JP3380459B2 - 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. The present invention has been made in view of the above problems, and has as its object to read out all pixels obtained by an image pickup device by one exposure to form a high-quality still image, and It is an object of the present invention to provide an electronic endoscope apparatus capable of faithfully reproducing a motion and preventing an incomplete image from being displayed or a screen from being blurred when switching from a moving image to a still image. . 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 device comprising: a memory for storing at least the moving image data; and still image data read from the imaging element when the all-pixel reading method is selected is written to the memory as moving image data. The write-protection period is set so that there is no write-protection period, and either one of the odd-numbered field and the even-numbered field that has already been written to the memory is written in the write-protection period. Control means for continuously reading as frame data;
It is characterized by having. As a detailed configuration, for example, for all pixel signals accumulated in the image sensor by one exposure, first, an image signal of either an odd or even line is read, and then an image signal of the remaining lines is read. Element driving circuit for controlling the image signal, a preceding-stage (for still image data) memory for storing the odd-line image signal and the even-line image signal obtained from the image sensor when the all-pixel readout method is executed. During execution of the all-pixel readout method, a phase adjustment memory for adjusting the phase of the image signal of the predetermined line and the image signal of the other line previously stored in the former stage memory; and A mixing circuit for mixing the read-out pixel signals of the odd line and the even line at the same exposure time to form a still image signal; and a pixel mixture readout output from the image sensor. An image switching circuit that switches a moving image signal of a system and a still image signal output from the mixing circuit based on an operation of a freeze switch, and a subsequent memory that stores moving image data and still image data output from the image switching circuit, In the subsequent memory, control means for prohibiting writing of still image data as moving image data, and for continuously reading one of odd or even field data already written, instead of this data, Is characterized by the following. According to the above arrangement, when the freeze switch is pressed, the all-pixel reading method is selected, thereby forming a still image. For example, charges accumulated by exposure (exposure time is arbitrary) within a predetermined (first) 1/60 second period (vertical synchronization period) are imaged in a second period (1/60 second). The odd lines of the element (CCD) are read and stored in a predetermined memory (read from the transfer line), and the remaining even lines are read in a third (at the next exposure) period, which is also stored in the predetermined memory. It is memorized. 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 related art. 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.
In a frame, image processing is performed on half the normal moving image data, 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, a write inhibit signal is output to the subsequent memory for storing moving image data, and the still image data obtained by the all-pixel reading method is not written to the memory as moving image data. At the same time, for example, only the odd field data is continuously read. According to this, the moving image data of the immediately preceding odd field that has already been obtained is used in place of the incomplete still image data, and the display of an inappropriate image that occurs when switching to the still image is prevented. Further, in this case, the image blur can be suppressed by reading the odd (or even) field data at least twice (for one frame) continuously. That is, as the data replacing the still image data, the immediately preceding data for both the odd field and the even field can be used again. In this case, since the image is displayed with the data that is temporally earlier or later, for example, the subject When moves right and left, the display screen will be blurred. However, according to the present invention, as described above, only one of the odd number data and the even number data is read out and the image is displayed, so that the field data which is temporally earlier or later is not used, and the blur of the screen is eliminated. . 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 driving circuit 18 for driving the CCD 12 is connected to the CCD 12. The driving circuit 18 includes a timing generator 19, memories (23 to 25,
A microcomputer (microcomputer-control means) 20 for performing various controls including writing and reading of (30, 31) is connected, and an operation signal of the freeze switch 16 is input to the microcomputer 20. The CCD drive circuit 18
Receives a timing signal based on the control of the microcomputer 20, and performs a pixel-mixing readout method at the time of CCD output for a moving image;
The driving control of the all-pixel reading method for a still image is performed. 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. An A / D converter 22 for inputting the output signal of the CCD 12 is provided.
In the subsequent stage, a first memory 23 for storing the image data of the odd lines, a second memory 24 for storing the image data of the even lines, and the first memory 2 for reading all the pixels.
