JP2004272156A - Image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display which realizes favorable gradation reproducibility in any viewing environment. <P>SOLUTION: The apparatus is equipped with: an ambient illuminance measuring unit 21 which measures the ambient illuminance; a microcomputer 22 which detects the minimum luminance possible to be displayed on a screen (screen minimum luminance) based on the ambient illuminance data by the ambient illuminance measuring unit 21 and on the light controlling data by a back light controlling circuit 8 and which varies and controls the reference gradation voltage responding to the input image data to drive a liquid crystal display panel 2; and a storage unit 23 for the data of the reference gradation voltage, such as a ROM, which stores in the memory a plurality of reference gradation voltages generated by a reference gradation voltage generating unit 5 for each screen minimum luminance. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image display device that displays an image corresponding to input image data, and more particularly to an image display device that can achieve good tone reproducibility regardless of the viewing environment.
[0002]
[Prior art]
In recent years, lighter and thinner display devices such as personal computers and television receivers have been required to be lighter and thinner. In accordance with such demands, liquid crystal display devices (LCDs) have been used instead of cathode ray tubes (CRTs). ) And flat panel displays such as plasma display devices (PDPs) have been developed.
[0003]
For example, an LCD applies an electric field to a liquid crystal layer having an anisotropic dielectric constant injected between two substrates, and controls the intensity of the electric field to control the amount of light transmitted through the substrate. This is a display device for obtaining a desired image signal. Such LCDs are typical of portable simple flat panel displays. Among them, TFT LCDs using thin film transistors (TFTs) as switching elements are mainly used.
[0004]
Such a conventional liquid crystal display device will be described with reference to FIGS. FIG. 12 is a block diagram showing a schematic configuration of a conventional liquid crystal display device, in which 1 is an LCD controller, 2 is a liquid crystal display panel, 3 is a signal line driving circuit, 4 is a scanning line driving circuit, and 5 is a reference. A gradation voltage generator, 6 is a backlight, 7 is an inverter circuit for driving the backlight, and 8 is a backlight control circuit.
[0005]
The image data is input to the LCD controller 1 as gradation data and synchronization data. The gradation data is, for example, an RGB signal, and the synchronization data is data including a vertical synchronization signal, a horizontal synchronization signal, a data enable signal (DE), a clock, and the like. The LCD controller 1 generates gradation data and a signal-side control signal to be output to the signal line driving circuit 3 based on the input gradation data and synchronization data, and controls the scanning line to be output to the scanning line driving circuit 4. A signal is generated, and image display control on the liquid crystal display panel 2 is performed.
[0006]
Further, the LCD controller 1 controls the inverter circuit 7 via the backlight control circuit 8 to adjust the backlight lighting period (backlight duty) and the backlight drive current, thereby controlling the backlight 6 by the backlight 6. Dimming control of the brightness of the illumination light.
[0007]
Here, the configuration of the liquid crystal display panel 2 (active matrix type LCD) will be described with reference to FIG. The liquid crystal display panel 2 includes first and second glass substrates (not shown). On the first glass substrate, n scanning lines G1 to Gn and m signal lines S1 to Sm are arranged. A thin film transistor (TFT) 11, which is a non-linear element (switching element), is provided near each intersection.
[0008]
The gate line of the TFT 11 is connected to the scanning lines G1 to Gn, the source electrode is connected to the signal lines S1 to Sm, and the drain electrode is connected to the pixel electrode. The second glass substrate is disposed at a position facing the first glass substrate, and a common electrode is formed on one surface of the glass substrate surface by a transparent electrode such as ITO. Each of the common electrodes is connected to a common electrode drive circuit 12, and the potential is set by the common electrode drive circuit 12. Then, a liquid crystal 13 is sealed between the common electrode and the pixel electrode formed on the first glass.
