JPH10228258A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of a disturbance pattern in a part that the same gradation level or a flat part with a minute gradation level difference continues by selecting a combination of sub-pixel display states in respective gradation levels and displaying it so that the number of sub-pixels changing the display states according to the change of the gradation level are reduced. SOLUTION: When the certain gradation level among the gradation levels more than two levels is expressible by plural ways of combinations of sub-pixels, the combination of the sub-pixel display states in respective gradation levels is selected so that the number of sub-pixels changing the display states according to the change of the gradation level are reduced. Then, a display is performed using an obtained sub-pixel series. In this device, an interface part consists of an A/D converter 101, a digital half-tone processor 102, an image area information table 109 and a sub-pixel selector 103, etc. The sub-pixel selector 103 selects the sub-pixel to be lighted from image area information stored in the image area information table 109 and the image data outputted from the digital halftone processor 102.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device using an area gradation, and more particularly to an image display device using a binary device such as a ferroelectric liquid crystal (FLC).

[0002]

2. Description of the Related Art In many image display devices typified by CRT displays, the smallest display element has a physical and chemical mechanism capable of taking continuous luminance values.
For example, in the case of a CRT display, the amount of light emitted by the phosphor is controlled by adjusting the amount of electrons that collide with a phosphor layer formed on a glass surface. Also TFT
In a liquid crystal display, the angle of a light vibrating surface is changed by adjusting an electric field applied to liquid crystal molecules, and the amount of light transmission, that is, brightness is controlled by combining the angle with a filter. Further, in a color display device having such a mechanism, each display element is composed of three basic colors of red (R), green (G), and blue (B), and the luminance is independently changed. Displays many colors.

On the other hand, some display devices include:
As mentioned above, there is no mechanism to change the brightness continuously,
Some types can only be switched between the ON state and the OFF state. For example, a display (FLCD) using a ferroelectric liquid crystal (hereinafter abbreviated as FLC)
While it has advantages as a general-purpose display, such as a simple structure and a wide viewing angle, the minimum display element can only express binary. Therefore, in order to increase the number of luminance values (gradation levels) that can be expressed by each pixel, a method completely different from a continuous (analog) luminance gradation method such as a CRT display is required. One of them is called an area gray scale method.

In the area gray scale method, a plurality of sub-pixels (sub-pixels) are provided by further subdividing a pixel having a certain finite area, and a lit sub-pixel (sub-pixel) is formed by combining the sub-pixels. The luminance corresponding to the sum of the areas of the sub-pixels whose display state is “bright” in the darkness is obtained stepwise. At this time, the area ratio of the sub-pixel is determined by the ratio of the size of each bit in the binary system,
That is, if the ratio is 1: 2: 4:...: 2 ^N, an evenly spaced luminance sequence is obtained by a combination thereof. Thus, for example, one pixel 212 is divided into four independently controllable sub-pixels as shown in FIG.
For simplicity, only one color is shown. The numbers 1, 2, 4, and 8 in the figure indicate the area ratios of the sub-pixels.
6 and 210 and 207 and 211, and the area ratio is 2
And one sub-pixel 208 and 209 are disposed above and below the sub-pixels 208 and 209. Then, those having the same number are turned on / off in synchronization with each other), so that each pixel has 16 RGB colors.
It is possible to have a gradation expressing ability at equal intervals of levels.

Since the FLCD has a memory effect of maintaining a display state (ON / OFF) even when there is no potential difference, a combination of horizontal electrodes and vertical electrodes is used instead of an active matrix structure in which a transistor is provided for each display unit. A sufficient contrast can be obtained even if a simple matrix structure is used. Because the active matrix structure is disadvantageous in terms of manufacturing cost during mass production, FLC
D often has a simple matrix structure.

In the case of adopting this area gradation method with a simple matrix structure, the number of horizontal and vertical electrodes tends to increase because the number of sub-pixels constituting one pixel is increased.
In the case of the FLCD, each display element switches at a very high speed. On the other hand, it is necessary to continuously apply a voltage of a certain threshold or more for a certain period of time until the ON / OFF state is completely switched. Therefore, the duty driving used in the STN liquid crystal display having the same simple matrix structure cannot be used in the FLCD. Therefore, there is a trade-off that increasing the number of horizontal lines decreases the refresh frequency of the display in inverse proportion thereto.

