having this amount of information, a digital VTR of the D1 format uses a track pattern as a track pattern.
In the PAL system, a segment system using 12 tracks is adopted. A recording tape having a width of 19 mm is used, and a tape thickness of 13 mm is used.
There are two types, i.e., μm and 16 μm, and three types of large (L), medium (M), and small (S) cassettes are provided for storing these. Since information data is recorded on these tapes in the format described above, the data recording density is about 20.4 μm ² / bit. When the above parameters are combined, the reproduction time of the cassette of each size of the digital VTR of the D1 format is as follows. That is, for an S size cassette, 13 minutes when the tape thickness is 13 μm, 11 minutes when the tape thickness is 16 μm, and for an M size cassette, the tape thickness is 13 minutes.
μm 42 minutes, 16 μm 34 minutes, L
For a cassette of a size, the time is 94 minutes when the tape thickness is 13 μm, and 76 minutes when the tape thickness is 16 μm.

[0006]

As described above, the digital VTR of the D1 format is sufficient as a VTR for a broadcasting station that requires the performance with the highest priority on image quality.
Even if a large cassette with a tape having a width of 19 mm is used, only about 1.5 hours of reproduction time can be obtained, which is extremely unsuitable for use as a home VTR. On the other hand, for example, if a signal having a shortest wavelength of 0.5 μm is recorded for a track width of 5 μm, a recording density of 1.25 μm ² / bit can be realized, and the amount of recorded information is reduced with less reproduction distortion By using the compression method in such a manner together, long-time recording / reproduction can be performed even when a narrow magnetic tape having a tape width of 8 mm or less is used.

As a magnetic tape for recording at such a high recording density, the use of a metal-deposited tape (ME tape) is being studied. The ME tape can be as narrow as 8 mm or less as described above. However, such a narrow ME tape has a problem that the bit error rate at the time of reproduction becomes extremely high because the ME tape is easily deformed at the time of storage. this is,
As the track pitch becomes narrower with the increase in recording density, the linearity of the track becomes worse due to expansion and contraction of the tape during storage, and it becomes difficult for the magnetic head to accurately trace each track during reproduction. It is.

Accordingly, an object of the present invention is to reproduce and output a digital image signal recorded on a magnetic recording medium even if the recording density of the data is increased to about 1 μm ² / bit and the width of the magnetic recording medium is reduced. It is an object of the present invention to provide a magnetic recording method of a digital image signal capable of reducing the bit error rate before performing the error correction to 1 × 10 ⁻⁴ or less.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention converts an input digital image signal into a block unit of a plurality of pixel data and blocks the data. In a magnetic recording method of a digital image signal, a compression encoding is performed in units, the compression encoded data is channel encoded, and the channel encoded data is recorded on a magnetic recording medium by a magnetic head mounted on a rotating drum. The magnetic recording medium has a magnetic layer formed of a metal magnetic thin film formed on a non-magnetic support, and the energy product of the product of the residual magnetic flux density, thickness and coercive force of the magnetic layer is 100 G · cm · Oe.
The surface roughness of the magnetic recording medium is the center line average roughness.
The ratio of the longitudinal heat shrinkage of the magnetic recording medium to the transverse heat shrinkage of the magnetic recording medium is 0.8 to 1.0 , and the transverse heat shrinkage The heat shrinkage in the longitudinal direction is 0.5 % or less.

Here, the heat shrinkage ratio is defined as (a-a ') when an object having an initial length a in a certain direction becomes a length a' after being left at 150 ° C. for 30 minutes. /
a is expressed in%. As described above, in the present invention , the surface roughness of the magnetic recording medium is the center line average roughness R.
_a is set to 0.003 μm (30 °) or less.

[0011]

The ratio of the vertical thermal shrinkage of the magnetic recording medium to the horizontal thermal shrinkage of the magnetic recording medium is 0.8 to 1.0 , and the horizontal thermal shrinkage and the vertical thermal shrinkage. When the rates are 0.5 % or less, it is possible to effectively suppress the deterioration of track linearity due to deformation during storage of the magnetic recording medium. Therefore, the data recording density is 1 μm
^{Even if the} height is increased to about ² / bit and the width of the magnetic recording medium is reduced, the magnetic head can accurately trace each track during reproduction. As a result, the bit error rate before error correction of the reproduction output of the digital image signal recorded on the magnetic recording medium can be reduced to 1 × 10 ⁻⁴ or less.

