Electronic Endoscope System

Abstract

To provide an electronic endoscope system capable of correcting an emission light amount of a light emitting element at arbitrary timing while a living body tissue is being illuminated by the light emitting element.SOLUTION: An electronic endoscope system includes: an electronic endoscope having an image pickup device configured so as to image a living body tissue; a light source device equipped with a light emitting element for emitting illumination light for illuminating the living body tissue; a processor configured so as to control timing of light exposure of the image pickup device and timing of lighting of the illumination light, and control the illumination light; and a light detector for detecting outgoing light emitted from the light emitting element. The processor includes a correction period setting part for setting a correction period between adjacent frames of an image acquired by the imaging by the image pickup device, and a correction part for executing control so that reference light is emitted from the light emitting element within the correction period, and correcting an amount of the illumination light emitted from the light emitting element on the basis of the reference light received by the light detector.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electronic endoscope system equipped with a light source device. [Background technology]

[0002] In the field of medical equipment, there is known an electronic endoscope system capable of generating an image suitable for diagnosing a lesion hidden in a body cavity by illuminating a biological tissue in a body cavity and capturing an image of the illuminated biological tissue in the body cavity as a subject. Conventionally, lamp light sources such as xenon lamps and halogen lamps that emit white light have been used as illumination light, but recently, instead of lamp light sources, semiconductor light sources having light emitting elements such as light emitting diodes (LEDs) and laser diodes (LDs) that emit light in a specific wavelength band have been used.

[0003] For example, it is known that the amount of emitted light of a light-emitting element such as an LED gradually decreases due to deterioration over time, etc. For this reason, it is common to correct the amount of emitted light from the light-emitting element by emitting light of a predetermined emission pattern before using the system (i.e., before capturing an image of a subject), or to correct the amount of emitted light from the light-emitting element by partially capturing the light emitted from the light-emitting element while using the system. As an example of the latter, Patent Document 1 describes that in a light source device, photodetectors for each of the RGB colors are provided, which are arranged near LEDs that emit each of the RGB colors, detect the amount of light of each color emitted from each LED during an exposure period, and generate and output a light amount detection signal indicating the detected light amount, and a control unit controls the driving of the LEDs that emit each of the RGB colors based on the light amount detection signal output during the exposure period and a light amount control pattern. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2016 / 056476 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is still room for improvement in the conventional method for correcting the amount of emitted light from a light emitting element. In the method of correcting the amount of light emitted from the light-emitting element by emitting light of a predetermined light-emitting pattern before using the system, if the correction is performed over the entire output range from weak light emission with a small amount of emitted light to strong light emission with a large amount of emitted light, the correction takes a long time and is inconvenient. On the other hand, in the method of Patent Document 1, which partially captures the emitted light from the light-emitting element while the system is in use and corrects the amount of light emitted from the light-emitting element, it may be difficult to correct the amount of light emitted from the light-emitting element over the entire output range depending on the usage conditions. For example, in observation of narrow cavities such as bronchi, the emitted light from the light-emitting element continues to be in a weak light emission state, making it difficult to correct over the entire output range.

[0006] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an electronic endoscope system capable of correcting the amount of light emitted from a light-emitting element at any timing while the light-emitting element is illuminating a living tissue. [Means for solving the problem]

[0007] One aspect of the present invention is an electronic endoscope system comprising: an imaging element configured to image biological tissue; a light source device having a light-emitting element that emits illumination light to illuminate the biological tissue; a processor configured to control the exposure timing of the imaging element and the timing of turning on the illumination light and to control the illumination light; and a photodetector that detects the light emitted by the light-emitting element. The processor has a correction period setting unit that sets a correction period between adjacent frames of an image obtained by imaging of the imaging element, and a correction unit that controls the emission of reference light from the light-emitting element within the correction period and corrects the amount of illumination light emitted from the light-emitting element based on the reference light received by the photodetector.

[0008] The imaging element may be configured to image the biological tissue by a rolling shutter method, and the processor may include an exposure period setting unit that sets an exposure period for each line of the imaging element by an electronic shutter. In this case, the correction period setting unit may set the correction period from an exposure end time of the scanning line of the Nth frame to an exposure start time of the electronic shutter of the N+1th frame.

[0009] The consecutive frames of the image obtained by imaging with the imaging element may include display frames used as display images and non-display frames not used as display images. In this case, the processor includes an exposure period setting unit that sets an exposure period for a scanning target line of the imaging element by an electronic shutter, and the correction period setting unit sets the correction period from an exposure end time of the scanning target line of the Nth display frame to an exposure start time of the electronic shutter of the N+1th display frame.

