JP3420931B2 - Electronic endoscope signal processing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit for an electronic endoscope, and more particularly, to a method for forming a moving image by a conventional pixel-mixing readout method and a method for storing a moving image in an image pickup device. The present invention relates to a configuration for adjusting an exposure amount when a still image is selected in an electronic endoscope that reads out pixels 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. 6 shows the arrangement of the above color filters. As shown in the figure, on the imaging surface of the CCD 1, for example, pixels of Mg (magenta), Cy (cyan), 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. 7 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. 6C, an odd field signal and an even field signal are obtained. For example, the (n−1) th odd field signal is obtained by the (0 + 1) line shown on the left side of FIG. A (2 + 3) line, (4 + 5) line... Are mixed signals, and the n-th even field signal is a (1 + 2) line, (3 + 4) line... [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 simultaneous electronic endoscope apparatus, as shown in FIG. 7C, an odd-numbered field image for forming one frame image and 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 the subject or the like by the pixel mixture readout in the CCD 1 described above, but in the case of a still image, the resolution is reduced. Therefore, the present applicant has provided a predetermined light-shielding period, and has adopted an all-pixel reading method of reading out data of all pixels obtained by one exposure using this light-shielding period. For example, there is a problem that the amount of exposure during a period in which all pixels are read is insufficient due to a delay in mechanical (gear or the like) response of the light shielding plate for setting the light shielding period. That is,
Since a complete light-shielding state is required in the light-shielding period for data reading, the light-shielding plate is operated slightly before the light-shielding period in consideration of its response time. Shortage of light amount). SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide an electronic endoscope capable of obtaining a high-quality still image and a moving image faithfully reproducing a motion, and reading all pixels.
It is an object of the present invention to provide a signal processing circuit of an electronic endoscope which can satisfactorily compensate for a shortage of light amount due to a response delay of a light shielding mechanism for an optical system . [0010] In order to achieve the above object, the present invention provides a method of forming a moving picture by mixing and outputting pixel signals accumulated in an image sensor between upper and lower lines (horizontal lines). an imaging element pixel mix reading system at the output of, a single exposure out read the signals of all pixels stored in the image pickup device, the electronic endoscope equipped with reading all pixels which form a still picture
In the signal processing circuit , when the all-pixel reading method is selected.
Next to the exposure field to read out all pixel signals
A light-shielding plate that shields light during the field period
In consideration of the response delay time of the light shielding plate,
A light-shielding unit that operates from before the light-shielding period;
A digital signal area is provided in a digital signal area for converting an image signal output from the image sensor into a digital signal based on a pixel readout method and processing the digital signal. an arithmetic circuit for multiplying the amount corresponding to the shortage, characterized in that the provided. 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 during 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 that of the pixel mixing 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 data obtained by one exposure. This is distinguished from the pixel mixed readout method at the time of element output. Then, 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, and A moving image that faithfully reproduces the movement of the object can be obtained. However, in the above-described light shielding operation for a still image, as described above, a light quantity shortage occurs during the exposure period for forming a still image due to, for example, a mechanical response delay of the light shielding plate. Therefore, in the present invention, a multiplier is provided in the digital domain,
This multiplier amplifies the digital image signal output from the image sensor by an amount corresponding to the light quantity shortage, thereby obtaining a proper light quantity and displaying a still image with good brightness. FIGS. 1 and 2 show a circuit configuration of an electronic endoscope apparatus as an embodiment. The 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. This scope 10 has a tip as shown in FIG.
