JP2693628B2 - Image playback method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image reproducing method for estimating the shape of an observation object using a signal wave such as a sound wave, and particularly to an image reproducing method capable of highly accurate image reproduction. It is about.

(Prior Art) Conventionally, as a technology of this kind of field, Document 1; “Oki R & D” 44 [2] (Sho 53-3) Oki Electric Industry Co., Ltd., P. 47-56, Document 2; Oki R & D ”50 [1] (Sho 58-6) Oki Electric Industry Co., Ltd., P.57-62.

FIG. 2 is a configuration block diagram showing an example of the configuration of the ultrasonic underwater imaging apparatus described in Document 1 for implementing the conventional image reproducing method.

In FIG. 2, first, when a signal such as a sine wave or a pulse wave for transmission is output from the signal generator 11, this signal becomes
The phase is controlled so that the signals of the ultrasonic waves and the like output from the wave transmitter array 14 and output from the wave transmitter array 14 are focused on a point on the observed object surface. The wave transmitter 13 converts the digital signal sent from the wave transmitter phase adjuster 12 into an analog signal, and sends the analog signal to each wave transmitter array 14. The analog signal from the transmitter 13 is, in the transmitter array 14,
It is converted into sound waves and output in water. The sound wave output from the transmitter array 14 propagates in water and is reflected by the observation object plane. The sound wave as the reflected wave is received by the wave receiver array 15 and converted into an analog electric signal. Subsequently, the analog signal is converted into a digital signal in the wave receiver 16, and the FFT signal processor 17 performs spatial processing by FFT (Fast Fouier Transformation) on the digital signal. The spatially processed digital signal is displayed on the display 18 as a reproduced image.

FIG. 3 is a configuration block diagram showing an example of the configuration of another ultrasonic underwater image device described in the above-mentioned Document 2 for implementing the conventional image reproducing method.

This ultrasonic underwater image device includes a signal generator 21, a wave transmitter phaser 22, a wave transmitter 23, a wave transmitter array 24, and a wave receiver array 2.
5, the configuration of the wave receiver 26 and the display 28 is the signal generator 11, the wave transmitter phaser 12, the wave transmitter 13, and the wave transmitter array shown in FIG.
14, the wave receiver array 15, the wave receiver 16 and the display 18 are the same in configuration, and only the wave receiver phaser 27 is a different component from FIG.

In the phase rectifier 27 for wave receiver, the phase and amplitude of the received sound wave are controlled to form a standby beam.
As a result, the product of both beam patterns becomes a total beam pattern, and this total beam is scanned to reproduce an image from the received wave level.

(Problems to be Solved by the Invention) However, the image reproducing method in the ultrasonic underwater imaging apparatus having the above configuration has the following problems.

In the image reproduction method of Reference 1, when spatial processing is performed on a digital signal, processing is performed using FFT. In this FFT, the estimated resolution of the azimuth depends on the number of receivers. Therefore, in order to obtain a high-resolution image, the receiver array 15
There was a problem that I had to increase the number of.

In the image reproducing method of Document 2, since the scanning resolution is the direct resolution, there are many scanning points and a great amount of time is required to obtain a highly accurate image. Further, when the directivity of the transmission / reception beam is not sufficiently narrow, there is a problem that an erroneous image is displayed.

Due to these points, it was difficult to obtain a highly accurate image.

The present invention provides an image reproducing method that solves the problem of the above-mentioned conventional technique that it is difficult to obtain a highly accurate image.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an image reproducing method, in which a signal wave such as a sound wave or a radio wave is transmitted from a wave transmitter array toward an object to be observed. The reflected wave from the object is received by the receiver array, the spatial frequency spectrum of the reflected wave at any time is obtained by a linear prediction method such as the maximum entropy method (hereinafter referred to as MEM), and the time of the spatial frequency spectrum is calculated. Taking the average, while controlling the amplitude and phase of the signal wave and scanning the directivity of the transmitter array, the spatial frequency spectrums that have been time-averaged are superposed to obtain the intensity of the spatial frequency spectrum. The intensity is converted into a grayscale display so that the image of the observation object is reproduced.

(Operation) Since the present invention configures the image reproducing method as described above, when the signal wave transmitted from the wave transmitter array is reflected by the observation object and the reflected wave arrives, the reflected wave is received by the wave receiver array. Is received by. From the received reflected wave, the spatial frequency spectrum at any time is obtained by the linear prediction method,
In order to suppress the spectrum variation due to the phase difference of the reflected wave, the time average of the spectrum is taken and the arrival direction of the reflected wave is obtained. Next, while scanning the directivity of the transmitter array, the time-averaged spatial frequency spectra are overlapped to obtain the intensity of the spectra, and this intensity is converted into a grayscale display to estimate the shape of the observation object. It

(Embodiment) FIG. 1 is a configuration block diagram of an ultrasonic underwater image device for carrying out an image reproducing method according to an embodiment of the present invention.

