JPH03133280A - Image pickup device for electronic endoscope - Google Patents

Abstract

PURPOSE:To make an output level of a video signal of a solid-state image pickup element constant by providing a charge storage time adjustment means varying an effective charge storage time so as to adjust the charge storage time of the solid-state image pickup element in response to the reflecting luminous quantity from an object. CONSTITUTION:A charge storage time in each field of a CCD 7 is constant. Part of a full charge storage time is invalid and an effective charge storage time extracted as a video signal is controlled to apply the sensitivity adjustment of the CCD 7 so that the level of the output video signal is made constant. A charge storage time control circuit 18 is provided to apply the undesired charge readout pulse. Then a photodetecting quantity detection means 19 calculates a deviation between a level of an actual output video signal in the CCD 7 and a prescribed reference level. The deviation signal is inputted to the charge storage time control circuit 18 to adjust the output timing of the undesired charge transfer pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an imaging device using a solid-state imaging device, and is particularly used as an observation system of an electronic endoscope device, etc. The present invention relates to an imaging device for photographing.

[Prior art 1] An electronic endoscope device used for medical or industrial purposes includes an endoscope main body, a processor, and a monitor device, and an insertion section of the endoscope main body is inserted into a body cavity or the like. Then, illumination light is emitted toward the subject from the lighting device built into the processor, and the reflected image from the subject is photographed by a solid-state image sensor such as a CCD, converted into an electrical signal, and this video signal is transmitted to the processor. The processor then performs predetermined signal processing and then displays the signal in color on a monitor device.

Here, in order to reduce the diameter of the insertion section of the endoscope main body, a single solid-state image sensor is normally used to obtain a color video signal. As a typical driving method of this solid-state image sensor, R,
A color filter array that transmits G and B wavelength light is arranged in a checkerboard pattern, and this solid-state image sensor is exposed to light to accumulate color video signals consisting of R, G, and B in each pixel in the light receiving section. By using a so-called simultaneous drive method that reads out this accumulated signal, and by passing the illumination light from the light source through a rotating color filter, illumination with light in the R, G, and B color wavelength ranges is sequentially repeated, and during this period, the solid-state image sensor By repeating charge accumulation and transfer, R,
There is a frame-sequential driving method in which G and B color image signals are formed for each field, and these color image signals are converted into simultaneous signals via a field memory to output a color video signal.

Regardless of whether it is a simultaneous drive method or a frame-sequential drive method, when driving a solid-state image sensor to capture an image of a subject, in order to obtain a clear, high-quality image, it is necessary to It must be illuminated with the same amount of light. However, 1. The appropriate amount of illumination light is not constant depending on the positional relationship between the subject and the tip of the insertion section provided with the illumination window and observation window, the reflectance of the subject, etc. For example, if the subject is far away,
Since the amount of reflected light from the subject decreases, the amount of light received by the solid-state image sensor also decreases, making the monitor screen darker. On the other hand, if the subject is close to the subject, the amount of light received by the solid-state image sensor will be too large and the solid-state image sensor will quickly become saturated, resulting in the so-called whitewashing phenomenon. Information is lost and image quality deteriorates.

Therefore, in the conventional technology, by adjusting the amount of illumination light emitted from the light source according to the position of the object, the light reflectance of the object, etc., the amount of light reflected from the object changes. A structure that adjusts changes in the amount of received light is used. The mechanism for adjusting the amount of illumination light includes a light aperture member provided between the light source and the light guide to mechanically control the amount of light from the light source, and a motor to control the light aperture member. A light amount diaphragm mechanism consisting of a servo mechanism equipped with a driving means such as the following is used. Then, it detects the video signal output from the solid-state image sensor, extracts the brightness information from it, compares this brightness level with a predetermined reference level, and inputs a drive signal to the servo mechanism based on the deviation. The servo mechanism operates the light amount diaphragm member to adjust the amount of illumination light to increase or decrease so that the brightness level of the video signal is approximately constant.

