JP3797518B2 - Image display device driving method and image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a driving method and an image display apparatus for an image display apparatus that expresses a plurality of gradations with one pixel.
[0002]
[Prior art]
There are image display devices that can express only two values per pixel, and those that can express multiple gradations.
Time gray scale or dither is known as a method of displaying a halftone image in a method that can express only binary values. Among these, in the time gradation, the time of the voltage applied for display is modulated to perform gradation display. In dithering, one pixel is divided into a plurality of minute pixels, a pseudo-random number (periodic random number) is superimposed on the image input signal, and then A / D conversion is performed, and the minute pixels are binarized to change the area gradation. Do.
[0003]
On the other hand, in a method capable of expressing a plurality of gradations, gradation expression is performed for each pixel. For example, in a liquid crystal using an active matrix driving method, thin film transistors (TFTs) are arranged in a matrix for each pixel, and a gate-on pulse is applied to the TFTs so that the source and the drain are in a conductive state. At this time, an image signal is applied from the source and accumulated in the capacitor. The liquid crystal is driven in correspondence with the stored image signal, and at the same time, the voltage of the video signal is modulated to perform gradation display.
[0004]
[Problems to be solved by the invention]
However, in order to accurately control the gray scale, in the case of the time gray scale, there is a problem that the drive frequency becomes high because the drive frequency becomes too fast.
Further, in the case of dithering, since the resolution has to be increased, there is a problem that the patterning cost of the element is increased.
[0005]
On the other hand, when expressing gradation with each pixel, each pixel must be accurately controlled, so that the control circuit becomes complicated, or gradation error correction by the display pattern of the element becomes necessary. Even in this case, there was a problem of increasing the cost.
[0006]
The present invention has been made in view of the above situation, and an object thereof is to provide a driving method of an image display apparatus and an image display apparatus capable of displaying a continuous gradation image at low cost.
[0007]
[Means for Solving the Problems]
According to another aspect of the invention, there is provided a driving method for an image display device, wherein the input image data is converted into a plurality of display dots having different brightness levels and displayed in gradation, and the gradation level of the image data is displayed. Is converted into the brightness of the display means, at least five characteristic curves of the gradation conversion table showing the relationship between the gradation value and the energy for displaying the display dots are set. In the gradation value, the energy value that is not the maximum or minimum energy is set to be at least three types, and the number of display points with the minimum energy is set at the minimum gradation value where the display point with the maximum energy exists. It is set to more than half of the total number of display points.
[0008]
In this driving method, one pixel is divided into minute pixels by dither and is subjected to area gradation, and further, individual minute pixels are displayed by gradation, and even when the pixel becomes rough due to division by using dither, The brightness will change continuously, and a smooth continuous tone will be obtained. Further, since the number of display points with the minimum energy is set to half or more of the total number of display points at the minimum gradation value where the display point with the maximum energy exists, the roughness becomes inconspicuous.
[0009]
An image display apparatus according to a second aspect of the present invention differs from an image processing apparatus that converts image data from a digital data output apparatus into a plurality of display dots each having different brightness, based on conversion data from the image processing apparatus. A display unit that performs gradation display with brightness, and the image processing apparatus stores a relationship between gradation values and energy for displaying display dots as a plurality of characteristic curve data; and At the time of converting the gradation level of the image data to the brightness of the display means, at least five characteristic curves of the gradation conversion table are set. The energy value is set so that there are at least three types of energy values that are not energy. The number of display points is small composed of a gradation processing unit for setting more than half of the total number of display points.
[0010]
In this image display device, when converting image data from the digital data output device into display dots having different brightness, the characteristic curve, energy value, and number of display points of the gradation conversion table are set by the image processing device, The brightness of the minute pixels divided by dither is continuously changed to display a smooth continuous tone on the display means.
[0011]
According to another aspect of the image display device of the present invention, the display means is displayed in gradation by modulating the light intensity of the display dots.
This image display device can display gradation of display dots by modulation of transmittance, reflectance, or emission intensity due to the difference in structure.
[0012]
According to a fourth aspect of the present invention, the display means is a ferroelectric liquid crystal display device. In this image display device, a ferroelectric liquid crystal display device is used as a display means, and a high-speed response with a memory property and a high-speed response that maintains the liquid crystal molecular orientation at the time of voltage application, which is a feature of the ferroelectric liquid crystal display device. Even in moving image display, the brightness of transmitted light is continuously changed to enable smooth continuous tone display.
[0013]
The image display device according to claim 5 is a display device in which the display means uses an EL. In this image display device, EL is used as the display means, and an AC voltage is applied to EL, which is a kind of capacitor with a phosphor sandwiched between insulators, and the AC voltage is controlled by the image processing device, thereby emitting light. By changing the brightness continuously, it is possible to display smooth continuous gradation.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an image display apparatus driving method and an image display apparatus according to the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of an image display device for carrying out a driving method according to the present invention, and FIG. 2 is a cross-sectional view of the ferroelectric liquid crystal display device shown in FIG.
[0015]
The dither display 1 as an image display device includes a digital data output device 3 at the previous stage, an image processing device 5, and a ferroelectric liquid crystal display device (liquid crystal display device) 7 as display means. The image processing device 5 uses gradation data from the digital data output device 3 as an object of image processing. The image processing apparatus 5 includes a data selector 9, a gradation processing unit 11, and a conversion table 13.
[0016]
In the liquid crystal display device 7, a transparent conductive film 17 and an alignment film 19 are formed on the surfaces of two transparent substrates 15a and 15b shown in FIG. The conductive film 17 serves as an electrode for applying an electric field to the ferroelectric liquid crystal (liquid crystal layer) 21 held between the substrates 15a and 15b. The alignment film 19 horizontally aligns the liquid crystal.
Substrates 15a and 15b are subjected to an orientation process, and then spacers are sandwiched between them and the periphery is fixed with a sealant 23 to form cells 25. The cell 25 is sealed by injecting ferroelectric liquid crystal (chiral smectic liquid crystal) heated to an isotropic phase. Outside the cell 25, two polarizing plates 27a and 27b are disposed so that the polarizing plates 27a and 27b are orthogonal to each other and form a certain angle with the orientation control direction of the substrates 15a and 15b.
[0017]
In the cell 25, a light source (not shown) is placed on one substrate 15b side, and light is transmitted to the opposite side. When used as a reflection type, a reflection plate may be provided outside the substrate 15b. In the cell 25, when a direct current (+ E) is applied to the conductive film 17, the spontaneous polarization of the liquid crystal coincides with the direction of the electric field, and the liquid crystal molecules are aligned in a constant direction of the tilt angle θ. Further, when the polarity of the electric field is reversed, the spontaneous polarization of the liquid crystal is also reversed, and the liquid crystal molecules are aligned in the tilt angle −θ direction. That is, by switching the polarity of the electric field, the tilt angle of the liquid crystal molecules is switched, and the cell 25 operates in a bright and dark state.
[0018]
At this time, the tilt angle of the liquid crystal molecules changes depending on the voltage of the conductive film 17. Therefore, the transmittance, that is, the brightness is changed by changing the tilt angle of the liquid crystal molecules by controlling the voltage of the conductive film 17. In the dither display 1, the brightness can be controlled by controlling the voltage applied to the conductive film 17 by the gradation processing unit 11.
[0019]
A method for driving the dither display 1 configured as described above will be described.
When the liquid crystal display device 7 is activated, digital image data is output from the digital data output device 3 to the image processing device 5. Of the image data (luminance data) input to the image processing device 5, only data of a predetermined gradation is selected by the data selector 9 and input to the gradation processing unit 11.
[0020]
The gradation processing unit 11 converts this input data using the gradation conversion table 13. Hereinafter, the conversion process using the conversion table 13 will be described. FIG. 3 shows an example of conversion characteristics that are the basis of the gradation conversion table 13. In FIG. 3, the horizontal axis indicates the gradation of the input screen, and the vertical axis indicates the applied energy corresponding to the brightness of the display dots. In this example, the gradation of the input image is 16 levels.
[0021]
The gradation conversion characteristics shown in FIG. 3 are set to at least five or more characteristic curves (16 lines A to P in FIG. 3) indicating the relationship between the gradation value of the input image and the energy for displaying the display dots. is doing. Each type indicates the transmissivity, that is, the brightness from the display threshold (the lowest part of the line) of the display dot.
In the gradation conversion characteristics shown in FIG. 3, at least three types of characteristic curves having energy values other than the maximum or minimum energy are set in a predetermined gradation value in the halftone area.
[0022]
Furthermore, the number of display points with the minimum energy is set to be half or more of the total number of display points at the minimum gradation value where the display point with the maximum energy exists.
[0023]
FIG. 4 is a matrix (unit block) showing which conversion curve is selected from a plurality of energy conversion characteristics. Each element in the matrix corresponds to a display point, and by repeating these matrices vertically and horizontally, a gradation-display energy conversion curve (characteristic curve) is determined for the display points of the entire image. . In this matrix, “1”, “2”, “3”,... Are display points corresponding to the characteristic curves “A”, “B”, “C”,. In the matrix, the resolution in the main scanning direction and the sub-scanning direction is 200 dpi, and the size of the number of these elements is 4 × 4.
[0024]
In this way, many gradation-display energy conversion curves (characteristic curves) are set, and in the halftone, the display points of intermediate energy values that are not the maximum or minimum energy are set to be three or more types. For this reason, even when dither is used and pixels become rough due to division, the brightness changes continuously and the roughness becomes inconspicuous. That is, it is possible to compensate for the disadvantages caused by dithering.
