JP2021131385A - Object detector - Google Patents

Abstract

To provide an object detector which can detect an object in a right unit more accurately.SOLUTION: The object detector divides an excessively coupled cluster in Step S111 if a cluster is determined to be excessively coupled in S108, and detects the part of the cluster which is in a point group corresponding to an image target as an object in S112. The object detector couples at least two clusters in the part in the point group corresponding to the image target in S116 when the cluster is determined to be excessively coupled in S113, and detects the cluster after the coupling as an object.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to an object detection device.

Patent Document 1 describes an object identification device that detects an object using a cluster generated by clustering a plurality of detection points detected by a laser radar. Specifically, the object identification device identifies a cluster representing an object by calculating the degree of coincidence between the cluster generated last time and the cluster generated this time. At this time, the object identification device calculates the degree of coincidence from the cluster of the root node to the cluster of the child node by utilizing the fact that the cluster has a tree structure.

Japanese Unexamined Patent Publication No. 2013-228259

However, as a result of detailed examination by the inventor, the following problems have been found. That is, if clustering is performed using only a point cloud as in the apparatus described in Patent Document 1, it is difficult to detect an object in a correct unit. For example, when a cluster smaller than the cluster that should be originally generated is generated as a cluster of root nodes for an object to be detected, it is difficult to detect a cluster larger than the cluster of root nodes as an object, and the object is overdivided. It ends up. Also, for example, if the cluster that was generated last time does not exist, that is, at the time of the first clustering, the degree of coincidence between the cluster that was generated last time and the cluster that was generated this time cannot be calculated. It is difficult to identify and the detection accuracy is low.

One aspect of the present disclosure provides an object detection device capable of detecting an object in a correct unit with higher accuracy.

One aspect of the present disclosure is an object detection device, which includes an irradiation unit (2), a light receiving unit (3), and a detection unit (51 to 54). The irradiation unit is configured to irradiate a predetermined ranging area with light. The light receiving unit is configured to receive the reflected light, which is the light reflected by the light emitted by the irradiation unit, and the ambient light. The detection unit is configured to detect a predetermined object based on a point cloud, which is information based on reflected light, and an image. The point cloud is a group of reflection points detected in the entire ranging area. The image is at least one of an ambient light image which is an image based on ambient light, a distance image which is an image based on the distance to an object detected based on reflected light, and a reflection intensity image which is an image based on the reflection intensity of reflected light. There is one.

According to such a configuration, the object can be detected with higher accuracy in the correct unit.

It is a block diagram which shows the structure of the object detection device. It is an example of a schematic diagram of an image target showing a pedestrian. It is an example of a schematic diagram of a part showing a pedestrian in a point cloud. It is an example of a schematic diagram of an image target showing a mixer truck. It is an example of a schematic diagram of a part showing a mixer truck in a point cloud. It is a flowchart which shows the first half part of the object detection process of 1st Embodiment. It is a flowchart which shows the latter half part of the object detection process of 1st Embodiment. It is a flowchart which shows the first half part of the object detection process of 2nd Embodiment. It is a flowchart which shows the object detection process of the modification of 2nd Embodiment.

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.
[1. composition]
The object detection device 1 shown in FIG. 1 is mounted on a vehicle and is used to irradiate light and receive reflected light from an object that reflects the irradiated light to detect an object existing in front of the vehicle.

As shown in FIG. 1, the object detection device 1 includes an irradiation unit 2, a light receiving unit 3, a storage unit 4, and a processing unit 5.
The irradiation unit 2 irradiates the ranging area in front of the vehicle with a laser beam. The ranging area is an area that extends in a predetermined angle range in each of the horizontal direction and the vertical direction. The irradiation unit 2 scans the laser beam in the horizontal direction.

The light receiving unit 3 detects the amount of incident light from the ranging area. The incident light detected by the light receiving unit 3 includes ambient light such as reflected light of sunlight as well as reflected light obtained by reflecting the laser light emitted by the irradiation unit 2 on an object.

The ranging area is divided into a plurality of divided areas, and the amount of incident light can be detected for each of the plurality of divided areas. When the ranging area is represented as a two-dimensional plane that is visually recognized when the light receiving unit 3 is viewed from the front (that is, the irradiation direction of the laser beam), the plurality of divided areas described above refer to the two-dimensional plane. It corresponds to each region divided into a plurality of stages in the horizontal direction and the vertical direction. Each of the divided areas is a space area having a length along a straight line extending from the light receiving unit 3 when viewed as a three-dimensional space. For each division area, the horizontal angle and the vertical angle of the straight line described above are associated and determined.

In the present embodiment, the ranging area is divided into finely divided areas as compared with the conventional general LIDAR. For example, the number of divided areas in the distance measuring area is designed to be divided into 500 in the horizontal direction and 100 in the vertical direction in the above-mentioned two-dimensional plane.

One or more light receiving elements are associated with each divided area. The size of the divided area (that is, the size of the area on the above-mentioned two-dimensional plane) changes depending on the number of light receiving elements associated with one divided area. The smaller the number of light receiving elements associated with one divided area, the smaller the size of one divided area and the higher the resolution. In order to realize such a configuration, the light receiving unit 3 includes a light receiving element array in which a plurality of light receiving elements are arranged. The light receiving element array is composed of, for example, SPAD and other photodiodes. SPAD is an abbreviation for Single Photon Avalanche Diode.

As described above, the incident light includes reflected light and ambient light. The reflected light reflected by the object from the laser beam emitted by the irradiation unit 2 represents the relationship between the time and the amount of incident light obtained by sampling the amount of incident light for a certain period starting from the irradiation timing of the laser light. In the received waveform, it is detected as a peak that is sufficiently distinguishable from ambient light. From the time from the irradiation timing of the laser light by the irradiation unit 2 to the detection timing of the reflected light, the distance to the reflection point where the laser light is reflected by the object is calculated. Therefore, the three-dimensional position of the reflection point is specified from the horizontal and vertical angles of the divided area and the distance from the object detection device 1. Since the three-dimensional position of the reflection point is specified for each divided area, the three-dimensional position of the point cloud, which is a group of reflection points detected in the entire ranging area, is specified. That is, the three-dimensional position of the object reflecting the laser beam and the horizontal and vertical sizes in the three-dimensional space are specified. The three-dimensional positions of the reflection points are converted into X, Y, and Z coordinate values for processing such as clustering, which will be described later.