[0012]

An embodiment of the present invention will be described below. This description is made in the following order. a. Signal processing unit b. Block coding c. Channel encoder and channel decoder d. Head / tape system e. Electromagnetic conversion system a. First, a signal processing unit of the digital VTR according to the embodiment will be described. FIG. 1 shows the configuration on the recording side as a whole. Input terminals indicated by reference numerals 1Y, 1U, and 1V are supplied with digital luminance signals Y and digital color difference signals U and V formed from, for example, three primary color signals R, G, and B from a color video camera. In this case, the clock rate of each signal is the same as the frequency of each component signal in the D1 format. That is, the respective sampling frequencies are 13.5 MHz and 6.75.
MHz, and the number of bits per sample is 8 bits. Therefore, the input terminals 1Y, 1
The data amount of the signal supplied to U and 1V is about 216 Mbps as described above. The data amount of the signal is reduced to about 1 by an effective information extracting circuit 2 which removes data of a blanking period from the signal and extracts only information of an effective area.
It is compressed to 67 Mbps. The luminance signal Y of the output of the effective information extraction circuit 2 is supplied to the frequency conversion circuit 3, and the sampling frequency is converted from 13.5 MHz to 3/4 of that. As the frequency conversion circuit 3, for example, a thinning filter is used so that aliasing distortion does not occur. The output signal of the frequency conversion circuit 3 is supplied to the blocking circuit 5, and the order of the luminance data is converted into the order of the blocks. The blocking circuit 5 is provided for a block coding circuit 8 provided at a subsequent stage.

FIG. 3 shows a block structure of a unit of encoding. This example is a three-dimensional block, for example, by dividing a screen spanning two frames, a large number of (4 lines × 4 pixels × 2 frames) unit blocks are formed as shown in FIG. In FIG. 3, a solid line indicates a line of an odd field, and a broken line indicates a line of an even field. In addition, two color difference signals U and V of the output of the effective information extraction circuit 2 are supplied to the sub-sampling and sub-line circuit 4, and the sampling frequency is 6.
After conversion from 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, the sub-sampling and sub-line circuit 4 provides a line-sequentialized digital color difference signal. FIG. 4 shows a pixel configuration of a signal sub-sampled and sub-lined by the circuit 4. In FIG. 4, ○ indicates a sampling pixel of the first chrominance signal U, △ indicates a sampling pixel of the second chrominance signal V, and × indicates a position of a pixel thinned out by sub-sampling.

A line-sequential output signal of the sub-sampling and sub-line circuit 4 is supplied to a blocking circuit 6. In the blocking circuit 6, similarly to the blocking circuit 5, the color difference data in the scanning order of the television signal is converted into the data in the block order. Like the blocking circuit 5, the blocking circuit 6 converts the color difference data into a block structure of (4 lines × 4 pixels × 2 frames). Output signals of the blocking circuits 5 and 6 are supplied to the synthesizing circuit 7.
In the synthesizing circuit 7, the luminance signal and the chrominance signal converted in the block order are converted into one-channel data, and the output signal of the synthesizing circuit 7 is supplied to the block encoding circuit 8. As the block coding circuit 8, a coding circuit (referred to as ADRC) adapted to a dynamic range of each block, a DCT circuit, or the like can be applied as described later.
An output signal of the block encoding circuit 8 is supplied to a framing circuit 9 and is converted into data having a frame structure. In the framing circuit 9, switching between the image system clock and the recording system clock is performed.

An output signal of the framing circuit 9 is supplied to an error correction code parity generation circuit 10 to generate an error correction code parity. An output signal of the parity generation circuit 10 is supplied to a channel encoder 11, and channel coding is performed so as to reduce a low-frequency portion of recording data. An output signal of the channel encoder 11 is supplied to magnetic heads 13A and 13B via recording amplifiers 12A and 12B and a rotary transformer (not shown), and is recorded on a magnetic tape. Although not shown, the audio signal is compression-encoded separately from the video signal and supplied to the channel encoder.

By the above-described signal processing, the input data amount of 216 Mbps is reduced to about 167 Mbps by extracting only the effective scanning period, and further, by the frequency conversion and the sub-sample and the sub-line, this is reduced to 84 Mbps.
bps. This data is compressed to about 25 Mbps by compression coding in the block coding circuit 8, and after adding additional information such as parity and audio signals, the recording data amount becomes 31.56 Mbps.
s.

Next, the configuration of the reproducing side will be described with reference to FIG. In FIG. 2, reproduction data from the magnetic heads 13A and 13B is supplied to a channel decoder 22 via rotary transformers (not shown) and reproduction amplifiers 21A and 21B. In the channel decoder 22, the channel coding is demodulated, and the channel decoder 2
2 is supplied to a TBC circuit (time axis correction circuit) 23. In the TBC circuit 23, the time axis fluctuation component of the reproduction signal is removed. The reproduction data from the TBC circuit 23 is supplied to the ECC circuit 24, and error correction using an error correction code and error correction are performed. An 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 coded data, and switches the recording system clock to the image system clock.
Each data separated by the frame decomposition circuit 25 is supplied to a block decoding circuit 26, and original data and corresponding restored data are decoded for each block, and the decoded data is supplied to a distribution circuit 27. In the distribution circuit 27, the decoded data is separated into a luminance signal and a color difference signal. These luminance signal and color difference signal are supplied to block decomposition circuits 28 and 29, respectively. The block decomposing circuits 28 and 29 convert the decoded data in the block order in the order of the raster scan, contrary to the blocking circuits 5 and 6 on the transmission side.