[0009]
The above-described scanning lines G1 to Gn and signal lines S1 to Sm are connected to the scanning line driving circuit 4 and the signal line driving circuit 3, respectively. The scanning line driving circuit 4 performs scanning by sequentially applying a high potential to the n scanning lines G1 to Gn, and turns on the TFT 11 connected to each of the scanning lines G1 to Gn. When the scanning line driving circuit 4 scans the scanning lines G1 to Gn, the signal line driving circuit 3 outputs a gradation voltage corresponding to image data to any of the m signal lines S1 to Sm. The gradation voltage is written to the pixel electrode via the TFT 11 in the ON state, and the light transmission amount is determined by the potential difference between the common electrode set to a constant potential and the pixel electrode to which the gradation voltage is applied. Is controlled.
[0010]
Here, since the backlight 6 provided on the back surface of the liquid crystal display panel 2 emits a certain luminance by being driven by the inverter circuit 7, the backlight 6 is operated according to the above-described operation principle of the liquid crystal display panel 2. The desired image display is performed by controlling the amount of transmission of the light emitted from the device.
[0011]
Further, the reference gray scale voltage generator 5 shown in FIG. 12 supplies the reference gray scale voltage to the signal line drive circuit 3. The reference gradation voltage is a voltage applied to the liquid crystal display panel 2 which is appropriately set according to the gradation level of the image data. FIG. 14 is an explanatory diagram showing an example of the relationship between the transmittance and the applied voltage of the liquid crystal. In order to display an image using the liquid crystal having the characteristics shown in FIG. 14, for example, as shown in FIG. 15, the relationship between the gradation level of the image data and the light transmittance becomes a curve of gamma 2.2. Is set to the reference gradation voltage.
[0012]
As shown in FIG. 14, for example, the reference gray scale voltage is set as a reference gray scale voltage obtained by dividing the maximum display gray scale into eight, and the remaining gray scale voltages are obtained by dividing the adjacent reference gray scale voltages. Generated. Specifically, all the display gradation voltages are set by the circuit divided by the resistance.
[0013]
The conventional liquid crystal display device has been described above. However, when an image is displayed on the conventional liquid crystal display device, it is affected by the viewing environment (illuminance). In response to this, there has been proposed a device that switches the γ correction characteristic related to the linearity of the display luminance, and particularly improves the display contrast at the halftone level.
[0014]
According to this, in a normal use environment such as indoors, the γ correction characteristic indicated by a polygonal line A in FIG. 16 is selected, and in an environment such as outdoors where the surroundings are bright, γ1 as shown by a polygonal line B in FIG. By increasing the amplification degree only for the signal levels of 信号 2, the brightness of the halftone level display can be increased, and the visibility of a normal video signal can be improved.
[0015]
[Patent Document 1]
JP-A-6-83287
[Problems to be solved by the invention]
By the way, in the liquid crystal display device as described above, as shown in FIG. 17 and FIG. 18, when the surrounding brightness (illuminance) is changed, the gradient does not change even when the surrounding illuminance changes. . However, according to an experiment performed by the inventor of the present application, it has been clarified that the gradation identification luminance difference near the luminance differs depending on the luminance to be displayed. The relationship is that the relationship between the logarithm of the display luminance and the logarithm of the discrimination limit luminance difference is proportional.
[0017]
That is, when the surroundings are dark and the brightness when displaying black on the screen is low, the gradation discrimination near black is improved (a small difference in luminance is possible). Conversely, when the surroundings are bright, the black Is displayed, only black with high luminance can be displayed due to the surface reflection of the screen. In such a case, the gradation discrimination is lower than in the case where the surrounding brightness is dark (a slight difference in luminance cannot be determined).
[0018]
As described above, with the change in the ambient illuminance, the visual tone reproducibility (discrimination limit brightness) particularly in a low tone portion is different. Since the amount of reflected light is small, the minimum luminance that can be displayed on the screen is also small, and it is possible to identify subtle luminance changes in low gradation areas.However, when the ambient illuminance is large, the liquid crystal display panel of the ambient light However, since the amount of light reflected on the surface is large, the minimum luminance that can be displayed on the screen is also large, and there has been a problem that it is difficult to distinguish a subtle luminance change in a low gradation portion.
