JPS63246985A - Image pickup system for electronic camera - Google Patents

Abstract

PURPOSE:To obtain a picture signal with a superior S/N even when an ambient temperature is high and a shutter time is long, by reading out an image pickup signal for several times separately so that a sum of noise charge and signal charge does not exceed the capacity of a charge accumulation part, and generating the picture signal finally by accumulating the image pickup signal 7 accumulated at every time. CONSTITUTION:When a time T set on a shutter is larger than a prescribed value, the time T is divided by a divisor N(N>=2), and a noise signal being generated before the opening operation of the shutter is accumulated. And after the time T/N of the opening operation of the shutter, a first image pickup signal is fetched, and the noise signal is subtracted from the first image pickup signal, and a subtracted signal is stored in a first memory 11, and furthermore, after the time T/N, a second image pickup signal is fetched, and the noise signal is subtracted from the second image pickup signal. Such operation is repeated for the number(N) of times of division, and after the closing operation of the shutter, the image pickup signal accumulated in the first memory 11 is accumulated in a second memory 12. In such a way, it is possible to obtain a still picture scarcely affected by a dark current.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention 1 (Field of Industrial Application) The present invention relates to an imaging system for an electronic camera that captures and records still images using a solid-state imaging device.

(Prior art) An imaging device using a solid-state imaging device consisting of COD+MO8, etc. has already been used as a video camera for moving pictures (stage).
C It has been made into a joke. Recently, this solid-state image sensor is used to capture still images. So-called electronic cameras are attracting a lot of attention.

- In the case of a video camera, the exposure time of the photosensitive surface is usually a constant r# period corresponding to one claim or one field of television photography, and is constant at ]/30 seconds or 1/60 seconds. . In contrast, the secondary camera uses a shutter, similar to conventional film-based cameras, and its exposure time varies over a wide range from several tens of seconds to several tenths of a second. For this reason, dark current, which was not much of a problem with video cameras, comes into play.

In other words, a solid-state image sensor emits light like a photodiode! A photosensitive surface is constructed by two-dimensionally arranging pixels consisting of conversion elements, and each pixel generates charges due to thermal excitation as noise in addition to signal charges caused by incident light. A current based on noise charges caused by this thermal excitation is called a dark current, and is a factor in reducing the S/N of the output image signal.

This dark current increases exponentially depending on the ambient temperature, and also increases in proportion to the charge accumulation time.

Therefore, especially when the ambient temperature is affected and the shutter time is long, the S/N reduction due to dark current becomes a serious problem, and in extreme cases, there is only dark current and no image signal can be extracted.

(Problem to be solved by the invention) As shown above, the occurrence of a dark stream that increases exponentially with the ambient temperature and increases in proportion to the charge accumulation time is a problem caused by the S/N of the image. causing a decline in.

Furthermore, failure may even occur if the image signal cannot be extracted.

The purpose of the present invention was to solve the above problems and to provide an electronic camera imaging method that can output a still image signal that is less affected by dark current, regardless of button changes or shutter time. It's all about providing.

[Structure of the invention]

(Means for Solving the Problems) The present invention captures and records still images using a solid-state image sensor having a photosensitive surface configured by two-dimensionally arranging pixels that accumulate electric charge according to the amount of incident light. In the imaging system of electronic cameras, the shutter is set before opening the shutter, which is placed in front of the photosensitive surface.

If the evening time is longer than a certain value, it divides the time so that it falls within a certain value, accumulates the noise signal that occurs independently of the incident light on the photosensitive surface, and opens the shutter for the set shutter time. , after a period of time when the signal charge caused by the light from the subject is accumulated on the photosensitive surface and divided.

Stop the signal charge ii! Read out as i7 image signal,
A still image signal is obtained by subtracting the noise signal from this still image signal, the noise signal is removed, and the still image signal is stored in the first memory, and the second signal charge is read out after one division after the first signal readout. is read out as a still image signal, the noise signal is subtracted from this still image signal, and the noise signal is removed.
The still image signal and the NYT button 1 already stored in the first memory.
The still image signal of the third time is added and the image is stored in the first memory again. The above operation is repeated according to the number of divisions, and the finally stored still image signal in the first memory is transferred to the second memory.

For example, it is recorded on a memory card.

(effect) Basically, the purpose is to reduce the influence of dark current.