The decoded luminance signal from the block decomposition circuit 28 is supplied to an interpolation filter 30. In the interpolation filter 30, the sampling rate of the luminance signal is from 3fs to 4fs.
(4fs = 13.5 MHz). The digital luminance signal Y from the interpolation filter 30 is taken out to an output terminal 33Y. On the other hand, the digital color difference signal from the block separation circuit 29 is supplied to the distribution circuit 31, and the line-sequentialized digital color difference signals U and V are converted into the digital color difference signal U.
And V respectively. The digital color difference signals U and V from the distribution circuit 31 are supplied to the interpolation circuit 32 and are interpolated. The interpolation circuit 32 interpolates the thinned line and pixel data using the restored pixel data. The interpolation circuit 32 obtains digital color difference signals U and V having a sampling rate of 4 fs.
It is taken out to output terminals 33U and 33V, respectively.

B. Block Coding The block coding circuit 8 shown in FIG. 1 is an ADRC (Adapter) disclosed in Japanese Patent Application Nos. 59-266407 and 59-269866 filed by the present applicant.
ive Dynamic Range Coding) encoder is used.
The ADRC encoder detects a maximum value MAX and a minimum value MIN of a plurality of pixel data included in each block, detects a dynamic range DR of the block from the maximum value MAX and the minimum value MIN, and detects the dynamic range DR of the block. The adaptive coding is performed, and the 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 coding circuit 8, the pixel data of each block is converted into a DCT (Discrete Cosine Transform).
form), the coefficient data obtained by the DCT may be quantized, and the quantized data may be run-length-Huffman-encoded and compression-encoded. Here, AD
An example of an encoder that uses an RC 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 input from an combining terminal 7 in FIG. Blocked data from an input terminal 41 is supplied to a maximum value / minimum value detection circuit 43 and a delay circuit 44. The maximum value / minimum value detection circuit 43 detects the minimum value MIN and the maximum value MAX for each block. The delay circuit 44 delays the input data by the time required for detecting the maximum value and the minimum value. The pixel data from the delay circuit 44 is supplied to the comparison circuits 45 and 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. The value of one quantization step width (Δ = (1/16) DR) when non-edge matching quantization is performed with a fixed length of 4 bits is supplied from the bit shift circuit 49 to the subtraction circuit 47 and the addition circuit 48. Is done. The bit shift circuit 49 shifts the dynamic range DR by 4 bits so as to perform the division of (1/16). From the subtraction circuit 47, (MAX-
Δ) is obtained, and (MI)
N + Δ). These subtraction circuits 47
And the threshold value from the adding circuit 48 is compared with the comparing circuits 45 and 4
6 respectively. The value Δ defining the threshold value is not limited to the quantization step width, and may be a fixed value corresponding to a noise level.

The output signal of the comparison circuit 45 is supplied to the AND gate 5
0 and the output signal of the comparison circuit 46 is supplied to the AND gate 51. Input data from the delay circuit 44 is supplied to the AND gates 50 and 51. Comparison circuit 4
5 is high when the input data is larger than the threshold value. Therefore, the output terminal of the AND gate 50 receives the pixel data of the input data included in the maximum level range of (MAX to 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. Therefore, the output terminal of the AND gate 51 receives the pixel data of the input data included in the minimum level range of (MIN to MIN + Δ). Is extracted.

The output signal of the AND gate 50 is supplied to an averaging circuit 52, and the output signal of the AND gate 51 is supplied to an averaging circuit 53. These averaging circuits 52 and 5
3 calculates an average value for each block.
Are supplied to these averaging circuits 52 and 53. The averaging circuit 52 obtains an average value MAX ′ of the pixel data belonging to the maximum level range of (MAX to MAX−Δ).
Can obtain the average value MIN ′ of the pixel data belonging to the minimum level range of (MIN to MIN + Δ). Average value M
The average value MIN ′ is subtracted from AX ′ by a subtraction circuit 55,
The dynamic range DR 'is obtained from the subtraction circuit 55. Further, the average value MIN ′ is supplied to the subtraction circuit 56,
From the input data passed through the delay circuit 57, the average value MIN '
Is subtracted in the subtraction circuit 56 to form the data PDI after the removal of the minimum value. The data PDI and the modified dynamic range DR ′ are supplied to the quantization circuit 58. In this embodiment, a variable length ADRC in which the number n of bits allocated to quantization is 0 bit (a code signal is not transmitted), 1 bit, 2 bits, 3 bits, or 4 bits, and edge matching is performed. Quantization is performed. The number n of allocated bits is determined for each block by the bit number determination circuit 59, and data of the number n of bits is supplied to the quantization circuit 58.

