KR100421835B1 - Circuit for controlling screen brightness - Google Patents

Abstract

PURPOSE: A circuit for controlling screen brightness is provided to automatically adjust the screen brightness by detecting a DC level of an inputted image signal and outputting a correction waveform according to the detected result. CONSTITUTION: A signal input unit including an A/D converting unit(41), a memory(42) and a D/A converting unit(43) converts an inputted image signal into a digital image signal, temporarily stores the digital image signal, converts the digital image signal into an analog image signal, and outputs the analog image signal to an LCD(Liquid Crystal Display) driving unit(49). A timing generating unit(45) separates a synchronous signal from the inputted image signal, generates various timing signals on the basis of the separated synchronous signal, and provides the various timing signals to the signal input unit. A DC level detecting unit(46) detects a DC level from the inputted image signal. A peak level detecting unit(47) detects a peak level in a frame according to the timing signal of the timing generating unit(45) from the digital image signal of the signal input unit. A gamma and gain control unit(48) detects a gamma correction value and a gain adjustment value using at least one or more of the DC level and the peak level, and outputs the gamma correction value and the gain adjustment value to the LCD driving unit(49) to correct an LCD output waveform.

Description

The screen brightness control circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display (LCD) projector, and more particularly, to a screen brightness control circuit for automatically adjusting screen brightness according to an input video signal.

In the conventional LCD projector, the LCD output is linearly non-linear with respect to the linearly input image signal as shown in FIG. 1A, due to the voltage-transmission (V-T) characteristic of the LCD as shown by the solid line in FIG.

Therefore, the correction value as shown by the dotted line in FIG. 1B is preset by experiments or the like, and then the correction waveform is supplied to the input image theoretically irrespective of the brightness, and the brightness of the screen is linearly corrected as shown in FIG. 1C.

However, since the correction waveform is supplied to the input image according to the inherent VT characteristic of the LCD itself as described above, the brightness control of the input image is always constant according to each screen, so that a relatively dark screen distinguishes the image It became difficult.

That is, the whole picture quality is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a display device which detects a direct current (DC) level of an input video signal and outputs a correction waveform according to the detection result, And a brightness control circuit.

Another object of the present invention is to provide a screen brightness control circuit for automatically adjusting brightness according to an area of a video signal within a screen by detecting a DC level and a peak level of an input video signal and outputting a correction waveform according to the detection result, .

According to an aspect of the present invention, there is provided a screen brightness control circuit for an LCD projector including an LCD driver for driving an LCD in a pixel unit, the circuit brightness control circuit comprising: A signal input means for temporarily storing the converted video signal and then converting it into an analog signal for driving the LCD and outputting it to the LCD driver; and a control means for separating the synchronizing signal from the input video signal and generating various timing signals based on the separated synchronizing signal A DC level detecting means for detecting a DC level in the input video signal; a digital-to-analog converter for converting the digital video signal of the signal input means into a peak in the frame A peak level detecting means for detecting a level of the detected DC level, Is a town correction value and the gain adjustment value to a point that is configured to include the gamma and gain control means for outputting to the LCD driver.

FIG. 1A is a graph showing the input video signal

1B is a graph showing the relationship between the LCD output and the LCD correction output for the input image of FIG. 1A

1C is a graph showing the output value after correction according to FIG.

2 is a block diagram showing a first embodiment of a screen brightness control circuit according to the present invention.

FIG. 3A shows a waveform of an overall dark screen of one frame

FIG. 3B is a waveform diagram showing the DC level detected in FIG. 3A; FIG.

FIG. 3C is a waveform diagram when a bright portion and a dark portion are present at the same time in one frame

4 is a block diagram showing a second embodiment of the screen brightness control circuit according to the present invention.

Figs. 5A to 5D are diagrams showing operating waveforms of respective parts of Fig. 4

6A is a waveform diagram when a bright portion and a dark portion exist in one frame at the same time

FIG. 6B is a diagram showing a correction waveform when DC and peak levels detected by FIG. 4 are applied at the same time

DESCRIPTION OF THE REFERENCE NUMERALS

21, 41: analog / digital conversion section 22, 42: memory

23, 43: digital / analog conversion unit 24, 44:

25, 45: timing control unit 26, 46: DC level detection unit

27, 48: gamma and gain controller 28, 49: LCD driver

47: peak level detector

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment

2 is a block diagram showing a first embodiment of a screen brightness control circuit according to the present invention.

2, there are shown an analog / digital (A / D) conversion unit 21 for converting an input analog image signal into a digital signal, a memory 21 for temporarily storing the digital output of the A / D conversion unit 21, A digital / analog (D / A) converter 23 for converting the output of the memory 22 into an analog signal, a synchronization separator 24 for separating a sync signal from the input video signal, And supplies the generated timing signals to the A / D conversion unit 21, the memory 22, and the D / A conversion unit 23 based on the sync signal separated by the sync separation unit 24, A DC level detection unit 26 for detecting a DC level in the input video signal, a gamma correction unit 24 for performing gamma correction or gain adjustment in accordance with the DC level detected by the DC level detection unit 26, The gamma and gain controller 27, and the gamma and gain controller 27, And an LCD driver 28 for correcting the output waveform of the LCD drive signal output from the D / A converter 23 with the corrected waveform.

In the first embodiment of the present invention configured as described above, the D / A converter 21 converts the analog video signal input according to the timing signal provided by the timing controller 25 into a digital signal and stores the digital signal in the memory 22 .

Further, the sync separator 24 separates only the sync signal from the input video signal, and the separated sync signal is input to the timing controller 25, which serves as a reference for generation of the timing signal.

The DC level detector 26 detects the DC level of the input video signal and outputs the detected DC level to the gamma and gain controller 27.

At this time, the digital video signal stored in the memory 22 is output to the D / A converter 23 according to the clock generated by the timing controller 25, and the D / A converter 23 converts the analog video signal And then output to the LCD driver 28 for driving the LCD in units of pixels.

The gamma and gain controller 27 controls the gamma correction and gain of the video signal input from the D / A converter 23 to the LCD driver 28 according to the detected DC level.

Here, the gain adjustment controls the peak-to-peak of the video signal, and the gamma correction linearly adjusts the non-linearity.

At this time, only gamma correction or gain adjustment may be performed according to the detected DC level, and gamma correction and gain adjustment may be performed at the same time.

Since the DC level detection unit 26 and the gamma and gain control unit 27 take a predetermined time to process the signal, the memory 22 controls the timing control unit 25 to delay the video signal for one field or one frame And then output to the LCD driver 28 through the A / D converter 23 so that the video signal input to the LCD driver 28 and the control value output from the gamma and gain adjuster 27 are synchronized in time.

As described above, in the first embodiment of the present invention, if one frame is entirely dark as in FIG. 3A, the entire DC level of the input image is detected to adjust the gamma correction and the gain as shown in FIG. 3B.

However, as shown in FIG. 3C, when a bright image and a dark image are simultaneously present in at least one frame, the DC level is converted into a DC level and the DC level when the dark image is converted into a DC level as a whole The correction values are also output in the same manner. Thus, when a dark image and a bright image coexist on one screen, the information of the image signal of the white portion is read out and the display is difficult. This is difficult.

Second Embodiment

FIG. 4 is a block diagram of a screen brightness correction circuit according to the second embodiment of the present invention. The DC level and the peak level of an input image are detected, and gamma correction and gain adjustment are performed. In the coexistence, the dark and bright portions are corrected differently so that image identification is facilitated even for a relatively dark screen.

4, an A / D converter 41 for converting an input analog image signal into a digital signal, a memory 42 for temporarily storing the digital output of the A / D converter 41, a memory 42 A sync separator 44 for separating a sync signal from the input video signal, a sync signal demultiplexer 42 for separating the sync signal separated by the sync separator 44 from a reference signal, A timing controller 45 for generating various timing signals to the A / D converter 41, the memory 42 and the D / A converter 43, A peak level detector 47 for detecting a peak level in a video signal converted into a digital signal by the A / D converter 41; a DC level detector 47 for detecting a DC level detected by the DC level detector 46; Gamma or gain adjustment is performed simultaneously or selectively according to the peak level detected by the peak level detector 47 An LCD for correcting an output waveform of an LCD drive signal output from the D / A converter 43 by the correction waveform generated by the gamma and gain controller 48; And a driving unit 49.

In the second embodiment of the present invention configured as described above, the D / A converter 41 converts an analog video signal input as shown in FIG. 5A into a digital signal according to a timing signal provided by the timing controller 45 And stores it in the post-memory 42.

Further, the sync separation unit 44 separates only the sync signal from the input video signal, and the separated sync signal is input to the timing control unit 45 and serves as a reference for generation of the timing signal.

The DC level detection unit 46 detects the entire DC level of the input video signal and outputs the detected DC level to the gamma and gain control unit 48.

The peak level detector 47 detects the amount of the peak level and the peak level inside the frame on a frame-by-frame basis in accordance with the timing signal of the timing controller 45 using a counter or the like, .

The digital video signal stored in the memory 42 is output to the D / A converter 43 as shown in FIG. 5C according to the clock generated by the timing controller 45, And is then output to the LCD driver 49. [0050]

Here, the reason for detecting the amount of the peak level, that is, the time occupied by the peak signal in the entire screen, is to ignore the peak value appearing once or twice.

The peak level detector 47 detects the amount of the white peak level and the peak level in the digital image signal converted by the A / D converter 41 because the image signal delayed in the memory 42 And the control timing outputted from the peak level detecting unit 47 can be easily adjusted as shown in Fig. 5D.

The gamma and gain controller 48 outputs the gamma correction and gain control values to the LCD driver 28 according to the detected DC level and peak level.

That is, when the DC level detected by the DC level detector 46 indicates a dark signal as a whole, the gamma and gain controller 48 performs gamma correction on the signal of the low portion and outputs a control signal for increasing the gain when the peak level is low .

Further, the peak level detector 47 outputs a white peak value, thereby controlling the gamma correction of the white portion at the time of gamma correction, and controlling the limit gain according to each peak value at the time of gain control. Therefore, white that can not be distinguished from the LCD does not occur.

At this time, since the correction is not performed for the portion where no signal exists (black), the distinction becomes clear.

Therefore, when a bright portion and a dark portion are present in one frame at the same time as in FIG. 6A, the correction value is outputted differently from the bright portion and the dark portion as shown in FIG. 6B, so that image identification is also easy for a relatively dark screen.

In other words, since the gain of the sub-average signal is increased and the gain of the white portion is reduced, the overall gain is kept constant, so that image identification is facilitated even for a relatively dark screen.

Since the DC level detection section 46, the peak level detection section 47 and the gamma and gain control section 48 take a predetermined time to process the signal, the memory 42 is controlled by the timing control section 45 to generate one field or The video signal is delayed for one frame and then output to the LCD driver 49 through the A / D converter 43 to adjust the video signal input to the LCD driver 49 and the correction signal output from the gamma and gain adjuster 27 Match the values in time.

As described above, according to the screen brightness control circuit of the present invention, There is an effect that the screen brightness is automatically adjusted according to the input video signal by detecting the DC level of the input video signal and outputting the correction waveform in accordance with the detection result.

Further, by detecting the DC level and the peak level of the input video signal and changing the drive level of the LCD drive signal according to the detection result, the brightness difference according to the region of the video signal in at least one frame can be corrected, There is an effect that the image can be easily identified even in a relatively dark screen when a dark screen and a bright screen coexist.

Claims (5)

1. A screen brightness control circuit of an LCD projector including an LCD driver for driving a liquid crystal display element (LCD) in units of pixels, A signal input unit for converting an input video signal into a digital signal, jogging the digital signal, converting the digital signal into an analog signal for driving the LCD, and outputting the analog signal to the LCD driver, A timing generator for separating a sync signal from the input video signal and generating various timing signals based on the separated sync signal and providing the generated timing signals to the signal input unit; A DC level detecting unit for detecting a DC level in the input video signal; A peak level detecting unit for detecting a peak level inside the frame in accordance with the timing signal of the timing generating means in the digital video signal of the signal inputting means; And a gamma and gain controller for detecting a gamma correction value and a gain adjustment value at least one of the detected DC level and peak level and outputting the gamma correction value and the gain adjustment value to the LCD driver to correct the LCD output waveform. Brightness control circuit. The method according to claim 1, And the gamma and gain control unit corrects the gamma of the white portion. The method according to claim 1, Wherein the gamma and gain control unit adjusts a gain by controlling a limit according to each peak value. The method according to claim 1, Wherein the gamma and gain control unit corrects gamma for a signal of a low portion when a dark signal is entirely inputted. The method according to claim 1, Wherein the gamma and gain control unit increases the gain when the detected peak level is low.