JP6000838B2 - Endoscope device - Google Patents

Description

  The present invention relates to an endoscope apparatus that acquires an analog image generated by imaging, converts the analog image into a digital image, and adjusts a gain.

  An endoscope needs to be able to observe with appropriate brightness and image quality from near point observation to far point observation. Therefore, in the case of an endoscope that detects very weak light, such as a fluorescent endoscope, it is important to ensure the brightness of the image during far-point observation.

  Methods for improving image brightness include increasing the amount of light emitted from the light source, using a bright imaging optical system, increasing the aperture when the aperture is variable, and analog obtained from the image sensor A method for analog amplification of a signal is known.

  However, increasing the maximum light amount of the light source not only increases the amount of heat generated by the light source itself, but also has a thermal effect on a subject such as a living body. There is a limit. When light is emitted with such a limited maximum light amount, the far-point image may become dark, and in this case, a bright image cannot be obtained only by controlling the light source. Also, if a bright imaging optical system is used or the aperture opening is enlarged, the depth of field becomes shallow, so that for example, a subject at a far point away from the focusing distance cannot be observed sufficiently sharply. Furthermore, the analog signal amplification increases not only the image pickup signal but also noise mixed in the image pickup signal, which causes an undesirable effect in terms of image quality.

  As a method for improving the brightness of an image, for example, Japanese Patent Laid-Open No. 2005-131129 discloses a CCD using a CMD (Charge Multiplying Device) that performs charge multiplication using ionization. Have been described.

  However, with the technique described in Japanese Patent Laid-Open No. 2005-131129, an image with sufficient brightness can be obtained unless a sufficiently high voltage is applied to the CCD disposed at the distal end of the endoscope. I can't. On the other hand, when a high voltage is applied to obtain a high amplification factor, it is necessary to sufficiently coat the high-voltage signal line for safety, and the outer diameter of the endoscope increases. I was doing it. In addition, since it is necessary to use a special image sensor, the cost also increases.

  On the other hand, as another method for improving the brightness of an image, for example, in Japanese Patent Application Laid-Open No. 2009-219719, an average luminance value or a peak value of an endoscopic image determines whether or not automatic control of a light source unit is appropriate. If it is out of the set luminance range even after a predetermined period of time, it is determined that appropriate light amount control by the control of the light source unit is impossible, and the endoscopic image Describes a technique for performing gain correction by adjusting a gain coefficient based on the average luminance value or peak value. Here, the gain correction is a digital gain correction performed on an endoscopic image acquired by an image acquisition means such as a DSP (digital signal processor).

  A method for increasing the signal intensity by applying digital gain to the digital image signal obtained by such imaging will be described with reference to FIG. FIG. 15 is a diagram illustrating a flow when an image for output (for example, for observation or storage) is obtained from an analog image signal obtained by imaging.

  An image signal obtained by photoelectric conversion at each pixel of the image sensor is an analog signal. Here, it is assumed that the obtained analog image signal is a signal obtained by photoelectrically converting weak light, and has a low histogram of signal values of many pixels. This analog signal is then A / D converted to a digital image signal.

  Here, in order to obtain an image that can be recognized as a smooth gradation change by the human naked eye, it is said that it is necessary to display 256 gradations, that is, 8 bits per color of the RGB signal. In addition, in a high-definition image that has become widespread in recent years, 1024 gradations with a single color and a larger number of gradations may be used. Therefore, it is assumed here that the output image is 10 bits.

  At this time, if signal processing in the middle is also performed with 10 bits, intermediate gradation may be lost when gradation conversion or the like is performed. Therefore, in the midway signal processing, processing with, for example, 12 bits having a gradation number larger than 10 bits is performed.

  Therefore, when an analog signal obtained from the image sensor is A / D converted, sampling is performed so that a 12-bit digital signal is output. Even when the image signal is digitized, the histogram has many pixels with low signal values, as in the case of an analog signal.

  Thereafter, the digital image signal is linearly amplified by multiplying an automatic gain control (AGC) signal value by a gain coefficient. When this process is performed, the dynamic range is expanded, but the gradation is impaired. For example, if a signal with values 0, 1, 2,... Is amplified four times, signals with values 0, 4, 8,... Are obtained, but there are no signals with values 2-3, 5-7,. Further, it can be seen that so-called gradation drop occurs and the gradation becomes ¼.

  Then, in order to convert to an image suitable for display, γ correction which is nonlinear conversion is performed. After or simultaneously with this gamma correction, a process of converting a 12-bit signal for processing into a 10-bit signal for output is also performed. Conversion to a 10-bit signal is preferably after or simultaneously with gamma correction because it is non-linear and gradation loss occurs. Here, since the conversion from 12 bits to 10 bits corresponds to a signal value amplification of ¼ times, if the signal amplification by AGC is up to four times, the gradation loss in the output image is substantially reduced. It turns out that it does not occur.

JP 2005-131129 A JP 2009-219719 A

  However, when trying to obtain an image with brightness suitable for observation, signal amplification of 4 times may not be sufficient. This point will be described with reference to FIG. FIG. 16 is a diagram illustrating an example in the case where the brightness of an image is insufficient with 4 times signal amplification.

  First, when adjusting the brightness of an image, in order to obtain the best image quality, priority is given to light source light amount adjustment with a gain fixed to 1. Next, if the brightness is insufficient even when the light source light amount is adjusted to the maximum, the gain adjustment by AGC is performed while maintaining the maximum illumination light amount so as to obtain an image having the necessary brightness. In the case where the processing signal is 12 bits and the output signal is 10 bits, an output image with no loss of gradation can be obtained up to a gain of 4 (4 times signal amplification). is there.

  When considering a subject of a point light source, the subject is observed brighter as it is closer, and darker as it goes farther. Then, it is possible to deal with a subject (near view) at a short distance by adjusting the light source light amount, and for a subject (middle scene) at a medium distance, it is necessary to adjust the gain by AGC as the maximum illumination light amount. In this case, when a subject distance that cannot obtain an image with appropriate brightness by gain adjustment up to 4 is reached, a subject (distant view) that is further away than the subject distance is an area with insufficient brightness. .

  For example, if a gain adjustment larger than 4, for example, is performed on such an insufficiently bright area, gradation loss occurs and the image quality deteriorates for the reason described above. In addition, for example, in the case of processing with 14 bits instead of processing with 12 bits as described above, even if gain adjustment up to 16 times is performed as AGC, gradation loss does not occur. In this case, since the amount of information of the readout signal from the image sensor increases significantly, there is a problem that the readout time of the image becomes long.

  The present invention has been made in view of the above circumstances, and provides an endoscope apparatus that ensures a wide brightness adjustment range so as to be compatible with a dark subject and does not deteriorate the image quality of a bright subject. The purpose is that.

In order to achieve the above object, an endoscope apparatus according to a first aspect of the present invention includes an analog image acquisition unit that acquires an analog image generated by imaging, and converts the analog image into a predetermined number of gradations. An A / D converter that converts the digital image, a digital gain adjuster that adjusts the gain of the digital image , and the number of gradations of the digital image that has been gain-adjusted by the digital gain adjuster. An output image generation unit that generates an output image by converting from a predetermined number of gradations to an output gradation number equal to or less than the predetermined number of gradations, and a brightness change unit that changes the brightness of the image If the predetermined of number of gradations by setting a threshold below divided by the number of tones for the output, the gain is determined whether there are more pre Ki閾 value, if the the threshold value or more The digital gain adjuster It is provided with a control unit that controls to increase the brightness of the image so as not to increase, and with respect to the brightness change unit than the value.

