JP2938264B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display for displaying images using a liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal image display device using a transmission type or projection type liquid crystal panel can obtain a bright display. Therefore, a direct-view type liquid crystal television receiver or a projection type liquid crystal projector is used as a display device instead of a cathode ray tube. And so on. However, a liquid crystal panel has a narrower input voltage range capable of expressing a gradation than a cathode-ray tube, and thus tends to cause underexposure and overexposure.

FIG. 4 is a graph of electro-optical characteristics showing a relative transmittance with respect to an applied voltage of the liquid crystal panel. The range of input voltage in which gradation control can be performed is indicated by ΔV in the figure, and the range is narrow.

[0004]

In a conventional liquid crystal video display device, when a video signal which is higher than the white saturation point of the liquid crystal panel is input, all the peak portions of the luminance signal are cut off. There is a problem that details are not reproduced at all, and there is a problem that details of a dark part are not reproduced on an overall dark screen including a portion close to a black saturation point.

[0005]

According to the present invention, there is provided a white peak value detecting means for detecting a white peak value of an input video signal from a digitized luminance signal derived from the input video signal. Average value detecting means for detecting an average video level of the input video signal, black level detecting means for detecting a black level of the input video signal, and pedestal level detecting means for detecting a pedestal level of the input video signal, Calculating means for calculating a video control signal for obtaining an appropriate video level based on a white peak value, an average video level, and a black level detected by the respective detecting means for a video signal equal to or higher than a pedestal level ; , the video control signal calculated by said calculating means, the liquid crystal image display device in which a control means for controlling the input video signal
Oite, average video level is the degree mu ₁₀ when a high value
Signal output means and average video level is low
Means for outputting a signal of degree mu _20, the average video level
Output degree mu ₃ signals when it is neither value is low high
Means and the degree when the black level of the luminance signal is a high value.
Means for outputting a signal if mu _11, the black level of the luminance signal
Means for outputting a signal of degree μ ₂₁ when the value is low ;
The lower signal of the multiplexer mu ₁₀ the degree mu ₁₁ as the degree mu ₁
Means for outputting, lower signal of the degree mu ₂₀ and the degree mu ₂₁
Means for outputting a degree mu ₂ to No. degree μ _1, μ _2, μ ₃
Output control values E ₁ , E ₂ , E ₃ respectively
And (μ ₁ E ₁ + μ ₂ E ₂ + μ ₃ E ₃ ) / (μ ₁ + μ ₂
+ Μ ₃ ) as brightness control signal
Means for outputting the brightness control signal.
Signal is high when the average video level is high and the black level is high.
Lower lightness, lower average video level and lower black level
Increase the brightness when the average video level is high.
Keep the brightness when it is not too low
Thus, the input video signal is controlled as described above.

[0006] means for outputting a signal of the degree μ _10, degree
means for outputting a signal of mu _20, and outputs a signal of the degree mu ₃
Means, means for outputting a signal of the degree mu _11, degree mu ₂₀ signals
Means for outputting, and the control values E _1, E _2, E ₃
All output means are composed of lookup tables.
Have been .

[0007]

According to the above arrangement, the white peak value, the average video level and the black level of the input video signal are detected, and the respective degrees are calculated by the calculating means based on the level of the normal video signal equal to or higher than the pedestal level. Since the input video signal is controlled by the video control signal, the driving of the liquid crystal display device can be optimized so that the details of the bright and dark portions of the video can be reproduced.

The brightness control signal
(Μ ₁ E ₁ + μ ₂ E ₂ + μ ₃ E ₃ ) / (μ ₁ + μ ₂ + μ ₃ )
When the power video signal is controlled, the average video level increases and the black level increases.
The brightness of the input video signal decreases when the
When the average video level is low and the black level is low, the
Brightness increased, average video level not high or low
The brightness of the input video signal is
State.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, an input video signal from a television signal demodulation circuit or the like supplied from a video input terminal T is quantized by sampling in an analog / digital (hereinafter, referred to as A / D) conversion circuit 1 to obtain an 8-bit signal. A digital signal is supplied to the Y / C separation circuit 2.

In a Y / C separation circuit 2, a luminance signal Y and a chrominance signal C are separated, and these are supplied to a video signal processing circuit 3 in the next stage and demodulated into R, G, B signals. It is supplied to the control circuit 24. The R, G, and B control circuits 24 use various control signals, such as a contrast control signal, a brightness control signal, and a gamma correction control signal, from the arithmetic circuit 23, which will be described later, in order to make it easy to see the image reproduced on the liquid crystal panel 25. Next, the level and bias of the R, G, and B signals supplied from the video signal processing circuit 3 are controlled, and the contrast and brightness are controlled.

