JP7493882B2 - Image Processing Unit - Google Patents

Description

This invention relates to an image processing unit, and in particular to image processing technology for receiving radar echoes, which are reflected signals of a radar signal, and displaying the radar echoes on a monitor or the like.

There is known a radar device that is mounted on a ship and displays a radar image that shows the image of targets around the ship based on the echo signal of the radio waves emitted from the radar antenna (see, for example, Patent Document 1).

JP 2008-014874 A

Pixel enlargement is one of the image processing methods used when displaying radar echoes on a monitor or the like. This processing is used to make targets appear larger because targets close to the center of the PPI (Plan Position Indicator) look small when displayed in PPI format. In conventional pixel enlargement processing, a dilation filter (i.e., an expansion filter) is used on an image generated for display in PPI format, so that pixels are enlarged/expanded in all directions, up and down and left and right (in other words, vertical and horizontal). However, when displaying radar echoes in PPI format, the pixel closest to the aircraft is used as the reference pixel in the radar echo to measure the distance from the aircraft to the target. However, in conventional pixel enlargement processing, pixels are enlarged/expanded in all directions, up and down and left and right (vertical and horizontal), so the position of the pixel closest to the aircraft is shifted (specifically, the pixel newly added by the pixel enlargement processing becomes closest to the aircraft), and the distance to the target cannot be measured accurately.

The objective of this invention is to provide an image processing unit that can accurately measure the distance from the aircraft to a target even when pixel enlargement processing is applied.

In order to solve the above problem, the invention described in claim 1 is an image processing unit characterized by having a pixel data generation unit that performs coordinate conversion of echo data in a polar coordinate system into echo data whose positions follow a Cartesian coordinate system and correspond to pixel positions in a PPI image, a pixel expansion unit that performs pixel expansion processing on the echo data that corresponds to pixel positions in the PPI image, a pixel deletion unit that deletes pixels that are closer than the original pixels from among the pixels added by the pixel expansion processing, and an image generation unit that generates image data using data output from the pixel deletion unit.

The invention described in claim 2 is characterized in that the image processing unit described in claim 1 is incorporated into a radar device mounted on a ship.

According to the invention described in claim 1, the echo data in the polar coordinate system is transformed into echo data that corresponds to the pixel position in the PPI image, and then pixel enlargement processing is performed, and pixels closer than the original pixels are deleted. This makes it possible to accurately measure the distance from the aircraft to the target even when pixel enlargement processing is applied.

According to the invention described in claim 2, an image processing unit is incorporated into the radar device mounted on the ship, so that the distance to targets that may be an obstacle to the safe navigation of the ship (specifically, for example, other ships or ice/icebergs) can be accurately measured, and accurate information regarding the distance from the ship to the targets can be provided to ensure the safe navigation of the ship.

1 is a functional block diagram showing a schematic configuration of a radar device including an image processing unit according to an embodiment of the present invention; 4 is a flowchart showing a processing procedure in a radar device including the image processing unit of FIG. 1 . 1A is a schematic diagram for explaining an example of pixel enlargement processing, and FIG. 1B is a schematic diagram for explaining pixel deletion processing, showing a state in which the enlarged echo data after the pixel enlargement processing of FIG. 1A is expressed in an azimuth-distance orthogonal coordinate system. 10A to 10C are schematic diagrams illustrating an example of pixel enlargement processing configured by multiple stages of processing. FIG. 4 is a schematic diagram showing the deleted echo data after the pixel deletion process of FIG. 3B displayed in PPI format. 1A is a diagram showing a specific example of an image display of echo data before pixel enlargement processing, FIG. 1B is a diagram showing an image display of data after conventional pixel enlargement processing is applied to the echo data of FIG. 1A, and FIG. 1C is a diagram showing an image display of deleted echo data after pixel enlargement processing is applied to the echo data of FIG. 1A by the image processing unit.

The present invention will be described below based on the illustrated embodiment.

