JP2009223345A - Image processing method and liquid crystal display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method and a liquid crystal display device using it in which an angle of view is widened and which are excellent in gradation and viewing angle characteristics with respect to an image processing method which enhances the quality of images to be display on a display device, and to provide a liquid crystal display device using it. <P>SOLUTION: In this image processing method, a high luminance pixel 1a which is driven so as to become higher luminance than the luminance data of an image to be displayed and a low luminance pixel 1b which is driven so as to become a lower luminance than the luminance data are combined and the luminance of the high luminance pixels 1a and the luminance of the low luminance pixels 1b and the area ratio of high luminance pixels 1a and low luminance pixels 1b are determined so that luminance roughly identical to a desired luminance based on the luminance data can be obtained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image processing method for improving the image quality of an image displayed on a display device, and a liquid crystal display device using the image processing method.

  FIG. 33 shows an example of the configuration of a vertical alignment type liquid crystal display device. FIG. 33A schematically shows a cross-sectional structure of the liquid crystal panel 101. The liquid crystal panel 101 includes a TFT substrate (array substrate) 102 on which a thin film transistor (TFT) or the like is formed, and a counter substrate 103 on which a common electrode or CF (color filter) is formed. And sealed with a peripheral sealing material 105. A gap (cell gap) between the TFT substrate 102 and the counter substrate 103 is maintained at a predetermined interval by a spacer 106. Polarizing plates 107 are arranged, for example, in crossed Nicols on the opposite surfaces of the TFT substrate 102 and the counter substrate 103, respectively. A mounting terminal 108 for mounting a liquid crystal driving IC (not shown) is formed on the TFT substrate 102.

  FIG. 33B shows the structure of one pixel 113 when the vertical alignment type liquid crystal display device is viewed in the normal direction of the display screen (hereinafter referred to as “front direction”). A pixel electrode pattern for driving a liquid crystal is formed on at least one substrate, for example, the TFT substrate 102. On the TFT substrate 102, a plurality of drain bus lines 111 and gate bus lines 112 are formed so as to intersect with each other through an insulating film, and a pixel driving TFT 110 connected to the pixel electrode 109 is formed at the intersecting portion. Is formed. Further, the pixel 113 has a storage capacitor electrode 116 for holding charges. A storage capacitor bus line 117 is formed below the storage capacitor electrode 116 via an insulating film.

  In the pixel electrode 109, a slit 114 is formed by removing an electrode material, and a linear protrusion 115 is formed on the counter substrate 103 side. The slits 114 and the protrusions 115 function as alignment regulating structures that regulate the direction in which liquid crystal molecules (not shown) of the liquid crystal layer 104 are tilted when a voltage is applied. In the pixel 113, the region is divided so that the liquid crystal molecules are tilted in four directions. By tilting the liquid crystal 103 in four directions, the viewing angle deviation is averaged compared to a liquid crystal display device that tilts in only one direction. This greatly improves the viewing angle characteristics. Such a technique is called an alignment division technique.

  FIG. 34 schematically shows a cross-sectional structure of a vertical alignment type liquid crystal display device using an alignment division technique. In FIG. 34A, the protrusion 115 of the alignment regulating structure is formed on both the counter electrode 118 formed on the TFT substrate 102 and the pixel electrode 109 formed on the counter substrate 103. An alignment film 119 is formed on the TFT substrate 102 and the counter substrate 103 including the protrusions 115. Although not shown, the protrusion 115 may be provided only on one substrate. FIG. 34A shows a state where no voltage is applied to the liquid crystal 104. FIG. 34B shows a state in which a voltage is applied to the liquid crystal 104, and the liquid crystal molecules 120 are aligned in two directions. FIG. 34C shows a state where the slit 114 is provided only on the TFT substrate 102 side and a voltage is applied to the liquid crystal 104. Also in this case, the liquid crystal molecules 120 are aligned in two directions. Note that the slit 114 may be provided only on the counter substrate 103 or may be provided on both the TFT substrate 102 and the counter substrate 103.

Further, unlike the LCD shown in FIGS. 33 and 34, in the initial state where no voltage is applied to the liquid crystal layer 104, the liquid crystal molecules 120 are substantially parallel to the TFT substrate 102 and the like, and the liquid crystal molecules 120 rise when a voltage is applied. There are also mode liquid crystal display devices. An example of the liquid crystal display device is a TN (Twisted Nematic) type. In the TN type, the alignment direction formed on the surfaces of the TFT substrate 102 and the counter substrate 103 is preliminarily subjected to rubbing to determine the alignment direction of the liquid crystal molecules 120. Therefore, the slit 114 and the protrusion 115 are not necessary. However, in order to divide the alignment, it is necessary to divide the direction in which the liquid crystal molecules 120 fall into several directions, and the alignment division is realized by a method of locally changing the pretilt. In addition to the TN type, there are various liquid crystal display modes such as IPS (In-Plane Switching) and ferroelectric liquid crystal in which the liquid crystal molecules 120 do not tilt with respect to the TFT substrate 102 etc., but other than IPS and ferroelectric liquid crystal The liquid crystal mode has a common problem that viewing angle characteristics are poor.

  FIG. 35 is a diagram for explaining a problem of a conventional liquid crystal display device. FIG. 35A shows the characteristics (TV characteristics) between the voltage applied to the liquid crystal layer and the transmittance in the vertical alignment type liquid crystal display device. In the graph, a curve A indicated by a solid line plotted with a mark ● indicates a TV characteristic in the front direction, and a curve B indicated by a solid line plotted with a mark * indicates an azimuth angle of 90 ° and a polar angle of 60 with respect to the display screen. The TV characteristics in the direction of ° (hereinafter referred to as “oblique direction”) are shown. Here, the azimuth angle is an angle measured counterclockwise from the approximate center of the display screen with respect to the horizontal direction. Further, the polar angle is an angle formed with a perpendicular line standing at the center of the display screen.

  In the portion indicated by the virtual circle C in FIG. 35 (a), the luminance change is distorted. For example, the transmittance in the oblique direction is higher than the transmittance in the front direction at a relatively dark luminance with an applied voltage of about 2.5V, but in the oblique direction at a relatively bright luminance with an applied voltage of about 4.5V. The transmittance is lower than the transmittance in the front direction. As a result, when viewed from an oblique direction, the luminance difference in the effective drive voltage range becomes small. This phenomenon appears most prominently in color changes. That is, when the display screen is viewed obliquely with respect to the front, the color of the image changes whitish. FIG. 35B shows a gradation histogram of three primary colors of a red (R), green (G), and blue (B) image of a video that is displayed on an MVA-LCD and is photographed with a digital camera under the same conditions from the front and obliquely. Is shown. The horizontal axis represents gradation (for example, 256 levels from 0 to 255, and the brightness becomes higher as it approaches 0), and the vertical axis represents the existence ratio (%). Although the respective distributions of R, G, and B are separated from each other in the front, it can be seen that the distributions are approaching from an oblique direction. As a result, the original display color is lost.

  Methods for improving this phenomenon are disclosed in Patent Document 1 to Patent Document 7. FIG. 36 shows a basic pixel structure disclosed in Patent Document 1. 36A shows a schematic diagram of a pixel structure in the normal direction relative to the display screen, FIG. 36B shows an equivalent circuit of the pixel 121, and FIG. 36C shows a cross-sectional structure of the pixel 121. ing. As shown in FIG. 33B, one pixel electrode 109 is normally connected to one TFT 110. However, as shown in FIG. 36A, one pixel 121 is divided into, for example, four subpixels 121a, 121b, 121c, and 121d. The subpixels 121a, 121b, 121c, and 121d are electrically capacitively coupled. When a voltage is applied to the pixel 121 through the TFT 122, charges are distributed according to the capacitance ratio of the subpixels 121a, 121b, 121c, and 121d, and different voltages are applied to the subpixels 121a, 121b, 121c, and 121d. Thereby, the distortion of the TV characteristic shown in FIG. 35A is dispersed by the sub-pixels 121a, 121b, 121c, and 121d, and the whiteness of the screen is alleviated. The principle of the dispersion of the TV characteristic distortion will be described later. Hereinafter, the method of dividing the pixel 121 into sub-pixels 121a, 121b, 121c, and 121d will be referred to as a capacitive coupling HT (halftone gray scale) method. The HT method using capacitive coupling is applied to a TN liquid crystal display mode.

In the HT method using capacitive coupling, the pixel structure becomes very complicated. First, one pixel must be divided into a plurality of pixels. When each sub-pixel comes into contact with a defective pattern, a point defect occurs. For capacitive coupling, as shown in FIG. 36C, the sub-pixels 121a, 121b, 121c, and 121d are three-dimensionally arranged between the counter electrode 118 and the control capacitor electrode 122 formed on the TFT substrate. If an interlayer short circuit or the like occurs, the whole becomes a point defect. In addition, when the distribution of capacity changes due to missing patterns or the like, the overall luminance changes, and in this case, a point defect also occurs. Furthermore, the aperture ratio is greatly reduced because the pixel is divided into sub-pixels. In the HT method based on capacitive coupling, a decrease in aperture ratio is inevitable, and in order to alleviate the decrease in aperture ratio as much as possible, it is necessary to form two layers of electrodes that form a capacitor with transparent electrodes. In this case, since the number of film forming steps increases, the influence on the process such as an increase in manufacturing cost and a decrease in process capability is large.

  Further, the HT method using capacitive coupling also has a problem that the drive voltage becomes high. This is because voltage loss occurs due to capacitive coupling, and the drive voltage increases as the number of divisions increases. As the drive voltage increases, power consumption increases. Further, a high withstand voltage driving IC is required, resulting in high cost. In addition, since the HT method based on capacitive coupling provides a potential difference depending on the sub-pixel, synthesis of TV characteristics becomes discontinuous. The display characteristics are deteriorated as compared with an ideal state in which the TV characteristics change continuously.

  As described above, the HT method based on capacitive coupling has an effect of improving the display characteristics, but has too many drawbacks and is not employed in liquid crystal display devices currently on the market. Further, the TN type liquid crystal display device has a problem that the black luminance increases and the contrast decreases when viewed obliquely. The HT method based on capacitive coupling is a technique for accurately expressing halftone gradation, but if the contrast is lowered, the effect of halftone color reproducibility cannot be fully exhibited.

  An object of the present invention is to provide an image processing method having a wide viewing angle and excellent gradation viewing angle characteristics, and a liquid crystal display device using the image processing method.

  The object is to combine a high-luminance pixel that is driven to have higher luminance than luminance data of an image to be displayed and a low-luminance pixel that is driven to have lower luminance than the luminance data, and to obtain a desired value based on the luminance data. An image processing method for determining a luminance of the high luminance pixel and a luminance of the low luminance pixel and an area ratio of the high luminance pixel and the low luminance pixel so that a luminance substantially equal to the luminance can be obtained. Achieved by:

  As described above, according to the present invention, an image processing method having a wide viewing angle and excellent gradation viewing angle characteristics and a liquid crystal display device using the image processing method can be realized.

