JP2011235021A - Electronic endoscope system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove reflected signal components from output signals of an imaging element.SOLUTION: The electronic endoscope system includes: an electronic endoscope which has the imaging element; a transmission cable which transmits output signals from the imaging element; a resistor which is connected with a base end of the transmission cable; and a signal processing circuit which processes the output signals transmitted by the transmission cable and generates observation images. The signal processing circuit is connected with the transmission cable and the resistor. When white balance is adjusted, from output signals from a first pixel within an effective pixel region and output signals from a second pixel within an optical black pixel region which are output subsequently to the output signals from the first pixel, the signal processing circuit calculates the signal quantity of reflected signals by the output signals from the first pixel included in the output signals from the second pixel. When observation images are shot, it removes reflected signals included in the output signals from the pixels of the imaging element on the basis of the signal quantity of the reflected signals.

Description

  The present invention relates to an electronic endoscope system for removing a reflected signal component generated when an output signal from an image sensor is propagated to a video processor via a transmission cable.

  2. Description of the Related Art Conventionally, electronic endoscope systems capable of observing and imaging a target site by inserting a long and narrow insertion portion into a patient's body cavity have been widely used. An image pickup device (CCD image sensor, CMOS image sensor, etc.) is provided at the distal end of the insertion portion of the electronic endoscope, and a pixel signal photoelectrically converted by the image pickup device is output as a signal transmission means such as a coaxial cable. The data is transmitted to a video processor connected to the electronic endoscope using a transmission cable.

  An example of such an electronic endoscope system is disclosed in Patent Document 1. Here, a conventional electronic endoscope system will be described with reference to FIG. FIG. 6 is a diagram illustrating a transmission system of an output signal from the image sensor 103 of the electronic endoscope 101 in the conventional electronic endoscope system 100. An output signal from the image sensor 103 is sent to the transistor 105 of the emitter follower. The transistor 105 forms a buffer amplifier together with the emitter resistor 107, and the base of the transistor 105 is connected to the signal output terminal of the image sensor 103 and the collector is connected to the power supply voltage 104. The transistor 105 sends the output signal to the transmission cable 108 via the output resistor 106. The transmission cable 108 extends from the distal end of the insertion portion of the electronic endoscope 101 to the video processor 102. The output signal transmitted by the transmission cable 108 is sent to the capacitor 109. The capacitor 109 constitutes an analog signal processing circuit together with the termination resistor 110, and an output signal is sent from the analog signal processing circuit to a preceding signal processing circuit (not shown) in the video processor 102, and various images are output to the output signal. Processing is performed.

Here, assuming that the resistance values of the output resistor 106 and the terminating resistor 110 and the characteristic impedance of the transmission cable 108 are R ₁ , R ₂ , and Z ₀ , respectively, if the condition R ₁ = Z ₀ = R ₂ is satisfied, the impedance Matching is achieved, and signal reflection of the output signal does not occur on the analog signal processing circuit side. However, when this condition is not satisfied, a reflected signal component due to reflection generated in the transmission cable is mixed in the signal output from the image sensor 103 due to variations in the characteristic impedance of the transmission cable 108 or the like. . The imaging device has an effective pixel region that receives light from the observation target and an optical black (OB) pixel region for dark current correction. Paying attention to the signal output at the transition point from the pixel of the effective pixel area of the image sensor to the pixel of the optical black pixel area, if the image is captured using illumination light of a certain intensity, if the impedance is matched, As shown in FIG. 4A, the observation image data output is obtained as the pixel output of the effective pixel region, and the black level data output is obtained as the pixel output of the optical black pixel region.

JP 2001-45071 A

  However, in the conventional electronic endoscope system as described above, since resistance is provided at both ends of the transmission cable in order to achieve impedance matching, the signal strength of the output signal may be reduced. Further, since the electronic endoscope is used by being inserted into the body cavity of the patient, it is desired that the electronic endoscope be further reduced in diameter in order to reduce the burden on the patient. In order to reduce the diameter of the electronic endoscope, the output resistor may not be arranged due to space saving at the distal end of the insertion portion. Furthermore, a transmission cable in an electronic endoscope is a long cable that transmits an output signal of an image sensor provided at a distal end portion of the electronic endoscope to a base portion that is a connection portion with a video processor. Therefore, the characteristic impedance may vary within the transmission cable. This variation in characteristic impedance affects the reflection loss of the output signal. In addition, with a certain resistance value of the output resistance or the termination resistance, it is impossible to eliminate the influence of the reflected signal generated by the variation in characteristic impedance.