3 is stored as it is, and the read timing is set to 1
/ 3 second memory 2 for phase adjustment for delaying by 60 seconds
5. A still image mixing circuit 26 is provided. That is, CCD
All the pixel signals obtained in step S12 are temporarily stored in the memories 23 and 24 in a state of being divided into odd-line data and even-line data. By delaying 60 seconds, the second
It has the same phase as the even-numbered line data stored in the memory 24. 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, an image switching circuit 27 for switching between a moving image and a still image is provided at a stage subsequent to the mixing circuit 26. In the image switching circuit 27, the A / D terminal for forming a moving image is provided at its a terminal. The output of the converter 22 is supplied via the L line, the output of the mixing circuit 26 is given to the other terminal b, and when the freeze switch 16 is pressed, the microcomputer 20 controls the terminal b to the terminal b. Switch to terminal. The image switching circuit 27 includes a DVP
(Digital video processor) 29 is connected,
In the DVP 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. At the subsequent stage of the DVP 29, a fourth memory 3 for storing data of odd-numbered fields and even-numbered fields is provided.
A switching circuit 32 for switching between the 0th and fifth memories 31 and the c terminal on the fourth memory 30 side and the d terminal on the fifth memory 31 side;
A D / A converter 33 is provided. For example, in the case of a still image, the fourth memory 30 stores odd field data obtained by converting the data in FIG.
The even field data obtained by converting the data of FIG. 2E into a color difference signal or the like is stored in the memory 31. In the fourth and fifth memories 30 and 31 during the moving image display process, the unprocessed (unmixed) still image data is not used as the moving image data stored therein. The microcomputer 20 prohibits writing for a predetermined period, and controls to additionally read, for example, odd field data for one frame. That is, a write signal that is write-inhibited during a period of time when incomplete still image data obtained by the all-pixel readout method is used as a moving image is transmitted to the memory 30,
The fourth memory 30 receives a read signal for omitting reading for a predetermined one field period, and the fifth memory 31 receives a read signal for reading the same data continuously for a predetermined three field period. On the other hand, in the light source section for supplying light to the light guide 15 disposed on 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 a diaphragm 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 (each figure coincides in 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 the CCD 12 accumulates electric charges corresponding to the image light. 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 27 to the terminal b side, 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, as shown in FIG. 3C, at the next rising edge of the O / E signal (t1). ), The light shielding plate 36 blocks the optical path only for 1/60 second, during which the light is blocked [FIG. 3 (D)]. Therefore, the image data from which all the pixels are read out becomes the electric charges accumulated in the CCD 12 in the exposure Lt in the 1/60 second period immediately before the light-shielded period. This charge is obtained in the portion g1 of the electronic shutter pulse shown in FIG. 3G, and the charges (data) of all the pixels are read out by the CCD drive circuit 18. That is, FIG. 3E shows the read pulse P1 of the odd-numbered line shown in FIG. 2B, and FIG. 3F shows the read pulse P1 of 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). Note that, as shown in FIG. 3G, even in the electronic shutter pulse, there is no rising period (sweep period) between the above-mentioned t1 and t2. The odd-numbered 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 (E), 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 understood from FIGS. 4E and 4F, the data of the odd-numbered lines and the data of the even-numbered 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 (G), the first memory 23 and the second memory 24 are write-protected. Then, pixel mixture conversion is performed in the same period [FIG. 4 (H)], 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. 4 (I)]. 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).
