U.S. patent application number 11/830619 was filed with the patent office on 2008-01-24 for endoscope system.
This patent application is currently assigned to OLYMPUS CORPORATION. Invention is credited to Nobuyuki Doguchi, Takayuki Hanawa, Katsuichi Imaizumi, Yasuo Komatsu, Kazunari Nakamura, Sakae Takehana.
Application Number | 20080021272 11/830619 |
Document ID | / |
Family ID | 15205503 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080021272 |
Kind Code |
A1 |
Doguchi; Nobuyuki ; et
al. |
January 24, 2008 |
ENDOSCOPE SYSTEM
Abstract
An endoscope 2 has a CCD 9 incorporated in the distal part of an
insertion unit 6 thereof. The sensitivity of the CCD 9 can be
varied by applying a plurality of pulsating driving signals so as
to change an electron multiplication rate. The endoscope 2 is
connected to a processor 3 so that it can be disconnected freely.
Information representing a type of endoscope stored in advance in a
ROM 48 is transmitted to a controller 21 incorporated in the
processor 3. The control means 21 uses a CCD sensitivity control
means 12 to control the sensitivity of the CCD 9 according to the
type of connected endoscope 2. Consequently, a view image of proper
brightness can be produced irrespective of the type of endoscope
2.
Inventors: |
Doguchi; Nobuyuki; (Tokyo,
JP) ; Komatsu; Yasuo; (Toyko, JP) ; Nakamura;
Kazunari; (Kanagawa, JP) ; Takehana; Sakae;
(Kanagawa, JP) ; Imaizumi; Katsuichi; (Tokyo,
JP) ; Hanawa; Takayuki; (Tokyo, JP) |
Correspondence
Address: |
SCULLY SCOTT MURPHY & PRESSER, PC
400 GARDEN CITY PLAZA
SUITE 300
GARDEN CITY
NY
11530
US
|
Assignee: |
OLYMPUS CORPORATION
43-2, Hatagaya 2-chome, Shibuya-ku
Tokyo
JP
151-0072
|
Family ID: |
15205503 |
Appl. No.: |
11/830619 |
Filed: |
July 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
10755559 |
Jan 12, 2004 |
7258663 |
|
|
11830619 |
Jul 30, 2007 |
|
|
|
09743994 |
Jan 17, 2001 |
6902527 |
|
|
10755559 |
Jan 12, 2004 |
|
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Current U.S.
Class: |
600/109 ;
348/E3.018; 348/E7.087; 600/118 |
Current CPC
Class: |
A61B 5/0071 20130101;
A61B 1/05 20130101; A61B 1/00059 20130101; A61B 1/0684 20130101;
G02B 23/24 20130101; A61B 1/045 20130101; G02B 26/008 20130101;
A61B 1/0646 20130101; A61B 1/043 20130101; A61B 5/0084 20130101;
H04N 2005/2255 20130101; G02B 23/2484 20130101; A61B 1/0638
20130101; H04N 7/183 20130101; G02B 23/2469 20130101 |
Class at
Publication: |
600/109 ;
600/118 |
International
Class: |
A61B 1/04 20060101
A61B001/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 1999 |
JP |
11137730 |
Claims
1-19. (canceled)
20. An endoscope system comprising an endoscope having a
solid-state imaging device comprising a charge multiplication
mechanism for varying a sensitivity by varying a charge
multiplication rate in accordance with the number of pulses or
amplitude of the pulses provided to the solid-state imaging device;
a signal processing unit for processing an output signal from the
solid-state imaging device; a light source unit for selectively
irradiating first light to perform ordinary light observation and
second light to perform special light observation to an object; an
observation mode switching device for switching between the
ordinary light observation by the first light and the special light
observation by the second light; and a light amount adjustment unit
for adjusting an amount of light irradiated from the light source
unit to the object based on the output signal from the solid-state
imaging device, wherein the light amount adjustment unit adjusts
the amount of light irradiated from the light source unit to the
object based on the output signal from the solid-state imaging
device, while keeping constant the charge multiplication rate of
the charge multiplication mechanism by varying the number of pulses
or the amplitude of the pulses provided to the solid-state imaging
device.
21. An endoscope system according to claim 20, further comprising
an irradiating light switching device for switching the light
irradiated to the object between the first light and the second
light in accordance with an output from the observation mode
switching device.
22. An endoscope system according to claim 21, wherein the charge
multiplication mechanism is provided at a preceding stage of a
detection amplifier.
23. An endoscope system according to claim 21, wherein the
solid-state imaging device detects an object image by the first
light and an object image by the second light.
24. An endoscope system according to claim 23, wherein the
effective period during which charges are accumulated in the
solid-state imaging device when the first light is irradiated to
the object is different from that when the second light is
irradiated to the object.
25. An endoscope system according to claim 21, wherein the
solid-state imaging device comprises a first solid-state imaging
device for detecting the object image by the second light and a
second solid-state imaging device for detecting the object image by
the first light.
26. An endoscope system according to claim 21, wherein the second
light is of wavelength falling within a wavelength band of
excitation light to perform observation under fluorescent
light.
27. An endoscope system according to claim 26, wherein the
effective period during which charges are accumulated in the
solid-state imaging device when the second light is irradiated to
the object is longer than that when the first light is irradiated
to the object.
28. An endoscope system according to claim 21, further comprising a
sensitivity control unit for controlling the number of pulses or
the amplitude of the pulses provided to the solid-state imaging
device in accordance with whether the first or second light is
irradiated to the object so that the charge multiplication rate of
the charge multiplication mechanism remains constant.
29. An endoscope system according to claim 21, further comprising
an input unit for setting the charge multiplication rate of the
charge multiplication mechanism.
30. An endoscope system according to claim 21, wherein the light
source unit includes a lamp and a filter unit provided in the
optical path between the object and the lamp and comprises a first
filter to transmit light from the lamp so as to irradiate the first
light to the object and a second filter to transmit light from the
lamp so as to irradiate the second light to the object, and the
irradiating light switching device comprises a filter switching
device for switching the filter unit provided in the optical path
between the first filter and the second filter.
31. An endoscope system according to claim 30, wherein the filter
unit is provided with a rotary filter rotated by a motor, and the
time that the second light is irradiated to the object via the
second filter is longer than the time that the first light is
irradiated to the object via the first filter.
32. An endoscope system according to claim 31, further comprising;
an iris diaphragm which adjusts light level of the light irradiated
to the object; and an iris diaphragm controller, wherein the iris
diaphragm controller controls the iris diaphragm such that the iris
diaphragm is opened when the light irradiated to the object is
switched by the filter switching device from the first light to the
second light.
33. An endoscope system according to claim 31, wherein the first
filter is provided along the periphery of the rotary filter, and
the second filter is provided along the periphery of the rotary
filter substantially in parallel to the first filter.
34. An endoscope system comprising: an endoscope having a
solid-state imaging device comprising a charge multiplication
mechanism for varying a sensitivity by varying a charge
multiplication rate in accordance with the number of pulses or
amplitude of the pulses provided to the solid-state imaging device;
a signal processing unit for processing an output signal from the
solid-state imaging device; a light source unit for selectively
irradiating first light to perform ordinary light observation and
second light to perform special light observation to an object; an
observation mode switching device for switching between the
ordinary light observation by the first light and the special light
observation by the second light; a sensitivity control device for
controlling the charge multiplication rate by varying the number of
pulses or the amplitude of the pulses provided to the solid-state
imaging device; an automatic-gain control circuit for amplifying
the output signal from the solid state imaging device when the
level of the output signal is less than a predetermined level; an
iris diaphragm for adjusting a level of the first or second light
irradiated to the object; and an iris diaphragm controller; wherein
the iris diaphragm controller controls the iris diaphragm based on
an output signal from the solid-state imaging device.
35. An endoscope system comprising: an endoscope having a
solid-state imaging device comprising a charge multiplication
mechanism for varying a sensitivity by varying a charge
multiplication rate in accordance with the number of pulses or
amplitude of the pulses provided to the solid-state imaging device;
a signal processing unit for processing an output signal from the
solid-state imaging device; a light source unit for selectively
irradiating first light to perform ordinary light observation and
second light to perform special light observation to an object; an
observation mode switching device for switching between the
ordinary light observation by the first light and the special light
observation by the second light; a sensitivity control device for
controlling the charge multiplication rate by varying the number of
pulses or the amplitude of the pulses provided to the solid-state
imaging device to vary the multiplication rate, the sensitivity
control device controlling the number of sensitivity control pulses
or amplitude of the sensitivity control pulses so that a level of
an output signal from the solid-state imaging device may be a
predetermined level; an automatic-gain control circuit for
amplifying the output signal from the solid state imaging device
when the level of the output signal is less than a predetermined
level; an iris diaphragm for adjusting a level of the first or
second light irradiated to the object; and an iris diaphragm
controller; wherein the iris diaphragm controller controls the iris
diaphragm based on an output signal from the solid-state imaging
device.
Description
TECHNICAL FIELD
[0001] The present invention relates to an endoscope system for
visualizing an object using a solid-state imaging device whose
sensitivity is controllable.
BACKGROUND ART
[0002] An endoscope system having a solid-state imaging device
consists mainly of an endoscope such as an electronic endoscope, a
processor, a light source unit, and a monitor. In the endoscope
system, the insertion unit of the endoscope is inserted into a body
cavity, and illumination light emanating from the light source unit
is irradiated to an object over a light guide lying through the
endoscope. The solid-state imaging device incorporated in the
distal part of the endoscope photoelectrically converts the light
to produce a video signal. The processor processes the signal and
displays an image on the monitor according to the signal.
[0003] Talking of the endoscope system, a field-sequential
endoscope system like the one disclosed in, for example, Japanese
unexamined Patent Application Publication No. 1-221135 is known as
a modality enabling observation under ordinary light by utilizing
illumination light of wavelengths falling within the visible
spectrum. In the endoscope system, as described in Japanese
Unexamined Patent Application Publication No. 9-70384, an endoscope
designed for fluorescence diagnosis is often employed in order to
discover an early-stage carcinoma or the like. Specifically,
excitation light is irradiated to a living tissue, and light
stemming from fluorescence exhibited by the living tissue is
observed in order to discover an early-stage carcinoma or the
like.
[0004] An imaging device included in such a fluorescence diagnosis
endoscope system is requested to offer so high sensitivity as to
enable observation of feeble light stemming from fluorescence. For
this reason, a pickup tube is often employed. Japanese Unexamined
Patent Application Publication No. 5-252450 has disclosed a
technology of controlling a drain voltage occurring due to overflow
in a solid-state imaging device according to an output signal of
the solid-state imaging device. The technology thus enables
visualization of a region whose image cannot be corrected by
controlling an amount of light using an iris diaphragm.
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005] In the foregoing endoscope system, various types of
endoscopes are switched for use according to a region to be
assessed or a method of assessment. For example, an endoscope
dedicated to examination of the bronchi is thinner than an
endoscope dedicated to examination of the large intestine.
[0006] The diameter of an endoscope affects the number of optical
fibers constituting a light guide lying through the endoscope, and
brings about a difference in the amount of irradiated light.
Moreover, an f-number varies depending on the purpose of use of an
endoscope. In particular, when an endoscope having a large f-number
set therefor is used to observe an object located at a far point,
the amount of light is so small that a view image is dark.
[0007] This causes a range, within which a proper amount of light
necessary for picking up image data is collected, to greatly vary
depending on a type of endoscope. On the other hand, as mentioned
above, the endoscope system is usable not only for observation
under ordinary light but also for observation under special light
such as light stemming from fluorescence intended to assess a
lesion. For the observation under light stemming from fluorescence,
very feeble light stemming from auto-fluorescence must be
collected. Therefore, a solid-state imaging device to be
incorporated in the distal part of an endoscope is requested to
offer much higher sensitivity than a solid-state imaging device
designed for observation under ordinary light.
[0008] In general, when the endoscope system is used to observe an
object that makes quick motion or to produce a still image, the
solid-state imaging device is driven using an electronic shutter.
In this case, the amount of irradiated light is increased in order
to optimize an exposure value. However, when an iris diaphragm is
fully opened in order to adjust the amount of irradiated light, if
the electronic shutter is activated, the exposure value becomes
insufficient. This results in a dark image. Automatic gain control
(AGC) may be utilized to compensate the insufficient exposure
value. However, this poses a problem in that a noise is
intensified.
[0009] An object of the present invention is to provide an
endoscope system capable of producing a view image of proper
brightness irrespective of a type of endoscope. Specifically, the
sensitivity of a solid-state imaging device is controlled depending
on the type of endoscope, that is, the diameter of an insertion
unit of an endoscope, an f-number set for an endoscope, or whether
an endoscope is designed for observation under ordinary light or
observation under special light such as light stemming from
fluorescence.
[0010] Another object of the present invention is to provide an
endoscope system capable of offering a proper exposure value by
controlling the sensitivity of a solid-state imaging device
according to movement information concerning the light source,
whether an amount of light supplied from a light source is
insufficient or not.
[0011] Still another object of the present invention is to provide
an endoscope system capable of producing a view image less affected
by a noise by controlling the sensitivity of a solid-state imaging
device according to the driven state of the solid-state imaging
device.
