JP2002055675A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device which can display image of bright impression, while suppressing the power consumption, and to provide an image display device with which the distribution of brightness in a screen is hardly perceived with the aid of a kind of psychological illusion, even when the luminance of peripheral parts is low. SOLUTION: The image display device has a position-detecting means 51, a luminance level detecting means 52 to detect the signal level for every pixel of a video signal, a first look-up table 53 which stores a first multiplication gain to modulate luminance, so that it has a prescribed luminance inclination from a near center to peripheral parts of the display screen, a second lookup table 54, which stores a second multiplication gain for optimizing grayscale characteristics, a multiplication means 55 to multiply the signal level of the video signal by the second multiplication gain, and a multiplication means 56, to multiply the multiplication result of the multiplication means 55 by the first multiplication gain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device.

[0002]

2. Description of the Related Art Image display devices can be broadly classified into a light receiving type and a self light emitting type. The light receiving type has an external light supply unit, and displays an image by modulating the light of the light supply unit with a display element. For example, it is a liquid crystal monitor, a liquid crystal projector, or the like. The self-luminous type has no external light supply means, and the display element itself emits light to display an image. For example, CRT, P
DP, FED, organic EL and the like correspond to this.

In these conventional image display devices, high luminance, high contrast, high resolution, and low power consumption have been desired for higher image quality. Above all, luminance is the most important parameter that has a large effect on the visual impression of the image.

Therefore, various devices have been conventionally devised to make the luminance uniform within the screen. For example, in the case of the light receiving type, it has been attempted to realize a uniform screen luminance by changing characteristics of the light supply means, and in the case of the self light emitting type, by appropriately changing the video signal.

A method conventionally used for equalizing the luminance in a screen will be described with reference to a liquid crystal display device as an example.
The liquid crystal display device has a liquid crystal display element 19 as shown in FIG.
01, a backlight 1902, and driving means 1903 for the liquid crystal display element 1901. Backlight 19
02 is a transparent light guide plate 1 for supplying at least the light source 1904 and the light from the light source to the liquid crystal display element 1901, for example.
905, a reflection cover 1906 covering the light source. A large number of small scattering dots 1907 are formed on the back surface of the light guide plate, and the in-plane luminance is controlled by the shape and forming position of the small scattering dots 1907.

That is, the light output from the light source 1904 is incident from the end face of the light guide plate 1905, repeats total reflection, and propagates inside the light guide plate. At that time, all or a part of the light incident on the small scattering dots 1907 formed on the back surface changes its traveling direction, and the light incident on the upper surface of the light guide plate at an angle smaller than the critical angle is taken out as output light and is displayed on the liquid crystal display. Element 1
901.

Therefore, the distribution of the small scattering dots on the rear surface determines the luminance distribution in the surface. In the conventional backlight 1902, the dot area is increased from the peripheral portion to the central portion of the screen. The distribution of in-plane luminance is set to 80% or more, and uniform brightness is displayed. For example, consider a case where light sources are horizontally arranged on end faces of a light guide plate located above and below a screen. If the area of the small scattering dots on the back surface is uniform over the entire screen,
It is known that the luminance distribution is formed mainly in the vertical (y-axis) direction, and becomes a distribution in which the vicinity of the center becomes dark as shown in FIG. This is because most of the light is scattered at a portion near the light source and is output from the light guide plate.

In order to compensate for such a luminance distribution, it has been proposed to change the area of the fine scattering dots so as to be proportional to the reciprocal of the luminance distribution when the area of the fine scattering dots is made uniform over the entire area of the screen. Have been. That is, the area of the minute scattering dots is changed in the vertical direction in the screen, and the area of the minute scattering dots is increased toward the center. As a result, the brightness uniformity in the screen is 80%.
It can be higher than that.

Next, a self-luminous type will be described as an example.
In the case of the self-luminous type, it is particularly considered to correct unevenness of the display element itself. In other words, the luminance is compensated for each pixel by an amount that varies to compensate for the variation in the luminance of each pixel.

Generally, the driving means of the display device comprises a video signal decoding means 2101, a signal correction means 2102, and a display element interface means 2103 as shown in FIG. The video signal decoding unit 2102 is for generating RGB primary color signals and horizontal and vertical synchronizing signals from normal NTSC signals. The signal correction means 2102 is RGB
The correction of the gradation characteristics is originally performed in consideration of the input / output characteristics of the display element 2104.
The display element interface unit 2103 is for adjusting the corrected signal so that the signal level of the display element matches.

Although the signal correction means 2102 is originally intended to realize good gradation, the image display means 2104
In the case where there is a factor causing luminance unevenness for some reason, a means for correcting the luminance unevenness is also provided. For example, there may be a case where the luminance varies for each pixel, for example, due to the accuracy in producing the display element. In this case, the brightness in the screen is made uniform by changing the gradation for each pixel so that the brightness is adjusted to a certain level. More specifically, the signal correction means is provided with a look-up table which determines the gradation for each pixel as a built-in memory, and the luminance is appropriately modulated by referring to this in accordance with the synchronization signal.

As described above, in the conventional display device, various devices have been devised to make the brightness in the screen uniform.

In recent years, the size of the display screen has been increasing, and an image of 20 inches or more has been desired for a home TV. However, the power consumption of a conventional display device has increased significantly with the increase in the screen size. There was a problem of doing. When the luminance is kept constant, the power consumption increases in proportion to the area. In addition, as the resolution increases as the screen size increases, the area per pixel becomes smaller and the efficiency generally decreases. Therefore, when the screen size is increased and the resolution is increased without changing the luminance, the power consumption further increases. I do.

Therefore, an increase in power consumption is an unavoidable problem while keeping the luminance in the screen uniform. However, simply reducing the luminance can suppress an increase in power consumption, but gives a dark impression to an image observer.

[0015]

SUMMARY OF THE INVENTION It is an object of the first invention of the present application to solve the above-mentioned problems and to provide a display device capable of displaying a bright impression image while suppressing power consumption. That is, in order to solve the above-mentioned problem, the first invention of the present application does not impair a bright impression by gradually decreasing luminance from the center of the screen to the periphery and not perceiving the luminance gradient by a certain illusion phenomenon. It is possible to reduce power consumption.

A second object of the present invention is to provide an image display device in which the distribution of brightness in a screen is hardly perceived by a kind of psychological illusion even when the brightness of the peripheral portion is reduced. .

