Patent Publication Number: US-2022217260-A1

Title: Signal processing device, imaging device, and signal processing method

Description:
TECHNICAL FIELD 
     The present technology relates to a signal processing device, an imaging device, and a signal processing method, and particularly, to a technical field with respect to adjustment of the brightness of a captured image. 
     BACKGROUND ART 
     With respect to adjustment of the brightness of a captured image, an iris (optical diaphragm) is mainly used for adjustment of a brightness, for example, in a live camera for broadcasting stations. As reasons therefor,
         When an electronic shutter is used, continuity between frames is lost to easily cause a ruffling image, which is not desirable.   An S/N ratio (signal-to-noise ratio) decreases when a digital gain is increased and a dynamic range is narrowed when a digital gain is decreased.   An analog gain mostly has a narrow variable range in general.   A neural density (ND) filter is provided for each light transmissivity and thus it is difficult to continuously change ND filters (although a variable ND filter has recently appeared, brightness decreases by half even when transmissivity is maximized in many cases), and the like may be conceived.       

     However, in a case where brightness adjustment according to an iris is performed, when the iris is excessively opened (that is, F value is excessively decreased), the phenomenon that resolution abruptly decreases halfway is seen in many lenses. In a broadcasting B4 mount lens, in general, the resolution is maximized at about F4.0 and abruptly decreases therefrom over F1.8 of opening. 
     To prevent such resolution decrease, it is conceived that, when an F value is not more than a certain threshold value F_th, brightness is adjusted by maintaining the F value of a lens (F_th) and changing a gain of a captured image. 
     As a specific example, a brightness indication operation performed by a user may be an F value indication operation as before, but as internal processing, an iris is controlled when an F value indication value is greater than the threshold value F_th, and the gain is increased while the F value is fixed to F_th when the F value indication value is equal to or less than F-_th. 
     PTL 1 described below discloses a technology in which a user inputs position information of a volume for which a brightness will be indicated, an amplification factor is fixed and an iris opening diameter is controlled such that it becomes a value changing in response to the position information when the position information is within an iris control region, and the iris opening diameter is fixed and the amplification factor is controlled such that it becomes a value changing in response to the position information when the position information is within an amplification factor control region. 
     When brightness adjustment according to the iris is assumed to be “optical brightness adjustment” and brightness adjustment according to a gain is assumed to be “electronic brightness adjustment,” the technology disclosed in PTL 1 can be called switching between optical brightness adjustment and electronic brightness adjustment in response to the size of a brightness indication value in other words. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     JP 2015-111746 A 
     SUMMARY 
     Technical Problem 
     However, when a method of switching between optical brightness adjustment and electronic brightness adjustment is employed, a phenomenon that a speed of change of brightness abruptly increases or decreases at a timing of switching between them occurs. Generation of such a brightness change speed difference is caused by a difference between response characteristics with respect to change in an indication value between the iris and the gain. 
     When a brightness change speed difference is generated as described above, a user or an output image observer is caused to feel discomfort. 
     In addition, for the user, difficulty of the operation of adjusting a brightness such that it does not abruptly change increases to cause deterioration of operability with respect to brightness adjustment. 
     Accordingly, an object of the present technology is to mitigate a discomfort of a user or an output image observer during brightness adjustment switching and to promote curbing of deterioration in operability with respect to brightness adjustment while promoting curbing of resolution decrease due to execution of only optical brightness adjustment. 
     Solution to Problem 
     A signal processing device according to the present technology includes a switching unit that performs, in response to change in an indication value indicating the brightness of a captured image obtained by an imaging device, control of switching between optical brightness adjustment that is brightness adjustment according to an iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on the indication value to the captured image, and a first delay unit that delays change in the gain with respect to change in the indication value in the electronic brightness adjustment. 
     By delaying change in the gain with respect to change in the indication value in electronic brightness adjustment, prevention of abrupt change in a degree of change in brightness is promoted even when the indication value has changed to be a threshold value or less and thus brightness adjustment has switched from optical brightness adjustment to electronic brightness adjustment. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the indication value is a target value of an F value may be conceived. 
     Accordingly, it is not necessary to convert a brightness indication value other than the F value into an F value in execution of optical brightness adjustment. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the switching unit performs the switching control on the basis of a result of comparison between the indication value and a threshold value may be conceived. 
     Accordingly, optical brightness adjustment is performed having a predetermined F value as a limit. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the indication value is a target value of an F value, and the switching unit performs switching control such that optical brightness adjustment is performed on a side on which the target value of the F value is large and electronic brightness adjustment is performed on a side on which the target value of the F value is small, with respect to the threshold value may be conceived. 
     That is, optical brightness adjustment is performed in a region where the F value is large and resolution is high and electronic brightness adjustment instead of optical brightness adjustment is performed in a region where the F value is small and resolution tends to be low. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the first delay unit changes a gain change speed within a period in which the gain is changed in the electronic brightness adjustment may be conceived. 
     Accordingly, it is possible to approximate brightness change characteristics according to electronic brightness adjustment to brightness change characteristics according to optical brightness adjustment. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the first delay unit suppresses a gain change speed to a predetermined speed or less in electronic brightness adjustment may be conceived. There is an upper limit in a speed of change of brightness in optical brightness adjustment due to characteristics of the iris. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the first delay unit delays the gain according to delay characteristics imitating inertia in the electronic brightness adjustment may be conceived. 
     Accordingly, it is possible to cause brightness change characteristics according to electronic brightness adjustment to be change characteristics to which inertia acting on the iris has been added. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the switching unit is configured to be able to switch between a switching mode in which control of switching between optical brightness adjustment and electronic brightness adjustment is performed in response to change in the indication value and a non-switching mode in which switching control is not performed with respect to change in the indication value and optical brightness adjustment is executed may be conceived. 
     Accordingly, the F value can be decreased to a minimum value. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation may be conceived. 
     Accordingly, it is possible to perform switching between the switching mode and the non-switching mode on the basis of an intention of a user. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation of the remote controller may be conceived. 
     Accordingly, a burden of operation of switching between the switching mode and the non-switching mode is not imposed on a cameraman. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the first delay unit is configured to be able to change delay characteristics of the gain in the electronic brightness adjustment may be conceived. Accordingly, it is possible to change brightness change characteristics according to electronic brightness adjustment to characteristics corresponding to brightness change characteristics according to optical brightness adjustment in response to a case in which iris characteristics change due to a certain circumstance. 
     In the aforementioned signal processing device according to the present technology, a configuration in which the imaging device is a lens interchangeable type imaging device, and the first delay unit delays change in the gain according to delay characteristics based on information acquired from a lens device mounted in the imaging device may be conceived. 
     Accordingly, it is possible to cause change characteristics of brightness according to electronic brightness adjustment to be characteristics suitable for a lens device in response to a case in which iris characteristics vary according to lens devices to be mounted. 
     In the aforementioned signal processing device according to the present technology, a configuration including a second delay unit that delays change in the F value with respect to change in the indication value in optical brightness adjustment may be conceived. 
     Accordingly, it is possible to cause change characteristics of the F value with respect to change in the indication value to be desired characteristics. 
     In addition, an imaging device according to the present technology includes an imaging element that receives incident light through an iris to acquire a captured image, a switching unit that performs, in response to change in an indication value indicating the brightness of the captured image, switching between optical brightness adjustment that is brightness adjustment according to the iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on the&#39; indication value to the captured image, and a first delay unit that delays change in the gain with respect to change in the indication value in the electronic brightness adjustment. 
     The same operation as that of the aforementioned signal processing device according to the present technology can be acquired by the imaging device according to the present technology. 
     Further, a signal processing method according to the present technology is a signal processing method that performs, in response to change in an indication value indicating the brightness of a captured image obtained by an imaging device, switching between optical brightness adjustment that is brightness adjustment according to an iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on the indication value to the captured image, and delays change in the gain with respect to change in the indication value in the electronic brightness adjustment. 
     The same operation as that of the aforementioned signal processing method according to the present technology can also be obtained by this signal processing method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration example of an imaging system including an imaging device according to the present technology. 
         FIG. 2  is a perspective view illustrating a configuration example of the exterior of a remote controller included in an imaging system of an embodiment. 
         FIG. 3  is a conceptual diagram of an example of switching between optical brightness adjustment and electronic brightness adjustment. 
         FIG. 4  is a flowchart illustrating an example of processing of switching between optical brightness adjustment and electronic brightness adjustment. 
         FIG. 5  is a diagram schematically representing brightness change characteristics when an iris is used. 
         FIG. 6  is an explanatory diagram with respect to abrupt change in a speed of change of brightness during switching between optical brightness adjustment and electronic brightness adjustment. 
         FIG. 7  is a functional block diagram representing a function for brightness adjustment in an embodiment. 
         FIG. 8  is a diagram for describing an effect of delaying of a gain. 
         FIG. 9  is a diagram for describing a configuration of an imaging system as a first modified example. 
         FIG. 10  is a diagram for describing a configuration of an imaging system as a second modified example. 
         FIG. 11  is an explanatory diagram with respect to a modified example of a filter unit. 
         FIG. 12  is an explanatory diagram with respect to a modified example of performing control relating to brightness adjustment as an embodiment in camera control unit (CCU). 
         FIG. 13  is a diagram schematically illustrating an overall configuration of an operating room system. 
         FIG. 14  is a diagram illustrating a display example of an operation screen in a centralized operation panel. 
         FIG. 15  is a diagram illustrating an example of a state of an operation to which an operating room system is applied. 
         FIG. 16  is a block diagram illustrating an example of a functional configuration of a camera head and a CCU illustrated in  FIG. 15 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be described in the following order. 
     &lt;1. Configuration of imaging system&gt;
 
&lt;2. Brightness adjustment method as embodiment&gt;
 
[First example of delay characteristics]
 
[Second example of delay characteristics]
 
[Third example of delay characteristics]
 
[With respect to mode switching]
 
&lt;3. Modified examples&gt;
 
[3-1. First modified example]
 
[3-2. Second modified example]
 
[3-3. Other modified examples]
 
&lt;4. Conclusion of embodiments&gt;
 
     &lt;5. Application Examples&gt; 
     &lt;6. Present technology&gt; 
     1. Configuration of Imaging System 
       FIG. 1  is a diagram illustrating a configuration example of an imaging system including an imaging device  1  that is an embodiment of a signal processing device according to the present technology. 
     The imaging system in the present embodiment is, for example, a broadcasting live camera system and is used inside a broadcasting station or outside in the case of sports broadcasting. As illustrated, the imaging system includes the imaging device  1 , a lens device  10 , a camera control unit (CCU)  20 , and a remote controller  30 .
 
