JPH0779250B2 - Subband filter and subband coding method - Google Patents

Description

The present invention relates to a subband coding system used for digital transmission of high-definition image signals, and an input digital signal in a plurality of band signals in the subband coding system. It relates to a subband filter that is divided into.

[Conventional technology]

The subband coding method is a method in which an input signal is divided into a plurality of band signals by a subband filter (band division filter), and each band signal is independently coded by an optimum method and transmitted. The coding method may be, for example, differential PCM (DPCM) or other predictive coding method, or DCT.
(Discrete Cosine Transform) Other transform coding methods are used.

A conventional sub-band filter used for band division in such a sub-band coding method is a quadrature mirror filter (QMF: Quadrarure Mirror
lter) or perfect reconstruction low-order filter (SSKF: S
ymmetric Shork Kemel Filter) is used.

FIG. 5 is a block diagram showing a configuration example of a conventional subband filter using a second-order perfect reproduction type filter.

In the figure, an input signal (X (t)) 51 is a digital signal converted by an analog / digital converter (A / D converter) not shown. When the 8-bit A / D converter is used, the input signal (X (t)) 51 takes an integer value in the range of 0 to 255.

The input signal (X (t)) 51 is a multiplier 52 ₁ that multiplies a coefficient of 1.0.
Input to the input signal (X
(T-1)) is input to the multiplier 52 ₂ which multiplies the coefficient 1.0. The outputs of the multipliers 52 ₁ and 52 ₂ are added by the adder 54 ₁ and taken out as a low frequency signal (L (t)) 55. That is, the multipliers 52 ₁ , 52 ₂ , the delay circuit 53, and the adder 54 ₁ output coefficient values (1,
The low pass filter (LPF) 56 of 1) is configured.

Further, the input signal (X (t)) 51 is input to a multiplier 52 ₃ for multiplying the factor of 1.0, further input signal via a delay circuit 53 (X (t-1) ) is multiplied by a coefficient -1.0 multiplication Input to the device 57. The outputs of the multipliers 52 ₃ and 57 are added by the adder 54 ₂ and taken out as a high frequency signal (H (t)) 58. That is, the multipliers 53 ₃ and 57, the delay circuit 53 and the adder 54 ₁ output the coefficient value (1,
A high pass filter (HPF) 59 of -1) is configured.

Such a second-order perfect reproduction type sub-band filter is
Two consecutive input signal sequences X (t) and X (t-
1) From L (t) = X (t) + X (t-1) H (t) = X (t) -X (t-1), the low frequency signal (L (t)) 55 and the high frequency signal are obtained. This is a configuration in which the range signal (H (t)) 58 is divided and output.

Although not shown, each signal is down-sampled (decimated) to 1/2, independently encoded, and transmitted to the transmission line.

On the reception (decoder) side, restoration processing is performed by the subband synthesis filter corresponding to the transmission (coder) side subband filter.

FIG. 6 is a block diagram showing a configuration example of a conventional subband synthesis filter.

In the figure, a low-frequency signal (L (t)) 61 that has undergone decoding processing corresponding to encoding on the transmission side is represented by multipliers 62 ₁ and 62 with a coefficient of 0.5.
Entered in ₂ . Similarly, the decoded high frequency signal (H
(T) 63 is input to the multiplier 62 _{3 having a} coefficient of 0.5 and the multiplier 64 having a coefficient of −0.5. The outputs of multipliers 62 ₁ and 62 ₂ are adders
Is added at 65 _1, the output of the multiplier 62 ₂ and the multiplier 64 are added by the adder 65 ₂ is input to the switch circuit 66, respectively. The switch circuit 66 switches at a predetermined timing and multiplexes two signals to obtain an output signal 67.

Such a sub-band synthesis filter is used for high frequency signals (H
(T)) and the low frequency signal (L (t)) X (t) = 0.5 * {L (t) + H (t)} X (t-1) = 0.5 * {L (t) -H (t )} Is used to reproduce the signal sequences X (t) and X (t-1).

[Problems to be Solved by the Invention]

As for the sub-band coding method, the optimum coding method can be selected independently for each band signal, so if the visually important components are concentrated in the low-frequency signal such as an image signal, that characteristic is used. As a result, the coding bit rate of the high frequency signal is reduced and the overall coding bit rate can be reduced.

