JP3378790B2 - Electronic endoscope device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic endoscope apparatus, and more particularly, to a method for forming a moving image by a conventional pixel-mixed readout method.
The present invention relates to a configuration of an electronic endoscope apparatus that reads out all pixels stored in an image sensor and forms a still image. 2. Description of the Related Art In an electronic endoscope apparatus, for example, a CCD (Charge Coupled Device) is used as a solid-state image pickup device. In this CCD, charges stored in pixels are read out by a photoelectric conversion element. Thus, an image signal (video signal) is obtained. And
For example, in a simultaneous electronic endoscope device, a color filter is arranged in pixel units on the upper surface of the CCD, thereby obtaining a color image. FIG. 7 shows the arrangement of the above color filters. As shown in the figure, for example, Mg (magenta), Cy (cyan) pixels, G (green) and Ye (yellow) pixels are arranged on odd lines. In the CCD 1, accumulated charges (pixel signals) in pixel units are passed through these color filters.
Is obtained. [0004] According to the conventional color difference line sequential mixed reading method, the accumulated charges of the pixels on the upper and lower lines are added and mixed and read. For example, at the first exposure, a mixed signal of 0 line and 1 line, a mixed signal of 2 lines and 3 lines,
.. Are read out, and a mixed signal of 1 line and 2 lines, a mixed signal of 3 lines and 4 lines, and so on in the second exposure are read out. The video signal is read. Therefore, the mixed signal of the two lines of the CCD 1 becomes a signal of one line of the field image, and odd or even one field data can be obtained by one exposure. FIG. 8 shows the operation of a signal read from the CCD 1. In the electronic endoscope apparatus, as shown in FIG. 1A, 1/60 second (vertical synchronization period)
An odd field and an even field are formed based on each O (Odd) / E (Even) signal (field signal). Therefore, as shown in FIG. 3B, signal accumulation is performed according to the accumulation (exposure) time T of the electronic shutter during the 1/60 second period, and the accumulated mixed signal is accumulated in the next 1/60 second period. Is read. As a result, as shown in FIG. 7C, an odd (Odd) field signal and an even (Even) field signal are obtained. For example, the (n-1) th odd field signal is shown on the left side of FIG. (0 + 1) line, (2 + 3) line, (4+
5) A mixed signal of lines..., And the n-th even-numbered field signal has (1 + 2) lines and (3) shown on the right side of FIG.
+4) A mixed signal of lines... [0006] The odd field signal and the even field signal are interlaced and formed as an image of one frame, and this image is displayed as a moving image on a monitor. Further, in the endoscope apparatus, a freeze switch is disposed on the operation unit, and when the freeze switch is pressed, a still image at that time is formed and displayed. However, in the above-mentioned simultaneous electronic endoscope apparatus, as shown in FIG. 8C, an odd field image for forming one frame image and an odd field image for forming one frame image are used. 1/60 between even field image
If there is a time lag of seconds and the endoscope itself shakes or the object moves during this time, there is a problem that when displaying a still image, the image quality (resolution, color shift, etc.) is reduced. .
In other words, in the case of a moving image, it is often better to faithfully reproduce the movement of a subject or the like by the above-described mixed reading method in the CCD 1, but in the case of a still image, the resolution is reduced. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to obtain a high-quality still image and a moving image faithfully reproducing a motion, and at the time of switching from a moving image to a still image. To prevent incomplete images from being displayed,
Another object of the present invention is to provide an electronic endoscope apparatus that stabilizes a black level clamping process and prevents a decrease in image quality. In order to achieve the above object, the present invention mixes and outputs pixels stored in an image sensor between upper and lower lines (horizontal lines) to form a moving image. A pixel mixed readout method at the time of output of an image sensor, and an all-pixel readout method of reading a signal of all pixels stored in the image sensor in one exposure using a light-shielding period set by a light-shielding means and forming a still image An electronic endoscope apparatus comprising: a delay means for delaying a predetermined period of moving image data obtained by the pixel mixture readout method; and a clamp circuit for clamping an image signal output from the image sensor by a clamp signal. Switching control means for directly inputting a moving image signal obtained by the pixel mixture readout method at the time of output of the image sensor without passing through the delay means, and controlling to extract a black information signal of the moving image signal And a signal processing circuit that forms a clamp signal from the black information signal obtained under the control of the switching control means and feeds back the clamp signal to the clamp circuit. In the above-mentioned switching control means, a switching circuit for switching and selecting three of, for example, a still image signal, a moving image signal output from the delay means, and a through moving image signal directly output from the image sensor is provided, and the moving image signal (or the still image Signal), the switching can be controlled so as to extract the through video signal during the optical black period. According to the above arrangement, when the freeze switch is pressed, the all-pixel reading method is selected and a still image is formed. For example, 1/60 of a predetermined (first)
The charge accumulated by exposure (exposure time is arbitrary) within a second period (vertical synchronization period) is equal to the charge accumulated during the second period (1/60).