It is a figure which shows the example which set the bright pixel 1a and the dark pixel 1b with respect to the nine pixels 1 by Example 1-1 of the 1st Embodiment of this invention. It is a graph which shows the measurement result of the applied voltage-transmittance characteristic of the front direction and the diagonal 60 degree direction by Example 1-1 of the 1st Embodiment of this invention. It is a figure which shows an example of the gradation conversion table by Example 1-1 of the 1st Embodiment of this invention, and the image before and behind conversion. It is a graph which shows the relationship between the ratio of the area of the bright pixel and dark pixel by Example 1-1 of the 1st Embodiment of this invention, and a distortion influence evaluation number. It is a figure which shows the subjective evaluation result of whether the rough feeling of the pixel by Example 1-1 of the 1st Embodiment of this invention is visually recognizable. It is a figure which shows the image processing method by Example 1-2 of the 1st Embodiment of this invention. It is a figure which shows typically the pixel 4 of the predetermined area | region by Example 1-3 of the 1st Embodiment of this invention. It is a figure which shows the result of having visually evaluated the influence of the roughness by Example 1-3 of the 1st Embodiment of this invention. It is a figure which shows the result of having evaluated visually the influence of the roughness in the moving image display by Example 1-3 of the 1st Embodiment of this invention. It is a figure which shows the effect by the 1st Embodiment of this invention. It is a figure which shows the measurement result of the brightness | luminance of the diagonal direction which performed the image process to the 127/255 gradation unprocessed image by the 2nd Embodiment of this invention. It is a block diagram of the system apparatus and liquid crystal display device by the 2nd Embodiment of this invention, Comprising: It is a figure explaining the site | part which performs the said gradation conversion process. It is a figure explaining the other effect by the 2nd Embodiment of this invention, Comprising: It is a figure which shows the cross-section of the pixel 33 typically. When the brightening frame period and the darkening frame period according to Example 2-1 of the second embodiment of the present invention are divided at a ratio of 1: 1, the gradation of the unprocessed image is set to what gradation after the image processing. It is a figure which shows the gradation conversion table for calculating | requiring whether to set. It is a figure which shows the other gradation conversion table by Example 2-1 of the 2nd Embodiment of this invention. It is a graph which shows the gradation-luminance characteristic seen from the front direction of the screen by the Example 2-1 of the 2nd Embodiment of this invention, and the diagonal 60 degree direction. It is a graph which shows the gradation-luminance characteristic seen from the front direction of the screen by the Example 2-1 of the 2nd Embodiment of this invention, and the diagonal 60 degree direction. It is a graph which shows the gradation-luminance characteristic seen from the front direction of a screen, and the diagonal 60 degree direction at the time of using the several gradation conversion table by Example 2-1 of the 2nd Embodiment of this invention simultaneously. . It is a flowchart which shows the method of changing a gradation conversion table for every RGB by Example 2-2 of the 2nd Embodiment of this invention, and changing a gradation. It is a flowchart which shows the method of converting a gradation by changing a gradation conversion table with the luminance difference of RGB by Example 2-3 of the 2nd Embodiment of this invention. It is a figure explaining the image conversion method by Example 2-5 of the 2nd Embodiment of this invention. It is a flowchart which shows the gradation conversion method by changing a gradation conversion table with the luminance difference of RGB by Example 2-5 of the 2nd Embodiment of this invention. It is a figure explaining the generation | occurrence | production principle of the display abnormality improved in the 3rd Embodiment of this invention. It is a figure explaining the principle of the image conversion by Example 3-1 of the 3rd Embodiment of this invention. It is a figure explaining the image processing method by Example 3-1 of the 3rd Embodiment of this invention. It is a figure explaining the image processing method by Example 3-2 of the 3rd Embodiment of this invention. It is a figure explaining the selection transition of the gradation conversion table with respect to the input gradation by Example 3-2 of the 3rd Embodiment of this invention. It is a figure which shows the simulation result of the equiluminance distribution of the combination of the brightness difference of light and dark on the setting conditions by Example 3-2 of the 3rd Embodiment of this invention. It is a figure which shows the gradation conversion table by Example 3-3 of the 3rd Embodiment of this invention. It is a figure which shows the simulation result of the equiluminance distribution before and behind adjustment of the output tone-luminance characteristic of source driver IC by Example 3-4 of the 3rd Embodiment of this invention. According to Example 3-4 of the third embodiment of the present invention, R is 136/255 gradation, B is 0/255 gradation, and G is from 0/255 gradation from edge to edge of the image. It is a graph which shows the measurement result of the brightness | luminance change of G pixel when the image which moves changing to 255/255 is displayed. It is a figure explaining the gradation setting method in the low gradation vicinity of the HTD technique by Example 3-5 of the 3rd Embodiment of this invention. It is a figure which shows the structure of the conventional vertical alignment type liquid crystal display device. It is a figure which shows typically the cross-sectional structure of the vertical alignment type liquid crystal display device using the conventional alignment division | segmentation technique. It is a figure explaining the problem which the liquid crystal display device by a conventional drive has. It is a figure which shows the conventional pixel structure.

[First Embodiment]
An image processing method and a liquid crystal display device using the image processing method according to the first embodiment of the present invention will be described with reference to FIGS. Hereinafter, the embodiments will be described in detail. In all the embodiments, the liquid crystal display device is an MVA type, and a vertical alignment mode liquid crystal panel (vertical alignment type liquid crystal display device) in which black luminance is kept low. Used.

[Example 1-1]
An image processing method of Example 1-1 according to the present embodiment and a liquid crystal display device using the image processing method will be described with reference to FIGS. First, the principle of the image processing method according to this embodiment will be described with reference to FIG. In this embodiment, a plurality of pixels are regarded as one unit, and a part of the plurality of pixels is made brighter than the luminance of an original image that has not been subjected to image processing (hereinafter referred to as “unprocessed image”), and the remaining pixels Part or all is darker than the brightness of the unprocessed image. Darken the pixels to be brightened (hereinafter referred to as high-brightness pixels) so that the front brightness does not change before and after image processing, and the total area of the pixels to be darkened is equal to or larger than the total area of the pixels to be brightened. A ratio with a pixel (hereinafter referred to as a low luminance pixel) is set. FIG. 1 shows an example in which nine pixels 1 in a 3 × 3 matrix are regarded as one unit, and one high luminance pixel 1a and eight low luminance pixels 1b are set. In contrast to the luminance of the nine pixels 1 shown in FIG. 1A, only the central pixel 1a is brightened and the remaining surrounding pixels 1b are darkened in FIG. 1B.

  The inventors of the present invention have a distortion influence evaluation number (60 °) = (T60 / T0) × (the degree of the influence of the distortion of the applied voltage-transmittance (TV) characteristic of the vertical alignment type liquid crystal display device on the visual observation. It was found that it can be expressed by (T60-T0). Note that T0 is the luminance (or brightness) in the front direction of the display screen, and T60 is the luminance (or brightness) in a direction having an angle of 60 ° with respect to the front direction (an oblique 60 ° direction).

  FIG. 2 is a graph showing the results of measuring the characteristics of the liquid crystal applied voltage versus the brightness in the front direction and at an angle of 60 ° when an image is displayed on the liquid crystal display device using this embodiment. FIG. 2A shows the characteristics of liquid crystal applied voltage versus brightness obtained in front of the liquid crystal panel. The horizontal axis represents, for example, the voltage applied to the liquid crystal of the high luminance pixel 1a, and the vertical axis represents brightness (arbitrary unit). (Au)). A curve A indicated by a solid line in the graph indicates a liquid crystal applied voltage vs. brightness characteristic of one high luminance pixel 1a, and a curve B indicated by a broken line indicates a characteristic of the liquid crystal applied voltage vs. brightness of eight low luminance pixels 1b. Show. A curve C indicated by an alternate long and short dash line indicates a characteristic of liquid crystal applied voltage versus brightness in the combination of the curve A and the curve B.

A voltage higher than the applied voltage of the unprocessed image is applied to the high brightness pixel 1a, and a voltage lower than the applied voltage of the unprocessed image is applied to the low brightness pixel 1b. The total area of the high luminance pixels 1a in the entire display screen is smaller than the total area of the low luminance pixels 1b, and the maximum brightness is the sum of the eight low luminance pixels 1b in one high luminance pixel 1a. It is set to be lower than the maximum brightness.

  As a specific example, for example, V-1 (volt) is applied to the liquid crystal of the low luminance pixel 1b with respect to the voltage V (volt) applied to the liquid crystal of the high luminance pixel 1a. However, in FIG. 2A, the V-1 (volt) characteristic of the low-luminance pixel 1b is shifted by +1 volt and shown at the position of V (volt). Further, if the total area of the high luminance pixels 1a in the entire display screen is 1, the total area of the low luminance pixels 1b is 8 (see FIG. 1). Further, as shown by curves A and B in FIG. 2A, the brightness of one high-luminance pixel 1a at an applied voltage of 5 volts for white display is 0.03 (au). The total brightness of the eight low-luminance pixels 1b is about 0.27 (au), nine times that of the low-luminance pixel 1b.

  In the combination of one high luminance pixel 1a and eight low luminance pixels 1b having such a relationship, the curve A and the curve B are combined to obtain the liquid crystal applied voltage vs. brightness characteristic of the curve C indicated by a one-dot chain line. It is done. The characteristic indicated by the curve C has substantially the same shape as the characteristic in the front direction in the applied voltage to transmittance characteristic (TV characteristic) applied to the liquid crystal layer when the unprocessed image shown in FIG. It becomes a curve.

  FIG. 2B shows a characteristic change of the liquid crystal panel having the applied voltage versus brightness characteristic shown in FIG. The horizontal axis represents, for example, the voltage applied to the liquid crystal of the high luminance pixel 1a, and the vertical axis represents the brightness (arbitrary unit (au)). A curve D indicated by a solid line in the graph indicates a liquid crystal applied voltage vs. brightness characteristic of one high luminance pixel 1a in an oblique 60 ° direction, and a curve E indicated by a broken line indicates an oblique 60 ° direction of eight low luminance pixels 1b. The liquid crystal applied voltage vs. brightness characteristics are shown. A curve F indicated by a two-dot chain line indicates characteristics of liquid crystal applied voltage versus brightness in an oblique 60 ° direction synthesized with the curves D and E. The characteristic indicated by the curve F is substantially the same as the characteristic in the oblique 60 ° direction in the applied voltage versus transmittance characteristic (TV characteristic) applied to the liquid crystal layer in the case of displaying the unprocessed image shown in FIG. It becomes a shape curve. For comparison, FIG. 2 (b) also shows a curve C (dashed line) showing the characteristics of the combined liquid crystal applied voltage versus brightness in the same front direction as shown in FIG. 2 (a). is there.

  As shown in FIG. 2 (b), when the curve C indicating the characteristic in the front direction is compared with the curve F indicating the characteristic in the oblique 60 ° direction, the curve F is more in two places, the virtual circle G and the virtual circle H. It can be seen that there is a distortion whose brightness is higher than that of the curve C. In the virtual circle G, it is the curve D among the curves D and E that have higher brightness than the curve C. Therefore, the cause of the distortion is the high luminance pixel 1a. However, since the brightness of the high luminance pixel 1a is originally sufficiently low in the virtual circle G, the distortion cannot be visually observed. This has the effect that the difference between the front brightness T0 and the brightness T60 from 60 ° is small, that is, the term (T60−T0) in the equation of the distortion influence evaluation number (60 °) is reduced. ing.

