JPH08186810A - Electronic endoscope - Google Patents

Abstract

PURPOSE: To make a reference black level of a digital video signal obtained through A/D conversion constant by providing a feedback circuit section which compares a black level of a digital video signal with a prescribed digital value and gives the black level in response to the result of comparison to a blanking circuit to the endoscope. CONSTITUTION: A digital video signal from an A/D converter 117 is given to a comparator 122 of a feedback circuit section 120, in which the signal is compared with a prescribed digital value. When the black level of the digital video signal is higher than the k prescribed digital value, the output VCTRL of an integration device 121 is gradually decreased, when the black level of the digital video signal is smaller than the prescribed digital value, the output VCTRL of the integration device 121 is gradually increased, and when the black level of the digital video signal is equal to the prescribed digital value, the output VCTRL of the integration device 121 reaches a prescribed level. The output VCTRL of the integration device 121 controlled in this way is given to a preblanking circuit 214, and the black level of the video signal processed by the circuit 214 is equal to a level corresponding to the output voltage VCTRL of the integration device 121. That is, the output VCTRL of the integration device 121 is fed back so that the black level of the video signal is equal to a prescribed digital value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention digitizes and processes a video signal from an image pickup device attached to the tip of a scope, and displays an image obtained by the image pickup device on a monitor for diagnosis inside a body cavity. The present invention relates to an electronic endoscope to serve.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a configuration of an electronic endoscope according to a conventional example. A solid-state image sensor (CCD) 103 is provided at the tip of the scope 102, and a light guide 102b is provided at the tip of the scope 102 to guide the light from the light source 112 to illuminate the inside of the body cavity and the CCD 103 to image the image inside the body cavity. The output can be output to the processor 110.

The CSD circuit 113 is a circuit that performs correlated double sampling of the video signal from the CCD 103 and performs processing for noise reduction of the video signal. This circuit is CC
It is usually used for the output of D.

Pre-blanking circuit 11 according to a conventional example
Reference numeral 4 is a circuit for blanking the video signal subjected to noise reduction processing by the CSD circuit 113. That is, it is a circuit for setting the level of the video signal to a constant black level by applying the optical black of the video signal, and FIG. 6 shows an example of its configuration.

The inputs of the pre-blanking circuit 114 of FIG. 6 are an emitter follower composed of a transistor TR2 and a resistor R2, and a transistor TR1 which is a switch for turning on / off the connection with the constant voltage source circuit E _CP by a clamp pulse CP1. The clamp circuit by is connected. The output of this clamp circuit is connected to the transistor via resistor R4.
TR5 is connected to a buffer formed by an emitter follower formed of a transistor TR4 and a resistor R5. The transistor TR5 functions as a switch for turning on / off between the base of the transistor TR4 and the constant voltage source circuit E _PB by the pre-blank pulse P _BLK .

FIG. 7 shows the pre-blanking circuit 11 of FIG.
4 is a timing chart of FIG. For the video signal from the pre-blanking circuit 114 as shown in FIG. 7A, the clamp pulse CP1 becomes active (“H” level) in the optical black of the video signal as shown in FIG. TR1 turns on. The output of the clamp circuit is clamped by the voltage of the constant voltage source circuit E _CP . Then, the pre-blank pulse P _BLK has a waveform that becomes active (“H” level) in the horizontal blanking period during the period other than the image period of the image signal, as shown in FIG. 7C. While this pulse is active, transistor TR5
Is turned on, and the level of the video signal becomes the voltage of the constant voltage source circuit E _PB as shown in FIG. Thus, the output from the buffer by the transistor TR4 becomes a constant black level given by the voltage of the constant voltage source circuit E _PB while the pre-blank pulse P _BLK is active during the period other than the video.

The gain control amplifier 115 shown in FIG.
Is for amplifying the video signal output from the pre-blanking circuit 114 to a desired level, and its amplification factor can be controlled externally and adjusted so that the level becomes constant.