In the pixel division shown in FIG. 11, two lines of the upper and lower horizontal electrodes 203 and 20 of the upper, middle and lower lines are used.
5 are selected at the same time, and independently of this, the horizontal electrode 204 of the middle line is selected, and the common ON
By applying the / OFF voltage to the vertical electrodes 201 and 202, 16 levels can be displayed. further,
203 and 205 are individually selected and independently
If N / OFF is controlled, the refresh frequency is lowered for the above-described reason, but the number of grayscale levels by area grayscale can be further increased. At this time, by changing the area ratio of the upper and lower lines as shown in FIG. 12, it is possible to obtain a greater number of gradation levels.

The advantages of the sub-pixel configuration shown in FIG. 12 are as follows: (1) Simultaneous selection of three lines → 4-level high-speed display of uniform-level 4-level gradation display depending on how the upper, middle, and lower lines are selected. (2) Simultaneous selection of upper and lower lines → 16 levels of gray scale display at equal intervals are displayed at half the speed of mode (1).
Level middle speed mode ”(3) Independent selection of line → 29 level gradation display at approximately equal intervals at 1/3 the speed of mode (1)“ 29
The point is that any one of the “level low-speed mode” can be selected. The above three modes include a mode having a large number of levels and a mode having a small number of levels in terms of a representable luminance value (gradation level). Therefore, in the mode with a large number of levels, the same sub-pixel combination is inherited for the same luminance value as that in the mode with a smaller number of levels, and for the luminance value that could not be expressed in the mode with a smaller number of levels, a new You can decide the combination.

There is one problem in the gradation expression by the area gradation method. That is, in the case of the “29-level low-speed mode” in the above (3), as shown in FIG. 13, there are a plurality of combinations of sub-pixels expressing the same level, and depending on the selection, the image quality of the display image may be impaired. There is a point.

For example, there are three combinations of sub-pixels that can express level 16, as shown in FIG. Although the sum of the areas of the lighting sub-pixels is the same, the spatial positions occupied by the lighting sub-pixels are greatly different.

FIG. 15 shows a configuration of one pixel of the conventional image display device. The pixel shown in the figure has a sub-pixel configuration of the same size and common shape for the three primary colors of RGB, has a gradation expression capability of 4 bits (16 levels) for each color of RGB, and has a lighting pattern of the sub-pixel (a lighting sub-pixel). FIG. 16
As shown in FIGS. 17 and 17, a fixed pattern (one-to-one correspondence) was obtained for one gradation level. Therefore, when there is a flat portion having a small difference in gradation level between pixels adjacent to the input image signal, pixels having a specific and identical lighting pattern may be concentrated on a certain portion of one screen. FIG.
(A) and (b) show an example in which the same luminance value of the lighting areas 7.5 (gradation level 14) and 7 (gradation level 13) are continuous in a certain portion of one screen, respectively. is there.

This is an example in which the pattern of the lighting / non-lighting sub-pixels in the vertical direction has periodicity, and the pattern having the periodicity extends in the horizontal direction. Depending on the lighting pattern of (1), a visual interference pattern of vertical stripes) may occur. Also, in an image whose luminance value changes slowly like a gray scale,
As in the example shown in FIG. 18, since the pixels having the same lighting pattern are consecutive, a visual obstruction pattern that does not exist in the original image in the horizontal or vertical direction may occur, thereby impairing the original smoothness of the original image. there were.

However, in the conventional method using a fixed pattern corresponding to each luminance value (that is, gradation level) on a one-to-one basis, a lighting pattern of a sub-pixel in one pixel for an input signal of the same gradation level is as follows. Since it is impossible to select, a pattern that is not present in the original image signal due to the same sub-pixel lighting pattern continuing in the two-dimensional direction in a flat portion or gradation pattern with the same hue and a gradation level That is, there is a drawback that occurrence of a visual obstruction pattern cannot be avoided.

[0014]

SUMMARY OF THE INVENTION The present invention is directed to a portion where flat portions having the same gradation level such as a luminance value level flat portion or gradation pattern portion of the same hue or a flat portion having a small difference in gradation level continue. Suppress the occurrence of interference patterns,
It is an object of the present invention to enable visually natural image expression without impairing the smoothness of an original image.

[0015]

In order to achieve the above object, when the gradation level of an image is uniform and all pixels perform the same gradation display, the plurality of sub-pixel patterns described above are used. It has been found that the most visually preferable one from among (sub-pixel display state combinations) may be selected and used. Here, as the visually preferable sub-pixel pattern, for example, a binary image (N, M: a natural number of 2 or more) obtained by arranging pixels having the same sub-pixel pattern two-dimensionally is used. In the spatial frequency distribution in which the lighting sub-pixel portion is 1 and the others are 0), the spatial frequency distribution with the lowest low-frequency component is selected. Alternatively, the two-dimensionally arranged N × M
Select a sub-pixel pattern that optimizes the balance of the center of gravity of the pixel.

