JPH04295627A - Magnetic recording of digital image signal - Google Patents

Abstract

PURPOSE:To obtain a copying magnetic recording medium which allows copying at a high speed and in large quantities by a magnetic transference and moreover, with a high transfer output. CONSTITUTION:A magnetic recording medium has a magnetic layer comprising a metal magnetic thin film is formed on a non-magnetic support body. An energy product of the magnetic layer is set at 100G.cm.0e or more. The magnetic recording medium has a magnetic layer comprising a metal magnetic thin film formed on a non-magnetic support body. A mother magnetic recording medium M with a magnetization facilitating shaft e.a. selected in a direction of 20 deg.+ or -15 deg. to an in-plane direction and a magnetic recording medium C are arranged to be laminated on the surfaces thereof on the sides of the magnetic layers in such a manner that the columns CL of the magnetic layers are opposite to each other in inclination. Under such a condition, an internal bias magnetic field HB is applied in a direction of about 110 deg.+ or -15 deg. to the in-plane direction of the mother magnetic recording medium M to transfer a recording magnetization on the mother magnetic recording medium M onto the magnetic recording medium C.

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 for digital image signals suitable for recording digital image signals such as digital video signals on a magnetic tape.

0002

[Background Art] In recent years, digital VT that digitizes color video signals and records them on recording media such as magnetic tape has been developed.
As for R, D1 format component type digital VTRs and D2 format composite type digital VTRs for broadcasting stations have been put into practical use. The former D1 format digital VTR transmits the luminance signal and the first and second color difference signals at 13.5 MHz, respectively.
After A/D conversion at a sampling frequency of 6.75 MHz, predetermined signal processing is performed and recorded on a magnetic tape.Since the ratio of the sampling frequencies of these component components is 4:2:2, It is also called the :2:2 method. The latter D2 format digital VTR samples a composite color video signal using a signal with a frequency four times the frequency fsc of the color subcarrier signal, performs A/D conversion, performs predetermined signal processing, and then outputs it to a magnetic tape. I try to record it.

[0003] These digital VTRs are both designed with the assumption that they will be used for broadcasting stations.
Image quality is given top priority, and one sample is converted to 8 bits, for example.
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 explained. The amount of information of a color video signal is approximately 216 Mbps (megabits/second) when A/D conversion is performed at 8 bits per sample at the above-mentioned sampling frequency. Of these, excluding the data for the horizontal and vertical blanking periods, the number of effective pixels for the luminance signal in one horizontal period is 720, and the number of effective pixels for the color difference signal is 36.
0, and the number of effective scanning lines for each field is 250 in the NTSC system (525/60), so the data amount Dv of the video signal for one second is Dv = (720 + 360 + 360) x 8 x 250.
×60=172.8 Mbps.

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 amount of data is NT
It can be seen that this is equivalent to the SC method. When redundant components for error correction and formatting are added to this data, the total bit rate of the video data is approximately 205.
It becomes 8Mbps. In addition, audio data Da is approximately 12.8 Mbps, and additional data Do such as editing gaps, preambles, and postambles is approximately 6 Mbps.
．． Since the speed is 6 Mbps, the information amount Dt of the entire recording data in the case of the NTSC system is as follows. Dt=Dv+Da+Do =172.8 +12.8+6.6 =192.2 M
bps

[0005] In order to record data having this amount of information, D1 format digital VTRs employ a segment method in which one field has 10 tracks in the NTSC system and 12 tracks in the PAL system. . In addition, the recording tape used is 19mm wide, and there are two types of tape thickness: 13μm and 16μm, and the cassettes that store it are large (L), medium (M), and small (S). Three types are available. Since information data is recorded on these tapes in the format described above, the data recording density is approximately 20.4 μm 2 /bit. Combining the above parameters, the playback time of each size cassette of a D1 format digital VTR is as follows. In other words, for an S size cassette, when the tape thickness is 13 μm, it takes 13 minutes, and when the tape thickness is 16 μm.
11 minutes when the tape thickness is 13 μm for M size cassettes, 42 minutes when the tape thickness is 16 μm, and 34 minutes when the tape thickness is 16 μm.
For an L size cassette, the tape thickness is 94 minutes when the tape thickness is 13 μm, and 76 minutes when the tape thickness is 16 μm.