The lens device  10  is detachably mounted on the imaging device  1  through a mounting part that is not illustrated. In the imaging system, the imaging device  1  having the lens device  10  mounted thereon is mainly used by a user as a cameraman.
 
Further, the CCU  20  and the remote controller  30  are disposed, for example, in a room separate from a studio in a broadcasting station or disposed inside an outside broadcast van when used outside and mainly used by a user such as a video engineer.
 
Here, although the broadcasting live camera system generally employs a configuration including a plurality of sets of the imaging device  1 , the CCU  20 , and the remote controller  30 , only one of the plurality of sets is illustrated here for convenience of illustration.
 
     The lens device  10  is, for example, a lens device based on the B4 mount standard and includes lenses such as a cover lens, a zoom lens, and a focus lens, an iris (optical diaphragm), and the like as optical components. In addition, the lens device  10  includes an iris driving unit  11  having an actuator such as a motor for driving the iris, for example. 
     The lens device  10  concentrates light (incident light) from a subject and guides the concentrated light to an imaging element  2  which will be described later in a state in which it is mounted on the imaging device  1 . Here, the incident light from the subject is received by the imaging element  2  through the iris. 
     The imaging device  1  includes the imaging element  2 , a first correction processing unit  3 , an amplification unit  4 , a second correction processing unit  5 , a development processing unit  6 , and a control unit  7 . 
     The imaging element  2  is, for example, an image sensor such as a complementary metal oxide semiconductor (CMOS) type or a charge coupled device (CCD) type, photoelectrically converts received light, executes, for example, correlated double sampling (CDS) processing, automatic gain control (AGC) processing, and the like on an electrical signal obtained by photoelectric conversion, and additionally performs analog/digital (A/D) conversion processing. Then, a captured image signal (captured image data) as digital data is output to the first correction processing unit  3  at the following stage.
 
The first correction processing unit  3  performs image correction processing, such as defective pixel correction, ambient light amount decrease correction, and lens aberration correction, on the captured image signal from the imaging element  2 .
 
     The amplification unit  4  amplifies the captured image signal input through the first correction processing unit  3  on the basis of a gain G indicated by the control unit  7 . Amplification of the captured image signal by the amplification unit  4  is performed as, for example, amplification of a luminance value. Here, when the gain G=1, a signal amplification factor of the amplification unit  4  is 1, and thus the brightness of a captured image does not change between before and after processing of the amplification unit  4 . 
     The second correction processing unit  5  performs predetermined image correction processing different from image correction processing in the first correction processing unit  3  on the captured image signal input through the amplification unit  4 . 
     The development processing unit  6  performs predetermined image signal processing, for example, γ correction processing, on the captured image signal input through the second correction processing unit  5 .
 
In the imaging system of this example, the captured image signal processed by the development processing unit  6  is input to the CCU  20  as an output image signal of the imaging device  1 .
 
     The CCU  20  is configured to be able to perform wired communication via a cable or wireless communication with the imaging device  1 , transfers the captured image signal output from the imaging device  1  to, for example, an external device such as a video editing device which is not illustrated, and controls the imaging device  1  on the basis of an input signal and the like from the remote controller  30 . Here, the video editing device that processes an output image from the CCU  20  can switch between captured images from a plurality of imaging devices  1  or combine a plurality of captured images in the case of a system including a plurality of imaging devices  1  and CCUs  20 . 
     The control unit  7  includes a microcomputer (arithmetic operation processing device) including, for example, a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and the like and controls operation of the imaging device  1 , for example, by executing processing according to a program stored in the ROM. 
     The control unit  7  controls various operations of the imaging device  1  on the basis of an operation input from the remote controller  30 . 
       FIG. 2  is a perspective view illustrating a configuration example of the exterior of the remote controller  30 . 
     As illustrated, operators such as a plurality of buttons and knobs are formed in the remote controller  30 . Particularly, an adjustment operator  30   a  for performing brightness adjustment of a captured image is formed in the remote controller  30 .
 
In this example, the adjustment operator  30   a  is, for example, a lever type operator, and an indication value of the brightness of a captured image can be changed by an operation of rotating the adjustment operator  30   a.  Specifically, the indication value indicates a darkest brightness (a maximum value in the case of an F value which will be described later) at a position at which the adjustment operator  30   a  reaches one end and indicates a brightest brightness (a minimum value in the case of the F value which will be described later) at a position at which the adjustment operator  30   a  reaches the other end. In addition, the indication value changes by monotonically increasing or monotonically decreasing (e.g., linearly) from one end toward the other end.
 
Meanwhile, the adjustment operator  30   a  is not limited to a lever type operator and can be an operator of other types, for example, a rotary type operator and a slide type operator.
 
     Here, it is assumed that indication of the brightness of a captured image is performed as indication of an F value in the imaging system of this example. Accordingly, the remote controller  30  in this example outputs an operation state of the adjustment operator  30   a,  specifically, a target value (hereinafter denoted as “target value F_target”) of an F value in response to a rotation angle of the adjustment operator  30   a  to the CCU  20  as a brightness indication value. Here, an F value may be a value indicating a brightness corresponding to an F value in response to change in an effective aperture of a lens according to driving of the iris and may not necessarily be the F value itself in response to change in the effective aperture of the lens according to driving of the iris. 
     The CCU  20  transfers the target value F_target input through the remote controller  30  to the control unit  7  in the imaging device  1 . 
     Meanwhile, although an example in which the remote controller  30  outputs the target value F_target has been described above, a configuration in which the CCU  20  generates the target value F_target on the basis of an operation input signal (e.g., a signal indicating a value in response to a rotation angle of the adjustment operator  30   a ) from the remote controller  30  and transfers the target value F_target to the control unit  7  can also be employed. 
     In  FIG. 1 , the control unit  7  outputs the F value to the iris driving unit  11  and outputs the gain G to the amplification unit  4  to adjust the brightness of the captured image on the basis of the target value F_target input from the CCU  20 . Specific processing executed by the control unit  7  to adjust the brightness of the captured image will be described in detail below. 
     Meanwhile, although the imaging device  1  performs correction processing (processing of the first correction processing unit  3  and the second correction processing unit  5 ) and development processing (processing of the development processing unit  6 ) in  FIG. 1 , some processing may be omitted or a processing order may be changed. 
     2. Brightness Adjustment Method as Embodiment 
     Specific processing performed by the control unit  7  to adjust the brightness of a captured image will be described. 
     Meanwhile, in the following description, the brightness of a captured image may be simply abbreviated as “brightness.”
 
In brightness adjustment of this example, in response to change in an indication value (target value F_target in this example) indicating brightness, switching between “optical brightness adjustment” that is brightness adjustment according to the iris and “electronic brightness adjustment” that is brightness adjustment according to application of a gain depending on the indication value to a captured image is performed.
 
As described above, the target value F_target of the F value is input to the control unit  7  as a brightness indication value in response to operation of the adjustment operator  30   a  in the remote controller  30  in this example. In this example, a threshold value F_th for this target value F_target of the F value as a brightness indication value is fixed, and the control unit  7  performs switching between optical brightness adjustment and electronic brightness adjustment on the basis of a result of comparison between the target value F_target and the threshold value F_th.
 
       FIG. 3  and  FIG. 4  are diagrams for describing an example of switching between optical brightness adjustment and electronic brightness adjustment,  FIG. 3  is a conceptual diagram of an example of this switching, and  FIG. 4  illustrates an example of processing executed by the control unit  7  for this switching. 
     As illustrated in  FIG. 3 , a minimum value of the F value is, for example, F1.8, and F4.0 is set as the threshold value F_th (refer to  FIG. 3 ). The control unit  7  determines whether the target value F_target is the threshold value F_th or less (step S 101  in  FIG. 4 ), and if the target value F_target is not the threshold value F_th or less, sets an F value indicated to the iris driving unit  11  to the target value F_target and sets a target value G_target of a gain G indicated to the amplification unit  4  to “1” (step S 102 ).
 
In this manner, when the target value F_target is not the threshold value F_th or less, brightness adjustment according to the gain G is not performed because the target value G_target is set to “1”, whereas brightness adjustment according to the iris is performed because the F value is set to the target value F_target (refer to  FIG. 3 ). That is, when the target value F_target is greater than the threshold value F_th, electronic brightness adjustment is not performed and optical brightness adjustment is performed.
 
     On the other hand, when the target value F_target is the threshold value F_th or less, the control unit  7  sets the F value indicated to the iris driving unit  11  to the threshold value F_th and sets the target value G_target of the gain G to a value depending on a difference between a brightness at the target value F_target and a brightness at the threshold value F_th, specifically, a value of (brightness at the target value F_target)/(brightness at the threshold value F_th) (step S 103 ). That is, when the target value F_target is the threshold value F_th or less, brightness adjustment according to the iris is not performed because the F value is set to the threshold value F_th, whereas brightness adjustment according to the gain G is performed because the target value G_target changes depending on the size of the target value F_target of the F value (refer to  FIG. 3 ). 
     Here, the brightness at the target value F_target is inversely proportional to “F_target×F_target” and the brightness at the threshold value F_th is inversely proportional to “F_th×F_th” with respect to processing of step S 103 . Accordingly, the target value G_target of the gain G in step S 103  is obtained according to G_target=(F_th×F_th)/(F_target×F_target). 
     By performing brightness adjustment switching based on the aforementioned threshold value F_th, optical brightness adjustment is performed having a predetermined F value as a limit. 
     Accordingly, it is possible to promote curbing of resolution decrease occurring when only optical brightness adjustment is performed. 
     Here, since optical brightness adjustment requires driving of a mechanical part (diaphragm blade and the like) in the iris, change in brightness tends to be gentle with respect to change in the target value F_target. 
       FIG. 5  schematically represents change characteristics (thick solid line in the figure) of brightness with respect to the target value F_target (thick broken line in the figure) when the iris is used. Specifically, the illustrated example represents change characteristics when the target value F_target has been changed to a value corresponding to a brightness Bx at a specific speed from a point in time T0 to a point in time T1.
 