The variable length ADRC has a dynamic range D
Efficient encoding can be performed by reducing the number of allocated bits n in a block with a small R 'and increasing the number of allocated bits n in a block with a large dynamic range DR'. That is, the threshold values for determining the number of bits n are T1 to T4 (T1 <T2 <T3 <
T4), the code signal is not transmitted to the block of (DR ′ <T1), only the information of the dynamic range DR ′ is transmitted, and the block of (T1 ≦ DR ′ <T2) is (n = 1) The block of (T2 ≦ DR ′ <T3) is set to (n = 2), the block of (T3 ≦ DR ′ <T4) is set to (n = 3), and the block of (DR ′ ≧ T4) is set to (n = 3). The block is set to (n = 4). Such variable length AD
In the RC, the amount of generated information can be controlled (so-called buffering) by changing the threshold values T1 to T4. Therefore, the variable length ADRC can be applied to a transmission line such as the digital VTR of the present invention in which the amount of generated information per field or frame is required to be a predetermined value.

In FIG. 5, reference numeral 60 denotes a buffering circuit for determining threshold values T1 to T4 for setting the amount of generated information to a predetermined value. In the buffering circuit 60,
A plurality of, for example, 32 sets of thresholds (T1, T2, T3, T4) are prepared, and these sets of thresholds are determined by parameter codes Pi (i = 0, 1, 2,..., 31). Be distinguished. The amount of generated information is set to decrease monotonically as the number i of the parameter code Pi increases. However, as the amount of generated information decreases, the image quality of the restored image deteriorates. The threshold values T1 to T4 from the buffering circuit 60 are supplied to the comparison circuit 61, and the dynamic range DR 'via the delay circuit 62 is supplied to the comparison circuit 61. The delay circuit 62 determines the time required for the buffering circuit 60 to determine the set of thresholds,
Delay R '. In the comparison circuit 61, the dynamic range DR 'of the block is compared with each threshold value, the comparison output is supplied to the bit number determination circuit 59, and the number n of bits allocated to the block is determined. In the quantization circuit 58, the data PDI from which the minimum value has been removed via the delay circuit 63 is converted into a code signal DT by edge matching quantization using the dynamic range DR 'and the number of allocated bits n. The quantization circuit 58 is constituted by, for example, a ROM. The modified dynamic range DR 'and average value MIN' are output via the delay circuits 62 and 64, respectively, and further a parameter code Pi indicating a set of the code signal DT and the threshold value is output. In this example, since the signal once subjected to the non-edge match quantization is subjected to the edge match quantization based on the new dynamic range information, the image degradation when dubbing is reduced.

C. Next, the channel encoder 11 and the channel decoder 22 shown in FIG. 1 will be described. For details of these circuits, refer to Japanese Patent Application No. 1-143491 filed by the present applicant.
The specific configuration is disclosed in FIG. 1, and the schematic configuration will be described with reference to FIG. 6 and FIG. In FIG. 6, reference numeral 71 denotes an adaptive scrambling circuit to which the output of the parity generation circuit 10 of FIG. 1 is supplied, in which a plurality of M-sequence scrambling circuits are prepared. Is configured to select an M-sequence that gives the least output of Code 7
Reference numeral ² denotes a precoder for the partial response class 4 detection method, which performs an arithmetic operation of 1 / 1-D ² (D is a unit delay circuit). This precoder output is recorded by the recording amplifier 1
Recording and reproduction are performed by the magnetic heads 13A and 13B via 2A and 12B, and the reproduction output is amplified by the reproduction amplifiers 21A and 21B.

FIG. 7 showing the structure of the channel decoder 22.
, The code 73 is a partial response class 4
And a calculation circuit 1 + D is performed on the outputs of the reproduction amplifiers 21A and 21B. Symbol 74
Denotes a so-called Viterbi decoding circuit, in which data strong against noise is decoded by an arithmetic operation using the correlation and certainty of data with respect to the output of the arithmetic processing circuit 73. The output of the Viterbi decoding circuit 74 is output to a descramble 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 improves the reproduction C / N by 3 dB as compared with the case where decoding is performed for each bit.

D. Tape Head System As shown in FIG. 8A, the magnetic heads 13A and 13B are attached to the rotating drum 76 at an interval of 180 ° facing each other. Alternatively, as shown in FIG. 8B, the magnetic heads 13A and 13B are attached to the drum 76 in an integrated structure. On the peripheral surface of the drum 76, 180
The magnetic tape (not shown) is obliquely wound at a winding angle slightly larger than or slightly smaller than °. In the head arrangement shown in FIG. 8A, the magnetic heads 13A and 13B contact the magnetic tape almost alternately, and in the head arrangement shown in FIG. 8B, the magnetic heads 13A and 13B scan the magnetic tape at the same time.

The extending directions (referred to as azimuth angles) of the gaps of the magnetic heads 13A and 13B are different. For example, as shown in FIG.
And 13B, an azimuth angle of ± 20 ° is set. Due to this difference in azimuth angle,
A recording pattern as shown in FIG. 10 is formed. As can be seen from FIG. 10, adjacent tracks TA and TB formed on the magnetic tape are formed by magnetic heads 13A and 13B having different azimuth angles, respectively. Therefore, during reproduction, the amount of crosstalk between adjacent tracks can be reduced due to azimuth loss.