DISCLOSURE OF INVENTION
[0012] The present invention has paid attention to a technology of
multiplying charge through ionization to improve sensitivity as
described in the U.S. Pat. No. 5,337,340 entitled "Charge
Multiplying Detector (CMD) Suitable for Small Pixel CCD Image
Sensors." According to the technology, an electric field of
sufficient strength is produced, and conduction electrons are
collided against atoms in the electric field. The electrons are
thus released from a valence band, and escaped from an area in
which the conduction electrons collide against the atoms. Owing to
the ionization, charge carriers are multiplied.
[0013] According to the present invention, there is provided an
endoscope system consisting mainly of an endoscope, a signal
processing unit, a light source unit, and a sensitivity control
means. The endoscope has a solid-state imaging device whose
sensitivity can be varied by applying a plurality of different
driving pulses to change an electron multiplication rate. The
signal processing unit processes a signal output from the
solid-state imaging device. The light source unit irradiates light
to an object so that an object image will be projected on the
solid-state imaging device. The sensitivity control means varies a
sensitivity control pulse, applies it to the solid-state imaging
device, and thus controls the electron multiplication rate for the
solid-state imaging device.
[0014] According to the present invention, there is provided an
endoscope system consisting mainly of an endoscope, a signal
processing unit, a light source unit, a switching means, and a
sensitivity control means. The endoscope has a solid-state imaging
device whose sensitivity can be varied by applying a plurality of
different pulsating driving signals to change an electron
multiplication rate. The signal processing unit processes a signal
output from the solid-state imaging device. The light source unit
irradiates white light or special light of a specified wavelength
band to an object with the intensity of light varied. The switching
means switches observation in an ordinary light mode in which the
white light is irradiated and observation in a special light mode.
The sensitivity control means varies a sensitivity control pulse,
applies it to the solid-state imaging device, and controls an
electron multiplication rate for the solid-state imaging
device.
[0015] According to the present invention, the sensitivity control
means included in the endoscope system is controlled based on at
least one of a designating signal output from a designating means,
an information signal output from a connected endoscope and
representing a feature of the endoscope, a movement information
signal output from the light source unit, a signal representing a
driving condition for the solid-state imaging device, and an output
signal of the signal processing unit.
[0016] In the endoscope system according to the present invention,
the sensitivity can be controlled freely by adjusting an amplitude
of a sensitivity control pulse (CMDgate pulse) or the number of
applications of the sensitivity control pulse per unit time. Since
the sensitivity can be controlled, a high-sensitivity solid-state
imaging device can be realized without a noise derived from
multiplication and without the necessity of cooling. This results
in an endoscope capable of offering high image quality and being
inserted smoothly.
[0017] In the endoscope system according to the present invention,
the sensitivity control means is included in the signal processing
unit. The sensitivity of the solid-state imaging device is
determined based on a type of endoscope or a property of each
solid-state imaging device. Consequently, a view image of proper
brightness can be produced irrespective of the type of endoscope or
the property of each solid-state imaging device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 to FIG. 6 are concerned with Example 1 of the present
invention;
[0019] FIG. 1 is a block diagram showing the overall configuration
of an endoscope system;
[0020] FIG. 2 is a block diagram showing the configuration of a
signal pre-processing means included in a signal processing
means;
[0021] FIG. 3 is a block diagram showing the configurations of a
field-sequential signal synchronizing means and a signal
post-processing means which are included in the signal processing
means;
[0022] FIG. 4 is an explanatory diagram showing various types of
endoscopes employed in the present example;
[0023] FIG. 5 is an explanatory diagram concerning the purposes of
use of the endoscopes;
[0024] FIG. 6 is an explanatory diagram concerning actions;
[0025] FIG. 7 is a block diagram showing the overall configuration
of an endoscope system in accordance with Example 2 of the present
invention;
[0026] FIG. 8 is a block diagram showing the overall configuration
of an endoscope system in accordance with Example 3 of the present
invention;
[0027] FIG. 9 is a block diagram showing the overall configuration
of an endoscope system in accordance with Example 4 of the present
invention;
[0028] FIG. 10 is a block diagram showing in detail the
configuration of a video signal processing means;
[0029] FIG. 11 is a block diagram showing the overall configuration
of an endoscope system in accordance with Example 5 of the present
invention;
[0030] FIG. 12 is a block diagram showing in detail the
configuration of a signal pre-processing means;
[0031] FIG. 13 to FIG. 16 are concerned with Example 6 of the
present invention;
[0032] FIG. 13 is a block diagram showing the overall configuration
of an endoscope system;
[0033] FIG. 14 is a block diagram showing in detail the
configuration of a signal pre-processing means;
[0034] FIG. 15 shows in detail the structure of a CCD;
[0035] FIG. 16 is an explanatory diagram indicating an action
performed with ordinary sensitivity and an action performed with
electrons multiplied;
[0036] FIG. 17 to FIG. 23 are concerned with Example 7 of the
present invention;
[0037] FIG. 17 is a block diagram schematically showing the
configuration of an endoscope system;
[0038] FIG. 18 is an explanatory diagram showing the arrangement of
two filter sets constituting a rotary filter;
[0039] FIG. 19 is a block diagram showing a signal pre-processing
signal included in a signal processing means;
[0040] FIG. 20 is a block diagram showing a field-sequential
synchronizing means and a signal post-processing means which are
included in the signal processing means;
[0041] FIG. 21 is a timing chart indicating the timings of signals
used to drive a CCD;
[0042] FIG. 22 is a graph indicating the relationship between the
illuminance on the imaging surface of a CCD and a signal-to-noise
ratio;
[0043] FIG. 23 is a graph indicating the relationship between the
illuminance on the imaging surface of the CCD and an output voltage
level;
[0044] FIG. 24 to FIG. 27 are concerned with Example 8 of the
present invention;
[0045] FIG. 24 shows the structure of a rotary filter;
[0046] FIG. 25 is a timing chart indicating the timings of signals
used to drive a CCD in a special light mode;
[0047] FIG. 26 is a graph indicating the relationship between the
illuminance on the imaging surface of the CCD and a signal-to-noise
ratio (long exposure);
[0048] FIG. 27 is a graph indicating the relationship between the
illuminance on the imaging surface of the CCD and an output voltage
level (long exposure);
[0049] FIG. 28 and FIG. 29 are concerned with Example 9 of the
present invention;
[0050] FIG. 28 is a block diagram schematically showing an
endoscope system; and
[0051] FIG. 29 is a block diagram showing a signal pre-processing
means included in a signal processing means.
BEST MODE FOR CARRYING OUT THE INVENTION
[0052] Examples of the present invention will be described with
reference to the drawings below.
EXAMPLE 1
[0053] FIG. 1 to FIG. 6 are concerned with Example 1 of the present
invention. FIG. 1 is a block diagram schematically showing the
configuration of an endoscope system of Example 1. FIG. 2 and FIG.
3 show a signal pre-processing means included in a signal
processing means. FIG. 4 shows various types of endoscopes employed
in the present example. FIG. 5 describes the purposes of use of the
endoscopes and others. FIG. 6 is an explanatory diagram concerning
actions.
[0054] As shown in FIG. 1, an endoscope system 1 of Example 1 of
the present invention consists mainly of an electronic endoscope
(hereinafter, for brevity's sake, an endoscope) 2, a processor 3,
and a monitor 5. A solid-state imaging device is incorporated in
the endoscope 2. The endoscope 2 is connected to the processor 3 so
that it can be disconnected freely, and a signal processing unit 4
and a field-sequential light source unit 22 are incorporated in the
processor 3. The monitor 5 is connected to the processor 3, and a
video signal processed by the processor 3 is output to the monitor
5.
[0055] The endoscope 2 has an elongated insertion unit 6 that is
inserted into a body cavity. An objective 8 through which an object
image is projected is incorporated in the distal part 7 of the
insertion unit 6. A solid-state imaging device, for example, a
charge-coupled device (hereinafter a CCD) is located on the image
plane of the objective 8. The CCD 9 is connected to a CCD driving
means 11 and a CCD sensitivity control means 12, which are included
in the signal processing unit 4 incorporated in the processor 3,
over a signal line. Exposure and reading are controlled based in a
driving signal and a sensitivity control signal produced by the CCD
driving means 11 and CCD sensitivity control means 12
respectively.
[0056] In the CCD 9, as described in the U.S. Pat. No. 5,337,340
entitled "Charge Multiplying Detector (CMD) suitable for Small
Pixel CCD Image Sensors," an electric field of sufficient strength
is produced, and conduction electrons are collided against atoms in
the electric field. The electrons are released from a valence band
and escaped from an area in which the conduction electrons collide
against the atoms. Owing to the ionization, charge carriers are
multiplied, and the sensitivity of the CCD is improved. Moreover,
the sensitivity of the CCD is freely controllable by adjusting an
amplitude of an external control pulse (CMDgate pulse) and the
number of applications of the control pulse per unit time.
[0057] Consequently, a high-sensitivity CCD is realized without a
noise derived from multiplication performed for improving
sensitivity and without the necessity of cooling. The CCD is
therefore ideal for realization of an endoscope offering excellent
image quality and being inserted smoothly. The CCD 9 is connected
to a signal processing means 14 included in the processor 3 via a
buffer 13. An object image projected on the imaging surface of the
CCD 9 through the objective 8 is converted into an electric signal
by the CCD 9, and read from the CCD 9. The output of the CCD 9 is
then fed to the signal processing means 14.
[0058] A light guide 15 over which illumination light is propagated
lies through the endoscope 2. An illumination lens 16 is located in
front of the distal end of the light guide 15. Illumination light
propagated through the endoscope 2 over the light guide 15 is
irradiated to an object through the illumination lens 16.
[0059] The signal processing means 14 consists of a signal
pre-processing means 17, a field-sequential signal synchronizing
means 18, and a signal post-processing means 19. The signal
pre-processing means 17 performs various kinds of signal processing
on an output signal of the CCD 9. The field-sequential signal
synchronizing means 18 synchronizes field-sequential signal
components output from the signal pre-processing means 17. The
signal post-processing means 19 performs various kinds of signal
processing on an output signal of the field sequential signal
synchronizing means 18 so that the output signal can be output to
the monitor 5. An output signal read from the CCD 9 is converted
into a television signal, and the television signal is output to
the monitor 5.
[0060] The CCD driving means 11, CCD sensitivity control means 12,
and signal processing means 14 are connected to a (first) control
means 21. The control means 21 extends control.
[0061] The control means 21 is connected to a (second) control
means 26 for controlling an iris diaphragm 23, a diaphragm control
means 24, and an RGB rotary filter control means 25 which are
included in the field-sequential light source unit 22 for supplying
field-sequential illumination light rays to the endoscope 2.
Interlocked with the RGB rotary filter control means 25, the
control means 21 controls the CCD driving means 11 and signal
processing means 14.
[0062] Moreover, the field-sequential light source unit 22 includes
a lamp 27, a condenser lens 28, and a RGB rotary filter 29. The
lamp 27 generates illumination light. The condenser lens 28
converges the illumination light on the rear end of the light guide
15. The RGB rotary filter 29 is interposed between the lamp 27 and
condenser lens 28.
[0063] The rotary filter 29 is coupled to the rotation shaft of a
motor 30 so that it can rotate. The rotary filter 29 is controlled
by the RGB rotary filter control means under control of the control
means 26 so that it will rotate at a predetermined rotating speed.
Consequently, red, green, and blue field-sequential light rays are
supplied to the rear end of the light guide 15.
[0064] The signal processing means 14 has the signal pre-processing
means 17 thereof configured as shown in, for example, FIG. 2.
Field-sequential signal components output from the endoscope are
input to the signal pre-processing means 17.
[0065] In the signal pre-processing means 17, the output signal of
the CCD 9 passes through a CDS circuit 31, a low-pass filter (LPF)
32, and a clamping circuit 33, and is then digitized by an A/D
converter 34. The resultant digital signal is isolated from a
patient circuit and transmitted to a secondary circuit by a
photocoupler 35a.
[0066] The secondary circuit includes a white balance control
circuit 36, a tone control circuit 37, and a gamma correction
circuit 38. After subjected to white balance control, tone control,
and gamma correction are carried out, an expansion circuit 39
performs electronic zooming to achieve expansion. An output signal
of the expansion circuit 39 is input to the field sequential signal
synchronizing means 18 via a contour enhancement circuit 40.
[0067] The control means 21 outputs a control signal used to
control the white balance control circuit 36, tone control circuit
37, expansion circuit 39, and contour enhancement circuit 40 which
are included in the secondary circuit. Moreover, the control means
21 outputs a control signal, which is used to control the clamping
circuit 33 included in the patient circuit, via a photocoupler 35b
serving as an isolating/transmitting means.
[0068] Red, green, and blue field-sequential signal components
output from the signal pre-processing means 17 are input to
synchronizing means 43a, 43b, and 43c via selector switches 41,
42A, and 42B included in the field-sequential signal synchronizing
means 18 shown in FIG. 3.
