JPH04160878A - Image pickup device - Google Patents

Abstract

PURPOSE:To display a picture on a TV monitor continuously without interruption at a low speed shutter by storing a picture signal outputted from an image pickup element into a memory and reading repetitively the picture signal stored precedingly until a succeeding picture signal is written. CONSTITUTION:A picture signal outputted from an image pickup element 3 whose charge storage time is variable is stored in a memory 6 and until a succeeding picture signal is written by a control means 9, the picture signal stored precedingly is repetitively read from the memory 6. Then prescribed signal processing is implemented in response to the charge storage time of the image pickup element 3. Thus, in the case of long time exposure over 1/(field frequency) or over, a picture on a TV monitor is not interrupted and a bright pattern without a sense of disorder is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an imaging device, and more particularly, to an imaging device capable of high-sensitivity imaging using long-time exposure.

[Prior Art] An imaging device that displays an image capture screen on a TV monitor displays a moving image as continuous images with the period of the vertical synchronization signal (hereinafter abbreviated as 1/(field frequency)) as the exposure time. (JP-A-59-17772, JP-A-59-17773, JP-A-57-78281)
(Refer to each publication). However, in recent years, by controlling the charge accumulation time and charge transfer timing of an image sensor such as a CCD, it is possible to improve dynamic resolution by exposing for a time shorter than 1/(field frequency), or to variable control the exposure time. It has also become possible to control exposure by

[Problems to be Solved by the Invention] Incidentally, when the subject illuminance is dark, it is necessary to improve the sensitivity of the imaging device, and there are two methods for this as described below. That is, the first method is to increase the circuit gain by increasing the amplification degree of each circuit in the imaging device, but in order to maintain a stable high gain in the frequency characteristics of the video band, the circuit scale is large. Moreover, when the amplification level of the circuit is increased, the noise component generated by the circuit itself also increases, resulting in SZ
This is not preferable because it will deteriorate the N ratio. The second method is to increase the exposure time by increasing the exposure time.
According to the above means, the above S can be achieved without increasing the circuit scale.
This is very advantageous because the sensitivity of the imaging device can be improved without deterioration of the /N ratio.

In this way, by making the exposure time longer than 17 (field frequency), it is possible to improve the sensitivity of the imaging device while maintaining the above-mentioned advantages even when the subject is dark. There are problems like this. In other words, in the current television standards, image information can only be read out at field frequency intervals, so the exposure time can be reduced by 1/2.
(field frequency), normal TV display will not be possible. Therefore, in conventional imaging devices, when the subject illuminance decreases, the aperture is opened and the shutter time is lengthened, but when the exposure time reaches 1/(field frequency), this 1/(field frequency) The shutter speed was fixed at the time. Therefore, TV
I had no choice but to accept that the image information on the monitor would be dark.

In order to avoid the image information on the TV monitor from becoming dark, if the shutter time is made longer than 1/(field frequency), the image information on the TV monitor will become 1/(field frequency) during readout.
(field frequency) is displayed on the monitor, information is lost during the remaining time period, resulting in intermittent image display.

Therefore, an object of the present invention is to solve the above-mentioned problems, so that even if a long-time exposure of 1/(field frequency) or more is performed, the image on the TV monitor will not be interrupted, and therefore a bright screen that does not give an unnatural feeling can be displayed. To provide an imaging device.

[Means and Effects for Solving the Problems] The imaging device of the present invention includes an imaging device whose charge accumulation time is variable, a memory that stores an image signal output from the imaging device, and a memory that stores at least the next image. It is characterized by comprising a control means for repeatedly reading out previously stored image signals from the memory until the signal is written, and predetermined signal processing is performed according to the charge accumulation time of the image sensor.

[Example] The present invention will be specifically described below with reference to the drawings. 1st
The figure is a block configuration diagram of an imaging device showing an embodiment of the present invention.
An image is formed on the light-receiving surface of the CCD 3 that constitutes the image sensor. The video signal photoelectrically converted by the CCD 3 is processed by a signal processing circuit 4, and converted into a digital signal by an A/D converter 5. This digital signal is captured and stored in a field memory 6, which will be described later, and the digital signal read out from the memory 6 is converted into a D/D signal.
It is converted back to an analog signal by A converter 7 and sent to encoder 8.
The signal is then encoded into, for example, an NTSC signal and sent to an external device (not shown) as a video output.

Note that when the output of the signal processing circuit 4 is divided into a luminance signal and a color difference signal, the A/D converter 5. Two sets of field memory 6 and D/A converter 7 are required.