[0006]

[Problems to be Solved by the Invention] As described above, the D1 format digital VTR is sufficient as a VTR for broadcasting stations that requires performance with top priority on image quality.
Even if a large cassette equipped with a tape having a width of 19 mm is used, only a playback time of about 1.5 hours can be obtained at most, making it extremely unsuitable for use as a home VTR. On the other hand, for example, if a signal with the shortest wavelength of 0.5 μm is recorded with respect to a track width of 5 μm, a recording density of 1.25 μm2/bit can be achieved, and the amount of recorded information can be reduced with less reproduction distortion. By using a method of compression in a similar manner, long-time recording and reproduction becomes possible even when using a narrow magnetic tape with a tape width of 8 mm or less.

By the way, when copying a large amount of recorded content on a magnetic tape, a bias magnetic field is applied to the mother tape (master tape) containing the original recording, and this mother tape is brought into contact with or close to the copy tape (slave tape). Therefore, a magnetic transfer method is generally employed in which the recorded contents of a mother tape, that is, recorded magnetization, is transferred to a copy tape. According to this magnetic transfer method, since transfer can be performed at high speed, copy tapes can be copied in large quantities at high speed. Conventionally, in this magnetic transfer method, in order to suppress the demagnetization of the mother tape due to the bias magnetic field and to facilitate the transfer of recorded contents to the copy tape, the coercive force (HC) of the mother tape is applied to the copy tape. It was set to be 2.5 to 3 times the coercive force HC.

However, for example, if a metal coated tape with high coercive force, which is currently the best coated magnetic tape, is used as a mother tape, barium ferrite (Ba-F)
Even when the tape was used as a copy tape, demagnetization could not be completely suppressed, and a high value for the transfer output of the copy tape could not be obtained. In particular, when the recording wavelength is shortened to achieve higher recording density,
The transfer output becomes a very low value. For these reasons, it has been difficult to mass-produce soft tapes for digital VTRs, which require high output, by magnetic transfer. Therefore, an object of the present invention is to provide a method for magnetically recording digital image signals, which allows high-speed, large-scale copying by magnetic transfer, and which also allows use of a copy magnetic recording medium with a high transfer output as the magnetic recording medium. be.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the first invention converts an input digital image signal into block-based data consisting of a plurality of pixel data and blocks it, and converts the input digital image signal into blocks. Magnetic recording of digital image signals in which the data is compressed and encoded block by block, the compressed encoded data is channel encoded, and the channel encoded data is recorded on a magnetic recording medium by a magnetic head attached to a rotating drum. In this method, the magnetic recording medium is formed by forming a magnetic layer made of a metal magnetic thin film on a nonmagnetic support, and the energy product consisting of the product of the residual magnetic flux density, thickness, and coercive force of the magnetic layer is 100 G cm O.
e or more, and the magnetic recording medium is formed by forming a magnetic layer made of a metal magnetic thin film on a non-magnetic support, and the axis of easy magnetization is selected in a direction making an angle of 20° ± 15° with the in-plane direction. The in-plane direction of the mother magnetic recording medium and the magnetic recording medium are stacked with their magnetic layer side surfaces so that the column inclinations of their magnetic layers are opposite to each other. This is a copy magnetic recording medium in which recorded magnetization on a mother magnetic recording medium is transferred to a magnetic recording medium by applying an external bias magnetic field in a direction forming an angle of approximately 110°±15°.

[0010] In a second invention, in the first invention, the ratio HCM/HCC of the coercive force HCC of the copy magnetic recording medium to the coercive force HCM of the mother magnetic recording medium is 1.5 or less. In a preferred embodiment of the present invention, the surface roughness of the magnetic recording medium is a center line average roughness Ra of 3
It is assumed to be 0 Å or less.