Seconds), the odd lines of the image sensor (CCD) are read out (read from the transfer line) and stored in a predetermined memory,
In the third (during the next exposure) period, the remaining even-numbered lines are read out and stored in a predetermined memory. Then, in order to be able to read out the even-numbered lines, the light source light in the second period is blocked by the light blocking means. That is, if the charges of the next exposure are accumulated in the second period in which the accumulated charges of the odd lines are sequentially read out, the remaining even lines cannot be read.
Therefore, in the present invention, the light output in the second period is eliminated, and the accumulated charges in the even-numbered lines are read in the third period. Thus, signals for all pixels of the image sensor obtained by one exposure can be read. Next, the video signal of, for example, the odd line first stored in the above-mentioned memory is further stored in the phase adjustment memory and is delayed by 1/60 second. A pixel mixing process is performed with the data of the even-numbered lines. That is, this pixel mixing process
As a result, a signal equivalent to the pixel mixture readout method at the time of output of the image sensor, which is performed at the time of signal output from the image sensor, is formed, but the pixel is mixed based on information obtained in one exposure. This is distinguished from the pixel mixed readout method at the time of element output. [0013] Odd and even field signals are formed by the pixel mixture signal, and a still image is displayed based on these video signals. Therefore, a still image is formed based on signals of all pixels obtained by one exposure, and becomes a high quality image. On the other hand, in a normal state in which the freeze switch is not pressed, the pixel mixture readout method at the time of output of the image sensor is selected, and pixels of two horizontal lines read from the image sensor are mixed and output as in the conventional case. Is done. However, when switching from a moving image to a still image, the illumination light is blocked and switching to reading of all pixels is performed. The process is performed, and a phenomenon occurs in which an incomplete image (an image with half luminance and an inappropriate color) is displayed. Therefore, in the present invention, for example, moving image data is entirely delayed by a processing time for one frame by a delay memory, for example, so that a moving image is not formed by image data obtained at the time of shading. This prevents display of an inappropriate image that occurs when switching from a moving image to a still image. In the above-described image processing, a clamp process for matching the black level is performed every horizontal scanning period, as is well known. In the above-described clamp process for the moving image, the image data once stored in the delay memory and the still image Since the display process is performed with the image data stored in the memory also in the clamp process of, the clamp signal is formed based on the old data. Therefore, stable control of the black level cannot be performed, and in this case, color reproducibility deteriorates. In the present invention, the black information signal of the current moving image signal directly output from the image pickup device is extracted separately from the processing signal for the moving image (or still image). Thus, a clamp signal is formed, and a clamp process is performed. Therefore, a large change in the black level due to a time lag is eliminated, and a good image can be displayed even when a moving image is selected or when the display is switched from a still image display to a moving image display. FIG. 1 shows a circuit configuration of an electronic endoscope apparatus as an example of an embodiment. This electronic endoscope apparatus has a scope (electronic endoscope) 10. Is connected to a processor device or a light source device having an image processing circuit. The scope 10 is provided with a CCD 12 having a color filter similar to that described with reference to FIG. 7 at its distal end, and a light guide 15 for guiding the light of the light source 14 to the distal end. The operation unit of the scope 10 has a freeze switch 16 for displaying a still image.
Is provided. A CCD drive circuit 18 for driving the CCD 12 is connected to the CCD 12. The drive circuit 18 includes a timing generator 19, and a microcomputer (microcomputer) for performing various controls including writing and reading of a memory. ) 20 is connected, and an operation signal of the freeze switch 16 is input to the microcomputer 20. CC above
The D drive circuit 18 inputs a timing signal based on the control of the microcomputer 20, and performs drive control of a pixel mixed readout method at the time of CCD output for a moving image and an all pixel readout method for a still image. For example, in the case of this all-pixel reading method,
Two kinds of pulses for reading out the accumulated data for all the pixels accumulated in the CCD 12 in one exposure by dividing the data into odd lines and even lines (shifted in terms of time) are also used for the CCD.