FIGS. 11A and 11B show the magnetic head 13.
A more specific configuration when A and 13B are formed as an integral structure (a so-called double azimuth head) will be described. For example, 15
Upper drum 7 rotated at a high speed of 0 rps (NTSC system)
6, the magnetic heads 13A and 13B having an integral structure are attached, and the lower drum 77 is fixed. Therefore, data of one field is recorded on the magnetic tape 78 while being divided into five tracks. With this segment system, the length of the track can be shortened, and the linearity error of the track can be reduced. The winding angle θ of the magnetic tape 78 is, for example, 166 °, and the drum diameter φ is 1
It is 6.5 mm. Simultaneous recording is performed using a double azimuth head. Normally, the eccentricity of the rotating portion of the upper drum 76 causes vibration of the magnetic tape 78,
Track linearity errors occur. As shown in FIG. 12A, the magnetic tape 78 is pressed down, and as shown in FIG. 12B, the magnetic tape 78 is pulled upward, which vibrates the magnetic tape 78 and deteriorates the linearity of the track. I do. However, by performing simultaneous recording with a double azimuth head, the linearity error amount can be reduced as compared with a case where a pair of magnetic heads are arranged facing each other at 180 °. Further, the double azimuth head has an advantage that the pairing adjustment can be performed more accurately because the distance between the heads is small. With such a tape head system, recording / reproducing of a narrow track can be performed.

E. Next, the electromagnetic conversion system used in the present invention will be described. First, a magnetic tape (ME tape) as a recording medium
Is manufactured by the following method. In the first method, for example, polyethylene terephthalate (PE) having a thickness of 10 μm is used.
T) A solution containing, for example, an emulsion mainly composed of an acrylate latex is applied to a base made of a film, followed by drying to form fine projections made of the above emulsion fine particles on one main surface of the base. I do.
The surface roughness of the base subjected to such a treatment was, for example, about 15 ° in center line average roughness _Ra , and the density of the fine projections was, for example, about 5 million / mm ² . In addition, SiO ₂ , TiO ₂ , A
l ₂ O ₃ or the like is used. Thereafter, a magnetic layer containing Co as a main component is formed on the base by oblique deposition in an oxygen atmosphere using a vacuum deposition apparatus as shown in FIG. 13 as follows.

In FIG. 13, reference numerals 81a and 81b denote vacuum vessels, 82 denotes a partition plate, and 83 denotes a vacuum exhaust valve. Reference numeral 84 denotes a supply roll for the base B, 85 denotes a take-up roll, 86 denotes a guide roll, and 87a and 87b denote cylindrical cooling cans for guiding the base B. Reference numerals 88a and 88b denote Co evaporation sources, and reference numerals 89a and 89b denote electron beams for heating the evaporation sources 88a and 88b, respectively. Reference numerals 90a and 90b denote shielding plates for regulating the incident angle of the evaporated metal with respect to the base B, and reference numerals 91a and 91b denote oxygen gas introduction pipes. In the vacuum evaporation apparatus configured as described above, the base B is transferred from the supply roll 84 to the cooling can 87a, the guide roll 86, the cooling can 87b, and the winding roll 85 in this order. At this time, in the cooling cans 87a and 87b, a magnetic layer composed of two Co layers is formed by oblique evaporation in an oxygen atmosphere.

In this vacuum vapor deposition, while keeping the vacuum chambers 81a and 81b at, for example, a degree of vacuum of 1 × 10 ^-4 Torr, oxygen gas is supplied into these vacuum chambers 81a and 81b by, for example, 250 cc / min by introducing pipes 91a and 91b. Perform while introducing at a ratio. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, in a range of 45 to 90 °. The Co layer is deposited on the cooling cans 87a and 87b to a thickness of, for example, 1000 そ れ ぞ れ, and the total thickness δ of the magnetic layer is 2 mm.
000Å. The composition of the ingot used for the evaporation sources 88a and 88b is, for example, 100% Co.
After applying a back coat made of, for example, carbon and an epoxy binder and a top coat of a lubricant made of perfluoropolyether to the base B on which the magnetic layer made of the two Co layers is formed, 8 mm
Cut to width to produce magnetic tape. The properties of the finally obtained magnetic tape are as follows: residual magnetic flux density B _r = 4150 G;
Coercivity H _c = 1760Oe, was squareness ratio R _s = 79%. The surface roughness of the magnetic tape reflected the surface roughness of the base B, and was extremely small as center line average roughness _Ra of 20 °. Furthermore, the energy product in this case is _Br
Δ · H _c = 146.1 G · cm · Oe The measurement of the surface roughness is usually performed according to JIS B0601, but this measurement was performed under the following conditions. Measuring device: Taristep (manufactured by Rank Taylor) Needle diameter: 0.2 × 0.2 μm, square needle Needle pressure: 2 mg High pass filter: 0.33 Hz

