JPH07226863A - Television receiver - Google Patents

Abstract

PURPOSE:To obtain a television receiver whereby tone reproduction at a low luminance part in a video signal with APL (average luminance) being lower than a prescribed value is improved and also a blooming phenomenon at a high luminance part is prevented. CONSTITUTION:The voltage of a connection point 12 is supplied to a control signal generating circuit 13 as the APL detecting signal of an incoming video signal. The control signal generating circuit 13 judges whether or not the APL value of the video signal is lower than the prescribed APL value in accordance with the APL detecting signal and outputs a control signal when the value is low. A contrast control circuit 3 and a video processing circuit 2 emphasize contrast in accordance with the control signal for improving tone reproduction at the low luminance part. At the same time, a non-linear circuit 15 conducts gammacorrection to a luminance output in accordance with the control signal for preventing the blooming phenomenon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver capable of preventing a blooming phenomenon in a high luminance portion of a video signal having a low average luminance (APL) and improving gradation reproducibility of the low luminance portion. .

[0002]

2. Description of the Related Art Conventionally, a color television receiver is provided with a manual adjuster capable of adjusting the contrast of a displayed image. FIG. 8 shows a change in the luminance output characteristic of the picture tube with respect to the image input when the contrast adjustment is performed.

Generally, in contrast adjustment, when a video signal of a prescribed level (for example, a signal of 1 Vp-p) is received, the maximum contrast is obtained from the black portion to the white portion in the video signal. The input-output characteristic shown in 8-B is adjusted (the setting having this characteristic is the initial setting of the contrast). Figure 8-
In the input-output characteristic shown in A, the adjustment is for insufficient contrast, and in the state of FIG. 8-C, it is for excessive contrast. Since the portion of the vertical axis in the figure that is higher than the maximum brightness is the area where the beam current of the picture tube is saturated, if the contrast is increased too much as shown in FIG. Will occur.

When the level from the black portion to the white portion of the incoming video signal is almost the same as the prescribed video signal,
With the optimal contrast value once set (FIG. 8-B), the best reproduced image is always obtained.

However, since the level of the video signal varies depending on the content of the video, there are cases where the same contrast adjustment value remains unsuccessful, and manual re-adjustment of the contrast is required. there were. In particular,
More than the lowest average brightness (reference average brightness) that is set to obtain sufficient image quality with the default contrast value,
When the average luminance of the incoming video signal is low, most of the video signal is a low-luminance component, so if the contrast adjustment with the characteristics shown in FIG. The gradation reproduction of will become insufficient. In such a case, conventionally, the contrast is readjusted manually so that the characteristics shown in FIG.

[0006]

However, by adjusting the contrast having the characteristics shown in FIG. 8C, a small area high brightness component such as white characters is included in the video signal having a low average brightness (APL). If so, the high-brightness part may cause a blooming phenomenon, and the image quality may be impaired.

An object of the present invention is to provide a television receiver capable of both improving the gradation reproducibility in a low luminance portion of a video signal having a low APL and preventing the blooming phenomenon in a high luminance portion. There is.

[0008]

In order to solve the above problems, the present invention detects the average luminance of an incoming video signal in a television receiver having a circuit for contrast adjustment, An APL detection / control signal generation circuit that outputs a control signal according to the detected value when the detected value is lower than a predetermined average luminance value, and a gamma correction to the luminance signal in the video signal according to the control signal. And a contrast control circuit for instructing the circuit for contrast adjustment to instruct the contrast adjustment circuit to increase the contrast above an initial setting value in accordance with the control signal. Machine.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The feature of the television receiver of the present invention is that the average luminance (APL) of an incoming video signal is a predetermined value (for example, the lowest average value set when a sufficient image quality is obtained with a default contrast value). When the brightness is lower than the brightness (reference average brightness), the contrast is automatically increased from the initial setting value to improve the gradation reproducibility in the low brightness area, and the gamma (γ) is automatically added to the video signal. The point is that correction is performed (for example, the correction having the characteristics shown in FIG. 2-B) to prevent the blooming phenomenon in the high-luminance portion and obtain a higher quality image.

