JPS6027276A - Shading correcting circuit - Google Patents

Abstract

PURPOSE:To obtain a uniform luminance even in a dark place by changing a reference potential to a polarity opposite to that of a shading waveform in a tube type video camera device. CONSTITUTION:If a signal where shading occurs is applied to a terminal 3, a transistor (TR) Q2 is made conductive for a period of a clamp pulse (CP) corresponding to a BLK period, and the signal is clamped in the clamp potential applied to an emitter. The clamp voltage is applied to a signal processing circuit 5, and a black part level is detected by a sample holding circuit 15 and is compared with a potential VCL from a reference potential generating circuit 16, and a voltage corresponding to the difference is applied as the clamp voltage to the emitter of the TR for clamp. By this circuit constitution, the black level of an amplifying circuit 14 is stabilized. A correcting signal is superposed to a reference DC potential to change the black level clamp voltage, thus correcting shading in the dark part.

Description

[Detailed description of the invention] [Field of application of the invention] The non-invention relates to the waveform correction force method for video cameras.

I am particularly impressed with the brightness and vertical shading correction of the dark areas of tube video cameras.

[Background of the invention]

Figure 1 shows an overview of the signal processing circuit of a single-carrier frequency separation type single-tube color video camera, which has been widely used as a home-use tube color video camera (for example, Journal of the Television Sciron Society, June 11, 1981 VoL). 35.
/163. It is a gray diagram showing p184). In this figure, from the target of the image pickup tube 1, the luminance signal is transmitted as a baseband signal, and the color signal is transmitted onto the photoconductive surface of the image pickup tube.
Vertical direction.

It is extracted as a frequency multiplexed carrier color signal (the red and blue signals are each quadrature modulated) determined by the configuration of two sets of color trig filters (for example, a red cut filter and a blue cut filter) arranged at opposite slopes. Ru. The extracted signal is applied to the preamplifier 2. After the black level is clamped and DC-regenerated by the clamp circuit 4, the No. 4g processing circuit 5 performs to-ranking processing, automatic gain control,
Performs various signal processing such as The output signal of the signal processing circuit 5 is passed through a low-pass filter 6 (for example, a cutoff frequency jc:
5M11z) through the luminance signal yy, low pass filter 7
(fc: 500KH1) to obtain the low frequency component 1'z of the luminance signal for obtaining the color difference signal. Furthermore, the blue component,
A carrier color signal whose red component is orthogonally modulated is extracted by a bandpass filter (for example, bandpass 5.58±o, 5J#z) 8. Here, by utilizing the principle of vertical correlation of images, the signals passed through one horizontal time delay line (1HDL) 9 and the signals not passed are added to an adder 10. The subtracter 12 adds and subtracts the signal to separate it into a red signal and a blue signal, and then,
The detection circuits 11 and 12 detect the width of the image and detect red (
R) @ number, affirmative signal CB) has been obtained. Above, Y, R, B
An overview of No. 46 processing until the signal is obtained is described. However, in general, in the case of an image pickup tube, Ic1 is determined by the time constant determined by the scanning electron beam impedance and the storage capacity of the photoconductive film.
Since the charge is not fully charged and discharged during the first scan, there is an afterimage due to the charge being left behind. This phenomenon is large at low illuminance, and in the case of a single carrier frequency separation method, this afterimage becomes magenta and green layer color afterimages, degrading the image quality. In order to reduce this afterimage, a method is to add bias light using an LED from the front or back side of the photoconductive film even when there is no light incident on the lens, increasing the target backside potential in the dark and lowering the beam impedance. It has been put into practical use. However, it is difficult to uniformly and evenly irradiate a photoconductive film with a bias light, so shading occurs in dark areas. Furthermore, with the deflection, r, c
5 Shading occurs in dark areas due to non-uniformity in sensitivity, reducing the quality of an image.

Shading has a parabolic component and a sawtooth component. FIG. 2 is a waveform diagram showing the state of shading, and for simplicity, only the parabolic shading waveform that occurs in the vertical direction is shown. In the figure, B L lc' (ELACK
) is the black level obtained by blanking the cathode of the image pickup tube, and is uniform in this case. In the dark area, the waveform shown in FIG. 2 is obtained at the output 3 of the preamplifier 20, and is passed through the clamp circuit 4 and clamped at the BLK level section, so the luminance signal Y output to the low-pass filter 6 in FIG. It appears in the shape shown in Figure 2, giving a sense of ink in the dark area.

[Purpose of the invention]

The object of the present invention is to provide the above-mentioned dark area shape ink.

In particular, shading in the vertical direction is corrected to obtain uniform brightness even in dark areas.

