JP2008237634A - Electronic endoscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic endoscope enlarging the dynamic range of an image sensor by adding neither mechanical members and nor a calculation circuit. <P>SOLUTION: In the electronic endoscope in which the image sensor is incorporated in the distal end of an invivo insertion part, primary color filters are arranged in front of a light receiving element group in a predetermined arrangement in the image sensor, and ND filters 35 limiting the transmitting light quantity are arranged in front of red color filters 34R of the primary color filters. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electronic endoscope, and more particularly, to an electronic endoscope including an image sensor with an expanded dynamic range of a video signal.

  Conventionally, an electronic endoscope apparatus has illumination light emitted from an external light source guided to the distal end of the body insertion section through a light guide, or illumination emitted by a semiconductor light emitting element such as an LED provided at the distal end of the body insertion section. The inside of the body cavity is illuminated with light and imaged. Since the general usage target of the electronic endoscope apparatus is in a body cavity such as the gastrointestinal tract of a human body, the ratio of the distances of the imaging targets that enter the same imaging screen is very large. For this reason, the image is likely to cause whiteout or blackout. If the dynamic range of the image sensor is expanded, such overexposure and underexposure can be reduced, but this is not easy.

Therefore, in order to expand the dynamic range, a technique has been proposed in which the dynamic range is expanded by switching between two types of illumination light and intensity, and combining the two types of light and dark data after image correction processing (Patent Document 1). ). In addition, a technique has been proposed in which an ND filter is arranged on every other line on the CCD image pickup surface and a dynamic range is expanded by synthesizing video signals obtained from two types of image pickup units (Patent Document 2). .
Japanese Patent Laid-Open No. 11-155808 JP-A-11-331710

  However, the invention for switching between two types of intensity light requires an illumination light switching device for switching the illumination light, and there is a problem that the light source device becomes large. The invention for synthesizing two video signals has a problem that a complicated arithmetic circuit for synthesizing the video signals is required.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide an electronic endoscope that can expand the dynamic range of an image sensor without adding mechanical members or arithmetic circuits. To do.

  The present invention has been made by paying attention to the fact that there are many red components in the body cavity, which is the observation target of the electronic endoscope.

  The present invention for solving such a problem is an electronic endoscope in which an image sensor is built in a distal end portion of an in-vivo insertion portion, and the image sensor has primary color filters arranged in a predetermined arrangement in front of a light receiving element group. In the primary color filter, a light amount limiting member for limiting the amount of incident light is provided in front of the light receiving element on which the light transmitted through the red filter is incident.

  In the electronic endoscope of the present invention, the light quantity limiting member can be constituted by an ND filter provided on the front surface or the back surface of the red filter. The ND filter is preferably formed integrally with the front surface or the back surface of the red filter.

In the electronic endoscope of the present invention, the light quantity limiting member can be configured by a red filter having a narrow band of the wavelength characteristic.
In the electronic endoscope of the present invention, the image sensor includes a light-shielding curtain that shields a portion between the light-receiving element and the light-receiving element disposed behind the primary color filter, and the light quantity limiting member includes the red light-limiting member. It can be formed by a light-shielding curtain covering the light receiving element so as to reduce the opening area of the filter or the light receiving area of the light receiving element on which the red light transmitted through the red filter is incident.

  Another aspect of the present invention is characterized in that the wavelength characteristics of the red filter in the primary color filters arranged in a predetermined arrangement on the imaging surface of the image sensor are narrowed.

  Another aspect of the present invention is an image sensor in which a primary color filter is arranged in front of a large number of light receiving elements, and the light receiving element on which the light transmitted through the red filter is incident is the light transmitted through the other primary color filters. It is characterized by being smaller than the incident light receiving element.

  According to the electronic endoscope of the present invention, the amount of the red component incident on the light receiving element of the image sensor is limited in photographing a subject having a large red component such as in a body cavity, so that the dynamic range can be substantially expanded. become. In addition, since a mechanical mechanism and a driving unit are not required, the configuration is easy, and an image synthesis process is not required, so that image calculation and processing circuits are not complicated.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration of an electronic endoscope 10 to which the present invention is applied, which is used together with a video processor 100. FIG. 2 shows an imaging system of the electronic endoscope 10 to which the present invention is applied and a video processor 100. The main part of the main circuit is shown. The electronic endoscope 10 includes a CCD imaging device 30 as an image sensor at the distal end portion 12 of the flexible in-vivo insertion portion 11 and extends from the operation portion 13 connected to the proximal end of the in-vivo insertion portion 11. A connector portion 15 connected to the connector portion of the video processor 100 is attached to the distal end of the universal cable 14 to be connected.

  The electronic endoscope 10 incorporates a light guide 16 extending from the distal end portion 12 into the light guide sleeve 17 of the connector portion 15 via the in-vivo insertion portion 11, the operation portion 13, and the universal cable 14. The end surface of the light guide sleeve 17 protruding from the connector portion 15 is coincident with the illumination light incident end surface 16a of the light guide 16, and when the connector portion 15 is connected to the connector portion of the video processor 100, the illumination light incident end surface 16a. Are optically connected to the endoscope light source. In this embodiment, the illumination light emitted from the lamp 122 which is an endoscope light source built in the video processor 100 is converged by the condenser lens 123 and enters from the illumination light incident end face 16a. Illumination light incident from the illumination light incident end face 16 a is guided through the light guide 16, emitted from the illumination light exit end face 16 b located in the vicinity of the end face of the distal end portion 12, and a light distribution lens 18 provided on the end face of the distal end portion 12. Is emitted outward with a predetermined light distribution.

  Further, an objective lens 19 is provided on the end face of the distal end portion 12, and a CCD image pickup device 30 is disposed behind the objective lens 19. The reflected light from the subject illuminated by the illumination light emitted from the light guide 16 is projected as a subject image by the objective lens 19, the projected subject image is projected by the objective lens 19, and the projected subject image is captured by the CCD. The element 30 captures an image, converts it into an electrical video signal, and outputs it. This video signal is amplified and A / D converted by the AFE circuit 21 and output to the video signal processing circuit 101 of the video processor 100 via the electrical connector 22 of the connector unit 15.

  The video signal input to the video signal processing circuit 101 is subjected to white balance correction by the white balance adjustment circuit 101a, edge enhancement correction by the edge enhancement circuit 101b, and gamma correction by the gamma correction circuit 101c. Further, the corrected video signal is encoded into a predetermined video format by the encoder 103 and visualized by the TV monitor 110.

  The video processor 100 includes a control circuit 105 that controls the entire system. When the lamp switch SWL is turned on, the lamp power supply 121 is activated to turn on the lamp 122. When the power switch SWM is turned on, the constant voltage is supplied to the video signal processing circuit 101 and the encoder 103, the constant voltage is further supplied to the AFE circuit 21, the AFE circuit 21 is activated, and imaging by the CCD image pickup device 30 is started. Let The moving image captured by the CCD image sensor 30 is displayed on the TV monitor 110.

  The above are general functions of the electronic endoscope 10 and the video processor 100. Next, features of the present invention will be described with reference to FIGS. The CCD image sensor 30 is a so-called CCD image sensor.

  FIG. 3 is a front view of the first embodiment of the CCD image sensor 30 to which the present invention is applied. In the CCD image pickup device 30, a primary color filter 34, in this embodiment, red, green, and blue RGB primary color filters 34R, 34G, and 34B are arranged on an image pickup surface 32. The arrangement of the RGB primary color filters 34R, 34G, and 34B in this embodiment is a Bayer arrangement. Below each of the RGB primary color filters 34R, 34G, 34B, a photodiode (PD) 33 is provided for converting light incident through the RGB primary color filters 34R, 34G, 34B into signal charges (FIG. 5). reference).

Thus, in this embodiment, an ND filter 35 as a light amount limiting member is provided so as to overlap the red (R primary color) filter 34R. The ND filter 35 limits the red light component that passes through the red filter 34R and enters the photodiode 33. The video signal obtained from the CCD image pickup device 30 has a red component smaller than that obtained with a normal image sensor without the ND filter 35. In this embodiment, an ND filter 35 that reduces the amount of transmitted light is provided, and the amount of red light is limited to about ½.
The ND filter 35 may be provided on either the front surface or the back surface side of the red filter 34R, and may be integrally formed on the front surface or the back surface of the red filter 34R.

  In the second embodiment of the image sensor of the present invention, although not shown in detail, only the wavelength characteristic of the R primary color filter is narrowed. The spectral characteristics of the R primary color filter and the normal GB primary color filter thus formed are graphed and shown in FIG. As is apparent from this graph, the red spectral sensitivity is low. This characteristic is substantially equivalent to the RGB primary color filters 34R, 34G, 34B of the first embodiment in which the ND filter 35 is provided only in the red filter 34R.