The field memory 6 is a key point of the present invention, and is, for example, M5M4C500L-5°-6, -10 (Mitsubishi Electric Generator).
To explain this using an example of configuring a field memory using a memory IC (hereinafter referred to as a memory IC), this memory IC is a dual-port field memory that can be written while reading, and has a configuration of 320 rows x 256 columns x 6 bits. It consists of a memory array, a serial input memory with a 256x6 bit configuration, and a serial output memory with a 256x6 bit configuration. If new write data is not input from the outside, the memory data already stored in the memory area is repeatedly read out in synchronization with a vertical synchronization signal as a clock pulse. On the other hand, when write data is input from the outside, the data is synchronized with the vertical synchronization signal and replaces the already stored memory data.
This new write data is read out in synchronization with the next vertical periodic signal. In other words, while data is read from the memory area within the memory IC, data is written from outside at the same time to update the screen.

The signal processing circuit 4 and encoder 8 are supplied with a synchronization signal from an SSG (synchronization signal generator) 10 that controls the operation timing of each part of this imaging device, and this synchronization signal is transmitted to the CCD. The signal is also supplied to the drive circuit 11 and memory timing generation circuit 9. The CCD drive circuit 11 and the memory timing generation circuit 9 are supplied with a shutter signal sent from a shutter signal generation circuit 12 that can vary the shutter time with a shutter time setting variable resistor 13. 11
The drive timing of the CCD 3 is determined by the memory timing generation circuit 9, and the A/D converter 5. Field memory 6 and D/A converter 7 are each controlled.

A freeze switch 14 for temporarily fixing the image information read from the field memory 6 and a reset switch 15 for releasing the frozen state are connected to the memory timing generating circuit 9, respectively.

Further, connected to the shutter signal generation circuit 12 is a video signal detection block 16 having a low-pass filter 18 that passes the luminance signal from the signal processing circuit 4 through a buffer 17 and detects the average level. And the same block 1
At 6, a comparator 19 is connected to compare a certain specified threshold level voltage,
This signal output is input to the shutter signal generation circuit 12.

The operation of this embodiment constructed in this way will be explained with reference to the timing charts of FIGS. 2-3. First, according to Figure 2, 1
The operation of each part during a low-speed shutter for exposing for a time longer than /(field frequency) will be described, and then the operation of each part during a high-speed shutter will be described with reference to FIG.

FIGS. 2(A) to 2(E) show the timing of normal operation during low-speed shutter. In FIG. 2(A), when the shutter open time A of the shutter signal 21 ends at time tt, as shown in FIG. Then, the signal output from the CCD 3 during the shutter signal A period (
Hereinafter, the CCD (A,) output 23 is the second
The output is as shown in Figure (C). This CCD (A1)
After the output signal 23 is converted into a digital signal by the A/D converter 5, it is stored in the field memory 6 as a memory write (A2) signal 24, as shown in FIG. 2(E). Therefore, the memory read signal read from this field memory 6 to form the display screen is a memory read signal read out from the memory write (A2) signal 24 in synchronization with the vertical synchronization signal 25 output at time t3. (A2) The signal becomes 26. In this case, the memory read signal before time t3 is the shutter (A) signal 21
is the shutter (Ao) signal at a time before .

By the way, in the field memory 6 used in the conventional imaging device, the stored information is not repeatedly read out, so after the memory read (A2) signal 26 is output, the memory read (A2) signal 26a, 26b, 26
Since c is not repeatedly output and there is no information during this period T1, the image is displayed intermittently.

On the other hand, according to this embodiment, the field memory 6 uses something like the above-mentioned IC memory, the image signal output from the image sensor is stored in the internal memory, and at least the next image signal is stored in the memory. The memory write (A2) signal 24 is repeatedly read out until the memory write (A2) signal 24 is written, and an image is displayed as the memory read (A2) signals 26a, 26b, and 26c. Therefore, even during long exposure at a rate of 1/(field frequency), the display screen on the TV monitor does not appear intermittently as in the conventional case, but rather during memory read (A
2) Several signals are displayed in succession, so to speak, as a continuous screen similar to a moving image.

When the shutter (B) signal 27 that opens the shirt shutter at time t and closes the shirt shutter at time t4 is output, the shutter (B) signal 27 is output in synchronization with the first vertical synchronization signal 28 after closing the shirt shirt. Corresponding CCD (B1) output signal 2
9 is output. This CCD (B1) output signal 29 is the memory write (B2) signal 30 which is the field memory 6 (
(see Figure 1). Then, the memory is read out in synchronization with the vertical synchronization signal 30 at time t6. In this way, the shutters (C), (D), (
The above operations corresponding to the E), , and (F) signals are repeatedly executed.

The above is an explanation of the normal operation during low-speed shutter operation. Next, we will explain the freeze operation in Figures 2 (F), (G), (
This is explained by H). Freeze switch 14 of the memory timing generation circuit 9 shown in FIG. The input terminals to which the reset switches 15 are connected are pulled up to the power supply voltage by pull-up resistors (not shown).
When the freeze switch 14 is turned on, the switch power 32 goes to the "L" level, as shown in FIG. 2(F). Then, the field memory 6 receives the memory read (A2) at this point via the memory timing generation circuit 9.
) to output a signal 26 to form a display screen. The display screen then displays the memory read (A2) signals 26, 26a, . . . , 26 until the reset switch input 33 is applied.
1 will be refrozen. When the reset switch input 33 is applied, this frozen state is released, so the memory read (C2) signal 3 at this point
4 is output, and thereafter the normal operation is resumed. Therefore, in an electronic camera having an EVF (electronic view finder), by making the timing of this freeze operation coincide with the shutter timing, it is possible to take a picture while checking the screen of the scene to be photographed.

FIG. 3 is a timing chart when a high-speed shutter is used, that is, when the shutter time is shorter than 1/(field frequency). Shutter open signals At and B shown in FIG. 3(A)
/,... Q Corresponding to /, the vertical synchronizing signal VD shown in FIG. 3(B) is sent out next to each of these signals.
VD..., 1'2' synchronized with VD7, the CCD output A' shown in FIG. 3(C)
B'..., G'1 are each output 1'
I can do it. These CCD outputs A'B'1° 1
""'G'1 is each subjected to signal processing and A/D conversion,
Memory write signal A'B' shown in FIG. 3(D)
..., Fieldme 2' as G'2
2' Stored in memory 6.

Then, the memory write signal A'B'2°
The memory shown in FIG. 3(E) is read out in synchronization with the vertical synchronizing signals VDVD..., VDS applied next to 2'..., G'2, respectively. Read signal A'
B'..., G'2, and the display screen becomes 2
゛ 2 ' is formed.

As described above, according to this embodiment, all operations start from the fall of the shutter signal, and the exposure time width exceeds the next vertical synchronization signal, as shown in FIG. For example, if the long exposure shown in Figure 2 does not exceed 3.
Since each of the short exposures shown in the figure is performed, a bright screen display that does not give an unnatural feeling on the TV monitor can be obtained regardless of whether the shutter time is longer or shorter than 1/(field frequency). Moreover, it can be displayed on a monitor as a pseudo moving image, and high-sensitivity photography using long exposure is possible. Therefore, when taking still images with an electronic camera or the like having an EVF, according to this embodiment, the exposure time is not restricted by the television standard, so the desired image can be transferred to the floppy disk while checking the screen of the shooting scene on the electronic viewfinder. It can be recorded on a disc, etc.

Next, an application example in which the imaging device according to the present invention is used as a video camera will be described. The video signal detection block 16 in FIG. 1 receives the luminance signal Y from the signal processing circuit 4.
is passed through the buffer circuit 17 to a low-pass filter (LP
F) Detect the average signal level at 18. At this time, if the subject is bright, the output of the comparator 19 (see Figure 1) with an appropriately set threshold level will exceed this threshold level, so the shutter signal will be shortened, and if the subject is dark, the output will reach the threshold level. Therefore, a feedback loop is formed to lengthen the shutter time, and exposure control is thereby performed to keep the video output constant. Although the shutter light signal is controlled using the output luminance signal, a photometric element may be provided separately, and the shutter time may be similarly controlled by calculating the output of this element.

By the way, in conventional video cameras, it was possible to vary the shutter speed for exposure control, but in that case, due to restrictions in television standards, the shutter speed could not be set longer than 1/(field frequency). When viewed on a TV monitor, the brightness remains constant until the shutter speed reaches 1/(field frequency), but after that,
The screen becomes dark. However, according to the video camera in this application example, the exposure time can theoretically be set as long as the subject becomes darker, so it is possible to always obtain a constant video output even if the subject illuminance changes. The screen can be easily viewed.

[Effects of the Invention] As described above, according to the present invention, an image signal output from an image sensor such as a CCD is stored in a memory, and the previously stored image signal is stored until the next image signal is written. Since the image is read out repeatedly, when displaying on the screen, there is a remarkable effect that the image on the TV monitor can be displayed continuously without interruption even when the shutter speed is low, that is, the shutter timing is higher than 1/(field frequency). Demonstrated.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of an imaging device showing an embodiment of the present invention. FIGS. 2 and 3 are timing charts of the operation of each part in FIG. , 3rd
The figures each show the high-speed shutter mode.

Claims (1)

[Claims] (1) An image sensor with variable charge accumulation time, a memory that stores image signals output from the image sensor, and images stored first in the memory until at least the next image signal is written into the memory. An imaging device comprising: a control means for repeatedly reading out a signal;