[0025]
This driving method divides one pixel into a plurality of display dots, performs gradation control by changing the brightness of the display dots, and further performs a process of overlapping different brightness for each display dot. Both still images and moving images can be applied, and the same effect can be obtained by using, for example, EL (electroluminescence) as a display unit in addition to the liquid crystal display device 7 used in the above embodiment.
[0026]
In addition, this driving method is a cantilever that performs display by moving a cantilever-shaped cantilever as a display means other than the liquid crystal and EL described above by moving electrostatic force to a pixel area. The present invention is applicable to all display systems using transmitted light, light emission, or reflected light, such as a DMD system, an LED system, a CRT system, and a magnetic display system using an active semiconductor device having a deflectable mirror. Particularly preferred are liquid crystal, EL, etc., capable of high resolution display, but there are applications that are not particularly affected by the resolution of the element, such as when the screen is enlarged display or projection type, so it is limited to these. is not.
[0027]
Furthermore, even when the dither display 1 driven by this driving method is used as a surface exposure light source in a printer head, the dither display 1 has an effect of compensating for the disadvantages caused by dithering as described above.
[0028]
【The invention's effect】
As described above, according to the driving method of the image display device according to the present invention, at least five types of characteristic curves of the gradation conversion table indicating the relationship between the gradation values and the energy for displaying the display dots are set. In halftones, the predetermined gradation value is set so that there are at least three energy values that are not the maximum or minimum energy. Therefore, even when the pixel becomes rough due to the division, the brightness is reduced. It is possible to change continuously, obtain a smooth continuous tone, and at the minimum tone value where there is a display point with the maximum energy, the number of display points with the minimum energy is all Since the number of display points is set to half or more, the roughness can be made inconspicuous. As a result, it is possible to display a continuous gradation image at low cost.
[0029]
According to the image display device of the present invention, the image processing device that converts the image data from the digital data output device into a plurality of display dots each having different brightness, and the brightness that is different based on the conversion data from the image processing device. A gradation conversion table, comprising: a display means for performing gradation display; and a gradation conversion table for storing the relationship between gradation values and energy for displaying display dots as a plurality of characteristic curve data. The characteristic curve is set to at least five types, and in the halftone, the predetermined gradation value is set so that there are at least three types of energy values that are not the maximum or minimum energy, and the display point at which the energy is maximized is set. It is composed of a gradation processing unit that sets the number of display points with the smallest energy at the minimum existing gradation value to half or more of the total number of display points. Because, it is possible to continuously change the brightness of the small pixels obtained by dividing the dither, can be displayed on the display means a smooth continuous tone.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an image display device for carrying out a driving method according to the present invention.
2 is a cross-sectional view of the ferroelectric liquid crystal display device shown in FIG.
FIG. 3 is an explanatory diagram showing conversion characteristics as a basis of a gradation conversion table.
FIG. 4 is an explanatory diagram showing a conversion curve selected from energy conversion characteristics in a matrix.
[Explanation of symbols]
1 Dither display (image display device)
3 Digital data output device 5 Image processing device 7 Ferroelectric liquid crystal display device (display means)
11 Gradation processing unit 13 Gradation conversion table

Claims (5)

In the driving method of the image display device for converting the input image data into a plurality of display dots having different brightness and displaying the gradation, when converting the gradation level of the image data to the brightness of the display means,
Set at least five characteristic curves of the gradation conversion table showing the relationship between gradation values and energy for display dot display,
In the halftone, a predetermined gradation value is set so that there are at least three energy values that are not the maximum or minimum energy,
A driving method of an image display device, wherein the number of display points with the minimum energy is set to be half or more of the total number of display points at the minimum gradation value where the display point with the maximum energy exists. An image processing device that converts image data from a digital data output device into a plurality of display dots each having different brightness, and display means that performs gradation display at different brightnesses based on the converted data from the image processing device And
The image processing apparatus is
A gradation conversion table for storing the relationship between gradation values and energy for display dot display as a plurality of characteristic curve data, and the gradation when the gradation level of the image data is converted to brightness of display means The characteristic curve of the conversion table is set to at least five types, and in the case of halftones, at a predetermined gradation value, the energy value that is not the maximum or minimum energy is set to at least three types, and the energy is maximized. An image display device comprising: a gradation processing unit configured to set the number of display points with the minimum energy to half or more of the total number of display points at a minimum gradation value where dots exist. 3. The image display apparatus according to claim 2, wherein the display means displays a gradation by modulating the light intensity of the display dots. 4. The image display device according to claim 2, wherein the display means is a ferroelectric liquid crystal display device. 4. The image display device according to claim 2, wherein the display means is a display device using an EL.

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