JP2017217056A - Endoscope system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endoscope system advantageous in suppressing blur of a captured image in a case where a distance from a scope to a subject changes.SOLUTION: An endoscope system includes an objective optical system for capturing a subject image, an image pickup device for generating an image signal of the subject image captured by the objective optical system, filter processing means for subjecting the image signal to correction filter processing, distance determination means for determining a distance from the objective optical system to the subject, and filter switching means for switching a correction filter used in the correction filter processing according to the distance.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an endoscope system that performs still (freeze) processing of a captured moving image.

  As an endoscope system for observing a subject in a body cavity such as a human esophagus or intestine, an endoscope system including a scope unit, a processor unit, and a monitor is known. An objective optical system and an imaging device are provided at the distal end of the scope unit. Object light from the subject passes through the objective optical system, is received by the image sensor, and is output as an image signal. The processor unit performs predetermined image processing on the image signal output from the scope unit to generate a video signal. A captured image of the subject based on the video signal is displayed on the monitor. In this type of endoscope system apparatus, an electronic zoom function is provided so that an operator can easily observe a subject. The electronic zoom function is a function for electrically enlarging a captured image and displaying it on a monitor.

  Patent Document 1 discloses an endoscope system that performs spatial frequency restoration processing on an image signal in order to obtain a high-resolution captured image. In the endoscope system described in Patent Document 1, a spatial frequency restoration process is performed on an image signal in accordance with the spatial frequency of the objective optical system of the scope unit. Thereby, the captured image can be converted into a high-resolution image.

JP 2000-5127 A

  A photographic image of a subject obtained by the endoscope system is blurred depending on the characteristics (spatial frequency) of the objective optical system and the distance from the optical system to the subject. In the endoscope system of Patent Document 1, what kind of spatial frequency restoration processing is performed on an image signal is switched according to the objective optical system to be used and the focal length of the objective optical system. However, when a blur occurs in the captured image due to a change in the distance from the objective optical system to the subject, the endoscope system described in Patent Document 1 eliminates the blur and obtains a high-resolution captured image. There was a case that could not be.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an endoscope system that is advantageous in suppressing blurring of a captured image when the distance from a scope to a subject changes. .

  In order to achieve the above object, an endoscope system according to an embodiment of the present invention includes an objective optical system that captures a subject image, an image sensor that generates an image signal of the subject image captured by the objective optical system, and an image Filter processing means for performing correction filter processing on the signal, distance determination means for determining the distance from the objective optical system to the subject, and filter switching means for switching the correction filter used in the correction filter processing according to the distance Consists of.

  According to such a configuration, since the correction filter used for the correction filter process is changed according to the distance from the objective optical system to the subject, blurring caused by the change in the distance is effectively suppressed. be able to.

  In one embodiment of the present invention, the endoscope system further includes, for example, a light source unit that emits illumination light that illuminates a subject, and a dimming unit that dimmes the illumination light emitted from the light source unit. Prepare. In this case, the distance determination unit determines the distance based on the degree of dimming by the dimming unit.

  In one embodiment of the present invention, the light control means has, for example, a variable diaphragm that adjusts the amount of illumination light, and controls the opening of the variable diaphragm based on the luminance of the image signal. In this configuration, the distance determination unit determines the distance based on the opening degree.

  In one embodiment of the present invention, the distance determination unit includes, for example, a light emitting element that emits measurement light and a light receiving element that receives the measurement light reflected by the subject. In this configuration, the distance determination unit determines the distance based on the measurement light received by the light receiving element.

  In one embodiment of the present invention, the correction filter process is an image correction process using a Wiener filter, for example.

  In one embodiment of the present invention, for example, the objective optical system can be exchanged, and the filter switching unit switches the correction filter used in the correction filter processing according to the objective optical system to be used and the distance.

  In an embodiment of the present invention, an endoscope system, for example, further includes an electronic enlargement processing unit that performs an electrical enlargement process on the image signal that has been subjected to the correction filter process.

  ADVANTAGE OF THE INVENTION According to this invention, when the distance from a scope part to a to-be-photographed object changes, the endoscope system advantageous for suppressing the blur of a picked-up image is provided.

