JP2001238137A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce effect of a dark current and to improve an S/N of a picked up image in an imaging apparatus provided with an imaging device where an image pickup face is constituted of an image exposure area and a non- exposure area. SOLUTION: An image signal which is image-picked up by a CCD imaging device 1 fitted to the tip of the scope part o an electronic endoscope is inputted to an A/D conversion circuit 2 via a transmission cable 9, is digitally converted and is preserved in an image memory 3. The dark current correction control part 8 reads a dark current image signal which is image-picked up by the non- exposure area of the CCD imaging device 1 from the image memory 3 and calculates the dark current image signal of the image exposure area from the dark current image signal of the non-exposure area. A subtracter 4 is controlled and the dark current image signal of the image exposure area is subtracted from the image signal which is image-picked up in the image exposure area, which is prevented in the image memory 3, an image signal from which a signal equivalent to the dark current is removed is preserved in an image memory 5. The image signal is D/A-converted in a D/A conversion circuit 6 and is displayed no a CRT 7 as a fluorescent image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus for picking up a two-dimensional image of an observation section, and more particularly, to an image pickup surface comprising an image exposure area used for imaging the observation section and a non-exposed area which is shielded from light. The present invention relates to an imaging device that is in use.

[0002]

2. Description of the Related Art In recent years, C is added to an observation site such as a body cavity or the like.
Insert a scope section on which an image sensor such as a CD is provided, form an image of an object on an image pickup surface of the image sensor with an optical system, convert the electric signal into an electric signal, and transmit the electric signal by a transmission cable penetrating the scope section. The development of an electronic endoscope that sends the signal to a signal processing unit and displays the signal on a monitor or the like is underway. In this electronic endoscope, since an optical image is captured by an image sensor and an image signal is transmitted by a transmission cable, there are advantages such as improvement in image resolution and reduction in the diameter of a scope.

[0003] Similarly, development of a colposcope, a surgical microscope, and the like, which incorporate an image pickup device for directly picking up an optical image by an image pickup device, is also in progress.

[0004] When observing the inside of a body cavity or the like using these devices, the temperature near the image pickup device may be reduced due to the influence of body temperature or the like.
May rise to near 0 degrees. In a normal high-sensitivity imaging device or the like, a cooling device is often provided to keep the temperature of the imaging device at a low temperature. However, in an imaging device in which the imaging device is disposed at the tip of a scope section or the like, a space around the imaging device is provided. , It is difficult to provide a cooling device. For this reason,
There is a problem that noise included in the image signal is significantly increased. It is considered that most of this noise is due to dark current that increases due to a rise in the temperature of the image sensor.

Usually, in such an image pickup apparatus, the dark current value included in the image signal is regarded as being uniform over the entire image pickup surface, and a constant dark current value is removed from the image signal picked up by each pixel. As a result, the effect of dark current was reduced.

[0006]

However, when the present inventors repeated dark current measurement experiments on the image sensor and analyzed the dark current value, the dark current value was not uniform over the entire imaging surface. However, it became clear that the distribution of the concave shape was lowered in the center. FIG. 14 shows the signal intensity of the dark current on the imaging surface 51, and FIG. 14B shows the signal intensity distribution of the dark current on the line A in FIG. c) is the signal intensity distribution at line B. That is, the signal intensity of the dark current is small in the central portion of the imaging surface, and the signal intensity is large in the peripheral portion.

For this reason, simply removing a constant dark current value from an image signal picked up by the image pickup element causes an excess or deficiency in dark current removal, and lowers the S / N of the picked-up image. It turned out that there was a problem.

In view of the above problems, the present invention reduces the influence of dark current from an image signal picked up in an image exposure area of an image sensor whose image pickup surface is composed of an image exposure area and a non-exposure area. It is an object of the present invention to provide an imaging device with an improved S / N.

[0009]

According to the present invention, there is provided an imaging apparatus comprising an imaging device having an imaging surface having an image exposure area and a non-exposure area. It is characterized by having a dark current correction means for performing two-dimensional correction.

The dark current correction means includes a dark current image acquisition means for acquiring an exposure area dark current image signal corresponding to a dark current included in an image signal captured in the image exposure area, and an image captured in the image exposure area. It is preferable to include a dark current image removing unit that removes an exposure area dark current image signal from the image signal.

The dark current image acquisition means may calculate the exposure area dark current image signal based on the signal intensity distribution of the non-exposure area dark current image signal imaged in the non-exposure area of the image sensor.