[Problems to be Solved by the Invention] By the way, when the above-mentioned light aperture mechanism is used, not only does the structure of the light source become complicated and large, but also the response of the aperture mechanism is poor, and the aperture speed controllability is deteriorated. Hunting phenomenon may occur due to such problems and the image may not be stable.Furthermore, depending on the type of light aperture member, color balance may deteriorate, and furthermore, due to the use of a mechanical operating mechanism, failures may occur. Therefore, there is a drawback that sufficient reliability cannot be obtained in the light amount adjustment mechanism of the illumination light.

The present invention has been made in view of the above points, and the output video signal level can be adjusted by adjusting the sensitivity of the solid-state image sensor according to the amount of light received without using a mechanically operated aperture mechanism. It is an object of the present invention to provide an imaging device for an electronic endoscope that can be adjusted to maintain a constant value.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention includes a light source that emits illumination light toward a subject, and an image of the subject is photographed under illumination from the light source. a solid-state imaging device disposed at the distal end of the insertion section; a received-light amount detection means for detecting the amount of received light from the video signal level output from the solid-state imaging device and calculating a deviation from a reference level; and the amount of received light. charge accumulation time adjusting means for changing the effective charge accumulation time by setting a part of the total charge accumulation time of the solid-state image sensor as an invalid accumulation time based on a light intensity deviation signal from the detection means; A feature of the present invention is that the charge accumulation time of the solid-state image sensor is adjusted according to the amount of light reflected from the subject.

[Operation l] In this way, by controlling the charge accumulation time in the solid-state image sensor and adjusting its sensitivity, the amount of light received by the solid-state image sensor can be adjusted according to the position and condition of the subject without changing the light source itself. can be adjusted, and the output level of the video signal of the solid-state image sensor can be made constant with high precision. That is, in a solid-state image sensor, the total charge accumulation time in one field is constant (usually 1/60 second);
Rather than extracting all of the charge accumulated within this total charge accumulation time, a portion of it is swept out as invalid charge, thereby limiting the effective charge accumulation time and automatically increasing the sensitivity of the solid-state image sensor. For example, if the subject is close, increase the invalid charge accumulation time,
By reducing the effective charge accumulation time and discharging excess charge to the solid-state image sensor, it is possible to prevent the solid-state image sensor from becoming harmonized. Furthermore, when the subject is far away and the amount of light reflected from the subject is small, increasing the effective charge accumulation time increases the sensitivity of the solid-state image sensor and improves the output level of the overall output video signal. I can do it.

Here, in order to limit the effective charge accumulation time, an unnecessary charge transfer pulse that sweeps out the accumulated charge is applied to the solid-state image sensor in the middle of the total charge accumulation time, and the charge accumulated up to that point is swept out once. After applying a pulse to sweep out this unnecessary charge, only the accumulated charge is taken out and transmitted to the video signal processing circuit. By changing the application timing of this unnecessary charge sweep pulse, the effective charge accumulation time can be changed. The timing of applying the unnecessary charge sweep pulse to the solid-state image sensor is determined by detecting the output video signal from the solid-state image sensor, extracting its luminance signal, and comparing it with a predetermined reference level, as in the conventional technology. Determined by

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

First, FIG. 1 shows a schematic configuration of an imaging device for an electronic endoscope using a solid-state imaging device driven in a frame-sequential manner.

In the figure, 1 indicates an illumination lamp, and the illumination lamp 1
The one that emits white light is used. The illumination light emitted from the illumination lamp 1 is incident on the light guide 5 via the condensing lens 39 and the rotating color filter 4, and the illumination light can be irradiated from the output end of the light guide 5 toward the subject. It looks like this. Here, as shown in FIG. 2, the rotating color filter 4 has filter regions 4R, 4G, 4 that transmit only light in the R, G, and B wavelength regions.
B is formed, and a light shielding area is formed between each filter area 4R, 4G, and 4B. The reflected image from this object is transmitted to a CC as a solid-state image sensor via an objective lens 6 provided at a position close to the output end of the light guide 5.
It is incident on D7, photoelectrically converted by the CCD7, and R
, G, and B color image signals can be obtained.