It is a block diagram of an endoscope system in an embodiment of the present invention. It is a figure for demonstrating the focus position of the objective optical system in embodiment of this invention. It is a figure for demonstrating PSF of the objective optical system in embodiment of this invention. It is a figure for demonstrating PSF of the objective optical system in embodiment of this invention. It is a figure for demonstrating PSF of the objective optical system in embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration of an endoscope system 100 according to an embodiment of the present invention. The endoscope system 100 of this embodiment is a medical imaging system used for observing a subject in a human body cavity. As shown in FIG. 1, the endoscope system 100 includes a scope unit 110, a processor unit 120, and a monitor 130. The scope unit 110 is detachably connected to the processor unit 120.

  The scope unit 110 includes a connector unit 111 and an insertion tube 112. An imaging unit 10 and a light distribution lens 11 are provided at the distal end portion of the insertion tube 112. In the scope section 110, a light guide fiber 13 and a plurality of wirings 14 are provided from the connector section 111 to the tip section.

  The processor unit 120 includes a light source unit 121, a light source driving circuit 122, an image processing unit 123, a controller 124, an input device 125, an image sensor driver 126, and a memory 127.

  The light source unit 121 includes a light source 20, a light control unit 22, and a condenser lens 23. The light source 20 is driven by a light source driving circuit 122 and emits white illumination light. The illumination light emitted from the light source 20 is incident on the light control unit 22.

  The dimmer 22 has a variable aperture. The amount of illumination light passing through the light control unit 22 (the degree of light control) is adjusted by the opening of the variable aperture (aperture value or F value). The illumination light modulated by the light control unit 22 is collected on the end surface of the light guide fiber 13 by the condenser lens 23 and is incident on the light guide fiber 13. The illumination light that has entered the light guide fiber 13 is guided to the tip of the insertion tube 112. The illumination light guided to the distal end portion of the insertion tube 112 is emitted from the distal end portion of the insertion tube 112 via the light distribution lens 11 and is irradiated onto the subject in the body cavity. The illumination light applied to the subject is reflected by the subject and enters the imaging unit 10 as object light.

  The imaging unit 10 includes an objective optical system 10a and an imaging element 10b. The image sensor 10b is a single-plate color CCD (Charge Coupled Device) image sensor having a Bayer pixel arrangement. The image sensor 10b accumulates the subject image formed by each pixel on the light receiving surface as a charge corresponding to the amount of light, and generates and outputs R (Red), G (Green), and B (Blue) image signals. To do. The imaging element 10b is not limited to a CCD image sensor, and may be replaced with a complementary metal oxide semiconductor (CMOS) image sensor or other types of imaging devices. The image sensor 10b may also be one having a complementary color filter.

  The object light incident on the imaging unit 10 is received by the imaging device 10b via the objective optical system 10a. The object light received by the image sensor 10 b is converted into an image signal at a predetermined frame rate and transmitted to the image processing unit 123 of the processor unit 120 through the wiring 14.

  The image processing unit 123 includes a preprocessing unit 40, an image processing unit 42, and a post processing unit 44.

  The preprocessing unit 40 performs predetermined signal processing such as white balance adjustment processing, color interpolation processing, matrix calculation processing, and the like on the image signal received from the image sensor 10 b and outputs the processed signal to the image processing unit 42.

  The image processing unit 42 includes a correction filter processing unit 42a and an enlargement processing unit 42b. The correction filter processing unit 42a performs correction filter processing on the image signal. The enlargement processing unit 42b performs an electric enlargement process on the image signal. Details of the correction filter process and the enlargement process will be described later.

  The post-processing unit 44 performs gamma correction processing and conversion processing to a video signal on the image signal output from the image processing unit 42. In the gamma correction processing, gamma correction that matches the characteristics of the monitor 130 is performed. In the conversion process to the video signal, monitor display screen data is generated based on the image signal, and the generated monitor display screen data is converted into a video signal of a predetermined video format. The converted video signal is output to the monitor 130. The monitor 130 displays a captured image of the subject based on the video signal.

  Next, correction filter processing and enlargement processing in the image processing unit 42 will be described.