Figure 1 is a functional block diagram showing the schematic configuration of a radar device including an image processing unit according to an embodiment of the present invention. Figure 2 is a flowchart showing the processing procedure in a radar device including an image processing unit according to an embodiment.

A radar device is a mechanism that is mounted on a ship, for example, to transmit radar signals and receive radar echoes, which are reflected signals of the radar signals, and detects targets present around the ship based on the radar echoes. The radar device mainly comprises an antenna unit 1, an image processing unit 2, a memory unit 3, and a display unit 4.

The antenna unit 1 is a mechanism for transmitting radar signals and generating echo data, and includes a radar antenna 11, a transceiver unit 12, and an A/D converter unit 13.

The radar antenna 11 is a transceiver that wirelessly transmits (in other words, radiates) a radar signal as a pulsed radio wave and captures radar echoes (specifically, reflected signals of the radar signal), which are reflected waves of the transmitted/radiated radio wave. The radar antenna 11 scans 360° around the aircraft by repeatedly transmitting/radiating radio waves and capturing radar echoes while rotating horizontally at a predetermined horizontal rotation period and changing the direction of the front of the antenna (step S1).

The transmitter/receiver 12 is a communication circuit that has the function of generating a radar signal, transmitting the generated radar signal via the radar antenna 11, and receiving a radar echo, which is a reflected signal of the transmitted radar signal, via the radar antenna 11. The transmitter/receiver 12 transmits the radar signal at a predetermined time interval (specifically, a time interval shorter than the horizontal rotation period of the radar antenna 11) and receives and outputs the radar echo (step S2).

The A/D conversion unit 13 is a converter that has the function of converting the received radar echo, which is an analog signal, into a digital signal. The A/D conversion unit 13 sequentially converts the radar echo supplied from the transceiver unit 12 at the predetermined time interval into a digital signal and outputs an echo signal (step S3).

The echo signal output from the antenna unit 1 is associated with position information according to a polar coordinate system with the radar antenna 11 as the origin in a horizontal plane, specifically, with the actual distance r between the radar antenna 11 and the echo source, and the angle θ of the radar antenna 11 facing forward when the radar signal is transmitted. In other words, the antenna unit 1 outputs echo data associated with a position (r, θ) in the polar coordinate system.

The actual distance r to the echo source corresponding to the echo intensity at a time t after the radar signal (radio wave) is transmitted via the radar antenna 11 (in other words, the actual distance between the radar antenna 11 and the echo source; the radio wave travels the actual distance r back and forth during the time t) is calculated according to the following formula 1:
(Equation 1) r = c × t / 2
Here, r: actual distance to the echo source corresponding to the echo intensity [m]
c: speed of light [m/s]
t: Time from transmitting the radar signal to capturing the radar echo [s]
(In other words, the time elapsed since the radar signal was transmitted [s])

The front-facing angle θ of the radar antenna 11 is defined, for example, as an azimuth angle with a predetermined direction as the reference direction (i.e., 0°) and a positive direction in the planar view when the radar antenna 11 rotates horizontally. The front-facing angle θ of the radar antenna 11 changes by a predetermined angle for each series of operations of transmitting a radar signal and receiving a radar echo. In this embodiment, the front-facing angle θ of the radar antenna 11 is defined as an azimuth angle with a north direction as the reference direction (i.e., 0°) and a positive direction in the clockwise direction in the planar view.

In addition, the echo signal output from the A/D conversion unit 13 may be subjected to a predetermined signal processing as necessary. Specifically, for example, a sensitivity adjustment process or a process for removing unnecessary echoes (i.e., clutter) due to sea surface reflections, land reflections, rain and snow reflections, etc., contained in the radar echo may be performed.

The memory unit 3 is a memory element/memory circuit that has the function of storing programs and data used when executing processes related to the generation of PPI images, and is composed of, for example, a volatile memory or a hard disk.

The display unit 4 is a display device that has the function of displaying images generated by the image generation unit 24, and is configured, for example, by a liquid crystal display.