This ultrasonic underwater imaging device includes a transmitter 50 and a receiver 60. The transmission unit 50 includes a signal generator 51, a wave transmitter phaser 52, a digital / analog converter (hereinafter, referred to as a D / A converter) 53, a transmission frequency converter 54, and a wave transmitter array 55. These are sequentially connected.

The signal generator 51 has a function of generating a signal such as a sine wave, a pulse wave, or a chop signal to be transmitted to the observation object, and the wave transmitter phaser 52 is a signal output from the wave transmitter array 55. It has the function of controlling the amplitude and phase of waves. The D / A converter 53 is a circuit that converts the digital signal output from the wave transmitter phaser 52 into an analog signal. The transmission frequency converter 54 has a function of converting the output of the D / A converter 53 into a high frequency, and as shown in FIG. 4, a carrier signal generator 54a for generating a carrier signal of an angular frequency ω _C and , Multiplier 5
4b and a bandpass filter 54c. The wave transmitter array 55 has a function of converting an electric signal sent from the transmission frequency converter 54 into a sound wave which is a signal wave by a speaker of each array and outputting the sound wave into water.

The receiver 60 includes a receiver array 61, a reception frequency converter 62,
An analog / digital converter (hereinafter referred to as A / D converter) 63, a spatial signal processor 64, and a display 65,
These are sequentially connected.

The wave receiver array 61 has a function of converting the received sound wave (reflected wave) into an electric signal by the microphone of each array and sending the electric signal to the reception frequency converter 62. The reception frequency converter 62 has a function of converting the output of the receiver array 61 into a low frequency, and as shown in FIG. 5, a carrier signal generator 62a for generating a carrier cosine signal of an angular frequency ω _C , Multipliers 62b and 62e, low-pass filters 62c and 62f, and phase shifter 62
It consists of d. A / D converter 63 is a reception frequency converter
The analog signal output from the 62
It has the function of converting to a digital signal after passing through a low-pass filter with a cutoff frequency of 1/2 or less. The spatial signal processor 64 has a function of performing spatial processing on the digital signal. The display device 65 has a function of displaying a two-dimensional image for the observer to see. Further, the spatial signal processor 64, as shown in FIG. 6, uses a MEM to obtain a spatial frequency spectrum of the output of the A / D converter 63, and a MEM analysis unit 64a and a time average value of the spatial frequency spectrum. A time averaging unit 64b, a spatial synthesizing unit 64c that superimposes temporally averaged spectra, a grayscale converting unit 64d that transforms the intensity of the spectrum obtained by the processing result of the spatial synthesizing unit 64 into a grayscale display, and a grayscale display The image processing unit 64e that performs image processing such as edge extraction and filtering on the generated image.

An image reproducing method of the present invention will be described using the ultrasonic underwater imaging device configured as described above.

First, in the signal generator 51, an acoustic wave signal for transmitting to the observation object is generated, and the acoustic wave signal is transmitted to the wave transmitter phaser.
Send to 52. The wave transmitter phaser 52 controls the amplitude and phase of the wave transmission signal output from each wave transmitter array 55 so that the amplitude and phase of the sound wave match at one point on the surface of the observation object to be observed. To do. For example, if the focus of the transmitted signal is set on the position vector P, the amplitude and phase value wi applied to the i-th transmitter array 55 at the position vector Si is wi = | p-si | exp (jω | p−si | / v) where v is the speed of the sound wave, ω is the angular frequency of the sound wave (1), and the sound wave transmitted from the i-th transmitter array 55 is received at the position vector p. ri (p) is ri (p) = wi * (a / | p-si | * exp (j [omega] (t- | p-si | / v)) = a * exp (j [omega] t + b) where a; The amplitude of the signal b; the initial phase of the transmitted signal becomes (2) and has a value that does not change depending on the position of the transmitter array 55. In other words, in the wave form device 52 for the wave transmitter, each wave transmitter array is used.
In 55, the value shown in the above equation (1) and the signal generator 51
Performs signal processing that takes the product of the signals sent from.

