JP2605425B2 - Electronic endoscope imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging apparatus using a solid-state imaging device, and more particularly, to an imaging system used as an observation system for an electronic endoscope, which captures an object under irradiation of illumination light. The present invention relates to an imaging device for performing the above.

[Prior Art] Electronic endoscope devices used for medical and industrial purposes are:
An endoscope body, a processor, and a monitor device are provided. An insertion portion of the endoscope body is inserted into a body cavity or the like, and illumination light is directed from a lighting device incorporated in the processor to a subject via a light guide. Illuminated, a reflected image from the subject is photographed by a solid-state imaging device such as a CCD, converted into an electric signal, and this video signal is transmitted to a processor, and the processor performs predetermined signal processing. A color display is performed on the monitor device.

Here, in order to reduce the diameter of the insertion portion of the endoscope body,
Normally, a color image signal is obtained using one solid-state imaging device. Then, the illumination light from the light source is decomposed into light of each wavelength of R, G, and B via a rotating color filter, and illumination with each light of each color is sequentially and repeatedly repeated in a time-series manner. By repeating charge accumulation and transfer by the image pickup device, R, G, and B color image signals are formed for each field, and these color image signals are converted into a simultaneous signal to form a color video signal. The subject image is displayed as a color image on the screen of the monitor device based on the color image signal.

As described above, when a solid-state imaging device is driven to capture a video of a subject, in order to obtain a clear and high-quality video,
It must be illuminated with the proper amount of illumination. However, the appropriate amount of illumination light is not constant depending on the positional relationship between the subject and the distal end of the insertion section provided with the illumination window and the observation window. For example, when the subject is at a distant position, the amount of reflected light from the subject is small, and the amount of light received by the solid-state imaging device is also small,
The monitor screen becomes dark and the affected part to be observed cannot be seen. On the other hand, if the subject is in a close position, the amount of light received by the solid-state imaging device is too large, and the solid-state imaging device is immediately saturated, causing a whiteout phenomenon and detailed information on a white portion of the monitor image. Are lost, and the image quality is also deteriorated.

For this reason, in the related art, a configuration is used in which a change in the amount of light received by the solid-state imaging device due to a change in the amount of light reflected from the subject is adjusted by adjusting the amount of light of the illumination light source. I have. As a mechanism for adjusting the illumination light amount, provided between the light source and the light guide,
In order to control the light amount stop member, a light amount stop mechanism including a servo mechanism including a driving unit such as a motor is used to control the light amount stop member. Then, a video signal output from the solid-state imaging device is detected to extract accuracy information, a drive signal is input to a servo mechanism in accordance with the luminance level, and the light amount aperture member is operated by the servo mechanism to output an output video signal. Adjustment is made so as to increase or decrease the amount of illumination so that the level becomes almost constant.

[Problems to be Solved by the Invention] By the way, when the light amount aperture mechanism as described above is used,
Not only is the configuration of the light source section complicated and large, but also the response is poor, the hunting phenomenon may occur due to the problem of adjusting the aperture speed, and the image stability may be lost. Has a problem that the color balance is deteriorated. Furthermore, since there is a possibility that a failure may occur due to the use of a mechanical operating mechanism, there is a drawback that sufficient reliability cannot be obtained in the illumination light amount adjusting mechanism.

In addition, the reflectance of each of the R, G, and B wavelength lights differs depending on the subject to be observed. For example, in a medical endoscope which is inserted into a human body or the like and is used for diagnosis and observation inside the body, the reflectance of light of a red wavelength component from a subject is extremely high, and green light and green light are reflected. Since the blue wavelength component is absorbed on the subject side, the amount of reflected light of R becomes significantly larger than the amount of reflected light of other wavelengths, resulting in a significant difference in the amount of light received by the solid-state imaging device. Further, even in the case of an industrial endoscope, the reflectance of light of wavelengths of R, G, and B greatly changes depending on the surface condition of a subject to be observed.
For this reason, among the R, G, and B color image signals formed in the solid-state imaging device, the specific signal level becomes too high, and the width up to the saturation voltage is reduced, so that the dynamic range is reduced. Further, the possibility of occurrence of a whiteout phenomenon, bleaming, smear and the like increases.

The present invention has been made in view of the above points, and does not use a mechanically operated diaphragm mechanism, but adjusts the sensitivity according to the amount of light received by a solid-state imaging device to thereby improve the brightness of an output video signal. It is an object of the present invention to provide an imaging apparatus for an electronic endoscope that can be adjusted so as to maintain a constant level and can obtain a high-quality image.

