Patent Publication Number: US-2022237747-A1

Title: Monitoring camera and image quality improving method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2021-008987 filed on Jan. 22, 2021, the contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a monitoring camera and an image quality improving method. 
     BACKGROUND ART 
     Patent Literature 1 discloses an imaging device that appropriately controls a processing of reducing a noise component on image data in consideration of an intensity of subject light. The imaging device includes a photometric unit that measures subject light, a noise reduction processing unit that executes a noise reduction processing on image data obtained by exposure in an imaging element to reduce a noise component caused by noises generated in the imaging element, and a control unit that controls an intensity of the noise reduction processing based on an exposure time of the exposure in the imaging element and an intensity of the subject light measured by the photometric unit. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP-2014-68253-A 
     In the configuration disclosed in Patent Literature 1, the intensity of the noise reduction processing is determined in accordance with a temporal change amount of a luminance value of a captured image, and the noise reduction processing with the determined intensity is uniformly executed on the entire captured image data. Therefore, the same signal noise ratio (SNR) may be obtained or an afterimage may be generated for both an attention subject and a non-attention subject in the image data. 
     For example, in a case where the surroundings are bright, when image data is captured in which a moving body portion (an example of an attention target) such as a person or a vehicle and a still portion (an example of a non-attention target) are mixed, since the gain of an image sensor is low and the amplification of a noise level is small, it is possible to distinguish a temporal change of luminance due to an actual movement from a temporal change due to noises. 
     Even when a noise reduction processing is uniformly executed on the entire image data, an afterimage of the moving body portion is not noticeable. However, in a case where image data (see the above description) in which a moving body portion and a still portion are mixed is captured in a low-illuminate environment (for example, at night or in a dark room), the gain of the image sensor increases. As a result, when the noise reduction processing is executed at a high intensity so as to improve the SNR, an afterimage of the moving body component is increased. On the contrary, when the noise reduction processing is executed at a low intensity so as to prevent an afterimage, the SNR deteriorates. This is because it is difficult to distinguish between a motion and a noise in the image data, and it is difficult to execute an appropriate noise reduction processing. 
     SUMMARY OF INVENTION 
     The present disclosure has been made in view of the circumstances described above in the related art, and an object of the present disclosure is to provide a monitoring camera, an image quality improving method, and a program for preventing an afterimage of a subject to be focused in a captured image, reducing noises, and improving recognition accuracy of the subject, regardless of a surrounding environment. 
     The present disclosure provides a monitoring camera including an imaging unit configured to capture an image of an imaging area, and a processor configured to determine a first intensity and a second intensity to be different each other. The first intensity indicates an intensity of a noise reduction processing executed on an attention portion in the captured image of the imaging area, and the second intensity indicates an intensity of a noise reduction processing executed on a non-attention portion in the captured image. The first intensity is lower than the second intensity. The processor is configured to execute the noise reduction processing on the attention portion based on the determined first intensity, to execute the noise reduction processing on the non-attention portion based on the determined second intensity, and to output an image after the noise reduction processing. 
     The present disclosure provides an image quality improving method to be executed by a monitoring camera. The image quality improving method includes capturing an image of an imaging area; determining a first intensity and a second intensity to be different from each other, the first intensity indicating an intensity of a noise reduction processing executed on an attention portion in the captured image of the imaging area, and the second intensity indicating an intensity of a noise reduction processing executed on a non-attention portion in the captured image; executing the noise reduction processing on the attention portion based on the determined first intensity, and executing the noise reduction processing on the non-attention portion based on the determined second intensity; and outputting an image after the noise reduction processing. The first intensity is lower than the second intensity. 
     Also, it should be noted that these comprehensive or specific aspects may be achieved by a system, a device, a method, an integrated circuit, a computer program, or a recording medium, or may be achieved by any combination of a system, a device, a method, an integrated circuit, a computer program, and a recording medium. 
     Further advantages and effects of an aspect of the present invention will become apparent from the specification and the drawings. These advantages and/or effects are respectively provided by features described in several embodiments, the specification, and the drawings, and it is not necessary to provide all of the advantages and/or effects in order to obtain one or more identical features. 
     According to the present disclosure, it is possible to prevent an afterimage of a subject to be focused in a captured image, reduce noises, and improve recognition accuracy of the subject, regardless of a surrounding environment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a system configuration example of a monitoring camera system according to a first embodiment. 
         FIG. 2  is a block diagram showing a hardware configuration example of a monitoring camera according to the first embodiment. 
         FIG. 3  is a block diagram showing an example of a functional configuration of a processor and an AI processing unit. 
         FIG. 4  is a diagram showing an example of an attention level table indicating a type of a detected object and an attention level (j) for each type. 
         FIG. 5  is a graph showing an example of a relationship between an image space direction and an attention level after a spatial filter processing. 
         FIG. 6  is a graph showing an example of a relationship between time and an attention level after a time filter processing. 
         FIG. 7  is a diagram showing an example of a correspondence relationship between a detection area of an object on captured image data detected by an AI detection unit  1611  and an attention level (j) of the detection area. 
         FIG. 8  is a diagram showing an example of a correspondence relationship between a detection assumption area of captured image data and an attention level of the detection assumption area. 
         FIG. 9  is a diagram showing an example of an attention level table indicating an attention level (j) of each detection assumption area of the captured image data in  FIG. 8 . 
         FIG. 10  is a diagram showing an example of a correspondence relationship among a noise reduction intensity, an SNR, and an afterimage prevention effect. 
         FIG. 11  is a flowchart showing an example of an operation procedure of the monitoring camera according to the first embodiment. 
         FIG. 12  is a diagram showing an example of a comparison result between a captured image after an NR processing in a case where there is no attention area and a captured image after an NR processing in a case where attention is focused on a face of a person. 