The signal is supplied from the drive circuit 18, and based on the signal, control for sequentially reading out the odd-line signal and the even-line signal separately from the CCD 12 is performed. Incidentally, in the pixel mixed readout method at the time of CCD output, one kind of readout pulse is applied to each line. Further, there is provided a clamp circuit 21 which receives the output signal of the CCD 12 and performs a clamp process for controlling the black level to be constant.
Is provided together with a correlated double sampling circuit, an automatic gain circuit, and the like. In the subsequent stage of the clamp circuit 21, a first memory 23 for storing the image data of the odd lines and a second memory for storing the image data of the even lines for reading all the pixels through an A / D converter 22. 24, a third memory 25 for phase adjustment for storing the data in the first memory 23 as it is and delaying the read timing by 1/60 second, and a still image mixing circuit 26 are provided. That is, C
All pixel signals obtained by the CD 12 are temporarily stored in the respective memories 23 and 24 in a state of being divided into odd-line data and even-line data.
By delaying the odd line data of 1/60 second,
The same phase as that of the even-numbered line data stored in the second memory 24 is set. As a result, both image data can be read at the same time, and the next-stage mixing circuit 26 adds and mixes the pixel data of the odd-numbered line of the third memory 25 and the pixel data of the even-numbered line of the second memory 24. (Still image pixel mixing process). Therefore, in the case of a still image, a pixel mixture signal equivalent to that of the conventional color difference line sequential mixture readout system is formed by the mixing circuit 26. FIG. 2 shows the contents of still image data formed by the circuits from the CCD 12 to the mixing circuit 26 described above. As shown in FIG. 1A, the CCD 12 is provided with horizontal lines from 0 to N lines corresponding to the number of scanning lines, and the pixel data of this horizontal line is transferred to a transfer line and read. Is done. The data of the odd lines (1, 3, 5,...) Of the CCD 12 are stored in the first memory 23 (and the third memory 25) of FIG. Are stored in the second memory 24 in FIG. The data in the memories 25 and 24 are mixed by the mixing circuit 26 as described above, as shown in FIGS.
, Pixels are mixed with each other, and as shown in FIG. 4D, 0 line + 1 line, 2 line + 3 line, 4 line
The addition operation data of line + 5 lines... Is odd (Odd)
Output as field data. Further, in the state where the read line in FIG.
1), pixel mixture is performed between the lines in FIG. (B) and FIG. (E), and as shown in FIG.
2 lines, 3 lines + 4 lines, 5 lines + 6 lines ...
Is output as even field data. In this example, the odd number of lines of the CCD 12 is ODD, the even number is EVEN, the odd number of the field to be interlaced is Odd, and the even number is Ev.
It is distinguished as en. In FIG. 1, the other output line of the A / D converter 22 is connected to a sixth memory as a delay memory for moving image data.
The memory 27A and the seventh memory 27B are connected. That is,
In this example, the two memories 27A and 27B store the moving image data for one frame (two fields) in time so that an incomplete moving image is not formed by the still image data obtained by the CCD 12 due to the light shielding operation. Speaking of 1/30 second. This eliminates the timing at which the incomplete still image data is displayed as a moving image, and prevents the display of an incomplete moving image. The seventh memory 27B and the mixing circuit 2
6 is an image switching circuit 28 for switching between a moving image and a still image
(A, b terminals), and this image switching circuit 28
Switches from the terminal a to the terminal b under the control of the microcomputer 20 when the freeze switch 16 is pressed. Further, the image switching circuit 28 has the above-described A
The moving image signal output from the / D converter 22 is directly supplied via a TL line (through line), and the optical black period of the moving image signal is used. A DVP (Digital Video Processor) 29 is connected to the image switching circuit 28.
At 29, color signal processing is performed by the same pixel mixture readout method as in the related art, and for example, a color difference signal and a luminance signal are formed. In the DVP 29, a video signal is supplied with an optical black pulse (OBP) to extract a voltage during an optical black period (black setting period).
