Endoscope apparatus with solid-state pick-up Number:7,393,321 from the United States Patent and Trademark Office (PTO) owispatent An endoscope apparatus includes an endoscope that has a solid-state image-pickup device in which charges are accumulated in order to pick up an object image. The endoscope apparatus further comprises a memory in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the solid-state image-pickup device is stored, and a drive unit that controls the accumulation period, during which charges are accumulated in the solid-state image-pickup device, on the basis of the pieces of information on the accumulation period stored in the memory. The endoscope further includes an optical member whose surface is shaped rotationally asymmetric. Correction information stored in a memory and associated with the optical element is used to correct an output signal of the solid-state image-pickup device.<H apparatus, Endoscope, Endoscope, appar, 7393321.html, Patent, pto, 7393321

Title: Endoscope apparatus with solid-state pick-up

Abstract: An endoscope apparatus includes an endoscope that has a solid-state image-pickup device in which charges are accumulated in order to pick up an object image. The endoscope apparatus further comprises a memory in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the solid-state image-pickup device is stored, and a drive unit that controls the accumulation period, during which charges are accumulated in the solid-state image-pickup device, on the basis of the pieces of information on the accumulation period stored in the memory. The endoscope further includes an optical member whose surface is shaped rotationally asymmetric. Correction information stored in a memory and associated with the optical element is used to correct an output signal of the solid-state image-pickup device.

Patent Number: 7,393,321 Issued on 07/01/2008 to Doguchi, et al.

Inventors: Doguchi; Nobuyuki (Hino, JP), Takahashi; Yoshinori (Hachioji, JP), Imaizumi; Katsuichi (Hachioji, JP), Ozawa; Takeshi (Sagamihara, JP), Takehana; Sakae (Sagamihara, JP), Hirao; Isami (Hachioji, JP)
Assignee: Olympus Corporation (Tokyo, JP)

Appl. No.: 10/871,223

Filed: June 18, 2004

Foreign Application Priority Data


Jun 18, 2003 [JP]			2003-174001

Current U.S. Class: 600/109 ; 348/70; 348/74; 600/118; 600/160

Current International Class: A61B 1/045 (20060101)

Field of Search: 600/109,118,160 348/65,70,72,74,296,297

References Cited [Referenced By]

U.S. Patent Documents


4007488	February 1977	Morishita et al.
5001556	March 1991	Nakamura et al.
5337340	August 1994	Hynecek
5912764	June 1999	Togino
6425858	July 2002	Minami
6638215	October 2003	Kobayashi
6873360	March 2005	Kawashiri
2002/0042556	April 2002	Sugimoto et al.
2003/0001952	January 2003	Iida et al.
2003/0050532	March 2003	Doguchi
2004/0210107	October 2004	Tani et al.

Foreign Patent Documents


102 26 582	Dec., 2002	DE
0 534 1998	Mar., 1993	EP
1 258 221	Nov., 2002	EP
1 294 186	Mar., 2003	EP
10-309282	Nov., 1998	JP
11-032982	Feb., 1999	JP
11-137515	May., 1999	JP
2000-5127	Jan., 2000	JP
2001-29313	Feb., 2001	JP

Primary Examiner: Leubecker; John P
Attorney, Agent or Firm: Scully, Scott, Murphy & Presser, P.C.

Claims

What is claimed is:

1. An endoscope apparatus having a solid-state image-pickup device that picks up images of an object, comprising: an endoscope including the solid-state image-pickup device in which charges are accumulated in order to pick up an image of the object during an accumulation period; a memory in which a plurality of pieces of information on the accumulation period, during which charges are accumulated in the solid-state image-pickup device, is stored; a drive unit that controls the accumulation period, during which charges are accumulated in the solid-state image-pickup device, according to the pieces of information on the accumulation period stored in the memory; an optical member which is included in an optical system that forms an optical image on the solid-state image-pickup device and whose surface is shaped rotationally asymmetric; a correction information memory in which correction information associated with the optical property of the optical member is stored; and a correction unit that corrects an output signal of the solid-state image-pickup device according to the contents of the correction information memory.

2. The endoscope apparatus according to claim 1, wherein the pieces of information on the accumulation period are determined for respective wavelength bands of images formed by lights to be picked up by the solid-state image-pickup device.

3. An endoscope apparatus according to claim 1, wherein: a first image pickup mode in which normal light whose wavelengths fall within the visible region is employed, a second image pickup mode in which special light whose wavelengths fall within a band different from the wavelength band of normal light is employed, and the pieces of information on the accumulation period are determined relative to each of the first image pickup mode and second image pickup mode.

4. The endoscope apparatus according to claim 1, wherein the solid-state image-pickup device includes a facility for multiplying produced charges with application of a pulse-type signal so as to vary the sensitivity of the solid-state image-pickup device.

5. The endoscope apparatus according to claim 4, wherein the solid-state image-pickup device includes a charge multiplying detector that multiplies produced charges through impact ionization derived from application of the pulse-type signal by controlling the amplitude of the pulse-type signal or the number of pulses of the pulse-type signal, and that thus varies the sensitivity of the solid-state image-pickup device.

6. The endoscope apparatus according to claim 5, wherein the charge multiplying detector is interposed between a horizontal transfer register and a floating diffusion amplifier that are incorporated in the solid-state image-pickup device, or disposed at each of pixel locations in the solid-state image-pickup device.

7. The endoscope apparatus according to claim 1, further comprising a light source unit that illuminates the object.

8. The endoscope apparatus according to claim 7, wherein the light source unit illuminates the object by switching normal light employed in normal light observation and a plurality of special lights employed in special light observation.

9. The endoscope apparatus according to claim 8, wherein the special light observation refers to fluorescence observation employing fluorescence.

10. The endoscope apparatus according to claim 8, wherein the plurality of special lights include blue excitation light to be used for fluorescence and narrow-band lights whose wavelengths fall within the green or red region to be used for reflected light.

11. The endoscope apparatus according to claim 8, wherein the special light observation refers to narrow-band light observation employing narrow-band light.

