JP3229052B2 - Data compression circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data compression circuit suitable for a Holter system (long-time electrocardiograph).

[0002]

2. Description of the Related Art Conventionally, it has been known to record an electrocardiographic waveform signal from an electrocardiographic measuring device on a magnetic tape or the like in the form of an analog signal. However, there are problems such as poor reproduction accuracy due to head characteristics and the like. Therefore, it has been conventionally proposed to record an electrocardiographic waveform signal on a magnetic tape, a semiconductor memory or the like in the form of a digital signal in order to improve the reproduction accuracy.

[0003]

By the way, the Holter system continuously records electrocardiographic waveform signals for, for example, 24 hours. The amount of recorded data is very large, and a recording medium corresponding to the amount is required. problems such that there is.

Accordingly, an object of the present invention is to provide a data compression circuit capable of greatly reducing the amount of data.

[0005]

According to the present invention, there is provided an adjacent data difference detecting means for detecting a difference between adjacent data of input data, and when the most significant bit of output data of the adjacent data difference detecting means is a logical one. Calculates the two's complement, shifts one bit to the upper bit side, adds a sign bit of logic 1 to the least significant bit, and when the most significant bit of the output data is logic 0, adds 1 to the upper bit side A code bit shifting means for shifting the bit and adding a sign bit of logic 0 to the least significant bit; and classifying the output data of the code bit shifting means into a plurality of bit data having different effective bits, thereby performing a data common processing Input to the data sharing means and the adjacent data difference detecting means.
Input data, adjacent data supplied to the sign bit moving means.
Data output means or data sharing means
For the output data of the supplied sign bit moving means,
When only the central data of the three consecutive data of the input data is different , a data correcting means for substantially performing the same processing of the central data as the preceding and succeeding data is provided.

[0006]

In the present invention, the adjacent data difference detecting means 2
1, sign bit moving means 22 and data correcting means 23
After the similar data is processed so as to increase, similar data is put together by the data sharing means 24 and the data is shared, so that the data amount can be significantly reduced. Further, since similar data is output as compressed data from the data sharing means 24, 100% of the Huffman method or LZW (Lample-Ziv-Welch) method is used.
When data is compressed using a decompressible compression method, the compression efficiency can be increased.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. This example is an example applied to a recording system of a Holter system for recording an electrocardiographic waveform signal by a digital VTR.

FIG. 1 is a block diagram showing the overall configuration of the Holter system. In the figure, an analog electrocardiographic waveform signal SH output from an electrocardiographic waveform measuring device (not shown)
Is supplied to the A / D converter 1 and the sampling frequency is 2
It is converted to a digital signal at 50 Hz and 10 bits per sample. The data of each sample is treated as 16-bit data in the following processing.

The electrocardiographic waveform data DH output from the A / D converter 1 is subjected to data compression processing by a data compression circuit 2 and then supplied to a digital VTR 3 for recording. The data compression circuit 2 includes a microcomputer (hereinafter, referred to as a “microcomputer”), and the data compression processing is performed by the microcomputer as software.

FIG. 2 shows the configuration of the data compression circuit by functional blocks. In the figure, the electrocardiographic waveform data DH output from the A / D converter 1 is supplied to the adjacent data difference detecting means 21. The detecting means 21 detects a difference between adjacent data of the data DH. In this case, when the difference is positive, the signal is output from the detection means 21 as it is, and when the difference is negative, the signal is output as a two's complement.

Next, the data DH1 output from the detecting means 21 is supplied to the sign bit moving means 22. In this moving means 22, the data DH1 (b15, b14,...,
b0 16-bit data) most significant bit (MSB) b1
Processing is performed as follows according to the logical state of 5.

That is, the most significant bit b of the data DH1
When 15 is logic 1, the 2's complement of the data DH1 is obtained, then shifted to the upper bit by 1 bit, and a sign bit of logic 1 is added to the least significant bit (LSB) b0.

For example, when the data DH1 is "FFFFH", the bit b15 is a logical one, and when the two's complement is obtained, it becomes "0001H". If a bit is added, it becomes "0003H". Here, "H" indicates hexadecimal display. The same applies to the following.

On the other hand, when the most significant bit b15 of the data DH1 is logic 0, the data is shifted by one bit to the higher bit side and a sign bit of logic 0 is added to the least significant bit b0.

For example, when the data DH1 is "0001H", the bit b15 is a logical 0, and after shifting by one bit to the upper bit side, adding a sign bit of a logical 0 to the bit b0 becomes "0002H".

FIG. 3 shows the correspondence between the data DH1 outputted from the detecting means 21 and the data DH2 outputted from the moving means 22.