Here, “calculating the exposure area dark current image signal based on the signal intensity distribution of the non-exposure area dark current image signal” means that the present inventors have apparently performed experiments over the entire imaging surface. It means that the signal intensity distribution of the exposed area dark current image signal is estimated and calculated from the signal intensity distribution of the known non-exposed area dark current image signal so that the concave dark current distribution becomes lower at the center. I do.

Further, the dark current image acquisition means may obtain an exposure area dark current image signal from an image signal captured in a state where the image exposure area is shielded from light.

A temporary storage section for storing an exposure area dark current image signal; a dark current correction section for rewriting an exposure area dark current image signal stored in the temporary storage section; Rewriting determining means for determining whether to rewrite the exposure area dark current image signal stored in the temporary storage section based on the presence or absence of a change in the area dark current image signal. The exposure area dark current image signal stored in the section may be used as the exposure area dark current image signal.

Here, "determining whether or not to rewrite the exposure area dark current image signal stored in the temporary storage unit based on the presence or absence of a change in the non-exposure area dark current image signal" means, for example, When a change occurs in the dark current, such as the average value of the signal intensity of the non-exposure area dark current image signal, the signal intensity of a predetermined portion, or the signal intensity distribution, a change that exceeds the predetermined value occurs. In this case, it is determined that the exposure area dark current image signal is to be rewritten. If no change equal to or more than the predetermined value has occurred, it is determined that the exposure area dark current image signal is not to be rewritten.

A first storage unit for storing the image sensor temperature and the relationship between the non-exposure area dark current image signal imaged under the temperature in association with each other; and a temperature of the image sensor and an exposure area dark corresponding to the temperature. A second storage unit that stores the current image signal in association with the current image signal, wherein the dark current correction unit is configured to perform a dark current correction based on the non-exposure area dark current image signal and the correspondence stored in the first storage unit. A temperature calculating unit for calculating a temperature of the image sensor, wherein the dark current removing unit includes a temperature of the image sensor calculated by the temperature calculating unit in the exposure area dark current image signal stored in the second storage unit. May be used as the exposure area dark current image signal.

The exposure area dark current image signal may be a thinned image signal.

The image sensor may be of any type, such as a CCD image sensor or a MOS image sensor, as long as it converts an optical signal into an electric signal by a pixel.

[0019]

In the above-mentioned image pickup apparatus, the space in which the optical system is arranged is narrow, and the size of the lens that can be used is limited. Therefore, unlike a CCD camera or the like, which normally captures a part of an optical image formed by an optical system, the entire optical image formed by the optical system is captured by an image sensor. The imaging surface of the imaging device is often formed in a quadrangular shape. Therefore, usually, only a part of a circular or nearly polygonal region of the imaging surface is used for imaging as an image exposure region.

According to the above-described imaging apparatus of the present invention,
By correcting the dark current of the image signal captured in the image exposure region of the image sensor two-dimensionally, it is possible to reduce the influence of the dark current generated at the time of capturing and improve the S / N of the captured image.

[0021] Further, by removing an exposure area dark current image signal corresponding to a dark current included in the image signal captured in the image exposure area from the image signal captured in the image exposure area, Even if the dark current value included in the image signal captured by the method is not a uniform value, the dark current can be removed from the image signal without excess or deficiency. Further, even when the imaging conditions such as the imaging temperature and the imaging time change and the dark current value changes, appropriate dark current correction can be performed, and the S / N of the captured image can be improved. it can.

In the case where the exposure area dark current image signal is calculated based on the signal intensity of the non-exposure area dark current image signal captured in the non-exposure area of the image sensor, the image signal of the image signal captured in the normal operation is used. Since the exposure area dark current image signal is calculated from the middle non-exposure area dark current image signal, the normal imaging operation is not hindered to obtain the exposure area dark current image signal, and the convenience of the imaging apparatus is improved. be able to.

When the exposure area dark current image signal is obtained from an image signal captured in a state where the image exposure area of the image sensor is shielded from light, the exposure area dark current image actually captured in the image exposure area is used. Since a signal can be obtained, accurate dark current correction can be performed, and the S / N of a captured image can be improved.