The knee circuit 116 is a circuit for compressing high brightness, and the input / output characteristics of this circuit 116 are as follows.
It looks like a fold. As a result, the video signal from the gain control amplifier 115 is clipped when it reaches a large level, and the saturation of the white level of the video signal is suppressed.

The A / D converter 117 is a circuit for digitizing the video signal from the knee circuit 116 and converting it into a digital video signal, and the signal processing circuit 118 performs signal processing on the digital video signal to perform NTSC conversion. It is a circuit for outputting to the monitor 119 as a video signal.

The CCD drive pulse generation circuit 111 has a CC
A drive pulse of D is given to the CCD 103 to drive the CCD 103, and at the same time, pulses necessary for the processor 110 such as a clamp pulse CP1 and a pre-blank pulse P _BLK are generated. As a result, the operation of the entire processor 110 is synchronized.

Next, the operation of the entire apparatus will be described. By the drive pulse of the CCD drive pulse generation circuit 111, the signal charge of the CCD 103 is converted into a video signal by the CCD 1.
03, the video signal is subjected to noise reduction processing by the CSD circuit 113, and the pre-blanking circuit 11
Given to 4. Then, the pre-blanking circuit 114
The video signal input to is processed so as to have a constant black level while the pre-blank pulse P _BLK is active in the period other than the video. The pre-blanked video signal is adjusted in level by the control amplifier 115 and then passed through the knee circuit 116 to A /
It is converted into a digital video signal by the D converter. The signal processing circuit 118 converts it into an NTSC video signal, and the CCD 1
The image captured in 03 is displayed on the monitor 119.

CDS which is a video signal from the CCD 103
In the output of the circuit 113, there is a period in which the signal level is the reference black level during the blanking period, and when the reference black level fluctuates due to noise on the period of the reference black level, color reproduction is performed. Can not be done accurately. In particular, like an electronic endoscope, the CCD 103 to CS
When the distance to the D circuit 113 is large and the wiring between them tends to be long, noise easily occurs on the wiring between them,
This noise causes the reference black level of the video signal from the CCD 103 to randomly change.

On the other hand, in this apparatus, the pre-blanking circuit 114 keeps the blanking period including the period of the reference black level at a constant black level so that the noise is crushed to a certain fixed DC value. I have to. This is intended to reproduce an accurate image.

[0014]

As described above, the black level of the video signal serves as a reference for luminance,
If this black level changes depending on the size of noise,
The brightness and color of the image displayed on the monitor 119 are different from those actually obtained by the CCD 103. The cause of the change in the black level is not only the magnitude of noise, but also the variation of the device such as the temperature change and the size of the AGC of the gain control amplifier 115, which are different for each device, and the angle is applied. The difference will vary depending on the operation, and the change will be significant.

However, in the apparatus of FIG. 5 described above, pre-blanking is performed only in the next stage of the CSD circuit 113, and it does not take into consideration variations in the apparatus as described above. The reference black level is not always constant in the subsequent stage of the circuit 114. for that reason,
The reference black level of the digital video signal obtained by A / D conversion changes, and the above-described inconvenience is observed. Therefore, it is an object of the present invention to provide an electronic endoscope in which the reference black level of a digital video signal obtained by A / D conversion becomes constant.

[0016]

An electronic endoscope according to the present invention digitizes and processes a video signal from an image pickup device attached to the tip of a scope, and displays an image obtained by the image pickup device on a monitor. In the electronic endoscope that
A pre-blanking circuit that sets a black level to a video signal output from the image sensor during a blanking period; And a feedback circuit section for comparing the black level of the digital video signal with a predetermined digital value and giving a black level according to the comparison result to the pre-blanking circuit.

[0017]

According to the electronic endoscope of the present invention configured as described above, the feedback circuit section compares the black level of the digital video signal with a predetermined digital value,
The black level corresponding to the comparison result becomes the black level of the video signal by the pre-blanking circuit, which is digitized by the A / D converter and compared by the feedback circuit section, forming a feedback loop. Therefore, the black level of the digital video signal is automatically controlled to be a constant value that is equal to the predetermined digital value, and the black level of the digital video signal is stabilized, so that an image with accurate color reproduction can be monitored. Can be displayed on the screen and variation can be suppressed.

