JP4276416B2 - Image signal fluctuation compensation circuit and electronic endoscope image signal processing circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to signal processing of an image photographed using a light source for illumination, and more particularly to an image signal processing circuit of an electronic endoscope apparatus using a light source of a discharge tube type.
[0002]
[Prior art]
The electronic endoscope apparatus is used for observation in a lumen that cannot be photographed by a normal camera, such as in a body or a tube. The electronic endoscope apparatus processes an image signal from an electronic endoscope (electronic scope) having an elongated insertion portion having flexibility and being inserted into a lumen, and an imaging device provided at the distal end of the insertion portion. Image signal processing device (processor) for image capturing and an image display device (TV monitor) for monitoring captured images. Usually, external light does not reach the inside of the lumen, so it is necessary to illuminate the subject in the lumen for imaging. However, since the distal end of the insertion portion of the electronic endoscope is required to be small, it is difficult to directly provide the light source portion at the distal end of the insertion portion. Therefore, light is supplied from the external light source provided outside the electronic scope such as in the processor to the distal end of the insertion portion via the optical fiber bundle (light guide) provided in the electronic scope. Thus, since illumination light is supplied via a light guide, a high-intensity lamp is used to obtain sufficient illumination intensity at the distal end of the insertion portion.
[0003]
[Problems to be solved by the invention]
As a high-intensity lamp, for example, a discharge tube type light source such as a xenon lamp is often used. However, in a discharge tube type light source using discharge between electrodes, the radiation intensity fluctuates due to the influence of convection of the enclosed gas, and the luminance distribution of illumination light becomes unstable. Such fluctuations are particularly prominent near the center of high brightness, and appear as flickering on the TV monitor.
[0004]
It is an object of the present invention to obtain a fluctuation compensation circuit for compensating for an influence on a video image due to fluctuations in radiation intensity of a light source, and an image signal processing circuit for an electronic endoscope in which the fluctuation compensation circuit is mounted. .
[0005]
[Means for Solving the Problems]
An image signal fluctuation compensation circuit according to the present invention includes an amplifying unit that amplifies a first image signal and outputs a second image signal, and a first sampling unit that samples the first image signal at a first period. A second sampling means for sampling the second image signal in a second period relatively shorter than the first period, a first signal level sampled by the first sampling means, and a second And a gain control means for controlling the gain of the amplifying means on the basis of the second signal level sampled by the sampling means, and the second period is an illumination used for taking an image of the first image signal. It corresponds to the fluctuation cycle of the radiation intensity of the light source.
[0006]
The gain control means controls the gain based on the difference between the first signal level and the second signal level. At this time, the difference between the first signal level and the second signal level related to the gain control is as follows: The range of fluctuation due to fluctuations in the radiation intensity of the illumination light source is limited. The gain control range is, for example, a range from 0.8 to 1.2, and the first period corresponds to the fluctuation period of the image signal due to a change in the photographing condition. As a result, it is possible to more effectively remove or reduce only the fluctuation component due to the fluctuation of the illumination light source from the image signal and to prevent the S / N ratio from deteriorating. In addition, when the illumination light source is a discharge tube type lamp, the effect of the present invention is more remarkably exhibited.
[0007]
Furthermore, an image signal processing circuit for an electronic endoscope according to the present invention is characterized by including the above-described fluctuation compensation circuit.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing an outline of an electrical configuration of the electronic endoscope apparatus according to the first embodiment of the present invention.
[0009]
The electronic endoscope apparatus according to this embodiment includes, for example, an electronic endoscope (electronic scope) 10, an image signal processing apparatus (hereinafter referred to as a processor) 20, and a TV monitor 40. The electronic scope 10 is detachably connected to the processor 20 via the connector 11, and the TV monitor 40 is connected to the video output terminal of the processor 20 via a video signal cable. In the present embodiment, only the TV monitor 40 is shown as a peripheral device connected to the processor 20, but peripheral devices such as a VCR, a video printer, and a computer may be connected simultaneously.
[0010]
The electronic scope 10 is provided with an elongated and flexible insertion portion 12, and an imaging element 13 such as a CCD is provided at the tip thereof. A light guide 14 made of an optical fiber bundle is disposed in the electronic scope 10. One end of the light guide 14 is connected to the light source unit in the processor 20 via the connector 11, and the other end is disposed at the distal end of the insertion unit 12. Light supplied from the light source unit in the processor 20 is emitted as illumination light from the tip of the light guide 14 disposed at the tip of the insertion unit via the illumination lens 15. That is, when the insertion portion 12 of the electronic scope 10 is inserted into the lumen or the like, the imaging device 13 uses the light emitted from the light guide 14 as illumination, and the subject in the lumen through the imaging lens 16. Take an image.
