JPS6138677B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an encoding/decoding device for composite color television signals such as NTSC and PAL systems.

In color television signals such as the NTSC system, a carrier color signal (hereinafter referred to as C signal), which is a subcarrier modulated with a color signal, is frequency multiplexed so that the frequency spectrum is interleaved with a luminance signal (hereinafter referred to as Y signal). signal format is used. As a method for efficiently encoding such a composite color television signal, the composite color television signal is directly encoded without being demodulated into baseband signals (for example, luminance signal Y, chrominance signal I, and chrominance signal Q in the NTSC system). Methods include direct coding methods such as high-order predictive DPCM and orthogonal transform coding such as Hadamard transform. The direct encoding method directly encodes a composite color television signal containing a C signal with a frequency spectrum concentrated in the high frequency region, so when sampling a signal, the sampling frequency s is within the signal band. It is necessary to set the value to more than twice the subcarrier frequency sc, and conventionally the value is about 2.5 to 3 times the subcarrier frequency sc (9 to 11 MHz for NTSC color television signals).
was selected. For this reason, the transmission bit rate required to transmit the encoded signal tends to be large because the sampling frequency is high. In addition, if sampling is performed at a frequency lower than twice the frequency of the signal band (hereinafter referred to as the Nyquist frequency), the frequency spectrum will be folded and overlapped, resulting in distortion of the waveform and the color signal may not be reproduced correctly. Waveform distortion caused by spectral folding is referred to as aliasing distortion.) The configuration of a filter circuit to remove aliasing distortion (in the frequency domain, the folded frequency spectrum, or folded spectrum) is complex.

The purpose of the present invention is to set the sampling frequency s under special conditions (approximately 2(m+n)/2n+1 times sc , where m and n are positive integers) to easily configure a filter circuit that removes aliasing distortion, and provides an encoding/decoding device that realizes highly efficient band compression encoding with a simple device. It's about doing.

The encoding/decoding device of the present invention has a sampling frequency s lower than twice the subcarrier frequency sc in the frequency domain, and approximately 2(m+n)/2n+1 times the subcarrier frequency sc (m and n are positive integers). ) is controlled to sample a composite color television signal at a frequency such that the frequency characteristic is
A filter containing the function sin(2(m+n)/2π/s) (where m is the same value as m above) and a low-pass filter that passes from 0 to 1/2s are used to remove aliasing distortion and create a composite color. and a decoding device that has the function of reproducing television signals.

According to the present invention, it is possible to directly sample a composite color television signal at a sampling frequency s lower than twice the subcarrier frequency sc, that is, lower than the Nyquist frequency, thereby eliminating aliasing distortion of the decoding device. The structure of the filter circuit to be removed is simplified, and an efficient encoding/decoding device can be obtained.

The case where the signal format is an NTSC composite color television signal will be explained below using the drawings as an example.

In the NTSC frequency multiplexed color television signal system, in order to reduce image quality deterioration due to mutual interference between the Y signal and the C signal, the frequency range of the frequency spectrum of the C signal is shifted to the high range where the amplitude of the frequency spectrum of the Y signal is small. selected in the frequency part, and the frequency spectrum of the C signal (hereinafter referred to as the spectrum of the C signal) is selected between the frequency spectrum of the Y signal (hereinafter referred to as the spectrum of the Y signal). The subcarrier frequency sc is in a frequency interleaved relationship with the horizontal scanning frequency _H. In other words, in the case of NTSC system, sc=
Selected as 455/2・_H. The distribution of the frequency spectrum of a color television signal generally spreads over the entire frequency band, but in a normal video signal, the spectrum of the Y signal is centered around a frequency that is an integer multiple of _H , and is concentrated in the vicinity and in the low frequency range. However, the amplitude of the frequency spectrum in the high frequency range is very small. Also, the spectrum of the C signal is in the frequency range near sc.
It can be considered that the waves are concentrated at frequencies that are odd multiples of _H /2. Therefore, a composite color television signal with an amplitude distribution of entangled frequency spectra as shown in Figure 1a is expressed as (1)
If sampling is performed at a sub-Nyquist frequency s that satisfies the equation s<2sc (1), a folded spectrum will be generated by the sampling as shown by the broken line in FIG. 1b.

If this signal is transmitted and the received signal is resampled at the sampling frequency of 2s on the receiving side, a signal with the spectral distribution shown in Figure 1c is obtained.From this, the aliasing component is removed using an interpolation filter. For the Y signal, a low-pass filter H _L (Z) that passes from 0 to 1/2 s blocks at least the vicinity of (s-sc) for the C signal, and sc
An interpolation filter Hc(Z) is required to pass the vicinity of .

