JPH08172588A - Luminance control signal generation circuit - Google Patents

Abstract

PURPOSE: To generate a control signal acting so as to reversely decrease luminance intensity as increasing the average brightness of a video. CONSTITUTION: This circuit comprises an APL detecting part 1 consisting of an integrator constituted of a resistor and a capacitor and which obtains a mean voltage by integrating an inputted pedestal-clamped video signal, a level setting part 4 consisting of an operational amplifier in which a level setting voltage K is connected to inversion input so as to supply the mean voltage to non-inversion input, a limiter part 2 which sets prescribed lower limit value L1 and upper limit value L2 and limits the mean voltage supplied from the level setting part 4, and an arithmetic part 3 consisting of the operational amplifier connected so as to supply a luminance control voltage V2 supplied from a microcomputer (not shown in figure) to the non-inversion input by dividing it by resistors R2 and R1 and to supply the output V1 of the limiter part 2 to the inversion input via the resistor R2 and also, to which a feedback resistor R1 is connected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brightness adjustment signal generating circuit for generating a control signal for adjusting the brightness of a display device according to the average level (APL) of a video signal.

[0002]

2. Description of the Related Art For example, in a display device using liquid crystal or the like, the brightness of an image is inferior (the display dynamic range is narrow) as compared with a cathode ray tube. Therefore, the contrast ratio is smaller than that of a cathode ray tube, and particularly when displayed in a bright place, the entire image becomes an unnatural image in which the entire image is whitish and the black portion is raised.

Further, in a conventional display device using liquid crystal or the like, the brightness of the display may be slightly insufficient.
In order to make an image signal appear to be a bright screen by gamma correction, for example, a correction has been performed in which a white portion is centered and the entire image is shifted to a brighter side. When the screen resulting from such a correction is displayed in a bright place, the expression of the bright part is improved, but the black part is further raised, resulting in a difficult-to-see screen display with less contrast. In any case, the conventional display device using liquid crystal or the like has a problem that the black portion appears to be raised.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to prevent the black portion from rising by moving the black level of the display according to the brightness of the screen, and to make the screen easy to see. It is an object of the present invention to provide a luminance adjustment signal generation circuit designed to obtain the above.

[0005]

In order to achieve the above object, an APL detecting section for obtaining an average voltage of a pedestal clamped video signal, and a predetermined value which sets the average voltage supplied by the APL detecting section. A limiter unit consisting of an upper limiter for limiting and a lower limiter for limiting to a set predetermined value, an average voltage limited by the limiter unit, and a luminance control voltage supplied by another unit are calculated to generate a luminance adjustment signal. And a calculation unit that

Further, an APL detecting section for obtaining an average voltage of the pedestal clamped video signal, an AD converting section for converting the average voltage into digital data, and the digital data being supplied to an address, brightness adjustment data is also supplied. It is composed of a ROM for storing in a look-up table format and a DA converter for converting the brightness adjustment data into an analog voltage.

[0007]

With the above-described structure, the APL detection unit detects the average voltage of the video signal, the limiter unit limits the average voltage between a predetermined lower limit value and a predetermined upper limit value, and the calculation unit operates as shown in FIG.
As shown in, the limited average voltage and the brightness control voltage are calculated to generate a brightness adjustment signal that is inversely proportional to the average voltage.

Further, the APL detector detects the average voltage of the video signal, the AD converter converts the average voltage into digital data, and the digital data is supplied to the address of the ROM. Since the required data is stored in the ROM in the look-up table format corresponding to the relationship shown in FIG. 2,
The look-up table is read according to the supplied address and converted into an analog signal by a DA converter.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A brightness adjustment signal generation circuit according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of a brightness adjustment signal generation circuit according to the present invention. An APL detector 1 is an integrator composed of a resistor and a capacitor, and integrates the input pedestal clamped video signal to obtain an average voltage. Reference numeral 4 denotes a level setting unit composed of an operational amplifier connected so that the level setting voltage K is supplied to the inverting input and the average voltage is supplied to the non-inverting input. Two
Sets the value L1 to the lower limit and the value L to the upper limit
The limiter unit limits the average voltage supplied by the level setting unit 4 within the range between the value L1 and the value L2 by setting 2. Reference numeral 3 denotes a brightness control voltage V2 supplied from a microcomputer (not shown), which is divided by resistors R2 and R1 and supplied to a non-inverting input, and an output V1 of the limiter unit 2 is supplied to the resistor R
The operation unit is configured to be connected so as to be supplied to the inverting input via 2 and to which the negative feedback resistor R1 is connected.