  According to the endoscope apparatus of the present invention, it is possible to ensure a wide brightness adjustment range so as to be able to deal with a dark subject and to prevent deterioration in image quality of a bright subject.

The block diagram which shows the structure of the endoscope apparatus of Embodiment 1 of this invention. The figure which shows the procedure of the brightness adjustment in the said Embodiment 1. FIG. In the said Embodiment 1, the figure which shows the example of the mode of a change of the brightness histogram on the signal processing path | route when the image imaged on an image sensor is a little bright and dark. 5 is a flowchart showing brightness adjustment processing in the first embodiment. The figure which shows the procedure of the brightness adjustment in Embodiment 2 of this invention. FIG. 6 is a diagram showing a pixel array of an image sensor in Embodiment 2. The figure which shows the example of the addition object pixel in the binning process of the said Embodiment 2. FIG. The figure which shows the procedure of the brightness adjustment in Embodiment 3 of this invention. 6 is a timing chart showing an operation in a normal exposure mode in the fluorescence observation mode of the third embodiment. 6 is a timing chart showing an operation in a long exposure mode in the fluorescence observation mode of the third embodiment. The timing chart which shows operation | movement of the long exposure mode in the fluorescence observation mode of Embodiment 4 of this invention. The figure which shows the procedure of the brightness adjustment in Embodiment 5 of this invention. In the said Embodiment 5, the figure which shows the state of the objective aperture at the time of small diameter aperture opening. In the said Embodiment 5, the figure which shows the state of the objective aperture at the time of large diameter aperture opening. The figure which shows the flow when obtaining the image for an output from the analog image signal obtained by imaging conventionally. The figure which shows the example in case the brightness of an image is insufficient in the signal amplification of 4 times conventionally.

Embodiments of the present invention will be described below with reference to the drawings.
[Embodiment 1]

  1 to 4 show the first embodiment of the present invention, and FIG. 1 is a block diagram showing the configuration of the endoscope apparatus 1.

  As shown in FIG. 1, an endoscope apparatus 1 includes an endoscope 2 that is an analog image acquisition unit, a video processor 3, a light source device 4, an observation monitor 5, a digital filing device 6, and an input unit 7. It is equipped with.

  The endoscope 2 has an imaging optical system 11, an objective aperture 12, an actuator 13, an imaging element 14, and an illumination optical system at the distal end of an elongated insertion portion that extends from the operation unit on the hand side and is inserted into a subject. 15 is provided. The endoscope 2 further includes a light guide 16 that extends from the insertion portion and the operation portion and is connected to the light source device 4, and includes a mode switching instruction switch 17 and a scope ID memory 18 in the operation portion. .

  The light guide 16 is configured by an optical fiber bundle or the like, and transmits illumination light supplied from the light source device 4 to the illumination optical system 15.

  The illumination optical system 15 irradiates the transmitted illumination light toward a subject as a subject.

  The imaging optical system 11 forms an optical image of the illuminated subject on the imaging element 14.

  The objective aperture 12 is an optical element that changes and adjusts the brightness of an optical image formed by the imaging optical system 11, and includes a plurality of apertures with different aperture diameters (see FIGS. 13, 14, etc.). ).

  The actuator 13 drives the objective aperture 12 to change the aperture diameter. The actuator 13 also drives to insert / extract an excitation light cut filter (not shown) on the light receiving optical path of the image sensor 14. Here, the excitation light cut filter is an optical element for cutting excitation light (blue light emitted from the B-LED 22b as will be described later) reflected from the subject when performing fluorescence observation.

  The imaging element 14 generates an analog image from the optical image formed by the imaging optical system 11. The imaging device 14 is configured by arranging a plurality of pixels 14p (see FIG. 6) on the imaging surface, and in this embodiment, includes an FD amplifier (Floating Diffusion Amplifier) that is an analog amplifying unit. It has become. This FD amplifier converts a charge signal into a voltage signal when reading a signal from a floating diffusion (FD) for temporarily accumulating the charge generated by the photodiode (PD), and amplifies the signal during this conversion. It is a kind of thing that changes brightness by processing an image. The FD amplifier can control the amplification factor when the analog image is amplified (the amplification factor control is performed by the image sensor driver 41 as will be described later). Such an image sensor 14 is controlled so as to acquire an analog image in a time series in units of frames for each frame period.

  The mode switching instruction switch 17 is a switch for performing an input instruction for switching the observation mode. In the present embodiment, it is assumed that the observation mode includes a normal light observation mode and a fluorescence observation mode, and an instruction signal for setting the normal light observation mode according to the operation state of the mode switching instruction switch 17. And an instruction signal for setting the fluorescence observation mode are output to a mode switching circuit 43 (to be described later) of the video processor 3.

  The scope ID memory 18 is a storage medium that stores the product model number and serial number of the endoscope 2 or other information unique to the endoscope 2 in a nonvolatile manner.

  The light source device 4 includes a light emitting unit 21, a collimating lens 24, an LED drive circuit 25, and a power source 26.

  The light emitting unit 21 includes, as light sources, an R-LED 22r that emits red (R) light, a G-LED 22g that emits green (G) light, and a B-LED 22b that emits blue (B) light. Yes. Of these, the blue light emitted by the B-LED 22b is also used as excitation light when performing fluorescence observation. The green light emitted from the G-LED 22g is also used as reference light when performing fluorescence observation.

  As a specific example, blue light having a wavelength of 390 to 470 nm becomes excitation light for observing autofluorescence from a fluorescent substance such as collagen existing in the mucous membrane. Further, green light having a wavelength of 540 to 560 nm is reference light absorbed by hemoglobin in blood. When irradiated with blue excitation light, tumor tissue has a characteristic that autofluorescence is attenuated compared to normal tissue. For this reason, in fluorescence observation (AFI: Auto Fluorescence Imaging), by irradiating these excitation light and reference light, tumorous lesions and normal mucous membranes are highlighted in different colors, and early development of fine lesions such as cancer. It is possible to support discovery.

  The light emitting unit 21 further includes a first beam splitter 23r, a second beam splitter 23g, and a third beam splitter 23b.

  The first beam splitter 23r functions as a reflection mirror that reflects red light emitted from the R-LED 22r.

  The second beam splitter 23g transmits the red light reflected by the first beam splitter 23r and reflects the green light irradiated from the G-LED 22g.

  The third beam splitter 23b reflects red light and green light from the second beam splitter 23g and transmits blue light emitted from the B-LED 22b.

  The collimating lens 24 irradiates the incident end of the light guide 16 with the RGB light from the third beam splitter 23b as a parallel light beam.

  The LED drive circuit 25 controls which LED 22r, 22b, 22g of the light emitting unit 21 emits light at what timing based on the control signal input from the AGC gain detection circuit 37. . At this time, the LED drive circuit 25 controls the light emission timing of each LED 22r, 22b, 22g according to whether the observation mode notified from the mode switching circuit 43 is the normal light observation mode or the fluorescence observation mode. It is like that.