By subtracting from the still image signal a noise signal caused by the same amount of noise charge as the small amount of noise charge that accumulates during imaging, the noise signal is always
/N, but if the ambient temperature is high and the shutter time is long, the dark current will increase significantly after subtracting the noise signal and the charge accumulation in one pixel or transfer section will increase. If this noise charge is accumulated in the part and the signal charge is not accumulated sufficiently, the image pickup signal is read out several times so that the noise charge and the signal charge do not exceed the capacity of each charge storage section, and the image pickup signal of each time is read out. are accumulated to form the final image signal.Thus, even if the ambient temperature is high and the shutter time is long, a good image signal of 8/N can be obtained.

(Example) An embodiment of the present invention will be described below in detail with reference to the drawings.

Figure 1 shows the entire configuration of an electronic camera according to a sister example of the present invention.

In the figure, light 1 from the subject is offset by 2 degrees from the imaging lens 3
The light is guided to the solid-state image sensing device 5 via a built-in shutter 4 and the like. The shutter 4 may be mechanical or may be a so-called optical shutter whose transparency can be changed by external control.

As the solid-state image sensor 5, for example, a known interline transfer type COD image sensor as shown in FIG. 2 is used. This photographic element consists of a two-dimensional array of pixels 2 consisting of photoelectric conversion elements such as photodiodes to form a photosensitive surface 22, which accumulates charges in each pixel 21 according to the edge of the incident light. The electric charge Fm 23 Vc is vertically transferred by the electric charge shift pulse Ps, and is outputted as an electric signal (image signal) from the output circuit 25 via the horizontal transfer section 24. In addition, the generated charge of each [1i7 element 21 is
Actually, charges are transferred by sequentially changing the depth of the potential well by changing nl accumulated in the potential well below it and by changing the transfer lock pulses Pv and Ph of the transfer section 23, 24+-1.

After the output signal of the solid-state image sensor 5 is amplified by an amplifier 6, a clamp circuit 7 clamps the potential of, for example, a horizontal blanking level to a constant value, and the signal is digitized by an A/D converter 8. The output of the p,/D converter 8 is input to a digital subtracter 9 that subtracts the image signal and the noise signal from the memory for storing noise signals. 10 and the output is stored in memo 1312. Further, the output of the memory 12 serves as another input to the digital subtracter 10, and is also input to a digital memory for transmission, such as a memo I/J output 13.

The timing control circuit 15 also controls the shutter button 16.
This is a circuit that controls the operation of each part based on signals from the camera and information on automatically or manually set tl, shutter speed, aperture value, etc.

The imaging operation in this actual cutting example will be described below with reference to the time chart of FIG. 3.

When capturing a still image, first, the brightness of the subject is measured using a photometer (not shown), and based on the brightness, the aperture value and shutter speed are determined, for example, manually.

Let t be the signal readout time of all pixels of the image sensor 5, and let T be the shutter time set above. Then, compare this T with a constant (Ill, (2t)) and find '1'
If <2t, N=1, that is, no division, and if T≧2t, t
Calculate N (≧2) such that ≦−<2t, and divide all of this T so that the shutter time falls within a constant value. In other words, the above N indicates the number of divisions.

Next, press the button 16 to remove unnecessary residual charges from the pixels of the solid-state image sensor 5 and the transfer section.
17) 74-old shift pulse p day 1 shown in FIG.
is supplied to the solid-state image sensor 5, the residual charge of each pixel 21 is transferred to the vertical transfer section 23, and further transferred to the vertical transfer section 23 and the horizontal transfer section 24. Lock pulses Pn and Pu'i are supplied to each pixel 21 and The electric charges in the transfer portions 23 and 24 are discharged to the outside.・Figure 13 shows the case where this residual charge is swept away once, but if the residual charge is swept away insufficiently, the above-mentioned sweep-out method may be used. During this operation, the clock pulse Spl f is not supplied to the vi% A/D 8, and no subsequent equalization processing is performed.

Next, the first field shift pulse P82 ends and the second field shift pulse P82 is supplied to the solid-state image sensor 5 after the T/N second time period has elapsed.

As a result, each pixel 21 (f) is accumulated in T,/N seconds.
' The noise charge is read out and transferred cock pulse Pn
.

Due to Pu, the dark current data (not including the transfer section) of the solid-state image sensor 5L is output as a noise signal. 'd in Figure 3
This dark current data shows the case of N=2. After the end of the second field shift pulse P62 stored in the memory 11 via the A/D converter 8, the shutter 4 opens and charges are accumulated in each pixel 21 from the object (signal ' due to optical input). T/N thinning, the third field pulse Ps3 is supplied, the signal charge is transferred to the vertical transfer section 23, and the first still image one-image signal is output from the solid-state image sensor 5. This still image signal is A/D
After conversion, it is input to a digital subtracter 9. At the read timing of each pixel signal, the dark current data stored before the memory 11 is read out, and the digital subtracter 9
to use human power. A subtractor 9v'i, the first silence: subtract the dark current data from the elephant signal, and digital 7J [lx unit 1
Enter o. When reading for the first time, nothing is 7JI]
The output data of the subtracter 9 without X is output to the adder 10. This output is stored in memory 12. T/N seconds mi after the end of the third field shift pulse Pa3
4 field shift pulse P84 is supplied to the solid-state image sensor 5, and the second readout is performed. - At the same time as the sword Ps4 is supplied, the shutter 4 is closed. Similar to the first signal readout, the second still image signal is A/
Memo II after D conversion 11 data money subtraction digital 71
It is supplied to a zero calculator 10. 7J11 The input of the X device 1O becomes the data of the memory 12. The read timing of the memory 12 is made to match the read timing of each pixel signal, and the first still image signal and the second still image 1#I are
The signals are added by the signal adder 10 and rewritten in the memory 12. After all the signals are written into the memory 12, the data in the memory 12 is read and all data is written into the external transfer memory 13.

In the above explanation, the case where N=2 was shown, but in other cases as well, the operation from the second time onwards may be repeated. Also, N=
1, the second operation is not performed and memory 12'7)
The data may be transferred to the memory 13 immediately.

It is of course possible to set N so that t≦, <21; but other values are also possible.

If you fight, the sound of the solid-state image sensor 5 (shown in FIG. 4) will be heard.
If the maximum value in the range of the toilet temperature of item a changes as shown in (a) with respect to the exposure time, then the output of the solid-state image sensor 5 will become saturated with only the noise signal as the exposure time becomes longer. Therefore, it is also possible to set N gold so that (Igi signal) + (noise) does not become saturated.

In the above explanation (well, the noise signal of each pixel is stored in the memory 11 and subtracted from each pixel signal, but the memory 11'fr is not used and the average noise signal of all pixels is subtracted from each pixel. Also good.

This invention is not limited to the embodiments described above,
For example, after pressing the shutter button 16.

You can easily set photometry, aperture, shutter speed, and number of readouts.
The first field pulse Pel may be applied after that.

Also, after 1 is led into memory 12, finally memory 13
Although the data is delivered to the memory 12, a part of the memory 13 may be used instead. Similarly, for the memory 11, it is also possible to substitute a part of the memory 13.

Although the noise data was digitally subtracted from the signal data, the output of the memory 11 was D/A converted.

Subtraction may be performed in an analog manner before A/D conversion.

〔Effect of the invention〕

As explained above, according to the invention, a still image signal output with less influence of dark current can be obtained regardless of changes in ambient temperature or shutter time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an electronic camera according to an embodiment of the present invention, FIG. 2 is a diagram conceptually showing the structure of a solid-state image sensor in the embodiment, and FIG. 13 is a diagram showing the operation of the embodiment. Timing chart, for explanation. FIG. 4 is a diagram showing the relationship between the exposure time and the output voltage of the solid-state image sensor shown in FIG. 2. 1... Subject light, 2... Imaging lens, 3... Aperture, 4... Shading, 5... Solid-state image sensor, 6...
Amplifier, 7... Clamp circuit, 8... A/D converter, 9... Subtractor, 10... Adder, 11.1
2.13...Memory, 15...Timing control circuit. Agent Patent Attorney Norihiro Chika Uichi 1

Claims (2)

[Claims] (1) In an electronic camera imaging system in which the shutter is opened and closed for a set time (T) by the release operation, and an imaging signal corresponding to the incident light is captured from a solid-state imaging device and recorded by the shutter operation. When the set time (T) of the shutter is longer than a certain value, this time (T) is divided by the number of divisions (N≧2), and before the shutter opening operation, the divided time T/N and the input are set. A noise signal generated independently of the body throw is accumulated in advance, and after the shutter opening operation time T/N, a first imaging signal is captured, and the noise signal is extracted from this first imaging signal. subtract, store this subtracted signal in a first memory, and further time T
/N, the second imaging signal is taken in, the noise signal is subtracted from the second imaging signal, and this subtracted signal is added to the first imaging signal stored in the first memory. , the operation of newly accumulating the added image signal in the first memory is repeated the number of divisions (N), and after the shutter closing operation, the image signal accumulated in the first memory is stored in the first memory. 2. An electronic camera imaging system characterized by storing information in a second memory. (2) The constant value is 2t when the readout time of all pixel signals of the solid-state image sensor is t, and when the shutter time is T, the number of divisions N is: If T<2t, N=1 If T≧2t, the constant value is 2t. An imaging system for an electronic camera according to claim 1, wherein N satisfies t≦T/N<2T.