JPH11326852A - Gray scale driving method of array type light modulation element and flat display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gradation drive method of arrayed optical modulation elements and a flat display device using the arrayed optical modulation elements even by γ-corrected image signals of a broadcasting system in an electrostatic stress type flat display device. SOLUTION: In a tone drive method of an arrayed optical modulator 14 in which an optical modulating part deforming a flexible thin film 9 by an electrostatic stress and changing an optical transmittance is arranged in a linear or two-dimensional matrix form, the optical modulating part is to be driven based on an input signal provided with inverse γ-correction. In such a case, the tone drive of the arrayed optical modulator 14 may obtain the gradation by varying a transmission time of the light of the optical modulating part. Moreover, the gradation drive of the arrayed optical modulator 14 may obtain the gradation by integrated gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a gray scale of an array type light modulating device and a flat panel display using the array type light modulating device, and more particularly, to operating in a binary modulation mode by electrostatic stress. The present invention relates to an improvement in a multi-grayscale driving method in an array type light modulation element.

[0002]

2. Description of the Related Art Conventionally, various types of thin flat display devices have been proposed, and typical ones include, for example, a liquid crystal display device, a plasma display device, and a field emission display (FED).

[0003] A liquid crystal display device encloses and seals a nematic liquid crystal between a substrate on which a pair of conductive transparent films are formed and oriented so as to be parallel to the substrate and twisted by 90 ° between the two substrates. It has a structure in which this is sandwiched between orthogonal polarizing plates. The display by this liquid crystal display device utilizes the fact that by applying a voltage to the conductive transparent film, the major axis direction of the liquid crystal molecules is oriented perpendicular to the substrate and the transmittance of light from the backlight changes. It is done. This liquid crystal display device
Since light from the backlight is transmitted through multiple layers of the polarizing plate, the transparent electrode, and the color filter, there is a problem that the light use efficiency is reduced. Also, inject liquid crystal between the two substrates,
There is a drawback that it is difficult to increase the area because it must be oriented. Further, since light is transmitted through the aligned liquid crystal molecules, there is a disadvantage that the viewing angle is narrowed.

On the other hand, a plasma display device has a large number of regularly arranged orthogonal electrodes corresponding to an anode and a cathode disposed between two glass plates in which a rare gas such as neon gas is sealed.
It has a structure in which the intersection of each counter electrode is a unit pixel. The display by the plasma display device is based on image information, by selectively applying a voltage to the opposing electrodes for specifying the respective intersections, thereby causing the intersections to discharge and emit light, and exciting the phosphor by the generated ultraviolet light. This is performed by emitting light. This plasma display device requires the formation of partition walls for generating plasma for each pixel and a high degree of vacuum sealing, and thus has the disadvantage of increasing the manufacturing cost and increasing the weight. There is also a disadvantage that the driving voltage is high and the driving IC becomes expensive.

Further, the FED has a structure as a flat display tube in which a pair of panels are arranged to face each other with a very small space therebetween and the periphery of these panels is sealed. A fluorescent film is provided on the inner surface of the panel on the display surface side, and field emission cathodes are arranged on the back panel for each unit light emitting region. The field emission cathode has a field emission type microcathode having a conical shape called a micro-sized emitter tip. FED
The display by means of taking out electrons using an emitter tip,
This is performed by irradiating the phosphor with accelerated irradiation to excite the phosphor. The FED requires a high vacuum inside the panel in order to stabilize the discharge with high efficiency, and has the disadvantage that the manufacturing cost is high as in the plasma display device. Further, since the field-emitted electrons are accelerated and irradiated to the phosphor, there is a disadvantage that a high voltage is required.

On the other hand, a flat display device having a light modulation element driven by electrostatic stress has been proposed. In this light modulation element, a support is provided on a substrate, and a transparent flexible thin film parallel to the substrate is provided at an upper end of the support. A pair of transparent electrodes serving as a scanning electrode and an image signal electrode are opposed to the substrate and the flexible thin film. In this light modulation element, by applying a voltage to the transparent electrode, the flexible thin film is displaced (electromechanically operated) by electrostatic stress, so that light from the substrate can be modulated. According to such an electrostatic stress type flat display device, high-speed light modulation can be performed by driving a flexible thin film at high speed by electrostatic stress. In addition, since light only passes through the transparent flexible thin film and the transparent electrode, higher light use efficiency can be obtained as compared with a liquid crystal display device that transmits light through multiple layers. Further, since high-level vacuum sealing is not required, a large screen and low cost can be realized.

[0007]

In the above-mentioned flat display device of the electrostatic stress type, the light modulation element takes a binary light modulation mode. In this case, as a method of obtaining a gradation, a technique is known in which the high-speed property is used to change the light transmission time of each pixel at a high speed within one field time so that flicker is not felt. In this case, if the input image signal is directly replaced with the transmission time, the image signal and the luminance have a substantially proportional relationship. However, in general, image signals of a broadcast system are γ-corrected in advance in consideration of a γ characteristic of a CRT (a characteristic representing a relationship between a signal voltage of the CRT and a light emission output). Therefore, if the image signal and the luminance are in a substantially proportional relationship, the displayed image is an image that has been subjected to the γ correction, and has a tight image quality (such as a decrease in contrast) that is difficult to see. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an electrostatic stress type flat display device, a gray scale drive of an array type light modulation element capable of obtaining high image quality even with a broadcast-system image signal which has been γ-corrected in advance. It is an object of the present invention to provide a method and a flat display device using the array type light modulation element.

[0008]

According to a first aspect of the present invention, there is provided a method of driving a gray scale of an array type light modulating device, the method comprising the steps of: In a gradation driving method of an array-type light modulation element in which light modulation units that change the light intensity are arranged in a one-dimensional or two-dimensional matrix, the light is modulated based on a signal obtained by performing an inverse γ correction on an input image signal. The modulation unit is driven.

In this method of driving the array-type light modulation element, the input image signal is inverse-gamma-corrected corresponding to the array-type light modulation element, and the array-type light modulation element is corrected based on the inverse-gamma-corrected signal. Is controlled, so that the γ correction is canceled.

According to a second aspect of the invention, there is provided a method for driving a gradation of an array type light modulation element, wherein the inverse γ correction is performed by setting the signal bit number M after the inverse γ correction to be larger than the bit number N of the input image signal. I do.

In the gradation driving method for an array type light modulation element, the relationship between image input signal data and visual brightness is
It becomes more continuous in the low-luminance area, the gradation skip is reduced, and the occurrence of false contour is reduced.

According to a third aspect of the invention, there is provided a gradation driving method for an array type light modulation element, wherein inverse gamma correction is performed using a non-monotonic increasing function set by an error diffusion method.

[0013] In this gradation driving method for an array type light modulation element, discrete changes in gradation in a low luminance region are further reduced, and the occurrence of false contours after inverse γ correction is further reduced.

According to a fourth aspect of the present invention, there is provided a method of driving a gradation of an array type light modulation element, wherein a gradation is obtained by changing a light transmission time of the light modulation section.

In this method of driving a gradation of an array type light modulation element, a signal subjected to inverse γ correction is converted as data for light transmission time control, and the light transmission time of the light modulation section is changed, so that the intermediate level is changed. The tone is obtained.

According to a fifth aspect of the invention, there is provided a gradation driving method for an array type light modulating element, wherein one pixel is divided into a plurality of regions, and the light modulating unit is provided corresponding to the divided regions. It is characterized in that a gray scale is obtained by an area gray scale to be selectively operated.

According to the gradation driving method for the array type light modulation element, the signal subjected to the inverse γ correction is converted as area gradation control data, and the number of light modulation sections to be driven, that is, the driving area in one pixel is reduced. By being variable, an intermediate gradation can be obtained.

The flat panel display according to the sixth aspect is the first to fifth aspects.
A planar light source is light-modulated using the array-type light modulation element driven by the driving method described above, and the modulated light causes a phosphor to emit light.