As a specific example, in the present invention, a means (sub-pixel selecting means) capable of selecting one or more sub-pixel lighting patterns for each expressible gradation level, and N ×
A table is provided in which M pixel (N, M: a natural number of 2 or more) is set as one unit, and a sub-pixel lighting pattern in which the center of gravity is optimized is recorded for each gradation level, and a natural image (an image other than a text image) is provided. In the case where the same gradation level or a similar gradation level (flat image signal) is continuously input, the optimum lighting pattern for the current gradation level is read out from the table in which the optimum sub-pixel lighting pattern is recorded and displayed. Let it. This makes it possible to suppress a visual obstruction pattern mainly caused by the lighting pattern of the sub-pixel in the flat portion of the image or the image having the gentle gradation.

However, the above selection method is effective when the values of the pixels to be displayed are uniform. On the other hand, the image includes continuous tones, which are further converted to pseudo intermediates such as error diffusion (ED) and dither. When the display is performed with the tone processing, the effect cannot be expected because the assumption that “pixel values (gradation levels or lighting sub-pixel areas) are uniform” does not hold. In fact, when performing pseudo halftone processing on a continuous tone image, an artificial image which is not included in the original image is a portion where the tone level gradually changes due to the positional relationship of the lighting sub-pixels between the upper and lower tones. Contour lines or band-like patterns may occur.
This is because the gradation level is switched, and a portion where the lighting sub-pixels are concentrated and a portion where the sub-pixels are depleted occur in a portion where pixels of different gradation levels are adjacent to each other, thereby significantly changing the spatial frequency characteristic of the image. It is considered that visually unpleasant components occur. In the case where the previously mentioned gradation level is 16, if the lighting patterns in the "16-level medium speed mode" are taken over at the adjacent levels 15 and 17, the combination of the sub-pixels shown on the left and right in FIG. In other words, in this case, the position of the lighting sub-pixel greatly changes in any of the three possible sub-pixel patterns at level 16. Therefore, when an image that gradually changes from level 15 to level 16 or from level 16 to level 17 is displayed, the boundary of the level change presents a rough texture, resulting in an artificial contour.

As described above, in the display means for performing the gradation expression by the area gradation method, the generation of the above-described rough artificial contour or pattern in a portion where the gradation level changes gradually is suppressed. In particular, there is a problem in that it is best to select a combination as in the case where a combination of a plurality of sub-pixels exists for one level. According to the present invention, a method for suppressing the generation of artificial contour lines or band-like patterns which are not included in the original image when the image is displayed by adding a pseudo halftone process such as error diffusion (ED) or dither. In an image display device in which one pixel can perform display of more than two levels by a combination of a plurality of sub-pixels capable of binary display, a certain gray level among the two or more gray levels When the level can be represented by a combination of a plurality of sub-pixels, the combination of sub-pixel display states (sub-pixels) at each gradation level is set so that the number of sub-pixels whose display state changes as the gradation level changes is minimized. The display is performed using the sub-pixel combination series obtained by selecting the pixel display pattern. Alternatively, there is provided a sub-pixel selecting means for selecting one of the plurality of combinations of sub-pixels according to local characteristics of an image to be displayed. This suppresses the generation of the rough artificial contour or pattern as described above.

In the first embodiment of the present invention, the local features of the image are defined by the characteristics of the spatial change of the image data in a sufficiently small area around the pixel of interest. In the case where the relatively gradual change component is dominant in the characteristics of the spatial change of the image data in a sufficiently small area around the pixel of interest, the sub-pixel whose lighting state changes with the change in the gradation level From the first sub-pixel combination series in which the number of sub-pixels is as small as possible, a combination of sub-pixels expressing a gradation level to be output is selected for the target pixel, while a flat component and an extremely When one or both of the steep components are dominant, the gradation level to be output is expressed from the second sub-pixel combination series in which the lighting sub-pixels are more dispersed within the pixel. The sub-pixel combination to be selected is selected for the target pixel. The first sub-pixel combination series includes at least one of the gradation levels that can be originally expressed by the pixel so that the number of sub-pixels whose lighting state changes with the change in the gradation level is as small as possible. And halftone processing means for performing digital halftone processing using the number of grayscale levels of the first and second subpixel combination series as an output value. Examples of the halftone processing method include a dither method and an error diffusion method.

