Endoscope system and interface adapter

Abstract

Provided are: an interface adapter that allows for a reduction in the cost for constructing a system that enables the display of images, which are formed based on imaging signals obtained using a scope, on a general-purpose portable information terminal; and an endoscope system including the interface adapter. An interface adapter (4) comprises: a first communication interface (41) for communicating with a scope (1) including an imaging sensor (23) and a light source device (5); a second communication interface (43) for communicating with a portable information terminal (7); and a processor (a signal processing unit (42) and a system control unit (44)). The processor causes the imaging sensor (23) to perform imaging while controlling the amount of illumination light of the scope (1) to a constant amount, controls the imaging sensitivity and the light exposure time of the imaging sensor (23) on the basis of the brightness of an imaged site determined on the basis of an imaging signal obtained through the imaging, converts the imaging signal into image data that can be displayed by the portable information terminal (7), and transmits the image data to the portable information terminal (7).

Description

Endoscope system and interface adapter

[0001] The present invention relates to an endoscope system and an interface adapter.

[0002] In recent years, disposable endoscopes that can be used hygienically and safely for a single time have been attracting attention. Patent Document 1 describes an endoscope in which an image signal is transmitted from the camera of the endoscope to a control operation unit, and the image signal is then sent from the control operation unit to a video display via an electric wire. Patent Document 2 describes a laparoscope system in which a laparoscope communicates with a dongle, and the dongle transmits image data to a television display.

[0003] Japanese Patent Publication No. 2012-511357 Japanese Patent Publication No. 2020-18876

[0004] An object of the present disclosure is to construct, at low cost, a system that can display images based on imaging signals obtained by a scope on a general-purpose portable information terminal.

[0005] An interface adapter according to one aspect of the present disclosure comprises a first communication interface for communicating with a scope including an imaging sensor and a light source device that generates illumination light for imaging by the imaging sensor, a second communication interface for communicating with a portable information terminal, and a processor, wherein the processor causes the imaging sensor to perform imaging while controlling the amount of illumination light to be constant, converts an imaging image signal obtained by the imaging sensor into image data that can be displayed by the portable information terminal, transmits the image data to the portable information terminal, derives brightness of the image data based on the imaging image signal, and controls the imaging sensitivity of the imaging sensor and the exposure time of the imaging sensor based on the brightness.

[0006] According to the present disclosure, a system can be constructed at low cost that enables images based on imaging signals obtained by a scope to be displayed on a general-purpose portable information terminal.

[0007] 1 is a diagram illustrating an example of an endoscope system 100 according to an embodiment of the present invention. FIG. 1 is a diagram illustrating an example of an interface adapter 4. FIG. 2 is a diagram illustrating an example of an interface adapter 4. FIG. 1 is a diagram illustrating an example of a state before the interface adapter 4 and the portable information terminal 7 are housed in the frame 8. FIG. 2 is a diagram illustrating an example of a state before the interface adapter 4 and the portable information terminal 7 are housed in the frame 8. FIG. 1 is a diagram illustrating an example of a state after the interface adapter 4 and the portable information terminal 7 are attached to a rear case 82. FIG. 2 is a diagram illustrating an example of a state after the interface adapter 4 and the portable information terminal 7 are attached to the rear case 82. FIG. 1 is a diagram illustrating an example of a state after a front cover 81 is attached to the rear case 82. FIG. 2 is a diagram illustrating an example of a state after the front cover 81 is attached to the rear case 82. FIG. 3 is a diagram illustrating an example of the internal configuration of the scope 1 and the interface adapter 4. FIG. 4 is a diagram illustrating an example of the hardware configuration of the portable information terminal 7. FIG. 5 is a flowchart for explaining detailed examples of photometry processing and exposure control performed by a system control unit 44. 5 is a schematic diagram illustrating the relationship between the magnitude of the exposure change amount ΔEV [Log] and the exposure time SS and the amplification factor DG. FIG. 6 is a schematic diagram for explaining gamma correction processing. FIG. 7 is a schematic diagram illustrating an example of an image displayed on the display unit 7a when the scope 1 is a bronchial endoscope. FIG. 8 is a diagram illustrating an example of display of image data that has been gamma corrected so as to have the output gradation characteristics of the solid line shown in graph 53. FIG. 9 is a diagram illustrating an example of a gain correction table.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] <Endoscope system 100 according to one embodiment of the present invention> Fig. 1 is a diagram showing an example of an endoscopic system 100 according to one embodiment of the present invention. The endoscopic system 100 includes a scope 1, an interface adapter 4 connected to the scope 1, and a frame 8 that houses a portable information terminal 7 connected to the interface adapter 4. In Fig. 1, the interface adapter 4 is located behind the portable information terminal 7 and is covered by the frame 8, so it is not visible. The endoscopic system 100 may further include the portable information terminal 7.

[0010] The scope 1 is an endoscope that includes an insertion section 10, which is a tubular member extending in one direction and is inserted into a subject, and an operation section 11 that is provided at the base end of the insertion section 10 and is used to perform various operations on the scope 1. The operation section 11 includes, for example, an angle knob that is rotated to bend the insertion section 10. The operation section 11 may also include operation members for switching the observation mode of the scope 1, image capture and recording, forceps operation, air and water supply operation, suction operation, and the like.

[0011] The scope 1 is connected to the interface adapter 4 via a communication cable 13. The scope 1 is detachable from the interface adapter 4 via the communication cable 13 and can be used once (i.e., disposable). For example, the communication cable 13 may be detachable from the interface adapter 4, or the scope 1 may be detachable from the communication cable 13.

[0012] Although not shown in FIG. 1, various channels may be provided inside the operation unit 11 and the insertion unit 10, such as a forceps hole for inserting forceps to collect biological tissue such as cells or polyps, a channel for supplying air and water, and a channel for suction.

[0013] The insertion section 10 is composed of a flexible soft section 10A, a bending section 10B provided at the tip of the soft section 10A, and a rigid tip section 10C provided at the tip of the bending section 10B. The bending section 10B is configured to be bendable by operating an operation section 11 (e.g., an angle knob). This bending section 10B can be bent in any direction and at any angle depending on the part of the subject on which the scope 1 is used, and the tip section 10C can be pointed in a desired direction.

[0014] The interface adapter 4 connects the scope 1 and the portable information terminal 7. Specifically, the interface adapter 4 is communicatively connected to the scope 1 via, for example, a communication cable 13. The interface adapter 4 is also communicatively connected to the portable information terminal 7 via a wired or wireless connection.

[0015] The interface adapter 4 also receives from the scope 1 an imaging signal obtained by imaging the inside of the subject with the imaging sensor of the scope 1, and converts the received imaging signal into image data that can be displayed on the portable information terminal 7. The interface adapter 4 then transmits the converted image data to the portable information terminal.

[0016] The portable information terminal 7 is a general-purpose portable information terminal such as a tablet terminal or a smartphone. The portable information terminal 7 has a display unit 7a that can display images based on image data. The portable information terminal 7 receives captured images, etc., obtained by capturing images of the inside of a subject using the scope 1 from the interface adapter 4, and displays the received captured images on the display unit 7a. The display unit 7a has a display surface on which display pixels are arranged two-dimensionally, and pixel data that constitutes image data is drawn on each display pixel of this display surface, thereby displaying an image based on this image data. The portable information terminal 7 also serves as a user interface that controls the interface adapter 4.

[0017] <Interface adapter 4> Figures 2 and 3 are diagrams showing an example of the interface adapter 4. Figures 2 and 3 show the interface adapter 4 viewed from different directions. As shown in Figures 2 and 3, the interface adapter 4 has a substantially rectangular parallelepiped shape and has a video input terminal 4a and a video output terminal 4b.

[0018] The video input terminal 4a and the video output terminal 4b can each be a terminal of various communication standards capable of transmitting video signals, such as USB (Universal Serial Bus), HDMI (High-Definition Multimedia Interface), DVI (Digital Visual Interface), etc. HDMI is a registered trademark.

[0019] The video input terminal 4a is a terminal for connecting so as to be able to communicate with the scope 1. For example, the video input terminal 4a is an HDMI terminal, and an HDMI terminal is also provided on the scope 1. The communication cable 13 is an HDMI cable, and the video input terminal 4a and the HDMI terminal of the scope 1 are connected by the communication cable 13.

[0020] However, the connection between the interface adapter 4 and the scope 1 is not limited to HDMI connection, and may be a wired connection other than HDMI, such as USB or DVI, or a wireless connection such as Bluetooth or short-range wireless communication. Bluetooth is a registered trademark. The connection between the interface adapter 4 and the scope 1 may also be made via a conversion adapter that converts communication standards.

[0021] The video output terminal 4b is a terminal for communicatively connecting to the portable information terminal 7. For example, the video output terminal 4b is a USB terminal, and the portable information terminal 7 is also provided with a USB terminal. The video output terminal 4b and the USB terminal of the portable information terminal 7 are connected by a USB cable.

[0022] However, the connection between the interface adapter 4 and the portable information terminal 7 is not limited to a USB connection, and may be a wired connection other than USB, such as HDMI or DVI, or a wireless connection such as Bluetooth or short-range wireless communication. Furthermore, the connection between the interface adapter 4 and the portable information terminal 7 may be made via a conversion adapter that converts communication standards.

[0023] The interface adapter 4 also includes circuits for controlling the scope 1 and converting the image signal from the scope 1 into image data that can be displayed on the portable information terminal 7. The internal configuration of the interface adapter 4 will be described later (see, for example, FIG. 10).

[0024] <State of Interface Adapter 4 and Portable Information Terminal 7 Before Being Housed in Frame 8> Figures 4 and 5 are diagrams showing an example of the state of the interface adapter 4 and the portable information terminal 7 before being housed in the frame 8. Figures 4 and 5 show the interface adapter 4, the portable information terminal 7, and the frame 8 viewed from different directions. As shown in Figures 4 and 5, the frame 8 includes a front cover 81 and a rear case 82.

[0025] The front cover 81 is a member that protects the front surface of the portable information terminal 7. The front cover 81 has an opening 81a for exposing the display unit 7a (touch panel) of the portable information terminal 7 from the front cover 81 so that display on the display unit 7a and touch operation on the display unit 7a are possible.

[0026] The rear case 82 is a member that protects the back surface of the portable information terminal 7. The rear case 82 is also provided with a cable insertion hole (not shown) so that a communication cable 13 can be connected from outside the frame 8 to the video input terminal 4a of the interface adapter 4 housed in the frame 8, and the rear case 82 is provided with a cable insertion hole cover 82a that covers this cable insertion hole. The rear case 82 is also provided with a notation viewing hole 82b so that notations such as standard compliance on the housing of the interface adapter 4 can be seen from outside the frame 8.

[0027] The interface adapter 4 is housed in the frame 8 together with the portable information terminal 7, thereby fixing the interface adapter 4 to the frame 8. In the example of Figures 4 and 5, the interface adapter 4 is attached to the back surface of the portable information terminal 7 fixed by the frame 8, thereby fixing the interface adapter 4 to the frame 8 via the portable information terminal 7.

[0028] The interface adapter 4 is attached to the portable information terminal 7, for example, by screws using screw holes provided on the back surface of the portable information terminal 7. Alternatively, the interface adapter 4 may be attached to the portable information terminal 7 via a metal plate or the like formed to match the shape of the back surface of the interface adapter 4.

[0029] Furthermore, the interface adapter 4 is not limited to being fixed to the frame 8 via the portable information terminal 7, and may be attached directly to the frame 8. For example, the interface adapter 4 may be attached to the rear case 82 of the frame 8.

[0030] A stand 82c may be provided on the outside of the rear case 82. The stand 82c is provided on the rear case 82 via a hinge, for example, and by pulling out a part of the stand 82c from the rear case 82, the frame 8 can be placed upright on a horizontal surface such as a table top.

[0031] Furthermore, in addition to or instead of the stand 82c, the rear case 82 may be provided with screw holes that can be used to attach the frame 8 to a wall mount, an arm, a stand, etc. These screw holes may be compliant with, for example, the VESA (Video Electronics Standards Association) standard.

[0032] In the state shown in FIGS. 4 and 5, the video output terminal 4b of the interface adapter 4 and the portable information terminal 7 are connected via a communication cable (for example, a USB cable).

[0033] <State in which the interface adapter 4 and the portable information terminal 7 are attached to the rear case 82> Figures 6 and 7 are diagrams showing an example of a state in which the interface adapter 4 and the portable information terminal 7 are attached to the rear case 82. Figures 6 and 7 show the interface adapter 4, the portable information terminal 7, and the frame 8 as viewed from different directions.

[0034] 4 and 5, with the interface adapter 4 attached to the back of the portable information terminal 7, the portable information terminal 7 and the interface adapter 4 are attached to the inside of the rear case 82 as shown in Figures 6 and 7. This exposes the markings such as standard compliance on the housing of the interface adapter 4 from the marking viewing hole 82b. Furthermore, by removing the cable insertion hole cover 82a, the video input terminal 4a of the interface adapter 4 is exposed from the cable insertion hole of the rear case 82.

[0035] <State in which the front cover 81 is attached to the rear case 82> Figures 8 and 9 are views showing an example of a state in which the front cover 81 is attached to the rear case 82. Figures 8 and 9 show the frame 8 and the like as viewed from different directions.