  On the other hand, in the virtual circle H, the brightness that is higher than that of the curve C is the curve E out of the curves D and E. Therefore, the cause of the distortion is the eight low-luminance pixels 1b. However, since the total luminance reached by the high-luminance pixel 1a that does not cause distortion is sufficiently high, the ratio of the brightness T60 from 60 ° to the front brightness T0 is closer to 1 than in the past. That is, it has the effect of reducing the term (T60 / T0) in the equation of the distortion influence evaluation number (60 °).

  As shown in FIG. 2B, by using the image processing method according to this embodiment, (T60 / T0) in the virtual circle C indicating the distortion region in the TV characteristic shown in FIG. While the level is ˜4 times, in this embodiment, the level can be reduced to less than 2 times. As a result, it is possible to greatly suppress the occurrence of a white-brown image observed when viewed from an oblique direction.

  FIG. 3 shows an example of gradation conversion table creation and images before and after conversion. FIG. 3A shows an example of creating a gradation conversion table for determining gradations to be set for the high luminance pixel 1a and the low luminance pixel 1b after image processing based on the gradation of the unprocessed image. . FIG. 3A illustrates a case where the ratio of the number of pixels of the high luminance pixel 1a and the low luminance pixel 1b is 1:10. The horizontal axis represents the gradation (composite gradation) of the unprocessed image, and the vertical axis represents the gradation (element gradation) to be set after conversion. For example, when the luminance of the unprocessed image is 100/255 gradations, the luminance after conversion actually displayed on the liquid crystal panel is 10 out of 11 pixels from the curve A indicated by the solid line plotted with ■ in the graph. The low luminance pixel 1b (10/11 pixel) has 70/255 gradations. The curve A has x = 0 on the horizontal axis and y on the vertical axis, where y = 0 (where 0 ≦ x ≦ 73.3), y = (255 / (255-73.3)) × ( x−73.3) (where 73.3 ≦ x ≦ 255).

  Furthermore, it can be seen from the curve B indicated by the solid line plotted with the asterisks in the graph that one high luminance pixel 1a out of 11 pixels should have 215/255 gradations. The curve B has a horizontal axis x and a vertical axis y, y = (187.7 / 73.3) × (x) (where 0 ≦ x ≦ 73.3), y = ( (255-187.7) / (255-73.3)) × (x-73.3) +187.7 (where 73.3 ≦ x ≦ 255).

  Ten low-luminance pixels 1b in 11 pixels are converted from 100 gradations to 70 gradations, so that the luminance (brightness) decreases. One high-brightness pixel 1a out of 11 pixels is converted from 100 gradations to 215 gradations, and the luminance (brightness) increases to compensate for the decrease in luminance in the 10 low-brightness pixels 1b. Therefore, the front luminance after image processing can maintain the luminance of the unprocessed image.

  FIG. 3B shows enlarged photographs of images before and after conversion. Image C shows an unprocessed image. Image D shows an enlarged view of an image obtained by converting the area ratio between the high luminance pixel 1a and the low luminance pixel 1b to 1: 3, and the image E shows the area ratio between the high luminance pixel 1a and the low luminance pixel 1b at 1:15. The enlarged view of the image converted into is shown.

  FIG. 4 shows the relationship between the area ratio of the high luminance pixel 1a and the low luminance pixel 1b and the distortion effect evaluation number. FIG. 4A is a graph showing the relationship between the ratio of the area of the high luminance pixel 1a and the low luminance pixel 1b and the distortion effect evaluation number, and the horizontal axis represents the gradation of the video signal input to the liquid crystal display device ( Input gradation), and the vertical axis represents the distortion effect evaluation number. In FIG. 4 and the subsequent figures, the symbol “◎” represents a good state, the symbol “◯” represents a slightly superior state, and the symbol “x” represents an inferior state. A normal panel not subjected to image processing according to the present embodiment is affected by distortion in a wide range with a peak of 40/255 gradation (curve A shown by a solid line plotted with ♦ in the graph). On the other hand, when the image processing according to the present embodiment is applied, the influence of distortion is dispersed in two places, and the value of the distortion influence evaluation number is small (curves B, C, D, and E). This means that the degree of influence of distortion is reduced.

  FIG. 4B shows the result of visual evaluation of the influence of distortion when the area ratio of the high luminance pixel 1a and the low luminance pixel 1b is changed for the two types of images F and G. The effect can be obtained in a wide range of the area ratio of the high-luminance pixel 1a and the low-luminance pixel 1b (hereinafter abbreviated as “light / dark area ratio”) from 1: 1 to 1:15. A great effect is obtained over 1: 3. When the area ratio of light and dark is out of the range, the effect of dispersion cannot be obtained because the strain distribution is biased to one side. In this way, only by electrically processing the image, the influence of the distortion of the viewing angle can be greatly reduced without changing the pixel structure of the liquid crystal panel.

By the way, the image processing of the present embodiment is performed after a video signal is input from a system side device such as a personal computer to the liquid crystal display device. Specifically, image processing is performed by an interface circuit such as a control IC mounted on the liquid crystal display device, and a video signal is transmitted to a source driver IC that drives the liquid crystal panel. However, similar image processing is not necessarily performed at this stage. For example, by providing the image processing function with a video processing chip provided in a system side device such as a personal computer, the cost can be reduced. It is also possible to realize the image processing function in the OS or software.

  FIG. 5 is a diagram showing a subjective evaluation result as to whether or not a feeling of roughness of pixels can be visually recognized when image processing is performed on a liquid crystal panel having a vertical pixel pitch of 0.3 mm. When the subject leaves the screen, the luminance difference between adjacent pixels becomes difficult to see, so the roughness becomes inconspicuous. Further, when the area ratio is close to 1: 1, the gap between the bright pixels and the dark pixels becomes small, so that the roughness becomes inconspicuous. In a public display device or the like on the street, since it is sufficient to assume that the person and the display device are used at a distance of 1 to 2 m, a sufficient effect can be obtained even with a 0.3 mm pitch panel. Moreover, since it will be used in the state where the distance between the user and the screen is close in applications such as a personal computer monitor, it must be assumed that the distance between the user and the screen is about 20 cm. When the pixel brightness ratio is 4:12, roughness is visually recognized up to a distance of about 60 cm. However, if the pixel pitch is a liquid crystal panel of about 0.1 mm, it can be considered to be sufficiently applicable to this application.

[Example 1-2]
Next, Example 1-2 according to the present embodiment will be described with reference to FIG. In the embodiment 1-1, a so-called spatial image processing method is performed in which a predetermined pixel area is divided into a high-luminance pixel and a low-luminance pixel. However, in this embodiment, the image is brightened or darkened at predetermined time intervals. It has a feature in that it is a so-called temporal image processing method.

  FIG. 6 is a diagram for explaining the image processing of this embodiment. A frame (hereinafter, referred to as a high luminance frame) T1 that is brighter than the luminance level A of an unprocessed image and a frame (hereinafter, referred to as a low luminance frame) T2 that is darkened are provided for one pixel. In frame T1, luminance level B (luminance level B> luminance level A) is assumed, and in frame T2, luminance level C (luminance level C <luminance level A) is assumed. The luminance level in each frame is set so that the average luminance by the combination of the high luminance frame T1 and the low luminance frame T2 is the same as the luminance of the unprocessed image. According to the temporal image processing method according to the present embodiment, it is possible to realize the relaxation of distortion in the same manner as in the embodiment 1-1.

  FIG. 6 shows an example in which conversion to light and dark is performed temporally at a ratio of 1: 3. One low-brightness frame T1 is continuously followed by three low-brightness frames T2. The one set of high luminance frame T1 and the three low luminance frames T2 is set as one set T, and the set T is repeated in time series. If this is performed on the entire screen, it is possible to suppress screen roughness and the like as in Example 1-1, but on the other hand, flicker is visually recognized. It is known that flicker cannot be seen if it becomes a 60 Hz component. When driving at a frame frequency of 60 Hz, a flicker of 15 Hz components due to the high luminance frame T1 is visually recognized. If the ratio of the high-luminance frame T1 and the low-luminance frame T2 is 1: 1, the flicker factor can be set to 30 Hz, so that the flicker can be considerably reduced. Furthermore, if the ratio of the high-luminance frame T1 and the low-luminance frame T2 is 1: 1 and the frame frequency is increased to 120 Hz, the flicker factor becomes 60 Hz, so that flicker cannot be seen by human eyes.

  It should be noted that the image processing method according to the present embodiment may be performed on the LCD side or the system side as described in the embodiment 1-1.

[Example 1-3]
Next, Example 1-3 according to the present embodiment will be described with reference to FIGS. This embodiment is characterized in that both the roughness and the flicker are made more difficult to see by combining the image processing method of the embodiment 1-1 and the image processing method of the embodiment 1-2. In the present embodiment, the brightness of the entire screen is not changed at once for each frame as in the embodiment 1-2, but the high-luminance pixel and the low-luminance pixel in the predetermined pixel unit as in the embodiment 1-1. And the brightness is changed for each frame.

  FIG. 7 schematically shows a predetermined pixel group in the display area of the LCD in order to explain the image processing method of the present embodiment. Specifically, 16 pixels in a 4 × 4 matrix are represented by 1 An example in which the brightness of each pixel is set is shown as one unit. In FIG. 7A, the contrast of 16 pixels in each frame is divided into a ratio of 1: 3 while preventing the high-brightness pixels from being adjacent to each other at the edges. In FIG. These 16 pixels are divided into 1: 1 ratios so that the high luminance pixels are not adjacent to each other at the edges. Further, the brightness for each pixel is changed for each predetermined number of frames. For example, in FIG. 7A, the brightness for each frame is set to change at a cycle of 1: 3 for each pixel. For example, paying attention to the pixel 5, the pixel 5 changes from bright to dark to dark to dark from the first frame to the fourth frame.

  In FIG. 7B, the brightness for each frame is set to change at a cycle of 1: 1 for each pixel. For example, when attention is paid to the pixel 6, the pixel 6 changes from light-dark-light-dark from the first frame to the fourth frame.

  When the period from the first frame to the fourth frame was set to 60 Hz and the light / dark time ratio was set to 1: 1, and the display quality was confirmed, it was possible to realize a display in which the feeling of roughness was sufficiently relaxed and flicker was not visually recognized. .

  FIG. 8 shows the result of visual evaluation of the effect of roughness in this example. It can be seen that the roughness is greatly reduced as compared with FIG. Therefore, the present invention can also be applied to the case where the liquid crystal display device is used close to the user like a monitor for a personal computer, and an improvement effect having a high viewing angle dependency can be obtained in most applications.

  Furthermore, when the display is limited to a moving image display such as a TV application, it is more difficult to recognize the roughness because the image is moving. FIG. 9 shows the result of visual evaluation of the effect of roughness in moving image display, and the result shows that the image processing method of this embodiment can be used without worrying about the feeling of roughness when applied to a product limited to moving image display applications. ing.

  It should be noted that the image processing method according to the present embodiment may be performed on the LCD side or the system side as described in the embodiment 1-1.

FIG. 10 shows the same video as in FIG. 35B on the MVA-LCD, and the red (R), green (G), and blue (B ) A gradation histogram of three primary colors is shown. The horizontal axis represents gradation (for example, 256 levels from 0 to 255, and the brightness becomes higher as it approaches 0), and the vertical axis represents the existence ratio (%). In FIG. 35 (b) showing the problem of the prior art, the color distribution in the oblique direction approaches and the display of the original color is lost. However, when this embodiment is applied, as shown in FIG. In particular, it can be seen that the distribution of green (G) moves away from red (R) and approaches the original color. The reason why it is relatively dark compared to the front is that the luminance distribution of the backlight is oblique and dark compared to the front, and is not caused by the LCD.
As described above, according to the present embodiment, an image processing method having a wide viewing angle and excellent color reproducibility and a liquid crystal display device using the image processing method can be realized very easily.