In this flat display device, the array-type light modulation element is driven so that the γ correction of the input image signal is canceled, and the image signal of the broadcasting system which has been γ corrected in advance for the CRT can be obtained. This γ correction is canceled, and a high-quality display is obtained.

According to a seventh aspect of the present invention, the light emitted from the flat light source is ultraviolet light.

In this flat display device, the ultraviolet light emitted from the flat light source is light-modulated by the array-type light modulation element to cause the phosphor to emit light. That is, by using a planar light source that emits ultraviolet light, an inexpensive light source and a device configuration using a general phosphor can be realized.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a gradation driving method for an array type light modulation device and a flat panel display device according to the present invention will be described below in detail with reference to the drawings. First, before describing a method of driving a gray scale of an array-type light modulation device according to the present invention, a flat display device using an array-type light modulation device will be described. FIG. 1 is a cross-sectional view of the first embodiment of the flat panel display according to the present invention, and FIG. 2 is a view taken along the line AA of FIG.

A plurality of strip-shaped transparent electrodes (signal electrodes) 3 are arranged in parallel on the light guide plate 1, which is a plane light source, at intervals. On the light guide plate 1, there are formed columns 5 that partition adjacent signal electrodes 3 from each other. The support 5 is, for example, the light guide plate 1.
It is formed by etching a material of the same quality as above.
An ultraviolet lamp (low-pressure mercury lamp) 7 serving as a light source is provided on a side surface of the light guide plate 1, and light from the low-pressure mercury lamp 1 is guided to the surface of the light guide plate 1 (upper surface in FIG. 1).

A transparent flexible thin film 9 is joined to the upper end surface of the support 5 at a position away from the signal electrode 3. Therefore, a gap 11 is formed between the signal electrode 3 and the flexible thin film 9. On the upper surface of the flexible thin film 9, a plurality of transparent strip-shaped electrodes (scanning electrodes) 13 long in a direction orthogonal to the signal electrodes 3 are arranged in parallel at intervals. That is, as shown in FIG. 2, the signal electrodes 3 and the scanning electrodes 13 are arranged in a grid arranged in a direction orthogonal to each other. The signal electrode 3 and the scanning electrode 13 are matrix electrodes that can specify a specific counter electrode unit (light modulation unit) by selecting a predetermined one. The light guide plate 1, the signal electrode 3, the flexible thin film 9, and the scanning electrode 13 constitute an array type light modulation device 14.

A power supply 15 is connected to each of the signal electrodes 3 and the scanning electrodes 13, and the power supply 15 can selectively apply a voltage to a predetermined one based on image information.

Further, above the scanning electrodes 13, strip-shaped phosphors 16a, 16b, 16c of three primary colors (R, G, B) are provided.
Is provided so as to face the signal electrode 3. This phosphor 1
A black matrix (not shown) for improving the contrast ratio of the phosphor may be disposed between 6a, 16b, and 16c.

In this example, the phosphors 16a, 16b, 16
Above c, a fiber-shaped front plate 17 is provided.
The front plate 17 may be of a fiber shape or a diffusion film. Further, the front plate 17 may be provided with a color filter equivalent to the phosphor emission color.

The flat display device 19 constructed as described above
The light guide plate 1 can be formed of a transparent glass plate or a resin film such as polyethylene terephthalate or polycarbonate.

The signal electrode 3 and the scanning electrode 13 are made of a transparent conductive material. The signal electrode 3 arranged on the light guide plate 1 side is preferably made of a material that transmits ultraviolet light for excitation or has optical characteristics. Further, the phosphor 16a,
It is preferable that the scanning electrodes 13 disposed on the 16b and 16c sides transmit a UV ray for excitation and more preferably have a material or an optical property that reflects a phosphor emission wavelength.

The power supply circuit connected to the signal electrode 3 and the scanning electrode 13 can be patterned at the same time when the signal electrode 3 and the scanning electrode 13 are formed.