12. The endoscope apparatus according to claim 8, wherein the plurality of special lights include lights whose wavelengths fall within the blue, green, or red region, and at least one of the lights whose wavelengths fall within the blue, green, or red region is narrow-band light.

13. The endoscope apparatus according to claim 8, wherein the special light observation refers to infrared light observation employing infrared light.

14. The endoscope apparatus according to claim 8, wherein the plurality of special lights include light whose wavelengths fall within the near infrared region.

15. The endoscope apparatus according to claim 1, wherein a plurality of illumination periods occur, the plurality of acclumation periods refers to accumulation periods during which charges are accumulated responsively to a plurality of lights respectively during special light observation.

16. The endoscope apparatus according to claim 15, wherein the special light observation refers to fluorescence observation employing fluorescence.

17. The endoscope apparatus according to claim 16, wherein during the fluorescence observation, the accumulation period during which charges are accumulated responsively to fluorescence is different from the accumulation period during which charges are accumulated responsively to reflected light.

18. The endoscope apparatus according to claim 17, wherein the accumulation period during which charges are accumulated responsively to fluorescence is longer than the accumulation period during which charges are accumulated responsively to reflected light.

19. The endoscope apparatus according to claim 15, wherein the special light observation refers to narrow-band light observation employing narrow-band light.

20. The endoscope apparatus according to claim 19, wherein the accumulation period during which charges are accumulated responsively to narrow-band light, of which wavelengths fall within the blue region, during narrow-band light observation is longer than the accumulation period during which charges are accumulated responsively to narrow-band light of green or red.

21. The endoscope apparatus according to claim 8, wherein the special light observation refers to infrared light observation employing infrared light.

22. The endoscope apparatus according to claim 1, wherein a plurality of illumination periods occur, the plurality of accumulation periods refers to accumulation periods during which charges are accumulated responsively to respective lights of red, green, and blue in a normal light mode.

23. The endoscope apparatus according to claim 1, wherein a plurality of illumination periods occur, the plurality of accumulation periods refers to accumulation periods during which charges are accumulated responsively to respective lights of red, green, and blue in a normal light mode or responsively to plural kinds of wavelength during a special light mode.

24. The endoscope apparatus according to claim 1, further comprising a sensitivity control unit that controls an amplification factor, at which charges in the solid-state image-pickup device are amplified, by varying a pulse-type signal.

25. The endoscope apparatus according to claim 24, wherein the sensitivity control unit includes an automatic gain control circuit that increases or decreases the amplification factor, at which charges in the solid-state image-pickup device arc amplified, by controlling the amplitude of an applied pulse such that an output signal of the solid-state image-pickup device will assume a predetermined level during special light observation.

26. The endoscope apparatus according to claim 1, wherein the drive unit applies to the solid-state image-pickup device arm electronic shutter signal that releases charges accumulated in the solid-state image-pickup device during an exposure period longer than a designated accumulation period, and thus the drive unit controls and sets the accumulation period as an alternative designated accumulation period that is longer that the designated accumulation period.

27. The endoscope apparatus according to claim 1, wherein the memory is incorporated in the endoscope.

28. An endoscope for picking up an object image, comprising: a solid-state image-pickup device in which charges are accumulated in order to pick up an image of the object; a memory in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the solid-state image-pickup device are stored in order to transmit the pieces of information on the accumulation period to driving means that controls the accumulation period during which charges are accumulated in the solid-state image-pickup device; an optical member which is included in an optical system that forms an optical image on the solid-state image-pickup device and whose surface is shaped rotationally asymmetric; a correction information memory in which correction information associated with the optical property of the optical member is stored; and a correction unit that corrects an output signal of the solid-state image-pickup device according to the contents of the correction information memory.

29. An endoscope apparatus including a solid-state image-pickup device for picking up an object image, comprising: an endoscope having the solid-state image-pickup device in which charges are accumulated in order to pick up an image of an object; memory means in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the solid-state image-pickup device is stored; driving means for controlling the accumulation period, during which charges are accumulated in the solid-state image-pickup device, on the basis of the pieces of information on the accumulation period stored in the memory means; an optical member which is included in an optical system that forms an optical image on the solid-state image-pickup device and whose surface is shaped rotationally asymmetric; a correction information memory in which correction information associated with the optical property of the optical member is stored; and a correction unit that corrects an output signal of the solid-state image-pickup device according to the contents of the correction information memory.

30. An endoscope apparatus including an image pickup device for picking up an object image, comprising: an endoscope having the image pickup device that picks up an image of the object and an optical system that includes an optical member whose surface is shaped rotationally asymmetric; a memory in which restoration data for use in restoring a change in optical performance caused by the optical member is stored; and a signal processing unit that restores an output signal of the image pickup device to its original state on the basis of the restoration data stored in the memory and that performs signal processing.

31. An endoscope apparatus including an image pickup device for picking up an object, comprising: an endoscope having an image pickup device that picks up an image of the object and an optical system that includes an optical member whose surface is shaped rotationally asymmetric; a memory in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the image pickup device and restoration information for use in restoring a change in optical performance caused by the optical member are stored; a drive unit that controls the accumulation period, during which charges are accumulated in the image pickup device, on the basis of the pieces of information on the accumulation period stored in the memory; and a signal processing unit that performs signal processing to restore an output signal of the image pickup device to its original state on the basis of the restoration information stored in the memory.

Description

This application claims the benefit of Japanese Application No. 2003-174001 filed on Jun. 18, 2003, the contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope apparatus that acquires an image using an image pickup device in which charges are accumulated in order to pick up an object image.

2. Description of the Related Art

In general, endoscope apparatus for use in endoscopic examinations comprise an endoscope such as an electronic endoscope including a solid-state image-pickup device, a processor, a light source unit, and a monitor.

The conventional endoscope apparatus has an insertional unit of an endoscope inserted into a body cavity. Illumination light emanating from a light source unit is transmitted over a light guide, which is built in the endoscope, to illuminate an object. Light reflected from the object forms an optical image on a solid-state image-pickup device by an objective lens incorporated in the distal section of the endoscope. The solid-state image-pickup device photoelectrically converts the optical image. An output signal resulting from the photoelectric conversion is inputted in a processor serving as a signal processing apparatus. The processor performs signal processing. A video signal resulting from the signal processing is transmitted to a monitor to be displayed.