[0017]

According to a first aspect of the present invention, there is provided a display device including at least a luminance gradient forming unit and an image display unit, wherein the luminance gradient forming unit includes: It is characterized in that a luminance gradient that decreases substantially monotonously from a substantially center to a peripheral portion of a display image when an all-white signal is displayed is formed.

That is, the display device according to the first aspect of the present invention does not make the luminance in the screen substantially uniform over the entire surface, but applies a luminance gradient that decreases substantially monotonously from the center of the screen to the peripheral portion by the luminance gradient forming means. The power consumption is reduced as compared with the case where the entire surface has substantially uniform luminance.

At this time, it is preferable that the luminance of the display image is reduced substantially monotonously so that the luminance gradient is hardly perceived by the observer. In this case, it is more inconspicuous if the luminance gradient has symmetry, so it is preferable to monotonously decrease the luminance in the horizontal or vertical direction from the center of the screen. For the same reason, it is preferable that the luminance gradient is a luminance gradient that is substantially symmetric with respect to the horizontal axis or the vertical axis of the display image.

From the above viewpoint, several preferable examples of the distribution shape of the luminance gradient are considered. For example, when the luminance gradient is concentrically distributed, the luminance gradient can be extremely inconspicuous. The concentric luminance distribution is a distribution in which lines connecting portions having substantially the same luminance are substantially circular with the center of the screen being substantially at the center. Hereinafter, the luminance distribution shape is similarly defined.

The reason why the luminance distribution is less noticeable in this manner is considered to be as follows. Since the human pupil is a circle, the area where the screen can be perceived at a time is almost circular. Therefore, when the luminance gradient distribution shape in the screen is a circle, the area that can be perceived by humans at once and the distribution shape of the luminance gradient become almost similar, so the kind of illusion reduces the psychological effect on the luminance gradient. is there. Since the same effect is obtained even if the luminance distribution shape is not a substantially circular shape but an elliptical shape or a diamond shape, it is also preferable to form these luminance distribution shapes.

In the case of an elliptical luminance gradient, the luminance gradient can also be made inconspicuous by making the ratio of the major axis to the minor axis substantially equal to the ratio of the length of the display screen in the horizontal and vertical directions. . This is because the contour of the display image and the distribution shape of the luminance gradient are close to similar shapes, and thus a kind of illusion phenomenon reduces the psychological influence on the luminance gradient. For the same reason, a rectangular luminance distribution is also one of the preferable luminance distributions for making the luminance gradient inconspicuous.

Such a luminance gradient can be defined using a function. Now, with the approximate center of the displayed image as the origin,
A luminance gradient function f (x, x) substantially equal to the luminance B of an in-screen point at a distance x in the horizontal direction and y in the vertical direction from the origin.
Consider y). At this time, if the luminance gradient function f (x, y) is represented by f (x, y) = f (r) using a luminance distribution shape function r (x, y) that defines the distribution shape, the luminance gradient will be more simply described. be able to. For example, it is preferable that the luminance gradient function f (r) monotonously decreases with respect to the variable r of the luminance distribution shape function because the gradient of the luminance gradient is not noticeable if the gradient is gentle. As an example of this, a case in which it decreases linearly can be considered. In addition, a luminance gradient that decreases exponentially with respect to r is also conceivable.

In this case, as compared with the case where the luminance decreases linearly, the gradient of the luminance gradient is small near the center of the screen and becomes large toward the outside, so that the effect of making the luminance gradient more difficult to perceive is more preferable. . The reason is that when a human observes an image, he or she usually tends to focus mainly on the center of the screen. In other words, the luminance gradient in the portion of interest is small, and the luminance gradient is large in the peripheral portion of the screen where observation is rarely performed, so that the luminance gradient in the screen is not easily perceived. For the same reason, a luminance gradient in which the luminance decreases in accordance with the power of r and a luminance gradient in which the luminance decreases monotonically sinusoidally toward the peripheral portion are also hardly perceived, and are preferable configurations.

It is preferable that the extent to which the brightness gradient is formed is acceptable to the image observer (how much the brightness of the peripheral portion can be reduced) is based on the subjective evaluation result based on ergonomics. That is, it is preferable that the luminance gradient in the screen has a property that coincides with various boundary values defined as a result of the subjective evaluation. These results are generally referred to as detection limit, tolerance limit, and gaman limit (practical limit). According to the results of the subjective evaluation experiment by the inventors, the detection limit of the boundary value luminance defined by the luminance ratio between the diagonal angle of view of 0.9 and the central part at the time of displaying the all white signal has a detection limit of 55% ± 15% and an allowable limit. Is 30%
± 10%, Gaman limit (practical limit) is 15% ± 5%. Therefore, it is preferable to set such that the luminance gradient satisfies the above condition.

The luminance gradient satisfying the detection limit condition (diagonal 0.
If the luminance at the nine angles of view is about 55% of the center of the screen), the luminance gradient can be set so as not to be perceived by 50% of the observer. 50% if the brightness gradient satisfies the allowable limit condition
And the power consumption can be further reduced as compared with the case where the detection inclination condition is satisfied. Similarly, by satisfying the limit condition, the power consumption can be further reduced.

The method of reducing the power consumption by forming the luminance gradient on the screen by the luminance gradient forming means as described above is as follows.
The present invention can be applied to any display device having a light receiving type and a self light emitting type image display means. In the case of a display device having a light receiving type image display means, a light gradient supplying means for supplying light to the light receiving type image display means may be provided. For example, in the case of a display device using a transmissive liquid crystal panel as the light receiving type image display means, it has a light source and a light guide plate as the light supply means. At this time, a desired luminance distribution can be formed by the distribution of the scattering dots formed on the back surface of the light guide plate.

In either the light receiving type display means or the self-luminous type display means, a desired luminance gradient can be formed by modulating the input signal by the luminance gradient forming means. At this time, the luminance gradient in the screen can be formed in a desired shape by using a configuration in which the luminance gradient forming means is provided with a look-up table that determines the gradation of each pixel. Similarly, a configuration in which a luminance gradient forming means for changing the gain of the level shift is provided in an interface portion with the display element is also possible. When the image display means is an FED, a desired luminance gradient can be formed in the screen by providing the extraction voltage varying means as the luminance gradient forming means.