[0010] When multiple consecutive frames of an image obtained by imaging with the imaging element include display frames that are used as display images and non-display frames that are not used as display images, the correction period setting unit may set the correction period within a period for generating the non-display frames.

[0011] The display frames may be even-numbered or odd-numbered frames, and the non-display frames may be odd-numbered or even-numbered frames.

[0012] The correction unit may control the emission of multiple reference light beams having different output levels from the light-emitting element during multiple correction periods, and may correct the amount of illumination light emitted from the light-emitting element based on the multiple reference light beams received by the photodetector. Effect of the Invention

[0013] According to the above-mentioned electronic endoscope system, the amount of light emitted from the light emitting element can be corrected at any timing while the living tissue is being illuminated by the light emitting element. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of a configuration of an endoscope system according to an embodiment; [Diagram 2] 1 is a block diagram showing an example of a configuration of a power supply device according to an embodiment; [Diagram 3] 1 is a block diagram showing a configuration for correcting the amount of illumination light in an endoscope system according to one embodiment. FIG. [Figure 4] 10 is a timing chart showing an example of timing for turning on a reference light; [Diagram 5] 10 is a timing chart showing an example of timing for turning on a reference light; [Figure 6] 10 is a timing chart showing an example of timing for turning on a reference light; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the electronic endoscope system will be described in detail with reference to the accompanying drawings. An electronic endoscope system according to one embodiment includes an electronic endoscope, a light source device, and a processor. The electronic endoscope includes an imaging element configured to capture images of biological tissue. The light source device includes a light-emitting element (such as a light-emitting diode or a laser diode) that emits illumination light to illuminate the biological tissue. The processor is configured to control the timing of exposure of the imaging element and the timing of turning on the illumination light by the light-emitting element of the light source device, and to control the illumination light. An electronic endoscope system according to one embodiment includes a photodetector that detects outgoing light emitted by a light-emitting element, in order to correct the amount of illumination light from the light-emitting element at any timing while illuminating the living tissue, such as when an operator is observing the living tissue of a patient. In order to perform correction within a wide range of the amount of outgoing light regardless of the amount of illumination light required for observing the living tissue, a correction period is set between adjacent frames of an image so as not to affect an image generated by an imaging element. The light-emitting element is controlled to emit reference light, which is outgoing light for correction, within this correction period. The emitted reference light is detected by the photodetector, and the detection result is used to correct the amount of light from the light-emitting element.

[0016] 1 is a block diagram showing an example of a configuration of an electronic endoscope system 1 according to an embodiment. As shown in FIG. 1, the electronic endoscope system 1 includes an electronic scope 100, an electronic endoscope processor 200, and a monitor 300.

[0017] The electronic endoscope processor 200 includes a system controller 202 and a timing controller 206. The system controller 202 executes various programs stored in a memory 204 and comprehensively controls the entire electronic endoscope system 1. The system controller 202 also changes various settings of the electronic endoscope system 1 in response to instructions from a user (surgeon or assistant) inputted to an operation panel 208. The timing controller 206 outputs clock pulses to each circuit in the electronic endoscope system 1 to adjust the timing of the operation of each part.

[0018] The electronic endoscope processor 200 includes a light source device 230 that supplies illumination light to the electronic scope 100. The light source device 230 is configured so that the illumination light is focused by a focusing lens (not shown) and then incident on an entrance end of an LCB (Light Carrying Bundle) 102, which is a bundle of optical fiber strands of the electronic scope 100, via a dimming device (not shown). The light source device 230 includes a plurality of light-emitting diodes (hereinafter referred to as "LEDs") that emit light of a predetermined color wavelength band. Laser diodes can be used instead of LEDs. LEDs and laser diodes have characteristics such as low power consumption and low heat generation compared to other light sources, and therefore have the advantage of being able to obtain bright images while suppressing power consumption and heat generation. The ability to obtain bright images can improve the accuracy of evaluation of the extent of the lesion in the affected area. 1, the light source device 230 is built into the electronic endoscope processor 200, but may be provided in the electronic endoscope system 1 as a device separate from the electronic endoscope processor 200. The light source device 230 may also be provided at the tip of the electronic scope 100, which will be described later. In this case, the LCB 102 for guiding the illumination light is not necessary.

[0019] Illumination light entering the LCB 102 from the entrance end propagates through the LCB 102, exits from the exit end of the LCB 102 located in the tip of the electronic scope 100, and is irradiated onto the subject via a light distribution lens 104. Light reflected from the subject forms an optical image on the light receiving surface of an image sensor 108 via an objective lens 106.

[0020] The imaging element 108 is, for example, a single-chip color CCD (Charge-Coupled Device) image sensor with various filters, such as an IR (Infra Red) cut filter 108a and a Bayer array color filter 108b, arranged on the light-receiving surface, and generates primary color signals of R (Red), G (Green), and B (Blue) according to the optical image formed on the light-receiving surface. Instead of a single-chip color CCD image sensor, a single-chip color CMOS (Complementary Metal Oxide Semiconductor) image sensor can also be used.

[0021] A driver signal processing circuit 152 is provided in the connection section of the electronic scope 100. The driver signal processing circuit 152 performs predetermined signal processing such as color interpolation and matrix calculation on the primary color signals input from the image sensor 108 to generate image signals (luminance signal Y, color difference signals Cb, Cr), and outputs the generated image signals to the image processing unit 220 of the electronic endoscope processor 200. The driver signal processing circuit 152 also accesses the memory 154 to read out the unique information of the electronic scope 100. The unique information of the electronic scope 100 recorded in the memory 154 includes, for example, the number of pixels and sensitivity of the image sensor 108, the operable frame rate, the model number, etc. The driver signal processing circuit 152 outputs the unique information read out from the memory 154 to the system controller 202. In this way, the electronic scope 100 uses the image sensor 108 to capture images of biological tissue in a body cavity.

[0022] The system controller 202 performs various calculations based on the unique information of the electronic endoscope 100 and generates a control signal. Using the generated control signal, the system controller 202 controls the operation and timing of each circuit in the electronic endoscope processor 200 so that processing suitable for the electronic endoscope 100 connected to the electronic endoscope processor 200 is performed.

[0023] The timing controller 206 generates a timing signal composed of clock pulses in accordance with timing control by the system controller 202, and supplies this timing signal to the imaging element 108, the driver signal processing circuit 152, the image processing unit 220, and the light source device 230. The driver signal processing circuit 152 drives in accordance with the clock pulses of the timing signal supplied from the timing controller 206.

[0024] Under the control of the system controller 202, the image processing unit 220 generates a video signal for displaying an endoscopic image, etc. on the monitor based on the image signal input from the driver signal processing circuit 152 in accordance with a timing signal, and outputs the video signal to the monitor 300.

[0025] 2 shows a block diagram of the light source device 230. The light source device 230 includes first to fourth LEDs 111 to 114. The first to fourth LEDs 111 to 114 are individually controlled in terms of light emission by first to fourth LED drive circuits 141 to 144, respectively.

[0026] The first LED 111 is a purple light emitting diode (LED) that emits light in a purple wavelength band (for example, a wavelength of 395 to 435 nm). The second LED 112 is a blue LED that emits light in a blue wavelength band (for example, a wavelength of 430 to 470 nm). The third LED 113 has a blue LED that emits light in a blue wavelength band (for example, a wavelength of 425 to 455 nm) and a phosphor. The phosphor is excited by the blue LED light emitted from the blue LED and emits fluorescence in a green wavelength band (for example, a wavelength of 460 to 600 nm). The fourth LED 114 is a red LED that emits light in a red wavelength band (for example, a wavelength of 620 to 680 nm).

[0027] Collimator lenses 121 to 124 are disposed in front of the light emission direction of each of the LEDs 111 to 114. The purple LED light emitted from the first LED 111 is converted into parallel light by the collimator lens 121 and is incident on the dichroic mirror 131. The LED light emitted from the second LED 112 is converted into parallel light by the collimator lens 122 and is incident on the dichroic mirror 131. The dichroic mirror 131 combines the optical path of the light emitted from the first LED 111 and the optical path of the light emitted from the second LED 112. In detail, the dichroic mirror 131 has a cutoff wavelength in the vicinity of 430 nm, and has a characteristic of transmitting light with a wavelength shorter than the cutoff wavelength and reflecting light with a wavelength equal to or longer than the cutoff wavelength. Therefore, the purple LED light emitted from the first LED 111 passes through the dichroic mirror 131, and the blue LED light from the second LED 112 is reflected by the dichroic mirror 131. This causes the optical paths of the purple LED light and the blue LED light to be combined. The light whose optical paths have been combined by the dichroic mirror 131 is incident on the dichroic mirror 132.