The digital signal which is the output of the phase adjuster 52 for the transmitter is D /
It is input to the A converter 53, converted into an analog signal, and passed through a low-pass filter. The transmission frequency converter 54 includes an output of the D / A converter 53 and a carrier signal generator 54 in the multiplier 54b.
The product of the carrier signal (a sine wave) from a is taken, and the result is passed through a bandpass filter 54c to be converted into a high frequency and sent in parallel to each transmitter array 55. That is, the product signal a (t) of the output α · cos (jωt−β) of the D / A converter 53 and the carrier signal of the angular frequency ω _c output from the carrier signal generator 54a is a (t) = α · cos (ωt-β ) · cos (ω c t-γ) α / 2 · (cos ((ω c -ω) t + β-γ) + cos ((ω c + ω) t-β-γ) ...... (3)

If the central angular frequency of the bandpass filter 54c is ω _c + ω, the first term of the above equation (3) is removed, so that the output signal is b (t) = α / 2 · cos ((ω _c + ω ) T-β-γ) (4) and the frequency is converted.

The electric signal frequency-converted by the transmission frequency converter 54 is input to the wave transmitter array 55, converted into a sound wave, and output in water.

The sound wave transmitted by the wave transmitter array 55 propagates in water and is reflected by the observation object plane. The sound wave as the reflected wave is received by the wave receiver array 61 and converted into an analog electric signal. The analog electrical signal is received frequency converter
It is sent to 62 and converted to a lower frequency. That is, the multiplier
The output αcos ((ω _c + ω) t of the receiver array 61 by 62b
-Β) and the angular frequency ω generated by the carrier signal generator 62a
The product of _{c and} the carrier cosine signal is taken, and the result is c (t)
And At the same time, the output from the multiplier 62d is α cos ((ω _c +
ω) t−β) and the cosine signal obtained by (−π / 2) phase shift by the phase shifter 62d, and the result is d
(T). These c (t), d (t ) is, c (n) = αcos ( (ω c + ω) t-β) · cos (ω c t-γ) = α / 2 · (sin ((2ω c + ω) t-β-γ) + cos (ωt-β + γ)) ...... (5) d (t) = αcos ((ω c + ω) t-β) · sin (ω c t-γ) = α / 2 · (cos to become _{((2ω c + ω) t} -β-γ) + sin (ωt-β + γ)) ...... (6).

If this signal is passed through bandpass filters 62c and 62f,
The first terms of equations (5) and (6) are removed, and the output signal is e (t) = α / 2 · cos (ωt−β + γ) (7) f (t) = α / 2 · sin (ωt−β + γ) (8), which is converted to a low frequency.

After that, the low frequency analog signal output from the reception frequency converter 62 is converted into a digital signal by the A / D converter 63.

The spatial signal processor 64 performs spatial processing on the digital signal. First, the MEM analysis unit 64a obtains a spatial frequency spectrum at an arbitrary time. Next, the time averaging unit 64d calculates the time average of the spectrum in order to suppress the spectrum fluctuation due to the phase difference of the received signal. Further, while scanning the beam of the transmitter array 55, the time-averaged spectra are corrected in the arrival angle by the scanning angle and overlapped by the space synthesis unit 64c.

Then, the intensity of the obtained spectrum is converted into the intensity conversion unit 64d.
At, the image is converted into a grayscale display, the grayscale-displayed image is subjected to image processing by the image processing unit 64e, and then sent to the display unit 65. The display 65 was regenerated to show it to the observer.
Display a three-dimensional image.

In order to show the advantages of the present embodiment, the results of characteristic comparison between the image reproducing method disclosed in Document 1 which is a conventional technique and the image reproducing method disclosed in the present embodiment will be described below.

FIG. 7 is an installation condition diagram of a characteristic evaluation test showing a positional relationship between an array for characteristic evaluation and an observed object.

In FIG. 7, the array has both transmission and reception and is omnidirectional, and 64 arrays are arranged on a straight line at 5.4 mm intervals. The frequency of the transmitted signal is a 384 KHz sine wave,
Q1 and Q2 have a width of 19.5 mm, and two of them with a width of 200 mm are arranged in parallel with the array at a distance of 2 m from the center of the array.

When the characteristics are evaluated under the above-mentioned installation conditions, the result of the conventional method of Document 1 is as shown in FIG. 8, and the result of the method of the present embodiment is as shown in FIG. FIG. 9 is a diagram showing an output of the space synthesis unit 64c in FIG. 6, and FIG. 8 is a diagram showing an output of an equivalent signal in the conventional document 1. The line segments q1 and q2 and the line segment q drawn in the figure
Observed objects exist in each range of 3, q4.