The ambient light is detected as a received light waveform during the period when the reflected light is not detected. For example, the received light waveform after the period set for detecting the reflected light of the laser light has elapsed may be detected as the ambient light. As described above, since the light receiving unit 3 detects the amount of incident light from each divided area, it is a grayscale image having a resolution of 500 pixels in width and 100 pixels in height and multi-gradation based on the received ambient light. Is generated as an ambient light image. That is, the ambient light image is the same as when the front of the vehicle is photographed by the camera. In addition, since the angular position of each reflection point in the point cloud and the position of each pixel in the ambient light image have a one-to-one correspondence, the object recognized by image analysis of the ambient light image and the point cloud The correspondence between the recognized object and the object can be identified with high accuracy. The ambient light image is generated by the image generation unit 61, which will be described later.

The storage unit 4 stores the type information, the distance threshold value, and the size threshold value.
The type information is the type of the object to be detected. The object to be detected includes an object that the driver should pay attention to when driving, such as a pedestrian and a preceding vehicle.

The distance threshold value is a threshold value set for each type of object as a guideline for a distance range in which an object to be detected can be detected. For example, when it is extremely unlikely that a pedestrian can be detected at a position separated by a predetermined distance or more due to factors such as the performance of the object detection device 1 and the traveling environment, the predetermined distance is set as a distance threshold value for the pedestrian. The distance threshold used may be changed according to the traveling environment and the like.

The size threshold value is a threshold value set for each type of object as a guideline for an appropriate size of the object to be detected. For example, the upper limit of each height and width range that is likely to be a pedestrian and is extremely unlikely to be a pedestrian if it exceeds that range is for a pedestrian. Set as a size threshold. By not setting the lower limit value, it is possible to determine that the person is a pedestrian, for example, even when only the upper body of the pedestrian is imaged.

The processing unit 5 is mainly composed of a well-known microcomputer having a CPU, ROM, RAM, flash memory, etc. (not shown). The CPU executes a program stored in ROM, which is a non-transitional substantive recording medium. When the program is executed, the method corresponding to the program is executed. Specifically, the processing unit 5 executes the object detection processing shown in FIGS. 6 and 7 described later according to the program. The processing unit 5 may be provided with one microcomputer or may be provided with a plurality of microcomputers.

The processing unit 5 is a functional block realized by the CPU executing a program, that is, as virtual components, a point cloud generation unit 51, a cluster generation unit 52, an identification unit 53, and an object detection unit 54. , A switching unit 55, and an image generation unit 61. The method for realizing the functions of each unit included in the processing unit 5 is not limited to software, and some or all of the functions may be realized by using one or more hardware. For example, when the above function is realized by an electronic circuit which is hardware, the electronic circuit may be realized by a digital circuit, an analog circuit, or a combination thereof.

The point cloud generation unit 51 generates a point cloud based on the received light waveform. The point cloud is a group of reflection points detected in the entire ranging area. The reflection point represents a point where the laser beam reflected by the irradiation unit 2 is reflected, and is acquired for each of the above-mentioned divided areas. By changing the number of light receiving elements associated with one divided area, it is possible to switch the point cloud resolution in the point cloud. The point cloud resolution is the number of units (that is, division areas) for detecting a plurality of reflection points constituting the point cloud.

The cluster generation unit 52 generates a plurality of clusters by clustering the point clouds generated by the point cloud generation unit 51.
The image generation unit 61 generates an ambient light image, a distance image, and a reflection intensity image. The distance image is an image showing the distance to the reflection point reflected by the object by the laser beam emitted by the irradiation unit 2 for each pixel. The reflection intensity image is an image showing the intensity of the laser light emitted by the irradiation unit 2 reflected by the object and received by the light receiving unit 3 for each pixel. The resolution of each image can be switched.

The identification unit 53 analyzes the ambient light image and detects an image target, which is a portion identified as an object to be detected, in the ambient light image. That is, the identification unit 53 detects an object that matches the type information stored in the storage unit 4 from the ambient light image. As a method for detecting an image target, for example, Deep Learning, machine learning, or the like is used.

The object detection unit 54 detects a cluster corresponding to the image target detected by the identification unit 53 in the point cloud. The detection of clusters corresponding to image targets will be described in detail later.
The switching unit 55 switches the resolution as a switching process. Regarding the resolution in the vertical direction, the resolution is increased by reducing the number of light receiving elements used for one pixel in the light receiving unit 3 and increasing the number of pixels in the vertical direction. The object detection device 1 has a first resolution in which the first number of light receiving elements among the plurality of light receiving elements is one pixel, and a second number of light receiving elements that is smaller than the first number among the plurality of light receiving elements. It is configured to be switchable to a second resolution in which the light receiving element is one pixel. In the present embodiment, the object detection device 1 has a default resolution in which a total of 24 light receiving elements (6 horizontal × 4 vertical) are used as one pixel, and a total of 12 light receiving elements (6 horizontal × 2 vertical). It is configured to be switchable to a high level resolution of one pixel. On the other hand, regarding the resolution in the horizontal direction, the resolution is increased by narrowing the interval for scanning the laser beam in the irradiation unit 2 and increasing the number of pixels in the horizontal direction. In the present embodiment, in the case of a high level resolution, an image having a resolution of 1000 pixels in the horizontal direction and 200 pixels in the vertical direction is generated as an ambient light image. Further, in the present embodiment, the point cloud resolution is set to match the resolution of the above-mentioned image. Specifically, in the case of a high level, a point cloud is generated as a group of reflection points detected in 1000 divided areas in the horizontal direction and 200 in the vertical direction.

Here, with reference to FIGS. 2 and 3, a scene in which a wall and a pedestrian are close to each other will be described as an example. In the ambient light image of FIG. 2, even when the pedestrian 22 is detected as an image target separately from the wall 21, the wall 23 and the pedestrian 24 are not distinguished in the point cloud of FIG. 3, and one cluster. May be detected as. Here, a state in which a plurality of clusters that should be distinguished by the unit of an object are connected to one cluster is said to be over-coupled.

Further, a mixer truck will be described as an example with reference to FIGS. 4 and 5. As shown in FIG. 4, even when the mixer truck 25 is detected as an image target in the ambient light image, in the point cloud of FIG. 5, the mixer truck is 2 in the front portion 26 of the vehicle body and the tank portion 27. It may be detected as one cluster. Here, a state in which one cluster that should be distinguished by the unit of an object is divided into a plurality of clusters is said to be overdivided.