[Summary of the invention]

As a method for correcting vertical shading, the present invention focuses on the fact that the black level after clamping is clamped to a set level (Vct)K in the clamp circuit 4. That is, by superimposing a correction waveform of opposite polarity to the shading on the DC clamp potential, 1. By changing the clamp potential (Vct) as shown in FIG. 3, a signal corrected for black level and post-flag shading is obtained.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. 4 below. In Figure 4,
Front stage amplifier output terminal 6. Clamp circuit 4. The signal processing circuit 5 is the same as that shown in FIG.

The clamp circuit 4 shown in FIG. 4 is a feedback clamp circuit. A signal with shading as shown in FIG. 2 is obtained at terminal 3 in the same figure.

Transistor Ql, emitter resistor R1, capacitor C1
, a clamp circuit 4K consisting of a transistor Q2.

Therefore, the clamp pulse applied to the base of transistor Q2 makes transistor Q2 conductive for a clamp pulse (cp) period corresponding to the BLK period in FIG. 2, and is clamped to the clamp potential applied to its emitter.

The clamped signal II passes through the Kaoru amplifier circuit 14.

While applying the voltage to the signal processing circuit 5, the black part (BLK part) level is detected by the sample and hold circuit 15, and compared with the potential VCL from the reference potential generation circuit 16 by the comparator 17, and a voltage corresponding to the difference is output.
It is applied as a clamp voltage to the emitter of the crank transistor. That is, a feedback system is constructed with respect to the black level (BLK) by the main path configuration, and the focus level of the amplifier circuit 14 is stabilized. Its level is stabilized at VCL determined by the reference potential generation circuit 16, and absorbs the DC offset voltage of the amplifier circuit 14 and the like. The reference potential generation circuit 16 has two input terminals of the operational amplifier 18;
A; Connect variable resistors VR1 and VB2 respectively, and output a parabolic wave signal for shading correction from the sliding terminal of the variable resistor,
Input sawtooth signal and output any level to the op amp.

A correction signal of a parabolic wave signal of arbitrary polarity, a sawtooth wave signal, or a mixed wave thereof can be obtained. This signal is superimposed on the reference DC potential, and the black level frang voltage is changed according to the shape ink condition to correct dark area shading as explained with the waveform in FIG. 6.

FIG. 5 shows another embodiment in which the clamp circuit 4 is the same as that in FIG. 4, but the DC voltage of the amplifier circuit 14 is not stabilized because a feedback system is constructed in the point level section.

A reference DC voltage is provided by resistors R2 and R4, and the resistor R
4, a correction wave is superimposed.

As explained above, the present invention effectively utilizes the clamp circuit to correct shading, and can be easily put into practice. Although it is not explained in detail in the main text, the horizontal shape ink correction is performed by changing the output cleaning wave of the front stage amplifier 2 for one day -C
It is common to make corrections.

[@Ming effect]

As mentioned above, the misfired #JK waviness can be corrected to the extent that it is not a problem with the dark dVS sheet ink in the vertical direction, and when combined with the shape ink correction in the horizontal direction, it is possible to paste a good 71 image. Furthermore, in realizing the present invention, it is only necessary to superimpose a correction wave on the clamp reference potential;
It has the advantage of being easy to configure.

Figure 1 is a block diagram showing an overview of the signal processing circuit of a conventional single-carrier frequency separation type single-circuit camera; Figure 2 is a dark area shape ink waveform diagram; Dark part shape・
The waveform diagrams after the amplifier is corrected, FIGS. 4 and 5, are circuit configuration diagrams showing an embodiment of the shape ink correction circuit according to the present invention.

1: Image pickup tube 2: Pre-stage amplifier 4: 22 filter 1 circuit 5: Signal processing circuit 6: Low-pass filter for luminance signal passage (fc: 51dll
z ) 7: Low-pass filter for passing the low-frequency components of the luminance signal (fc
: 500KHz) 8: Bandpass filter for carrier color signal passage (bandwidth: 3.5B±
500 nlz) 9:1H delay line 11.13: Detection circuit 14: Amplification circuit 15: Sample hold circuit 16: Clamp voltage generation circuit 17: Comparator 71 Figure 5 product 420-

Claims (2)

[Claims] (1) In a tube video camera device equipped with a signal processing circuit that clamps the point level rt of the video image to a predetermined reference potential, the clamping operation is performed by changing the base S potential to the polarity opposite to that of the shape ink waveform. By l'
ii. Part 1: A shading correction circuit that does not correct shading. (2) Each allowable tN) range In the shading correction circuit described in item 1, a parabolic waveform signal, a toothed waveform A6, or a composite wave of both signals is added to the reference DC voltage as the reference potential. A shading correction circuit characterized in that: