Patent Application
20240420657
This application claims the benefit of priority to Japanese Patent Application Number 2023-098584 filed on Jun. 15, 2023. The entire contents of the above-identified application are hereby incorporated by reference.
The present disclosure relates to liquid crystal display devices.
A liquid crystal display device is a display device that utilizes a liquid crystal composition for display and typically produces a display by applying a voltage to a liquid crystal composition enclosed between a pair of substrates and changing the alignment of liquid crystal molecules in the liquid crystal composition in accordance with the applied voltage, to control the transmission of light. Such liquid crystal display devices are used in a wide variety of fields by taking advantage of their features such as small thickness, light weight, and low power consumption.
Conventionally, it has been studied to improve the viewing angle characteristics of a liquid crystal display device so that the same image can be observed in both a narrow viewing angle range and a wide viewing angle range. On the other hand, from a viewpoint of privacy protection, a display method has been studied by which images are observable in a narrow viewing angle range, but the images are difficult to observe in a wide viewing angle range. For example, Japanese Unexamined Patent Application Publication No. 2021-67852 discloses a liquid crystal display device that can switch between narrow viewing angle mode and wide viewing angle mode by controlling the voltage applied to a third electrode provided on a color filter substrate.
According to the study by the inventors of the disclosure, when the liquid crystal display device is switched between the public mode and the privacy mode by applying a voltage to the third electrode disposed on the opposite substrate side, for example, the front luminance and coloration of the liquid crystal panel could differ between the public mode and the privacy mode.
The disclosure has been made in view of these issues and has an object to provide a liquid crystal display device that is capable of switching between the privacy mode and the public mode and also of restraining changes in luminance and coloration of the liquid crystal panel between the privacy mode and the public mode.
The disclosure can provide a liquid crystal display device that is capable of switching between the privacy mode and the public mode and also of restraining changes in luminance and coloration of the liquid crystal panel between the privacy mode and the public mode.
The following will describe embodiments of the disclosure. The disclosure is not limited to the contents described in the following embodiments, and design changes can be appropriately made within a range satisfying the configuration of the disclosure. Note that in the following description, the same portions or portions having similar functions are denoted by the same reference numerals in different drawings as appropriate, and description thereof is not repeated as appropriate. The aspects of the disclosure may be appropriately combined without departing from the scope of the disclosure.
In the present specification, a side closer to a screen (display surface) of a liquid crystal display device is also referred to as a “viewer side (front side),” and a side farther from the screen (display surface) of the liquid crystal display device is also referred to as a “rear side.” The case of observing from the normal direction of the front side is also referred to as a “plan view.”
In the present specification, the term, “horizontal,” indicates that the liquid crystal molecules have a tilt angle (including a pretilt angle) of from 0° to 5°, preferably from 0° to 3°, and more preferably from 0° to 1°, relative to the surface of a first substrate 10 or a second substrate 30. The tilt angle of liquid crystal molecules refers to the angle by which the major axis of the liquid crystal molecules is inclined to the surface of the first substrate 10.
A liquid crystal display device in accordance with Embodiment 1 includes a liquid crystal panel and a control unit for driving the liquid crystal panel. The liquid crystal panel includes a first substrate, a liquid crystal layer, and a second substrate, all of which are provided in this order. The first substrate includes either a first electrode and a second electrode stacked via a first insulating layer or a first electrode and a second electrode disposed opposite each other. The second substrate includes a third electrode. The control unit includes a display mode switching unit, a gamma correction table memory unit, a gamma correction unit, and an image data output unit. The display mode switching unit switches between narrow viewing angle mode and wide viewing angle mode by controlling a voltage applied to the third electrode. The gamma correction table memory unit stores a gamma correction table associating a gray level with a voltage applied to the first electrode and/or the second electrode. The gamma correction unit acquires a gamma correction table for narrow viewing angle mode and a different gamma correction table for wide viewing angle mode from the gamma correction table memory unit, performs gamma correction on original image data on the basis of both gamma correction tables, and outputs the obtained gamma-corrected image data to the image data output unit. The image data output unit outputs a liquid crystal panel drive signal to the liquid crystal panel to adjust the voltage applied to the first electrode and/or the second electrode.
A description is given below of a structure of the liquid crystal panel with reference to
Referring to
The plurality of picture elements preferably have optical openings each structured so as to allow light to travel through the liquid crystal panel 100. The optical opening is the region surrounded by a dotted line inside in the picture element shown in
Referring to
Note that the first substrate may have an IPS (in plane switching) electrode structure (not shown) that includes a first electrode and a second electrode disposed opposite each other. In the IPS scheme, these first and second electrodes may be disposed on the same layer (e.g., the first support substrate 11 or the first insulating layer 13).
The first support substrate 11 and a second support substrate 31 (which will be described later) are not limited in any particular manner and may be made of, for example, a resin such as polycarbonate or glass.
The first insulating layer 13 may be made of, for example, an inorganic material such as a silicon oxide or a silicon nitride.
Either one or both of the first electrode and the second electrode may include a linear electrode section that is provided in each picture element and that extends in a first direction.
