JP3210566B2 - Solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a solid-state imaging device using a solid-state imaging device such as a charge-coupled imaging device (hereinafter, referred to as a CCD imaging device).

[0002]

2. Description of the Related Art A solid-state imaging device using a CCD imaging device has been used as an image information input device for various systems in various fields because of its features such as low cost, small size, light weight, and easy handling. “Sensitivity” is one of the performances of television cameras. However, television cameras used for surveillance and other purposes often have poor lighting conditions for subjects, which is more than 10 times that of ordinary indoor use. More than double sensitivity is required. As one of the methods for high sensitivity,
There is a method in which the light accumulation time in a photodiode, which is a photoelectric conversion unit on a CCD image sensor, is ten times or more in accordance with the degree of increasing sensitivity.

FIG. 7 is a diagram for explaining the timing of reading out signal charges stored in the photodiode of the CCD image pickup device. FIG. 7A shows an example of a vertical blanking pulse, and FIG. 7B shows an example of a charge readout pulse during normal imaging, in which signal charges are read out from a photodiode for each field. FIG. 13C shows another example of the charge readout pulse, in which the signal charge is read out from the photodiode once every four fields.

When the signal charges are read out at the timing shown in FIG. 1C, the light sensitivity is quadrupled. In this case,
In order to maintain the continuity of the playback image as a frame image,
An image pickup signal read from the CCD image pickup device is taken into a memory in the course of signal processing. In a field having no charge readout pulse, a process of reading and reproducing an image signal from the memory is generally performed.

[0005] In the method of improving light sensitivity used in the above-described solid-state imaging device, the following problems in image quality occur. That is, the higher the sensitivity, the longer the interval between the charge readout pulses. If the subject moves during this time, the outline of the reproduced image becomes unclear, and the image becomes a trailing image as an afterimage phenomenon, making the image unsightly.

[0006]

As described above, in the conventional solid-state imaging device, if the sensitivity is increased, the processing is performed with a longer interval for reading out the signal charges accumulated in the photodiode. The outline of the reproduced image becomes unclear, and the image becomes a trailing image as an afterimage phenomenon, making the image unsightly. That is, the motion resolution characteristic deteriorates.

Accordingly, the present invention provides a solid-state image pickup device capable of effectively suppressing the deterioration of the motion resolution characteristic even when the subject moves or pans or tilts while operating in the high sensitivity mode. The purpose is to provide.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention reads out a signal from a photoelectric conversion unit in accordance with the amount of movement of a subject output from a motion detection unit for detecting the movement of the subject. The first light sensitivity adjusting means for adjusting the light sensitivity performance by controlling the interval adds the ratio contributing to the light sensitivity performance and the pixel signal in one field (or frame) in units of a predetermined number of pixels. The second light sensitivity adjusting means for adjusting the light sensitivity performance changes the ratio contributing to the light sensitivity performance.

According to such means, it is possible to prevent the motion resolution characteristic from deteriorating at the time of high-sensitivity imaging, and to effectively improve the motion resolution characteristic of the solid-state imaging device according to the amount of movement of the subject while maintaining the high sensitivity characteristic. Can be improved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. The optical information collected by the imaging lens 11 forms an image on the imaging surface of the CCD imaging device 12. The CCD image pickup device 12 is driven by a drive pulse from a CCD drive circuit 13 that operates based on a pulse output from a pulse generation circuit 14.

Referring now to FIG. 2, the CCD image pickup device 1
2 will be described. This CCD image sensor 12
Is, for example, about 500 pixels in the vertical direction and about 80 pixels in the horizontal direction.
An array in which 0 pixels are arranged is used. And one vertical transfer CCD for television interlace
Two photodiodes 31 and 32 correspond to 35, and the signal charges accumulated in the photodiode 31 are sent to the vertical transfer CCD 35 via the read gate 33 during the vertical blanking period. Similarly, the signal charges accumulated in the photodiode 32 are read by the read gate 34.
Through the vertical transfer CCD 35. One more
The vertical transfer CCD 35 as one cell has four electrodes 36.
To 39, but each electrode has four terminals V1
To V4, to which four-phase vertical transfer pulses φV1 to φV4 are supplied, respectively. These vertical transfer pulses φV1 to φV4 are output from the CCD drive circuit 13 described above. At this time, for example, the first or third electrode 36, 38
When a pulse having a voltage level of VFS (field shift pulse) is applied to the corresponding photodiodes 32 and 31,
Can be read out to the vertical transfer CCD 35. In the first field of one frame, for example, signal charges of lines 1, 2,... Shown in FIG. 2 are read out, and in the second field, lines 264, 26
.. Are read out.