A display device according to a second aspect of the present invention is a display device having at least a luminance gradient forming means and an image display means, wherein the brightness index defined by (Equation 1) extends from substantially the center of the screen to the periphery. It is characterized by a substantially monotonous decrease. (Equation 1) BI = a × L + b × CR + d × γM + g = a × L + b × L / (OFF + BG) + d × γM + g = a × L + b / (1 / Cr + BG / L) + d × γM + g where L is the value when all white signals are used. Brightness, CR is bright place contrast, Cr is dark place contrast, γM is gradation coefficient, OF
F indicates the luminance at the time of full black display without the influence of external light, and BG indicates the luminance increase due to the influence of external light.

(Equation 1) has been found through a subjective evaluation experiment by the inventors, and is a scale showing a very good agreement with a psychological impression of brightness. As described in the first invention of the present application, a monotonous decrease in luminance from the center of the screen to the periphery means that the brightness index also monotonically decreases. This is effective for reducing power consumption as described in the first invention of the present application. However, on the other hand, since the brightness index decreases, the psychological impression of brightness decreases according to the mathematical formula. Therefore, in the first invention of the present application, the shape of the luminance gradient is devised, and the gradient of the luminance gradient is monotonously reduced, thereby making it difficult to be perceived as luminance unevenness.

On the other hand, the second invention of the present application improves the impression of brightness by improving the lightness index which decreases according to the mathematical formula. In other words, it is an object of the second invention of the present application to make it more difficult to perceive a luminance gradient by improving a decrease in brightness impression caused by a decrease in luminance by optimizing gradation. In this case, the characteristic is that the power consumption is not basically increased because only the gradation is changed.

At this time, by compensating the brightness index substantially uniformly throughout the entire area of the screen, the brightness of the peripheral portion can be basically reduced without lowering the impression of brightness. Not only can the brightness index of the entire area within the screen be substantially uniformly compensated, but also, for example, the brightness index can be substantially uniformly compensated within a range of 0.5 diagonal angles of view. This is because the most noticeable point when a human observes an image is in the vicinity of the center of the screen, and the range that can be observed at a time is generally within the range of 0.5 diagonal angles of view. By optimizing the gradation in the screen in this way, the distribution of the lightness index is improved, so that the power consumption can be reduced without impairing the impression regarding brightness.

It is also preferable to correct the distribution shape of the brightness index in the screen, for example. For example, when the brightness is deviated from the above-mentioned preferred brightness shape due to individual differences of display elements, the brightness index is improved by the brightness index improving means into a desired distribution shape, that is, the above-mentioned highly symmetric distribution shape. It becomes possible to make the luminance gradient hard to perceive.

Similarly, even when the luminance gradient deviates from the desired luminance gradient, it is possible to make the luminance gradient more difficult to perceive by making the brightness index coincide with the desired luminance gradient. In addition, it is possible to make inconspicuous luminance unevenness in a screen, which often becomes a problem in a liquid crystal display device having a direct backlight. In a direct-type backlight, which has a configuration in which several light sources are arranged directly below the liquid crystal display element, when an image is observed, the light immediately above the lamp is bright,
The part between the lamps was dark.

However, the brightness index can be made uniform in the screen by appropriately adjusting the gradation so as to compensate for the decrease in brightness by the brightness index improving means of the second invention of the present application. It is also possible to improve image quality degradation due to distribution.

[0036]

(Embodiment 1) FIG. 1 shows a display device according to an embodiment of the present invention.
It is a block diagram in the case of using a light receiving type image display means. The output light flux emitted from the light source 10 is formed by the luminance gradient forming means 12 into a luminance gradient that decreases substantially monotonically from the center of the screen toward the periphery, for example, and is input to the image display means 13. The image display means 13 displays an image by modulating the incident image. With such a configuration, the above-described gradient (luminance distribution) is formed in the luminance when an all-white signal is displayed. Here, the case where a transmissive liquid crystal panel is used as the image display means will be described in more detail. FIG. 2 shows a configuration diagram of a display device according to the present invention using a liquid crystal panel as an image display means. Examples of the display device include a liquid crystal monitor and a liquid crystal projector. The display device basically includes a backlight 17 having both a light source 15 and minute scattering dots 16, and a transmissive liquid crystal panel 18 as image display means. The luminous flux of the light source 15 is input from the end face of the transparent light guide plate 19 and propagates total reflection repeatedly between upper and lower surfaces.

A plurality of minute scattering dots 16 are arranged on the back surface of the transparent light guide plate 19, and a part or all of the light incident on the portion where the minute scattering dots 16 are formed changes its traveling direction and is shifted from the critical angle. Light incident on the upper surface of the transparent light guide plate 19 at a small angle is output (light ray 20 in the figure) and is incident on the transmission type liquid crystal panel 18. And this output light 20
Is input to the transmissive liquid crystal panel 205 and converted into an image as display light 21.

The fine scattering dots 16 may be formed by screen printing a medium in which fine particles of silicon oxide and titanium oxide are dispersed on the back surface of the transparent light guide plate 19. Alternatively, it can be realized by forming a projection on the back surface by injection molding.

At this time, the amount of peripheral light is converged on the center of the image according to the area and formation position of the fine scattering dots 16 formed on the back surface of the transparent light guide plate 19 to form a desired luminance gradient. FIG. 3 is a plan view of the small scattering dots 16 formed on the transparent light guide plate. As shown in the figure, by changing the area of the scattering dots 16, it is possible to form a luminance gradient in which the luminance decreases monotonously from the center to the periphery of the screen. Therefore, an aggregate of the small scattering dots 16 having the distribution shown in FIG. 3 among the constituent members of the backlight 17 corresponds to the luminance gradient forming means 12 of the present invention.

The distribution of such minute scattering dots 16 is as follows.
For example, it can be obtained by changing the radius of the scattering dots 16 in proportion to the result of dividing the desired luminance distribution by the in-plane luminance distribution when the radius of the minute scattering dots 16 is uniform. Assume that the luminance distribution generated when the radius of the minute scattering dots 16 is the same in the entire area in the plane is φ0 (x, y). However, the x axis is parallel to the horizontal direction of the screen, the y axis is parallel to the vertical direction of the screen, and the origin is the center of the screen.

At this time, the luminance distribution to be realized is represented by f (x,
y), the area S (x, y) of the minute scatterer is (Equation 2)
Required by (Equation 2) S (x, y) = a × f (x, y) / φ 0 (x, y). Here, a is a proportional coefficient.