In the second method, the vacuum evaporation apparatus shown in FIG.
A magnetic layer made of, for example, a Co ₉₀ Ni ₁₀ alloy layer is formed by oblique deposition in an oxygen atmosphere. However, in this case, 230 cc of oxygen gas is supplied to the vacuum chambers 81a and 81b.
/ Oblique deposition is performed while introducing at a rate of / min. Also, C
The o ₉₀ Ni ₁₀ alloy layer is vapor-deposited on the cooling cans 87a and 87b to a thickness of, for example, 900 °, so that the entire magnetic layer has a thickness of 1800 °. Thereafter, a magnetic tape having a width of 8 mm was produced in the same manner as in the first method. Characteristics of the finally obtained magnetic tape, B _r = 4100G, H
_c = 1440Oe, it was R _s = 81%. The surface roughness of this magnetic tape was 20 ° in _Ra . Further, the energy product in this case is _Br · δ · _Hc = 10
It was 6.3 Gcm Oe.

In the third method, a magnetic layer containing Co as a main component is formed on a base B formed by a method similar to the first method using a vacuum deposition apparatus shown in FIG. It is formed by oblique deposition in an oxygen atmosphere. 14, reference numerals 81c and 81d denote vacuum chambers, 82 denotes a partition plate,
84 is a supply roll of the base B, 85 is a take-up roll,
86a and 86b are guide rolls, 87 is a cylindrical cooling can for guiding the base B, 88 is an evaporation source, 89
Denotes an electron beam for heating the evaporation source 88; 90, a shielding plate for regulating the incident angle of the evaporated metal with respect to the base B;
Is an oxygen gas introduction pipe, and 92 is an electron gun. In the vacuum evaporation apparatus configured as described above, the base B is transferred from the supply roll 84 to the guide roll 86a, the cooling can 87, the guide roll 86b, and the winding roll 85 in this order. At this time, in the cooling can 87, a single magnetic layer made of, for example, a Co ₉₀ Ni ₁₀ alloy layer is formed by oblique evaporation in an oxygen atmosphere. In this vacuum deposition, the vacuum chambers 81c and 81d are set to, for example, a degree of vacuum of 1 × 10 ^−4.
While maintaining the pressure at Torr, oxygen gas is introduced into these vacuum chambers 81c and 81d by the introduction pipe 91, for example, at 250 cc / min.
Perform while introducing at the rate of. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, in a range of 45 to 90 °. The thickness of the magnetic layer is, for example, 2000 °. Thereafter, a magnetic tape having a width of 8 mm is manufactured in the same manner as in the first method. The properties of the finally obtained magnetic tape are _Br =
3900 G, H _c = 1420 Oe, and squareness ratio R _s = 78%. The surface roughness of this magnetic tape is
Reflecting the surface roughness of, the _Ra was extremely small at 20 °. Further, the energy product in this case is _Br · δ · _Hc
= 110.76 G · cm · Oe.

In the fourth method, a single magnetic layer made of, for example, a Co ₉₅ Ni ₅ alloy layer is formed on the base B in an oxygen atmosphere using the vacuum evaporation apparatus shown in FIG. 14 in the same manner as the third method. It is formed by oblique deposition in the inside. However, in this case, oxygen gas, for example, 220 cc is supplied to the vacuum chambers 81c and 81d.
/ Oblique deposition is performed while introducing at a rate of / min. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, 50 to
The range is 90 °. The thickness of the magnetic layer is, for example, 20
00 °. Then, 8 mm in the same manner as in the first method.
Make a magnetic tape of width. Characteristics of the finally obtained magnetic _{tape, B r = 4160G, H c} = 1690Oe, was squareness ratio R _s = 77%. The surface roughness of this magnetic tape was 20 ° in _Ra . Furthermore, energy product in this case is _{B r · δ · H c =} 140.6G · cm · Oe
Met.

In the above-described method for producing a magnetic tape, when a magnetic layer is formed on the base B by vapor deposition, so-called cupping (curling of the tape in the width direction) usually occurs. Therefore, in order to correct the cupping after this vapor deposition, thermal annealing of the base B is caused by performing an annealing after applying the back coat and the top coat, and further, the tape is cut by performing the hot roll treatment and then performing the cutting. Become

FIG. 15 shows the results of measurement of the amount of cupping, MD / TD and bit error rate of the magnetic tape produced through such a process, together with comparative examples. The width of the magnetic tape was 8 mm. The bit error rate in this case is set to 40 ° C., 8
It was measured after being left for 8 days in an environment of 0% RH. In FIG. 15, the magnetic tape of Example 1 was coated at 60 ° C. and 50% R after applying a back coat and a top coat.
Annealing in an environment of H for 24 hours caused heat shrinkage of the base B made of a PET film to correct cupping, and then further corrected the cupping by hot roll treatment, and then cut the tape. Things. In this hot roll treatment, the contact time between the base B and the hot roll was 0.5 seconds, and the temperature was 1
50 ° C. On the other hand, the magnetic tape according to Comparative Example 1 was formed into a tape by performing heat shrinkage of the base B and correcting cupping in the same manner as in Example 1, and then performing cutting.