Now, set the sampling frequency s so that the values of s-sc and sc become s-sc≒2m-1/4s (2) sc≒2n+1/4s (3) , n is a positive integer) (4). If s is selected in this way, the vibration characteristics will be sin(2π・i・/2c) as shown by the broken line in Figure 1d.
= | (1-Z ^-2(m+n) ) |/2 By using a digital filter that includes a factor, a bandpass filter H _CB (Z) that passes s-sc and the vicinity of sc can be easily constructed. can.

Here, i=n+m.

Therefore, it passes from 0 to 1/2s and from 1/2s to s
Low-pass filter H _L (z) and HCB that prevent
(z), the C signal interpolation filter H _C (z), which has an amplitude characteristic that blocks at least the vicinity of s-sc and passes the vicinity of sc, as shown in Figure 1d, becomes H _C (z )=H _L (z) (1-2H _CB (z))
+H _CB (z) (6) can be easily configured. The characteristics of these H _L (z) and H _CB (z) can be made closer to the required characteristics as the order increases, but the hardware requirements become larger. Therefore, as a simple example, let H _L (z) and H _CB (z) be Z ^-1
= e ⁱ² 〓 ^{/2 s} as H _L (z)=Z ⁻¹ +2+Z ¹ /4+k × −Z ⁻³ +Z ⁻¹ +Z ⁻¹ −Z ³ /4(7) H _CB (z)=−Z ^{−2 (m+n)} +2-Z ^2(m+n)
/4(8). However, the value of k is selected so that =s-sc and the amplitude of H _L (z) is close to 1.

As an example, a case will be explained in which n=m=1 in equation (4), that is, the sampling frequency is selected as s≈4/3 sc (9).

At this time, H _L (z) and H _CB (z) will be as follows if (7) and (8) are used.

H _L (z)=Z ^-1 +2+Z ⁺¹ /4+3/16 × -Z ^-3 +Z ^-1 +Z ₊₁ -Z ^-3 /4(10) H _CB (z)=-Z ^-4 +2-Z ⁺⁴ /4 (11) At this time, the C signal interpolation filter H _C using equation (6)
From equations (10) and (11), (z) is H _C (z) = [-3Z ^-3 +19Z ^-1 +32+19Z
⁺¹ -3Z ⁺³ /64] × [Z ^-4 +Z ⁺⁴ /2] +-Z ^-4 +2-Z ⁺⁴ /4
(12), and the amplitude characteristics are as shown in Figure 1d.
From this, the first embodiment uses a filter of H _C (z) to fold back the C signal in the vicinity of s-sc from the sub-Nyquist sampled signal, and to look into the vicinity of sc from 1/2s to s. A method of removing folding of the Y signal in the frequency range and obtaining a 2s sampling signal having almost the same spectral distribution as that on the transmitting side will be shown.

In other words, the sub-Nyquist sampled signal at the sampling frequency given by equation (9) can be removed using the interpolation filter H _C (z) with a simple configuration given by equation (12), resulting in NTSC color. Can decode TV signals.

In this case, the interpolation filter H _C (z) alone does not completely remove the aliased spectrum (for example, the Y signal spectrum aliased near sc), so the way to remove it is to sample at the sub-Nyquist frequency s. It is conceivable to band-limit the Y signal and C signal beforehand. For example, a composite color television signal sampled at a sampling frequency of 2 s is band-limited using a digital filter with the same transfer characteristic as the interpolation filter H _C (z) used on the receiving side, and then resampled at s. . In this way, a composite color television signal with even less deterioration can be decoded on the receiving side.
As a second method to further reduce image quality deterioration,
Focusing on the fact that the spectra of the Y signal and C signal of a composite color television signal are in a frequency interleaved relationship, the spectrum of the Y signal is mainly concentrated near integral multiples of _H (hereinafter referred to as the Y component). ), and the spectrum of the C signal is mainly concentrated in the vicinity of odd multiples of _H /2 (hereinafter referred to as the C component). We will show you how to use limits and interpolation to eliminate wrapping. In other words, a received signal with an aliased component is separated into a Y component (mainly including the Y signal) and a C component (mainly including the C signal) using a comb filter. The aliasing is removed using a low-pass filter H _L (z) that passes up _to If removed, it is possible to reproduce the Y component from 0 to 1/2 seconds without deteriorating the frequency characteristics near s-sc, and the Y component can be reproduced more easily than in the first method. The frequency band is expanded.