In recent years, a technique as follows has come to prevail: excitation light is irradiated to a region to be observed in a living-body tissue; and light caused by auto-fluorescence of the living-body tissue induced by the excitation light or light caused by fluorescence induced by an chemical agent injected into a living body is captured as a two-dimensional image by a solid-state image-pickup device. The fluorescence image is used to assess the condition of a lesion such as a carcinoma (kind of lesion or humectant range). Development of a fluorescence observation system for enabling observation of fluorescence is under way.

In auto-fluorescence, when excitation light is irradiated to a living-body tissue, the fluorescence is generated at the long wavelength side due to the excitation light. Fluorescence materials contained in a living body include, for example, nicotinamide adenine dinucleotide (NADH), flavine mononucleotide (FMN), and collagen. Recently, the correlation between diseases and materials that are intrinsic to living bodies and that generate fluorescence is being investigated. Observation of fluorescence enables diagnosis of carcinomas or the like.

Talking of chemifluorescence or fluorescence caused by a chemical agent, fluorescence substances to be injected into a living body include hematoporphyrin (HpD), photofrin, and .alpha.-amino levulinic acid (ALA). These chemical agents have a specific property of accumulating in a carcinoma or the like. Therefore, when any of the agents is injected preliminarily into a living body in order to observe fluorescence, a lesion can be diagnosed. Other technique is such that a fluorescence substance is administered to a monoclonal antibody and accumulated in a lesion by utilizing antigen-antibody reaction.

A fluorescence observation system disclosed in Japanese Unexamined Patent Application Publication No. 2001-29313 aims at acquisition of a fluorescence monochrome image, in the system, the sensitivity of a CCD incorporated in the distal section of an endoscope is varied and controlled such that the average brightness values exhibited by a fluorescence image, that is, the average brightness of an image displayed on a monitor will remain constant.

According to the conventional fluorescence observation system, when excitation light is irradiated to the mucosa of the bronchus or the alimentary tract, auto-fluorescence occurs. The intensity of light caused by auto-fluorescence is much feebler than that of reflected light resulting from irradiation of normal illumination light. Moreover, the ratio of the intensity of auto-fluorescence to the intensity of reflected light may greatly vary depending on a region such as the superior alimentary tract (esophagus and stomach) or the inferior alimentary track (large intestine).

SUMMARY OF THE INVENTION

An-endoscope apparatus in accordance with the present invention comprises: an endoscope having a solid-state image-pickup device in which charges are accumulated in order to pick up an object image; a memory in which a plurality of pieces of information on the accumulation period during which charges are accumulated in the solid-state image-pickup device are stored; and a drive unit that controls the accumulation period, during which charges are accumulated in the solid-state image-pickup device, on the basis of the pieces of information on the accumulation period stored in the memory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 11B are concerned with a first embodiment of the present invention; FIG. 1 is a block diagram schematically showing the configuration of an endoscope apparatus in accordance with a first embodiment of the present invention;

FIG. 2 is a block diagram showing a solid-state image-pickup device realized with a charge-coupled device and employed in the first embodiment of the present invention;

FIG. 3A, FIG. 3B, and FIG. 3C are timing charts indicating the timings of a sensitivity control pulse .phi.CMD and horizontal transfer pulses .phi.S1 and .phi.S2;

FIG. 4 is an explanatory diagram showing the relationship between a CMD applied voltage and a CMD amplification factor that relate to the sensitivity of a CCD;

FIG. 5A to FIG. 5F indicate timings to signify the actions to be performed in order to drive a CCD in a special light mode;

FIG. 6A to FIG. 6F indicate timings to signify the actions to be performed in order to drive a CCD in a normal light mode;

FIG. 7 is a graph indicating the property or sensitivity of a CCD (output signal to be sent to a monitor);

FIG. 8 is a graph indicating the property or sensitivity of a CCD (signal-to-noise ratio);

FIG. 9 is a plan view showing the structure of an RGB rotary filter;

FIG. 10 is a graph indicating the spectral characteristic of light emitted from a light source unit during fluorescence observation;

FIG. 11A is a graph indicating the spectral characteristics of fluorescence and reflected light employed in fluorescence observation;

FIG. 11B is a flowchart describing the outline of a process to be executed in the first embodiment;

FIG. 12 is a block diagram schematically showing the configuration of an endoscope apparatus in accordance with a second embodiment of the present invention;

FIG. 13 is a block diagram schematically showing the configuration of an endoscope apparatus in accordance with a third embodiment of the present invention;

FIG. 14 to FIG. 18 are concerned with a fourth embodiment of the present invention;

FIG. 14 is a block diagram schematically showing an endoscope apparatus in accordance with the fourth embodiment of the present invention;

FIG. 15A to FIG. 15E indicate timings to signify the actions to be performed in order to drive a CCD;

FIG. 16 is a plan view showing the structure of an RGB rotary filter;

FIG. 17 is a graph indicating the spectral characteristic of light emitted from a light source unit during narrow-band light observation;

FIG. 18 is a graph indicating the spectral characteristic of reflected light employed in narrow-band light observation;

FIG. 19 is a block diagram schematically showing the configuration of an endoscope apparatus in accordance with a fifth embodiment of the present invention; and

FIG. 20 is a block diagram schematically showing the configuration of an endoscope apparatus in accordance with a sixth embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, embodiments of the present invention will be described below.

First Embodiment

Referring to FIG. 1 to FIG. 11, a first embodiment of the present invention will be described below.

(Configuration)

To begin with, the configuration of the first embodiment will be described below.

As shown in FIG. 1, an endoscope apparatus 1 in accordance with the first embodiment comprises an electronic endoscope (hereinafter, an endoscope) 2, a processor 3, and a monitor 6.

The endoscope 2 is freely detachably connected to the processor 3. Moreover, the processor 3 includes a signal processing unit 4 and a light source unit 5. The light source unit may be separated from the processor.

The monitor 6 is connected to the processor 3. A video signal treated by the processor 3 is transmitted to the monitor 6.