[0019]
In addition, the minimum luminance that can be displayed on the screen is affected by the amount of backlight transmitted through the liquid crystal display panel in addition to the above-described reflection of ambient light on the surface of the liquid crystal display panel. Means that the minimum luminance that can be displayed on the screen is also small, and it is possible to identify subtle luminance changes in the low gradation part. However, if the backlight emission luminance is large, the minimum luminance that can be displayed on the screen is low. And it becomes difficult to identify a subtle change in luminance in a low gradation portion.
[0020]
Note that, as described above, the change in gradation reproducibility that occurs according to the minimum luminance that can be displayed on the screen is almost negligible in the middle and high gradation parts, and is noticeable in the low gradation part. It is thought to be due to human visual characteristics.
[0021]
The present invention has been made in view of the above problems, and an object of the present invention is to provide an image display device capable of realizing good tone reproducibility under any viewing environment.
[0022]
[Means for Solving the Problems]
A first invention of the present application is an image display device that displays an image corresponding to input image data, comprising: a detecting unit that detects a minimum luminance that can be displayed on a screen; Control means for controlling the display luminance of the low gradation corresponding to the input image data based on the minimum luminance.
[0023]
The second invention of the present application is characterized in that the detecting means detects a minimum luminance that can be displayed on a screen based on ambient illuminance.
[0024]
A third invention of the present application is characterized in that the detecting means detects a minimum luminance that can be displayed on a screen based on a backlight emission luminance.
[0025]
A fourth invention of the present application is the reference gradation voltage circuit, wherein the control means varies a gradation voltage applied to a liquid crystal display panel in accordance with the input image data based on a minimum luminance that can be displayed on the screen. It is characterized by being.
[0026]
A fifth invention of the present application is the image display device, wherein the control unit is a gradation correction circuit that changes a gradation level of the input image data based on a minimum luminance that can be displayed on the screen.
[0027]
According to the image display device of the present invention, it is possible to control the low-gradation display luminance corresponding to the input image data based on the minimum luminance that can be displayed on the screen, which is obtained from the ambient illuminance and the backlight emission luminance. Accordingly, when the minimum luminance that can be displayed on the screen is small, the display luminance of the low gradation becomes dark (the luminance change becomes small), and when the minimum luminance that can be displayed on the screen is large, the low gradation is displayed. Automatic adjustment can be performed so that the display luminance of the gradation becomes bright (the luminance change becomes large). This makes it possible to maintain good visual gradation reproducibility at low gradations in any viewing environment.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a case where the first embodiment of the image display device of the present invention is applied to a liquid crystal display device will be described in detail with reference to FIGS. 1 to 7. The description is omitted. Here, FIG. 1 is a block diagram showing a schematic configuration of the liquid crystal display device of the present embodiment, FIG. 2 is a schematic explanatory diagram showing an example of the contents of a reference gradation voltage data storage unit in the liquid crystal display device of the present embodiment, and FIG. FIG. 4 is an explanatory diagram showing a relationship between display gradation and display luminance in the liquid crystal display device of the present embodiment.
[0029]
FIG. 4 is an explanatory diagram showing the relationship between the screen minimum luminance and the inclination near black in the liquid crystal display device of the present embodiment, and FIG. 5 is a schematic configuration of a reference gray scale voltage generation unit in the liquid crystal display device of the present embodiment. FIG. 6 is a circuit diagram showing a schematic configuration of a main part of a signal line driving circuit in the liquid crystal display device of the present embodiment, and FIG. 7 is a schematic explanatory diagram showing gamma characteristics in the liquid crystal display device of the present embodiment.
[0030]
As shown in FIG. 1, the liquid crystal display device according to the present embodiment includes an ambient illuminance measuring unit 21 that detects ambient brightness, ambient illuminance data detected by the ambient illuminance measuring unit 21, and a backlight control circuit 8. A microcomputer that detects the minimum luminance that can be displayed on the screen (the minimum luminance of the screen) based on the dimming control data, and variably controls a reference gradation voltage for driving the liquid crystal display panel 2 according to the input image data. And a reference gradation voltage data storage unit 23 such as a ROM that stores a plurality of values of the reference gradation voltage generated by the reference gradation voltage generation unit 5 for each screen minimum luminance.
[0031]
Here, the reference gradation voltage generator 5 supplies a reference gradation voltage to the signal line driving circuit 3 based on the reference gradation voltage data stored in the reference gradation voltage data storage 23. is there. Here, as shown in FIG. 2, the reference gradation voltage data storage unit 23 stores, in another area of the ROM, reference gradation voltage data corresponding to the screen minimum luminance obtained based on the ambient illuminance / backlight emission luminance. These are selected and instructed by the microcomputer 22 and output to the reference gray scale voltage generator 5.
[0032]
That is, the relationship between the display gradation of the input image data and the display luminance of the liquid crystal display panel 2 is as shown in FIG. 3, but in the liquid crystal display device of the present embodiment, as shown in FIG. When the backlight is bright or when the backlight is bright, the reference gradation voltage is variably controlled so that the inclination when displaying the vicinity of black becomes large (the luminance change becomes large = the display luminance of the low gradation becomes bright). When the surroundings are dark or the backlight is dark, the reference gradation voltage is variably controlled so that the inclination when displaying the vicinity of black becomes small (the luminance change becomes small = the display luminance of the low gradation becomes dark). .
[0033]
For this reason, the reference gradation voltage data storage unit 23 stores low gradations in accordance with the minimum luminance (screen minimum luminance) that can be displayed on the screen, which is determined by the brightness of the ambient light and the brightness of the backlight illumination light. Three types of reference gray-scale voltage data are provided which have different inclinations in the vicinity. In the present embodiment, the inclination near black is variably controlled as described above by focusing on a low gradation portion where the minimum luminance of the screen greatly affects the visual gradation reproducibility. Of course, the middle and high gradation portions are also appropriately adjusted in order to ensure continuity with the vicinity of black.
[0034]
Here, for example, when the number of display signal levels, that is, the number of display data is 256 gradations of 8 bits, the voltage data V0, V32,... Corresponding to 0, 32, 64, 96, 128, 160, 192, 224, 255 gradations. .., V255 are set / stored. With respect to gradations other than the stored reference gradation, the reference gradation voltage is linearly divided by resistance, so that all the gradations to be applied to the liquid crystal display panel 2 are applied. A regulation voltage is required.
[0035]
As shown in FIG. 5, the reference gradation voltage generator 5 performs D / A conversion of digital data of V0, V32,..., V255 acquired from the reference gradation voltage data storage 23 by the DA converter 5a. Thereafter, the reference gradation voltages VA0, VA32,..., VA255 adjusted by appropriately amplifying by the amplifier unit 5b are supplied to the signal line driving circuit 3 including a source driver and the like. As shown in FIG. 6, the signal line drive circuit 3 has the input terminals of the reference gradation voltages VA0, VA32,..., VA255, which are connected by resistance division, and generates all gradation voltages corresponding to image data. Thus, 8-bit image data can be displayed.
[0036]
Here, gray scale voltages for nine reference gray scales of 32 gray scales of 0, 32, 64, 96, 128, 160, 192, 224, 255 are generated, and the other gray scale voltages are divided by resistance. However, the present invention is not limited to this, and it goes without saying that the present invention may be applied to, for example, a device that generates a gradation voltage for a reference gradation every 16 gradations. Further, in the present embodiment, three types of reference grayscale voltage data are switched according to the screen minimum luminance for the sake of simplicity, but it is obvious that the number of switched data is not limited to this.
[0037]
As described above, any one of the reference gradation voltage data stored in the reference gradation voltage data storage unit 23 is read out to the reference gradation voltage generation unit 5 by the switching control signal from the microcomputer 22. Based on the reference gradation voltage data, the gradation voltage applied to the liquid crystal display panel 2 is determined corresponding to each gradation level of the input image data.
[0038]
Thereby, as shown in FIG. 7, when the screen minimum luminance is small, it is possible to make the inclination when displaying the vicinity of black gentle (decrease the luminance change) (curve a in FIG. 7). When the screen minimum luminance is large, it is possible to increase the inclination near black (increase the luminance change) (curve c in FIG. 7). Therefore, even if the minimum screen luminance becomes large, it is possible to easily identify a subtle luminance change in a low gradation portion, and it is possible to suppress the occurrence of image quality deterioration due to a change in gamma characteristics.