That is, in the scenes shown in FIGS. 2 to 5, even if the object can be detected in the correct unit in the ambient light image, it may be difficult to detect the object in the correct unit in the point cloud.

On the contrary, even if the object can be detected in the correct unit in the point cloud, it may be difficult to detect the object in the correct unit in the ambient light image. For example, in an ambient light image, a part of a wall having a mottled pattern, an arrow painted on a road surface, or the like may be detected as an image target indicating a pedestrian.

Therefore, the object detection device 1 of the present embodiment executes an object detection process for improving the object detection accuracy by using both the ambient light image and the point cloud.
[2. process]
The object detection process executed by the processing unit 5 of the object detection device 1 will be described with reference to the flowcharts of FIGS. 6 and 7. The object detection process is executed every time the distance measurement of the entire distance measurement area is completed. At the start of the object detection process, the resolution is set to the default resolution. In the description of this process, the term "resolution" includes both the image resolution and the point cloud resolution of the point cloud.

First, in S101, the processing unit 5 generates a point cloud. Note that S101 corresponds to the processing as the point cloud generation unit 51.
Subsequently, in S102, the processing unit 5 generates a plurality of clusters by clustering the point cloud. Each generated cluster does not have type information as an initial value. Note that S102 corresponds to the processing as the cluster generation unit 52.

Subsequently, in S103, the processing unit 5 detects an image target from the ambient light image. By detecting the image target, the type of the image target is also recognized. When there are a plurality of objects to be detected in the ambient light image, the processing unit 5 detects a plurality of image targets from the ambient light image. Subsequent processing is executed for each image target. If the image target is not detected in S103 even though the clusters are generated in S102, the processing unit 5 shifts to S112 and detects each of the generated clusters as an object, and then in FIG. The object detection process is terminated. At this time, each generated cluster is detected as an object having no type information. Note that S103 corresponds to the processing as the identification unit 53.

Subsequently, in S104, the processing unit 5 detects the image target corresponding cluster. Specifically, first, the processing unit 5 surrounds the image target detected in S103 in the ambient light image with a rectangle. In addition, the processing unit 5 regards the point cloud as a two-dimensional plane having information on the angular position of each reflection point, and surrounds the plurality of clusters generated in S102 in the point cloud with a rectangle. Next, the processing unit 5 detects the rectangle of the cluster that overlaps with the rectangle of the image target, and detects the cluster as the image target compatible cluster. Here, when there are a plurality of cluster rectangles that overlap with the image target rectangle, the rectangle of the cluster having the maximum overlap rate with the image target rectangle is detected, and the cluster is detected as the image target compatible cluster. .. That is, the processing unit 5 associates the image target with the cluster. If there is no cluster rectangle that overlaps with the rectangle of the image target, the image target is invalidated and the object detection process of FIG. 6 ends.

Subsequently, in S105, the processing unit 5 determines whether or not the distance to the object indicated by the image target is appropriate. Specifically, when the distance to the object indicated by the image target is within the distance threshold value, the processing unit 5 determines that the distance is appropriate. Whether or not the distance to the object is appropriate cannot be determined only by the ambient light image, but it can be determined by using a point cloud having information on the distance to the reflection point. That is, since the image target and the cluster are associated with each other, for example, the distance between the center point of the image target compatible cluster and the object detection device 1 can be used as the distance between the image target and the object detection device 1. can. In the following description, the pixel or the number of pixels of the image target corresponding cluster means the number of divided areas or divided areas which is a unit for detecting a plurality of reflection points constituting the point cloud.

When the processing unit 5 determines in S105 that the distance to the object indicated by the image target is appropriate, the processing unit 5 proceeds to S106 and determines whether or not the size of the object indicated by the image target is appropriate. do. Specifically, when the size of the object indicated by the image target falls within the size threshold value, the processing unit 5 determines that the size is appropriate. Whether or not the size of the object is appropriate cannot be determined only by the ambient light image, but it can be determined by using a point cloud having information on the three-dimensional position of the reflection point. The size of the object indicated by the image target is estimated based on the part in the point cloud corresponding to the image target. The portion in the point cloud corresponding to the image target is a portion of the point cloud at an angular position corresponding to the position of each pixel of the image target. For example, when the number of pixels of the image target-compatible cluster is larger than the number of pixels of the image target, the size of the part of the image target-compatible cluster in the point group corresponding to the image target is the size of the image target. Estimated to be the size of the indicated object. For example, when the number of pixels of the image target cluster is smaller than the number of pixels of the image target, the ratio of the number of pixels of the image target to the number of pixels of the image target cluster is multiplied by the image target cluster. The size of the cluster is estimated to be the size of the object indicated by the image target.

When the processing unit 5 determines in S106 that the size of the object indicated by the image target is appropriate, the processing unit 5 shifts to S107, and determines the number of pixels of the image target, the number of pixels of the cluster corresponding to the image target, and the number of pixels of the image target cluster. Is equal or not. Specifically, in the processing unit 5, the difference obtained by subtracting the number of pixels in the image target from the number of pixels in the cluster corresponding to the image target is equal to or greater than the upper limit value and the lower limit value in the pixel number threshold indicating the range of a predetermined number of pixels. If it fits in, it is determined that the number of pixels of the image target and the number of pixels of the cluster corresponding to the image target are equivalent. For example, when the pixel number threshold value indicates a range of plus or minus 10 pixels, the upper limit value indicates plus 10 and the lower limit value indicates minus 10.

When the processing unit 5 determines in S107 that the number of pixels of the image target and the number of pixels of the image target compatible cluster are not equal, the process proceeds to S108 to determine whether the clusters are overcoupled. To judge. Whether or not the clusters are over-coupled depends on whether there is an over-coupled cluster in the point cloud corresponding to the image target, which is a cluster having a larger size than the part in the point group corresponding to the image target. It is judged by whether or not. For example, when the difference obtained by subtracting the number of pixels in the image target from the number of pixels in the cluster corresponding to the image target is larger than the upper limit value in the pixel number threshold value, it is determined that the overcoupled cluster exists. When an over-coupled cluster exists, the processing unit 5 determines that the cluster is over-coupled.

When the processing unit 5 determines in S108 that the clusters are over-coupled, the processing unit 5 shifts to S109 and determines whether or not the switching process has been performed. In the present embodiment, the processing unit 5 determines whether or not the resolution has been switched. The process of switching the resolution is executed in S110 or S115 described later.