As an example of using a comb-shaped filter, when the composite color television signal is in the NTSC format, the folding of the Y signal overlaps with the spectrum of the Y signal (when sampling is performed with the sampling frequency s being a frequency multiple of the frequency of _H ). ) and cases in which the return of the Y signal falls between the spectrum of the Y signal and the spectrum of the C signal (sampling is performed with the sampling frequency s set to an odd multiple of 1/4 _H ), etc. .

When the composite color television signal is in the PAL format (in the PAL format, the spectrum of the C signal is concentrated at frequencies that are odd multiples of 1/4 _H ), the folding of the Y signal is made to overlap the spectrum of the Y signal. (
When s is an integer multiple of _H ) and when the folded spectrum of the Y signal is made to overlap at a frequency that is an odd multiple of _H /2 (when s is a frequency that is an odd multiple of _H /2), etc. It will be done.

Next, as an example of the above-mentioned method as a second embodiment, if the composite color television signal is an NTSC system and the sampling frequency s is a frequency near 4/3sc (m = 1, n = 1 in equation (4)). A comb filter, a band-limiting filter, and an interpolation filter selected so that s=l _H (13) (where l is an integer number) will be explained. When s is in the vicinity of 4/3sc, the value of l is l=341, 341±1, . . . . When sampling is performed at such s, the relationship between the aliasing distortion of the Y signal and the C signal is as shown in FIG. 2a, when the frequency spectrum distribution is closely examined. The folded spectrum of the C signal is concentrated near frequencies that are odd multiples of 1/2 _H , as shown by the broken line, for the Y signal, which has a frequency spectrum concentrated near frequencies that are integral multiples of _H , as shown by the solid line. and then turned around. From this, in order to separate the Y component, as shown in Figure 2b, at frequencies that are integral multiples of _H , its amplitude, or absolute value, is approximately 1, and at odd multiples of 1/2 _H , its magnitude is It is sufficient to pass the signal through a filter having a frequency characteristic that is approximately 0. An example of a filter having the characteristics shown in FIG. 2b is a 1H type comb filter that passes the Y signal. This filter is Z ^-1 = e ^-j2 〓 ^/2
If ^s is expressed using Z transformation, the transfer function H
This frequency characteristic ^H
() becomes H()=|cosπ/ _H |, and its magnitude is 1 for integral multiples of _H and 0 for odd multiples of 1/2 _H. Similarly, for C component, H(z)=1−Z ^−H /
2 comb-shaped filters may be used. That is, by using these comb-shaped filters, a composite color television signal can be separated into a Y component and a C component.

Although the frequency spectrum of the Y signal of the input signal is explained here as up to the frequency of 1/2 s, if the amplitude of the spectrum of the Y signal of 1/2 s or more is large and its influence cannot be ignored, the sampling frequency is 2 s. The converted signal is band-limited in advance (for example, by using a comb-shaped filter and a low-pass filter _H Frequency components of the Y signal up to s are blocked. Thereafter, subsampling is performed to convert the signal to a signal with a sampling frequency of s, and the signal is sent to the transmission path.

As an interpolation filter for removing aliasing of the Y component signal, a low-pass filter with a pass band from 0 to 1/2 seconds is required, and for example, there is a digital filter H _L (z) given by equation (10).

Since the sampling frequency s satisfies equation (4), an interpolation filter for removing folding of the C component signal may be, for example, the transfer function H shown in the first embodiment.
Digital filter H _C where (z) is given by equation (12)
It can be easily configured by using (z).

If aliasing distortion is removed by performing filtering suitable for each signal distribution using these filters, it is possible to decode a color television signal with little deterioration in image quality.

Note that s should be selected so that the folded spectrum of the C signal falls approximately in the middle of the spectrum of the Y signal, and therefore, it is sufficient that it approximately satisfies equation (13).

As is clear from the above description, the principle of the present invention is to encode and decode a composite color television signal by selecting the sampling frequency s to be a value smaller than twice the subcarrier frequency sc, that is, a frequency lower than the Nyquist frequency. In the method of This method allows the filter to be easily configured using a digital filter having a frequency characteristic of sin ((m+n)π/s) and a low-pass filter that passes low frequencies.

By using such a method, it is possible to directly sample and transmit a composite color television signal at a frequency equal to or lower than the Nyquist frequency without demodulating the composite color television signal into a baseband signal using a simple device configuration.