[0018]

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of an electronic endoscope according to a first embodiment of the present invention. This electronic endoscope has a scope 102 having a CCD 103 at its tip and a light guide 102b for guiding light to its tip, as in the above-mentioned conventional example.
In addition to illuminating the inside of the body cavity, the CCD 103 outputs an image inside the body cavity as a video signal to the processor 110 so that the inside of the body cavity can be observed by the monitor 119.

Further, in the configuration of the processor 110 for controlling the drive of the light source 112 and the CCD 103 and processing the video signal, the CCD drive pulse generation circuit 111 and the CDS circuit 1 are included.
13, gain control amplifier 115, knee circuit 11
6, the A / D converter 117 and the signal processing circuit 118 are also the same as those in the conventional example described above, and the processor 110 as a whole operates in synchronization by the pulse from the CCD drive pulse generating circuit 111. However, this electronic endoscope
The internal configuration of the pre-blanking circuit 214 is different from that of the feedback circuit section 120,
This is a feature.

The feedback circuit section 120 is a circuit which compares the black level of the digital video signal with a predetermined digital value and gives a voltage V _CTRL of the black level corresponding to the comparison result to the pre-blanking circuit 214. In this example,
This circuit is composed of a comparator 122 and an integrator 121.

FIG. 2 shows the circuit configuration of the feedback circuit section 120. In this embodiment, the comparator 1 is used.
22 is a digital comparator 122a and an inverter 1
It is composed of 22b. Digital comparator 122a
Means that when the digital video signal output from the A / D converter 117 is applied to the input A, the digital value set to the reference level value by a dip switch or a register is applied to the input B, and the input A is larger than the input B. Becomes "H". The comparison result is inverted by the inverter 122b.

The inverter 122b is controlled by the pre-blank pulse P _BLK from the CCD driving pulse generating circuit 111, the pulse within a period of only ie black level when active, the output is "ENABL
E ". When the pre-blank pulse P _BLK is active, the output of the inverter 122b becomes “L” when the input A is large and “H” when the input B is large,
If the pre-blank pulse P _BLK is not active,
High impedance state. Since the value of the digital video signal indicates the value of the black level when the pre-blank pulse P _BLK is active, the comparator 122 compares the black level value of the digital video signal with a predetermined digital value for each pixel, The comparison result is output in binary.

The integrator 121 is a circuit for integrating the binary output from the comparator 122, and in this embodiment, the integrator 12 is used.
1 is composed of an integrating circuit including a resistor 121a and a capacitor 121b and a buffer amplifier 121c. If the black level of the digital video signal is large output V _CTRL of the integrator 121 is small, if the black level of the digital video signal is small the output V _CTRL of the integrator 121 is increased.

Thus, the feedback circuit section 120
Compares the black level value of the digital video signal with a predetermined digital value, integrates the comparison result, and supplies a black level output V _CTRL corresponding thereto to the pre-blanking circuit 214.

FIG. 3 shows a circuit configuration of the pre-blanking circuit 214. The input of the pre-blanking circuit 214 is a buffer composed of a transistor TR2, a resistor R2, a transistor TR3 and a resistor R3, and a transistor TR1 which is a switch for turning on / off the connection with the constant voltage source circuit E _CP by a clamp pulse CP1. The clamp circuit by is connected. The output of this clamp circuit is connected to transistor TR5 and transistor TR5 via resistor R4.
It is connected to a buffer formed by an emitter follower composed of TR4 and a resistor R5. Transistor TR5 acts as a switch that turns on and off between the output V _CTRL base integrator 121 of the transistor TR4 by the pre-blank pulse P _BLK.