Further, a temporary storage unit for storing an exposure area dark current image signal is provided, and at the time of imaging, the exposure area dark current image stored in the temporary storage unit is stored based on the presence or absence of a change in the non-exposure area dark current image signal. It is determined whether or not to rewrite the current image signal, and only when the non-exposure area dark current image signal changes by a predetermined value or more, the exposure area dark current image signal stored in the temporary storage unit is determined. Rewriting, when the non-exposed area dark current image signal has not changed by a predetermined value or more, that is, since the dark current value has not changed,
If it is not necessary to rewrite the exposure area dark current image signal,
If the rewriting is not performed and the exposure area dark current image signal stored in the temporary storage unit is removed from the image signal captured in the image exposure area, the number of rewriting of the exposure area dark current image signal is reduced. Therefore, the processing time for the dark current correction processing can be reduced.

It has been confirmed by experiments by the inventors that the dark current value and the dark current distribution change depending on the temperature. For this reason, if the temperature of the image sensor and the characteristics of the non-exposed area dark current image signal imaged in the non-exposed area at that temperature are stored in advance in correspondence, the non-exposed area dark current image signal From the characteristics described above, the temperature of the image sensor can be obtained.

Utilizing this, a first storage unit that stores in advance the temperature of the image sensor and the non-exposed area dark current image signal imaged in the non-exposed area of the image sensor at the temperature, A second storage unit that stores the temperature of the image sensor and the exposure area dark current image signal corresponding to the temperature in association with each other, and stores the non-exposure area dark current image signal and the first storage unit during imaging. Based on the corresponding relationship, the temperature of the image sensor is calculated, and the temperature of the image sensor in the exposure area dark current image signal stored in the second storage unit is calculated from the image signal captured in the image exposure area of the image sensor. As long as the image signal that removes the dark current image signal in the exposure region corresponding to the above, it is possible to appropriately correct the dark current according to the temperature change of the image sensor. In addition, since the temperature of the imaging device can be obtained, signal processing can be appropriately performed according to the temperature of the imaging device, and the convenience of the imaging device is improved.

If the exposure area dark current image signal is a thinned-out image signal, the signal processing time can be reduced when acquiring the exposure area dark current image signal. Also,
When storing the exposure area dark current image signal, the required storage area can be reduced.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, an electronic endoscope as a first specific embodiment to which the imaging device according to the present invention is applied will be described with reference to FIGS. FIG. 1 is a schematic configuration diagram of an electronic endoscope to which an imaging device according to the present invention is applied. This electronic endoscope captures an image of an observation unit with a CCD imaging device attached to a distal end of a scope unit.
The dark current image signal of the image exposure area is calculated from the dark current image signal captured in the non-exposure area of the image sensor, and then the dark current image signal of the image exposure area is calculated from the image signal captured in the image exposure area. An image in which the dark current has been corrected by subtraction is obtained, and is displayed on a CRT (Cathode-Ray Tube).

The electronic endoscope comprises a CCD image pickup device 1 attached to the distal end of a scope (not shown), an A / D conversion circuit 2 for digitizing an image signal picked up by the CCD image pickup device 1, and a digital An image memory 3 for storing the converted image signal, a subtractor 4 for subtracting the dark current image signal from the image signal stored in the image memory 3, and an image memory 5 for storing the image signal output from the subtractor 4. And a D / A conversion circuit 6 for DA-converting the image signal output from the image memory 5
And a CRT 7 for displaying an image, and a dark current correction control unit 8 connected to the image memory 3 and the subtractor 4.
Note that the CCD image pickup device 1 and the A / D conversion circuit 2 are connected by a transmission cable 9 that passes through the inside of the scope. A controller for operation timing control, not shown, is connected to each part.

As shown in FIG. 2, the CCD image pickup device 1
It has an imaging surface 11 in which n vertical pixels and m horizontal pixels are arranged.
Image exposure area where the inside of the circle inscribed at 11 is used for imaging
12, both sides of the image exposure area 12 are non-exposure areas 13. The non-exposed area 13 is shielded by a thin metal film or the like.

Hereinafter, the operation of the electronic endoscope having the above configuration to which the imaging device according to the present invention is applied will be described.

In the CCD image pickup device 1, a light image of the observation section is formed on the image exposure area 12 of the image pickup surface 11. On the imaging surface 11 composed of the image exposure area 12 and the non-exposure area 13, photoelectric conversion is performed in each pixel, and electric signals corresponding to the intensity of incident light are accumulated. The signal charges accumulated in all the pixels of the imaging surface 11 at predetermined time intervals are output to the A / D conversion circuit 2 via the transmission cable 9 as image signals.