The first electrode 12 may be a plate-like electrode (may be referred to as a solid electrode) with no slits or openings at least in regions overlapping the optical openings of the picture elements in a plan view. The first electrode 12 may be provided in each of a plurality of picture elements, commonly across a plurality of picture elements, or across the entire display area irrespective of the boundaries of the picture elements. The first electrode 12 may be made of, for example, a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).
One second electrode 14 is provided in each picture element. Referring to
There may be provided a plurality of first linear electrode sections 14a. Adjacent first linear electrode sections 14a may have ends thereof coupled together by an electrode material and have openings surrounded by an electrode material. In addition, the second electrode 14 may be such a comb-teeth electrode that adjacent first linear electrode sections 14a have open ends or may have a slit between adjacent first linear electrode sections 14a.
The first linear electrode section 14a may have a width of, for example, from 2 to 5 μm. The slit or opening has a width of, for example, from 2 to 5 μm. The width of the first linear electrode section 14a and the width of the slit or opening is measured perpendicular to the first direction D1.
The second electrode 14 may be made of, for example, a transparent conductive material such as ITO or IZO. The second electrode 14 may be, for example, electrically connected to an associated one of the source lines 2 via a semiconductor layer in the TFT 3.
Any one of the first electrode 12 and the second electrode 14 is preferably disposed electrically coupled, straddling the plurality of picture elements. “Straddling the plurality of picture elements” indicates such an arrangement as to overlap the plurality of picture elements across the boundaries of the plurality of picture elements. This electric coupling straddling the plurality of picture elements enables a fixed voltage that is common to the plurality of picture elements to be applied to either one of the first electrode 12 and the second electrode 14.
The liquid crystal layer 20 contains liquid crystal molecules. The liquid crystal molecules preferably have a dielectric anisotropy (Δε) with a positive value (positive type) as defined by the following formula (L). In addition, the liquid crystal molecules preferably have a homogeneous alignment under zero applied voltage (in the absence of applied voltage). The direction of the major axis of the liquid crystal molecules in the absence of applied voltage may alternatively be referred to as the direction of the initial alignment of the liquid crystal molecules. This absence of applied voltage comprehensively refers to the liquid crystal layer being placed under an applied voltage that is below the threshold value of the liquid crystal molecules.
Δε=(Permittivity of Liquid Crystal Molecules in Major Axis Direction)−(Permittivity of Liquid Crystal Molecules in Minor Axis Direction) (L)
The second substrate 30 includes a third electrode 34. The liquid crystal display device in accordance with Embodiment 1 switches between narrow viewing angle mode and wide viewing angle mode by controlling the voltage applied to the third electrode. Specifically, the liquid crystal display device switches between privacy mode and public mode by applying a drive voltage to the third electrode 34, hence generating an electric field in the thickness direction of the liquid crystal layer 20. A display method will be described later.
Referring to
Referring to
The second linear electrode section 34a may be disposed between two picture elements that are adjacent to each other in the column direction. The above-described gate lines 1 may extend in the second direction D2, which is the extension direction of the second linear electrode section 34a. Referring to
The second linear electrode section 34a has a width W34a of preferably from 25 μm to 35 μm, both inclusive, more preferably from 27 μm to 33 μm, both inclusive, and even more preferably from 29 μm to 31 μm, both inclusive. The width W34a is an electrode width of the second linear electrode section 34a in the direction that is perpendicular to the second direction D2.
The third electrode 34 may further include a third linear electrode section 34b that is disposed between the plurality of second linear electrode section 34a. The third linear electrode section 34b is preferably provided so as to extend in the second direction D2 and also to overlap the optical openings of the picture elements, in a plan view. By the third electrode 34 including the third linear electrode section 34b, the high frontal contrast can be maintained, and the contrast can be further restrained when viewed from oblique directions. In locations overlapping the optical openings of the picture elements, there may be provided either a single third linear electrode section 34b or a plurality of third linear electrode sections 34b.
The third linear electrode section 34b preferably has a smaller width W34b than does the second linear electrode section 34a. By providing the third linear electrode section 34b with a smaller width than the second linear electrode section 34a, the frontal contrast can be increased, and the contrast for oblique directions can be further restrained, in privacy mode.
The width W34b is preferably from 2.5 μm to 15 μm, both inclusive, more preferably from 3 μm to 13 μm, both inclusive, and even more preferably from 4 μm to 10 μm, both inclusive. The width W34b is an electrode width of the third linear electrode section 34b in the direction perpendicular to the second direction D2.
When there is provided a plurality of third linear electrode sections 34b, the third linear electrode sections 34b are preferably disposed at equal intervals. Adjacent third linear electrode sections 34b are separated by a distance d1 that is preferably from 3 μm to 20 μm, both inclusive, and more preferably from 9 μm to 15 μm, both inclusive.
The second linear electrode section 34a and the third linear electrode section 34b are preferably electrically connected to each other. The second linear electrode section 34a and the third linear electrode section 34b may be preferably, for example, coupled together by a connecting portion at an end of the liquid crystal panel, so that the entire third electrode 34 is placed under an equal voltage.