  The present invention has been made in view of the above circumstances. An object of the present invention is to simplify the circuit configuration of an electronic endoscope and to remove a reflected signal component from the output signal without reducing the signal intensity of the output signal from the image sensor. Is to provide a system.

  An electronic endoscope system according to an embodiment of the present invention includes an electronic endoscope having an imaging device having an effective pixel region and an optical black pixel region, a transmission cable for transmitting an output signal from the imaging device, and a transmission cable. And a signal processing circuit that generates an observation image by processing the output signal transmitted by the signal processing circuit, wherein the signal processing circuit starts from the first pixel in the effective pixel region during white balance adjustment. The output signal from the second pixel is included in the output signal from the second pixel from the output signal from the second pixel in the optical black pixel region that is output following the output signal from the first pixel. The signal amount of the reflected signal generated in the transmission cable by the output signal from the pixel is calculated from each pixel of the image sensor based on the signal amount of the reflected signal when the observation image is captured. Removing a reflected signal included in the output signal.

  Preferably, at the time of white balance adjustment, the signal processing circuit includes a signal amount of a reflection signal based on an output signal from the first pixel and an output signal from the first pixel included in the output signal from the second pixel. From the reflection coefficient calculation circuit for calculating a predetermined coefficient, a memory for storing the predetermined coefficient, and a predetermined coefficient stored in the memory for the signal amount of the previous pixel signal with respect to the output signal from each pixel. A reflection signal removal circuit that performs a process of removing the signal amount calculated by applying the signal amount as the signal amount of the reflection signal from the target pixel signal.

  More preferably, the reflected signal removal circuit applies a predetermined coefficient stored in the memory to the output signal from each pixel and a delay circuit that delays the output signal from each pixel, and reduces the signal amount of the reflected signal. A reflection signal amount calculation circuit to be calculated, and a subtraction unit that subtracts the signal amount of the output signal from the reflection signal amount calculation circuit from the signal amount of the output signal from the delay circuit.

Further, the reflection coefficient calculation circuit obtains a predetermined coefficient by the following equation (1),
α = A / B (1)
Here, α is a predetermined coefficient, A is the signal amount of the output signal from the first pixel, and B is the signal amount of the reflected signal by the output signal from the first pixel included in the output signal from the second pixel. Is,
The reflection signal removal circuit obtains the signal amount of the reflection signal to be removed from the target pixel signal by the following equation (2).
C _ref = α × C (2)
Here, C _ref is the signal amount of the reflected signal to be removed from the target pixel signal, and C is the signal amount of the previous pixel signal.

Furthermore, the time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the target pixel signal is given by the following equation (3):
ΔT = 2 × T × L (3)
Here, ΔT is the elapsed time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the pixel signal of interest, T is the signal transmission delay time in the transmission cable, and L is the cable of the transmission cable Is long,
The reflected signal removal circuit removes the reflected signal from the target pixel signal at the position specified by ΔT in Expression (3).

The signal transmission delay time T in the transmission cable is given by the following equation (4).
T = (μ ₀ × μ _r × ε ₀ × ε _r ) ^1/2 (4)
Here, μ ₀ is the magnetic permeability of the vacuum, μ _r is the magnetic permeability of the conductor of the transmission cable, ε ₀ is the dielectric constant of the vacuum, and ε _r is the dielectric constant of the dielectric of the transmission cable.

  Alternatively, a configuration may be adopted in which white pixels are provided in the optical black pixel region and an output signal from the white pixel is used instead of the output signal from the first pixel in the signal processing circuit. In this case, the coefficient α can be set and updated periodically when the observation image is captured without performing the work of adjusting the white balance and determining the predetermined coefficient α.

  According to the electronic endoscope system of the present invention, it is possible to remove the reflected signal component included in the signal when the output signal from the image sensor is transmitted by the transmission cable. Furthermore, for example, even when the characteristic impedance of the transmission cable changes with deterioration of the transmission cable due to long-term use of the electronic endoscope, the reflection component can be removed by periodically updating the coefficient. In addition, since it is not necessary to provide a resistor between the imaging element and the transmission cable at the distal end portion of the electronic endoscope, the circuit configuration can be simplified as compared with the conventional electronic endoscope.