In both methods, the spectrum in the direction in which the observed object is present is strong. However, in the present embodiment shown in FIG. 9, the difference between the height of the spectrum of the line segments q1, q2, q3, q4 indicating the existence of the observed object and the other directions is larger. Therefore, the output after processing this output by the grayscale conversion unit 64d is clearly clearer in the reproduced image according to the present embodiment.

Further, in the above-described embodiment, since the MEM is used to calculate the spatial frequency spectrum of the received sound wave, high resolution can be obtained in spectrum estimation.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. For example, there are the following modifications.

(A) In the above embodiment, the D / A converter 53 is provided, but it may be omitted if analog signal processing is performed in the signal generator 51 and the wave transmitter phaser 52.

(B) In the above embodiment, the bandpass filter 54c is provided in the transmission frequency converter 54, but it may be omitted if the output of the D / A converter 53 is a complex signal.

(C) Although the signal wave in the above embodiment is a sound wave, it may be a radio wave, for example.

(D) In the above embodiment, the signal wave is transmitted in water, but it may be transmitted in the air.

(E) In the above embodiment, the reception frequency converter 62 and the A / D converter 63 are sequentially provided on the output side of the wave receiver array 61,
As long as the frequency of the received sound wave is within the range in which the A / D converter 63 operates normally, the installation order of the reception frequency converter 62 and the A / D converter 63 may be exchanged.

(F) In the above embodiment, MEM was used as the linear prediction method, but the present invention is not limited to this, and the same effect as in the above embodiment can be expected by using the autocorrelation method or the like.

(Effect of the Invention) As described in detail above, according to the present invention, a signal wave is transmitted from a wave transmitter array toward an observation object, and a reflected wave from the observation object is received by a wave receiver array. Since the spatial frequency spectrum of the reflected wave is obtained by the linear prediction method and the time average of the spatial frequency spectrum is obtained, the arrival direction of the reflected wave can be accurately obtained. After that, the temporally averaged spatial frequency spectra are overlapped to obtain the intensities of the spectra, and the intensities are converted into a grayscale display to reproduce the image of the observation object. The position, number, shape, etc. of an arbitrary observation object can be estimated in time, and high-accuracy image reproduction becomes possible. In addition, since the directivity of the transmitter array is scanned by controlling the amplitude and phase of the signal wave, any directivity can be realized with a small number of transmitter arrays, and the device configuration can be further simplified.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an ultrasonic underwater imager according to an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a conventional ultrasonic underwater imager, and FIG. 3 is another conventional ultrasonic underwater imager. 4 is an internal configuration block diagram of the transmission frequency converter 54 in FIG. 1, FIG. 5 is an internal configuration block diagram of the reception frequency converter 62 in FIG. 1, and FIG. 1 is a block diagram of the internal configuration of the spatial signal processor 64 in FIG. 1, FIG. 7 is a diagram of installation conditions of a characteristic evaluation test showing a positional relationship between an array for characteristic evaluation and an observation object, and FIG. FIG. 9 is a diagram showing the results, and FIG. 9 is a diagram showing the characteristic evaluation results of the examples of the present invention. 51 …… Signal generator, 52 …… Transponder phaser, 54 …… Transmission frequency converter, 55 …… Transmitter array, 61 …… Receiver array, 62 …… Reception frequency converter, 63 …… A / D converter, 64…
... Spatial signal processor, 64a ... MEM analysis section, 64b ... Time averaging section, 64c ... Spatial synthesis section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Fukasawa 1-7-12 Toranomon, Minato-ku, Tokyo Oki Denki Kogyo Co., Ltd. (56) Reference JP-A-61-187606 (JP, A) JP JP-A-60-501874 (JP, A) JP-A-63-19133 (JP, A) JP-A-2-500464 (JP, A) Practical application Sho-63-90178 (JP, U)

Claims (2)

(57) [Claims] 1. A signal wave is transmitted from a wave transmitter array to an observed object, a reflected wave from the observed object is received by a wave receiver array, and an arbitrary time of the reflected wave is obtained by a linear prediction method. Of the spatial frequency spectrum, the time average of the spatial frequency spectrum is obtained, the amplitude and the phase of the signal wave are controlled, and the directivity of the transmitter array is scanned to obtain the spatial averaged frequency spectrum. An image reproducing method comprising: superimposing the spatial frequency spectrum to obtain an intensity, converting the intensity into a grayscale display, and reproducing an image of the observation object. 2. The image reproducing method according to claim 1, wherein the signal wave is a sound wave or a radio wave, and the linear prediction method is
Image reproduction method with maximum entropy method.