Patent ID: 6059720
Filing Date: 2000-05-09
Classification: A61B,H04N

Abstract:
An endoscope system for observing a fluorescent image, comprising:an endoscope unit which emits an excitation light to an object to be observed and receives a fluorescent light emitted by said object;a filtering optical element, which extracts a predetermined color component of said fluorescent light received by said endoscope unit;an image capturing device, which receives an image formed by said predetermined color component of said fluorescent light and outputs an image signal;a variable gain amplifier, a gain of which changes in accordance with said image signal output by said image capturing device;said variable gain amplifier comparing said image signal output by said image capturing device with a plurality of reference values defining a plurality of signal level ranges;said gain of said variable gain amplifier being changed stepwisely in accordance with a signal level range in which said image signal is included;said variable gain amplifier comprising a first amplifying circuit which amplifies said output signal of said image capturing device and outputs a first output signal, said first output signal fluctuating with respect to a predetermined value;a second amplifying circuit which amplifies said first output signal at a predetermined gain and outputs a second output signal;a first circuit which prepares said first output signal with a first higher reference value which is higher than said predetermined value, said first circuit lowering said gain of said second amplifying circuit if said first output signal has a higher value than said first higher reference value; anda second circuit which compares said first output signal with a first lower reference value which is lower than said predetermined value, said second circuit lowering said gain of said second amplifying circuit if said first output signal has a lower value than said first lower reference value.