[Means for Solving the Problems] In order to achieve the above-described object, the present invention repeatedly illuminates a subject with light of each of R, G, and B wavelengths in a time-sequential manner at predetermined time intervals. A solid-state imaging device disposed at the distal end of the insertion portion and repeatedly accumulating and transferring electric charges under illumination from the light source to capture images of the subject in R, G, and B colors. Maximum light amount detecting means for detecting a light amount of a maximum output level among output video signals of each color of R, G, and B from the solid-state imaging device and calculating a deviation from a reference level; Based on the light amount deviation signal from the light amount detecting unit, an invalid accumulation time is set in a part of the total charge accumulation time of the solid-state imaging device, and a sweep-out transfer pulse is used to change the effective charge accumulation time. The charge accumulation time adjusting means for transmitting the It is characterized in that the charge accumulation time of the solid-state imaging device at the time of capturing an image of each color of R, G, B is adjusted in accordance with the maximum amount of reflected light from the body.

[Operation] As described above, by controlling the charge accumulation time in the solid-state imaging device and adjusting its sensitivity, the amount of light received by the solid-state imaging device can be adjusted according to the position and state of the subject. Even if the amount of reflected light changes, the output level of the video signal of the solid-state imaging device can be accurately aligned. In general, a solid-state imaging device has a fixed total charge accumulation time in one field (usually 1/60 second), but does not take out all the charge accumulated during the total charge accumulation time, but partially removes the charge. By sweeping out as invalid charges, the sensitivity of the solid-state imaging device is automatically corrected by limiting the effective charge accumulation time.

Here, in order to limit the effective charge accumulation time, an invalid sweep pulse for sweeping out the accumulated charge is applied to the solid-state imaging device during the entire charge accumulation time, and the accumulated charge is swept once. The charge accumulated after the application of the invalid sweep pulse is extracted as effective charge and transmitted to the video signal processing circuit. By changing the application timing of the invalid sweep pulse, the effective charge accumulation time can be changed.

The timing of applying the sweep pulse to the solid-state imaging device is determined by detecting an output video signal from the solid-state imaging device, extracting the video information, and comparing the video information with a predetermined reference level. The level of the video signal output from the solid-state imaging device is not always the same for all of the R, G, and B video signals. Therefore, in the present invention, the output video signal having the maximum output level among the output video signals from the solid-state imaging device is detected, and the video level of the output video signal having the maximum level is compared with the reference level. As a result, by controlling the video signal of the maximum output level in the solid-state imaging device, the range until saturation at the time of accumulation is increased, and the overexposure phenomenon and the like can be prevented. can get.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

First, FIG. 1 shows a schematic configuration of an image pickup device of an electronic endoscope using a solid-state image pickup device driven by a frame sequential method.

In the figure, reference numeral 1 denotes an illumination lamp, and the illumination lamp 1 emits white light. This lighting lamp 1
Illumination light emitted from the light guide 5 enters the light guide 5 through the condenser lens 3 and the rotating color filter 4, so that the illumination light can be emitted toward the subject from the emission end of the light guide 5. ing. Here, as shown in FIG. 2, the rotating color filter 4 is formed with filter regions 4R, 4G, and 4B that transmit only light of each wavelength of R, G, and B, and each of the filter regions 4R and 4G. , 4B, a light shielding area is formed.
And the indexes 6R, 6G, 6B are provided in the light shielding area at the transition part of each of these filter areas 4R, 4G, 4B,
The indexes 6R, 6G, and 6B are detected by the photo sensor 7 and output the respective enable signals of R, G, and B.

In this way, by performing illumination with the R, G, and B wavelength lights, the reflected light from the subject is provided at a position close to the emission end of the light guide 5 at the distal end of the insertion portion of the endoscope. CCD 9 as a solid-state imaging device via objective lens 8
, And form an image on the light receiving portion of the CCD 9 to accumulate the charges. By reading out the accumulated charges, R, G, and B color image signals can be obtained.

In order to drive the signal read from the CCD 9, a synchronization signal generation circuit 10 is provided.
The synchronization signal output from the
Is input to the CCD drive circuit 12 via the
By applying a read drive signal to CCD9 from R,
Video signals of colors for each of the G and B fields are read. Then, the video signals of the colors of each field of R, G, B are A / D converted by an A / D converter 14 via a video signal processing circuit 13, and each memory area 15R, 15G, 15B in the field memory 15 is processed. R, G, and B color image signals are sequentially stored, respectively, and when any color is stored in the field memory 15 for two fields, these color image signals are read out simultaneously and become simultaneous signals. The analog signals are converted by the D / A converters 16R, 16G, 16B, and these R, G, B
The composite video signal is output from the video signal of each color via the encoder 17 so that the image of the subject can be displayed in color on the monitor device.