  FIG. 5 is a sectional view showing a CCD image pickup element 302 according to a third embodiment of the present invention in a longitudinal section. The arrangement of the RGB primary color filters 34R, 34G, and 34B is the same as that of the first embodiment shown in FIG. The CCD image pickup element 302 is provided with a light shielding curtain 36 between the RGB primary color filters 34R, 34G, 34B and the substrate 31 to shield a portion between the photodiode 33 and the photodiode 33 (such as a charge transfer unit). In the third embodiment, the light shielding curtain 35 is extended below the red filter 34R to restrict the opening of the red filter 34R to a small size and to limit the light receiving area of the photodiode 33 that receives red light to a small size. In the second embodiment, the opening area of the red filter 34R is limited to about ½ of the normal, and spectral characteristics substantially similar to the spectral characteristics shown in FIG. 4 are obtained.

  The first and second embodiments are not limited to the CCD type image sensor, but may be any image sensor using a primary color filter, and can be applied to a CMOS type image sensor. The third embodiment can be easily applied to any image sensor provided with a light-shielding curtain between the photodiodes.

  FIG. 7 is a graph showing the relationship between the output level of each color signal and the brightness of the subject when the inside of the body cavity is imaged by the image sensor, and (A) is a case where the image is captured by the conventional image sensor. (B) shows a case where the image is picked up by the CCD image pickup devices 30 and 302 according to the first to third embodiments of the present invention. The image of the conventional image sensor has a large signal level change rate with respect to the change in the brightness of the subject by the red signal level. Therefore, as the subject brightness increases, the green and blue signal levels are well below the threshold value. Only the red signal level reached the threshold at the stage. That is, since the red signal level is higher than the brightness of the subject and is saturated, the substantial dynamic range is narrowed.

  On the other hand, when the image is picked up by the CCD image pickup devices 30 and 302 according to the embodiment of the present invention, the change rate of the red, green, and blue signal levels with respect to the change in the brightness of the subject is approximate. Even if the brightness increases, the red, green and blue signal levels rise almost evenly and reach the threshold value with almost the same brightness. That is, it can be seen that the substantial dynamic range is expanded.

  As described above, according to the electronic endoscope of the present invention, the red light component incident on the image sensor is limited or the amount of received light is reduced in imaging inside a body cavity with a large amount of red component. The saturation brightness is high and the dynamic range is expanded. In addition, mechanical devices such as switching light sources and image processing such as combining images are unnecessary.

It is a figure which shows the whole structure of the electronic endoscope to which this invention is applied. It is a figure which shows the principal part of the main circuit of the imaging system and video processor of an electronic endoscope to which this invention is applied. It is a front view of a first embodiment of an image sensor of an electronic endoscope to which the present invention is applied. It is a figure which graphs and shows the spectral sensitivity of 2nd embodiment of the image sensor of the electronic endoscope to which this invention is applied. It is sectional drawing which shows longitudinally 3rd embodiment of the image sensor of the electronic endoscope to which this invention is applied. It is a figure explaining the relationship between each color signal level of the image sensor of an electronic endoscope and the brightness of a subject in a graph, where (A) shows a conventional case and (B) shows a case of the present invention. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electronic endoscope 11 Insertion | insert part 12 End part 13 Operation part 14 Universal cable 15 Connector part 16 Light guide 18 Light distribution lens 19 Objective lens 30 302 CCD image pick-up element 31 Board | substrate 32 Image pick-up surface 33 Photodiode 34R 34G 34B RGB primary color filter 35 ND filter 36 Light-shielding curtain 100 Video processor 101 Video signal processing circuit

Claims (6)

An electronic endoscope in which an image sensor is built in the distal end portion of the body insertion portion,
In the image sensor, primary color filters are arranged in a predetermined arrangement in front of the light receiving element group,
An electronic endoscope comprising a light amount limiting member for limiting an incident light amount in front of a light receiving element on which light transmitted through a red filter is incident among the primary color filters. The electronic endoscope according to claim 1, wherein the light amount limiting member is an ND filter provided on a front surface or a back surface of the red filter. The electronic endoscope according to claim 1, wherein the ND filter is integrally formed on a front surface or a back surface of the red filter. The electronic endoscope according to claim 1, wherein the light amount limiting member is a red filter in which the wavelength characteristic is narrowed. 2. The electronic endoscope according to claim 1, wherein the image sensor includes a light-shielding curtain that shields a portion between the light-receiving element and the light-receiving element disposed behind the primary color filter, and the light amount limiting member includes the red light limiting member. An electronic endoscope which is a light shielding curtain covering a light receiving element so as to reduce an opening area of the filter or a light receiving area of the light receiving element on which red light transmitted through the red filter is incident. An electronic endoscope in which an image sensor is built in the distal end portion of the body insertion portion,
An electronic endoscope characterized in that a light receiving element on which light transmitted through a red filter enters is smaller than a light receiving element on which light transmitted through another primary color filter enters.

Images