By the way, in order to realize high-quality coding, it is necessary to reduce the coding distortion of each band signal as much as possible, but if a code code is assigned to each level that the band signal can take, it will be completely distorted in coding. It is known that transmission can be performed without causing

In addition, at this time, a short code to a high frequency level,
If the entropy coding that allocates a long code to a level with low occurrence frequency is applied, the coding bit rate can be reduced.

On the other hand, when the conventional sub-band filter is used, even if the number of levels that can take an input signal is 256 (0 to 255), each band signal (low band signal (L (t)) and high band signal ( The number of levels that H (t) can take is 511 (0 to 510,-
255-255), which is double the size.

Therefore, when a code code is assigned to each possible level of each band signal, entropy is large, and even if the coding bit rate is reduced according to the bias of the signal distribution, the effect is canceled out. There was a point.

It is an object of the present invention to provide a subband filter and a subband coding method that reduce the entropy of a band signal to be separated and that can reduce the overall coding bit rate.

[Means for Solving the Problems]

FIG. 1 is a block diagram showing the basic configuration of the present invention.
Incidentally, FIG. 1 (a) is a basic configuration of the subband filter according to claim 1 and claim 2, and FIG.
Is a basic configuration of the subband coding method according to claims 3 and 4.

In the invention according to claim 1, the coefficient value is (1, 1). 2
It has a second low-pass filter and a second-order high-pass filter having a coefficient value of (1, -1), and inputs a predetermined integer digital signal into each of the low band and the high band. In the sub-band filter that divides into a signal and outputs, when each band signal has an odd value, band signal entropy reducing means for converting at least one band signal into a predetermined even value is provided.

According to a second aspect of the present invention, in the subband filter according to the first aspect, the band signal entropy reducing means converts at least one band signal into a predetermined odd value when each band signal has an even value. It is a composition.

In the invention according to claim 3, the coefficient value is (1, 1). 2
It has a second low-pass filter and a second-order high-pass filter having a coefficient value of (1, -1), and inputs a predetermined integer digital signal into each of the low band and the high band. A sub-band filter that divides into a signal and outputs, a coding means that encodes each band signal by a corresponding coding method, multiplexes and transmits, and a demultiplexing received signal that corresponds to the coding method. Decoding means for decoding and outputting as respective low band and high band signals, and a sub-band synthesis filter for taking in each decoded band signal and reproducing a digital signal by processing corresponding to the sub-band filter In the sub-band coding method, the sub-band filter has a band signal signal which, when each band signal has an odd value, converts one of the band signals into a predetermined even value and outputs it to the coding means. The sub-band synthesis filter includes a tropy reducing means, and the sub-band synthesis filter converts one band signal to the original odd value when the other band signal takes an odd value with respect to the even band signal. It is configured including means.

According to a fourth aspect of the present invention, in the subband coding method according to the third aspect, the band signal entropy reducing means of the subband filter outputs one of the band signals when each band signal has an even value. It is configured to convert to a predetermined odd value and output to the encoding means, the band signal restoration means of the sub-band synthesis filter, when the other band signal to one of the odd band signal takes an even value, The configuration is such that one band signal is converted to the original even value.

[Work]

In the sub-band filter of the present invention, the band signal entropy reducing means converts an odd value of at least one band signal into a predetermined even value or an even value into a predetermined odd value.

That is, at least one of the band signals can take only an even value or an odd value, the number of levels can be reduced by half in encoding, and entropy can be reduced.

By the way, the input signal sequence X (t) of the subband filter
And one of X (t-1) is even and the other is odd, the low-frequency signal (L
(T)) and the high frequency signal (H (t)) are always odd numbers.

When the input signal sequences X (t) and X (t-1) are both even or odd, the low-frequency signal (L (t)) and high-frequency signal (L (t)) corresponding to the sum and difference thereof are H
Both (t) are always even numbers.

In the sub-band coding method of the present invention, the band signal entropy reducing means of the sub-band filter converts all one band signal into an even value or an odd value for coding. In the band signal restoration means of the sub-band synthesis filter, the other band signal transmitted in the same state is monitored and the above-mentioned property is utilized to make one band signal even-numbered or odd-numbered depending on its numerical state. Perform the operation to return to the original numerical value.

That is, the original band signal can be accurately reproduced in decoding, and one band signal can take only even values or odd values, so that the number of levels can be reduced by half in encoding to achieve entropy. Can be reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing the configuration of an embodiment of the subband filter of the present invention.