When the processing unit 5 determines in S109 that the resolution has not been switched, the processing unit 5 shifts to S110, performs switching processing, that is, switches the resolution to a high level resolution, and then returns to S101. That is, the processing unit 5 executes the processing in S101 to S108 again in a state where the resolution of the image and the point cloud is higher.

On the other hand, when the processing unit 5 determines that the resolution has been switched in S109, the processing unit 5 shifts to S111. That is, the processing unit 5 executes the processing in S101 to S108 again in a state where the resolution of the image and the point cloud is higher, and when it is determined that the clusters are still overcoupled, the process proceeds to S111.

The processing unit 5 divides the overcoupled cluster in S111. In the processing unit 5, the shortest distance between the target cluster, which is the part of the overbound cluster corresponding to the image target, and the adjacent cluster, which is the part of the overconnected cluster excluding the part corresponding to the image target, is set. Overcoupled so that it is greater than the maximum distance between two adjacent points in the target cluster and greater than the maximum distance between two adjacent points in the adjacent cluster. Split the cluster. The processing unit 5 may divide the portion of the over-coupled cluster corresponding to the image target as it is into one cluster.

Subsequently, the processing unit 5 detects a cluster of parts in the point cloud corresponding to the image target as an object in S112. That is, when the processing unit 5 determines that the clusters are over-coupled in S108 and divides the over-coupled cluster in S111, the processing unit 5 has the type information of the cluster of the portion corresponding to the image target in the over-coupled cluster. Detect as an object. In addition, in S112, the processing unit 5 detects the adjacent cluster divided from the overbound cluster as an object having no type information. After that, the processing unit 5 ends the object detection process of FIG.

On the other hand, when the processing unit 5 determines in S108 that the clusters are not over-coupled, the processing unit 5 shifts to S113 and determines whether or not the clusters are over-divided. Whether or not the clusters are overdivided is determined by whether or not there are two or more clusters in the part of the point cloud corresponding to the image target. Specifically, the difference obtained by subtracting the number of pixels in the image target from the number of pixels in the cluster corresponding to the image target is smaller than the lower limit value in the pixel number threshold, and the image is in the part in the point group corresponding to the image target. When there is one or more clusters other than the target cluster, the processing unit 5 determines that the clusters are overdivided.

When the processing unit 5 determines in S113 that the cluster is over-divided, the processing unit 5 shifts to S114 and determines whether or not the switching process has been performed. In the present embodiment, the processing unit 5 determines whether or not the resolution has been switched.

When the processing unit 5 determines in S114 that the resolution has not been switched, the processing unit 5 shifts to S115, performs switching processing, that is, switches the resolution to a high level resolution, and then returns to S101. That is, the processing unit 5 executes the processing in S101 to S108 and S113 again in a state where the resolution of the image and the point cloud is higher. Note that S110 and S115 correspond to the processing as the switching unit 55.

On the other hand, when the processing unit 5 determines that the resolution has been switched in S114, the processing unit 5 shifts to S116. That is, the processing unit 5 executes the processing in S101 to S108 and S113 again in a state where the resolution of the image and the point cloud is higher, and if it is determined that the cluster is still overdivided, the process proceeds to S116.

The processing unit 5 joins two or more clusters existing in the part of the point cloud corresponding to the image target in S116, and then shifts to S112. That is, when two or more clusters are combined in S116, the processing unit 5 detects the combined cluster as an object having type information. After that, the processing unit 5 ends the object detection process of FIG.

When the processing unit 5 determines in S113 that the cluster is not over-divided, the processing unit 5 shifts to S112, detects the cluster corresponding to the image target as an object, and then ends the object detection process of FIG. At this time, the image target cluster is detected as an object having no type information. Even if the processing unit 5 determines in S113 that the clusters are not overdivided, if there are a plurality of cluster rectangles that overlap the image target rectangle in S104, the image target rectangle is used. The cluster having the next largest overlap rate with the rectangle is set as the image target compatible cluster, and the processing after S105 is repeated.

On the other hand, when the processing unit 5 determines in S107 that the size of the image target compatible cluster is appropriate, the processing unit 5 shifts to S112 and supports the image target as a cluster of parts in the point cloud corresponding to the image target. After detecting the cluster as an object having type information, the object detection process of FIG. 6 is terminated. This means that the number of pixels in the image target cluster is almost the same as the number of pixels in the image target, and the image target cluster is neither overdivided nor overcoupled. That is, it means that both the object indicated by the image target and the cluster of parts in the point cloud corresponding to the image target are detected in the correct unit.

On the other hand, when the processing unit 5 determines in S106 that the size of the object indicated by the image target is not appropriate, the processing unit 5 invalidates the target image. Further, the processing unit 5 shifts to S112, detects the image target cluster as an object, and then ends the object detection process of FIG. At this time, the image target cluster is detected as an object having no type information.

Further, the processing unit 5 also invalidates the target image when it is determined in S105 that the distance to the object indicated by the image target is not appropriate. Further, the processing unit 5 shifts to S112, detects the image target cluster as an object, and then ends the object detection process of FIG. At this time, the image target cluster is detected as an object having no type information. Note that S104 to S108, S111 to S113, and S116 correspond to the processing as the object detection unit 54.

[3. effect]
According to the embodiment described in detail above, the following effects can be obtained.
(3a) The object detection device 1 detects a predetermined object based on the point cloud and the ambient light image. According to such a configuration, it is easy to identify the type and unit of the object in the point cloud as compared with the case where a predetermined object is detected in the point cloud without using the ambient light image. In addition, compared to the case where the degree of coincidence between the cluster generated last time and the cluster generated this time is calculated and the object is detected, the accuracy at the first distance measurement is the same as that at the second and subsequent distance measurements. Objects can be detected. Therefore, according to the object detection device 1, it is possible to detect an object with higher accuracy in the correct unit.

(3b) When the object detection device 1 determines that two or more clusters out of a plurality of clusters generated by clustering the point cloud exist in a part of the point cloud corresponding to the image target, the two or more clusters are present. Detect the cluster as one object. According to such a configuration, even when the cluster is overdivided in the point cloud, the object detection device 1 can detect the object in the correct unit.

