JPH05110941A - Black level step correcting circuit - Google Patents

Abstract

PURPOSE:To automatically correct an OB step with simple circuit configuration by providing a read control circuit to read output data for one line from a photosensitive part again synchronously to a horizontal synchronizing signal. CONSTITUTION:When reading a video signal, the charge of the photosensitive part is transferred to a transfer part by a charge transfer pulse T synchronously to a horizontal synchronizing signal HF and afterwards, a read pulse RV is inputted to the transfer part. Then, the output data for each field are outputted from the photosensitive part through the output register of the transfer part as video signals. Synchronously to the next horizontal synchronizing signal just after the output of the video signal for one field as mentioned above, a read control circuit 11 inputs the charge transfer pulse T, black level step detecting charge read pulse RB to the transfer part and reads the charge of the photosensitive part only for one line again. Thus, a signal for black level step correction is outputted to a line next to the final line of the video signal part for each field. In this line, namely, in a line VB for black level step correction, the charges for one line are stored.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black level difference correction circuit, and more particularly, it relates to a difference between an optical black level of a two-dimensional CCD image pickup device and a black level of a video signal in a television camera using the two-dimensional CCD image pickup device. The present invention relates to a black level step correction circuit that corrects a certain black level step.

[0002]

2. Description of the Related Art In a television camera using a two-dimensional CCD image pickup device, a black level step which is a difference between an optical black level of the two-dimensional CCD image pickup device and a black level of a video signal is a black level reference of a video signal. It is the offset level for the signal.

In the amplification of an output video signal of a television camera, an AGC amplifier which reduces the gain in order to compress an unnecessary white level in high illuminance and increases the gain in order to secure sensitivity in low illuminance. Is commonly used.

At low illuminance, the output video signal of the television camera is amplified by the AGC amplifier by about 30 dB. Since this amplification is performed with the black level reference signal level as a reference, if there is a black level step, this is amplified and output as a variation in the pedestal of the video signal, resulting in deterioration of the video quality. For example, if the black level difference is 5 mV, the fluctuation of the pedestal of the video signal is about 160 mV, which cannot be ignored.

As shown in FIG. 3, a conventional manually adjusted black level difference correction circuit is a CCD sensor 1, an addition circuit 2, and an AGC for amplifying a video signal from the CCD sensor 1.
An amplifier 3 which is an amplifier, and an analog switch 4 which is opened during a video signal period by a gate pulse from an input terminal TI,
The variable resistance 7 for generating the correction voltage is provided.

Next, the operation will be described.

First, when manually adjusting the black level step, the video signal from the CCD sensor 1 amplified by the amplifier 3 is observed at the output terminal TO with an oscilloscope or the like,
This is done by adjusting the variable resistor 7 so that the black level step becomes 0 and adjusting the correction voltage applied to the adder circuit 2.

Next, a conventional automatic adjustment type black level step correction circuit, as shown in FIG. 4, a CCD sensor 1, an adder circuit 2, and an amplifier A for amplifying a video signal from the CCD sensor 1.
An amplification unit 3 which is a GC amplifier, and an analog switch 4 which is opened during a video signal period by a gate pulse from an input terminal TI
, Clamp circuit 5, sample hold circuit 6, A
The D / A conversion circuit 8, the memory 9, and the D / A conversion circuit 10 are provided.

Next, the operation will be described.

First, when the television camera is started, the analog switch 4 is opened by a gate pulse from the input terminal TI with the lens diaphragm closed in advance. Then,
The video signal from the CCD sensor 1 in the video signal period naturally corresponds to the optical black level, and the black step level which is the difference between this level and the black level reference signal level of the video signal is clamped by the clamp circuit 5 and the sample hold. The circuit 6 samples and holds. The sampled and held black step level is converted into digital data by the A / D conversion circuit 8 and stored in the memory 9.

Next, during normal operation of the television camera, the black level difference data read from the memory 9 is D /
The A conversion circuit 10 converts the analog signal and the addition circuit 2 adds it to the video signal from the CCD sensor 1 to correct the offset due to the black level step.

Further, since the black level step changes with temperature, it is necessary to frequently change the setting of the correction value so that a correction error does not occur.

[0013]

The conventional black level difference correction circuit described above has a drawback that it is troublesome because it is necessary to manually adjust the variable resistance. Further, in the case of automatic correction, an A / D conversion circuit and a D / A conversion circuit are required, which has a drawback that the circuit scale becomes large. Furthermore, when changing the setting of the correction value so that a correction error due to temperature does not occur, it is necessary to readjust the variable resistor in the case of manual operation, and to restart the television camera in the case of automatic operation. There was a drawback that

[0014]

The black level difference correction circuit of the present invention has no light input to the two-dimensional CCD image pickup device in a television camera using a two-dimensional CCD image pickup device having a photosensitive section and a transfer section. In the black level step difference correction circuit for correcting the black level step difference which is the level difference between the optical black level which is the electrical output level at this time and the black level of the video signal, output data for each one field of the photosensitive section is transferred to the transfer section. Read through the above 1
The read control circuit is configured to read the output data for one line of the photosensitive section again in synchronization with the first horizontal synchronizing signal after reading the output data for each field.

[0015]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the black level difference correction circuit of the present invention.

The black level difference correction circuit of this embodiment is shown in FIG.
As shown in FIG. 2, a two-dimensional CCD having a photosensitive section and a transfer section
A CCD sensor 1 as an image pickup device, an adder circuit 2,
The amplification unit 3 which is an AGC amplifier for amplifying the video signal from the CCD sensor 1, the analog switch 4 opened during the video signal period by the gate pulse from the input terminal TI, the clamp circuit 5, the sample hold circuit 6, and the CCD sensor The reading control circuit 11 controls reading of output data from one photosensitive section.

The read control circuit 11 reads the output data for each field of the photosensitive section of the CCD sensor 1 via the transfer section, and synchronizes with the first horizontal synchronizing signal after reading the output data for each field. It again has a function of reading the output data for one line of the photosensitive section. A circuit having such a function can be configured by a well-known analog switch circuit and a timing circuit for controlling the horizontal and vertical synchronizing signals, and the like, and therefore detailed description thereof will be omitted.

Next, the operation of this embodiment will be described.

FIG. 2 is an operation time chart of the read control circuit 11 of the present embodiment shown in FIG.

As is well known, a two-dimensional CCD image pickup device such as the CCD sensor 1 is generally a transfer unit which outputs a photosensitive portion formed of a photodiode array and information charges accumulated in the photosensitive portion via an output register as a video signal. It is composed of parts and parts.

When the video signal is read, the read pulse RV is input to the transfer section after the charge of the photosensitive section is transferred to the transfer section by the charge transfer pulse T in synchronization with the horizontal synchronizing signal HF, and the read pulse RV is input to each transfer section of the photosensitive section. The output data is output as a video signal via the output register of the transfer unit.

The read control circuit 11 inputs the charge transfer pulse T and the black level step detection charge read pulse RB to the transfer section in synchronization with the next horizontal synchronizing signal immediately after the output of the video signal for one field. , The charges of the photosensitive portion are read again for one line. As a result, a signal for black level difference correction is output to the line next to the last line of the video signal portion for each field. In this line, that is, the black level difference correction line VB, the charges for one line are accumulated.

For example, the CCD sensor 1 uses the NTSC system, which is a standard television system, and the CCD sensor 1 has a standard illuminance of 20.
If there is a 0 mV video output and the illuminance is about 1/4 of that, the output of the black level step correction line is as follows.

(200/4) × 60 / (15.7 × 1000) = 0.2 (mV) Since this value of 0.2 mV substantially corresponds to the black level of the video signal, this black level and optical It is possible to detect a difference from a different black level.

In FIG. 1, the CCD sensor 1 outputs a video signal V including a black level step correction line VB by a read control circuit 11. This video signal V is extracted by the analog switch 4 controlled by the gate pulse from the terminal TI, only the black level step correction line VB for each field. The extracted black level step correction line VB is input to the clamp circuit 5. The clamp circuit 5 and the sample hold circuit 6 sample and hold the difference between the black level of the black level step correction line VB in the optical black level period and the black level in the video signal period, that is, the black level step. This sample hold circuit 6 has a capacitor C1
By using the black level level difference correction signal obtained for each field scan, a simple function such as charging and discharging of the capacitor C1 is sufficient. Next, the sampled and held black level step data is added to the video signal V from the CCD sensor 1 by the adder circuit 2 to correct the black level step. The video signal in which the black level step is corrected is amplified by the amplifier 3 and output from the terminal TO.

[0027]

As described above, the black level difference correcting circuit of the present invention is re-sensitized in synchronization with the first horizontal synchronizing signal after reading the output data for each field from the photosensitive section of the CCD sensor. Since a black level difference correction signal obtained for each field scan corrects the black level difference by providing a read control circuit for reading the output data for one line of the same section, no manual adjustment is required and automatic correction is performed. There is an effect that the circuit for holding the black level difference in is simple enough to use a capacitor and sufficiently functions. Further, there is an effect that it is possible to follow and correct the fluctuation of the black level difference due to the temperature fluctuation during the operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a black level difference correction circuit of the present invention.

FIG. 2 is a time chart showing an example of the operation of the read control circuit of the black level difference correction circuit of the present embodiment.

FIG. 3 is a block diagram showing a first example of a conventional black level difference correction circuit.

FIG. 4 is a block diagram showing a second example of a conventional black level difference correction circuit.

[Explanation of symbols]

 1 CCD Sensor 2 Addition Circuit 3 Amplification Section 4 Analog Switch 5 Clamp Circuit 6 Sample Hold Circuit 7 Variable Resistance 8 A / D Conversion Circuit 9 Memory 10 D / A Conversion Circuit 11 Read Control Circuit C1 Capacitor

Claims (1)

[Claims] 1. A two-dimensional CCD having a photosensitive section and a transfer section.
Black for correcting a black level step difference which is a level difference between an optical black level which is an electrical output level and a black level of a video signal when there is no light input to the two-dimensional CCD image pickup device in a television camera using the image pickup device. In the level difference correction circuit, output data for each field of the photosensitive unit is read out via the transfer unit, and again in synchronization with the first horizontal synchronizing signal after reading the output data for each field, the photosensitive unit of the photosensitive unit is read again. A black level difference correction circuit comprising a read control circuit for reading output data for one line.