[0028] Also, the light emitted from the third LED 113, i.e., the blue LED light and the green fluorescent light, is converted into parallel light by the collimating lens 123 and enters the dichroic mirror 132. The dichroic mirror 132 combines the optical path of the light incident from the dichroic mirror 131 and the optical path of the light emitted from the third LED 113. In detail, the dichroic mirror 132 has a cutoff wavelength in the vicinity of a wavelength of 500 nm, and has the property of transmitting light with a wavelength shorter than the cutoff wavelength and reflecting light with a wavelength equal to or longer than the cutoff wavelength. Therefore, the optical paths of the purple LED light and the blue LED light incident from the dichroic mirror 131 and the green fluorescent light among the light emitted from the third LED 113 are combined by the dichroic mirror 132. The light whose optical paths are combined by the dichroic mirror 132 enters the dichroic mirror 133.

[0029] Moreover, the red LED light emitted from the fourth LED 114 is converted into parallel light by the collimator lens 124 and is incident on the dichroic mirror 133. The dichroic mirror 133 combines the optical path of the light incident from the dichroic mirror 132 with the optical path of the red LED light emitted from the fourth LED 114. In detail, the dichroic mirror 133 has a cutoff wavelength in the vicinity of a wavelength of 600 nm, and has the property of transmitting light with a wavelength shorter than the cutoff wavelength and reflecting light with a wavelength equal to or longer than the cutoff wavelength. Therefore, the optical paths of the light incident from the dichroic mirror 132 and the red LED light emitted from the fourth LED 114 are combined by the dichroic mirror 133, and are emitted from the light source device 230 as the illumination light L.

[0030] Illumination light L emitted from light source device 230 is condensed by condenser lens 25 onto the incident end surface of LCB 102 and enters LCB 102 . The photodetector 156 is configured to detect a portion of the illumination light L. The photodetector 156 photoelectrically converts the detected portion of the illumination light L into an electrical signal. The converted electrical signal is sent to the system controller 202 and used to correct the amount of illumination light L emitted from the light source device 230.

[0031] Next, a configuration for correcting the amount of light of illumination light L emitted from light source device 230 will be described with reference to Fig. 3. Fig. 3 is a functional block diagram including an internal configuration of system controller 202 and parts other than system controller 202 that are related to light amount correction. As shown in FIG. 3, the system controller 202 includes an exposure period setting unit 21, a correction period setting unit 22, and a correction unit . The exposure period setting unit 21 sets an exposure period for each line of the image sensor 108 by using an electronic shutter. The correction period setting unit 22 sets a correction period between adjacent frames of an image obtained by imaging with the imaging element . The correction unit 23 controls the LED of the light source device 230 to emit the reference light within the correction period T, and corrects the amount of illumination light emitted from the LEDs 111 to 114 based on the reference light received by the photodetector 156. Each of these units may be realized, for example, by a microcontroller built into the system controller 202 executing a program, or may be realized by hardware such as an FPGA (Field Programmable Gate Array).

[0032] In one embodiment, the image sensor 108 is a CMOS image sensor and is configured to image biological tissue using a rolling shutter method. In this embodiment, when imaging using the rolling shutter method, a correction period is set between adjacent frames by adjusting the timing of exposure. Since this correction period is set as a period during which exposure is not performed, a reference light for correcting the amount of illumination light by the light source device 230 can be emitted.

[0033] A specific method for setting the correction period will be described with reference to FIG. For reference, Fig. 4(a) shows the exposure timing when no timing adjustment is performed. Fig. 4(b) shows the exposure timing of one embodiment. The vertical direction in Fig. 4(a) and Fig. 4(b) is the line scanning direction. In each figure after Fig. 4, RO indicates the charge readout timing for each line of one frame. 4(c) shows the timing of turning on (ON) and off (OFF) the illumination light in one embodiment. The vertical axis of the timing chart in FIG. 4(c) represents the driving pulse current P applied to the LED for the reference light emitted during the correction period. n-1 ,P n ,P n+1 It also shows the level of