[0011]

[Operation] The magnetic layer consisting of a metal magnetic thin film of the mother magnetic recording medium and the copy magnetic recording medium used in the present invention is obtained by obliquely depositing a magnetic metal on a non-magnetic support at an incident angle of 45° to 90°. It is formed. In the magnetic layer formed in this manner, columnar growth grains, so-called columns, having an inclination angle of approximately 45° with respect to the in-plane direction are formed in a curved manner. According to the findings of the present inventors, the substantial axis of easy magnetization of this magnetic layer does not coincide with the growth direction of this column, but is slightly inclined in the in-plane direction from the column growth direction, and is not aligned with the in-plane direction. The directions form an angle of approximately 20°±15°. In this invention, such an axis of easy magnetization is approximately 11 degrees with respect to the in-plane direction of the mother magnetic recording medium, which is a direction forming an angle of approximately 20°±15° with the in-plane direction.
An external bias magnetic field is applied in a direction forming an angle of 0°±15°. This direction corresponds to the direction of the hard axis of magnetization of the mother magnetic recording medium. Therefore, when the recorded magnetization of the mother magnetic recording medium is magnetically transferred to the magnetic recording medium, demagnetization of the mother magnetic recording medium can be prevented, and the transfer output of the copy magnetic recording medium can be increased. Even when the recording wavelength is as short as, for example, 0.5 μm, a sufficiently high value can be obtained as the transfer output of the copy magnetic recording medium. Furthermore, by setting the ratio HCM/HCC of the coercive force HCC of the copy magnetic recording medium to the coercive force HCM of the mother magnetic recording medium to be 1.5 or less, it is possible to relatively increase the coercive force HCC of the copy magnetic recording medium. It is possible to make the transfer output sufficiently high.

0012

[Embodiment] An embodiment of the present invention will be described below. This description is given in the following order. a. Signal processing section b. 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 of this embodiment will be explained. FIG. 1 shows the overall configuration of the recording side. For example, the three primary color signals R from a color video camera are input to the input terminals indicated by symbols 1Y, 1U, and 1V.
, G, and B, and digital color difference signals U and V are supplied. 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, the respective sampling frequencies are 13.5MHz and 6.75M
Hz, and the number of bits per sample is 8 bits. Therefore, input terminals 1Y, 1U
, 1V is approximately 216 Mbps, as described above. The effective information extraction circuit 2 removes the data in the blanking period from this signal and extracts only the information in the effective area, reducing the amount of data to about 16
Compressed to 7Mbps. 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 thereof. For example, a thinning filter is used as the frequency conversion circuit 3 to prevent aliasing distortion from occurring. 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 a screen spanning two frames, for example, many unit blocks of (4 lines x 4 pixels x 2 frames) are formed as shown in FIG. 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 V are supplied to the sub-sampling and sub-line circuit 4, and the sampling frequency is 6.
After being converted from 75 MHz to half that, the 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 sub-line circuit 4. FIG. 4 shows the pixel configuration of the signal converted into sub-samples and sub-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 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, 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). The output signals of the blocking circuits 5 and 6 are supplied to a 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. As this block encoding circuit 8, an encoding circuit adapted to the dynamic range of each block (referred to as ADRC), a DCT circuit, etc. can be applied, as will be described later. 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 to generate the parity of the error correction code. 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 the magnetic heads 13A, 13B via recording amplifiers 12A, 12B and a rotary transformer (not shown), and is recorded on the 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 of 216 Mbps is reduced to approximately 167 Mbps by extracting only the effective scanning period, and further reduced to 84 Mbps by frequency conversion, sub-sampling, and sub-line.
bps. This data is compressed to approximately 25 Mbps by compression encoding in the block encoding circuit 8, and with the addition of additional information such as parity and audio signals, the recorded data amount is 31.56 Mbps.
It will be about s.