[Second Embodiment]
Next, an image processing method according to a second embodiment of the present invention and a liquid crystal display device using the same will be described with reference to FIGS. The purpose of this embodiment is to improve halftone color reproducibility using a vertical alignment type liquid crystal display device in which the black luminance is least affected by the viewing angle, and in particular, the slant that is a drawback of the liquid crystal display device. Provided are an image processing method and a liquid crystal display device using the image processing method, which can sufficiently reduce a change in display direction by an easy method.

  In this embodiment, an image conversion processing method that can convert an input video signal of the same gradation into a plurality of different gradations and easily obtain an effect of improving gradation viewing angle characteristics will be described. First, the basic principle of the image processing method of the present embodiment will be described with reference to FIGS. 6 and 7 again. The image processing method according to the present embodiment does not change the brightness of the entire screen for each frame as in the case of Example 1-2, but is a bright pixel within a predetermined pixel unit as in Example 1-3. The basic concept is to improve the gradation viewing angle characteristics by dividing the pixel into dark pixels and changing the brightness for each frame.

  Such image processing is performed when, for example, a 6-bit source driver IC has a small number of output gradations and outputs a gradation number greater than the output gradation number, for example, 8-bit multi-gradation display (256 gradations). And is known as the dithering method. The dithering method can provide only two gradations of contrast, whereas the image processing method of the present embodiment is characterized in that contrast of two or more gradations can be added. Depending on the conditions, it is possible to add a luminance difference of 250/255 gradations, which is a completely different technique from the conventional dithering method.

  If a luminance difference is provided between the high-luminance pixel and the low-luminance pixel, the luminance when viewed from an oblique direction can be changed without changing the luminance at the front. FIG. 11 shows the result of measuring the luminance obtained in the oblique direction of the screen by performing image processing on the 127/255 gradation unprocessed image. The horizontal axis represents the gradation difference between the high luminance pixel and the low luminance pixel, and the vertical axis represents the luminance in the oblique direction of 127/255 gradation. As apparent from FIG. 11, the luminance in the oblique direction tends to decrease as the gradation difference between the high luminance pixel and the low luminance pixel increases. By controlling the gradation difference between high- and low-luminance pixels at the time of gradation conversion for each gradation of the unprocessed image using this characteristic, the diagonal image can be viewed without affecting the quality of the front image. It becomes possible to improve the quality of the viewed image.

  FIG. 12 is a block diagram of a system side device such as a personal computer (hereinafter referred to as “system device”) and a liquid crystal display device, and is a diagram for explaining a gradation conversion processing unit. FIG. 12A shows an example in which the gradation conversion processing is performed by the interface circuit 25 that is a component of the liquid crystal display device 24. In this case, since all image processing is performed on the liquid crystal display device 24 side, the interface specification between the system device 26 and the liquid crystal display device 24 is not different from the conventional one, and the liquid crystal display device 24 maintains compatibility with the conventional liquid crystal display device. be able to. FIG. 12B shows an example in which image processing is performed by an image conversion device 27 provided in the system device 26, and a video signal after image processing is output to the liquid crystal display device 28. For example, internal processing of an image processing LSI provided in a video card of a personal computer, a video camera / deck, or the like is applicable. FIG. 12C shows a method for converting a video signal between the liquid crystal display device 30 and the system device 26 by using, for example, a video card 29 or the like. FIG. 12 (d) shows an example in which a physical mechanism such as a video card is not provided, the software is processed by the program of the system device 31 and then output to the liquid crystal display device 32. In any case of FIGS. 12A to 12D, the same effect can be obtained on the display screen.

In this embodiment, the same effect as that of Example 1-1 can be obtained. In other words, the effect of distortion is distributed to two locations by dividing the frame into a high-luminance frame and a low-luminance frame, and the value of the distortion effect evaluation number becomes small, so that the white-brown image observed when viewed from an oblique direction Occurrence can be greatly suppressed.

  FIG. 13 is a diagram for explaining another effect in the present embodiment, and is a schematic diagram of a cross-sectional structure of the pixel 33. In the pixel 33 of the vertical alignment type liquid crystal display device, liquid crystal is injected between the counter substrate 34 and the TFT substrate 35. A counter electrode 36 is formed on the counter substrate 34, and a protrusion 40 that defines the direction in which the liquid crystal molecules 39 are tilted is formed on the counter electrode 36. An alignment film 37 is formed on the counter electrode 36 and the protrusions 40. A pixel electrode 38 and an alignment film 37 are stacked on the TFT substrate 35. A slit 41 is formed on the TFT substrate 35 side, and defines the direction in which the liquid crystal molecules 39 are tilted in the same manner as the protrusion 40. In the structure of the pixel 33, when the liquid crystal responds at a high speed, a slight difference in response occurs in the pixel 33 region, and the response difference affects display quality. In the vicinity of the projection 40, the slit 41, and the like shown in the virtual circle A, the liquid crystal molecules 39 have a clear response direction because the direction in which the liquid crystal molecules 39 are tilted is clear. However, in the region indicated by the virtual circle B away from the protrusion 40, the slit 41, etc., the liquid crystal response is slow because the direction in which the liquid crystal molecules 39 fall is unclear. Therefore, if light and dark are repeated at high speed, even if the same voltage is applied to the pixel 33, the angle at which the liquid crystal molecules 39 fall within the pixel 33 is different from the ideal state, and the luminance is divided in a very fine area. Area halftone phenomenon occurs. When the area halftone phenomenon occurs, the dispersion of distortion occurs as described with reference to FIG.

  As described above, according to the present embodiment, the distortion caused by the luminance when viewed from an oblique angle is higher than the luminance when viewed from the front is reduced, thereby suppressing the phenomenon that the entire display becomes whitish. Can do. Furthermore, the present embodiment can obtain the same effect by means much easier than the HT method based on the conventional capacitive coupling called image processing.

  If the effect of this embodiment is used, the image quality at an oblique viewing angle can be improved without increasing the drive voltage or decreasing the aperture ratio as in the HT method by capacitive coupling. When converting an unprocessed image into a high luminance pixel and a low luminance pixel, the luminance difference between the high luminance pixel and the low luminance pixel is changed. In the conversion, the vividness of the image can be adjusted by changing only the gradation characteristics in the oblique direction without affecting the display quality of the front.

Hereinafter, it demonstrates more concretely using an Example.
[Example 2-1]
Example 2-1 according to the present embodiment will be described with reference to FIGS. FIG. 14 is a gradation conversion table for determining the gradation of the unprocessed image to be set after image processing when the high-luminance frame period and the low-luminance frame period are divided at a ratio of 1: 1. is there. In the graph, a curve A indicated by a solid line represents a gradation conversion characteristic of a high luminance frame, a curve B indicated by a broken line represents a gradation conversion characteristic of a low luminance frame, and a curve C indicated by a one-dot chain line represents Ref (reference). ing. For example, when the luminance of the unprocessed image is 128/255 gradation, the high luminance frame is converted from the curve A to 215/255 gradation, and the low luminance frame is converted from the curve B to 0/255 gradation. The ratio of each frame period is 1: 1, and the luminance after conversion actually displayed on the liquid crystal panel is the combined luminance of both frames. Even if the conversion is performed, the luminance of the front surface maintains the luminance of the unprocessed image. Further, the effect of the image conversion process becomes weaker as the curve C is approached.

The gradation conversion table is only an example. The only restriction in gradation conversion is that the front luminance does not change before and after gradation conversion. If the restriction is satisfied, there are many gradation conversion tables in addition to the gradation conversion table. FIG. 15 shows another gradation conversion table. The horizontal axis represents input gradation, and the vertical axis represents output gradation. Curves A, B, and C in the figure again show the same curves as in FIG. A curve plotted with a mark ■ shown between the curve A and the curve C is a gradation conversion characteristic for a high-luminance frame, and plotted with a mark ● shown between the curve B and the curve C. The curve shown is the tone conversion characteristic for the low-luminance frame.
FIG. 11 shown above shows the measurement result of the luminance in the oblique 60 ° direction when image processing is performed on an unprocessed image of 127/255 gradation. The image processing of FIG. 11 uses the gradation conversion table of FIG. 15, and the brightness difference between the high brightness frame and the low brightness frame is set so that the front brightness maintains the brightness of the unprocessed image. As apparent from FIG. 11, the luminance in the oblique 60 ° direction becomes darker as the luminance difference between the high luminance frame and the low luminance frame increases, and becomes brighter as the luminance difference decreases.

  In this embodiment, the frame periods of the high-luminance frame and the low-luminance frame are set to be equal. However, when the ratio of the frame periods is changed, for example, the number of low-luminance frames is increased and the high-luminance frame is shortened, the oblique direction The brightness adjustment range can be expanded. However, if the ratio is deviated from 1: 1, the frame period of the high-luminance frame and the low-luminance frame is extended, so that flicker is visible. In this case, the user may feel uncomfortable. The flicker can be reduced by increasing the frame frequency. For example, when the ratio of each frame of a high-luminance frame and a low-luminance frame is 1: 1, a minimum of 60 Hz is necessary, and preferably 70 Hz or more. When the ratio is 1: 3, a minimum of 120 Hz is required, and preferably 150 Hz or higher.

  Next, a method for converting to a clearer image using the gradation conversion table will be described. FIG. 16 is a diagram showing the gradation-luminance (GL) characteristics viewed from the front direction of the screen and from an oblique 60 ° direction. A curve A indicated by a solid line plotted with □ in the graph indicates the GL characteristics of the unprocessed image, and curves B and C indicated by solid lines plotted with an asterisk (*) and a triangle (Δ) are gradation conversion tables (not shown). The G-L characteristic seen from the direction of 60 ° obliquely after the conversion is shown, and the curve D shown only by the solid line shows the GL characteristic in the front direction. Curve B and curve C are converted by different gradation conversion tables. When the characteristics of curve A, curve B, and curve C are compared, curve A is brightest, and curve C and curve B are darker in this order. Further, the gradation conversion table is designed so that the curve B and the curve C become closer to the curve A toward the higher gradation side and become brighter. In the curve A where image processing is not performed, the luminance in the oblique 60 ° direction is higher than the luminance in the front direction on the low gradation side indicated by the range E, and lower than the luminance in the front direction on the high gradation side. Furthermore, color purity will fall. However, in the curves B and C converted using the gradation conversion table, the brightness on the low gradation side is reduced without reducing the brightness on the high gradation side, so that the vividness of the image can be maintained.

  However, in the case of an image having gradation as shown in FIG. 17, even if the gradation conversion table based on the curve B or C is used, the effect of improving the image quality is small. For example, in the case of FIG. 17A, the luminance of all three gradations marked with ● in the figure is lowered, so that the image quality is not clear. In order to improve this, it is necessary to use a gradation conversion table closer to the curve A than the curve C. However, in this case, as shown in FIG. 17B, all are the same as the curve A, so that no improvement effect can be obtained. Therefore, when conversion is performed using one type of gradation conversion table, there is a possibility that an improvement effect cannot be obtained depending on the display image. Therefore, in this embodiment, as shown in FIG. 18, by using a plurality of gradation conversion tables at the same time, if the magnitude of gradation conversion is changed for each display image, the sharpness inherent in the image is viewed from an oblique direction. Can also be realized.