In the second embodiment of the present invention, when a plurality of sub-pixel patterns (sub-pixel lighting patterns) can be selected per one gradation level, the sub-pixel selecting means may include N × M pixels. Are lit at the same gradation level, the area W of the lit sub-pixel (sub-pixel)
A table listing patterns in which the distribution of the lit sub-pixels in the N × M pixels is most uniform, using the distance r from the center of the N × M pixels and the lit sub-pixels as a parameter; When two selectable adjacent gray levels are mixed in N × M pixels, the area W of the lit sub-pixel and the distance r from the center of the lit sub-pixel and the N × M pixel Is provided as a parameter, and a table listing patterns in which the distribution of the sub-pixels lit in N × M pixels is most uniform is provided.
Then, the lighting sub-pixel pattern of the table is applied to the display screen. Also, according to the input pixel signal, N ×
When selecting a lighting sub-pixel pattern in units of M pixels, the level information of the image signal input within the processing range of the N × M pixels is stored, but the pixel position to be lit corresponding to the level is: Arbitrary selection is possible within the processing range of N × M pixels.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 shows an interface section of a digital image signal display apparatus according to a first embodiment of the present invention. In FIG. 1, 101 is an A / D converter, 102 is a digital halftone processor, 104 is a frame memory, 105 is a frame memory controller for controlling writing and reading to and from the frame memory 104, and 107 is a ferroelectric liquid crystal display. (FLCD) 106 displays the display data obtained from the frame memory 104 via the frame memory controller 105 as F
An FLCD scanning controller that transfers the data to the LCD 107 and controls its scanning. On the other hand, reference numeral 108 denotes an image area discriminator for judging the type of an image in units of a certain area (N × M pixels), and includes “computer image / discontinuous tone area (D)” and “natural image / continuous tone area”. (C) ". Reference numeral 109 denotes an image area information table for holding image area distribution information in a display image based on the result of the image area determination by the image area discriminator 108; 103, image area information stored in the image area information table 109 and digital intermediate information; A sub-pixel selector that selects a sub-pixel to be lit from image data output from the tone processor 102. The arrangement of the sub-pixels constituting one pixel of the FLCD 107 is the same as that of the conventional example shown in FIG. Each sub-pixel can independently control ON / OFF.

In the interface unit shown in FIG. 1, an input moving image signal is sequentially converted into a digital moving image signal by an A / D converter 101 and output. The output signal is input to the digital halftone processor 102 and the image area discriminator 108. The image area discriminator 108 outputs an image included in each “tile area” including a predetermined number (N and N) of pixels (pixels) in the vertical and horizontal directions.
Whether the discontinuous tone image is dominant (D) or the natural image /
It is determined whether the continuous tone image is dominant (C), and a 1-bit result of D (= 1) or C (= 0) is output. Here, the size of the tile is set to 32 × 32, but other values can be used depending on the processing speed of the circuit and restrictions on the memory capacity. The determination method is to determine the difference between pixel data between adjacent pixels and determine the difference from the distribution state. That is, if the value of the difference value is concentrated on several values with the peak at 0, the computer image / discontinuous tone image is dominant (D), and the difference values are relatively gently distributed. If so, it is determined that the natural image / continuous tone image (C) is dominant. Since many calculations are required to determine the image area, a considerable processing speed and / or circuit scale is required to obtain a complete result for each frame of a moving image. However, it is generally considered that, with a few exceptions, the image area in a moving image continuously changes in the order of the frame frequency. Therefore, it is not always necessary to determine the image area on a frame basis. For example, if the image area information of each tile area in the image is updated once every 5 to 10 frames, it is possible to sufficiently cope with a case where the mouse cursor passes through the natural image area. Then, the circuit scale and the processing speed can be reduced.

The image area information output by the image area discriminator 108 is stored in an image area information table 109. This information is read out at any time and supplied to the digital halftone processor 102 and the sub-pixel selector 103. Digital halftone processor 10
2 is 8 bits (0 to 2) for each R / G / B channel.
The input pixel data of 55) is subjected to halftone processing by the dither method to output a 4-bit (0 to 15) value.
In this process, the image area information at the position of the pixel currently being processed is obtained from the image area information table 109, and the processing branches as follows according to the content, that is, "D" or "C". (1) In the case of "D": For each of the 29 gradation levels, as shown in FIG. 2, a sub-pixel to be lit is selected.
In this method, sub-pixels are selected such that ON / OFF is vertically symmetrical at an odd-numbered gradation level among the 29 levels. This is because the upper and lower lines are synchronized
This is the same combination as the N / OFF mode of 16 colors for each channel.