When the iris is used, brightness barely changes in a starting period immediately after the point in time T0 and thus a delay with respect to the target value F_target occurs according to the influence of inertia acting on the mechanical part. After the starting period, a speed of change of brightness gradually increases to reach a change speed approximately equal to a change speed of the target value F_target. Thereafter, the aperture in the iris continuously extends according to the influence of inertia and brightness also continuously changes even when change in the target value F_target ends at the point in time T1. The speed of change of brightness slowly decreases after a certain time from the point in time T1, and then change in brightness ends.
 
In this manner, change characteristics of brightness when the iris is used has a delay with respect to change in the target value F_target.
 
     On the other hand, in electronic brightness adjustment, driving of a mechanical part such as the iris is not performed and a delay in brightness change is barely generated with respect to change in the target value F_target. 
     Accordingly, when switching between optical brightness adjustment and electronic brightness adjustment is performed, a phenomenon that a speed of change of brightness abruptly increases or decreases at a switching timing occurs.
 
 FIG. 6  is an explanatory diagram with respect to this, and it is assumed that a brightness is changed to B1 according to optical brightness adjustment from a point in time T0 to a point in time T1, as shown in  FIG. 6A , and a logarithm of a gain is changed from 0 to B2 according to electronic brightness adjustment from the point in time T1 to a point in time T2, as shown in  FIG. 6B . In this case, although change characteristics of brightness from the point in time T0 to the point in time T2 correspond to a combination of these change characteristics of  FIG. 6A  and  FIG. 6B  and become characteristics as shown in  FIG. 6C , a part in which a speed of change of brightness abruptly changes is generated, as indicated by “X” in the figure, caused by a difference between the change characteristics of  FIG. 6A  and  FIG. 6B  at the point in time T1 that is a timing of switching between optical brightness adjustment and electronic brightness adjustment.
 
     Such a brightness change speed difference causes a user or an output image observer to feel discomfort. In addition, for the user, difficulty of the operation of adjusting a brightness such that it does not abruptly change increases to cause deterioration of operability with respect to brightness adjustment. 
     Accordingly, in the present embodiment, change in the gain G is delayed with respect to change in a brightness indication value. 
     Accordingly, the control unit  7  has a function as a filter unit  7   b  shown in  FIG. 7 . While  FIG. 7  is a functional block diagram representing a function of the control unit  7  for brightness adjustment, the control unit  7  has a function as a switching unit  7   a  and the function as the filter unit  7   b,  as illustrated.
 
The switching unit  7   a  switches between optical brightness adjustment and electronic brightness adjustment by performing processing shown in  FIG. 4 .
 
The filter unit  7   b  is a digital filter realized by software processing and serves as a delay filter that delays the target value G_target of the gain G input from the switching unit  7   a.  The target value G_target delayed by this filter unit  7   b  is output to the amplification unit  4  as the gain G.
 
     Here, although various examples may be conceived with respect to filter characteristics (delay characteristics) of the filter unit  7   b,  first to third examples will be given as a part thereof below. 
     [First Example of Delay Characteristics] 
     The first example is an example in which a difference between the target value G_target and a current value G(t) of the gain G is multiplied by a proportional coefficient p and a multiplication result is added to the current value G(t) of the gain G, as represented by the formula below. 
         G ( t+ 1)= G ( t )+( G _target− G ( t ))× p  
 
     [Second Example of Delay Characteristics] 
     The second example is an example of limiting a change speed. 
     There is an upper limit in a change speed in an actual iris. Accordingly, an upper limit is also provided to a change speed in delay characteristics according to the filter unit  7   b  such that the delay characteristics further approximate characteristics of the iris. 
     Although the method of adding a value obtained by multiplying a difference between the target value G_target and the current value G(t) of the gain G by the proportional coefficient p to the current value G(t) of the gain G is basically used in the second example as in the first example, the value (represented as “ΔG(t)” below) added to G(t) is limited on the basis of an upper limit value ΔG_max of a variation of the gain G in the second example. 
     Specifically, ΔG(t) is defined as follows. 
       Δ G ( t )= G _target− G ( t )× p  
 
       Then, 
       when |Δ G ( t )|&gt;Δ G _max,
 
       Δ G ′( t ) G′ ( t )=Δ G _max×Δ G ( t )/|Δ G ( t )|
 
     and, when |ΔG′(t)|≤ΔG_max, 
       Δ G′ ( t )=Δ G ( t ),
 
       and thus 
     G(t+1)=G(t)+ΔG′(t) is obtained. 
     [Third Example of Delay Characteristics] 
     The third example considers inertia acting on the iris. 
     The actual iris is driven having a weight and thus it has inertia and is barely accelerated when it starts to move. Accordingly, delay characteristics imitating the inertia acting on the iris are set such that they approximate the characteristics of the iris. 
     Specifically, a current variation of the gain G is set to Gs(t) and a variation of the gain G at the next time is set to Gs(t+1). Then, 
         F ( t )=( G _target− G ( t ))× p−Gs ( t )× d  and
 
         Gs ( t+ 1)= Gs ( t )+ F ( t ) 
       and thus 
         G ( t+ 1)= G ( t )+ Gs ( t+ 1) is obtained. 
       FIG. 8  is a diagram for describing an effect of delaying of the gain G, and the gain G responds to change in the target value F_target with a delay in this example, as can be ascertained from a comparison between  FIG. 6B  and  FIG. 8B . 
     In this example, change characteristics of the gain G with respect to change in the target value F_target, that is, change characteristics of a brightness in electronic brightness adjustment become curved characteristics instead of linear characteristics even in a case where any of the aforementioned first to third example is employed. Specifically, even in a case where any of the first to third example is employed, the change speed of the gain G gradually changes and thus a change state of the gain G becomes a curved change state within a period (a period after the point in time T1 in the example of the figure) in which the gain G is changed in optical brightness adjustment.
 
Particularly, in a case where the third example considering inertia is employed, a response period in which the gain G barely changes with respect to change in the target value F_target is acquired near the point in time T1 that is a timing of switching to electronic brightness adjustment.
 
     In addition, although change characteristics of a brightness according to brightness adjustment of this example become change characteristics as shown in  FIG. 8C  which correspond to a combination of change characteristics of brightness according to optical brightness adjustment shown in  FIG. 8A  and change characteristics of brightness according to electronic brightness adjustment shown in  FIG. 8B , abrupt change in the speed of change of brightness, as represented in  FIG. 6C , is curbed in this example because brightness change characteristics according to electronic brightness adjustment approximate brightness change characteristics according to optical brightness adjustment by providing the filter unit  7   b  shown in  FIG. 7 , and thus change in brightness can be smoothened even when switching between optical brightness adjustment and electronic brightness adjustment is performed (refer to a part represented by “X” in  FIG. 8C ). 
     Here, the filter unit  7   b  functions as a filter having a delay time and thus it also serves as a low pass filter. Since the filter unit  7   b  also functions as a low pass filter in this manner, prevention of change in the value of the gain G little by little is promoted even when the adjustment operator  30   a  is operated little by little in this example. That is, prevention of change in brightness little by little is promoted. 
     There is also a case in which, although a user wants to change the target value F_target at a constant speed, the speed changes, for example, due to tremor of a hand, and the like. In such a case, brightness adjustment can be realized according to intention of the user and improvement in operability with respect to brightness adjustment is promoted by curbing a response to operation performed little by little. 
     [With Respect to Mode Switching] 
     Here, the control unit  7  in this example is configured to be able to switch between a switching mode in which control of switching between optical brightness adjustment and electronic brightness adjustment as described above is performed and a non-switching mode in which control of switching is not performed and optical brightness adjustment is executed as brightness adjustment modes in response to the target value F_target indicated by operation of the adjustment operator  30   a.  Between these modes, the non-switching mode can be referred to as a mode of changing the F value in response to change in the target value F_target even when the target value F_target becomes the threshold value F_th or less in other words. 
     In this example, the control unit  7  executes switching between the switching mode and the non-switching mode as described above on the basis of operation of the remote controller  30 . 
     For example, the remote controller  30  is provided with an operator, for example, a button or the like, by which switching between the switching mode and the non-switching mode is instructed, and outputs corresponding operation input information to the CCU  20  in response to operation of the operator. This operation input information is transferred to the control unit  7  via the CCU  20 . 
     Here, when the aforementioned non-switching mode is provided such that the F value can be decreased to a minimum value in response to operation of the adjustment operator  30   a,  the following advantages are obtained. 
     One advantage is that efficiency of an adjustment work in flange back adjustment (adjustment of a distance from an installation plane of the lens device  10  to an imaging plane) can be promoted. Flange back adjustment is performed while observing blur generated in a captured image, and when the F value cannot be decreased during adjustment, it is difficult to perform flange back adjustment because blur is hardly generated. Accordingly, it is possible to facilitate generation of blur in a captured image and to promote efficiency of the adjustment work by performing switching to the non-switching mode such that the F value can be set to be less than the threshold value F_th.
 
Another advantage is that response to intention to create an image, such as intention to generate background blur, can be promoted. A user of the imaging system may desire to create fantastic image content with a blurred background, and it is possible to respond to such a desire.
 
     Meanwhile, an operation of switching between the switching mode and the non-switching mode is not limited to the operation of the remote controller  30  and can also be an operation for the imaging device  1 . 
     When the mode switching operation is set as an operation of the remote controller  30 , a mode switching operation burden is not imposed on a cameraman.
 
Here, since the above-described flange back adjustment is performed by the cameraman, it is not desirable to impose an extra operation burden on the cameraman during flange back adjustment in terms of efficiency of the adjustment work. By setting the mode switching operation as an operation of the remote controller  30 , it is possible to cause a person other than a cameraman such as a video engineer to perform the mode switching operation to promote reduction in an operation burden on the cameraman during flange back adjustment and to promote efficiency of the adjustment work.
 