The image processing unit 2 is a mechanism for generating image data to be displayed on the display unit 4, and includes a pixel data generation unit 21, a pixel enlargement unit 22, a pixel deletion unit 23, and an image generation unit 24.

The image processing unit 2 according to the embodiment includes a pixel data generating section 21 that converts echo data in a polar coordinate system into echo data whose positions follow a Cartesian coordinate system and correspond to pixel positions in the PPI image, a pixel enlargement section 22 that performs pixel enlargement processing on the echo data that corresponds to pixel positions in the PPI image, a pixel deletion section 23 that deletes pixels that are closer than the original pixels from among the pixels added by the pixel enlargement processing, and an image generating section 24 that generates image data using the data output from the pixel deletion section 23.

The pixel data generating unit 21 is a processing circuit having a function of converting data having position information in a polar coordinate system into data having position information in a Cartesian coordinate system to generate pixel data constituting a PPI image (i.e., a radar image when radar echoes are displayed in PPI format). The pixel data generating unit 21 converts echo data having position information in a polar coordinate system output from the antenna unit 1 into echo data having position information in a Cartesian coordinate system to generate pixel data constituting a PPI image (step S4).

The Cartesian coordinate system is set as a coordinate system that represents the positions of a large number of pixels that are arranged vertically and horizontally in a grid/matrix pattern to compose an image. In this embodiment, the positions of pixels are represented according to an XY Cartesian coordinate system in which the upper left corner of the image is the origin, the horizontal direction is the X axis, and the vertical direction is the Y axis. The range of values in the X axis direction (i.e., the X coordinate value) and the range of values in the Y axis direction (i.e., the Y coordinate value) of the Cartesian coordinate system are determined, for example, based on the size of the display area of the display unit 4.

The pixel data generating unit 21 calculates the pixel position (x, y) in the PPI image, which is a position according to the XY Cartesian coordinate system corresponding to the position (r, θ) in the polar coordinate system, for each piece of echo data output from the antenna unit 1 and associated with the position (r, θ) in the polar coordinate system. In other words, the pixel position (x, y) in the PPI image is the drawing coordinate when the echo data in the polar coordinate system is displayed on the display unit 4 in PPI format. The method of converting the position (r, θ) in the polar coordinate system to the position (x, y) in the XY Cartesian coordinate system is well known, so details will be omitted, but in summary, after setting the position coordinates of the aircraft in the image, the X coordinate x can be calculated using the actual distance r (or time t) and sin θ, and the Y coordinate y can be calculated using the actual distance r (or time t) and cos θ.

The pixel data generating unit 21 outputs echo data associated with a position (x, y) in an XY Cartesian coordinate system, i.e., echo data associated with a pixel position (x, y) in the PPI image, which is a position according to the XY Cartesian coordinate system. The echo data associated with a pixel position (x, y) in the PPI image output from the pixel data generating unit 21 is, in other words, the pixel data constituting the PPI image.

The pixel expansion unit 22 is a processing circuit that has the function of performing dilation processing (i.e., enlargement/expansion processing; called "pixel expansion processing") on the pixels of the echo data that appear in the PPI image. The pixel expansion unit 22 performs pixel expansion processing on the echo data that is associated with the pixel position (x, y) in the PPI image and is output from the pixel data generation unit 21 (step S5).

The method of pixel enlargement processing by the pixel enlargement unit 22 is not limited to a specific procedure or method, so long as the processing basically enlarges the pixels of the echo data appearing in the PPI image in both the X-axis and Y-axis directions.

For example, as shown in FIG. 3(A), the pixels of the echo data appearing in the PPI image may be enlarged in the direction of increase and decrease in the X-axis direction as well as in the direction of increase and decrease in the Y-axis direction. In FIG. 3 to FIG. 5, "X(+)" indicates the direction of increase in the X-axis direction, and "Y(+)" indicates the direction of increase in the Y-axis direction. In FIG. 3 and FIG. 5, the solid-lined circles indicate the boundaries of the radar range in the PPI display, and the black dot at the center of the circles is the center of the PPI display (i.e., the origin in the polar coordinate system) and indicates the position of the aircraft (specifically, the radar antenna 11).