  The power source 26 is a power source that supplies power to the light emitting unit 21 and the LED drive circuit 25.

  The video processor 3 includes a process circuit 31, an A / D conversion circuit 32, an image processing circuit 33, D / A conversion circuits 38a, 38b, and 38c, an encoding circuit 39, an image sensor driver 41, and actuator control. A circuit 42, a mode switching circuit 43, a dimming control parameter switching circuit 44, and a dimming circuit 45 are provided.

  An analog imaging signal output from the imaging element 14 is input to the process circuit 31.

  The process circuit 31 performs analog process processing on the input imaging signal.

  The A / D conversion circuit 32 samples (quantizes) the analog imaging signal output from the process circuit 31 and converts it into a digital image signal having a predetermined gradation number N (N is an integer of 2 or more) for image processing. An A / D conversion unit for conversion. In the present embodiment, the A / D conversion circuit 32 is described as converting to a digital image signal having 12 bits, that is, a gradation number of 2 12.

  In this embodiment, the A / D conversion circuit 32 is provided in the video processor 3 on the assumption that the image pickup device 14 is an analog image pickup device. However, if the image pickup device 14 is a digital image pickup device, it is provided in the image pickup device 14. (At this time, the process circuit 31 may be further provided in the imaging device 14, or the processing corresponding to the process circuit 31 may be performed digitally in the video processor 3).

  The image processing circuit 33 performs various types of digital signal processing on the digital image signal output from the A / D conversion circuit 32, and includes an AGC (auto gain control) processing circuit 34, a binning frame addition circuit 35, and a color. A matrix circuit 36 and an AGC gain detection circuit 37 are provided.

  The AGC processing circuit 34 is a digital gain adjusting unit that performs amplification by adjusting the gain of a digital image signal, and can control the gain (gain).

  The binning frame addition circuit 35 performs binning processing or frame addition processing on the image signal.

  Here, the binning process is a process of adding a plurality of spatially adjacent pixel signals and handling them as one pixel. As some examples, 2 × 2 binning handling 2 × 2 pixels as one pixel, 3 × 3 × 3 binning that handles × 3 pixels as one pixel, and the like. In this embodiment, an example in which the binning process is performed by the binning frame addition circuit 35 in the video processor 3 will be described. However, the binning process may be performed by the image sensor 14 having a binning processing function. As will be described later in the second embodiment, the binning process includes a process in which the number of pixels is reduced to 1 / k (here, k is a positive integer) and a process in which the number of pixels is hardly reduced.

  The frame addition process is a process of handling image signals of a plurality of frames as one frame image signals by adding image signals output in units of frames from the image sensor 14 at the same pixel position. Some examples of frame addition processing include two-frame addition that adds two frames to generate one frame, three-frame addition that adds one frame to generate one frame, and the like. It is done. For example, even in the case of adding two frames, the first addition frame is generated by adding the first frame and the second frame, and then the second addition frame is generated by adding the third frame and the fourth frame. There are cases where the second frame and the third frame are added to generate a second addition frame. In the former case, the number of frames is halved, but in the latter case, the total number of frames is only reduced by one frame, for example.

  The color matrix circuit 36 performs output (for observation, storage, etc.) by performing color space conversion or γ conversion of an image signal on the digital image after gain adjustment by the AGC processing circuit 34. It is an output image generation part which produces | generates this image. Here, the color space conversion is, for example, conversion from an RGB signal to a YCbCr signal. As is well known, the γ conversion is a process of converting a signal value nonlinearly so as to match the display characteristics of the observation monitor 5, and typically expands the gradation of a low-brightness signal. Then, conversion is performed so as to compress the gradation of the high luminance signal. In this γ conversion, conversion is also performed from the gradation number N for digital image processing to the gradation number M for output (M is an integer of 2 or more and N or less). In the present embodiment, description will be made on the assumption that γ conversion is performed to convert the number of gradations to 10 bits, that is, 2 to the 10th power.

  As will be described later, the AGC gain detection circuit 37 acquires the illumination light amount of the light emitting unit 21 from the dimming circuit 45, determines whether or not the light amount of the light emitting unit 21 has reached the maximum illumination light amount, and becomes the maximum illumination light amount. If the brightness needs to be increased further, the AGC processing circuit 34 is controlled to increase the gain.

  The AGC gain detection circuit 37 further acquires the gain of the AGC processing circuit 34 and determines whether the illumination light amount is the maximum illumination light amount and the gain is equal to or greater than a threshold value Th set based on a predetermined number of gradations. When the maximum illumination light quantity is equal to or greater than the threshold Th (when the first brightness adjustment level is reached), the AGC processing circuit 34 is prevented from increasing the gain beyond the threshold Th and the brightness. It is a control part which controls so that the brightness of an image may be increased with respect to a change part.

  The brightness changing unit controlled by the AGC gain detection circuit 37 changes the brightness of the image, and is an FD amplifier (or an analog amplifying unit provided in the video processor 3) built in the image sensor 14. , A binning processing function provided in the binning frame addition circuit 35 (or a binning processing function provided in the image sensor 14), a frame addition processing function provided in the binning frame addition circuit 35, an image sensor driver 41 that controls the frame rate as will be described later, There is an objective aperture 12 or the like, and a different configuration is adopted for each embodiment as described below.

  Therefore, as an image whose brightness is changed by the brightness changing unit, an analog image obtained by photoelectric conversion by the photodiode (PD) of the image sensor, an analog image obtained by analog amplification of the analog image by an FD amplifier or the like. There is a digital image obtained by converting an analog image by the A / D conversion circuit 32.

  The brightness changing unit in this embodiment is assumed to be an FD amplifier of the image sensor 14. Therefore, the AGC gain detection circuit 37 controls the amplification factor of the FD amplifier via the image sensor driver 41.

  At this time, the change in brightness by the brightness changing unit may not be continuous but discontinuous. For example, in the case of binning or frame addition, an integer multiple is a unit, and analog amplification by an FD amplifier, a frame rate changing step, and an aperture diameter of the objective aperture 12 are also stepwise (discontinuous) changes. There seems to be something. In such a case, the brightness changed by the brightness changing unit so that the brightness of the output image is maintained substantially the same without suddenly changing before and after the brightness is changed by the brightness changing unit. The AGC gain detection circuit 37 performs a process of causing the AGC processing circuit 34 to adjust the gain by the amount that cancels out the error. Therefore, after the brightness is increased by the brightness changing unit, the gain is considered to be less than the threshold value Th. Therefore, it is possible to control the brightness at a finer level by changing the gain by the AGC processing circuit 34. Again possible.

  In the case where the brightness has already been increased by the brightness changing unit, even when the gain of the AGC processing circuit 34 becomes 1, the brightness needs to be further reduced (the second brightness adjustment level is reached). The AGC gain detection circuit 37 controls the brightness changing unit to decrease the brightness. At this time, the AGC gain detection circuit 37 performs the process of causing the AGC processing circuit 34 to adjust the gain as much as the brightness reduced by the brightness changing unit is cancelled. Therefore, after the brightness is reduced by the brightness changing unit, the gain is considered to be larger than 1. Therefore, the AGC processing circuit 34 can change the gain and control the brightness at a finer level. Again possible.