[0036] With the portable information terminal 7 and the interface adapter 4 attached to the rear case 82 as shown in Figures 6 and 7, the front cover 81 is attached to the rear case 82 as shown in Figures 8 and 9. This allows the portable information terminal 7 and the interface adapter 4 to be housed in the frame 8.

[0037] 8 and 9, the frame 8 has a waterproof structure that prevents the intrusion of water, dust, and the like from the outside. For example, a packing is provided between the front cover 81 and the rear case 82 to fill the joint between the front cover 81 and the rear case 82. In addition, the frame of the opening 81a of the front cover 81 is sealed so as to fit closely to the display unit 7a of the portable information terminal 7, and the opening 81a is closed by the display unit 7a.

[0038] The frame of the notation viewing hole 82 b of the rear case 82 is sealed so as to fit closely to the housing of the interface adapter 4 , and the notation viewing hole 82 b is closed by the housing of the interface adapter 4 .

[0039] Furthermore, the frame of the cable insertion hole of the rear case 82 is sealed so as to fit tightly against the housing of the interface adapter 4, and when the cable insertion hole cover 82a is removed from the rear case 82, the cable insertion hole of the rear case 82 is blocked by the housing of the interface adapter 4. Furthermore, when the cable insertion hole cover 82a is removed from the rear case 82, the periphery of the cable insertion hole of the rear case 82 is sealed so that the cable insertion hole of the rear case 82 is blocked by the communication cable 13 inserted from the cable insertion hole of the rear case 82.

[0040] That is, the frame 8 has a waterproof structure that prevents water, dust, and the like from entering the inside of the frame 8 by utilizing the interface adapter 4 and portable information terminal 7 accommodated therein. As a result, even when the portable information terminal 7, interface adapter 4, and frame 8 are used in an outdoor environment or the like, the intrusion of water, dust, and the like into the inside of the frame 8 can be prevented, and the interface adapter 4 and portable information terminal 7 can be protected.

[0041] In this way, the endoscopic system 100 is configured such that the interface adapter 4, which converts the imaging signal obtained by the imaging sensor 23 of the scope 1 into image data that can be displayed on the portable information terminal 7, is fixed to the frame 8 that houses the portable information terminal 7.

[0042] As a result, the interface adapter 4 converts the image signal obtained by the imaging sensor 23 of the scope 1 into image data, allowing the portable information terminal 7 to be a general-purpose portable information terminal such as a tablet terminal, making it easy to procure, replace, update, etc. the portable information terminal 7.

[0043] Furthermore, because the interface adapter 4 is fixed to the frame 8 that houses the portable information terminal 7, the portable information terminal 7 and the interface adapter 4 are integrated by the frame 8. This makes it easy to operate the scope 1 while observing, on the portable information terminal 7, an image based on an imaging signal obtained by the imaging sensor 23 of the scope 1.

[0044] For example, a user of the endoscope system 100 (e.g., a doctor) can operate the scope 1 while observing an image without having to worry about the position of the interface adapter 4 between the scope 1 and the portable information terminal 7. Furthermore, when the user operates the scope 1 while observing an image, it is possible to prevent an accident such as the interface adapter 4 between the scope 1 and the portable information terminal 7 dropping and pulling the scope 1.

[0045] Furthermore, by providing an interface adapter 4 between the scope 1 and the portable information terminal 7, it is not necessary to provide the scope 1 with an image processing circuit (e.g., a signal processing unit 42) that converts the image signal obtained by the imaging sensor 23 of the scope 1 into image data, thereby reducing the manufacturing cost of the scope 1 and making it easier to operate the scope 1 for single use.

[0046] <Internal Configuration of Scope 1 and Interface Adapter 4> Fig. 10 is a diagram showing an example of the internal configuration of the scope 1 and the interface adapter 4. As shown in Fig. 10, the tip portion 10C of the scope 1 is provided with an imaging optical system including an objective lens 21 and a lens group 22, an imaging sensor 23 that images a subject through this imaging optical system, a memory 25 such as a RAM (Random Access Memory), a communication interface (I / F) 26, an imaging driver 27, a light source device 5, and an illumination lens 50.

[0047] A CCD (Charge Coupled Device) image sensor, a CMOS (Complementary Metal Oxide Semiconductor) image sensor, or the like is used as the image sensor 23. The image sensor 23 may be one that performs imaging using a rolling shutter system or one that performs imaging using a global shutter system.

[0048] The image sensor 23 has a light-receiving surface on which a plurality of pixels are arranged two-dimensionally, and converts an optical image formed on this light-receiving surface by the imaging optical system into an electrical signal (image signal) at each pixel. The image sensor 23 then converts the converted image signal from an analog signal to a digital signal with a predetermined number of bits and outputs the digital image signal to the memory 25. The image sensor 23 is equipped with color filters of, for example, primary colors or complementary colors. The collection of image signals output from each pixel on the light-receiving surface of the image sensor 23 is called an image signal.

[0049] The memory 25 temporarily records the digital image signal output from the image sensor 23. The communication interface (I / F) 26 is connected to a first communication interface (I / F) 41 of the interface adapter 4. The communication interface 26 transmits the image signal recorded in the memory 25 to the interface adapter 4 through a signal line in the communication cable 13.

[0050] The imaging driver 27 is connected to the system controller 44 of the interface adapter 4 via the communication interface 26. The imaging driver 27 drives the imaging sensor 23 and the memory 25 based on commands from the system controller 44 received via the communication interface 26.

[0051] The light source device 5 can emit, as illumination light, normal light, such as white light, having an emission spectrum suitable for recognition by a person such as a doctor. Furthermore, the light source device 5 can also emit, as illumination light, special light, which has an emission spectrum different from that of normal light and is suitable for image analysis by a computer, such as IEE (Image-Enhanced Endoscopy). As the light source of the light source device 5, for example, a semiconductor light source is used.

[0052] The light source device 5 is connected to the system control unit 44 of the interface adapter 4 via the communication interface 26. The light source device 5 emits illumination light based on commands from the system control unit 44 received by the communication interface 26.

[0053] The illumination lens 50 irradiates the illumination light emitted from the light source device 5 toward an object (e.g., the inside of a subject) to be imaged by the imaging sensor 23 and imaging optical system. An aperture may be included between the illumination lens 50 and the light source device 5 or in the imaging optical system, but it is preferable that an aperture not be included from the perspective of reducing the manufacturing cost of the scope 1. Not including an aperture in the scope 1 simplifies exposure control of the scope 1, and therefore reduces the manufacturing cost of the interface adapter 4.