The clamp pulse CP1 and the pre-blank pulse _PBLK are shown in FIGS.
The waveform is as shown in (1) and is given from the CCD drive pulse generation circuit 111. This pre-blanking circuit 21
4 operates at the timing shown in FIG. 7, and the clamp pulse
The transistor TR1 is turned on by the CP1 at the blanking start portion of the video signal, and the output of the clamp circuit is clamped by the voltage of the constant voltage source circuit E _CP . Then, by the pre-blank pulse P _BLK , the transistor
TR5 is turned on, and the level of the video signal in the blanking period becomes equal to the output voltage _VCTRL of the integrator 121. Thus, the output from the buffer by transistor TR4 is
During the blanking period, while the pre-blank pulse P _BLK is active, the black level becomes a constant black level given by the voltage of the constant voltage source circuit E _PB .

The signal processing circuit 118 is a circuit similar to the conventional example, but FIG. 1 shows its configuration. The signal processing circuit 118 is a brightness signal processing unit 1 for obtaining a brightness signal from the digital video signal from the A / D converter 117.
18a, a color signal processing unit 118b for obtaining a color difference signal from a digital video signal, and a luminance signal and a color difference signal obtained by the luminance signal processing unit 118a and the color signal processing unit 118b are converted into NTSC image signals It is composed of a YL / color difference processing unit 118c for outputting a signal to the monitor 119. Ye, Cy, G, and Mg from the CCD 103
Since the signal from the complementary color filter is output, the digital video signal is a data string in which complementary color image data are arranged in a predetermined order. Signal processing circuit 1
In 18, a process of obtaining a luminance signal and a color difference signal from this digital video signal and a process of converting these signals into an NTSC video signal are performed digitally, and the monitor 119
Is output as an analog video signal.

Next, the operation of the entire apparatus will be described. By the drive pulse of the CCD drive pulse generation circuit 111, the signal charge of the CCD 103 is converted into a video signal by the CCD 1.
03, the video signal is subjected to noise reduction processing by the CDS circuit 113 and subjected to the pre-blanking circuit 21.
Given to 4. Then, the pre-blanking circuit 214
The video signal input to is input to the integrator 1 during the blanking period.
21 is processed so as to have a level according to the output voltage V _CTRL of the reference numeral 21, and noise in the period is crushed. Output voltage V by pre-blanking circuit 214
A video signal given a level according to _CTRL is adjusted in signal level by the control amplifier 115, and then converted into a digital video signal by the A / D converter through the knee circuit 116. An image picked up by the CCD 103 is displayed on the monitor 119 after being converted into an NTSC video signal by the signal processing circuit 118.

Here, the digital video signal from the A / D converter 117 is the comparator 1 of the feedback circuit section 120.
22 and this digital video signal is compared with a set predetermined digital value. Then, when the black level of the digital video signal is higher than a predetermined digital value, the output V _CTRL of the integrator 121 gradually decreases, and when the black level of the digital video signal is lower than the predetermined digital value, integration is performed. The output V _CTRL of the integrator 121 gradually increases, and when equal, the output of the integrator 121 becomes a constant level. The output V _CTRL of the integrator 121 controlled in this way is given to the pre-blanking circuit 214, and the black level of the video signal processed by this circuit is integrator 121.
Of the output voltage V _CTRL . After passing through the control amplifier 115 and the knee circuit 116, A /
The signal is D-converted and given to the feedback circuit section 120 of the digital video signal, the black level of the digital video signal is compared with a predetermined digital value, and the output _VCTRL of the integrator 121 is fed back so that they become equal. .

As a result, the pre-blanking circuit 21
The black level of the video signal processed in step 4 is controlled to be a constant black level according to a predetermined digital value, and the A / D
The value of the black level of the digital video signal from the converter 117 is controlled to be equal to the set predetermined digital value. In addition, the pre-blanking circuit 2 detects changes in temperature and the magnitude of the AGC of the gain control amplifier 115.
Even if there is a factor that changes the level between 14 and the A / D converter 117, the value of the black level is controlled to be equal to the set predetermined digital value and becomes a constant value.