The image signal is digitally converted by the A / D conversion circuit 2 and stored in the image memory 3. FIG. 3 shows the signal strength of the image signal captured on the line A in FIG. 2 in the image signal stored in the image memory 3. The image signal 14 stored in the image memory 3 includes an image signal 15 captured in the image exposure area 12 and a dark current image signal 16 captured in the non-exposure area 13.
It is composed of Also, the image signal 15 is
This is a signal in which a dark current image signal 17 corresponding to 12 dark currents and an image signal 18 corresponding to a light image of the observation section are superimposed.

Next, the operation of the dark current correction controller 8 will be described with reference to the flowchart shown in FIG.

First, in step 101, the dark current correction controller 8 reads out the dark current image signal 16 picked up by the non-exposed area 13 of the CCD image pickup device 1 from the image memory 3.

In step 102, based on the dark current image signal 16, a dark current image signal 17 'reflecting the dark current value of the image exposure area 12 is calculated. Normally, as shown in FIG. 14, the dark current value shows a concave dark current distribution with the center lowered, so that the signal intensity distribution of the dark current image signal 16 approximates the actual dark current image signal 17. Dark current image signal 17 '
Can be estimated and calculated.

In step 103, the subtractor 4 is controlled,
The dark current image signal 17 ′ calculated in step 102 is subtracted from the image signal 15 captured in the exposure area 12 stored in the image memory 3 and stored in the image memory 5. Therefore,
The image memory 5 stores an image signal 18 'shown in FIG. 5, that is, an image signal corresponding to the light image of the observation unit. Thereafter, returning to the top of the flowchart, the same operation is repeated from step 101 at the next image reading timing.

The image signal 18 'stored in the image memory 5
Is D / A converted by the D / A conversion circuit 6 and displayed on the CRT 7.

Steps 101, 102 and 103 of the flow chart shown in FIG. 4 constitute the dark current correcting means of the present invention. In particular, steps 101 and 102 constitute the dark current acquiring means, and step 103 is the dark current removing means. Is configured. The dark current image signal 16 corresponds to the non-exposed area dark current image signal of the invention, and the dark current image signal 17 'corresponds to the exposed area dark current image signal.

By the above operation, the dark current contained in the image signal 15 picked up by the image exposure area 12 of the CCD image pickup device 1 can be corrected two-dimensionally, so that the influence of the dark current can be reduced, S / N of the obtained image can be improved.

After the image pickup by the CCD image pickup device 1, the dark current image signal 16 picked up by the non-exposure area 13 of the CCD image pickup device 1 is read out from the image memory 3, and the dark current image signal 16 is read.
Image signal captured in the image exposure area 12 from the signal intensity distribution of
Calculate the dark current image signal 17 ′ included in the image signal 15
By subtracting the dark current image signal 17 ′ from the image signal, the dark current image signal can be removed from the image signal 15 without excess and deficiency, and an image corresponding to the light image of the observation unit can be displayed on the CRT 7. In addition, the dark current image signal
Since the calculation of 17 ′ is performed, appropriate correction of the dark current can be performed even when the imaging conditions such as the imaging temperature and the imaging time change and the dark current value changes.

Further, the dark current image signal 17 'is
The dark current image signal 16 captured by the normal operation of the D imaging device 1
Since the calculation is performed based on the signal intensity distribution of, the ordinary imaging operation for acquiring the dark current image signal 17 ′ is not hindered, and the convenience of the imaging apparatus can be improved.

As a modification of the first embodiment, a method in which the dark current image signal 17 is obtained from an image signal captured in a state where the image exposure area of the CCD image sensor 1 is shielded from light is considered. Although the imaging operation is complicated, a dark current image signal actually captured in the image exposure area can be obtained, so that accurate dark current correction can be performed and the S / N of the captured image is further improved. be able to.

Next, an electronic endoscope according to a second specific embodiment to which the imaging apparatus according to the present invention is applied will be described with reference to FIGS. FIG. 6 is a schematic configuration diagram of an electronic endoscope to which the imaging device according to the present invention is applied. This electronic endoscope captures an image of an observation unit with a CCD imaging device attached to the end of the endoscope. The average value of the signal intensity of the dark current image signal captured in the non-exposure area of the CCD image sensor is calculated. If the average value does not change, the average value is stored in the storage unit from the image signal captured in the image exposure area. The dark current image signal is subtracted, and if the average value changes, a new dark current image signal is obtained, the dark current image signal stored in the storage unit is rewritten, and then the image exposure is performed. The dark current corrected image is obtained by subtracting the dark current image signal stored in the storage unit from the image signal picked up in the area.
It is displayed above. The same elements as those in the first specific embodiment shown in FIG.
The description thereof will be omitted unless it is particularly necessary.

