Endoscope System

Abstract

To provide a technology to secure sufficient light volume while avoiding a distortion and an artifact caused by a rolling shutter, and to make unevenness of brightness and horizontal stripes inconspicuous even when a change in a pulse emission organ extends into a rolling shutter period.SOLUTION: A light source device for generating illumination light that a subject is irradiated with includes a plurality of semiconductor light emitting elements for emitting lights with different wavelength bands and a control part for controlling light emission profiles of the plurality of semiconductor light emitting elements and driving the plurality of semiconductor light emitting elements. The light emission profile includes a strong light emission period in which light is emitted by a predetermined light intensity, and a weak light emission period in which light is emitted by a light intensity weaker than the predetermined light intensity. The control part executes reduction control processing for replacing light emission volume in the weak light emission period with light emission volume in the strong light emission period while keeping constant a total amount of the light emission volume in the strong light emission period and the light emission volume in the weak light emission period.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] This disclosure , within This invention relates to endoscope systems. [Background technology]

[0002] In a typical endoscopic device equipped with a rolling shutter type image sensor, the light source is turned off during the effective pixel readout period (rolling shutter period) of the image sensor and turned on (pulse emission control) during the other period (quasi-global exposure period) to perform quasi-global exposure and avoid undesirable phenomena caused by the rolling shutter, such as distortion and artifacts.

[0003] On the other hand, if the light source is completely turned off during the rolling shutter period, the amount of light may be insufficient depending on the subject (site to be observed), and a good image cannot be obtained. For example, Patent Documents 1 to 3 disclose light source control that includes part of the rolling shutter period in the pulse emission period in order to solve this lack of light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-182580 A [Patent Document 2] Patent No. 5379932 [Patent Document 3] Patent No. 6239220 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when light source control such as that described in Patent Documents 1 to 3 is performed, the difference in exposure time between lines in adjacent frames causes uneven brightness and horizontal stripes on the screen. Then, there is a problem that the uneven brightness and horizontal stripes move up and down on the display screen due to the change in the pulse emission period for each frame, which is an eyesore. In addition, when offset emission is performed during the rolling shutter period to solve the lack of light, if the offset emission becomes strong to a certain extent, an unnatural image is generated, as if a long-exposure image and a high-speed exposure image are double-exposed.

[0006] The present disclosure has been made in consideration of these circumstances, and proposes a technology that ensures a sufficient amount of light while avoiding the occurrence of distortion and artifacts caused by the rolling shutter, and makes uneven brightness and horizontal stripes less noticeable even when changes in the pulse light-emitting device extend over the rolling shutter period. [Means for solving the problem]

[0007] In order to solve the above problems, the present embodiment proposes a light source device that generates illumination light to be irradiated onto a subject, the light source device comprising: a plurality of semiconductor light-emitting elements that emit light having different wavelength bands; and a control unit that controls the light emission profile of the plurality of semiconductor light-emitting elements and drives the plurality of semiconductor light-emitting elements, the light emission profile including a strong light emission period in which light is emitted at a predetermined light intensity and a weak light emission period in which light is emitted at a light intensity weaker than the predetermined light intensity, and the control unit executes a reduction control process that replaces the amount of light emitted in the weak light emission period with the amount of light emitted in the strong light emission period while maintaining the total amount of light emitted in the strong light emission period and the weak light emission period constant.

[0008] Moreover, the present embodiment proposes an endoscopic system for inserting an endoscope into an object to be observed and acquiring an image of the object, the endoscopic system comprising: a plurality of semiconductor light-emitting elements that emit light of different wavelength bands; an imaging element that irradiates the object with illumination light and detects reflected light from the object to generate an image signal; a processor that processes the image signal to generate an image of the object and displays it on a monitor; a main control unit that generates a control signal for controlling an emission profile of the plurality of semiconductor light-emitting elements based on the image signal; and a light source control unit that receives a control signal from the main control unit and drives the plurality of semiconductor light-emitting elements with a drive signal according to the emission profile, the emission profile including a strong emission period during which light is emitted at a predetermined light intensity and a weak emission period during which light is emitted at a light intensity weaker than the predetermined light intensity, and the main control unit determines the emission profile by executing a reduction control process that replaces the amount of light emitted in the weak emission period with the amount of light emitted in the strong emission period while maintaining the total amount of light emitted in the strong emission period and the weak emission period constant.

[0009] Further features related to the present disclosure will become apparent from the description of the present specification and the accompanying drawings, and the present disclosure may be realized and realized by the elements and combinations of various elements and aspects of the following detailed description and the appended claims. It should be understood that the descriptions in this specification are exemplary and illustrative only and are not intended to limit the scope or application of the claims in any manner. Effect of the Invention

[0010] According to the present disclosure, it is possible to ensure a sufficient amount of light while avoiding the occurrence of distortion and artifacts caused by the rolling shutter, and to make uneven brightness and horizontal stripes less noticeable even when changes in the pulse light-emitting element extend over the rolling shutter period. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing an example of the overall appearance of an endoscope system according to an embodiment of the present invention; [Diagram 2]1 is a diagram showing an example of a schematic internal configuration of an endoscope system according to an embodiment of the present invention; [Diagram 3] 2 is a diagram showing an example of the internal configuration of a light source device 201 provided inside a processor 200. FIG. [Figure 4] FIG. 13 is a diagram showing the spectra (wavelength characteristics) of the LEDs 2011 to 2015. [Diagram 5] 13 is a diagram showing the characteristics of illumination light (light that illuminates an observation area) generated by transmitting each LED through cross prisms 2017 and 2018. FIG. [Figure 6] FIG. 1 is a diagram showing an example of the configuration of a light source using LEDs with different light distributions. [Figure 7] FIG. 13 is a graph showing the ratio of emitted light intensity to current for each LED. [Figure 8] 1 is a diagram showing an effective pixel area and an ineffective area of ​​a rolling shutter type imaging element, with a CMOS sensor being an example. [Figure 9] 9A and 9B are diagrams showing phenomena (characteristics) that appear in an image captured using an imaging element having the imaging surface shown in FIG. 8 when a general dimming control process is executed. [Figure 10] 13A to 13C are diagrams showing operations when extension control (time control only) of the pulse emission period is performed and the corresponding state of an acquired image. [Figure 11] FIG. 2 is a diagram showing an overview of an improved dimming control process according to the present embodiment. [Figure 12] 1A and 1B are diagrams for explaining the influence of the difference in intensity between strong light emission and weak light emission. [Figure 13] FIG. 12 is a diagram showing the dimming control process of FIG. 11 in more detail, and is a diagram for explaining an example of inappropriate dimming control process. [Figure 14] 13 is a diagram for explaining offset light emission processing (weak pulse) in a non-light emission period (or a weak light emission period in which the light emission intensity is so weak that the light emission is not visible). FIG. [Figure 15] 13 is a diagram for explaining offset light emission processing (weak continuous light) in a non-light emission period (or a weak light emission period in which the light emission intensity is so weak that the light emission is not visible). FIG. [Figure 16]11A and 11B are diagrams showing differences in captured images that appear depending on whether or not offset emission is performed when an image sensor suddenly approaches a subject. [Figure 17] 5 is a flowchart for explaining a dimming control process according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. Note that, in the following, an endoscope system will be described as an example of one embodiment of the present disclosure.