As described above, by feeding back and controlling the pre-blanking level, which is the black level, from the digital video signal obtained by A / D conversion, the black level such as noise, temperature change, and variation due to the difference in scope can be controlled. Even if there is a factor that causes fluctuation, the fluctuation is automatically adjusted, and a digital video signal having a constant black level value is obtained. Since the digital video signal has such a stable black level value, it is possible to display an image in which colors are accurately reproduced on the monitor 119. Also, since the black level is automatically adjusted, even if there are variations in each, there is no color variation or dark coloring in each scope or processor, so there is no need to adjust each scope or processor. Like This reduces the time required for installation and image quality adjustment.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a block diagram showing the configuration of the electronic endoscope according to the second embodiment of the present invention. Each component of the scope 102 and processor 110 of this electronic endoscope, light source 112, CCD drive pulse generation circuit 111, C
DS circuit 113, gain control amplifier 115, knee circuit 116, A / D converter 117, signal processing circuit 11
8. As the feedback circuit unit 120 (comparator 122 / integrator 121), the same one as in the first embodiment is used,
These are given the same reference numerals as in the first embodiment.

In this embodiment, a feedback clamp circuit 217b and an adder 217a are provided so as to perform feedback clamp using the digital video signal from the A / D converter 117. The feedback clamp circuit 217b has the same configuration as the feedback circuit unit 120, compares the digital video signal from the A / D converter 117 with a predetermined digital value, and determines the black level value of the digital video signal as the predetermined digital value. It is a circuit that gives a lower voltage to the adder 217a when the value is larger than the predetermined value, and a higher voltage when the value of the black level is smaller than a predetermined digital value. The adder 217a adds the video signal from the knee circuit 116 and the output from the feedback clamp circuit 217b in an analog manner. With this feedback clamp, the value of the black level of the digital video signal from the A / D converter 117 is changed to the feedback clamp circuit 217b.
It is controlled to be equal to the predetermined digital value set in.

In this embodiment, the signal processing circuit 11
It is characterized in that the digital luminance signal obtained by the color signal processing unit 118b of No. 8 is given to the comparator 122.
The signal processing circuit 118 is a circuit similar to the conventional example, but FIG. 4 shows its configuration in more detail. The color signal processing unit 118b of the signal processing circuit 118 includes the color separation processing unit 11
81, YL / LPF unit 1182, matrix unit 118
3, white balance adjustment unit 1184, γ processing unit 118
It is composed of 6. Here, the color separation processing unit 1181
Is for separating the color difference signals 2R-G and 2B-G from the digital video signal from the A / D converter 117, and the YL / LPF unit 1182 is a digital video signal from the A / D converter 117. From the color difference signals 2R-G and 2B-G and the narrow band luminance signals to the red, green, and red color signals.
This is for obtaining the blue narrow band signals RL, GL and BL. The white balance adjusting unit 1184 outputs the difference signals RL and G
The white balance adjustment is performed from L and BL to convert into a color difference signal, and the γ processing unit 1186 performs gamma correction of the color difference signal and outputs the gamma correction signal. The digital video signal is output to the monitor 119 as a composite video signal from the YL / color difference processing unit 118c after undergoing these processes.

The bandwidth of the digital video signal from the A / D converter 117 is about 7 MHz when converted into analog, whereas the bandwidth of the luminance signal obtained by the color signal processing unit 118b is about 1.5 MHz, which is a narrow band. However, it is the same in that all the digital signals are digital video signals having substantially the same black level value. Therefore, as in the first embodiment described above, the black level value of the digital video signal is controlled to be equal to the predetermined digital value set by the comparator 122.