(2) In the case of "C": As shown in FIG.
A sub-pixel to be turned on for each gradation level is selected. In this method, there is no sub-pixel pattern expressing the gradation levels 5, 8, 15, 20, and 23. Each is expressed by dither using a combination of two upper and lower gradation levels. For example, gradation level 8 is represented by a combination of gradation levels 7 and 9.

In the sub-pixel selection of "D" among the above two options, an image obtained by arranging the same sub-pixel lighting pattern in a two-dimensional manner selects the one having the lowest low frequency component. This is because, in the case of "D", that is, in a computer image / discontinuous tone image, a portion where the tone level is flat occupies most, and it is appropriate to select an optimal pattern on the assumption that the tone level is the same. Because it is possible.

On the other hand, in the sub-pixel selection of "C", the change in the display state of the sub-pixels between the upper and lower adjacent gradation levels is smaller than the smoothness of the flat image, so that the position of the lit sub-pixel is smaller. Emphasis is placed on reducing change. As described above, the gradation levels 5, 8, 15, 20,
There is no sub-pixel pattern corresponding to 23 for the following reason. Regarding the gradation levels 5, 8, 15, 20, and 23 in which the above-mentioned sub-pixel pattern does not exist, any of the sub-pixel patterns shown in FIG. There are three sub-pixels whose display state changes between. As a result, the sub-pixel lighting pattern changes, and as a result, artificial contour lines are likely to occur. If the number of sub-pixels whose display state changes by not using a sub-pixel pattern corresponding to a certain gradation level decreases, the number of colors calculated on the desk decreases, but the artificial contour as described above is used. The generation of lines is suppressed, which is rather preferable.

The number of sub-pixels whose display state changes is the smallest when one sub-pixel is newly turned on by increasing the gradation level by one level. This is a case where another sub-pixel is turned on at the same time as turning off the light. In the present embodiment, the number of sub-pixels whose display state changes between levels is suppressed to one or two except for one exception (17 to 18). In the sub-pixel configuration of this embodiment, it is not possible to reduce the number of pixels to two or less at all levels.
Only at １８18, three sub-pixels are changed. However, as compared with the case shown in FIG. 2, the number of sub-pixels whose display state changes between gradation levels is very small as a whole.

The digital halftone processor 102 performs dither processing for generating output values according to the two cases (1) and (2). That is, (1) can output output values of 29 gray levels, and (2) can output output values of 24 gray levels excluding levels 5, 8, 15, 20, and 23 from the 29 gray levels of (1). Perform dither processing. FIG. 4 shows the distribution of the level values that the output values can take in both cases and the corresponding pixel data (luminance value). In each case, there is a portion where the interval of the luminance value between the levels is different at some levels. As described above, in the case of (2) above, there are levels that are not output, and the total number of gradation levels is reduced to 24. In any case, in such multi-valued dithering, the threshold matrix is applied hierarchically between two adjacent output gray levels to simply compare the input pixel data with the threshold value. Then, one of the two upper and lower gradation levels is output.

The digital halftone processor 102 does not know the position of the sub-pixel, but only performs halftone processing according to the distribution of output values. Digital halftone processor 10
The sub-pixel selector 103 determines ON / OFF of each sub-pixel from the output value of 2. The sub-pixel selector 103 obtains image area information at the position of the pixel currently being processed from the image area information table 109, and ON / OFF of each sub-pixel based on the obtained information and the output value of the digital halftone processor 102.
Determine OFF. Further, the result is transferred to the frame memory controller 105 and written into the corresponding bid in the frame memory 104 as 1/0 data.

The FLCD scanning controller 106 sequentially reads out bit data corresponding to each sub-pixel from the frame memory 104 via the frame memory controller 105, and
107 is displayed.

According to the present embodiment, in the output device using the area gradation method, the generation of artificial contours or texture patterns which are likely to occur in the portion of the input original image where the luminance changes gradually is suppressed. It is possible to display a smooth image of the image.