This electronic endoscope is attached to the distal end of a scope (not shown) and has a mechanical shutter function, a CCD image pickup device 21, an A / D conversion circuit 2, an image memory 3, and a subtractor 4. An image memory 5, a D / A conversion circuit 6, a CRT 7, a storage unit 23 as a temporary storage unit, and a storage unit 24 for storing an average value of signal intensities of dark current image signals picked up in a non-exposed area. , A CCD image pickup device 21, an image memory 3, a subtractor 4, a storage unit 23, and a dark current correction control unit 22 connected to the storage unit 24. The CCD image pickup device 21 and the A / D conversion circuit 2 are connected by a transmission cable 9,
Further, the CCD image pickup device 21 and the dark current correction control unit 22 are connected by a control line 25 penetrating the scope unit. A controller for operation timing control (not shown) is connected to each part.

As shown in FIG. 7, the CCD image pickup device 21
It has an imaging surface 31 in which n vertical pixels and m horizontal pixels are arranged.
The inside of the circle inscribed at the right end of 31 is an image exposure area 32 used for imaging, and a portion other than the image exposure area 32 on the imaging surface 31 is a non-exposure area 33. The non-exposed area 33 is shielded by a thin metal film or the like. Further, a mechanical shutter mechanism (not shown) is provided in the CCD image pickup device 21.

Hereinafter, the operation of the electronic endoscope having the above configuration to which the imaging apparatus according to the present invention is applied will be described. In the CCD imaging device 21, a light image of the observation unit is formed on an image exposure area 32 of an imaging surface 31. On the imaging surface 31, in each pixel,
The photoelectric conversion is performed, an electric signal corresponding to the intensity of the incident light is accumulated, and is output to the A / D conversion circuit 2 via the transmission cable 9 as an image signal of the entire area of the imaging surface 31 every predetermined time. .

The image signal is digitally converted by the A / D conversion circuit 2 and stored in the image memory 3. FIG. 9 shows the signal strength of the image signal captured on the line A in FIG. 7 in the image signal stored in the image memory 3. The image signal 34 stored in the image memory 3 includes an image signal 35 captured in the image exposure area 32 and a dark current image signal 36 captured in the non-exposure area 33.
It is composed of Further, the image signal 35 corresponds to the image exposure area.
This is a signal obtained by superimposing a dark current image signal 37 corresponding to a dark current 32 and an image signal 38 corresponding to a light image of the observation unit.

Next, the operation of the dark current correction controller 22 will be described with reference to the flowchart shown in FIG. First, in step 201, the dark current correction control unit 22 reads from the image memory 3 the dark current image signal 36 imaged in the non-exposure region 33 of the CCD image sensor 21, and in step 202, the signal intensity of the dark current image signal 36 An average value a is calculated.

In step 203, the average value a is stored in the storage unit.
It is determined whether or not the average value A stored in 24 is within the range of ± d. If the average value a falls within the range of the average value A ± d, the process proceeds to step 207. If the average value a is not within the range of the average value A ± d, the process proceeds to step 204.
That is, when the average value a does not change by a predetermined value or more,
Since it is considered that no change has occurred in the dark current image signal 37, the process proceeds to step 207, and the dark current image signal stored in the storage unit 23 is directly used as the dark current image signal. On the other hand, if the average value a has changed by a predetermined value or more, it is considered that the dark current image signal 37 has also changed. Therefore, in steps 204 to 206, a new dark current image signal is detected and Overwrites the dark current image signal stored in.

First, in step 204, the dark current correction control unit 22 controls the CCD image pickup device 21, closes the mechanical shutter, and performs image pickup with the image pickup surface 31 being shielded from light.

In step 205, an image signal picked up by the CCD image pickup device 21 with the mechanical shutter closed is read from the image memory 3. This image signal is, as shown in FIG. 10, a dark current image signal captured in the image exposure area 32.
37 ′ and an image signal 39 including a dark current image signal 36 captured in the non-exposure area 33.