         FIG. 13  is a diagram showing an example of a comparison result between a captured image after an NR processing in a case where there is no attention area and a captured image after an NR processing in a case where attention is focused on a vehicle traveling in a monitoring camera direction. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments specifically disclosing a monitoring camera, an image quality improving method, and a program according to the present disclosure will be described in detail with reference to the drawings as appropriate. Unnecessarily detailed description may be omitted. For example, detailed description of a well-known matter or repeated description of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding for those skilled in the art. It is to be understood that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the range of the claims. 
       FIG. 1  is a diagram showing a system configuration example of a monitoring camera system  100  according to a first embodiment. The monitoring camera system  100  includes a monitoring camera  1 , a power on Ethernet (PoE (registered trademark)) hub  20 , a recorder  30 , a monitor  40 , and a monitoring computer  50 . The monitoring camera  10 , the recorder  30 , and the monitoring computer  50  constitute a network in which the monitoring camera  10 , the recorder  30 , and the monitoring computer  50  can communicate with one another via the PoE hub  20 . 
     The network is a wired or wireless network. The wired network is, for example, a universal serial bus (USB) cable, a wired local area network (LAN), and the like, and is not limited thereto. On the other hand, the wireless network is, for example, any one of a wireless LAN such as Wi-Fi (registered trademark), Bluetooth (registered trademark), and Wireless Gigabit (WiGig), and is not limited thereto. In the following description, an image captured by the monitoring camera  10  (hereinafter referred to as a “captured image”) includes not only data of the captured image but also camera identification information and imaging date and time information of the monitoring camera  10  that captured the image. 
     The monitoring camera  10  may be installed outdoors or indoors. When the monitoring camera  10  is installed outdoors, the monitoring camera  10  is fixedly installed by being mounted to, for example, a pole installed on a road side or a parking lot. On the other hand, when the monitoring camera  10  is installed indoors, the monitoring camera  10  is fixedly installed on a ceiling surface in the vicinity of an automatic door in a building such as a store, a museum, and an art museum. It is needless to say that an installation location of the monitoring camera  10  is not limited to those described above. 
     The monitoring camera  10  includes at least an imaging unit CAP 1  and an artificial intelligence (AI) processing unit  16 . The imaging unit CAP 1  of the monitoring camera  10  captures an image (that is, a captured image) of a subject TRG 1  including an object (that is, a moving body) present in an imaging area (that is, a monitoring area) within a predetermined angle of view. The AI processing unit  16  of the monitoring camera  1  can execute a processing by artificial intelligence (AI) and detects a moving body (an example of an attention portion) from a captured image obtained from the imaging unit CAP 1  by using the artificial intelligence. A detailed configuration example of the imaging unit CAP 1  and the AI processing unit  16  will be described later with reference to  FIG. 2 . The moving body is an object to be monitored by the monitoring camera  10 , and is, for example, a person, a face of a person, a vehicle, a two-wheel vehicle such as a motorcycle, a bicycle, a three-wheel vehicle, or a kick scooter. The moving body is not limited to these examples, and the object may not be limited to a moving body. 
     In the monitoring camera  10 , a learning model for enabling AI to detect an object is stored in a learning model memory  162  (see  FIG. 2 ). The learning model is a parameter group having a characteristic of an AI processing function that can be executed by the AI processing unit  16 . That is, the learning model is a parameter group for detecting a portion of a moving body to be detected from the entire captured image (hereinafter, also referred to as a “frame”). The learning model may be, for example, a parameter group for determining an AI constituent element (for example, a neural network) constructed in the monitoring camera  10 . The parameter group for determining a constituent element of the neural network includes, for example, information indicating a connection relationship between units of the neural network, a weight coefficient, and the like. The learning model is, for example, transmitted from the monitoring computer  50  to the monitoring camera  10  via the PoE hub  20 , and is stored before the monitoring camera  10  starts to operate. 
     That is, the monitoring camera  10  constructs a corresponding neural network for each moving body (object) to be detected, and can detect the object by using the corresponding neural network. For example, the monitoring camera  10  constructs a neural network for detecting a person (specifically, the whole body of the person), a neural network for detecting the face of a person, and a neural network for detecting a vehicle, and can detect a corresponding moving body (object). 
     The PoE hub  20  transmits captured image data from the monitoring camera  10  to the recorder  30  and the monitoring computer  50 . For example, when the PoE hub  20  is connected to the monitoring camera  10  via a wired network (not shown, see the above description), the PoE hub  20  supplies driving power to the monitoring camera  10 . 
     When the recorder  30  receives, from the PoE hub  20 , the captured image data transmitted from the monitoring camera  10 , the recorder  30  stores the captured image data in association with storing date and time and camera identification information of the monitoring camera  10 . As described above, the captured image data includes the camera identification information of the monitoring camera  10  that is a generation source of the captured image data and imaging date and time information, in addition to the captured image data. Although not shown in  FIG. 1 , a plurality of recorders  30  may be connected to the PoE hub  20 . 
     The monitor  40  is a display device configured with, for example, a liquid crystal display (LCD) or an organic electroluminescence (EL). The monitor  40  displays the captured image data transmitted from recorder  30 , for example, when the captured image stored in recorder  30  is instructed to be displayed by an operation of a user (for example, an operator of the monitoring camera system  100 ). 
     The monitoring computer  50  is, for example, not only a desktop or notebook personal computer, but also an information processing device such as a smartphone, a tablet terminal, or a server computer machine having high-performance specifications. The monitoring computer  50  receives, for example, an operation of a user (see the above description), and receives captured image data of an imaging area (in other words, a monitoring area) captured by the monitoring camera  10  from the PoE hub  20  and displays the captured image data in accordance with the operation of the user. 
       FIG. 2  is a block diagram showing a hardware configuration example of the monitoring camera  10  according to the first embodiment. The monitoring camera  10  includes at least the imaging unit CAP 1 , a processor  13 , a memory  14 , a communication interface (IF) unit  15 , and the AI processing unit  16 . The imaging unit CAP 1  includes a lens  11  and an image sensor  12 . The AI processing unit  16  includes an AI calculation processing unit  161  and the learning model memory  162 . 