     Meanwhile, although not particularly mentioned in the above description, the threshold value F_th used for switching between optical brightness adjustment and electronic brightness adjustment can be caused to be variable, for example, according to operation input, the type of the lens device  10 , or the like. A case in which the F value at which resolution starts to decrease changes according to the type or entity of the lens device  10  may also be conceived, and in such a case, the effect of curbing resolution decrease can be improved by varying the threshold value F_th according to the type of the lens device  10 , and the like. 
     3. Modified Examples 
     [3-1. First Modified Example] 
     Meanwhile, embodiments are not limited to the aforementioned specific examples and various modified examples may be conceived. 
     For example, the filter characteristics of the filter unit  7   b,  that is, delay characteristics of the gain G can be caused to be variable.
 
As an example, it is conceivable that these delay characteristics are caused to be variable in response to characteristics of the iris in the lens device  10 .
 
       FIG. 9  is a diagram for describing a configuration of an imaging system as a first modified example. Meanwhile, in the following description, parts similar to those that have already been described above will be denoted by the same reference numerals and signs, and description thereof will be omitted. 
     Here, illustration of the CCU  20  and the remote controller  30  is omitted in  FIG. 9 . 
     In the first modified example, a lens device  10 A in which information representing the filter characteristics of the filter unit  7   b  is stored is used. The lens device  10 A differs from the lens device  10  in that it includes a storage unit  12  as a nonvolatile memory. The storage unit  12  stores filter characteristic information  12   a  representing the filter characteristics of the filter unit  7   b  corresponding to characteristics of an iris of the lens device  10 A. 
     In the imaging system in this case, the imaging device  1 A is provided instead of the imaging device  1 . The imaging device  1 A differs from the imaging device  1  in that a control unit  7 A is provided instead of the control unit  7 . The control unit  7 A acquires the filter characteristic information  12   a  from the storage unit  12  of the lens device  10 A mounted on the imaging device  1 A and delays the target value G_target according to delay characteristics (i.e., the filter characteristics of the filter unit  7   b ) in accordance with the acquired filter characteristic information  12   a  in electronic brightness adjustment. 
     Accordingly, change characteristics of brightness according to electronic brightness adjustment can be caused to be characteristics suitable for the lens device in response to a case in which iris characteristics vary according to the lens device  10 A to be mounted. That is, it is possible to promote mitigation of a discomfort of a user during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment in response to a case in which iris characteristics vary according to a lens device to be mounted. 
     Here, as a specific example of the filter characteristic information  12   a,  information such as a tap coefficient and the number of taps may be conceived, for example, when a finite impulse response (FIR) filter is used as the filter unit  7   b.    
     An example in which the delay characteristics of the gain G is changed in response to the iris characteristics is not limited to the aforementioned example in which the filter characteristic information  12   a  is stored in the lens device  10 A. For example, a configuration in which entity identification information (e.g., information such as the model number and the manufacture&#39;s serial number of the lens device  10 A) for each lens device  10 A is stored in the storage unit  12  and the control unit  7 A delays the target value G_target according to delay characteristics corresponding to the entity identification information acquired from the lens device  10 A can also be employed. 
     In this case, in the imaging device  1 A, a predetermined storage means (e.g., a memory or the like included in the control unit  7 A) is caused to store table information representing a corresponding relationship between entity identification information and delay characteristics, and the control unit  7 A performs processing of delaying the target value G_target according to delay characteristics specified from the table information on the basis of acquired entity identification information. 
     Meanwhile, although an example in which the delay characteristics of the gain G are caused to be variable for each lens device  10 A to be mounted has been given above, instead of this, it is also conceivable to cause the delay characteristics of the gain G to be variable in response to iris characteristic change with time (e.g., characteristic change associated with aging degradation of a mechanical part), for example. 
     In any case, it is possible to change brightness change characteristics according to electronic brightness adjustment to characteristics corresponding to brightness change characteristics according to optical brightness adjustment in response to a case in which iris characteristics change due to a certain circumstance by configuring the delay characteristics of the gain to be variable. That is, it is possible to promote mitigation of a discomfort of a user during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment in response to a case in which iris characteristics changes due to a certain circumstance. 
     [3-2. Second Modified Example] 
     In addition, it is also conceivable to delay not only the gain G side but also the iris side (F value side). Specifically, a filter unit  7   c  that delays the F value output from the switching unit  7   a  is provided along with the filter unit  7   b  that delays the target value G_target of the gain G as in a control unit  7 B shown in  FIG. 10 . According to this configuration, change in the F value with respect to change in the target value F_target as a brightness indication value is delayed in optical brightness adjustment. Although not illustrated, the F value (represented by “F”&#39; in the figure) that has passed through the filter unit  7   c  is indicated to the iris driving unit  11  in the imaging system in this case. 
     According to this, on the assumption that there are ideal iris response characteristics, for example, it is possible to cause total characteristics of “iris+filter” to be identical to the ideal iris response characteristics by applying a filter to the gain G such that characteristics thereof becomes identical to the ideal response characteristics and, for an iris that does not have ideal response characteristics, providing a filter before the iris. 
     Accordingly, the ideal response characteristics can be realized in both optical brightness adjustment and electronic brightness adjustment, and thus it is possible to promote mitigation of a discomfort of a user with respect to brightness adjustment and curbing of deterioration in operability with respect to brightness adjustment. 
     [3-3. Other Modified Examples] 
     Meanwhile, although an example in which filter processing for delaying the gain G is performed as software processing of the control unit  7  has been given above, a filter unit  8  that performs the filter processing can also be provided as an external circuit as in an imaging device  1 C shown in  FIG. 11 , for example. 
     Here, the control unit  7 C differs from the control unit  7  in that it includes the switching unit  7   a  shown in  FIG. 7  as a functional unit with respect to brightness adjustment and the filter unit  7   b  is omitted. The filter unit  8  performs filter processing for delaying change in the target value G_target output from the control unit  7  (switching unit  7   a ) with respect to change in the target value F_target of the F value and outputs a gain G acquired through the filter processing to the amplification unit  4 . 
     In addition, although an example in which the control unit  7  in the imaging device  1  executes control with respect to brightness adjustment as an embodiment has been given in the above description, the control can also be performed by the CCU  20 .  FIG. 12  shows a configuration example of the imaging system in such a case. 
     In the imaging system in this case, an imaging device  1 D is provided instead of the imaging device  1  and a CCU  20 D is provided instead of the CCU  20 . The CCU  20 D includes, for example, a control unit  20   a  composed of a microcomputer including a CPU, a ROM, a RAM, and the like. This control unit  20   a  performs operation control of the imaging device  1 D, for example, on the basis of operation input information or the like from the remote controller  30 .
 
Although not illustrated, functional units with respect to brightness adjustment shown in  FIG. 7  are provided for the control unit  20   a  of the CCU  20 D in the imaging system in this case. Specifically, the functional units are the switching unit  7   a  and the filter unit  7   b.  
 
In this case, the F value output from the switching unit  7   a  included in the control unit  20   a  and the gain G output from the filter unit  7   b  included in the control unit  20   a  are respectively indicated to the iris driving unit  11  and the amplification unit  4  via the control unit  7 D included in the imaging device  1 D. Meanwhile, the control unit  7 D differs from the control unit  7  in that the switching unit  7   a  and the filter unit  7   b  are omitted.
 
     4. Conclusion of Embodiments 
     As described above, the signal processing device (imaging device  1  or CCU  20 D) of an embodiment includes a switching unit (switching unit  7   a ) that performs, in response to change in an indication value indicating the brightness of a captured image obtained by the imaging device, switching between optical brightness adjustment that is brightness adjustment according to an iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on the indication value to the captured image, and a first delay unit (filter units  7   b  and  8 ) that delays change in the gain with respect to change in the indication value in the electronic brightness adjustment. 
     By delaying change in the gain with respect to change in the indication value in electronic brightness adjustment, a degree of change in brightness is prevented from abruptly changing even when the indication value has changed to be a threshold value or less and thus brightness adjustment has switched from optical brightness adjustment to electronic brightness adjustment.
 
Accordingly, it is possible to promote mitigation of a discomfort of a user or an output image observer during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment while promoting curbing of resolution decrease due to execution of only optical brightness adjustment.
 
     In addition, in the signal processing device of the embodiment, the indication value is a target value F_target of an F value. 
     Accordingly, it is not necessary to convert a brightness indication value other than the F value into an F value in execution of optical brightness adjustment. Therefore, it is possible to promote reduction in a processing load with respect to brightness adjustment. 
     Further, in the signal processing device of the embodiment, the switching unit performs switching control on the basis of a result of comparison between the indication value and a threshold value. 
     Accordingly, optical brightness adjustment is performed having a predetermined F value as a limit.
 
Therefore, it is possible to improve the effect of curbing resolution decrease.
 
     In addition, in the signal processing device of the embodiment, the indication value is a target value of an F value, and the switching unit performs switching control such that optical brightness adjustment is performed on a side on which the target value of the F value is large and electronic brightness adjustment is performed on a side on which the target value of the F value is small, with respect to the threshold value. 
     That is, optical brightness adjustment is performed in a region where the F value is large and resolution is high and electronic brightness adjustment instead of optical brightness adjustment is performed in a region where the F value is small and resolution tends to decrease.
 
Accordingly, it is possible to promote curbing of resolution decrease associated with brightness adjustment.
 
     Furthermore, in the signal processing device of the embodiment, the first delay unit changes a gain change speed within a period (period after the point in time T1 in  FIG. 8B ) in which the gain is changed in electronic brightness adjustment. Accordingly, it is possible to approximate brightness change characteristics according to electronic brightness adjustment to brightness change characteristics according to optical brightness adjustment. 
     Therefore, seamlessness of change in brightness during brightness adjustment switching is improved, and thus it is possible to enhance the effect of mitigating a discomfort of a user or an output image observer with respect to change in brightness and the effect of curbing deterioration of operability with respect to brightness adjustment. 
     In addition, in the signal processing device of the embodiment, the first delay unit suppresses a gain change speed to a predetermined speed or less in electronic brightness adjustment. 
     There is an upper limit in a speed of change of brightness in optical brightness adjustment due to characteristics of the iris.
 