As can be seen from FIG. 15, in Comparative Example 1,
MD / TD = 0.6% / 1.0% = 0.6, and the bit error rate at that time is as large as 4.0 × 10 ⁻⁴ , whereas in the first embodiment, MD / TD = 0.6% / 1.0%. 0.4% / 0.
5% = 0.8, and the bit error rate at that time is 4.2 × 10 ⁻⁵ , one digit smaller than that of Comparative Example 1. As described above, the correction of cupping is performed by the annealing process and the hot roll process to obtain MD / TD = 0.4% /
By setting 0.5% = 0.8, the bit error rate can be significantly reduced as compared with the case where the cupping correction is performed only by the annealing process.

FIG. 16 shows the measurement results of the amount of magnetic tape cupping, MD / TD and bit error rate according to the second embodiment, together with comparative examples. The method of manufacturing the magnetic tape according to the second embodiment is as follows. That is, as the base B, MD and TD are each set to 0.2.
% Of a 10 μm-thick polyamide film. And this base B in oxygen atmosphere
By performing oblique deposition on the upper surface at an incident angle of 45 to 90 °,
A magnetic layer made of a Co ₈₀ Ni ₂₀ alloy layer having a thickness of 2000 ° is formed. In Example 1, in order to correct the cupping generated by this vapor deposition, the base B was further subjected to heat shrinkage and then subjected to a hot roll treatment. However, in Example 2, the MD and TD were both 0.2% as described above, and the heat shrinkage of the base B was extremely small. Then, a polyurethane binder having a glass transition temperature T _g = 30 ° C. and a nitrocellulose-based binder (trade name: NC 1 / 2H: manufactured by Asahi Kasei Corporation) were mixed at a ratio of 80% by weight and 20% by weight, respectively. A back coat was applied using a mixture of carbon at a B ratio of 2.0 as a coating agent. As a result, the cupping amount of the magnetic tape was 0.3 mm, which was a value having no practical problem.

On the other hand, the magnetic tapes according to Comparative Examples 2 and 3
A magnetic layer composed of a Co ₈₀ Ni ₂₀ layer was formed on a base B composed of a PET film by oblique deposition in an oxygen atmosphere. MD / TD on base B by annealing
= 2.0% / 2.0% heat shrinkage, which was further subjected to hot roll treatment to correct cupping.

As can be seen from FIG. 16, MD / TD =
In the magnetic tape of Example 2 where 0.2% / 0.2% = 1.0, the bit error rate was very small at 3.1 × 10 ⁻⁵ , while MD / TD = 1.0. % / 1.2% =
The magnetic tape of Comparative Example 2 and MD / TD = 0.83 =
In the magnetic tape of Comparative Example 3 where 1.2% / 1.4% = 0.86, the bit error rate was 6.0 × 10
^-4 and 3.5 × 10 ^-4 .

FIG. 17 shows an example of a magnetic head used in the present invention. As shown in FIG. 17, this magnetic head has single crystal Mn—Zn ferrite cores 101A and 101A.
Fe-Ga-Si- formed on B by sputtering
A gap 104 is provided between the Ru-based soft magnetic layers 102 and 103. Glasses 105 and 106 are filled on both sides of the gap 104 in the track width direction, whereby the track width is regulated to, for example, about 4 μm width. 10
Reference numeral 7 denotes a winding hole, in which a recording coil (not shown) is wound. The effective gap length of this magnetic head is 0.20 μm. The magnetic head, since the saturation magnetic flux density B _s in the vicinity of the gap 104 is used Fe-Ga-Si-Ru soft magnetic layers 102 and 103 of 14.5 kG, even for high coercive force of the magnetic tape Recording can be performed without causing magnetic saturation of the head.

By using the ME tape and the magnetic head as described above, a recording density of 1.25 μm ² / bit or less can be realized. That is, as described above, 1.25 μm ² / bit is realized by recording a signal having a minimum wavelength of 0.5 μm with respect to a track width of 5 μm.
However, it is known that the C / N of the reproduction output deteriorates as the recording wavelength and the track width decrease, and the tape and the head having the above-described configuration are used to suppress the deterioration. The present applicant prototyped a digital VTR having a track pitch of 15 μm and a minimum wavelength of 0.5 μm using an 8 mm wide ME tape in 1988, but this time using a 40 mm diameter rotary drum at 60 rpm. Was rotated to perform recording and reproduction. In this system, a C / N of 5 ldB was obtained for a recording wavelength of 1 μm. The bit error rate of the system was 4 × 10 ^-5 . As in the embodiment of the present invention, 5
When using a track with a width of μm, about 44d
Only C / N of B is obtained, and the image quality is degraded. In order to compensate for the 7 dB C / N deterioration, the configuration of the embodiment of the present invention described above is used.