In the example shown in FIG. 3(A), specifically, for pixel a, which is the original pixel before enlargement, pixel 3 is added by enlarging in the X-axis direction in an increasing direction and pixel 4 is added by enlarging in the decreasing direction, while pixel 2 is added by enlarging in the Y-axis direction in an increasing direction and pixel 1 is added by enlarging in the decreasing direction. Also, for pixel b, which is the original pixel before enlargement, pixel 7 is added by enlarging in the X-axis direction in an increasing direction and pixel 8 is added by enlarging in the decreasing direction, while pixel 6 is added by enlarging in the Y-axis direction in an increasing direction and pixel 5 is added by enlarging in the decreasing direction.

The pixel enlargement process may be performed by performing a multi-stage process, as shown in FIG. 4. In FIG. 4, each of the squares defined by the dashed lines is arranged vertically and horizontally in a lattice/matrix pattern, and each position corresponds to a pixel represented by a position (x, y) in the XY Cartesian coordinate system.

In the example shown in FIG. 4, specifically, the first stage of enlargement processing is first performed by enlarging the area surrounding the pixels of the echo data appearing in the PPI image. That is, for pixel c, which is the original pixel shown in FIG. 4A, pixels 11 to 18 are added by enlarging the area surrounding pixel c, as shown in FIG. 4B. Note that in FIG. 4B, the shaded pixels are the pixels added by the first stage of enlargement processing.

Next, the second stage enlargement process is performed by moving pixels in both the increasing and decreasing directions along the X axis and enlarging the pixels in both the increasing and decreasing directions along the Y axis. As a specific example, as shown in FIG. 4(C), pixels 19-21 are added by enlarging the pixel group (specifically, a block of pixels c and pixels 11-18) after the first stage enlargement process in the increasing direction along the X axis, pixels 22-24 are added by enlarging the pixel group in the decreasing direction, pixels 25-27 are added by enlarging the pixel group in the increasing direction along the Y axis, and pixels 28-30 are added by enlarging the pixel group in the decreasing direction. Note that in FIG. 4(C), the shaded pixels are the pixels added by the second stage enlargement process.

Furthermore, the third stage enlargement process is performed by moving pixels in both the increasing and decreasing directions along the X axis and enlarging the pixels in both the increasing and decreasing directions along the Y axis. As a specific example, as shown in FIG. 4(D), the group of pixels after the second stage enlargement process (specifically, a block of pixels c and pixels 11-30) is enlarged by moving them in the increasing direction along the X axis, adding pixels 31-35, and by enlarging them in the decreasing direction, adding pixels 36-40, and by enlarging them in the increasing direction along the Y axis, adding pixels 35, 40, and 41-43 (note that pixels 35 and 40 overlap with the addition by the enlargement by moving them in the X axis), and adding pixels 31, 36, and 44-46 by enlarging them in the decreasing direction (note that pixels 31 and 36 overlap with the addition by the enlargement by moving them in the X axis). Note that in FIG. 4(D), the shaded pixels are the pixels added by the third stage enlargement process.

In the example shown in FIG. 4, the enlargement process may end at the first or second stage, or the number of stages of the enlargement process for moving in the X-axis or Y-axis direction may be increased, or the number of stages of the enlargement process for moving in the X-axis or Y-axis direction may be selectable by the user.

The pixel enlargement unit 22 acquires the position (x, y) of each pixel added by the pixel enlargement process in the PPI image, which is a position according to the XY Cartesian coordinate system, and outputs data (called "enlarged echo data") for each pixel group after the pixel enlargement process, in which the positions according to the XY Cartesian coordinate system and the pixel positions (x, y) in the PPI image are associated with each of the pixels constituting the pixel group (i.e., the original pixels and the pixels added by the pixel enlargement process).

The pixel deletion unit 23 is a processing circuit that has a function of performing a process (called a "pixel deletion process") on the enlarged echo data to delete pixels that are closer than the original pixels. The pixel deletion unit 23 performs the pixel deletion process on the enlarged echo data output from the pixel enlargement unit 22 (step S6).

