JPS62193465A - Correction device for peripheral luminance of television receiver - Google Patents

Abstract

PURPOSE:To obtain the optimum contrast adjustment fitted for the brightness of a picture by making operate a peripheral luminance correction suppression circuit, and nullifying the output of a peripheral luminance correction circuit, when the average luminance level of the picture is below a prescribed level regulated in advance. CONSTITUTION:A peripheral luminance correction device 11 supplies a parabola wave having a horizontal or a vertical scanning cycle to a contrast adjusting circuit 6 which changes the contrast of the picture in a television receiver, and makes operate a peripheral luminance correction suppression circuit 12, and nullifies the output of a peripheral luminance correction circuit 7 which corrects luminance at the periphery of the picture, when the average luminance level is below the prescribed level regulated in advance. In this way, when the whole of the picture is dark though having a peak at a center, and the average luminance level is low, it is possible to prevent the brightness in peak from being suppressed inconveniently, and the optimum contrast adjustment fitted for the brightness of the picture can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a peripheral brightness correction device for a television receiver that suppresses peripheral brightness correction when the average brightness level of the screen is low.

``Conventional technology J Rin 11'l! ITI +-('di r+-1)h 1. y5- ・-Xl, jff+ -+-h Direct-view type, which has a picture tube screen directly, is the mainstream. However, there is an increasing demand for projection television receivers in which images can be enlarged and displayed on a screen using a projection tube, and various improvements have been made to improve image quality and productivity.

The television receiver 1 shown in FIG. 3 is of a projection type,
Three projection tubes 3r, 3g, and 3b provided in the projector 2 and corresponding to the three primary colors of red, green, and blue project images magnified through magnifying lenses onto a screen 4 in front of the projector 2, respectively.

The video processing circuit 5 in the projector 2 includes a screen 4
A contrast adjustment circuit 6 is provided to vary the contrast of the upper screen. Generally, projection tubes 3r, 3g, a
With the magnifying lens used in b, the amount of transmitted light decreases at the periphery, so the periphery of the screen appears darker than the center.

Therefore, as a measure to prevent the image from becoming blurred due to a decrease in the amount of light around the magnifying lens, in this example, the contrast setting value of the contrast adjustment circuit 6 is adjusted using a parabolic filter of the horizontal scanning period and the direct scanning period. A peripheral brightness correction circuit 7 is connected to the /P tatami mat 1 for correcting a decrease in brightness around the screen. 7h is a parabolic wave generating circuit that generates a parabolic wave with a horizontal scanning period, and 7V is a parabolic wave generating circuit that generates a parabolic wave with a vertical scanning period. These 2
The parabolic wave generation circuits 7h and 7v are connected to the contrast adjustment circuit 6 via signal lines 8 provided with coupling capacitors Ch and Cv and coupling capacitors Co, respectively.

[Problems to be Solved by the Invention] In the above-mentioned conventional contrast adjustment circuit 6, when the average brightness level of the screen is high, the peripheral brightness correction circuit 7 is effective in correcting the peripheral brightness, but there is a peak at the center of the screen. If the entire object is dim and the average brightness level is low, the peak brightness is suppressed by peripheral brightness correction, which has the opposite effect.

[Means for Solving the Problems] The present invention solves the above problems, and includes a contrast adjustment circuit that changes the contrast of the screen of a television receiver, and a horizontal or vertical scanning control circuit for this contrast adjustment circuit. a peripheral brightness correction circuit that supplies a periodic paraholographic wave and corrects brightness at the periphery of the screen;
The apparatus is characterized by comprising a peripheral brightness correction suppression circuit that operates when the average brightness level of the recorded screen is below a predetermined level and invalidates the output of the peripheral brightness correction circuit. be.

[Function] The present invention provides a peripheral brightness correction circuit that corrects the brightness at the periphery of the screen by supplying a parabolic wave having a horizontal or vertical scanning period to a contrast adjustment circuit that changes the contrast of the screen of a television receiver. On the other hand, when the average brightness level of the screen is below a predetermined level, the peripheral brightness correction suppressing circuit operates, invalidates the output of the peripheral brightness correction circuit, and stops the peripheral brightness correction that would have the opposite effect.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic circuit diagram showing an embodiment of the peripheral brightness correction device for a television receiver according to the present invention;
FIG. 2 is a diagram showing the output characteristics of the brightness limiting circuit shown in FIG. 1.

In FIG. 1, the peripheral brightness correction device 11 has a peripheral brightness correction suppression circuit I2 connected to a signal line 8 connecting the foot trust a adjustment circuit 6 and the peripheral brightness correction circuit 7. The peripheral brightness correction suppression circuit 12 includes a brightness limiting circuit I3 and a switch circuit 1 that is switched according to the output of the brightness limiting circuit 13.
It consists of 4. The brightness limiting circuit I3 functions as a protection circuit to prevent damage to the horizontal output transistor by detecting the average brightness level of the screen and suppressing excessive beam current flowing through the picture tube. As shown in FIG. 2, the output voltage V of the brightness limiting circuit I3 used in this embodiment is kept constant at the maximum value Vo when the lower average brightness level P of the screen is low brightness equal to or higher than Pa. However, when the average brightness level P h < P o is exceeded, it exhibits a characteristic that it decreases linearly.

