JPS58125960A - Signal processing circuit of electronic camera - Google Patents

Abstract

PURPOSE:To obtain an electrostatic picture with clear contrast which is not disturbed by a dark current in a small-sized and inexpensive camera device, by recording separately the signal component obtained from a solid-state image pickup element with the dark current component detected with increased storing time. CONSTITUTION:With a push of a shutter push-button 12, a pulse A is instantaneously produced and supplied to a pulse generating circuit 11. Thus an optical shutter 7 is opened, and an output pulse C is supplied to the circuit 11 from a position detecting circuit 13 of the shutter 7. In this case, the dark current stored in a period T1 during which the shutter 7 is open is read out along with a signal. Thus the signal is read out in a period T2 with a pulse D given from the circuit 11 and recorded to a recorder 10 via a signal processing circuit 9. Then the working of an element 8 is stopped for a period T3 longer than the period T1. The dark current of this period is turned into a T1/T3-fold value to be written to a device, then subtracted from an optical signal after reproduction.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to an electronic camera device exclusively for still images that is capable of photographing still images and recording and reproducing them in an image recording device.

(2) Prior Art With the development of television cameras and magnetic recording devices, attempts have been made to replace conventional film cameras with all-electronic cameras.

A typical example is a system that combines a video tape recorder (VTR) and a television camera, and is capable of recording and playing back images in various forms, such as moving images, slow motion images, and still images.

However, the above-mentioned VTR system requires a multi-leaf recording medium to record and play back the video information of Prevision Eirin.
The device becomes complicated and large.

Therefore, a method of recording static images on an audio cassette tape recorder as shown in FIG. 1 has been proposed. (
(Japanese Patent Publication No. 55-20283) This is achieved by recording a wideband image signal of several MHz obtained from a television camera 1 at a high speed in a field or frame memory 2, and reading out the memory information at a low speed. This is a method in which the signal is converted into a negative signal and recorded on a magnetic tape 5 through a recording amplifier 3 and a magnetic head 4.

Since a small magnetic tape device such as an audio tape recorder can record only a frequency of several tens of kilohertz, it is not possible to directly record an image signal having a frequency band of several megahertz.

Therefore, it is necessary to use a field memory 2 for time axis conversion as shown in the conventional example shown in FIG.

However, the amount of information for one image is very large, and the field memory device is also large, making it impossible to downsize the electronic camera.

(3) Purpose and general explanation of the invention The purpose of the present invention is to provide a small and inexpensive electronic camera device exclusively for still images, in which the solid-state sensor fC, uses optical information accumulated in a compensation tube to It is characterized in that the frequency band of the image signal is compressed by reading out the image signal and recording it on the recording device.

In order to enable the above-mentioned signal readout, the image pickup element itself must have an image storage effect.

Compensation tubes such as PIZICO/ etc. also have an image storage effect, but the explanation will be given here using the MO8 type solid-state bond sensor shown in FIG. 2 as an example.

In FIG. 2, 16 is a photodiode, 17° and 18 are shift registers for horizontal and vertical scanning, 19 is a video signal output terminal, 20.2111 is a horizontal and vertical readout switch, 22 is a vertical readout line, 23 is a horizontal readout line, 24
is a video bias voltage source, and 25 is a load resistance.

There is a parasitic capacitance 26 in the photodiodes 16 arranged in a matrix. Photocharges corresponding to the intensity of light are stored in the capacitor 26. These photocharges drop @readout switch 21
By sequentially switching the horizontal readout switch 20 and the horizontal readout switch 20, the VC is configured such that the time series signal is read out to the video signal output terminal 19 through the signal output lines 22 and 23.

The vertical and horizontal readout switches are opened and closed by the output pulses of the vertical and horizontal shift registers 18.17.

Further, the vertical and horizontal shift registers each receive two-phase clock pulses CY and Cx and an input pulse -Vy.

It is driven by Vx.

As mentioned above, the MO8 type solid-state image sensor shown in FIG.
Parasitic capacitance in photodiode for electrical conversion 1. It is possible to store signals for a certain period of time.

Therefore, the sensor itself can be used as a field or frame memory.

However, when the temperature of the sensor substrate increases, the dark current flowing through the photodiode increases, making it impossible to store signals for a long time.

Therefore, in the electronic camera of the present invention, as a measure against the dark current of the photodiode, the dark current component is removed before the shutter 7 is opened, and the signal is read out and recorded immediately after the shutter is closed. Next, dark current is accumulated for a certain period of time, and n is read out and recorded.

After reproducing these signals, the gain of the dark current component is adjusted and then subtracted from the signal to cancel out the dark current component contained in the signal.

As a result, dark current can be removed without increasing random noise.

(4) Examples Hereinafter, the invention will be explained in detail with reference to examples.

FIG. 3 shows the configuration of an electronic camera device according to the invention.

6 is a lens, 7 is an optical shutter, 8 is a photographic element 9 which is a signal processing circuit, and 10 is a recording device typified by a magnetic tape. Further, 11 is a drive pulse generation circuit that generates pulses for driving the sensor element, signal processing circuit, and pulses to be supplied to the recording device, 12 is a push button for operating the shutter, and 13 is a position detection circuit for the shutter 7.

The photodetector has a dark current, and electric charges are accumulated in the parasitic capacitance 26 of the photodiode even when no light is irradiated. When the ground lines of the vertical and horizontal shift registers 18 and 17 are raised to a level higher than the voltage of the video bias power supply 24, all the vertical and horizontal switches are turned on. As a result, charges due to the dark current are extracted through the signal output lines 22 and 23.

It is also possible to read out the dark current by scanning the vertical and horizontal shift registers 18.degree. 17 at high speed.

FIG. 4 shows a timing chart of the embodiment.

(A) is a pulse generated at the moment the shutter button is pressed, (B) is a pulse to remove the dark current of the sensor 8, and (C) is a pulse generated when the shutter 7 is opened or closed. This is an output pulse generated by the position detection circuit. In this case, if the time during which the shutter is open is 5 cmT1, t dark current accumulated during this period will be read out together with the signal. (D) is a pulse for operating the image sensor 8, signal processing circuit 9, and recording device;
During the period T2, the optical signal is read out and recorded on the recording device. Next, the operation of the image sensor is stopped for a period T during which the shutter is open, which is a longer period T.

Dark current accumulates during the period T, but the longer the time T, the greater the dark Vl#L becomes. This signal is T,
The signal is multiplied by /T3 and written to the recording device, and subtracted from the optical signal after reproduction. For example, one frame memory may be stored in the signal reproducing circuit and a portion of this memory may be used for dark current.

If T, = T, then the random noise of the circuit system is also -
Since gK calculation is required, the signal-to-noise ratio deteriorates by 3 dB.

However, if T is large, a large dark current becomes T,
/T, since the random noise in the circuit system also becomes smaller, it can be seen that even if this dark current is subtracted in the reproduction circuit, the signal-to-noise ratio hardly deteriorates.

Further, it is not necessary to record the dark current every time, but it is sufficient to record the dark current at a rate of about once every several dozen sheets and write this in one part of the one-frame memory of the reproducing circuit.

The gist of the present invention has been described above, but the signal component obtained from the solid-state compensation element and the dark current component detected by increasing the storage time are all recorded separately, and after playback, the calculation (reduced by As a result, a clear still image without dark DL flow disturbance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional method for recording still images on an audio cassette, Fig. 2 is a diagram showing the structure of an MO8 type sensor, and Fig. 3 is an embodiment for realizing the invention. , FIG. 4 is a timing chart for operating an embodiment of the present invention.

Claims (1)

[Claims] Remarks 1. An electronic camera device comprising an optical shutter mechanism that controls the amount of optical information captured by the shutter mechanism, and a photographing device that converts the optical information captured by the shutter mechanism into an electrical signal, A signal processing circuit for an electronic camera, characterized in that a signal component containing a dark current obtained from the above-mentioned compensation device and the dark current component are separately read out, and the two signals are independently recorded in a recording device.