     The lens  11  as an example of the imaging unit CAP 1  includes, for example, a focus lens and a zoom lens. When incident light that is light reflected by a subject TRG 1  present in an imaging area is incident onto the lens  11 , the lens  11  forms an optical image of the subject TRG 1  on a light receiving surface (in other words, an imaging surface) of the image sensor  12 . The lens  11  includes lenses having various focal lengths or imaging ranges in accordance with an installation location, the imaging use, or the like of the monitoring camera  10 . 
     The image sensor  12  as an example of the imaging unit executes a photoelectric conversion for converting light received on a light receiving surface (in other words, an imaging surface) into an electric signal. The image sensor  12  is configured with, for example, a charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS). The image sensor  12  transmits an electric signal (analog signal) corresponding to the light received on the light receiving surface (in other words, the imaging surface) to the processor  13  at predetermined time intervals (for example, 1/60 (seconds)). That is, a frame rate of monitoring camera  10  is, for example, 60 frames per second (fps). This value is an example, and the frame rate is not limited to 60 fps. The analog signal is converted into captured image data in a digital format by the processor  13 . As a result, the captured image data is generated by the processor  13 . The conversion from the analog signal to the digital format may be executed by the image sensor  12 . In this manner, the monitoring camera  10  can acquire captured image data in a digital format at predetermined time intervals (for example, 1/60 (seconds)). 
     The processor  13  includes, for example, a central processing unit (CPU), a digital signal processor (DSP), a graphical processing unit (GPU), or a field programmable gate array (FPGA). The processor  13  functions as a controller that governs the overall operation of the monitoring camera  10 , and executes a control processing for governing the operation of each unit of the monitoring camera  10 , a data input and output processing among units of the monitoring camera  10 , a data calculation processing, and a data storing processing. The processor  13  operates in accordance with a program and data stored in the memory  14 . The processor  13  uses the memory  14  at the time of operation, and temporarily stores data or information generated or acquired by the processor  13  in the memory  14 . 
     For example, the processor  13  generates captured image data in a digital format by executing a predetermined signal processing on the electric signal output from the image sensor  12 , and transmits the captured image data to the AI processing unit  16 . As described above, the processor  13  can acquire captured image data in a digital format at predetermined time intervals (for example, 1/60 (seconds)), and transmits the acquired captured image data to the AI processing unit  16 . 
     The processor  13  executes a noise reduction processing on current captured image data (frame) generated by the image sensor  12  or the processor  13  by using a processing result (see the following description) of the AI processing unit  16 . Accordingly, in the current captured image data, the monitoring camera  10  can execute a noise reduction processing at a low intensity on an attention portion (for example, a portion of a moving body such as a face of a person detected by the AI processing unit  16 ) appearing in the captured image data to reduce an influence of an afterimage due to a movement, and can execute a noise reduction processing at a high intensity on a non-attention portion (for example, a portion where no movement occurs) present on the same captured image data to generate image data having a high signal noise ratio (SNR). Details of the noise reduction processing executed by the processor  13  will be described later with reference to  FIG. 3 . 
     The memory  14  is configured with, for example, a random access memory (RAM) and a read only memory (ROM), and temporarily stores a program necessary for executing an operation of the monitoring camera  10  and data or information generated during the operation. The RAM is, for example, a work memory used when monitoring camera  10  operates. The ROM pre-stores, for example, a program according to the present disclosure for controlling the monitoring camera  10 . In other words, the processor  13  can execute various processings related to the image quality improving method according to the present disclosure in the monitoring camera  10  that is a computer by executing the program stored in the ROM. 
     For example, the memory  14  stores a detection result (see the following description) of a moving body (object) such as a face of a person detected by the AI processing unit  16  based on captured image data generated by the image sensor  12  or the processor  13  in the past. 
     The communication IF unit  15  as an example of a communication unit executes data communication (transmission and reception) with the PoE hub  20  connected via a network (see the above description). For example, the communication IF unit  15  transmits the captured image data subjected to a noise reduction processing (see the following description) by the processor  13  to the PoE hub  20  via the network (see the above description). The communication IF unit  15  receives data or information transmitted from the monitoring computer  50  via the network (see the above description). 
     The AI processing unit  16  detects an object (for example, a moving body such as a face of a person) that is an attention portion from the captured image data transmitted from the processor  13  by using artificial intelligence (AI). The AI processing unit  16  is configured with, for example, a processor such as a CPU, a DSP, a GPU, and an FPGA, and a memory such as a flash memory. 
     The AI calculation processing unit  161  forms artificial intelligence (AI) based on a learning model stored in the learning model memory  162 . For example, the AI calculation processing unit  161  forms a neural network (see the above description) based on the learning model. The AI calculation processing unit  161  inputs the captured image data generated by the processor  13 , and detects an object (for example, a moving body such as a face of a person) that is an attention portion from the input captured image data by the neural network based on the learning model. A detailed configuration example of the AI calculation processing unit  161  will be described later with reference to  FIG. 3 . 
     The learning model memory  162  is configured with, for example, a memory such as a RAM, a ROM, and a flash memory. The learning model memory  162  stores a learning model that is used for a detection processing for each object (moving body) and is generated in advance by a learning processing. The AI calculation processing unit  161  executes a learning model for each object (moving body) from the learning model memory  162  to form a corresponding neural network (see the above description), thereby detecting an object (moving body) reflected in the captured image data. 
       FIG. 3  is a block diagram showing an example of a functional configuration of the processor  13  and the AI processing unit  16 . The processor  13  includes a frame buffer FB 1 , a cyclic coefficient deriving unit  131 , and a blending processing unit  132 . The AI calculation processing unit  161  of the AI processing unit  16  includes at least an AI detection unit  1611  and a pixel unit attention level deriving unit  1612 . The AI calculation processing unit  161  may further include a motion vector deriving unit  1613 . Although the learning model memory  162  is not shown in  FIG. 3 , at least the AI detection unit  1611  is functionally configured based on a learning model read from the learning model memory  162 . 