[0069] The synchronizing means 43a, 43b, and 43c each have a memory
in which data for at least one field can be stored. The red, green,
and blue field-sequential signal components that are input in that
order are stored in the memories associated with the respective
colors. The stored field-sequential signal components are read
simultaneously and output as synchronous signal components.
[0070] As an example of the synchronizing means 43a, 43b, and 43c,
each synchronizing means 43i (where i denotes a, b, or c) shown in
FIG. 3 consists of image memories 44a and 44b in each of which data
for at least two fields can be stored. Herein, writing and reading
of an image signal in and from the image memories 44a and 44b are
alternately switched for the purpose of synchronization.
[0071] Synchronous signal components output from the synchronizing
means 43a, 43b, and 43c are input to still image memories 45a, 45b,
and 45c, in each of which a still image signal component is stored,
included in the signal post-processing means 19, and also input to
a selector 46.
[0072] The synchronous signal components output from the
synchronizing means 43a, 43b, and 43c are fed as motion picture
signal components to the monitor 5 via the selector 46 and a 75-ohm
driver 47 installed as a succeeding stage of the selector 46. The
output terminals of the still image memories 45a, 45b, and 45c are
connected to the other input terminals of the selector 36.
[0073] The control means 21 controls writing and reading of an
image signal component in and from the still image memories 45a,
45b, and 45c. In response to an external Freeze instruction, the
control means 21 controls the still image memories 45a, 45b, and
45c so that image signal components to be frozen will be stored
therein. The control means 21 controls the selector 46 so that the
selector 46 will select still image signal components and feed them
to the monitor 5 via the 75-ohm driver 47 on the succeeding stage.
Herein, the selector 46 selects either of the motion picture signal
components output from the synchronizing means 43a, 43b, and 43c
and the still image signal components output from the still image
memories 45a, 45b, and 45c.
[0074] A ROM 48 in which information inherent to the endoscope 2 is
stored is incorporated in the endoscope 2. At the time when the
endoscope 2 is connected to the processor 3, the information is
transmitted to the control means 21 included in the signal
processing unit 4 incorporated in the processor 3. The sensitivity
of the CCD 9 is then controlled. In short, the RON 48 serves as a
designating means for designating the sensitivity of the CCD 9.
[0075] As shown in FIG. 4, aside from the endoscope 2, various
types of endoscopes 2I (where I denotes A, B, or C) are available
for different regions to be observed or different purposes of use.
Specifically, the endoscope 2A has a smaller number of optical
fibers constituting the light guide 15 than the endoscope 2 to thus
have a smaller diameter. The endoscope 2B offers a larger f-number
than the endoscope 2 to thus offer a larger depth of field. The
endoscope 2C has a filter 49, which transmits only light stemming
from fluorescence exhibited by a living body for the purpose of
observation under light stemming from fluorescence, disposed in
front of the CCD 9. The various types of endoscopes 2I can be
connected to the processor 3 so that they can be disconnected
freely.
[0076] FIG. 5 lists the features of the endoscopes 2 and 2I.
Information of the features (for example, information representing
the number of applications of a sensitivity control pulse .phi.CMD
per unit time) is stored in advance in the RON 48. The information
read from the ROM 48 incorporated in the endoscope 2 or 2I
connected to the processor 3 is sent to the control means 21. The
control means 21 determines the sensitivity of the CCD 9 serving as
a solid-state imaging device so that the endoscope 2, 2A, or 2B
designed for observation under ordinary light can offer a proper
exposure value.
[0077] Herein, a sensitivity control value with which the
sensitivity of the CCD 9 is controlled is calculated on the
assumption that the amount of light supplied from the light source
unit 22 to the rear end of the light guide 15 remains constant. The
sensitivity control value causes the voltage level of an output
signal of the CCD 9 to remain intact irrespective of the number of
optical fibers constituting the light guide and the f-number set
for an endoscope. When the number of optical fibers constituting
the light guide and the f-number are different, information
representing the different number of optical fibers and a different
f-number is supplied.
[0078] For example, when the number of optical fibers constituting
the light guide is small, control is extended to make the
sensitivity of the CCD 9 higher than it is when the number of
optical fibers is large.
[0079] When the endoscope 2C designed for observation under light
stemming from fluorescence is employed, information representing
the fact that the endoscope 2C is employed is transmitted in
advance. The sensitivity is set to a predetermined value. Based on
the set value, the control means 21 controls the CCD driving means
11 and CCD sensitivity control means 12. FIG. 6 shows driving
signals and a sensitivity control signal output from the CCD
driving means 11 and CCD sensitivity control means 12
respectively.
[0080] FIG. 6 indicates an exposure period and an interception
period (reading period) determined by the RGB rotary filter. FIG. 6
also indicates the relationship among a sensitivity control pulse
.phi.CMD, a vertical transfer pulse .phi.IAG, and a horizontal
transfer pulse .phi.SR which are applied to the CCD 9 and an output
signal of the CCD.
[0081] The sensitivity of the CCD 9 may be controlled by adjusting
either the number of applications of the pulse .phi.CMD per unit
time or the amplitude thereof. Herein, the number of applications
of the pulse .phi.CMD per unit time is adjusted in order to attain
desired sensitivity. In this case, the sensitivity control pulse
.phi.CMD is applied to the CCD 9 during the interception (reading)
period succeeding the exposure period in order to improve the
sensitivity of the CCD 9. The vertical transfer pulse .phi.IAG and
horizontal transfer pulse .phi.SR are then applied to the CCD 9 in
order to acquire an output signal of the CCD 9.
[0082] For example, the number of applications of the sensitivity
control pulse .phi.CMD per unit time is varied depending on
whichever of the endoscopes 2 and 2I is connected for the purpose
of use described in FIG. 5. Sensitivity of a level required by any
of the endoscopes 2 and 2I is thus attained readily.
[0083] Incidentally, for brevity's sake, electrons shall be
multiplied by 1% with each application of the pulse .phi.CMD listed
in FIG. 5.
[0084] In the endoscope 2C designed for observation under light
stemming from fluorescence, the filter 49 having a property of
passing light which stems from fluorescence exhibited by a living
body and of which wavelengths range from 480 nm to 600 nm is
disposed in front of the CCD 9. Only feeble light stemming from
fluorescence exhibited by a living body excited with a blue
field-sequential light ray (whose wavelengths range from 400 nm to
500 nm) is converted into a video signal by the CCD 9 whose
sensitivity has been raised.
[0085] The synchronizing means 43a, 43b, and 43c included in the
processor 3 store signal components derived from the blue light ray
alone simultaneously in the memories associated with the three
colors. The synchronizing means 43a, 43b, and 43c read the stored
field-sequential signal components simultaneously and output them
as monochrome image signal components.
[0086] The foregoing control is extended by the control means 21.
Signal processing intended to enable observation under ordinary
light and signal processing intended to enable observation under
light stemming from fluorescence are switched based on information
read from the ROM 48 incorporated in any of the endoscopes 2, and
2A to 2C.
[0087] As mentioned above, according to the present example, the
sensitivity of a solid-state imaging device is controlled based on
the type of endoscope connected, that is, whichever of the
endoscopes 2 and 2I is connected. Consequently, the endoscope
system 1 can produce a view image of proper brightness.
[0088] Information read from the ROM 48 may represent a parameter
such as a light distribution curve or an angle of view or a
correction value with which a difference in brightness from one
solid-state imaging device to another. Needless to say, a set value
of the sensitivity of the CCD 9 may be transmitted to the processor
3.
[0089] According to the present example, the sensitivity of the CCD
9 incorporated in the endoscope 2 or 2I is designated based on
information stored in the ROM 48 incorporated therein. In case of
an endoscope (for example, the endoscope 2D) not having the ROM 48,
an input means such as a keyboard (or a sensitivity designating
means) may be connected to the control means 21 incorporated in the
signal processing unit 4. In this case, the input means is used to
enter a value of sensitivity permitting the endoscope 2D to produce
a proper view image. The CCD sensitivity control means 12 controls
the sensitivity of the CCD 9 incorporated in the endoscope 2D under
control of the control means 21.
[0090] Instead of entering a value of sensitivity using the input
means, a feature of the endoscope 2D, or more particularly, the
number of optical fibers constituting the light guide or an
f-number listed in FIG. 5 may be entered. The control means 21 then
calculates the required number of applications of the sensitivity
control pulse .phi.CMD per unit time, and instructs the CCD
sensitivity control means 12 to control the sensitivity of the CCD
9.
EXAMPLE 2
[0091] FIG. 7 shows the configuration of an endoscope system 51 in
accordance with Example 2 of the present invention. The description
of components identical to those shown in FIG. 1 will be
omitted.
[0092] In Example 1, the field-sequential light source unit 22 is
incorporated in the processor 3 together with the signal processing
unit 4 including the signal processing means 14. In Example 2, a
field-sequential light source unit 52 is included independently of
the signal processing unit 4.
[0093] In the field-sequential light source unit 52, a half mirror
53 is disposed in front of the lamp 27. The half mirror 53 splits
light emitted from the lamp 27. Light reflected from the half
mirror 53 is routed to a light level sensor 54.
[0094] The amount of light emitted from the lamp 27 decreases with
an increase in a lamp lighting time. The light level sensor 54
converts the decrease in the amount of light into numerical data.
The numerical data is sent to the control means 21 via the control
means 26. The control means 21 calculates a set value of the
sensitivity of the CCD 9, which can compensate the decrease in the
amount of light emitted from the lamp 27, according to the
numerical data, and thus controls the CCD sensitivity control means
12.
[0095] The diaphragm control means 24 sends information to the
control means 21 via the control means 26. The information
represents whether light can be adjusted using the iris diaphragm
23 or whether the iris diaphragm 23 is fully opened or closed.
[0096] When the iris diaphragm 23 is fully opened, the control
means 21 controls the CCD sensitivity control means 12 so that the
CCD sensitivity control means 12 will raise the set value of the
sensitivity of the CCD 9. When the iris diaphragm 21 is fully
closed, the control means 21 controls the CCD sensitivity control
means 12 so that the CCD sensitivity control means 12 will lower
the set value of the sensitivity of the CCD 9. The set value of
sensitivity may be varied stepwise or continuously. The other
components are identical to those of Example 1.
[0097] Example 2 exerts the same operations as Example 1. In
addition, a means for eliminating the influence of a change in the
amount of light emitted actually from the lamp 27 by controlling
the sensitivity of the CCD 9 using the CCD sensitivity control
means 12 is included in consideration of the time-passing change in
the amount of light emitted from the lamp 27.
[0098] According to Example 2, even if the amount of light emitted
from the lamp 27 incorporated in the light source unit 52 decreases
or light cannot be adjusted using the iris diaphragm 23, the
endoscope system 51 can produce a view image of proper brightness.
This is because the sensitivity of the CCD 9 serving as a
solid-state imaging device is controlled based on information sent
from the light source unit 52.
EXAMPLE 3
[0099] FIG. 8 shows the configuration of an endoscope system 51' in
accordance with Example 3 of the present invention. The description
of components identical to those shown in FIG. 1 and FIG. 7 will be
omitted below. In Example 3, an LED light source unit 52' shown in
FIG. 8 may be substituted for the field-sequential light source
unit 52 of Example 2 shown in FIG. 7.
[0100] The LED light source unit 52' shown in FIG. 8 includes a red
LED 57a, a green LED 57b, a blue LED 57c, and a condenser lens 28.
The red LED 57a, green LED 57b, and blue LED 57c are connected to
an LED control means 56 and lit sequentially. The condenser lens 28
converges the illumination light on the rear end of the light guide
15. Thus, field-sequential light rays are fed to the rear end of
the light guide 15.
[0101] The iris diaphragm 23 is interposed between the red LED 57a,
green LED 57b, and blue LED 57c and the condenser lens 28, and
controlled by the diaphragm control means 24. The diaphragm control
means 24 and an LED control means 56 are connected to the control
means 26.
[0102] Moreover, the control means 21 incorporated in the signal
processing unit 4 is connected to the control means 26. The control
means 26 instructs the LED control means 56 to control glowing of
the red LED 57a, green LED 57b, and blue LED 57c incorporated in
the LED light source unit 52 for supplying field-sequential
illumination light rays to the endoscope 2. The control means 21
controls the CCD driving means 11 and signal processing means 14
while being interlocked with glowing of the LEDs.
[0103] When the field-sequential light source unit 52 is connected
to the endoscope, information indicating that a xenon lamp is used
is sent from the control means 26 incorporated in the light source
unit to the control means 21. When the LED light source unit 52' is
connected to the endoscope, information indicating that LEDs are
used is sent from the control means 26 incorporated in the light
source unit to the control means 21. When a light source unit,
which is not shown, including a halogen lamp is connected to the
endoscope, information indicating that the halogen lamp is used is
sent from the control means 26 incorporated in the light source
unit. The control means 21 controls the CCD sensitivity control
means 12 according to the information.
[0104] According to Example 3, even if an absolute value of the
amount of emitted light differs between the light source units 52
and 52', the sensitivity of a solid-state imaging device is
controlled to compensate the difference in the amount of emitted
light according to information sent from a connected light source
unit. This results in an endoscope system capable of producing a
view image of proper brightness.