In the above embodiment, the configuration of the sub-pixel shown in FIG. 15 is premised. However, as a countermeasure against the problem dealt with by the present invention, a method of changing the configuration of the sub-pixel itself can be considered. That is, as shown in FIG. 5, by making the R, G, and B sub-pixels approach each other, the switching of the sub-pixels due to the change in the gradation level is made inconspicuous. In the configuration of FIG. 5, there is no choice of a pixel configuration of higher resolution (double each in the vertical and horizontal directions) with the dashed line in FIG. 15 as a boundary, but it is effective to suppress the generation of artificial contours and texture patterns. There is. However, even if this method is used, not all problems in image quality are solved, and a smoother image can be obtained by using the method disclosed in the present invention together.

Second Embodiment FIG. 6 shows a configuration of an interface section of a digital image signal display device according to a second embodiment of the present invention. 6, reference numeral 601 denotes an A / D converter; 602, a frame memory; 603, a controller for controlling writing and reading to and from the frame memory 602; 604, a digital halftone processing block; 610, a motion (change) detection block for an image; Reference numeral 609 denotes an image area determination block that determines the type of an image using a certain area as a unit, and mainly has a function of determining an area between a text and a natural image.

Reference numeral 607 denotes a zone table indicating the distribution of images in a frame (one screen) based on the image area determination result of the image area determination block 609, and 608 denotes an image area determination code of the zone table 607 and the digital intermediate code. From the halftone-processed image data from the tone processing block 604,
Display sub-pixel (sub-pixel) which is a feature of this embodiment
605 is a partial rewrite control block for controlling a rewrite signal based on the result of the motion detection of the motion detection block 610 for the image, 605
Numeral 1 has a resolution of 4 bits each for RGB, and for each signal level, a lighting sub-pixel pattern shown in FIGS. 7 to 9 (a combination of sub-pixels whose display state is “bright” of bright and dark).
606, a digital image display capable of selecting
Is a display controller for controlling the display output to the digital image display 611, and 612 is an N × M which can be selected by the display 611 in a flat portion of an image or the like.
9 is a sub-pixel (sub-pixel) pattern table listing lighting sub-pixel patterns in pixel units.

The local characteristic of the image is flat, that is, a table of the lighting sub-pixel pattern for the flat portion of the image is constructed in which each pixel has a single gradation level when viewed locally. One example of the method is shown in FIG.

FIG. 10 shows N = M = 5 (5 pixels × 5 pixels)
Of 25 pixels each with a lighting area of 7.5 (gray level 1
This is an example of a uniform pattern that is turned on in 4). 5x
For 5 = 25 pixels, there are 4 <25> lighting sub-pixel patterns in the lighting area 7.5, so
For each lighting sub-pixel pattern, as shown in the following equation (1), for each of the other 24 pixels excluding the center pixel from each lighting sub-pixel of the center pixel of 5 × 5 pixels, The square of the area W and the distance r _n from the lighting sub-pixel of the center pixel to each lighting sub-pixel of the other 24 pixels excluding the center pixel,
The sum of the products with the reciprocal of the power is independently calculated for the 24 pixels, and the sum of the quotients (average values) obtained by dividing the sum of the products by the number of lighting sub-pixels k for each pixel (for 24 pixels) is minimized. The least biased pixels (sub-pixels) of the limited sub-pixel pattern
This is to select the arrangement.

[0037]

(Equation 1)

The input image signal is converted into a digital image signal by the A / D converter 601 and input to the frame memory controller 603, the image area determination block 609, and the motion detection block 610. The digital image signal input to the frame memory controller 603 is stored in the frame memory 602 as comparison data for motion detection of the next frame, and at the same time, input to the halftone processing block 604 and subjected to digital halftone processing. , Partial rewrite control block 605 and sub-pixel
The data is input to the selector 608.

The image area determination block 609 determines the type of image for each certain area (for example, 4 × 4 pixels), writes the result in the zone table 607, and determines the distribution of the image in one screen (frame). Construct a map to represent. The information in the zone table 607 includes the sub-pixel
The data is passed to the selector 608 and the motion detection block 610.

The motion detection block 610 determines a screen (frame) from the current image signal immediately after A / D conversion, the image area determination result from the zone table 607, and the image data of the previous frame stored in the frame memory 602. ), A portion that has moved (changed) from the previous frame to the present is detected, and the result is output to the partial rewrite control block 605.