[0054] The interface adapter 4 includes a first communication interface 41 connected to the communication interface 26 of the scope 1 via a communication cable 13 , a signal processing unit 42 , a second communication interface (I / F) 43 , and a system control unit 44 .

[0055] The first communication interface 41 is for communicating with the scope 1, and has, for example, the video input terminal 4a shown in Figures 2 and 3, and receives the imaging signal transmitted from the communication interface 26 of the scope 1 via the communication cable 13 and transmits it to the signal processing unit 42.

[0056] The signal processing unit 42 has a built-in memory such as RAM for temporarily recording the digital imaging signals received from the first communication interface 41, and processes the captured image signals, which are a collection of imaging signals recorded in the memory (image processing such as amplification processing for amplifying each imaging signal, demosaic processing, white balance processing, or gamma correction processing), to generate image data in a format that can be displayed on the portable information terminal 7, which is a general-purpose terminal. To enable white balance processing to be set for each imaging sensor, the white balance gain may be written to a memory installed in the scope 1 during manufacturing, and the white balance gain may be read from this memory and used during white balance processing. From the perspective of reducing manufacturing costs, a fixed white balance gain may be used in white balance processing.

[0057] The second communication interface 43 is for communicating with the portable information terminal 7, and has, for example, the video output terminal 4b shown in Figure 3, etc., and transmits image data generated by the signal processing unit 42 to the portable information terminal 7.

[0058] The system control unit 44 controls each unit of the interface adapter 4, sends commands to the scope 1, and performs overall control of the endoscope system 100. For example, the system control unit 44 is an example of a control unit of the image sensor 23 that controls image capture by the image sensor 23 via the image capture driver 27. The system control unit 44 is also an example of a control unit of the light source device 5 that controls the emission of illumination light by the light source device 5. In this embodiment, the system control unit 44 causes the image sensor 23 to capture an image while controlling the light intensity of the illumination light emitted from the light source device 5 to be constant.

[0059] The system control unit 44 also performs photometry processing to derive a photometric value (hereinafter referred to as brightness Y) indicating the brightness of the image data based on the captured image signal obtained by the imaging sensor 23, and exposure control to control the imaging sensitivity of the imaging sensor 23 (specifically, the amplification factor of the imaging signal in the amplification processing) and the exposure time of the imaging sensor 23 based on the brightness Y obtained by the photometry processing. For example, the system control unit 44 derives the brightness YA of the captured image signal based on the captured image signal before amplification processing by the signal processing unit 42, amplifies this brightness YA by the amplification factor used in the amplification processing, and controls the imaging sensitivity of the imaging sensor 23 and the exposure time of the imaging sensor 23 so that the brightness Y approaches a brightness (hereinafter referred to as target brightness Yt) suitable for recognition by a person such as a doctor.

[0060] The signal processing unit 42 and the system control unit 44 each include various processors that execute programs to perform processing, a RAM, and a ROM (Read Only Memory). The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes programs to perform various processing, a programmable logic device (PLD), such as an FPGA (Field Programmable Gate Array), whose circuit configuration can be changed after manufacturing, or a dedicated electrical circuit, such as an ASIC (Application Specific Integrated Circuit), which is a processor having a circuit configuration designed specifically to perform specific processing. More specifically, the structure of these various processors is an electrical circuit that combines circuit elements such as semiconductor elements.

[0061] The signal processing unit 42 and the system control unit 44 may be configured with one of various processors, or may be configured with a combination of two or more processors of the same or different types (for example, a combination of multiple FPGAs or a combination of a CPU and an FPGA). From the viewpoint of reducing the cost and size of the interface adapter 4, it is preferable that the signal processing unit 42 and the system control unit 44 be configured with only FPGAs.

[0062] <Hardware Configuration of Portable Information Terminal 7> Fig. 11 is a diagram showing an example of the hardware configuration of the portable information terminal 7. The portable information terminal 7 can be realized, for example, by a general-purpose information terminal 110 shown in Fig. 11. The information terminal 110 includes a processor 111, a memory 112, a communication interface 113, and a user interface 114. The processor 111, the memory 112, the communication interface 113, and the user interface 114 are connected by, for example, a bus 119.

[0063] The processor 111 is a circuit that performs signal processing, and is, for example, a central processing unit (CPU) that controls the entire information terminal 110. The processor 111 may be realized by other digital circuits such as a field programmable gate array (FPGA) or a digital signal processor (DSP). The processor 111 may also be realized by combining multiple digital circuits.

[0064] The memory 112 includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM. The main memory is used as a work area for the processor 111.

[0065] The auxiliary memory is a non-volatile memory such as a magnetic disk, an optical disk, a flash memory, etc. The auxiliary memory stores various programs that operate the information terminal 110. The programs stored in the auxiliary memory are loaded into the main memory and executed by the processor 111.

[0066] The auxiliary memory may also include a portable memory that is removable from the information terminal 110. Portable memories include USB flash drives and memory cards such as SD (Secure Digital) memory cards.

[0067] The communication interface 113 is a communication interface that communicates with the outside of the information terminal 110 (for example, the interface adapter 4). For example, the communication interface 113 is a wired communication interface that has a terminal that can be connected to the video output terminal 4b of the interface adapter 4 via a communication cable. Alternatively, the communication interface 113 may be a wireless communication interface that can communicate wirelessly with the interface adapter 4. The communication interface 113 is controlled by the processor 111.

[0068] The user interface 114 includes, for example, an input device that accepts operation input from the user and an output device that outputs information to the user. For example, the input device and the output device are realized by the display unit 7a configured as a touch panel. The user interface 114 may also include keys, a remote control, etc. as input devices. The user interface 114 may also include a speaker, a vibrator, etc. as output devices. The user interface 114 is controlled by the processor 111.

[0069] For example, the touch panel included in the user interface 114 displays image data received from the interface adapter 4 via the communication interface 113. This allows an image based on an imaging signal obtained by the imaging sensor 23 of the scope 1 to be displayed to a user such as a doctor.

[0070] Furthermore, the touch panel included in the user interface 114 receives, through user operation, instructions for imaging by the imaging sensor 23 of the scope 1 and instructions for irradiating illumination light by the light source device 5 of the scope 1. Control signals indicating the user operations received by the user interface 114 are transmitted to the system control unit 44 of the interface adapter 4 via the communication interface 113. Based on the received control signals, the system control unit 44 controls imaging by the imaging sensor 23 of the scope 1 and irradiating illumination light by the light source device 5 of the scope 1.