     The AI detection unit  1611  detects an object of an attention portion (for example, a moving body such as a face of a person) from the captured image data generated by the image sensor  12  or the processor  13  based on an AI learning model read from the learning model memory  162 . The AI detection unit  1611  derives, as a detection result, a detection area (k) of an object, an attention level (j) for each type of a detected object, a weight coefficient (s) based on a size of a detection area among a predetermined size of the captured image data, and an AI score (a) that indicates accuracy (certainty) of a detected object. 
     The detection area (k) has a value of “0” or “1” for each pixel among the number of pixels of the captured image data (for example, 1920×1080 pixels in the case of full high definition). The detection area (k) is “1” in the case of a pixel in which an object is detected, and the detection area (k) is “0” in the case of a pixel in which no object is detected. 
     The attention level (j) for each type of a detected object is a value indicating an attention level (j) predetermined for each type of an object (a moving body) to be focused in the captured image data. Here, the attention level (j) for each type of a detected object will be described with reference to  FIG. 4 .  FIG. 4  is a diagram showing an example of an attention level table indicating a type of a detected object and an attention level (j) for each type. 
     In the attention level table, a type of an object detected by the AI detection unit  1611  and a value of an attention level (j) predetermined for each type are associated with each other. An attention level (j) of a non-detection area in which no object is detected is “0”, that is a minimum value. Similarly, an attention level (j) of a vehicle of which a license plate is not detected (for example, a vehicle traveling in a lateral direction when viewed from the monitoring camera  10 ) is also “0” that is a minimum value. An attention level (j) of an animal is “0.4”. An attention level (j) of a person whose whole body is reflected is “0.6”. An attention level (j) of a person for whom only head portion is reflected is “0.6”. An attention level (j) of a two-wheel vehicle is “0.8”. An attention level (j) of a vehicle of which a license plate is detected (for example, a vehicle traveling in a direction of the monitoring camera  10 ) is “1” that is a maximum value. An attention level (j) of a face of a person is “1” that is a maximum value. 
     The weight coefficient (s) is a value derived by the AI detection unit  1611  according to a ratio of a detected object to a size of the captured image data, and specifically, has a value from “0” to “1”. For example, when the ratio of an object to the size of the captured image data is less than a lower limit value of a predetermined range, the weight coefficient (s) is “0”, and when the ratio of an object to the size of the captured image data is larger than an upper limit value of the predetermined range (see the above description), the weight coefficient (s) is “1”. 
     The AI score (a) is a value indicating the accuracy (that is, certainty) of a detected object, and specifically has a value from “0” to “1”. For example, when the accuracy of the object is larger than an upper limit value (that is, 80%) of a predetermined ratio range (for example, 30% to 80%), the AI score (a) is “1”, and when the certainty of the object is less than a lower limit value (that is, 30%) of the predetermined ratio range (for example, 30% to 80%), the AI score (a) is “0”. 
     The pixel unit attention level deriving unit  1612  derives an attention level for each pixel (that is, a pixel unit attention level) of the captured image data (hereinafter, also referred to as a “current frame”) that is a target of a detection processing by the AI detecting unit  1611 , by using a detection result from the AI detecting unit  1611 , and transmits a derivation result for each pixel to the cyclic coefficient deriving unit  131 . When the pixel unit attention level is high, the pixel unit is an attention portion in the captured image data. For example, the pixel unit attention level deriving unit  1612  derives (calculates) an attention level for each pixel (that is, a pixel unit attention level) in the current frame as F(k, s, a, j)=k×s×a×j. Therefore, the pixel unit attention level deriving unit  1612  derives, for example, an attention level of a non-detection area of an object or a vehicle (a license plate is not detected) as “0”. This is because the attention level (j) of the non-detection area and the attention level (j) of the vehicle (a license plate is not detected) are both “0”. 
     The pixel unit attention level deriving unit  1612  may derive an attention level for each pixel (that is, a pixel unit attention level) in the current frame by using not only the detection result from the AI detection unit  1611  but also a derivation result of a motion vector from the motion vector deriving unit  1613 . 
     The motion vector deriving unit  1613  calculates (an example of deriving) a motion vector indicating a moving direction and a moving amount of a moving body (for example, a person) in the captured image data based on a processing result of the AI detection unit  1611  (for example, a detection position in a current frame and a detection position in a previous frame of a moving body in the captured image data within the same angle of view). The motion vector deriving unit  1613  transmits the calculation (derivation) result to the pixel unit attention level deriving unit  1612 . 
     When the pixel unit attention level deriving unit  1612  acquires the derivation result of the motion vector from the motion vector deriving unit  1613 , the pixel unit attention level deriving unit  1612  derives (calculates) an attention level for each pixel (that is, a pixel unit attention level) in the current frame as F(k, s, a, j, v)=k×s×a×j×v. The pixel unit attention level deriving unit  1612  transmits the derivation result of F(k, s, a, j, v)=k×s×a×j×v (that is, the pixel unit attention level) to the cyclic coefficient deriving unit  131 . 
     The frame buffer FB 1  is configured with a semiconductor memory such as a RAM, and temporarily stores the captured image data (that is, a current frame (=cur_frame)) generated by the image sensor  12  or the processor  13  at predetermined time intervals (for example, 1/60 seconds). 
     The cyclic coefficient deriving unit  131  uses the derivation result of the pixel unit attention level from the pixel unit attention level deriving unit  1612  and a previous frame and a current frame read from the frame buffer FB 1  to execute a spatial filter processing on the derivation result of the pixel unit attention level in the current frame, and further executes a time filter processing using the pixel unit attention level in the current frame and a pixel unit attention level in the previous frame. Accordingly, the cyclic coefficient deriving unit  131  can derive a cyclic coefficient a using an NR (noise reduction) processing executed by the blending processing unit  132  (see  FIGS. 5 and 6 ). Specifically, the cyclic coefficient deriving unit  131  derives (calculates) the cyclic coefficient α=G(t, x)={γF(t)+(1−γ)G(t−1, x)}×{(m−x)/m}, and transmits the derivation result to the blending processing unit  132 . γ is a cyclic coefficient of a time filter, has a fixed value, and has a value of 0 to 1. 