The third electrode 34 (second linear electrode section 34a and the third linear electrode section 34b) may be termed a horizontal stripe electrode with respect to the first direction D1. By designing the third electrode 34 as a horizontal stripe electrode, privacy protection can increased, for example, over when the third electrode 34 is disposed in the same direction as the first direction D1 (when the third electrode 34 is a vertical stripe electrode) and over when the third electrode 34 has the same shape as a black matrix. Specifically, when the display is in privacy mode, the frontal contrast can be increased, and the contrast for oblique directions (e.g., when viewed from an azimuth of from 0° to 180° and a polar angle of from 35° to 55°) can be reduced. In addition, by designing the third electrode 34 as a transverse stripe, there is provided a portion where the third electrode 34 does not overlap the optical opening, and when the display is in public mode, a vertical electric field does not readily act in the opening of the picture element. Therefore, a high transmittance and a high contrast can be achieved.
The first direction D1 and the second direction D2 make an angle θ1 that is preferably from 80° to 100°, both inclusive, and more preferably from 85° to 95°, both inclusive. The second direction D2 may be parallel to either an absorption axis 62A of a second polarizer 62 or an absorption axis 61A of a first polarizer 61. In Embodiment 1, the second direction D2 is parallel to the absorption axis 62A of the second polarizer 62 (azimuth of from 0° to 180°) as shown in
The third electrode 34 may be made of a transparent conductive material. The transparent conductive material may be, for example, ITO or IZO.
Referring to
The black matrix 33 is disposed between a plurality of picture elements. The black matrix 33 may be disposed between the optical openings that are adjacent to each other in either the row direction or the column direction or may be disposed around the optical openings in a plan view. The black matrix 33 may be a black matrix commonly used in the field of liquid crystal display devices and is made preferably of a resin and more preferably of a black resin containing a black pigment or dye.
Alignment films (not shown) may be disposed, one between the first substrate 10 and the liquid crystal layer 20 and another between the second substrate 30 and the liquid crystal layer 20. The alignment films control the initial alignment direction of the liquid crystal molecules in the absence of applied voltage. The alignment films are preferably horizontal alignment films. The horizontal alignment film is preferably specified so that the liquid crystal molecules have an initial (which refers to absence of applied voltage across liquid crystal layer) pretilt angle of from 0° to 1° with respect to the surface of the alignment film.
In addition, the first polarizer 61 and the second polarizer 62 may be disposed respectively opposite the liquid crystal layer 20 in the first substrate 10 and opposite the liquid crystal layer 20 in the second substrate 30. The first polarizer 61 and the second polarizer 62 are preferably disposed in a crossed Nicol position so that the absorption axis 61A of the first polarizer 61 and the absorption axis 62A of the second polarizer 62 are perpendicular to each other. In
The liquid crystal panel 100 may include a dielectric layer (not shown) between the third electrode 34 and the liquid crystal layer 20. The provision of the dielectric layer enables restraining the generation of a vertical electric field that is generated between the third electrode 34 and the electrode on the first substrate side in public mode. As a result, in-plane switching drive becomes possible almost without having to cause the liquid crystal molecules to stand upright. Therefore, the transmittance and frontal contrast can be increased for the front direction in a white display when the display is in public mode.
The dielectric layer is a layer other than the alignment films and is a layer made of, for example, a resin that is transparent to light. The dielectric layer preferably has a total light transmittance of greater than or equal to 80%. In the present specification, the total light transmittance is the total light transmittance measured in accordance with JIS K7361-1. The dielectric layer contains, for example, an acrylic-based resin, a polyimide-based resin, or another like resin. The dielectric layer preferably has a thickness of from 0.5 μm to 4 μm, both inclusive.
The liquid crystal display device in accordance with Embodiment 1 may include a backlight 300 on the rear side (first substrate 10 side) of the liquid crystal panel. The backlight 300 is not limited in any particular manner and may be any backlight commonly used in the field of liquid crystal display devices. The backlight 300 may be, for example, an edge-light type where a light source is disposed on an end face of a light-guide plate or a direct type where a large number of light sources are disposed in a plane along with a diffusion plate for increased uniformness.
As shown in
Referring to
The display mode switching unit 201 switches between narrow viewing angle mode and wide viewing angle mode by controlling the voltage applied to the third electrode 34. In wide viewing angle mode (public mode), the third electrode drive circuit 103 applies, as a fixed voltage, a prescribed AC voltage to the third electrode 34 on the basis of the display mode signal 212. In narrow viewing angle mode (privacy mode), the third electrode drive circuit 103 applies a drive voltage that has a different effective value from the fixed voltage to the third electrode 34 on the basis of the display mode signal 212.
In the present specification, the display mode for displaying a first image that can be viewed from a narrow viewing angle range, including the normal to liquid crystal panel, is referred to as narrow viewing angle mode, and the display mode where the first image can be viewed from a wide viewing angle range that covers the narrow viewing angle range is referred to as wide viewing angle mode. In addition, in the present specification, narrow viewing angle mode may alternatively be referred to as privacy mode, and wide viewing angle mode may alternatively be referred to as public mode.