Next, the data DH2 output from the moving means 22 is supplied to the data correcting means 23. Correction means 2
In step 3, when only the central data is different among the three consecutive data DHs output from the A / D converter 1, the central data is made substantially the same as the preceding and succeeding data. Is performed.

For example, if the data DH2 is 0002H 000
When it is continuous with 3H, or when it is continuous with 0003H 0002H, it is set to 0000H 0000H.

As described above, when the sampling frequency in the A / D converter 1 is set to 250 Hz, the sampling frequency is 125 which is 1/2 of the sampling frequency according to the well-known sampling theorem.
Hz. However, in the case of an electrocardiographic waveform, it is not considered necessary to have a frequency band up to 125 Hz.
The frequency component of z can be removed, and similar data can be increased.

Note that the above-described correction processing is performed by A / D
Of course, it can be performed on the data DH output from the converter 1 or the data DH1 output from the detection means 21. When performing on the data DH output from the A / D converter 1, for example, 03F3H 03F4
When H 03F3H continues, 03F3H 03F3H0
3F3H. Further, when the operation is performed on the data DH1 output from the detection means 21, for example, FFFFH
When 0001H and 0001H FFF
When it is continuous with FH, it is set to 0000H 0000H.

[0021]

Next, the data DH3 output from the correction means 23 is supplied to the data sharing means 24 and
Is performed.

The data DH 3 is classified into three types of data of valid 4 bits, valid 8 bits, and valid 16 bits based on the valid bits. For example, "0004
"H" and "0005H" are valid 4-bit data,
“0080H”, “0090H”, etc. are valid 8-bit data, and “0100H”, “0200H”, etc. are valid 16 bits.
Bit data. When this classification is performed, a header is placed before each type of data so that the content of each type is known.

Here, the header is composed of bits b7 to b0, for example.
Of 1 byte data. The header has the following meaning, for example. That is, 2 of “b7b6”
The bit indicates the type of data. For example,
“00” indicates valid 4-bit data, “01” indicates valid 8-bit data, and “10” indicates valid 16-bit data. In addition, the number of bit data blocks is represented by 6 bits “b5 to b0”. The number is from 01H to 3FH
(1 to 63).

The effective 4-bit data is in 8-bit units. In this case, when the same data is not continuous, the bits b15 to b8 are removed to obtain 8-bit data. When the same data continues, 8-bit data "b7 to b0" is formed as follows. That is, the continuous number of the same data is represented by the four bits “b7 to b4”. Here, 0H to FH (0 to 15) are shown, but 0 to 15 is considered to represent 1 to 16. Further, 4-bit data is represented by 4 bits of "b3 to b0".

For example, 0004H 0005H 0005H
The data of 0005H 0005H 0005H 0006H is 04H 45H 06H.

The effective 8-bit data is in 8-bit units. In this case, bits b15 to b8 are removed and 8
Bit data.

For example, 0010H 0020H 0030H
The data of 0040H 0050H 0060H is 10H 2
0H 30H 40H 50H 60H.

As described above, in the data sharing means 24,
Are performed. For example, 0004H 0005
H 0005H 0005H 0005H 0005H 0006
The data of H 0080H 0090H 0100H 0200H is 03H 04H 45H 06H 42H 80H 90H 82
H 0100H 0200H. Here, 03H, 42
H and 82H are headers.

Next, the data DH4 output from the common unit 24 is converted to a lossless compression unit 25.
Supplied to In the compression means 25, data compression processing is performed using a compression method capable of 100% expansion such as a conventionally known Huffman method or LZW (Lample-Ziv-Welch) method.
The data DH5 output from the compression means 25 is supplied to the digital VTR 3 as an output of the data compression circuit 2.

As described above, in this embodiment, the detecting means 2
1. The common means 2 is processed by the moving means 22 and the correction means 23 so that similar data is increased.
4, the similar data is put together and the data is shared, so that the data amount can be significantly reduced. Further, since similar data is output from the common unit 24 as compressed data, the Huffman method or the LZ
The compression efficiency of data compression by a compression method such as the W (Lample-Ziv-Welch) method can be increased.

For example, the output data DH of the A / D converter 1
4 is as shown in FIG. 4, the output data DH1 to DH4 of the detecting means 21, the moving means 22, the correcting means 23 and the commoning means 24 are as shown in FIGS. In this case, the input 768 bytes (see FIG. 4) become 191 bytes (see FIG. 8) by the processing of the detection means 21 to the commonization means 24, which means that 191/768 ≒ 1/4 has been compressed. In FIGS. 4 to 8 and FIG. 12 described later, the symbol “H” is not attached, but the hexadecimal display is used.