In step 206, the image signal detected in step 205 is stored in the storage unit 23 as a new dark current image signal.
And the dark current image signal is rewritten. In the following step 207, the average value a is set as the average value A,
To memorize. That is, the average value A is rewritten and the new average value reference is stored. Thereafter, the process proceeds to step 208.

In step 208, the subtractor 4 is controlled,
From the image signal 34 stored in the image memory 3, the storage unit
The dark current image signal 39 stored in 23 is subtracted and stored in the image memory 5. The image signal 38 'shown in FIG. 11, that is, the image signal corresponding to the light image of the observation unit is stored. Returning to step 201, the same operation is repeated from step 201 at the next image reading timing.

The image signal stored in the image memory 5 is D /
The signal is converted into an analog signal by the A conversion circuit 6 and displayed on the CRT 7.

Step 20 of the flowchart shown in FIG.
1 to 208 constitute the dark current correction means of the invention, in particular, Steps 201 to 203 and Step 207 constitute the rewriting judgment means, Steps 204 to 206 constitute the dark current image rewriting means, and Step 208 constitutes the dark current image rewriting means. It constitutes a current image removing means.

The dark current image signal 36 corresponds to the non-exposed area dark current image signal of the present invention, and the dark current image signal 37 'corresponds to the exposed area dark current image signal.

According to the above operation, if the average value of the signal intensity of the dark current image signal 36 imaged in the non-exposure area 33 of the CCD image sensor 21 does not change, the image exposure area 32
The dark current image signal stored in the storage unit 23 is directly subtracted from the image signal picked up in step 3 and displayed on the CRT 7, and the average value of the signal intensity of the dark current image signal 36 picked up in the non-exposed area 33 is obtained. If a change has occurred, first the storage unit 23
After rewriting the dark current image signal stored in the CRT 7, the dark current image signal stored in the storage unit 23 is subtracted from the image signal captured in the image exposure area 32 and displayed on the CRT 7.

For this reason, it is possible to reduce the number of operations of acquiring and rewriting dark current image signals corresponding to dark current in the image exposure area. Further, by obtaining this dark current image signal from an image signal captured in a state where the image exposure region 32 of the CCD image sensor 21 is shielded from light, an accurate dark current image signal can be obtained, and an accurate dark current image signal can be obtained. Current correction can be performed, and the S / N of a captured image can be improved.

As a modification of the second embodiment, the dark current image signal of the image exposure area is
Of the image signals picked up by the normal image pick-up operation described above may be calculated from the signal intensity distribution of the dark current image signal picked up in the non-exposure area. In this case, it is possible to improve the convenience of the imaging apparatus without interrupting the normal imaging operation for acquiring the dark current image signal of the image exposure area.

In steps 202 and 203 of the flowchart shown in FIG. 9, the average value of the signal intensity of the dark current image signal 36 is calculated to determine whether or not the average value has changed. Even if it is determined whether or not there is a change in a value that causes a change in a dark current, such as a signal strength of a part or a signal strength distribution of the dark current image signal 36,
Similar effects can be obtained.

Next, an electronic endoscope according to a third specific embodiment to which the imaging apparatus according to the present invention is applied will be described with reference to FIGS. FIG. 12 is a schematic configuration diagram of an electronic endoscope to which the imaging device according to the present invention is applied. This electronic endoscope includes a temperature of a CCD imaging device and a dark current image signal imaged in a non-exposed area under the temperature. And a storage unit that stores the temperature of the CCD image sensor and the dark current image signal imaged in the image exposure area under the temperature in association with each other. First, an image of the observation unit is captured by a CCD image sensor attached to the tip of the scope unit. First, a temperature of the CCD image sensor is calculated based on a dark current image signal captured in a non-exposure area of the CCD image sensor. The dark current image signal captured in the image exposure area corresponding to the temperature is read out from the storage unit, and the dark current image signal read out from the storage unit is subtracted from the image signal captured in the image exposure area to obtain the dark current image signal. Current corrected image CR
It is displayed on T. The same elements as those in the first specific embodiment shown in FIG. 1 are denoted by the same reference numerals, and a description thereof will be omitted unless necessary.

The electronic endoscope comprises a CCD image pickup device 1, an A / D conversion circuit 2, an image memory 3, a subtractor 4, an image memory 5,
, A D / A conversion circuit 6, a CRT 7, a storage unit 42 as a first storage unit, a storage unit 43 as a second storage unit, an image memory 3, a subtractor 4, a storage unit 42, and a storage unit 43. And a dark current correction control unit 41 connected to the control unit. The CCD imaging device 1 and the A / D conversion circuit 2 are connected by a transmission cable 9. A controller (not shown) is connected to each part to control the operation timing.

