JPS58162176A - Method for recording digital video signal - Google Patents

Abstract

PURPOSE:To remove a DC component effectively and to obtain code sequence appropriate to digital recording, by inverting regularly the code of a picture element in every subcarrier frequency period or picture element, or furthermore inverting the least significant bit of the picture element. CONSTITUTION:One of a digitally encoded television signal is applied to a selecting circuit 2 as it is and the other is inverted by a code inverting circuit 1 and then applied to the selecting circuit 2. The selecting circuit 2 selects a non- code conversion signal or a code conversion signal by a selection controlling signal and outputs the selected signal. The selection controlling circuit selects a code-inverted signal in every period of subcarrier frequency e.g. or code-inverted signal in every picture element. In a reproducing device, one of a reproduced digital code is applied to a selecting circuit 4 and the other is once inverted by a code inverting circuit 1 and then applied to the selecting circuit 4. Code sequence having no code inversion is obtained from the selecting circuit 4.

Description

[Detailed description of the invention] The present invention relates to a recording and reproducing method for magnetic recording, and in particular to a recording and reproducing method for magnetic recording. Converts signals such as television signals to f'tal signals.

The present invention relates to a recording modulation method for magnetic recording for recording and reproducing.

Conventionally, in magnetic recording, in order to avoid the influence of direct current interruption during recording, some kind of recording modulation is performed to remove the direct current component. Even in so-called digital VTRs, which digitize image information such as television signals and record and reproduce this digitized information, modulation is performed to avoid the effects of direct current interruption during recording.

8-10 conversion is known as this modulation method. This modulation method converts an 8-bit code into a 10-bit code with the same number of 1'' as It_OJ#, and records this 10-bit code.The 10-bit code is ``''
Since the numbers of ``0'' and ``1'' are equal, the code becomes a DC-balanced code in units of 10 bits, making it possible to remove the DC component. On the other hand, 8-10 conversion has the problem that the number of bits U required for recording increases by a factor of 1.25 (10/8), but as another modulation method that maintains DC balance,
A block is constructed in units of several tens of bits, and the sign of the entire block is appropriately inverted so that the difference in number between "0" and 11" is reduced (here, sign inversion is at On, zo1"
). However, in this method, the sign inversion position of the block differs depending on the input information, so the sign inversion is performed for each block. It is necessary to add a new code to identify the presence or absence of block inversion, and if the presence or absence of block inversion is incorrectly identified during playback, the entire block may become a code error.

The purpose of the present invention is to solve the above-mentioned problems by performing regular sign inversion on a pixel-by-pixel basis using the characteristics of television signals, and is suitable for DC-balanced digital magnetic recording without increasing the number of bits. The object of the present invention is to provide a recording modulation means.

The principle of the present invention will be explained. Here, an NTSC television signal will be explained as an example. In the NTSC system, the television signal is a so-called composite signal in which color difference signals (2) and (Q) amplitude-modulated at a subcarrier frequency fme are superimposed on a luminance signal Y. 4f for this television signal. When the signal is sampled and converted into digital information at a sampling frequency of , a signal as shown in the first diagram is obtained at each sample point.

Table 1 Sampling point X4 m X4 ll+, X4 n+2
X4 +++3Y4- +I4- Y4-+1+04
-+I Y4-ya, -ri,. 2χ,. ,-Q,. 3 sample values, that is, sampling point X, (n=0.1...
...) then Y411+■4, I X4□, then YH,
+Q4□1 + X411+1 is Y 4 l1at
I 41++t + x, m. .

You can obtain values such as UY4 men Q, 4, and so on. Here, Y represents a luminance signal, and I and Q represent amplitudes of color difference signals. Therefore, these Y+I, Y+Q.

Values such as Y-I and Y-Q are calculated every 4 samples, i.e.
It occurs every period of the subcarrier frequency fss. By the way, the correlation between pixels in television signals is extremely strong. Therefore, by inverting the sign of the pixels as shown in the second row for each subcarrier frequency, it is possible to obtain a DC-balanced code system within two cycles of the subcarrier frequency.

In other words, in the present invention, the effect of removing the DC component is obtained by inverting the sign of the pixel every cycle of the subcarrier frequency. In the inversion of pixels for each cycle of the subcarrier frequency in this invention, the regularity is determined in advance, for example, as shown in Table 2 (a), all pixels in one subcarrier cycle have sign inversion. During playback, the code can be converted to the original code sequence by code reversal according to this regularity, so no special code is required for identification of code reversal. Further, since only sign inversion is performed, there is no need to increase the number of recording bits as seen in 8-10 conversion.

On the other hand, in a so-called component television signal in which the luminance signal Y and the color difference signals I and Q are independent, each component signal has an extremely strong correlation between adjacent pixels. Therefore, as shown in Table 3, the effect of removing the DC component can be obtained by, for example, displacing the sign-inverted sound for each pixel.