[0039]
In the above-described embodiment, the reference gradation voltage for driving the liquid crystal display panel 2 is varied according to the minimum luminance that can be displayed on the screen (the minimum screen luminance). However, the present invention is not limited to this. For example, a configuration may be adopted in which the gradation level of the input image data is converted at the preceding stage of the LCD controller 1 so as to variably control the low-gradation display luminance corresponding to the input image data.
[0040]
This will be described with reference to FIGS. 8 to 11 as a second embodiment of the present invention, and the same parts as those in the above-described first embodiment will be denoted by the same reference numerals and description thereof will be omitted. Here, FIG. 8 is a block diagram illustrating a schematic configuration of the liquid crystal display device of the present embodiment, and FIG. 9 is a schematic explanatory diagram illustrating input / output characteristics (first example) of a gradation correction unit in the liquid crystal display device of the present embodiment. FIG. 10 is a schematic explanatory view showing the input / output characteristics (second example) of the gradation correction unit in the liquid crystal display device of the present embodiment. FIG. 11 is the input / output characteristics of the gradation correction unit in the liquid crystal display device of the present embodiment. It is a schematic explanatory drawing showing (the 3rd example).
[0041]
As shown in FIG. 8, the liquid crystal display device according to the present embodiment, based on the ambient illuminance data detected by the ambient illuminance measurement unit 21 and the dimming control data by the backlight control circuit 8, controls the minimum displayable on the screen. A microcomputer 32 for detecting luminance (minimum screen luminance) and variably controlling the gradation level of the input image data; and a floor such as a ROM storing a plurality of output image data values for the input image data for each minimum screen luminance. A tone correction data storage unit 33 and a tone correction circuit 34 for changing the tone level of the input image data according to the minimum screen brightness.
[0042]
Here, the gradation correction circuit 34 converts the gradation level based on the gradation correction data stored in the gradation correction data storage unit 33, and then outputs the image data to the LCD controller 1. . Here, in the gradation correction data storage unit 33, gradation correction data corresponding to the screen minimum luminance obtained based on the ambient illuminance / backlight emission luminance is stored in another area of the ROM. Is selected and used by the tone correction circuit 34 for tone conversion processing.
[0043]
That is, in the liquid crystal display device of the present embodiment, as shown in FIGS. 9 to 11, when the screen minimum luminance is large (when the surroundings are bright or the backlight is bright), the inclination when displaying the vicinity of black is reduced. (The curve a in FIGS. 9 to 11), and the screen minimum luminance is set so that the input image data becomes larger (the change in luminance becomes larger = the display luminance of the lower gradation becomes brighter). When the image data is small (when the surroundings are dark or the backlight is dark), the input image data is set so that the inclination when displaying the vicinity of black becomes small (the luminance change becomes small = the display luminance of low gradation becomes dark). (A curve c in FIGS. 9 to 11).
[0044]
Thus, when the screen minimum luminance is small, it is possible to make the inclination when displaying the vicinity of black gentle (the luminance change is small), and when the screen minimum luminance is large, the inclination near the black is increased. (Increase the change in luminance). Therefore, even if the screen minimum luminance is increased, it is possible to easily identify a subtle luminance change in a low gradation portion, and it is possible to suppress the occurrence of image quality deterioration due to a change in gamma characteristics.
[0045]
As described in detail above, according to the image display device of the present invention, based on the minimum luminance that can be displayed on the screen, the display brightness of the low gradation corresponding to the input image data is appropriately variably controlled. Regardless of the viewing environment, it is possible to maintain good visual gradation reproducibility in a low gradation portion, and to always realize high-quality image display.
[0046]
In the first and second embodiments of the present invention described above, the minimum luminance (screen minimum luminance) that can be displayed on the screen is obtained from the ambient illuminance and the backlight emission luminance, and the low gradation corresponding to the input image data is obtained. Is adjusted, but it is needless to say that the minimum screen brightness may be obtained based on, for example, either the ambient illuminance or the backlight emission brightness. Further, it is apparent that the present invention is not limited to a liquid crystal display device, but can be applied to various image display devices such as a CRT and a PDP.