FIG. 1 is a schematic diagram showing an outline of an electronic endoscope system according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a part of the electronic endoscope system according to the embodiment of the present invention. FIGS. 3A and 3B are schematic views showing the configuration of the image sensor of the electronic endoscope system in the embodiment of the present invention. 4A to 4D are graphs showing signal waveforms when an output signal from the image sensor is transmitted through a transmission cable. FIG. 5 is a flowchart showing the reflected signal removal processing in the second embodiment of the present invention. FIG. 6 is a schematic diagram showing a part of the configuration of a conventional electronic endoscope system.

  Hereinafter, an electronic endoscope system according to an embodiment of the present invention will be described with reference to the drawings. In the electronic endoscope, the distal end side of the insertion portion is defined as the distal end side, and the base side connected to the video processor is defined as the proximal end side. Further, when the same member is shown across a plurality of drawings, the same number is attached.

  FIG. 1 schematically shows an electronic endoscope system according to the first embodiment of the present invention. The electronic endoscope system 200 includes an electronic endoscope 1, a video processor 2, and a monitor 3. The light source unit 22 includes a light source such as a halogen lamp, a xenon lamp, or a white LED. In the video processor 2, a condensing optical system 20 that condenses light from the light source at an incident end of a light guide 24 that is a propagation path of illumination light, a light amount stop 21 for adjusting the amount of illumination light, and a light amount stop A motor 19 that controls the motor 21 and a motor driver 18 that drives and controls the motor 19 are provided. In the present embodiment, the simultaneous method is adopted as the imaging method. Therefore, the white light from the light source unit 22 is propagated through the light guide 24 as it is to irradiate the site to be observed, the complementary color signal is separated by the on-chip complementary color filter on the image sensor 6, and the complementary color signal is converted into R, R, It converts into the primary color signal of G and B, and a luminance signal and a color difference signal are obtained from this primary color signal. Of course, a simultaneous system in which primary color signals are output using color filters of the three primary colors R, G, and B instead of the complementary color filters may be used. Note that the imaging method may employ a frame sequential method instead of the simultaneous method. That is, a rotating color filter for sequentially separating the white light from the light source into red (R), green (G), and blue (B) light is provided between the light source unit 22 and the light guide 24, and the image The color filter is rotated in synchronization with a timing pulse or a vertical synchronization signal when writing a signal to the frame memory. Further, an external light source device may be used instead of the light source unit 22.

  The light emitted from the light source unit 22 travels to the end surface of the light guide 24 via the condensing optical system 20 and the light amount diaphragm 21. When the electronic endoscope 1 is connected to the video processor 2, the light guide 8 of the electronic endoscope 1 and the light guide 24 of the video processor 2 are optically connected. Therefore, the light emitted from the light source unit 22 is propagated to the tip of the electronic endoscope 1 by the light guides 8 and 24. The light emitted from the tip of the light guide 8 travels to the target site as illumination light through the light distribution optical system 4. The illumination light is reflected by the target part and enters the objective optical system 5 and then reaches the imaging surface of the imaging device 6. Therefore, the image of the target part is connected to the imaging surface of the imaging device 6 by the objective optical system 5. The illumination light received by the image sensor 6 is photoelectrically converted, amplified by an amplifier 7, and then transmitted as a pixel signal via a transmission cable 9 via a base 1a which is a connection portion with the video processor 2 of the video processor 2. It is transmitted to the analog signal processing circuit 10. As will be described later, in this embodiment, an output resistor is not provided between the imaging element 6 and the transmission cable 9 in order to remove the reflected signal component generated in the transmission cable 9 in the pre-stage signal processing circuit 11. For this reason, the circuit configuration of the distal end portion of the electronic endoscope 1 can be simplified.

  The analog signal processing circuit 10 performs various processes such as sample and hold processing and noise removal on the input signal, converts it into an image signal composed of the luminance signal Y and the color difference signals Cb and Cr, and converts it into a digital signal. Thereafter, the signal is sent to the preceding signal processing circuit 11. In the pre-stage signal processing circuit 11, the luminance signal Y and the color difference signals Cb and Cr are converted into primary color signals R, G and B by a matrix circuit (not shown). The converted R, G, and B signals are respectively sent to a VCA (Voltage Controlled Amplifier) circuit (not shown) to control the amplification degree. Further, the pre-stage signal processing circuit 11 performs a process of removing the reflected signal component included in the received image signal. Details of the processing in the pre-stage signal processing circuit 11 will be described later. The R, G, and B signals are stored in the image memory 12. A signal for one frame is read from the image memory 12, a horizontal synchronizing signal and a vertical synchronizing signal output from the timing controller 15 are added, and the signal is sent to the subsequent signal processing circuit 13. The timing controller 15 controls the scanning timing of the image sensor 6 by the drive circuit 14. The timing controller 15 controls the operation timings of the analog signal processing circuit 10, the pre-stage signal processing circuit 11, the image memory 12, and the post-stage signal processing circuit 13 in synchronization with the frame rate of the image sensor 6.

