JPH0248864A - Shading correction circuit - Google Patents

Abstract

PURPOSE:To correct shading of an output of an image pickup element changed due to temperature by detecting the temperature of the image pickup element and varying the slope of a tilt signal correcting a video output in response to the result of detection. CONSTITUTION:A video processing circuit 3 applies prescribed processing to an output 13 of an image pickup element 2. A sawtooth wave generating circuit 5 receives a vertical drive signal 7 from the video processing circuit 3 and sends a shading correction signal 6 synchronously with the vertical drive signal 7. A shading correction signal 6 is given to the video processing circuit 3 and the video signal is modulated and corrected by the shading correction signal 6. A temperature detection section 4 detects the temperature of the image pickup element 2 to control the sawtooth wave generating circuit 5. Thus, the shading of the output of the image pickup element varied with temperature is corrected.

Description

[Detailed Description of the Invention] The present invention relates to a shading (Shadinv) correction circuit, and particularly to a CCD (Charge Couple) correction circuit.
The present invention relates to a shading correction circuit in a television camera using an ed device (solid-state image sensor).

BACKGROUND ART Conventionally, in the vertical shading correction circuit of this type of television camera, a method has been adopted in which a sawtooth wave having one period of one vertical scanning period is created and added to the original signal (video signal).

In addition, in a COD with a frame interline structure in which a memory section that can store charges for one field is added to a normal interline structure, the vertical register of the COD is transferred at high speed, and the data accumulated in the vertical register is It is known that in the method of reading signal charges after clearing the accumulated charges, linear vertical shading occurs due to the 11I current of the vertical register.

In this case, the dark current accumulation time of the vertical register is short at the top of the screen, that is, near the horizontal register, but the dark current accumulation time increases in proportion to the distance from the horizontal register, so the dark current accumulation time of the vertical register increases. Shading due to dark current linearly increases every vertical period, and the magnitude of shading is proportional to the magnitude of dark current of the image sensor.

In general, the dark current of an image sensor has a temperature characteristic in which it doubles when the temperature increases by 10° C., which causes deterioration of image quality at high temperatures.

However, since the above-described conventional shading correction circuit does not have a temperature correction element, it has the disadvantage that it cannot correct the shading of the output of the image sensor that changes depending on the temperature.

An object of the present invention is to provide a shading correction circuit that can correct shading caused by temperature changes.

A shading correction circuit of the present invention is a shading correction circuit that modulates and corrects a video output from an image sensor using a gradient signal, and includes a temperature detection means for detecting the temperature of the image sensor, and a temperature detection means for detecting the temperature of the image sensor. It is characterized by comprising a correction means for changing the slope of the slope signal according to the detection result of the means.

X Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of a shading correction circuit according to the present invention. In FIG. 13, a temperature detection section 4, and a sawtooth wave generation circuit 5. In addition, 1 is a lens, 1
2 is an output terminal.

The sawtooth wave generating circuit 5 includes operational amplifiers 10 and 11, resistors R1 and R2, a variable resistor VR, a capacitor C, a field effect transistor 8, and power supplies 91 and 92.

Further, this sawtooth wave generating circuit 5 receives a vertical drive signal 7 from the video processing circuit 3 as an input, and this vertical drive signal 7
The shading correction signal 6 is sent out in synchronization with the shading correction signal 6.

Furthermore, the shading correction signal 6 sent from the sawtooth wave generation circuit 5 is input to the video processing circuit 3, and the video signal is modulated and corrected by this shading correction signal 6.

The temperature detection section 4 includes a transistor,
Similar to the dark current of the image sensor 2, the current flowing between the emitter and base of this transistor is approximately 2 when the temperature rises by 10°C.
It has the property of being doubled. The sawtooth wave generating circuit 5 is controlled by the current from the temperature detecting section 4.

Next, the relationship between temperature changes and the shading correction signal 6 will be explained using FIG. FIG. 2 is a time chart showing the relationship between the temperature change of the image sensor 2 and the shading correction signal 6. In FIG. 0, a sawtooth wave shading correction signal 6 synchronized with the vertical drive signal 7 is shown.

The figure also shows the amplitude of the shading correction signal 6 when the image sensor 2 is at a low temperature (■) and when it is at a high temperature (■).

First, at low temperatures (■) when the dark current of the image sensor 2 is small and the amount of shading is small, the amplitude of the shading correction signal 6 is also small.

On the other hand, at high temperatures (■), when the dark current increases and the amount of shading increases, the current from the temperature detection section 4 also increases accordingly.

Therefore, changes in the amount of shading of the image sensor 2 due to temperature can be effectively offset.

In this embodiment, vertical sawtooth wave shading correction is performed, but even if the parabolic shading changes depending on the temperature, the product of the output of the temperature detection section 4 and the parabolic signal is used as the shading correction signal. 6
It is clear that temperature compensation can be effectively achieved if used as

As explained above, the present invention detects the temperature change of the image sensor and changes the magnitude of the shading correction signal accordingly, thereby reducing the amount of shading caused by the change in the dark current of the image sensor. This has the effect of being able to compensate for changes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a shading correction circuit according to an embodiment of the present invention, and FIG. 2 is a time chart showing the relationship between the temperature change of the image sensor shown in FIG. 1 and the shading correction signal. Explanation of symbols of main parts 2...Image sensor 3...Video processing circuit...Temperature detection section

Claims (1)

[Claims] (1) A shading correction circuit that modulates and corrects a video output from an image sensor using a gradient signal, the circuit comprising: temperature detection means for detecting the temperature of the image sensor; A shading correction circuit comprising: correction means for changing a signal slope.