  When such processing is performed, the first brightness adjustment level at the time when the brightness is increased by the brightness changing unit (the illumination light amount adjustment by the light emitting unit 21, the gain adjustment by the AGC processing circuit 34, and the brightness change). Unlike the second brightness adjustment level at the time when the brightness is reduced by the brightness changing unit, the first brightness adjustment level is basically It becomes more than the 2nd brightness adjustment level.

  In particular, when the brightness change by the brightness changing unit is discontinuous, the first brightness adjustment level is higher than the second brightness adjustment level. Therefore, the path shape when the brightness adjustment level is increased is different from the path when the brightness adjustment level is decreased, and the path shape is similar to a so-called hysteresis curve (FIGS. 2, 5, 8, and 12). Etc.).

  The discontinuous change in brightness caused by the brightness changer can be considered as switching in the so-called brightness adjustment mode. However, when following the path of the hysteresis shape as described above, once the mode is changed, Even if the subject's brightness changes slightly due to changes in subject distance due to blurring or movement of the subject (that is, unless the subject's brightness changes significantly), it will not return immediately to the original mode, but frequently There is an advantage that mode switching is difficult to occur.

  As will be described later, the brightness change (mode switching) by the brightness changing unit may be accompanied by a change in image quality. However, if mode switching occurs frequently, the image quality of the output image changes frequently. In addition, the observer feels uncomfortable. Therefore, such a sense of incongruity can be reduced.

  Furthermore, the brightness change (mode switching) by the brightness changing unit may require reset of the image sensor 14 as will be described later. At this time, if mode switching is performed, a frame drop occurs. Therefore, by employing a hysteresis-shaped brightness adjustment path that is unlikely to cause mode switching, the number of occurrences of frame dropping can be significantly suppressed.

  The AGC gain detection circuit 37 is used when the brightness changing unit does not increase the brightness and the gain of the AGC processing circuit 34 is “1” and the brightness needs to be further reduced. Then, the light control circuit 45 is controlled to reduce the illumination light quantity of the light emitting unit 21.

In addition, the AGC gain detection circuit 37 performs a process of setting the threshold Th based on the above-described number of gradations N (predetermined number of gradations) for image processing. As a specific example, the AGC gain detection circuit 37 further includes the output gradation number M described above and the gradation number L at which gradation drop does not occur when γ conversion is performed (since γ conversion is non-linear conversion). Based on the above, the threshold value Th is set as shown in the following Equation 1.
[Equation 1]
Th = λ × min [N, L] / M
Here, λ is a predetermined coefficient of 1 or less multiplied to adjust the value, and min [N, L] indicates that the smaller one of N and L is taken.

In addition, when simplifying Formula 1 so as not to consider gradation drop in γ conversion, Formula 1 is written as Formula 2 below.
[Equation 2]
Th = λ × N / M

  When the threshold Th is set as shown in Equation 2, the AGC gain detection circuit 37 uses the gradation number N for image processing and the gradation number M for output. As a specific numerical example, in this embodiment, N is a gradation expressed by 12 bits, and M is a gradation expressed by 10 bits. Therefore, if λ = 1, Th = 4 It becomes. Therefore, the AGC gain detection circuit 37 controls the brightness changing unit to increase the brightness of the image when the gain of the AGC processing circuit 34 becomes “4”. The gain “4” is a maximum gain value at which no gradation drop occurs when a signal having the gradation number N for image processing is converted to a signal having the gradation number M for output.

  The D / A conversion circuits 38a, 38b, and 38c convert digital image signals output from the color matrix circuit 36 into analog image signals. For example, output signal components (RGB components, YCbCr components, etc.) ) Is provided for each.

  The encoding circuit 39 performs encoding processing (specifically, compression processing) on the digital image signal output from the color matrix circuit 36.

  The image sensor driver 41 drives and controls the image sensor 14 to perform exposure and reading. The image sensor driver 41 also controls the amplification factor of the FD amplifier built in the image sensor 14. Further, the image sensor driver 41 also controls the frame rate when the image sensor 14 captures an image. In addition, when the image sensor 14 has a binning processing function, the image sensor driver 41 also controls the function.

  The actuator control circuit 42 controls the actuator 13 to drive the objective aperture 12 to change the aperture diameter of the aperture, or to insert / extract the excitation light cut filter on the optical path of the imaging optical system 11.

  The mode switching circuit 43 switches the observation mode of the endoscope apparatus 1 in accordance with the instruction signal input from the mode switching instruction switch 17. That is, when an instruction signal for setting the fluorescence observation mode is input from the mode switching instruction switch 17, the mode switching circuit 43 applies an excitation light cut filter to the actuator 13 via the actuator control circuit 42. While being inserted into the optical path, the dimming circuit 45 is caused to set parameters for fluorescence observation via the dimming control parameter switching circuit 44. Further, when an instruction signal for setting the normal light observation mode is input from the mode switching instruction switch 17, the mode switching circuit 43 applies an excitation light cut filter to the actuator 13 via the actuator control circuit 42. Are evacuated from the optical path and the dimming circuit 45 is caused to set parameters for normal light observation via the dimming control parameter switching circuit 44.

  The dimming control parameter switching circuit 44 switches the dimming control parameter set in the dimming circuit 45 according to the observation mode set by the mode switching circuit 43.

  The dimming circuit 45 detects the brightness of the image based on the imaging signal output from the process circuit 31 (that is, the signal before the processing by the AGC processing circuit 34 is performed), and the brightness of the image is appropriate. Thus, the amount of illumination light emitted by the light source device 4 is adjusted. Accordingly, the light control circuit 45 sets the light emission amounts of the R-LED 22r, G-LED 22g, and B-LED 22b, that is, the light emission balance is adjusted.

  The dimming circuit 45 includes a dimming control parameter therein, and switches the parameter set based on the control from the dimming control parameter switching circuit 44. Specifically, a parameter set that permits light emission of all of the R-LED 22r, the G-LED 22g, and the B-LED 22b is used in the normal light observation mode, and the light emission of the R-LED 22r is prohibited and excited in the fluorescence observation mode. A parameter set that allows light emission of the B-LED 22b that emits light and the G-LED 22g that emits reference light is used.

  Further, the dimming circuit 45 changes the parameter value set in each parameter set within a settable range so that the brightness of the image detected from the output of the process circuit 31 is appropriate. And the light control circuit 45 outputs a light control signal to the light emission unit 21 based on the parameter value of the parameter set according to observation mode, and supplies it from the power supply 26 to R-LED22r, G-LED22g, B-LED22b. Set the current. Thus, when a light emission signal indicating the light emission timing is output from the LED drive circuit 25 to the light emitting unit 21, the light emitting unit 21 emits illumination light at an appropriate timing according to the observation mode and an appropriate amount of illumination light. In addition, the dimming circuit 45 outputs information indicating the illumination light amount of the light emitting unit 21 to the AGC gain detection circuit 37.

  Next, FIG. 2 is a diagram showing the procedure of brightness adjustment.

  First, brightness adjustment mode switching in the present embodiment is performed by using a low amplifier mode (for example, an analog amplification gain of 1) and a high amplifier mode (for example, an analog amplification gain of 3) in an FD amplifier built in the image sensor 14. Etc.).

  And priority is given to adjustment of the brightness by the illumination light quantity of the light emitting unit 21 which is a light source. Therefore, as basic settings, the gain of the AGC processing circuit 34 is 1, and the mode of the FD amplifier is the low amplifier mode.