The endoscope 2 has an elongated insertional unit 11 that is inserted into a patient's body cavity.

For examination of the alimentary tract, bronchus, cranio-cervix (pharynx), or bladder, the insertional unit 11 is formed with a soft member. For examination of the abdominal or thoracic cavity or the uterus, the insertional unit 11 is formed with a rigid member.

Moreover, the endoscope 2 has a charge-coupled device (hereinafter CCD) 19, which includes a facility for varying an amplification factor as described later, as a solid-state image-pickup device incorporated in the distal section 15 of the insertional unit 11.

A light guide 12 by which illumination light is transmitted, a CCD driving signal line 13 by which a CCD driving signal is transmitted and which is coupled to the CCD 19, and a CCD output signal line 14 by which a CCD output signal resulting from photoelectric conversion performed by the CCD 19 is transmitted are run through the insertional unit 11.

The distal end of the light guide 12 is fixed in the distal section 15 of the insertional unit 11. An illumination lens 16 is arranged on an illumination window opposite to the distal end of the light guide.

By the light guide 12, illumination light emanating from the light source unit 5 is transmitted to the distal end of the light guide 12. An object such as an intracavitary lesion is illuminated with the illumination light emitted from the distal end through the illumination lens 16.

An objective lens 17, an excitation light cut filter 18, and the CCD 19 are arranged behind an observation (image picking-up) window adjoining the illumination window in the distal section 15.

The objective lens 17 forms an optical image of an object on the image picking-up (light receiving) surface of the CCD 19 that serves as an image sensor and that is located at the position of the image plane.

The excitation light cut filter 18 is located in front of the CCD 19, and passes light, of which wavelengths fall within a specific band, that is, fluorescence alone. According to the present embodiment, the excitation light cut filter 18 has a property of passing auto-fluorescence (whose wavelengths are equal to or higher than 500 nm) caused by fluorescence of a living-body tissue but of intercepting excitation light.

In other words, according to the present embodiment, light reflected from an object and auto-fluorescence caused by fluorescence of the object form images on the light receiving surface of the CCD 19 via the objective lens 17 and excitation light cut filter 18.

Referring to FIG. 1, an illumination and image-pickup optical system, that is, an optical system including the illumination lens 16, objective lens 17, CCD 19, and the like is disposed in order to realize an endoscope of a direct-vision type that emits illumination light forward in the longitudinal direction of the insertional unit 11 and that offers a field of view for observation (image picking-up) in the forward direction. Alternatively, the optical system may be disposed in order to realize an endoscope of an oblique-vision or side-vision type.

Moreover, the CCD 19 is connected to CCD driving means 31 included in the signal processing unit 4 incorporated in the processor 3 via the driving signal line 13. When a driving signal produced by the CCD driving means 31 is applied to the CCD 19, an electronic shutter is controlled, signal charges are accumulated, the sensitivity of the CCD 19 is controlled, and image data is read.

An object image formed on the light receiving surface of the CCD 19 by the objective lens 17 and excitation light cut filter 18 is photoelectrically converted pixel by pixel by the CCD 19. Thereafter, the resultant signal is transferred and transmitted from a floating diffusion amplifier. The output signal of the CCD 19 is transferred to an analog processing circuit 33 included in the signal processing unit 4 incorporated in the processor 3 via the CCD output signal line 14.

Moreover, a storage device 20 is incorporated inside, for example, a connector 29 formed at the proximal end of the endoscope 2. The storage device 20 may be incorporated inside, for example, an operating unit or the like other than the connector 29. The storage device 20 comprises a CPU 21 and a memory 22.

The memory 22 is formed with, for example, a nonvolatile EEPROM, a flash memory, or any other electrically reprogrammable semiconductor memory. Data can be electrically written in or read from the memory 22.

The CPU 21 controls reading or writing of data in or from the memory 22, and controls transmission or reception (communication) of data to or from the processor 3.

The accumulation periods (electronic shutter speeds) during which charges are accumulated responsively to three kinds of wavelength of red, green, and blue in a normal light mode, and the accumulation periods (electronic shutter speeds) during which charges are accumulated responsively to three kinds of wavelength Ex1 (fluorescence), Ex2 (green reflected light), and Ex3 (red reflected light) in a special light mode (fluorescence observation) are stored in the memory 22.

Instead of the accumulation periods, a charge clear period, a ratio of the accumulation periods during which charges are accumulated responsively to three kinds of wavelength of red, green, and blue or three kinds of wavelength Ex1, Ex2, and Ex3 may be stored in the memory 22.

As for the accumulation periods during which charges are accumulated responsively to a fluorescence wavelength and two kinds of reflected light wavelength and which are stored in the memory 22, the accumulation period during which charges are accumulated responsively to fluorescence is set longer than those during which charges are accumulated responsively to two kinds of respective reflected light wavelength.

The accumulation periods during which charges are accumulated responsively to three kinds of wavelength of red, green, and blue in the normal light mode and which are stored in the memory 22 are set shorter than those determined for an endoscope including a typical CCD other than a sensitivity-valiable CCD serving as the CCD 19.

The accumulation periods during which charges are accumulated responsively to three kinds of wavelength in the special light mode and which are stored in the memory 22 are set to optimal values according to whichever of types of endoscopes (for examination of the bronchus, superior alimentary tract, inferior alimentary tract, cranio-cervix, or bladder) is adopted. This is because the intensities of fluorescence and reflected light differ from region to region. The accumulation periods are determined for the three kinds of wavelength in relation to each region such that the intensities will remain at equal levels.

Aside from the accumulation periods, other data relevant to the endoscope is stored in the memory 22.

The stored data includes, for example, an endoscope model (type) name, an endoscope serial number, white balance set values (for normal lights and for special lights (fluorescence observation)), the number of times by which the endoscope is connected to the processor and the power supply thereof is turned on, information on a forceps channel lying through the endoscope, the outer diameter of the distal section of the endoscope, and the outer diameter of the insertional unit of the endoscope.