Next, the configuration on the playback side will be explained with reference to FIG. 2. In FIG. 2, reproduced data from magnetic heads 13A and 13B is supplied to a channel decoder 22 via a rotary transformer (not shown) and reproduction amplifiers 21A and 21B. In the channel decoder 22, the channel coding is demodulated, and the channel decoder 2
The output signal No. 2 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 supplied to the ECC 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. These luminance signals and color difference signals 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 3 fs to 4 fs.
s (4fs = 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 V are separated into digital color difference signals U and V, respectively. The digital color difference signals U and V from the distribution circuit 31 are supplied to an interpolation circuit 32, where they are interpolated. The interpolation circuit 32 interpolates the thinned out line and pixel data using the restored pixel data, and the interpolation circuit 32 outputs 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 As the block encoding circuit 8 in FIG. 1 described above, the ADRC (Ad
aptive Dynamic Range Codi
ng) 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, detects the dynamic range DR of the block from these maximum values MAX and minimum value MIN, and applies the dynamic range DR to this dynamic range DR. Adaptive encoding is performed, 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, the pixel data of each block is processed by DCT (Discrete Coding).
sine Transform), then this DCT
It is also possible to use a configuration in which the coefficient data obtained in 1 is quantized, and the quantized data is 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 input from the synthesis circuit 7 of FIG. 1 to an input terminal indicated by reference numeral 41. The blocked data from the input terminal 41 is the maximum value, the minimum value detection circuit 43 and the delay circuit 4
4. The maximum value/minimum value detection circuit 43 detects the minimum value MIN and maximum value MAX for each block. Delay circuit 44 delays the input data for the time required for the maximum and minimum values to be detected. Pixel data from the delay circuit 44 is supplied to a comparison circuit 45 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=(1/16)DR) when performing non-edge matching quantization with a fixed length of 4 bits from the bit shift circuit 49. be done. The bit shift circuit 49 is configured to shift the dynamic range DR by 4 bits so as to perform division by (1/16). From the subtraction circuit 47, (MAX-Δ
) is obtained, and from the adder circuit 48, the threshold value of (MIN
+Δ) is obtained. The threshold values from these subtraction circuits 47 and addition circuits 48 are applied to comparison circuits 45 and 46.
are supplied 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 the comparison circuit 45 is applied to the AND gate 5.
0, and the output signal of the comparison circuit 46 is supplied to the AND gate 51. AND gates 50 and 51 are supplied with input data from delay circuit 44 . Comparison circuit 4
The output signal of 5 becomes high level when the input data is larger than the threshold value. Therefore, the output terminal of the AND gate 50 receives pixel data of the input data included in the maximum level range of (MAX to MAX-Δ). 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 51 receives pixel data of the input data included in the minimum level range of (MIN to MIN+Δ). 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 5
3 calculates the average value for each block, and the terminal 54
A block period reset signal is supplied to these averaging circuits 52 and 53 from . The averaging circuit 52 obtains the average value MAX' of pixel data belonging to the maximum level range of (MAX to MAX-Δ), and the averaging circuit 53 obtains the average value MAX' of pixel data belonging to the minimum level range of (MIN to MIN+Δ). The average value MIN' of the data is obtained. Average value MA
The average value MIN' is subtracted from X' 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 the subtraction circuit 56, and the average value MIN' is subtracted from the input data via the delay circuit 57 in the subtraction circuit 56, and the data P after the minimum value is removed is
A DI is formed. This data PDI and the modified dynamic range DR' are supplied to a quantization circuit 58. In this example, the number of bits allocated for quantization n
is 0 bit (does not transmit code signal), 1 bit, 2
The ADRC has a variable length of bit, 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.

[0024] The variable length ADRC has a dynamic range D
Efficient encoding can be performed by reducing the number n of allocated bits for a block with a small R' and increasing the number n of allocated bits for a block with a large dynamic range DR'. That is, the threshold value for determining the number of bits n is T1 to T4 (T1<T2<T3<T
4), the code signal is not transmitted to the block with (DR'<T1) and only the information of the dynamic range DR' is transmitted, and the block with (T1≦DR'<T2) is
(n=1), (T2≦DR'<T3) blocks are (n=2), (T3≦DR'<T4) blocks are (n=3), (DR The block where '≧T4) is (n=4). Such variable length ADRC
Now, by changing the threshold values T1 to T4, the amount of generated information can be controlled (so-called buffering). Therefore, variable length AD is also suitable for transmission paths 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.
RC can be applied.

In FIG. 5, reference numeral 60 indicates a buffering circuit that determines threshold values T1 to T4 for setting the amount of generated information to a predetermined value. In the buffering circuit 60,
For example, 32 sets of threshold values (T1, T2, T3, T4) are prepared, and these sets of threshold values are determined by parameter code Pi (i=0, 1, 2, . . . , 31). 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 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 threshold values, D.
Delay R'. 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 determining circuit 59, which determines the number n of allocated bits for 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 value MIN' are outputted via delay circuits 62 and 64, respectively, and furthermore, a parameter code Pi indicating a combination of code signal DT and threshold value is outputted. In this example, since the signal that has been 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 in FIG. 1 will be explained. For details of these circuits, see Japanese Patent Application No. 1-143491 filed by the applicant.
Although its specific configuration is disclosed in the No. 1, its schematic configuration will be explained with reference to FIGS. 6 and 7. In FIG. 6, reference numeral 71 is an adaptive scrambling circuit to which the output of the parity generation circuit 10 of FIG. The configuration is such that the M sequence that provides the least output is selected. code 72
is a precoder for the partial response class 4 detection method, and arithmetic processing of 1/1-D2 (D is a circuit for unit delay) is performed. Amplifier 1 records this precoder output.
Recording and reproduction are performed by magnetic heads 13A and 13B via magnetic heads 2A and 12B, and the reproduced output is amplified by reproduction amplifiers 21A and 21B.