In the figure, the configuration of a low-pass filter and a high-pass filter surrounded by a chain line, its input signal (X (t)) 51,
Further, the low-frequency signal (L (t)) 55 and the high-frequency signal (H (t)) 58 that are output are the same as in the conventional configuration shown in FIG.

The band signal entropy reducing means provided in the subband filter of the present embodiment, when the low band signal (L (t)) 55 and the high band signal (H (t)) 58 are odd numbers, the low band signal (L). (T) is characterized by adding 1 or -1 to 55 to make it even.

By the way, when one of the input signal sequences X (t) and X (t−1) is an even number and the other is an odd number, the low-frequency signal (L
(T)) 55 and high frequency signal (H (t)) 58 are both odd numbers. Therefore, here, the odd number discriminating circuit 21 detects whether or not the high frequency signal (H (t)) 58 is an odd number, and when it becomes an odd number, 1 or -1 is output, and an even number. If it becomes 0, 0 is output. The adder 23 is
The output value of the odd number discriminating circuit 21 is added to the low frequency signal (L (t)) 55 and converted into the low frequency signal (L '(t)) 25 which takes only even values.

It should be noted that either 1 or -1 may be added when converting the low-frequency signal (L (t)) 55 having an odd value into an even number, but one is set in advance in conformity with the subband synthesis filter. I'll do it.

As described above, by providing the band signal entropy reducing means in the sub-band filter, the low band signal (L (t)) of each band signal can be set to an even value only in this embodiment. Therefore, the number of levels that the low frequency signal (L (t)) can take is 512/2 = 256, which can be reduced to about half of the conventional level number 511 of the low frequency signal (L (t)). , It is possible to significantly reduce the entropy.

By the way, the embodiment shown above is a configuration example in which the low-frequency signal (L (t)) is made even, but the same is true when the high-frequency signal (H (t)) is made even. In the case of an image signal, the effect of making the high-frequency signal (H (t)) even is smaller than that of making the low-frequency signal (L (t)) even, because of its characteristics. (L (t)) is the target of even numbering.

On the other hand, even if the even value of one band signal is made odd, the entropy reduction is the same, and the effect of the present invention can be obtained.

FIG. 3 is a block diagram showing an embodiment configuration of the subband synthesis filter.

In the figure, the basic components of the sub-band synthesis filter surrounded by the alternate long and short dash line, and the low-frequency signal (L (t)) input thereto
61, the high frequency signal (H (t)) 63, and the output signal 67 are the same as those in the conventional configuration shown in FIG.

The band signal restoration means provided in the sub-band synthesis filter of the present embodiment, when the high frequency signal (H (t)) 63 transmitted in the same state is an odd number, the low frequency signal (L
(T)) is also an odd number, and is characterized by a configuration in which 1 or -1 is added to the low-frequency signal (L '(t)) 31 having an even value to return it to the original odd value.

That is, the odd number discrimination circuit 33 determines that the high frequency signal (H (t))
It is detected whether 63 is an odd number, and when it becomes an odd number, 1 or -1 is output corresponding to the odd value discrimination circuit 21 of the subband filter, and when it becomes an even number, 0
Shall be output. The adder 35 outputs a low frequency signal (L '
(T)) 31 is added with the output value of the odd number discriminating circuit 33, and when the high frequency signal (H (t)) 63 takes an odd value, the low frequency signal (L (L ( t)) 61 is obtained.

In this way, in the subband coding method that uses pairs in the subband filter and the subband synthesis filter, one of the band signals is made even or odd at the transmission (coder) side and transmitted as it is at the reception (decoder) side. From the state of the other band signal to be converted, the even or odd band signal can be converted into the original numerical value.

That is, the sub-band coding method of the present invention can accurately reproduce the original band signal and can significantly reduce the coding bit rate when coding one band signal, and It is possible to reduce the overall coding bit rate.

By the way, in the above-mentioned embodiment, only the low frequency signal (L (t)) having an odd value (even value) is made even (odd).
1 or -1, which is the minimum value of the numerical values for adding, and if the error can be tolerated on the receiving side, the band signal restoring means as shown in FIG. Need not be added. Also,
In such a case, the sub-band filter does not need to limit the band signal to be even (odd) to only one, and both the low band signal (L (t)) and the high band signal (H (t)). Can be made even (odd) to further reduce the encoding bit rate.

