JPS6187494A - Method of digital processing video signal - Google Patents

Abstract

PURPOSE:To process a signal by the same circuit with respect to an NTSC system and a PAL system by setting a sampling frequency in case of converting an analog video signal to a digital video signal, to a frequency of N times of a horizontal synchronizing signal frequency of the analog video signal. CONSTITUTION:In a frequency converter 3, at the time of recording, the frequency is converted from 3.58MHz to 9.9375MHz, and at the time of reproducing, the frequency is converted from 629kHz to 3.9375MHz, and a PS demodulation processing of a color signal is executed. A sampling frequency (fs) of this time is set to 15.75MHz. Particularly explaining, the frequency (fs) is set to a frequency of N times of a horizontal synchronizing signal frequency of an analog video signal {N is an integer, and also such a number as an integer P of P=M+Q becomes an even number, when the remainder obtained by dividing its integer N by 4 is denoted as M (N=4K+M, K is an integer, and M is a number of one of '0', 1, 2 and 3), and the remainder obtained by dividing the integer N by 3 is denoted as Q (N=3L+Q, L is an integer, and Q is a number of one of '0', +1 and -1)}.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a video signal digital processing method, and in particular to a video signal digital processing method.
TSC and PAL format signals can be processed in the same circuit. For example, when color signal processing for a magnetic recording/reproduction device BFF (VTR) is performed using digital signal processing, the signal can be processed using decimation processing. The present invention relates to a video signal digital processing method that can reduce the scale of processing circuits.

(Prior Art) In recent years, a method has been developed in which a video signal is digitized and then this digital signal is processed.
Reducing the number of capacitors, resistors, coils, or
This is an excellent method from the perspective of eliminating the need for adjustments to equipment, and many research and development efforts have been made in this regard, and some manufacturers are commercializing it as a "digital television."

In addition, the current television broadcasting system is NTS
The C, PAL, and 5ECAH systems mainly exist, but the market for the NTSC and PAL systems is especially large, and the color signal multiplexing system is said to be similar compared to the 5ECAH system. It has characteristics.

Therefore, both the NTSC and PAL systems are the same (
Alternatively, if signal processing could be performed using a circuit (almost equivalent), the benefits would be enormous.

Furthermore, since there is no major difference in luminance signals between the NTSC and PAL systems other than the frequency band, if the color signal processing circuits were standardized, it would be possible to use the same circuit for the NTSC and PAL systems. Become.

(Object of the Invention) The present invention has been made in view of the above-mentioned prior art, and an object thereof is to be able to process signals of the NTSC system and the PAL system in the same circuit, and to provide a magnetic recording/reproducing apparatus (VTR), for example. ) When carrying out color signal processing using digital signal processing, it is an object of the present invention to provide a video signal digital processing method capable of reducing the 1yA size of a signal processing circuit by using decimation processing.

(Means for Solving the Problems) In order to achieve the above object, the present invention sets the sampling frequency to a frequency N times the horizontal synchronizing signal frequency of the analog video signal (N is an integer, and Integer N is 4
The remainder divided by M (N=4K+M, where M is an integer and M is 0
．． 1, 2.3), and the remainder when dividing the integer N by 3 is Q (N = 3L 10, L is an integer, Q is O, +1゜-1) ), then P=M+Q
This invention provides a video signal digital processing method characterized in that the integer P is an even number.

(Example) Regarding the video signal digital processing method according to the present invention,
This will be explained below.

Generally, the frequency at which a video signal is sampled is
According to the "sampling theorem", it must be higher than twice the highest frequency included in the analog signal, usually about 10MHz.
z or higher is suitable (condition ■).

In addition, to configure a comb filter for color signal processing, the sample points must be arranged vertically on the screen.In other words, the sampling frequency must be an integral multiple of the horizontal synchronization signal frequency. (Condition ■).

Furthermore, in the case of the N rsc method, the comb filter is
A delay circuit (delay line: memory) for one line (horizontal scanning period) is required (in the case of PAL system, for two lines), but as the sampling frequency increases, more memory is used to make up the filter. It turns out. Therefore, since the band of the color signal is narrower than that of the luminance signal, it is effective to perform decimation processing.

By making the subcarrier (color subcarrier) frequency common between the NTSC system and the PAL system, color signal processing can be performed for both systems using substantially the same circuit.