In the narrow viewing angle range, the contrast is preferably less than or equal to 5 when the liquid crystal panel is observed from an oblique direction (at an azimuth of 0° or 180°) at a polar angle. As an example, when the direction vertical to the surface of the liquid crystal panel is taken to be a 0° polar angle, and the direction horizontal to the surface of the liquid crystal panel is taken to be a 90° polar angle, this polar angle is preferably greater than or equal to 60°, more preferably greater than or equal to 45°, and even more preferably greater than or equal to 30°. The wide viewing angle range above refers to the range of polar angles larger than the polar angles in the narrow viewing angle range.
To produce a black display in public mode, a liquid crystal panel drive signal 217 is outputted from the image data output unit 204 to the gate driver 101 and the source driver 102 while applying a prescribed AC voltage as a fixed voltage to the third electrode 34. Note that a black display is a display state where a minimum luminance is reached in each display mode, and a white display is a display state where a maximum luminance is reached in each display mode.
As an original image signal 213 is inputted to an original image data generation unit 205, an original image data 214 is outputted. When no gamma correction is performed, the original image data 214 is outputted to the image data output unit 204, and the image data output unit 204, for example, controls so as to apply a common voltage to the second electrode 14 and the first electrode 12 on the basis of the original image data 214. The common voltage is common to the fixed voltage with the fixed voltage being equal to 0 V. Note that either the common voltage applied to the second electrode 14 and the first electrode 12 may be equal to the fixed voltage or a voltage lower than a threshold value of the liquid crystal molecules with respect to the fixed voltage may be applied. Such a state may be referred to as the absence of applied voltage.
In the absence of applied voltage, since no electric field for driving the liquid crystal molecules is generated in the liquid crystal layer 20 shown in
To produce a white display in public mode, for example, while a fixed voltage is being applied to the third electrode 34, the liquid crystal panel drive signal 217 is outputted so as to apply a fixed voltage (common voltage) from the image data output unit 204 to any one of the first electrode 12 and the second electrode 14 and as to apply an AC voltage that has a different effective value from the common voltage to the other one of the first electrode 12 and the second electrode 14. A fringe field is generated between the first electrode 12 and the second electrode 14, whereas the electric field in the thickness direction of the liquid crystal layer 20 is small, which differs from privacy mode (detailed later). Therefore, the liquid crystal molecules are aligned parallel to the first substrate 10, and at the same time change their alignment direction, in the electric field generated between the first electrode 12 and the second electrode 14. By the liquid crystal molecules rotating in the plane of the liquid crystal layer 20 and hence changing their initial alignment direction, the major axis direction of the liquid crystal molecules forms an angle with the absorption axis 61A of the first polarizer and the absorption axis 62A of the second polarizer so as to transmit light from the rear face of the liquid crystal panel, hence producing a white display.
To produce a black display in privacy mode, the third electrode drive circuit 103 applies, to the third electrode, a drive voltage that differs in effective value from the fixed voltage, and the image data output unit 204 controls so as to apply the fixed voltage (common voltage) to the second electrode 14 and the first electrode 12. An oblique electric field is generated between the third electrode 34 and a combination of the first electrode 12 and the second electrode 14. The liquid crystal molecules incline with respect to the first substrate 10 in the oblique electric field.
Since the liquid crystal molecules do not change their alignment direction in the plane of the liquid crystal layer 20, the liquid crystal panel does not transmit light from the rear face, and meanwhile, the liquid crystal molecules incline with respect to the first substrate, the liquid crystal panel appears more whitish than the black display observed from a narrow viewing angle range when the liquid crystal panel is observed from a wide viewing angle range.
To produce a white display in privacy mode, while the third electrode drive circuit 103 is applying a drive voltage to the third electrode 34, the image data output unit 204 applies the fixed voltage (common voltage) to any one of the first electrode 12 and the second electrode 14 and controls so as to apply an AC voltage that differs in effective value from the common voltage to the other one of the first electrode 12 and the second electrode 14. The drive voltage applied to the third electrode 34 preferably differs in effective value from the AC voltage applied to the first electrode 12 or the second electrode 14 and more preferably has a greater effective value than the AC voltage applied to the first electrode 12 and the second electrode 14. A fringe field is generated between the first electrode 12 and the second electrode 14, and an oblique electric field with respect to the thickness direction of the liquid crystal layer 20 is generated either between the third electrode 34 and the first electrode 12 or between the third electrode 34 and the second electrode 14. As a result, an electric field that is a sum of the fringe field and the oblique electric field is generated in the liquid crystal layer 20. Therefore, under the electric field generated between the combination of the first electrode 12 and the second electrode 14 and the third electrode 34, the liquid crystal molecules incline with respect to the first substrate 10 and at the same time change their alignment direction, thereby producing a white display. Since the liquid crystal molecules incline with respect to the first substrate, the first image is observable from a narrow viewing angle range. On the other hand, when the liquid crystal panel is observed from a wide viewing angle range, the image decreases extremely in contrast or undergoes other changes, which renders it difficult to observe the first image.
The liquid crystal display device can switch between the white display in privacy mode and the white display in public mode described above by applying a voltage to the third electrode. Similarly, the liquid crystal display device can switch between the black display in privacy mode and the black display in public mode by applying a voltage to the third electrode. This description equally applies to grayscale displays.
In the liquid crystal display device in accordance with the embodiment, when the liquid crystal panel is observed from an oblique direction, high-level privacy protection is achieved by switching from wide viewing angle mode (public mode) to narrow viewing angle mode (privacy mode) as described above. Note that the oblique direction above refers to cases when the liquid crystal panel is observed from an azimuth of 0° and 180° and a polar angle of 35° to 55° when the right-hand direction of the liquid crystal panel on which a desired image is being displayed is taken to be 0°, and the angle increases counterclockwise.
According to the study by the inventors of the disclosure, when the liquid crystal display device switches between narrow viewing angle mode and wide viewing angle mode by controlling the voltage applied to the third electrode on the opposite substrate side as described above, for example, the luminance and coloration can differ between narrow viewing angle mode and wide viewing angle mode when the liquid crystal panel is observed from the front (normal direction).
Referring to
The gamma correction unit 203 acquires different gamma correction tables 215 from the gamma correction table memory unit 202 for narrow viewing angle mode and for wide viewing angle mode in accordance with the inputted display mode signal 212.
The gamma correction table memory unit 202 contains gamma correction tables that associate gray levels to application voltages to the first electrode and/or the second electrode. The gamma correction tables can be prepared by, for example, the following method. First, VT curves are generated on the basis of actual measured values by producing displays in narrow viewing angle mode and in wide viewing angle mode without gamma correction. The VT curve is a graph representing a relationship between the application voltage (V) and the luminance ratio (T). In the present specification, the “application voltage” for the VT curve refers to, when a common voltage to an electrode that is either one of the first electrode and the second electrode is taken to be 0 V, the voltage applied to the other electrode with this 0 V being taken as the reference. In the present specification, the luminance ratio is such that luminance is 0 at gray level 0 and 1 at gray level 255 when the luminance of a picture element is expressed by 256 gray levels (gray levels 0 to 255).
A gamma correction table is prepared by calculating the relationship between gray levels and predetermined voltages on the basis of the VT curve measured above in advance in such a manner that the grayscale characteristics defined by grayscale and luminance ratios have particular gamma values. Note that the graph representing a relationship between grayscale and luminance ratios may alternatively be referred to as the γ curve. In Embodiment 1, gamma correction tables are individually prepared respectively for wide viewing angle mode and for narrow viewing angle mode. A predetermined voltage is a voltage specified to be outputted from the image data output unit 204 and refers to, when a common voltage to an electrode that is either one of the first electrode and the second electrode is taken to be 0 V, the voltage applied to the other electrode with this 0 V being taken as the reference.
The relationship between the luminance ratio L, gray level G, and gamma value γ is given by following equation (1).
The gamma correction table memory unit 202 may contain a gamma correction table that shows a constant gamma value between gray levels 0 and 255. The gamma value is preferably from 1.8 to 2.6 both inclusive, more preferably from 2.0 to 2.4 both inclusive, and even more preferably equal to 2.2.
In the following, the gamma correction table used in narrow viewing angle mode may alternatively be referred to as the “gamma correction table for use in narrow viewing angle mode,” and the gamma correction table used in wide viewing angle mode may alternatively be referred to as the “gamma correction table for use in wide viewing angle mode.” The gamma correction table for use in narrow viewing angle mode and the gamma correction table for use in wide viewing angle mode may contain the same gamma value. The gamma values for wide viewing angle mode and the gamma values in the gamma correction table are preferably from 1.8 to 2.6 both inclusive, more preferably from 2.0 to 2.4 both inclusive, and even more preferably equal to 2.2.
In addition, the gamma correction table for use in narrow viewing angle mode and the gamma correction table for use in wide viewing angle mode may contain different gamma values. The gamma value in the gamma correction table used in narrow viewing angle mode is preferably lower than the gamma value in the gamma correction table used in wide viewing angle mode. This configuration can further increase privacy protection in narrow viewing angle mode.
The gamma values in the gamma correction table for use in wide viewing angle mode are preferably from 1.8 to 2.6 both inclusive, more preferably from 2.0 to 2.4 both inclusive, and even more preferably equal to 2.2. The gamma values in the gamma correction table for use in narrow viewing angle mode need only to be lower than the gamma values in the gamma correction table for use in wide viewing angle mode, but the gamma values in the other gamma correction table are preferably 1.8 or more with a view to efficiently restraining changes in coloration from the front.
For instance, when the gamma value in the gamma correction table for use in wide viewing angle mode is 2.2, the gamma value in the gamma correction table for use in narrow viewing angle mode may be 2.2. With a view to improving privacy protection from oblique directions, the gamma values in the gamma correction table for use in narrow viewing angle mode may be 2.0 or may be 1.8.
The gamma value in the gamma correction table used in narrow viewing angle mode preferably differs from the gamma value in the gamma correction table used in wide viewing angle mode by no more than 0.4. By rendering these gamma value differences no more than 0.4, it is possible to both improve privacy protection from oblique directions and lower coloration from the front. This is because although privacy protection from oblique directions improves with an increasing foregoing difference from the gamma value, if the foregoing difference from the gamma value is too large, differences in coloration grow between display modes when the liquid crystal panel is observed from the front. The foregoing difference from the gamma value is more preferably no more than 0.2.
The gamma correction unit 203 performs gamma correction respectively on original image data on the basis of different gamma correction tables in narrow viewing angle mode and in wide viewing angle mode and outputs obtained gamma-corrected image data 216 to the image data output unit 204. The gamma correction unit 203 outputs the gamma-corrected image data 216 to the image data output unit 204 in reference to the correspondence information between the gray levels and predetermined voltages in the gamma correction tables with respect to the grayscale information in the original image data 214, to obtain a desirable luminance ratio. For example, the gamma correction is performed using a gamma correction table (Table 1) for use in wide viewing angle mode shown in
The image data output unit 204 outputs the liquid crystal panel drive signal 217 to the liquid crystal panel 100 to adjust the application voltage to the first electrode and/or the second electrode described above.
By taking the VT curve characteristics of the liquid crystal panel into consideration, gamma correction is performed using different gamma correction tables respectively in narrow viewing angle mode and in wide viewing angle mode. For example, gamma correction may be performed so as to achieve such grayscale characteristics as γ=2.2, both in narrow viewing angle mode and in wide viewing angle mode. Hence, the shape of the γ curve becomes the same in narrow viewing angle mode and in wide viewing angle mode, and differences in, for example, luminance and coloration can be reduced even when the liquid crystal panel is switched between narrow viewing angle mode and wide viewing angle mode.
The luminance ratio of the γ curve is the value with the luminance at gray level 0 being equal to 0 and the luminance at gray level 255 being equal to 1 when the luminance from the front of the liquid crystal panel outputted in accordance with the gamma correction table is expressed by 256 gray levels (gray levels 0 to 255).
In Embodiment 2, the gamma correction table memory unit contains a gamma correction table in which the gamma value has a plurality of values between gray levels 0 to 255.
In Embodiment 2, either one or both of the gamma correction table for use in wide viewing angle mode and the gamma correction table for use in narrow viewing angle mode need(s) only to contain a gamma value that has a plurality of values between gray levels 0 to 255. Either one of the gamma correction table for use in wide viewing angle mode and the gamma correction table for use in narrow viewing angle mode may contain a gamma value that is constant between gray levels 0 to 255, and the other gamma correction table may contain a gamma value that has a plurality of values between gray levels 0 to 255. This configuration can render the amount of change in the luminance ratio at intermediate gray levels in narrow viewing angle mode smaller than the amount of change in the luminance ratio at intermediate gray levels in wide viewing angle mode, thereby further restraining luminance changes from the front.
More preferably, the gamma correction table used in wide viewing angle mode contains a gamma value that is constant between gray levels 0 to 255, and the gamma correction table used in narrow viewing angle mode contains a gamma value that has a plurality of values between gray levels 0 to 255.
Letting X be any gray level from 0 to 255, the gamma value in the gamma correction table used in narrow viewing angle mode may be smaller than the gamma value in the gamma correction table used in wide viewing angle mode at gray levels from 0 inclusive to X exclusive and larger than the gamma value in the gamma correction table used in wide viewing angle mode at gray levels from X to 255 both inclusive.
For instance, when the gamma value in the gamma correction table for use in wide viewing angle mode is equal to 2.2 (constant) at gray levels 0 to 255, the gamma value in the gamma correction table for use in narrow viewing angle mode may be 2.2 or lower at gray levels from 0 inclusive to X exclusive and may exceed 2.2 at gray levels from X to 255 both inclusive. The gamma correction table for use in narrow viewing angle mode preferably contains a gamma value of 2.0 or lower for gray levels from 0 inclusive to X exclusive and more preferably of 1.8 or higher with a view to achieving both visibility in narrow viewing angle mode and restraining of changes in coloration from the front. The gamma correction table for use in narrow viewing angle mode preferably contains a gamma value of 2.4 or higher for gray levels from X to 255 both inclusive and more preferably of 2.6 or lower with a view to achieving both visibility in narrow viewing angle mode and restraining of changes in coloration from the front. Arbitrary gray level X described above may be any of 64, 128, and 192. There is a trade-off between the viewing angle control capability and the effect of restraining changes in coloration from the front between narrow viewing angle mode and wide viewing angle mode.
Letting X represent any one of gray levels 0 to 255, and Y be the gray level higher than X, the gamma value in the gamma correction table used in narrow viewing angle mode may be smaller than the gamma value in the gamma correction table used in wide viewing angle mode at gray levels from 0 inclusive to X exclusive, and the gamma value in the gamma correction table used in narrow viewing angle mode may be larger than the gamma value in the gamma correction table used in wide viewing angle mode at gray levels from Y to 255 both inclusive.
For instance, when the gamma value in the gamma correction table for use in wide viewing angle mode is equal to 2.2 (constant) at gray levels 0 to 255, the gamma value in the gamma correction table for use in narrow viewing angle mode may be 2.2 or lower at gray levels from 0 inclusive to X exclusive and higher than 2.2 at gray levels from Y to 255 both inclusive. The gamma correction table for use in narrow viewing angle mode preferably contains a gamma value of 2.0 or lower at gray levels from 0 inclusive to X exclusive and more preferably of 1.8 or higher with a view to achieving both visibility in narrow viewing angle mode and restraining of changes in coloration from the front. The gamma correction table for use in narrow viewing angle mode preferably contains a gamma value of 2.4 or higher at gray levels from Y to 255 both inclusive and more preferably of 2.6 or lower with a view to achieving both visibility in narrow viewing angle mode and restraining of changes in coloration from the front.