EXAMPLE 4
[0105] FIG. 9 shows the configuration of an endoscope system 61 in
accordance with Example 4 of the present invention. Example 4 is a
simultaneous endoscope system having a color filter 65 placed on
the face of the CCD 9.
[0106] The description of components identical to those shown in
FIG. 1 or FIG. 7 will be omitted. Example 4 consists mainly of a
simultaneous endoscope 62, a light source unit 63, a signal
processing unit 64, and a monitor 5. The light source unit 63
supplies white illumination light to the endoscope 62. The signal
processing unit 64 (independent of the light source unit 63) drives
the CCD 9 and processes signals. An image is displayed on the
monitor 5 according to a video signal output from the signal
processing unit 64.
[0107] The simultaneous endoscope 62 has the color filter 65 placed
on the face of the CCD 9 incorporated in the endoscope 2 included
in Example 1.
[0108] The light source unit 63 does not include the RGB rotary
filter 29 intervened in the path of illumination light in the
field-sequential light source unit 22 shown in FIG. 1. White light
emitted from the lamp 27 is converged by the condenser lens 28
through the iris diaphragm 23, and supplied to the rear end of the
light guide 15. Therefore, the light source unit 63 includes
neither the motor 30 shown in FIG. 1 nor the RGB rotary filter
control means 25 shown therein.
[0109] Moreover, the signal processing unit 64 in Example 4 has a
signal pre-processing means 66 and a signal post-processing means
67 included in the signal processing means 14 unlike the signal
processing means 14 shown in FIG. 1.
[0110] Specifically, the signal processing means 14 consists of the
signal pre-processing means 66 for performing various kinds of
signal processing on an output signal read from the CCD 9, and the
signal post-processing means 67 for performing various kinds of
signal processing on an output signal of the signal pre-processing
means 66 so as to output the output signal to the monitor 5. The
output signal read from the CCD 9 is converted into a television
signal and output to the monitor 5.
[0111] The CCD driving means 11, CCD sensitivity control means 12,
and signal processing means 14 are connected to the control means
21 and controlled by the control means 21.
[0112] The control means 21 is also connected to the control means
26 for controlling the iris diaphragm 23, which is incorporated in
the light source unit 63 for supplying white illumination light to
the endoscope 62, and the diaphragm control means 24.
[0113] The signal processing means 14 employed in Example 4 has,
for example, the configuration shown in FIG. 10. A signal output
from the endoscope 62 is fed to the signal pre-processing means
66.
[0114] In the signal pre-processing means 66, an output signal of
the CCD 9 having color signal components superposed on one another
is digitized by the A/D converter 34 after passing through the CDS
circuit 31, low-pass filter 32, and clamping circuit 33. The
digital signal is isolated from a patient circuit and transmitted
to a secondary circuit by the photocoupler 35a.
[0115] The output signal passing through the photocoupler 35a is
split into a luminance signal Y and chrominance signals R-Y and B-Y
by a luminance/chrominance signal separation circuit 68 included in
the secondary circuit. The luminance signal Y and chrominance
signals R-Y and B-Y are converted into red, green, and blue signals
by a matrix circuit 69. The red, green, and blue signals are
subjected to white balance control, tone control, and gamma
correction by means of the white balance control circuit 36, tone
control circuit 37, and gamma correction circuit 38. Thereafter,
the red, green, and blue signals are subjected to electronic
zooming by the expansion circuit 39. An output of the expansion
circuit 39 is fed to the signal post-processing means 67 via the
contour enhancement circuit 40.
[0116] An output of the contour enhancement circuit 40 is fed to
the still image memories 45a, 45b, and 45c, in which still image
signal components are stored, included in the signal
post-processing means 67. The output of the contour enhancement
circuit 40 is also input to the selector 46, and then fed as motion
picture signal components to the monitor 5 via the 75-ohm driver 47
on the succeeding stage.
[0117] The output terminals of the still image memories 45a, 45b,
and 45c are connected to the other input terminals of the selector
46. The control means. 21 controls writing and reading of image
signal components in and from the still image memories 45a, 45b,
and 45c. In response to a Freeze instruction entered by an
operator, the control means 21 controls the still image memories
45a, 45b, and 45c so that image signal components to be frozen will
be stored in the memories.
[0118] Moreover, the control means 21 controls the CCD driving
means 11 so that an electronic shutter will be activated in
response to the Freeze instruction. The control means 21 controls
the CCD sensitivity control means 12 so that the CCD sensitivity
control means 12 will raise a set value of the sensitivity of the
CCD. The set value of sensitivity is set to compensate a decrease
in an exposure time determined by the electronic shutter. When the
electronic shutter is opened for 1/120 sec, the sensitivity of the
CCD 9 is set to a value that is twice as large as the one set when
the electronic shutter is opened for a normal exposure time of 1/60
sec.
[0119] As mentioned above, according to the present example, when
the electronic shutter is employed, the sensitivity of a
solid-state imaging device is controlled based on the driven state
of the solid-state imaging device. This results in an endoscope
system capable of producing a view image of proper brightness.
Variant of Example 4
[0120] A variant of Example 4 of the present invention will be
described with reference to FIG. 9 showing Example 4. The present
variant is a simultaneous endoscope system connectable to both an
NTSC (60 Hz) monitor and a PAL (50 Hz) monitor. The signal
processing unit 64 uses a switch that is not shown to select a
television system. When the NTSC system is selected, the control
means 21 controls the CCD driving means 11, signal pre-processing
means 66, and signal post-processing means 67 so that an image
signal will be read from the. CCD 9 at a rate equivalent to the
frequency of 60 Hz and converted into an NTSC television
signal.
[0121] When the PAL system is selected, the control means 21
controls the CCD driving means 11, signal pre-processing means 66,
and signal post-processing means 67 so that an image signal will be
read from the CCD 9 at a rate equivalent to the frequency of 50 Hz
and converted into a PAL television signal. At this time, when the
reading rates are switched, the control means 21 changes the set
value of the sensitivity of the CCD 9. The control means 21
controls the CCD sensitivity control means 12 so that a video
signal of the same voltage level will be produced between the
reading rates equivalent to the frequencies of 60 Hz and 50 Hz.
[0122] As mentioned above, according to the present variant, when
the reading rate or exposure time is changed, the sensitivity of a
solid-state imaging device is controlled based on the driven state
of the solid-state imaging device. This results in an endoscope
system capable of producing a view image of proper brightness.
EXAMPLE 5
[0123] FIG. 11 shows the configuration of an endoscope system in
accordance with Example 5 of the present invention. The description
of components identical to those shown in FIG. 1 or FIG. 9 will be
omitted. In Example 5, an endoscope system 61' consists mainly of
an endoscope 62, a light source unit 63', a signal processing unit
64', and the monitor 5.
[0124] In Example 5, the light source unit 63' does not have,
unlike the light source unit 63 included in the endoscope system 61
shown in FIG. 9, the iris diaphragm 23, diaphragm control means 24,
and control means 26. Illumination light emitted from the lamp 27
is converged by the condenser lens 28 and supplied to the rear end
of the light guide 15.
[0125] Specifically, the light source unit 64', has no light
narrowing mechanism. Irradiation light of the same amount is always
fed to the rear end of the light guide 15.
[0126] Moreover, the signal processing unit 64' employed in the
present example has a signal processing means 14 that includes a
signal pre-processing means 66' partly different from the signal
pre-processing means 66 included in the signal processing means 14
of the signal processing unit 64 shown in FIG. 9. FIG. 12 shows the
configuration of the signal pre-processing means 66'.
[0127] The signal pre-processing means 661 shown in FIG. 12 has, in
addition to the same components as those of the signal
pre-processing means 66 shown in FIG. 10, an average detection
filter circuit 70 to which a luminance signal Y is input.
[0128] The average detection filter circuit 70 calculates an
average of voltage levels assumed by the luminance signal Y that is
one of the components of an output signal of the CCD 9 provided
during one field, and sends the luminance average to the control
means 21. The control means 21 calculates the set value of the
sensitivity of the CCD 9, which permits production of a view image
of proper brightness, according to the luminance average, and
controls the CCD sensitivity control means 12.
[0129] As mentioned above, according to the present example, the
sensitivity of a solid-state imaging device is controlled based on
an output signal of the solid-stage imaging device. Consequently,
the endoscope system 61' can produce a view image of proper
brightness. Moreover, the configuration of the light source unit
63' can be simplified.
EXAMPLE 6
[0130] FIG. 13 shows the configuration of an endoscope system in
accordance with Example 6 of the present invention. The description
of components identical to those shown in FIG. 1 will be
omitted.
[0131] An endoscope system 71 consists mainly of the endoscope 2,
the field-sequential light source unit 22, a video processor 73
with a built-in signal processing unit 74, and the monitor 5.
[0132] According to the present example, information (data)
representing a difference in an electron multiplication rate from
one pixel location in the CCD 9 to another is stored in the ROM 48
incorporated in the endoscope 2.
[0133] The signal processing unit 74 employed in the present
example includes, in addition to the same components as those of
the signal processing unit shown in FIG. 1, a memory means 75, a
switch 76, and an arithmetic means 78. Data read from the ROM 48 is
stored in the memory means 75. The switch 76 is used to freely
designate the sensitivity of the CCD 9. The arithmetic means 78
performs arithmetic operations to calculate correction data that
compensates the above difference in the electron multiplication
rate. Moreover, the signal processing means 74 includes a signal
pre-processing means 17' whose configuration is partly different
from the signal pre-processing means 17 shown in FIG. 1. The
correction data calculated by the arithmetic means 78 is sent to
the signal pre-processing means 17'. Even when the sensitivity of
the CCD 9 differs from one CCD to another, the sensitivity can be
set to a value designated using the switch 76.
[0134] Similarly to Example 1, when the endoscope 2 is connected to
the processor 73, the information in the ROM 48 is sent to the
memory means 75 incorporated in the processor 73 and stored
therein. Information representing a set value of sensitivity
designated using the switch 56 formed, for example, on the panel of
the processor 73 and used to freely designate the sensitivity of
the CCD 9 is input to the control means 21. The control means 21
controls the CCD sensitivity control means 12 according to the
information.
[0135] In the present example, the number of applications of a
pulse .phi.CMD per unit time is adjusted in order to control the
sensitivity. The arithmetic means 78 calculates correction data
according to the difference in the electron multiplication rate
from one pixel location to another, which is stored in the memory
means 75, and the number of applications of the pulse .phi.CMD per
unit time.
[0136] Assuming that a reference electron multiplication rate is X,
an electron multiplication rate for a certain pixel location is kX,
and the number of applications of the pulse .phi.CMD per unit time
is n, the correction data for data read from the pixel location is
expressed as 1/(kX) n.
[0137] The output signal read from the CCD 9 is multiplied by the
correction data for each pixel location by means of a multiplier 79
included in the signal pre-processing means 17' shown in FIG. 14.
Thus, the difference in the electron multiplication rate from one
pixel location to another is corrected. The resultant signal is
sent to the circuit on the succeeding stage. The signal
pre-processing means 17' shown in FIG. 14 has, in addition to the
same components as those of the signal pre-processing means 17
shown in FIG. 2, the multiplier 79 interposed between the
photocoupler 35a and white balance control circuit 36.
[0138] FIG. 15 shows the structure of the CCD 9 employed in the
present example. A serial register 81 and an FDA 82 for converting
charge into a voltage are located below a light receiving surface
80. Six dummy pixel locations 83 are preserved between the serial
register 80 and FDA 82.
[0139] Based on a set value designated using the switch 76, the
control means 21 extends control differently between when the CCD 9
exhibits ordinary sensitivity and when electrons flowing in the CCD
are multiplied.
[0140] Specifically, when the electrons flowing in the CCD are not
multiplied, that is, when the sensitivity of the CCD is not raised
but ordinary sensitivity, the control means 21 sends a timing
signal to the clamping circuit 33 according to the set value
designated using the switch 76. Based on the timing signal, the
clamping circuit 33 clamps an output signal of the CCD (output
signal of the CDS circuit) composed of signal components read from
OB pixel locations 84 during an OB period shown in FIG. 16A.
[0141] In contrast, when the electrons flowing in the CCD are
multiplied in order to raise the sensitivity of the CCD, a dark
current flowing in the OB pixel locations 84 is multiplied as shown
in FIG. 16B. This affects a specified voltage to be clamped. For
avoiding this incident, a timing signal representing a different
timing of clamping is sent to the clamping circuit 33 so that the
clamping circuit will clamp an output signal of the CCD composed of
signal components read from the dummy pixel locations 83 during a
dummy period.
[0142] As mentioned above, according to the present example, an
output signal of a solid-state imaging device is corrected based on
a difference in an electron multiplication rate from one pixel
location in the solid-state imaging device to another and a set
value of the sensitivity of the solid-state imaging device. This
results in an endoscope capable of producing an excellent view
image.
[0143] Moreover, the output signal of the solid-state imaging
device is processed based on the set value of the sensitivity of
the solid-state imaging device. Consequently, a correct black level
of a gray scale is reproduced. Eventually, an excellent view image
can be produced.
