JPS6180977A - Television receiver - Google Patents

Abstract

PURPOSE:To always keep a contrast of a slave picture constant, and to always read the contents of an image without any trouble by controlling the contrast of the slave picture without making it depend on a master picture. CONSTITUTION:A video signal 12 sent out from a synthesizing circuit 8 is supplied to a cathode ray tube 6, and also supplied to a master picture contrast controlling circuit 13 and a slave picture contrast holding circuit 14. The master picture contrast controlling circuit 13 uses an average current of the cathode ray tube 6 as a control signal and controls a contrast of the video signal 12. The slave picture contrast holding circuit 14 is brought to an on-off control by a gate pulse 11, and holds a contrast of only a slave picture image signal in the video signal 12, in a constant state. Outputs of these circuits 13, 14 are selected by a switch 15 which is brought to opening and closing control by the gate pulse 11, and fed back to the synthesizing circuit 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an in-picture television receiver.

[Technical background of the invention and its problems]

FIG. 3 shows a schematic diagram of a picture-in-picture type television receiver. 1 is a television broadcast signal receiving antenna, 2 is a checkerboard, 3 is a video intermediate frequency amplifier, 4 is a video detection circuit, 5 is a video amplification circuit, and 6 is a cathode ray tube, which receives the video signal of a normal television signal. The entire television receiver circuit is configured to display the received image (main screen). Reference numeral 7 denotes a sub-screen image signal teacher circuit which generates a sub-UMJ normal image video signal to be displayed on a part of the main screen.

The sub-screen video signal 10 is often a television signal obtained through a channel other than the channel 2, or is generated from a character generator built into the television receiver. Various things can be considered, such as characters, figures, etc. These small screen video signals 10
is superimposed on a part of the main screen video signal 9 via the sweet-acid circuit 8.
The synthesis circuit 8 blown out is a circuit that performs luminance +;'fg:, contrast adjustment, etc. on each of the supplied main screen and sub-screen video signals, and outputs both video signals by fully superimposing them. The above superimposition method will be explained with reference to FIG. 4. In order to project a child screen on the main screen, the child screen video signal 10 is time-axis compressed into a part of the main screen sandwich signal 9, and the main screen OfI It is sufficient to insert it instead of the 1 ice signal 9. The gate pulse 11 is a pulse that defines this push-in position, and the main screen == double signal corresponding to the pulse generation position is deleted, and the sub-screen video signal 10 is inserted in its place.

At this time, the contrast of the child screen video signal 10 is the main picture d.
It is restricted to that of O. This is to make small characters etc. easier to see by suppressing the contrast of the main screen video signal 9.

Even so, the child screen displayed in the above state becomes difficult to see when the contrast ratio between the parent and child images becomes large. Therefore, in the past, as described in Japanese Patent Publication No. 56-39594, the average brightness level (APL) of the main screen is detected, and the ratio of the brightness of the main screen and the sub-screen is controlled according to this brightness level. Therefore, it has been proposed to keep the contrast ratio of both picture mounds constant. However, according to this method, when the contrast of the main screen decreases, the contrast of the sub-screen also decreases, so the displayed response on the sub-screen, which is originally small, becomes illegible. It was inconvenient.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a television receiver that can always display a sub-screen displayed on a main screen in a state where the contents are sufficiently legible. purpose.

[Summary of the invention]

In order to achieve the above object, the present invention controls the contrast of the child screen without depending on the parent screen (tt), and performs feedback control to keep the contrast of 1,000 ryo (2) approximately constant at the time of trial. Make it the gist.

[The invention is hilarious]

FIG. 1 shows a schematic configuration of a television receiver according to the present invention. The video signal 12 sent from the combined g1g circuit 8 is supplied to the Pi electrode ray tube 6, and is also supplied to the main screen contrast side end circuit 13 and the sub screen contrast holding circuit 14. is fed back to the synthesis circuit 8 via a switch 15 whose opening and closing are controlled by a gate pulse 11.

The main picture l contrast control circuit 13 controls the contrast of the supplied video signal 12 using the average current of the cathode ray u6 as a control signal. That is, a circuit is used to maintain and output the contrast of only the 〇-plane image signal 10, which performs control to increase cathode rays. The outputs of these circuits 13 and 14 are selected by a switch 15 which is opened and closed by the gate pulse 11 and fed back to the combining circuit 8. The switch 15 is set during the supply period of the gate pulse 11 (sub-screen video signal period).
The output of the sub-l contrast holding circuit 14 is selected, and the output of the main screen contrast ratio retaining circuit 13 is selected during the seventh other period (main screen image signal period).

The above-mentioned seven contrast-controlled main screen image signals and sub-side image single signal are fed back to the synthesis circuit 8 to be output in a superimposed manner and displayed on the display screen of the cathode ray tube 6.

FIG. 2 shows a specific example of the circuit configuration of the small screen contrast holding circuit 14. The emitter of the transistor Q1, to which the video signal 12 is supplied to the pace, is connected to the collector of the transistor Q2 via a resistor R1. The emitter of this transistor Q2 is connected to the reference potential, and the gate pulse 11 is supplied to its pace. Therefore, the amplification of the video signal 12 in the transistor QIK is performed during the supply period of the gate pulse 11, that is, the sub-screen video signal 1.
This will be done only during the input period of 0.

Danpuku child screen I5! - Image signal 1O1a is output from the collector of transistor Q1 and supplied to the pace of transistor Q3. A resistor R2 is connected to the pace and power injection amount of this transistor Q3, and the collector is connected to a reference potential. Further, a series circuit in which a capacitor C and a resistor R3 are connected in series and a resistor R4 are connected in parallel between the emitter of the transistor Q3 and the power supply -+-tQB. By setting the capacitance t of the capacitor C to a large value, the contrast is averaged over a certain period of time, and the contrast of the small screen video signal 10 is maintained at a constant value.

The above contrast-controlled signal is sent to the Banfa amplifier OP.
It is output through I and is subsequently selected by switch 15.

〔Effect of the invention〕

According to the present invention, the contrast of the child screen is kept constant regardless of the parent screen and regardless of the pattern of the mouthpiece of the child screen. That is, when the contrast of the sub-screen painter signal is large, the contrast is increased to kM, and conversely, when the contrast is small, the contrast is increased. Of course, if the contrast on the image display is low, the video content will become unclear, but since the sub-screen is formed by a small screen on the display screen, even if the contrast is high, it will cause visual problems. According to the present invention, since the contrast of the sub-screen is limited to a certain level, the above-mentioned problem is solved, and the image contents can be read without any trouble at all times.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a television receiver according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a sub-screen contrast holding circuit according to the present invention, and FIG. 3 is a diagram of a conventional television receiver. The schematic configuration diagram and FIG. 4 are waveform diagrams of video signals. 6...Vi pole ray tube 7...Small screen video number generation circuit 8...Synthesis diagram 11...Gate pulse 12...
Sub-screen contrast retention circuit 15...Switch agent Patent attorney Nori Chika Atsushi Figure 1 Figure 2 Figure 3'@ Figure 4

Claims (1)

[Claims] If another image (main screen) is displayed on the display screen (main screen)
1. A television receiver capable of displaying a sub-screen (sub-screen), characterized in that the contrast of the sub-screen video signal is constant.