[0011]
In the electronic endoscope apparatus according to this embodiment, for example, simultaneous imaging is performed by using the image sensor 13 as a color single-plate image sensor provided with a predetermined complementary color filter, and white illumination light is emitted from the light guide 14. Always irradiated. That is, in the light source unit of the processor 20, a condensing lens 22 is disposed between the light guide 14 and the lamp 21, and light emitted from the lamp 21 is incident on the incident end of the light guide 14 by the condensing lens 22. It is focused on. The lamp 21 is, for example, a xenon lamp, and power is supplied to the lamp 21 from a power source 27.
[0012]
On the other hand, the image pickup device 13 of the electronic scope 10 is driven and controlled by a drive pulse supplied from a timing circuit 26 in the processor 20, and the drive is performed in synchronization with a vertical synchronization signal or the like. Thereby, the image sensor 13 continuously captures images for one screen.
[0013]
An image signal output from the image pickup device 13 is transmitted to a luminance signal (Y signal) and two color difference signals (RY signal, BY) by a process circuit (not shown) provided near the connector 11 in the electronic scope 10. Signal). These luminance signals and color difference signal groups are transmitted as analog image signals to the pre-stage signal processing circuit 28, and predetermined signal processing such as gamma correction, color separation processing, and enhancement processing, fluctuation compensation processing, and conversion into RGB image signals. Is applied, A / D conversion is performed. The image signal converted into the digital signal is temporarily held in the RGB memory 29 for each RGB image. When RGB digital images for one screen are arranged in the RGB memory 29, the RGB image data are synchronized and output to the subsequent signal processing circuit 30 to be a color image for one screen. The subsequent signal processing circuit 30 performs predetermined signal processing on the image signal, encodes it into a video signal of a standard for television broadcasting such as NTSC and PAL, and outputs it to the TV monitor 40 or the like. The front-stage signal processing circuit 28, the RGB memory 29, and the rear-stage signal processing circuit 30 are driven based on the synchronization signal from the timing circuit 26.
[0014]
Next, the fluctuation compensation circuit in the first embodiment will be described with reference to FIG. FIG. 2 is a block diagram in which circuit configurations relating to fluctuation compensation processing are extracted from the front-stage signal processing circuit 28, the RGB memory 29, and the rear-stage processing circuit 30 in FIG. Therefore, the circuit configuration that is not related to the fluctuation compensation process is omitted.
[0015]
Analog image signals (Y signal, RY signal, BY signal) sent from the image sensor 13 are first appropriately amplified by the preamplifiers 281a, 281b, 281c of the pre-stage signal processing circuit 28, respectively. The Y signal is input to a VCA (Voltage Controlled Amplifier) 282 and a first clamp circuit 283a, and the RY signal and the BY signal are input to a matrix circuit 288.
[0016]
In the first clamp circuit 283a, the input image signal is clamped based on the clamp signal CP1 from the timing circuit 26. That is, the signal level (for example, the black level) of the image signal is DC-reproduced based on a predetermined reference voltage and output to the first luminance level detection circuit 284a. In the first luminance level detection circuit 284a, the Y signal is sampled and held at the first sampling period T1 based on the sample hold signal S / H1 from the timing circuit 26, and the luminance level of the screen at that time is detected. . The luminance level signal detected in the first sampling period T1 is output to, for example, the REF voltage circuit 285 that is a buffer circuit, biased to the + side by the predetermined voltage Vr, and then held as the REF voltage for the period T1, and added. Is input to the positive terminal of the device 286.
[0017]
On the other hand, the Y signal input to the VCA 282 is amplified based on the value of the control voltage Vc from the adder 286 and output to the matrix circuit 288 and the second clamp circuit 283b. The Y signal, RY signal, and BY signal input to the matrix circuit 288 are converted into RGB image signals, then converted into digital signals by the A / D converter 287, and R, G, and B digital signals are converted. Are temporarily stored in the memory (R) 29R, the memory (G) 29G, and the memory (B) 29B in the RGB memory 29, and then the signal processing circuit (R) 30R of the subsequent processing circuit, The signals are output to the circuit (G) 30G and the signal processing circuit (B) 30B, respectively.