If the signal system is not NTSC but another system, e.g.
In the case of the PAL system, it can be processed in the same way as NTSC, considering that the spectrum of the C signal is concentrated near frequencies that are odd multiples of _H /4.

In other words, in the case of the first sake example, the NTSC method is also used.
The same applies to the PAL system.

In the case of the second embodiment, since the spectral distribution of the C signal is different, it is necessary to change the configuration of the comb filter that separates the Y component signal and the C component signal.

The configuration of an embodiment in the case where the signal format is the NTSC system will be described below.

FIG. 3 is a block diagram showing the structure of the first and second embodiments of the narrowband color television signal encoding apparatus of the present invention. In this embodiment, a case will be explained in which the sampling frequency s is selected to be approximately 4/3 times the subcarrier frequency sc (approximately 4.8 MHz). This is the case where m=1 and n=1 in equation (4).
The oscillation circuit 4 is a circuit that generates a clock with a frequency of 2 s, and in the case of the first embodiment, free oscillation may be used, and in the case of the second embodiment, the frequency is such that the frequency satisfies equation (13), for example, s = 342 _H That is, 2s=
It is necessary to control the oscillation frequency of 2s to _684H .

Obtaining an oscillation frequency synchronized with the scanning frequency of a television signal can be easily achieved using known techniques. The clock signal with a frequency of 2s generated by the oscillation circuit 4 is supplied to the A/D converter 1 and the band limiter circuit 2, and is divided by half from the frequency of 2s to the frequency of s in the frequency divider circuit 11, and the sub The signal is supplied to the sample circuit 6. Further, the clock generating circuit 8 is a circuit that generates a clock having a frequency of 2 seconds in synchronization with the clock frequency of the transmission line, and can be easily realized using already known technology. The generated 2s clock is supplied to each section. The analog NTSC color television signal supplied to the A/D converter 1 is converted by the A/D converter 1 into a PCM (pulse code modulation) signal with a sampling frequency of 2 s, and is supplied to the band limiting circuit 2. The band limiting circuit 2 limits the frequency band of signal components unnecessary for signal reproduction, and supplies the band limited PCM signal with a sampling frequency of 2 s to the sub-sampling circuit 3. The sub-sampling circuit 3 resamples the signal having a sampling frequency of 2s every other sampling value and converts it into a signal having a sampling frequency s, and the converted composite color television signal is supplied to a transmission path.

On the receiving side, the PCM signal of sampling frequency s received from the transmission line is supplied to the interpolation circuit 5. The interpolation circuit 5 interpolates sample values with a value of 0 between each sample value from the PCM signal with the sampling frequency s to obtain a PCM signal with the sampling frequency of 2s, and the average amplitude is equal for the frequencies of s and 2s. The magnitude of the signal is doubled so that the signal is supplied to the removal filter circuit 6. The removal filter circuit 6 uses a filter to remove aliasing distortion unnecessary for signal reproduction, thereby obtaining a band-limited composite color television PCM signal with a sampling frequency of 2 seconds. PCM with sampling frequency of 2s obtained by removal filter circuit 6
The signal is converted into an analog composite color television signal by a D/A converter 7.

FIG. 4 shows an example of a specific configuration of the band limiting circuit 2 and removal filter circuit 6 of FIG. 3 in the case of the first embodiment. In this embodiment, both the band limiting circuit 2 and the removal filter 6 are constructed of digital filters whose transfer function H(z) is given by equation (12).

In FIG. 4, reference numerals 401 to 425 are shift registers operating at a clock frequency of 2 s, and each input signal is outputted to the output of each shift register with a delay of one clock period. 431 to 438 are adders, and 441 to 448 are multipliers. 441-448
The multiplier values from 441 to 448 are 1/2, -3, 19, 32, 1/64, -1, 2, and 1/4, but these are due to the digit shift of the signal and the sign of the signal. It can be easily constructed using means of inversion and addition.

The operation of each component is a well-known configuration of a digital filter and can be clearly understood from the drawings, so a description thereof will be omitted. The output signal of this digital filter is delayed by seven clock cycles with respect to the input signal.

FIG. 5 shows an example of a specific configuration of the sub-sample circuit 3 and interpolation circuit 5 shown in FIG. 3. The sub-sample circuit 3 is composed of a switch 51.