Then, the sub-pixel selector 608
Monitors the image signal output of the halftone processing block 604 when the information from the zone table 607 indicates a natural image (not a text), and corresponds to the image output level of the halftone processing block 604. If the sub-pixel pattern to be performed is a single (uniform) pattern, the uniform pattern corresponding to the single level obtained by the method shown in FIG.
Read from pixel pattern table 612, N
The display image signal is replaced by a display image signal in units of × M pixels and displayed.

According to the present embodiment, without changing the display 611 (with the sub-pixel pattern as it is), it is caused by the lighting pattern of the sub-pixel which becomes a problem in the flat part of the picture, the gray scale and the like. It is possible to suppress or reduce the occurrence of the visual obstruction pattern, and to display the original smooth image of the original image.

[0043]

As described above, according to the present invention,
In an output device using the area gradation method, it is necessary to suppress the occurrence of artificial contours or texture patterns that are likely to occur in a portion where the luminance changes gradually in the input original image, and to display a smooth image of the original image. Becomes possible. In particular, the effect is greater when a pseudo halftone process such as a dither method or an error diffusion method is performed and output.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an image display device including a sub-pixel selector according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a sub-pixel selection sequence applied to a portion where the image area information of a pixel is “D” in the apparatus of FIG. 1, and is also a diagram illustrating a conventional sub-pixel selection sequence.

FIG. 3 is a diagram showing a sub-pixel selection sequence applied to a portion where the image area information of a pixel is “C” in the apparatus of FIG. 1;

FIG. 4 is a diagram showing a halftone processing output value of a portion where the image area information of a pixel is “C” in the apparatus of FIG. 1;

FIG. 5 is a diagram showing a sub-pixel configuration in which sub-pixels of each color are concentrated as a modification of the pixel configuration in the device of FIG.

FIG. 6 is a block diagram of an interface circuit of a digital image display device including a sub-pixel selector according to a second embodiment of the present invention.

7 is a diagram showing a list of sub-pixel lighting patterns which can be selected on the display of FIG. 6 having a resolution of 4 bits for each RGB per pixel having a sub-pixel selector function.

8 is a diagram showing a list of sub-pixel lighting patterns that can be selected on the display of FIG. 6 having a resolution of 4 bits for each RGB per pixel having a sub-pixel selector function.

9 is a diagram showing a list of sub-pixel lighting patterns that can be selected on the display of FIG. 6 having a resolution of 4 bits for each RGB per pixel having a sub-pixel selector function.

10 is an explanatory diagram of an example of a sub-pixel pattern optimization method applied to a single (uniform) level flat image signal portion in the apparatus of FIG. 6;

FIG. 11 is a diagram showing a conventional sub-pixel configuration capable of displaying 16 gradations with an area ratio of 1: 2: 4: 8.

FIG. 12 is a diagram showing a sub-pixel configuration which is a modification of the sub-pixel configuration of FIG. 11 and enables display of more gradations.

13 is a diagram illustrating selection of a sub-pixel that expresses each gradation level obtained by the sub-pixel configuration of FIG.

14 is a diagram illustrating selection of sub-pixels at gradation levels of 15 to 17 in the case of the sub-pixel configuration in FIG.

FIG. 15 shows an example of applying the sub-pixel configuration of FIG.
A sub-pixel configuration capable of color display having three channels of green (G) and blue (B) is shown.

16 is a table showing correspondence between each gradation level and selectable lighting sub-pixel patterns of a conventional digital image display having a resolution of 4 bits for each RGB having one sub-pixel configuration shown in FIG.

17 is a table showing correspondence between each gradation level and a selectable lighting sub-pixel pattern of a conventional digital image display having a resolution of 4 bits for each RGB having one pixel having the sub-pixel configuration shown in FIG. 15;

FIG. 18 shows the lit sub-pixel of FIGS. 16 and 17.
A conventional digital image display having a resolution of 4 bits for each of RGB having a pattern and a lighting sub-pixel when displaying a gray flat portion with a lighting area of 7.5 and 7.0.
It is explanatory drawing of a pattern.

[Explanation of symbols]

101: A / D converter, 102: digital halftone processor, 103: sub-pixel selector, 104: frame memory,
105: frame memory controller, 106: FLCD scanning controller, 107: FLCD (ferroelectric liquid crystal display) 108: image area discriminator, 109: image area information table,
201, 202: vertical electrodes, 203, 204, 205:
Horizontal electrodes, 206, 207, 208, 209, 210,
211: sub-pixel, 601: A / D converter, 602:
Frame memory, 603: Frame memory controller, 604: Digital halftone processing block, 605:
Partial rewrite control block, 606: display controller, 607: zone table (image area display map), 608: sub-pixel selector, 609: image area determination block, 610: image motion (change) detection block, 611: Digital Image Display, 612: Sub-pixel pattern table.