Further, the signal charges sent to the vertical transfer CCD are sequentially transferred in the vertical direction using a horizontal blanking period. Then, the signal charges transferred to the last stage of the vertical transfer CCD are simultaneously transferred to the horizontal transfer CCD 40 during the horizontal blanking period.

The horizontal transfer CCD 40 has two terminals H
1, H2. Terminals H1 and H2 are supplied with two-phase horizontal transfer pulses φH1 and φH2 from the CCD drive circuit 13. As a result, the signal charges are sequentially transferred in the horizontal direction, and the signal charges are converted into voltages by the output unit 41 and are taken out.

Returning to FIG. 1, the description will be continued. An image pickup output signal from the CCD image pickup device 12 is amplified to a predetermined level by a preamplifier 15 and then amplified by a camera process circuit 16.
To perform normal camera signal processing such as so-called gamma correction.

In the camera process circuit 16, the input signal is converted into a digital signal and a part of the input signal is written into the frame memory 17, and before that, the input signal is written into the frame memory 17 as a video signal of the immediately preceding frame. The video signal is written to the frame memory 18. Output signals of the frame memories 17 and 18 are input to a motion vector detection circuit 19. Also, the frame memory 17
Are also input to the pixel addition circuit 20.

The motion vector detecting circuit 19 detects an image motion vector using the video signals from the two frame memories, and sends the result to the microcomputer, that is, the system control unit 21. The system control unit 21 controls the interval of reading image signals from the photodiodes, that is, the interval of field shift pulses, and the number of pixels to be subjected to pixel addition in accordance with the input motion vector.

According to this control, the pixel addition circuit 20 performs pixel addition within a predetermined neighboring pixel of each pixel to increase the video signal level, and then inputs the video signal level to the camera process circuit 16. In order to maintain continuity of the reproduced image as a frame image, in a field without field shift and no pulse, a process of reading and reproducing an image signal from a memory is performed. Then, the final video signal is output from the output terminal 22.

The operation of the above embodiment will be further described. Now, consider the case where the sensitivity setting of the camera is 16 times the normal value. When the subject is at rest, the system control unit 21 sets the readout interval of the image pickup signal from the photodiode on the CCD image pickup device 12, that is, the interval of the field shift pulse to 16 times, and the pixel addition circuit 20 No addition is performed. Next, when the amount of motion of the subject gradually increases and the amount of motion from the motion vector detection circuit 19 exceeds a predetermined value, the system control unit 21 shortens the interval of the field shift pulse, thereby reducing the sensitivity. The decrease in the video signal level due to the above is compensated for by pixel addition, and control is performed so as to maintain the target 16-fold higher sensitivity, which is now the objective. For example, the interval between the field shift pulses is set to four times the normal value, and the number of pixel additions is set to four pixels. The interval of the field shift pulse is 16
Since the time is shortened from 2 times to 4 times, the phenomenon that the outline of the subject becomes unclear on the reproduced image and the afterimage phenomenon of the moving subject are reduced.

FIG. 3A shows a vertical blanking pulse V
BLK and vertical transfer pulses φV1 to φB4 are shown. φV1 and φV3 have levels of VFS, VH and VL.
The value pulses φV2 and φV4 are binary pulses having levels VH and VL. By applying a field shift pulse FS3 of level VFS as φV3 to the third electrode V3 shown in FIG. 2, a signal of the first field in one frame can be read from the photodiode as shown in FIG. . Similarly, a field shift pulse FS1 of level VFS is set as φV1 and the first electrode V1 in FIG.
, The signal of the second field in one frame can be read from the photodiode.

The vertical transfer pulses φV1 to φV4 include a pulse P1 for vertically transferring signal charges in each vertical transfer CCD in units of one transfer stage in a horizontal blanking period (omitted in FIG. 3). Similarly, the pulse P2
Similarly to P1, the pulse is transferred in the vertical direction in units of one transfer stage within the horizontal blanking period. However, since two types of field shift pulses FS1 and FS3 are generated only every eight fields, the signal charge is not applied during this period. Has not transferred. For comparison, FIG. 3B shows a timing chart of the vertical transfer pulse in the normal operation without increasing the sensitivity.

In FIG. 3B, the same parts as those in FIG. 3A are denoted by the same reference numerals. It can be seen that the interval between the field shift pulses in FIG. 7A is four times the interval between the field shift pulses in FIG.