Here, as described above, at the time of observation, the amount of light reflected from the subject and received by the CCD 9 from the relationship between the distance between the light guide 5 and the exit end of the CCD 9 and the subject and the reflectance of light at the subject. Changes. In the present invention, the light amount itself of the illumination lamp 1 as a light source is not always constant irrespective of the position or state of the subject, and the charge accumulation of the CCD 9 is provided without providing a light amount stop means in this light source unit. By controlling the time, sweeping out a part of the total charge accumulation time as invalid, and controlling the effective charge accumulation time taken out as a video signal, the CCD 9 is adjusted in sensitivity so that even if the amount of reflected light from the subject changes. In addition, the image of the subject displayed on the monitor device is displayed with a substantially constant brightness, so that a high-quality image is obtained. Moreover, in setting the invalid charge accumulation time, the R, G, and B wide output video signals are set based on the maximum level of the output video signal, so that the R, G, and B color wavelength light Even when the amount of light reflected from the subject fluctuates when illumination is performed, the amount of light received by the CCD 7 does not become excessive.

Therefore, the CC of the frame interline transfer method is described below.
A method of adjusting the output level of each field when D is used will be specifically described.

In order to drive the CCD 9, as is well known, signal light is accumulated in the light receiving unit by causing the light receiving unit of the CCD 9 to receive light during sequential illumination in each field. Here, the charge accumulation time by this CCD9 is usually
This is 1/60 second, so that the stored charge is read out every 1/60 second. However, when a certain arbitrary time has elapsed among the total charge storage time, an unnecessary charge transfer pulse is applied to the CCD to sweep out the stored charge, and the charge stored in the light receiving unit during this time is transferred to the unnecessary charge. To drain to the drain. After the application of the unnecessary charge transfer pulse, the signal charge newly accumulated in the light receiving section is extracted as a video signal by applying a transfer pulse to the CCD 9 during the vertical blanking period.

As apparent from FIG. 1, a charge accumulation time control circuit 18 is provided to apply the sweeping pulse. The charge accumulation time control circuit 18 is provided based on a signal output from the charge accumulation time control circuit 18. The output timing of the unnecessary charge reading pulse applied during the time can be set. The charge accumulation time control circuit 18 is connected to a maximum light amount detection unit 19, and the maximum light amount detection unit 19 sets the maximum level of the actual output video signal in the CCD 9 to a predetermined reference level. The difference is calculated by comparing the difference signal from the maximum light amount detection means 19 with the charge accumulation time control circuit 18.
, The output timing of the unnecessary charge readout pulse is adjusted.

For this purpose, the maximum light amount detecting means 19 is connected to the video signal processing circuit 13. The video signal processing circuit 13 includes a low-pass filter 13a, a white balance circuit 13b, and a γ correction circuit 13c, and sequentially processes color image signals of R, G, and B fields output from the CCD 9, Light intensity detection means 19
Is the low-pass filter 13a and white balance circuit 1.
3b, and R, G, B color image signals are taken in. The color image signal thus captured is amplified by the amplifier 19a and converted into an R, G, B enable signal output from the photo sensor 7 that reads the indexes 6R, 6G, 6B provided on the rotating color filter 4. The R, G, and B color image signals are input to the maximum value detection circuit 19c in a separated state via the switching means 19b that operates based on this. Therefore, by detecting the maximum value detection circuit 19c, a signal having the maximum luminance level is extracted from each of the color image signals, and the luminance level is detected. Then, the maximum luminance level of the image output signal from the CCD 9 detected in this way is compared with a reference level preset by the reference level setting unit 19d in the comparator 19e, and a deviation signal relating to the level difference is charged. It is input to the accumulation time setting circuit 18 and determines the output timing of the unnecessary charge readout pulse based on the deviation signal. The unnecessary charge readout pulse set as described above is
It is configured to be transmitted from the timing pulse generation circuit 11 to the CCD drive circuit 12 to be transferred to the CCD drive signal applied from the CCD drive circuit 12 to the CCD 9 and applied to the CCD 9 at a predetermined timing.