  As described above, according to this embodiment, by performing image processing using a plurality of gradation conversion tables, only the luminance on the low gradation side can be reduced without reducing the luminance on the high gradation side of the input video signal. As a result, the gradation characteristics in the oblique direction change, and the display screen viewed from an oblique direction can be prevented from being whitish and good display characteristics can be obtained.

[Example 2-2]
Next, Example 2-2 according to the present embodiment will be described with reference to FIG. This embodiment is characterized in that a gradation conversion table is provided for each color (red, green, blue: RGB), and image processing is performed by changing the gradation conversion table for each RGB. The phenomenon that the luminance increases when viewed from an oblique angle as compared to when viewed from the front is due to the birefringence of the liquid crystal. The influence of birefringence varies depending on the wavelength of light, and the lower the wavelength, the greater the influence. Therefore, it is affected by birefringence in the order of blue, green and red. Therefore, red uses the gradation conversion table with the smallest luminance difference between the high luminance pixels and the low luminance pixels, blue uses the gradation conversion table with the largest luminance difference, and green has a larger luminance difference than red and blue. A smaller intermediate tone conversion table is used. For example, in FIG. 18, red is converted so as to obtain a characteristic like curve A, green is converted so that a characteristic like curve B is obtained, and blue is converted so that a characteristic like curve C can be obtained. To do. It is also effective to reduce the brightness difference by red. This is because humans react sensitively to colors based on red, such as flesh and skin color. It is also effective to increase the luminance difference by green. This is because human visibility is the highest for green. Although this embodiment can greatly improve the vividness of an image, the entire image is slightly colored in a specific color when viewed from an oblique direction. For example, when red is converted by reducing the luminance difference in order to increase the luminance when viewed from an oblique direction, gray or the like is colored red and an overall red impression is received.

  Next, the gradation conversion method of this embodiment will be specifically described with reference to FIG. FIG. 19 is a flowchart of the gradation conversion method of this embodiment. First, a video signal is input (step S1). Next, when the color of the input video signal is determined to be red (step S2), a gradation conversion table having the minimum luminance difference between the high luminance pixel and the low luminance pixel is selected (step S3), and the conversion process is performed. Performed (step S7). When it is determined that the color of the input video signal is green (step S4), a gradation conversion table having a medium luminance difference between the high luminance pixels and the low luminance pixels is selected (step S5), and conversion processing is performed (step S7). . When the input video signal is neither red nor green, the high luminance pixel and the low luminance pixel are set (step S7). The gradation conversion is performed by repeating the above operation.

  As described above, according to the present embodiment, image processing is performed by changing the gradation conversion table for each RGB, so that the display screen viewed from an angle can be prevented from being blurred and display characteristics with excellent color purity can be obtained. be able to.

[Example 2-3]
Next, Example 2-3 according to the present embodiment will be described with reference to FIG. This embodiment is characterized in that the gradation conversion table is used for each color by comparing the RGB luminance differences. The comparison of the luminance difference between RGB may be performed on the entire screen, may be performed within a predetermined range, or may be performed on RGB constituting one pixel. For the color in which the gradation of the unprocessed image is distributed on the highest luminance side, a gradation conversion table having the smallest luminance difference between the high luminance pixels and the low luminance pixels is used. If the luminance difference between RGB is very large, the conversion process need not be performed. A gradation conversion table having a large luminance difference is used for colors other than the color distributed on the highest luminance side. As a result, not only the color tone of the entire image but also the screen with different color tone locally, etc., the vividness increases on all screens, and a very beautiful video can be obtained even when viewed from an oblique direction.

Next, the gradation conversion method of the present embodiment will be specifically described with reference to FIG. FIG. 20 is a flowchart of the gradation conversion method of this embodiment. First, a video signal is input (step S11). Next, among the colors of the input video signal, a color whose gradation is distributed on the highest luminance side is determined (step S12). When it is determined in step S12 that the gradation is distributed to the highest luminance side, the luminance of the color determined to be the highest luminance side is compared with the luminance of other colors (step S13). If there is no color having the same luminance among the other colors, a gradation conversion table having a minimum luminance difference between the high luminance pixel and the low luminance pixel is selected (step S14), and conversion processing is performed (step S15). If there is a color having the same luminance in step S13, a gradation conversion table having the maximum luminance difference between the high luminance pixel and the low luminance pixel is selected (step S16), and conversion processing is performed (step S15). In step S12, a gradation conversion table in which the luminance difference between the high luminance pixel and the low luminance pixel is the largest is selected for the other colors whose gradation is not determined to be distributed on the highest luminance side (step S16). Conversion processing is performed (step S15). The gradation conversion is performed by repeating the above operation.

  As described above, according to the present embodiment, since the RGB luminance difference is compared and the gradation conversion table is used for each color and image processing is performed, it is possible to prevent the display screen from being viewed obliquely. Thus, display characteristics with better color purity can be obtained.

[Example 2-4]
Next, Example 2-4 according to the present embodiment will be described. In the present embodiment, the same processing is performed for the luminance of a specific pixel with respect to the luminance distribution within a predetermined range, not for each RGB color. Another feature is that the luminance difference is changed depending on the relationship between the luminance of a certain pixel and the luminance of 1 to n pixels adjacent to the pixel. This embodiment is effective when emphasizing gradation of black and white brightness without emphasizing color. It is also effective for monochrome display images and monochrome display image devices that do not have RGB pixels.

[Example 2-5]
Next, Example 2-5 according to the present embodiment will be described with reference to FIGS. The present embodiment is characterized in that it is an optimal image conversion method when the relationship between the levels of gradation is switched within a range where the gradation difference of the unprocessed image is extremely small. FIG. 21 is a diagram for explaining an image conversion method. As shown in FIG. 21A, in the predetermined locations (1), (2), and (3) of the display area, the red gradation is 1 to 3 higher than the green gradation. Conversion is performed using a gradation conversion table having a large luminance difference from the luminance pixel, and green is converted using a gradation conversion table having a medium luminance difference. Since the luminance of red and green is equal in the predetermined location (4) in the display area, both the red and green are converted by the gradation conversion table having a medium luminance difference. In the predetermined locations (5), (6), and (7) of the display area, the green gradation is 1 to 3 larger than the red gradation, so green is converted by a gradation conversion table with a large luminance difference, and red is Conversion is performed using a gradation conversion table having a medium luminance difference. As described above, in the case of an image in which the gradation conversion table is switched in a range where the gradation difference of RGB is small, depending on the gradation, the luminance difference due to the switching of the gradation conversion table becomes larger than the original gradation difference, which is unnatural. May result in a nasty image. For example, when the screen is viewed obliquely, a green-red-green-red stripe may be displayed. In the figure, the luminance of the place (4) is lower than the luminance of the places (3) and (5), resulting in an unnatural display. Therefore, when the gradation difference between RGB is small as shown in FIG. 21B, an intermediate gradation conversion table is used. If the gradation conversion table before and after the change of the RGB gradation is gradually switched, the luminance after gradation conversion does not become larger than the original luminance, so that the occurrence of display abnormality can be prevented.

  The gradation conversion table may be prepared in advance in the storage unit of the liquid crystal display device. Or you may calculate according to a gradation difference. In order to prepare the gradation conversion table in advance, it is preferable to derive it by calculation because the storage capacity for the gradation conversion table becomes large. The conversion can be easily realized by providing a function function that outputs an appropriate value from a combination of a high luminance pixel and a low luminance pixel that can be selected with respect to a gradation input in advance. For example, the function function may be a conversion equation approximated by a quadratic equation or the like. Alternatively, the storage unit may be provided with a gradation conversion table in advance.

Next, the gradation conversion method of this embodiment will be specifically described with reference to FIG. FIG. 22 is a flowchart of the gradation conversion method of this embodiment. First, a video signal is input (step S21). Next, it is determined whether there is a brighter color than the color of the input video signal (step S22). If it is determined in step S22 that there is no color brighter than the color of the input video signal, the process proceeds to step S23 to determine whether a color having the same luminance exists. If there is no color having the same luminance among the other colors, a gradation conversion table having a minimum luminance difference between the high luminance pixel and the low luminance pixel is selected (step S24), and a conversion process is performed (step S25).

  If there is a color having the same luminance in step S23, a gradation conversion table having a medium luminance difference between the high luminance pixel and the low luminance pixel is selected (step S29), and conversion processing is performed (step S25).

  If it is determined in step S22 that there is a brighter color than the color of the input video signal, the process proceeds to step S26 to determine whether there is a darker color than the color of the input video signal. If there is a darker color than the color of the input video signal, the process proceeds to step S29 to select a gradation conversion table in which the luminance difference between the high luminance pixel and the low luminance pixel is medium, and conversion processing is performed ( Step S25).

  If there is no darker color than the color of the input video signal in step S26, the process proceeds to step S27, and the brightness of the color determined to be the highest brightness side is compared with the brightness of other colors. If there is a color having the same luminance among the other colors, a gradation conversion table having a medium luminance difference between the high luminance pixel and the low luminance pixel is selected (step S29), and conversion processing is performed (step S25). . If there is no color having the same luminance in step S27, a gradation conversion table having the maximum luminance difference between the high luminance pixel and the low luminance pixel is selected (step S28), and conversion processing is performed (step S25).

  As described above, according to the present embodiment, if the gradation conversion table before and after the RGB gradation is switched is gradually switched, the luminance after gradation conversion does not become higher than the original luminance, so that the occurrence of display abnormality is prevented. be able to.

  As described above, according to the present embodiment, it is possible to realize an image processing method and a liquid crystal display device that can extremely reduce the display change in the oblique direction, which is a drawback of the liquid crystal display device, with an easy technique.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS. An object of the present embodiment is to provide an image processing method having a wide viewing angle and excellent color reproducibility in moving image display, and a liquid crystal display device using the image processing method.

  As described in the second embodiment, the luminance is separated into two values based on the gradation conversion table shown in FIG. 14, and the separated luminance is assigned to the pixels in the screen for display. By repeatedly displaying the separated luminance at a predetermined frame period, it is possible to control the luminance viewed from an oblique direction without changing the front luminance. Hereinafter, the new technology is referred to as a halftone drive (HTD) technology. The gradation conversion table for converting the gradation is exemplified in FIG. 15 described above, but there are innumerable other than this. Further, in the HTD technology, the gradation for each RGB pixel that performs color display is compared, and the darker color pixel is converted to increase the brightness difference between light and dark in the image processing, and the brighter color pixel is converted to decrease the luminance difference. As a result, the luminance difference for each color when viewed from an oblique direction becomes large, and a vivid color viewed from the front can be reproduced even when viewed from an oblique direction. Further, flicker can be prevented by a combination of HTD technology and drive polarity. The principle of the improvement effect of the HTD technique is the same as that of Example 2-1 described with reference to FIG.

Although the color loss phenomenon of an image when viewed from an oblique direction is greatly improved by the HTD technique, an abnormality may occur in the display of some images when a moving image is displayed. FIG. 23 is a diagram for explaining the principle of occurrence of the display abnormality. FIG. 23A shows the time transition of the luminance change of RGB pixels and G
It is a figure which shows the change of the brightness | luminance of the pixels 42 and 43. FIG. The horizontal axis represents time (frame), and the vertical axis represents luminance. In addition, a straight line A indicated by a solid line in the figure represents a luminance change of the G pixel, a straight line B indicated by a broken line represents a luminance change of the R pixel, and a straight line C indicated by a one-dot chain line represents a luminance change of the B pixel.

  As shown in FIG. 23A, there is an image in which the luminance of RGB is high in the order of green, red, and blue, and the luminance difference between red and green and blue is very large. A part of the image includes a moving image in which the luminance of green gradually decreases and becomes equal to the luminance of red, and then becomes lower than the luminance of red. When the moving image is moving in the screen, the G pixel has the second brightest brightness from the brightest brightness in the screen at the specific position when the nth frame changes to the (n + 1) th frame. Suddenly changes to state.

  Until the nth frame in which the G pixel has the brightest luminance, the HT process is performed using a gradation conversion table having a small luminance difference between the high luminance pixel and the low luminance pixel. However, from the (n + 1) th frame to the (n + 6) th frame in which the G pixel has the second brightest brightness, the HT process is performed using a gradation conversion table having a large brightness difference between the high brightness pixel and the low brightness pixel. Therefore, from the nth frame to the (n + 1) th frame, the gradation conversion of the HT process changes abruptly, and the luminance difference between the high luminance pixel and the low luminance pixel changes from small to large.

  FIG. 23B shows the optical response characteristics of the liquid crystals of the G pixels 42 and 43. The horizontal axis represents time (frame), and the vertical axis represents transmittance. Curves D and E indicated by solid lines in the figure represent optical responses of the G pixels 42 and 43, and straight lines F and G indicated by broken lines represent ideal luminance levels of the G pixels 42 and 43. As shown in FIG. 23B, during the period H in which the luminance difference between the high luminance pixel and the low luminance pixel is large, the response speed of the liquid crystal cannot completely follow the luminance change for each frame.

  However, in the nth frame, the luminance difference between the high luminance pixel and the low luminance pixel is small, so even in the low luminance pixel, the actual luminance is high and the actual luminance difference between the nth frame and the (n + 1) th frame is small. In the (n + 1) th frame, the response speed of the liquid crystal can follow the luminance change for each frame, and the luminance becomes higher than the period H after the frame. Therefore, bright abnormal display unevenness is displayed on the display screen when the gradation conversion table is switched. Even in the (n + 7) th frame in which green becomes brighter than red again, display abnormality occurs due to the same cause.

  In this way, display defects occur in the portion where the conversion table is suddenly switched by a slight gradation difference between RGB pixels. In addition, since the difference in brightness between high-brightness pixels and low-brightness pixels is naturally reduced in low-gradation images, the effect of preventing the phenomenon that the oblique brightness increases and the color falls off white is reduced. have.

  In this embodiment, in an image having a moving image in which the gradation of each color gradually approaches and the order is changed, the luminance of the high-luminance pixel and the low-luminance pixel converted with respect to the same input gradation It is characterized in that the display abnormality that occurs because the difference changes abruptly can be improved.

Examples will be described in detail below.
[Example 3-1]
Example 3-1 according to the third embodiment of the present invention will be described with reference to FIGS. FIG. 24 is a diagram for explaining the principle of image conversion according to the embodiment 3-1. When the pixel A, which has higher luminance than the pixel B in the nth frame, has a lower image luminance than the pixel B in the (n + 1) th frame, the n + 1th pixel so that the luminance difference between the high luminance pixel and the low luminance pixel does not change significantly for the pixel A. If a process for suppressing a change in luminance at a frame is performed, display defects can be prevented. Thus, in order to prevent display defects in a moving image, it is important to prevent a sudden luminance difference between a high luminance pixel and a low luminance pixel.

  In the present embodiment, in order to alleviate a sudden change in luminance between frames, a frame memory is used to evaluate the state of gradation change of the preceding and succeeding frames, and one or more frames without greatly changing the luminance difference. To alleviate the brightness change. FIG. 25 shows an embodiment of an image in which the luminance of RGB is higher in the order of green, red, and blue, and the green luminance of the moving image in which the luminance difference between red and green and blue is very large gradually decreases and becomes lower than the luminance of red. It is a figure for demonstrating the image conversion processing method of this. FIG. 25A shows the optical response of the liquid crystal when the conventional HT treatment is performed. The horizontal axis represents the frame, and the vertical axis represents the luminance. In addition, a straight line A indicated by a solid line in the figure represents a luminance change of the G pixel, a straight line B indicated by a broken line represents a luminance change of the R pixel, and a straight line C indicated by a one-dot chain line represents a luminance change of the B pixel. In addition, a curve D indicated by a solid line in the drawing represents the optical response of the G pixel 44, and a straight line F indicated by a broken line represents the luminance level of the G pixel 44.

  As described with reference to FIG. 23, abnormal display unevenness in which the luminance is increased occurs in the nth frame in which the luminance order is changed. Therefore, when the image data in the frame memory is compared and the luminance order of a certain color is lowered between frames and the luminance difference between the high luminance pixel and the low luminance pixel in the gradation conversion table becomes large, FIG. ) To forcibly lower the brightness as shown in FIG. In the first method, as shown in FIG. 25B, in the (n + 1) th frame immediately after the gradation conversion table is switched, the pixels to be high luminance pixels are forcibly darkened. In this way, the pixel remains in a dark state until the n + 3th frame for the next high luminance pixel.

  In the second method, as shown in FIG. 25C, the brightness of the high brightness pixel is lowered in the (n + 1) th frame immediately after the gradation conversion table is switched. In the third method, as shown in FIG. 25 (d), in the (n + 1) th frame immediately after the gradation conversion table is switched, the gradation that was originally input without performing HT processing for only one frame where the pixel should be a high luminance pixel is input. Outputs the street brightness. When these methods are implemented, even if a moving image having a portion where the gradation conversion table is switched moves in the image, display defects are not seen. It should be noted that display abnormality can also be prevented for the n + 7th frame by the same method.

  As described above, according to the present embodiment, it is possible to suppress a display abnormality that occurs when the luminance of RGB pixels is close to each other and the order of the luminance of the RGB pixels is switched. Obtainable.

[Example 3-2]
Next, Modification 3-2 according to the present embodiment will be described with reference to FIGS. In this embodiment, the luminance difference between the high-luminance pixel and the low-luminance pixel for gradation conversion is changed in the order of the luminance of the RGB pixels as in the conventional case, but the luminance difference of the conversion is changed as the luminance difference of the RGB pixels approaches. It has a feature in that it is gradually changed. FIG. 26 is a diagram for explaining an image conversion processing method in the present embodiment. In FIG. 26, a curve A indicated by a solid line indicates the gradation of the input video signal of the R pixel, a curve B indicated by a broken line indicates the gradation of the input video signal of the G pixel, and a straight line C indicated by the alternate long and short dash line indicates the B pixel. The gradation of the input video signal is shown. Furthermore, curves D and E plotted with ▲ and △ marks in the same figure indicate gradations after the HT processing of the R pixel, and curves F and G plotted with ■ and □ marks are after the HT processing of the G pixel. Curves H and I plotted with x and * indicate the gradation of the B pixel after the HT processing. As shown in FIG. 26, the luminance difference between the high luminance pixel and the low luminance pixel is gradually changed at the display positions 15 to 30, so that it can be seen that the gradation after the HT processing is also gradually changed. If the gradations are sufficiently separated, a basic gradation conversion table is used.

In the present embodiment, the display abnormality of an image whose luminance rapidly changes spatially is alleviated. That is, gradation conversion is performed in consideration of not only the luminance order of RGB colors but also luminance differences. By making the gradation difference smaller as the luminance difference is smaller, a sudden change can be mitigated.

  FIG. 27 is a diagram for explaining selection transition of the gradation conversion table with respect to the input gradation. FIG. 27A shows the gradation distribution of each RGB color of an image. The horizontal axis represents time, and the vertical axis represents gradation. In the figure, a straight line indicated by a solid line represents a change in gradation of the G pixel, a straight line indicated by a broken line represents a change in gradation of the R pixel, and a straight line indicated by a one-dot chain line represents a change in gradation of the B pixel. FIG. 27B shows a gradation conversion table switching method when the gradations of the respective colors gradually approach as shown in FIG. In this example, three sets of gradation conversion tables are prepared in accordance with the three colors of RGB, for a total of six tables. The gradation conversion table used by the brightest color is the high luminance side Ah (x) and the low luminance side Al (x), and the gradation conversion table has the smallest luminance difference compared to other gradation conversion tables. Is set to The gradation conversion tables used for the darkest color are the high-luminance side Ch (x) and the low-luminance side Cl (x), and are set so that the luminance difference is the largest compared to the other gradation conversion tables. . The gradation conversion table for the second brightest color is the high luminance side Bh (x) and the low luminance side Bl (x), which is larger than the luminance difference between the high luminance side Ah (x) and the low luminance side Al (x) and The gradation conversion table is set so as to be smaller than the luminance difference between the high luminance side Ch (x) and the low luminance side Cl (x).

  If the gradation difference between the G pixel and the R pixel is sufficiently separated, the gradation conversion table for the high luminance side Ah (x) and the low luminance side Al (x) is used for the G pixel. However, as shown in FIG. 27A, when the gradation between the G pixel and the R pixel gradually approaches and the gradation difference n between the G pixel and the R pixel becomes equal to or less than the set value N, the conversion value of the G pixel becomes R It approaches the pixel (period A). If the high luminance side of the conversion value of the G pixel at this time is Green_h, Green_h = Bh (x) − {Bh (x) −Ah (x)} × n / N. Further, when the low luminance side is Green_l, Green_l = Bl (x) + {Al (x) −Bl (x)} × n / N. Therefore, the high luminance side Green_h and the low luminance side Green_l are linearly interpolated by the gradation difference n as shown by solid lines in the figure, and when n = 0, intermediate Bh (x) and B1 (x ) Converges to the gradation conversion table.

  If the gradation difference between the R pixel and the B pixel is sufficiently separated, the gradation conversion table for the high luminance side Ch (x) and the low luminance side Cl (x) is used for the B pixel. However, as shown in FIG. 27A, when the gradation of the R pixel and the B pixel gradually approaches and the gradation difference n between the R pixel and the B pixel becomes equal to or less than the set value L, as shown in FIG. On the other hand, the conversion value of the B pixel approaches the R pixel (period B). If the high luminance side of the B pixel conversion value at this time is Blue_h, then Blue_h = Bh (x) + {Ch (x) −Bh (x)} × n / L. If the low luminance side is Blue_l, then Blue_l = Bl (x)-{Bl (x) -Cl (x)} * n / L. Therefore, the high luminance side Blue_h and the low luminance side Blue_l are interpolated linearly by the gradation difference n as shown by a broken line in the figure, and when n = 0, intermediate Bh (x) and B1 (x ) Converges to the gradation conversion table.

That is, when RGB gradations are close to each other, intermediate gradation conversion tables Bh (x) and Bl (x) are used as gradation conversion tables for all colors. The gradation conversion table includes a gradation conversion table Ah (x) and Al (x) for bright colors and a gradation conversion table Ch (x) and Cl (x) for dark colors as the gradation difference increases. It will approach one of them in a straight line. As a result, even in a moving image in which display abnormality is likely to occur, a luminance difference in the HT gradation conversion table does not suddenly occur, and thus display abnormality does not occur. As the setting values N and L are larger, the gradation conversion table changes more slowly, so that display defects are less likely to occur, but the effect of HTD is weakened. FIG. 27C shows the result of visual evaluation of the relationship between the set value N, the display defect prevention effect, and the HTD effect. The circles in the figure indicate that good display can be obtained for all images, the triangles indicate that display abnormalities may occur depending on the specific image, and the x marks indicate abnormal display for all images. Is generated. The setting value N is 2 or more and 64 for 255 gradation display.
The following is a good range.

  As described above, according to the present embodiment, it is possible to suppress a display abnormality that occurs when the luminance of RGB pixels is close to each other and the order of the luminance of the RGB pixels is switched. Obtainable.

  In some cases, it may not be sufficient to use a gradation conversion table that linearly interpolates, such as Green_h. FIG. 28 shows an actual luminance distribution measurement result by a combination of light and dark luminance differences under a certain setting condition. As shown in FIG. 28A, the equiluminance distribution is considerably curved. As shown in FIG. 28 (b), since the set value moves linearly in the luminance distribution in the linear interpolation, the front luminance changes across several bands, resulting in display unevenness. become.

The horizontal axis represents the gradation on the low luminance side, and the vertical axis represents the gradation on the high luminance side. The upper left band group in the figure shows the luminance distribution obtained by combining the low luminance side gradation and the high luminance side gradation. Areas with equal bands mean that front brightness is equal. Note that the combination of low gradations is not shown because the graph is complicated. Further, since the high luminance side gradation is higher than the low luminance side gradation, there is no data in the lower right region. If there is data, the high luminance side gradation and the low luminance side gradation indicated by Ref in the figure have line-symmetric characteristics with the same line.
As described above, the front brightness is the same within the band, but the oblique brightness is different. As it goes to the upper left, the difference in gradation between light and dark becomes larger. Therefore, in order to realize a display without display unevenness, some methods will be described in Example 3-3 and later.

[Example 3-3]
Next, Example 3-3 according to the present embodiment will be described with reference to FIG. In this embodiment, not only three sets of gradation conversion tables and six tables but also four sets of intermediate gradation conversion tables are set between the maximum luminance gradation conversion table and the intermediate luminance gradation conversion table. , With the feature of 8 tables. As shown in FIG. 29, as the number of gradation conversion tables is increased, the interpolation distance becomes shorter, and even if the curve is curved, the error is reduced and a great effect can be obtained. Therefore, it can be said that increasing the number of gradation conversion tables is a very effective method. In this embodiment, a plurality of gradation conversion tables must be stored in the storage unit. When the image processing is electrically performed by an interface circuit, the capacity of the storage unit increases, leading to high costs. Further, even if a gradation conversion table is not provided, interpolation with two or more straight lines or curves can be performed with a calculation algorithm, and the same effect as when image processing is performed with a plurality of gradation conversion tables. Can be obtained.

  As described above, according to the present embodiment, since a plurality of gradation conversion tables are used, display unevenness is generated without crossing the band of the equal luminance distribution in which the same gradation data after gradation conversion is curved. Can be prevented.

[Example 3-4]
Next, Example 3-4 according to the present embodiment will be described with reference to FIGS. This embodiment is characterized in that the luminance distribution is linear by adjusting the output tone-luminance characteristics of the source driver IC that drives the liquid crystal panel so that the luminance does not change by linear interpolation. is doing. FIG. 30A shows the luminance distribution before adjustment of the output gradation-luminance characteristics, and FIG. 30B shows the luminance distribution after adjustment. If the luminance distribution is linear, the gradation conversion table for linear interpolation does not cross the band of equal luminance distribution, so that a large burden is not imposed on the storage unit and the calculation algorithm, and the implementation is easy. If the luminance deviation is within 10%, a good display can be obtained with a moving image.

  Next, the effect of adjusting the input tone-luminance characteristic, that is, the gamma characteristic of the source driver IC will be described. In FIG. 31, the R pixel has 136/255 gradation, the B pixel has 0/255 gradation, and the G pixel moves from 0/255 gradation to 255/255 while changing from the edge of the screen to the end. This is a result of measuring how the luminance of the G pixel changes when a going image is displayed. In the figure, a curve A indicated by a solid line indicates normal (unprocessed) luminance, a curve B plotted by □ indicates non-adjusted gamma characteristic, and a curve C plotted by Δ indicates optimal gamma characteristic The curve D plotted with ● marks indicates the brightness when the gamma characteristic is optimized and the number of gradation conversion tables is increased. When the G pixel exceeds 136/255 gradations, the magnitude relationship between the luminance of the G pixel and the R pixel is reversed, so the gradation conversion table is switched, and the interpolation processing of the above embodiment is performed before and after the 136/255 gradations. . When the luminance distribution is curved in the relationship between the gradation combination and the luminance distribution (curve B), an abnormality occurs in the image because the luminance decreases by 10% or more. In the curve C in which the gamma characteristic is optimized, the luminance reduction is reduced. In curve D that optimizes the gamma characteristic and increases the number of gradation conversion tables, and narrows the interval between gradation conversion tables to facilitate linear interpolation, the decrease in luminance is greatly improved and straight line A of normal luminance is improved. You can see that Note that the smaller the decrease in luminance, the less the influence on the image, and it is necessary to suppress it to 10% or less.

  As described above, according to the present embodiment, the luminance distribution is linearized by adjusting the output gradation-luminance characteristics of the source driver IC. The generation of display unevenness can be prevented without the gradation data crossing the band of the equiluminance distribution.

[Example 3-5]
Next, Example 3-5 according to the present embodiment will be described with reference to FIG. This embodiment is characterized in that the effect of the HTD technique in the vicinity of a low gradation is enhanced. In the high gradation area, the ratio of the high luminance pixel to the low luminance pixel is 1: 1, but as the gradation becomes low, the high luminance pixels are thinned out to increase the existence ratio of the low luminance pixels. By doing so, the brightness difference naturally increases. When the brightness difference increases, the use of intermediate brightness with poor viewing angle characteristics decreases, so that viewing angle characteristics can be improved.

  FIG. 32 is a diagram for explaining a gradation setting method for enhancing the effect in the vicinity of the low gradation of the HTD technique. The existence ratio of high luminance pixels and low luminance pixels in the HTD is, for example, 1: 3 in the extremely low gradation (range A) from 0/128 gradation to 16/128 gradation, and from 17/128 gradation to 99/99. It is changed based on the input gradation so as to be 1: 2 for a low gradation of 128 gradations (range B) and 1: 1 for a medium gradation of 100/128 gradations or more (range C). FIG. 32B schematically shows the existence ratio of the high luminance pixels and the low luminance pixels in the vicinity of the low gradation. When the presence ratio of high-brightness pixels decreases, the brightness of high-brightness pixels increases and the brightness difference between high-brightness pixels and low-brightness pixels increases in order to maintain the brightness before the reduction of the presence ratio at that presence ratio. Can do. Thereby, an increase in luminance at an oblique viewing angle can be suppressed. The reason for reducing the existence ratio only on the low gradation side as in the present embodiment is that flickering becomes very noticeable if the existence ratio is reduced on the high gradation side. Since the absolute luminance is low on the low gradation side, the image is hardly adversely affected. In order to suppress flickering, it is desirable that the existence ratio of high luminance pixels and low luminance pixels is 1: 1 for all gradations. However, in this case, the effect of HT is weakened on the low gradation side. Therefore, it is effective to change the existence ratio within a range that does not adversely affect the image as in this embodiment.

  As described above, according to the present embodiment, since image processing can be performed only on the low gradation side without affecting the high gradation side, it is possible to suppress an increase in luminance in an oblique direction with almost no flickering. it can. As a result, it is possible to greatly reduce the whitishness that occurs when viewed from an oblique direction, and to obtain good display characteristics.

As described above, according to the present embodiment, suppression of display abnormality in moving images and improvement of characteristics on the low gradation side are achieved using the HTD technology that can improve the display change in which the color becomes whitish when viewed from an oblique direction. can do.

The image processing method and the liquid crystal display device using the image processing method according to the first embodiment of the present invention described above are summarized as follows.
(Appendix 1)
Combining a high-luminance pixel that is driven to be higher in luminance than the luminance data of the image to be displayed and a low-luminance pixel that is driven to be lower than the luminance data,
Determining a luminance of the high-luminance pixel and a luminance of the low-luminance pixel and an area ratio of the high-luminance pixel and the low-luminance pixel so that a luminance substantially equal to a desired luminance based on the luminance data is obtained. An image processing method.

(Appendix 2)
In the image processing method according to attachment 1,
The combination of the high luminance pixel and the low luminance pixel changes for each frame.

(Appendix 3)
In the image processing method according to attachment 1 or 2,
An area ratio between the high luminance pixel and the low luminance pixel is 1: 1 to 1:20.

(Appendix 4)
Combining a high-luminance frame that drives pixels with higher luminance than the luminance data of the image to be displayed, and a low-luminance frame that drives pixels with lower luminance than the luminance data,
The luminance of the pixel in the high luminance frame and the luminance of the pixel in the low luminance frame, and the luminance of the high luminance frame and the low luminance frame are obtained so that a luminance substantially equal to a desired luminance based on the luminance data is obtained. An image processing method characterized by determining an existence ratio.

(Appendix 5)
In the image processing method according to attachment 4,
The image processing method according to claim 1, wherein the existence ratio of the high-luminance frame and the low-luminance frame is 1: 1 to 1:20.

(Appendix 6)
In a liquid crystal display device comprising an array substrate opposed to each other with a predetermined cell gap and a liquid crystal sealed between the opposite substrates,
A liquid crystal display device comprising a drive circuit that implements the image processing method according to any one of appendices 1 to 5.

(Appendix 7)
In the liquid crystal display device according to appendix 6,
The liquid crystal has a negative dielectric anisotropy and is vertically aligned when no voltage is applied.

The image processing method and the liquid crystal display device using the image processing method according to the second embodiment of the present invention described above are summarized as follows.
(Appendix 8)
In the image processing method according to any one of appendices 1 to 5,
An image processing method characterized in that the rate of change in the correlation between the gradation in the diagonal direction of the screen and the luminance is greater after image processing than before image processing.

(Appendix 9)
In the image processing method according to attachment 8,
An image processing method, wherein the high luminance pixel and the low luminance pixel are mixed in the same frame.

(Appendix 10)
In the image processing method according to attachment 9,
The high luminance pixel and the low luminance pixel are mixed in an area ratio of 1: 1.

(Appendix 11)
In the image processing method according to any one of appendices 8 to 10,
An image processing method comprising: selecting an optimum conversion table based on a predetermined condition from a plurality of conversion tables for obtaining the luminance of the high luminance pixel and the luminance of the low luminance pixel from the input luminance data.

(Appendix 12)
In the image processing method according to attachment 11,
The image processing method, wherein the conversion table for the pixel of one color among the plurality of pixels provided for each color is different from the conversion table for the pixel of another color.

(Appendix 13)
In the image processing method according to attachment 12,
An image processing method characterized in that a difference between the luminance of the high luminance pixel and the luminance of the low luminance pixel of the red pixel is minimum at least in a predetermined luminance range.

