JPS6097786A - Television receiver - Google Patents

Abstract

PURPOSE:To obtain optical picture quality even in any external light conditions or scenes by detecting average luminance of the tube surface of a picture tube instead of detecting an APL, and by controlling to decreased nonlinear correction if the average luminance is high. CONSTITUTION:A luminance signal from an image detection circuit 21 is supplied to a picture control circuit 22, and this luminance signal amplitude is contolled by an ABL signal in accordance with luminance of the tube surface of a picture tube 25 from an image output circuit 24. This ABL signal is supplied to an average luminance detection circuit 26, and here, an average luminance dtection voltage SB is obtained and supplied to a multiplying circuit 29. On the other hand, an external luminous energy detecting signal SL, which is detected by a detection element 27 of the external luminous energy, is also added to the multiplying circuit 29, and is multiplied by the average luminance detection voltage SB. As a result, a multiplication signal S'M is obtained. When this is supplied to a correction circuit 23 as control voltage, the correction circuit 23 is corrected so that the larger the absolute value of the control voltage will be, the smaller the nonlinear properties will be.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to television receivers, and more particularly to techniques for improving contrast on their inner surfaces.

Background technology and its problems Generally speaking, television l! It is known that when viewing blood in the presence of external light, the contrast becomes worse as the luminance signal becomes black.

Figure 1 is a box graph showing the results of an experiment with low contrast, where the horizontal axis shows the level (instantaneous level) of the luminance signal, and the vertical axis shows the intensity of the signal that enters the eye from the surface of the picture tube. The amount of light (U) of the light emitted by the picture tube and the light reflected from the outside light on the tube surface.

In this anchor in Figure 1, curve L1 is the characteristic in a dark room, where the level of the luminance signal and the warmth of the light from the picture tube surface are ljl, so the contrast from black to white at the luminance signal level is The result is a consistently good screen.

On the other hand, curve L2 is a characteristic when there is external light, and as the luminance signal becomes black level, the contrast worsens, causing a phenomenon of falling in love. This phenomenon becomes stronger as the amount of external light increases.

Therefore, in the luminance signal system, curves Co, C1°C2 in Fig. 2 are used.
, C3 is provided with a non-linear correction circuit for normal human output characteristics, and when there is external light, the amplitude of the luminance signal in the black direction is expanded and the amplitude in the white direction is compressed. It was considered that the contrast could be improved by obtaining a characteristic similar to that of the curve L3 in FIG. 1.

That is, if the luminance signal before correction (horizontal axis) is X and the luminance signal after correction (vertical axis) is y, then y=xγ (+≦γ≦1)
At the same time, if we control the multiplier γ in accordance with the external light ML so that the brighter the external light amount is, the closer the compensation curve B is to the curve 03 side, the external light will increase ζ, or the external light amount will change. This means that good contrast can be obtained even if the contrast changes.

However, when performing non-linear correction based only on the amount of external light, it was effective in reducing non-electromagnetic effects in dark scenes, but it turned out to have the opposite effect in bright scenes, giving a whitish appearance. did.

This is because, although the presence or absence of external light does not have a large effect on the brightness of the tube at its own level, non-linear correction is performed from the black level to the white level, making the brightness signal level higher than necessary. This is because the contrast of the white level becomes small.

Therefore, a method was devised in which the average brightness level of the human input signal is detected, regardless of the amount of external light, and when the C1 average brightness level is low, the nonlinear correction is weakened.

Figure 3 shows an example of such a case, where the luminance signal Y from the video detection circuit (11) is supplied to the clamp circuit (12), subjected to Bedestal clamping, and then supplied to the nonlinear correction circuit (13). . This correction circuit (13) has correction characteristics as shown in FIG.

Further, a detection element for detecting the amount of external light, for example Cd5 (14), is provided, and the light detection output from this is supplied to a detection circuit (15), from which a detection signal St of the amount of external light is obtained. In this case, the detected f-signal SL is a signal with characteristics as shown in FIG. This signal SL is supplied to a multiplication circuit (16).

On the other hand, the luminance signal from the clamp circuit v8 (12) is APL
The detection signal SP of the average luminance level supplied to the detection circuit (17) is a signal with characteristics as shown in FIG. This signal Sp is also supplied to the multiplication circuit (16).

Therefore, from the multiplication circuit (16), the signal SL and the signal S
A signal SM multiplied by p is obtained, and this signal 3M is supplied to the correction circuit (13) to control its correction characteristic. In this case, the larger the amount of outside light, the larger the correction amount is.At this time, the larger the APL, that is, the more the average luminance level becomes the quotient, the smaller the correction amount is.
If is larger than a certain level, the correction amount is set to zero regardless of changes in the amount of external light.

The brightness signal supplemented in this way is then supplied to the ζ picture tube (20) via the picture control circuit (18) and the video output circuit (19). Output circuit (19)
The brightness signal amplitude is increased by the ABL signal corresponding to the brightness of the tube curve. Also picture volume (18
Similarly, the brightness signal amplitude can be changed by manipulating νP) by the user.