[0071] (Detailed Example of Photometry Processing and Exposure Control) FIG. 12 is a flowchart illustrating a detailed example of photometry processing and exposure control performed by the system control unit 44. Below, a detailed example of photometry processing and exposure control will be described assuming that the system control unit 44 is configured solely with an FPGA. Furthermore, below, the value obtained by converting each of the multiple exposure times that can be set in the image sensor 23 into information in logarithmic space using a logarithmic transformation lookup table (hereinafter referred to as the first LUT) will be referred to as the exposure time SS, and the value obtained by converting each of the multiple settable amplification factors (digital gains) used in the amplification processing performed by the signal processing unit 42 into information in logarithmic space using the first LUT will be referred to as the amplification factor DG. The first LUT is generated, for example, according to the formula y = Log(x) × a. In this formula, a is a predetermined coefficient, x is the value before conversion, and y is the value after conversion.

[0072] When the system control unit 44 acquires the captured image signal before being amplified by the signal processing unit 42 (step S1), it performs a photometric calculation on the captured image signal using a predetermined photometric method to derive brightness YA, and then multiplies the brightness YA by the currently set amplification factor for the amplification process to derive brightness Y (step S2). The photometric method is not particularly limited, but in the case of an endoscope, for example, a method of obtaining a photometric value by differently weighting the central and peripheral portions of the captured image signal can be preferably used. In this case, the following equation (1) is calculated to derive the image feature required to derive the photometric value.

[0073] Image feature quantity = {α × central brightness value + (100 - α) × peripheral brightness value} ÷ 100 (1) In equation (1), α is a coefficient for changing the weighting of the central and peripheral areas, and may be a fixed value determined by the system, or a variable value selected from multiple values ​​depending on the imaging mode, user preference, etc.

[0074] The division formula shown in formula (1) can be replaced with an arithmetic formula that does not include division, such as formula (2) below, by utilizing a bit shift operation: β is a coefficient corresponding to α.

[0075] Image feature amount = {β × central brightness value + (256 - β) × peripheral brightness value} >> 8 (2) If α in equation (1) is, for example, 20, β in equation (2) is 51. If α in equation (1) is, for example, 40, β in equation (2) is 102. If α in equation (1) is, for example, 60, β in equation (2) is 154. If α in equation (1) is, for example, 80, β in equation (2) is 205.

[0076] The system control unit 44 may derive the image feature quantity using either equation (1) or equation (2). However, if the system control unit 44 is configured solely with an FPGA, it is preferable to derive the image feature quantity using the calculation shown in equation (2) in step S2 and use the image feature quantity to derive the brightness Y (photometric value). The calculation shown in equation (2) does not include division, but is performed using only addition and multiplication. This makes it possible to reduce the circuit size of the FPGA and improve the calculation speed by the FPGA.

[0077] After deriving the brightness Y in step S2, the system control unit 44 derives (step S3) an exposure change amount ΔEV required to bring the image data to the target brightness Yt based on the brightness Y. The exposure change amount ΔEV can be derived, for example, by calculating the following equation (3).

[0078] Exposure change amount ΔEV=target brightness Yt / brightness Y (3)

[0079] By converting the target brightness Yt and the brightness Y into information in logarithmic space, equation (3) can be replaced with an arithmetic expression that does not include division, as in the following equation (4): [Log] indicates information in logarithmic space.

[0080] Exposure change amount ΔEV [Log] = target brightness Yt [Log] - brightness Y [Log] (4)

[0081] The target brightness Yt[Log] is a value obtained by converting the target brightness Yt into information in logarithmic space using the first LUT. The brightness Y[Log] is a value obtained by converting the brightness Y into information in logarithmic space using the first LUT.

[0082] The calculation shown in equation (4) does not include division and is performed only by subtraction. In other words, the calculation shown in equation (4) is performed only by subtraction out of division and subtraction. Therefore, when the system control unit 44 is configured using only an FPGA, it is possible to reduce the circuit size of the FPGA and improve the calculation speed by the FPGA.

[0083] Here, it is assumed that the system control unit 44 is configured only with an FPGA, and therefore in step S3, the system control unit 44 converts the brightness Y to brightness Y[Log] using the first LUT, converts the target brightness Yt to target brightness Yt[Log], and subtracts the brightness Y[Log] from the target brightness Yt[Log] to derive the exposure change amount ΔEV[Log]. The larger the value of the exposure change amount ΔEV[Log], the darker the image data is relative to the target brightness Yt.

[0084] Next, the system control unit 44 selects one of the multiple exposure times SS according to the magnitude of the exposure change amount ΔEV[Log] (step S4). For example, the system control unit 44 divides the exposure change amount ΔEV[Log] that is equal to or greater than zero into multiple ranges according to the magnitude of the exposure change amount ΔEV[Log].

[0085] Fig. 13 is a schematic diagram illustrating the relationship between the magnitude of the exposure change amount ΔEV [Log], the exposure time SS, and the amplification factor DG. In each graph in Fig. 13, the higher the value on the vertical axis, the larger the value. Fig. 13 shows an example in which six exposure times SS can be set. Note that, as an example, it is preferable to set the upper limit of the exposure time SS to 1 / 38 seconds and the lower limit to 1 / 800 seconds so that the observed image formed from the continuously acquired image data appears natural.

[0086] In the example of FIG. 13 , ranges RG1, RG2, RG3, RG4, RG5, RG6, and RG7 are set in order of increasing exposure change amount ΔEV[Log]. In step S4, if the exposure change amount ΔEV[Log] falls within ranges RG1 and RG2, the system control unit 44 selects the smallest value (lower limit value) of the six exposure times SS. If the exposure change amount ΔEV[Log] falls within range RG3, the system control unit 44 selects the second smallest value of the six exposure times SS. If the exposure change amount ΔEV[Log] falls within range RG4, the system control unit 44 selects the third smallest value of the six exposure times SS. If the exposure change amount ΔEV[Log] falls within range RG5, the system control unit 44 selects the fourth smallest value of the six exposure times SS. If the exposure change amount ΔEV[Log] falls within range RG6, the system control unit 44 selects the fifth smallest value among the six exposure times SS. If the exposure change amount ΔEV[Log] falls within range RG7, the system control unit 44 selects the largest value among the six exposure times SS (the upper limit of the exposure time SS).

[0087] 13, the range RG1 is the range in which the exposure cannot be reduced any further, and is the range in which the generated image data is brighter than or equal to the target brightness Yt. When the exposure change amount ΔEV[Log] falls within the range RG1, the lower limit value is selected for the exposure time SS, and a reference value (e.g., 1x) is selected for the amplification factor DG.

[0088] After selecting the exposure time SS in step S4, the system control unit 44 calculates the amplification factor DG by the following equation (5) (step S5): Amplification factor DG=exposure change amount ΔEV [Log]−exposure time SS (5)

[0089] When each value in equation (5) is converted from information in logarithmic space to information in real space, the following equation (6) is obtained.