  The processor unit 120 of this embodiment has an electronic zoom function. The electronic zoom function is a function for enlarging and displaying a captured image of a subject displayed on the monitor 130. When the surgeon performs an operation for designating a ratio (magnification) for enlarging the captured image on the input device 125, the enlargement processing unit 42b electrically enlarges the image signal according to the designated magnification. This electronic zoom function makes it easier for the surgeon to see a desired part of the subject.

  However, when the distance from the imaging unit 10 to the subject changes and the focus of the imaging unit 10 does not match the subject, blurring may occur in the captured image. Further, when the photographed image includes blur, the magnified processing unit 42b enlarges the photographed image in a state including blur. For this reason, even if enlargement processing is performed on the captured image, an image that is easy to see for the surgeon may not be obtained. Therefore, in the endoscope system 100 of the present embodiment, the correction filter processing unit 42a performs correction filter processing on the image signal, thereby removing blur included in the captured image.

  The correction filter processing unit 42a performs, for example, a Wiener Filter process as the correction filter process. The Wiener filter process is a filter process that uses a transfer function (OTF: Optical Transfer Function) of the objective optical system 10a and a power spectrum of inherent noise superimposed on an image signal, and suppresses blurring, noise, and artifacts of the image signal. Can do. Here, the OTF of the objective optical system 10a is calculated from a point spread function (PSF) of the objective optical system 10a. Further, for example, fixed pattern noise of the imaging device 10b to be used is used for the power spectrum of the inherent noise. The PSF of the objective optical system 10a and the fixed pattern noise of the imaging device 10b differ depending on the scope unit 110 to be used, and are measured in advance for each scope unit 110.

  The PSF of the objective optical system 10a corresponds to an object image on the image sensor 10b when an object of a point light source is imaged. The PSF of the objective optical system 10a changes according to the distance from the objective optical system 10a to the subject.

  FIG. 2 is a diagram for explaining a focus position of the objective optical system 10a. In FIG. 2, the axis O indicates the optical axis of the objective optical system 10a, and the position F indicates the in-focus position of the objective optical system 10a. When the subject is in the focus position F, the objective optical system 10a is in focus. 3 to 5 are diagrams for explaining the PSF of the objective optical system 10a. FIG. 3 shows the luminance distribution of the subject of the point light source. FIG. 4 shows the PSF of the objective optical system 10a when the subject is at the in-focus position F. FIG. 5 shows the PSF of the objective optical system 10a when the subject is closer to the objective optical system 10a than the in-focus position F. 3 to 5, the X axis and the Y axis indicate positions in a plane perpendicular to the optical axis O of the objective optical system 10a. The Z axis indicates the luminance of the subject and is normalized so that the integrated value of the luminance in the XY plane is 1.

  As shown in FIG. 3, the subject of the point light source has a luminance of 1 at (X, Y) = (0, 0) and zero at other locations. When the object of the point light source is at the in-focus position F of the objective optical system 10a, the PSF of the objective optical system 10a has a steep peak at (X, Y) = (0, 0) as shown in FIG. A Gaussian distribution with The PSF of the objective optical system 10a depends on the magnification of the objective optical system 10a. If the objective optical system 10a includes manufacturing errors and aberrations, the full width at half maximum of the PSF increases. Therefore, even if the subject is at the in-focus position F, the PSF shown in FIG. 4 is not the same as the distribution shown in FIG. When the subject of the point light source is located closer to the objective optical system 10a than the in-focus position F, the PSF of the objective optical system 10a is (X, Y) = (0, 0) as shown in FIG. Gaussian distribution with peaks. However, the half width of PSF is larger than the distribution shown in FIG.

  The half width of the PSF of the objective optical system 10a takes a minimum value when the subject is at the in-focus position F of the objective optical system 10a. The closer the subject is to the objective optical system 10a from the in-focus position F, or the farther the subject is, the larger the half width of the PSF becomes. This widening of the half width of the PSF appears as blur in the subject image. In the endoscope system 100 of the present embodiment, a change in the PSF of the objective optical system 10a according to the distance from the objective optical system 10a to the subject is measured in advance.

