JPH0344276A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To always eliminate an element substantial noise component accurately by closing tentatively the aperture of a lens for each prescribed period regardless of the contrast of an object so as to revise the element substantial noise component. CONSTITUTION:The device is provided with an aperture shut control means 14 closing tentatively the aperture of a lens for each prescribed period regardless of the contrast of an object during the pickup and an element substantial noise component revision means 7 latching the up-to-date element substantial noise component obtained from a solid-state image pickup element 3 while the aperture 13 of a lens 1 is closed with the an aperture shut control means 14. Thus, the element substantial noise component of the solid-state image pickup element (CCD) 3 is always eliminated from the picture signal obtained at long time exposure accurately to improve the picture quality.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a solid-state imaging device having a long exposure function,
In particular, it relates to the removal of background noise in solid-state image sensors.

(Prior Art) In an imaging device using a solid-state imaging device (hereinafter referred to as CCD), in order to image a subject with insufficient illuminance, long-time exposure can be performed to increase the sensitivity of the solid-state imaging device.

FIG. 3 is a block diagram showing an example of a conventional long exposure solid-state imaging device of this type. The subject image focused by the lens 1 has its light amount adjusted by the diaphragm 13, and then passes through the optical low-pass filter 2 and forms an image on the CCDB.

The CCD 3 photoelectrically converts the optical image using a drive signal from the CCDNA moving N and outputs the obtained signal to the matrix circuit 4 . The matrix circuit 4 creates a luminance signal Y, color difference signals RY, BY from the input signals, and outputs these image signals to the A/D conversion circuit 5. A/
The D conversion circuit 5 digitizes the input image signal and outputs it to the image memory 6 and the background noise memory 7.

Here, when the aperture 13 of the lens 1 is closed before imaging, the A/D conversion circuit 5 outputs the ground noise signal component of the CCD 3, so this is stored in the ground noise memory 7. During the period when the aperture 13 of the lens L is automatically controlled by the aperture control circuit 14 to the aperture according to the brightness of the subject after the start of the image processing, the A/D conversion circuit 5 outputs the image signal. , this image signal is temporarily stored in the image memory 6. The arithmetic circuit 8 subtracts the background noise signal component read out from the background noise memory 7 from the image signal read out from the image memory 6, and outputs the result to the D/A conversion circuit 9. The D/A conversion circuit 9 converts the input digital signal into an analog signal, and sends the analog luminance signal Y and the analog color difference signals R-Y, B-Y to the encoder circuit 1.
Output to 0. The encoder circuit 10 creates a video signal from the input luminance signal and color difference signal and outputs it.

The synchronization signal generation circuit 12 outputs various synchronization signals to a matrix circuit 4, an A/D conversion circuit #I5, an image memory 6, a background noise memory 7, an arithmetic circuit 8, a D/A conversion circuit 9, an encoder circuit 10, The signal is supplied to the CCD drive circuit 11 and the aperture control circuit 14 to adjust the operation timing of each circuit.

FIG. 4 is an example of an operation time chart of the conventional solid-state imaging device described above. (A> is when no long exposure is performed.
This shows a normal pulse (hereinafter referred to as a field shift pulse) that transfers a signal charge from the photoelectric conversion section 31 of the CCD 3 shown in FIG. 5 to the vertical transfer section 32. However, 21 indicates the vertical scanning period. (B) shows the field shift pulse when performing long-time exposure, (C) shows the output signal from the CCD when performing long-time exposure, and (D) shows the video signal when performing long-time exposure. ing.

When performing long-time exposure, the solid-state imaging device performs exposure for >n light during the period 22 shown in FIG. I am getting an output signal.

Incidentally, when the above-mentioned four-field exposure is performed, the sensitivity becomes four times as high as in the normal case. However, the output signal of the CCD 3 shown in FIG. 4(C) is output once every several fields. Therefore, the period 2 in which there is no output signal from the CCD 3
6, for example, the luminance signal and color difference signal obtained from the output signal a' of the CCD 3 are stored in the memory 6, and the video signal X as shown in FIG. 4 (D>) is generated from the stored luminance signal and color difference signal. Memory interpolation is performed by creating and outputting for a period 22. However, in the solid-state imaging device that performs long exposure using the method described above, the background noise of the CCD 3 becomes noticeable and the image quality deteriorates. The memory 7 and the arithmetic circuit 8 are used to remove background noise.

Here, to reconstruct this ground noise removal method, the aperture 13 is closed in advance before imaging, the ground noise component obtained from the CCD 3 is stored in the memory 7, and the image signal a' obtained after the start of imaging is stored in the memory 7. By storing them in the image signal a' and calculating them in the arithmetic circuit 8, the background noise signal component is removed from the image signal a'. However, the dark current of the CCD 3, which causes background noise, changes depending on the temperature and also on the exposure time, so the background noise changes depending on the time of power-on, the time of use, and the usage conditions. Therefore, with the conventional method of sampling the background noise only once before use, it is not possible to accurately remove the background noise component from the image signal at the time of use, and the disadvantage is that image quality may deteriorate in some cases. was there.

(Problems to be Solved by the Invention) As described above, in the method of subtracting the COD background noise from the image signal used in the conventional long-exposure solid-state imaging device to prevent image quality deterioration of the video signal, Since the image signal is sampled only once before imaging, there is a drawback that if the background noise changes depending on usage conditions or the like, the background noise component cannot be accurately removed from the image signal.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned drawbacks, and aims to provide a solid-state imaging device that can always accurately remove COD background noise components from image signals obtained during long-time exposure.

[Structure of the invention]

(Means for Solving the Problems) The present invention has a long-time exposure function that reads out signal charges accumulated over several field periods in a photoelectric conversion section of a solid-state image sensor in one field period, and a lens A function of retaining the base noise component obtained from the solid-state image sensor when the aperture of the lens is closed, and removing the retained base noise component from the image signal obtained from the solid-state image sensor when the aperture of the lens is open. In the solid-state imaging device, the aperture closing control means temporarily closes the aperture of the lens at predetermined intervals during imaging, regardless of the brightness of the subject, and the aperture of the lens is closed by the one-chain aperture control means. and a background noise updating means that holds the latest background noise obtained from the solid-state image sensor during the period of time.

(Function) In the solid-state imaging device of the present invention, during imaging, the aperture closure control means temporarily closes the aperture of the lens at predetermined intervals regardless of the brightness or darkness of the subject. The ground noise updating means holds the latest ground noise obtained from the solid-state image sensor during a period when the aperture of the lens is closed by the aperture closure control means.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings, in which the same parts as those of the conventional example are denoted by the same reference numerals. FIG. 1 is a block diagram showing an embodiment of the solid-state imaging device of the present invention. 1 is a lens that forms an optical image of the subject, 2 is an optical low-pass filter that removes high frequency components from the optical image focused by lens 1, 3 is a COD that photoelectrically converts the optical image, and 4 is output from CCD 3. A matrix circuit that creates a luminance signal Y and color difference signals R-Y, B-Y from the signals; 5 is an A/D conversion circuit that converts the analog image signal output from the matrix circuit 4 into a digital signal; 6 is an image signal 7 is a background noise memory that stores the background noise component; 8 is an arithmetic circuit that subtracts the background noise component from the image signal; 9 is a digital video signal output from the arithmetic circuit 88 as an analog video signal Convert to D/A
Conversion circuit, 10 is luminance signal Y, color difference signal R-Y, B-Y
11 is a CC encoder circuit that creates a video signal from
A CCD drive circuit that generates a drive signal for driving D3, 1
2 is a synchronization signal generation circuit that generates various synchronization signals for operating the device; 13 is an aperture that adjusts the amount of light collected by the lens 1; and 14 is an output of the opening degree of the aperture 13 from the D/A conversion circuit 9. A diaphragm control circuit performs control based on the brightness signal Y, and 15 is a control circuit that performs control for sampling background noise of the CCD 3.

Next, the background noise sampling operation of the CCD 3 of this embodiment will be explained. The optical image formed on the CCD 3 by the lens 1 is photoelectrically converted here, and then separated into a luminance signal Y, color difference signals R-Y, B-Y by the matrix circuit 4, and these signals are further converted into A/ The data is digitized by the D conversion circuit 5 and output to the memories 6 and 7.