  By adjusting the light source light amount under such basic settings, the light source light amount is decreased when the image is too bright, and the light source light amount is increased when the image is too dark. The brightness adjustment range at this time is from the minimum illumination light amount to the maximum illumination light amount.

  If the image is still dark even when the light source light amount is the maximum illumination light amount, the gain adjustment of the AGC processing circuit 34 is performed with the second priority. In the present embodiment, since the maximum gain value at which gradation drop does not occur is 4 as described above, the brightness adjustment range by gain is from 1 to 4.

  If the image is still dark even with a gain of 4, the FD amplifier mode is set to the high amplifier mode. When the FD amplifier is set to the high amplifier mode and the signal amplification of the analog image is performed, the noise level is also amplified. Therefore, when an FD amplifier that is an analog amplifying unit is used as the brightness changing unit, the S / N ratio is lowered instead of obtaining the brightness of the image. That is, the use of the FD amplifier as the brightness changing unit has a trade-off relationship between the brightness of the image and the image quality of the output image.

  Furthermore, at this time, the amount of increase in brightness associated with the transition from the low amplifier mode to the high amplifier mode so that the brightness of the output image does not change suddenly before and after the transition from the low amplifier mode to the high amplifier mode. The AGC gain detection circuit 37 performs a process of reducing the gain in the AGC processing circuit 34 by the amount that cancels out.

  Thereafter, the AGC gain detection circuit 37 sequentially increases the gain to the AGC processing circuit 34, and increases or decreases the gain within the adjustment range from 1 to 4, so that the output image has an appropriate brightness. Make adjustments.

  On the other hand, when the brightness is reduced from the maximum brightness state where the light source light amount is the maximum illumination light amount, the FD amplifier is in the high amplifier mode, and the gain of the AGC processing circuit 34 is 4, the following is performed.

  First, the AGC processing circuit 34 performs a process for reducing the gain.

  If the image is still bright even when the gain is 1, the FD amplifier mode is set to the low amplifier mode. At this time, in order to prevent the brightness of the output image from changing abruptly before and after the transition from the high-amplifier mode to the low-amplifier mode, the amount of decrease in brightness associated with the transition from the high-amplifier mode to the low-amplifier mode is Similar to the above, the AGC gain detection circuit 37 performs the process of increasing the gain by the AGC processing circuit 34 by the amount of offset.

  Thereafter, the AGC gain detection circuit 37 causes the AGC processing circuit 34 to sequentially decrease the gain. If the image is still bright even with a gain of 1, the brightness is adjusted so that the output image has an appropriate brightness by reducing the light amount of the light source.

  Next, FIG. 3 is a diagram illustrating an example of how the brightness histogram changes on the signal processing path when the image formed on the image sensor 14 is slightly bright and dark.

  When photoelectric conversion is performed by the image sensor 14 (ST1), when the image is slightly bright, pixels are distributed from low luminance to, for example, about medium luminance (ST1H), whereas when the image is dark, the luminance is mostly reduced. Pixels are distributed, and are hardly distributed over medium luminance (ST1L).

  When an image is read from the image sensor 14, amplification is performed by an FD amplifier (ST 2). For example, when the image is slightly bright, analog amplification is not performed (ST 2 H), and when the image is dark, analog amplification is performed ( ST2L). Then, not only when the image is slightly bright, but also when the image is dark, pixels are distributed from low luminance to, for example, about medium luminance.

  When the analog image output from the image sensor 14 is converted into a digital signal by the A / D conversion circuit 32 (ST3), the same sampling is performed both when the image is slightly bright and when the image is dark, and image processing is performed. This is a digital image signal having a predetermined gradation number N for use (ST3H, ST3L).

  If these digital image signals are subjected to digital gain adjustment by the AGC processing circuit 34 and gained up (ST4), the gradation width of any digital image is widened (ST4H, ST4L).

  Thereafter, gamma correction is performed by the color matrix circuit 36 (ST5), whereby any digital image is converted into a signal having an output gradation number M, and a brightness histogram is displayed on the observation monitor 5, for example. It changes to a suitable shape (ST5H, ST5L).

  FIG. 4 is a flowchart showing the brightness adjustment process as described above.

  When this process is started, it is first determined whether or not to end the brightness adjustment process (step S1).

  Here, if not yet finished, it is determined whether or not the brightness of the currently acquired image is too bright than the appropriate brightness (step S2).

  If it is determined that the brightness is not too bright, it is determined whether or not the brightness of the currently acquired image is too dark than the appropriate brightness (step S3).

  Here, when it is determined that the image is not too dark, the brightness is appropriate. Therefore, the process returns to step S1 in order to cope with future brightness changes, and the above-described processing is repeated. Do.

  If it is determined in step S3 that the light is too dark, it is determined whether the light emission amount of the light emitting unit 21 is the maximum illumination light amount (step S4).

  Here, when it is determined that the light amount is not the maximum illumination light amount, the adjustment by the illumination light amount is prioritized to increase the light emission amount of the light emitting unit 21 (step S5), and the process returns to the above-described step S1.

  On the other hand, when it is determined in step S4 that the light intensity is already the maximum illumination light amount, the AGC gain detection circuit 37 determines whether or not the gain value acquired from the AGC processing circuit 34 is equal to or greater than the threshold Th ( Step S6).

  Here, when it is determined that the gain is less than the threshold Th, it means that there is room for increasing the gain. Therefore, the AGC gain detection circuit 37 increases the gain to the AGC processing circuit 34 (step S1). S7), the process returns to step S1 described above.

  If it is determined in step S6 that the threshold value Th is equal to or greater than the threshold Th, the AGC gain detection circuit 37 increases the brightness of the image in the brightness changing unit (step S8). That is, in the present embodiment, as described above, the mode of the FD amplifier built in the image sensor 14 is shifted from the low amplifier mode to the high amplifier mode. At this time, as described above, it is preferable to cause the AGC processing circuit 34 to perform the process of decreasing the gain by the amount that offsets the increase in brightness accompanying the transition from the low amplifier mode to the high amplifier mode. Then, the process returns to the above-described step S1.

  On the other hand, if it is determined in step S2 that the brightness of the currently acquired image is too bright than the appropriate brightness, the AGC gain detection circuit 37 determines that the gain value acquired from the AGC processing circuit 34 is It is determined whether or not 1 (that is, no gain up). (Step S9).

  Here, when it is determined that the gain value is not 1, the AGC gain detection circuit 37 reduces the gain to the AGC processing circuit 34 (step S10), and then returns to the processing of step S1 described above.

  If it is determined in step S9 that the gain value is 1, the AGC gain detection circuit 37 determines whether or not the brightness change unit is increasing the brightness of the image. Determination is made (step S11).

  If it is determined that the brightness increasing process is being performed, the AGC gain detection circuit 37 causes the brightness changing unit to decrease the brightness of the image (step S12). That is, in the present embodiment, as described above, the mode of the FD amplifier built in the image sensor 14 is shifted from the high amplifier mode to the low amplifier mode. At this time, as described above, it is preferable to cause the AGC processing circuit 34 to perform the process of increasing the gain by the amount that offsets the decrease in brightness accompanying the transition from the high amplifier mode to the low amplifier mode. Then, the process returns to the above-described step S1.