(3c) In the object detection device 1, of the plurality of clusters generated by clustering the point cloud, the over-coupled cluster having a larger size than the part in the point cloud corresponding to the image target corresponds to the image target. When it is determined that it exists in a part of the point cloud, the part corresponding to the image target in the overbound cluster is detected as an object. According to such a configuration, the object detection device 1 can detect an object in a correct unit even when the clusters are overcoupled in the point cloud.

(3d) The object detection device 1 includes a target cluster which is a part of the over-coupled cluster corresponding to the image target, and an adjacent cluster which is a part of the over-coupled cluster excluding the part corresponding to the image target. The shortest distance is greater than the maximum distance between two adjacent points in the target cluster and greater than the maximum distance between two adjacent points in the adjacent cluster. Divide the overcoupled cluster as follows. According to such a configuration, the object detection device 1 detects an object in the correct unit as compared with the case where the portion of the overcoupled cluster corresponding to the image target is divided as it is into one cluster. Can be done.

(3e) When the object detection device 1 determines that the size of the object is within the preset size range according to the type of the object indicated by the image target, the object detection device 1 is in the point cloud corresponding to the image target. The part is detected as an object. That is, the object detection device 1 verifies the certainty of the object based on the size assumed for each type of the object. At this time, the object detection device 1 identifies the type of the object by using the ambient light image, and calculates the size of the object by using the point cloud. By combining not only the ambient light image but also the point cloud, the object detection device 1 can make it difficult for the object type to be misidentified.

(3f) When the object detection device 1 determines that the distance to the object is within the preset distance range according to the type of the object indicated by the image target, the point cloud corresponding to the image target Is detected as an object. That is, the object detection device 1 verifies the certainty of the object based on the existence position assumed for each type of the object. At this time, the object detection device 1 identifies the type of the object by using the ambient light image, and calculates the distance to the object by using the point cloud. By combining not only the ambient light image but also the point cloud, the object detection device 1 can make it difficult for the object type to be misidentified.

(3g) In the object detection device 1, the light receiving unit 3 has a plurality of light receiving elements, and has a first resolution in which the first number of light receiving elements among the plurality of light receiving elements is one pixel, and a plurality of light receiving elements. It is possible to switch to a second resolution in which a second number of light receiving elements, which is smaller than the first number, is one pixel. According to such a configuration, the object detection device 1 can detect an object with higher accuracy as compared with the case where the resolution cannot be switched between the first resolution and the second resolution.

In the present embodiment, the point cloud generation unit 51, the cluster generation unit 52, the identification unit 53, and the object detection unit 54 correspond to the processing as the detection unit.
[4. Second Embodiment]
[4-1. Differences from the first embodiment]
Since the basic configuration and processing of the second embodiment are the same as those of the first embodiment, the common configuration and processing will be omitted and the differences will be mainly described.

In the first embodiment, the image target is detected only from the ambient light image in S103 of the object detection process. On the other hand, in the second embodiment, the image target is detected from each of the ambient light image, the distance image, and the reflection intensity image. Further, in the second embodiment, the resolutions of the point cloud, the ambient light image, the distance image, and the reflection intensity image are switched according to the external brightness.

[4-2. process]
The object detection process executed by the processing unit 5 of the object detection device 1 of the second embodiment will be described with reference to the flowchart of FIG.

In S201, the processing unit 5 determines whether or not the external brightness is brighter than a predetermined threshold value. For example, the processing unit 5 determines that the outside is bright when the intensity of the ambient light is equal to or higher than a predetermined threshold value.

In S202, the processing unit 5 generates a point cloud having a point cloud resolution according to the external brightness. Specifically, when the processing unit 5 determines in S201 that the external brightness is brighter than the predetermined threshold value, the processing unit 5 determines in S201 that the external brightness is not brighter than the predetermined threshold value. Generates a point cloud with a relatively low point cloud resolution. On the other hand, when the processing unit 5 determines in S201 that the external brightness is not brighter than a predetermined threshold value, the processing unit 5 generates a point cloud having a relatively high point cloud resolution. The point cloud resolution matches the resolution of the distance image and the reflection intensity image generated in S203.

Subsequently, in S102, the processing unit 5 generates a plurality of clusters by clustering the point cloud.
Subsequently, in S203, the processing unit 5 generates an image having a resolution corresponding to the external brightness. Specifically, when the processing unit 5 determines in S201 that the external brightness is brighter than the predetermined threshold value, the processing unit 5 determines in S201 that the external brightness is not brighter than the predetermined threshold value. An ambient light image having a relatively high resolution is generated, and a distance image and a reflection intensity image having a relatively low resolution are generated. On the other hand, when the processing unit 5 determines in S201 that the external brightness is not brighter than a predetermined threshold value, the processing unit 5 generates an ambient light image having a relatively low resolution, and a distance image and a reflection intensity having a relatively high resolution. Generate an image.

Further, in S203, the processing unit 5 detects an image target from each of the ambient light image, the distance image, and the reflection intensity image, and integrates the image target. The integration is to generate one image target used in the processing performed following S203 based on the image target detected using the three types of images. For example, when the image target is detected from any of the three types of images, the processing unit 5 adopts it as the image target. The method of integrating image targets is not limited to this. For example, an image target detected from only one of the three types of images does not have to be adopted as an image target. That is, in this case, the processing proceeds assuming that the image target has not been detected. Further, for example, an image target detected from only one of two of the three types of images does not have to be adopted as the image target. When different image targets are detected in the three types of images, the image targets are determined based on the priority determined in advance for each image, or the image targets detected in the two images are integrated. It may be used as an image target. After this S203, the process proceeds to S104. The processing of S104 to S106 is the same as the processing of S104 to S106 shown in FIG.

When the processing unit 5 determines in S106 that the size of the object indicated by the image target is appropriate, the processing unit 5 shifts to S204, and determines the number of pixels of the image target and the number of pixels of the cluster corresponding to the image target. Determines if is supported.