  In the subsequent signal processing circuit 13, the signal sent from the image memory 12 is converted into a digital video signal, an RGB video signal, a composite video signal, an S video signal, etc., and then output to the monitor 3 as an observation image. The surgeon observes and treats the target part while confirming the observation image displayed on the monitor 3. The luminance signal processed in the analog signal processing circuit 10 is also sent to the motor driver 18 via the system controller 17. The motor driver 18 drives and controls the motor 19 to adjust the aperture amount of the light amount aperture 21 so that the brightness of the observation image is optimized based on the received luminance signal.

  The video processor 2 is provided with a front panel 16 having operation buttons and setting switches for performing various adjustments related to the display of an observation image, dimming of a light source, and the like. The surgeon operates each operation button and each setting switch on the front panel 16 to change the setting value of the process in each circuit in the electronic endoscope 1 and the video processor 2, and the saturation, brightness, and enhancement of the observation image. Make adjustments. For example, a signal output from a dimming setting switch on the front panel 16 is sent to the system controller 17, and the system controller 17 performs dimming control of the light source power source 23 based on the received dimming signal. The system controller 17 relates to the identification information of the electronic endoscope 1 and the image sensor 6 that are necessary for performing various controls on the video processor 2 side when the electronic endoscope 1 is connected to the video processor 2. Information and the like are acquired from the memory 25 of the electronic endoscope 1.

  FIG. 3A schematically shows the configuration of the image sensor 6 used in this embodiment. The image sensor 6 has an effective pixel area 6a and an optical black pixel area 6b. The effective pixel region 6a receives light reflected from a target region to be observed and accumulates electric charges according to the amount of light received. The optical black pixel region 6b is a region where each pixel is shielded from light by, for example, an aluminum vapor deposition film, and outputs a signal corresponding to the black level.

4B to 4D show schematic waveforms of pixel signals received by the video processor 2 from the electronic endoscope 1 via the transmission cable 9 in this embodiment. The signal waveforms shown in FIGS. 4B and 4C are output following the output signal (effective pixel signal) from one pixel in the effective pixel region 6a of the image sensor 6 and the output signal from the pixel. The signal waveform of the output signal (optical black pixel signal) from the pixels in the optical black pixel region 6b is extracted. In the present embodiment, signal reflection occurs in the transmission cable 9 due to the absence of an output resistor between the image sensor 6 and the transmission cable 9. Therefore, as shown in FIGS. 4B and 4C, the reflected signal component of the effective pixel signal appears in the optical black pixel signal that is subsequently output. When the following formula (5) is satisfied, the reflected signal is superimposed on the optical black pixel signal without inverting its phase, and the waveform shown in FIG. 4B appears.
R> Z (5)
Here, R is the resistance value of the terminating resistor, and Z is the value of the characteristic impedance of the transmission cable 9. When the following expression (6) is satisfied, the reflected signal is superimposed on the optical black pixel signal with its phase inverted, so that the waveform shown in FIG. 4C appears.
R <Z (6)

If the time from when the effective pixel signal appears in the transmission cable 9 until the reflected waveform of the effective pixel signal appears in the optical black pixel signal is ΔT, ΔT can be obtained by the following equation (7).
ΔT = 2 × T × L (7)
Here, T is the signal transmission delay time in the transmission cable 9, and L is the cable length of the transmission cable 9. Further, the delay time T can be obtained by the following equation (8).
T = (μ ₀ × μ _r × ε ₀ × ε _r ) ^1/2 (8)
Here, μ ₀ is the magnetic permeability of vacuum, μ _r is the magnetic permeability of the conductor of the transmission cable 9, ε ₀ is the dielectric constant of vacuum, and ε _r is the dielectric constant of the dielectric of the transmission cable 9. By obtaining ΔT, the position where the reflection signal of the effective pixel signal appears in the optical black pixel signal can be specified in advance. In the present embodiment, the reflection signal of the pixel signal that is output first also appears at a position specified by ΔT in the pixel signal that is subsequently output for the adjacent pixels in the effective pixel region 6a. Can be considered.