[0144] The description has been made on the assumption that the
endoscope is an electronic endoscope having the CCD 9 incorporated
in the distal part of the insertion unit 6. The present invention
is not limited to this type of endoscope. The present invention can
be applied to a TV camera-mounted endoscope having a TV camera, in
which a CCD is incorporated, mounted on an eyepiece unit of an
optical endoscope.
[0145] In this case, as described in conjunction with Example 1,
for example, an input means (designating means) may be used to
enter a value of the sensitivity of the CCD 9 so that the value
will be fed to the control means 21. Alternatively, a feature of a
TV camera may be entered together with a feature (the number of
optical fibers constituting a light guide) of an optical endoscope.
The control means 21 may calculate the number of applications of a
sensitivity control pulse .phi.CMD per unit time required for use
of the optical endoscope and TV camera, and instruct the CCD
sensitivity control means 12 to control the sensitivity of the CCD
9.
EXAMPLE 7
[0146] FIG. 17 to FIG. 23 are concerned with Example 7 of the
present invention. FIG. 17 is a block diagram schematically showing
the configuration of an endoscope system. FIG. 18 is an explanatory
diagram schematically showing the arrangement of two filter sets
constituting a rotary filter. FIG. 19 is a block diagram showing a
signal pre-processing means included in a signal processing means.
FIG. 20 is a block diagram showing a field-sequential synchronizing
means and a signal post-processing means included in the signal
processing means. FIG. 21 is a timing chart showing the timings of
signals used to drive a CCD. FIG. 22 is a graph showing the
relationship between the illuminance of an imaging surface of a CCD
and a signal-to-noise ratio. FIG. 23 is a graph showing the
relationship between the illuminance of the imaging surface of the
CCD and an output voltage level.
[0147] As shown in FIG. 17, an endoscope system 101 of Example 7
consists mainly of an electronic endoscope (hereinafter an
endoscope) 102, a processor 103, and a monitor 105. The endoscope
102 has a solid-state imaging device incorporated therein. The
endoscope 102 is connected to the processor 103 so that it can be
disconnected freely. A signal processing unit 104 and a
field-sequential light source unit 122 are incorporated in the
processor 103. The monitor 105 is connected to the processor 103. A
video signal processed by the processor 103 is output to the
monitor 105.
[0148] The endoscope 102 has an elongated insertion unit 106 that
is inserted into a body cavity. An objective 108 through which
object light is projected is incorporated in the distal part 107 of
the insertion unit 106. For example, a charge-coupled device
(hereinafter a CCD) 109 that is a solid-state imaging device is
used as an image sensor and located on the image plane of the
objective 108. The CCD 109 is connected to a CCD driving means 111
and a CCD sensitivity control means 112, which are included in the
signal processing unit 104 incorporated in the processor 103, over
signal lines. Exposure, multiplication of produced charge carriers,
and reading are performed based on driving signals and a
sensitivity control signal produced by the CCD driving means 111
and CCD sensitivity control means 112 respectively. The image
sensor may be realized with a CMOS image sensor. A filter 110 for
transmitting light of a certain specific wavelength band is placed
on the face of the CCD 109. The filter 110 has a spectral property
of transmitting light stemming from fluorescence exhibited by a
living tissue but cutting off (not transmitting) excitation
light.
[0149] The CCD 109 is realized with a CCD described in the U.S.
Pat. No. 5,337,340 entitled "Charge Multiplying Detector (CMD)
Suitable for Small Pixel CCD Image Sensors." The CCD is
characterized in that an electron multiplication mechanism (that
is, a charge multiplying detection (CMD)) is formed at each pixel
location or as a preceding stage of a detection amplifier (as a
succeeding stage of a horizontal transfer register). When an
electric field (energy whose level falls within a band that is
approximately 1.5 times larger than an energy gap) is induced in
the electron multiplication mechanism (CMD), charge carriers
(electrons) collide against electrons in the valence band of the
electron multiplication mechanism. The electron multiplication
mechanism is thus excited to enter a conduction band. Impact
(secondary) ionization brings about a hole-electron pair. In other
words, when a pulse of certain strength (amplitude) is applied
sequentially, impact ionization sequentially brings about a
hole-electron pair. Namely, charge carriers are multiplied to an
extent proportional to the number of applications of the pulse.
[0150] The CCD 109 is connected to a signal processing means 114
incorporated in the processor 103 via a buffer 113 over a CCD cable
120 (signal line). An object image projected on the imaging surface
of the CCD 109 via the objective 108 and filter 110 is converted
into an electric signal by the CCD 109 and read from the CCD 109.
This output signal is fed to the signal processing means 114.
[0151] FIG. 21 indicates an exposure period and an interception
period (CCD reading period) determined with a rotary filter 129 to
be described later. FIG. 21 also indicates the relationship among a
sensitivity control pulse .phi.CMD, a vertical transfer pulse
.phi.IAG, and a horizontal transfer pulse .phi.SR that are applied
to the CCD 109, and an output signal of the CCD. The charge
multiplying detector (CMD) may be located at each pixel location in
the CCD 109 or as a preceding stage of a detection amplifier
therein. Herein, the CMD shall be located at each pixel location.
The sensitivity (CMD multiplication rate) of the CCD 109 can be
controlled by adjusting either the number of applications of the
pulse .phi.CMD per unit time or the amplitude (voltage level)
thereof. Herein, the number of applications of the pulse .phi.CMD
per unit time is adjusted to attain desired sensitivity (CMD
multiplication rate). In this case, the sensitivity control pulse
.phi.CMD is applied to the CCD 109 during the interception period
(reading period) succeeding the exposure period, whereby the
sensitivity (CMD multiplication rate) of the CCD 109 is raised.
Produced charge carriers are multiplied. Thereafter, the vertical
transfer pulse .phi.IAG and horizontal transfer pulse .phi.SR are
applied to the CCD 109. An output signal of the CCD 109 is then
acquired. Namely, the number of applications of the sensitivity
control pulse .phi.CMD per unit time is varied in order to enable
the CCD 109 to exert desired sensitivity (CMD multiplication
rate).
[0152] The endoscope 102 has a light guide 115 over which
illumination light of wavelengths ranging from the ultraviolet
spectrum to the near-infrared spectrum can be propagated. An
illumination lens 116 is located in front of the distal end of the
light guide 115. Illumination light that may be ordinary light or
special light propagated through the endoscope 102 over the light
guide 115 is irradiated to an object through the illumination lens
116. An SLF fiber (product name) or a quartz fiber may be used to
realize the light guide 115.
[0153] The signal processing means 114 consists of a signal
pre-processing means 117, a field-sequential synchronizing means
118, and a signal post-processing means 119. The signal
pre-processing means 117 performs various kinds of processing on an
output signal read from the CCD 109. The field-sequential
synchronizing means 118 synchronizes field-sequential signal
components output from the signal pre-processing means 117. The
signal post-processing means 119 performs various kinds of
processing on an output signal of the field-sequential
synchronizing means 118, and outputs the signal to the monitor 105.
In short, the output signal read from the CCD 109 is converted into
a television signal and output to the monitor 105.
[0154] The CCD driving means 111, CCD sensitivity control means
112, and signal processing means 114 are connected to a (first)
control means 121. The control means 121 extends control. The
control means 121 is connected to a (second) control means 126 for
controlling an iris diaphragm 123, a diaphragm control means 124,
and an RGB rotary filter control means 125 which are included in a
field-sequential light source unit 122 for routing field-sequential
illumination light rays to the endoscope 102. The control means 121
controls the CCD driving means 111 and signal processing means 114
while being interlocked with the RGB rotary filter control means
125.
[0155] The field-sequential light source unit 122 includes a lamp
127, a condenser lens 128, and an RGB rotary filter 129. The lamp
127 generates illumination light of wavelengths falling within a
wide band that ranges from the ultraviolet spectrum to the infrared
spectrum. The condenser lens 128 converges the illumination light
on the rear end of the light guide 115. The RGB rotary filter 129
is interposed between the lamp 127 and condenser lens 128. A xenon
lamp, a halogen lamp, a metal halide lamp, an LED, or a
high-pressure mercury lamp may be used as the lamp 127.
[0156] The rotary filter 129 is attached to the rotation shaft of a
motor 130 so that it can rotate. The rotary filter 129 is
controlled to rotate at a specified rotating speed by the RGB
rotary filter control means 125 under control of the control means
126. Field-sequential light rays of red, green, and blue are routed
to the rear end of the light guide 115.
[0157] The rotary filter 129 consists of two filter sets as shown
in FIG. 18, that is, a pair of filter sets 133 and 134 formed as an
inner circumferential part and outer circumferential part. The
inner circumferential first filter set 133 consists of three
filters that pass light rays R1, G1, and B1 required for an
ordinary light mode (observation under ordinary light). The outer
circumferential second filter set 134 consists of three filters
that pass light rays R2, G2, and B2 required for a special light
mode (observation under special light). The first filter set 133
and second filter set 134 each have a spectral property of
transmitting light suitable for each purpose of observation. The
first filter set 133 has filters 133a, 133b, and 133c, which pass
red (R1), green (G1), and blue (B1) light rays required for the
ordinary light mode (observation under ordinary light), shaped like
sectors and arranged circumferentially discretely. Filters 134a,
134b, and 134c that pass red (R2), green (G2), and blue (B2) light
rays required for the special light mode (observation under special
light) are discretely arranged outside the filters 133a, 133b, and
133c respectively.
[0158] Portions of the first filer set 133 among the filters 133a,
133b, and 133c that pass the red (R1), green (G1), and blue (B1)
rays required for the ordinary light mode (observation under
ordinary light) are interceptive areas. The interceptive areas
determine the interception period (reading period) during which the
CCD 109 is read. The filters 133a, 133b, and 133c and the
interceptive areas are arranged nearly equidistantly. The same
applies to the second filter set 134.
[0159] The filter 134b is realized with an excitation filter that
passes light of wavelengths ranging from the ultraviolet spectrum
to the blue spectrum and being used in the special light mode. The
light passing through the filter 134b causes a living tissue to
exhibit fluorescence. The filters 134a (R2) and 134c (B2) are
blocked in the present example, and no light passes through these
filters.
[0160] A rotary filter switching mechanism 131 is disposed on the
ray axis of illumination light linking the lamp 127 and light guide
115 in order to select either the inner circumferential filter set
133 or outer circumferential filter set 134. In the ordinary light
mode, light P1 emanating from the lamp 127 (indicated with a solid
line in FIG. 18) falls on the inner circumferential filter set 133.
In the special light mode, the rotary filter mechanism 131 switches
the filter sets by moving the whole rotary filter 129 so that light
P2 (indicated with a dot-dash line in FIG. 22) will fall on the
outer circumferential filter set 134. The rotary filter switching
mechanism 131 moves the motor 130 and rotary filter 129 relatively
to the lamp 127. Alternatively, the lamp 127 may be moved in an
opposite direction.
[0161] The processor 103 is connected to a mode switching means
135. When it is instructed to switch the observation modes
(ordinary light mode and special light mode), a rotary filter
switching instruction signal is fed to the rotary filter switching
mechanism 131 and control means 126. When the filter sets of the
rotary filter 129 are switched, if the special light mode is
selected, the iris diaphragm 123 is automatically fully closed by
the diaphragm control means 124.
[0162] The rotary filter switching instruction signal is also fed
to the control means 121. The control means 121 controls the signal
processing means 114, CCD driving means 111, and CCD sensitivity
control means 112 so that these means will act in a selected mode
(ordinary light mode or special light mode).
[0163] The signal processing means 114 has the signal
pre-processing means 117 thereof configured as shown in, for
example, FIG. 19. Referring to FIG. 19, an output signal of the CCD
109 is fed to the signal pre-processing means 117. In the signal
pre-processing means 117, the output signal of the CCD 109 passes
through a preamplifier 140, a CDS circuit 141, a low-pass filter
143, a clamping circuit 144, an automatic gain control (AGC)
circuit 145. An A/D converter 146 then digitizes the signal. The
digital signal is isolated from a patient circuit and transmitted
to a secondary circuit by a photocoupler 147a. The secondary
circuit includes a white balance control circuit 148, a tone
control circuit 149, and a gamma correction circuit 150. After
white balance control, tone control, and gamma correction are
carried out, an expansion circuit 151 performs electronic zooming
for the purpose of expansion.
[0164] An output signal of the expansion circuit 151 is fed to the
field-sequential synchronizing means 118 via a contour enhancement
circuit 152. A photometry means 142 is connected as a succeeding
stage of the CDS circuit 141. An average of voltage levels assumed
by the output signal of the CCD 109 during one field is calculated
and fed to the control means 121. The control means 121 outputs a
control signal to each of the white balance control circuit 148,
tone control circuit 149, expansion circuit 151, and contour
enhancement circuit 152 which are included in the secondary
circuit. Moreover, the control means 121 outputs a control signal,
which is used to control the clamping circuit 144 included in the
patient circuit, via the photocoupler 147b serving as an
isolation/transmission means.