Claims (13)

[Claims] 1. One pixel is composed of a plurality of sub-pixels capable of displaying two levels, and by combining the display states of the plurality of sub-pixels, it is possible to express the number of gradation levels greater than the two levels. In an image display device including at least one gray level which can be expressed by a plurality of combinations of sub-pixel display states among the gray levels higher than the two levels, when the gray levels change sequentially, An image display apparatus, wherein display is performed using a sub-pixel combination sequence obtained by selecting the sub-pixel display state combination so that the number of changing sub-pixels is as small as possible. 2. In order to limit the number of sub-pixels whose display state changes when said gradation level sequentially changes to at least a predetermined number, at least one of gradation levels that can be originally expressed by said pixel. 2. The image display apparatus according to claim 1, wherein the gradation level is excluded, and the excluded gradation level is expressed by predetermined digital halftone processing using the preceding and following gradation levels. 3. One pixel is constituted by a plurality of sub-pixels capable of displaying two levels, and by combining the display state of each of the plurality of sub-pixels, the number of gradation levels higher than the two levels can be expressed. An image display device including at least one gray level that can be expressed by a plurality of combinations of sub-pixel display states among the gray levels higher than the two levels, An image display device comprising a sub-pixel selecting means for selecting one from a plurality of combinations of sub-pixel display states. 4. The image display device according to claim 3, wherein the local feature of the image is defined by a characteristic of a spatial change of the image data in a sufficiently small area around the target pixel. 5. The image processing apparatus according to claim 1, wherein said sub-pixel selecting means changes a gradation level when a relatively gradual change component is dominant in spatial change characteristics of image data in a sufficiently small area around said target pixel. From among the first sub-pixel combination series in which the number of sub-pixels whose display state changes with the minimum, a sub-pixel display state combination expressing a gradation level to be output is set for the target pixel. If one or both of the flat component and the very steep component are dominant, select from the second sub-pixel combination sequence in which the sub-pixel display state is more dispersed within the pixel. ,
5. The image display device according to claim 4, wherein a sub-pixel display state combination expressing a gradation level to be output is selected for the target pixel. 6. The first sub-pixel combination series includes a plurality of sub-pixels whose display state changes with a change in the gradation level as small as possible. 6. The image display device according to claim 5, wherein at least one level is excluded. 7. An image display according to claim 6, further comprising a halftone processing means for performing digital halftone processing using the number of grayscale levels of the first and second subpixel combination series as an output value. apparatus. 8. The digital halftone process according to claim 2, wherein the digital halftone process is a process using a dither method.
The image display device as described in the above. 9. The image display apparatus according to claim 2, wherein said digital halftone processing is processing using an error diffusion method. 10. The sub-pixel selecting means selects all pixels in an area consisting of N × M pixels (N and M are positive integers) in the same sub-pixel display state combination capable of selecting the sub-pixel display state combination. When expressed by a gradation level, the area W of the sub-pixel displaying one of the two levels and the distance r of the sub-pixel displaying the one level from the center of the area are used as parameters in the area. When the sub-pixel display state combination in which the distribution of the sub-pixels displaying one level is the most uniform and two adjacent gradation levels that can select the sub-pixel display state combination are mixed in the region, the area W And a table which lists sub-pixel display state combinations in which the distribution of sub-pixels displaying the one level is the most uniform in the area using the distance r as a parameter and the same or similar gradation levels. In successive images, the image display apparatus according to claim 4, wherein the display sub-pixel display state combinations of the table in the region of the screen. 11. The method according to claim 1, wherein the sub-pixel selecting means determines a position of a pixel to be displayed in accordance with the gradation level information of the image signal input within the processing range of the N × M pixels. 11. The image display device according to claim 10, wherein the image display device can be arbitrarily selected within a processing range. 12. The one pixel is formed by collecting a plurality of sub-pixels each having two or more types of display areas and capable of displaying at two levels, and the two pixels are selected from the sub-pixels constituting one pixel. 12. The image display device according to claim 1, wherein by selecting the number of sub-pixels for displaying one of the levels, more than two gradation levels can be displayed. 13. The display device according to claim 1, wherein a plurality of types of the spatial resolution and the number of gradations that can be expressed per pixel can be selected by selecting the number of sub-pixels constituting one pixel. The image display device according to any one of the above.