In S107 of the first embodiment described above, in order to compare the sizes of the image target and the image target compatible cluster, the number of pixels of the image target compatible cluster and the image target is compared. However, in the second embodiment, the point cloud resolution and the image resolution may be different, so that a simple comparison cannot be made. Therefore, the ratio of the point cloud resolution to the image resolution is obtained based on the point cloud resolution of the point cloud generated in S202 and the resolution of the image generated in S203. For example, if the resolution of the image is 500 pixels in the horizontal direction and 200 pixels in the vertical direction, and the resolution of the point group is 1000 pixels in the horizontal direction and 200 pixels in the vertical direction, the area of one pixel of the image is 2 of the area of one pixel of the point group. It is double. In this case, if the number of pixels of the image target corresponding cluster is twice as large as the number of pixels of the image target, it can be said that the area has the same range in the distance measuring area. In this way, the above-mentioned ratio is obtained, and after considering the ratio, it is determined whether or not the size of the image target and the size of the cluster corresponding to the image target are equivalent. The above method is an example, and when the number of pixels of the image target cluster and the image target are different, various methods capable of comparing their sizes can be adopted.

When the processing unit 5 determines in S204 that the number of pixels of the image target and the number of pixels of the image target compatible cluster do not correspond, the process proceeds to S108. On the other hand, when it is determined that the number of pixels of the image target and the number of pixels of the image target compatible cluster correspond to each other, the process proceeds to S112. Since the processing after S108 is the same as the processing of S108 to S116 shown in FIG. 7, the description thereof will be omitted.

[4-3. effect]
According to the second embodiment described in detail above, the following effects can be obtained.
(4a) When the object detection device 1 determines that the external brightness is bright, the object detection device 1 has a relatively high resolution ambient light image and a relatively high resolution as compared with the case where it is determined that the external brightness is not bright. The object is detected based on the low-distance image and the reflection intensity image. According to such a configuration, in the ambient light image, the image target is detected from the high-resolution ambient light image, so that the image recognition accuracy is improved. Further, in the distance image and the reflection intensity image, the detection distance tends to be extended because the SN is improved. Therefore, it is possible to detect an object farther away. The SN is the ratio of the signal to the noise.

(4b) When the object detection device 1 determines that the external brightness is not bright, the object detection device 1 has a relatively low resolution ambient light image and a relatively high resolution as compared with the case where the external brightness is determined to be bright. The object is detected based on the high-distance image and the reflection intensity image. According to such a configuration, the reliability of the ambient light image is low when the outside is not bright in the first place, so that even if the resolution of the ambient light image is lowered, the reliability is unlikely to be affected. Therefore, it is possible to generate an ambient light image while suppressing the processing load. Further, in the distance image and the reflection intensity image, when the intensity of the ambient light is low, the noise is reduced, so that the detection distance tends to be long. Therefore, even if the resolution is increased, it is possible to suppress a decrease in the detection distance.

(4c) In the object detection device 1, the point cloud resolution matches the resolution of the distance image and the reflection intensity image. According to such a configuration, since the angular position of each reflection point in the point group and the position of each pixel in the distance image and the reflection intensity image have a one-to-one correspondence, the distance image and the reflection intensity image are analyzed. It becomes easy to take a correspondence between the object recognized in the above and the object recognized in the point group.

(4d) In the object detection device 1, the processing unit 5 generated a point cloud having a point cloud resolution corresponding to the external brightness in S202, and generated an image having a resolution corresponding to the external brightness in S203. In addition, when the processing unit 5 determines in S108 that the clusters are overcoupled, the processing unit 5 switches to a high level point cloud resolution and resolution in S110. The processing unit 5 also switched to a high level point cloud resolution and resolution in S115 even when it was determined in S113 that the cluster was overdivided. According to such a configuration, the object can be detected with higher accuracy as in the first embodiment.

In this embodiment, S201 corresponds to the processing as the determination unit.
[4-4. Modification example of the second embodiment]
(I) In the above embodiment, the object is detected based on three types of images: an ambient light image, a distance image, and a reflection intensity image. However, the number of image types used is not limited to this. For example, at least one of an ambient light image, a distance image, and a reflection intensity image may be used. Further, an ambient light image and at least one of a distance image and a reflection intensity image may be used.

(Ii) In the above embodiment, when it is determined that the external brightness is bright, the resolution of the ambient light image is relatively high as compared with the case where it is determined that the external brightness is not bright, and the point cloud The point cloud resolution was relatively low. Further, when it is determined that the external brightness is not bright, the resolution of the ambient light image is relatively low as compared with the case where the external brightness is determined to be bright, and the point cloud resolution of the point cloud is relative. It was expensive. That is, when the point cloud resolution of the point cloud is relatively low, the resolution of the ambient light image is relatively high, and when the point cloud resolution of the point cloud is relatively high, the resolution of the ambient light image is set relatively low. Was done. However, the method of setting the point cloud resolution and the resolution is not limited to this. For example, the resolution of the ambient light image may be switched between high and low while keeping the point cloud resolution of the point cloud constant, and the point cloud resolution of the point cloud may be set high or low while keeping the resolution of the ambient light image constant. You may switch. Further, for example, when the point cloud resolution of the point cloud is low, the resolution of the ambient light image may be switched to be low, and when the point cloud resolution of the point cloud is high, the resolution of the ambient light image is also high. You may switch as follows.

Similarly, for the distance image and the reflection intensity image, for example, the resolution of the distance image and the reflection intensity image may be switched to high or low while keeping the point group resolution of the point group constant, or the distance image and the reflection intensity may be switched to high or low. The point group resolution of the point group may be switched between high and low while keeping the image resolution constant. Further, for example, when the point group resolution of the point group is low, the resolution of the distance image and the reflection intensity image may be switched to be low, or when the point group resolution of the point group is high, the distance image and the reflection intensity may be low. You may switch so that the resolution of the image is also high.
According to such a configuration, the point cloud resolution of the point cloud and the image resolution can be independently set to appropriate values.

(Iii) In the above embodiment, the resolution of the ambient light image is different from that of the distance image and the reflection intensity image. That is, the object was detected based on the ambient light image having the third resolution and the distance image and the reflection intensity image having the fourth resolution different from the third resolution. However, the resolutions of the ambient light image and the distance image and the reflection intensity image may be the same. According to such a configuration, it becomes easy to correspond to the image target detected from each image.

(Iv) In the above embodiment, the point cloud resolution was consistent with the resolution of the distance image and the reflection intensity image. However, the resolution of the point group may not match the resolution of the distance image and the reflection intensity image, or may match only the resolution of one of the distance image and the reflection intensity image.

(V) In the above embodiment, a point cloud and an image having a resolution corresponding to the external brightness are generated. However, the resolution of the point cloud and the image may be set according to the requirements other than the external brightness. For example, the resolution may be set according to the time, whether or not the headlights are turned on, the attributes of the road on which the vehicle travels, and the like.