Next, the basic operation of the flat display device 19 thus configured will be described with reference to FIG. FIG. 3 is a sectional view showing a state of the flat display device according to the present invention during operation. In the flat display device 19, when a voltage is applied between the signal electrode 3 and the scanning electrode 13 by the power supply 15, the flexible thin film 9 is attracted by the electrostatic stress and is bent toward the gap 11. The bending operation of the flexible thin film 9 due to the electrostatic stress is hereinafter referred to as an electromechanical operation. Thus, the light transmitted from the light guide plate 1 and emitted through the flexible thin film 9 is modulated. Therefore, by selectively applying the voltage of the power supply 15 to each of the signal electrodes 3 and the scanning electrodes 13 based on the image information, desired exposure control becomes possible, and the light whose exposure has been controlled is emitted from the phosphors 16a and 16b. , 16c to form an image.

Next, a procedure for performing inverse gamma correction on an analog image signal from a broadcast system and performing gradation driving by light transmission time control will be described. FIG. 4 is a block diagram of a circuit configuration for performing light transmission time control. The analog image signals (R, B, G) are digitally converted by the A / D converter 31. The digitally converted image signal is input-selected together with the digital image signal (R, B, G), and becomes N-bit input image data Iin, which is a look-up table (L).
UT) 33. This LUT 33 is, for example, R
It is configured by a memory such as an OM and a RAM.

The LUT 33 performs an inverse γ correction for converting the input image data Iin into an applied voltage signal that matches the characteristics of the array type light modulation device 14. The LUT 33 performs inverse γ correction on the input image data Iin, and outputs the result to the two-dimensional image memory 35 as M-bit inverse γ correction data Iout. At this time, a memory address is generated by the input image synchronization signal, and the inverse γ correction data Iout output according to the memory address is stored in the two-dimensional image memory 35.
That is, the digital data of the input image signal is used as an address,
Since the inverse gamma correction data corresponding to the address is stored in the two-dimensional image memory 35, if the LUT is addressed by digital data of the input image signal, the inverse gamma correction data corresponding to the input image signal is stored in the two-dimensional image memory. It becomes possible to output from 35.

The two-dimensional image memory 35 receives a row to be displayed from the time division gray scale scanning timing sequencer 37 based on the display synchronization signal. The two-dimensional image memory 35
The inverse gamma correction data corresponding to this display row is output to the binary data generator 39. At the same time, the binary data generator 39 receives a gray scale bit from the time division gray scale scanning timing sequencer 37.

Time division gray scale scanning timing sequencer 3
7 scans the rows of the two-dimensional array type light modulation element 14 of the flat panel display 19 via the scanning drive circuit 41. In accordance with this row, the image data driving circuit 43
Γ is applied to the image signal electrode of the array type
When the correction data Iout is applied, the flat panel display is driven in gradation by light transmission time control.

Next, a specific example of the inverse γ correction will be described. Inverse γ
The correction converts an input image signal, which is digital data of each color of RGB, into a γ characteristic equivalent to that of a CRT (inverse γ correction processing). Here, assuming that the input image signal Iin of each color is N bits, the gradation data is Iin = 0, 1, 2, 3,..., 2 ^N -1.

Further, M obtained by inverse γ correction of the input image signal Iin
^Assuming that a digital signal of bits is Iout, Iout = ( ^2M- 1) {Iin / ( ^2N- 1)} ^2.2 (where Iout is an integer rounded up to the decimal point).

The light transmittance of the array type light modulating element is controlled in accordance with the digital signal Iout having undergone the inverse γ correction. Iou
t is M-bit data. Therefore, the number of controllable gradations of the array type light modulation element, that is, the number of controllable transmittances is required to be at least ^2M .

When gradation is obtained by time division within one screen display period, the transmittance of the array type light modulation element, that is, the apparent display luminance Ld is substantially proportional to the data of Iout. If this proportionality constant is 1, Ld = Iout [arbitrary unit].

Here, the relationship between the display brightness as in a display device and the visual brightness Lh perceived by a human is close to the γ characteristic, and has a relationship substantially as in the following equation. Lh = Ld ^{(1 / 2.2)} = Iout ^{(1 / 2.2)} [arbitrary unit]

FIGS. 5 to 11 show the relations obtained by substituting the specific number of gradations as each condition in accordance with the above relations. FIG. 5 shows the relationship when the input image signal Iin is N = 6 bits (64 gradations), and the transmittance control data Iout of the array-type light modulation element subjected to inverse γ correction is M = 6 bits (64 gradations). FIG. 6 shows a case where the input image signal Iin is N = 6 bits (64 gradations) and the transmittance control data Iout of the array-type light modulation element subjected to inverse γ correction is M = 8 bits (256 gradations). FIG. 7 shows an input image signal Iin of N = 6 bits (64 gradations), and a transmittance control data Iout of an array-type light modulation element subjected to inverse γ correction of M = 10.
FIG. 8 is a graph showing the relationship when the input image signal Iin is N = 8 bits (256 tones), and the transmittance control data Iout of the array-type light modulation element subjected to the inverse γ correction is shown in FIG. 9 is a graph showing the relationship when M = 8 bits (256 gradations), FIG. 9 is an enlarged view of the low luminance area in FIG. 8, and FIG. 10 is a diagram in which the input image signal Iin is N = 8 bits (256 gradations).
FIG. 11 is a graph showing the relationship when the transmittance control data Iout of the array-type light modulation element subjected to inverse γ correction is M = 10 bits (1024 gradations). FIG. In each figure, (a) is a graph showing a relationship between input image signal data and inverse γ correction conversion data, (b) is a graph showing a relationship between inverse γ correction conversion data and visual brightness, and (c) is an input graph. 4 is a graph showing a relationship between image signal data and visual brightness.

As can be seen from (c) of each figure, the relationship between input image signal data and visual brightness becomes substantially linear due to transmittance control by inverse γ correction conversion. That is, it is possible to display the gradation curve of the input image signal data with a natural image quality.

Here, the relationship between the input image signal data and the visual brightness is discrete in a low-luminance region (gradation sharply changes), and the gradation of the input image signal data may not be reproduced. In this case, a gradation jump appears, and a pseudo contour occurs in the display image. When displaying 64 gradations, FIG.
According to (c), FIG. 6 (c), and FIG. 7 (c), such a pseudo contour generation phenomenon is reduced as the number of bits M of Iout subjected to inverse γ correction is increased. Therefore, the number of bits M is preferably larger than the number of bits N of the input image signal data.

Similarly, when displaying 256 gradations, FIG.
10 (c) and FIG. 10 (c), when the number of bits M of the inverse γ-corrected Iout is 10 bits, the pseudo contour is reduced more than 8 bits, and almost no problem occurs in the image quality.

In practice, when 10-bit transmittance control is performed by weighted time division, the image quality switching frequency is set to, for example, 60
If the number of scanning lines is 2000 and the number of scanning lines is 2000, the required response time of the element is about 0.8 μs. This time length can be adequately dealt with in the above-mentioned array type light modulation element 14 of the electrostatic stress deformation type.

In the inverse γ correction conversion of the above-mentioned gradation driving method, a monotone increasing function as shown in FIG. 12A is used as a conversion function. May occur, before and after the discrete change, inverse γ correction may be performed using a non-monotonic increasing function converted to approach a continuous change by a method such as an error diffusion method. Here, the non-monotonic increasing function means a function which is an increasing function as a whole but may sometimes decrease as shown in FIG. 12 (b). When the input gradation data is quantized by the error diffusion method, the change point 50
The + pulse 51 and the -pulse 52 are inserted before and after the change point 50 so that the average value of the converted data before and after becomes zero. As a result, image quality deterioration due to discontinuous change points is reduced, and pseudo contours are further reduced.

Next, another embodiment of the gradation driving method according to the present invention will be described. In this embodiment, a region having an area corresponding to one pixel is further divided into a plurality of regions of m rows and n columns to form a small matrix. That is, one pixel is m
× n display elements. The light modulator is provided corresponding to the one display element. In this embodiment, by selectively operating and adjusting the number of display elements, a so-called area gray scale in which the gray scale of one pixel is controlled in area is enabled. That is, in the above-described embodiment, the array-type light modulation element is driven in gradation by light transmission time control by inverse γ correction conversion, whereas in this embodiment, the array-type light modulation element is It is driven by a gray scale. According to such gray scale driving based on area gray scale, stable and simple control can be performed as compared with the case of light transmission time control.