[0018]
In addition, the image signal input from the VCA 282 to the second clamp circuit 283b is subjected to clamp processing based on the clamp signal CP2 from the timing circuit 26. That is, the signal level (for example, black level) of the image signal is DC-reproduced based on a predetermined reference voltage and is output to the second luminance level detection circuit 284b. The second luminance level detection circuit 284b samples and holds the image signal at the second sampling period T2 (<T1) based on the sample hold signal S / H2 from the timing circuit 26, and the luminance level of the screen at that time Is detected. The luminance level signal detected in the second sampling period T2 is input to the negative terminal of the adder 286.
[0019]
The adder 286 adds the voltages input from the + side terminal and the − side terminal, and outputs a control voltage Vc corresponding to the calculation result to the VCA 282. An example of the relationship between the control voltage Vc from the adder 286 and the gain at the VCA 282 is shown in FIG.
[0020]
Next, the fluctuation compensation processing operation in the first embodiment for an image signal will be described with reference to FIG. FIG. 3A shows the sampling timing of the image signal by the sample hold signal S / H1 in the first luminance level detection circuit 284a, and FIG. 3B shows the image signal of FIG. The sampling timing in the second luminance level detection circuit 284b is represented by the sample hold signal S / H2. The waveform of the image signal shown in FIG. 3B corresponds to the case where the gain of the VCA 282 is fixed to 1 for convenience, but actually the gain of the VCA 282 is obtained by the fluctuation compensation processing described below. Therefore, fluctuations due to fluctuations are removed and reduced from the image signal output from the VCA 282.
[0021]
In the figure, the horizontal axis represents time, and the vertical axis corresponds to the direction of the luminance level of the image signal. 3A and 3B show image signals S1 to S10 for 10 screens as an example. FIGS. 3A and 3B are conceptual timing charts for explaining the fluctuation compensation processing operation, and do not represent an actual image signal sampling operation.
[0022]
As shown in FIG. 3A, in the first luminance level detection circuit 284a, the image signal is sampled by the sample hold signal S / H1 having a period T1, and for example, in FIG. The luminance signal levels (potentials) V1, V4, V7, and V10 of the image signals S1, S4, S7, and S10 are sampled and held, respectively. On the other hand, in the second luminance level detection circuit 284b of FIG. 3B, the image signal is sampled by the sample hold signal S / H2 of the period T2 (<T1), and for example, the image signals S1, S2,. The luminance signal levels (potentials) V1, V2,..., V10 in S10 are sampled and held. Note that the potential V0 in FIG. 3 is a reference voltage when the image signal is DC-reproduced by the first and second clamp circuits 283a and 283b.
[0023]
The period T1 is a period for sampling the REF voltage, which is the target value of the feedback loop including the first luminance level detection circuit 284a, and operates and moves the distal end of the insertion section of the electronic scope 10 (for example, the electronic scope operation section). Corresponds to a change in the brightness of the screen when using an angle lever or the like, for example on the order of 1 to 2 seconds. On the other hand, the period T2 corresponds to the fluctuation period of the image signal due to the fluctuation of the radiation intensity of the lamp 21, and is, for example, on the order of 0.3 to 0.5 seconds.
[0024]
That is, in the fluctuation correction processing operation of the present embodiment, only a relatively short-cycle image signal variation resulting from lamp fluctuation is subject to compensation, and a relatively long-cycle image signal generated by the operation of the electronic scope 10 is compensated. Is not subject to compensation, and the brightness of the screen changes within the range of automatic light control in accordance with changes in shooting conditions.
[0025]
In this embodiment, the relationship between the control voltage Vc and the gain in the VCA 282 is shown in FIG. 4, the gain range of the VCA 282 is 0.8 to 1.2, and the input range of the control voltage Vc is also 0.8. -1.2 (V). That is, assuming that the REF voltage input to the + side of the adder 286 is VR and the voltage input to the − side of the adder 286 is V, in this embodiment, the VCA 282 is | VR−V | <0.2 ( V) amplifying the variation in the range of gain range 0.8-1.2. In this embodiment, it is assumed that the fluctuation of the image signal due to the fluctuation of the radiation intensity of the lamp 21 is within a range of approximately ± 0.2 (V).