In order to drive the CCD 7, a synchronization signal generation circuit 10 is provided, and the synchronization signal outputted from the synchronization signal generation circuit 10 is sent to the CO2 via a timing pulse generation circuit 11.
By inputting the signal to the D drive circuit 12 and applying a read drive signal from the CCD drive circuit 12 to the CCD 7,
Color image signals for each field of R, G, and B are read out. The color image signals of each field of R, G, and B are sent to the A/D through the video signal processing port and path 13.
A/D conversion is performed by the converter 14, and each R, G, and B color image signal is sequentially stored in each memory area 15R, 15G, and 15B in the field memory 15, and any color image signal is stored in two fields. When stored in the minute field memory 15, these color image signals are simultaneously read out to become simultaneous signals, which are converted into analog signals by D/A converters 16R, 16G, and 16B, respectively.
By superimposing these R, G, and B color video signals via the encoder 17, a composite video signal is output, and the image of the subject can be displayed in color on a monitor device.

Here, as already explained, the light guide 5 and CC
The amount of light reflected from the subject and received by the CCD 7 changes during photographing due to the relationship between the distance between the output end of the D7 and the subject, the reflectance of light on the subject, and the like. However, in the present invention, the light amount of the illumination lamp 1 as a light source is constant regardless of the position or condition of the subject, and no light amount diaphragm mechanism is provided on the light source side. Instead, the sensitivity can be adjusted by controlling the charge accumulation time of the CCD 7, so that even if the amount of reflected light from the subject changes, the image of the subject displayed on the monitor device can be maintained at approximately constant brightness. So that it is displayed in the state,
It is configured to obtain high-quality images.

That is, although the charge accumulation time in each field of the CCD 7 is constant, a part of this total charge accumulation time is invalidated,
By controlling the effective charge accumulation time taken out as a video signal, the sensitivity of the CCD 7 is adjusted so that the level of the output video signal is constant.

Therefore, below is the COD of the frame interline transfer method.
A method for adjusting the output level of each field when using the following will be explained in detail.

To drive the CCD 7 using the frame interline transfer method, as is well known, the light receiving section of the CCD 7 receives light while sequential illumination in each frame is performed, thereby accumulating signal charges in the light receiving section. Let it happen. Here, the charge accumulation time by the CCD 7 is normally 1760 seconds, and therefore the accumulated charges are read out every 1760 seconds. However, when a certain arbitrary period of time has elapsed out of this total charge accumulation time, an unnecessary charge readout pulse is applied to the light receiving section to sweep out the accumulated charge, and the charge H&ed in the light receiving section during this period is drained as unnecessary charge. Have it swept away. After applying this unnecessary charge readout pulse, the signal charge newly accumulated in the light receiving section is extracted as a video signal by applying a forward transfer pulse to the CCD 7 during the vertical blanking period.

Therefore, in order to add this unnecessary charge readout pulse, the first
As is clear from the figure, a charge accumulation time control circuit 18 is provided, and the output timing of the unnecessary charge read pulse added during the charge accumulation time is set based on the signal output from the charge accumulation time control circuit 18. It is now possible to do so. This charge accumulation time control circuit 18 is connected to a received light amount detection means 19, and the received light amount detection means 19 detects the deviation between the level of the actual output video signal in the CCD 7 and a predetermined reference level. By inputting the deviation signal from the received light amount detection means 19 to the charge accumulation time control circuit 18, the output timing of the unnecessary charge transfer pulse is adjusted.