In the above two embodiments, the time division control and the area gray scale method are used as means for obtaining the intermediate gray scale. However, the gray scale driving method for the array type light modulation element according to the present invention uses this method. In addition, a spatial dither method, a spatial or temporal error diffusion method, or the like may be used in combination. Such combined use of the multiple gradation methods is particularly effective when the number of display gradations is increased for the purpose of reducing the pseudo contour by the above-described inverse γ correction.

[0049]

As described above in detail, according to the gradation driving method of the present invention, in an array type light modulating element of an electrostatic stress type, an input image signal is inverted in correspondence with the array type light modulating element. Since the γ correction is performed and the gradation of the array-type light modulation element is controlled based on the inverse γ corrected signal, the γ correction can be canceled.

In the flat display device using the electrostatic stress type array type light modulating element according to the present invention, the array type light modulating element is driven so as to cancel the γ correction of the input image signal. High image quality can also be obtained by a broadcast image signal that has been γ-corrected for CRT.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of a flat panel display according to the present invention.

FIG. 2 is a view as viewed in the direction of arrows AA in FIG. 1;

FIG. 3 is a cross-sectional view showing a state of the flat display device according to the present invention during operation.

FIG. 4 is a block diagram of a circuit configuration for performing light transmission time control.

FIG. 5 is a graph showing a relationship when the input image signal is 6 bits and the transmittance control data of the array-type light modulation element subjected to the inverse γ correction is 6 bits.

FIG. 6 is a graph showing a relationship when the input image signal is 6 bits and the transmittance control data of the array-type light modulation element subjected to the inverse γ correction is 8 bits.

FIG. 7 is a graph showing the relationship when the input image signal is 6 bits and the transmittance control data of the array-type light modulation element subjected to inverse γ correction is 10 bits.

FIG. 8 is a graph showing the relationship when the input image signal is 8 bits and the transmittance control data of the array-type light modulation element subjected to the inverse γ correction is 8 bits.

FIG. 9 is an enlarged view of a low luminance area in FIG. 8;

FIG. 10 is a graph showing the relationship when the input image signal is 8 bits and the transmittance control data of the array-type light modulation element subjected to the inverse γ correction is 10;

FIG. 11 is an enlarged view of a low luminance area in FIG.

FIG. 12 is a diagram illustrating a monotone increasing function and a non-monotonic increasing function.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light guide plate (flat light source) 9 flexible thin film 14 array-type light modulator 16 a, 16 b, 16 c phosphor 19 flat display device Iin input image signal Iout signal subjected to inverse γ correction

Claims (7)

[Claims] 1. A flexible thin film is deformed by electrostatic stress,
In a gradation driving method of an array type light modulating element in which light modulating units for changing light transmittance are arranged in a one-dimensional or two-dimensional matrix, a signal obtained by performing inverse γ correction on an input image signal And driving the light modulation section based on the gray scale driving method of the array type light modulation element. 2. The gray scale of an array-type light modulation element according to claim 1, wherein said inverse γ correction sets the number M of signal bits after the inverse γ correction to be larger than the number N of bits of the input image signal. Drive method. 3. The method according to claim 1, wherein the inverse γ correction is performed using a non-monotonic increasing function set by an error diffusion method. . 4. The gradation driving method for an array-type light modulation element according to claim 1, wherein a gradation is obtained by changing a light transmission time of the light modulation unit. . 5. A method according to claim 1, wherein one pixel is divided into a plurality of regions, said light modulator is provided corresponding to said divided regions, and gray scale is obtained by an area gray scale for selectively operating said light modulator. 4. The gradation driving method for an array-type light modulation device according to claim 1, wherein: 6. A planar light source, wherein a light source for a planar light source is light-modulated using the array-type light modulating element driven by the driving method according to claim 1, and a phosphor is displayed by the modulated light. Display device. 7. The flat display device according to claim 6, wherein light emitted from the flat light source is ultraviolet light.