Shadow ≧ 1 However, in the present invention, it is not necessarily guaranteed that DC balance is achieved in areas where the correlation between pixels in the horizontal direction is weak. Since the proportion thereof is extremely small, it hardly poses a problem in practice.

If the means described below are used in combination, it is possible to almost completely remove the direct current component. That is, by further adding means such as inverting the least significant bit of the pixel to the code sequence obtained by the present invention, a completely DC-balanced code sequence can be obtained. In other words, when there are many '1's, as shown in the fourth column, for example, for a pixel whose least significant bit is 'Pa1', '0' is added to the least significant bit '1', 't'''0', and '0'.
If there are many numbers, for example, for a pixel whose least significant bit is '0', the DC component is removed by inverting the least significant bit to '0ζzo1'. However, in television signals, a code error in the least significant bit is a visual problem at all (9) Table 4
00 code sequence ↓ Inversion X1l
X Il+I X +++2 pixels lowest bit 01
011110 10011010 01100001 It is not reversed.

As described above, in the present invention, the DC component is effectively suppressed by inverting the sign of the pixels regularly, for example, in each subcarrier wave number period or for each pixel, or by further inverting the lowest order of the pixel. It is possible to obtain a complete code sequence suitable for digital magnetic recording.

Embodiments of the present invention will be described below with reference to FIG.

FIG. 1(a) shows the structure of the recording modulation section, and FIG. 1(b) shows the structure of the reproducing system.

One of the digitally encoded television signals is sent to the 11 selection circuit 2, and the remaining one is sent to the sign inversion circuit 1, where the sign of 0'' is inverted to 1'' and the sign of '1' to '0'''. After that, it is added to the selection circuit 2.

The selection circuit 2 selects (10
) The signal with no signal and the signal with sign inversion are all selectively selected and output. This selection control signal is such that, for example, a subcarrier frequency whose sign is inverted every cycle is selected, or a subcarrier frequency whose sign is inverted for each pixel is selected.

On the other hand, in the reproducing apparatus, one of the reproduced digital codes is sign-inverted in the selection circuit 4 and the remaining one is applied to the selection circuit 4 after being sign-inverted in the sign-inverting circuit 1. Then, the 1 selection circuit 4 performs selection control using the selection control signal so that the code inversion circuit 3 outputs the code-inverted pixels, thereby obtaining the original code sequence without sign inversion.

FIG. 2 shows a second embodiment of the invention. This example is
This is an example in which a function of inverting the lowest pixel by 1 is added to a code sequence whose sign is regularly inverted. Between the signal whose sign has been inverted by the sign inverting circuit 5 and the signal as it is, a selection circuit 6 selects a pixel with sign inversion and a pixel without sign inversion according to the regularity of sign inversion. This code sequence is applied to the least significant bit inversion circuit 7. In the lowest (11) bit inversion circuit, if there are many occurrences of '0', the lowest bit of the pixel is set to '1', and when there are many occurrences of '1', the lowest bit of the pixel is set to '1'. The inversion operation of the least significant bit is performed by the control signal of the inversion control circuit 8.The inversion control circuit 8 determines the number of occurrences of '0' and '1' kl measurement
This is done by using a control signal that causes the least significant bit inversion circuit to perform an inversion operation when the difference in the number of occurrences between M0$7 and '1'' exceeds a certain threshold.

As described above, according to the present invention, direct current components can be removed with a simple configuration, and the effects obtained are extremely large.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams showing the structure of an embodiment of a code converter in a magnetic recording apparatus that implements the entire method according to the present invention. 1.3.5... Sign inversion circuit, 2, 4.6... Selection circuit, 7... Least significant bit inversion circuit, 8... Inversion control circuit. (12)

Claims (1)

[Claims] 1. A digital signal converted from a video signal is sign-inverted, the digital signal and the sign-inverted n'i signal are selected at a constant period, and a predetermined signal selected for each pixel is obtained. A method for recording a digital video signal, the method comprising: recording a digital video signal; 2. In the method described in item 1, a pixel whose sign is inverted and a pixel whose sign is not inverted are alternately generated every cycle of the subcarrier frequency as a predetermined signal selected for each pixel. A method for recording digital video signals. 3. A method for recording a digital video signal, characterized in that in the method described in item 1, the predetermined signal selected for each pixel is a pixel whose adjacent pixel is inverted in sign. 4. In the method described in item 1, if the difference in the number of occurrences between '1' and '0' exceeds a specific value, '1' and '0'
A method for recording a digital video signal, comprising inverting the polarity of a specific bit of a pixel so as to reduce the difference between the two bits.