A clamp signal for controlling the black level to be constant is formed, and this clamp signal is fed back to the clamp circuit 21. In such a clamping process, in this example, the image switching circuit 2 by the microcomputer 20 is used.
Even if a video signal (a still image signal at b) is selected at the terminal a by the switching control of No. 8, the black level remains
Switching to the terminal c instantaneously extracts the voltage of the moving image signal during the optical black period. As a result, even when the moving image is delayed by, for example, one frame by the memories 27A and 27B, stable control of the black level in consideration of the current state is performed, and good color reproducibility can be secured. In the subsequent stage of the DVP 29, a fourth memory 3 for storing data of odd fields and even fields is provided.
A switching circuit 32 and a D / A converter 33 for switching between the 0th and fifth memories 31, a fourth memory 30 side terminal and a fifth memory 31 side terminal are provided. For example, in the case of a still image,
The odd field data obtained by converting the data of FIG. 2D into a color difference signal or the like is stored in the memory 30.
1 stores even field data obtained by converting the data of FIG. 2E into a color difference signal or the like. On the other hand, in the light source section for supplying light to the light guide 15 provided in the scope 10, the light source 14
A stop 35 and a light shielding plate 36 are arranged between the light guide 15 and the entrance end of the light guide 15. The light-shielding plate 36 is configured to rotate, for example, a semicircular plate, and a driving circuit 38 is connected to drive the light-shielding plate 36 to rotate. In this example, the light-shielding plate 36 is used by the freeze switch 16 in the field O / E signal at a cycle of 1/60 second.
The light is blocked for a predetermined 1/60 second after the is pressed. The diaphragm 35 has an aperture control circuit 3
9. A lamp driving circuit 40 is connected to the light source 14, and the aperture control circuit 39 drives the aperture 35 based on the luminance signal obtained by the DVP 29 to adjust the output light amount of the light source 14. ing. This example has the above-mentioned configuration, and its operation will be described with reference to FIGS. 3 to 6 (FIGS. 3 to 5 coincide with time at point Q). As shown in FIG. 3B, a timing signal for forming a one-field image in 1/60 second is used as a field O (Odd) / E (Even) signal as in the related art. In the normal state, it is set so as to execute the moving image processing, that is, the pixel mixture readout method at the time of CCD output. The light shielding plate 36 shown in FIG. Irradiated from the tip into the body to be observed via the. By this light irradiation, an image of the inside of the body to be observed is captured by the CCD 12 at the distal end, and charges corresponding to the image light are accumulated in the CCD 12. The accumulated charges are read out by adding the pixels between the upper and lower lines by the driving pulse from the CCD driving circuit 18, and the pixel mixed signal described with reference to FIG. 7 is output. The subsequent moving image processing will be described later, and the still image processing will be described first. Freeze switch 1 of scope 10 in FIG.
When the button 6 is pressed, the microcomputer 20 switches the image switching circuit 28 to the terminal b, and switches from the mixed pixel reading method to the all pixel reading method for a still image. For example, as shown in FIG. 3A, if a trigger Tr1 (or Tr2) by the freeze switch 16 is given, the next rising edge of the O / E signal (t1).
The light shielding plate 36 blocks the optical path only for 1/60 second from that time, and during that time, the light is blocked as shown in FIG. Therefore, the image data from which all the pixels are read out has the light output Lt in the 1/60 second period immediately before the light-shielded period.
And becomes the electric charge accumulated in the CCD 12. This electric charge is obtained by exposing the g1 portion of the electronic shutter pulse shown in FIG.
It is read by the drive circuit 18. That is, FIG. 3D shows the read pulse P1 of the odd-numbered line shown in FIG. 2B, and FIG. 3E shows the read pulse P1 in FIG.
The read pulse P2 of the even-numbered line shown in FIG. 4A, and the read pulse P1 without the pulse at t2 and the read pulse P2 without the pulse at t1, as shown in FIG.
Odd (ODD) line data and even (EV)
EN) Line data is sequentially read. Therefore, the reading of the odd-numbered lines is performed during the light-shielding period (t1 to t2), and the reading of the even-numbered lines is performed during the next period (t2 to t3). As shown in FIG. 3 (F), there is no rising period (sweeping period) between t1 and t2 in the electronic shutter pulse. The odd line data is stored in the first memory 2 as shown in FIG.
3 and the even line data is written to the second memory 24 as shown in FIG. Next, FIG.