That is, it is generally known that the signal output level decreases as the spacing between the tape and the magnetic head during recording and reproduction increases, and the amount of this spacing depends on the flatness of the tape. It is also known to do. In the case of a coating type tape, it is known that the flatness of the tape depends on the coating agent, whereas in the case of the ME tape, it depends on the surface flatness of the base itself. In the above example, an experimental result was obtained in which the C / N was increased by 1 dB by selecting the surface roughness of the base film as small as possible. Further, by using the vapor deposition material and the vapor deposition method of the above-described embodiment, a C / N improvement of 3 dB was obtained as an experimental result with respect to the magnetic tape used in the trial production in 1988. From the above, by using the head and the tape of the present invention, it is possible to achieve a 4
This means that an increase in dB C / N was obtained. In addition, according to the present invention, since Viterbi decoding is used for channel decoding, it has been confirmed that an increase of 3 dB can be obtained with respect to decoding for each bit used in the previous prototype. As described above, the C / N degradation of 7 dB can be compensated as a whole, and the recording density of 1.25 μm ² / bit is 1988.
A bit error rate equivalent to that of the year prototype will be obtained. Regarding the reproduction output, it is necessary that the bit error rate in the stage before the error correction code correction processing is 10 ^-4 or less, when the error correction code having a redundancy of about 20% is used. This is to suppress errors in the amount.

[0046]

As described above, according to the present invention,
Even if the data recording density is increased to about 1 μm ² / bit and the width of the magnetic recording medium is reduced, the magnetic head can accurately trace each track at the time of reproduction, whereby the data is recorded on the magnetic recording medium. The bit error rate before error correction of the reproduced output of the digital image signal can be reduced to 1 × 10 ⁻⁴ or less.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration on a recording side of a signal processing unit in a digital VTR according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration on a reproduction side of a signal processing unit.

FIG. 3 is a schematic diagram illustrating an example of a block for block encoding.

FIG. 4 is a schematic diagram used for explaining subsampling and sublines.

FIG. 5 is a block diagram illustrating an example of a block encoding circuit.

FIG. 6 is a block diagram schematically illustrating an example of a channel encoder.

FIG. 7 is a block diagram schematically illustrating an example of a channel decoder.

FIG. 8 is a schematic diagram used for explaining a head arrangement.

FIG. 9 is a schematic diagram used to explain azimuth of a head.

FIG. 10 is a schematic diagram used for describing a recording pattern.

FIG. 11 is a top view and a side view showing an example of a tape head system.

FIG. 12 is a schematic diagram for explaining that tape vibration occurs due to eccentricity of a drum.

FIG. 13 is a schematic diagram used for describing a method of manufacturing a magnetic tape.

FIG. 14 is a schematic diagram used for describing a method of manufacturing a magnetic tape.

FIG. 15 is a table showing characteristics of a magnetic tape.

FIG. 16 is a table showing characteristics of a magnetic tape.

FIG. 17 is a perspective view showing an example of the structure of a magnetic head.

[Explanation of symbols]

 1Y Component signal input terminal 1U Component signal input terminal 1V Component signal input terminal 5 Blocking circuit 6 Blocking circuit 8 Block coding circuit 11 Channel encoder 13A Magnetic head 13B Magnetic head 22 Channel decoder 26 Block decoding circuit 28 Block decomposition Circuit 29 Block decomposition circuit B base

Continuation of the front page (72) Inventor Yuichi Arisaka 6-5-6 Kita Shinagawa, Shinagawa-ku, Tokyo Inside Sony Magne Products Co., Ltd. (72) Inventor Yukari Yamada 6-5-6 Kita Shinagawa, Shinagawa-ku, Tokyo So (56) References JP-A-63-95791 (JP, A) JP-A-60-93626 (JP, A) JP-A-1-220218 (JP, A) JP-A 64-53329 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 5/02-5/09

Claims (1)

(57) [Claims] An input digital image signal is converted into a block of data consisting of a plurality of pixel data and divided into blocks. The block-divided data is compression-coded in block units, and the compression-coded data is converted into a channel. In a magnetic recording method of a digital image signal, wherein the encoded data is recorded on a magnetic recording medium by a magnetic head mounted on a rotating drum, the magnetic recording medium comprises a metal on a non-magnetic support. A magnetic layer composed of a magnetic thin film is formed. An energy product of a product of a residual magnetic flux density, a thickness and a coercive force of the magnetic layer is 100 G · cm · Oe or more, and a surface roughness of the magnetic recording medium is Center line average roughness 0.0
03 μm or less, the ratio of the longitudinal thermal shrinkage of the magnetic recording medium to the lateral thermal shrinkage of the magnetic recording medium is 0.8 to 1.0 , and the lateral thermal shrinkage and A magnetic recording method of a digital image signal, wherein the thermal shrinkage in the vertical direction is 0.5 % or less.