FIG. 7 shows the configuration of the channel decoder 22.
, code 73 is partial response class 4
2 shows an arithmetic processing circuit on the playback side, in which the 1+D calculation is performed on the outputs of the playback amplifiers 21A and 21B. code 74
indicates a so-called Viterbi decoding circuit, in which noise-resistant data is decoded by calculation using data correlation, probability, etc. on the output of the calculation processing circuit 73. The output of this Viterbi decoding circuit 74 is transmitted to the descrambling circuit 75.
The data that has been rearranged by scrambling processing 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. Alternatively, as shown in FIG. 8B, the magnetic heads 13A and 13B are attached to the drum 76 as an integral structure. On the circumferential surface of the drum 76, there are 180
A magnetic tape (not shown) is wound diagonally with a winding angle that is slightly larger 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 simultaneously scan the magnetic tape.

The extending directions (referred to as azimuth angles) of the gaps of the magnetic heads 13A and 13B are different from each other. For example, as shown in FIG. 9, a magnetic head 13A
An azimuth angle of ±20° is set between and 13B. Due to this difference in azimuth angle, magnetic tape has
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 is shown when A and 13B are made into an integral structure (so-called double azimuth head). For example 150
Upper drum 7 rotates at high speed of rps (NTSC system)
6, integrated magnetic heads 13A and 13B are attached, and the lower drum 77 is fixed. Therefore, one field of data is recorded on the magnetic tape 78 while being divided 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 angle θ of the magnetic tape 78 is, for example, 166°, and the drum diameter φ is 1
It is said to be 6.5mm. It also uses a double azimuth head for simultaneous recording. Normally, the upper drum 76
Due to eccentricity of the rotating portion of the magnetic tape 78, vibrations occur in the magnetic tape 78, causing errors in track linearity. 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, which causes the magnetic tape 78 to vibrate and deteriorate the linearity of the track. do. However, by performing simultaneous recording with a double azimuth head, the amount of error in linearity can be reduced compared to when a pair of magnetic heads are arranged facing each other at 180 degrees. Further, the double azimuth head has the advantage that the distance between the heads is small, so that pairing adjustment can be performed more accurately. Such a tape head system allows recording and reproduction of narrow tracks.

[0031] e. Electromagnetic Conversion System Next, the electromagnetic conversion system used in the present invention will be explained. First, magnetic tape (ME tape) as a recording medium
is manufactured by the following method. In the first method, for example, polyethylene terephthalate (PET) with a thickness of 10 μm is used.
) A liquid containing an emulsion containing, for example, acrylate latex as a main component is applied onto a base made of film, and then dried to form microprotrusions made of the emulsion fine particles on one main surface of the base. . The surface roughness of the base subjected to such treatment was, for example, about 15 Å in center line average roughness Ra, and the density of microprotrusions was, for example, about 5 million pieces/mm 2 . Note that fillers added to the base include SiO2, Ti
O2, Al2 O3, etc. are used. Thereafter, using a vacuum evaporation apparatus as shown in FIG. 13, for example, 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, reference numerals 81a and 81b are vacuum chambers, 82 is a partition plate, and 83 is a vacuum exhaust valve. Reference numeral 84 is a supply roll for the 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. Further, reference numerals 88a and 88b are Co evaporation sources, and 89a and 89b are electron beams that heat the evaporation sources 88a and 88b, respectively. Symbols 90a and 90b are shielding plates for regulating the incident angle of the evaporated metal with respect to the base B, and 91a and 91b are oxygen gas introduction pipes. In the vacuum deposition apparatus configured in this manner, 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 take-up roll 85 in this order. At this time, in the cooling cans 87a and 87b, a magnetic layer consisting of two Co layers is formed by oblique vapor deposition in an oxygen atmosphere.