The switch 51 is a switch that opens and closes at a clock frequency s, and by opening and closing the switch, the sampling frequency 2s supplied to the sub-sampling circuit 3 changes.
A PCM signal having a sampling frequency s is outputted to the output of the switch 51 by passing the PCM signal in a diagonal manner every other sampling value. That is, the PCM signal of the sampling frequency s is outputted from the sub-sampling circuit 3.

The interpolation circuit 5 is composed of a switch 52 and a multiplier 53. The PCM signal of sampling frequency s supplied to the interpolator 5 is sent to one input of a switch 52 which switches at a clock frequency of 2s. The other input is given the value 0 by the 0 level generator 54.
PCM signal is supplied. 2 in synchronization with the input signal
By switching the switch 52 at a frequency of s, a PCM signal having a sampling frequency of 2s with a zero value interpolated therein is obtained at the output of the switch 52. This signal is sent to the multiplier 53, doubled, and output so that the average value of the signal is equal when the sampling frequency is s and 2s. A multiplier with a magnification of 2 can be easily constructed by shifting the input signal one digit higher and outputting it.

FIG. 6 shows a specific configuration example of the band limiting circuit 2 of FIG. 3 in the case of the second embodiment.

A PCM signal with a sampling frequency of 2 seconds is supplied to a signal separation circuit 61. The signal separation circuit 61 uses a comb filter to separate the signal into a Y component signal and a C component signal, the Y component signal is sent to a band limit filter circuit 62, and the C component signal is sent to a delay circuit 63. The Y component signal band-limited by the band-limiting filter circuit 62 so that the frequency component is 0 to 1/2 s is sent to the adder 64, where it is passed to the delay circuit 6.
3 and is added to the phase-compensated C component signal. As a result, the output of the adder 64 is a signal having a sampling frequency of 2s in which the high frequency component of the Y component signal is band-limited.

FIG. 7 shows an example of a specific configuration of the signal separation circuit 61 shown in FIG. 6. In this embodiment, a case is shown in which a so-called 1H type comb filter is used to separate the Y component signal using the correlation between the current sample value and the sample value one scanning line before. PCM with sampling frequency of 2s sent from A/D converter 1
The signals are supplied to line memory 71, adder 72 and subtracter 73, respectively. line memory 71
is a circuit that provides a delay of one horizontal scanning period, and can be constructed from a storage element such as a shift register.

The output of line memory 71 is supplied to adder 72 and subtracter 73. The input signal and the signal delayed by one horizontal scanning period are added by an adder 72 and multiplied by 1/2 by a multiplier 74, thereby outputting a Y component signal at the output of the multiplier 74. Further, the subtracter 73 subtracts the input signal delayed by one horizontal scanning period from the input signal, and the multiplier 75 multiplies the input signal by 1/2, thereby outputting the C component signal as the output of the multiplier 75. do. Multipliers 74 and 75 are simply constructed by shifting each input signal one bit downward by one digit and outputting the resultant signal.

FIG. 8 shows an example of a specific configuration of the band-limiting filter circuit 62 shown in FIG. The filter characteristics used in this example are shown by equation (10).

H _L (z)=-3Z ^-3 +19 ^-1 +32+19Z ⁺¹
-3Z ^+3/64 (15) This frequency characteristic H _L () is H _L () = 1/2 + 19/32cos (2π/2s) -3/32cos (2π·3/2s) (15). As is clear from equation (15), this filter is a low-pass filter that passes frequencies from approximately 0 to 1/2 seconds.

In FIG. 8, reference numerals 801 to 806 are shift registers operating at a clock frequency of 2 s, and each input signal is outputted with a delay of one clock cycle to the output of each shift register. 811 to 814 are adders;
821 to 824 are multipliers whose magnifications are −3, 19, 32, and 1/64 in this order. Multipliers with respective magnification factors can be easily constructed using means of digit shifting, inversion, and addition of each signal.

The operation of each component is a well-known configuration of a digital filter and can be clearly understood from the drawings, so a description thereof will be omitted.

When the digital filter of equation (10) shown in FIG. 8 is used, the output signal of the band-limiting filter circuit 62 is delayed by three clock cycles with respect to the input signal. Therefore, the delay circuit 63 is constructed by connecting three stages of shift registers operating at a clock frequency of 2 seconds, and the output of the delay circuit 63 is delayed by three clock cycles depending on the input, and compensation for the delay is performed.

FIG. 9 shows a specific configuration example of the removal filter circuit 6 of FIG. 3 in the case of the second embodiment. The sampling frequency of 2s supplied from the interpolation circuit 5
The PCM signal is sent to a signal separation circuit 91 and separated into a Y component signal and a C component signal containing aliasing distortion using a comb filter that utilizes line correlation.