[0047]
【The invention's effect】
Since the liquid crystal display device of the present invention is configured as described above, by controlling the display luminance of the low gradation corresponding to the input image data based on the minimum luminance that can be displayed on the screen, Even in a viewing environment, it is possible to maintain good visual gradation reproducibility at low gradations, and to always realize high-quality image display.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image display device according to a first embodiment of the present invention.
FIG. 2 is a schematic explanatory diagram showing an example of the contents of a reference gradation voltage data storage unit in the first embodiment of the image display device of the present invention.
FIG. 3 is an explanatory diagram showing a relationship between display gradation and display luminance in the first embodiment of the image display device of the present invention.
FIG. 4 is an explanatory diagram showing the relationship between the screen minimum luminance and the inclination near black in the first embodiment of the image display device of the present invention.
FIG. 5 is a block diagram illustrating a schematic configuration of a reference gradation voltage generation unit in the first embodiment of the image display device of the present invention.
FIG. 6 is a circuit diagram showing a schematic configuration of a main part of a signal line driving circuit in the first embodiment of the image display device of the present invention.
FIG. 7 is a schematic explanatory diagram showing gamma characteristics in the first embodiment of the image display device of the present invention.
FIG. 8 is a block diagram illustrating a schematic configuration of an image display device according to a second embodiment of the present invention.
FIG. 9 is a schematic explanatory diagram showing input / output characteristics (first example) of a gradation correction unit in a second embodiment of the image display device of the present invention.
FIG. 10 is a schematic explanatory diagram showing input / output characteristics (second example) of a gradation correction unit in a second embodiment of the image display device of the present invention.
FIG. 11 is a schematic explanatory diagram illustrating input / output characteristics (third example) of a gradation correction unit in a second embodiment of the image display device of the present invention.
FIG. 12 is a block diagram illustrating a schematic configuration of a conventional liquid crystal display device.
FIG. 13 is an explanatory diagram (equivalent circuit diagram) illustrating a schematic configuration of a liquid crystal display panel.
FIG. 14 is an explanatory diagram showing an example of the relationship between the transmittance and the applied voltage of the liquid crystal.
FIG. 15 is a schematic explanatory diagram showing gamma characteristics in a liquid crystal display device.
FIG. 16 is a schematic explanatory view showing γ correction characteristics in a conventional liquid crystal display device.
FIG. 17 is an explanatory diagram showing gradation-luminance characteristics when the ambient illuminance is changed in a conventional liquid crystal display device.
FIG. 18 is an enlarged view of a low gradation portion in FIG. 17;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 LCD controller 2 Liquid crystal display panel 3 Signal line drive circuit 4 Scan line drive circuit 5 Reference gradation voltage generation part 6 Backlight 7 Backlight inverter circuit 8 Backlight control circuit 21 Ambient illuminance measurement part 22, 32 Microcomputer 23 Reference floor Voltage adjustment data storage unit 33 Gradation correction data storage unit 34 Gradation correction circuit

Claims (5)

An image display device that displays an image according to input image data,
Detecting means for detecting the minimum luminance that can be displayed on the screen;
An image display device comprising: a control unit that controls display luminance of a low gradation corresponding to input image data based on the detected minimum luminance that can be displayed on a screen. The image display device according to claim 1,
The image display device, wherein the detecting means detects a minimum luminance that can be displayed on a screen based on ambient illuminance. The image display device according to claim 1,
The image display device, wherein the detecting means detects a minimum luminance that can be displayed on a screen based on a backlight emission luminance. The image display device according to any one of claims 1 to 3,
The control means is a reference gradation voltage circuit that varies a gradation voltage applied to a liquid crystal display panel in accordance with the input image data based on a minimum luminance that can be displayed on the screen. Display device. The image display device according to any one of claims 1 to 3,
The image display device, wherein the control means is a gradation correction circuit that changes a gradation level of the input image data based on a minimum luminance that can be displayed on the screen.

Images