  On the other hand, when it is determined in step S11 that the brightness increase process is not being performed, the AGC gain detection circuit 37 determines whether or not the light emission amount of the light emitting unit 21 is the minimum illumination light amount (step S13).

  Here, when it is determined that the light amount is not the minimum illumination light amount, the light emission amount of the light emitting unit 21 is decreased (step S14). When it is determined that the light amount is the minimum illumination light amount, the above-described step S1 is performed as it is. Return to the process.

  Thus, if it is determined in step S1 that the process is to end, the brightness adjustment process ends.

  In the above description, the analog image is amplified by the FD amplifier built in the image pickup device 14. However, the present invention is not limited to such a configuration. For example, the video processor 3 includes an analog amplification unit. It does not matter.

  The analog image acquisition unit is not limited to the configuration including the imaging device 14 such as the endoscope 2, and may be any unit that acquires an analog image generated by imaging. Therefore, the analog image acquisition unit may be an analog image input unit in an image processing apparatus corresponding to the video processor 3, for example.

  In the above description, the normal light observation mode and the fluorescence observation mode are given as examples of the observation mode. However, for example, an NBI (Narrow Band Imaging: registered trademark) observation mode may be set.

  In the above description, the analog amplification is discontinuous two-stage switching between the low amplifier mode and the high amplifier mode. However, the present invention is not limited to this. For example, the gain changing step of analog amplification may be reduced so as to approach more continuous switching. Furthermore, the range of analog amplification may be increased. As a specific example, the analog amplification gain may be set in a range from 1 to 8, for example, in fine change steps divided into 256 steps. In this case, when the brightness is increased, the analog amplification gain is gradually increased when the digital gain by the AGC processing circuit 34 reaches 4, and conversely, when the brightness is decreased. In addition, the analog amplification gain may be decreased step by step, and the digital gain by the AGC processing circuit 34 may be decreased from 4 when the analog amplification gain has reached 1 (however, the process may be considered). The process is not limited to this process, and may be a process for maintaining the above-described hysteresis-shaped brightness adjustment path).

  According to the first embodiment, since the brightness adjustment by adjusting the light source light amount is prioritized, the output image is within a range (for example, near point) that can be handled only by adjusting the light source light amount. The image quality of the camera does not deteriorate.

  Further, when adjusting the brightness by the gain adjustment by the AGC processing circuit 34, since the adjustment is performed within the range of the threshold value Th indicating the upper limit that does not cause gradation drop in the output image, it is digitally performed. Even if the gain is adjusted, it is possible to prevent the image quality of the output image from deteriorating.

  Further, when the brightness is insufficient even when the gain reaches the threshold value Th, the brightness of the output image is reduced because the FD amplifier as the brightness changing unit is shifted from the low amplifier mode to the high amplifier mode. A wide adjustment range can be secured, and it is possible to handle far-point observation.

  On the other hand, if the brightness is excessive even when the digital gain is 1, the FD amplifier as the brightness changing unit is shifted from the high amplifier mode to the low amplifier mode. It is possible to return to a high level. For example, the image quality during near-point observation can be maintained at a high level.

  Then, when the amplifier mode of the FD amplifier is changed, the gain of the AGC processing circuit 34 is changed by an amount corresponding to the amount of change in brightness accompanying the change of the amplifier mode. Can be prevented from changing abruptly so that the viewer does not feel uncomfortable.

  In addition, the first brightness adjustment level when the FD amplifier is shifted from the low amplifier mode to the high amplifier mode is higher than the second brightness adjustment level when the FD amplifier is shifted from the high amplifier mode to the low amplifier mode. Thus, in other words, since the path shape is similar to a so-called hysteresis curve, the number of occurrences of mode switching and thus the number of changes in image quality can be reduced, thereby reducing the viewer's uncomfortable feeling.

In this way, it is possible to secure a wide brightness adjustment range so as to be able to deal with a dark subject such as far-point observation, and to obtain an endoscope apparatus that does not deteriorate the image quality of a bright subject such as near-point observation. .
[Embodiment 2]

  FIGS. 5 to 7 show Embodiment 2 of the present invention, FIG. 5 is a diagram showing a procedure of brightness adjustment, FIG. 6 is a diagram showing a pixel arrangement of the image sensor 14, and FIG. 7 is a binning process. It is a figure which shows the example of an addition object pixel.

  In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted as appropriate, and only different points will be mainly described.

  In the first embodiment described above, an FD amplifier is used as the brightness changing unit. However, in the present embodiment, the binning processing function provided in the binning frame addition circuit 35 or the image sensor 14 is used.

  As shown in FIG. 6, the image sensor 14 has a two-dimensional pixel arrangement in which the pixels 14p are arranged in, for example, the horizontal direction and the vertical direction.

  In the present embodiment, as the binning process, for example, four pixels are added as shown in FIG. 7, that is, 2 × 2 pixels (four pixels 14p) adjacent in the horizontal direction and the vertical direction are added to obtain one pixel ( It is assumed that 2 × 2 binning is performed as the pixel 14b) after binning (thus increasing the brightness of the image). Therefore, the binning process is a kind of process for changing the brightness by processing an image obtained from each pixel of the image sensor.

  Here, the binning processing can be performed in the imaging device 14 when the imaging device 14 having the binning processing function is used, or can be performed by the binning frame addition circuit 35 in the image processing circuit 33. It is.

  For example, when binning processing is performed in the image sensor 14, the number of pixels after binning processing is reduced to ¼ in the case of 2 × 2 binning as an example, and the number of readout pixels can be reduced. There is an advantage that the frame rate can be improved by shortening the period.

  On the other hand, when binning processing is performed in the binning frame addition circuit 35, it is possible to generate an image after binning processing while preserving the image before binning processing. Instead of moving in units of two pixels, it moves in units of one horizontal pixel, and when one horizontal line ends, it moves in units of one vertical pixel and moves again in units of one horizontal pixel. The number of pixels after the binning process is (m−1) × (n−, where m and n are positive integers and all pixels of the image sensor 14 are m × n pixels. 1) It becomes a pixel).

  In this way, the brightness adjustment procedure when the binning processing function is used as the brightness changing unit is substantially the same as that shown in FIG. 2 of the first embodiment described above, as shown in FIG. That is, it is only necessary to perform binning processing for four-pixel addition instead of shifting to the high amplifier mode of the first embodiment, and to turn off pixel addition by binning processing instead of shifting to the low amplifier mode.

  When the binning processing function is used as the brightness changing unit, instead of obtaining the brightness of the image, a decrease in the number of pixels (especially in the case of the binning processing in the image sensor 14) or the sharpness of the image. Degradation (for example, in the case of binning processing in the binning frame addition circuit 35 (to add pixel signals spatially close to each other)) is caused. Therefore, the use of the binning processing function as the brightness changing unit has a trade-off relationship between the brightness of the image and the image quality of the output image.

  If it is desired to avoid a decrease in the number of pixels, processing such as pixel interpolation may be added. On the other hand, when it is desired to suppress a reduction in sharpness, sharpness enhancement processing may be additionally performed.