[0090] Amplification rate DG [real number] = exposure change amount ΔEV [real number] ÷ exposure time SS [real number] (6)

[0091] In this embodiment, the amount of illumination light is constant, and the exposure value is determined by multiplying the amplification factor by the exposure time, so the above formula (6) holds. When each value in formula (6) is converted into information in logarithmic space, formula (5) holds. Therefore, the amplification factor DG can be calculated by calculating formula (5). Thus, in step S5, only subtraction is performed, out of division and subtraction. This makes it possible to reduce the circuit size of the system control unit 44 and improve the speed at which the amplification factor DG is derived.

[0092] In the example of FIG. 13 , when the exposure change amount ΔEV [Log] is within each range from RG2 to RG7, the system control unit 44 determines a larger value for the amplification factor DG as the exposure change amount ΔEV [Log] increases. Furthermore, within ranges RG2 to RG6, the amplification factor DG is varied within a range from a reference value to a preset value that is smaller than the upper limit of the amplification factor DG. Furthermore, within ranges RG2 to RG6, the closer the range is to range RG1, the larger the fluctuation range of the amplification factor DG (the difference between the reference value and the preset value). Meanwhile, within range RG7, the amplification factor DG is varied between the reference value and the upper limit.

[0093] After deriving the amplification factor DG in step S5, the system control unit 44 converts the exposure time SS selected in step S4 into a setting value for the image sensor 23 using a lookup table, and sets the setting value in the register of the image sensor 23 (step S6). As a result, in the next imaging frame, the exposure time of the image sensor 23 becomes a value corresponding to the exposure time SS selected in step S4.

[0094] Furthermore, the system control unit 44 converts the gain DG derived in step S5 into a setting value for the signal processing unit 42 using a lookup table, and sets the setting value in a register of the signal processing unit 42 (step S7). As a result, in the next imaging frame, the gain of the imaging signal during the amplification process becomes a value equivalent to the gain DG derived in step S5.

[0095] 13 , the exposure time of the image sensor 23 is changed discretely based on the brightness Y of the image data, and the amplification factor during the amplification process is changed continuously based on the brightness Y of the image data. By changing the exposure time discretely, it is possible to reduce the cost of the image sensor 23 and the cost of controlling it. On the other hand, by being able to change the amplification factor continuously, it is possible to fine-tune the brightness of the image data and improve the quality of the image displayed on the portable information terminal 7.

[0096] Furthermore, in the example of FIG. 13 , the maximum value of the gain DG decreases as the exposure change amount ΔEV[Log] moves from range RG2 to range RG6. For example, when the exposure change amount ΔEV[Log] is in range RG6, the image data is dark, and increasing the gain may result in noticeable noise. Therefore, in such a situation, the signal-to-noise ratio can be improved by narrowing the range of change in the gain. When the exposure change amount ΔEV[Log] is in range RG7, the exposure time SS has reached its upper limit, and the only way to increase the exposure is to increase the gain DG. Therefore, by varying the gain DG between the reference value and the upper limit, the image data can be brought closer to the target brightness, even in a very dark imaging environment.

[0097] 13, the gain DG varies depending on the magnitude of the exposure change amount ΔEV[Log] in each of the ranges RG2 to RG6, but this is not limiting. For example, the gain DG may remain at a reference value (equivalent to 1x) in each of the ranges RG2 to RG6. In this case, the signal-to-noise ratio can be improved over a wide range from the range RG1 to the range RG6.

[0098] (Preferred form of image processing) It is preferable that the signal processing unit 42 performs the above-mentioned gamma correction processing to generate image data so that when a pixel value that is less than or equal to the first threshold value TH1 is input to the display unit 7a, the output value of the display unit 7a is greater than that pixel value, and when a pixel value that exceeds the first threshold value TH1 is input to the display unit 7a, the output value of the display unit 7a matches that pixel value.

[0099] 14 is a schematic diagram illustrating gamma correction processing. Graph 51 shows the gamma characteristic of the display unit 7a (e.g., γ=2.2). The dashed straight line in graph 51 indicates an ideal characteristic in which input and output are directly proportional. Generally, when performing gamma correction, the gamma characteristic of graph 51 is taken into consideration, and gamma correction is performed on the image data before correction using correction data C1 shown in graph 52 so that when pixel values ​​of the corrected image data are input to the display unit 7a, the pixel values ​​and the output values ​​(display luminance values) of those pixel values ​​match.

[0100] In this embodiment, for example, gamma correction is performed on the image data before correction using the correction data C2 shown in graph 52. Graph 53 shows the relationship between the pixel values ​​(input values) of the image data obtained by gamma correction in accordance with the correction data C2 and the output values ​​of the display unit 7a when the pixel values ​​are input to the display unit 7a.

[0101] As shown in graph 53, the output gradation characteristics of the image data after gamma correction approximately match the straight line of the ideal characteristics in the range where the pixel value exceeds the first threshold value TH1, but deviate higher from the straight line of the ideal characteristics in the range where the pixel value is equal to or less than the first threshold value TH1. In other words, in the image data after gamma correction, when a pixel value equal to or less than the first threshold value TH1 is input to the display unit 7a, the output value of the display unit 7a is larger than that pixel value, and when a pixel value exceeding the first threshold value TH1 is input to the display unit 7a, the output value of the display unit 7a matches that pixel value.

[0102] Graph 53 shows the pixel values ​​of the image data after gamma correction, with the first range R1 being the range from the minimum value (=0) to a second threshold TH2 that is smaller than the first threshold TH1, and the second range R2 being the range from a third threshold TH3 between the first threshold TH1 and the second threshold TH2 to the second threshold TH2.

[0103] In the image data after gamma correction, the difference between the output value of the display unit 7a when pixel values ​​in the second range R2 are input to the display unit 7a and the pixel value is larger than the difference between the output value of the display unit 7a when pixel values ​​in the first range R1 are input to the display unit 7a and the pixel value. In other words, when the image data after gamma correction is divided into a very dark area with very small pixel values ​​(a area with pixel values ​​in the first range R1) and a slightly darker area with slightly small pixel values ​​(a area with pixel values ​​in the second range R2), the slightly darker area is displayed relatively brighter.

[0104] Fig. 15 is a schematic diagram showing an example of an image displayed on the display unit 7a when the scope 1 is a bronchial endoscope. Fig. 15 shows an example in which the output gradation characteristics of image data after gamma correction are ideal characteristics. A displayed image 70 shows a thick tube 73, a thin tube 71, and a branch tube 72 inside the thin tube 71. The thin tube 71 is brighter than the branch tube 72, but the difference in brightness between the two is very slight.