[0034] As shown in Fig. 4(a), when no timing adjustment is performed, the exposure timing of each line is set so that the exposure periods of all lines do not overlap. On the other hand, in one embodiment, as shown in Fig. 4(b), the effective lines are set to EL1 to ELN By limiting the exposure period to this period, a global exposure period (period from time t1 to t2, period from time t3 to t4, period from time t5 to t6, ...) is set and the electronic shutter is also set. The period during which the electronic shutter is open is between timings SS and SE. By setting in this way, it is possible to periodically provide correction periods T that do not affect the image displayed on the monitor 300 from times t1, t3, t5, ... until the electronic shutter opens. In FIG. 4(b), the lighting period F of the (N-1)th frame n-1 , the lighting period F of the Nth frame n , the lighting period F of the N+1th frame n+1 where the correction period T is set between the lighting periods of adjacent frames. That is, in one embodiment, the exposure period setting unit 21 sets an exposure period by an electronic shutter for each line of the image sensor 108. The correction period setting unit 22 sets a correction period T from the exposure end time SE of the scanning target line of the Nth frame to the timing SS when the electronic shutter of the (N+1)th frame opens.

[0035] As shown in FIG. 3, the correction unit 23 controls the LED driving circuits 141-144 in the light source device 230 based on an electrical signal (a signal obtained by photoelectrically converting a portion of the illumination light L) sent from the photodetector 156, thereby correcting the amount of illumination light emitted from the LEDs 111-114. Preferably, the correction unit 23 controls the LED drive circuits 141-144 so that the LEDs 111-114 emit a plurality of reference beams having different output levels during a plurality of correction periods T, and corrects the amount of illumination light emitted from the LEDs 111-114 based on the plurality of reference beams received by the photodetector 156. For example, in FIG. 4, different drive pulse currents P are supplied to the LEDs in order to emit reference beams having different output levels during each correction period T. n-1 ,P n ,P n+1 By emitting reference light having a different output level, the correction unit 23 can correct the linearity of the LED output (light amount) with respect to the pulse current.

[0036] Multiple different driving pulse currents P n-1 ,P n ,P n+1 When correcting the amount of illumination light by the reference light emitted by the LED, the correction unit 23 stores in advance data indicating the relationship between the pulse current and the target value of the amount of reference light by the pulse current. Then, based on the difference between the target value of the amount of reference light corresponding to the value of the pulse current given to the LED in the correction period T and the amount of reference light detected by the photodetector 156 (detection value), the correction unit 23 corrects parameters such as the signal amplification factor in the LED drive circuit.

[0037] Figure 4(b) shows the effective lines EL1 to EL N In this example, the global exposure period is set to a value between 0 and 100, but the global exposure period can also be set by performing binning readout. In binning readout, surrounding pixels of the same color are added before charge transfer, so the apparent number of pixels after addition is reduced and the charge transfer time is shorter than in normal readout, making it possible to set the global exposure period.

[0038] As another embodiment, a method of setting the correction period T without depending on the electronic shutter can be adopted. In other words, it is not essential to provide the exposure period setting unit 21. The method of setting the correction period T without depending on the electronic shutter will be described with reference to FIG. 5. In the embodiment shown in FIG. n-1 ,F n+1 ) are even-numbered or odd-numbered frames, non-display frames are odd-numbered or even-numbered frames, and the image sensor 108 is driven in 1 / 60 second units. In this case, display on the monitor 300 is performed at, for example, 30 fps (frames per second). As in FIG. 4(b), in FIG. 5(a), the effective lines are EL1 to EL NBy limiting the period between t1 and t2 and t5 and t6, a global exposure period is set between times t1 and t2 and between times t5 and t6, and the illumination light is turned on during this period (ON in FIG. 5(b)). A correction period T is set during the period of the non-display frame (times t3 to t4 in the example shown in FIG. 5), and the driving pulse current P n is given to each LED. Note that the display frames and non-display frames are not limited to being set alternately for each frame. For example, a plurality of non-display frames may be arranged between adjacent display frames.

[0039] As yet another embodiment, a method can be adopted in which the global exposure period is not set and the correction period T is set. This method will be described with reference to FIG. In this embodiment, similarly to the embodiment of FIG. 5, the display frames (the lighting period for each frame is F n-1 ,F n+1 The frames for non-display are either odd-numbered or even-numbered frames, and the image sensor 108 is driven in 1 / 60 second increments. In this case, display on the monitor 300 is performed at, for example, 30 fps (frames per second). The embodiment of Fig. 6 differs from the embodiment of Fig. 5 in that the effective lines are not limited, and a global exposure period is not set. Instead, the exposure period setting unit 21 sets an exposure period for the scanning target lines of the image sensor 108 using the electronic shutter. Specifically, as shown in Fig. 6(a), the electronic shutter is set during the exposure period for the display frame. The period during which the electronic shutter is open is between timings SS and SE. Then, the correction period setting unit 22 sets a correction period T between the timing of the rear end of all scanning target lines (time t2) and the electronic shutter start end (time t3).