As described above, the field shift pulse F
The video signal of the first field read out from the photodiode in S3 is vertically transferred one after another by the transfer pulse P1 following the transfer, and the horizontal transfer CCD 40 shown in FIG.
And output from the CCD imaging device 12 via the output unit 41. The digital signal is input to the camera process circuit 16 through the preamplifier 15 shown in FIG. In the subsequent vertical blanking period, the imaging signal of the second field read by the field shift pulse FS1 is vertically transferred one after another by the subsequent transfer pulse P1, and is similarly written into the frame memory 17. The video signal for one frame is stored in the frame memory 17.
The video signal (eight fields before) previously written to the frame memory 17 is transferred to the frame memory 18 prior to the operation of writing to the frame memory 18.

In accordance with the timing at which the contents of the frame memory are updated, the frame memories 17 and 1
The motion vector of the subject is calculated by the motion vector detection circuit 19 using the video signal 8. The system control unit 21 controls the signal charge readout interval from the photodiode and the pixel addition number in accordance with the detected amount of motion, and the motion of the subject decreases when the amount of motion is smaller than a first predetermined value. Then, the interval between the field shift pulses is controlled to shift to a longer one, and the control is performed in a direction to reduce the number of pixel additions in order to maintain the final sensitivity. Conversely, when the motion amount is equal to the second predetermined value (first predetermined value <
If it is larger than (the second predetermined value), it is determined that the subject is moving greatly, and the interval of the field shift pulse is controlled to be shorter this time and the direction of increasing the pixel addition number is controlled. When the motion amount is between the first predetermined value and the second predetermined value, control is performed such that the current state is maintained for the field shift pulse interval and the number of added pixels.

FIG. 4 is a diagram showing an example of a combination in the case of performing pixel addition. Now, as shown in FIG. 4A, lines 1 (hereinafter, referred to as L1), L264, L2, L26
.., A line continues, and each line has a pixel 1 (hereinafter, D
1), D2, D3, D4,... At this time, the combination of pixel addition is (L1D1 + L1D2 + L264D1 +) in the (2k + 1) th (k = 0, 1, 2,...) Field as shown in FIG.
L264D2), (L1D2 + L1D3 + L264D2
+ L264D3),..., (L2D1 + L2D2 + L26
5D1 + L265D2), (L2D2 + L2D3 + L2
65D2 + L265D3), and so on.
Here, for example, “L1D1” means pixel 1 on line 1, and so on. On the other hand, as shown in FIG.
In the (2k) (k = 0, 1, 2,...) Field,
(L264D1 + L264D2 + L2D1 + L2D
2), (L264D2 + L264D3 + L2D2 + L2
D3),..., (L265D1 + L265D2 + L3D1)
+ L3D2), (L265D2 + L265D3 + L3D
2 + L3D3),...

In general, when an addition operation is performed using neighboring pixels, the operation is performed as a low-pass filter, so that the resolution is deteriorated. However, the deterioration of the resolution can be reduced by shifting the combination of addition as described above. .

As described above, in the above-described embodiment, in the solid-state imaging device capable of adjusting the light sensitivity performance by controlling the interval at which the signal from the photodiode is read, the motion detecting section 19 for detecting the motion of the subject. The first light sensitivity adjustment means for adjusting the light sensitivity by controlling the interval at which the signal from the photodiode is read out in accordance with the amount of movement of the subject output from the device contributes to the light sensitivity performance, Alternatively, the second light sensitivity adjusting means for adjusting the light sensitivity performance by adding the pixel signals in a frame) in units of a predetermined number of pixels changes the ratio contributing to the light sensitivity performance.

The position of the optical center of gravity determined by the combination of pixels to be added is switched at a predetermined cycle by switching the combination of pixels for performing the above-described pixel addition for each field (or frame).

This means that even when the solid-state imaging device is operated in the high-sensitivity mode, the ratio of the two means for increasing the sensitivity is changed in accordance with the amount of movement of the subject. It is possible to effectively suppress the degradation of the resolution characteristic due to the moving image such that the outline of the reproduced image becomes unclear or reproduced as an afterimage phenomenon. Further, since the combination of pixels for pixel addition is switched for each field (or frame), deterioration in resolution can be reduced while maintaining high sensitivity characteristics.

Although an example of four-pixel addition has been described with reference to FIG. 4, the present invention is not limited to this method. FIG. 5 shows another pixel addition method. Like FIG. 4, FIG. 5 (A) shows the line of the base line and the arrangement of pixels, and FIG. 5 (B) shows the (2k +
1) (k = 0, 1, 2,...) Indicates a combination of field addition. Line 1 in FIG. 2B is the same as FIG.
(D1 + D2 + D3 + D4) is the first pixel, (D2 + D3 + D4 + D5) is the second pixel, etc. from each pixel of line 1 of.
Thus, the optical centroid of the combination of addition is shifted by one pixel in the horizontal direction and the addition is performed, and the following lines and each line in FIG. In the example shown in FIG. 5, similarly to the example in FIG. 4, when the sensitivity is increased by the pixel addition, the deterioration of the resolution can be reduced.