For this purpose, the received light amount detection means 19 is connected to the video signal processing circuit 13. This video signal processing circuit 13 is
As shown in FIG. 3, it has a low-pass filter 13a, a white balance circuit 13b, and a γ correction circuit 13c.
The color image/image signals of each field of R, G, and B output from the CD 7 are sequentially processed, and the video signal transmitted from the white balance circuit 13b to the γ correction circuit 13c is taken out and amplified by the amplifier 19a. Then, the detection circuit 1
9b to detect the output luminance level. And CC detected in this way
The brightness level of the image output signal from D7 is compared with a reference level preset by the reference level setter 19c in the comparator 19d, and a light amount deviation signal related to the level difference is input to the charge accumulation time setting circuit 18. , the output timing of the unnecessary charge read pulse is determined based on this deviation signal. The unnecessary charge read pulse whose timing has been set in this way is transmitted from the timing pulse generation circuit 11 to the CCD drive circuit 12, and the CCD drive circuit 1
2 to the CCD drive signal applied to CCD7.

The configuration is such that the voltage is applied to the CCD 7 at a predetermined timing.

As shown in FIG. 4(a), the illumination light from the illumination lamp 1 passes through the rotating color filter 4 and is illuminated with light of each wavelength of R, G, and B. A field period F in which the CCD 7 is exposed to light and a vertical blanking period B in which light is shielded between the field periods F of each color are sequentially repeated. Then, as shown in FIG. 4(b), signal charges are accumulated in the CCD 7 during each field period F, and by applying a transfer pulse TP during the vertical blanking period B, the CCD 7 The signal charge accumulated in the light receiving section is transferred to the accumulation section.

However, instead of transferring the entire charge accumulation time during the field period F described above to the storage section, an invalid accumulation time FD is provided, and during charge accumulation in the CCD 7, the charges accumulated up to that point are used as unnecessary charges. Only the signal charges accumulated during the effective charge accumulation time FE after the invalid accumulation time FD are extracted as a video signal.

Therefore, the video signal output from the CCD 7 is taken into the detection circuit 19a constituting the received light amount detection means 19, the detection circuit 19a detects the brightness level of the output video signal, and this signal level is input to the comparator 19d. Then, it is compared with the reference level set by the reference level setter 19c, the level difference is calculated, and the deviation signal is inputted to the charge accumulation time control circuit 18. Based on this deviation signal, the charge accumulation time control circuit 18 determines the application timing of the unnecessary charge read pulse RP. The unnecessary charge read pulse RP determined in this way is transmitted to the timing circuit 11 and C
When the charges are sequentially input to the CCD 7 via the CD drive circuit 12, the charges accumulated in the light receiving section of the CCD 7 up to that point are transferred to the accumulation section. After this unnecessary charge is transferred, charge is accumulated in the light receiving section during the effective charge accumulation time FE, and when the vertical blanking period B starts, the charge is accumulated by applying a photodiode read pulse TP to the CCD 7. Transferred to the storage section. However, in order to prevent unnecessary charges from remaining in the storage section when this photodiode readout pulse TP is applied, a transfer pulse DP for sweeping out unnecessary charges is added before the photodiode readout pulse TP. It is swept out into the drain. Sara·
Then, by applying an effective charge transfer pulse HP, the effective charges from which the signal charges have been transferred to the vertical transfer section are transferred to the storage section, and the signal charges are sequentially read out.

The R, G, and B color image signals read out in this manner are written to each memory area 15R, 15G, and 15B of the field memory 15 via the A/D converter 14, and
When these R, G, and B color image signals are recorded, they are simultaneously read out and combined by the encoder 17 to form a composite video signal.

As a result, the intensity of the reflected light from the subject can be corrected without adjusting the light intensity of the light source, and control can be performed so that a nearly constant video signal can be obtained, as shown by the solid line in Figure 4(c). can do. In this way, by changing the application timing of the unnecessary charge readout pulse RP based on the amount of reflected light from the subject, it is possible to detect cases where the subject is nearby and the amount of reflected light is large, as shown by the dotted line in the figure. Even if the output level is high, or if the subject is far away and the amount of reflected light is low, and the output level is low as shown by the dashed line, the subject will be displayed with approximately the same brightness on the monitor screen. be able to. In addition, since the level of the output video signal is adjusted by providing an invalid accumulation time during the total charge accumulation time of the CCD 7,
It goes without saying that the amount of illumination light emitted from the illumination lamp 1 needs to be maintained at a level that allows a sufficient video signal level to be obtained even when the amount of reflected light is small at a remote location.