Accordingly, it is possible to approximate brightness change characteristics according to electronic brightness adjustment to brightness change characteristics according to optical brightness adjustment by suppressing the gain change speed to the predetermined speed or less in electronic brightness adjustment, and thus it is possible to enhance the effect of mitigating a discomfort of a user or an output image observer with respect to change in brightness and the effect of curbing deterioration of operability with respect to brightness adjustment.
 
     Further, in the signal processing device of the embodiment, the first delay unit delays the gain according to delay characteristics imitating inertia in electronic brightness adjustment. 
     Accordingly, it is possible to cause brightness change characteristics according to electronic brightness adjustment to be change characteristics to which inertia acting on the iris has been added.
 
Therefore, it is possible to approximate brightness change characteristics according to electronic brightness adjustment to brightness change characteristics according to optical brightness adjustment, and thus it is possible to enhance the effect of mitigating a discomfort of a user or an output image observer with respect to change in brightness and the effect of curbing deterioration of operability with respect to brightness adjustment.
 
     Furthermore, in the signal processing device of the embodiment, the switching unit is configured to be able to switch between a switching mode in which control of switching between optical brightness adjustment and electronic brightness adjustment is performed in response to change in the indication value and a non-switching mode in which switching control is not performed with respect to change in the indication value and optical brightness adjustment is executed. Accordingly, the F value can be decreased to a minimum value. 
     Therefore, it is possible to promote efficiency of a flange back adjustment work. Further, it is possible to promote response to intention to create an image such as intention to generate background blur. 
     In addition, in the signal processing device of the embodiment, the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation. 
     Accordingly, it is possible to perform switching between the switching mode and the non-switching mode on the basis of an intention of a user.
 
Therefore, it is possible to promote improvement of convenience of the user.
 
     Further, in the signal processing device of the embodiment, the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation of the remote controller (remote controller  30 ). 
     Accordingly, a burden of operation of switching between the switching mode and the non-switching mode is not imposed on a cameraman.
 
Since flange back adjustment is performed by the cameraman, it is not desirable to impose an extra operation burden on the cameraman during flange back adjustment in terms of efficiency of an adjustment work. If mode switching is performed on the basis of the operation of the remote controller as described above, a person other than the cameraman such as a video engineer can be caused to perform the mode switching operation and thus it is possible to promote reduction in an operation burden of the cameraman during flange back adjustment to promote efficiency of the adjustment work.
 
     Furthermore, in the signal processing device of the embodiment, the first delay unit is configured to be able to change delay characteristics of the gain in electronic brightness adjustment. 
     Accordingly, it is possible to change brightness change characteristics according to electronic brightness adjustment to characteristics corresponding to brightness change characteristics according to optical brightness adjustment in response to a case in which iris characteristics change due to a certain circumstance.
 
That is, it is possible to promote mitigation of a discomfort of a user or an output image observer during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment in response to a case in which iris characteristics change due to a certain circumstance.
 
     In addition, in the signal processing device of the embodiment, the imaging device is a lens interchangeable type imaging device, and the first delay unit delays change in the gain according to delay characteristics based on information acquired from a lens device mounted in the imaging device. 
     Accordingly, it is possible to cause change characteristics of brightness according to electronic brightness adjustment to be characteristics suitable for a lens device in response to a case in which iris characteristics vary according to lens devices to be mounted.
 
That is, it is possible to promote mitigation of a discomfort of a user or an output image observer during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment in response to a case in which iris characteristics vary according to lens devices to be mounted.
 
     Further, the signal processing device of the embodiment includes a second delay unit (filter unit  7   c ) that delays change in the F value with respect to change in the indication value in optical brightness adjustment. 
     Accordingly, it is possible to cause change characteristics of the F value with respect to change in the indication value to be desired characteristics.
 
Therefore, it is possible to promote mitigation of a discomfort of a user or an output image observer with respect to brightness adjustment and curbing of deterioration in operability with respect to brightness adjustment.
 