The pixel deletion unit 23 calculates the actual distance from the aircraft (specifically, the radar antenna 11; i.e., the black dot in FIG. 3/origin in the polar coordinate system) for each pixel constituting each pixel group as the magnified echo data. This process of calculating the actual distance corresponds to the inverse process of the coordinate conversion process in step S4, which calculates the position (x, y) of the pixel in the PPI image according to the XY orthogonal coordinate system, which corresponds to the position (r, θ) in the polar coordinate system represented by the actual distance r and the forward angle θ of the radar antenna 11.

The process of calculating the actual distance can also be said to be equivalent to the conversion process when displaying in PPI format in B-scope format.

The pixel deletion unit 23 then removes, for each pixel group after the pixel enlargement process, pixels added by the pixel enlargement process that have an actual distance shorter than the actual distance of the original pixel based on the calculated actual distance.

For example, in the example shown in FIG. 3(A), when pixels 1 to 4 are added by performing pixel enlargement processing on the original pixel a, the actual distance from the aircraft is calculated for each of the added pixels 1 to 4. Then, the actual distance r of the original pixel a is compared with the actual distance of each of the added pixels 1 to 4, and among the added pixels 1 to 4, pixels whose actual distance is shorter than the actual distance r of the original pixel a are deleted. Specifically, when the pixel group consisting of the original pixel a and the added pixels 1 to 4 is confirmed in FIG. 3(B) reflected in the azimuth distance orthogonal coordinate system (note that this figure corresponds to a display in the B-scope format), the actual distance of the added pixels 1 to 3 is equal to or greater than the actual distance r of the original pixel a, so pixels 1 to 3 are not deleted, but the actual distance of the added pixel 4 (the shaded pixel in the figure) is less than the actual distance r of the original pixel a, so pixel 4 is deleted.

In the example shown in FIG. 3(A), when pixels 5 to 8 are added by performing pixel enlargement processing on the original pixel b, the actual distance from the aircraft is calculated for each of the added pixels 5 to 8. Then, the actual distance r of the original pixel b is compared with the actual distance of each of the added pixels 5 to 8, and the added pixels 5 to 8 whose actual distance is shorter than the actual distance r of the original pixel b are deleted. Specifically, when the pixel group consisting of the original pixel b and the added pixels 5 to 8 is checked in FIG. 3(B) which reflects the azimuth distance orthogonal coordinate system, the actual distance of the added pixels 5 and 8 is equal to or greater than the actual distance r of the original pixel b, so the pixels 5 and 8 are not deleted, whereas the actual distance of the added pixels 6 and 7 (shaded pixels in the figure) is less than the actual distance r of the original pixel b, so the pixels 6 and 7 are deleted.

When the pixel enlargement process is performed by multiple stages as in the example shown in FIG. 4, it is preferable to perform pixel deletion processing at each stage of the enlargement process in order to improve the efficiency of the process and reduce the computational load by reducing the number of pixels to be processed. In other words, it is preferable to alternately perform pixel enlargement processing (step S5) and pixel deletion processing (step S6) in a loop. For example, in the example shown in FIG. 4, when the upper left corner is set as the center of the PPI, among the pixels 11 to 18 added by the first stage of the enlargement process shown in FIG. 4 (B), pixels 11, 12, 14, and 16, which are closer than the original pixel c, are deleted, and in the second stage of the enlargement process shown in FIG. 4 (C), it is preferable that the deleted pixels 11, 12, 14, and 16 are not to be enlarged, and pixels 22, 23, 24, 25, 28, and 29 are not added.

For each pixel group after the pixel deletion process, the pixel deletion unit 23 outputs data (called "deletion echo data") that corresponds to the position of the pixel in the PPI image (x, y) according to the XY Cartesian coordinate system for each pixel that composes the pixel group (i.e., the original pixels and the remaining pixels obtained by subtracting the pixels deleted by the pixel deletion process from the pixels added by the pixel enlargement process).