[0013] Target sites for observation in an endoscope system include, for example, the respiratory system, digestive system, etc. Examples of the respiratory system include the lungs, bronchi, and ears, nose, and throat. Examples of the digestive system include the large intestine, small intestine, stomach, esophagus, duodenum, uterus, bladder, etc. When observing target sites such as those described above, it is more effective to utilize images that highlight specific biological structures.

[0014] <Endoscope system configuration> Fig. 1 is a diagram showing an example of the overall appearance of an endoscope system of this embodiment, and Fig. 2 is a diagram showing an example of a schematic internal configuration of the endoscope system of this embodiment. The endoscope system 1 includes an endoscope device (electronic scope) 100, a processor 200, and a monitor 300. The processor-side end of the endoscope device 100 is provided with a scope connector (hereinafter, sometimes simply referred to as "connector") 400 including a connector circuit according to this embodiment.

[0015] The endoscope device 100 includes a long and thin tubular insertion section 11 to be inserted into the inside of a subject. The endoscope device 100 includes, for example, an LCB (Light Carrying Bundle) 101 for guiding irradiation light from a light source device 201 described later, a light distribution lens 102 provided at the emission end of the LCB 101, an imaging unit 103 for receiving return light from an irradiated portion (observation site) via an objective lens (not shown), a driver signal processing circuit 105 for driving the imaging unit 103, and a first memory 106.

[0016] Illumination light from the light source device 201 enters the LCB 101 and propagates by repeating total reflection within the LCB 101. The illumination light (illumination light) propagated within the LCB 101 is emitted from the emission end of the LCB 101 disposed within the tip 12 of the insertion section 11, and illuminates the observation site via the light distribution lens 102. Return light from the irradiated area forms an optical image at each pixel on the light receiving surface of the imaging unit 103 via the objective lens.

[0017] The imaging unit 103 is disposed in the tip 12 of the insertion section 11, and may be a CMOS (Complementary Metal Oxide Semiconductor) image sensor, which is a rolling shutter type image sensor. The imaging unit 103 accumulates an optical image (return light from biological tissue) formed at each pixel on the light receiving surface as an electric charge according to the amount of light, and generates and outputs R, G, and B image signals. The imaging unit 103 is not limited to a CMOS image sensor, and may be replaced with other types of imaging devices as long as they are based on the rolling shutter type. The signal output from the imaging unit 103 is processed by a scope connector circuit 401 provided in the scope connector 400, as described later.

[0018] The processor 200 is a device that integrally includes a signal processing device that processes signals from the endoscope device 100, and a light source device that illuminates the inside of a body cavity where natural light does not reach via the endoscope device 100. In another embodiment, the signal processing device and the light source device may be configured as separate devices. The processor 200 includes a light source device 201, a system controller 202, a photometry unit 203, a front-stage signal processing circuit 205, a color conversion circuit 206, a rear-stage signal processing circuit 207, and a second memory 208.

[0019] The processor 200 may include an operation panel (not shown). The operation panel may be configured in various forms. Specific configurations of the operation panel include, for example, hardware keys for each function mounted on the front surface of the processor 200, a touch panel type GUI (Graphical User Interface), a combination of hardware keys and a GUI, etc. The operator (practitioner) can use the operation panel to perform mode switching operations described below.

[0020] The photometry unit 203 acquires luminance information of the image signal obtained by capturing an image from a gain circuit included in the color conversion circuit 206, compares it with a predetermined appropriate luminance value (for example, information on the appropriate luminance value can be stored in advance in an internal memory (not shown) of the photometry unit 203), and notifies the system controller 202 of the comparison result (whether the current luminance value is appropriate, high, or low).

[0021] The system controller 202 executes various programs stored in a memory (not shown) and comprehensively controls the entire endoscope system 1. The system controller 202 uses control signals to control the operation and timing of various circuits in the processor 200 so that processing suitable for the endoscope device 100 connected to the processor 200 is performed. The system controller 202 may be connected to the above-mentioned operation panel.

[0022] In addition, the system controller 202 receives the comparison result with the appropriate brightness value from the photometry unit 203, determines whether the current exposure should be maintained, whether the exposure should be increased (including the level value to increase), or whether the exposure should be decreased (including the level value to decrease), and outputs the result to the light source device 201 as an exposure control signal.

[0023] Furthermore, the system controller 202 changes each operation of the endoscope system 1 and parameters for each operation according to an instruction from an operator inputted from an operation panel. For example, when the operator selects an observation mode through the operation panel (mode switching operation), the system controller 202 outputs a mode selection signal to the light source device 201 for causing a light source corresponding to the observation mode to emit light. As will be described later, the light source device 201 may be, for example, a plurality of LEDs (Light Emitting Diodes) each emitting light of a different wavelength band (see FIG. 3). When the operator selects an observation mode (for example, a normal observation mode, a special light observation mode, a SatO2 mode, etc.) by operating a mode selection switch provided in the processor 200, for example, the system controller 202 generates a mode selection signal corresponding to the selected mode and supplies the signal to a light source control unit 2016 of the light source device 201 (see FIG. 3). The light source control unit 2016 determines the combination of LEDs to be illuminated and their intensity and light amount based on the mode selection signal (for example, the combination of light-emitting LEDs corresponding to the mode selection signal is stored in advance in an internal memory (not shown)), and outputs the required LED control signal to each of the LEDs 2011 to 2015. When each of the LEDs 2011 to 2015 emits light of each wavelength band based on the LED control signal supplied from the light source control unit 2016, the emitted lights are combined by a cross prism to generate irradiation light (combined light).