The switch circuit 14 includes a pair of transistors Qa whose emitters are commonly connected to form a differential pair.

It has Qb. Rca and Rcb are transistors Q
a and Qb are collector resistances, and Re is a common emitter resistance. The base of one transistor Qa is connected to the brightness limiting circuit 13, and the base of the other transistor Qb is connected to a voltage dividing point of a resistive voltage dividing circuit 14a consisting of resistors Ra and Rh. A resistor R is connected to the signal line 15 connecting the collector of the transistor Qa and the signal line 8.
.

are connected in parallel. The resistive voltage divider circuit 14a divides the power supply voltage of the DC power supply element B by a voltage division ratio Rb/Ra + Rb, and its divided voltage output is approximately 60% of the maximum average brightness level of the brightness limiting circuit I3. The corresponding voltage output Vc is set.

Now, the average brightness level P of the screen on screen 4 is Pa
In this case, in the switch circuit 14, the transistor Qb is in a conductive state, so the output of the peripheral brightness correction circuit 7 is supplied to the contrast adjustment circuit 6 via the signal line 8, and the peripheral brightness is corrected. be exposed.

On the other hand, the average brightness level P of the screen on the screen 4 is Pc
When the output voltage V of the brightness limiting circuit 13 becomes lower than
Since the voltage exceeds Vc, the transistor Qa in place of the transistor Qb in the switch circuit 14 becomes conductive. As a result, the signal line 8 connecting the peripheral brightness correction circuit 7 and the contrast adjustment circuit 6 is grounded by the switch circuit 14, thereby invalidating the correction output of the peripheral brightness correction circuit 7.

Therefore, it is possible to prevent an inconvenience in which a bright image at the center of the screen becomes blurred due to peripheral brightness correction being performed even though the average brightness level of the screen is low.

In this way, the peripheral brightness correction device 11 of the television receiver supplies a parabolic wave having a horizontal or vertical scanning period to the contrast adjustment circuit 6 that changes the contrast of the screen of the television receiver, thereby changing the contrast of the screen. For the peripheral brightness correction circuit 7 that corrects the brightness in the periphery, when the average brightness level of the screen is below a predetermined level, the peripheral brightness correction suppression circuit I2 acts and disables the output of the peripheral brightness correction circuit 7. Because of this configuration, if there is a peak in the center of the screen but the entire screen is dim and the average brightness level is low, the peripheral brightness? It is possible to effectively prevent the inconvenience that the peak brightness is suppressed by ff iE, and as a result, only when the average brightness level of the screen is high, the peripheral brightness correction circuit 7 allows peripheral brightness correction, and the screen This enables optimal contrast adjustment according to brightness.

[Effects of the Invention] As explained above, the present invention supplies a parabolic wave having a horizontal or vertical scanning period to a contrast adjustment circuit that changes the image quality of the screen of a television receiver, and adjusts the brightness at the periphery of the screen. For the peripheral brightness correction circuit that corrects
The peripheral brightness correction suppression circuit operates when the average brightness level of the screen is below a predetermined level and disables the output of the peripheral brightness correction circuit, so even though there is a peak at the center of the screen, the entire It is possible to effectively prevent the inconvenience that the brightness of the repeater is suppressed by peripheral brightness correction when the screen is dimly lit and the average brightness level is low. It allows peripheral brightness correction by the brightness correction circuit, and has excellent effects such as making it possible to optimally adjust the contrast according to the brightness of the screen.

[Brief explanation of drawings]

FIG. 1 is a schematic circuit diagram showing an embodiment of the peripheral brightness correction device for a television receiver according to the present invention, and FIG. 2 is a diagram showing the output characteristics of the brightness limiting circuit shown in FIG. FIG. 3 is a schematic circuit configuration diagram showing an example of a peripheral brightness correction circuit of a conventional television receiver. 693. Contrast adjustment circuit, 7. , ,peripheral luminance correction circuit, 11. ,,peripheral brightness correction device. +2. ,,peripheral luminance correction suppression circuit.

Claims (1)

[Claims] a contrast adjustment circuit that changes the contrast of a screen of a television receiver; a peripheral brightness correction circuit that supplies parabolic waves with a horizontal or vertical scanning period to the contrast adjustment circuit to correct brightness at the periphery of the screen; A peripheral brightness correction device for a television receiver, comprising a peripheral brightness correction suppression circuit that operates when the average brightness level of the peripheral brightness correction circuit is lower than a predetermined level, and invalidates the output of the peripheral brightness correction circuit.