     Here, the spatial filter processing will be described with reference to  FIG. 5 , and the time filter processing will be described with reference to  FIG. 6 .  FIG. 5  is a graph showing an example of a relationship between an image space direction and an attention level after the spatial filter processing.  FIG. 6  is a graph showing an example of a relationship between time and an attention level after the time filter processing. In  FIG. 5 , a horizontal axis represents the image space direction, and a vertical axis represents an attention level after the spatial filter processing. In  FIG. 6 , a horizontal axis represents time, and a vertical axis represents an attention level after the time filter processing. 
     An area ATT 1  of a face of a person and the vicinity of the face of the person in the captured image data shown in  FIG. 5  is, for example, an attention portion (that is, a portion from AI in to AI out) indicating an object (a moving body) detected by the AI detection unit  1611 . The cyclic coefficient deriving unit  131  executes the spatial filter processing in the image space direction (that is, multiplies {(m−x)/m} of the expression G(t, x) described above). The spatial filter processing has a characteristic of gradually reducing (for example, linearly reducing) an attention level toward the periphery (for example, a peripheral area PERI) of the attention portion (in the area ATT 1 ). In  FIG. 5 , x represents a distance from an attention portion detected by the AI detection unit  1611 , and m represents a space effective range which is a predetermined fixed value (that is, a range indicating that a range from the attention portion to where is regarded as effective as the attention portion). Therefore, the cyclic coefficient deriving unit  131  can prevent the occurrence of a phenomenon in which an attention level is rapidly reduced at the moment when a portion becomes a non-attention portion in the image space direction by executing the spatial filter processing. Accordingly, the cyclic coefficient deriving unit  131  appropriately maintains the continuity between an attention portion and a peripheral area of the attention portion in the captured image data (for example, the fact that an afterimage is less likely to occur in the image space direction) when the noise reduction processing (blending processing) to be described later is executed. 
     In the horizontal axis shown in  FIG. 6 , a time point t 1  indicates a time point at which an end portion (for example, a contour portion) of an attention portion starts to be detected by the AI detection unit  1611 , a time point t 2  indicates a time point at which a central portion of the attention portion starts to be detected by the AI detection unit  1611 , a time point t 3  indicates a time point at which the detection of the attention portion by the AI detection unit  1611  is completed, and a time point t 4  indicates a time point at which the detection processing by the AI detection unit  1611  is completed. The cyclic coefficient deriving unit  131  uses the pixel unit attention level F(t) in the current frame and the pixel unit attention level G(t−1) after the spatial filter and the time filter are applied in the previous frame to execute the time filter processing having the characteristics shown in  FIG. 6  in a time direction (that is, multiplies {γF(t)+(1−γ)G(t−1, x)} of the expression G(t, x) described above). Therefore, the cyclic coefficient deriving unit  131  can appropriately maintain the temporal continuity of the captured image data (for example, the fact that an afterimage is less likely to occur in the time direction) so as to prevent a rapid change of the attention portion in a temporal front-back direction. 
     Here, a relationship among the cyclic coefficient a, the intensity of the noise reduction processing executed by the blending processing unit  132 , an SNR effect, and an afterimage prevention effect will be described with reference to  FIG. 10 .  FIG. 10  is a diagram showing an example of a correspondence relationship among the noise reduction intensity, the SNR, and the afterimage prevention effect. 
     The cyclic coefficient a used in the noise reduction processing has a value of 0 to 1. When the cyclic coefficient a is small, the weight (influence) on the noise reduction processing by the previous frame is large, and the intensity of the noise reduction processing is high. In other words, a noise reduction effect in the current frame is enhanced due to the influence of the previous frame, thus the SNR is improved, and an afterimage prevention effect is reduced since it is likely to be influenced by the previous frame (see  FIG. 10 ). 
     On the other hand, when the cyclic coefficient a is large, the weight (influence) on the noise reduction processing by the current frame is large, and the intensity of the noise reduction processing is low. That is, a noise reduction effect in the current frame is reduced due to the influence of the current frame, thus an SNR improvement effect is reduced, and an afterimage prevention effect is increased since it is less likely to be influenced by the previous frame (see  FIG. 10 ). 
     The blending processing unit  132  executes a noise reduction processing on the current frame by using the derivation result of the cyclic coefficient a from the cyclic coefficient deriving unit  131 , the previous frame, and the current frame. Specifically, the blending processing unit  132  executes an image processing (a noise reduction processing) of α×current frame (cur_frame)+(1−α)×previous frame (pre_frame) and outputs a result. In the first embodiment, the cyclic coefficient α is not a uniform (same) value over the entire (all) predetermined size of the current frame (captured image data), and the cyclic coefficient a is derived in a manner in which an attention portion has a high cyclic coefficient α (that is, the intensity of the noise reduction processing is low) and a non-attention portion has a low cyclic coefficient a (that is, the intensity of the noise reduction processing is high). 
     Therefore, the blending processing unit  132  can enhance the afterimage prevention effect by executing the noise reduction processing on the attention portion (for example, a moving body such as a face of a person) in the current frame (captured image data) at a lower intensity than an intensity (a reference intensity) at the time of a normal noise reduction processing. On the other hand, the blending processing unit  132  can enhance the SNR improvement effect by executing the noise reduction processing on the non-attention portion (for example, a background portion in which no moving body is present) in the current frame (captured image data) at a higher intensity than the intensity (the reference intensity) at the time of a normal noise reduction processing. The reference intensity is, for example, a median value (0.5) of the cyclic coefficient a, and is not limited to this value as long as the reference intensity is a value larger than “0” and less than “1” at which the effect of the noise reduction processing is obtained. 
       FIG. 7  is a diagram showing an example of a correspondence relationship between detection areas AR 1 , AR 2 , AR 3 , AR 4 , AR 5 , AR 6 , AR 7 , and AR 8  of objects in captured image data IMG 1  detected by the AI detection unit  1611  and attention levels (j) of the detection areas AR 1 , AR 2 , AR 3 , AR 4 , AR 5 , AR 6 , AR 7 , and AR 8 . 