The separated Y component signal is sent to a Y filter circuit 92.
It passes only the frequency components with frequencies from 0 to 1/2s, and removes the folded spectrum of the Y signal of 1/2s or more caused by folding, which is almost the same as the band-limited original Y signal. A Y signal with a sampling frequency of 2s consisting of the same frequency spectrum is obtained.
Further, the separated C component signal is passed through a C filter circuit 93.
(s-sc)
The folded spectrum of the C signal in the vicinity of the frequency of is removed, and a C signal with a sampling frequency of 2s, which has almost the same frequency spectrum as the original C signal, is obtained. The Y signal and C signal, which have been compensated for the difference in delay time due to filtering, are supplied to an adder 94 and added to obtain a composite color television signal with a sampling frequency of 2 s.

As an example of a specific configuration of the signal separation circuit 91 shown in FIG. 9, a circuit having the same function as the signal separation circuit shown in FIG. 7 is used.

FIG. 10 shows an example of a specific configuration of the Y filter circuit 92 shown in FIG. 9. The Y component signal of the input signal to the Y filter circuit 92 has its aliasing component removed by a Y interpolation filter 101, is delayed by a delay circuit 102 to match the phase with the output signal of the C filter circuit 93, and is output. As an example of a specific configuration of the Y interpolation filter circuit 101, a low-pass filter circuit having the same function as the band-limiting filter circuit shown in FIG. 8 is used. The delay circuit 102 is composed of four stages of shift registers operating at a clock frequency of 2 s, and outputs the input signal with a delay of 4 clock cycles. Therefore, the output of the Y interpolation filter circuit 92 is delayed by seven clock cycles with respect to the input.

As an example of a specific configuration of the C filter circuit 93 shown in FIG. 9, a filter having the same function as the removal filter circuit shown in FIG. 4 is used.

Although the first and second embodiments have been described above, the range limiting circuit shown in FIG. There is also a way to add bandwidth restrictions to the network.

The signal separation circuit of the embodiment shown in FIG.
Although this is a 1H type configuration, the configuration is not limited to this method, and it is also possible to use other methods, for example, a so-called 2H type configuration using front and rear scanning lines.

The embodiments of the Y filter circuit 92 and the C filter circuit 93 in FIGS. 4, 8, and 9 are not limited to these embodiments, and may be configured to satisfy the required frequency characteristics. Any suitable filter circuit may be used.

The embodiment of the interpolation circuit shown in FIG. 5 and the removal filter circuit shown in FIG. 52 between the signal separation circuit 91 and the Y filter circuit 92, and between the signal separation circuit 91 and the C filter circuit 9.
It is also possible to configure such a configuration that they are respectively placed between 3 and 3. In this way, the number of delay elements required for the signal separation circuit can be reduced.

Furthermore, in the first and second embodiments, the case where the sampling frequency s is approximately equal to 4/3 sc (when m = 1, n = 1 in equation (4)) was explained, but in the case of other values, the band limit is The frequency characteristics of each filter circuit in the circuit 2 and the removal filter circuit 6 may be changed to a desired characteristic.

FIG. 11 is a block diagram showing the configuration of a third embodiment of the present invention. This embodiment is a combination of the first or second embodiment with a band compression encoding method, and includes an A/D conversion 1, a band limiting circuit 2, a sub-sampling circuit 3, an oscillation circuit 4, an interpolation circuit 5, and a removal circuit. Filter circuit 6, D/A converter 7, clock generation circuit 8
The frequency dividing circuits 11 and 12 are the A/D converter 1, band limiting circuit 2, sub-sampling circuit 3, oscillation circuit 4, interpolation circuit 5, removal filter circuit 6, and
It has the same functions as the D/A converter 7, the clock generation circuit 8, and the frequency dividing circuit 11.

The band compression encoding circuit 9 receives the PCM signal of sampling frequency s supplied from the sub-sampling circuit 3.
This is a circuit that performs band compression encoding such as DPCM (differential PCM) and Hadamard transform. The signal encoded by the band compression encoding circuit 9 is sent out to a transmission path.

The band compression decoding circuit 10 is a circuit that decodes a band compressed signal sent from a transmission path to a PCM signal of sampling frequency s. The decoded signal is interpolated by an interpolation circuit 5, aliased components are removed by a removal filter circuit 6, and then sent to a D/A converter 7.
is converted into an analog signal.