Arbitrary gray levels X, Y described above may be any of 64, 128, and 192. Specific examples of X, Y combinations may include Y=192 at X=64, Y=128 at X=64, and Y=192 at X=128. Between gray levels X to Y, a gamma value may be specified suitably for each gray level so that the luminance ratio smoothly rises from gray level X toward gray level Y.
In Embodiment 3, privacy protection can be further improved by combining a veil view function of displaying a second image overlapping a first image as well as switching the display mode for the ordinary display of the first image. A description is given below of an exemplary method of displaying an image by the veil view function with reference to
Referring to
As the veil view switching unit 207 is fed with a veil view display switching signal 218, the veil view switching unit 207 acquires veil view pattern data 219 from the database 206 and outputs a veil view pattern image signal 220 to the above-described image data output unit 204. The image data output unit 204 combines the gamma-corrected image data 216 outputted from the above-described gamma correction unit 203 and the veil view pattern image signal 220 to output the liquid crystal panel drive signal 217 to the gate driver 101 and the source driver 102.
Since the display by the veil view function can further increase privacy protection by being combined with narrow viewing angle mode, the veil view display switching signal 218 may be inputted from the aforementioned the display mode switching unit 201 to the veil view switching unit 207 when narrow viewing angle mode is selected.
For instance, when the common voltage is applied to the second electrode 14, with respect to the first electrode 12, different voltages are applied respectively to the first electrodes 12 corresponding to the first picture element 70 and the second picture element 71 so that the second image can be viewed from a wide viewing angle range. In such cases, one first electrode 12 is preferably provided in each picture element. On the other hand, when the common voltage is applied to the first electrode 12, with respect to the second electrode 14, different voltages are applied respectively to the second electrodes 14 corresponding to the first picture element 70 and the second picture element 71 so that the second image can be viewed from a wide viewing angle range.
The first picture element 70 and the second picture element 71 may be regarded as a single picture element respectively as shown in
To produce a color display, the liquid crystal panel preferably includes a red display unit 72R including the first red picture element 70R and the second red picture element 71R, a green display unit 72G including the first green picture element 70G and the second green picture element 71G, and a blue display unit 72B including the first blue picture element 70B and the second blue picture element 71B. A color element 73 may include a red display unit 72R, a green display unit 72G, and a blue display unit 72B. The first and second picture elements of each color overlap the color filter 32R of each color in optical openings respectively.
Letting, for example, Data1 be luminance data values of an original image that one wants to display as the first image, a method for displaying an image by the veil view function involves dividing Data1 equally into two data values Data2 and Data3, inputting data values Data1+Data2 to any one of the first picture element 70 and the second picture element 71, and inputting data values Data1−Data3 to the other one of the first picture element 70 and the second picture element 71. When the liquid crystal panel is observed from a narrow viewing angle range, the luminance of the first picture element 70 and the luminance of the second picture element 71 are spatially averaged out and perceived as the luminance of the original image; on the other hand, when the liquid crystal panel is observed from a wide viewing angle range, the luminance is perceived as Data1+Data2 or Data1−Data3.
By combining the display pattern of color elements shown in
The second image is preferably a veil view pattern. The veil view pattern is a display image displayed over the first image to render it difficult to visually recognize the first image. The display of the veil view pattern can further improves privacy protection. The veil view pattern is not limited in any particular manner and may be, for example, a geometric pattern such as stripes or a checkered pattern, characters, or an image.
The following will describe effects of the disclosure by way of examples and comparative examples: the disclosure is however not limited by these examples.
Example 1 was a specific example of Embodiment 1 and included the structure shown in
The third electrode 34 was disposed on the second substrate 30. The third electrode 34 included the second linear electrode section 34a disposed along the upper and lower ends of the picture element and the two, third linear electrode sections 34b overlapping the optical openings. The second linear electrode section 34a had a width W34a of 31 μm, and the third linear electrode section 34b had a width W34b of 5 μm. The distance d1 by which adjacent third linear electrode sections 34b were separated from each other was 11 μm.
The angle θ1 made by the extension direction (first direction D1) of the first linear electrode section 14a and the extension direction (second direction D2) of the second linear electrode section 34a and the third linear electrode section 34b of the third electrode was 80°.
The fixed voltage (common voltage) was applied to the third electrode In wide viewing angle mode. As the fixed voltage, a constant voltage of 0 V was applied. An AC voltage of 4 V was applied to the third electrode with respect to the fixed voltage in narrow viewing angle mode. A grayscale display was produced by applying the common voltage (0 V) to the first electrode 12 and changing the voltage applied to the second electrode 14 both in wide viewing angle mode and in narrow viewing angle mode.
In Example 1, since the grayscale characteristics were corrected so that γ=2.2 in post-gamma correction wide viewing angle mode and in post-gamma correction narrow viewing angle mode, the resultant γ curve in wide viewing angle mode matched with the resultant γ curve in narrow viewing angle mode. Therefore, the luminance and coloration of the liquid crystal panel did not change when switched between wide viewing angle mode and narrow viewing angle mode.