FIG. 1 shows a block configuration of an embodiment of the present invention. The difference from the conventional example is that the control signal generating circuit 13 is
A non-linear circuit 15 and a control signal generating circuit 13 are newly provided.
This is the point where the output signal of is supplied to the contrast control circuit 3.

In FIG. 1, a video signal input from a terminal 1 is supplied to a video processing circuit 2 to be decoded and output as a luminance signal Y and color difference signals R-Y, BY and G-Y. It Then, the three color difference signals are directly supplied, and the luminance signal is respectively supplied to the video output circuit 6 via the non-linear circuit 15, and added and amplified to become R, G, B signals,
It is supplied to the picture tube 7.

Contrast control circuit (constituted by CPU etc.)
When a signal for contrast adjustment (adjustment signal for initial setting described in the conventional example) is supplied from the control terminal 5, the reference numeral 3 outputs the contrast control signal 4 to the video processing circuit 2. The video processing circuit 2 adjusts the contrast according to the contrast control signal, and controls the luminance signal Y so that it has the instructed contrast value. (In this embodiment, the contrast is initially set so that the brightness output characteristic shown in FIG. 6A is obtained.)

The video signal processing circuit 2 also supplies a synchronizing signal to the deflection / high voltage circuit 9. The deflection / high voltage circuit 9 supplies a high voltage to the picture tube (CRT) 7 according to the synchronizing signal. The beam current IA supplied to the electron gun of the picture tube 7 (the resistance RA from the DC power supply 11 and the deflection / high voltage circuit 9
(Current supplied to the picture tube 7 via) flows.

Now, assume that the voltage of the DC power supply 11 is VCC. The voltage VA at the connection point 12 between the resistor RA, the deflection / high voltage circuit 9 and the control signal generation circuit 13 becomes VA = VCC-RA.IA due to the beam current IA flowing in the picture tube 7. Therefore, the voltage VA changes in inverse proportion to the beam current IA.

Since the beam current IA is proportional to the APL (average brightness) of the video signal, the voltage VA is inversely proportional to the APL, and the voltage VA increases as the APL decreases. These relationships are shown in FIG. 5 (note that VDa,
VC1 will be described later).

In this embodiment, the voltage VA at this connection point 12 is
Is used as the APL detection signal of the video signal. The control signal generating circuit 13 to which this voltage VA (APL detection signal) is supplied, changes the A of the incoming video signal according to the value of the voltage VA.
It is determined whether PL is lower than a predetermined value. If it is determined to be low, the control signal 14 for automatically performing the contrast correction and the γ correction is output. The value of the control signal 14 changes according to the value of the voltage VA. The control signal generation circuit 13 and the resistor RA form an APL detection / control signal generation circuit 17.

FIG. 3 shows an example of a concrete circuit configuration of the control signal generating circuit 13. Voltage VA supplied from connection point 12
The (APL detection signal) is input to the buffer circuit composed of the npn transistor Qa and the resistor ra, and is level-shifted by the voltage VDa by the Zener diode Da. Then, it is amplified by an amplifier circuit composed of npn transistor Qb, pnp transistor Qc, and resistors rb, rc, rd, and output as control signal 14. When the voltage of the control signal 14 is VC1, the relationship between the voltage VA and the voltage VC1 is as shown in FIG. Point a at which voltage VC1 becomes zero
Is a point corresponding to the lowest APL (reference average luminance) set so that sufficient image quality can be obtained with the default contrast value. When it is lower than APL corresponding to this point a, the control signal 14 (voltage VC1) is output.

The control signal 14 is the contrast control circuit 3
And non-linear circuit 15 respectively. The contrast control circuit 3 responds to the voltage value VC1 of the control signal 14 by
In order to improve the gradation reproducibility in the low luminance portion, the contrast control signal 4 for increasing the contrast above the initial setting value is output to the video processing circuit 2. The image processing circuit 2 adjusts the contrast according to the contrast control signal, and the contrast is strengthened as the APL decreases (that is, the voltage value VC1 of the control signal 14 increases). For example, as shown in FIG. 6, control is performed so that the luminance output characteristic changes from the initial setting characteristic A to the characteristic B1 → B2 → B3.