[0024] Data communication between the endoscope device 100 and the processor 200 may be performed using a wired electrical communication method or a wireless optical communication method.

[0025] 2, the endoscope device 100 and the processor 200 are connected via a scope connector 400. The connector 400 includes an LCB that constitutes a part of the LCB 101 that continues from the processor 200 to the endoscope device 100, and a scope connector circuit 401. Note that in this embodiment, the scope connector circuit 401 is provided in the scope connector 400, but it does not necessarily have to be provided inside the scope connector 400. For example, a circuit equivalent to the scope connector circuit 401 may be provided in a connector section on the processor 200 side or inside the processor 200.

[0026] <Example of internal configuration of light source device 201> FIG. 3 is a diagram showing an example of the internal configuration of a light source device 201 provided inside the processor 200, for example.

[0027] The light source device 201 includes a green LED 2011 that emits green light, a blue LED 2012 that emits blue light, a red LED 2013 that emits red light, an amber LED 2014 that emits amber light, a UV LED 2015 that emits UV light, a light source control unit 2016 that controls the light emission of each of the LEDs 2011 to 2015, and cross prisms 2017 and 2018.

[0028] When the light source control unit 2016 receives an exposure control signal from the system controller 202, it controls the light emission period and applied current value of each currently emitting LED (the combination of LEDs to emit light is determined depending on the observation mode), thereby changing the light emission profile of each LED to adjust the exposure (adjust the amount of light) (see Figs. 11 and 13 described below). For example, after changing the light emission profile by one step, the light source control unit 2016 determines whether to change the light emission profile again to adjust the exposure, based on an exposure control signal determined by the photometry result (comparison result with the appropriate luminance value) by the photometry unit 203.

[0029] Furthermore, the light source control unit 2016 determines the combination of LEDs to emit light based on a mode selection signal indicating an observation mode selected by an operator. At the start of light emission, the light source control unit 2016 controls the light emission of each LED based on, for example, a predetermined light emission profile (default light emission period and drive current value), and thereafter performs exposure adjustment as described above.

[0030] <About each LED light source> Fig. 4 is a diagram showing the spectrum (wavelength characteristics) of each of the LEDs 2011 to 2015. Fig. 5 is a diagram showing the characteristics of illumination light (light that illuminates an observation site) generated by transmitting each of the LEDs through the cross prisms 2017 and 2018.

[0031] The green LED 2011 has a transmission wavelength band of 540 nm to 575 nm, a peak wavelength of 550 nm, and a half width of 30 nm. The green LED 2011 is equipped with a phosphor, which emits light with a transmission wavelength band of about 400 nm to 780 nm, as shown in FIG. 4. In other words, the green LED and the phosphor essentially emit white light, but this white light is an intermediate product, and as described later, the transmission wavelength band is narrowed by the cross prism 2018, and green light is irradiated onto the observation site. The blue LED 2012 has a transmission wavelength band of 460 nm to 490 nm, a peak wavelength of 456 nm, and a half width of 21 nm. The red LED 2013 has a transmission wavelength band of 630 nm to 1000 nm, a peak wavelength of 650 nm, and a half width of 20 nm. The transmission wavelength band of the Amber LED2014 is 600nm to 615nm, with a peak wavelength of 613nm and a half-width of 19nm. The transmission wavelength band of the UV LED2015 is 385nm to 425nm, with a peak wavelength of 405nm and a half-width of 14nm.

[0032] When each light (white light, blue light, red light, amber light, and UV light as intermediate products) emitted from each of the LEDs 2011 to 2015, including the green LED 2011 equipped with a phosphor, passes through the cross prisms 2017 and 2018, it becomes each light with the characteristics shown in FIG. 5 and is irradiated onto the observation area. In detail, the white light emitted from the green LED 2011 + phosphor has its transmission wavelength band limited by the cross prism 2018, and becomes green light of 520 nm to 595 nm. The blue light emitted from the blue LED 2012 becomes blue light of 440 nm to 500 nm by the cross prisms 2017 and 2018. Also, the red light emitted from the red LED 2013 becomes red light of 620 nm to 630 nm by the cross prisms 2017 and 2018. The amber light emitted from the amber LED 2014 becomes amber light of 580 nm to 630 nm through the cross prisms 2017 and 2018. Furthermore, the UV light emitted from the UV LED 2015 becomes UV light of 380 nm to 450 nm through the cross prism 2018.

[0033] <Correction of linearity differences between LEDs> When the light source device 201 is configured with a plurality of LEDs, not only the wavelength of the light emitted by each of the LEDs 2011 to 2015 but also the light distribution (luminous intensity distribution in each direction) may differ (see FIG. 6: an example of a light source configuration using LEDs with different wavelengths), and this may cause a change in the color and light distribution of the light emitted from each of the LEDs 2011 to 2015. Furthermore, depending on the type of LED, when the forward voltage is lowered to lower the drive current value, the drive current value drops sharply and the LEDs no longer emit light, so that the drive current value cannot be lowered significantly. To deal with such a situation, it becomes necessary to dynamically correct the difference in linearity of the emitted light amount / current ratio of each of the LEDs 2011 to 2015 in accordance with the drive current control of each of the LEDs 2011 to 2015.

[0034] However, since the process of dynamically correcting the difference in linearity is complicated, it is preferable to determine the drive current value in advance so that there is no difference in linearity. Therefore, in this embodiment, a correction table for correcting the linearity of the emitted light amount / current ratio is prepared in advance, and the drive current value of each LED 2011 to 2015 is determined using this correction table. FIG. 7 is a diagram showing a graph of the emitted light amount / current ratio of each LED. In FIG. 7, the relationship of only two LEDs (LED1 and LED2) is shown as an example, but the same applies to the case where five LEDs 2011 to 2015 are used as shown in this embodiment. The relationship of the emitted light amount / current ratio of each LED as shown in FIG. 7 can be obtained by measuring each LED in advance. For this reason, a correction table is prepared in advance (stored in memory) in which the reciprocal of the relationship of the emitted light amount / current ratio is used as a correction parameter as a correction value, and the light source control unit 2016 calculates a corrected drive current value by multiplying the correction parameter corresponding to the desired emitted light amount (target emitted light amount obtained by exposure adjustment) and drives each LED. By doing so, even if the wavelengths or light distributions of the emitted light from each LED are different, it is possible to appropriately control the linearity of the emitted light amount / current ratio.