The storage unit 42 stores the CC value for each predetermined temperature in advance.
It stores the temperature of the D image sensor 1 and the dark current value and dark current distribution of the dark current image signal imaged in the non-exposure area 13 of the CCD image sensor 1 under the temperature. In addition, the storage unit 43 previously stores, for each predetermined temperature, the temperature of the CCD image sensor 1 and a dark current image signal captured by the image exposure area 12 of the CCD image sensor 1 under the temperature.

Hereinafter, the operation of the electronic endoscope having the above configuration to which the imaging device according to the present invention is applied will be described. In the CCD image pickup device 1, an image signal picked up is output to an A / D conversion circuit 2 via a transmission cable 9, digitally converted by the A / D conversion circuit 2, and stored in an image memory 3. The image signal stored in the image memory 3 is, as in the first embodiment, a dark current image signal (dark current image signal) shown in FIG.
16 + dark current image signal 17) and an image signal 18 corresponding to the optical image of the observation unit.

Next, the operation of the dark current correction controller 41 will be described with reference to the flowchart shown in FIG.

First, in step 301, the dark current correction control section 41 reads out the dark current image signal 16 picked up by the non-exposure area 13 of the CCD 1 from the image memory 3.

In step 302, the dark current image signal
The temperature t of the CCD 1 is obtained from the 16 dark current values and the dark current distribution and the correspondence stored in the storage unit 42.

In step 303, a dark current image signal corresponding to the temperature t is read from the storage section 43.

In step 304, the subtractor 4 is controlled,
From the image signal 15 captured in the image exposure area 12 of the CCD image sensor 1 stored in the image memory 3, a step 303 is performed.
Subtracts the dark current image signal read out in step (1) and stores it in the image memory 5. That is, the image memory 5 stores the image signal 18 'shown in FIG. 5, that is, the image signal corresponding to the optical image of the observation unit. Thereafter, the flow returns to step 301, and the same operation is repeated from step 301 at the next image reading timing.

The image signal stored in the image memory 5 is D /
The signal is converted into an analog signal by the A conversion circuit 6 and displayed on the CRT 7.

Steps 301 to 304 in the flowchart shown in FIG. 13 constitute the dark current correcting means of the present invention.
In particular, steps 301 and 302 constitute a temperature calculating means, and steps 303 and 304 constitute a dark current removing means.

By the above operation, at the time of image pickup, the CCD image pickup device based on the dark current value and the dark current distribution as characteristics of the dark current image signal 16 picked up in the non-exposure area and the correspondence stored in the storage section 42. 1 is calculated, and then, from among the dark current image signals stored in the storage unit 43 for each temperature, CC is calculated.
By reading out a dark current image signal corresponding to the temperature of the D image pickup device 1 and removing the dark current image signal from the image signal 15 picked up in the exposure area, it is possible to perform appropriate correction of the dark current according to the temperature change of the CCD image pickup device 1. it can. Further, since the temperature of the CCD image sensor 1 can be obtained, signal processing can be appropriately performed according to the temperature of the image sensor, and the convenience of the imaging device is improved.

In this embodiment, the temperature of the CCD image sensor and the non-exposure area 13 of the CCD image sensor 1 under the temperature are determined in advance.
A storage unit 42 for storing a correspondence relationship with the dark current image signal 16 imaged in the above, and a storage unit 43 for storing a dark current image signal of the exposure area of the CCD image sensor 1 corresponding to the temperature. As a modified example, a storage unit 42 for storing the correspondence between the temperature of the CCD image sensor and the dark current image signal 16 imaged in the non-exposure area of the CCD image sensor 1 under the temperature, and a predetermined storage in which nothing is stored Only a portion is provided in advance, and during imaging, a method of calculating a dark current image signal of an image exposure region from a dark current image region of a non-exposure region, or a method of capturing a dark current image signal while shielding light is used. A dark current image signal of the image exposure area of the CCD image pickup device 1 is acquired and stored in a predetermined storage unit in correspondence with the temperature, and a new dark current image signal of the image exposure area is appropriately acquired. Dark current stored in the storage unit The case where an image signal is used can be properly used. The storage area of the predetermined storage unit required for storing the dark current image signal can be reduced without storing the dark current image signal outside the operating temperature range of the imaging device.