[0105] 16 is a diagram showing an example of displaying image data that has been gamma-corrected to achieve the output gradation characteristics shown by the solid line in graph 53. Between thin tube 71 and branch tube 72, thin tube 71, which is relatively bright, is displayed brighter. As a result, the state of branch tube 72 visible within thin tube 71 is easier to see than in FIG. 15.

[0106] Note that the signal processing unit 42 does not need to use the correction data C2 of graph 52 to generate image data having the output gradation characteristics shown by the solid line of graph 53. For example, the output gradation characteristics shown in graph 53 may be obtained by performing gamma correction using the correction data C1 and then applying a gain greater than 1 to small pixel values ​​according to the gain correction table shown in Fig. 17. More preferably, the output gradation characteristics shown in graph 53 may be obtained by performing gamma correction using the correction data C1, converting pixel values ​​to luminance values, and applying a gain greater than 1 to luminance values ​​smaller than a predetermined value according to the gain correction table shown in Fig. 17.

[0107] In the above explanation, the imaging sensitivity of the imaging sensor 23 is changed by changing the amplification factor used in the amplification process performed by the signal processing unit 42. However, for example, the imaging sensitivity may be changed by changing the amplification factor of an amplifier that amplifies the analog signal contained in the imaging sensor 23.

[0108] As explained above, this specification describes the following items. Note that the elements in parentheses correspond to those in the above-described embodiments, but are not limited to these.

[0109] (1) An interface adapter comprising: a first communication interface (first communication interface 41) for communicating with a scope (scope 1) including an imaging sensor (imaging sensor 23) and a light source device (light source device 5) that generates illumination light for imaging by the imaging sensor; a second communication interface (second communication interface 43) for communicating with a portable information terminal; and a processor (system control unit 44 and signal processing unit 42), wherein the processor: causes the imaging sensor to capture an image while controlling the amount of the illumination light to be constant; converts an image signal obtained by the imaging sensor into image data that can be displayed by the portable information terminal; transmits the image data to the portable information terminal; derives brightness of the image data based on the image signal; and controls the imaging sensitivity of the imaging sensor and the exposure time of the imaging sensor based on the brightness.

[0110] According to (1), exposure control is performed by adjusting two parameters, imaging sensitivity and exposure time, while the amount of illumination light is constant. Because the number of adjustments required for exposure control is limited to two, a highly capable processor is not required. As a result, a system can be realized at low cost that allows a general-purpose portable information terminal connected via the second communication interface to display and check images captured by the scope. This also enables the interface adapter to be made smaller and lighter.

[0111] (2) An interface adapter according to (1), wherein the processor increases the fluctuation range of the imaging sensitivity when controlling the exposure time to an upper limit value (when the exposure change amount ΔEV[Log] is in the range R7) compared to when controlling the exposure time to less than the upper limit value (when the exposure change amount ΔEV[Log] is in the range RG2 to RG6).

[0112] According to (2), the fluctuation range of the imaging sensitivity is small until the exposure time reaches the upper limit, thereby improving the signal-to-noise ratio of the imaging signal. On the other hand, after the exposure time reaches the upper limit, the fluctuation range of the imaging sensitivity can be increased, thereby enabling a dark subject to be captured brightly.

[0113] (3) The interface adapter according to (2), wherein the processor discretely changes the exposure time and continuously changes the imaging sensitivity.

[0114] According to (3), there is no need for a high-performance imaging sensor (one that can precisely control the exposure time), which reduces the manufacturing cost of the scope and the interface adapter by simplifying the scope control, thereby reducing the system construction cost.

[0115] (4) An interface adapter according to (2), wherein the processor sets the exposure time to a different value for each of a plurality of ranges of brightness (each range of brightness in which the exposure change amount ΔEV [Log] is in the range from RG2 to RG7), and when the exposure time is controlled to be less than the upper limit value, the processor changes the imaging sensitivity between a reference value (amplification factor DG = 1x) and a value lower than the upper limit value of the imaging sensitivity according to the brightness.

[0116] According to (4), a high-performance imaging sensor (one that can precisely control the exposure time) is not required, which reduces the manufacturing cost of the scope and the interface adapter by simplifying the scope's control, thereby reducing the system construction cost. Furthermore, even when an arbitrary exposure time is set, the exposure can be precisely adjusted to suit the subject by changing the imaging sensitivity, improving the quality of image data.

[0117] (5) An interface adapter according to any one of (1) to (4), wherein the processor performs an amplification process to amplify the digital captured image signal output from the imaging sensor, and the imaging sensitivity is an amplification factor set in the amplification process.

[0118] According to (5), the brightness of the image data can be controlled by amplifying the digital signal, which allows for more accurate exposure control than controlling the amplification factor when amplifying an analog signal inside the image sensor. Also, since an image sensor with high analog signal amplification performance is not required, the manufacturing cost of the scope can be reduced.

[0119] (6) The interface adapter according to any one of (1) to (5), wherein the processor is a programmable logic device.

[0120] According to (6), the cost of the interface adapter can be reduced, and the cost of building the system can be reduced.

[0121] (7) An interface adapter according to (6), wherein the processor performs only subtraction out of division and subtraction as the calculation process required to determine the combination of the imaging sensitivity and the exposure time to bring the brightness (brightness Y) closer to a target brightness (target brightness Yt).

[0122] According to (7), since division is not performed to determine the imaging sensitivity and exposure time, it is possible to reduce the circuit scale and calculation time of the processor, thereby reducing the manufacturing cost of the interface adapter.

[0123] (8) An interface adapter according to (7), wherein the logarithmic conversion of each of a plurality of exposure times that can be set in the imaging sensor is used as an exposure time logarithmic value (exposure time SS), and the processor: subtracts the logarithmic conversion value of the brightness (brightness Y[Log]) from the logarithmic conversion value of the target brightness (target brightness Yt[Log]) to derive a first subtraction value (exposure change amount ΔEV[Log]), selects one from the plurality of exposure time logarithmic values ​​depending on the magnitude of the first subtraction value, subtracts the selected exposure time logarithmic value from the first subtraction value to derive a second subtraction value (amplification factor DG[Log]), converts the selected exposure time logarithmic value into a setting value of the exposure time using a conversion table (lookup table), and converts the second subtraction value into a setting value of the imaging sensitivity using the conversion table (lookup table).

[0124] According to (8), since division processing is not performed to determine the imaging sensitivity and exposure time, it is possible to reduce the circuit scale of the processor and the calculation time.

[0125] (9) The interface adapter according to any one of (6) to (8), wherein the processor performs the calculation required to determine the brightness by bit shift calculation.

[0126] According to (9), division processing is not required to determine brightness, which makes it possible to reduce the circuit scale of the processor and the calculation time.

