JPS62289060A - Control circuit for picture quality in television receiver - Google Patents

Abstract

PURPOSE:To always set picture quality optimum by changing a DC voltage for controlling picture quality in accordance with the brightness of a screen and setting the picture quality sharper as the screen is darker. CONSTITUTION:A DC-reproduced picture signal being a luminance signal is added to a variable resistor 1 for controlling picture quality, whereby the volt age for controlling picture quality is changed in accordance with the picture signal. In the picture signal on the black screen, the voltage of an input terminal for controlling picture quality in a video chroma circuit 2 rises, and picture quality is controlled sharp. In the picture signal on the white screen, the voltage for controlling picture quality drops and picture qulaity becomes soft. When the screen is bright, picture quality is set soft, whereby a blooming can be prevented, and the easy-to-see and sharp picture can be reproduced. When the screen is dark, picture quality is set sharp, whereby the easy-to-see picture can be reproduced, which can precisely be seen even if the screen is dark.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention Field of Industrial Application The present invention relates to an image quality control circuit used in a television receiver.

BACKGROUND TECHNOLOGY In recent years, each circuit of a television receiver has been integrated into an IC, and a circuit that controls the sharpness of the image quality using a DC control voltage that is also applied to an image quality control circuit is used.

First, a conventional image quality control circuit will be described with reference to the drawings.

FIG. 3 shows an example of a conventional image quality control circuit.
In the figure, a variable resistor 2 for controlling image quality is an IC video chroma circuit having a built-in circuit for controlling image quality and having an input terminal for a DC voltage for control.

In this circuit, the frequency characteristics of the video signal when the movable terminals of the variable resistor 1 for controlling image quality are at points A, B, and 0 are shown in FIG. As is clear from Figure 4, the video
When the DC control voltage applied to the image quality control voltage input terminal of the chroma circuit 2 is high, the high frequency components of the video signal are compensated and the image quality becomes sharp, and when the DC control voltage applied is low, the image quality becomes soft.

Problems to be Solved by the Invention However, in the conventional circuit configured as described above, the reproduced image is controlled to the same constant image quality whether the screen is dark or bright, and plumping occurs when the screen is bright. However, when the screen is dark, the sharpness is insufficient and the image becomes difficult to see.

SUMMARY OF THE INVENTION Therefore, the present invention aims to solve the above-mentioned conventional inconveniences, and provides an image quality control circuit that can change the image quality to be always easy to see and free from blooming, etc., depending on the brightness of the screen of the reproduced image. This is the purpose.

Means for Solving the Problems The image quality control circuit of the television receiver of the present invention detects the brightness of the screen of the reproduced image, and uses the detection output to change the DC control voltage for image quality control, thereby adjusting the brightness of the screen. The image quality is controlled so that the darker the image, the sharper the image quality.

Effects According to the structure of the present invention, when the screen is bright, the image quality is softened to prevent the occurrence of pluming, and when the screen is dark, the image quality is sharpened to make the screen easy to view. You can play back videos with optimal image quality.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an image quality control circuit in one embodiment of the present invention. In Fig. 1, 3 is a transistor whose collector is connected to the 10B power supply line, whose base is connected to the video signal (luminance signal) line, and whose emitter is grounded via a resistor 4, as well as a variable resistor for image quality control. One end of 1 is connected to the emitter. As a result, a video signal (luminance signal) that changes depending on the brightness of the screen is passed through an impedance conversion circuit composed of a transistor 3 and a resistor 4 as a screen brightness detection output of a reproduced image, and is connected to a variable resistor 1 for image quality control. We are trying to supply it to

In the image quality control circuit configured as described above, it is assumed that the video signal is as shown in FIG. This signal is the signal immediately before driving the cathode ray tube, and by applying this video signal, which is a DC-regenerated luminance signal, to a variable resistor for image quality control, it is possible to change the image quality control voltage according to the video signal. can. When the video signal is for a black screen, the voltage at the image quality control input terminal of the video chroma circuit 2 is raised to control the image quality sharply, and for the video signal for a white screen, the image quality control voltage is lowered so that the image quality is soft. controlled.

Therefore, according to this embodiment, by softening the image quality when the screen is bright, it is possible to suppress pluming, and it is possible to reproduce a clear and easy-to-see image. Furthermore, by sharpening the image quality when the screen is dark, it is possible to reproduce an image that is easy to see in detail even on a dark screen.

Effects of the Invention As described above, according to the present invention, the brightness of the screen can be adjusted by changing the DC voltage for image quality control according to the brightness of the screen using a video signal, etc., and sharpening the image quality of a dark screen. This has great practical effects, as it can always maintain optimal image quality depending on the situation, eliminates blooming, and reproduces images that are clear and easy to see even in dark areas.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an image quality control circuit of a television receiver according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the video signal in FIG. 1, and FIG. 3 is a conventional image quality control circuit. The circuit diagram and FIG. 4 are characteristic diagrams showing the voltage of the image quality control terminal and the frequency-amplitude characteristics of the clear image signal. 1...Variable resistor for image quality control, 2...Video chroma circuit, 3...Transistor, 4...
·····resistance. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 71 ＼ Public J゛ 1゛J Figure 3 Figure 4

Claims (1)

[Claims] An image quality control circuit that controls the sharpness of the image quality of a reproduced image by an applied DC control voltage, and a detection circuit that detects the brightness of the reproduced image, and reproduces by changing the DC control voltage according to the output of the detection circuit. An image quality control circuit for a television receiver, characterized in that the darker the image, the sharper the image quality.