This vacuum evaporation is carried out by introducing pipes 91a, 91 into these vacuum chambers 81a, 81b while maintaining the vacuum chambers 81a, 81b at a degree of vacuum of, for example, 1×10 −4 Torr.
This is carried out while introducing oxygen gas at a rate of, for example, 250 cc/min. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, 45 (θmin) to 90° (θ
max). Further, the Co layer has a thickness of, for example, 1000 Å in each of the cooling cans 87a and 87b.
The total thickness of the magnetic layer δ is 2000 Å. The composition of the ingot used for the evaporation sources 88a and 88b is, for example, 100% Co. Base B on which a magnetic layer consisting of two Co layers was formed in this way.
For example, after applying a back coat consisting of carbon and epoxy binder, a rust preventive treatment, and a lubricant top coat consisting of perfluoropolyether, this is
A magnetic tape is produced by cutting it into mm width. The characteristics of the finally obtained magnetic tape are that the residual magnetic flux density Br = 415
0G, coercive force Hc = 1760Oe, squareness ratio Rs = 7
It was 9%. Further, the surface roughness of this magnetic tape was extremely small, reflecting the surface roughness of the base B, with a center line average roughness Ra of 20 Å. Furthermore, the energy product in this case is Br・δ・Hc=146.1G・cm・Oe
Met. Note that surface roughness is usually measured using JIS B
0601, but this measurement was performed under the following conditions. Measuring device: Talystep (manufactured by Rank Taylor) Needle diameter: 0
．． 2 x 0.2μm, square needle needle pressure: 2mg High pass filter: 0.33Hz

In the second method, two layers are deposited on the base B in the same manner as the first method using the vacuum evaporation apparatus shown in FIG.
A magnetic layer made of, for example, a Co90Ni10 alloy layer is formed by oblique vapor deposition in an oxygen atmosphere. However, in this case, oxygen gas is supplied to the vacuum chambers 81a and 81b, for example, at 23
Oblique vapor deposition is performed while introducing at a rate of 0 cc/min. In addition, the Co90Ni10 alloy layer has cooling can 8
The magnetic layers 7a and 87b are each deposited to a thickness of 900 Å, for example, so that the total thickness of the magnetic layer is 1800 Å. Thereafter, a magnetic tape with a width of 8 mm was produced in the same manner as in the first method. The characteristics of the magnetic tape finally obtained are Br
=4100G, Hc =1440Oe, Rs =81
%Met. In addition, the surface roughness of this magnetic tape is Ra
It was 20 Å. Furthermore, the energy product in this case was Br.delta.Hc =106.3G.cm.Oe.

In the third method, a magnetic layer containing Co as the main component is deposited on the base B formed by the same method as the first method using the vacuum evaporation apparatus shown in FIG. Formed by oblique vapor deposition in an oxygen atmosphere. In FIG. 14, numerals 81c and 81d are vacuum chambers, 82 is a partition plate, 8
4 is a supply roll of base B, 85 is a take-up roll, 8
6a and 86b are guide rolls, 87 is a cylindrical cooling can that guides the base B, 88 is an evaporation source, 89 is an electron beam that heats the evaporation source 88, and 90 is for regulating the incident angle of the evaporated metal with respect to the base B. 91 is an oxygen gas introduction pipe, and 92 is an electron gun. In the vacuum evaporation apparatus configured in this way, the base B is connected from the supply roll 84 to the guide roll 86a to the cooling can 8.
7, the guide roll 86b and the take-up roll 85 are transported in this order. At this time, in the cooling can 87,
A magnetic layer consisting of a single layer of, for example, a Co90Ni10 alloy layer is formed by oblique vapor deposition in an oxygen atmosphere. In this vacuum evaporation, the vacuum chambers 81c and 81d are, for example, 1×10 −
These vacuum chambers 81c, 81 are maintained at 4 Torr.
Oxygen gas is introduced into the interior of
This is done while introducing at a rate of c/min. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, 45 (θmi
n) to 90° (θmax). Further, the thickness of the magnetic layer is, for example, 2000 Å. Thereafter, a magnetic tape with a width of 8 mm is produced in the same manner as in the first method. The characteristics of the finally obtained magnetic tape are Br = 3900
G, Hc = 1420 Oe, squareness ratio Rs = 78%. In addition, the surface roughness of this magnetic tape was extremely small at Ra of 20 Å, reflecting the surface roughness of the base B. Furthermore, the energy product in this case is Br ・δ・H
c = 110.76 G·cm·Oe.