     The AI detection unit  1611  detects a vehicle traveling along the direction of the monitoring camera  10  in the detection area AR 1 , detects a driver of a two-wheel vehicle traveling along the direction of the monitoring camera  10  in the detection area AR 2 , detects a face of a pedestrian (person) walking along the direction of the monitoring camera  10  in the detection area AR 3 , and detects a two-wheel vehicle traveling along the direction of the monitoring camera  10  in the detection area AR 4 . In addition, the AI detection unit  1611  detects two persons riding on a two-wheel vehicle traveling along the direction of the monitoring camera  10  in the detection area AR 5 , detects a face of a pedestrian (person) who stands still while facing the monitoring camera  10  in the detection area AR 6 , detects the whole body of the pedestrian (person) who stands still while facing the monitoring camera  10  in the detection area AR 7 , and detects a two-wheel vehicle traveling along the direction of the monitoring camera  10  in the detection area AR 8 . A non-detection area AR 9  is an area in which no object (moving body) to be focused is detected by the AI detection unit  1611 . 
     The pixel unit attention level deriving unit  1612  refers to the attention level table in  FIG. 4  and derives attention levels (j) of pixels corresponding to portions AT 1 , AT 2 , AT 3 , AT 4 , AT 5 , AT 6 , AT 7 , and AT 8  of the objects (moving bodies) detected in the detection areas AR 1 , AR 2 , AR 3 , AR 4 , AR 5 , AR 6 , AR 6 , AR 7 , and AR 8  as “1”, “0.6”, “1”, “0.8”, “0.6”, “1”, “0.6”, and “0.8”. The pixel unit attention level deriving unit  1612  derives an attention level (j) of a pixel corresponding to the non-detection area AR 9  as “0”. In this manner, the pixel unit attention level deriving unit  1612  generates an attention level map MP 1  in which an attention level (j) for each pixel corresponding to the captured image data IMG 1  shown in  FIG. 7  is expanded, and stores the attention level map MP 1  in the memory  14 . The pixel unit attention level deriving unit  1612  derives the pixel unit attention level F(k, s, a, j) or the pixel unit attention level F(k, s, a, j, v) with reference to the attention level map MP 1  described above. 
     The pixel unit attention level deriving unit  1612  may select a high attention level (j) when deriving an attention level (j) of a pixel in a portion where two or more detection areas overlap with each other. For example, the detection areas AR 2  and AR 4  overlap with each other in partial areas, as shown in  FIG. 7 , the pixel unit attention level deriving unit  1612  selects the attention level (j)=“0.8” of the detection area AR 4  that is higher than the attention level (j)=“0.6” of the detection area AR 2  as an attention level (j) in the overlapped partial areas. Similarly, a higher attention level (j) may be selected in other overlapped areas (for example, an area in which the detection areas AR 1  and AR 4  overlap with each other). 
       FIG. 8  is a diagram showing an example of a correspondence relationship between detection assumption areas AR 11 , AR 12 , and AR 13  of captured image data IMG 2  and attention levels of the detection assumption areas AR 11 , AR 12 , and AR 13 .  FIG. 9  is a diagram showing an example of an attention level table indicating an attention level (j) for each detection assumption area of the captured image data in  FIG. 8 . 
     In the first embodiment, the pixel unit attention level deriving unit  1612  may use the attention level table (see  FIG. 9 ) provided in advance for each position (coordinate) in the captured image data IMG 2 , instead of the “attention level (j) for each type of a detected object” included in a detection result from the AI detection unit  1611 . 
     In the attention level table in  FIG. 9 , a detection assumption area in which it is assumed that an object (moving body) is detected in view of a mounting position of the monitoring camera  10  is associated with a value of an attention level (j) predetermined for each detection assumption area. For example, in the captured image data IMG 2  in  FIG. 8 , an attention level (j) is set to a low value of “0.1” in view of the fact that the probability of detecting an object (a moving body) in a portion “other than a road” is low. Similarly, an attention level (j) is set to “0.5” (median value) in view of the fact that an object (a moving body) is detected on a road provided at a position far from the monitoring camera  10  in a portion “road (far)”. An attention level (j) is set to “1” (maximum value) in view of the fact that an object (a moving body) is likely to be detected on a road provided at a position close to the monitoring camera  10  in a portion “road (near)”. 
     Therefore, the pixel unit attention level deriving unit  1612  refers to the attention level table in  FIG. 9 , and fixedly derives attention levels (j) of pixels corresponding to contour portions AT 11 , AT 12 , and AT 13  of the detection assumption areas AR 11 , AR 12 , and AR 13  as “0.5”, “0.1”, and “1”. In this manner, the pixel unit attention level deriving unit  1612  generates an attention level map MP 2  in which an attention level (j) for each detection assumption area corresponding to the captured image data IMG 2  shown in  FIG. 8  is expanded, and stores the attention level map MP 2  in the memory  14 . The pixel unit attention level deriving unit  1612  derives the pixel unit attention level F(k, s, a, j) or the pixel unit attention level F(k, s, a, j, v) with reference to the attention level map MP 2  described above. 
     Next, an operation procedure of the monitoring camera  10  according to the first embodiment will be described with reference to  FIG. 11 .  FIG. 11  is a flowchart showing an example of an operation procedure of the monitoring camera  10  according to the first embodiment. Each operation (step) shown in  FIG. 11  is mainly executed by the processor  13  or the AI processing unit  16  of the monitoring camera  10 . 
     In  FIG. 11 , the processor  13  acquires captured image data (that is, a current frame) generated by the image sensor  12  or the processor  13 , and stores the captured image data in the memory  14  (St 1 ). The AI processing unit  16  (for example, the AI detection unit  1611 ) detects an object of an attention portion (for example, a moving body such as a face of a person) from the captured image data acquired in step St 1 , based on an AI learning model read from the learning model memory  162  (St 2 ). The AI processing unit  16  (for example, the motion vector deriving unit  1613 ) may derive a motion vector indicating a moving direction and a moving amount of the moving body (for example, a person) in the captured image data based on the detection result in step St 2  (for example, a detection position in a current frame and a detection position in a previous frame of the moving body in the captured image data within the same angle of view) (St 2   a ). 