FIG. 2 is a block diagram of each component that performs processing for executing the removal of the reflected signal generated in the transmission cable 9 in the present embodiment. The image sensor 6 scans pixels at an operation timing controlled by the drive circuit 14 and outputs a pixel signal. The analog signal processing circuit 10 sends an image signal obtained by performing various processes on the input pixel signal as described above to the previous signal processing circuit 11. The pre-stage signal processing circuit 11 includes a reflection coefficient calculation circuit 30, a delay circuit 31, a subtraction unit 32, a reflection signal amount calculation circuit 33, and a reflection coefficient memory 34. In this embodiment, the signal amount of the reflected signal is measured from the effective pixel signal and the optical black pixel signal during white balance adjustment, and the reflection coefficient α is calculated from the measured signal amount of the reflected signal. If the signal amount of the effective pixel signal is A and the signal amount of the reflected signal appearing in the optical black pixel signal is B, the reflection coefficient α can be obtained by the following equation (9).
α = A / B (9)
The signal amount B of the reflected signal takes a positive value when the reflected signal is superimposed on the optical black pixel signal without inverting its phase, and the reflected signal is superimposed on the optical black pixel signal with its phase inverted. If you want to take a negative value.

  The image signal from the analog signal processing circuit 10 is sent to the reflection coefficient calculation circuit 30, the delay circuit 31, and the reflection signal amount calculation circuit 33. In this embodiment, ΔT is calculated from the equation (9) by the system controller 17. In addition, the timing controller 15 sends a signal for operating the reflection coefficient calculation circuit 30 in accordance with the timing of scanning the effective pixel and the optical black pixel adjacent to the effective pixel. Therefore, based on the timing instructed from the timing controller 15, the reflection coefficient calculation circuit 30 calculates the reflection coefficient by taking in only the pixel signals from the two pixels of the effective pixel and the optical black pixel adjacent to the effective pixel. The reflection coefficient calculation circuit 30 obtains the reflection coefficient α from the signal amount of the effective pixel signal and the signal amount of the reflection signal that appears at a position determined by ΔT in the optical black pixel signal, using the equation (9), and the obtained reflection coefficient α is calculated. Stored in the reflection coefficient memory 34.

Next, the white balance adjustment is finished and imaging of the target part is started. FIG. 4D shows a waveform when a pixel signal output from any two adjacent pixels of the image sensor 6 is transmitted by the transmission cable 9. Here, a signal output and transmitted first among the two pixels is a previous pixel signal, and a signal output and transmitted subsequent to the previous pixel signal is a target pixel signal. In FIG. 4D, it is assumed that the reflected signal of the previous pixel signal is superimposed on the target pixel signal without its phase being inverted. However, even when the phase is reversed and superimposed, the reflected signal can be removed by performing the same processing as described below. The reflection signal amount calculation circuit 33 uses the signal amount C of the input previous pixel signal and the reflection coefficient α stored in the reflection coefficient memory 34 to generate a signal amount α × C (= C _ref ) is obtained and sent to the subtraction unit 32. The delay circuit 31 performs the above calculation processing by the reflection signal amount calculation circuit 33 and outputs the output result C _ref to the subtraction unit 32, and the target pixel signal from which the reflection signal component is to be removed is the subtraction unit 32. The timing input to is matched. Specifically, the delay circuit 31 receives from the analog signal processing circuit 10 so that the signal amount C _{ref of the} reflected signal is subtracted from the signal amount at the position in the target pixel signal specified by ΔT in the subtractor 32. Delay the delayed signal. The subtracting unit 32 subtracts the signal amount of the reflected signal calculated by the reflected signal amount calculating circuit 33 from the signal amount of the target pixel signal output from the delay circuit 31. That is, assuming that the signal amount before the reflected signal is removed at the position specified by ΔT in the target pixel signal is D and the signal amount after the removal is D ′, D ′ is expressed by the following equation (10). Desired.
D ′ = D−C _ref (10)

  The reflected signal removal process described above is repeatedly performed on the output signals from the respective pixels of the image sensor 6 to remove the reflected signals contained in the respective output signals. The pixel signal from which the reflected signal has been removed by the subtracting unit 32 is sent to another circuit in the preceding-stage signal processing circuit 11 to convert or amplify the luminance signal and the color difference signal to the three primary color signals as described above. After various processing is performed, it is output to the image memory 12. Therefore, since various image processing is performed on the pixel signal after removing the reflection of the signal generated in the transmission cable 9, an observation image that is not affected by the reflection of the signal can be generated.

  Next, a second embodiment of the present invention will be described. The configuration of the electronic endoscope system in the present embodiment is the same as that in FIGS. 1 and 2 in the first embodiment. The signal waveforms shown in FIGS. 4B and 4C in the first embodiment are the same in this embodiment, except that the signal amount A of the effective pixel signal is output from the white pixel. (White pixel signal). FIG. 3B schematically shows the configuration of the image sensor 6 used in this embodiment. The image sensor 6 has an effective pixel area 6c, an optical black pixel area 6d, and a white pixel 6e. In the present embodiment, unlike the first embodiment, instead of calculating the reflection coefficient α using the output signal at the time of white balance adjustment, a white pixel signal output from the white pixel 6e at the time of imaging the target part, The reflection coefficient α is calculated from the optical black pixel signal output from the pixel in the optical black pixel area 6d output subsequent to the pixel signal.

  The pixel coordinates of the position where the white pixel 6e is arranged are known. Therefore, for example, the system controller 17 acquires the coordinates of the white pixel 6e from the memory 25 in the electronic endoscope 1, and controls the timing controller 15 based on the coordinates. Based on the control of the system controller 17, the timing controller 15 sends a signal for operating the reflection coefficient arithmetic circuit 30 in accordance with the scanning timing of the white pixel 6e and the optical black pixel adjacent to the white pixel 6e. The reflection coefficient calculation circuit 30 takes in the white pixel signal and the optical black pixel signal at the timing instructed by the timing controller 15 and calculates the reflection coefficient α. Note that the signal amount of the white pixel signal is significantly different from the signal amount of the optical black pixel signal. Therefore, when the system controller 17 receives an output signal exceeding a predetermined signal amount when receiving a signal output from each pixel in the optical black pixel area 6d, the signal is output from the white pixel 6e. It is also possible to regard the coordinates of the pixel that has output the signal as the coordinates of the white pixel 6e. Thus, the coordinates of the white pixel 6e can be specified without acquiring the coordinates of the white pixel 6e from the memory 25.

  FIG. 5 shows a flowchart of the reflection signal removal processing in this embodiment. First, the electronic endoscope 1 is connected to the video processor 2 and the electronic endoscope 1 is turned on. When the power of the electronic endoscope 1 is turned on, output of pixel signals from the image sensor 6 starts (S101). As shown in FIG. 4B, the system controller 17 displays the reflected waveform of the white pixel signal in the optical black pixel signal after the white pixel signal appears in the transmission cable 9, as in the first embodiment. The time ΔT until it appears in is determined (S103). Next, the reflection coefficient calculation circuit 30 operates based on the control of the timing controller 15 as in the first embodiment. That is, a signal for operating the reflection coefficient arithmetic circuit 30 is sent in accordance with the timing of scanning the white pixel and the optical black pixel adjacent to the white pixel. Accordingly, the reflection coefficient calculation circuit 30 calculates only the two pixel signals of the target white pixel signal and optical black pixel signal based on the timing instructed from the timing controller 15 and calculates the reflection coefficient. Then, the reflection coefficient calculation circuit 30 calculates the reflection coefficient α using the signal amount of the white pixel signal and the signal amount of the reflection signal that appears at a position determined by ΔT in the optical black pixel signal, and stores it in the reflection coefficient memory 34 ( S105).

Also in the present embodiment, a signal output and transmitted first among arbitrary two pixels adjacent to the image sensor 6 is a previous pixel signal, and a signal output and transmitted subsequent to the previous pixel signal is a target pixel signal. And When the reflection coefficient α is determined, the reflection signal removal process included in the pixel signal is started (S107). Here, the reflection signal removal processing will be described in detail. The reflection signal amount calculation circuit 33 calculates the signal amount α × C (= C) of the reflection signal that appears in the target pixel signal from the signal amount C of the input previous pixel signal and the reflection coefficient α stored in the reflection coefficient memory 34. _ref ) is obtained and sent to the subtraction unit 32. The delay circuit 31 includes a timing at which the output result C _ref subjected to the above calculation processing by the reflection signal amount calculation circuit 33 is input to the subtraction unit 32 and a target pixel signal from which the reflection signal component is to be removed. The timing input to is matched. Specifically, the delay circuit 31 delays the signal from the analog signal processing circuit 10 so that the signal amount of the reflected signal is subtracted from the signal amount at the position in the target pixel signal specified by ΔT. The subtracting unit 32 subtracts the signal amount of the reflected signal calculated by the reflected signal amount calculating circuit 33 from the signal amount of the target pixel signal output from the delay circuit 31. The reflected signal removal process described above is repeatedly performed on the output signals from the respective pixels of the image sensor 6 to remove the reflected signals contained in the respective output signals.

  The pixel signal from which the reflected signal has been removed by the subtracting unit 32 is sent to other circuits in the pre-stage signal processing circuit 11 to perform various processes such as conversion and amplification from the luminance signal and the color difference signal to the three primary color signals. Is output to the image memory 12. Therefore, since various image processing is performed after removing the reflection of the signal generated in the transmission cable 9 with respect to the pixel signal, an observation image that is not affected by the reflection of the signal can be generated.

  In the present embodiment, the reflection coefficient α is calculated by the reflection coefficient calculation circuit 30 every time the white pixel 6e is scanned under the control of the system controller 17, so the reflection coefficient α stored in the reflection coefficient memory 34 is Updated regularly. Accordingly, in the present embodiment, the reflected signal amount calculation circuit 33 can calculate the signal amount of the reflected signal using the periodically updated reflection coefficient α, so that the reflected signal component is real-time and more reliable. Can be removed.

  The above is the description regarding the embodiment of the present invention. The present invention is not limited to the above-described configuration, and various modifications can be made within the scope of the technical idea of the present invention. For example, in the first embodiment, it is also possible to use a reflection coefficient obtained by performing white balance adjustment at the time of manufacture instead of at the time of operation and acquired as a set value at the time of factory shipment.

DESCRIPTION OF SYMBOLS 1 Electronic endoscope 2 Video processor 6 Image pick-up element 6a, 6c Effective pixel area 6b, 6d Optical black pixel area 6e White pixel 9 Transmission cable 11 Pre-stage signal processing circuit 22 Light source part 30 Reflection coefficient calculation circuit 31 Delay circuit 32 Subtraction part 33 Reflection signal amount calculation circuit 34 Reflection coefficient memory

Claims (12)