In the fourth method, using the vacuum evaporation apparatus shown in FIG. 14, a magnetic layer consisting of a single layer of, for example, a Co95Ni5 alloy layer is diagonally deposited on the base B in the same manner as in the third method in an oxygen atmosphere. Formed by vapor deposition. However, in this case, oxygen gas is supplied to the vacuum chambers 81c and 81d, for example, at
Oblique vapor deposition is performed while introducing at a rate of 0 cc/min. In this case, the incident angle of the evaporated metal with respect to the base B is, for example, in the range of 50 (θmin) to 90° (θmax). Further, the thickness of the magnetic layer is, for example, 2000 Å. Thereafter, a magnetic tape with a width of 8 mm is produced in the same manner as in the first method. The properties of the magnetic tape finally obtained are:
Br = 4160G, Hc = 1690Oe, squareness ratio R
s = 77%. Further, the surface roughness of this magnetic tape was 20 Å in terms of Ra. Furthermore, the energy product in this case is Br・δ・
Hc = 140.6 G·cm·Oe. According to the magnetic tape manufactured by the above method, the bit error rate of the playback output before error correction is 1×10−4.
It can be reduced to:

Next, a magnetic transfer method for the magnetic tape manufactured as described above will be explained with reference to FIG. 15. As shown in FIG. 15, a mother tape M with original records and a copy tape C with magnetic transfer (both
E tape) are stacked on top of each other with their magnetic layer side surfaces so that the inclinations of their columns CL are opposite to each other. In FIG. 15, only the magnetic layers of the mother tape M and the copy tape C are illustrated, and the illustration of the base and the like is omitted.

The magnetic layers of these mother tapes M and copy tapes C are formed by oblique vapor deposition as described above, and the growth direction of the columns CL forms an angle of, for example, 45° with respect to the in-plane direction. It is the direction. In this case, the easy axis of magnetization e of the magnetic layer of the mother tape M. a. The angle φ that it makes with the in-plane direction is 20°±15°, and the hard magnetization axis h. a
．． The angle that it makes with the in-plane direction is 110°±15°. Then, the bias magnetic field HB is applied to the hard magnetization axis h. a.
The recorded magnetization on the mother tape M is transferred onto the copy tape C by applying the magnetization in the direction of . Note that the value of the bias magnetic field HB is selected as required, but for example, it is several kOe.

FIG. 16 shows the measurement results of the transfer output of copy tapes copied using various combinations of mother tapes and copy tapes having different magnetic layer materials and film structures. In any of the embodiments shown in FIG.
) was formed by oblique vapor deposition. In addition, Figure 16
In the film structure column, "single layer" refers to the case where the magnetic layer is formed by a single layer of metal magnetic thin film, and "double layer" refers to the case where the magnetic layer is formed by two layers of metal magnetic thin film laminated together. Indicates when

As shown in FIG. 16, in Examples 1 to 7,
Both HCM/HCC are 1.5 or less, and a sufficiently large value of 2.1 to 6.8 dB is obtained as a copy tape transfer output. Then, the recording wavelength is set to, for example, 0.
Even when the length is shortened to about 5 μm, a sufficiently high value can be ensured for the transfer output of a copy tape for practical purposes. In addition, in the comparative example shown in FIG. 16, the magnetic layer is made of 100% Co.
The case is shown in which a mother tape M, which is of the same type, is used, and a metal-coated Ba-F tape is used as a copy tape C. HCC and Br for this Ba-F tape refer to HC1 and Br1, respectively.

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 101B.
Fe-Ga-Si-R formed on top by sputtering method
A gap 104 is provided between the u-based soft magnetic layers 102 and 103. Both sides of this gap 104 in the track width direction are filled with glasses 105 and 106, thereby regulating the track width to, for example, about 4 μm. 107
is a winding hole 107, and a recording coil (not shown) is wound around this winding hole 107. The effective gap length of this magnetic head is 0.20 μm. This magnetic head has an F with a saturation magnetic flux density Bs of 14.5 kG near the gap 104.
Since the e-Ga-Si-Ru soft magnetic layers 102 and 103 are used, recording can be performed even on a magnetic tape with high coercive force without causing magnetic saturation of the head.