Further, when making one band signal even or odd by the sub-band filter, it is necessary to determine whether the band signal has an even value or an odd value, but in the configuration shown in FIG. Signal sequences X (t) and X (t-
1) When one is an even number and the other is an odd number, the fact that each band signal is an odd number is used to take advantage of the high band signal (H
(T)) is being monitored.

However, as shown in FIG. 4 (a), it is possible to monitor one of the band signals which are made even or odd, or, as shown in FIG. 4 (b), the odd number discriminating circuit 41 is continuous. Two input signal sequences X (t) and X (t-1)
Is monitored directly, and when only one of them is an odd number, the band signal takes an odd value, the same is true. In the latter case, to detect that the band signal has an even value, two consecutive input signal sequences X (t) and X (t-1) are both even or odd. Determine that.

In any case, the configuration of the subband synthesis filter is the same as that shown in FIG. 3, and can be handled by the band signal restoring means according to the subband filter.

〔The invention's effect〕

As described above, the subband filter of the present invention can significantly reduce the entropy of at least one band signal.

That is, by using this subband filter, it is possible to reduce the overall coding bit rate.

Further, the sub-band coding system of the present invention is made even (odd) by adding band signal entropy reducing means to the conventional sub-band filter and adding band signal restoring means to the sub-band synthesis filter. It is possible to accurately reproduce the band signal of 1 and the entropy of one band signal can be significantly reduced.

That is, it is possible to reduce the overall coding bit rate while maintaining high quality characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention. FIG. 2 is a block diagram showing the configuration of an embodiment of the subband filter of the present invention. FIG. 3 is a block diagram showing an embodiment configuration of a subband synthesis filter. FIG. 4 is a block diagram showing the configuration of another embodiment of the subband filter of the present invention. FIG. 5 is a block diagram showing a configuration example of a conventional subband filter using a second-order perfect reproduction type filter. FIG. 6 is a block diagram showing a configuration example of a conventional subband synthesis filter. 21, 33, 41 …… Odd value identification circuit, 23, 35 …… Adder, 2
5, 31 ... Low-frequency signal (L '(t)), 51 ... Input signal (X (t)), 52, 57 ... Multiplier, 53 ... Delay circuit, 54
…… Adder, 55 …… Low-pass signal (L (t)), 56 …… Low-pass filter (LPF), 58 …… High-pass signal (H (t)), 5
9 …… High-pass filter (HPF), 61 …… Low-pass signal (L
(T)), 62, 64 ... Multiplier, 63 ... High frequency signal (H
(T)), 65 ... Adder, 66 ... Switch circuit, 67 ...
Output signal.

Claims (4)

[Claims] 1. A second-order low-pass filter having a coefficient value of (1, 1) and a second-order high-pass filter having a coefficient value of (1, -1), which are input. In a sub-band filter that divides a predetermined integer digital signal into low-band and high-band signals and outputs them, at least one band signal has a predetermined even value when each band signal has an odd value. A subband filter characterized in that it is provided with a band signal entropy reducing means for converting to. 2. The subband filter according to claim 1, wherein the band signal entropy reducing means is configured to convert at least one band signal into a predetermined odd value when each band signal has an even value. Sub-band filter characterized by the following. 3. A second-order low-pass filter having a coefficient value of (1, 1) and a second-order high-pass filter having a coefficient value of (1, -1) are input. A sub-band filter that divides a predetermined integer digital signal into low-band and high-band band signals and outputs the signals, and coding means that codes each band signal by a corresponding coding method, multiplexes the signals, and transmits the signals. Decoding means for demultiplexing the received signal, decoding corresponding to the above-mentioned coding method, and outputting as respective band signals of the low band and the high band; In a sub-band coding system including a sub-band synthesis filter that reproduces the digital signal by a process corresponding to the filter, the sub-band filter includes one of the sub-band filters when one of the band signals has an odd value. The sub-band synthesis filter includes a band signal entropy reducing unit that converts the band signal into a predetermined even value and outputs the band signal to the encoding unit. A subband coding method, comprising band signal restoring means for converting the one band signal into an original odd value when taking a numerical value. 4. The sub-band coding method according to claim 3, wherein the band signal entropy reducing means of the sub-band filter sets one band signal to a predetermined odd value when each band signal has an even value. And outputs to the encoding means, the band signal restoring means of the sub-band synthesis filter, when the other band signal with respect to the one of the odd band signal takes an even value, Sub-band coding method characterized in that the band signal is converted to the original even value.