[0026]
The fluctuation of the image signal due to the fluctuation of the radiation intensity of the lamp 21 is sufficiently smaller than the fluctuation due to the change of the photographing condition. Further, when the image signal is amplified with a large gain, the S / N ratio is deteriorated. Therefore, the range of | VR−V | effective for gain control and the gain control range of VCA 282 are determined in consideration of the magnitude of fluctuation of the video signal due to the fluctuation of the light source, the deterioration of the S / N ratio due to amplification, and the like. The
[0027]
As described above, according to the present embodiment, since the target value of the feedback loop is changed according to the brightness of the image, the fluctuation of the radiant intensity of the lamp is maintained while maintaining the change in brightness due to the change in the photographing condition. It is possible to compensate for the fluctuations in the video signal caused by it. Accordingly, it is possible to suppress flickering of the screen due to lamp fluctuation, which occurs when a discharge tube type lamp is used as an illumination light source. In addition, short-cycle fluctuations due to fluctuations in the image signal lamp are sampled in a short period corresponding to the fluctuation period, and long-period fluctuations due to changes in imaging conditions etc. The range of | VR−V | effective for VCA gain control is suppressed to a range of fluctuation caused by fluctuations smaller than fluctuations of the image signal due to changes in imaging conditions, and sampling is performed at a period. It is possible to compensate only the fluctuation component due to.
[0028]
Next, a second embodiment of the present invention will be described with reference to FIG. Since the second embodiment is substantially the same as the first embodiment, only the parts different from the first embodiment will be described. In FIG. 5, the same reference numerals are used for the same components.
[0029]
In the first embodiment, the signal output from the VCA 282 is directly input to the second clamp circuit 283b. However, in the second embodiment, the signal is input via the band-pass filter (BPF) 289. The bandpass filter 289 is a filter that selectively passes only signal components corresponding to fluctuations in the radiation intensity of the light source. That is, only a signal corresponding to the fluctuation of the radiation intensity of the light source is input to the second clamp circuit 283b.
[0030]
As described above, also in the second embodiment, substantially the same effect as in the first embodiment can be obtained.
[0031]
In this embodiment, the fluctuation compensation circuit is provided in the previous signal processing circuit in the processor. However, the fluctuation compensation circuit may be provided at an appropriate position between the image sensor and the image display device. It may be provided in the scope. Furthermore, although the fluctuation compensation circuit of the present embodiment is configured with an analog circuit, it may be configured with a digital circuit. For example, a media processor such as a DSP (Digital Signal Processor) may be used as the digital circuit.
[0032]
【The invention's effect】
As described above, according to the present invention, the fluctuation compensation circuit for compensating for the influence on the video signal due to the fluctuation of the radiation intensity of the light source, and the image signal processing circuit for an electronic endoscope in which the fluctuation compensation circuit is mounted. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an electrical configuration of an electronic endoscope apparatus according to a first embodiment of the present invention.
2 is a block diagram excerpting a configuration related to a fluctuation compensation circuit in the previous stage signal processing circuit of FIG. 1; FIG.
FIG. 3 is a conceptual timing chart for explaining a sampling operation in the fluctuation compensation processing operation of the present embodiment.
FIG. 4 is a graph showing a relationship between a VCA control voltage and a gain.
FIG. 5 is a block diagram excerpting an electrical configuration related to a fluctuation compensation circuit of an electronic endoscope apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
10 Electronic Scope 13 Image Sensor 21 Lamp 282 VCA
283a First clamp circuit 283b Second clamp circuit 284a First luminance level detection circuit 284b Second luminance level detection circuit 285 REF voltage circuit 286 Adder

Claims (7)

Amplifying means for amplifying the first image signal and outputting the second image signal;
First sampling means for sampling the first image signal at a first period;
Second sampling means for sampling the second image signal at a second period relatively shorter than the first period;
Gain control means for controlling the gain of the amplification means based on the first signal level sampled by the first sampling means and the second signal level sampled by the second sampling means; ,
The fluctuation compensation circuit for image signals, wherein the second period corresponds to a fluctuation period of radiation intensity of an illumination light source used for taking an image of the first image signal. 2. The image signal fluctuation compensation circuit according to claim 1, wherein the gain control means controls the gain based on a difference between the first signal level and the second signal level. 3. The difference between the first signal level and the second signal level related to the gain control is limited to a range of fluctuation due to fluctuations in radiation intensity of the illumination light source. A fluctuation compensation circuit for an image signal according to 1. 2. The fluctuation compensation circuit for an image signal according to claim 1, wherein the control range of the gain is in a range of 0.8 to 1.2. 2. The fluctuation compensation circuit for an image signal according to claim 1, wherein the first period corresponds to a fluctuation period of an image signal due to a change in photographing conditions. 2. The image signal fluctuation compensation circuit according to claim 1, wherein the illumination light source is a discharge tube type lamp. An image signal processing circuit for an electronic endoscope comprising the fluctuation compensation circuit according to claim 1.

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