According to the present embodiment, the signal processing unit 4 comprises a CPU 30, CCD driving means 31, a CCD sensitivity control means 32, an analog processing circuit 33, an analog-to-digital (A/D) converter 34, a digital processing circuit 35, a digital-to-analog (D/A) converter 36, and a photometry means 37.

The light source unit 5 comprises a lamp 40, a diaphragm 41, diaphragm control means 42, an RGB rotary filter 43, a motor 44, a condenser lens 45, a rotary filter switching means 46, an RGB rotary filter control means 47, and a mode switching means 50.

When a user connects the endoscope 2 to the processor 3, the CPU 30 controls to read various kinds of data from the memory 22 via the CPU 21. In this case, the various kinds of data stored in the memory 22 are transmitted to the CPU 30 via the CPU 21. The CPU 30 reads various kinds of data from the memory 22.

Moreover, the CPU 30 transmits to the CCD driving means 31 the data representing accumulation periods, during which charges are accumulated responsively to three kinds of wavelength in the normal light mode and special light mode alike (fluorescence observation), and which are obtained from the memory 22.

Furthermore, the CPU 30 transmits the endoscope model name, serial number, white balance set values (for normal light and for special light), and others to the digital processing circuit 35.

Next, the CCD 19 will be described below.

The CCD 19 employed in the present embodiment is realized with a sensitivity-variable CCD that utilizes an impact ionization phenomenon and that is described in, for example, the U.S. Pat. No. 5,337,340 "Charge Multiplying Detector (CMD) suitable for small pixel CCD image sensors."

The CCD 19 has a charge multiplying detector interposed between a horizontal transfer register and a floating diffusion amplifier therein or disposed at each of pixel locations therein. When the processor 3 applies a pulse of a high-strength electric field to the charge multiplying detector, each signal charge gains energy from the high-strength electric field and collides with electrons in the valence band. Consequently, impact ionization occurs to produce a new signal charge (secondary electron).

For example, when an avalanche condition is utilized, application of one pulse causes a chain reaction to produce a secondary electron. When impact ionization is utilized, application of a relatively low-voltage pulse causes production of a hole-electron pair.

If the CCD 19 has the charge multiplying detector disposed in a stage preceding the floating diffusion amplifier, the number of signal charges can be freely increased by controlling the voltage level (amplitude) of a pulse to be applied.

On the other hand, when the charge multiplying detector is disposed at each of the pixel locations, the number of signal charges can be freely increased by controlling the voltage level (amplitude) of a pulse to be applied or the number of pulses to be applied.

In the present embodiment, a monochrome CCD of a full frame transfer (FFT) type having, as shown in FIG. 2, a charge multiplying detector interposed between a horizontal transfer register and a floating diffusion amplifier is adopted as the CCD 19.

The CCD 19 includes an image area 60, an optical black (OB) section 61, a horizontal transfer register 62, a dummy 63, a charge multiplying detector 64, and a floating diffusion amplifier 65. The charge multiplying detector 64 comprises nearly the same number of cells as the number of cells included in the horizontal transfer register 62 or comprises the number of cells that is twice larger than the number of cells included in the horizontal transfer register 62.

Signal charges produced at the respective pixel locations in the image area 60 are transferred to the horizontal transfer register 62 in response to vertical transfer pulses .phi.P1 and .phi.P2, which is shown in FIG. 5B, in units of signal charges juxtaposed on one horizontal line.

The signal charges transferred to the horizontal transfer register 62 are transferred to the dummy 63 and charge multiplying detector 64 in response to horizontal transfer pulses .phi.S1 and .phi.S2 that are shown in FIG. 3B and FIG. 3C (and FIG. 5D). A sensitivity control pulse .phi.CMD shown in FIG. 3A or FIG. 5C is applied to each of the plurality of cells constituting the charge multiplying detector 64, whereby the signal charges are transferred from one cell to an adjoining cell and are sequentially amplified step by step. The resultant signal charges are sequentially transferred to the floating diffusion amplifier 65.

The floating diffusion amplifier 65 converts the signal charges received from the charge multiplying detector 64 into a voltage signal, and transmits the signal as a CCD output signal to a component outside the CCD 19. Namely, the CCD output signal sent from the floating diffusion amplifier 65 is transferred to the processor 3 via the CCD output signal line 14.

According to the present embodiment, the phase correlation between the sensitivity control pulse .phi.CMD and the horizontal transfer pulses .phi.S1 and .phi.S2 are, as shown in FIG. 3A to FIG. 3C, such that: before the horizontal transfer pulse .phi.S1 rises, the sensitivity control pulse .phi.CMD rises; and before the horizontal transfer pulse .phi.S1 falls, the sensitivity control pulse .phi.CMD falls. Moreover, when the sensitivity control pulse .phi.CMD falls, the horizontal transfer pulse .phi.S2 rises. When the sensitivity control pulse .phi.CMD rises, the horizontal transfer pulse .phi.S2 falls.

Sensitivity or an amplification factor obtained by the charge multiplying detector 64 can be varied by changing the voltage level (amplitude) of the sensitivity control pulse .phi.CMD applied from the CCD driving means 31 to the charge multiplying detector 64.

When the voltage to be applied to the charge multiplying detector 64 exceeds a certain threshold Vth, charge amplification starts and the sensitivity or amplification factor offered by the charge multiplying detector 64 exponentially increases as indicated in FIG. 4.

When the sensitivity control pulse .phi.CMD ranges from (0)V to the threshold Vth, signal charges are not amplified but are merely transferred from the charge multiplying detector 64. The threshold that causes charge amplification to start or the sharpness in an increase in the sensitivity or amplification factor relative to the applied voltage can be varied in the stage of designing.

The CCD 19 has an electronic shutter facility. The principles of an electronic shutter lie in, like those of an electronic shutter included in a typical CCD, a substrate discharge technique that utilizes a change in an overflow characteristic caused by a variation of the voltage level (amplitude) of a pulse to be applied to an overflow drain.

During a period during which an electronic shutter pulse .phi.OFD to be applied to the overflow drain is transferred to the CCD 19 (H-level), the signal charge at each of the pixel locations in the CCD 19 (including a noise charge) is released into a substrate. No signal charge is accumulated in each of the pixel locations in the CCD 19.