[0035] <Example of the configuration of the imaging surface of an image sensor> FIG. 8 is a diagram showing the effective pixel area and the invalid area of ​​a rolling shutter type imaging element, taking a CMOS sensor as an example. The CMOS sensor includes an effective pixel area where imaging is possible and an invalid area where imaging is not possible. In addition, a part (periphery) of the effective pixel area is masked, and is an area from which image signals cannot be acquired. When imaging is performed using such an imaging element (in the case of global exposure), various phenomena (characteristics) appear in the captured image. In this embodiment, the period when no image is displayed on the screen is the global exposure period, but the idea of ​​this embodiment is not limited to this case.

[0036] <General dimming control process> FIG. 9 is a diagram showing a phenomenon (characteristic) that appears in an image captured by an image sensor having an imaging surface shown in FIG. 8 when a general dimming control process is performed. As shown in FIG. 9a, when pulsed light is emitted during the readout period of a line that is not displayed on the screen, pseudo-global exposure can be realized. Also, when pulsed light is emitted as shown in FIG. 9b, the top line of the effective pixel area has less exposure than the other lines by the period from readout to reset, and the top line appears slightly darker, but if the period from readout to reset is sufficiently shorter than the pseudo-global exposure period (for example, less than 1%), the darkening is not noticeable. Also, when pulsed light is emitted as shown in FIG. 9c, about the upper half of the effective pixel area becomes slightly darker, but the darkening of that area becomes even less noticeable by the amount of the total exposure of each line that has increased. In this way, the longer the pulsed light emission period, the wider the area with different exposure amounts becomes, but the difference in brightness caused by the different exposure amounts becomes less noticeable. Furthermore, as shown in FIG. 9d, when the pulsed light emission period is further extended, the ratio changes smoothly from the bottom to the top of the screen when the previous pulse component increases. This makes artifacts and distortion (undesirable phenomena) less noticeable.

[0037] Fig. 10 is a diagram showing the operation when performing extension control (time control only) of the pulse emission period and the corresponding state of the captured image. Fig. 10 is a diagram showing in more detail the effect of the above-mentioned pulse emission period extension. As shown in Fig. 10A, when the pulse emission period is changed between adjacent frames, the difference in exposure amount becomes large in the lines read before and after the pulse end, resulting in a phenomenon in which horizontal stripes are seen to move up and down on the image. On the other hand, as shown in Fig. 10B, when the weak emission intensity is changed between adjacent frames, the horizontal stripes on the image become less noticeable.

[0038] However, simply extending the exposure period as shown in Figures 9 and 10 is not enough. When the exposure is increased, there is a possibility that the image will have whiteout (bright areas appearing as whiteout) depending on the surrounding environment of the observation point. Therefore, it is necessary to avoid distortion and artifacts while maintaining the appropriate exposure (an image that is not too dark and does not have whiteout).

[0039] <Improved dimming control process> Fig. 11 is a diagram showing an outline of the improved dimming control process according to this embodiment, and Fig. 12 is a diagram for explaining the influence of the difference in intensity between strong and weak light emission.

[0040] When controlling the light emission operation of the light source so that the intensity of the light (strong emission) during the pseudo-global exposure period is equal to or greater than the intensity of the light (weak emission) during the rolling shutter period, and adjusting the weak emission intensity to control dimming, it is common to change the strong emission intensity or strong emission period within the range of the pseudo-global exposure period if the weak emission during the rolling shutter period is below a predetermined threshold.

[0041] However, as shown in FIG. 12A, if the intensity difference between strong and weak light emission is large and the ratio (integral value ratio) of the "product of the intensity and period of strong light emission (strong light emission integral value)" to the "product of the intensity and period of weak light emission (weak light emission integral value)" is not large enough, an unnatural image like a double exposure of a short exposure image and a long exposure image is observed, and this phenomenon is likely to be uncomfortable for the operator, especially for a moving subject. In addition, when the light source is composed of multiple LEDs with different wavelengths or different light distributions (as in the present embodiment), the color and light distribution of the emitted light will change unless the emitted light amount of each LED is set to a constant ratio. Therefore, as described above, in order to control the drive current value when there is variation in the linearity of the light emission amount / current ratio of each LED, it is necessary to correct the difference in linearity of the light emission amount / current ratio of each LED, which makes the processing complicated.

[0042] Therefore, in order to reduce the complexity of the processing, in addition to correcting the linearity of the light emission amount / current ratio of each LED using the above-mentioned correction table, if the intensity of the weak light emission is lower than a predetermined threshold, one of the following processing steps 1 to 3 is executed. Process 1: Process to extend the strong light emission period while reducing the weak light emission intensity Process 2: Process to shorten the weak light emission period while extending the strong light emission period Process 3: Process to increase the intensity of weak light emission while shortening the weak light emission period

[0043] In other words, all of the processes 1 to 3 are processes that gradually replace weak light emission with strong light emission over time (reduction control process) while keeping the total light emission integral value (strong light emission integral value + weak light emission integral value) the same before and after the process, so that there is no change in the brightness of the observation screen, no phenomenon in which horizontal stripes move up and down the image, and no fading of the screen (reduction in brightness). By using any of these processes, it becomes possible to eliminate inconveniences such as the formation of unnatural images that look like double exposure over time, and changes in the color and distribution of the emitted light. For example, it is possible to change from the state of FIG. 12A (an image with double exposure and horizontal stripes) to the state of FIG. 12E (an image without horizontal stripes, with no double exposure or uneven brightness / color).

[0044] The processes 1 to 3 will be described in detail with reference to FIG. 11. First, the light source control unit 2016 performs dimming control for each of the LEDs 2011 to 2015, setting the LEDs to high light emission during the pseudo-global exposure period and low light emission during the rolling shutter period until the exposure reaches an appropriate level. As shown in FIG. 11(1), when the light emission intensity is reduced from a state in which light is emitted with uniform intensity during the entire period (pseudo-global exposure period and rolling shutter period), dimming control is performed such that the light emission intensity during the rolling shutter period (weak light emission period) is reduced, and when the rolling shutter period becomes a non-light emission state, the pseudo-global exposure period is shortened or the light emission intensity during the pseudo-global exposure period is reduced. On the other hand, as shown in FIG. 11(2), when the light emission intensity is increased, dimming control is performed such that the light emission period during the pseudo-global exposure period is extended or the light emission intensity during the pseudo-global exposure period is increased, and when the light emission period and light emission intensity during the pseudo-global exposure period reach their maximum, the light emission intensity during the rolling shutter period (weak light emission period) is sequentially increased.