Also, the electrocardiographic waveform signal has two channels, a sampling frequency of 250 Hz, and a sample of 10 bits (actually handled as 16-bit data).
When it is 4 bytes, the number of data after compression by the data compression circuit 2 of this example is 59707 bytes, and the compression ratio is 8.8.
It was 5. However, this is a case where the LZW method is used in the lossless compression means 25.

In the reproduction system, as shown in FIG. 9, after the reproduction data of the digital VTR 3 is expanded by the data expansion circuit 4, it is converted into an analog signal by the D / A converter 5 and output. The decompression process in the data decompression circuit 4 is performed as shown in FIG.
So that the reverse processing is performed to the processing by each unit of. However, the reverse process of the correction unit 23 is omitted.

FIG. 10 shows an electrocardiogram waveform based on an electrocardiogram waveform signal which has been subjected to the compression processing of the present embodiment. The compression process does not significantly affect reproduction accuracy.

As described above, the correction means 23 does not always need to be provided. FIG. 12 shows that the output data DH of the A / D converter 1 is as shown in FIG.
2 shows output data DH4 of the data sharing means 24 when no data is provided. In this case, the input 768 bytes (see FIG. 4) are converted into 23 bits by the processing of the detecting unit 21, the sign bit moving unit 22, and the data sharing unit 24.
It becomes 9 bytes (see FIG. 12) and 239 / 768７1 /
This means that 3.2 compression has been performed.

As described above, when the correction means 23 is not provided, the compression ratio is lower than when the correction means 23 is provided. This is because the correcting means 23 is not provided, so that the commonizing means 24
It is considered that similar data is reduced in the data DH3 input to the DH3.

Although the above-described embodiment is applied to a Holter system for recording an electrocardiographic waveform signal, the present invention has many other signals, for example, a portion having a small level change like an electrocardiographic waveform signal. This is suitable for data compression processing when recording a signal.

[0039]

According to the present invention, after the similar data is processed by the adjacent data difference detecting means, the sign bit moving means and the data correcting means so as to increase the similar data, the similar data is collected by the data sharing means. Since the data is shared, the data amount can be significantly reduced. Further, since similar data is output as compressed data from the data sharing means, the Huffman method or LZ
When data compression is performed using a compression method that can expand 100%, such as the W method, the compression efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an embodiment of the present invention.

FIG. 2 is a functional block diagram illustrating a configuration of a data compression circuit.

FIG. 3 is a diagram showing a correspondence relationship between output data DH1 of an adjacent data difference detecting means and output data DH2 of a sign bit moving means.

FIG. 4 is a diagram illustrating an example of output data DH of an A / D converter.

FIG. 5 is a diagram showing output data DH1 of an adjacent data difference detecting means.

FIG. 6 is a diagram showing output data DH2 of the code bit moving means.

FIG. 7 is a diagram showing output data DH3 of the data correction means.

FIG. 8 is a diagram showing output data DH4 of the data sharing means.

FIG. 9 is a diagram showing a configuration of a reproduction system.

FIG. 10 is a diagram showing an electrocardiographic waveform based on data subjected to compression processing.

FIG. 11 is a diagram showing an electrocardiographic waveform based on data that has not been subjected to compression processing.

FIG. 12 is a diagram showing output data DH4 of a data sharing unit (without a data correction unit).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D converter 2 Data compression circuit 3 Digital VTR 21 Adjacent data difference detection means 22 Code bit movement means 23 Data correction means 24 Data sharing means 25 Lossless compression means

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03M 7/30 A61B 5/0432

Claims (1)

(57) [Claims] 1. An adjacent data difference detecting means for detecting a difference between adjacent data of input data, and, when the most significant bit of output data of the adjacent data difference detecting means is logic 1, after obtaining a two's complement. The output data is shifted by one bit to the upper bit side, and a sign bit of logic 1 is added to the least significant bit. When the most significant bit of the output data is logic 0, it is shifted by one bit to the upper bit side and a sign bit moving means for adding the sign bit of logic 0, and the data sharing means for the common processing of data classified into output data valid bit each different bit data of the code bit moving means, the The above input data input to the adjacent data difference detecting means
The adjacent data supplied to the code bit moving means.
Output data of the data difference detecting means or the above data commoning means
To the output data of the sign bit moving means supplied to
To, when only the center of the data of the three consecutive data of the input data are different, comprising: a data correcting means for processing, with the same substantially around the center of the data Data Data compression circuit.