On the other hand, during a period during which the electronic shutter pulse .phi.OFD is not transferred to the CCD 19, a signal charge is accumulated in each of the pixel locations in the CCD 19.

Moreover, since the pulse duration of the pulse .phi.OFD and the number of pulses .phi.OFD can be set to any values, the accumulation period during which signal charges are accumulated in the CCD 19 can be controlled to any period.

FIG. 5A to FIG. 5F indicate the timings of driving signals that are applied to the CCD 19 responsively to one of three kinds of wavelength in the special light mode, and the timing of an output signal of the CCD 19.

FIG. 5A indicates the action of the RGB rotary filter 43 in the special light mode. FIG. 5B indicates the timing of vertical transfer pulses .phi.P1 and .phi.P2 in the special light mode. FIG. 5C indicates the timing of a sensitivity control pulse .phi.CMD in the special light mode. FIG. 5D indicates the timing of horizontal transfer pulses .phi.S1 and .phi.S2 in the special light mode. FIG. 5E indicates the timing of an electronic shutter pulse .phi.OFD in the special light mode. FIG. 5F indicates the timing of an output signal of the CCD 19 in the special light mode.

FIG. 6A to FIG. 6F indicate the timings of driving signals that are applied to the CCD 19 responsively to one of three kinds of wavelength in the normal light mode, and the timing of an output signal of the CCD 19. FIG. 6A indicates the action of the rotary filter 43 in the normal light mode. FIG. 6B indicates the timing of the vertical transfer pulses .phi.P1 and .phi.P2 in the normal light mode. FIG. 6C indicates the timing of the sensitivity control pulse .phi.CMD in the normal light mode. FIG. 6D indicates the timing of the horizontal transfer pulses .phi.S1 and .phi.S2 in the normal light mode. FIG. 6E indicates the timing of an electronic shutter pulse .phi.OFD in the normal light mode. FIG. 6F indicates the timing of an output signal of the CCD 19 in the normal light mode.

The CCD driving means 31 transmits as driving signals the vertical transfer pulses .phi.P1 and .phi.P2, sensitivity control pulse .phi.CMD, horizontal transfer pulses .phi.S1 and .phi.S2, and electronic shutter pulse .phi.OFD.

In FIG. 5A to FIG. 5F and FIG. 6A to FIG. 6F, one cycle refers to one cycle of one of three kinds of wavelength. Namely it refers to a one-third of one rotation of the action of the RGB rotary filter 43.

A period TE (special light mode) and a period TE' (normal light mode) refer to exposure periods. During the exposure period, the CCD 19 photoelectrically converts light that is reflected from an object and falls on the light receiving surface of the CCD 19, and then accumulates resultant signal charges.

During the period TD (special light mode) or TD' (normal light mode), the signal charges accumulated in the image area 60 during the period TE or TE' are transferred to the horizontal transfer register 62 in units of the signal charges juxtaposed on one horizontal line in response to the vertical transfer pulses .phi.P1 and .phi.P2. The signal charges are then transferred to the dummy 63, charge multiplying detector 64, and floating diffusion amplifier 65 in response to the horizontal transfer pulses .phi.S1 and .phi.S2. The floating diffusion amplifier 65 converts the charges into voltage levels, and a signal assuming the voltage levels is then transmitted.

In the special light mode, for the RGB rotary filter 43, the exposure period TE and interception period TD are, as shown in FIG. 5A, determined to constitute a one-cycle period.

The electronic shutter pulse .phi.OFD shown in FIG. 5E has a pulse duration TC, during which it remains in H-level, at the beginning of the exposure period TE shown in FIG. 5A, whereby the charges at the respective pixel locations in the CCD 19 are cleared. Thereafter, the electronic shutter pulse .phi.OFD goes low to thus indicate the start of a charge accumulation period TA during which charges are accumulated at the respective pixel locations in the CCD 19.

During the interception period TD that is a CCD 19 reading period shown in FIG. 5A, the CCD driving means 31 transmits the vertical transfer pulses .phi.P1 and .phi.P2 shown in FIG. 5B, the sensitivity control pulse .phi.CMD shown in FIG. 5C, and the horizontal transfer pulses .phi.S1 and .phi.S2 shown in FIG. 5D. Consequently, the CCD 19 is read and an output signal of the CCD 19 shown in FIG. 5F is obtained.

The CCD driving means 31 varies the voltage level (amplitude) of the sensitivity control pulse .phi.CMD shown in FIG. 5C according to data sent from the CCD sensitivity control means 32. The CCD driving means 31 transmits the sensitivity control pulse .phi.CMD shown in FIG. 5C to the CCD 19, the sensitivity control pulse .phi.CMD being in a certain phase relation with the horizontal transfer pulses .phi.S1 and .phi.S2 as shown in FIG. 5D (see FIG. 3A to FIG. 3C for details).

Consequently, in the special light mode, the CCD driving means 31 changes the voltage level (amplitude) of the sensitivity control pulse .phi.CMD to be applied to the charge multiplying detector 64 and controls the CCD 19 such that a desired sensitivity or amplification factor can be attained.

In the normal light mode, for the RGB rotary filter 43, the exposure period TE' and interception period TD' are determined as shown in FIG. 6A within a one-cycle period.

The electronic shutter pulse .phi.OFD shown in FIG. 6E has a pulse duration TC', during which it remains in H-level, at the beginning of the exposure period TE' shown in FIG. 6A, whereby the charges at the pixel locations in the CCD 19 will be cleared. Thereafter, the electronic shutter pulse .phi.OFD goes low to thus indicate the start of the charge accumulation period TA' during which charges are accumulated at the respective pixel locations in the CCD 19.

During the interception period TD' shown in FIG. 6A that is the CCD 19 reading period TD', the CCD driving means 31 transmits the vertical transfer pulses .phi.P1 and .phi.P2 shown in FIG. 6B and the horizontal transfer pulses .phi.S1 and .phi.S2 shown in FIG. 6D. Consequently, the CCD 19 is read and an output signal of the CCD 19 shown in FIG. 6F is obtained.