Here, FIG. 2 is a diagram showing an example of an operation time chart of the solid-state imaging device described above. (A) shows the field shift pulse output from the CCD drive circuit 11 during normal operation, (B) shows the field shift pulse output from the CCD drive circuit 11 during long exposure, and (C) shows the field shift pulse output from the CCD drive circuit 11 during long exposure. (D> indicates the output signal from the CCD 3 during long exposure, (E)
indicates the video signal output from the encoder circuit 10 at that time. Incidentally, FIG. 2 shows a long-time exposure operation when exposure is performed four times as much as normal.

During long exposure, the CCD drive circuit 11 applies field shift pulses to the CCD 3 at the timing shown in FIG. 2(B).
Output to. The CCD 3 performs long-time exposure using the photoelectric conversion section 31 shown in FIG. 5, and during the period when the aperture 13 is open, image signals a and b are output every four fields as shown in FIG. 2(D).

At this time, memory interpolation is performed using the memory 6 from the image signals a and b, and the encoder circuit 10 outputs video signals A and B as shown in FIG. 2(E).

By the way, the control circuit 15 completely closes the diaphragm 13 via the diaphragm control circuit 14 during a period (between 4 fields) 23 as shown in FIG.
In order to output the background noise signal C as shown in
A corresponding ground noise signal is obtained from the conversion circuit 5, and
This is stored in the memory 7. The control circuit 15 is shown in FIG.
During the period 24 shown in C), the aperture control circuit 14 is operated normally, an image signal corresponding to the subject is obtained from the A/D conversion circuit 5, and this is stored in the memory 6.

During this time, the arithmetic circuit 8 subtracts the background noise signal read from the memory 7 from the image signal read from the memory 6,
The D/A conversion circuit 9 converts the image signal containing no background noise components into the D/A conversion circuit 9.
Output to. That is, since the arithmetic circuit 8 subtracts the ground noise signal from the image signals d, e, f, g, h, i, and j shown in FIG.
It outputs video signals E, F, G, H1, and J as shown in . The control circuit 15 periodically closes the aperture 13 as described above every few fields and stores the C0D3 base noise signal at that time in the memory 7.
The base noise signal that the arithmetic circuit 8 subtracts from the image signal is
It always depends on the state of the CCD 3 at that time.

According to this embodiment, the control circuit 15 samples the ground noise signal of the CCD 3 every few fields and stores it in the memory 7, and the arithmetic circuit 8 samples the background noise signal of the CCD 3 and stores it in the memory 7.
Since the background noise signal is subtracted from the image signal using the background noise signal according to the state of the CD3, it is possible to always accurately subtract the background noise signal from the image signal, regardless of the operating temperature of the CCD3 or the length of the exposure time. Yes, the image signal C
The background noise component of CD3 can be completely removed. Therefore, deterioration in the image quality of the video signal due to the mixing of the background noise component can be completely prevented.

〔Effect of the invention〕

As described above, according to the solid-state imaging device of the present invention, CCD background noise components can always be accurately removed from image signals obtained during long-time exposure.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the solid-state imaging device of the present invention, FIG. 2 is an operation time chart of the device shown in FIG. 1, and FIG. 3 is an example of a conventional solid-state imaging device. FIG. 4 is a block diagram showing an operation time chart of the device shown in FIG. 3, and FIG. 5 is a block diagram showing an example of a detailed configuration of the CCD shown in FIG. 1 or FIG. 3. 3...CCD 4...Matrix circuit 6.7...Memory 8...Arithmetic circuit 10...Encoder circuit 14...Aperture control circuit 15...Control circuit

Claims (1)

[Claims] It has a long exposure function that reads out signal charges accumulated over several field periods in the photoelectric conversion section of the solid-state image sensor in one field period. In a solid-state imaging device, the solid-state imaging device has a function of retaining a background noise component that is generated by the lens and removing the retained background noise component from an image signal obtained from the solid-state image sensor while the aperture of the lens is open. an aperture closing control means that temporarily closes the aperture of the lens for each period regardless of the brightness or darkness of the subject; and an aperture closing control means that obtains the latest image from the solid-state image sensor during a period in which the aperture of the lens is closed by the aperture closure control means. What is claimed is: 1. A solid-state imaging device comprising: a base noise updating means for retaining noise.