Here, the sump song frequency (fs) that satisfies the above conditions (1) and (2) is as shown in the following table.

In the above table, f is: f, = 15.734265 in the case of NTSC system
kH.

In the case of PAL method f H = 15.625 k
) l.

NTSC system, PAL at any frequency fs in the table
For example, if a composite video signal of both methods is sampled using the same circuit, the luminance signal (Y)
In order to separate the color signal (C) and the color signal (C), the frequencies of the subcarriers of the color signal may be converted so that they become common to each other. By making the above common, the subsequent processing circuits can also be made common.

At that time, if the frequency of the subcarrier to be converted is, for example, 10fS, the D
Both P (differential phase) and DG (differential gain) are minimized.

Here, decimation processing, which is one type of digital signal processing, will be explained. This decimation process converts the sampled data into one piece on the time axis.
Alternatively, it means leaving every two, three, etc. as significant data and lowering the sampling frequency to -h, +, -i,....

Furthermore, in digital signal processing of video signals, filters are configured depending on various uses, and the higher the sampling frequency, the larger the filter configuration.

For example, a PA that converts a 2-day comb filter into an 8-bit digital signal at a sampling frequency of 15.75 MHz.
When applied to L format video signal, 2 x 1008 x 8
(16,128 bits) of memory is required. On the other hand, if you use old decimation (leaving every second data and setting the sampling frequency to 5.25MHz for blue), the memory required is 5376 bits for blue, reducing the memory by 10,752 bits. This is enough to compensate for the additional circuitry required by the decimation process.

By performing decimation processing in this way,
It will be possible to significantly reduce the circuit scale, and it can be said that this will have a significant impact on cost, power consumption, reliability, etc.

When performing the above decimation processing, as shown in Fig. 2, if the subcarrier has a positive sampling frequency (fs), the previous decimation (as shown in Fig. 2 (a)) J - In other words, in the operation of validating every other sample point, the signal loops back at +fs, resulting in the signal looping back to the subcarrier itself.

In addition, with positive decimation (as shown in Figure 2 (C)), that is, an operation in which every third sample point is valid, the subcarrier component disappears and returns to the baseband, making subsequent signal processing difficult. Become.

Therefore, a lucky decimation process as shown in FIG. 2(b) can be considered. In other words, since the decimation process returns after fs, the signal component does not overlap with the original signal, and the band is sufficient (stop fs), making it the most effective. Furthermore, the circuit can be reduced to a smaller size by processing by decimation.

Here, even if we perform blue decimation, still
The frequency at which sample points for each line (horizontal scanning line) are arranged vertically on the screen is only when the horizontal synchronizing signal frequency is an integer of 3. Otherwise, the sample points for each line (horizontal scanning line) will shift. This is PAL
This is because the NTSC system always has a frequency that is a multiple of 3 (in the examples in the table above), whereas this is not necessarily the case for the NTSC system.

By the way, in the color signal processing circuit of a magnetic recording/reproducing device (VTR), the phase of the color signal is divided into one line (
The so-called P S (Phase
5hift) processing, or so-called P I (Pha
se Invert) processing etc.

This demodulation can also be performed by digital processing, and can be performed by a frequency converter in a digital signal processing circuit of a digital magnetic recording and reproducing apparatus, which will be described later.

In addition, processing for removing crosstalk from adjacent signal tracks is performed by demodulating the PS processed or PI processed signal and performing addition processing between two adjacent lines (horizontal scanning lines). This is because the phase of the crosstalk component is reversed and canceled by PS processing or PI processing.
The condition for the above-mentioned addition process is that the lines be in phase. Therefore, if the sample points shift due to decimation, the above addition process cannot be performed even if the phases are aligned.

Conversely, even if the sample points are shifted, the phase will match (
Iiyl), you can perform addition processing.

Here, let us consider the phase relationship of the NTSC system.

Note that the sampling frequency fs is the horizontal synchronizing signal frequency "
Multiply H by an integer N, and divide the integer N by 4, and the remainder is M
(N=4K+M, where M is an integer, M is any number from 0.1.2.3), and the remainder when the integer N is divided by 3 is Q (N=3L10).

is an integer and Q is any number of 0, +1, -1), then P=M+Q. (P is also an integer) Figure 3 shows the sampling frequency f s = 1.5.75 MHz (= f
+X1001. M= 1 (1001=4x 25
0+1).

Q--1 (1001=3x 334-1), P=1-
1 = O), and the subcarrier frequency is +f
s (3,9375 MHz), indicating that one line has 250.25 subcarriers.

Also, FIG. 3(a) is the nH line, and FIG. 3(b) is the (n
+1) H line, Figure 3 (C) is (n -1-262)
)-1 line, in the figure, 0 indicates a sample point at a sampling frequency of 15.75 MH, and O indicates a sample point after decimation.

In the same figure, the n)-1 line in FIG. 3<a') and the (n+1)H line in FIG. 3(b) below it are 3.9
As shown by the thick solid lines I and I' waves of 375 MH2,
The phase has advanced by 90 degrees compared to 1H before.

Also, in the figure, the wave with the longer wavelength of 1.3L25MHz ■.

II' (solid line) is blue decimated and 1
．． 3L25 M) This is a subcarrier looped back to lz.

Also, between the nH line and the (n+1)H line, 15
．． The phases of the 75MH, waves (thick solid line and I') are 906 different from each other, but the 1.3L25MH waves (I') are different in phase from each other by 906.
The phases of the solid lines n, n') differ from each other by 30°.

However, the sample phases after decimation for the 1.3L25 MH wave on both lines are 0° and 90°.

It is the same at 180° and 270°, and the closest points are in the same phase (for example, point X and point X' in the figure, or point y
point and y' point, 7 point and 2° point, etc.

Further, the above phase relationship also applies to (n + 262)H, which is the crosstalk component in FIG. 3(C).

Strictly speaking, the sample points are not arranged vertically, but since they are only shifted by 63 ns (that is, 1/1001 of one line) in time, there is no problem as long as the phases match.

From the above, it can be seen that even if the sample points are shifted, by matching the phases, crosstalk between two lines can be eliminated.

The above was an example of 15.75MH, but in general, subcarriers are -l-f for sampling frequency fs.
s, the number of waves in one line A and its remainder B
is expressed as fs = fHX4XA+8.4>B≧0, and when B is not O, the phase of the subcarrier is shifted by +×B for each line. Further, the number of samples C in one line after decimation and its remainder D can be expressed as fs÷f+=3Xc+D, 3>D≧O, and like B, the sampling points are also shifted by D from line to line.

When B and D match, a 1H comb filter or the like in the above-mentioned PS processing can be constructed. Further, even if B and D do not match, if B-D=2, it can be easily configured by using a subtraction circuit instead of the addition circuit of the comb-shaped filter. As a specific example, 13.50 MH2 (M=2.
An example is when 0=O-, P=2).

Figure 4 shows the sampling frequency f s = 13.50.
MHz (-fHX 858. M=2 (858=4
x 214+2>.

Q=O (858=3x, 286+O), P=2+0
= 2), and the subcarrier frequency is i-
fs (3,375 MHz), indicating that there are 214.5 rib carrier waves in one line.

Also, FIG. 4(a) is the nH line, and FIG. 4(b) is the (n
+1) H line is shown; in the figure, O indicates a sample point with a sampling frequency of 13.50 MH, and ○ indicates a sample point after decimation.

In the figure, the n)(line in Figure 4(a) and the (n+1)H line in Figure 4(b) below it are 3.375
As shown by the thick solid lines I and I' waves of M1lz, 11''
The phase has advanced by 180° compared to before.

Also, in the figure, the wave ■ has a long wavelength of 1.125 MH.

n'<m solid line) is decimated, and 1.
This is a subcarrier that has been folded back to 125MHz.

Also, between the nH line and (n+1.))-1 line,
The phases of the 3.375 MH waves (thick solid lines ■ and I') differ by more than 180 degrees, but the phases of the 1.125 Moz waves (thick solid lines u, n') also differ by 180 degrees from each other. .

However, the Zamble phase after decimation in the 1.125 MHz wave of both lines is Q'', 90°.

It is the same at 180° and 270°, and the closest holes are in opposite phases (for example, the points X and X' in the figure, and the points y and y'
point, 2 points and Z' point, etc.).

Including the above two cases, generalizing the case when there is no remainder in the number of waves (that is, the number of subcarriers in one line is an integer multiple) and the sampling point after decimation does not shift, the sampling The frequency should be selected as follows.