[0040] As described above, the electronic endoscope system of the embodiment includes an electronic endoscope having an image sensor configured to capture images of biological tissue, a light source device having an LED that emits illumination light for illuminating the biological tissue, and a processor configured to control the exposure timing of the image sensor and the illumination light turning on timing, as well as to control the illumination light. The electronic endoscope system further includes a photodetector that detects the light emitted by the LED of the light source device, and the processor corrects the amount of illumination light emitted from the LED based on the reference light received by the photodetector. At this time, the processor sets a correction period between adjacent frames of the image obtained by the imaging element. Therefore, according to the electronic endoscope system of the embodiment, the amount of light emitted from the LED can be corrected at any timing while the LED is illuminating the living tissue. Therefore, even in a situation where the LED continues to emit weak light, such as when observing a narrow cavity such as a bronchi, the amount of light emitted from the LED can be corrected in real time over the entire output range.

[0041] The electronic endoscope system of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0042] 1. Electronic endoscope system 100...Electronic scope 102…LCB 104...Orientation lens 106…Objective lens 108...Image sensor 108a...Cut filter 108b…Bayer array color filter 152...Driver signal processing circuit 21...Exposure period setting unit 22...Correction period setting section 23...Compensation section 25…Condenser lens 100...Electronic scope 104...Light distribution lens 106…Objective lens 111~114...LED 121~124...Collimating lens 131~133…Dichroic mirror 141~144…LED drive circuit 152...Driver signal processing circuit 154…Memory 156...Photodetector 200...Electronic endoscope processor 202…System controller 204…Memory 206...Timing controller 208…Operation panel 220...Image processing unit 230...Light source device 300…Monitor

Claims

1. an electronic endoscope having an imaging element configured to capture an image of a living tissue; a light source device including a light emitting element that emits illumination light for illuminating the biological tissue; A processor configured to control a timing of exposure of the image sensor and a timing of turning on the illumination light, and to control the illumination light; a photodetector for detecting a portion of the emitted light from the light emitting element; Equipped with The processor, a correction period setting unit that sets a correction period between adjacent frames of images obtained by imaging using the imaging element; a correction unit that controls the light emitting element to emit a reference light for correction within the correction period, and corrects the amount of illumination light emitted from the light emitting element based on the amount of the reference light detected by the photodetector. Electronic endoscope system.

2. The imaging element is configured to image the biological tissue by a rolling shutter method, the processor includes an exposure period setting unit that sets an exposure period for each line of the image sensor by an electronic shutter; the correction period setting unit sets the correction period from an exposure end time of a scanning target line of an Nth frame to an exposure start time of an N+1th frame by the electronic shutter; 2. An electronic endoscope system according to claim 1.

3. the plurality of consecutive frames of an image obtained by imaging with the imaging element include display frames used as display images and non-display frames not used as display images, the processor includes an exposure period setting unit that sets an exposure period for a scanning target line of the image sensor by an electronic shutter; the correction period setting unit sets the correction period from an exposure end time of a scanning target line of an Nth display frame to an exposure start time of an N+1th display frame by the electronic shutter; 2. An electronic endoscope system according to claim 1.

4. the plurality of consecutive frames of an image obtained by imaging with the imaging element include display frames used as display images and non-display frames not used as display images, the correction period setting unit sets the correction period within a period for generating the non-display frames.

4. An electronic endoscope system according to claim 1.

5. the display frames are even-numbered or odd-numbered frames, and the non-display frames are odd-numbered or even-numbered frames; 5. An electronic endoscope system according to claim 3 or 4.

6. the correction unit controls the light emitting element to emit a plurality of the reference beams having different output levels during a plurality of the correction periods, and corrects the amount of illumination light emitted from the light emitting element based on the amount of light of the plurality of the reference beams detected by the photodetector.

6. An electronic endoscope system according to claim 1.

7. The correction unit applies a plurality of driving pulse currents different from each other to the light-emitting element during each of a plurality of correction periods, thereby causing the light-emitting element to emit a plurality of reference beams each having a different output level.

7. An electronic endoscope system according to claim 6.

Images