[0165] The red, green, and blue field-sequential signal components
output from the signal pre-processing means 117 are fed to
synchronizing means 163a, 163b, and 163c via selector switches 160,
162A, and 162B included in the field-sequential signal
synchronizing means 118 shown in FIG. 20. The synchronizing means
163a, 163b, and 163c each have a memory in which data for at least
one field can be stored. The red, green, and blue field-sequential
signal components that are fed in that order are stored in the
memories associated with the colors. The stored field-sequential
signal components are read simultaneously, and output as
synchronized signal components.
[0166] FIG. 20 shows synchronizing means 163I (where I denotes a,
b, or c) as an example of the synchronizing means 163a, 163b, and
163c. The synchronizing means 163I is each realized with a means
composed of image memories 164a and 164b in which data for at least
two fields can be stored. The synchronizing means 163a is
associated with a video signal component acquired with light
passing through the filter 133a or 134a of the rotary filter 129.
Likewise, the synchronizing means 163b is associated with a video
signal component acquired with light passing through the filter
133b or 133a of the rotary filter 129. The synchronizing means 163c
is associated with a video signal component acquired with light
passing through the filter 133c or 134c of the rotary filter
129.
[0167] Writing and reading of an image signal component in and from
the image memories 164a and 164b are switched alternately, whereby
signal components are synchronized. Synchronized signal components
output from the synchronizing means 163a, 163b, and 163c are fed to
still image memories 165a, 165b, and 165c, in which still image
signal components are stored, included in the signal
post-processing means 119, and also fed to a selector 166. The
synchronized signal components output from the synchronizing means
163a, 163b, and 163c pass through the selector 166, and are fed as
motion picture signal components to the monitor 105 via a 75-ohm
driver 167 disposed as a succeeding stage of the selector 166. The
other input terminals of the selector 166 are connected to the
still image memories 165a, 165b, and 165c.
[0168] The control means 121 controls writing and reading of an
image signal component in and from the still image memories 165a,
165b, and 165c. In response to an external Freeze instruction, the
control means 121.extends control so that image signal components
to be frozen will be stored in the still image memories 165a, 165b,
and 165c respectively. Moreover, the control means 121 controls the
selector 166 so that the selector will feed still image signal
components, which are output from the still image memories 165a,
165b, and 165c, to the monitor 105 via the 75-ohm driver 167 on the
succeeding stage of the selector. Herein, the selector 166 selects
either of the still image signal components and the motion picture
signal components output from the synchronizing means 163a, 163b,
and 163c.
[0169] A ROM 170 in which information inherent to the endoscope 102
is stored is incorporated in the endoscope 102. When the endoscope
102 is connected to the processor 103, the information is
transmitted to the control means 121 included in the signal
processing unit 104 incorporated in the processor 103. The
sensitivity (CMD multiplication rate) of the CCD 109 is then
controlled. In short, the ROM 170 serves as a designating means for
designating the sensitivity of the CCD 109.
[0170] (Operations)
[0171] Operations to be exerted in the ordinary light mode and
special light mode will be described below.
[0172] To begin with, assume that the ordinary light mode
(observation under ordinary light) is designated. In this case, the
first filter set 133 of the rotary filter 129 is placed on the path
of illumination light. The CMD multiplication rate for the CCD 109
is set to a fixed value. The set value (fixed value) of the CMD
multiplication rate for the CCD 109 predefined for the ordinary
light mode is transmitted from the ROM 70 to the processor 103 when
the endoscope 102 is connected to the processor 103.
[0173] The CCD sensitivity control means 112 receives the set
(fixed) value of the COD multiplication rate for the CCD 109, which
is transmitted from the ROM 70, via the control means 121. The CCD
sensitivity control means 112 calculates the number of applications
of a pulse per unit time associated with the set (fixed) value of
the CMD multiplication rate predefined for the ordinary light mode.
The CCD sensitivity control means 112 then outputs the calculated
number of applications of the pulse per unit time to the CCD 109
during an exposure period or an interception (reading) period
during which the CCD 109 receives light or is read.
[0174] An input means (or designating means) such as a keyboard may
be connected to the control means 121 included in the signal
processing unit 104. A user may manually enter any value as the CMD
multiplication rate at the input means. In this case, the CCD
sensitivity control means 112 sets the CMD multiplication rate for
the CCD 109 to the user-entered value under control of the control
means 121. The same applies to the special light mode.
[0175] Illumination light emitted from the lamp 127 passes through
the first filter set 133. Red, green, and blue field-sequential
illumination light rays are successively irradiated to a living
tissue. Reflected rays of the red, green, and blue rays are
projected on the CCD 109, and red, green, and blue image signal
components (video signal components) are input to the signal
processing means 114. Consequently, a view image produced with
ordinary light is displayed on the monitor 105.
[0176] The photometry means 142 calculates an average of voltage
levels assumed by an output signal of the CCD 109 during one field,
and outputs the average to the control means 121. The control means
121 outputs the average to the second control means 126. A
diaphragm control command is output based on the average, whereby
the iris diaphragm 123 is opened or closed. If an object is too
bright relative to a predefined reference brightness level, the
output signal of the CCD 109 assumes a high voltage level.
Consequently, the iris diaphragm 123 is closed (the intensity of
light routed to the rear end of the light guide decreases). In
contrast, if the object is dark, the output signal of the CCD 109
assumes a low voltage level. Consequently, the iris diaphragm 123
is opened (the intensity of light routed to the rear end of the
light guide increases). Thus, the intensity of light irradiated to
a living tissue is varied (automatic light adjustment).
[0177] When an input means (or designating means) such as a
keyboard is connected to the control means 121 included in the
signal processing unit 104, a user can set the brightness
(reference value) of an image displayed on the monitor 105 to any
level at the input means. The automatic gain control circuit 145
can electrically amplify the output signal of the CCD 109 so that
the brightness of an image displayed on the monitor 105 will be set
to the designated level. When an object is too dark, even if the
automatic light adjustment is performed, the brightness of an image
displayed on the monitor 105 may not reach the designated level. In
this case, the output signal of the CCD 109 is electrically
amplified (automatic gain control).
[0178] The intensity of reflected light of (red, green, and blue)
field-sequential light rays irradiated to a living tissue
(alimentary canal or bronchus) falls within a domain larger than 1
lux in the graphs of FIG. 22 and FIG. 23. As seen from FIG. 22 and
FIG. 23, when the CMD multiplication rate for the CCD 109 is set to
a larger value, a signal-to-noise ratio and an output voltage level
are higher than those attained when electrons flowing in each CMD
in the CCD 109 are not multiplied.
[0179] Assume that the ordinary light mode (observation under
ordinary light) is designated. In this case, even if the brightness
of an object (living tissue), or in other words, the intensity of
light reflected from an object varies, a view image of proper
brightness whose level is designated by a user is always displayed
on the monitor 105. This is attributable to the automatic light
adjustment and automatic gain control. Moreover, when the CMD
multiplication rate for the CMD 109 is raised, the signal-to-noise
ratio improves. Namely, in the ordinary light mode (observation
under ordinary light), a view image of proper brightness can be
produced without impairment of image quality owing to the automatic
light adjustment. If the automatic light adjustment fails to
provide sufficient brightness, the automatic gain control is
activated.
[0180] In contrast, assume that the special light mode (observation
under special light) is designated. In this case, a user
manipulates, for example, a mode selection switch included in the
mode switching means 135. The rotary filter switching mechanism 131
is thus activated to place the second filter set 134 of the rotary
filter 129 on the path of illumination light. At this time, the
iris diaphragm 129 is fully opened. Consequently, the most intense
excitation light falls on the rear end of the light guide 115. The
sensitivity of the CCD 109, that is, the CMD multiplication rate
for the CCD 109 is set to a fixed value predefined for the special
light mode. The set value (fixed value) of the CMD multiplication
rate for the CCD 109 is a value transmitted from the ROM 170 and is
larger than that predefined for the ordinary light mode
(observation under ordinary light).
[0181] The CCD sensitivity control means U2 receives the set
(fixed) value of the CMD multiplication rate for the CCD 109 from
the ROM 170 via the control means 121. The CCD sensitivity control
means then calculates the number of applications of a pulse
associated with the set (fixed) value of the CMD multiplication
rate predefined for the special light mode. The CCD sensitivity
control means outputs the calculated number of applications of the
pulse to the CCD 109 during an exposure or interception (reading)
period during which the CCD 109 receives light or is read.
[0182] Excitation light (of wavelengths ranging from the
ultraviolet spectrum to the blue spectrum in the present example)
emitted from the lamp 127 passes through the second filter set 134.
In the present example, only excitation light passing through the
filter 134b (G2) is irradiated intermittently to a living tissue.
In the present example, the filters 134a (R2) and 134c (B2) are
blocked. No light therefore passes through the filters 134a (R2)
and 134c (B2).
[0183] Light reflected from a living tissue to which excitation
light is irradiated, and light stemming from fluorescence exhibited
by (for example, NADH or flavin contained in) the living tissue
excited by the excitation light falls on the objective 108. The
filer 110 cuts off the reflected light of the excitation light. The
light stemming from fluorescence enters the CCD 109. An image
signal picked up from the light stemming fluorescence by the CCD
109 is fed to the signal processing means 114. The signal
processing means 114 processes the image signal derived from the
light passing through the filter 134b (G2), and outputs the
resultant signal to the monitor 105.
[0184] The automatic gain control circuit 145 electrically
amplifies the output signal of the CCD 109 to a set voltage level.
Specifically, assume that an object is so dark that the output
signal of the CCD 109 is still lower than the set voltage level
despite multiplication of electrons flowing in each CMD in the CCD
109. In this case, the output signal is electrically amplified in
order to increase the magnitude of the output signal (automatic
gain control). Consequently, a view image of proper brightness
produced with special light can always be displayed on the monitor
105. Incidentally, when an input means (or designating means) such
as a keyboard is connected to the control means 121 included in the
signal processing unit 104, a user can set the brightness
(aforesaid reference level) of an image displayed on the monitor
105 to any level at the input means.
[0185] Now, a description will be made of a signal-to-noise ratio
relative to a signal representing a view image (in the present
example, an image produced with light stemming from fluorescence)
displayed on the monitor 105, and the brightness of the view image.
The signal-to-noise ratio and brightness are attained with the CMD
multiplication rate for the CCD 109 raised (set to be 3 or 10) (see
FIG. 22 and FIG. 23).
[0186] The signal-to-noise ratio reflects how well a dark object
can be visualized or with what image quality the dark object can be
visualized. Especially when an image signal is picked up from
feeble light such as light stemming from fluorescence, the
signal-to-noise ratio relative to the image signal is a very
important parameter. Moreover, the output voltage level of the
image signal reflects the brightness of an image displayed on a
monitor, and is therefore a very important parameter, too. When a
solid-state imaging device employed is a typical CCD (without a
multiplication mechanism), the signal-to-noise ratio relative to a
signal representing a view image to be display on the monitor 105
and the brightness of the view image substantially correspond to
those attained when the CMD multiplication rate for the CCD 109 is
set to 1 (electrons flowing in each CMD in the CCD 109 are not
multiplied).
[0187] When light of wavelengths ranging from the ultraviolet
spectrum to the blue spectrum is irradiated to a living tissue
(alimentary canal or bronchus), light stems from fluorescence
exhibited by NADH, flavin, or collagen contained in the living
tissue. However, the intensity of the light stemming from
fluorescence is very low (falls within a domain smaller than 1 lux
in the graphs of FIG. 22 anf FIG. 23). It is hard for a typical CCD
to pick up an image signal from such light. As seen from FIG. 22
and FIG. 23, when the CMD multiplication rate for the CCD 109 is
set to a higher value, the signal-to-noise ratio and output voltage
level are much higher than they are when the typical CCD is
employed.
[0188] The relationship among the illuminance (reflecting the
brightness of an object) of an imaging surface of the CCD 109, a
signal-to-noise ratio detected on an output stage of the processor
103, and an output voltage level detected thereon will be described
in relation to the sensitivity of the CCD 109.
[0189] Assume that an endoscope system concerned includes the
endoscope 101 (including the CCD 109 and CCD cable 120) and the
processor 103 (including the signal processing means 114). The
signal-to-noise ratio S/N and output voltage level S detected on
the output stage (signal processing means 114) of the processor 103
are calculated theoretically. S / N = .times. S / { N .times.
.times. CCD 2 + N .times. .times. CV 2 } 1 / 2 = .times. { A n K (
1 - .beta. ) G } / { ( A 2 F 2 ( n + D ) + R 2 ) .times. K 2 ( 1 -
.beta. ) 2 G 2 + N .times. .times. CV 2 } 1 / 2 = .times. { n K ( 1
- .beta. ) G } / { ( F 2 ( n + D ) + R 2 / A 2 } .times. K 2 ( 1
.beta. ) 2 G 2 + N .times. .times. CV 2 / A 2 } 1 / 2 S = .times. A
n K ( 1 - .beta. ) G .function. [ mV ] ( 1 ) ( 1 - 2 ) ( 1 - 3 ) (
2 ) ##EQU1## where S denotes the output voltage level of an image
signal (detected on the output stage of the processor 103). Herein,
for brevity's sake, the pedestal level of the signal shall be 0.