     The AI processing unit  16  (for example, the pixel unit attention level deriving unit  1612 ) derives an attention level for each pixel (that is, a pixel unit attention level) of the captured image data (the current frame) to be processed in step St 2  or steps St 2  and St 2   a  by using the processing result in step St 2  or steps St 2  and St 2   a  (St 3 ). 
     When the processor  13  (for example, the cyclic coefficient deriving unit  131 ) determines that the derivation result in step St 3  (that is, the pixel unit attention level F(k, s, a, j) or F(k, s, a, j, v)) is 0 (St 4 , YES), the processor  13  determines an intensity of the noise reduction processing (that is, the cyclic coefficient α) to be a predetermined maximum value because the pixel is not an attention portion (St 5 ). 
     On the other hand, when the processor  13  (for example, the cyclic coefficient deriving unit  131 ) determines that the derivation result in step St 3  (that is, the pixel unit attention level F(k, s, a, j) or F(k, s, a, j, v)) is not 0 (St 4 , NO), the processor  13  determines an intensity of the noise reduction processing (that is, the cyclic coefficient α) according to a pixel unit attention level so that the intensity of the noise reduction processing is less than a maximum value because the pixel is an attention portion (St 6 ). 
     The processor  13  (for example, the blending processing unit  132 ) executes a noise reduction processing on the current frame using the derivation result of the cyclic coefficient α derived in step St 5  or step St 6 , the previous frame, and the current frame (St 7 ). When the operation of the monitoring camera  10  is completed after step St 7  (St 8 , YES), the operation of the monitoring camera  10  is ended. 
     On the other hand, when the operation of the monitoring camera  10  is not completed after step St 7  (St 8 , NO), the processing of the monitoring camera  10  is returned to step St 1 . That is, the monitoring camera  10  repeatedly executes the processings in steps St 1  to St 8  until the operation of the monitoring camera  10  is completed. 
     Next, an image comparison when the noise reduction processing is executed on captured image data in a comparative example and the first embodiment will be described with reference to  FIGS. 12 and 13 .  FIG. 12  is a diagram showing an example of a comparison result between a captured image after an NR processing in a case where there is no attention area and a captured image after an NR processing in a case where attention is focused on a face of a person.  FIG. 13  is a diagram showing an example of a comparison result between a captured image after an NR processing in a case where there is no attention area and a captured image after an NR processing in a case where attention is focused on a vehicle traveling in a monitoring camera direction. In both captured image data IMG 21  and IMG 22  shown in  FIG. 13 , a part of a vehicle is partially extracted. 
     In  FIG. 12 , it is assumed that a face of a person is detected in a room (indoors) in both captured image data IMG 11  and IMG 12 . Different from the first embodiment, the noise reduction processing is uniformly executed on both a moving body portion AR 21   z  (for example, a face of a person) and a portion other than the moving body portion AR 21   z  in the captured image data IMG 11  in the comparative example. Therefore, as shown in an enlarged view ExT 11  of the moving body portion AR 21   z , an intensity of the noise reduction processing is higher than the reference intensity, and thus an afterimage remains, and the image quality of the captured image data IMG 11  deteriorates. Therefore, the recognition accuracy of the moving body portion (for example, a face of a person) in the captured image data after the noise reduction processing is reduced. 
     On the other hand, the intensity of the noise reduction processing on an attention portion AR 21  that is a moving body portion in the captured image data IMG 12  and the intensity of the noise reduction processing on a portion other than the attention portion AR 21  (that is, a non-detection area) are different from each other in the first embodiment. Accordingly, since the monitoring camera  10  according to the first embodiment executes the noise reduction processing on the attention portion AR 21  at a lower intensity than the reference intensity, the afterimage prevention effect on the attention portion AR 21  that is a moving body portion is improved. Therefore, as shown in an enlarged view ExT 12  of the attention portion AR 21  that is a moving body portion, since the intensity of the noise reduction processing is lower than the reference intensity, the afterimage prevention effect is improved, blurs of the moving body portion is reduced, and the image quality is improved. Since the monitoring camera  10  executes the noise reduction processing on the portion other than the attention portion AR 21  (that is, the non-detection area) at a higher intensity than the reference intensity, the SNR improvement effect is improved. Accordingly, the recognition accuracy of the attention portion AR 21  (for example, a face of a person) in the captured image data after the noise reduction processing is improved. 
     In  FIG. 13 , it is assumed that a vehicle is detected in both of the captured image data IMG 21  and IMG 22 . Different from the first embodiment, the noise reduction processing is uniformly executed on both an attention portion (for example, a vehicle traveling toward the monitoring camera) and a portion other than the attention portion in the captured image data IMG 21  and IMG 22  in the comparative example. Therefore, as shown in an enlarged view ExT 21  of the captured image data IMG 22 , an intensity of the noise reduction processing is higher than the reference intensity, and thus an afterimage remains over the entire captured image data IMG 22 , and the image quality of the captured image data IMG 22  deteriorates. Although the captured image data IMG 21  is not shown in the enlarged view ExT 21 , the image quality of the captured image data IMG 21  deteriorates because the noise reduction processing is executed at a uniform intensity over the entire captured image data IMG 21  in a similar manner. Therefore, the recognition accuracy of a license plate in the captured image data IMG 21  and IMG 22  after the noise reduction processing is reduced. 