According to the second embodiment, the same effects as those of the first embodiment described above can be obtained by performing the binning process.
[Embodiment 3]

  8 to 10 show Embodiment 3 of the present invention, FIG. 8 is a diagram showing the procedure of brightness adjustment, FIG. 9 is a timing chart showing the operation in the normal exposure mode in the fluorescence observation mode, and FIG. These are timing charts showing the operation in the long exposure mode in the fluorescence observation mode.

  In the third embodiment, the same parts as those in the first and second embodiments are denoted by the same reference numerals and the description thereof is omitted as appropriate, and only different points will be mainly described.

  In the present embodiment, an image sensor driver 41 that controls the frame rate (that is, changes in the frame period) is used as the brightness changing unit.

  As described above, the imaging device driver 41 sets the frame rate when imaging is performed by the imaging device 14 as necessary, regardless of whether the observation mode is the normal light observation mode, the fluorescence observation mode, or the NBI observation mode. It can be controlled.

  That is, for example, in the normal exposure mode in the fluorescence observation mode, as shown in FIG. 9, the light source device 4 alternately emits the excitation light and the reference light at a predetermined timing. The image sensor 14 performs exposure while the excitation light or the reference light is emitted (exposure period EXP). When the exposure period EXP in the normal exposure mode ends, the image sensor driver 41 outputs a read start signal to the image sensor 14. Upon receiving the readout start signal, the image sensor 14 shifts to the readout period RD, and sequentially outputs the captured images in units of pixels or lines.

  On the other hand, in the long exposure mode in the fluorescence observation mode as shown in FIG. 10, the light source device 4 alternately emits the excitation light and the reference light in the same manner as in the normal exposure mode. However, the reflected light from the subject obtained as a result of irradiating the reference light can be expected to have normal brightness, whereas the subject obtained via the excitation light cut filter as a result of irradiating the excitation light. The fluorescence from is considered to be extremely weak. Therefore, the AGC gain detection circuit 37 causes the excitation light irradiation period in the long exposure mode (that is, the excitation light exposure period EXP) to be longer than the excitation light irradiation period in the normal exposure mode via the LED drive circuit 25. The light emitting unit 21 is controlled to be longer. A specific example is a period of two frames in the normal exposure mode (roughly, (exposure period EXP for two frames in the normal exposure mode) + (readout period RD for one frame in the normal exposure mode)). .

  Accordingly, the AGC gain detection circuit 37 controls the light emission timing of the light emitting unit 21 via the LED drive circuit 25 and also controls the timing of the readout start signal output from the image sensor driver 41 to the image sensor 14. Yes.

  In this way, the brightness adjustment procedure when the image sensor driver 41 that controls the frame rate is used as the brightness changing unit, as shown in FIG. 8, is substantially the same as that shown in FIG. 2 of the first embodiment described above. It is. That is, the shift to the long exposure mode may be performed instead of the shift to the high amplifier mode of the first embodiment, and the shift to the normal exposure mode may be performed instead of the shift to the low amplifier mode.

  Note that, when the image sensor driver 41 that controls the frame rate is used as the brightness changing unit, instead of obtaining the brightness of the image, a decrease in the frame rate, occurrence of blurring, and the like are caused. Therefore, the use of the image sensor driver 41 that controls the frame rate as the brightness changing unit is based on the brightness of the image, at least one of the frame rate of the analog image acquired by the image sensor 14 and the image quality of the output image. This is a trade-off relationship.

  According to the third embodiment, the same effects as those of the first and second embodiments can be obtained by performing the process of changing the frame rate.

In addition, mode switching for changing the frame rate may require resetting of the image sensor 14, and in this case, frame dropping occurs with mode switching. Therefore, there is an advantage that the number of occurrences of frame dropping can be greatly suppressed by adopting a brightness adjustment path having a hysteresis shape in which mode switching hardly occurs as described above.
[Embodiment 4]

  Next, FIG. 11 shows Embodiment 4 of the present invention and is a timing chart showing the operation in the long exposure mode in the fluorescence observation mode.

  In the fourth embodiment, the same parts as those in the first to third embodiments are denoted by the same reference numerals and the description thereof is omitted as appropriate, and only different points will be mainly described.

  In the present embodiment, the frame addition processing function included in the binning frame addition circuit 35 is used as the brightness changing unit.

  First, also in this embodiment, the normal exposure mode and the long exposure mode can be set as the exposure mode. Of these, the exposure and readout operations in the normal exposure mode are the same as the operations shown in FIG. 9 of the third embodiment.

  On the other hand, the exposure and readout operations in the long exposure mode in the present embodiment are performed as shown in FIG. 11, for example.

  That is, similarly to the processing shown in FIG. 9, the frame rate at the time of imaging remains constant (therefore, resetting of the imaging element 14 is unnecessary). However, in the process of FIG. 9, the exposure is performed by alternately irradiating the excitation light and the reference light. In the present embodiment, for example, the excitation light, the excitation light, and the reference light (brighter excitation light image) When it is desired to obtain the light emission, the number of continuous light emission times of the excitation light may be increased), and exposure is performed by controlling so that the light emission order is repeated. Thus, the frame image obtained by the exposure in the emission period of the continuous excitation light in the acquired frame images (images of a plurality of frames close in time) is subjected to frame addition in the binning frame addition circuit 35 (accordingly, The frame rate of the output image is reduced).

  By performing such processing, it is possible to alternately obtain an image of reference light having a normal exposure time and an image of excitation light having a long exposure time.

  Note that, when the frame addition processing function provided in the binning frame addition circuit 35 is used as the brightness changing unit, the relationship between the brightness of the image and the trade-off is the same as in the third embodiment described above. It is at least one of image quality.

According to the fourth embodiment, the same effects as those of the third embodiment described above can be obtained, and the light emission order of the light source device 4 and the image processing content of the video processor 3 need to be changed. Since there is no need to change the frame rate at the time of imaging, there is an advantage that no frame drop occurs even if mode switching is performed.
[Embodiment 5]

  FIGS. 12 to 14 show Embodiment 5 of the present invention, FIG. 12 is a diagram showing the procedure of brightness adjustment, FIG. 13 is a diagram showing the state of the objective aperture 12 when the small-diameter aperture is opened, and FIG. These are figures which show the state of the objective aperture stop 12 at the time of large diameter aperture opening.

  In the fifth embodiment, the same parts as those in the first to fourth embodiments are denoted by the same reference numerals and the description thereof is omitted as appropriate, and only different points will be mainly described.

  In the present embodiment, the objective aperture 12 is used as the brightness changing unit.

  More specifically, the objective aperture 12 is configured as shown in FIGS. 13 and 14, for example.

  In other words, the objective diaphragm 12 includes a diaphragm substrate 12a having a light beam passage opening 12b, and a diaphragm frame 12c that is pivotally supported by the diaphragm substrate 12a via a rotation shaft 12e. . The diaphragm frame 12c is attached to the rotating shaft 12e via a shaft support part 12d, and includes a small-diameter diaphragm opening 12s and a large-diameter diaphragm opening 12l.

  The small-diameter aperture 12s is mainly used when the brightness of the subject is not insufficient (for example, near-point observation), and the image formed on the image sensor 14 is darker than in the case of the large-diameter aperture 12l. However, it has a deep depth of field.

  On the other hand, the large-diameter aperture opening 12l is mainly used when the brightness of the subject is insufficient (for example, far-point observation), and the image formed on the image sensor 14 is more than the case of the small-diameter aperture 12s. However, the depth of field is shallower than when the small-diameter aperture 12s is used.