The image generation unit 24 is a processing circuit having a function of generating image data (i.e., raster data) consisting of multiple pixel data for displaying an image on the display unit 4. The image generation unit 24 generates image data using the deleted echo data output from the pixel deletion unit 23 and displays the image data on the display unit 4 (step S7).

The image generating unit 24 generates one image data sheet by combining the deleted echo data for each pixel group output from the pixel deleting unit 23, and transfers the generated image data to the display unit 4. The image data transferred from the image generating unit 24 is then displayed on the display unit 4.

When pixel deletion processing is performed on the enlarged echo data after pixel enlargement processing shown in FIG. 3(A), as described above, pixel 4 is deleted from pixels 1 to 4 added by pixel enlargement processing for the pixel group related to original pixel a, and pixels 6 and 7 are deleted from pixels 5 to 8 added by pixel enlargement processing for the pixel group related to original pixel b, so that the pixel group shown in FIG. 5 (in other words, the deleted echo data) is displayed on the display unit 4. The display unit 4 may display the deleted echo data in PPI format as shown in FIG. 5, or in B-scope format.

Figure 6 shows an example of verification of the effect of the image processing unit described above. Figure 6 (A) shows a specific example of an image display of echo data before pixel enlargement processing, (B) shows an image display of the data after the echo data has been subjected to conventional pixel enlargement processing, and (C) shows an image display of deleted echo data after the echo data has been subjected to pixel enlargement processing by the image processing unit described above.

From the results shown in Figure 6 (B), it is confirmed that in conventional pixel enlargement processing, the front end position of the target after pixel enlargement processing (i.e., the position of the pixel closest to the aircraft) is shifted (specifically, closer to the aircraft) from the front end position of the target before pixel enlargement processing (i.e., the position of the pixel closest to the aircraft), and therefore it is confirmed that the distance from the aircraft to the target cannot be measured accurately.

On the other hand, from the results shown in Figure 6 (C), it is confirmed that in the pixel enlargement process by the image processing unit as described above, the front end position of the target after the pixel enlargement process (i.e., the position of the pixel closest to the aircraft) is the same as the front end position of the target before the pixel enlargement process (i.e., the position of the pixel closest to the aircraft), and therefore it is confirmed that the distance from the aircraft to the target can be accurately measured.

With the image processing unit described above, the echo data in the polar coordinate system is transformed into echo data that corresponds to the pixel position in the PPI image, and then pixel enlargement processing is performed, while pixels closer than the original pixels are deleted. This makes it possible to accurately measure the distance from the aircraft to the target even when pixel enlargement processing is applied.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes within the scope of the invention that do not deviate from the gist of the invention, they are included in the invention.

For example, in the above embodiment, the image processing unit 2 according to the present invention is installed in a radar device that is mounted on a ship and uses radio waves, but the mechanism for installing the image processing unit 2 according to the present invention is not limited to a radar device mounted on a ship, and is also not limited to a radar device that uses radio waves. For example, the image processing unit 2 according to the present invention may be installed in a sonar that uses sound waves.

REFERENCE SIGNS LIST 1 Antenna unit 11 Radar antenna 12 Transmitter/receiver 13 A/D converter 2 Image processing unit 21 Pixel data generator 22 Pixel enlargement unit 23 Pixel deletion unit 24 Image generator 3 Storage unit 4 Display unit

Claims (2)

a pixel data generating unit that converts the echo data in the polar coordinate system into echo data having a position according to a rectangular coordinate system and corresponding to a pixel position in the PPI image;
a pixel enlargement unit that performs pixel enlargement processing on the echo data associated with a pixel position in the PPI image;
a pixel deleting unit that deletes pixels that are closer to the original pixel from among the pixels added by the pixel enlargement process;
an image generating unit that generates image data using the data output from the pixel deleting unit,
1. An image processing unit comprising: It will be incorporated into radar equipment installed on ships,
2. The image processing unit according to claim 1.