In each of the above embodiments, it is possible to use a thinned image signal as a dark current image signal. If the thinned image signals are used, the signal processing time can be reduced when acquiring a dark current image signal. Further, when storing the dark current image signal, the required storage area can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic endoscope as a first specific embodiment to which an imaging device according to the present invention is applied;

FIG. 2 is a schematic configuration diagram of an imaging surface of a CCD imaging device used in the electronic endoscope according to the first specific embodiment.

FIG. 3 is a diagram showing a signal intensity distribution of an image signal captured by the CCD image sensor.

FIG. 4 is a flowchart illustrating a flow of an operation of a dark current correction control unit.

FIG. 5 is a diagram showing a signal intensity distribution of an image signal after dark current correction.

FIG. 6 is a block diagram of an electronic endoscope as a second specific embodiment to which the imaging device according to the present invention is applied;

FIG. 7 is a schematic configuration diagram of an imaging surface of a CCD imaging device used in an electronic endoscope according to a second specific embodiment.

FIG. 8 is a diagram showing a signal intensity distribution of an image signal captured by the CCD image sensor.

FIG. 9 is a flowchart illustrating a flow of an operation of a dark current correction control unit.

FIG. 10 is a diagram showing a signal intensity distribution of a dark current image signal.

FIG. 11 is a diagram illustrating a signal intensity distribution of an image signal after dark current correction.

FIG. 12 is a block diagram of an electronic endoscope as a third specific embodiment to which the imaging device according to the present invention is applied;

FIG. 13 is a flowchart illustrating a flow of an operation of a dark current correction control unit.

FIG. 14 is a diagram showing a signal intensity distribution of a dark current.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CCD image sensor 2 A / D conversion circuit 3,5 Image memory 4 Subtractor 6 D / A conversion circuit 7 CRT 8,22,41 Dark current correction control part 9 Transmission cable 11,31,51 Imaging surface 12,32 Image Exposure area 13,33 Non-exposure area 23,24,42,43 Storage 25 Control line

Claims (7)

[Claims] 1. An image pickup apparatus including an image pickup device having an image pickup surface composed of an image exposure region and a non-exposure region, wherein a dark current of an image signal of the image pickup device taken in the image exposure region is two-dimensionally corrected. An imaging device comprising a dark current correction unit. 2. The dark current image acquisition unit, wherein the dark current correction unit acquires an exposure region dark current image signal corresponding to a dark current included in an image signal captured in the image exposure region, and the image exposure region 2. The imaging apparatus according to claim 1, further comprising: a dark current image removing unit configured to remove the exposure area dark current image signal from the image signal captured in the step (a). 3. The method according to claim 1, wherein the dark current image acquisition unit calculates the exposure area dark current image signal based on a signal intensity distribution of a non-exposure area dark current image signal imaged in a non-exposure area of the imaging device. The imaging device according to claim 2, wherein: 4. The dark current image acquisition unit according to claim 2, wherein the dark current image acquisition unit is configured to determine the exposure area dark current image signal from an image signal captured in a state where the image exposure area is shielded from light. Imaging device. 5. A dark current image rewriting means having a temporary storage section for storing the exposure area dark current image signal, wherein the dark current correction means rewrites an exposure area dark current image signal stored in the temporary storage section. And a rewriting determination unit that determines whether to rewrite the exposure area dark current image signal stored in the temporary storage unit based on whether or not the non-exposure area dark current image signal has changed. The image removing means uses an exposure area dark current image signal stored in the temporary storage unit as the exposure area dark current image signal. Imaging device. 6. A first storage unit which stores in advance a relationship between a temperature of the image sensor and a non-exposed area dark current image signal imaged under the temperature, A second storage unit that stores the exposure area dark current image signal corresponding to the temperature in association with the temperature, wherein the dark current correction unit stores the non-exposure area dark current image signal at the time of imaging, and the first storage unit A temperature calculating unit configured to calculate a temperature of the image sensor based on the stored correspondence, wherein the dark current removing unit includes an exposure area dark current image signal stored in the second storage unit. 5. An exposure area dark current image signal corresponding to the temperature of the image sensor calculated by said temperature calculation means is used as an exposure area dark current image signal. An imaging device according to any one of the preceding claims. 7. The imaging apparatus according to claim 2, wherein the exposure area dark current image signal is a thinned image signal.