[0045] For example, assume that the light emission pattern P1 has an appropriate exposure level (for example, a predetermined appropriate level ±α: α is a margin) due to the dimming control of FIG. 11(1). If an image is captured while continuing this state, a double-exposed image will be generated as shown in FIG. 12A. This is because images with different brightness are obtained by strong light emission and weak light emission, and they overlap. Therefore, the dimming control process is shifted to one of FIG. 11(3-1) to (3-3) while maintaining the exposure level of the light emission pattern P1. Here, FIG. 11(3-1) corresponds to the above process 1, FIG. 11(3-2) corresponds to the above process 2, and FIG. 11(3-3) corresponds to the above process 3. In processes 1 to 3, if the weak light emission intensity is equal to or lower than a predetermined threshold, a process is performed in which the weak light emission intensity is gradually replaced with a strong light emission period in each frame. This makes it possible to eliminate the weak light emission period without generating horizontal stripes in the captured image, and to avoid the generation of unnatural images and changes in the color and distribution of light from each light source.

[0046] More specifically, in process 1 (FIG. 11(3-1)), the value of the light emission intensity x light emission period in the weak light emission (weak light emission area) is gradually replaced with the strong light emission period so that the total area (total light emission integrated value) of the strong light emission period and the weak light emission period becomes the same, and dimming control is performed by the light emission pattern Q1 (reduction process). For example, the light emission of the reduction parts 1001 to 1004 in FIG. 11 exposes the area below the top line of the effective pixel area (see FIG. 8) of the image sensor (CMOS sensor) in the frame in which the corresponding reduction process is performed. Therefore, in the frame, the image part corresponding to the top line becomes dark, but in the next frame, an image signal corresponding to the top line can be acquired.

[0047] Process 2 (FIG. 11(3-2)) and process 3 (FIG. 11(3-3)) are dimming control processes in a form (embodiment) different from process 1. That is, process 2 and process 3 are processes (reduction process) in which the value of the light emission intensity x light emission period in the weak light emission (weak light emission area) is gradually replaced by the strong light emission period so that the total area (total light emission integral value) of the strong light emission period is the same as process 1. In process 2, the weak light emission level is kept constant, and the light emission integral value corresponding to the weak light emission area reduced by the period reduction is gradually assigned to the strong light emission period, thereby extending the strong light emission period. In process 3, the weak light emission period is shortened, and the light emission integral value corresponding to the weak light emission area reduced by the period reduction is assigned to the weak light emission, and the weak light emission intensity is gradually increased, thereby extending the strong light emission period. Processes 1 to 3 result in the execution of light emission patterns Q1 to Q3. Note that the light emission patterns Q1 to Q3 are all the same pattern.

[0048] By executing the change in light emission by any of the light adjustment controls from process 1 to process 3 (FIG. 11 (3-1) to (3-3)) slowly enough, it is possible to avoid the generation of unnatural images such as double exposure without giving the operator a sense of discomfort. For example, when light adjustment control is executed by the light emission patterns Q1 to Q3, the obtained image is as shown in FIG. 12E, and double exposure is eliminated.

[0049] When the subject is illuminated with light from each light source in the light emission patterns Q1 to Q3, if the subject moves (including the camera's movement: relative movement) and the exposure level rises, making the subject too bright (the exposure level deviates from the appropriate value), the appropriate exposure level is searched for by the process shown in Fig. 11 (4-1). For example, if the exposure level is determined to be appropriate in the case of light emission profile P2 (when the exposure level that was too bright becomes appropriate: as described above, whether the exposure level is appropriate is determined based on the photometry results by the photometry unit 203), a reduction process (any of processes 1 to 3) is executed from the state of light emission profile P2, and the weakly luminous parts are reduced to strong light emission. On the other hand, when lighting is performed in the state of lighting profile P2, if the exposure level drops and becomes too dark (the exposure level deviates from the appropriate value) due to the movement of the subject (including the movement of the camera: relative movement), the exposure level is corrected to the appropriate exposure level by the process shown in Fig. 11 (4-2) (the process of increasing the weak lighting level shown in Fig. 11 (4-2) is executed sequentially until the appropriate exposure level is reached). For example, when the appropriate exposure level is reached with lighting profile Q4, one of the reduction processes from process 1 to process 3 is executed from the exposure level state of lighting profile Q4 as shown in Fig. 11 (5).

[0050] <Details of light control process and response to sudden movements of the endoscope> FIG. 13 is a diagram showing the dimming control process of FIG. 11 in more detail, and is a diagram for explaining an example of an inappropriate dimming control process.

[0051] In FIG. 13, for example, when an object is illuminated with light of the light emission profile P11 and an image is captured, if it is determined that the image is overexposed (if the exposure level of P11 is not appropriate), the intensity of the weak light emission during the rolling shutter period is successively lowered (moving from the profile P11 to the profile on the right). Here, for example, if the appropriate exposure level (exposure level where overexposure is eliminated and the image is easy to see) is reached with the light emission profile P16, the above-mentioned reduction process (any of processes 1 to 3) is then executed, and the weak light emission period is replaced with a strong light emission period. Then, the captured image changes from the state of FIG. 12A (illuminating an object with the light emission profile P16 results in an unnatural image that looks like it has been double-exposed) to the state of FIG. 12E, and phenomena such as overexposure and double exposure are eliminated. If there is no change in the brightness of the captured image (if the change is within a predetermined threshold), the light sources 2011 to 2015 emit light with the light emission profile P66.

[0052] In FIG. 13, the light emission profile P11 moves to the right in sequence to become light emission profile P16, and then the light emission profile P66 is dimmed by the reduction process. However, other routes (for example, a route such as P11 → P12 → P13 → P24 → P25 → P36 → P46 → P56 → P66, which moves diagonally (but moves only slowly in the vertical direction), that is, a route that moves while performing dimming control and reduction process simultaneously) may be followed. However, dimming control process cannot be executed in the route of light emission profile P11 → P22 → P33 → P44 → P55 → P66. This is because the strong light emission period is simply controlled in time, and the phenomenon of the bright part of the image moving up and down (horizontal stripe movement reduction) appears as shown in FIG. 10A. In order to prevent this phenomenon from occurring, it is necessary to slowly reduce the intensity distribution of weak light emission to strong light emission (reduction process) over a long period of time.

[0053] For example, when it is necessary to make the light even brighter than the light emission profile P66 in Fig. 13, the intensity level of weak light emission is first increased, since extending the intensity distribution of strong light emission in the time direction would cause the above-mentioned horizontal stripe movement phenomenon. For example, the light emission profile is changed from P66 to P56, and then dimming control is performed to change the light emission profile to P55. However, since a rapid shift in the light emission profile in the vertical direction is equivalent to a rapid shift in the profile in the time direction, it is important to move the profile horizontally to adjust it to an appropriate exposure level in response to a sudden movement of the endoscope (image sensor), and then perform reduction processing vertically.

[0054] On the other hand, when it is necessary to darken from the state of the light emission profile P66, it is not possible to immediately switch to the light emission profile P77. For this reason, the strong light emission level during the rolling shutter period is temporarily lowered to switch to the state of the light emission profile P76 as a weak light emission period, and then a reduction process is performed to switch to the state of the light emission profile P77.

[0055] After the appropriate exposure level is determined, the dimming control process is executed up to the emission profile (Pkk; k=1, 2, . . ., n: n is an integer equal to or greater than 1) where the up arrow and the down arrow meet.

[0056] 13, the current value Imin indicates the correction limit of the linearity of the light emission amount / current ratio of each light source described above, or the current value at which each LED turns off. Therefore, in this embodiment, when performing dimming control to reduce the light emission intensity of weak light emission, after reducing the light emission intensity to Imin, the brightness is adjusted by shortening the light emission period instead of reducing the light emission intensity. In this case, if Imin is sufficiently small compared to the strong light emission intensity x time, horizontal stripes will not be visible.

[0057] <Offset light emission processing> Figures 14, 15, and 16 are diagrams for explaining offset light emission processing during a no-light emission period (or a weak light emission period in which the light emission intensity is so weak that the light emission cannot be visually recognized). Figure 14 shows offset light emission using a weak pulse. Figure 15 shows offset light emission using weak continuous light. Figure 16 is a diagram showing the differences in captured images that appear with and without offset light emission when the imaging element rapidly approaches the subject. Note that "weak" here means a light emission intensity that is sufficiently lower than the light emission intensity during a strong light emission period so as not to result in a double exposure image, but which allows the subject to be imaged with a brightness that is visible when the subject and the tip of the endoscope are close to each other.

[0058] The offset light emission process is executed separately (in the background of the light control process) from the conventional light control process (FIG. 9, etc.) and the light control process according to the present embodiment (see FIG. 11 and FIG. 13), and is a process of emitting a weak offset light during a non-light emission period. The weak offset light emission is considered to be in the form of a pulsed light emission (see FIG. 14) or a continuous light emission (see FIG. 15), but may be in a light emission pattern other than these. For example, a light emission pattern may be configured by combining a pulsed light emission and a continuous light emission, or a light emission pattern with an irregular pulse width may be configured. Such a weak offset light emission can be regarded as 0 (zero) when the intensity of the light emission by the light control process (which applies to any light control process) is equal to or greater than a predetermined value. On the other hand, when the intensity of the light emission by the light control process is less than a predetermined value (or when the light emission intensity is zero), the subject is illuminated only by the offset light emission. As a result, an event that occurs during a non-light emission period cannot be captured as an image, but the offset light emission makes it possible to capture an event during a non-light emission period.

[0059] 16 is a diagram showing differences in captured images depending on whether weak offset emission (pulsed light, continuous light) is present or not when the imaging element rapidly approaches the subject. When there is no weak offset emission, the captured image of frame Fk is the same as that of frame Fk-1. On the other hand, when weak offset emission is performed, regardless of whether pulsed light or continuous light is used, the captured image of frame Fk is clearly different from that of frame Fk-1, and it can be seen that the event when the imaging element rapidly approaches the subject is captured in frame Fk. It can also be seen that there is no difference in the captured image of frame Fk+1 depending on whether weak offset emission is present or not.

[0060] <Flowchart of Dimming Control Process> 17 is a flowchart for explaining the dimming control process according to this embodiment. The process of each step below is explained with the system controller 202 as the main operating entity, but this is not limiting and a control unit (processor) that controls operation and performs arithmetic processing may be provided separately and executed by it. Also, the function of the system controller 202 may be provided in the light source control unit 2016 of the light source device 201. Therefore, the dimming (reduction) control process may be part of the overall operation of the endoscope system 1, or may be part of the operation of the light source device 201. In the latter case, the light source control unit 2016 is the main operating entity of the process of each step.

[0061] (i) Step 1701 The light source control unit 2016 receives a mode selection signal corresponding to the observation mode selected by the operator from the system controller, and corrects the linearity of the emission light amount / current ratio of each light source to be emitted (any combination of the green LED 2011 to the UV LED 2015) using the above correction table.

[0062] (ii) Step 1702 The light source control unit 2016 drives each light source by the drive current after linearity correction of the emitted light amount / current ratio to emit light to generate illumination light, and irradiates the subject with this illumination light. Note that the emission profile at this time (period of strong emission and level and period of weak emission) can be a predetermined value (default value), or the emission profile used in the last operation when the endoscope was used the previous time can be used.

[0063] (iii) Step 1703 An imaging element (e.g., a CMOS sensor) of the imaging unit 103 detects reflected light from the subject (observation site) generated by irradiating the subject with the illumination light generated in step 1702, and transmits a captured image signal to the processor 200 via the scope connector circuit 401. The photometry section 203 obtains luminance information of the current captured image signal from a gain circuit included in the color conversion circuit 206, compares it with a predetermined appropriate luminance value (e.g., obtains a difference value), and passes the comparison result to the system controller 202. Note that the photometry section 203 may obtain only the luminance information of the current captured image signal from the gain circuit, and the comparison with the appropriate luminance value may be performed by another processing section such as the system controller 202.

[0064] (iv) Step 1704 The system controller 202 compares the comparison result received from the photometry unit 203 (or the system controller 202 may calculate the comparison result (difference value)) with a predetermined threshold value (threshold value for determining whether the exposure level is appropriate) and determines whether the current exposure level is appropriate. For example, if the comparison result (difference value) is equal to or less than the predetermined threshold value, it can be determined to be appropriate. If it is determined that the current exposure level is not appropriate (No in step 1704), the process proceeds to step 1705. On the other hand, if it is determined that the current exposure level is appropriate (Yes in step 1704), the process proceeds to step 1706.

[0065] (v) Step 1705 The system controller 202 changes the current light emission profile (information indicating a strong light emission period, a weak light emission period, and a weak light emission level) used for illuminating the subject with illumination light.

[0066] For example, if the current exposure level is high and the image is too bright (such as when the image is blown out), the system controller 202 generates an exposure control signal to adjust the exposure level by lowering the weak light emission level in the light emission profile. Also, if the weak light emission level is zero in the current light emission profile, the system controller 202 generates an exposure control signal to further shorten the strong light emission period to adjust the exposure level.

[0067] On the other hand, if the current exposure level is low and the image is too dark, the system controller 202 extends the strong light emission period if the strong light emission period in the light emission profile has not reached the pseudo-global period width, or if the strong light emission period in the current light emission profile has reached the pseudo-global period width, the system controller 202 generates an exposure control signal to further increase the weak light emission level and adjust the exposure level.

[0068] Once the light emission profile has been changed, the process proceeds to step 1702. Note that here, the light emission profile is gradually changed by one step at a time to adjust to the appropriate exposure level. However, for example, information (e.g., a table) indicating the relationship between the difference value (comparison value) between the luminance value of the captured image and the appropriate luminance value (luminance value corresponding to the appropriate exposure level) and the change width of the light emission profile (information indicating how many steps the light emission profile is changed) may be stored in an internal memory (not shown) of the system controller 202, and an appropriate light emission profile may be obtained directly from the difference value (comparison value).

[0069] (vi) Step 1706 The system controller 202 judges whether or not it is necessary to execute reduction control processing for the light emission profile exhibiting the appropriate exposure level. The judgment of whether or not reduction control processing is necessary can be based on, for example, whether or not the light emission profile has been changed since the previous reduction control processing was executed. If the light emission profile has not been changed, the subject is currently being captured at an appropriate exposure level (appropriate brightness) and appropriate dimming (dimming that does not cause horizontal stripes to appear), so there is no need to execute reduction control processing. On the other hand, if the light emission profile has been changed, there is a possibility that there is a weak light emission component that should be replaced with strong light emission, so whether or not reduction control processing is necessary is judged based on whether or not there is a weak light emission period in the changed light emission profile.

[0070] If it is determined that the refund control process needs to be executed (YES in step 1706), the process proceeds to step 1707. On the other hand, if it is determined that the refund control process does not need to be executed (NO in step 1706), the process proceeds to step 1708.

[0071] (vii) Step 1707 The system controller 202 executes any one of processes 1 to 3 in Fig. 11, gradually replacing weak light emission components with strong light emission components while keeping constant the light emission integral value (area of ​​the light emission profile) expressed by "strong light emission period x strong light emission intensity + weak light emission period x weak light emission intensity". For example, the reduction control process is executed over a period of about one second (a period corresponding to several tens of frames), and the light emission profile is changed to that shown in Fig. 10, for example, from Q1 to Q3. This makes it possible to obtain an image (Fig. 12E) that does not show horizontal stripes, instead of an image (Fig. 12A) that would otherwise be double-exposed if the exposure level were merely adjusted appropriately.

[0072] (viii) Step 1708 The light source control unit 2016 receives information on the light emission profile to be applied from the system controller 202, and based on the received light emission profile and mode selection signal, causes any one of the LEDs 2011 to 2015 to emit light to generate illumination light and irradiate the subject. Also, the imaging element (CMOS sensor) of the imaging unit 103 detects reflected light from the subject irradiated with the illumination light, generates an image capture signal, and transmits it to the processor. Also, the processor 200 performs a predetermined image processing on the image capture signal to generate display image data, and displays the display image data on the screen of the monitor (display device) 300.

[0073] (ix) Step 1709 The system controller 202 judges whether an instruction to end observation, such as to end imaging or turn off illumination, has been input from the operator. If an instruction to end observation has been input (YES in step 1709), the light adjustment control process ends. If an instruction to end observation has not been input (no instruction is detected) (NO in step 1709), the process proceeds to step 1703, where the determination and monitoring of whether the current exposure level is appropriate or not, the light adjustment control process, and the like are continued. The imaging unit 103 is installed at the tip 12 of the endoscope device 100, and moves within the body cavity of the subject. Therefore, the exposure level may change as the imaging unit approaches or moves away from the subject (observation site). Therefore, the luminance level of the captured image is constantly monitored, and the operation of the light source device 201 is controlled so as to maintain an appropriate exposure level.

[0074] <Effects of this embodiment> According to this embodiment, it is possible to capture an image of a subject while avoiding rolling shutter distortion and artifacts and securing a sufficient amount of light. In addition, even if the change in the pulse emission period extends to the rolling shutter period, the vertical movement of horizontal stripes can be made less noticeable. Furthermore, when multiple LEDs are used simultaneously as a light source, if the emission intensity changes, the ratio of the light amount of each LED will change unless the difference in the linearity of the emission light amount / current ratio of each LED is corrected and current control is performed, causing changes in the abandoned mine and changes in color. However, according to this embodiment, the emission intensity can be returned to the original value in a short time, making it possible to solve such problems.

[0075] <Specific matters of this disclosure> (1) Specific matters 1 A light source device that generates illumination light to be irradiated onto a subject, A plurality of semiconductor light emitting elements each emitting light of a different wavelength band; a control unit that controls the light emission profiles of the semiconductor light emitting elements and drives the semiconductor light emitting elements; the light emission profile includes a strong light emission period during which light is emitted at a predetermined light intensity and a weak light emission period during which light is emitted at a light intensity weaker than the predetermined light intensity; The control unit executes a reduction control process to replace the amount of light emitted during the weak light emission period with the amount of light emitted during the strong light emission period while maintaining the total amount of light emitted during the strong light emission period and the weak light emission period constant.

[0076] (2) Specific matters 2 In particular item 1, the control unit reduces the light intensity during the weak light emission period while keeping the length of the weak light emission period constant until the light intensity during the weak light emission period becomes zero, and replaces the reduced amount of light emission with the amount of light emission during the strong light emission period, thereby extending the strong light emission period.

[0077] (3) Specific matters 3 In particular item 1, The control unit shortens the weak light emission period while keeping the light intensity of the weak light emission period constant, and replaces the shortened amount of light emission with the amount of light emission of the strong light emission period to extend the strong light emission period.