CCD 12 with the same color filter as described in
And a light guide 15 for guiding the light of the light source lamp 14 to the tip. Further, a freeze switch 16 for displaying a still image is provided on the operation unit of the scope 10. The CCD 12 is connected to a CCD drive circuit 18 that drives the CCD and has an electronic shutter function. The drive circuit 18 includes a timing generator 1
9. A microcomputer (microcomputer) 20 for performing various controls including writing and reading of the memory is connected, and an operation signal of the freeze switch 16 is input to the microcomputer 20. The CCD 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 types of pulses are supplied from the CCD driving circuit 18 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 and also shifting in time. Based on this, control is performed to sequentially and sequentially read out the odd-line signal and the even-line signal from the CCD 12. 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 is provided downstream of the CCD 12, and the A / D converter 22 converts an analog image signal into a digital image signal. The A / D converter 22 has 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 a 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 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. 3 shows the contents of the 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 28 for switching between a moving image and a still image is provided at the subsequent stage of the mixing circuit 26. In the image switching circuit 28, the A / D is connected to the terminal a for forming a moving image. 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 28 includes a DV
A P (digital video processor) 29 is connected, and the DVP 29 forms a color difference signal and a luminance signal. FIG. 2 shows main circuits in the DVP 29. Red (R), green (G), and blue (B) matrix circuits 29a, R are provided on the processing lines for the color difference signal (C).
GB gain circuit 29b, for example, RY (luminance signal), B
A color difference matrix circuit 29c for calculating the -Y signal and a gamma correction circuit 29e are provided, and a luminance calculation circuit 29f and a gamma correction circuit 29h are provided on a processing line for the luminance signal (Y). Then, the above color difference matrix circuit 29c
And the gamma correction circuit 29e, and the luminance calculation circuit 29
Multipliers 29d, 29 between f and the gamma correction circuit 29h for eliminating the light quantity shortage due to the response delay of the light shielding mechanism.
g is connected. Under the control of the microcomputer 20, the multipliers 29d and 29g perform the above-described color difference signal and the above-described color difference signal only for the predetermined two-field period (vertical synchronization period) after the freeze switch 16 is pressed. The data size of the luminance signal is multiplied by (1 + α). As a result, the shortage of the light amount caused by the response delay of the light shielding plate 36 for the next light shielding period, that is, the shortage of the exposure amount for the still image immediately before the light shielding period is solved. 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.
0 and fifth memory 31, a switching circuit 32 for switching between the fourth memory 30 side terminal and the fifth memory 31 side terminal,
An 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 of FIG. 3D into a color difference signal or the like, and stores the data of FIG. Even field data converted into a signal or the like is stored. On the other hand, in the light source section for supplying light to the light guide 15 disposed on the scope 10, a stop 35 for adjusting the amount of emitted light and a light-shielding portion are provided between the light source lamp 14 and the incident end of the light guide 15. A plate (light shielding means) 36 is provided. 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. The light shielding plate 36 in this example is
Based on the field O / E signal (every 1/60 second), the light is blocked only for a predetermined 1/60 second after the freeze switch 16 is pressed. The diaphragm 35 has an aperture control circuit 3
9. A lamp drive circuit 40 is connected to the lamp 14, and the aperture control circuit 39 drives the aperture 35 based on the luminance signal obtained by the DVP 29, and adjusts the amount of light emitted from the lamp 14. The first example has the above configuration, and its operation will be described with reference to FIGS. As shown in FIG. 4B, fields O (Odd) / E (Eve)
n) As the signal, a timing signal for forming a one-field image in 1/60 second as in the related art is used. 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 in FIG.
The light from the body is radiated from the distal end portion through the light guide 15 into the body to be observed. By this light irradiation, an image of the inside of the object to be observed is captured by the CCD 12 at the distal end, and charges corresponding to the image light are accumulated. This accumulated charge is read out by adding pixels between the upper and lower lines by a drive pulse from the CCD drive circuit 18 and reading out the pixel mixture signal described with reference to FIG. The moving image signal is sent from the A / D converter 22 to the image switching circuit 28 via the through line L.
The video signal is supplied to the DVP 29 via the terminal a of the image switching circuit 28. This DV
The operation after P29 is the same as the conventional operation.