(Vi) In the above embodiment, the external brightness is determined based on the intensity of the ambient light. However, the method of determining the external brightness is not limited to this. For example, an illuminance sensor may be used.

(Vii) In the above embodiment, the processing unit 5 is divided by the processing of S107 to S111 and S113 to S116 when the cluster is over-coupled, and is combined when the cluster is over-coupled. .. However, the processing unit 5 does not have to divide or combine the clusters described above. For example, as shown in FIG. 9, after detecting the image target corresponding cluster in S104, the processing unit 5 determines in S205 whether the distance to the object indicated by the image target is appropriate. Specifically, the processing unit 5 determines in the same manner as in S105 of FIG.

Subsequently, in S206, the processing unit 5 determines whether the size of the object indicated by the image target is appropriate. Specifically, the processing unit 5 determines in the same manner as in S106 of FIG.
Subsequently, in S207, the processing unit 5 detects an object. At this time, if it is determined in S205 that the distance to the object indicated by the image target is appropriate, and in S206 it is determined that the size of the object indicated by the image target is appropriate, the image target compatible cluster is determined. , Detected as an object with type information. After that, the processing unit 5 ends the object detection process of FIG.

On the other hand, in S207, when it is determined in S205 that the distance to the object indicated by the image target is not appropriate, or in S206, it is determined that the size of the object indicated by the image target is not appropriate, the image target compatible cluster is determined. , Detected as an object without type information. After that, the processing unit 5 ends the object detection process of FIG.

Further, returning to FIG. 7, for example, the processing unit 5 may skip the processing of S109 and S110 after determining whether the clusters are overcoupled in S108. Further, the processing unit 5 may skip the processing of S114 and S115 after determining whether the cluster is overdivided in S113. That is, the processing unit 5 may divide or combine the clusters and detect them as an object having type information without performing the switching process.

[5. Other embodiments]
Although the embodiments of the present disclosure have been described above, it goes without saying that the present disclosure is not limited to the above-described embodiments and can take various forms.

(5a) In the above embodiment, a configuration including SPAD as a light receiving element is illustrated. However, any light receiving element may be used as long as it can detect a temporal change in the amount of incident light.

(5b) In the above embodiment, a configuration in which an ambient light image is used is illustrated. However, the types of images used are not limited to this. For example, at least one of a distance image and a reflection intensity image may be used in addition to or in place of the ambient light image. Since both the distance image and the reflection intensity image are generated according to the number of divided areas, the angular position of each reflection point in the point cloud and the position of each pixel in the distance image and the reflection intensity image are 1: 1. Correspond with. As a result, the correspondence between the object recognized by image analysis of the distance image and the reflection intensity image and the object recognized in the point cloud can be specified with high accuracy.

Here, when an ambient light image is used, the detection performance is high during sunny days, but the detection performance may decrease at night or in a tunnel. On the other hand, when a distance image and a reflection intensity image are used, they have the opposite characteristics. Therefore, the object detection device 1 can detect an object in a correct unit with higher accuracy by using these images together.

(5c) In the above embodiment, when there is a suspicion of over-division or over-coupling, after switching the resolution, distance measurement is performed again in the entire distance measurement area. However, the range in which distance measurement is performed again is not limited to this. The object detection device 1 may perform distance measurement again only in a part of the range measurement area, for example, a range in which overcoupling or overdivision is suspected. As a result, it is possible to suppress excessive detection of an object in a range where switching of resolution is unnecessary, and it is possible to easily prevent the detection timing from being delayed.

(5d) In the above embodiment, a configuration in which the resolution is switched between the first resolution and the second resolution by switching the number of light receiving elements per pixel is illustrated. However, the object detection device 1 may switch the resolution by switching the range of the ranging area. Specifically, the angle range of the laser beam emitted by the irradiation unit 2 in the horizontal direction is switched. For example, the object detection device 1 switches the angle range from −60 ° to + 60 ° to −20 ° to + 20 ° without changing the number of division areas. If the angle range is narrowed without changing the number of division areas, the number of division areas in the angle range becomes relatively large, and the resolution becomes relatively high. Therefore, a more detailed point cloud can be generated. Further, even in the ambient light image, since the range of one-third is expressed without changing the number of pixels, the resolution is relatively high.

Further, as a switching process, the object detection device 1 sets the number of times of irradiating the laser beam to each divided area from the first number of irradiations to the first number of irradiations in addition to or instead of switching the resolution. The SN may be improved by switching to the second irradiation frequency, which is often large. The number of times of irradiating the laser beam is the number of times that the object detection device 1 irradiates the laser beam to each of the divided areas during one cycle of the distance measurement in the distance measuring area. In the above embodiment, the first irradiation number is set to once, and the laser beam is irradiated once to each divided area. According to such a configuration, even when the mixer truck is detected as two clusters in the front part 26 and the tank part 27 in the vehicle body as shown in FIG. 5, the object detection device 1 can be used. By increasing the SN, it becomes easier to detect a part in the vehicle body that connects the front part 26 and the tank part 27. As a result, the object detection device 1 can detect the mixer truck as one cluster instead of two clusters.

In the above embodiment, the entire ranging area is set as the range to be irradiated with the laser beam, but if the number of times the laser beam is irradiated to each divided area is increased, the detection cycle becomes longer and the object It is possible that the timing of detecting is delayed. Therefore, the object detection device 1 may switch from the first number of irradiations to the second number of irradiations only in a part of the range-finding area, for example, a range in which overcoupling or overdivision is suspected. As a result, the object detection device 1 can detect the object with higher accuracy in the correct unit while suppressing the timing of detecting the object from being delayed.

(5e) In the above embodiment, a configuration in which only an upper limit value is set as a size threshold value is illustrated. However, as the size threshold value, a lower limit value may be set in addition to or in place of the upper limit value.
(5f) In the above embodiment, when the number of pixels of the image target corresponding cluster is larger than the predetermined number of pixels as compared with the number of pixels of the image target, it is determined that the overcoupled cluster exists. However, for example, the total score, which is the score of all the reflection points constituting the cluster existing in the part of the point cloud corresponding to the image target, and the partial score, which is the score of the reflection points of the portion corresponding to the image target. , And whether or not an overbound cluster exists may be determined by comparing. Further, for example, when the value obtained by dividing the total score by the partial score is greater than or equal to a predetermined value greater than 1, it may be determined that an overbound cluster exists.