  In the memory 127 of the processor unit 120, a plurality of correction filters are recorded for each scope unit 110 to be used. Each correction filter is determined using the PSF of the objective optical system 10a and the fixed pattern noise of the image sensor 10b. When the scope unit 110 is connected to the processor unit 120, the controller 124 reads out unique information of the scope unit 110 from a memory (not shown) in the scope unit 110. The unique information of the scope unit 110 includes the number of pixels and sensitivity of the image sensor 10b, an operable frame rate, a model number, and the like. Note that the correction filter may be recorded in the memory in the scope unit 110 as one of the unique information of the scope unit 110.

  Next, the controller 124 is used for correction filter processing from among the plurality of correction filters recorded in the memory 127 based on the connected scope unit 110 and the distance from the objective optical system 10a to the subject. Select a correction filter. As described above, each of the plurality of correction filters corresponds to the PSF of the objective optical system 10a. Further, the PSF of the objective optical system 10a changes according to the distance from the objective optical system 10a to the subject. Therefore, a correction filter corresponding to the distance can be selected based on the distance from the objective optical system 10a to the subject. The correction filter processing unit 42 a performs correction filter processing on the image signal using the correction filter selected by the controller 124.

  Next, a method for determining the distance from the objective optical system 10a to the subject will be described. In the endoscope system 100 of the present embodiment, the distance from the objective optical system 10a to the subject is estimated based on the opening (aperture value) of the variable diaphragm used in the light control unit 22.

  In the endoscope system 100 of the present embodiment, the opening of the variable diaphragm is automatically changed according to the luminance of the image signal output from the scope unit 110. Specifically, when the brightness of the image signal is larger than the target value, the variable aperture is controlled so that the opening of the variable aperture is decreased (so that the aperture value is increased), and when the brightness of the image signal is smaller than the target value The opening of the variable throttle is controlled to be large (so that the throttle value is small). In this way, by changing the opening of the variable aperture and adjusting the amount of illumination light applied to the subject, fluctuations in the luminance of the image signal can be suppressed.

  The ratio of the illumination light (object light) that is reflected by the subject and captured by the objective optical system 10a out of the illumination light irradiated to the subject via the light distribution lens 11 depends on the distance from the objective optical system 10a to the subject. Change. For example, when the distance from the objective optical system 10a to the optical system is shortened, the proportion of illumination light captured by the objective optical system 10a increases. Further, as the distance from the objective optical system 10a to the subject increases, the proportion of illumination light captured by the objective optical system 10a decreases. For this reason, when the distance from the objective optical system 10a to the subject is short, the ratio of the illumination light captured by the objective optical system 10a is large, so that the opening of the variable aperture is small in order to reduce the luminance of the image signal. Further, when the distance from the objective optical system 10a to the subject is long, the ratio of the illumination light captured by the objective optical system 10a is small, so the opening degree is large in order to increase the luminance of the image signal. From this, the distance from the objective optical system 10a to the subject can be estimated from the opening of the variable aperture.

  Note that the proportion of illumination light captured by the objective optical system 10a also depends on changes in the reflectance and reflection characteristics (reflected light distribution) of the subject. However, since the scope unit 110 is normally used depending on the application (subject), when observation is performed using one scope unit 110, the reflectance and reflection characteristics of the subject change rapidly depending on the shooting location. Is hard to think. For this reason, the distance from the objective optical system 10a to the subject can be estimated with high accuracy using the opening of the variable aperture without considering the change in the reflectance and reflection characteristics of the subject.

  Further, the relationship between the distance from the objective optical system 10a to the subject and the opening of the variable aperture differs depending on the scope unit 110 to be used. For example, the relationship between the distance and the ratio of the illumination light captured by the objective optical system 10a changes depending on the characteristics of the light distribution lens 11, the distribution of illumination light distribution, the characteristics of the objective optical system 10a, etc. The degree of opening also changes. Therefore, the estimation method (calculation formula) for the distance from the objective optical system 10a to the subject using the opening of the variable aperture differs for each scope unit 110 to be used.

  When the distance from the objective optical system 10a to the subject is estimated, a correction filter corresponding to the distance is read from the memory 127 and used for correction filter processing. As a result, the blur generated in the image signal due to the change in the distance from the objective optical system 10a to the subject is removed, and a captured image that is easy for the operator to view can be obtained. Further, when the image signal enlargement process is performed by the electronic zoom function, the image signal from which the blur is removed by the correction filter process is enlarged. As a result, it is possible to obtain an enlarged photographed image that is easier for the operator to view.

  Further, while the subject is observed using the endoscope system 100, the distance from the objective optical system 10a to the subject always changes. Therefore, the optimal correction filter can be applied in real time by always estimating the distance from the objective optical system 10a to the subject and switching the correction filter to be used according to the change in distance. For example, the correction filter to be applied may be switched for each frame.

  The above is the description of the exemplary embodiments of the present invention. Embodiments of the present invention are not limited to those described above, and various modifications are possible within the scope of the technical idea of the present invention. For example, the embodiment of the present invention also includes contents appropriately combined with embodiments or the like clearly shown in the specification or obvious embodiments.

  For example, in the above-described embodiment, the endoscope system 100 has an electronic zoom function, but the present invention is not limited to this. The endoscope system 100 may have an optical zoom function, or may have both an optical zoom function and an electronic zoom function. The optical zoom function is realized by using a zoom lens for the objective optical system 10a. When a zoom lens is used for the objective optical system 10a, the PSF of the objective optical system 10a varies depending on the magnification of the zoom lens. Therefore, in the correction filter processing in the correction filter processing unit 42a, the correction filter to be used depends on the magnification of the zoom lens in addition to the scope unit 110 (objective optical system 10a) to be used and the distance from the objective optical system 10a to the subject. Can be switched.

  In the above-described embodiment, the distance from the objective optical system 10a to the subject is determined using the opening (aperture value) of the variable diaphragm, but the present invention is not limited to this. For example, the scope unit 110 may include a measurement light source that emits measurement light for distance measurement at the distal end of the insertion tube 112 and a light receiving element that receives the measurement light reflected by the subject. As the measurement light source, for example, a solid light emitting element such as a light emitting diode or a laser is used. The light receiving element outputs a measurement signal corresponding to the received measurement light. In this case, the controller 124 calculates the distance from the objective optical system 10a to the subject based on the measurement signal output from the light receiving element.

DESCRIPTION OF SYMBOLS 10 Imaging unit 10a Objective optical system 10b Image pick-up element 11 Light distribution lens 13 Light guide fiber 14 Wiring 20 Light source 22 Light control part 23 Condensing lens 40 Preprocessing part 42 Image processing part 42a Correction filter processing part 42b Enlargement processing part 44 Post process Unit 100 endoscope system 110 scope unit 111 connector unit 112 insertion tube 120 processor unit 121 light source unit 122 light source drive circuit 123 image processing unit 124 controller 125 input device 126 image sensor driver 127 memory 130 monitor

Claims (7)

An objective optical system for capturing a subject image;
An image sensor for generating an image signal of a subject image captured by the objective optical system;
Filter processing means for performing correction filter processing on the image signal;
Distance determining means for determining a distance from the objective optical system to a subject;
Filter switching means for switching a correction filter used in the correction filter processing according to the distance;
An endoscope system having A light source that emits illumination light to illuminate the subject;
A dimming means for dimming the illumination light emitted from the light source unit;
Further comprising
The distance determination means determines the distance based on the degree of light control by the light control means.
The endoscope system according to claim 1. The light control means includes
A variable aperture for adjusting the amount of illumination light;
Control the opening of the variable aperture based on the brightness of the image signal,
The distance determination means includes
Determining the distance based on the opening;
The endoscope system according to claim 2. The distance determination means includes
A light emitting element that emits measurement light;
A light receiving element that receives the measurement light reflected by the subject,
Determining the distance based on the measurement light received by the light receiving element;
The endoscope system according to claim 1. The correction filter process is an image correction process using a Wiener filter.
The endoscope system according to any one of claims 1 to 4. The objective optical system is replaceable,
The filter switching means switches a correction filter used in the correction filter processing according to the objective optical system to be used and the distance.
The endoscope system according to any one of claims 1 to 5. Further comprising electronic enlargement processing means for performing electrical enlargement processing of the image signal subjected to the correction filter processing.
The endoscope system according to any one of claims 1 to 6.

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