Electronic endoscope

Details Electronic endoscope Electronic endoscope

1999-06-21

2002-07-02

Britton, Howard (Department: 2713)

Television

Special applications

With endoscope

C600S160000, C600S180000

Reexamination Certificate

active

06414710

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electronic endoscope comprising a flexible conduit or scope and a video-signal processing unit to which the flexible scope is detachably connected at a proximal end.
2. Description of the Related Art
In such an electronic endoscope, the flexible conduit or scope includes an objective lens system provided at the distal end thereof, and a solid image sensor, such as a CCD (charge-coupled-device) image sensor, associated therewith. The flexible scope also includes an optical light guide extended therethrough, formed as a bundle of optical fibers, which is associated with a lighting lens system provided at the distal end of the flexible scope.
On the other hand, the video-signal processing unit includes a white-light source, such as a halogen lamp, a xenon lamp or the like. When the flexible scope is connected to the video-signal processing unit, the proximal end of the optical light guide is optically connected to the light source. Thus, an object to be photographed is illuminated by light radiating from the distal end of the optical light guide, and is focused as an optical image on a light-receiving surface of the CCD image sensor by the objective lens system.
The focused optical image is converted into a frame of analog image-pixel signals by the CCD image sensor. Then, the frame of analog image-pixel signals is read from the CCD image sensor, and is fed to the video-signal processing unit, in which the image-pixel signals are suitably processed, thereby producing a video signal including image-pixel signals and various synchronizing signals. Then, the video signal is fed from the video-signal processing unit to a TV monitor to reproduce the photographed object on the monitor on the basis of the video signal.
In general, the objective lens system, used in the electronic endoscope, exhibits a large depth of focus, because a close-range object image and/or a distant-range object image to be photographed must be focused on the light-receiving surface of the CCD image sensor by the objective lens system, before the photographed close-range object image and/or distant-range object image can be sharply reproduced on the monitor.
In this case, to maintain a constant overall brightness of a reproduced object image on the monitor, the radiation of the illuminating-light from the distal end of the optical light guide should be regulated in accordance with a distance between the photographed object image and the distal end of the optical light guide. For example, when only a medical image of a patient is to be reproduced as a close-up image by placing the distal end of the flexible scope close to the medical image, the radiation of the illuminating-light should be lowered to a minimum level in order to generate the medical image at a predetermined brightness on the monitor. Then, as the distal end of the flexible scope is moved away from the medical image, the radiation of the illuminating-light should be gradually increased from the minimum level to prevent the brightness of the reproduced medical image from being reduced.
Conventionally, for a regulation of radiation of the illuminating-light from the distal end of the optical light guide, an aperture-stop is associated with the white-light source, and is automatically controlled such that an overall brightness of the reproduced object image is always maintained at a constant level. In particular, a frame of luminance signals is extracted from the video signal at given regular time-intervals, and an average luminance level is calculated from the extracted luminance signals. Then, the radiation of the illuminating-light from the distal end of the optical light guide is regulated by controlling the aperture-stop such that the average luminance level coincides with a predetermined reference level.
Nevertheless, in the conventional electronic endoscope, there is room for improvement in a responsiveness of the regulation of the radiation of the illuminating-light from the distal end of the optical light guide, because a calculation time for calculating the average luminance level is relatively long, and because the calculation must be repeated at very short-time intervals. For example, in an electronic endoscope using the NTSC system, the calculation must be repeated at regular time-intervals of {fraction (1/30)} sec, and, in an electronic endoscope using the PAL system, the calculation must be repeated at regular time-intervals of {fraction (1/25)} sec.
On the other hand, in general, an electronic endoscope is constituted such that a photographed image is reproduced as a color image. In this case, a frame of red image-pixel signals, a frame of green image-pixel and a frame of blue image-pixel signals are cyclically read out from the CCD image sensor, and are then subjected to a white-balance correction processing such that the photographed color image is reproduced on a monitor with a proper color balance. As is well-known, the white-balance correction processing is performed by processing respective gains of red, green and blue image-pixel signals with red, green and blue correction factors, which exhibit inherent values with respect to each individual CCD image sensor used in an electronic endoscope. Thus, the correction factors are determined during manufacture of the electronic endoscope.
In particular, a manufactured flexible scope concerned is connected to a so-called master video-signal processor, and a distal end of the flexible scope is inserted into a tubular-like envelope, an inner wall surface of which is coated with a standard white pigment layer. Then, a frame of red image-pixel signals, a frame green image-pixel signals and a frame of blue image-pixel signals are obtained from the CCD image sensor, and a red correction factor, a green correction factor and a blue correction factor are determined on the basis of the obtained color image-pixel signals such that gains of red, green and blue image-pixel signals are equal to each other.
Nevertheless, an electronic characteristic of the master video-signal processor does not necessarily coincide with that of a manufactured and used video-signal processor to which the flexible endoscope concerned is connected. Thus, the determined correction factors are not necessarily proper with respect to the manufactured and used video-signal processor. Further, the color correction factors should be periodically readjusted and redetermined in accordance with deterioration of a white-light lamp which harmfully affects the white-balance correction processing. Namely, there is a demand for an improved electronic endoscope in which the redetermination of the color correction factors can be easily carried out.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an electronic endoscope in which a responsiveness of a regulation of radiation of an illuminating-light from a distal end of an optical light guide can be favorably improved.
Another object of the present invention is to provide an electronic endoscope in which it is possible to easily readjust and redetermine color correction factors for a white-balance correction.
In accordance with the present invention, there is provided an electronic endoscope which comprises a flexible scope, and a video-signal processing unit to which a proximal end of the flexible scope is detachably connected. The flexible scope has an image sensor provided at a distal end of the scope, and an optical light guide extending through the scope. The video-signal processing unit processes image-pixel signals successively read from the image sensor, and is provided with a light source such that light, emitted from the light source, is guided through the optical light guide and radiates from the distal end of the flexible scope. The electronic end scope features a light-emission regulator which may be an aperture-stop associated with the light source, and the aperture-stop regulates the radiation of light from the distal end of the flexible scope. The electr

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