In this way, by limiting the effective charge accumulation time of the CCD 7, the sensitivity is automatically corrected and the level of the output video signal is adjusted. Compared to conventional technology, the structure of the light source can be made smaller and more compact, which is not only advantageous in terms of cost, but also eliminates the hunting and color shift phenomena that are characteristic of mechanical aperture mechanisms. In addition, since no mechanical drive member is used, the operation is stable and highly reliable.

Furthermore, there are various types of endoscopes, such as gastroscopes, duodenoscopes, colonoscopes, etc., and depending on the type of endoscope, the size of the COD image formed differs, so the light source side Even if the amount of light is the same, the level of the video signal output from this CCD changes. Therefore, if the reference level set by the reference level setter 19c is configured to be able to be changed as appropriate, it is possible to adjust the video signal at the optimal output level according to the image formation size of the 0CCD. You will be able to do it.

In the above-mentioned embodiment, a CCD using a frame interline transfer method has been described, but the signal charge accumulation time can be controlled in the same manner as described above in a COD or MOS CCD using an interline transfer method. for example,
If a VOFD-type interline transfer COD is used and a pulse is applied to the light receiving section to sweep out unnecessary charges every horizontal scanning period, this unnecessary charge will be swept out to the substrate during the horizontal blanking period, and this sweeping out will be possible. The signal charge accumulation time of R2O and B can also be controlled by controlling the pulse application time. Further, the driving method of the CCD is not limited to the above-described frame sequential driving method, but the same control can be performed even in the case of a simultaneous driving method COD. Furthermore, RlG
, B color image signals, but if the invalid accumulation time is changed for each R, G, and B field, R, G.

B: The color balance of the output video signal for each field can also be improved, and image reproducibility becomes extremely good.

[Effects of the Invention] As explained above, according to the present invention, the amount of reflected light received from the subject is detected by the reflected light amount detection means from the video signal level output from the solid-state image sensor, and the output signal is detected by the reflected light amount detection means. level is compared with a reference level, and based on the deviation signal, a part of the total charge accumulation time of the solid-state image sensor is set as an invalid charge accumulation time, and the effective charge accumulation time is changed to change the effective charge accumulation time of the solid-state image sensor. Since the configuration is configured to control the effective charge accumulation time, the output level of the video signal can be kept almost constant even if the reflected light from the subject changes, without the need for a mechanical aperture mechanism in the light source. You will be able to do this.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the overall configuration of an imaging device according to the present invention using a field sequential method in an endoscope, FIG. 2 is an explanatory diagram of the configuration of a rotating color filter, and FIG. 3 is an image of the image shown in FIG. An explanatory diagram of the configuration of the signal processing circuit and charge accumulation time control signal setting means, FIG. 4(a) shows the irradiation cycle of illumination light, FIG. c) is an explanatory diagram showing the output timing of the COD video signal. l: illumination lamp, 4: rotating color filter, 4R:R
Filter area, 4G: G filter area, 4B: B filter area, 7: CCD, 10: Synchronization signal generation circuit, 11: Timing pulse generation circuit, 12: CCD drive circuit, 18: Charge accumulation time control circuit, 19: Light reception Quantity detection means. Figure 2 Figure 2 Figure 2

Claims (1)

[Claims] A light source that emits illumination light toward a subject, a solid-state image sensor disposed at the tip of the insertion section that captures an image of the subject under illumination from the light source, and a video signal output from the solid-state image sensor. A received light amount detecting means detects the received light amount from the level and calculates the deviation from the reference level, and a light amount deviation signal from the received light amount detecting means is used to detect the received light amount from the total charge accumulation time of the solid-state image sensor. The charge accumulation time adjustment means changes the effective charge accumulation time by setting a part of the charge accumulation time to an invalid accumulation time, and the structure is configured to adjust the charge accumulation time of the solid-state image sensor according to the amount of light reflected from the object. An electronic endoscope imaging device characterized by: