JPH04178082A - Ccd camera - Google Patents

Abstract

PURPOSE:To obtain a video signal without a dark current by storing shading by a dark current of a CCD image sensor, outputting the result as an analog signal and synthesizing it with an output of a temperature sensor so as to use the synthesized signal for gain control. CONSTITUTION:For example, a dark current signal obtained when a lens cap is put on the camera is given to an LPF 4 and an A/D converter 6, and a dark current signal by one TV frame is stored in a frame memory 7 by depressing a switch 10. The signal is converted into an analog signal by a D/A converter 8 and the signal is adjusted at a control circuit 12 with respect to a normal temperature change by the control of a temperature sensor 11 and the result is fed to an inverting input of a subtractor circuit 9. The circuit 12 is acted so that the gain is doubled with respect to a temperature rise of 8 deg.C. Thus, the output of the subtractor 9 is a video signal not including a dark current even in the presence of a temperature change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a CCD camera, which is a television camera using a CCD that generates television video signals.

[Conventional technology]

FIG. 3 is an image system diagram of a conventional monochrome camera using a CCD.

The output signal of the CCD image sensor 1 is first optically sampled by the CCD by the sample/hold circuit 2, and the obtained P A M (Pu1se, ^-pli-tu
de Modulation) signal as a continuous video signal, which is amplified by a buffer amplifier 3 and then further processed by an LPF (LPF).
ow Pa5s Filter) 4 removes high frequency components produced as a result of sample and hold. Thereafter, gamma correction, white clipping, and pedestal adjustment are performed in the process amplifier 13, and the video signal is output through the output video amplifier 14 at the final stage.

Compared to Ill detonator type cameras, CCD cameras do not produce microphonic noise or burn-in.
It has features such as a semi-permanent lifespan, but on the other hand, CC
There are problems such as white scratches, dark current, and smear that are unique to D image sensors. In a CCD image sensor, unevenness and slight shading occur in the dark current. For this reason, conventionally, a parabolic waveform or a sawtooth waveform is used to create and add a waveform having an opposite phase to the CCD output waveform in the dark, thereby performing LLN style shading correction.

[Problem to be solved by the invention]

The dark current generated within the CCD is caused by the photodiode, which is a photoelectric conversion element, and a unique dark current is generated in each two-dimensionally arranged photodiode.

Two-dimensional dark i4-style shading may occur due to process problems. Further, the dark current changes greatly depending on the temperature, and usually increases twice by increasing the temperature by 8°C. For this reason, the method of performing shading correction using the parabolic waveform or sawtooth waveform described above cannot cope with temperature changes and cannot perform complete shading correction.

An object of the present invention is to provide CC
D camera.

[Means to solve the problem]

The CCD camera of the present invention includes: an fAlf sensor that detects the temperature of the CCD image sensor; a frame memory; an A/D converter that converts the output of the LPF from analog to digital and writes it into the frame memory; A D/A converter that converts the output into digital/analog; and a CC whose output is detected by a temperature sensor.
A gain control circuit that increases or decreases according to the temperature of the D image sensor; a subtraction circuit that subtracts the output of the gain control circuit from the output of the PF and outputs it to the output video amplifier; and a frame memory write switch. .

[Effect]

The present invention uses a memory (frame memory) that stores one frame of a video signal to record dark current shading, and also provides a temperature sensor to the CCD image sensor to increase the temperature of the CCD image sensor. , the output of the frame memory is increased or decreased by the drop, and then subtracted from the normal video signal in order to cancel out the shading that varies due to temperature changes.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Figure 1 is a system diagram of a CCD camera according to an embodiment of the present invention, and Figures 2 (a), (b), and (c) are a video signal consisting only of dark current with shading, a shading correction signal, and a post-correction signal. FIG. 2 is a waveform diagram of a video signal of FIG.

The CCD camera of this embodiment is a CCD camera of the conventional example shown in FIG.
The J-mera includes a buffer amplifier 5 that amplifies the output of the I-P F 4, a temperature sensor 11 that detects the temperature of the CCD image sensor 1, a frame memory 7, and an analog/digital converter for the output of the buffer amplifier 5. , an A/D converter 6 for writing into the frame memory 7, a D/A converter 8 for converting the output of the frame memory 7 from digital to analog, and a temperature sensor 11 detecting the output of the D/A converter 8. A gain control circuit 12 that increases or decreases depending on the temperature of the CCD image sensor 1, a subtraction circuit 9 that subtracts the output of the gain control circuit 12 from the output of the buffer amplifier 5, and a write switch 10 for the frame memory 7 are added. It is configured.

In this embodiment, the signal after passing through the L P F 4 is passed through a buffer amplifier 5, then digitized by an A/D converter 6 and stored in a frame memory 7. frame memory 7
The video signal accumulated in the camera is not a normal video signal, but a signal obtained when a lens cap is attached, that is, a video signal containing only dark current.

By pressing the write switch 10, it is sufficient to store video signals for only one TV frame.

It is assumed that the signal accumulated at this time has dark current shading, for example, as shown in FIG. 2(a).

After this signal is D/A converted by the D/A converter 8 to become an analog signal, it is constantly increased or decreased by the gain control circuit 12 according to temperature changes by ill'm of the temperature sensor 11, and then subtracted. It is supplied to the negative human power of circuit 9. At this time, the gain control circuit 12 is set so that the gain doubles for every 8° C. rise in temperature. On the other hand, during normal imaging operation, the video signal given to the plus input of the subtraction circuit 9 is a signal corresponding to the light irradiated through the lens to the dark current with shading, as shown in FIG. 2(b). This is the signal obtained by adding . Therefore, as shown in FIG. 2(C), the output of the subtraction circuit 9 is as follows.
Even if there is a temperature change, it is possible to obtain a video signal that does not contain dark current.

〔Effect of the invention〕

As explained above, this development has a frame memory that stores the dark current shading of the CCD image sensor, while a temperature sensor constantly detects the temperature of the CCD image sensor, and the output signal of the frame memory is converted into an analog signal. By controlling the gain of the decoded signal using the output of the temperature sensor and subtracting it from the output of the CCD image sensor during normal imaging operation, it is possible to obtain a video signal with no F@zero current.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a CCD camera according to an embodiment of the present invention, FIG. 2(a) is a video signal consisting only of dark current with shading, FIG. 2(b) is a shading correction signal,
FIG. 2(C) is a diagram showing the corrected video signals, and FIG. 3 is a system diagram of a conventional CCD camera. 1... CCD image sensor, 2... Sample/hold circuit, 3.5... Buffer amplifier, 4... LPF. 6...A/D strange! ! ! ! 7... Frame memory, 8... D/A converter, 9... Subtraction circuit, 10... Write switch, 11... Temperature sensor, 12... Gain control circuit, 13. ...Process amplifier, 14...Output video amplifier. Patent application filed by To1hon Electric Co., Ltd. Patent attorney Susumu Uchihara

Claims (1)

[Claims] 1. A CCD camera, which is a television camera using a CCD, includes a temperature sensor that detects the temperature of a CCD image sensor, a frame memory, and a frame memory that converts the output of an LPF from analog to digital. an A/D converter for converting the output of the frame memory into digital/analog; and a D/A converter for converting the output of the D/A converter into a CC detected by a temperature sensor.
A gain control circuit that increases or decreases according to the temperature of the D image sensor, a subtraction circuit that subtracts the output of the gain control circuit from the output of the LPF and outputs it to an output video amplifier, and a frame memory write switch. Features a CCD camera.