In other words, "the frequency is N times the horizontal synchronization signal frequency (N is an integer and is 1, and the remainder when dividing the integer N by 4 is M
(N=4K+M, where M is an integer, 0, 1.2.
3), and the remainder when dividing the integer N by 3 is Q (N=3L+Q, L is an integer, Q is 0, +1,
-1), an integer P such that P=M+Q
is an even number). FIG. 1 is a diagram showing an embodiment of a circuit to which the video signal digital processing method of the present invention is applied. The circuit applied to the digital signal processing circuit will be explained below.

In the figure, 1 is an input terminal, and this input terminal 1
is associated with a composite video signal, which is converted into a digital signal by an AD converter 2 and then frequency-converted by a frequency converter 3. Here, the frequency converter 3 converts the frequency from 3.58 MHz to 3.937 MHz during recording.
The frequency is converted to 5 MHz, and during playback, the frequency is converted from 629kHz to 3.9375MHz, and the P of the color signal is
S demodulation processing is performed. J3, and the sampling frequency fs at this time is 15.75 MH.

Furthermore, a bandpass filter (BPF) for YC separation
After being subjected to decimation (thinning) processing in the decimation processing circuit 5 via the digital processing circuit 4, the digital processing circuit 6 performs ACC (automatic color signal level control) and AP processing.
Digital processing such as C (automatic phase control) is performed, and then the interpolation circuit 9 passes through a signal processing filter 7 and a comb-shaped filter 8 for canceling crosstalk during playback.
Then, decimation processing (interpolation processing) opposite to that of the decimation processing circuit 5 is performed to restore the decimation to its original state.

Then, the signal is frequency-converted again by a frequency converter 11 via an interpolation band-pass filter (BPF) 10. Here, in the frequency converter 11, at the time of recording, 3.937
The frequency is converted from 5 MHz to 629 kHz, and during playback, the frequency is converted from 3.9375 MHz to 3.58 MHz. Finally, it is converted into an analog video signal by the DA converter 12 and output from the output terminal 13.

In addition, 14 and 16 are data generation oscillators for supplying data for frequency conversion to the frequency converters 3 and 11, and 15 is a data generation oscillator for supplying data for frequency conversion to the frequency converters 3 and 11.
This is a control section that supplies control signals to the digital processing circuit 6 and the oscillators 14 and 16 in response to a TSC mode instruction signal. Reference numeral 17 denotes an oscillator that supplies a clock signal (sampling frequency fs) to each of the digital signal processing circuits described above.

By configuring as described above, the circuit configuration can be simplified, and the sampling frequency fs can be set to a frequency (N times the horizontal synchronizing signal frequency of the analog video signal as described above) (
N is an integer, and the remainder when dividing the integer N by 4 is M (N=4K+M).

K is an integer, M is any number from 0, 1.2.3),
The remainder when the integer N is divided by 3 is Q(N-3L-1-
When Q and L are integers (Qt, t0, +1, -1), the NTSC system and PAL system can be made the same by setting P = M + Q, such that the integer P is an even number). It becomes possible to process signals using circuits.

(Effects of the Invention) As described above, according to the video signal digital processing circuit of the present invention, it is possible to process signals for the NTSC system and the PAL system in the same circuit.
When color signal processing for a VTR is performed by digital signal processing, the use of decimation processing has the advantage that the scale of the processing circuit can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of a circuit to which the video signal digital processing method according to the present invention is applied, Fig. 2(a) to Fig. 3(C), and Fig. 3(a) to Fig. 3(C). and Figure 4(a)~
FIG. 2B is a diagram for explaining the principle of the video signal digital processing method according to the present invention. 1... Input terminal, 2... AD converter, 3.11...
・Frequency converter, 4, 10... BPF, 5... Decimation processing circuit, 6... Digital processing circuit, 7... Filter, 8.
...Comb filter, 9...Interpolation circuit, 12...D
A converter, 13... Output terminal, 14, 16.17...
- Oscillator, 15...control unit.

Claims (1)

[Claims] The sampling frequency when converting an analog video signal to a digital video signal is set to a frequency N times the horizontal synchronization signal frequency of the analog video signal {N is an integer, and
The remainder when the integer N is divided by 4 is M (N=4K+M, K is an integer, and M is any number of 0, 1, 2, or 3), and the remainder when the integer N is divided by 3 is Q. When (N = 3L + Q, L is an integer, Q is any number of 0, +1, -1),
A video signal digital processing method characterized in that the integer P is an even number such that P=M+Q.