     In addition, an imaging device (imaging devices  1 ,  1 A,  1 C, and  1 D) of the embodiment includes an imaging element (imaging element  2 ) that receives incident light through an iris to acquire a captured image, a switching unit (switching unit  7   a ) that performs, in response to change in an indication value indicating brightness of the captured image, switching between optical brightness adjustment that is brightness adjustment according to the iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on an indication value to the captured image, and a first delay unit (filter units  7   b  and  8 ) that delays change in the gain with respect to change in the indication value in electronic brightness adjustment. 
     According to the imaging device according to this embodiment, it is possible to obtain similar operation and effects as those of the signal processing device according to the foregoing embodiment. 
     5. Application Examples 
     The technology according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be applied to an operating room system. 
       FIG. 13  is a diagram schematically illustrating an overall configuration of an operating room system  5100  to which the technology according to the present disclosure is applied. Referring to  FIG. 13 , the operating room system  5100  is configured by connecting a group of devices provided in an operating room in a coordinated manner via an audiovisual controller (AV Controller)  5107  and an operating room control device  5109 . 
     Various devices can be installed in the operating room. In  FIG. 13 , as an example, various device groups  5101  for endoscopic surgery, a ceiling camera  5187  provided on a ceiling of the operating room to image hands of a surgeon, an operating room camera  5189  provided on the ceiling of the operating room to image a state of the entire operating room, a plurality of display devices  5103 A to  5103 D, a recorder  5105 , a patient bed  5183 , and lighting  5191  are illustrated. 
     Here, among these devices, the device groups  5101  belong to an endoscopic surgery system  5113 , which will be described later, and include an endoscope, a display device that displays an image captured by the endoscope, and the like. Each device belonging to the endoscopic surgery system  5113  is also referred to as a medical device. On the other hand, the display devices  5103 A to  5103 D, the recorder  5105 , the patient bed  5183 , and the lighting  5191  are devices provided in the operating room, for example, separately from the endoscopic surgery system  5113 . Each device that does not belong to the endoscopic surgery system  5113  is also referred to as a non-medical device. The audiovisual controller  5107  and/or the operating room control device  5109  controls operations of these medical devices and non-medical devices in cooperation with each other. 
     The audiovisual controller  5107  controls overall processing related to image display in the medical devices and non-medical devices. Specifically, among the devices included in the operating room system  5100 , the device groups  5101 , the ceiling camera  5187 , and the operating room camera  5189  may be devices (hereinafter, also referred to as source devices) having a function of transmitting information to be displayed during surgery (hereinafter, also referred to as display information). Further, the display devices  5103 A to  5103 D may be devices for outputting the display information (hereinafter, also referred to as output destination devices). In addition, the recorder  5105  may be a device that belongs to both the source devices and the output destination devices. The audiovisual controller  5107  has a function of controlling operations of the source devices and the output destination devices, acquiring the display information from the source devices, and transmitting the display information to cause the output destination devices to display or record it. Also, the display information includes various images captured during surgery, various information related to surgery (for example, physical information of a patient, test results in the past, information on a surgical procedure, etc.), and the like. 
     Specifically, as the display information, information about images of a surgical part in the patient&#39;s body cavity captured by the endoscope may be transmitted from the device groups  5101  to the audiovisual controller  5107 . Also, as the display information, information about images in the vicinity of the operator captured by the ceiling camera  5187  may be transmitted from the ceiling camera  5187 . Also, as display information, information about images showing a state of the entire operating room captured by the operating room camera  5189  may be transmitted from the operating room camera  5189 . In a case in which the operating room system  5100  has another device having an imaging function, the audiovisual controller  5107  may also acquire information about images captured by the other device from the other device as the display information. 
     Alternatively, for example, the information about these images captured in the past is recorded in the recorder  5105  by the audiovisual controller  5107 . The audiovisual controller  5107  can acquire the information about the images captured in the past from the recorder  5105  as the display information. Also, various information about surgery may be recorded in advance in the recorder  5105 . 
     The audiovisual controller  5107  causes at least one of the display devices  5103 A to  5103 D, which are the output destination devices, to display the acquired display information (that is, the images captured during surgery and various information about surgery). In the illustrated example, the display device  5103 A is a display device suspended from and installed at the ceiling of the operating room, the display device  5103 B is a display device installed on a wall surface of the operating room, the display device  5103 C is a display device installed on a desk in the operating room, and the display device  5103 D is a mobile device having a display function (for example, a tablet personal computer (PC)). 
     Further, although not illustrated in  FIG. 13 , the operating room system  5100  may include devices outside the operating room. The devices outside the operating room may be, for example, a server connected to a network constructed inside or outside a hospital, a PC used by medical staff, and a projector installed in a conference room of the hospital. When such an external device is outside the hospital, the audiovisual controller  5107  can also display the display information on a display device of another hospital via a video conferencing system or the like for telemedicine. 
     The operating room control device  5109  controls overall processing other than the processing related to image display in the non-medical devices. For example, the operating room control device  5109  controls driving of the patient bed  5183 , the ceiling camera  5187 , the operating room camera  5189 , and the lighting  5191 . 
     The operating room system  5100  is provided with a centralized operation panel  5111 , and a user can give an instruction about image display to the audiovisual controller  5107  and an instruction about operations of the non-medical devices to the operating room control device  5109  via the centralized operation panel  5111 . The centralized operation panel  5111  is configured by providing a touch panel on a display surface of a display device. 
       FIG. 14  is a diagram illustrating a display example of an operation screen in the centralized operation panel  5111 . In  FIG. 14 , as an example, an operation screen corresponding to a case in which the operating room system  5100  is provided with two display devices as output destination devices is shown. Referring to  FIG. 14 , the operation screen  5193  is provided with a source selection area  5195 , a preview area  5197 , and a control area  5201 . 
     In the source selection area  5195 , the source devices provided in the operating room system  5100  and thumbnail screens showing the display information held by the source devices are linked and displayed. The user can select the display information to be displayed on a display device from any of the source devices displayed in the source selection area  5195 . 
     In the preview area  5197 , previews of screens displayed on the two display devices (Monitor 1 and Monitor 2), which are the output destination devices, are displayed. In the illustrated example, four images are P in P displayed on one display device. The four images correspond to the display information transmitted from the source devices selected in the source selection area  5195 . Among the four images, one is displayed relatively large as a main image and the remaining three are displayed relatively small as sub-images. The user can switch the main image and the sub images by appropriately selecting an area in which the four images are displayed. Further, a status display area  5199  is provided below the area in which the four images are displayed, and status related to surgery (for example, elapsed time of surgery, physical information of the patient, etc.) may be appropriately displayed in the area. 
     The control area  5201  is provided with a source operation area  5203  in which graphical user interface (GUI) components for operating the source devices are displayed and an output destination operation area  5205  in which the GUI components for performing operations on the output destination devices are displayed. In the illustrated example, the source operation area  5203  is provided with the GUI components for performing various operations (pan, tilt, and zoom) on cameras in the source devices having an imaging function. The user can operate operations of the cameras in the source devices by appropriately selecting these GUI components. Also, although not shown, in a case in which the source device selected in the source selection area  5195  is the recorder (that is, in a case in which an image recorded in the recorder in the past is displayed in the preview area  5197 ), the source operation area  5203  may be provided with GUI components for performing operations such as playing, stopping, rewinding, and fast-forwarding the image. 
     Further, the output destination operation area  5205  is provided with GUI components for performing various display operations (swap, flip, color adjustment, contrast adjustment, and switching between 2D display and 3D display) on display devices that are the output destination devices. The user can operate the display on the display devices by appropriately selecting these GUI components. 
     Also, the operation screens displayed on the centralized operation panel  5111  are not limited to the illustrated example, and the user may be able to input operations to each device provided in the operating room system  5100 , which can be controlled by the audiovisual controller  5107  and the operating room control device  5109 , through the centralized operation panel  5111 . 
       FIG. 15  is a diagram illustrating an example of a state of the surgery in which the operating room system described above is applied. The ceiling camera  5187  and the operating room camera  5189  are provided on the ceiling of the operating room, and can image hands of a surgeon (doctor)  5181  who treats an affected part of a patient  5185  on the patient bed  5183  and a state of the entire operating room. The ceiling camera  5187  and the operating room camera  5189  may be provided with a magnification adjustment function, a focal length adjustment function, an imaging direction adjustment function, and the like. The lighting  5191  is provided on the ceiling of the operating room and irradiates at least the hands of the surgeon  5181 . In the lighting  5191 , an amount of irradiation light, a wavelength (color) of the irradiation light, an irradiation direction of the light, and the like may be appropriately adjusted. 
     The endoscopic surgery system  5113 , the patient bed  5183 , the ceiling camera  5187 , the operating room camera  5189 , and the lighting  5191  are connected so that these can cooperate with each other via the audiovisual controller  5107  and the operating room control device  5109  (not illustrated in  FIG. 15 ), as illustrated in  FIG. 13 . The centralized operation panel  5111  is provided in the operating room, and the user can appropriately operate these devices present in the operating room through the centralized operation panel  5111 , as described above. 
     Hereinafter, a configuration of the endoscopic surgery system  5113  will be described in detail. As shown in the drawing, the endoscopic surgery system  5113  includes an endoscope  5115 , other surgical instruments  5131 , a supporting arm device  5141  that supports the endoscope  5115 , and a cart  5151  on which various devices for an endoscopic surgical operation are mounted. 
     In the endoscopic surgery, instead of cutting an abdominal wall to open the abdomen, a plurality of tubular laparotomy devices called trocars  5139   a  to  5139   d  are punctured into the abdominal wall. Then, from the trocars  5139   a  to  5139   d,  a lens-barrel  5117  of the endoscope  5115  and other surgical tools  5131  are inserted into the body cavity of the patient  5185 . In the illustrated example, as other surgical tools  5131 , a pneumoperitoneum tube  5133 , an energy treatment tool  5135 , and forceps  5137  are inserted into the body cavity of patient  5185 . Further, the energy treatment tool  5135  is a treatment tool that cuts and peels tissue, seals a blood vessel, or the like by using a high-frequency current or ultrasonic vibration. However, the illustrated surgical tools  5131  are merely exemplary, and as the surgical tools  5131 , various surgical tools generally used in the endoscopic surgery such as a tweezer and a retractor may be used. 
     An image of a surgical part within the body cavity of the patient  5185  imaged by the endoscope  5115  is displayed on a display device  5155 . The surgeon  5181  performs treatment such as cutting-out of an affected part, using the energy treatment tool  5135  or the forceps  5137  while viewing the image of the surgical part displayed on the display device  5155  in real time. Meanwhile, although not shown in the drawing, the pneumoperitoneum tube  5133 , the energy treatment tool  5135 , and the forceps  5137  are supported by the surgeon  5181 , an assistant, or the like during a surgical operation. 
     (Supporting Arm Device) 
     The supporting arm device  5141  includes an arm portion  5145  extending from a base portion  5143 . In the example shown in the drawing, the arm portion  5145  includes joint portions  5147   a,    5147   b,  and  5147   c  and links  5149   a  and  5149   b,  and is driven under the control of an arm control device  5159 . The endoscope  5115  is supported by the arm portion  5145 , and the position and posture thereof are controlled. Thereby, fixation of the stable position of the endoscope  5115  can be realized. 
     (Endoscope) 
     The endoscope  5115  includes the lens-barrel  5117  configured such that a region having a predetermined length from a tip end thereof is inserted into the body cavity of the patient  5185 , and a camera head  5119  connected to a base end of the lens-barrel  5117 . In the example shown in the drawing, the endoscope  5115  configured as a so-called hard mirror including a hard lens-barrel  5117  is shown, but the endoscope  5115  may be configured as a so-called soft mirror including a soft lens-barrel  5117 . 
     An opening in which an objective lens is fitted is provided at a tip of the lens-barrel  5117 . A light source device  5157  is connected to the endoscope  5115 , and light generated by the light source device  5157  is guided to the tip of the lens-barrel by a light guide extending inside the lens-barrel  5117 , and is radiated toward an observation target in the body cavity of the patient  5185  through the objective lens. The endoscope  5115  may be a direct endoscope, a perspective endoscope, or a side endoscope. 
     An optical system and an imaging element are provided inside the camera head  5119 , and reflected light (observation light) from the observation target is condensed on the imaging element by the optical system. The observation light is subjected to photoelectric conversion by the imaging element, and an electrical signal corresponding to the observation light, that is, an image signal corresponding to an observation image is generated. The image signal is transmitted to a camera control unit (CCU)  5153  as RAW data. Meanwhile, the camera head  5119  is equipped with a function of adjusting magnification and a focal length by appropriately driving the optical system. 
     Meanwhile, for example, in order to cope with stereoscopic vision (3D display) and the like, the camera head  5119  may be provided with a plurality of imaging elements. In this case, a plurality of relay optical systems are provided inside the lens-barrel  5117  in order to guide observation light to each of the plurality of imaging elements. 
     (Various Devices Mounted on Cart) 
     The CCU  5153  includes, for example, a central processing unit (CPU) and a graphics processing unit (GPU), and generally controls operations of the endoscope  5115  and the display device  5155 . Specifically, the CCU  5153  performs various image processing for displaying an image based on an image signal, such as development processing (demosaic processing), on the image signal received from the camera head  5119 . The CCU  5153  provides the image signal subjected to the image processing to the display device  5155 . In addition, the audiovisual controller  5107  shown in  FIG. 13  is connected to the CCU  5153 . The CCU  5153  also provides the image signal subjected to the image processing to the audiovisual controller  5107 . Further, the CCU  5153  transmits a control signal to the camera head  5119  and controls drive thereof. The control signal may include information about imaging conditions such as a magnification and a focal length. The information regarding the imaging conditions may be input via an input device  5161  or may be input via the centralized operation panel  5111  described above. 
     The display device  5155  displays an image based on an image signal having been subjected to image processing by the CCU  5153  under the control of the CCU  5153 . In a case where the endoscope  5115  is an endoscope dealing with high-resolution imaging such as 4K (the number of horizontal pixels  3840 ×the number of vertical pixels  2160 ) or 8K (the number of horizontal pixels  7680 ×the number of vertical pixels  4320 ) and/or is an endoscope dealing with 3D display, a display device capable of performing high-resolution display and/or 3D display may be used for the respective endoscopes as the display device  5155 . In a case where the endoscope  5115  is an endoscope dealing with high-resolution imaging such as 4K or 8K, a further immersive feeling can be obtained by using a display device having a size of 55 inches or more as the display device  5155 . In addition, a plurality of display devices  5155  having different resolutions and sizes may be provided depending on the application thereof. 
     The light source device  5157  is configured of a light source such as a light emitting diode (LED) and supplies the endoscope  5115  with irradiation light for imaging the surgical part or the like. 
     The arm control device  5159  is constituted by a processor such as a CPU and operates in accordance with a predetermined program to control the driving of the arm portion  5145  of the supporting arm device  5141  in accordance with a predetermined control method. 
     The input device  5161  is an input interface for the endoscopic surgery system  5113 . A user can input various information and an instruction to the endoscopic surgery system  5113  through the input device  5161 . For example, the user inputs various information on a surgical operation, such as body information of a patient or information on an operative method of the surgical operation, through the input device  5161 . In addition, for example, the user inputs an instruction indicating that the arm portion  5145  is driven, an instruction indicating that imaging conditions of the endoscope  5115  (the type of irradiation light, magnification, a focal distance, and the like) are changed, an instruction indicating that the energy treatment tool  5135  is driven, or the like through the input device  5161 . 
     The type of input device  5161  is not limited, and the input device  5161  may be various known input devices. As the input device  5161 , for example, a mouse, a keyboard, a touch panel, a switch, a foot switch  5171 , a lever, and/or the like can be applied. In a case where a touch panel is used as the input device  5161 , the touch panel may be provided on a display surface of the display device  5155 . 
     Alternatively, the input device  5161  is a device put on the user, such as a glasses-type wearable device or a head mounted display (HMD), and various inputs are performed in accordance with the user&#39;s gesture and line of sight detected by these devices. Further, the input device  5161  includes a camera capable of detecting movement of the user, and various inputs are performed in accordance with the user&#39;s gesture and line of sight detected from images captured by the camera. Further, the input device  5161  includes a microphone capable of picking up the user&#39;s voice, and various inputs are performed by means of voice through the microphone. In this way, the input device  5161  is configured to be able to input various information in a non-contact manner, so that the user particularly in a clean area (for example, the surgeon  5181 ) can operate a device in a dirty area in a non-contact manner. In addition, the user can operate the device without taking his/her hand off the surgical tools that he/she has, which improves the convenience for the user. 