An electronic endoscope having an image pickup device having an effective pixel region and an optical black pixel region, a transmission cable for transmitting an output signal from the image pickup device, and an observation image obtained by processing the output signal transmitted by the transmission cable An electronic endoscope system having a signal processing circuit for generating
The signal processing circuit includes:
During white balance adjustment, an output signal from the first pixel in the effective pixel area and an output signal from the second pixel in the optical black pixel area that is output following the output signal from the first pixel And calculating the signal amount of the reflected signal generated in the transmission cable by the output signal from the first pixel, which is included in the output signal from the second pixel,
Removing the reflected signal included in the output signal from each pixel of the image sensor based on the signal amount of the reflected signal when capturing the observation image;
An electronic endoscope system characterized by that. The signal processing circuit includes:
At the time of white balance adjustment, a predetermined amount is obtained from an output signal from the first pixel and a signal amount of the reflected signal by the output signal from the first pixel, which is included in the output signal from the second pixel. A reflection coefficient calculation circuit for calculating a coefficient;
A memory for storing the predetermined coefficient;
For the output signal from each pixel, the signal amount calculated by applying the predetermined coefficient stored in the memory to the signal amount of the previous pixel signal is removed from the target pixel signal as the signal amount of the reflected signal. A reflected signal removal circuit that performs processing to perform,
The electronic endoscope system according to claim 1. The reflected signal removal circuit includes:
A delay circuit that delays an output signal from each pixel;
A reflected signal amount calculation circuit that calculates the signal amount of the reflected signal by applying the predetermined coefficient stored in the memory to an output signal from each pixel;
A subtractor that subtracts the signal amount of the output signal from the reflected signal amount calculation circuit from the signal amount of the output signal from the delay circuit,
The electronic endoscope system according to claim 2. The reflection coefficient calculation circuit obtains the predetermined coefficient by the following equation (1):
α = A / B (1)
Here, α is the predetermined coefficient, A is the signal amount of the output signal from the first pixel, and B is the reflection by the output signal from the first pixel included in the output signal from the second pixel. The signal amount of the signal,
The reflection signal removal circuit obtains the signal amount of the reflection signal to be removed from the pixel-of-interest signal by the following equation (2):
C _ref = α × C (2)
Here, C _ref is the signal amount of the reflected signal to be removed from the target pixel signal, and C is the signal amount of the previous pixel signal.
The electronic endoscope system according to claim 2 or claim 3, wherein The time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the target pixel signal is given by the following equation (3):
ΔT = 2 × T × L (3)
Here, ΔT is the time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the target pixel signal, T is the signal transmission delay time in the transmission cable, and L is The cable length of the transmission cable,
The reflected signal removing circuit removes the reflected signal from the pixel-of-interest signal at a position specified by ΔT in Expression (3);
The electronic endoscope system according to any one of claims 2 to 4, wherein the electronic endoscope system is characterized in that: The signal transmission delay time T in the transmission cable is given by the following equation (4).
T = (μ ₀ × μ _r × ε ₀ × ε _r ) ^1/2 (4)
Here, μ ₀ is the magnetic permeability of vacuum, μ _r is the magnetic permeability of the conductor of the transmission cable, ε ₀ is the dielectric constant of vacuum, and ε _r is the dielectric constant of the dielectric of the transmission cable.
The electronic endoscope system according to claim 5. An electronic endoscope having an image pickup device having an effective pixel region and an optical black pixel region, a transmission cable for transmitting an output signal from the image pickup device, and an observation image obtained by processing the output signal transmitted by the transmission cable An electronic endoscope system having a signal processing circuit for generating
A white pixel is provided in the optical black pixel region;
The signal processing circuit includes:
Included in the output signal from the third pixel from the output signal from the white pixel and the output signal from the third pixel in the optical black pixel area output following the output signal from the white pixel A signal amount of a reflected signal generated in the transmission cable by an output signal from the white pixel is calculated,
Based on the signal amount of the reflected signal, the reflected signal included in the output signal from each pixel of the image sensor is removed.
An electronic endoscope system characterized by that. The signal processing circuit includes:
A reflection coefficient calculation circuit that calculates a predetermined coefficient from the output signal from the white pixel and the signal amount of the reflection signal by the output signal from the white pixel, which is included in the output signal from the third pixel;
A memory for storing the predetermined coefficient;
For the output signal from each pixel, the signal amount calculated by applying the predetermined coefficient stored in the memory to the signal amount of the previous pixel signal is removed from the target pixel signal as the signal amount of the reflected signal. A reflected signal removal circuit that performs processing to perform,
The electronic endoscope system according to claim 7. The reflected signal removal circuit includes:
A delay circuit that delays an output signal from each pixel;
A reflected signal amount calculation circuit that calculates the signal amount of the reflected signal by applying the predetermined coefficient stored in the memory to an output signal from each pixel;
A subtractor that subtracts the signal amount of the output signal from the reflected signal amount calculation circuit from the signal amount of the output signal from the delay circuit,
The electronic endoscope system according to claim 8. The reflection coefficient calculation circuit obtains the predetermined coefficient by the following equation (5):
α = A / B (5)
Here, α is the predetermined coefficient, A is the signal amount of the output signal from the white pixel, and B is the signal amount of the reflected signal due to the output signal from the white pixel included in the output signal from the third pixel. Is,
The reflected signal removal circuit obtains the signal amount of the reflected signal to be removed from the pixel-of-interest signal by the following equation (6).
C _ref = α × C (6)
Here, C _ref is the signal amount of the reflected signal to be removed from the target pixel signal, and C is the signal amount of the previous pixel signal.
The electronic endoscope system according to claim 8 or 9, characterized by the above. The time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the target pixel signal is given by the following equation (7):
ΔT = 2 × T × L (7)
Here, ΔT is the time from when the previous pixel signal appears in the transmission cable until the reflected signal of the previous pixel signal appears in the target pixel signal, T is the signal transmission delay time in the transmission cable, and L is The cable length of the transmission cable,
The reflected signal removing circuit removes the reflected signal from the pixel-of-interest signal at a position specified by ΔT in Expression (7);
The electronic endoscope system according to any one of claims 8 to 10, wherein the electronic endoscope system is configured as described above. The signal transmission delay time T in the transmission cable is given by the following equation (8):
T = (μ ₀ × μ _r × ε ₀ × ε _r ) ^1/2 (8)
Here, μ ₀ is the magnetic permeability of vacuum, μ _r is the magnetic permeability of the conductor of the transmission cable, ε ₀ is the dielectric constant of vacuum, and ε _r is the dielectric constant of the dielectric of the transmission cable.
The electronic endoscope system according to claim 11.

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