JP2000217044A - On-screen data luminance adjustment circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve contrast of a luminance of a screen and on-screen data regardless of a very simple circuit configuration. SOLUTION: The subject adjustment circuit is provided with a charge discharge circuit 33 that changes a DC level of a video signal V depending on a mean value of the signal and with an OSD insertion circuit 36 that superimposes OSD signals α1, α2 of a prescribed DC level onto the video signal V. The charge discharge circuit 33 decreases the black level of the video signal V when the screen is bright and increases the black level when the screen is dark and the OSD insert circuit 36 superimposes the OSD signals α1, α2 of the prescribed DC level on the video signal V as above. Since the luminance of the on-screen data displayed on the screen is proportional to a voltage of the on-screen data signal on the basis of the black level of the video signal, the luminance of the on-screen data is relatively increased when the screen is bright, but relatively decreased when the screen is dark.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-screen data brightness adjusting circuit for adjusting the brightness of on-screen data to be displayed on a part of a screen.

[0002]

2. Description of the Related Art Most modern television receivers include:
A function of displaying on-screen data such as a reception channel on the screen is provided. However, if on-screen data is displayed at a constant luminance regardless of the screen, it has been pointed out that the data is difficult to see on a bright screen, and conversely, the data is bright and blurred on a dark screen.

In order to improve this problem, Japanese Utility Model Application Laid-Open No.
As disclosed in Japanese Patent Publication No. 266, a circuit has been proposed which detects the amplitude of a video signal and varies the luminance of on-screen data according to the detection result. 2-90577
A similar circuit is proposed in Japanese Patent Publication No. 62-395 and Japanese Patent Publication No. 62-6395.

[0004]

However, in the case of the above-mentioned conventional example, the contrast of the luminance between the screen and the on-screen data is improved, so that the on-screen data is easy to see, but the amplitude of the video signal is detected. Since it is necessary to vary the brightness of the on-screen data according to the detection result, the circuit configuration tends to be complicated, and there is an essential disadvantage that it is difficult to reduce the cost.

The present invention has been made in view of the above background, and has as its object to improve the brightness contrast between the screen and the on-screen data while having a very simple circuit configuration. It is an object of the present invention to provide an on-screen data brightness adjustment circuit capable of performing the above-mentioned operations.

[0006]

According to the present invention, there is provided an on-screen data brightness adjusting circuit for adjusting the brightness of on-screen data to be displayed on a part of a screen. And an on-screen data insertion circuit that superimposes an on-screen data signal of a constant DC level on the video signal.

In such a configuration, the charge / discharge circuit reduces the black level of the video signal on a bright screen, but increases it on a dark screen. An on-screen data signal of a constant DC level is superimposed. Since the brightness of the on-screen data displayed on the screen is proportional to the voltage of the on-screen data signal based on the black level of the video signal, the brightness of the on-screen data increases relatively when the screen is bright. On the other hand, when the screen is dark, the contrast is relatively lowered, and as a result, the contrast of the luminance between the screen and the on-screen data is improved.

More preferably, a clamp circuit is provided between the charge / discharge circuit and the on-screen data insertion circuit and fixes the white level of the video signal in order to limit the luminance of the on-screen data. With such a configuration, the brightness of the on-screen data does not increase to a certain level or more, and the on-screen data when the screen is at the intermediate brightness level is easy to see.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of an on-screen data brightness adjustment circuit provided in a television receiver, FIG. 2 is a diagram showing a voltage waveform of a video signal of a main part of the circuit, and FIG. 3 is a diagram showing a screen displayed on a CRT display. 9 is a graph showing a relationship between on-screen data and luminance.

The on-screen data brightness adjusting circuit described here by way of example is provided in a television receiver having a function of displaying on-screen data such as a receiving channel in a screen as shown in FIG. Is what it is. In the figure, reference numeral 10 denotes a video circuit for generating a video signal V (composite signal) and a synchronizing signal T, etc., 20 a microcomputer for controlling a main part of the television receiver, 30 an on-screen data brightness adjustment circuit, and 40 a CRT display. is there.

The microcomputer 20 receives a synchronization signal T and the like.
OSD (On Screen Data) signals α1, α for displaying on-screen data on the screen of the RT display 40
2 is generated and output. Here, as the on-screen data, not only the characters of the receiving channel such as CH2 but also the outline thereof are displayed.
The OSD signal α2 is a signal for displaying a character part (Y signal), while the OSD signal α1 is a signal for displaying a border part (blanking signal). It is output to the adjustment circuit 30.

On-screen data brightness adjustment circuit 30
Has a function of superimposing the OSD signals α1 and α2 on the video signal V and adjusting the brightness of the on-screen data to be displayed on a part of the screen of the CRT display 40. Circuit 32, charge / discharge circuit 33, clamp circuit 34, amplifier circuit 35, and O
An SD insertion circuit 36 (corresponding to an on-screen data insertion circuit) is provided.

The clamp circuit 31 includes resistors R10 and R11, a capacitor C2, and a diode D1, and is configured to fix the black level of the video signal V. Here, since the video signal V is input via a coupling capacitor (not shown), the black level of the signal fluctuates according to the average value. A clamp circuit 31 is provided to equalize the black level regardless of the average value of the video signal V, in other words, regardless of the brightness of the screen.

The clamped video signal V is input to a charge / discharge circuit 33 via an amplifier circuit 32 comprising a transistor Q1 and an emitter resistor R1.

The charge / discharge circuit 33 includes a capacitor C1 and a resistor R
2 is configured to change the DC level of the video signal V in accordance with the average value of the video signal V. That is, when the average value of the video signal V is high, in other words, when the screen is bright, the DC level of the video signal V is lowered, while when the average value of the video signal V is low, in other words, when the screen is dark, the video is low. The DC level of the signal V is increased. The substantial reason why the clamp circuit 31 is provided is that the charge / discharge circuit 33 proportionally changes the DC level of the video signal V in accordance with the average value of the signal. The rate of the change is determined by the circuit constant of the capacitor C1 and the resistor R2.

The video signal V output from the charge / discharge circuit 33
Is output to the OSD insertion circuit 36 via the clamp circuit 34 and the amplification circuit 35.

The clamp circuit 34 includes resistors R12 and R13, a capacitor C3, and a diode D2, and is configured to fix the white level of the video signal V. The circuit configuration is the same as that of the clamp circuit 31, except for the voltage to be clamped.

The amplifying circuit 35 includes a transistor Q2, bias resistors R3 and R4, and an emitter resistor R5. The amplifying circuit 35 amplifies the video signal V clamped by the clamp circuit 34 and outputs it to the OSD insertion circuit 36.

The OSD insertion circuit 36 is composed of a circuit block 361 for superimposing the OSD signal α1 on the video signal V and a circuit block 362 for superimposing the OSD signal α2 on the video signal V. The circuit block 362 is connected to the subsequent stage.

The circuit block 361 includes the semiconductor switch 3
When the OSD signal α1 is inactive, the video signal V is passed as it is. When the OSD signal α1 is active, the DC voltage v1 obtained by dividing the power supply voltage by the resistors R6, R7 is used. Output. That is, while the OSD signal α1 is active, the DC voltage v1 is output instead of the video signal V. As a result, the OSD signal α1 whose DC voltage level is v1 is superimposed on the video signal V. Is done. Note that the DC voltage v1 is the CRT display 4
It is set according to the luminance of the border of the character of the on-screen data to be displayed at 0.

The circuit block 362 includes the semiconductor switch 3
622 and resistors R8 and R9. When the OSD signal α2 is inactive, the video signal V or the like is passed as it is. When the OSD signal α1 is active, the DC voltage v2 obtained by dividing the power supply voltage by the resistors R8 and R9.
Is output. That is, while the OSD signal α2 is active, the DC voltage v2 is output instead of the video signal V or the like. As a result, the OSD signal α2 having the DC voltage level v2 with respect to the video signal V is output.
Are superimposed. Note that the DC voltage v2 is set according to the luminance of the characters of the on-screen data to be displayed on the CRT display 40.

The operation of the on-screen data brightness adjustment circuit configured as described above will be described with reference to FIGS. FIG. 2A shows the waveform of the video signal V at point A in FIG. 1. When the upper screen is a bright screen,
The lower part shows the case of a dark screen, respectively. The black level of the video signal V is fixed to a constant level regardless of the brightness of the screen by the clamp circuit 31.

FIG. 2 (b) shows the waveform of the video signal V at point B in FIG. 1.
The lower part shows the case of a dark screen, respectively. The charge / discharge circuit 33 allows the video signal V
The black level of the video signal V increases when the image is dark, while the black level of the video signal V decreases.

FIG. 2 (c) shows the waveform of the video signal V at point C in FIG. 1.
The lower part shows the case of a dark screen, respectively. Here, a period in which the border of the character of the on-screen data is displayed is shown, and OSD signals α1 and α2 whose DC voltage levels are v1 and v2 are superimposed on the video signal V.

The voltage of the OSD signal α1 based on the black level of the video signal V when the screen is bright is compared with the voltage of the OSD signal α1 based on the black level of the video signal V when the screen is dark. large. This is the charge / discharge circuit 33
This is because the black level of the video signal V decreases when the screen is bright, and increases when the screen is dark.

When the video signal V on which the OSD signal α1 is superimposed is output to the CRT display 40, C
On the RT display 40, the border of the character of the on-screen data is displayed on the screen of the video signal V. The brightness of the on-screen data displayed on the CRT display 40 depends on the OSD signal α1 based on the black level of the video signal V.
, The luminance of the border is high when the screen is bright, and is low when the screen is dark. This is exactly the same for the characters of the on-screen data. Therefore, the contrast of the brightness between the screen of the CRT display 40 and the on-screen data is improved, and the on-screen data becomes easy to see regardless of the brightness of the screen.

FIG. 3 is a graph showing the relationship between the screen displayed on the CRT display 40 and the luminance of the on-screen data. The solid line indicates the case where the clamp circuit 34 is provided, and the dotted line indicates the case where the clamp circuit 34 is not provided. ing. When there is no clamp circuit 34, the CRT display 40
The brightness of the on-screen data displayed on the screen changes in proportion to the brightness of the screen. This tends to make it difficult to see the on-screen data when the screen has an intermediate level of luminance.

To solve this problem, a clamp circuit 3
4 are provided. That is, by adjusting the circuit constants and the like of the charge / discharge circuit 33, the brightness of the on-screen data is set slightly brighter than the screen, and then the brightness of the on-screen data when the screen is bright is limited by the clamp circuit 34. This makes it easier to see the on-screen data when the screen has an intermediate level of luminance.

Further, in the on-screen data brightness adjustment circuit 30, since it is basically only necessary to change the DC level of the video signal V, the circuit configuration is very simple and the cost can be reduced. become.

The on-screen data brightness adjusting circuit according to the present invention is naturally applicable to a color television and the like, and the charge / discharge circuit, the clamp circuit and the OSD insertion circuit may have the same functions as described above. In this case, a circuit having a different circuit configuration may be used.

[0031]

As described above, according to the on-screen data brightness adjusting circuit according to the first aspect of the present invention, the brightness of the on-screen data increases relatively when the screen is bright, and decreases relatively when the screen is dark. With this configuration, the brightness contrast between the screen and the on-screen data becomes good, and the on-screen data becomes easy to see. Moreover, since it is only necessary to change the DC level of the video signal, the circuit configuration is inevitably very simple, and compared with the conventional example in which the detection of the amplitude of the video signal is indispensable, The number of points can be reduced, and cost can be reduced.

According to the on-screen data brightness adjusting circuit according to the second aspect of the present invention, since the brightness of the on-screen data does not become higher than a certain level,
As a result, the on-screen data when the screen is at the intermediate luminance level becomes easy to see, and the performance of the circuit can be further improved.

[Brief description of the drawings]

FIG. 1 is a diagram for describing an embodiment of the present invention, and is a circuit diagram of an on-screen data brightness adjustment circuit provided in a television receiver.

FIG. 2 is a diagram showing a voltage waveform of a video signal of a main part of the circuit.

FIG. 3 is a graph showing a relationship between a screen displayed on a CRT display and luminance of on-screen data.

[Explanation of symbols]

 Reference Signs List 30 on-screen data brightness adjustment circuit 31 clamp circuit 32 amplifier circuit 33 charge / discharge circuit 34 clamp circuit 35 amplifier circuit 36 OSD insertion circuit V video signal α1, α2 OSD signal 40 CRT display

Claims (2)

[Claims] 1. An on-screen data brightness adjustment circuit for adjusting brightness of on-screen data to be displayed on a part of a screen, a charge / discharge circuit for changing a DC level of the video signal according to an average value of the video signal, An on-screen data insertion circuit for superimposing an on-screen data signal having a constant DC level on the video signal. And a clamp circuit provided between the charge / discharge circuit and the on-screen data insertion circuit for fixing the white level of the video signal in order to limit the luminance of the on-screen data. The on-screen data brightness adjustment circuit according to claim 1.