Next, a luminance gradient function f (x,
y) will be described in detail. The luminance gradient is formed so as to decrease substantially monotonously in the horizontal and vertical directions from the substantially center of the display image when displaying the all-white signal. At this time, the luminance distribution is perceived by the observer by making the luminance gradient substantially symmetric with respect to the horizontal direction from the substantially center of the display image or the vertical direction from the substantially center of the display image and decreasing substantially monotonously. It can be difficult.

Such a luminance distribution is represented by a luminance gradient function f (x, y) = luminance at a point in the screen which is horizontally away from the origin by a distance x and vertically by a distance y from the origin of the image.
It can be easily represented by f (r). Here, r is a luminance distribution shape function, and at the same time, a luminance function f (x,
By defining the luminance shape function r as y) = f (r), the shape of the in-plane luminance distribution (the shape of the line connecting the same luminance in the plane) can be easily represented.

For example, in the present embodiment, it is preferable to have a concentric luminance distribution as shown in FIG. In this case, a concentric luminance gradient can be expressed by setting the luminance distribution shape function r to (x ² + y ² ) ^(1/2) .
The concentric luminance gradient means that a shape connecting points having the same luminance is substantially equal to a circle.

In addition, as shown in FIG.
A luminance gradient in which the luminance decreases from the periphery toward the periphery is also preferable.
In this case, the luminance shape function r is expressed as ((x / a)^Two+ (Y /
b)^Two) ^(1/2)(A and b are positive constants)
it can. At this time, the ratio between a and b is
It can also be made approximately equal to the ratio. For example, 4: 3, 1
6: 9, 5: 4, etc.

It is also preferable that the luminance shape is as shown in FIG. In this case, the brightness shape function r is changed to rect (x
/ (A × h), y / (b × v)), the luminance gradient can be expressed. Where a and b are positive constants,
h is the horizontal length of the screen, v is the vertical length, and rect (α, β) is 0 ≦ α ≦ as shown in FIG.
This is a special function that is defined by 1, 0 ≦ β ≦ 1, and represents a rectangle having a horizontal to vertical ratio of α: β. At this time, the ratio between a and b can be set to a general screen ratio as in the case of an ellipse.

Similarly, it is preferable to form a diamond-shaped luminance gradient as shown in FIG. In this case, the brightness shape function is r = rect (1 / (h × a × (x × cos θ−y × sin θ)),
1 / (v × b × (x × sin θ + y × cos θ))). However, θ is 45 °.

Further, by setting the luminance distribution shape function r to r = x or r = y, the luminance gradient can be symmetrical with respect to the horizontal axis passing through the center of the display screen or the vertical axis passing through the center of the display screen. it can.

Next, the change rate of the luminance, that is, the luminance gradient will be described. In the present invention, it is preferable that the luminance decreases substantially monotonously. That is, it is sufficient that the luminance gradient is such that f (r) decreases substantially monotonically with respect to r, and for example, a luminance gradient represented by the following function is preferable.

For example, if f (r) = − a × r + b (a and b are positive constants), the luminance decreases linearly with respect to r. Similarly, assuming that a, b, and c are positive constants, f (r)
= A × exp (−b × r), f (r) = a × exp ｛− (r / b) ² /
Similarly, a function represented by 2｝, f (r) = a × cos (2π / λ × b × r) can form a luminance gradient that monotonically decreases from the center of the screen toward the periphery. The luminance distribution shape and the luminance gradient do not need to exactly match the distribution and the gradient represented by the function.

Next, the effect of the present invention will be described by taking a specific luminance distribution as an example. In the display device configured as shown in FIG. 2, a concentric luminance distribution shape is used, and minute scattering dots, which are luminance gradient forming means, are formed such that the luminance gradient is monotonically reduced from a substantially center of the screen based on a substantially Gaussian function. . In this case, the fine scattering dots were adjusted so that the brightness at the diagonal angle of 0.9 was 0.55 with respect to the center.

This is determined based on the subjective evaluation described below. The inventors conducted a subjective evaluation experiment based on ergonomics, and examined the rate at which a change in luminance continuously changing from the center of the screen toward the periphery was perceived by an image observer. As a method of the experiment, the subject observed images in which the luminance was changed at various rates from the center to the periphery of the screen, and evaluated the unevenness of the luminance based on the double stimulus deterioration scale method which is a known technique. The degree of unevenness was represented by the ratio of the luminance at the screen diagonal of 0.9 and the luminance at the center of the screen.

An experiment was repeatedly performed on more than 100 subjects, and the following boundary value luminance was found. In other words, detection limit brightness, allowable limit brightness, and gamut limit brightness (practical limit)
Kind. With the detection limit luminance, 50% of observers do not notice the luminance gradient at all. In the case of the allowable luminance limit, the luminance gradient is such that 50% of observers slightly notice the existence of the luminance gradient but do not care at all. If the luminance is very limited (practical limit), 50% of the observers are slightly anxious, but the luminance gradient is acceptable.

From the results of the subjective evaluation, the detection limit luminance is 55% ± 1.
5%, allowable luminance 30% ± 10%, Gaman 15% ±
It was 5%.

Therefore, in the display device according to the present embodiment, the arrangement of the small scatterers is designed as shown in FIG. 3 so that the luminance at 0.9 angle of view becomes 0.55 with respect to the luminance at the center of the screen. did. In such a configuration, as shown in FIG. 9, the luminance at the center of the screen is increased by about 27% as compared with the case where the entire surface is designed to be uniform. This is because the light output from the peripheral portion is focused on the central portion. This means that if the power consumption is fixed, the luminance is improved by 27% compared to the conventional display device. Conversely, if the luminance at the center of the screen is the same as that of the conventional display device, the power consumption can be reduced by 27%. It means that it is possible. Moreover, since the luminance decreases monotonously and gradually from the center to the periphery of the screen, half of the observers do not notice the inclination at all.

As described above, according to the display device of the present invention, the power consumption can be reduced by about 30% as compared with the conventional liquid crystal display device without causing the image observer to perceive the luminance gradient.

Note that it is of course possible to use an allowable limit luminance and a gamut limit luminance as the boundary value luminance. In this case, the brightness gradient is more easily perceived than in the case of the detection limit, but the power consumption can be further reduced. This is extremely effective when further reduction in power consumption is required.

(Embodiment 2) FIG. 10 is a block diagram showing a display device according to another embodiment of the present invention.
The second embodiment is characterized in that a luminance gradient is formed by directly operating an input signal.
That is, in the first embodiment, the luminance gradient is formed by the formation position and the area of the minute scattering dots, but in the second embodiment, the luminance gradient is formed by the signal conversion processing of the video signal. .

The second embodiment can be applied to both the light receiving type display element and the self light emitting type display element. As self-luminous display elements, CRTs, PDPs (plasma displays), FEDs (abbreviations for field emission displays) that emit electrons and emits light using electrons emitted by the field effect, and ELs (organic and inorganic) are available. Any type of display that emits light by electroluminescence), LE in which LEDs are two-dimensionally arranged
D array and the like. In addition, the display device configured in this embodiment may include a luminance gradient unit that forms a luminance gradient by directly operating an input signal,
It is of course possible to use a light receiving type image display device.

Also in the display device of the present embodiment, it is preferable to realize the luminance distribution having the luminance distribution shape and the luminance gradient as described in the first embodiment. That is, it is preferable that the luminance decreases substantially monotonously from the center of the screen toward the periphery, and it is desirable to use any of the gradients that can be approximately approximated by the function described in the first embodiment. At this time, the shape of the luminance distribution (line connecting points in the screen having the same luminance)
Are generally horizontal and vertical axes of the screen, and concentric circles,
Preferably, it is substantially equal to any one of an ellipse, a rectangle, and a diamond.

In particular, by setting the luminance at the 0.9 angle of view to the detection limit luminance described in the first embodiment, it is possible to form a luminance gradient that is hardly perceived. Next, the luminance gradient forming means will be described in more detail. As shown in FIG. 10, the normal video signal is output from the video signal decoding unit 30, the signal correction unit 31,
The signal is input to the image display unit 13 via a signal processing circuit including the display element interface unit 32. The video signal decoding means 30 converts a normal NTSC signal into RGB primary color signals, a horizontal synchronizing signal H, and a vertical synchronizing signal V. The signal correction means 31 corrects each of the RGB signals, and originally corrects the gradation in consideration of the input / output characteristics of the display element. The display element interface means 32 is for adjusting the corrected signal so as to match the signal level of the image display means 13.

More specifically, the signal correcting means 31 of the present invention has a gradation adjusting means 33 for adjusting the gradation of each pixel. The gradation adjusting means 33 includes a memory,
The gradation data of each pixel is held as a look-up table and modulates a video signal according to a synchronization signal. That is, the signal correction unit 31 and the gradation adjustment unit 33 correspond to the luminance gradient forming unit 12.

The luminance gradient forming means 12 controls the gradation so as to obtain the desired luminance distribution shape as described in the first embodiment. That is, it is assumed that the luminance distribution in the current screen is approximately approximated by a luminance gradient function f (x, y) = f (r). At this time, for example, when the gradation at the center of the screen is represented by the curve shown in FIG. 11, the gradation at the place where the luminance is represented by f (x, y) is as shown in FIG. become. More specifically, the gradation characteristics are similar to each other, and the ratio may be approximately f (x, y) / f (0, 0).

By locally modulating the input signal itself, a desired luminance gradient can be freely formed in the screen. As a result, power consumption can be reduced by forming a luminance gradient that is not perceived even in the display device configured in this embodiment.

It is also conceivable that the display element interface means 32 functions as a luminance gradient forming means. For example, consider a case where a liquid crystal display element is used as the image display unit 13. The liquid crystal display element has input / output characteristics as shown in FIG. 13 in a so-called normally white mode. Therefore, the display element interface means 32 inverts the signal sent from the signal correction means 31 so as to obtain a desired signal. At this time, for example, the display element interface unit 32 changes the gain of the level shift for each pixel, for example, so that a luminance gradient similar to the effect of changing the gradation characteristic for each pixel can be formed.

When an FED is used as a display element, for example, as shown in FIG.
A luminance gradient can also be formed with 0. That is, the extraction voltage varying means 40 only has to receive the signal from the display element interface means 32 and modulate the extraction voltage so as to obtain a desired luminance gradient. In FIG. 14, 41 is a substrate, 42 is a phosphor, 43
Is an anode electrode, 44 is an extraction electrode, 45 is an electron gun,
46 indicates a drawing voltage, and 47 indicates an acceleration voltage.

FIG. 15 shows a specific configuration when a CRT is used as the image display means. In other words, this is a case where the image display means displays an image by causing the phosphor to emit light by scanning the cathode ray. The specific configuration will be described with reference to FIG. 15. The image display means basically includes an electron gun 51 and a fluorescent screen 52.
The electron beam 53 emitted from 1 is converted to a cathode ray deflector 54
Scans the fluorescent screen 52 while being deflected. The luminance gradient forming means 55 modulates the video signal so as to obtain the above-mentioned luminance distribution shape, and realizes a gentle luminance gradient from the center to the peripheral portion of the screen. Also in such a display device, it is preferable to realize the luminance distribution shape and the luminance gradient as described in the first embodiment. That is, it is preferable that the luminance decreases substantially monotonously from the center of the screen toward the periphery, and a gradient that can be approximately approximated by the function described in the first embodiment is desirable. At this time, the shape of the luminance distribution (the line connecting points in the screen having the same luminance) is symmetric about the horizontal and vertical axes of the screen, and is substantially equal to any of concentric circles, ellipses, rectangles, and rhombuses. Is preferred. Especially 0.9
By setting the luminance of the angle of view to the detection limit luminance described in Embodiment 1, it is possible to form a luminance gradient that is more difficult to perceive. It should be noted that also in the present display device, a bright image can be displayed without feeling the luminance gradient by forming the luminance gradient described in Embodiment 1 and setting the luminance at the diagonal angle of 0.9 as the boundary value luminance. In addition, by reducing the luminance of the peripheral portion, power consumption can be reduced without impairing the brightness.

(Embodiment 3) In Embodiments 1 and 2, an example is given in which a luminance gradient at which the luminance at a diagonal angle of view of 0.9 is substantially equal to the detection limit luminance (luminance of about 55% with respect to the center). Was explained. In this case, it is a level at which 50% or more observers do not notice the brightness unevenness from the result of the subjective evaluation. However, in order to further reduce the power consumption, in the display device described in the first to third embodiments, a gradient is formed from the luminance at the diagonal angle of view of 0.9 to the allowable luminance or the maximum luminance (practical limit). Of course, it is possible. However, in this case, it is naturally easy to detect the luminance gradient. Therefore, in the present embodiment, an embodiment of a display device in which the luminance gradient in such a case is more difficult to detect will be described in detail.

The luminance described in the present embodiment is a physical quantity that can be directly measured by a device and is used as an index indicating the brightness. However, it does not always coincide with the psychological impression of the image observer. Not something. That is, even if the luminance is the same, the psychological impression felt by the observer differs depending on the contrast and gradation.

As a result of the subjective evaluation, the inventors have found that a brightness index BI (Brightness Index) that agrees very well with a psychological impression.
x) [cd / m ² ] is found, which has a correlation between the measurable physical quantity and (Equation 3). (Equation 3) BI = a × L + b × CR + d × γM + g = a × L + b × L / (OFF + BG) + d × γM + g = a × L + b / (1 / Cr + BG / L) + d × γM + g

Here, L is the luminance when an all white signal is displayed.
CR is a bright place contrast, which means contrast in consideration of external light. Cr is a dark place contrast, and means contrast in a dark surrounding environment without external light (that is, a state where the illuminance is 0). OFF is the luminance when displaying all black signals when there is no influence of external light. BG indicates an increase in luminance due to the influence of external light. Therefore, the bright place contrast is CR = L
/ (OFF + BG). Further, the dark place contrast becomes Cr = L / OFF. Also, a, b, d, and g are coefficients and are in the following ranges. a = 0.00423339 ± 0.002671539 b = 0.007648902 ± 0.005754385 d = -79.52542076 ± 18.92439144 g = -0.7131531895 ± 0.16046239

Note that a = 0.00423339, b = 0.007648902,
d = -79.52542076 and g = -0.7131531895 are a, b,
The representative values of d and g are shown, ± 0.002671539, ±
0.005754385, ± 18.92439144, ± 0.16046239 indicate the upper and lower allowable value width of the representative value. Therefore, a, b, d, and g can take any values within a range from a lower allowable value to an upper allowable value.

Further, γM is a coefficient relating to gradation, and is defined by (Equation 4). (Equation 4) γM = ｛(L5-L4) / (s5-s4)-(L2-L
1) / (s2-s1)｝ / L7

Here, Li (i = 1 to 5) is the luminance of the i-th gradation obtained by dividing the luminance L into seven, as shown in FIG.
Is the input signal level for displaying the i-th gradation. However, the maximum value of the input signal level is normalized to 255. For reference, Table 1 shows the relationship between the characteristic values of normal gradation represented by an exponential type and the gradation defined in the present invention.

[0075]

[Table 1] The above-mentioned γM is used as a coefficient relating to the gradation in some cases (eg, an S-shaped display characteristic curve of a liquid crystal display element) having an input / output characteristic whose γ value is not always constant. This is for normalization to two γ values.

Here, as described in the first and second embodiments, when the luminance is reduced substantially monotonously from the center of the screen and the detection limit luminance is set at the diagonal angle of view of 0.9, the impression of the psychological brightness is reduced. The lightness index, which is approximately proportional, decreases according to (Equation 3). However, as described above, the brightness index decreases, but is hardly perceived as a luminance gradient. This is a kind of illusion phenomenon because a human observes the screen locally instead of observing the entire area at once.

Now, consider the case where a luminance gradient as shown in FIG. 17 is given. The horizontal axis represents the distance standardized diagonally, and the vertical axis represents the relative luminance when the luminance at the center is 1. Here, an example is described in which the angle of view is 0.9% with about 55% (detection limit luminance). When the light place contrast is set to 100 and the gradation is set to 2.2 in general, and these are made uniform in the screen, the lightness index decreases toward the periphery as shown in FIG. This is not a problem in the case of the detection limit luminance, but if the luminance of 0.9 angle of view is reduced below the detection limit luminance, the inclination of the luminance will be easily perceived gradually.

Therefore, for example, as shown in FIG. 19, all gradations are not set to γ = 2.2 over the entire area of the screen.
The purpose of the second invention of the present application is to compensate for a decrease in the brightness index due to a decrease in luminance by changing the gradation as shown in the drawing. As a result of changing the gradation as shown in FIG. 19, the brightness index becomes almost uniform up to about 0.5 diagonal view angle as shown in FIG. 20, and the impression of brightness does not change at all. . That is, by locally changing the gradation, it is possible to compensate for the impression of brightness resulting from the decrease in luminance.

As a result, even if the brightness at the diagonal angle of view of 0.9 is reduced to the detection limit brightness or less to further reduce the power consumption,
By changing the gradation in the screen as described above, it is possible to make the change in luminance more difficult to perceive.

For this purpose, the display device according to the present embodiment includes a brightness index improving unit. The brightness index improving means includes a gradation adjusting means in the same manner as the luminance gradient forming means described in the second embodiment.
It has a function of presetting it to be 9.

Hereinafter, a specific configuration will be described.
FIG. 21 is a block diagram illustrating a specific configuration of the signal processing unit of the display device according to the third embodiment. Decoder means 50 serves to separate the luminance signal and the horizontal / vertical synchronization signal from the composite video signal.
Reference numeral 51 denotes position detecting means for detecting the two-dimensional position coordinates of the pixel (or dot), and is realized by, for example, a counter. Reference numeral 52 denotes a luminance level detecting means for detecting a signal voltage level of each pixel of the video signal. Reference numeral 53 denotes a first look-up table. As shown in FIG. 22, the first look-up table 53 reduces the brightness index BI substantially monotonously from a substantially central portion to a peripheral portion of the display screen. A second multiplication gain according to the two-dimensional coordinate information is stored, and two-dimensional coordinate information from the position detecting means is input, and a first multiplication gain according to the input is output.
Numeral 54 denotes a second look-up table. The second look-up table 54 has a second look-up table 54 corresponding to the two-dimensional coordinates and the luminance level in order to change the γM value at the periphery of the display screen as shown in FIG. And the two-dimensional coordinate information from the position detecting means and the luminance level information from the luminance level detecting means are input, and a second multiplying gain corresponding to the input is output. 55 is a first multiplying means, and 56 is a second multiplying means.

Here, the second lookup table 54
Will be described in detail. As shown in FIG. 24A, three different positions r0,
Assuming r1 and r2, the γ value differs for each position r0, r1, r2 as shown in FIG. That is, at the position r0, for example, γ = 2.2, at the position r1, for example, γ = 1.8, and at the position r2, for example, γ = 1.5. Then, an output voltage corresponding to the video signal level was obtained from the γ curves for each position r0, r1, r2, and the ratio of the output voltage to the video signal level was defined as a second multiplication gain. Therefore, in this embodiment, the multiplication gain is determined by the two parameters of the pixel position and the signal level.

The calculation of the second multiplication gain is as follows.
The γ curve shown in FIG. 24C may be used instead of the γ curve shown in FIG. The operation and effect when the γ curve shown in FIG. 24C is used will be described later.

Next, the operation of the signal processing unit having the above configuration will be described with reference to FIGS. FIG. 25
27 show an example of signal conversion for a scanning line passing substantially at the center of the display screen. FIG. 25 shows a case where all signal levels of the scanning line are 100% luminance, and FIG. 26 shows all signal levels of the scanning line. 27 is 50% luminance, the signal level in the first half of the scanning line is 50% luminance and the signal level in the second half is 10 luminance.
The case of 0% is shown. First, referring to FIG. 25, in the case of the signal level shown in FIG. 25A, the second multiplication gain read from the second lookup table 54 is shown in FIG. Therefore, the output of the first multiplying means 55 is as shown in FIG. On the other hand, the first lookup table 53 outputs the first multiplication gain so as to decrease the brightness index BI substantially monotonously from the substantially central part of the display screen toward the peripheral part, and thus the first lookup table 53 outputs the entire scanning line. Shows the gain characteristic shown in FIG. Then, by the second multiplication means 56, FIG.
The luminance level shown in FIG. 25D is multiplied by the luminance level shown in FIG. 25C to obtain the luminance level shown in FIG.
That is, the luminance signal shown in FIG. 25A is converted into the luminance signal shown in FIG.

Similarly, in the case of the signal level shown in FIG. 26A, the signal is converted into a luminance signal shown in FIG. 26E. In this case, in the peripheral portions on both sides of the display screen, conversion is performed so as to increase the luminance level by changing the gradation of the middle floor.

Similarly, in the case of the signal level shown in FIG. 27A, the signal is converted into a luminance signal shown in FIG. 27E. In this case, the conversion is performed so that the luminance level is increased by the change in gradation at the left peripheral portion of the display screen.

As described above, the brightness index BI is substantially monotonously decreased from the substantially central portion of the display screen toward the peripheral portion, and the brightness index is improved such that the luminance level is increased in the peripheral portion. The power consumption can be reduced as compared with the case where the entire surface is made uniform brightness without reducing the impression of brightness. Further, it is possible to make it difficult to perceive a decrease in brightness impression due to a decrease in brightness in the peripheral portion without increasing power consumption by optimizing the gradation.

For reference, the multiplication gain is determined by one parameter only at the pixel position without providing the luminance detecting means, and the multiplication gain is multiplied by the signal level of the video signal. It is also conceivable to brighten the center of the screen and darken the periphery, but in such a case, the gain is the same for each gradation, that is, the reduction rate is the same for each gradation, and the luminance gradient becomes more conspicuous. In this regard, in a configuration in which the multiplication gain is determined by two parameters of the pixel position and the signal level as in the present invention, the gain differs for each gradation,
Therefore, by decreasing the gain as the gradation becomes lower, the luminance gradient can be made less noticeable.

Further, in the above example, the second multiplication gain is determined based on the γ curve shown in FIG. 24B, but instead of the γ curve shown in FIG.
May be used. In the case of the γ curve shown in FIG. 24B, the luminance was reduced in the peripheral portion in advance by the first multiplication gain, and the gradation was compensated in all the white level and halftone regions. On the other hand, γ shown in FIG.
In the case of a curve, the entire screen has a uniform brightness (or a very small decrease in the periphery), and the gray level is not compensated for the white level, and the gray level is compensated for the halftone area. is there. Even with the display by such gradation compensation, it is possible to sufficiently maintain the sense of brightness and reduce the power consumption. This is because, when a screen is displayed on the basis of a video signal, it is extremely rare that the entire surface is entirely displayed in white, so that γ shown in FIG.
This is because even if the gradation is compensated based on the curve, a sufficient brightness feeling can be maintained. Note that a specific configuration in the case of using the γ curve shown in FIG.
The first look-up table 53 is used such that the multiplication gains of all are substantially “1” at any position, and the gains that form the γ curve shown in FIG.
May be stored in the lookup table. Alternatively, only the second look-up table that stores the gains that result in the γ curve shown in FIG.
May be omitted.

(Embodiment 4) FIG. 28 shows Embodiment 4 of the present invention.
FIG. 3 is a block diagram illustrating a configuration of a signal processing unit of the display device according to the first embodiment. The fourth embodiment is similar to the third embodiment, and corresponding parts are denoted by the same reference numerals. Embodiment 4
Is characterized by compensating for fluctuations in the bright place contrast CR due to external light, and maintaining a sense of brightness without being affected by external light. Hereinafter, a specific configuration will be described with reference to FIG. In the display device according to the present embodiment, an external light detecting means 57 for detecting an external light level is added, and a third lookup table 58 is provided instead of the second lookup table 54. The third lookup table 58 is shown in FIG.
As shown in (3), a third multiplication gain is stored in order to compensate for the brightness index fluctuated by external light. The operation of this configuration is basically the same as the operation shown in FIGS. By the operations shown in FIGS. 25 to 27, the brightness index fluctuated by external light is improved, so that it is possible to maintain a sense of brightness without being affected by external light. In addition,
From the viewpoint of compensating for the influence of contrast due to external light, the first lookup table is not necessarily an essential component.

(Embodiment 5) FIG. 30 shows Embodiment 5 of the present invention.
FIG. 3 is a block diagram illustrating a configuration of a signal processing unit of the display device according to the first embodiment. The fifth embodiment is similar to the fourth embodiment and corresponding parts are denoted by the same reference numerals. The fifth embodiment is characterized in that fluctuations in peak luminance caused by the operation time of the display device are compensated, and it is possible to maintain a sense of brightness without being affected by the operation time. Things. In order to achieve such an object, in the fifth embodiment, the operation time detecting means 59 for detecting the operation time of the display device instead of the external light detecting means 57 in the fourth embodiment.
Are provided, and a fourth lookup table 60 is provided in place of the third lookup table 58. The fourth look-up table 60 stores a fourth multiplication gain for compensating for a peak luminance that varies with operation time. The operating time detecting means 59 is realized by, for example, a timer. The operation of this configuration is basically the same as the operation shown in FIGS. 25 to 27, and the brightness index fluctuated by the operation time of the display device is improved by such an operation, so that the operation time is affected. It is possible to maintain a sense of brightness without any problem.

Note that the first look-up table is not necessarily an essential component from the viewpoint of compensating for the peak luminance that varies with the display time.