FIG. 6 shows a program processing procedure constructed in a microcomputer inside the system control unit 21 according to another embodiment. The image signals of the frame memories 17 and 18 are compared with each other to determine whether or not there is any image motion, and an average motion vector for one entire screen is obtained (step S).
1 to S5). When the motion vector V is obtained, the threshold values Th1 and Th2 are compared with the motion vector V (where Th1 <Th2). When V <Th1, it is regarded as a still image, and the interval between the field shift pulses FS is increased. When V> Th2, it is regarded as a moving image, and the number of pixel additions is basically increased and the FS pulse interval is shortened. Here, if the setting is to obtain N times higher sensitivity, n1 times higher sensitivity can be obtained by increasing the number of added pixels.
Assuming that a high sensitivity of n2 times can be obtained by shortening the S pulse interval, the adjustment ratio of both is calculated in advance so that n1 * n2 = N. This setting is, for example, R
This is possible by storing the adjustment data in the AM. The present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the gist of the present invention.

[0031]

As described above, according to the present invention, even when the solid-state imaging device is operated in the high sensitivity mode, the ratio of the two means for increasing the sensitivity is changed according to the amount of movement of the subject. Therefore, even in the case of a moving subject, it is possible to effectively prevent the outline of the reproduced image from being blurred and the degradation of the motion resolution characteristic from being reproduced with a trail due to an afterimage phenomenon. Is done. Further, since the combination of pixels for pixel addition is switched for each field (or frame), deterioration in resolution can be reduced while maintaining high sensitivity characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a solid-state imaging device.

FIG. 3 is a timing chart shown for explaining an operation example of the imaging apparatus of FIG. 1;

FIG. 4 is an operation explanatory diagram of the imaging device of FIG. 1;

FIG. 5 is another operation explanatory view of the imaging device in FIG. 1;

FIG. 6 is a diagram showing the operation of another embodiment of the present invention.

FIG. 7 is a timing chart shown for explaining the operation of the conventional imaging apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Imaging lens 12 ... CCD imaging device 13 ... CCD drive circuit 14 ... Pulse generation circuit 15 ... Preamplifier 16 ... Camera process circuit 17, 18 ... Frame memory 19 ... Motion vector detection circuit 20 ... Pixel addition circuit 21 ... System control part.

────────────────────────────────────────────────── ─── Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/335 H04N 5/232-5/243

Claims (3)

(57) [Claims] 1. A solid-state imaging device capable of adjusting light sensitivity performance by controlling an interval at which a signal is read from a photoelectric conversion unit. The rate at which the first light sensitivity adjustment means adjusts the light sensitivity performance by controlling the interval at which the signal is read from the photoelectric conversion unit contributes to the light sensitivity performance, and the pixel signal within one field (or frame) is determined. A solid-state imaging device characterized in that a second light sensitivity adjusting unit that adjusts light sensitivity performance by adding the light sensitivity performance in units of a predetermined number of pixels changes a ratio contributing to the light sensitivity performance. 2. The light sensitivity adjusting means for adjusting the light sensitivity performance includes switching a pixel combination for adding a pixel signal in units of a predetermined number of pixels for each field (or frame). 2. The solid-state imaging device according to claim 1, wherein a position of an optical center of gravity determined by a combination of the pixels to be added is switched at a predetermined cycle. 3. A drive circuit for applying a signal readout pulse in field units to a photoelectric conversion unit, a processing circuit for performing pixel-by-pixel processing of an image pickup signal read from the photoelectric conversion unit,
A system control unit, wherein the system control unit controls the signal readout pulse interval of the photoelectric conversion unit and the number of pixel additions in the processing circuit according to an image motion amount obtained using the imaging signal. In this case, when the amount of image motion is smaller than the first predetermined value, it is determined that the motion of the subject is decreasing, and the signal readout pulse interval is controlled to shift to a longer one, and In order to maintain the final sensitivity, control is performed in the direction of decreasing the number of pixel additions. When the amount of image motion is larger than a second predetermined value (first predetermined value <second predetermined value), the subject becomes larger. It is determined that the image is moving, the interval between the signal readout pulses is controlled to be shorter, and the number of pixel additions is controlled to be increased, and the amount of image motion is equal to the first predetermined value and the second predetermined value. If it is in the middle, read the signal The solid-state imaging device according to claim 1, wherein the interval between the output pulses and the number of pixel additions maintain the current state.