The data is stored in the fifth memory 31 as field data. Then, at the same time when the odd field data and the even field data are read, the switching circuit 32 outputs the respective field data alternately as shown in FIGS. 4 (K) and 4 (L). The fourth memory 30 and the fifth memory 31 are selected. These field data are
The data is 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, even if the endoscope itself shakes or the object to be observed moves for 1/60 second, it is possible to observe a clear still image with a small influence. However, in the above-described still image processing, all the pixel data is 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, there is an inconvenience that a moving image is displayed by incomplete still image data immediately before switching to a still image. FIG. 5 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, a write inhibit signal is output to the memories 30 and 31 for storing moving image data,
For example, the data F1 and F2 for one frame are not used as a moving image, and this processing state is shown in FIG. At the time of this moving image formation, the image switching circuit 27 is switched to the terminal a side, and the video signal is subjected to predetermined processing in the DVP 29 in the same manner as in the case of a still image, and then stored in the fourth memory 30 at the subsequent stage. Odd field data is stored in the field data and the fifth memory 31. In FIG. 6, the odd-numbered line data O11 [FIG. 8B] and the even-numbered line data O12 [FIG. 9C] obtained in the period of O1 (O / E signal) in FIG. As shown in D), the pixel mixture readout is performed by the CCD 12, and an image signal is formed based on these signals. In the write signal to the fourth memory 30 at the subsequent stage, the write inhibit period S1 shown in FIG. 7E is set, and in the write signal to the fifth memory 31, the write inhibit period S2 shown in FIG. The unprocessed still image data F1 and F2 are not written to the fourth and fifth memories 30 and 31. By doing so, normally each memory 3
The same data is read out twice from 0 and 31, and returning to the previous figure, the data shown in FIGS. 5 (G) and (H) is obtained. That is, as shown in FIG. 5G, the data of E11 + E12 is read twice from the fourth memory 30 and the data of O21 + O22 is read twice from the fifth memory 31. As shown in FIG. The data of E11 + E12 is used during the period (E3) during which the still image data F1 is read, and the data O21 + O22 during the period (O3) during which the still image data F2 is read in FIG. Is used. Therefore, the still image data F1 and F2 are not used as moving image data, and incomplete moving image display is avoided. However, in the above-described read processing, FIG.
Focusing on the U portion of (G) and (H), the data E11 + E
Data O21 + O22 obtained temporally later (1/60 seconds later) than 12 will be read out first and displayed,
When the object to be observed or the endoscope itself is moving, the screen (image) is blurred. Therefore, in this example, as shown in FIGS. 6G to 6I, only data in either the odd field or the even field is used again. That is,
As shown in FIG. 9G, a read signal not to be read for a predetermined three-field period S3 is supplied to the fourth memory 30, and the same three signals are supplied to the fifth memory 31.
A read signal for reading in the field period S3 is provided. At the same time, a switching signal for selecting the fifth memory 31 (terminal d) for the three-field period S3 is supplied to the subsequent switching circuit 32, as shown in FIG. Then, as shown in FIG. 6H, the data of O21 + O22 is read out three times in succession, and is output from the switching circuit 32 to the monitor via the D / A converter 33. As a result, the moving image of the last one frame immediately before the switching to the still image is displayed as an image using only the data of O21 + O22, thereby preventing the image from being blurred due to the temporally preceding and succeeding data. You. In the above embodiment, the write inhibit period is one frame in total, and the continuous reading of odd field data is three fields. However, in the case of processing at different timings, the write inhibit period is correspondingly performed. In addition, the continuous reading period is appropriately set. Further, the data read continuously may be data of an even field. As described above, according to the present invention,
An electronic endoscope apparatus that forms a moving image by the pixel-mixing readout method at the time of output of the image sensor and forms a still image by the all-pixel readout method that reads out signals of all pixels stored in the image sensor. Is not written to the memory as moving image data, and one of the odd field data and the even field data already written to the memory as the frame data of the writing prohibited period is continuously read. As a result, a smooth image that faithfully reproduces motion is obtained for moving images, while a high-quality image without blur is obtained for still images, and incomplete images are displayed when switching from moving images to still images There is an advantage that no screen blur occurs.

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 still image forming operation in the embodiment and a continuation of FIG. 3; FIG. 5 is an explanatory diagram illustrating a moving image forming operation in which a problem occurs under certain conditions according to the embodiment; FIG. 6 is an explanatory diagram showing a moving image forming operation 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), 23 ... first memory,
24 ... second memory, 25 ... phase adjustment (third)
Memory, 26: mixing circuit, 28: image switching circuit, 30: fourth memory, 31: fifth memory,
32: switching circuit, 36: light shielding plate.

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

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 apparatus having an all-pixel reading method for reading out signals of all pixels stored in the image sensor using a light-shielding period set by a light-shielding unit and forming a still image, A memory for storing moving image data, and a write inhibit period set so that the still image data read from the image sensor when the all-pixel reading method is selected is not written to the memory as moving image data; Control means for continuously reading out data of either the odd field or the even field which has already been written as frame data of the write-inhibited period. Child endoscope apparatus.