[0078] (4) Specific matters 4 In particular item 1, the control unit shortens the length of the weak light emission period and increases the light intensity of the weak light emission period by the amount of light emitted by the shortened amount, thereby replacing the amount of light emitted in the weak light emission period with the amount of light emitted in the strong light emission period, thereby extending the strong light emission period.

[0079] (5) Specific matters 5 In any one of specific matters 1 to 4, The control unit determines an emission profile such that the luminance value in the captured image falls within a predetermined range, and then sets the determined emission profile as the target for starting the reduction control process.

[0080] (6) Specific matters 6 In any one of specific matters 1 to 5, The control unit further executes a process of correcting linearity of an emitted light amount / current ratio of the plurality of semiconductor light emitting elements.

[0081] (7) Specific matters 7 In any one of specific matters 1 to 6, The control unit controls the multiple semiconductor light-emitting elements to perform offset emission of an emission intensity that is sufficiently lower than the emission intensity during the strong emission period but is visible during a non-emission period other than the weak emission period and the strong emission period, or during a weak emission period in which the emission intensity is so weak that the emission is not visible.

[0082] (8) Specific matters 8 In particular item 7, The control unit executes the offset light emission using pulsed light or continuous light.

[0083] (9) Specific matters 9 An endoscope system for inserting an endoscope into an object to be observed and acquiring an image of the object, A plurality of semiconductor light emitting elements each emitting light of a different wavelength band; an image sensor that irradiates the subject with illumination light and detects reflected light from the subject to generate an image signal; a processor for processing the image signals to generate an image of the object for display on a monitor; a main control unit that generates a control signal for controlling a light emission profile of the plurality of semiconductor light emitting elements based on the image signal; a light source control unit that receives the control signal from the main control unit and drives the semiconductor light emitting elements with drive signals corresponding to the light emission profile, the light emission profile includes a strong light emission period during which light is emitted at a predetermined light intensity and a weak light emission period during which light is emitted at a light intensity weaker than the predetermined light intensity; The main control unit determines the emission profile by performing a reduction control process that replaces the amount of light emitted during the weak light emission period with the amount of light emitted during the strong light emission period while maintaining the total amount of light emitted during the strong light emission period and the weak light emission period constant.

[0084] (10) Specific matters 10 In particular item 9, the main control unit reduces the light intensity during the weak light emission period while keeping the length of the weak light emission period constant until the light intensity during the weak light emission period becomes zero, and replaces the amount of light emission corresponding to the decrease with the amount of light emission during the strong light emission period, thereby generating the control signal for extending the strong light emission period.

[0085] (11) Specific matters 11 In particular item 9, the main control unit generates the control signal for shortening the weak light emission period while keeping the light intensity of the weak light emission period constant, and for extending the strong light emission period by replacing the amount of light emission of the shortened weak light emission period with the amount of light emission of the strong light emission period.

[0086] (12) Specific matters 12 In particular item 9, the main control unit generates the control signal to extend the strong light emission period by shortening the length of the weak light emission period and increasing the light intensity of the weak light emission period by an amount of light emission corresponding to the shortened amount, thereby replacing the amount of light emission of the weak light emission period with the amount of light emission of the strong light emission period.

[0087] (13) Specific matters 13 In any one of specific matters 9 to 12, Further, a photometry unit is provided for acquiring luminance value information using the image signal, An endoscopic system in which the main control unit acquires the luminance information from the photometry unit, determines an emission profile such that the luminance value in the image signal is within a predetermined range, and then designates the determined emission profile as the target for starting the reduction control process.

[0088] (14) Specific matters 14 In any one of specific matters 9 to 13, the main control unit further generates a control signal for controlling the plurality of semiconductor light-emitting elements to perform offset emission of an emission intensity that is sufficiently lower than the emission intensity in the strong emission periods but is visible during non-emission periods other than the weak emission periods and the strong emission periods, or during weak emission periods where the emission intensity is so weak that the emission is not visible, and outputs the control signal to the light source control unit. [Explanation of symbols]

[0089] 1 Endoscope system 100 Endoscopic device 103 Imaging unit 200 processors 201 Light source device 2011 Green LED 2012 Blue LED 2013 Red LED 2014 Amber LED 2015 UV LED 2016 Light source control unit 2017, 2018 Cross Prism 202 System Controller 203 Photometry section 300 Monitors

Claims

1. An endoscope system for inserting an endoscope into an object to be observed and acquiring an image of the object, A plurality of semiconductor light emitting elements each emitting light of a different wavelength band; a rolling shutter type image sensor that irradiates the subject with illumination light and detects reflected light from the subject to generate an image signal; a processor that processes the image signal to generate an image of the subject and displays the image on a monitor; a main control unit that generates a control signal for controlling a light emission profile of the plurality of semiconductor light emitting elements based on the image signal; a light source control unit that receives the control signal from the main control unit and drives the semiconductor light emitting elements with drive signals corresponding to the light emission profile, the light emission profile includes a strong light emission period during which light is emitted at a predetermined light intensity and a weak light emission period during which light is emitted at a light intensity weaker than the predetermined light intensity; the main control unit generates the control signal for shortening the length of the weak light emission period and allocating the shortened light emission amount to the weak light emission period to increase the light intensity of the weak light emission period, thereby replacing the light emission amount of the weak light emission period with the light emission amount of the strong light emission period, and extending the strong light emission period; The main control unit determines the emission profile by performing a reduction control process that replaces the amount of light emitted during the weak light emission period with the amount of light emitted during the strong light emission period while maintaining the total amount of light emitted during the strong light emission period and the weak light emission period constant.

2. In claim 1, Further, a photometry unit is provided for acquiring luminance value information using the image signal, An endoscopic system in which the main control unit acquires the brightness value information from the photometry unit, determines an emission profile such that the brightness value in the image signal is within a predetermined range, and then sets the determined emission profile as the target for starting the reduction control process.

3. In claim 1 or 2, the main control unit further generates a control signal for controlling the plurality of semiconductor light-emitting elements so that, during non-light-emitting periods other than the weak light-emitting periods and the strong light-emitting periods, or during weak light-emitting periods where the light-emitting intensity is so weak that the light-emitting intensity is not visible, the light-emitting intensity is sufficiently lower than that during the strong light-emitting periods so as not to result in a double exposure image, but which allows the subject to be visible when the subject is approaching, and outputs the control signal to the light source control unit.

Images