(Appendix 14)
In the image processing method according to attachment 12,
An image processing method characterized in that image processing is not performed for red pixels.

(Appendix 15)
In the image processing method according to attachment 12,
A difference between the luminance of the high luminance pixel and the luminance of the low luminance pixel of the red pixel is minimum at least in a predetermined luminance range;
An image processing method characterized in that a difference between the luminance of the high luminance pixel and the luminance of the low luminance pixel of the blue pixel is maximum in at least a predetermined luminance range.

(Appendix 16)
In the image processing method according to attachment 12,
An image processing method characterized in that a difference between the luminance of the high luminance pixel and the luminance of the low luminance pixel of the green pixel is maximum at least in a predetermined luminance range.

(Appendix 17)
In the image processing method according to any one of appendices 11 to 16,
An image processing method comprising: comparing the luminance data of different colors and selecting the conversion table based on a luminance level.

(Appendix 18)
In the image processing method according to any one of appendices 11 to 16,
An image processing method comprising: comparing the luminance data of a plurality of pixels and selecting the conversion table based on a luminance difference.

(Appendix 19)
In the image processing method according to any one of appendices 8 to 18,
When the display device is viewed from an oblique direction, the decrease in luminance is small in the pixel (color) of the original gradation and bright, and large in the pixel (color) of the dark gradation, and from the oblique direction. An image processing method characterized in that the luminance difference of each pixel (color) does not exceed the luminance difference from the front.

(Appendix 20)
In the image processing method according to any one of appendices 19 to 26,
Compare the plurality of input luminance data, or compare the plurality of input luminance data for each color,
An image processing method characterized by not performing image processing on the brightest luminance data and the darkest luminance data among the luminance data.

(Appendix 21)
In the image processing method according to any one of appendices 11 to 20,
An image processing method comprising: comparing the plurality of input luminance data, or comparing the plurality of input luminance data for each color, selecting the conversion table, and performing image processing.

(Appendix 22)
In the image processing method according to any one of appendices 11 to 20,
Compare the plurality of input luminance data, or compare the plurality of input luminance data for each color,
A common conversion table is used when two or more colors or gradations of pixels are equal to each other.

(Appendix 23)
In the image processing method according to any one of appendices 11 to 20,
Compare the plurality of input luminance data, or compare the plurality of input luminance data for each color,
An image processing method using a conversion table obtained by interpolating from a plurality of the conversion tables when the gradation of two or more colors or pixels is within a predetermined range.

(Appendix 24)
In the image processing method according to any one of appendices 11 to 20,
Compare the plurality of input luminance data, or compare the plurality of input luminance data for each color,
An image processing method characterized in that when two or more colors or pixels have the same gradation, the conversion processing is different, and if the gradation of each color or pixel is within a predetermined range, the same gradation is processed.

(Appendix 25)
In the image processing method according to any one of appendices 8 to 24,
An image processing method characterized in that the gradation of the immediately preceding frame and the original image are compared, and if the gradation is changed more than an arbitrary number of gradations, the conversion processing to light and dark is not performed.

The above-described image processing method according to the third embodiment of the present invention and the liquid crystal display device using the same are summarized as follows.
(Appendix 26)
With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
For each of the RGB colors that are close in gradation, the gradation difference between light and dark is made different based on the gradation order of RGB, and the gradation is different depending on whether the gradation order is switched between frames or not. An image processing method characterized by using a conversion table.

(Appendix 27)
In the image processing method according to attachment 26,
An image processing method characterized in that when the gradation order is switched between frames and the gradation difference between light and dark becomes larger than that of the previous frame, the gradation of a pixel set to start from light luminance is corrected to be darker. .

(Appendix 28)
In the image processing method according to attachment 26,
When the gradation order is switched between frames and the gradation difference between light and dark becomes larger than that of the previous frame, even if the pixel is set to start from light luminance, one frame is set to dark luminance. An image processing method.

(Appendix 29)
In the image processing method according to attachment 26,
When the order of gradation is switched between frames, and the gradation difference between light and dark becomes larger than the previous frame, even if the pixel is set to start from bright brightness, gradation conversion is not performed for one frame. An image processing method characterized by maintaining the brightness of the toned gradation.

(Appendix 30)
With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
Multiple combinations of high-luminance and low-luminance gradation to be output with respect to the input gradation are determined in advance.
When the combination selected based on the order of gradation for each RGB color is switched, when the gradation difference between two colors AB is sufficiently separated, the high luminance side AH (x), BH (x), and the low luminance side AL ( x) and BL (x), and the gradation difference between the two colors approaches n,
The gradation on the high brightness side is
(BH (x) −AH (x)) × α / N
The gradation on the low brightness side is
(AL (x) −BL (x)) × α / N
As a result of performing correction corresponding to (α = n−m, where n = m> N, α = N, m is an arbitrary number of 0 or more), the relationship is gradually switched according to n. Conversion processing method.

(Appendix 31)
With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
There are three basic combinations of high luminance and low luminance to be output with respect to the input gradation, changing the magnitude of the luminance difference and A ≦ B ≦ C. Switch the combination selected from ABC so that the brightness difference is small, the dark color has a large brightness difference, and the intermediate color has an intermediate brightness difference. AH (x), BH (x), CH (x), low luminance side AL (x), BL (x), CL (x), and other colors have a tone difference n with respect to the intermediate luminance luminance. An image processing method characterized in that the relationship is gradually switched according to n when approaching.

(Appendix 32)
In the image processing method according to attachment 31,
In addition to the three basic combination tables for converting the gradations of the three colors, there is at least one auxiliary combination table positioned between them, and the gradation difference between colors approaches and gradually moves between the basic tables. When the process of switching to is performed, the basic table is divided into a plurality of sub tables by the auxiliary table, and converted to the gradation obtained by calculating so as to gradually switch between the basic and auxiliary or between auxiliary and auxiliary. An image processing method characterized by the above.

(Appendix 33)
In the image processing method according to attachment 31 or 32,
An image processing method, wherein a gradation width n for performing a process of gradually changing the gradation after conversion is within a range of 0/255 to 64/255 with respect to all gradations.

(Appendix 34)
With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
A plurality of combinations of high and low luminance gradations to be output with respect to the input gradation are determined in advance, and when switching the combination selected based on the gradation order for each color of RGB, high luminance and low luminance An image processing method characterized in that the average luminance is within 10% of the displacement when the input value is the same even if the combination of is changed.

(Appendix 35)
With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
An image processing method characterized in that the ratio between the bright luminance frequency A and the dark luminance frequency B tends to be B <A as the luminance of the image data to be displayed is darker.

(Appendix 36)
In the image processing method according to attachment 34,
Even if the combination of high luminance and low luminance changes, if the input value is the same, the gradation value of the driver-panel transmittance characteristic is set so that the average luminance is within 10% of the displacement. Image processing method.

(Appendix 37)
In a liquid crystal display device comprising an array substrate opposed to each other with a predetermined cell gap and a liquid crystal sealed between the opposite substrates,
A liquid crystal display device comprising a drive circuit for realizing the image processing method according to any one of appendices 8 to 36.

(Appendix 38)
In the liquid crystal display device according to attachment 37,
A liquid crystal display device having a frame frequency higher than 60 Hz.

(Appendix 39)
In the liquid crystal display device according to appendix 37 or 38,
A liquid crystal display device having at least two different response speeds in one pixel when the same voltage is applied, and a difference between the different response speeds being 3 ms or more.

(Appendix 40)
40. The liquid crystal display device according to any one of appendices 37 to 39,
Each pixel has a micro area where the alignment direction of the liquid crystal is different,
A liquid crystal display device, characterized in that the ratios of minute regions having different alignment directions of the liquid crystal are substantially equal.

(Appendix 41)
41. The liquid crystal display device according to any one of appendices 37 to 40,
The liquid crystal has a negative dielectric anisotropy and is vertically aligned when no voltage is applied.

1, 1a, 1b, 5, 6, 7, 19, 21, 33, 42, 113, 121 Pixel 2, 9, 111 Drain bus line 3, 8, 112 Gate bus line 4 Pixel region 10, 110 TFT
11, 20, 38, 109 Pixel electrode 12 Storage capacitor electrode 13, 40, 115, 116 Projection 14, 41, 114 Slit 15, 34, 103 Opposite substrate 16, 35, 102 TFT substrate 17, Dielectric 18, 36, 118 Counter electrode 20a, 20b, 20c Region 22, 37, 119 Alignment film 23, 39, 120 Liquid crystal molecule 24, 28, 30, 32 Liquid crystal display device 25 Interface circuit 26, 27, 29, 31 System device 101 Liquid crystal panel 104 Liquid crystal 105 Peripheral sealing material 106 Spacer 107 Polarizing plate 108 Mounting terminal 112 Gate bus line 117 Storage capacitor bus line 121a, 121b, 121c, 121d Subpixel 122 Control capacitor electrode 123 Insulating layers 123a, 123b, 123c, 123d Liquid crystal capacitors 124a, 124b , 24c, 124d control capacitor

Japanese Patent Laid-Open No. 3-122621 JP-A-4-348324 JP-A-5-66412 JP-A-5-107556 JP-A-6-332009 Japanese Patent Application No. 6-519211 Japanese Patent Application No.2-249025

Claims (9)

Combining a high-luminance pixel that is driven to be higher in luminance than the luminance data of the image to be displayed and a low-luminance pixel that is driven to be lower than the luminance data,
Determining the luminance of the high-luminance pixel and the luminance of the low-luminance pixel and the area ratio of the high-luminance pixel and the low-luminance pixel so that luminance substantially equal to desired luminance based on the luminance data is obtained. A featured image processing method. The image processing method according to claim 1,
The combination of the high luminance pixel and the low luminance pixel changes for each frame. The image processing method according to claim 1 or 2,
An area ratio between the high luminance pixel and the low luminance pixel is 1: 1 to 1:20. Combining a high-luminance frame that drives pixels with higher luminance than the luminance data of the image to be displayed, and a low-luminance frame that drives pixels with lower luminance than the luminance data,
The luminance of the pixel in the high luminance frame and the luminance of the pixel in the low luminance frame, and the luminance of the high luminance frame and the low luminance frame are obtained so that a luminance substantially equal to a desired luminance based on the luminance data is obtained. An image processing method characterized by determining an existence ratio. The image processing method according to claim 4.
The image processing method according to claim 1, wherein the existence ratio of the high-luminance frame and the low-luminance frame is 1: 1 to 1:20. The image processing method according to any one of claims 1 to 5,
An image processing method characterized in that the rate of change in the correlation between the gradation in the diagonal direction of the screen and the luminance is greater after image processing than before image processing. With respect to the luminance data of the image to be displayed, one frame is displayed with a luminance brighter than the luminance data, and the other frame is displayed with a dark luminance.
For each of the RGB colors that are close in gradation, the gradation difference between light and dark is made different based on the gradation order of RGB, and the gradation is different depending on whether the gradation order is switched between frames or not. An image processing method characterized by using a conversion table. In a liquid crystal display device comprising an array substrate opposed to each other with a predetermined cell gap and a liquid crystal sealed between the opposite substrates,
A liquid crystal display device comprising: a drive circuit that realizes the image processing method according to claim 1. The liquid crystal display device according to claim 8.
The liquid crystal has a negative dielectric anisotropy and is vertically aligned when no voltage is applied.

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