As described above, only increasing the contrast causes the blooming phenomenon in the high-luminance portion in the video signal. Therefore, in this embodiment, the non-linear circuit 15 corrects the luminance signal Y by γ to prevent the blooming phenomenon. The nonlinear circuit 15 has a voltage value V of the control signal 14 supplied from the control signal generation circuit 13.
As C1 increases (the APL decreases), for example, as shown in FIG. 7, the luminance output characteristic has the initial setting characteristic A
From the characteristics B1 → B2 → B3. A → B1 of the luminance output characteristic by γ correction shown in FIG.
The change from B2 to B3 corresponds to the change from A to B1 to B2 to B3 of the luminance output characteristic by contrast adjustment shown in FIG.

FIG. 4 shows an example of a concrete circuit configuration of the non-linear circuit 15. A control signal voltage VC1 is supplied to a connection point 16 with the control signal generation circuit 13. The voltage VC1 is voltage-converted by the npn transistor Qd and the resistors re and rf, and the impedance is lowered by the emitter follower circuit of the pnp transistor Qe and the resistor rg. As a result, the control signal voltage VC1 is applied to the emitter of the transistor Qe.
Then, the non-linear reference voltage VC2 corresponding to is generated. The voltage VY of the luminance signal output Y of the video processing circuit 2 is VY ≧ VC2 + VDb where VDb is the diode D
In the case of the forward voltage of b, the circuit of the resistor rh and the diode Db becomes conductive, so that the γ correction is added to the luminance signal output Y. With this operation of the non-linear circuit 15, the luminance output characteristic shown in FIG. 7 can be obtained, so that the blooming phenomenon can be prevented in this embodiment.

As described above, in this embodiment, the average brightness (APL) of the incoming video signal is set to a predetermined value (for example, the lowest average brightness (reference value) which is set so that sufficient image quality can be obtained with the default contrast value. When it is lower than the average luminance)), the gradation reproducibility in the low luminance portion can be improved and the blooming phenomenon in the high luminance portion can be prevented, so that a higher quality image can be obtained. The predetermined value may be adjustable according to the usage situation or the like.

In the examples shown in FIGS. 6 and 7, the luminance output characteristic changes stepwise, but it may be controlled so as to change continuously. In the embodiment, the voltage VA inversely proportional to APL is used as the APL detection signal.
A signal proportional to PL may be used as the APL detection signal.

[0023]

As described above, in the color television receiver of the present invention, the average brightness (APL) of the incoming video signal is set to a predetermined value (for example, a default contrast value is set to obtain sufficient image quality). When the average brightness is lower than the minimum average brightness (reference average brightness), the contrast is automatically increased from the initial setting value to improve the gradation reproducibility in the low brightness area and automatically By intentionally performing gamma (γ) correction, the blooming phenomenon in the high-luminance portion can be prevented, so that a higher quality image can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a block configuration of an embodiment.

FIG. 2 is a diagram showing an outline of γ correction characteristics.

FIG. 3 is a diagram showing an example of a circuit configuration of a control signal generation circuit.

FIG. 4 is a diagram showing an example of a circuit configuration of a non-linear circuit.

5 is a diagram for explaining the circuit operation of the embodiment shown in FIG.

FIG. 6 is a diagram showing a change in luminance output characteristic due to contrast adjustment.

FIG. 7 is a diagram showing changes in luminance output characteristics when γ correction is applied.

FIG. 8 is a diagram for explaining contrast adjustment.

[Explanation of symbols]

 2 video processing circuit 3 contrast control circuit 4 contrast control signal 13 control signal generation circuit 14 control signal 15 non-linear circuit 17 APL detection / control signal generation circuit

Claims (1)

[Claims] 1. A television receiver provided with a circuit for contrast adjustment, wherein the average brightness of an incoming video signal is detected, and when the detected value is lower than a predetermined average brightness value, the detected value is detected. An APL detection / control signal generation circuit that outputs a control signal according to the control signal; a non-linear circuit that applies gamma correction to a luminance signal in the video signal according to the control signal; and a contrast adjustment according to the control signal. And a contrast control circuit that gives an instruction to increase the contrast above an initial setting value.