As shown in (J), the odd line data of the first memory 23 and the even line data of the second memory 24 are read twice, and the odd line data is
It is stored in the third memory 25 for adjusting the phase of the second. Therefore, as can be understood from FIGS. 3J and 3K, the data of the odd lines and the data of the even lines are aligned in the same phase (timing). Each data read from the memories 25 and 24 in this way is mixed by the mixing circuit 26. In this example, in order to enable this, FIG.
As shown in (L), the first memory 23 and the second memory 24 are write-protected. Then, pixel mixture conversion is performed in the same period [FIG. 3 (M)], and first, as shown in FIG.
0 line + 1 line, 2 line + 3 line, 4 line +
Output data of 5 lines... Is output, and this is an odd number (Od).
d) It is stored in the fourth memory 30 as field data [FIG. 3 (N)]. Next, the addition data of 1 line + 2 lines, 3 lines + 4 lines, 5 lines + 6 lines... Shown in FIG. 2 (E) is output, and this is an even number (Even).
It is stored in the fifth memory 31 as field data [FIG. 3 (O)]. Then, at the same time that the odd field data and the even field data are read, the switching circuit 32 selects the fourth memory 30 and the fifth memory 31 so that each field data is output alternately. . These field data are output to a monitor via the D / A converter 33, and an image is displayed on the monitor by interlaced scanning. As a result, a still image is displayed based on all pixel data obtained at the same exposure, and a high-quality image is obtained. Therefore, 1
Even if the endoscope itself is shaken for 60 seconds or the object to be observed is moved, it is possible to observe a clear still image with little influence. However, in the above-described still image processing, all the pixel data are read out during the two-field period after the one-field period is shielded, so that the display is delayed by one frame as compared with the case of the moving image. Become. Therefore, when moving image data is used as it is without using the delay memories (27A, 27B), there is a disadvantage that moving image display is performed by incomplete still image data immediately before switching to a still image. FIG. 4 shows a state of such moving image processing. For example, O1 (O / E) shown in FIG.
Signal), the odd line data O11 and the even line data O12 shown in FIGS.
The moving image data output from the CCD 12 is O11 + O12 as shown in FIG.
It is stored in the memory 31 and is read out and supplied to the monitor during the period shown in FIG. E1 and O2 in FIG.
In the same manner, the data of E11 + E12 and O21 + O22 are output to the monitor. However, the next E2 (tO to t) shown in FIG.
1), during the period of O3 (t1 to t2), all pixels are read out while being shielded from light during this period of O3.
As shown in (C), only the odd-numbered line data F1 (ODD line) is obtained during the period E2,
In this period, only even line data F2 (EVEN line) is obtained. These data F1 and F2 are also used as field data of a moving image immediately before a still image is displayed as shown in FIGS. These data F1 and F2 are normal field data (such as luminance).
, And the moving image at this time does not hold as an image. Therefore, in this example, the sixth memory 27A and the seventh memory 27B are arranged to delay the moving image data by one frame processing period so that the data F1 and F2 are not used as moving images. This processing state is shown in FIG.
Is shown in When forming a moving image, the image switching circuit 28 is switched to the terminal a side, and the video signal is subjected to predetermined processing by the DVP 29 in the same manner as in the case of a still image, and then stored in the memories 30 and 31 at the subsequent stage. Is done. In FIG. 5, the odd line data O11 [FIG. (B)] and the even line data O12 [FIG. (C)] obtained during the period of O1 (O / E signal) in FIG. As shown in (D), the delay is delayed by one field (1/60 second) in the sixth memory 27A, and further delayed by one field in the seventh memory 27B as shown in (E). Therefore,
O11 + O12 read from the seventh memory 27B [FIG. (F)] and becoming moving image data is compared with the case of FIG.
This is temporally delayed by one frame (1/30 second). This is because E11 + E obtained in the next period of E2 and O3.
12, the same applies to O21 + O22, and all moving image data is delayed by one frame. Therefore, as shown in FIG. 5H, in FIG. 4, the above-mentioned E11 + E12 is used during the period (E3) during which the still picture data F1 is extracted, and as shown in FIG. In FIG. 5, the period during which the still image data F2 is extracted (O3
) Uses the above O21 + O22. As a result, the still image data F1 and F2 are not used as moving image data, and incomplete moving image display is avoided. FIG. 6 shows the operation of the clamp process in the image processing. In this example, as described above, the moving image data is stored in the sixth and seventh memories 27A and 27A.