     On the other hand, the intensity of the noise reduction processing on an attention portion in the captured image data IMG 22  (for example, a vehicle traveling toward the monitoring camera  10 ) and the intensity of the noise reduction processing on a portion (for example, a portion other than the vehicle) other than the attention portion are different from each other in the first embodiment. Accordingly, the monitoring camera  10  according to the first embodiment executes the noise reduction processing on the attention portion at a lower intensity than the reference intensity, and thus the afterimage prevention effect of the vehicle traveling toward monitoring camera  10  is improved. Therefore, as shown in an enlarged view ExT 22  of the captured image data IMG 22 , since the intensity of the noise reduction processing is lower than the reference intensity, the afterimage prevention effect of the vehicle portion is improved, blurs of the vehicle that is a moving body portion is reduced, and the image quality is improved. Since the monitoring camera  10  executes the noise reduction processing on a portion other than the attention portion (that is, a portion other than the vehicle) at a higher intensity than the reference intensity, the SNR improvement effect is improved. 
     As described above, the monitoring camera  10  according to the first embodiment includes the imaging unit CAP 1  that captures an image of an imaging area, and the processor  13  that determines a first intensity indicating an intensity of the noise reduction processing executed on an attention portion (for example, the detection area AR 1 ) in the captured image of the imaging area and a second intensity indicating an intensity of the noise reduction processing executed on a non-attention portion (for example, the non-detection area AR 9 ) in the captured image to be different from each other. The first intensity is lower than the second intensity. The processor  13  executes the noise reduction processing on the attention portion based on the determined first intensity, executes the noise reduction processing on the non-attention portion based on the determined second intensity, and outputs an image after the noise reduction processing. 
     Accordingly, the monitoring camera  10  can prevent an afterimage of a subject to be focused in the captured image data regardless of the brightness and darkness of an environment around an installation location of the monitoring camera  10 , and can reduce noises in the entire image (that is, the entire size of the captured image data). Therefore, the monitoring camera  10  can improve the recognition accuracy of a subject in the captured image data after the noise reduction processing by executing the noise reduction processing on the attention portion and the non-attention portion at different intensities. 
     The monitoring camera  10  further includes the AI detection unit  1611  that detects an attention portion in the captured image of the imaging area by using an artificial intelligence (AI) learning model. Accordingly, the monitoring camera  10  can detect an attention portion (for example, a moving body such as a face of a person) in the captured image data with high accuracy. 
     The processor  13  determines at least one of the first intensity and the second intensity based on an attention level for each type of a subject indicated by an attention portion of the captured image data. Accordingly, the monitoring camera  10  can execute highly accurate image editing such that an afterimage is not noticeable even when the noise reduction processing is executed on an object (a moving body) having a high ratio (tendency) to be focused in a recognition processing of the captured image data. 
     The processor  13  determines at least one of the first intensity and the second intensity based on the presence or absence of an attention portion (for example, the detection area (k)), an attention coefficient for each type of a subject indicated by an attention portion (for example, the attention level (j) for each type of a detected object), a weight coefficient (for example, the weight coefficient (s)) based on a size of an attention portion, and the certainty (for example, the AI score (a)) of a subject detected by the AI learning model. Accordingly, the monitoring camera  10  can adaptively determine the intensity of the noise reduction processing to be executed on an attention portion (for example, a moving body such as a face of a person) in accordance with various pieces of attribute information of the attention portion reflected in the captured image data. 
     The processor  13  determines the second intensity to be a maximum value. As a result, the monitoring camera  10  can reduce a noise component of a non-attention portion in the captured image data or a portion of the captured image data that is less likely to be focused by the noise reduction processing, and thus can improve the SNR of the entire captured image data. 
     The processor  13  drives an attention level of a current frame based on the presence or absence of an attention portion (for example, the detection area (k)), an attention coefficient for each type of a subject indicated by an attention portion (for example, the attention level (j) for each type of a detected object), a weight coefficient (for example, the weight coefficient (s)) based on a size of an attention portion, and the certainty (for example, the AI score (a)) of a subject detected by the AI learning model, and determines the first intensity by executing a spatial filter processing and a time filter processing using the derived attention level of a current frame and an attention level of a previous frame immediately before the current frame. As a result, the monitoring camera  10  can prevent the occurrence of a phenomenon in which an attention level is rapidly reduced at the moment when a portion becomes a non-attention portion in the image space direction, and can appropriately maintain the continuity between an attention portion and a peripheral area of the attention portion in the captured image data (for example, the fact that an afterimage is less likely to occur in the image space direction) when the noise reduction processing (the blending processing) is executed. The monitoring camera  10  can appropriately maintain the temporal continuity of the captured image data (for example, the fact that an afterimage is less likely to occur in the time direction) so as to prevent a rapid change of the attention portion in a temporal front-back direction. 
     The processor  13  determines the first intensity based on an attention level determined for each coordinate in the captured image of the imaging area. Accordingly, the monitoring camera  10  can easily select an attention level for each pixel according to a position (coordinates) of the captured image data of the imaging area, and thus can easily determine the first intensity. 
     The processor  13  further determines the first intensity based on the motion vector (v) of a subject. Accordingly, for example, even when an attention portion (for example, a face of a person) is detected by the AI detection unit  1611 , in a case where no motion occurs based on a value of the motion vector, image quality is less likely to deteriorate even when the monitoring camera  10  executes the noise reduction processing at an intensity the same as a still portion. 
     The attention portion is a moving body moving in the imaging area. Accordingly, the monitoring camera  10  can improve the afterimage prevention effect by executing the noise reduction processing at a low intensity on a focused moving body moving in the imaging area, and can improve the SNR by executing the noise reduction processing at a high intensity on a portion that does not move in the imaging area. 
     Although various embodiments have been described above with reference to the drawings, it is needless to say that the present disclosure is not limited to such examples. It will be apparent to those skilled in the art that various alterations, modifications, substitutions, additions, deletions, and equivalents can be conceived within the scope of the claims, and it should be understood that such changes also belong to the technical scope of the present disclosure. Components in various embodiments described above may be combined freely within a range not deviating from the spirit of the invention. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is useful as a monitoring camera, an image quality improving method, and a program for preventing an afterimage of a subject to be focused in a captured image, reducing noises, and improving recognition accuracy of the subject, regardless of a surrounding environment.