A moving image is displayed on the monitor based on the odd and even field signals stored in the memories 30 and 31. On the other hand, when the freeze switch 16 of the scope 10 shown in FIG. 1 is pressed, the microcomputer 20 switches the image switching circuit 28 to the terminal b side, and switches from the mixed pixel reading method to the all pixel reading method for a still image. Can be switched to For example, as shown in FIG. 4A, the trigger Tr1 (or Tr2) by the freeze switch 16 is used.
Is given, the rising edge of the next O / E signal (t
1) Only about 1/60 second from the time before (details will be described later)
The light shielding plate 36 blocks the optical path [FIG.
(C)] During that time, the output light from the light source unit is shut off as shown in FIG. Therefore, the image data from which all the pixels are read out becomes the electric charge accumulated in the CCD 12 by the light output Lt in the 1/60 second period immediately before the light-shielded period. FIG. 4E shows the read pulse P1 of the odd-numbered line shown in FIG. 3B, and FIG. 4F shows the read pulse P1 shown 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). FIG. 4G shows the operation of the electronic shutter. Here, the accumulated charges in the rising period of the pulse are swept out, and the accumulated charges in the falling period are read.
Accordingly, the still image data (accumulated charge) is strictly obtained by exposing the g1 portion after the charge has been swept out, and the charges of all the pixels are read out by the CCD drive circuit 18. . Further, the light shielding period (t) after the above g1
In 1 to t2), the sweep is omitted. By the way, in the above-mentioned light-shielding period, since the odd-numbered line data is read out, a complete light-shielding state is set.
It is necessary to prevent charges from being accumulated in D12, and for that purpose, the control of the light shielding plate shown in FIG. 5 is performed. FIG.
FIG. 5 is an enlarged view of a part (B, C, D, and G) of FIG. 4, and the light shielding plate control pulse shown in FIG.
In consideration of the mechanical response delay time ta of the drive unit (gear or the like), a pulse that falls earlier by that time ta is formed. Then, when the light shielding plate 36 is driven, the light emitted from the light source unit attenuates in a quadratic curve in the response period ta as shown in FIG. Will move to Therefore, in the light output Lt for a still image, a loss of the light amount La occurs, and as shown in FIG. 9G, even in the exposure of the g1 portion obtained in the actual charge accumulation time Ts, compared with the case of the moving image. Then, the light amount L
The light quantity becomes insufficient by a. In this example, the insufficient light quantity is compensated for by the multipliers 29d and 29g in the DVP 29.
This will be described later. The odd line data obtained from the CCD 12 in the above exposure control is controlled by the microcomputer 20 to
As shown in FIG. 4H, the data is written to the first memory 23, and the even-numbered line data is written to the second memory 24 as shown in FIG. Next, as shown in FIGS. 4 (J) and 4 (K), the odd line data of the first memory 23 and the even line data of the second memory 24 are read out twice each. The data is stored in the third memory 25 for the phase adjustment of / 60 seconds. Therefore, FIG.
As can be understood from (L) and (L), the data of the odd lines and the data of the even lines are aligned with the same phase (timing). Each data read out from the memories 25 and 24 in this way is mixed by the mixing circuit 26. In this example, in order to make this possible, FIG.
As shown in (M), the first memory 23 and the second memory 24 are write-protected. Then, pixel mixture conversion is performed during the same period [FIG. 4 (N)], and first, as shown in FIG.
... Addition data of 0 line + 1 line, 2 line + 3 line... Is output, and becomes odd (Odd) field data. Next, the addition data of 1 line + 2 lines, 3 lines + 4 lines... Shown in FIG. 3E is output, and this becomes the even (Even) field data. These field data are stored in the DSP 29
Where the color difference signal (C) and the luminance signal (Y) are formed. These signals are output from the multiplier 29 in FIG.
d, 29g, and here, FIG.
As shown in the above, each signal is multiplied by (1 + α) for a period of two fields from t3 to t5. That is, α is a ratio of the shortage to the required light amount, and the signal output of the ratio α causes the light output Lt at the time of forming a still image [FIG.
(D)] makes it possible to compensate for the insufficient light quantity La. The multiplied color difference signal and luminance signal are supplied to gamma correction circuits 29e and 29h, where gamma correction is performed to reproduce a faithful color on a color TV. The signal amplification for the light quantity shortage by the multipliers 29d and 29g is preferably performed before the gamma correction circuit 46, so that the effect of the gamma correction can be prevented from being diminished. The odd field data output from the DVP 29 is stored in the fourth memory 30 [FIG. 5 (P)], and the even field data is stored in the fifth memory 3.
1 [FIG. 5 (Q)]. Thereafter, the odd field data and the even field data are alternately read out by the switching operation of the switching circuit 32, converted into analog signals by the D / A converter 33, and output to the monitor. An image is displayed by interlaced scanning. As a result, a still image is displayed based on all pixel data obtained during the same exposure, and an image with high quality and optimal brightness can be 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. As described above, according to the present invention,
Forming a video pickup element pixel mix reading system at the output, in the electronic endoscope to form a still image in all <br/> pixel reading scheme, the digital signal processing area of the all-pixel reading scheme
The light-shielding period is set by a multiplier that multiplies the amount of light corresponding to the lack of light due to the response delay of the light- shielding plate operation. Obtain a complete light-blocking state with an endoscope by reading all pixels
Therefore, it is possible to compensate for the shortage of light amount caused by the operation of the light-shielding plate performed before the light-shielding period, and there is an advantage that a still image with good brightness can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an overall configuration of a signal processing circuit of an electronic endoscope according to an embodiment of the present invention. FIG. 2 is a block diagram showing a configuration inside the digital video processor of FIG. 1; FIG. 3 is a diagram showing image data read from the CCD of FIG. 1 to the mixing circuit. FIG. 4 is a diagram showing a still image forming operation in the circuit of FIG. 1; FIG. 5 is an enlarged waveform diagram showing a part of the operation of FIG. 4; FIG. 6 is a diagram illustrating a configuration of a color filter in a conventional CCD and pixel mixture readout. FIG. 7 is an explanatory diagram showing an operation in a conventional CCD. [Description of Signs] 1,12 CCD, 10 scope, 14 light source lamp, 16 freeze switch, 18 CCD drive circuit, 20 microcomputer (control means), 23, 24, 25, 30, 31 memory 26, a mixing circuit, 28, an image switching circuit, 29, a DVP (digital signal processor), 29d, 29g, a multiplier, 35, an aperture, 36, a light shielding plate.

Continuation of the front page (56) References JP-A-63-82619 (JP, A) JP-A-63-290540 (JP, A) JP-A-1-191822 (JP, A) JP-A-2-193633 (JP) JP-A-9-90244 (JP, A) JP-A-10-85174 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) A61B 1/00

Claims (1)

(57) [Claims] 1. Pixels stored in an image sensorsignalUp and down la
Image sensor output that mixes and outputs video signals to form moving images
Pixel mixture readout method and one exposure
Stored signal of all pixelsReadTo form a still image
Electronic endoscope with all-pixel readout methodSignal processing circuitso
So,Read out all pixel signals when selecting the above all pixel readout method
The next field period of the exposure field is the light shielding period
A light-shielding plate that shields light is provided as a gap, and the response delay of this light-shielding plate
The shading plate is moved from just before the shading period in consideration of time.
Light blocking means to make Based on the above all pixel readout method Output from the above image sensor
Digital signal that converts the converted image signal into a digital signal and processes it.
The digital image signal is provided in the
And the light amount associated with the response delay of the light shielding operation by the light shielding means.
An arithmetic circuit that multiplies the amount corresponding to the shortageWhen,Electronic
Endoscope signal processing circuit.