  In the endoscope field, observation is often performed at a near-to-midpoint distance of, for example, about several tens of millimeters, and the imaging optical system 11 is often designed according to such a subject distance. Therefore, if observation from a far point of about 100 mm is performed through the large-diameter stop aperture 121, it is considered that the subject image near the far point is blurred due to the shallow depth of field. Therefore, an auxiliary lens 11a for adjusting the focus position is attached to the large-diameter aperture 12l so that the subject is not out of focus during far-point observation (however, the imaging optical system 11 has a focus adjustment function). If so, this function may be used).

  The actuator 13 drives the objective aperture 12 as described above, and a small aperture mode in which the small diameter aperture 12s as shown in FIG. 13 is positioned on the light beam passage aperture 12b, and a large diameter aperture as shown in FIG. The brightness of the optical image formed on the image sensor 14 is changed by switching between the large aperture mode in which 12l is positioned on the light beam passage opening 12b.

  In this way, the procedure of brightness adjustment when the objective aperture 12 is used as the brightness changing unit is substantially the same as that shown in FIG. 2 of the first embodiment described above, as shown in FIG. That is, the shift to the large aperture mode may be performed instead of the shift to the high amplifier mode of the first embodiment, and the shift to the small aperture mode may be performed instead of the shift to the low amplifier mode.

  When the objective aperture 12 is used as the brightness changing unit, the depth of field is reduced as described above instead of obtaining the brightness of the image. Therefore, the use of the objective aperture 12 as the brightness changing unit has a trade-off relationship between the brightness of the image and the image quality of the output image.

  According to the fifth embodiment, even when the objective aperture 12 is used, substantially the same effects as those of the first to fourth embodiments described above can be achieved.

  Of course, a combination of a plurality of configurations of the brightness changing unit of each embodiment described above may be used. In this case, there is an advantage that the dynamic range of brightness can be further expanded.

  Further, the present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope in the implementation stage. In addition, various aspects of the invention can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, you may delete some components from all the components shown by embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined. Thus, it goes without saying that various modifications and applications are possible without departing from the spirit of the invention.

DESCRIPTION OF SYMBOLS 1 ... Endoscope apparatus 2 ... Endoscope (analog image acquisition part)
3 ... Video processor (may include analog amplification unit as brightness changer)
DESCRIPTION OF SYMBOLS 4 ... Light source device 5 ... Observation monitor 6 ... Digital filing device 7 ... Input part 11 ... Imaging optical system 11a ... Auxiliary lens 12 ... Objective aperture (brightness change part)
DESCRIPTION OF SYMBOLS 12a ... Diaphragm board 12b ... Light-beam passage opening 12c ... Diaphragm frame 12d ... Shaft support 12e ... Rotary shaft 12l ... Large diameter diaphragm opening 12s ... Small diameter diaphragm opening 13 ... Actuator 14 ... Image sensor (analog image acquisition part, brightness change) (Including FD amplifier as part)
14b ... Pixel after binning 14p ... Pixel 15 ... Illumination optical system 16 ... Light guide 17 ... Mode switching instruction switch 18 ... Scope ID memory 21 ... Light emitting unit 22r ... R-LED
22b ... B-LED
22g ... G-LED
23b, 23g, 23r ... beam splitter 24 ... collimating lens 25 ... LED drive circuit 26 ... power source 31 ... process circuit 32 ... A / D converter (A / D converter)
33: Image processing circuit 34: AGC processing circuit (digital gain adjustment unit)
35 ... Binning frame addition circuit (brightness changing section)
36 .. Color matrix circuit (output image generation unit)
37 ... AGC gain detection circuit (control unit)
38a, 38b, 38c ... D / A conversion circuit 39 ... Coding circuit 41 ... Image sensor driver (brightness changing unit)
42 ... Actuator control circuit 43 ... Mode switching circuit 44 ... Dimming control parameter switching circuit 45 ... Dimming circuit

Claims (11)

An analog image acquisition unit for acquiring an analog image generated by imaging;
An A / D converter that converts the analog image into a digital image having a predetermined number of gradations;
A digital gain adjuster for adjusting the gain of the digital image;
An image for output by converting the number of gradations of the digital image gain-adjusted by the digital gain adjustment unit from the predetermined number of gradations to an output gradation number equal to or less than the predetermined number of gradations An output image generation unit for generating
A brightness changing unit that changes the brightness of the image;
It said predetermined by the number of gradations by setting a threshold below divided by the number of tones for the output, when the gain is determined whether there are more pre Ki閾 value is the threshold or more, A control unit that controls the digital gain adjustment unit so as not to increase the gain above the threshold and to increase the brightness of the image with respect to the brightness change unit;
An endoscope apparatus characterized by comprising:   The control unit causes the digital gain adjustment unit to adjust the gain when controlling the brightness change unit, so that the brightness of the image for output before and after the control of the brightness change unit is maintained substantially the same. The endoscope apparatus according to claim 1, further controlled to be controlled. The output image generation unit further performs γ conversion on the digital image gain-adjusted by the digital gain adjustment unit to generate an output image,
  The control unit is configured such that the predetermined number of gradations is N, the number of gradations at which gradation drop does not occur when performing the γ conversion is L, the number of gradations for output is M, and a predetermined coefficient equal to or less than 1. Assuming that λ and the smaller one of N and L are represented by min [N, L], the threshold Th is
                    Th = λ × min [N, L] / M
The endoscope apparatus according to claim 2, wherein the endoscope apparatus is set as follows. When the change in brightness by the brightness change unit is discontinuous, the control unit determines that the brightness adjustment level by the digital gain adjustment unit and the brightness change unit is bright in the brightness change unit. When the second brightness adjustment level that is lower than the first brightness adjustment level when the brightness is increased, the brightness changing unit is further controlled to reduce the brightness. The endoscope apparatus according to claim 3. The brightness changing unit has a trade-off relationship with at least one of the image quality of the image for output and the frame rate of the analog image acquired by the analog image acquisition unit. The endoscope apparatus according to claim 4, wherein the brightness is changed. The endoscope apparatus according to claim 5, wherein the brightness changing unit changes the brightness by processing the image. The brightness change unit includes an analog amplification unit that amplifies the analog image, and changes the brightness by changing an amplification factor of the analog image. Endoscopic device. The analog image acquisition unit includes an image sensor in which a plurality of pixels are arranged,
  The endoscope apparatus according to claim 6, wherein the brightness changing unit increases the brightness of the image by performing a binning process on an image obtained from each pixel of the image sensor. . The analog image acquisition unit acquires an analog image in a time series in units of frames,
  The endoscope apparatus according to claim 6, wherein the brightness changing unit changes the brightness by adding images of a plurality of frames that are temporally close to each other. The analog image acquisition unit acquires an analog image for each frame period,
  The endoscope apparatus according to claim 5, wherein the brightness changing unit changes the brightness by changing the frame period. The analog image acquisition unit includes: an imaging element that generates the analog image from an optical image; an imaging optical system that forms an optical image on the imaging element; and an objective aperture that changes the brightness of the optical image. Prepared,
  The endoscope apparatus according to claim 5, wherein the brightness changing unit changes the brightness by changing the brightness of the optical image by the objective aperture.

Images