In the normal light mode, the CCD driving means 31 does not transmit the sensitivity control pulse .phi.CMD as shown in FIG. 6C. Otherwise, the CCD driving means 31 may transmit a sensitivity control pulse .phi.CMD whose voltage level is equal to or lower than the threshold Vth.

Consequently, in the normal light mode, the charge multiplying detector 64 does not amplify charges and the sensitivity or amplification factor is set to 1 or a magnification of 1.

Incidentally, when a typical endoscope in which a sensitivity-valiable CCD such as the CCD 19 is not included is connected to the processor 3, the CCD driving means 31 performs actions defined for the normal light mode shown in FIG. 6.

The electronic shutter pulse .phi.OFD shown in FIG. 5E and FIG. 6E is used to release the charges accumulated at the pixel locations into a substrate. The electronic shutter pulse .phi.OFD having any pulse duration or any number of electronic shutter pulses .phi.OFD is transmitted from the start of the exposure period (start of the interception period) to the end thereof.

The periods TE and TE' shown in FIG. 5A to FIG. 5F and FIG. 6A to FIG. 6F are periods during which charges are accumulated in the image area 60 of the CCD 19 according to an object image. During the periods TC and TC' corresponding to the pulse duration shown in FIG. 5E and FIG. 6E, no signal charge is accumulated.

When no electronic shutter pulse .phi.OFD shown in FIG. 5E and FIG. 6E transmits, accumulation of signal charges at the respective pixel locations in the CCD 19 is started. The period TA (=period TE-period TC) (special light mode) or TA' (=period TE'-period TC') (normal light mode) from the start of the accumulation to the start of the interception period refers substantially to the accumulation period.

The electronic shutter pulse .phi.OFD to be applied responsively to each light wavelength is transmitted to the CCD 19. Herein, the pulse duration and the number of electronic shutter pulses .phi.OFD are determined based on the accumulation period, during which charges are accumulated responsively to each light wavelength from the CPU 30.

For example, assume that the three kinds of wavelength employed in the special light mode are three kinds of wavelength Ex1, Ex2, and Ex3, and that the accumulation periods during which charges are accumulated responsively to the three kinds of wavelength in the special light mode and which are stored in the memory 22 are TA(Ex1)=TE, TA(Ex2)=0.2*TE, and TA(Ex3)=0.1*TE respectively. In this case, these data representing the accumulation periods are transmitted to the CCD driving means 31 via the CPU 30. The pulse duration that is transmitted from the CCD driving means 31 to the CCD 19 in order to clear charges is set to OFD(Ex1)=0*TE, OFD(Ex2)=0.8*TE, or OFD(Ex3)=0.9*TE.

Moreover, assume that the accumulation periods during which charges are accumulated responsively to three kinds of wavelength in the normal line mode and which are stored in the memory 22 are, for example, TA'(R)=0.7*TE', TA'(G)=0.7*TE', and TA'(B)=0.7*TE' respectively. In this case, these data representing the accumulation periods are transmitted to the CCD driving means 31 via the CPU 30. The pulse duration that is transmitted from the CCD driving means 31 to the CCD 19 in order to clear charges is set to OFD(R)=OFD(G)=OFD(B)=0.3*TE'.

The analog processing circuit 33 includes a preamplifier that amplifies a CCD output signal of the CCD 19 and a Correlated Double Sampling (CDS) circuit that performs correlated double sampling so as to minimize a CCD noise. A signal resulting from CDS performed in the analog processing circuit 33 is transmitted to an A/D converter 34, and then converted into a digital form. An output of the A/D converter 34 is transmitted to the digital processing circuit 35.

The digital processing circuit 35 performs signal processing, such as clamping, white balance adjustment, color conversion, electronic zooming, gamma conversion, and image enhancement, on a video signal received from the A/D converter 34, and transmits the resultant signal to a D/A converter 36.

The D/A converter 36 converts the video signal received from the digital processing circuit 35 from the digital form into an analog form, and transmits the resultant signal.

Based on the analog video signal transmitted from the D/A converter 36, various kinds of images are displayed on the monitor 6. Moreover, the video signal transmitted from the D/A converter 36 is also transferred to an image recorder that is peripheral equipment and that is hot shown.

White balance adjustment and color conversion are different between the normal light mode and special light mode (fluorescence observation). The digital processing circuit 35 performs white balance adjustment and color conversion that are differentiated based on a mode switching signal sent from the mode switching means 50.

During color conversion in the special light mode (fluorescence observation), image data items produced based on a fluorescence wavelength and two kinds of reflected light wavelength are respectively multiplied by certain matrix coefficients. Consequently, a synthetic image is constructed based on the fluorescence wavelength and two kinds of reflected light wavelength.

Moreover, during white balance adjustment, white balance set values stored in the memory 22 are inputted to the digital processing circuit 35 via the CPU 30. Consequently, a white balance is attained in a different manner between the normal light mode and special light mode (fluorescence observation).

The photometry means 37 receives a video signal from the analog processing circuit 33, and calculates respective averages of brightness values exhibited by a screen image produced based on three kinds of wavelength of the normal light mode and special light mode (fluorescence observation).

Herein, the photometry means 37 calculates the average of brightness values by changing methods, which are associated with the normal light mode and special light mode (fluorescence observation), according to a mode switching signal sent from the mode switching means 50.

In the normal light mode, the photometry means 37 calculates a luminance signal level on the basis of the averages of the brightness values exhibited by screen images produced based on the three kinds of wavelength of red, green, and blue. The photometry means 37 then transmits the luminance signal to the diaphragm control means 42 included in the light source unit 5.

In the special light mode (fluorescence observation), the photometry means 37 calculates average values of brightness values exhibited by screen images produced based on three kinds of wavelength Ex1, Ex2, and Ex3, and generates an average of brightness values exhibited by a synthetic image constructed from the screen images produced based on the fluorescence wavelength and two kinds of reflected light wavelength. The generated average value is transmitted to the CCD sensitivity control means 32 and diaphragm control means 42 respectively.