By using the ME tape and magnetic head as described above, a recording density of 1.25 μm 2 /bit or less can be achieved. That is, as mentioned above, 5 μm
By recording a signal with the shortest wavelength of 0.5 μm for a track width of 1.25 μm 2 /bit. 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
We prototyped a digital VTR with a track pitch of 15 μm and a shortest wavelength of 0.5 μm using a wide ME tape.At this time, we used a rotating drum with a diameter of 40 mm and rotated this drum at 60 rpm for recording and playback. Ta. This system has a C/N of 5 ldB for a recording wavelength of 1 μm.
was gotten. The bit error rate of that system was 4 x 10-5. 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 dB C/N deterioration, the configuration of the embodiment of the invention described above is used.

In other words, it is generally known that the signal output level decreases as the spacing between the tape and the magnetic head during recording and playback increases, and the amount of spacing depends on the flatness of the tape. It is also known to do. Furthermore, in the case of coated tape, the flatness of the tape depends on the coating agent, but in the case of ME tape, it is known that 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 to be as small as possible. Further, 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 magnetic tape used in the prototype in 1988. From the above, by using the head and tape of this invention, it is possible to improve
This means that an increase in C/N of dB was obtained. 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. As a result of the above, it is possible to compensate for the C/N deterioration of 7 dB as a whole, and the recording density of 1.25 μm2/bit is 198 dB.
This results in a bit error rate equivalent to that of the 2008 prototype. Regarding playback output, it is necessary that the bit error rate at the stage before the correction process of the error correction code is 10-4 or less. This is to reduce errors in quantity.

[0044]

[Effects of the Invention] As described above, according to the present invention,
A copy magnetic recording medium that allows high-speed, large-scale copying by magnetic transfer and has a high transfer output can be used as the magnetic recording medium.

[Brief explanation of the drawing]

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

FIG. 2 is a block diagram showing the configuration of the reproduction side of the signal processing section.

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

FIG. 4 is a schematic diagram used to explain subsampling and sublines.

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

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

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

FIG. 8 is a schematic diagram used to explain the head arrangement.

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

FIG. 10 is a schematic diagram used to explain 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 vibration of the tape occurs due to eccentricity of the drum.

FIG. 13 is a schematic diagram used to explain a method for manufacturing a magnetic tape.

FIG. 14 is a schematic diagram used to explain a method of manufacturing a magnetic tape.

FIG. 15 is a schematic diagram used to explain a magnetic transfer method.

FIG. 16 is a table showing the transfer output of copy tapes copied using various combinations of mother tapes and copy tapes having different magnetic layer materials and film structures.

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 encoding 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 M Mother tape C Copy tape CL Column

Claims (2)

[Claims] Claim 1: Converting an input digital image signal into block-by-block data consisting of a plurality of pixel data, compressing and encoding the blocked data in block units, and transmitting the compression-encoded data to a channel. In a magnetic recording method for digital image signals, the channel-encoded data is recorded on a magnetic recording medium by a magnetic head mounted on a rotating drum. A magnetic layer made of a magnetic thin film is formed, and the energy product consisting of the product of the residual magnetic flux density, thickness, and coercive force of the magnetic layer is 100.
G cm Oe or more, and the magnetic recording medium has a magnetic layer made of a metal magnetic thin film formed on a nonmagnetic support, and the axis of easy magnetization is at an angle of 20°±15° with the in-plane direction. The mother magnetic recording medium and the above magnetic recording medium are stacked with their magnetic layer sides so that the column inclinations of their magnetic layers are opposite to each other. Approximately 1 point with the in-plane direction of the recording medium
A digital image signal characterized in that it is a copy magnetic recording medium in which recorded magnetization on the mother magnetic recording medium is transferred to the magnetic recording medium by applying an external bias magnetic field in a direction forming an angle of 10°±15°. magnetic recording method. Claim 2: Coercive force HC of the mother magnetic recording medium.
2. The method for magnetically recording digital image signals according to claim 1, wherein the ratio HCM/HCC of the coercive force HCC of the copy magnetic recording medium to M is 1.5 or less.