     A treatment tool control device  5163  controls driving of the energy treatment tool  5135  for cauterizing or incising tissue, sealing a blood vessel, or the like. A pneumoperitoneum device  5165  sends a gas into the body cavity through the pneumoperitoneum tube  5133  in order to inflate the body cavity of the patient  5185  for the purpose of securing a visual field for the endoscope  5115  and a working space for the operator. A recorder  5167  is a device capable of recording various information about surgery. A printer  5169  is a device capable of printing various information about surgery in various formats such as text, images, and graphs. 
     Hereinafter, particularly characteristic configurations in the endoscopic surgery system  5113  will be described in more detail. 
     (Supporting Arm Device) 
     The supporting arm device  5141  includes the base portion  5143  which is a base, and the arm portion  5145  extending from the base portion  5143 . In the example shown in the drawing, the arm portion  5145  includes the plurality of joint portions  5147   a,    5147   b,  and  5147   c  and the plurality of links  5149   a  and  5149   b  connected to each other by the joint portion  5147   b,  but the configuration of the arm portion  5145  is simply shown in  FIG. 15  for the purpose of simplification. Actually, the shapes, number, and arrangement of the joint portions  5147   a  to  5147   c  and the links  5149   a  and  5149   b,  the directions of rotation axes of the joint portions  5147   a  to  5147   c,  and the like can be appropriately set so that the arm portion  5145  has a desired degree of freedom. For example, the arm portion  5145  can be configured to preferably have a degree of freedom of  6  or more degrees of freedom. Thereby, the endoscope  5115  can be freely moved within a movable range of the arm portion  5145 , and thus it is possible to insert the lens-barrel  5117  of the endoscope  5115  into the body cavity of the patient  5185  from a desired direction. 
     Actuators are provided at the joint portions  5147   a  to  5147   c,  and the joint portions  5147   a  to  5147   c  are configured to be rotatable around predetermined rotation axes by driving the actuators. By controlling driving of the actuators using the arm control device  5159 , the rotation angles of the joint portions  5147   a  to  5147   c  are controlled, and driving of the arm portion  5145  is controlled. As a result, control of the position and the posture of the endoscope  5115  can be realized. In this case, the arm control device  5159  can control the driving of the arm portion  5145  using various known control methods such as force control or position control. 
     For example, the surgeon  5181  appropriately performs an operation input through the input device  5161  (including the foot switch  5171 ), whereby the driving of the arm portion  5145  may be appropriately controlled by the arm control device  5159  in response to the operation input, and the position and posture of the endoscope  5115  may be controlled. By the control, the endoscope  5115  which is a tip end of the arm portion  5145  can be moved from any position to any position and then fixedly supported at a position after the movement. Meanwhile, the arm portion  5145  may be operated by a so-called master slave method. In this case, the arm portion  5145  can be remotely operated by a user through the input device  5161  installed at a location separated from a surgical operating room. 
     Further, in a case where force control is applied, the arm control device  5159  may perform so-called power assist control for receiving an external force from a user and driving the actuators of the joint portions  5147   a  to  5147   c  so that the arm portion  5145  moves smoothly according to the external force. Thereby, when the user moves the arm portion  5145  while directly touching the arm portion  5145 , the user can move the arm portion  5145  with a relatively small force. Thus, it is possible to more intuitively move the endoscope  5115  with a simpler operation and improve the convenience of the user. 
     Here, in general, in an endoscopic surgical operation, the endoscope  5115  is supported by a doctor called a scopist. On the other hand, the position of the endoscope  5115  can be fixed more reliably without depending on manpower by using the supporting arm device  5141 , and thus it is possible to stably obtain an image of a surgical part and smoothly perform a surgical operation. 
     Meanwhile, the arm control device  5159  may not be necessarily provided in the cart  5151 . In addition, the arm control device  5159  may not necessarily be one device. For example, the arm control device  5159  may be provided in each of the joint portions  5147   a  to  5147   c  of the arm portion  5145  of the supporting arm device  5141 , and the driving control of the arm portion  5145  may be realized by a plurality of arm control devices  5159  cooperating with each other. 
     (Light Source Device) 
     The light source device  5157  supplies irradiation light at the time of imaging a surgical part to the endoscope  5115 . The light source device  5157  is configured of, for example, an LED, a laser light source, or a white light source configured of a combination thereof. At this time, in a case where a white light source is constituted by a combination of RGB laser light sources, the intensity and timing of output of each color (each wavelength) can be controlled with high accuracy, and thus it is possible to adjust white balance of a captured image in the light source device  5157 . Further, in this case, an object to be observed is irradiated with a laser beam emitted from each of the RGB laser light sources in a time-division manner, and the driving of an imaging element of the camera head  5119  is controlled in synchronization with an irradiation timing thereof, whereby it is also possible to capture images corresponding to RGB in a time-division manner. According to the method, it is possible to obtain a color image without providing a color filter in the imaging element. 
     In addition, the driving of the light source device  5157  may be controlled so as to change the intensity of output light at predetermined time intervals. The driving of the imaging element of the camera head  5119  is controlled in synchronization of a timing of the change of the light intensity to acquire images in a time-division manner, and the images are composed, whereby it is possible to generate an image having a high dynamic range without so-called blackout and overexposure. 
     Further, the light source device  5157  may be configured to be able to supply light in a predetermined wavelength band corresponding to special light observation. In the special light observation, for example, so-called narrow band imaging for imaging predetermined tissue such as blood vessels in the surface of the mucosa with high contrast by emitting light of a narrow band as compared with irradiation light at the time of normal observation (that is, white light) by using wavelength dependency of light absorption in body tissue is performed. Alternatively, in the special light observation, fluorescence observation for obtaining an image using fluorescence generated by emitting excitation light may be performed. In the fluorescence observation, body tissue may be irradiated with excitation light to observe fluorescence from the body tissue (autofluorescence observation), or a reagent such as indocyanine green (ICG) may be locally injected into the body tissue, and the body tissue may be irradiated with excitation light corresponding to a fluorescence wavelength of the reagent to obtain a fluorescence image. The light source device  5157  can be configured to be able to supply narrow band light and/or excitation light corresponding to such special light observation. 
     (Camera Head and CCU) 
     Functions of the camera head  5119  of the endoscope  5115  and the CCU  5153  will be described in more detail with reference to  FIG. 16 .  FIG. 16  is a block diagram showing an example of functional configurations of the camera head  5119  and the CCU  5153  shown in  FIG. 15 . 
     Referring to  FIG. 16 , the camera head  5119  includes a lens unit  5121 , an imaging unit  5123 , a driving unit  5125 , a communication unit  5127 , and a camera head control unit  5129  as the functions thereof. In addition, the CCU  5153  includes a communication unit  5173 , an image processing unit  5175 , and a control unit  5177  as the functions thereof. The camera head  5119  and the CCU  5153  are connected to each other by a transmission cable  5179  so as to be able to bidirectionally communicate with each other. 
     First, a functional configuration of the camera head  5119  will be described. The lens unit  5121  is an optical system provided in a connection portion with respect to the lens-barrel  5117 . Observation light taken in from the top end of the lens-barrel  5117  is guided to the camera head  5119  and is incident on the lens unit  5121 . The lens unit  5121  is constituted by a combination of a plurality of lenses including a zoom lens and a focus lens. Optical characteristics of the lens unit  5121  are adjusted so that observation light is condensed on a light receiving surface of an imaging element of the imaging unit  5123 . In addition, the zoom lens and the focus lens are configured such that the positions thereof on the optical axes are movable in order to adjust the magnification and focus of a captured image. 
     The imaging unit  5123  is constituted by an imaging element and is disposed at a stage after the lens unit  5121 . Observation light having passed through the lens unit  5121  is condensed on the light receiving surface of the imaging element, and an image signal corresponding to an observation image is generated by photoelectric conversion. The image signal generated by the imaging unit  5123  is provided to the communication unit  5127 . 
     For the imaging element constituting the imaging unit  5123 , for example, a complementary metal oxide semiconductor (CMOS) type image sensor having a Bayer array and capable of color photographing can be used. Also, for the imaging element, for example, an imaging element capable of photographing a high-resolution image of 4K or higher may be used. By obtaining the image of the surgical part with high resolution, the surgeon  5181  can ascertain the state of the surgical part in more detail, and surgery can proceed more smoothly. 
     In addition, the imaging element constituting the imaging unit  5123  is configured to include a pair of imaging elements for acquiring an image signal for a right eye and an image signal for a left eye corresponding to 3D display. By the execution of the 3D display, the surgeon  5181  can more accurately ascertain the depth of biological tissue in the surgical part. Meanwhile, in a case where the imaging unit  5123  is configured as a multi-plate type, a plurality of systems of the lens units  5121  are also provided corresponding to the imaging elements. 
     Further, the imaging unit  5123  does not necessarily have to be provided on the camera head  5119 . For example, the imaging unit  5123  may be provided immediately after an objective lens inside the lens-barrel  5117 . 
     The driving unit  5125 , which is constituted by an actuator, moves the zoom lens and the focus lens of the lens unit  5121  along an optical axis by a predetermined distance under the control of the camera head control unit  5129 . Thereby, the magnification and focus of a captured image obtained by the imaging unit  5123  can be appropriately adjusted. 
     The communication unit  5127  is configured of a communication device for transmitting or receiving various information to or from the CCU  5153 . The communication unit  5127  transmits an image signal obtained from the imaging unit  5123  to the CCU  5153  through the transmission cable  5179  as RAW data. At this time, it is preferable that the image signal be transmitted by optical communication in order to display a captured image of a surgical part with low latency. This is because the surgeon  5181  performs a surgical operation while observing the state of an affected part by the captured image during the surgical operation, and thus it is required that a moving image of a surgical part is displayed in real time as much as possible for a safer and more reliable surgical operation. In a case where optical communication is performed, the communication unit  5127  is provided with a photoelectric conversion module that converts an electrical signal into an optical signal. An image signal is converted into an optical signal by the photoelectric conversion module and is then transmitted to the CCU  5153  through the transmission cable  5179 . 
     In addition, the communication unit  5127  receives a control signal for controlling the driving of the camera head  5119  from the CCU  5153 . The control signal includes information on imaging conditions such as information indicating designation of a frame rate of a captured image, information indicating designation of an exposure value during imaging, and/or information indicating designation of magnification and focus of a captured image. The communication unit  5127  provides the received control signal to the camera head control unit  5129 . Meanwhile, the control signal received from the CCU  5153  may also be transmitted by optical communication. In this case, the communication unit  5127  is provided with a photoelectric conversion module that converts an optical signal into an electrical signal, and the control signal is converted into an electrical signal by the photoelectric conversion module and is then provided to the camera head control unit  5129 . 
     Meanwhile, the above-described imaging conditions such as a frame rate, an exposure value, magnification, and focus are automatically set by the control unit  5177  of the CCU  5153  on the basis of an acquired image signal. That is, the endoscope  5115  is equipped with a so-called auto exposure (AE) function, auto focus (AF) function, and auto white balance (AWB) function. 
     The camera head control unit  5129  controls the driving of the camera head  5119  on the basis of the control signal from the CCU  5153  received via the communication unit  5127 . For example, the camera head control unit  5129  controls the driving of the imaging element of the imaging unit  5123  on the basis of information indicating designation of a frame rate of a captured image and/or information indicating designation of exposure during imaging. In addition, for example, the camera head control unit  5129  appropriately moves the zoom lens and the focus lens of the lens unit  5121  through the driving unit  5125  on the basis of information indicating designation of magnification and focus of a captured image. The camera head control unit  5129  may further have a function of storing information for identifying the lens-barrel  5117  and the camera head  5119 . 
     Meanwhile, components such as the lens unit  5121  and the imaging unit  5123  are disposed within a sealed structure with high airtightness and waterproofness, and thus the camera head  5119  can be made resistant to autoclave sterilization. 
     Next, a functional configuration of the CCU  5153  will be described. The communication unit  5173  is configured of a communication device for transmitting and receiving various pieces of information to and from the camera head  5119 . The communication unit  5173  receives an image signal transmitted from the camera head  5119  via the transmission cable  5179 . At this time, as described above, the image signal can be suitably transmitted through optical communication. In this case, for the optical communication, the communication unit  5173  is provided with a photoelectric conversion module that converts an optical signal into an electric signal. The communication unit  5173  provides the image signal converted into the electric signal to the image processing unit  5175 . 
     Further, the communication unit  5173  transmits a control signal for controlling the driving of the camera head  5119  to the camera head  5119 . The control signal may also be transmitted by optical communication. 
     The image processing unit  5175  performs various image processing on the image signal which is the RAW data transmitted from the camera head  5119 . Examples of the image processing include various known signal processing such as development processing, high image quality processing (band enhancement processing, super-resolution processing, noise reduction (NR) processing, and/or camera shake correction processing), and/or enlargement processing (electronic zoom processing). In addition, the image processing unit  5175  performs detection processing on an image signal for performing AE, AF, and AWB. 
     The image processing unit  5175  is constituted by a processor such as a CPU or a GPU, and the above-described image processing and detection processing can be performed by the processor operating in accordance with a predetermined program. Meanwhile, in a case where the image processing unit  5175  is constituted by a plurality of GPUs, the image processing unit  5175  appropriately divides information related to an image signal and performs image processing in parallel by the plurality of GPUs. 
     The control unit  5177  performs various control related to imaging of a surgical part and display of a captured image thereof which are performed by the endoscope  5115 . For example, the control unit  5177  generates a control signal for controlling the driving of the camera head  5119 . At this time, in a case where imaging conditions are input by a user, the control unit  5177  generates a control signal on the basis of the user&#39;s input. Alternatively, in a case where the endoscope  5115  is equipped with an AE function, an AF function, and an AWB function, the control unit  5177  appropriately calculates an optimal exposure value, focal distance, and white balance in accordance with results of the detection processing performed by the image processing unit  5175  to generate a control signal. 
     In addition, the control unit  5177  displays an image of a surgical part on the display device  5155  on the basis of an image signal having been subjected to image processing by the image processing unit  5175 . At this time, the control unit  5177  recognizes various objects in a surgical part image using various image recognition techniques. For example, the control unit  5177  can recognize surgical instruments such as forceps, specific biological parts, bleeding, mist at the time of using the energy treatment tool  5135 , and the like by detecting the shape, color, and the like of an edge of an object included in a surgical part image. The control unit  5177  displays various surgical operation supporting information so as to be superimposed on an image of a surgical part by using recognition results thereof at the time of displaying the image of the surgical part on the display device  5155 . The surgical operation supporting information is displayed to be superimposed and is presented to the surgeon  5181 , and thus it is possible to proceed with a surgical operation more safely and reliably. 
     The transmission cable  5179  connecting the camera head  5119  and the CCU  5153  to each other is an electric signal cable that supports electric signal communication, an optical fiber that supports optical communication, or a composite cable thereof. 
     Here, in the example shown in the drawing, communication is performed in a wired manner using the transmission cable  5179 , but communication between the camera head  5119  and the CCU  5153  may be performed in a wireless manner. In a case where communication therebetween is performed in a wireless manner, the transmission cable  5179  does not need to be built in a surgical operating room, and thus a situation where the movement of a medical staff in the surgical operating room is hindered by the transmission cable  5179  can be solved. 
     The example of the operating room system  5100  to which the technology according to the present disclosure may be applied has been described above. Also, although the case in which a medical system to which the operating room system  5100  is applied is the endoscopic surgery system  5113  has been described here as an example, the configuration of the operating room system  5100  is not limited to such an example. For example, the operating room system  5100  may be applied to a flexible endoscopic system for examination or a microsurgery system instead of the endoscopic surgery system  5113 . 
     The technology according to the present disclosure can be suitably applied to imaging of the hands of a surgeon using the ceiling camera  5187 , imaging of a state of the entire operating room using the operating room camera  5189 , imaging of a surgical side the using the endoscope  5115 , and the like among the above-described configurations. Specifically, the technology according to the present disclosure can be applied by a control unit (e.g., CCU  5153 ) adjusting irises (optical diaphragms) provided in the ceiling camera  5187 , the operating room camera  5189 , and the endoscope  5115  and a gain of an imaging device on the basis of an operation input of a user from a controller (e.g., input device  5161 ). By applying the technology according to the present disclosure to such imaging, it is possible to promote mitigation of a discomfort of a user during brightness adjustment switching and curbing of deterioration in operability with respect to brightness adjustment while promoting curbing of resolution decrease due to execution of only optical brightness adjustment with respect to capturing of images with respect to surgery. Particularly, when the technology according to the present disclosure is applied to imaging using the endoscope  5115 , abrupt change in brightness with respect to a captured image of a surgical site is curbed, and thus artifacts of the surgical site can be curbed to improve stability of surgery. 
     Meanwhile, the effects described in the present specification are merely exemplary and other effects may be obtained. 
     6. Present Technology 
     Meanwhile, the present technology can employ the following configurations. 
     (1)
 