Moreover, N CCD denotes the voltage level of a noise occurring in
the CCD 109 (detected on the output stage of the processor 103). N
CV denotes the total voltage level of a noise occurring along the
CCD cable 120 and a noise occurring in the processor 103 (detected
on the output stage of the processor 103).
[0190] [Parameters]
[0191] (1) CCD-Related Parameters
[0192] n [e/pixel]: the number of charge carriers per pixel
location (before electrons flowing in each CMD are multiplied)
n=M.times.(4.1.times.10.sup.9).times..mu..sup.2.times..eta..times.RA.time-
s.T [e/pixel/flame] where M [lux] denotes the illuminance of the
imaging surface of the CCD, .mu. denotes the size of each pixel
location, .eta. denotes a quantum efficiency, RA denotes a rate of
hole area, and T denotes an exposure time.
[0193] A: CMD multiplication rate
[0194] D [e/pixel/s]: dark current occurring at each pixel
location
[0195] R [eRMS]: a noise derived from reading (occurring in a
detection amplifier)
[0196] K [mv/e]: charge-voltage conversion factor set in the
detection amplifier
[0197] A: CMD multiplication rate
[0198] F.sup.2: CMD excess noise factor
[0199] (2) Parameters relevant to components other than CCD
[0200] .beta.[.times.100%]: attenuation ratio of a signal
propagated over the CCD cable 120
[0201] G: gain produced by the processor (G=voltage level of output
of processor/voltage level of input thereof)
[0202] Ncv [mV]: total voltage level of a noise occurring along the
CCD cable 120 and a noise occurring in the processor 103
[0203] (Signal to Which a Gain is Given)
[0204] FIG. 22 shows the relationship between an illuminance on the
imaging surface of a CCD and a signal-to-noise ratio which is
established with the CMD multiplication rate set to 1, 3, and 10.
The illuminance and signal-to-noise ratio are calculated by
assigning parameter values to the formulae (1-2) and (2). FIG. 23
shows the relationship between the illuminance of the imaging
surface of the CCD and an output voltage level. In FIG. 22, the
signal-to-noise ratio (axis of ordinates) is calculated as
S/N=20.times.log {formula (1-2)} (unit: dB).
[0205] (Advantages)
[0206] When the special light mode (observation under special
light) is designated, an object from which feeble light is returned
and which cannot be visualized by a typical CCD can be visualized
owing to multiplication of electrons flowing in each CMD in the CCD
and automatic gain control. Moreover, the signal-to-noise ratio
relative to an image signal and the output voltage level of the
image signal are improved. This results in a view image of
excellent image quality (high signal-to-noise ratio) and proper
brightness.
[0207] Information read from the ROM 170 may represent a type of
endoscope or the brightness of an image displayed on the monitor
105 (output voltage level provided by the processor 103) instead of
the CMD multiplication rates for CCD 109 predefined for the
ordinary light mode and special light mode. Otherwise, correction
data for a difference in the CCD multiplication rate for the CCD
109 from one pixel location to another may be transmitted to the
processor 103.
[0208] Two CCDs may be incorporated in the distal part of an
endoscope, and the first CCD of the CCDs may be used exclusively
for the ordinary light mode (observation under ordinary light) and
the second CCD thereof may be used exclusively for the special
light mode (observation under special light). In this case, the CCD
109 employed in the present example is used as the second CCD. The
first CCD dedicated to the ordinary light mode may be realized with
the CCD 109 or the typical CCD.
[0209] The rotary filter 129 includes three filters associated with
the special light mode. The number of filters associated with the
special light mode need not be 3 but may be two or less or four or
more.
[0210] The filters of the rotary filter 129 associated with the
special light mode have the property of transmitting light whose
wavelengths range from the ultraviolet spectrum to the blue
spectrum. Alternatively, the filters may transmit light of
wavelengths falling within the ultraviolet or blue spectrum alone.
The filters may be used to perform auto-fluorescence imaging.
[0211] The spectrum of light transmitted by the filters of the
rotary filter 129 associated with the special light mode ranges
from the ultraviolet spectrum to the blue spectrum. The filters may
transmit light of wavelengths falling within the visible spectrum.
In this case, a drug (such as HpD, porphyrins, NPe6, ALA, m-THPC,
ATX-S10, BPD-MA, ZnPC, SnET2, etc.) may be administered in order to
perform drug fluorescence imaging for the purpose of photodynamic
diagnosis.
[0212] The spectrum of light transmitted by the filters of the
rotary filter 129 associated with the special light mode ranges
from the ultraviolet spectrum to the blue spectrum. The filters may
transmit light of wavelengths falling within the near-infrared
spectrum. In this case, a drug (for example, indocyanine green that
is a derivative marker antibody) may be administered in order to
perform drug fluorescence imaging.
[0213] The spectrum of light transmitted by the filters of the
rotary filter 129 associated with the special light mode ranges
from the ultraviolet spectrum to the blue spectrum. The filters may
transmit light of wavelengths ranging from the visible spectrum to
the near-infrared spectrum. An image signal may be picked up from
the reflected light of the light. In this case, the filter 110 need
not be included.
[0214] The mode switching means 135 is included in the processor
103 but may be included in the endoscope 102.
[0215] The processor 103 has the signal processing unit 104 and
field-sequential light source unit 122 integrated thereinto.
Alternatively, the signal processing unit 104 and field-sequential
light source unit 122 may be provided as stand-alone
apparatuses.
EXAMPLE 8
[0216] In Example 8, automatic light adjustment and automatic gain
control are carried out for observation under ordinary light. For
observation under special light, the CMD multiplication rate is
manually set to a fixed value, automatic gain control is extended
to a processor, an exposure time is made long, and light is emitted
fully.
[0217] In Example 7, the exposure time is the same between the
ordinary light mode (observation under ordinary light) and special
light mode (observation under special light).
[0218] In Example 8, the exposure time is longer in the special
light mode than in the ordinary light mode. Moreover, a high
signal-to-noise ratio and a high output voltage level are
attained.
[0219] (Constituent Features)
[0220] FIG. 24 shows the structure of a rotary filter. FIG. 25 is a
timing chart showing the timings of signals used to drive a CCD in
the special light mode. FIG. 26 is a graph indicating the
relationship between the luminance on the imaging surface of the
CCD and a signal-to-noise ratio (long exposure). FIG. 27 is a graph
indicating the relationship between the luminance on the imaging
surface of the CCD and an output voltage level (long exposure).
[0221] The description of a rotary filter 129A and other components
identical to those of Example 7 will be omitted.
[0222] The rotary filter 129A consists, as shown in FIG. 24, of two
filter sets, that is, filter sets 133 and 134A serving as inner and
outer circumferential parts of the rotary filter 129A. The inner
circumferential first filter set 133 consists of three filters
133a, 133b, and 133c used for the ordinary light mode (observation
under ordinary light) as they do in Example 7. The outer
circumferential second filter set 134A consists of two filters
134aA and 134c used for the special light mode (observation under
special light). The filter sets 133 and 134A have spectral
transmission properties thereof matched with respective purposes of
observation.
[0223] In the present example, a filter for passing excitation
light used to cause auto-fluorescence (light of wavelengths ranging
from the ultraviolet spectrum to the blue spectrum) is adopted as
the filter 134aA. The filter 134c is blocked. The second filter set
134A of the rotary filter 129A is divided into three areas R2, G2,
and B2 as shown in FIG. 24. The filter 134aA occupies the whole
area R2 and a half of the area G2. The filter 134c occupies nearly
a half of the area B2 and is shaped like a sector. The filter 134aA
and filter 134c are arranged circumferentially. The portion of the
second filter set 134A other than the filters 134aA and 133c is
blocked and determines an interception time (reading time) during
which the CCD 109 is read. The control means 121 controls the CCD
driving means 111 in response to a command output from the mode
switching means 135 so that the CCD driving means will drive the
CCD in line with a selected mode (ordinary light mode or special
light mode).
[0224] FIG. 25 is a timing chart indicating the timings of signals
used to drive the CCD in the special light mode. FIG. 25 indicates
an exposure period and an interception period (reading period)
determined by the second filter set (outer circumferential part) of
the rotary filter 129A. Moreover, FIG. 25 indicates the
relationship among a sensitivity control pulse .phi.CMD, a vertical
transfer pulse .phi.IAG, and a horizontal transfer pulse .phi.SR
that are applied to the .phi.CCD 109, and an output signal of the
CCD. The magnitudes of turns R2, G2, and B3 made by the rotary
filter correspond to the sizes of the areas R2, G2, and B2 of the
rotary filter 129A. The sensitivity control pulse .phi.CMD,
vertical transfer pulse .phi.IAG, and horizontal transfer pulse
.phi.SR are output from the CCD sensitivity means 112 and CCD
driving means 111 respectively during the interception period
(reading period) succeeding the exposure period only when a gate
pulse assumes an on voltage level. The COD 109 provides the output
signal during the interception period.
[0225] In Example 8, the gate pulse assumes the on voltage level
only when the rotary filter 129A makes the turns G2 and B2. When
the rotary filter 129A makes the turn R2, the gate pulse assumes an
off voltage level. The CCD 109 does not provide the output signal.
An exposure time is therefore equal to the sum of a period
determined with the area R2 and a period determined with an
exposure area of the area G2. The exposure time is therefore as
long as nearly the triple of the one in Example 7. An image signal
read from the CCD 109 during a period determined with an
interceptive area of the area G2 is fed to the image memories
included in the synchronizing means 163a and 163b. An image signal
read from the CCD 109 during a period determined with an
interceptive area of the area B2 is fed to the image memory
included in the synchronizing means 163c. Incidentally, the gate
pulse assumes the on voltage level in the ordinary light mode.
After an object is exposed to light passing through the first
filter set composed of the filters 133a, 133b, and 133c, the CCD
109 is read.
[0226] (Operations)
[0227] Operations exerted in the special light mode will be
described below. Operations exerted in the ordinary light mode are
identical to those in Example 7.
[0228] Excitation light (of wavelengths ranging from the
ultraviolet spectrum to the blue spectrum in the present example)
emitted from the lamp 127 passes through the second filter set
134A. According to the present example, only the excitation light
passing through the filter 134aA is intermittently irradiated to a
living tissue. In the present example, no light passes through the
filter 134c and is irradiated to the living tissue. An exposure
time during which light passing through the filter 134aA is
irradiated is generally three times longer than that in Example 7.
Charge carriers are received and accummulated in the CCD 109 during
a period during which excitation light passing through the filter
134aA of the second filter set is irradiated to the living tissue.
The charge carriers are read during an interception period (reading
period) determined with the interceptive area of the area G2. An
image signal output from the CCD is fed to the signal processing
means 114. The signal processing means 114 processes the signal
read during the period determined with the interceptive area of the
area G2. Consequently, a view image produced with special light is
displayed on the monitor 105.
[0229] Now, a description will be made of a signal-to-noise ratio
relative to a signal representing the view image displayed on the
monitor 105 (image produced with light stemming from
auto-fluorescence in the present example) and the brightness of the
view image. The signal-to-noise ratio and brightness are attained
with an exposure time extended and the CMD multiplication rate for
the CCD 109 raised.
[0230] In Example 8, an exposure time T' shall be approximately
three times longer than the exposure time T in Example 1. Moreover,
the COD multiplication rate for the CCD 109 shall be set to 3 and
10. FIG. 26 and FIG. 27 graphically show the relationship between
the illuminance on the imaging surface of the CCD and the
signal-to-noise ratio or the output voltage level which is
established under the above conditions.
[0231] As seen from FIG. 26 and FIG. 27, when a living tissue is
exposed for a longer exposure time (irradiation time) with the CMD
multiplication rate for the CCD 109 held constant, the
signal-to-noise ratio and output voltage level get higher. When the
CMD multiplication rate is raised and the exposure time is
extended, the signal-to-noise ratio and output voltage level get
higher.
[0232] (Advantages)
[0233] In the special light mode (observation under special light),
even if light returning from an object is too feeble to visualize
the object using a typical CCD, the object can be visualized owing
to multiplication of electrons flowing in each CMD in the CCD,
extension of an exposure time, and automatic gain control.
Moreover, a signal-to-noise ratio and an output voltage level are
raised. Consequently, a view image of excellent image quality (high
signal-to-noise ratio) and proper brightness can be produced.
[0234] Information read from the RON 170 may represent a type of
endoscope or the brightness of an image displayed on the monitor
105 (output voltage level of processor 103) instead of the CMD
multiplication rate for the CCD 109 defined for the ordinary light
mode or special light mode. Otherwise, correction data for a
difference in the CMD multiplication rate for the CCD 109 from one
pixel location to another may be transmitted to the processor
103.
[0235] Two CCDs may be incorporated in the distal part of an
endoscope. The first CCD of the two CCDs may be used exclusively
for the ordinary light mode (observation under ordinary light), and
the second CCD thereof may be used exclusively for the special
light mode (observation under special light). In this case, the CCD
109 employed in the present example is adopted as the second CCD.
The first CCD dedicated to the ordinary light mode may be realized
with the CCD 109 or a typical CCD.