The CCD sensitivity control means 32 controls the charge multiplying detector 64 included in the CCD 19 to execute automatic gain control (AGC) in the special light mode. The CCD sensitivity control means 32 controls the sensitivity or amplification factor offered by the charge multiplying detector 64 included in the CCD 19 such that an average of the levels of an output signal of the CCD 19 will be set to a desired value according to a change in the intensity of light reflected from an object and incident on the light receiving surface of the CCD 19.

The CCD sensitivity control means 32 receives from the photometry means 37 the average of brightness values, which are exhibited by a synthetic image constructed of a fluorescence image and reflected light images, and compares the average with an operator-designated monitor brightness level of an image to be displayed on the monitor.

An operator can designate a target value of a brightness level of a screen image to be displayed on the monitor using a brightness designating means 39 included in the light source unit 5. Incidentally, the brightness designating means 39 may be included in the signal processing unit 4.

The CCD sensitivity control means 32 compares the average of brightness values exhibited by a screen image with the operator-designated value (target value) of a brightness level. Based on the result of the comparison (whether the average of brightness values is larger or small), the CCD sensitivity control means 32 calculates the voltage level (amplitude) of the sensitivity control pulse .phi.CMD, which the CCD driving means 31 transmits to the charge multiplying detector 64 included in the CCD 19, and transmits the voltage level to the CCD driving means 31.

An AGC method adopted by the CCD sensitivity control means 32 will be described below.

The relationship between the voltage level of the sensitivity control pulse .phi.CMD to be transmitted to the charge multiplying detector 64 and the sensitivity or amplification factor, which is shown in FIG. 4, is approximated by the following expression: M(V)=CExp{.alpha.(V-Vth)} (1) Wherein, M(V) denotes the sensitivity or amplification factor attained when the voltage level (amplitude) of the sensitivity control pulse .phi.CMD is V(v), and Vth denotes a threshold voltage that initiates charge amplification. C, .alpha., and Vth denote constants inherent to each device and variable in the stage of designing.

When an image formed by light reflected from an object exhibiting a certain light intensity is picked up by a CCD, an average of brightness values exhibited by a screen image varies exponentially along with an increase or decrease in the voltage level of the sensitivity control pulse .phi.CMD. Based on this fact, the CCD sensitivity control means 32 varies (increases or decreases) the voltage level (amplitude) of the sensitivity control pulse .phi.CMD along with the changes in the intensities of light resulting from fluorescence of the object and of light reflected from the object such that the average of brightness values exhibited by a fluorescence image and an operator-designated target value of a brightness level of an image to be displayed on the monitor will be agreed with each other. Moreover, the CCD sensitivity control means 32 controls the CCD driving means 31 such that when the voltage level of the sensitivity control pulse .phi.CMD is equal to or smaller than a threshold, an applied voltage will be 0(V).

FIG. 7 or FIG. 8, shows the relationship between an output signal to be transmitted to the monitor 6, or between a signal-to-noise, and the intensity of light reflected from an object, which is established when a sensitivity or an amplification factor is varied by changing the voltage level (amplitude) of the sensitivity control pulse .phi.CMD to be transferred to the charge multiplying detector 64.

As seen from the drawings, when the light reflected from an object is feeble (the intensity of light reflected from an object is low), if the sensitivity or amplification factor is set to 1 (no amplification), the brightness of an image on the monitor is low and the image quality (signal-to-noise ratio) thereof is low. As the sensitivity or amplification factor increases, the brightness of the image on the monitor increases and the image quality thereof gets higher.

The mode switching means 50 is a switch allowing an operator to freely select either of-observation modes, that is, either of the normal light mode and special light mode (fluorescence observation).

The mode switching means 50 may be located on the processor 3, light source unit 5, endoscope, 2 or all of them.

A mode switching signal sent from the mode switching means 50 is transmitted to each of the rotary filter switching means 46, RGB rotary filter control means 47, photometry means 37, CCD driving means 31, CCD sensitivity control means 32, and digital processing circuit 35.

Next, the light source unit 5 will be described below.

The lamp 40 emits illumination light which is constituted of a xenon lamp, a halogen lamp, an LED, an LD (semiconductor laser), or the like.

The condenser lens 45 concentrates illumination light, which is introduced from the lamp 40 via the diaphragm 41 and RGB rotary filter 43, on the back end of the light guide 12.

The diaphragm 41 and RGB rotary filter 43 are interposed between the lamp 40 and condenser lens 45. The RGB rotary filter 43 is coupled to the rotation shaft of the motor 44 such that it can be rotated, and controlled to rotate at a predetermined speed by the RGB rotary filter control means 47.

The RGB rotary filter control means 43 controls to a predetermined rotating speed the RGB rotary filter 43 (or the motor 44 that rotates the RGB rotary filter) according to the mode switching signal sent from the mode switching means 50. The RGB rotary filter control means 47 can make the rotating speed lower in the special light mode than in the normal light mode so as to extend an exposure period.

The diaphragm control means 42 receives an average of brightness values exhibited by a screen image from the photometry means 37, and compares the average of brightness values with an operator-designated target value of a brightness level of an image to be displayed on the monitor. An operator can freely designate the brightness of an image on the monitor using the brightness designating means 39 included in the light source unit 5.

Based on the result of the comparison (whether the average of brightness values is larger or smaller), the diaphragm control means 42 controls the opening or closing of the diaphragm 41 interposed between the lamp 40 and RGB rotary filter 43. Consequently, the diaphragm control means 42 controls an amount of light incident on the back end of the light guide 12.

The RGB rotary filter 43 has, as shown in FIG. 9, a double structure including two filter sets 48 and 49 that serve as an inner circumference side thereof and an outer circumference side thereof.

As shown in FIG. 1, the rotary filter switching means 46 selectively moves either of the first filter set 48 that is the inner circumference side or the second filter set 49 that is the outer circumference side of the RGB rotary filter 43 shown in FIG. 7 on the optical axis of illumination light that links the lamp 40 and the back end of the light guide 12. In this case, the rotary filter switching means 46 moves the whole of the RGB rotary filter 43 and disposes the first filter set 48 that is the inner circumference side or the secondary filter set 49 that is the outer circumference sid