In the first embodiment, the configuration example in which the voltage V _CTRL for pre-blanking is controlled by using only the black level period of the digital video signal is shown, but in the second embodiment, the color signal processing is performed. The luminance signal obtained by the unit 118b is used to control the voltage V _CTRL for pre-blanking and also perform feedback clamp. Therefore, not only the luminance signal but also the black level of the color difference signal becomes very stable. As a result, an image whose color is reproduced accurately can be displayed on the monitor 119, and it is not necessary to adjust each scope or processor.

Moreover, since the probe of the electronic endoscope can be replaced, the compatibility with the probe may be poor due to variations. However, in the electronic endoscope of the present invention, the black level is also extremely low. In order to obtain a stable image, there is no such problem with any connectable probe, and no adjustment is required.

The present invention is not limited to the above-mentioned embodiment, but various modifications can be made. The black level of the digital video signal is a standard of the level of the video signal, and in the present invention, the black level is calculated from the pedestal of the digital video signal (the output of the A / D converter, the narrow band luminance signal, etc.) during the horizontal blanking period. Is detected and the black level is stabilized by performing feedback control of this. Therefore, the black level detection can be modified to be equivalent to this. For example, in the second embodiment, the example in which the digital video signal from the YL / LPF unit 1182 is fed back is shown, but the output of the color signal processing unit 118b is given to the comparator 122 to detect the black level from the pedestal of the color difference signal. You may do it.

[0039]

As described above, according to the present invention, a feedback loop is formed. Therefore, the black level of the digital video signal is automatically controlled to be a constant value that is equal to the predetermined digital value, and the black level of the digital video signal is stabilized, so that an image with accurate color reproduction can be monitored. Can be displayed on the screen and variation can be suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an electronic endoscope according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a circuit configuration of a feedback circuit section.

FIG. 3 is a diagram showing a circuit configuration of a pre-blanking circuit.

FIG. 4 is a block diagram showing a configuration of an electronic endoscope according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of an electronic endoscope according to a conventional example.

FIG. 6 is a diagram showing a configuration example of a pre-blanking circuit according to a conventional example.

FIG. 7 is a timing diagram of a pre-blanking circuit.

[Explanation of symbols]

102 Scope 103 CCD 117 A /
D converter 118 signal processing circuit 118a luminance signal processing unit 118b color signal processing unit 118c YL / color difference processing unit 119 monitor 120 feedback circuit unit 121 integrator
122 comparator 214 pre-blanking circuit

Claims (4)

[Claims] 1. A video signal from an image pickup device attached to the tip of a scope is digitized and processed, and
In an electronic endoscope for displaying an image obtained by the image pickup device on a monitor, a pre-blanking circuit for setting a level of an optical black period of the video signal for a video signal output from the image pickup device to a given black level, An A / D converter that digitizes the video signal to which the black level is applied and converts the video signal into a digital video signal, compares the black level of the digital video signal with a predetermined digital value, and outputs the black corresponding to the comparison result. A feedback circuit section for giving a level to the pre-blanking circuit, and an electronic endoscope comprising: 2. The feedback circuit unit compares the digital video signal with a predetermined digital value and outputs a binary result of the comparison, and a voltage obtained by integrating the output of the comparator. The electronic endoscope according to claim 1, further comprising: an integrator that supplies the black level to the pre-blanking circuit. 3. The feedback circuit comprises the A / D
2. The electronic device according to claim 1, wherein the output of the converter is used as the digital video signal, the black level thereof is compared with the predetermined digital value, and the black level corresponding to the comparison result is given to the pre-blanking circuit. Endoscope. 4. A luminance signal processing unit for obtaining a luminance signal from the output of the A / D converter, a color signal processing unit for obtaining a color difference signal from the output of the A / D converter, and the luminance signal. And a signal processing circuit having YL / color difference processing unit for converting the color difference signal into a video signal and outputting the video signal to a monitor, wherein the feedback circuit has a narrow band luminance obtained by the color signal processing unit. 2. The electronic endoscope according to claim 1, wherein the signal is used as the digital video signal, the black level thereof is compared with the predetermined digital value, and the black level corresponding to the comparison result is given to the pre-blanking circuit. .