[0127] (10) An adapter according to any one of (1) to (9), wherein the processor performs gamma correction processing based on the gamma characteristics of the display unit (display unit 7a) of the portable information terminal as a process for converting the captured image signal into the image data, and in the gamma correction processing, when a pixel value that is equal to or less than a first threshold value (first threshold value TH1) is input to the display unit, the output value of the display unit is greater than that pixel value, and when a pixel value that exceeds the first threshold value is input to the display unit, the output value of the display unit matches that pixel value.

[0128] According to (10), when a specific portion of an image captured by an imaging sensor is dark, for example, it is possible to brighten the dark portion without relying on the gradation characteristics of the display device, thereby enabling efficient and highly accurate inspection using a scope.

[0129] (11) An interface adapter as described in (10), wherein a first range (first range R1) is a range of pixel values ​​of the image data from the minimum value to a second threshold (second threshold TH2) smaller than the first threshold, and a second range (second range R2) is a range from a third threshold (third threshold TH3) between the first threshold and the second threshold to the second threshold, and the processor generates the image data in the gamma correction process such that the difference between the output value of the display unit and the pixel value when pixel values ​​in the second range are input to the display unit is greater than the difference between the output value of the display unit and the pixel value when pixel values ​​in the first range are input to the display unit.

[0130] According to (11), when there are multiple dark regions in the image data with slight differences in brightness, the brighter regions among the multiple regions are displayed brighter, making the boundaries of the multiple regions easier to see. For example, when using a bronchoscope, if the trachea branches into two at the front, the branching points of the two can be clearly seen.

[0131] (12) The interface adapter according to any one of (1) to (11), which is fixed to a frame (frame 8) capable of accommodating the portable information terminal.

[0132] (13) An endoscope system (endoscope system 100) comprising: the interface adapter according to any one of (1) to (11); a frame (frame 8) capable of accommodating the portable information terminal; and the scope, wherein the interface adapter is fixed to the frame.

[0133] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0134] This application is based on a Japanese patent application (Patent Application No. 2023-025924) filed on February 22, 2023, the contents of which are incorporated herein by reference.

[0135] DESCRIPTION OF SYMBOLS 1 Scope 4 Interface adapter 4a Video input terminal 4b Video output terminal 5 Light source device 7 Portable information terminal 7a Display unit 8 Frame 10 Insertion section 10A Flexible section 10B Bending section 10C Tip section 11 Operation section 13 Communication cable 22 Lens group 23 Imaging sensor 25, 112 Memory 26, 113 Communication interface 41 First communication interface 27 Imaging driver 42 Signal processing section 43 Second communication interface 44 System control section 50 Illumination lens 81 Front cover 81a Opening 82 Rear case 82a Cable insertion hole cover 82b Notation viewing hole 82c Stand 100 Endoscope system 110 Information terminal 111 Processor 114 User interface 119 Bus RG1 to RG7 Range 51, 52, 53 Graph C1, C2 Correction data R1 First range R2 Second range 70 Display image 71 Narrow tube 72 Branch tube 73 Large tube

Claims

1. a first communication interface for communicating with a scope including an image sensor and a light source device for generating illumination light for image capture by the image sensor; a second communication interface for communicating with a portable information terminal having a user interface; a processor, The processor: causing the image sensor to capture an image while controlling the amount of illumination light to a constant level; converting the captured image signal obtained by the imaging sensor into image data that can be displayed by the portable information terminal, and transmitting the image data to the portable information terminal; deriving brightness of the image data based on the captured image signal; controlling the imaging sensitivity of the imaging sensor and the exposure time of the imaging sensor based on the brightness; An interface adapter controlled by the user interface of the portable information terminal.

2. 10. The interface adapter of claim 1, When the processor controls the exposure time to the upper limit value, the processor increases the fluctuation range of the imaging sensitivity compared to when the processor controls the exposure time to be less than the upper limit value.

3. 3. The interface adapter of claim 2, The processor discretely changes the exposure time and continuously changes the imaging sensitivity.

4. 3. The interface adapter of claim 2, The processor sets the exposure time to a different value for each of a plurality of ranges of brightness, and when the exposure time is set to a value less than the upper limit, changes the imaging sensitivity between a reference value and a value lower than the upper limit of the imaging sensitivity in accordance with the brightness.

5. 5. An interface adapter according to any one of claims 1 to 4, the processor performs an amplification process to amplify the digital captured image signal output from the image sensor; The imaging sensitivity is an amplification factor set in the amplification process.

6. 5. An interface adapter according to any one of claims 1 to 4, An interface adapter wherein the processor is a programmable logic device.

7. 7. The interface adapter of claim 6, an interface adapter, wherein the processor performs only subtraction out of division and subtraction as a calculation process required to determine a combination of the imaging sensitivity and the exposure time for bringing the brightness closer to a target brightness;

8. 8. The interface adapter of claim 7, a logarithmic conversion value of each of a plurality of exposure times that can be set in the image sensor is used as an exposure time logarithm value; The processor: deriving a first subtraction value by subtracting the logarithmic transformation value of the brightness from the logarithmic transformation value of the target brightness; selecting one of the plurality of logarithmic exposure time values ​​according to the magnitude of the first subtraction value; deriving a second subtraction value by subtracting the selected logarithmic value of the exposure time from the first subtraction value; an interface adapter that converts the selected logarithmic value of the exposure time into a setting value of the exposure time using a conversion table, and converts the second subtraction value into a setting value of the imaging sensitivity using a conversion table;

9. 7. The interface adapter of claim 6, The processor performs the calculation required to determine the brightness by bit shift calculation.

10. 5. The adapter according to claim 1, The processor: As a process for converting the captured image signal into image data, a gamma correction process is performed based on the gamma characteristic of a display unit of the portable information terminal; In the gamma correction process, the interface adapter generates image data such that when a pixel value that is equal to or less than a first threshold is input to the display unit, the output value of the display unit is greater than the pixel value, and when a pixel value that exceeds the first threshold is input to the display unit, the output value of the display unit matches the pixel value.

11. 11. The interface adapter of claim 10, a first range of pixel values ​​of the image data ranging from a minimum value to a second threshold value that is smaller than the first threshold value, and a second range of pixel values ​​ranging from a third threshold value between the first threshold value and the second threshold value to the second threshold value; In the gamma correction process, the processor generates the image data such that the difference between the output value of the display unit and the pixel value when pixel values ​​in the second range are input to the display unit is greater than the difference between the output value of the display unit and the pixel value when pixel values ​​in the first range are input to the display unit.

12. 5. An interface adapter according to any one of claims 1 to 4, An interface adapter is fixed to a frame capable of accommodating the portable information terminal.

13. An interface adapter according to any one of claims 1 to 4; a frame capable of accommodating the portable information terminal; the scope, The interface adapter is fixed to the frame.