Since B is delayed by one frame, the clamp signal is formed by past data delayed by one frame, and the black level greatly changes. Therefore, in this example, as described above, control is performed such that the clamp signal is always extracted from the through moving image signal. That is, in FIG. 6, the moving picture signal in FIG. 6A is supplied to the terminal a of the image switching circuit 28, and the through signal (moving picture signal from the through line TL) in FIG. The switching signal shown in FIG. 2C is supplied from the microcomputer 20 to the switching circuit 28. This switching signal is formed from an OBP (optical black pulse) shown in FIG. 4D, and the upper side is connected to the a (or b) terminal and the lower side is connected to the c terminal. According to this, even when the moving image (terminal a) is selected, by switching to the terminal c for a predetermined short period,
The optical black period K of the current video signal is 1H
It is extracted every time. The moving picture signal incorporating the black level period of the through signal is applied to the DVP 29
Then, the OBP of FIG. 6D is applied to form the clamp signal of FIG. 6E. This clamp signal is fed back to the clamp circuit 21, where the black level signal is reproduced. Therefore, the control of the black level is stably performed, and good color reproducibility is obtained. Even when a still image is selected, a signal of an optical black period of a through signal is used in the same manner. That is, even in a still image, the first memory 2
3. Since an image is displayed using the same signal stored in the second memory 24, a clamp signal is formed from old data in the past, and when switching to a moving image, the clamp signal does not match the current situation. , The black level greatly changes. Therefore, even when this still image processing is selected, in the same manner as described above, the signal is switched to the through signal (terminal c) so as to extract the signal in the optical black period, and the current black level voltage is extracted. As a result, constant control of the black level is performed. As described above, according to the present invention,
An electronic endoscope device that forms a moving image by the pixel mixture readout method at the time of output of the imaging element and forms a still image by the all-pixel readout method
The above moving image data is delayed by a predetermined period so that an incomplete image is not displayed when switching from a moving image to a still image, and based on the black level voltage of the current moving image signal always directly output from the image sensor. Clamping process produces smooth images that faithfully reproduce the motion of moving images, while high-quality images without blurring are obtained for still images.The black level clamping process is stable, and color reproducibility is reduced. This has the advantage of preventing

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a circuit configuration of an electronic endoscope apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing image data read from the CCD of FIG. 1 to a mixing circuit. FIG. 3 is an explanatory diagram showing a still image forming operation in the embodiment. FIG. 4 is an explanatory diagram showing a moving image forming operation when no delay memory is provided in the embodiment. FIG. 5 is an explanatory diagram illustrating a moving image forming operation in the embodiment. FIG. 6 is a waveform chart showing a clamp process in the embodiment. FIG. 7 is a diagram illustrating a configuration of a color filter in a conventional CCD and pixel mixture readout. FIG. 8 is an explanatory diagram showing an operation in a conventional CCD. [Description of Signs] 1,12 CCD, 10 scope, 16 freeze switch, 18 CCD drive circuit, 20 microcomputer (control means), 21 clamp circuit, 23, 24, 25, 27A, 27B, 30 , 31…
Memory, 26: Mixing circuit, 28: Image switching circuit, 29: DVP (signal processing circuit), 36: Light shielding plate

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 1/00 H04N 5/18

Claims (1)

(57) [Claim 1] A pixel-mixing readout method at the time of output of an image sensor for mixing and outputting pixels accumulated in an image sensor between upper and lower lines to form a moving image, and one exposure An electronic endoscope device including an all-pixel reading method for reading out signals of all pixels accumulated in the image sensor using a light-shielding period set by a light-shielding unit and forming a still image, Delay means for delaying the moving image data obtained by the mixed reading method by a predetermined period, a clamp circuit for clamping an image signal output from the image sensor by a clamp signal, and a pixel circuit obtained by the image sensor output-time pixel mixed reading method. Switching control means for directly inputting the moving picture signal without passing through the delay means, and controlling to extract a black information signal of the moving picture signal; and a black signal from the black information signal obtained by the control of the switching control means. An electronic endoscope apparatus comprising: a signal processing circuit that forms a ramp signal and feeds back the clamp signal to the clamp circuit.