JPH02265380A - Video reproducing device - Google Patents

Abstract

PURPOSE:To apply contour correction in response to a change in the brightness of a picture by providing a control voltage generating circuit using a detected voltage (brightness detection voltage) generated by an automatic brightness limit circuit to generate a control voltage and a gain control circuit controlling the gain for speed modulation operation through the control voltage. CONSTITUTION:When the brightness is low and a brightness detection voltage is higher than a Zener voltage of a constant voltage diode 14, an amplitude of a.video signal outputted from a collector of a transistor(TR) 12 is small. On the other hand, when the brightness is high and the brightness detection voltage is lower than the Zener voltage of the constant voltage diode 14, an amplitude of a video signal outputted from a collector of the TR 12 is high. Thus, the amplitude of the output video signal of a gain control circuit is constant when the brightness detection voltage is a prescribed value or over by supplying the output video signal of the gain control circuit 2 to the speed modulation circuit and the speed modulation gain is made constant. Since the amplitude of the output video signal of the gain control circuit is increased as the brightness detection voltage decreased with the brightness detection voltage being at a prescribed value or below, the gain of the speed modulation operation is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video reproducing device, and more particularly, to a video reproducing device that enhances the outline of an image using an electron beam scanning speed modulation method.

[Conventional technology]

In a video reproducing device, a speed modulation method is used to correct the outline of the image displayed on the cathode ray tube, which modulates the scanning speed of the electron beam of the cathode ray tube using a detection signal that detects the brightness change portion of the video signal. Video playback devices are known.

FIG. 3 shows a block diagram of the speed modulation circuit portion.

The video signal input from the video signal input terminal 1 is supplied to a first-order differential amplification circuit 5, which performs first-order differentiation of the video signal, amplifies the obtained signal, and supplies the amplified signal to the speed modulation coil 7. Japanese Patent Application Laid-Open No. 61-210769 focuses only on contour correction in a high-brightness portion of an image where the contrast is increased by contrast adjustment of the amplitude of a video signal. By supplying the output video signal of the contrast adjustment circuit as the video signal input to the speed modulation circuit, contour correction proportional to the contrast of the video signal is performed. The amount of contour correction of the image is proportional to the amplitude of the signal obtained by first-order differentiation of the video signal in the first-order differential amplifier circuit 5, that is, the amount of change in brightness of the video signal. Therefore, when the brightness of the image is high and plumping occurs, sufficient contour correction cannot be performed for signals whose brightness changes are small.

In addition, the video input terminal 1 generally includes a contrast adjustment circuit that adjusts the amplitude of the video signal applied to the cathode ray tube, and a clamp circuit that sets the pedestal level of the video signal to a predetermined level. A signal is provided. Therefore, even if the image projected on the cathode ray tube causes blooming in high-brightness portions due to the settings of the control 5th filter and pedestal level, sufficient contour correction cannot be performed.

The purpose of the present invention is to eliminate images that have blooming due to high brightness even if the brightness changes are small, and to adjust contrast and pedestal level settings to prevent images that have blooming due to high brightness. It is an object of the present invention to provide a video reproducing device capable of performing sufficient contour correction even on images that are difficult to understand.

[Means for solving problems]

The above purpose is achieved by using a speed modulation circuit that corrects the contour of the image by modulating the scanning speed of the electron beam of the cathode ray tube using a speed modulation coil, and a detection voltage that detects the seven node currents of the cathode ray tube and converts them into voltages. In a video playback device equipped with an automatic brightness limiting circuit that automatically limits the brightness of an image, the automatic brightness limiting circuit generates a control voltage using the detection voltage (hereinafter referred to as the brightness detection voltage). This is achieved by providing a generating circuit and a gain control circuit that controls the gain of the speed modulation operation using the control voltage.

[Effect]

The brightness detection voltage generated by the automatic brightness detection circuit normally has a sufficiently large time constant for one vertical scanning period of the video signal due to the integration circuit, and detects the average brightness of the video signal.

The brightness detection voltage and the video signal are supplied to a gain control circuit. The gain control circuit operates to thicken the amplification gain of the video signal of the gain control circuit as the brightness increases due to the brightness detection screw.On the other hand, as the brightness decreases, the gain control circuit operates to make the amplification gain smaller as the brightness decreases. However, when the brightness further decreases using a predetermined value of the brightness detection voltage as a threshold value, the amplification gain is kept constant.