[0236] In the present example, reading of the CCD is performed
twice during one full turn of the rotary filter. The gate pulse may
be applied only once while the rotary filter makes the turns R2,
G2, and B2. In this case, the exposure time set in Example 1 can be
extended to be five times longer at most. Two filters included in
the rotary filter 129A are associated with the special light mode.
The number of filters associated with the special light mode need
not be confined to two but may be one.
[0237] The filters of the rotary filter 129A associated with the
special light mode have the property of transmitting light whose
wavelengths range from the ultraviolet spectrum to the blue
spectrum. Alternatively, filters for transmitting light whose
wavelengths fall within the ultraviolet or blue spectrum alone may
be employed for auto-fluorescence imaging.
[0238] The filters of the rotary filter 129A associated with the
special light mode have the spectral property of transmitting light
whose wavelengths range from the ultraviolet spectrum to the blue
spectrum. Alternatively, the filters may transmit light of
wavelengths falling within the visible spectrum. In this case, a
drug (HpD, porphyrins, NPe6, ALA, m-THPC, ATX-S10, BPD-MA, ZnPC,
SnET2) is administered in order to perform drug fluorescence
imaging for the purpose of photodynamic diagnosis.
[0239] The filters of the rotary filter 129A associated with the
special light mode have the spectral property of transmitting light
whose wavelengths range from the ultraviolet spectrum to the blue
spectrum. Alternatively, the filters may transmit light of
wavelengths falling within the near-infrared spectrum. In this
case, a drug (for example, indocyanine green that is a derivative
marking antibody) is administered in order to perform drug
fluorescence imaging.
[0240] The filters of the rotary filter 129A associated with the
special light mode have the spectral property of transmitting light
whose wavelengths range from the ultraviolet spectrum to the blue
spectrum. Alternatively, the filters may transmit light of
wavelengths ranging from the visible spectrum to the near-infrared
spectrum. An image signal may then be picked up from the reflected
light of the light. In this case, the filter 110 need not be
included.
[0241] The mode switching means 135 is included in the processor
103, but may be included in the endoscope 102.
[0242] The processor 103 has the signal processing unit 104 and
field-sequential light source unit 122 integrated thereinto. The
signal processing unit 104 and field-sequential light source unit
122 may be included as stand-alone apparatuses.
EXAMPLE 9
[0243] Example 9 is such that the CMD multiplication rate is varied
automatically depending on whichever of observation under ordinary
light and observation under special light is designated.
[0244] In Example 7, the CMD multiplication rate for the CCD is set
to a fixed value. The CMD multiplication rate is adjusted manually.
For optimizing the brightness of an image displayed on the monitor,
the output signal of the CCD is electrically amplified and thus
adjusted through automatic gain control.
[0245] (Constituent Features)
[0246] FIG. 28 is a block diagram schematically showing the
configuration of an endoscope system. FIG. 29 is a block diagram
showing a signal pre-processing means included in a signal
processing means.
[0247] The description of components identical to those shown in
FIG. 17 will be omitted.
[0248] The automatic gain control circuit 145, iris diaphragm 123,
and diaphragm control means 124 included in Example 7 are excluded
in Example 9.
[0249] The photometry means 142 calculates an average of voltage
levels assumed by the output signal of the CCD 109 during one
field, and outputs the average to the CCD sensitivity control means
112 via the control means 121. The CCD sensitivity control means
112 calculates the number of applications of a pulse per unit time
associated with a CMD multiplication rate that permits the output
signal of the CCD 109 to assume a set voltage level. Consequently,
the pulse is applied to the CCD 109 by the calculated number of
times during an interception period (reading period) during which
the CCD 109 is read.
[0250] (Operations)
[0251] A user manipulates, for example, a mode selection switch
included in the mode switching means 135 so as to select a desired
mode (ordinary light mode or special light mode). In the
field-sequential light source unit 122A, the rotary filter
switching mechanism 131 turns the rotary filter 129 according to
the selected mode. Illumination light matched with the selected
mode is routed to the rear end of the light guide 115 via the
rotary filter 129, and irradiated to a living tissue. Since the
field-sequential light source unit 122a has no diaphragm, the
intensity of illumination light emitted from the distal end of the
endoscope 102 remains constant.
[0252] Field-sequential light rays (of red, blue, and green) are
reflected from a living tissue in the ordinary light mode, while
special light such as light stems from fluorescence exhibited by
the living tissue in the special light mode. The reflected light
rays or light stemming from fluorescence is projected on the CCD
109 in order to pick up an image signal. A resultant video signal
is fed to the signal processing means 114A. The signal processing
means 114A processes the output signal of the CCD 109.
Consequently, a view image is displayed on the monitor 105.
[0253] When an object (living tissue) exhibiting certain brightness
is imaged using the CCD 109, a signal-to-noise ratio (FIG. 22) and
an output voltage level (FIG. 23) vary depending on the CMD
multiplication rate for the CCD 109. The photometry means 142
calculates an average of voltage levels assumed by the output
signal of the CCD 109 during one field, and outputs the average to
the CCD sensitivity control means 112 via the control means 121.
The CCD sensitivity control means 112 calculates the number of
applications of a pulse per unit time associated with a CMD
multiplication rate for the CCD 109 that permits the output signal
of the CCD 109 to assume a voltage level and represent an image of
brightness of a user-designated level to be displayed on the
monitor 105. The CCD sensitivity control means 112 outputs the
number of applications of the pulse per unit time to the CCD 109.
Specifically, when the voltage level of a signal output from the
processor 103A is lower than a set valuer the CMD multiplication
rate for the CCD 109 is automatically raised. When the voltage
level of a signal output from the processor 103A is higher than the
set value, the CMD multiplication rate for the CCD 109 is
automatically lowered. A user can always view an image of
brightness of any user-designated level on the monitor 105.
[0254] Moreover, when light returning from an object is especially
feeble, the CMD multiplication rate for the CCD 109 is
automatically raised. For example, as seen from FIG. 22, when the
CMD multiplication ratio is set to a large value, a signal-to-noise
ratio is higher than it is when the CMD multiplication rate is set
to a small value. An excellent view image can therefore be
produced.
[0255] A signal output from the output stage of the processor 103A
is amplified by raising the CMD multiplication ratio for the CCD
109. Compared with when the signal output from the CCD 109 is
electrically amplified, influence of a noise can be suppressed.
This results in an image benefiting from a high signal-to-noise
ratio.
[0256] (Advantages)
[0257] The CMD multiplication ratio for a CCD is automatically
controlled based on the brightness of an object. This results in a
view image of excellent image quality (high signal-to-noise ratio)
and proper brightness. Moreover, the configuration of a light
source unit can be simplified.
[0258] An appendix and variant of the present example are identical
to those of Example 7.
[0259] In the present example, the CMD multiplication rate for the
CCD 109 is varied between the ordinary light mode and special light
mode in order to make the brightness of an image displayed on the
monitor 105 constant. Alternatively, in the ordinary light mode,
similarly to that in Example 1, the iris diaphragm included in the
light source unit may be controlled to vary the intensity of light
to be irradiated to a living tissue.
EXAMPLE 10
[0260] The present example is such that the CMD multiplication
ratio is automatically varied depending on whichever of observation
under ordinary light and observation under special light is
designated. For the observation under special light, an object is
exposed to light for a long period of time.
[0261] In Example 9, an exposure time is the same between the
ordinary light mode (observation under ordinary light) and special
light mode (observation under special light).
[0262] In contrast, in Example 10, an exposure time for the special
light mode is longer than that for the ordinary light mode. Thus,
the present example attempts to attain a higher signal-to-noise
ratio than that attained in Example 9.
[0263] A rotary filter (second filter set) is structured as shown
in FIG. 24. The timings of signals applied in order to drive the
CCD in the special light mode are defined as shown in FIG. 25.
[0264] (Constituent Features)
[0265] The description of components identical to those of Example
9 will be omitted.
[0266] Differences of Example 19 from Example 9 lie in the
structure of a rotary filter 129A and the timings of signals
applied to drive a CCD in the special light mode.
[0267] (Operations)
[0268] Operations to be exerted in the special light mode will be
described below. Operations to be exerted in the ordinary light
mode are identical to those in Example 9.
[0269] Excitation light emitted from the lamp 127 (light of
wavelengths ranging from the ultraviolet spectrum to the blue
spectrum) passes through the second filter set 134A. In the present
example, the excitation light passing through the filter 134aA is
intermittently irradiated to a living tissue. An irradiation
(exposure) time is approximately three times longer than that in
Example 9. No light passes through the filter 134c and is
irradiated in the present example. The CCD 109 receives light
stemming from fluorescence exhibited by the living tissue to which
the excitation light is irradiated. Accumulated charge carriers are
read from the CCD 109 during an interception period (reading
period) determined with the interceptive area of the area G2. An
acquired imaging signal is fed to the signal processing means 114A.
The signal processing means 114A processes the signal.
Consequently, a view image produced with special light is displayed
on the monitor 105.
[0270] Now, a description will be made of a signal-to-noise ratio
relative to a signal representing a view image displayed on the
monitor 105 (an image produced with auto-fluorescence in the
present example) and the brightness of the view image. The
signal-to-noise ratio and brightness are attained with an exposure
time extended and the CMD multiplication ratio for the CCD 109
raised.
[0271] In Example 10, an exposure time T' is approximately three
times longer than the exposure time T in Example 9. Moreover, the
CMD multiplication rate for the CCD 109 is set to 3 and 10. FIG. 26
and FIG. 27 graphically show the relationship between the
illuminance on the imaging surface of the CCD and a signal-to-noise
ratio or an output voltage level which is established under the
above conditions.
[0272] Assume that an object (living tissue) of certain brightness
is imaged using the CCD 109 with an exposure time extended. A
signal-to-noise ratio (FIG. 26) and output voltage level (FIG. 27)
vary depending on the CMD multiplication rate for the CCD 109. With
the CMD multiplication rate held unchanged, the longer the exposure
time is, the higher the signal-to-noise ratio and output voltage
level are. Namely, the signal-to-noise ratio and output voltage
level attained in the present example are higher than those
attained in Example 9. The photometry means 142 calculates an
average of voltage levels assumed by an output signal of the CCD
109 during one field, and outputs the average to the CCD
sensitivity control means 112 via the control means 121. The CCD
sensitivity control means 112 calculates the number of applications
of a pulse per unit time associated with the CMD multiplication
rate for the CCD 109 that permits the output signal to represent an
image of brightness of a certain user-designated level. The CCD
sensitivity control means 112 outputs the number of applications of
the pulse per unit time to the CCD 109. Specifically, when the
output voltage level provided by the processor 103A is lower than a
set value, the CMD multiplication rate for the CCD 109 is
automatically raised. When the output voltage level is higher than
the set value, the CMD multiplication rate for the CCD 109 is
automatically lowered. Consequently, a view image of brightness of
the user-designated level can always be viewed on the monitor.
[0273] Moreover, when light returning from an object is feeble, the
CMD multiplication rate for the CCD 109 is automatically raised. As
seen from FIG. 26, when the CMD multiplication rate is set to a
larger value, if an exposure time is extended, a signal-to-noise
ratio is much higher than it is when the CMD multiplication rate is
set to a small value.
[0274] A signal output from the output stage of the processor 103A
is amplified by raising the CMD multiplication rate for the CCD
109. Compared with when the output signal of the CCD 109 is
electrically amplified, influence of a noise is limited. This
results in an image benefiting from a high signal-to-noise
ratio.
[0275] (Advantages)
[0276] When the special light mode (observation under special
light) is designated, the CMD multiplication rate for the CCD is
automatically controlled based on the intensity of the feeble
light. Consequently, a view image of excellent image quality (high
signal-to-noise ratio) and proper brightness can be produced.
Moreover, when an exposure time is extended, a view image will
benefit from a higher signal-to-noise ratio. Moreover, the
structure of the light source unit can be simplified.
[0277] An appendix and variant of the present example are identical
to those of Example 8.
[0278] In the present example, the CMD multiplication rate for the
CCD 109 is controlled in order to make the brightness of an image
on the monitor 105 constant depending on whichever of the ordinary
light mode or special light mode is designated. When the ordinary
light mode is designated, similarly to Example 1, the iris
diaphragm included in the light source unit may be controlled in
order to vary the intensity of light to be irradiated to a living
tissue.
[0279] Examples composed of parts of the constituent features of
the aforesaid examples also belong to the present invention.
INDUSTRIAL APPLICABILITY
[0280] As described so far, according to the present invention, a
view image of proper brightness can be produced irrespective of the
type of endoscope. Moreover, a means for controlling the
sensitivity of a solid-state imaging device can freely control the
sensitivity by adjusting the. amplitude of a sensitivity control
pulse and the number of applications thereof per unit time. Owing
to the sensitivity control, a high-sensitivity solid-state imaging
device can be realized without a noise derived from multiplication
of electrons and without the necessity of cooling. Consequently, an
endoscope offering excellent image quality and capable of being
inserted smoothly can be realized. Moreover, the sensitivity
control means can set the sensitivity of the solid-state imaging
device according to a type of endoscope or the property of each
solid-state imaging device. Eventually, a view image of proper
brightness can be produced irrespective of the type of endoscope or
the property of each solid-state imaging device.
* * * * *