A signal processing device including; a switching unit that performs, in response to change in an indication value indicating the brightness of a captured image obtained by an imaging device, switching between optical brightness adjustment that is brightness adjustment according to an iris and electronic brightness adjustment that is brightness adjustment according to application of a gain depending on the indication value to the captured image; and
 
a first delay unit that delays change in the gain with respect to change in the indication value in electronic brightness adjustment.
 
(2)
 
The signal processing device according to (1), wherein the indication value is a target value of an F value.
 
(3)
 
The signal processing device according to (1) or (2), wherein the switching unit performs the switching control on the basis of a result of comparison between the indication value and a threshold value.
 
(4)
 
The signal processing device according to (3), wherein the indication value is a target value of an F value, and
 
the switching unit performs the switching control such that the optical brightness adjustment is performed on a side on which the target value of the F value is large and the electronic brightness adjustment is performed on a side on which the target value of the F value is small, with respect to the threshold value.
 
(5)
 
The signal processing device according to any one of (1) to (4), wherein the first delay unit changes a gain change speed within a period in which the gain is changed in the electronic brightness adjustment.
 
(6)
 
The signal processing device according to any one of (1) to (5), wherein the first delay unit suppresses the gain change speed to a predetermined speed or less in the electronic brightness adjustment.
 
(7)
 
The signal processing device according to any one of (1) to (6), wherein the first delay unit delays the gain according to delay characteristics imitating inertia in the electronic brightness adjustment.
 
(8)
 
The signal processing device according to any one of (1) to (7), wherein the switching unit is configured to be able to switch between a switching mode in which control of switching between the optical brightness adjustment and the electronic brightness adjustment is performed in response to change in the indication value and a non-switching mode in which the switching control is not performed with respect to change in the indication value and the optical brightness adjustment is executed.
 
(9)
 
The signal processing device according to (8), wherein the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation.
 
(10)
 
The signal processing device according to (9), wherein the switching unit performs switching between the switching mode and the non-switching mode on the basis of an operation of a remote controller.
 
(11)
 
The signal processing device according to any one of (1) to (10), wherein the first delay unit is configured to be able to change delay characteristics of the gain in the electronic brightness adjustment.
 
(12)
 
The signal processing device according to (11), wherein the imaging device is a lens interchangeable type imaging device, and
 
the first delay unit delays change in the gain according to delay characteristics based on information acquired from a lens device mounted in the imaging device.
 
(13)
 
The imaging device according to any one of (1) to (12), including a second delay unit that delays change in the F value with respect to change in the indication value in the optical brightness adjustment.
 
     REFERENCE SIGNS LIST 
       1  Imaging device 
       1 ,  1 A,  1 C,  1 D Imaging device 
       2  Imaging element 
       3  First correction processing unit 
       4  Amplification unit 
       5  Second correction processing unit 
       6  Development processing unit 
       7 ,  7 A,  7 B,  7 C,  7 D Control unit 
       7   a  Switching unit 
       7   b,    7   c,    8  Filter unit 
       10 ,  10 A Lens device 
       11  Iris driving unit 
       12  Storage unit 
       12   a  Filter characteristic information 
       20 ,  20 D Camera control unit (CCU) 
       20   a  Control unit 
       30  Remote controller 
       30   a  Adjustment operator