JPS61152167A - Contour compensating circuit - Google Patents

Abstract

PURPOSE:To prevent an output waveform from being distored beyond the dynamic range in a video amplifer of the succeeding stage even if the amplitude of a contour signal is changed, by reducing the amplitude of an original video signal when the amplitude of the contour signal to be added to the video signal is increased. CONSTITUTION:The inputted original video signal is inputted to a contour signal forming circuit 2 and a video signal variable gain circuit 6. The contour signal outputted from the circuit 2 has the amplitude changed by a contour signal variable gain circuit 3. Gains of circuits 6 and 3 are controlled by a gain control circuit 5 so that the amplitude of the video signal is reduced according as that of the contour signal is increased, and the resulting amplitude of addition between the contour signal and the video signal is made constant. The video signal and the contour signal are added by an adder 4, and the output is inputted to the video amplifier to the succeeding stage. Thus, the output waveform which does not exceed the dynamic range of the contour signal is obtained to perform good contour compensation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a contour compensation circuit for a television or display.

[Background of the invention]

Conventionally, a contour compensation circuit performs appropriate contour compensation by changing the amplitude of a contour signal added to a video signal to change the amount of compensation. With this method, there is no need to perform any manipulation on the amplitude of the video signal.
Therefore, if the amplitude of the contour signal to be added is increased,
No consideration was given to the fact that the video amplifier at the next stage would cause distortion. Incidentally, related circuits for this purpose include, for example, Japanese Patent Laid-Open Nos. 51-109722 and 1987-87524.

[Purpose of the invention]

An object of the present invention is to provide a contour compensation circuit in which the 1b power waveform is not distorted beyond the dynamic range in the next stage video amplifier even if the amplitude of the contour signal is changed. , when the amplitude of the added contour signal is increased,
This is a contour compensation circuit that reduces the amplitude of the original video signal so that the amplitude of the original video signal plus the contour signal falls within the dynamic range of the next-stage video amplifier.

A conventional contour compensation circuit will be described below with reference to FIG.

The video signal input to the terminal 1 is input to the contour signal forming circuit 2 and becomes a contour signal. This contour signal is input to the variable gain circuit 3 and becomes a contour signal whose amplitude can be varied. Then, the image signal and the contour signal are added by an adder 4, and the output is input to a video amplifier.

In this case, since contour compensation is performed by changing the amplitude of the contour signal without changing the amplitude of the original video signal, the output signal has an amplitude larger than the amplitude of the human input signal by the amount of the contour signal.

In the next-stage video amplifier, the dynamic range is fully utilized to obtain the maximum output voltage, as shown in FIG. 4<a>. When the contour signal is added, the dynamic range of the next-stage video amplifier is exceeded, as shown in FIG. 4(b), and the output waveform is distorted. In this case, it is not possible to obtain an effective contour compensation circuit on the cathode ray tube surface, and on the contrary, only the contour is emphasized thickly, which may have the opposite effect.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to FIG.

The original video signal input to the terminal 1 is input to the contour signal forming circuit 2 and the video signal variable gain circuit 6. The amplitude of the contour signal outputted by the contour signal forming circuit 2 can be freely changed by the contour signal variable gain circuit 3.

Therefore, if the gain control circuit 5 controls the respective gains of the video signal variable gain circuit 6 and the contour signal variable gain circuit 3, and the contour signal is increased, the amplitude of the video signal decreases accordingly, and the contour signal and the video signal are increased. Pressure is applied so that the amplitude of the added signal remains constant. In other words, the control circuit 5 works so that the amplitude of the contour signal and the amplitude of the video signal are inversely proportional to each other (.Then, the adder 4 adds the video signal and the contour signal, and the output is input to the next stage video amplifier. By doing so,
Regardless of the amplitude of the contour signal, it is possible to obtain an output waveform as shown in FIG. 4C, which does not distort beyond the dynamic range of the video amplifier in the next stage, and to perform good contour compensation.

Next, a specific circuit will be explained using FIG. 2.

The video signal input to the terminal 1 passes through a contour signal forming circuit 2 using two delay circuits, becomes a contour signal, and is input to a contour signal variable gain circuit 3. Further, the video signal that has passed through one delay circuit is input to the video signal variable gain circuit 6. If double-balanced mixers are used as these two variable gain circuits, the gain can be controlled by DC voltage, so it is possible to use a gain control circuit consisting of a variable DC power supply and resistors as shown in Figure 2. can. In other words, it is possible to simultaneously change the amplitude of the contour signal and the video signal while maintaining an inversely proportional relationship using one variable DC power supply. The amplitude of the sum of the contour signal and the video signal added by the adder 4 is constant regardless of the amount of contour compensation. This method has the advantage that the amount of contour compensation can be adjusted using the leader line to the outside.

〔Effect of the invention〕

According to the present invention, even if the amplitude of the contour signal is changed, the finger width of the original video signal changes in inverse proportion to it, and a constant amplitude is maintained by adding the video signal and the contour signal. This has the advantage that an output waveform that is not distorted beyond the dynamic range of the amplifier can be obtained, and that good contour compensation can be performed.

Therefore, if this circuit is used, it can be attached as an external circuit to televisions and displays that do not perform conventional contour compensation, and contour compensation can be performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a contour compensation circuit according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of an embodiment of the present invention, FIG. 6 is a block diagram of a conventional contour compensation circuit, and FIG. 4 is an output FIG. 2...contour signal forming circuit, 4...addition circuit,

Claims (1)

[Claims] 1. A contour compensation circuit comprising a circuit for forming a contour signal from a video signal, a circuit for amplifying the contour signal and varying its gain, and a circuit for adding the original video signal and the contour signal. A circuit for amplifying the video signal and varying its gain, and a circuit for controlling the gain of the video signal and the contour signal are provided, and the amplitude of the original video signal is changed in opposition to the change in the amplitude of the contour signal. Contour compensation circuit.