This can prevent the amplification gain from becoming too small in the case of instantaneous high-luminance signals to which the luminance detection voltage cannot respond. By supplying the output video signal of the gain control circuit to the speed modulation circuit, the gain of the speed modulation operation can be controlled depending on the brightness.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a video signal input terminal, 2 is a gain control circuit, 3 is a control voltage generation circuit, 4 is a speed modulation circuit, 5 is a first-order differential amplifier circuit, 6 is an output circuit, 7 is a speed modulation coil, 8
is a terminal that supplies the brightness detection voltage generated by the automatic brightness limiting circuit.

In this embodiment, the explanation will be made assuming that the brightness detection voltage decreases as the brightness of the image projected on the cathode ray tube increases, but it is clear that the present study can also be applied to the opposite case. The circuit diagram of the main part in Figure 1 is O. The constant voltage diode 14 of the control voltage generation circuit 3 has a Zener voltage that is the same as the brightness detection voltage corresponding to a predetermined brightness below which the gain of the speed modulation operation is constant. use. The gain control circuit 2 includes transistors 10. it,
12 differential amplifiers.

As the operating reference voltage of the differential pair transistors 11 and 12, a voltage lower than the Zener voltage of the constant voltage diode 14 is applied to the base of the transistor 12 by the power supply voltage and the resistor 15 and 16.

The resistors 17 and 18 divide the voltage at the cathode end of the constant voltage diode and the voltage applied to the base of the transistor 12 and apply it to the base of the transistor 11. Set to perform linear operation at . The video signal is input from the video signal input terminal 1 to the base of the current source transistor 10, and the collector current 8i! . The collector current of transistor 10 is shunted into the respective collector currents of differential pair transistors 11.12, and the potential difference between the bases of transistors 11.12 determines said shunting ratio. Therefore, by changing the potential difference between the bases, the amplitude of the video signal output to the collector of the transistor 12 can be controlled.

When the brightness is low and the brightness detection voltage is higher than the Zener pressure of the constant voltage diode 14, the base voltage of the transistor 11 is higher than the pace voltage of the transistor 12 and becomes a constant voltage, and the collector current of the transistor 12 is equal to the collector current of the transistor 11. Therefore, the amplitude of the video signal output from the collector of the transistor 12 is small.

On the other hand, the brightness is high and the brightness detection voltage is constant voltage diode 1.
If the Zener voltage is lower than 4, the voltage regulator diode 1
4 becomes non-conductive, and as the luminance detection voltage falls, the pace voltage of the transistor 11 also falls, and when it becomes lower than the pace voltage of the transistor 12, the collector current of the transistor 12 becomes larger than the collector current of the transistor 11. Therefore, by supplying the output video signal of the gain control circuit 2 to the speed modulation circuit 1, the amplitude of the output video signal of the gain control circuit becomes constant when the luminance detection voltage is equal to or higher than a predetermined value, and the speed modulation The operating gain is also constant. Further, below a predetermined value, the luminance detection voltage decreases E, and therefore the amplitude of the output video signal of the gain control circuit increases, so the gain of the speed modulation operation also increases. The brightness detection voltage generated by the brightness limiting circuit is supplied, and the output of the gain control circuit that controls the amplification gain of the video signal by the control voltage generated by the supplied brightness detection voltage is supplied to the speed modulation circuit, Since the configuration is configured to perform scanning speed modulation, it is possible to perform contour correction according to changes in the brightness of the image projected onto the cathode ray tube. By adjusting the contrast and setting the pedestal level, when the brightness is high, it is possible to perform sufficient contour correction even on images with blooming.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram of the main part of FIG. 1, and FIG. 3 is a block diagram of a conventional speed modulation circuit. 1... Video signal input terminal 2... Gain control circuit 3... Control voltage generation circuit 4
...speed modulation circuit 5...1 differential amplifier circuit 6...
・Output circuit 7...Speed modulation coil 8...Brightness detection voltage input terminal Fig. 1

Claims (1)

[Claims] 1. In a video playback device equipped with a speed modulation circuit that corrects the contour of an image by modulating the electron beam scanning speed of a cathode ray tube using a detection signal that detects a change in the brightness of a video signal, and an automatic brightness limiting circuit. 1. A video reproducing device comprising an operation control circuit that controls speed modulation operation using a brightness limit detection voltage.