Thus, as shown in FIG.
Is illuminated by light of each wavelength of R, G, and B by passing through the rotating color filter 4, and the light is shielded between a field period F in which the CCD 9 is exposed and a field period F of each color. , The vertical blanking period B is sequentially repeated. Accordingly, as shown in FIG. 3 (b), signal charges are accumulated in the CCD 9 during each field period F, and the photodiode read pulse TP is applied during the vertical blanking period B, thereby making the CCD readout. The signal charges stored in the light receiving section of the CCD 9 are transferred to the storage section.

However, instead of transferring the entire charge accumulation time in the above-described field period F to the accumulation unit, an invalid accumulation time FD is provided, and during the charge accumulation of the CCD 9, charges accumulated up to that point are regarded as unnecessary charges. The drain is drained, and only the signal charges accumulated during the effective charge accumulation time FE after the invalid accumulation time FD are taken out as a video signal.

Therefore, as described above, the maximum light amount detecting means 19
A deviation signal obtained by detecting the maximum luminance level of the output video signal of each color of R, G, B is input to the charge accumulation time control circuit 18, and based on the deviation signal, the unnecessary charge is calculated by the charge accumulation time control circuit 18. The application timing of the read pulse RP is determined. The unnecessary charge readout pulse RP determined in this manner is supplied to the timing circuit 11 and the timing circuit 11 during the horizontal blanking period.
CCD 9 which is in the process of accumulating charge via CCD drive circuit 12 sequentially
Is input to the vertical transfer unit. Then, after the transfer is once performed, the charge is again stored in the light receiving unit. The charges thus accumulated are applied with a photodiode read pulse TP for reading out effective charges when the vertical blanking period B is reached, and the effective charges are read out from the photodiodes to the transfer section. Before the application, the unnecessary charge sweeping transfer pulse DP is applied to discharge unnecessary charges accumulated in the accumulation unit to the drain, and the accumulation unit is emptied. The effective charges transferred to the storage unit as described above are transferred to the storage unit by applying a transfer pulse HP, sequentially read, and output to the A / D converter 14,
When the video signals of the respective colors of R, G, and B are recorded in the respective memory areas 15R, 15G, and 15B of the field memory 15, they are simultaneously read out, and the composite video synthesized by the encoder 17 is read out. A signal is formed.

As a result, as shown in FIG. 3 (c), the intensity of the reflected light from the subject is corrected without adjusting the light source light amount, and the R, G, and B color image signals become constant. Therefore, by changing the application timing of the sweeping rolling pulse RP based on the amount of reflected light from the subject, when the subject is near, the amount of reflected light increases and is indicated by a dotted line. When the output level is too high or the subject is far away, the amount of reflected light is small, and the output level does not become too low as indicated by the dashed line, and the brightness is almost the same on the monitor screen. Can be used to project the subject. Since the level of the output video signal is adjusted by providing the invalid accumulation time in the total charge accumulation time of the CCD 9 as described above, the amount of illumination light emitted from the illumination lamp 1 is far. It is needless to say that it is necessary to keep the position at such a level that a sufficient video signal level can be obtained even when the amount of reflected light is small.

As described above, by controlling the effective charge accumulation time of the CCD 9, the sensitivity is automatically corrected and the level of the output video signal is adjusted, so that the light source light amount is mechanically controlled. Compared to technology, the light source can be made smaller and more compact, which is advantageous not only in terms of cost, but also suppresses hunting and color shift phenomena peculiar to mechanical diaphragm mechanisms. In addition, since no mechanical driving member is used, the operation is stable and the reliability is improved.

In addition, depending on the nature of the subject, the reflectance in the case of performing illumination with light of each wavelength of R, G, and B is not equal. For example, in the case of a medical endoscope inserted into a human body or the like, the reflectance of red wavelength light is much higher than the reflectance of other wavelength light. Therefore, the signal used for setting the application timing of the unnecessary charge readout pulse RP described above is converted into a maximum value detection circuit in the maximum light amount detection means 19.
By 19c, the maximum one of the R, G, and B color image signals is detected. As a result, even in the state of being illuminated with the light having the highest reflectance, saturation is prevented at the time of exposure of the CCD 9, and so-called whiteout phenomenon, blooming, smear, etc. do not occur, and a high-quality image can be obtained. can get.

As described above, in the medical endoscope, the reflectance of the red wavelength light always becomes the maximum, and therefore, as shown in FIG. Switching means 19 that closes only when output is made
b ', and a detection circuit 19c' is provided on the output side of the switching means 19b '. If the maximum value detection is not necessarily performed, the image signal of the maximum luminance level is extracted from each color image signal. , The comparator 19e can compare with the reference level output from the reference level setting unit 19d. Note that the signal taken out by the maximum light amount detecting means 19 may be taken from between the white balance circuit 13b and the γ correction circuit 13c.

Further, as an endoscope, for example, a gastroscope, a duodenoscope,
There are various types such as colonoscopes, but depending on the type of endoscope, the imaging size of the CCD is different, so even if the light amount on the light source side is the same, the image output from this CCD The signal level changes. Therefore, if the configuration is such that the reference level set by the reference level setting unit 19c can be appropriately changed, it is possible to adjust so as to obtain a video signal of an optimal output level according to the imaging size of the CCD. become able to.

In the above-described embodiment, the CCD of the frame interline transfer method has been described. However, the same control of the signal charge accumulation time as described above can be performed in the CCD and the MOS CCD of the interline transfer method. For example, by using a VOFD type interline transfer CCD and applying a pulse for sweeping out unnecessary charges to the light receiving unit every horizontal scanning period, the unnecessary charges are swept to the substrate during the horizontal blanking period. It is also possible to control the signal charge accumulation time of R, G, and B by controlling the time for applying the sweep pulse. Further, there is a variation in output signals among the R, G, and B color image signals due to a rotation color filter, a sensitivity characteristic to a color of the CCD, and the like.
If the invalid accumulation time is changed for each of the G and B fields, the color balance of the output video signal for each of the R, G and B fields can also be improved, and the reproducibility of the image becomes extremely good. .

[Effects of the Invention] As described above, according to the present invention, R, G,
By irradiating the illumination with each color wavelength light of B sequentially and chronologically repeatedly at predetermined time intervals, and repeating the accumulation and transfer of electric charges under this illumination, the image of each color of R, G, B of the subject can be obtained. The solid-state imaging device to be photographed is disposed at the distal end position of the insertion section, and when photographing the image of the subject, the R, G, and B colors output from the solid-state imaging device based on the reflected light from the subject. Among the video signal levels, the maximum level is detected by the maximum light amount detection means, the level of the output signal is compared with the reference level, and based on the deviation signal,
A part of the total charge accumulation time of the solid-state imaging device is regarded as an invalid accumulation time, the effective charge accumulation time is limited, and the invalid accumulation time is set based on the transmission timing of the sweep-out transfer pulse by the charge accumulation time adjusting means. Since the effective charge storage time of the solid-state imaging device is controlled by changing the output voltage, the output level of the video signal can be kept substantially constant without changing the light-receiving time in the solid-state imaging device or the light source light amount. It is possible to adjust the sensitivity of the solid-state image sensor to the maximum level even if there is a variation in the light reflectance of each color wavelength light due to R, G, B in the subject, etc. This has the effect of increasing the dynamic range and preventing the occurrence of overexposure phenomena, blooming, smear, and the like, and obtaining a high-quality image.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory diagram of the entire imaging system of an endoscope imaging device according to the present invention, FIG. 2 is a structural explanatory diagram of a rotating color filter, and FIG.
FIG. 2B is an explanatory diagram showing the transfer and sweep pulse application timing, FIG. 2C is an explanatory diagram showing the output level of the CCD video signal, and FIG. 4 is an imaging system showing a second embodiment of the present invention. FIG. 3 is an explanatory diagram of a main part configuration of FIG. 1: 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: maximum light amount detection means.

Claims (1)

(57) [Claims] 1. A light source for irradiating a subject with illumination of each of R, G, and B color wavelength lights in a time-sequential manner repeatedly at predetermined time intervals, and a light source disposed at a distal end position of an insertion portion. A solid-state image sensor that captures an image of each color of R, G, B of the subject by repeating charge accumulation and transfer under illumination, and an output image of each color of R, G, B from the solid-state image sensor. A maximum light amount detecting means for detecting a signal having a maximum light output level among the signals and calculating a deviation from the reference level; and a light amount deviation signal from the maximum light amount detecting means. A charge accumulation time adjusting means for transmitting a sweep-out transfer pulse in order to change an effective charge accumulation time by setting an invalid accumulation time as a part of the charge accumulation time; and Depending on R, G,
B. An imaging apparatus for an endoscope, wherein the charge accumulation time of the solid-state imaging device at the time of capturing an image of each color is adjusted.