JP2010008836A - Electronic endoscope apparatus and focus adjustment method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time required for focusing when varying the optical magnification of an objective optical system. <P>SOLUTION: Just after varying the magnification of the objective optical system, an AF control part specifies an evaluation value searching range in accordance with the combination of the varied magnification, the brightness of the photographed image, the shape of the portion of an object to be observed, photographed just before varying the magnification. The focus lens is moved within a range capable of obtaining an AF evaluation value within the evaluation value searching range, then, the focus lens is set at the lens position obtaining the maximum AF evaluation value. The evaluation value searching range is decided as an AF evaluation value range probably to attain a focused state in accordance with each of combinations of magnification, brightness and shape. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electronic endoscope apparatus having a function of changing the focal length of an objective optical system and an autofocus function, and a focus adjustment method thereof.

  In recent years, examination using an electronic endoscope apparatus has been widely used in the medical field. The electronic endoscope apparatus includes a processor device, a light source device, a monitor, and the like in addition to an endoscope main body portion in which an objective optical system, an image sensor, and the like are incorporated in a distal end portion. At the time of inspection, an optical image of the observed region in the living body is imaged on the image sensor through the objective optical system under the illumination light from the light source device, and the obtained photographic signal is subjected to various image processing by the processor device. Display on the monitor.

  In the electronic endoscope apparatus as described above, an optical zoom mechanism including a zoom lens is incorporated in the objective optical system, and the focal length of the objective optical system is increased or decreased by moving the zoom lens in the optical axis direction. There is also known one in which an optical magnification is changed so that an observation site can be observed. Further, as in Patent Document 1, an electronic endoscope apparatus is also known that incorporates an autofocus mechanism that automatically performs focusing together with an optical zoom mechanism.

  In the electronic endoscope apparatus of Patent Document 1, a varifocal type optical zoom mechanism that requires focus adjustment for each zooming and a zooming lens that can be moved independently of the zooming lens. A focusing mechanism including a focusing lens is incorporated in the objective optical system. At the time of focus adjustment, a contrast detection method is adopted in which the lens position of the focusing lens that maximizes the contrast of the captured image is detected, and the focusing lens is moved to that lens position.

  In the contrast detection method as described above, a search process is performed in which shooting is performed while stepping the focusing lens, and evaluation values indicating the magnitude of contrast in the captured image are sequentially calculated for each lens position of the focusing lens. And the lens position where the AF evaluation value is maximized is detected. In the search process, for example, a focusing lens is set at one end of the movable range, and a whole area search is performed in which the focusing lens is moved from the near end to the other end. As one of contrast detection methods, a so-called hill-climbing method is also known in which a peak at which the AF evaluation value changes from increasing to decreasing is detected, and a focusing lens is set at the lens position where the AF evaluation value becomes the peak.

JP 2006-106520 A

  By the way, the search process as described above has a problem that it takes a considerable time since it is necessary to perform image capturing by the image sensor every time the focusing lens is moved stepwise. For this reason, when the optical magnification is changed by the optical scaling mechanism as described above, the search process is performed, so that an image in focus cannot be observed for a relatively long time. There was a problem that the inspection efficiency in the mirror device was lowered.

  In the hill-climbing method, the effect of shortening the time required for the search process by reducing the focusing lens movement step can be expected, but when the optical magnification is high or the contrast of the observed site itself is low, Since the detected AF evaluation value changes finely or does not change much, a clear peak cannot be detected, and it may be difficult to adjust the focus.

  The present invention has been made in view of the above problems, and an electronic endoscope apparatus capable of reducing the time required for focusing when changing the magnification by an optical zoom mechanism and performing quick focusing, and its An object is to provide a focus adjustment method.

  In order to achieve the above object, according to the focus adjustment method of the electronic endoscope apparatus according to claim 1, when the magnification change is performed by the movement of the zoom lens, the brightness of the photographed image and immediately before the magnification change are performed. The search range is specified as the range of evaluation values expected after the magnification change, corresponding to the combination of the characteristics of the image of the observed site recognized from the image taken at the same time and the magnification of the objective optical system after the magnification change. In addition, after moving the focusing lens to the lens position that matches the focus after the magnification change to the shooting distance corresponding to the lens position before the magnification change, the range of the lens position that maintains the search range specified by the evaluation value Then, the focusing lens is moved, and the focusing lens is moved to a lens position for focusing on the observed site obtained by evaluating each evaluation value obtained by this movement.

  The focus adjustment method of the electronic endoscope apparatus according to claim 2, wherein when the focusing lens is moved within a specified search range, the focusing lens is moved to a lens position having a maximum evaluation value. Is.

The electronic endoscope apparatus according to claim 3 is provided at a distal end of an insertion portion to be inserted into the body, and adjusts a focusing distance by moving a focusing lens, and zooms an optical image. An objective optical system incorporating an optical scaling mechanism, an image sensor that performs imaging of the observed site through the objective optical system, photoelectrically converts the captured image of the observed site into an imaging signal, and
Contrast detection means for detecting an evaluation value indicating the magnitude of contrast of the photographed image based on the photographing signal, brightness detection means for detecting the brightness of the photographed image based on the photographing signal, and based on the photographing signal , Recognition means for recognizing the characteristics of the image of the observed site, the brightness of the captured image, the characteristics of the image of the observed site immediately before the magnification change of the objective optical system, and the magnification of the objective optical system after the magnification change The search range specified in advance as the range of evaluation values expected after the magnification change, the brightness of the captured image, the characteristics of the image of the observed site before the magnification change, and the magnification after the magnification change Brightness of the captured image detected by the brightness detection means when the magnification of the objective optical system is changed by the optical scaling mechanism From the plurality of search ranges stored in the storage unit, a search range corresponding to the combination of the image feature of the observed site recognized by the recognition unit immediately before the magnification change and the magnification of the objective optical system after the magnification change is stored. A search range in which the evaluation value detected by the contrast detection means is specified after the focusing lens is moved to the lens position that matches the focus after the magnification change to the shooting distance corresponding to the lens position before the magnification change. The focusing lens is moved within the range of the lens position that maintains the inside, the evaluation values obtained by this movement are evaluated, the lens position for focusing on the observed site is determined, and the determined lens position And a focus control means for moving the focusing lens.

  In the electronic endoscope apparatus according to claim 4, the focus control unit is configured to focus the lens position that is the maximum evaluation value when the focusing lens is moved within the specified search range. This is determined as the lens position.

  According to the present invention, when the magnification change is performed by the optical magnification change mechanism, the combination of the characteristics of the observed region immediately before the magnification change, the brightness of the captured image, and the magnification of the objective optical system after the magnification change The range of the expected evaluation value corresponding to the search range is specified as the search range, the focusing lens is moved within the range of the lens position where the evaluation value is the search range, and the lens position for matching the focus from each evaluation value Therefore, even when the contrast change due to the movement of the focusing lens is small or the AF evaluation value changes finely, the focus can be achieved in a short time.

  In FIG. 1, the electronic endoscope apparatus 2 includes an endoscope main body 10, a processor device 11, a light source device 12, a monitor 14, and the like. The endoscope body 10 includes an insertion portion 15 to be inserted into a body cavity, an operation portion 16 provided at the proximal end of the insertion portion 15, and extends from the operation portion 16 to the processor device 11 and the light source device 12. And a universal cord 17 for connecting the mirror body 10.

  The insertion portion 15 includes a distal end portion 20, a bending portion 21, and a flexible tube portion 22 in order from the distal end. The distal end portion 20 incorporates an imaging unit 23 for in-vivo imaging. The bending portion 21 is bent in the vertical and horizontal directions when the wire passed through the insertion portion 15 is pushed and pulled in conjunction with the operation of the angle knob 24 provided in the operation portion 16. Thereby, the front-end | tip part 20 can be orient | assigned to the desired direction in a body cavity.

  The flexible tube portion 22 is a portion that connects the operation portion 16 and the bending portion 21 in a long shape, and has flexibility. In the flexible tube portion 22, in addition to the wire linked to the angle knob 24, a cable for electrically connecting the photographing unit 23 and the processor device 11, and the optical magnification (focal length) of the photographing unit 23 are set. A linear transmission member for transmitting a driving force for changing, a light guide for guiding illumination light from the light source device 12 to the distal end portion 20, a forceps tube, an air / water supply tube, and the like are provided.

  In addition to the angle knob 24, the operation unit 16 is provided with a scaling operation unit 25 that is operated when changing the optical magnification of the photographing unit 23. The zoom operation unit 25 includes an up button 25a for increasing the optical magnification and a down button 25b for decreasing the magnification. The optical magnification of the photographing unit 23 changes by one step for each magnification operation pressed by the up button 25a or the down button 25b.

  The processor device 11 is electrically connected to the endoscope main body 10 and the light source device 12, and comprehensively controls the operation of the electronic endoscope device 2. The processor device 11 is connected to the endoscope main body 10 via a cable passed through the universal cord 17 to control driving of the photographing unit 23 and input a photographing signal from the photographing unit 23. Then, various image processing is performed on the input photographing signal to generate image data of the photographed image. Based on the image data generated by the processor device 11, an image of the site to be observed as a captured image is displayed on the monitor 14 connected to the processor device 11. In addition, the processor device 11 performs focus control of the photographing unit 23 based on the contrast of the photographed image.

  As shown in FIG. 2, an observation window 31, an illumination window 32, a forceps outlet 33, and an air / water supply nozzle 34 are provided on the front surface 20 a of the distal end portion 20. A part of the optical system constituting the photographing unit 23 is exposed in the observation window 31, and photographing by the photographing unit 23 is performed through the observation window 31.

  Two illumination windows 32 are arranged so as to sandwich the observation window 31, and irradiate the illumination light from the light source device 12 into the body cavity. The forceps outlet 33 is connected to a forceps insertion port 35 (see FIG. 1) provided in the operation unit 16 via a forceps tube. Various treatment tools having an injection needle, a high-frequency knife or the like arranged at the tip are inserted from the forceps insertion port 35, and the tip is exposed from the forceps outlet 33. The air supply / water supply nozzle 34 ejects cleaning water or air toward the site to be observed by operating an air supply / water supply button (not shown) provided in the operation unit 16.

  As shown in FIG. 3, an objective optical system 40 is incorporated in the photographing unit 23. The objective optical system 40 includes, in order from the object side, a first fixed lens 41, a first variable lens 42 for zooming, a second variable lens 43, a second fixed lens 44, and a focusing lens for adjusting focus. 45 and an aperture 46 are provided, which is a varifocal photographic lens.

  A prism 47 that bends the optical axis PL of the objective optical system 40 by 90 degrees is disposed behind the stop 46, and an image sensor 48 is disposed on the folded optical axis PL. A cover glass 49 that protects the light receiving surface of the image sensor 48 is disposed between the prism 47 and the image sensor 48.

  The first fixed lens 41 is held by a fixed lens holder 51 and exposes the object side surface from the observation window 31 to the outside. The first variable magnification lens 42 and the second variable magnification lens 43 are held by lens holders 52 and 53, and are movable in directions along the optical axis PL. The second fixed lens 44 is held by a lens holder 54 that is fixed in the same manner as the first fixed lens 41. Further, the focusing lens 45 is held by the lens holder 55 and is movable in the direction along the optical axis PL.

  The variable power lenses 42 and 43 constitute a variable power mechanism 58 of the objective optical system 40 together with the cam shaft 57 and the like. Cam pins 52 a and 53 a are integrally provided on the lens holders 52 and 53, and these cam pins 52 a and 53 a are engaged with cam grooves 57 a and 57 b formed on the outer periphery of a cylindrical cam shaft 57. The cam shaft 57 is rotatably assembled, and one end of a linear transmission member 59 made of a multiple coil spring or the like is connected to the end of the cam shaft 57. The other end of the linear transmission member 59 is attached to a variable power motor 61 (see FIG. 4) provided inside the operation unit 16.

  By configuring the zoom mechanism 58 as described above, the rotation of the zoom motor 61 is transmitted to the cam shaft 57 via the linear transmission member 59 and the cam shaft 57 rotates. By the rotation of the cam shaft 57, the variable power lenses 42 and 43 move back and forth along the optical axis PL. Thereby, the focal length of the objective optical system 40 is changed, and the optical magnification is changed.

  The focusing lens 45 constitutes a focusing mechanism 62 that adjusts the focus by moving the focusing lens 45. The lens holder 55 that holds the focusing lens 45 is integrally provided with a cylindrical moving body 63. The moving body 63 is frictionally engaged with a drive shaft 64 passed through the inside thereof, and the drive shaft 64 has a small piezoelectric actuator 65 attached to one end thereof.

  The piezoelectric actuator 65 expands and contracts when the drive pulse from the processor device 11 is applied to move the drive shaft 64 back and forth. By the movement of the drive shaft 64 in the front-rear direction, the focusing lens 45 moves between a front end position where the moving body 63 contacts the stopper 66a and a rear end position where the moving body 63 contacts the stopper 66b. By the movement of the focusing lens 45, adjustment is made so that the focus of the objective optical system 40 is matched with the observation site. The moving direction and moving amount of the focusing lens 45 are controlled by the drive pulse pattern and the number of drive pulses applied to the piezoelectric actuator 65.

  In addition, the structure of the zooming mechanism 58 and the focusing mechanism 62 of the objective optical system 40 is not limited to the above structure, and various structures can be employed.

  In FIG. 4 showing the electrical configuration, the main control unit 70 of the processor device 11 controls the respective parts of the endoscope body 10 and the light source device 12 that are electrically connected together with each part of the processor device 11. To do. The endoscope body 10 is provided with a sensor driver 71, an analog signal processor 72, a motor driver 73, a focus driver 74 and the like in addition to the image sensor 48 described above.

  As the image sensor 48, for example, a CCD type is used. The sensor driver 71 includes a timing generator that generates various drive signals for driving the image sensor 48. The image sensor 48 is driven by a drive signal from the sensor driver 71 to capture 60 frames per second, for example, and photoelectrically converts an optical image formed on the light receiving surface via the objective optical system 40 and the prism 47. The converted shooting signal is output.

  The analog signal processing unit 72 includes a correlated double sampling (CDS) circuit that removes reset noise included in the photographic signal, an amplifier that performs amplification, an A / D converter that digitally converts the photographic signal, and the like. An imaging signal from the image sensor 48 is processed by the analog signal processing unit 72 and sent to the processor device 11.

  The motor driver 73 drives the magnification motor 61 under the control of the magnification control unit 76 of the processor 11 and changes the magnification of the objective optical system 40 by the magnification mechanism 58. The scaling control unit 76 drives the scaling motor 61 via the motor driver 73 every time a scaling operation signal corresponding to the scaling operation is input from the scaling operation unit 25. Thereby, the magnification of the objective optical system 40 is set to any one of 1 ×, 2 ×,. The focus driver 74 drives the piezoelectric actuator 65 under the control of the AF control unit 77 of the processor device 11 and moves the focusing lens 45.

  The light source device 12 includes a light source 78, a light source driver 79, and a condenser lens 81. The light source 78 includes, for example, a xenon lamp or a halogen lamp that outputs illumination light, and is driven by a light source driver 79. The condensing lens 81 condenses the light from the light source 78 and makes it incident on one end of the light guide 82. The light guide 82 guides the illumination light from the light source 78 to the distal end portion 20 and irradiates the illumination light toward the observation site via the illumination lens 83 and the illumination window 32.

  The photographing signal input from the analog signal processing unit 72 to the processor device 11 is sent to the image processing unit 84. The image processing unit 84 performs color interpolation, gain correction, white balance adjustment, gamma correction, image enhancement processing, and the like on the input shooting signal. The signal conversion unit 85 analog-converts the photographic signal processed by the image processing unit 84 and outputs it to the connected monitor 14. As a result, an image of the observed region imaged by the image sensor 48 is displayed on the monitor 14.

  The photographing signal from the analog signal processing unit 72 is also sent to the brightness detection unit 86, the evaluation value detection unit 87, and the feature recognition unit 88. The brightness detection unit 86 detects the brightness of the captured image (subject brightness) from the captured signal and sends it to the AF control unit 77.

  The evaluation value detection unit 87 generates an AF evaluation value indicating the magnitude of contrast of the captured image for each frame based on the captured signal, and sends the AF evaluation value to the AF control unit 77. This AF evaluation value is obtained by the same method as that used when focus adjustment is performed by a conventional contrast detection method, and is obtained as an accumulation of high-frequency components of a captured image. In this example, the AF area, which is the target range for obtaining the AF evaluation value, is set as the entire range of the captured image. However, an AF area smaller than the entire range may be set.

  The feature recognizing unit 88 recognizes the feature of the image of the observed region being imaged based on the imaging signal. In this example, the feature recognizing unit 88 recognizes the shape of the imaged site to be observed as a feature of the image of the site to be observed, and is the most among a plurality of shapes set in the evaluation value table described later. Identify near-shaped objects.

  This feature recognition unit 88 has a buffer memory that holds the shape for several frames, and updates the oldest shape of the buffer memory each time a shape is identified, thereby obtaining the latest shape for several frames. Hold. When a scaling operation is performed by the scaling operation unit 25, the feature recognition unit 88 sends the latest shape immediately before the magnification change stored in the buffer memory to the AF control unit 77 at the time of the operation. Thereby, the AF control unit 77 acquires the shape recognized from the captured image in focus just before the magnification change.

  The AF control unit 77 drives the piezoelectric actuator 65 via the focus driver 74 while referring to the AF evaluation value from the evaluation value detection unit 87, so that the focus is matched to the site to be observed. The lens position of the focusing lens 45 is controlled. Further, the AF control unit 77 is based on the number and pattern of drive pulses supplied to the piezoelectric actuator 65 with reference to the state where the focusing lens 45 is in contact with the stopper 66a or the stopper 66b. The lens position is detected.

  In a normal time, the AF control unit 77 adjusts the lens position of the focusing lens 45 so that the observation site is in focus by, for example, the entire area search process, and then the AF evaluation value is a small change amount but a constant amount. When the change has occurred, the lens position of the focusing lens 45 is finely adjusted by a fine search process so that the focus is maintained.

  In the entire area search process, the AF evaluation value is acquired while moving the focusing lens 45 in the entire movable range, and the focusing lens 45 is set at the lens position where the AF evaluation value is maximized. In the minute search process, the focusing lens 45 is moved back and forth in a predetermined minute region based on the lens position at the start of the process to detect the peak of the AF evaluation value so that the AF evaluation value becomes the peak. The lens position of the focusing lens 45 is adjusted. Note that when the AF evaluation value peak cannot be detected by the fine search process, the entire area search process is performed.

  Immediately after the magnification of the objective optical system 40 is changed, the AF control unit 77 performs a limited search process so that the focused lens 45 can be brought into focus in a short time so as to match the focus on the observation site in order to match the focus in a short time. Control the lens position. In the limited search process, the AF control unit 77 acquires the AF evaluation value while moving the focusing lens 45 in a limited section in which the AF evaluation value is within an evaluation value search range described later, and obtains the maximum AF evaluation value. The value is detected, and the focusing lens 45 is set at the lens position where the maximum value is detected.

The evaluation value search range is defined as a range of AF evaluation values. The evaluation value search range is determined according to the combination of the brightness of the photographed image, the magnification of the objective optical system 40 after the magnification change, and the shape of the observation site photographed immediately before the magnification change. An evaluation value search range corresponding to the brightness and shape is specified from the evaluation value table stored in the table memory 89.
In this example, when the evaluation value search range is specified, the brightness of the captured image is the one after the magnification change, but may be the one before the magnification change.

  The AF control unit 77 acquires the magnification of the objective optical system 40 when determining the evaluation value search range from the magnification control unit 76, and the brightness of the captured image from the brightness detection unit 86, and the shape of the observed region Is acquired from the feature recognition unit 88.

  The table memory 89 stores the evaluation value table as described above. In this evaluation value table, as shown in FIG. 5, an evaluation value search range is associated with each combination of the magnification of the objective optical system 40, the brightness of the captured image, and the shape of the site to be observed.

  The magnification of the objective optical system 40 is 1 ×, 2 ×,... 5 ×, and the brightness of the photographed image is, for example, “7 (IRE)”, “40 (IRE)”, “60 (IRE). ) ”Etc. Further, the shapes are obtained by patterning the shapes of various observed sites to be photographed. For example, a circular shape A, a square shape B, and a triangular shape C obtained by patterning the observed shape such as a polyp. Etc. are set.

  When photographing the site to be observed that is recognized as a specific shape, the AF evaluation value when the optical magnification is changed and the focus is matched is fairly high, and the specific shape and the post-change The value is within a relatively narrow specific range corresponding to the combination of the magnification of the optical system and the brightness of the image. Accordingly, in response to a combination of arbitrary shape, magnification, and brightness, a specific range of AF evaluation values expected after the magnification change is obtained as an evaluation value search range corresponding to the combination for various combinations, They are stored in the evaluation value table in association with these combinations.

  Next, the operation of the above configuration will be described. When observing the inside of a body cavity with the electronic endoscope device 2, first, the endoscope body 10 is connected to the processor device 11 and the light source device 12. Next, the power of each part is turned on, and the insertion part 15 is inserted into the body cavity. The illumination window 32 is irradiated with illumination light from the light source device 12 when the power is turned on. Then, under the illumination light, the image sensor 48 performs photographing at a predetermined frame rate through the objective optical system 40 exposed from the observation window 31. An imaging signal obtained by this imaging is sent to the processor device 11, and a captured image of the site to be observed in the body cavity is displayed on the monitor 14 connected to the processor device 11.

  While photographing by the image sensor 48 is being performed, every time a photographing signal for one frame is input, an AF evaluation value is obtained by the evaluation value detection unit 87, and this is sent to the AF control unit 77. When the magnification of the objective optical system 40 is constant, the focus adjustment of the objective optical system 40 using the entire area search process and the fine search process is performed under the control of the AF control unit 77.

  For example, when the distal end portion 20 is pointed to an observation site in an appropriate direction and the imaging distance has changed greatly and the peak of the AF evaluation value cannot be detected by the fine search processing, the entire area search processing is performed. In the entire area search process, first, the focusing lens 45 is moved to one end of the movable range, for example, the front end position. Thereafter, after the image sensor 48 performs photographing, the focusing lens 45 is moved stepwise toward the rear end position, and photographing is performed again.

  As described above, while the focusing lens 45 is moved toward the rear end position, shooting is performed for each movement, and the AF evaluation value is sequentially detected by the evaluation value detection unit 87 from the shooting signal obtained by each shooting. The After the AF evaluation value at the rear end position is obtained, the AF control unit 77 determines the AF evaluation value that is the maximum among the AF evaluation values, and the lens position corresponding to the maximum AF evaluation value is determined as piezoelectric. It is specified from the number of drive pulses supplied to the actuator 65. Then, under the control of the AF control unit 77, the piezoelectric actuator 65 is driven and the focusing lens 45 is moved to the specified lens position. As a result, the focus of the objective optical system 40 is brought into agreement with the previously observed site to which the tip 20 is directed.

  As described above, after the entire area search process is brought into focus, if the shooting distance changes due to the movement of the tip 20 or the movement of the part to be observed, a focus shift occurs, which is a change in the AF evaluation value. It is detected by the AF control unit 77. Then, when the amount of change in the AF evaluation value exceeds a certain amount, the AF control unit 77 performs a fine search process.

  When the minute search process is started, first, the focusing lens 45 is moved back and forth within a minute range centered on the lens position of the current focusing lens 45, and an AF evaluation value at each lens position is acquired. Then, a peak of the AF evaluation value in a range in which the focusing lens 45 is moved is detected from each AF evaluation value, and the focusing lens 45 is moved to the lens position where the peak is reached, and the focus is matched. When the peak of the AF evaluation value cannot be detected, the above-described whole area search process is performed and the focus is matched, assuming that the change in the shooting distance is large.

  As described above, the observation site is observed under the control to be in focus with the observation site, but the observation site is magnified and observed without changing the position of the tip 20. In order to do this, the up button 25a of the scaling operation unit 25 is operated. Similarly, when observing a wide range, the down button 25b of the scaling operation unit 25 is operated.

  When the magnification changing section 25 is operated, the magnification changing motor 61 is driven under the control of the magnification changing control section 76 to rotate the cam shaft 57. As the cam shaft 57 rotates, the first variable magnification lens 42 and the second variable magnification lens 43 move in the front-rear direction, and the magnification of the objective optical system 40 changes. Since the control is performed so that the camshaft 57 is rotated by a certain amount for each operation of the magnification operation unit 25, the magnification is increased or decreased by one step for each operation. Accordingly, for example, when the magnification of the objective optical system 40 is 1, when the up button 25a is pressed once, the first and second variable magnification lenses 42 and 43 move, and the magnification of the objective optical system 40 is 2. Doubled.

  When the magnification is changed in this way, focus shift occurs. The cause of the focus shift includes not only the movement of the focal position of the objective optical system 40 due to the movement of the first and second variable magnification lenses 42 and 43 but also the change in the distribution of the photographing distance due to the change of the photographing range. As an example of the latter, for example, most of the shooting range is occupied by a long shooting distance, and when there is a small protrusion with a relatively short shooting distance at the center, the focus is almost matched with the long shooting distance. However, when the magnification is changed to a high magnification and most of the photographing range is a small protrusion, the small protrusion is not in focus even if the focal position of the objective optical system 40 does not move. There are cases where

  When the AF control unit 77 receives notification from the magnification control unit 76 that the magnification of the objective optical system 40 has been changed, the AF control unit 77 starts the limited search process shown in FIG. First, the AF control unit 77 acquires the shape of the site to be observed identified from the captured image immediately before the magnification change by the feature recognition unit 88. Subsequently, the brightness of the observed region after the magnification change detected by the brightness detection unit 86 is acquired, and further, the magnification after the magnification change is acquired from the magnification control unit 76.

  When the shape immediately before the magnification change and the brightness and magnification after the magnification change are acquired as described above, the AF control unit 77 accesses the table memory 89 and corresponds to the combination of the acquired shape, brightness, and magnification. The evaluation value search range to be specified is obtained from the evaluation value table.

  On the other hand, a pre-movement process is performed, and the focusing lens 45 is moved to a lens position that matches the focus after the magnification change to the photographing distance corresponding to the lens position before the magnification change. The lens position after the magnification change corresponding to the magnification change is acquired based on the number of pulses, the pattern, and the like of the driving pulse supplied to the piezoelectric actuator 65 so far, and the lens position of the focusing lens 45 is in focus. The lens position of the focusing lens 45 that is in focus after the magnification change is determined from the matching shooting distance. Then, a drive pulse is supplied to the piezoelectric actuator 65 so that the specified lens position is obtained.

  If the respective magnifications before and after the magnification change and the photographing distance before the magnification change are known, it can be obtained from the lens position of the focusing lens 45 after the magnification change that matches the photographing distance. In addition, a data table that associates the lens position under the magnification after the magnification change corresponding to the lens position under each magnification before the magnification change is prepared in advance, and a pre-movement process is performed with reference to the data table. Also good.

  After performing the pre-movement process as described above, a pre-AF evaluation value that is an AF evaluation value after the pre-movement process is acquired, and it is confirmed that the pre-AF evaluation value is within the acquired evaluation value search range. Then, the moving direction determination process is performed. In this moving direction determination process, it is determined in which direction the focusing lens 45 can be moved to a lens position that is the lower limit value of the evaluation value search range with a small amount of movement.

  For example, the focusing lens 45 is moved back and forth with an appropriate step width around the lens position after the pre-movement process, and the relationship between the moving direction of the focusing lens 45 and the increase or decrease of the AF evaluation value at that time is examined. The direction in which the AF evaluation value decreases is the direction in which the focusing lens 45 should be moved. For example, if the AF evaluation value decreases when the focusing lens 45 is moved toward the rear end position, the direction in which the focusing lens 45 is moved is the direction in which the focusing lens 45 is to be moved. In addition, it is good also considering the arbitrary one direction as the direction which should move the focusing lens 45 irrespective of such a process.

  After determining the moving direction, the focusing lens 45 is set at the lens position that is the lower limit value of the evaluation value search range. Therefore, while acquiring the AF evaluation value, the piezoelectric actuator 65 is driven, and the focusing lens 45 is moved in the previously determined direction to be moved. Then, when the acquired AF evaluation value becomes the lower limit value of the evaluation value search range, the movement of the focusing lens 45 is stopped and set. Note that it is not necessary to strictly set the focusing lens 45 at the lens position that is the lower limit value of the evaluation value search range. For example, the lens position may be an AF evaluation value close to the lower limit value, or the lens position when the AF evaluation value is equal to or lower than the lower limit value.

  As described above, after setting the focusing lens 45 so that the AF evaluation value becomes the lower limit value of the evaluation value search range, the AF control unit 77 starts processing for detecting the maximum value of the evaluation value search range. Is done. First, AF evaluation values are sequentially acquired while moving the focusing lens 45 one step at a time in the direction opposite to that when moving to the lower limit value in the moving direction determination process.

  When the acquired AF evaluation value becomes equal to or lower than the lower limit value of the evaluation value search range due to the movement of the focusing lens 45, the movement of the focusing lens 45 is stopped at that lens position. Thereby, AF evaluation values when the focusing lens 45 is moved within a range of lens positions where the AF evaluation values are maintained within the specified evaluation search range can be sequentially acquired.

  When the AF evaluation value for each lens position in the evaluation value search range is acquired, the AF control unit 77 determines the largest AF evaluation value among them, and specifies the lens position corresponding to the AF evaluation value. Is done. Then, the AF control unit 77 moves the focusing lens 45 to the lens position.

  By the way, when the pre-AF evaluation value acquired after the pre-movement process is outside the evaluation value search range, the AF evaluation value can be set within the evaluation value search range by moving the focusing lens 45 in any direction. A moving direction determination process is performed to determine whether or not it is possible. In this determination process of the moving direction, the focusing lens 45 is also moved back and forth with an appropriate step width around the current lens position, and the relationship between the moving direction of the focusing lens 45 and the increase or decrease of the AF evaluation value at that time Check out.

  When the pre-AF evaluation value is out of the evaluation value search range and the pre-AF evaluation value is smaller than the value in the evaluation value search range, the focusing lens 45 is moved in the direction in which the AF evaluation value increases. The direction should be. Then, while acquiring the AF evaluation value, the focusing lens 45 is moved in the direction to be moved. Then, the focusing lens 45 is set at a lens position where the AF evaluation value is the lower limit value of the evaluation value search range. In this case as well, it is not necessary to set the focusing lens strictly. For example, the lens position at the time when the AF evaluation value falls within the evaluation value search range may be used.

  After the focusing lens 45 is set at the lens position where the AF evaluation value is the lower limit value of the evaluation value search range, the AF control unit 77 performs the same operation as when the pre-AF evaluation value is within the evaluation value search range. Then, a process for detecting the maximum value of the evaluation value search range is performed. In this case, the focusing lens 45 may be moved in the same direction as when moving to the lower limit value of the evaluation value search range.

  The evaluation is performed when the pre-AF evaluation value is larger than the evaluation value search range or when the focusing lens 45 is moved to detect the maximum AF evaluation value in the evaluation value search range. When an AF evaluation value larger than the upper limit of the value search range is detected, it is certain that an AF evaluation value larger than the value of the evaluation value search range can be taken. Therefore, in such a case, the AF evaluation value is evaluated while moving the focusing lens 45, for example, by restricting the search range to a direction in which the AF evaluation value is increased from the pre-AF evaluation value, for example. Then, it may be controlled so that the focus of the objective optical system 40 matches the site to be observed.

  Further, when the pre-AF evaluation value is outside the evaluation value search range, if the pre-AF evaluation value does not fall within the evaluation value search range even if it moves in the determined movement direction, for example, the focusing lens reaches the front end position or the rear end position. At that time, the moving direction may be reversed and the focusing lens may be controlled to move toward the evaluation value search range.

  As shown in FIG. 7, the AF evaluation value for the lens position after the magnification change is represented by an AF evaluation value curve Ca, and the AF evaluation value for the lens position before the magnification change is represented by an AF evaluation value curve Cb. Before the magnification change, the focusing lens 45 is set at the lens position P0 corresponding to the maximum AF evaluation value. Further, when the magnification is changed, the focus position of the objective optical system 40 is moved or the photographing range becomes small, and the focus lens 45 is not changed at the lens position P0. However, the AF evaluation value is The maximum value in the AF evaluation value curve Ca is not reached.

  By the pre-movement process, the lens position P1 that matches the focus after the magnification change is specified from the photographing distance that is in focus at the lens position P0, and the focusing lens 45 is moved to the lens position P1. When the pre-moving process is performed in this way, the AF evaluation value (pre-AF evaluation value) is a combination of the shape of the observed region imaged before the magnification change, the magnification of the optical system after the magnification change, and the brightness of the image. Although it falls within the evaluation value search range specified according to the above, it is not always in a state of being in focus. This is because the shooting range becomes smaller and the distribution of shooting distances changes.

  The focusing lens 45 is moved back and forth within a range of ΔP with the lens position P1 as the center. Based on each AF evaluation value obtained at this time, the moving direction of the focusing lens 45 for setting the AF evaluation value as the lower limit value of the evaluation value search range decreases the AF evaluation value in the AF evaluation value curve Ca. It is determined as a direction.

  The focusing lens 45 is moved to the lens position P2 by being moved while referring to the AF evaluation value. Subsequently, while acquiring the AF evaluation value, the focusing lens 45 is moved backward by one step at a time, and the movement of the focusing lens 45 is stopped at a lens position where the AF evaluation value is equal to or lower than the lower limit value of the evaluation value search range. The In the illustrated example, the focusing lens 45 moves to the lens position P3. Then, the focusing lens 45 is moved to the maximum lens position P4 obtained while the focusing lens 45 is moved and the AF evaluation value is in the evaluation value search range in this way. The focus is matched to the observation site.

  As described above, the objective optical system 40 is focused after zooming so that the focus is matched to the site to be observed. At this time, the maximum value of the AF evaluation value within a narrow evaluation value search range according to the combination of the shape of the observed region imaged before the magnification change, the magnification of the optical system after the magnification change, and the brightness of the image Since the position of the lens that matches the focus is specified by detecting, the focus can be matched to the site to be observed in a short time.

  In the above embodiment, the focusing lens is moved and set to the lens position where the maximum AF evaluation value in the evaluation value search range is detected, but the peak of the AF evaluation value at which the AF evaluation value turns from increasing to decreasing is detected. However, a so-called hill-climbing method in which a focusing lens is set at the peak lens position may be employed. In this case, for example, the focusing lens is set at the first detected peak lens position. Even in this case, even if the AF evaluation value of the peak is not the maximum value, the evaluation value search range is narrow, so that it can be suppressed to a practical focus shift amount.

  In the above description, the varifocal type objective optical system whose focal position changes when the optical magnification is changed has been described as an example. However, the present invention is not limited to this, and the optical magnification is changed. It may be a zoom type objective optical system configured such that the focal position does not change.

  Furthermore, in the above-described embodiment, the shape of the observed region is recognized as a feature of the image of the observed region to be recognized from the captured image, and the shape is associated with the evaluation value search range. The characteristics of the image are not limited to the shape, but may be a pattern such as a pleat or a lattice, color and brightness, their distribution, distribution ratio, and the like. Alternatively, the evaluation value search range may be specified by combining any two of shape magnification and brightness.

It is explanatory drawing which shows the structure of an electronic endoscope apparatus. It is explanatory drawing which shows the front end surface of an endoscope main-body part. It is sectional drawing which shows the structure of an objective optical system. It is a block diagram which shows the electric constitution of an electronic endoscope apparatus. It is explanatory drawing which shows the example of the evaluation value table which matched the evaluation value search range with the combination of a shape, a magnification, and brightness. It is a flowchart which shows the process sequence of the limited search process performed when the optical magnification is changed. It is a graph which shows the relationship between the movement of the focusing lens at the time of change of optical magnification, and AF evaluation value.

Explanation of symbols

2 Electronic Endoscope 10 Electronic Endoscope 11 Processor Unit 40 Objective Optical System 42, 43 Variable Lens 45 Focusing Lens 48 Image Sensor 77 AF Control Unit 86 Brightness Detection Unit 87 Evaluation Value Detection Unit 88 Feature Recognition Unit 89 Table memory

Claims (4)

An objective optical system having a variable power lens that changes an optical image and a focusing lens that adjusts the focus, and an image sensor that takes an image of an observation site and outputs an imaging signal through the objective optical system are inserted into the body. In the focus adjustment method of the electronic endoscope apparatus that is provided at the distal end of the insertion portion and performs focus adjustment based on the evaluation value indicating the magnitude of contrast,
When the magnification is changed by moving the zoom lens, the brightness of the photographed image, the characteristics of the image of the observed region recognized from the image photographed immediately before the magnification change, and the magnification after the magnification change Corresponding to the combination with the magnification of the objective optical system, the search range is specified as the range of evaluation values expected after the magnification change, and the focus after the magnification change is matched to the shooting distance corresponding to the lens position before the magnification change After moving the focusing lens to the lens position to be moved, the focusing lens is moved within the range of the lens position that maintains the search range specified by the evaluation value, and each evaluation value obtained by this movement is evaluated. A focus adjustment method for an electronic endoscope apparatus, wherein the focusing lens is moved to a lens position for focusing on a portion to be observed.   2. The electronic endoscope apparatus according to claim 1, wherein when the focusing lens is moved within a range within the specified search range, the focusing lens is moved to a lens position having a maximum evaluation value. Focus adjustment method. Objective optics that incorporates a focusing mechanism that adjusts the focusing distance by moving the focusing lens and an optical scaling mechanism that scales the optical image. The system,
An image sensor that performs imaging of the observed site through the objective optical system, photoelectrically converts the captured image of the observed site into an imaging signal, and
Contrast detection means for detecting an evaluation value indicating the magnitude of contrast of the captured image based on the captured signal;
Brightness detection means for detecting the brightness of the shot image based on the shooting signal;
Recognition means for recognizing the characteristics of the image of the imaged site to be observed based on the imaging signal;
Evaluation value expected after the magnification change corresponding to the combination of the brightness of the captured image, the characteristics of the image of the observed region immediately before the magnification change of the objective optical system, and the magnification of the objective optical system after the magnification change Storage means for storing a search range preliminarily defined as a range of the image in association with a plurality of combinations of the brightness of the photographed image, the characteristics of the image of the observed region before the magnification change, and the magnification after the magnification change, and ,
When the magnification of the objective optical system is changed by the optical scaling mechanism, the brightness of the captured image detected by the brightness detection unit and the site to be observed recognized by the recognition unit immediately before the magnification change The search range corresponding to the combination of the image characteristics and the magnification of the objective optical system after the magnification change is specified from the plurality of search ranges stored in the storage means, and the lens position before the magnification change is supported The focus lens is moved to the lens position that matches the focus after the magnification change to the shooting distance, and then the focus is maintained within the range of the lens position that maintains the evaluation value detected by the contrast detection means within the specified search range. The focal lens is moved, each evaluation value obtained by this movement is evaluated, the lens position for focusing on the observation site is determined, and the determined lens position is determined. Electronic endoscope apparatus according to claim further comprising a focus control means for moving the focusing lens to.   The focus control means determines a lens position that has a maximum evaluation value when the focusing lens is moved within a specified search range as a lens position for focusing. The electronic endoscope apparatus according to claim 3.

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