As shown below, the APL of the human brightness signal is detected and the AP
By weakening the correction when L is quotient,
Improves screen appearance in bright scenes.

However, in the example in Figure 3, ? After the ili stop circuit,
As mentioned above, since there is a picture control circuit that controls the amplitude of the luminance signal, the amplitude of the signal corrected by this control circuit is changed by ABL etc., so the correspondence between the APL of the human input signal and the brightness of the screen surface is changed. This results in inconveniences such as the contrast correction not working even though the tube surface is very dark.

Purpose of the Invention The present invention improves the above-mentioned drawbacks and makes it possible to obtain a screen with good contrast in any scene under any outside light conditions.

Summary of the invention This invention detects the average luminance of the tube curve of the picture tube instead of detecting -4, and performs nonlinear correction if the amount of external light is large and the average luminance of the tube surface increases +Ili. By controlling the amount of meat to a minimum, optimal meat quality can be obtained even under harsh external light conditions and in harsh scenes.

Embodiment FIG. 6 is a diagram of an embodiment of the present invention. In this example, the luminance signal from the video detection circuit (21) is supplied to the picture control circuit II (22),
The amplitude of this brightness signal is controlled by an ABL signal from the video output circuit (24) that corresponds to the brightness of the tube surface of the picture tube (25). The output signal from this picture control circuit (22) is supplied to a nonlinear correction circuit (23) having a correction characteristic as shown in FIG. Then, after being subjected to non-linear correction as described below, it is supplied to the picture tube (25) through the video output circuit (24). (22VR) is traceable by the user.
This is the picture volume for adjustment.

The ABL signal from the video output circuit (24) is then fed to the average luminance detection circuit (26) on the tube surface.

This detection circuit (26) consists of, for example, an integrating circuit consisting of a resistor (26R) and a capacitor (26C), and the tube surface average brightness detection voltage sB from this circuit increases as the brightness increases, as shown in Figure 7. The output is made so that the value becomes smaller.

The average luminance detection voltage of the tube surface obtained in this way is calculated by the multiplier circuit (
29).

On the other hand, the signal from the external light amount detection element (27) is supplied to the detection circuit (28), and from this, an external light amount detection signal St having characteristics as shown in FIG. (29) is supplied to Jl,ru.

Therefore, a multiplication signal SM' of the signal sB and the signal St is obtained from the multiplication circuit 118 (29), and this signal SN'
is supplied as a control voltage to the °C correction circuit (23).

In this case, the complementary 1F circuit (23) is corrected so that the greater the absolute value of the controlled vehicle jL, the stronger the nonlinearity becomes.

Therefore, with this control, even if the external light 9 is strong, if the tube surface average luminance is equal to the average brightness, the nonlinear complement +E is made weak.

In this example, a clamp circuit is not provided, but this is because the tube surface average brightness detection voltage is detected from the ABL voltage, which is already a DC voltage.

FIG. 8 shows another example of this invention, in which ζ is AB
Picture control circuit (22) instead of L voltage
The output voltage ratio of 43 is supplied to the tube surface average brightness detection circuit (26).Others are the same as in the example shown in FIG.

However, in this example, a clamp circuit (
31) will be established. This example uses the BLL signal to control picture+-b! This is an example that takes advantage of the fact that the output of J road (22) is controlled to have a constant ABL amount.

In the examples shown in FIGS. 6 and 8, if the user is using the control volume at the picture control circuit (22) and using external light,
Since the absolute value of the average brightness detection voltage on the tube surface is a quotient, this is combined with the fact that the amplitude of the human input signal in compensation circuit IIJt (23) is small. It also works.

Effects of the Invention According to the present invention, instead of detecting the APL of the luminance signal, the average luminance of the tube surface is detected, and non-linear correction is performed according to that and the amount of external light. Optimal contrast I- corresponding to the brightness of the tube surface when viewed
This can be corrected.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the results of this experiment regarding the low contrast of a television receiver in the presence of external light 1ζ.
3 is a block diagram of an example of a conventional television receiver, FIGS. 4 and 5 are explanatory diagrams, and 6 1 is a block diagram of one embodiment of the present invention, FIG. 7 is a diagram for explaining the same, and FIG. 8 is a block diagram ζ of another embodiment of the present invention. (23) is a nonlinear compensation circuit, (26) is an average brightness detection circuit for the tube surface of the picture tube, (27) is an external light amount detection element, (29)
) is a multiplication circuit that obtains the control voltage of the supplementary circuit (23).

Claims (1)

[Claims] A circuit for controlling the amplitude of a luminance signal in accordance with the brightness of the tube surface of a picture tube, and a nonlinear correction circuit provided at a subsequent stage of this control circuit for nonlinearly controlling the output level of the luminance signal. , has an external light amount detection circuit and a detection circuit that detects the average brightness of the tube surface, and the nonlinear correction circuit is controlled by the magnitude of the external light amount. A television receiver in which optimum contrast correction is performed corresponding to the brightness of the tube surface of a J-recording picture tube.