The operation of the brightness adjustment signal generation circuit according to the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing the relationship of the brightness adjustment signal generated by the brightness adjustment signal generation circuit according to the present invention with respect to the average voltage of the video signal. APL detector 1
Integrates the pedestal clamped video signal to obtain an average voltage. The level setting unit 4 sets the average voltage to a predetermined level (for example, the clamp level is 6V, and the minimum level of the necessary brightness adjustment voltage is required). If it is 2V, adjust the level by lowering the level by about 4V).
In the limiter unit 2, the average voltage is set to L1 so as to exclude a dark screen whose average voltage is equal to or lower than a predetermined value L1 and a screen where the average voltage is equal to or higher than the predetermined value L2 and the proportion of black portions is expected to be extremely small. Limit during L2. The arithmetic unit outputs a voltage V1 limited by L1 and L2 output from the limiter unit 2.
And the divided value of the brightness control voltage V2 and the resistors R2 and R1 are calculated to generate a brightness adjustment signal V0 as shown below. V0 = (V2-V1) * R1 / R2 Therefore, as shown in FIG. 2, when the average voltage is from 0 to L1, the brightness adjustment signal has a constant value A: (V2-L1) * R1.
/ R2, L1 to L2 are V0 values that are inversely proportional to the above-mentioned average voltage, and a constant value B above L2:
(V2-L2) * R1 / R2. The level setting unit 4 may be unnecessary when the level adjustment is not necessary, for example, when the clamp level is substantially equal to the minimum level of the brightness adjustment voltage.

FIG. 3 is a circuit diagram of another embodiment of the brightness adjustment signal generating circuit according to the present invention. In the figure, 11 is an AP for obtaining the average voltage of the pedestal clamped video signal.
It is an L detector. Reference numeral 12 is an AD converter that converts the average voltage into digital data. A ROM 13 is supplied with the digital data at an address and stores necessary adjustment data in a look-up table format at a predetermined address as shown in FIG. 14 is
The DA conversion unit converts the brightness adjustment data read from the ROM 13 into an analog voltage. In addition, FIG.
The adjustment data to be stored in the lookup table of 1 may have the relationship shown in FIG. 2 described above, or may realize the curve as shown in FIG.

[0012]

As described above, the present invention moves the black level of the display in accordance with the brightness of the screen to prevent the black portion from rising and to generate a brightness adjustment signal for obtaining an easy-to-see screen. Provide the circuit. Therefore, even if the conventional display device using liquid crystal or the like is brightly corrected by the gamma correction, it is possible to suppress the floating of the black portion and improve the contrast.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a brightness adjustment signal generation circuit according to the present invention.

FIG. 2 is a diagram showing a relationship of a brightness adjustment signal to be generated with respect to an average voltage of a video signal of the brightness adjustment signal generating circuit according to the present invention.

FIG. 3 is a circuit diagram of another embodiment of the brightness adjustment signal generation circuit according to the present invention.

FIG. 4 is a diagram showing a look-up table of the brightness adjustment signal generation circuit according to the present invention and a relationship of an adjustment value with respect to an average voltage stored in the look-up table.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 APL detection unit 2 Limiter unit 3 Calculation unit 4 Level setting unit 11 APL detection unit 12 AD conversion unit 13 ROM 14 DA conversion unit

Claims (8)

[Claims] 1. An APL detector for obtaining an average voltage of a pedestal clamped video signal, and an upper limiter for limiting the average voltage supplied by the APL detector to a preset value. Luminance characterized by comprising a limiter unit consisting of a lower limit limiter for limiting, an average voltage limited by the limiter unit, and a calculation unit for calculating the brightness control voltage supplied by the others to generate a brightness adjustment signal. Adjustment signal generation circuit. 2. An APL detecting section for obtaining an average voltage of a pedestal clamped video signal, a level setting section for adding or subtracting a predetermined voltage to the average voltage to generate an average voltage with a voltage level shift, and the level shift. A limiter unit for limiting the average voltage set within a range of a predetermined upper limit value and a lower limit value, an average voltage limited by the limiter unit, and a brightness control voltage supplied by another unit to calculate a brightness adjustment signal. And a brightness adjustment signal generation circuit. 3. The brightness adjustment signal generation circuit according to claim 1, wherein the APL detection unit is configured by an integration circuit. 4. The brightness adjustment signal generation circuit according to claim 2, wherein the level setting unit is composed of an operational amplifier connected to supply a predetermined voltage to an inverting input and an average voltage to a non-inverting input. . 5. The operational amplifier connected to supply the second DC level of the brightness control voltage to the non-inverting input of the average voltage of which the arithmetic unit is limited to the inverting input. The brightness adjustment signal generation circuit according to claim 2. 6. An APL detector for obtaining an average voltage of a pedestal clamped video signal, an AD converter for converting the average voltage to digital data, and the digital data supplied to an address and brightness adjustment data. A brightness adjustment signal generation circuit comprising a ROM for storing in a look-up table format and a DA converter for converting the brightness adjustment data into an analog voltage. 7. The brightness adjustment signal generation circuit according to claim 6, wherein a look-up table in which the address of the ROM and the brightness adjustment data to be stored are in an inversely proportional relationship is stored. 8. The brightness adjustment signal generation circuit according to claim 6, wherein a look-up table having a non-linear relationship between the ROM address and the brightness adjustment data to be stored is stored.