The oscillation circuit 4 and clock generation circuit 8 supply necessary clocks to each section.

The encoding device of this embodiment uses a band compression encoding method suitable for the PCM signal to transmit the PCM color television signal sampled at the sub-Nyquist sampling frequency s in the first or second embodiment. By combining them, a larger number of transmission bits can be compressed than in the first or second embodiment.

FIG. 12 shows an example of a specific configuration of the band compression encoding circuit 9 and the band compression decoding circuit 10 shown in FIG. 11. In this embodiment, a case will be described in which high-order DPCM using a high-order prediction function adapted to a color television signal including subcarriers is adopted as a band compression encoding method. If the prediction function is P(z) and the transfer function of the prediction error signal is H(z), then H(z)
= (1-P(z)), and in high-order DPCM, the prediction error signal transfer function H is such that the RMS value of the prediction error output is small with respect to the Y signal and carrier color signal in the low frequency part. (z) is sufficient.
As such a function, 1-Z ^-2H (Z ^-2H indicates the sampling time two horizontal scanning periods before) is used, which uses the value of the sampling time two lines ago, and as a correction function, (1-αZ ^{- 1} ). (Here, when s = l・_H as shown in equation (7), Z ^-2H is Z ^-2H = Z ^-2l
It is indicated by. ), that is, H(z) = (1-αZ ^-1 )
A prediction function P that is a transfer function of (1-Z ^-2H )
Consider (z)=1-H(z) as an example. From this, the prediction function P(z) becomes P(z)=αZ ⁻¹ +Z ^−2H −αZ ⁻¹ ·Z ^−2H (16). However, α is a constant and is selected as, for example, α=0.5.

The high-order DPCM encoder 9 includes a subtracter 141, a quantizer 142, an adder 43, a prediction filter 144, and a code converter 145. Consists of 148.

An input signal 141 to a higher order DPCM encoder is provided. The subtracter 141 subtracts the prediction signal output from the prediction filter 144 from the input signal and outputs a prediction error signal. The prediction error signal that is the output of the subtracter 141 is sent to the quantizer 142, where it is quantized with the quantization characteristic determined by the quantizer 142, and the quantized signal is sent to the adder 143 and code converter 145. Can be supplied. In the adder 143, the output of the quantizer 142 and the output signal of the prediction filter 144 are added to obtain a locally decoded signal, which is supplied to the input of the prediction filter 144. The prediction filter 144 has a transfer characteristic shown in equation (16), calculates a predicted value of the next sampling time from the locally decoded signal, and outputs it as a predicted signal. A code converter 145 converts the signal quantized by the quantizer 142 into a code corresponding to each quantization level, and sends the code to a transmission path.

In the high-order DPCM decoder 10, the code sent from the transmission path is converted to the quantizer 14 by the code inverse conversion circuit 146.
The signal level is converted to a signal level corresponding to the quantization level of 2 and sent to the adder 147. The adder 147 adds the signal sent from the sign inverse conversion circuit 146 and the prediction signal sent from the prediction filter 148 to obtain a decoded signal. The decoded signal is sent to a prediction filter 148, which calculates and outputs a predicted signal at the next sampling time. The prediction filter 148 is the prediction filter 14
It has the same transfer characteristics as 4.

FIG. 13 shows an example of a specific configuration of the prediction filters 144 and 148 in FIG. 12. In this embodiment, the function P(z) given by equation (16) is constructed from a non-recursive digital filter. 151 is a shift register operating at a clock frequency s, and 152 is a multiplier with a multiplication factor α.
If the magnification α is chosen to be α=0.5, the multiplier 152
is easily constructed by simply shifting the input signal one digit lower and outputting it. 153 is a subtractor,
155 is an adder, and 154 is a line memory.
The line memory 154 is a circuit that provides a delay of two horizontal scanning periods, and can be composed of a storage element such as a shift register. The operation of each component is a well-known component of a digital filter and can be clearly understood from the drawings, so a description thereof will be omitted.

As is clear from the above explanation, significant band compression can be achieved by combining the band compression coding method with the coding/decoding device that can code at a sampling frequency lower than the Nyquist frequency described in the first or second embodiment. An encoding/decoding device capable of encoding can be realized.

Moreover, since the decoded color television signal is not demodulated into a baseband signal, and all post-encoding processing can be performed using digital logic circuits, highly accurate and stable calculations can be performed.

Also, prediction filters 144 and 148 in FIG.
The transfer characteristic of is the prediction function P shown by equation (16)
(z), and any function may be used as long as it can efficiently predict both the luminance signal component and the carrier color signal component. For example, it can be configured with a prediction filter within the 1H line.

Furthermore, the band compression encoding method in the third embodiment is not limited to high-order DPCM, and may be an orthogonal transform encoding method such as Hadamard transform or an interframe encoding method. Alternatively, a method combining these with variable length encoding may be used.

In the first, second and third embodiments, if no band limitation is applied, A/D with a sampling frequency of 2s is used.
There is no need to convert, and s will suffice. Therefore, in this case, the band limiting circuit 2 and the sub-sampling circuit 3 are unnecessary, and the device configuration becomes simple.

In each embodiment, signal lines other than signal lines indicating the flow of information of television signals, clock signal lines, etc. are omitted except for important parts.

[Brief explanation of the drawing]

FIG. 1a is a diagram showing the envelope of the frequency spectral distribution of the Y signal and C signal of the input composite color television signal. Figure 1b is a diagram showing the frequency spectrum distribution of the input signal sampled at the sampling frequency s.
Figure c shows the frequency spectrum distribution of the input signal when a signal with a sampling frequency of s is resampled at a sampling frequency of 2s by interpolating 0 between each sample value.
FIG. d is a diagram showing the frequency characteristics of a filter for removing aliasing distortion of the C signal. FIG. 2a is a diagram showing the frequency spectrum functions of the Y signal and the folded C signal, and FIG. 2b is a diagram showing the frequency characteristics of a comb-shaped filter that passes the Y component signal. FIG. 3 is a block diagram showing the configuration of the first and second embodiments of the narrowband color television signal encoding/decoding apparatus of the present invention, and FIG. 4 shows the band limiting circuit 2 or its removal in the first embodiment. 5 is a block diagram showing an example of a specific configuration of the filter circuit 6, FIG. 5 is a block diagram showing an example of a specific configuration of the sub-sampling circuit 3 and the interpolation circuit 5, and FIG. 7 is a block diagram showing an example of a specific configuration of the signal separation circuit 61, and FIG. 8 is a block diagram showing an example of a specific configuration of the band limiting circuit 2 in the case of the embodiment. 9 is a block diagram showing an example of a specific configuration of the removal filter circuit 6 in the second embodiment of the present invention, and FIG.
FIG. 0 is a block diagram showing an example of a specific configuration of the Y filter circuit 92. FIG. 11 is a block diagram showing the configuration of the third embodiment of the present invention, FIG. 12 is a block diagram showing the configuration of the high-order DPCM encoder 9 and decoder 10, and FIG.
4,148 is a block diagram showing an example of a specific configuration of the No. 4,148. In the figure, 1 is an A/D converter, 2 is a band limiting circuit, 3 is a sub-sampling circuit, 4 is an oscillation circuit, and 5
is an interpolation circuit, 6 is a removal filter circuit, and 7 is a D/A
Converter, 8 is a clock generation circuit, 9 is a band compression encoding circuit, 10 is a band compression decoding circuit, 11 and 12 are frequency dividing circuits, 401 is a shift register, 4
11 is an adder, 413 is a multiplier, 51 is a switch, 54 is a 0 level generator, 63 is a delay circuit, 6
1 is a signal separation circuit, 62 is a band limiting filter circuit, 73 is a subtracter, 71 is a line memory, 91 is a signal separation circuit, 92 is a Y filter circuit, 93 is a C
Filter circuit, 101 is Y interpolation filter circuit, 1
42 is a quantizer, 144 and 148 are prediction filters, 145 is a code converter, 146 is an inverse code converter, 151 is a shift register, 152 is a multiplier,
154 each indicates a line memory.

Claims (1)

[Claims] 1. In an encoding/decoding device that encodes and transmits a composite color television signal obtained by frequency multiplexing color signals, the sampling frequency s is lower than 2sc (sc is the subcarrier frequency of the color signal). and 2(m+n)/2
an encoding device comprising means for sampling a composite color television signal at a sampling frequency s such that the value is n+1·sc (m·n is a positive integer) or a value in the vicinity thereof, and the sampling frequency s The frequency characteristics are calculated from the composite color television signal sampled by
sin((m+n)π/s) (where m and n are the m,
It consists of a decoding device equipped with means for removing aliasing distortion by using a filter with frequency characteristics that can be expressed by a function that includes (same value as n) and a filter that passes a low frequency range. An encoding/decoding device characterized in that a television signal is encoded at a sampling frequency lower than the Nyquist frequency.