In Comparative In Example 1, gamma correction was performed using the same liquid crystal panel as in Example 1 and using the same gamma correction table in narrow viewing angle mode and in wide viewing angle mode. In the comparative example, gamma correction was performed using gamma correction Table 1 shown in
In Example 2, gamma correction was performed using the same liquid crystal panel as in Example 1 and using Table 1 in wide viewing angle mode similarly to Example 1. In narrow viewing angle mode, gamma correction was performed by preparing a gamma correction table for use in narrow viewing angle mode (Table 3) specified on the basis of the VT curve for narrow viewing angle mode shown in
In Example 3, gamma correction was performed using the same liquid crystal panel as in Example 1 and using Table 1 in wide viewing angle mode similarly to Example 1. In narrow viewing angle mode, gamma correction was performed by preparing a gamma correction table for use in narrow viewing angle mode (Table 4) specified on the basis of the VT curve for narrow viewing angle mode shown in
In Example 3, again, the luminance ratio difference was smaller, and the sense of incongruity in coloration was reduced, between narrow viewing angle mode and wide viewing angle mode than in Comparative Example 1. In addition, in Example 3, the luminance ratio was higher at intermediate gray levels in narrow viewing angle mode than in Example 1, and when the liquid crystal panel was observed from an oblique direction, the visibility was lower, which indicates that privacy protection was improved over Example 1, albeit not as much as in Example 2.
Example 4 was a specific example of Embodiment 2 and used a gamma correction table containing a gamma value having a plurality of values between gray levels 0 to 255. In Example 4, gamma correction was performed using the same liquid crystal panel as in Example 1 and using Table 1 in wide viewing angle mode similarly to Example 1. Table 1 contained a constant γ value of 2.2 between gray levels 0 to 255. In narrow viewing angle mode in Example 4, gamma correction was performed by preparing a gamma correction table (Table 5) containing a γ value that varied from 2.0 to 2.4 between gray levels 0 to 255 as shown in Table 1 below.
As described above, in the liquid crystal panel 100, the visibility was reduced, and privacy protection was improved, by increasing the luminance for an oblique black display (gray level 0) in narrow viewing angle mode to extremely reduce the contrast for oblique direction. In Example 4, γ was not fixed and varied for each gray level, in narrow viewing angle mode so that γ=1.8 at gray levels less than or equal to 64 and that γ=2.6 at gray levels greater than or equal to 192. In Example 4, the contrast was reduced only at intermediate gray levels than in Example 1 by varying the γ value from 1.8 to 2.6 in the gray level range of 64 to 192. Since images in an ordinary display are often expressed by intermediate gray levels, the visibility was further reduced, and privacy protection was improved, by lowering the contrast at intermediate gray levels when the liquid crystal panel was observed from an oblique direction in narrow viewing angle mode.
Examples 5 to 7 were the same as Example 4, except that gamma correction was performed by preparing gamma correction tables (Table 6 to 8) containing a γ value that varied between gray levels 0 to 255 in narrow viewing angle mode as shown in Table 1 below.
In Example 5, the contrast was further reduced only at intermediate gray levels than in Example 1, by varying γ from 2.0 to 2.4 in the gray level range of 64 to 192. As a result, when the liquid crystal panel was observed from an oblique direction in narrow viewing angle mode, the visibility was further reduced, and privacy protection was improved.
In Examples 6 and 7, the amount of change in the luminance ratio was smaller in narrow viewing angle mode than in wide viewing angle mode respectively at gray levels 64 to 128 and at gray levels 128 to 192, and the front visibility was good in narrow viewing angle mode. In addition, in Examples 6 and 7, the contrast was reduced respectively at gray levels 64 to 128 and at gray levels 128 to 192 over Example 1.
A display image was displayed in narrow viewing angle mode on the liquid crystal display devices of the examples and the comparative example and observed from an oblique direction (from an azimuth of 0-180° and a polar angle of) 45°, to evaluate whether or not the display image was visually recognizable. Difficulty in visual recognition of the display image in narrow viewing angle mode in Comparative Example 1 was given 1 point, and the visibility in narrow viewing angle mode in each example was given from point 1 to point 3. A higher point indicates that the display image is difficult to visually recognize in narrow viewing angle mode and gives better privacy protection. The display image was a color landscape image.
The luminance was measured in the normal direction at gray level 255 in narrow viewing angle mode on the liquid crystal display devices of the examples and the comparative example, with the luminance in the normal direction at gray level 255 in wide viewing angle mode being equal to 100%. The front luminance in narrow viewing angle mode was given a ∘ mark if the front luminance was greater than or equal to 90% and a x mark if the front luminance was less than 90%.
The liquid crystal display devices of the examples and the comparative example were observed from the normal direction, and a display image was displayed. Five reviewers evaluated, by the following criteria, whether or not coloration gave a relative sense of incongruity in narrow viewing angle mode in comparison with wide viewing angle mode when the liquid crystal panel was switched between wide viewing angle mode and narrow viewing angle mode. The display image was a color landscape image.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2023-098584 | Jun 2023 | JP | national |
