Electronic endoscope

Details Electronic endoscope Electronic endoscope

1997-12-02

2001-01-30

Nguyen, Huy (Department: 2715)

Television

Special applications

With endoscope

C348S070000

Reexamination Certificate

active

06181368

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic endoscope having a solid state image pickup device at a front end of an insertion portion thereof. The pickup device converts an image viewed through the endoscope into electrical signals which can be sent to an external device to reproduce the image on a monitor, etc.
2. Description of Related Art
It is necessary to carry out a gamma correction of image signals supplied from a solid state image pickup device, provided at a front end of an insertion portion of an endoscope to reproduce a clear and natural image.
To this end, in a known endoscope, an output value which has been subjected to a gamma correction, corresponding to image signals (original signals) to be input to a gamma correction portion is written in advance in a look-up table in a memory. The image signals are applied as an address signal for the memory of the look-up table to produce a corresponding gamma-corrected value. The corrected signals are then reconverted to analog signals, processed and displayed on a monitor (see for example, Japanese Unexamined Patent Publication No. 1-178235).
However, the gamma-corrected value written in the look-up table has a greater value corresponding to the magnitude of the input original signals. Consequently, the look-up table requires a large memory size for data storage. This results in a substandard memory utilization efficiency and necessitates large and expensive circuits, thereby leading to increased manufacturing costs and power consumption.
Moreover, in the gamma correcting portion, when the original signal is amplified to obtain corrected signals, a noise component is superimposed on the original signal. Consequently, the S/N (signal-to-noise ratio) of the input original signal shown in
FIG. 26
, deteriorates particularly in a low brightness (dark) range having a high gain, as shown in FIG.
27
.
It is an object of the present invention to provide an electronic endoscope in which a gamma correction of an image signal can be effected without deteriorating the S/N.
Still further, in a nonlinear operation with reference to the look-up table, data which is not written in the look-up table, such as data
1
-
4
between the memory addresses
0
and
1
, shown in
FIG. 35
, is produced.
Consequently, there are large amounts of data which are not written in the look-up table in a low brightness range (dark area) in which data varies considerably depending on the address. Accordingly, a quantization error inherent in the operation of digital data occurs during the gamma correction.
It is a further object of the present invention to provide an electronic endoscope in which a gamma correction of digital image signals can be carried out without deteriorating the S/N or increasing a quantization error.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electronic endoscope having an increased memory utilization efficiency, wherein a look-up table for a gamma correction is a small and inexpensive memory.
To achieve the object mentioned above, according to the present invention, there is provided an electronic endoscope having a solid state image pickup device supplying an image signal, comprising; a look-up table for storing therein only data necessary for gamma correction with respect to the image signal a; gamma correcting device for adding the gamma correcting data to the image signal and outputting a gamma-correcting image signal.
According to another aspect of the present invention, there is provided an electronic endoscope having a solid state image pickup device supplying an image signal which is converted to a digital signal and is subject to a gamma correction in accordance with gamma correcting data stored in and read from a look-up table, wherein the look-up table stores therein data necessary for the gamma correction of the original signal, and wherein a low-pass filter eliminates a noise component from the original signal input to the look-up table, so that the data for the gamma correction is added to the original signal read from the look-up table to output a gamma-corrected signal.
According to a further aspect of the present invention, there is provided an electronic endoscope having a solid state image pickup device supplying an image signal which is converted to a digital signal and subject to a gamma correction in accordance with gamma correcting data stored in and read from a look-up table, wherein the look-up table stores therein data necessary for the gamma correction of the original signal input thereto, and wherein a low-pass filter removes a noise component from the signal supplied from the look-up table, so that the data for the gamma correction, read from the look-up table, is added through the low-pass filter to the original signal to output a gamma-corrected signal.
According to another aspect of the present invention, there is provided an electronic endoscope having a solid state image pickup device supplying an image signal is converted to a digital signal and subject to a gamma correction in accordance with gamma correcting data stored in and read from a look-up table, wherein the look-up table stores therein data necessary for the gamma correction of the original signal input thereto, and wherein a first low-pass filter removes a noise component from the signal supplied to the look-up table, and a second low-pass filter removes a noise component from the signal issued from to the look-up table, so that the data for the gamma correction, read from the look-up table and transmitted through the second low-pass filter, is added to the original signal to output a gamma-corrected signal.
The present disclosure relates to subject matter contained in Japanese patent application Nos. 06-75564 (filed on Apr. 14, 1994), 06-78278 (filed on Apr. 18, 1994), 06-78279 (filed on Apr. 18, 1994), and 06-79080 (filed on Apr. 19, 1994) which are expressly incorporated herein by reference in their entireties.


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