(5g) The functions of one component in the above embodiment may be dispersed as a plurality of components, or the functions of the plurality of components may be integrated into one component. Further, a part of the configuration of the above embodiment may be omitted. Further, at least a part of the configuration of the above embodiment may be added or replaced with the configuration of the other embodiment.

1 ... Object detection device, 2 ... Irradiation unit, 3 ... Light receiving unit, 51 ... Point cloud generation unit, 52 ... Cluster generation unit, 53 ... Identification unit, 54 ... Object detection unit.

Claims (16)

An irradiation unit (2) configured to irradiate a predetermined ranging area with light,
A light receiving unit (3) configured to receive the reflected light, which is the light reflected by the light emitted by the irradiation unit, and the ambient light.
A detection unit (51 to 54) configured to detect a predetermined object based on a point cloud which is information based on the reflected light, an image, and the like.
With
The point cloud is a group of reflection points detected in the entire ranging area.
The image is an ambient light image which is an image based on the ambient light, a distance image which is an image based on the distance to the object detected based on the reflected light, and a reflection intensity which is an image based on the reflection intensity of the reflected light. An object detector, which is at least one of the images. The object detection device according to claim 1.
The detection unit detects an image target which is a portion identified as the object in the image, and two or more clusters out of a plurality of clusters generated by clustering the point cloud are the image object. An object detection device that detects two or more clusters as one object when it is determined that the object exists in a portion of the point cloud corresponding to the target. The object detection device according to claim 1 or 2.
The detection unit detects an image target which is a portion identified as the object in the image, and among a plurality of clusters generated by clustering the point cloud, the detection unit corresponds to the image target. When it is determined that an overbound cluster having a larger size than the portion in the point cloud exists in the portion in the point group corresponding to the image target, it corresponds to the image target among the overbound clusters. An object detection device that separates parts and detects them as the object. The object detection device according to claim 3.
The shortest distance between the target cluster, which is the portion of the over-coupled cluster corresponding to the image target, and the adjacent cluster, which is the portion of the over-coupled cluster excluding the portion corresponding to the image target, is the said. The overcoupling is greater than the maximum distance between two adjacent points in the target cluster and greater than the maximum distance between two adjacent points in the adjacent cluster. An object detector that divides a cluster. The object detection device according to any one of claims 1 to 4.
The detection unit detects an image target which is a portion identified as the object in the image, and the size of the object is preset according to the type of the object indicated by the image target. An object detection device that detects a portion of the point group corresponding to the image target as the object when it is determined that the size is within the range. The object detection device according to any one of claims 1 to 5.
The detection unit detects an image target which is a portion identified as the object in the image, and the distance to the object is preset according to the type of the object indicated by the image target. An object detection device that detects a portion of the point group corresponding to the image target as the object when it is determined that the distance is within the range of the distance. The object detection device according to any one of claims 1 to 6.
The detection unit is based on the image having the first resolution and the point group having the resolution of the first point group indicating the number of units for detecting the plurality of reflection points constituting the point group. Based on the image having a second resolution higher than the first resolution and the point group having a second point group resolution higher than the first point group resolution. An object detection device that can detect an object. The object detection device according to claim 7.
The light receiving unit has a plurality of light receiving elements and has a plurality of light receiving elements.
The detection unit has the first resolution in which the first number of light receiving elements among the plurality of light receiving elements is one pixel, and the second detection unit has a smaller number than the first number of the plurality of light receiving elements. An object detection device capable of switching to the second resolution in which the number of light receiving elements is one pixel. The object detection device according to claim 7 or 8.
The detection unit detects an image target, which is a portion identified as the object in the image, and clusters the point cloud to generate a plurality of clusters.
The detection unit corresponds to the case where it is determined that two or more clusters out of the plurality of clusters exist in the part of the point cloud corresponding to the image target, or the detection unit corresponds to the image target among the plurality of clusters. When it is determined that a connected cluster having a larger size than the portion in the point cloud is present in the portion in the point cloud corresponding to the image target, the resolution of the image is derived from the first resolution. An object that switches to the second resolution, detects the image target, switches the point cloud resolution of the point cloud from the first point cloud resolution to the second point cloud resolution, and clusters the point cloud. Detection device. The object detection device according to any one of claims 1 to 9.
The irradiation unit can switch the number of times of irradiating light to at least a part of the range-finding area between the first irradiation number and the second irradiation number more than the first irradiation number. There is an object detector. The object detection device according to claim 10.
The detection unit detects an image target, which is a portion identified as the object in the image, and clusters the point cloud to generate a plurality of clusters.
The irradiation unit corresponds to the case where it is determined that two or more clusters out of the plurality of clusters are present in the part of the point cloud corresponding to the image target, or the irradiation unit corresponds to the image target among the plurality of clusters. When it is determined that an overbound cluster having a larger size than the portion in the point cloud is present in the portion in the point cloud corresponding to the image target, the second irradiation count is used. Switch to the number of irradiations,
When the number of times of irradiating light is switched from the first number of times of irradiation to the second number of times of irradiation, the detection unit detects the image target at the second number of times of irradiation and displays the point cloud. An object detector that clusters. The object detection device according to any one of claims 1 to 11.
The detection unit can detect the object based on the point cloud and the image having a resolution different from the point cloud resolution indicating the number of units for detecting the plurality of reflection points constituting the point cloud. There is an object detector. The object detection device according to claim 12.
The detection unit is an object detection device capable of detecting the object based on the point cloud and the ambient light image having a resolution different from the point cloud resolution of the point cloud. The object detection device according to any one of claims 1 to 13.
The detection unit is based on the ambient light image having a third resolution and at least one of the distance image and the reflection intensity image having a fourth resolution different from the third resolution. An object detection device that can detect an object. The object detection device according to claim 14.
An object detection device whose point cloud resolution indicating the number of units for detecting a plurality of the reflection points constituting the point cloud matches the resolution of at least one of the distance image and the reflection intensity image. The object detection device according to claim 14 or 15.
Further equipped with a brightness determination unit that determines the external brightness,
When the detection unit determines that the external brightness is brighter than the predetermined threshold value by the brightness determination unit, the detection unit is compared with the case where the external brightness is determined not to be brighter than the predetermined threshold value. An object detection device that detects the object based on the ambient light image having a relatively high resolution, and at least one of the distance image and the reflection intensity image having a relatively low resolution.

Images