In the liquid crystal panel 25, a plurality of pixels arranged in a matrix form a horizontal and vertical drive circuit (not shown).
Are driven line by line, and the R, G, B control circuit 2
4, a color image is displayed according to the corrected R, G, B signals.

On the other hand, a luminance signal Y composed of an 8-bit digital signal separated by the Y / C separation circuit 2 is passed through a screen area dividing section 4 to a peak detection circuit 5 for detecting a white peak value of the luminance signal. , An average value detection circuit 6 for detecting an average level of the luminance signal Y, a black level detection circuit 7 for detecting a black level of the luminance signal, and a pedestal detection circuit 8 for detecting a pedestal level of the luminance signal. You.

The peak value, average value, and black level of the luminance signal Y detected by the peak detection circuit 5, the average value detection circuit 7, and the black level detection circuit 7 are determined by the pedestal level detected by the pedestal detection circuit 8. The correction operation circuit 9 corrects and calculates the true video signal level excluding the synchronizing signal level, and stores them in the peak data register 10, the average value data register 11, and the black level data register 12, respectively.

In the figure, reference numeral 13 denotes the average value data register 11.
When the average picture level APL, which is stored has a high value in a look-up table for outputting a control signal of the degree mu ₁₀ as shown in FIG. 2 (a), 14 is stored in the average value data register 11 Average video level A
If PL is a low value, a lookup table which outputs a control signal of the degree mu ₂₀ as shown in FIG. 2 (b), 17 is the average picture level APL, which is stored in the average value data register 11 If higher is also no value less without a look-up table for outputting a control signal of the degree mu ₃ as shown in Figure 2 (c).

[0015] figure 15, when the black level of the luminance signal Y stored in the black level data register 12 has a high value, the control signal of the degree mu ₁₁ as shown in FIG. 2 (d) Reference numeral 16 denotes a lookup table to be output. When the black level of the luminance signal Y stored in the black level data register 12 is a low value, a control signal having a degree μ ₂₁ as shown in FIG. This is a lookup table to be output.

In the figure, reference numeral 18 denotes the lookup table 1
3 and compares the degree mu ₁₀ and mu ₁₁ of the control signal output from the 15, a comparator circuit for outputting a lower of degree as the degree mu ₁ of the control signal, 20 is a control derived from the comparison circuit 18 depending on the degree mu ₁ of the signal is a lookup table to derive the control value output E ₁ as shown in FIG. 3 (a).

Reference numeral 19 denotes a comparison circuit which compares the control signals outputted from the look-up tables 14 and 16 with the degrees μ ₂₀ and μ ₂₁ , and outputs the lower one as a control signal having a degree μ _2. depending on the degree mu ₂ control signal derived from the comparator circuit 19, a look-up table to derive the control value output E ₂ as shown in FIG. 3 (b), 22 is outputted from the look-up table 17 depending on the degree mu ₃ of a control signal, a look-up table to derive the control value output E ₃ as shown in Figure 3 (c).

Reference numeral 23 denotes a control signal of the degree μ ₁ , μ ₂ , μ ₃ and E ₁ , E ₂ , E ₃ output from the comparison circuits 18, 19 and the look-up tables 17, 20, 21, 22 as input signals. (Μ ₁ E ₁ + μ ₂ E ₂ + μ ₃ E ₃ ) / (μ ₁ + μ ₂ + μ
Performs weighting averaging operation of _3), an arithmetic circuit for outputting a brightness control signal E _BR, the arithmetic circuit 2
The brightness control signal E _BR from 3 is R, G,
It is supplied to a B control circuit 24 to control the brightness of the R, G, B signals.

Next, the operation when the brightness control of the R, G, B signals is performed by the above configuration will be described. First, the following rules A, B, and C are determined as conditions for determining the brightness control output. Rule A: If the average video level APL is high and the black level is high, lower the brightness. Rule B: Increase the brightness when the average video level APL is low and the black level is low. Rule C: When the average video level is neither high nor low, the brightness is not changed (standard value).

[0020] For rule A, the output of the look-up table 13, i.e., the average picture level APL is high degree mu _10, the output of the look-up table 15, i.e. compares the black level is high degree of mu _11, the degree the lower the the degree μ ₁ of rules a. The control values output E ₁ for the degree mu ₁ derived from the look-up table 20 as shown in FIG. 3 (a), supplied to the arithmetic circuit 23 together with the degree mu ₁ of said rules A.

Next, regarding rule B, the output of the look-up table 14, ie, the degree μ _{20 at} which the average video level APL is low, the output of the look-up table 16,
That is, the degree μ ₂₁ of the low black level is compared, and the lower degree is defined as the degree μ _{2 of the} rule B. The control values output E ₂ for the degree mu ₂ derived from the look-up table 21 as shown in FIG. 3 (b), supplied to the arithmetic circuit 23 together with the degree mu ₂ above rule B.

Regarding the rule C, FIG. 3C shows the output of the look-up table 17, that is, the degree μ ₃ shown in FIG. 2C where the average video level APL is neither high nor low. The control value output E ₃ having a constant value is derived from the look-up table 22,
It is supplied to the arithmetic circuit 23 together with the degree μ ₃ derived from the lookup table 17.

In the arithmetic circuit 23, the comparison circuit 1
8, 19 and the degrees μ ₁ , μ ₂ , μ ₃ supplied from the lookup table 17 and the lookup tables 20,
Based on the degrees E ₁ , E ₂ , E ₃ supplied from 21 and 22,
Perform a weighted average operation (μ ₁ E ₁ + μ ₂ E ₂ + μ ₃ E ₃ ) /
(Μ ₁ + μ ₂ + μ ₃ ) is the brightness control output E
_It is derived as _BR and supplied to the R, G, B control circuit 24 to control the brightness of the R, G, B signals.

Therefore, when the level of the rule A is the highest, the average video level APL is high, and when the black level is high, the brightness is lowered. When the white peak level is high, the contrast is lowered. The liquid crystal panel 25 can reproduce a bright portion of an image in detail within a driving range corresponding to ΔV in FIG.

Similarly, when the average video level APL is low and the black level is low, the brightness is increased. When the average video level is neither high nor low, the brightness is controlled to be the same, and the image is bright. Both parts and dark parts can be reproduced in detail.

Although the control of brightness has been described above, the control of contrast can also be performed by configuring the contrast control section 26 in the same manner as that for controlling brightness. The rules in this case are as follows, for example. I just need. Rule D: If the white peak luminance level is high, lower the contrast. Rule E: Low white peak level and average video level APL
If the contrast is low, increase the contrast. Rule F: If the white peak level is neither high nor low, the contrast is standardized.

Also, the gamma correction of the liquid crystal panel can be realized by configuring the gamma control unit 27 in the same manner as described above, so that an optimum display according to the contents of various images is performed. Can be.

[0028]

Since the present invention has the above configuration, even when a video signal that is higher than the white saturation point of the liquid crystal panel is input,
The peak portion of the luminance signal can be reproduced, and the details of the dark portion can be reproduced even on the entire dark screen including the portion close to the black saturation point, thereby significantly improving the display quality of the liquid crystal display. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a characteristic diagram of a first lookup table used in the present invention.

FIG. 3 is a characteristic diagram of a second lookup table used in the present invention.

FIG. 4 is a characteristic diagram of a liquid crystal display device.

Claims (2)

(57) [Claims] 1. A white peak value detecting means for detecting a white peak value of an input video signal from a digitized luminance signal derived from an input video signal, and an average value detection for detecting an average video level of the input video signal. Means, a black level detecting means for detecting a black level of the input video signal, a pedestal level detecting means for detecting a pedestal level of the input video signal, and each of the above detections for a video signal having a pedestal level or higher. Calculating means for calculating a video control signal for obtaining an appropriate video level based on the white peak value, average video level, and black level detected by the means; and an input video signal based on the video control signal calculated by the calculating means. Liquid crystal display device equipped with control means for controlling the
Oite, leaving the degree mu ₁₀ signal when the average is a video level higher values
Means for force, out of the signals of the degree mu ₂₀ when the average picture level is low
Means when the average image level is neither high nor low
Means for outputting a _third signal, the degree mu ₁₁ signal when the black level of the luminance signal is high value
Means for outputting a degree mu ₂₁ signal when the black level of the luminance signal is low
And means for outputting, the lower signal of the degree mu ₁₀ and the degree mu ₁₁ and degree mu ₁
Comparing means for outputting Te, the lower signal of the degree mu ₂₀ the degree mu ₂₁ the degree mu ₂ and
Comparing means for outputting Te, degree mu _1, mu _2, respectively control value in accordance with the mu ₃
The means for outputting E ₁ , E ₂ , and E ₃ and the calculation of (μ ₁ E ₁ + μ ₂ E ₂ + μ ₃ E ₃ ) / (μ ₁ + μ ₂ + μ ₃ )
Output and output as a brightness control signal
And the brightness control signal is an average image.
When the level is high and the black level is high, lower the brightness,
Brightness when average video level is low and black level is low
The average video level is neither high nor low.
Input video signal to keep the lightness as it is
A liquid crystal display device characterized by controlling the following . 2. A means for outputting a signal of the degree mu _10, degree
means for outputting a signal of mu _20, and outputs a signal of the degree mu ₃
Means, means for outputting a signal of the degree mu _11, degree mu ₂₀ signals
Means for outputting, and the control values E _1, E _2, E ₃
All output means are composed of lookup tables.
2. The liquid crystal display according to claim 1, wherein
Indicating device.