(Embodiment 6) FIG. 31 shows Embodiment 6 of the present invention.
FIG. 3 is a block diagram illustrating a configuration of a signal processing unit of the display device according to the first embodiment. The sixth embodiment is similar to the fifth embodiment and corresponding parts are denoted by the same reference numerals. In the sixth embodiment, the operation time detecting means 5 according to the fifth embodiment is used.
9 is provided with time-dependent change detecting means 61 for detecting a time-dependent change. Instead of the fourth look-up table 60, a fifth multiplication gain for compensating for peak luminance fluctuated due to time-dependent change is provided. A fifth look-up table 62 for storing is provided. The temporal change detecting means 61 is realized by, for example, an optical sensor for detecting the actual luminance of the display surface. Although the peak luminance which decreases with the elapse of a certain time in the operating time detecting means 59 depends on preset data, the temporal change detecting means 61 detects the actual decrease in the peak luminance. Are different. This FIG.
In the case of the configuration shown in (1), since the brightness index that fluctuates due to aging is improved, it is possible to maintain a sense of brightness without being affected by aging.

The first look-up table is not necessarily an essential component from the viewpoint of compensating for the peak luminance that changes with time.

(Supplementary Explanation of the Embodiment) (1) In the configurations of the embodiments 3 to 6, the brightness index BI is reduced substantially monotonously from the substantially central portion of the display screen toward the peripheral portion. Although the brightness is increased in the peripheral portion, the present invention is not limited to this, and the brightness index BI may be made constant over the entire surface by changing the storage data of the lookup table. Good.

(2) When actually determining γM, it is important to determine how much γM should be changed in consideration of gradation. For example, it is easy to completely maintain the brightness index of the entire area in the screen by obtaining the gradation coefficient γM by introducing the luminance into (Equation 3), but the gradation may be broken. . So as approximate prospect, it is preferable to keep at a value corresponding to gamma = 1.6 as shown in FIG. 18.

(3) As described above, an area that can be noticed at a time when a human observes an image is at most about 0.5 diagonal when the screen size is 15 "or more. It is also conceivable that the lightness index is made to substantially match the center of the screen only in the inside, and the lightness index is smoothly changed in the peripheral portion without extreme compensation.

(4) In the display device having the brightness gradient forming means of minute scattering dots like the liquid crystal display device described in the first embodiment, the asymmetry of the brightness distribution shape becomes strong for some reason. In this case, the brightness index naturally has an asymmetric distribution shape. Therefore, it is also possible to improve the symmetry of the lightness index in the screen by the lightness index improving means so as to obtain a desired lightness index distribution shape based on Expression 3.

(5) In the display device according to the present invention described in the first to sixth embodiments, even if the luminance distribution is deviated from a desired gradient due to a pixel defect or the like for some reason, the brightness index improving means can be used. By appropriately optimizing the tonality in the screen, the lightness index can be changed with a gentle desired gradient.

(6) As described above, when a gradual luminance gradient is applied from the center of the screen to the periphery, the gradation change is optimized in the screen according to (Equation 3), so that it is difficult to perceive the luminance change. can do. Therefore, even if the brightness at the diagonal 0.9 is reduced to a brightness equal to or lower than the detection limit brightness, it is possible to prevent the image observer from perceiving a change in brightness.
Even when the luminance is reduced only to a level equal to or higher than the detection limit luminance, it is of course possible to compensate the lightness index by the in-plane distribution of the gradation.

(7) It is also possible to make luminance unevenness in a screen which is often a problem in a liquid crystal display device having a so-called direct type backlight inconspicuous. That is, in a direct-type backlight having a configuration in which several light sources are arranged immediately below a liquid crystal display element, when an image is observed, a portion immediately above the lamp is bright and a portion located between the lamps is dark when an image is observed. I was However, Embodiments 3 to 6 above
The brightness index can be made uniform in the screen by appropriately adjusting the gradation so as to compensate for the decrease in brightness by the brightness index improving means in the above, so that the deterioration of the image quality due to such brightness distribution is improved. Is also possible.

Note that the present invention is not limited to the above-described first to sixth embodiments, and various modifications are possible by taking over the purpose.

[0103]

As described above, according to the structure of the present invention, each object of the present invention can be sufficiently achieved. The details are as follows.

(1) According to the first aspect of the present invention, it is possible to finally reduce the power consumption by gently decreasing the luminance from the center of the screen without causing the image observer to perceive the luminance by the luminance gradient forming means. Become.

(2) Further, according to the second aspect of the present invention, by changing the gradation in the screen by the brightness index improvement means, the impression of psychological brightness impaired by the inclination of the brightness is improved, and furthermore. It is possible to make it difficult to perceive the luminance gradient. Therefore, it is possible to further reduce power consumption by combining with the first invention of the present application.

[Brief description of the drawings]

FIG. 1 is a block diagram of a display device configured in Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram of a display device configured in Embodiment 1 of the present invention.

FIG. 3 is a plan view of a luminance gradient forming unit of the display device according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a luminance distribution shape of the display device configured in Embodiment 1 of the present invention.

FIG. 5 is an explanatory diagram of a luminance distribution shape of the display device configured in Embodiment 1 of the present invention.

FIG. 6 is an explanatory diagram of a luminance distribution shape of the display device configured in Embodiment 1 of the present invention.

FIG. 7 is an explanatory diagram of a brightness distribution shape function representing a brightness distribution shape of the display device configured in Embodiment 1 of the present invention.

FIG. 8 is an explanatory diagram of a luminance distribution shape of the display device configured in Embodiment 1 of the present invention.

FIG. 9 is an explanatory diagram of a luminance gradient of the display device configured in Embodiment 1 of the present invention.

FIG. 10 is a block diagram of a display device configured in Embodiment 2 of the present invention.

FIG. 11 is an explanatory diagram of the gradation at the center of the screen of the display device configured in Embodiment 2 of the present invention.

FIG. 12 is an explanatory diagram of a gradation property of the display device configured in Embodiment 2 of the present invention.

FIG. 13 is an explanatory diagram of input / output characteristics of an image display unit used in the display device according to the second embodiment of the present invention.

FIG. 14 is a configuration diagram of a display device configured in Embodiment 2 of the present invention.

FIG. 15 is a configuration diagram of another display device configured in Embodiment 2 of the present invention.

FIG. 16 is a diagram illustrating a method of calculating γM.

FIG. 17 is an explanatory diagram of a luminance gradient of the display device configured in Embodiment 3 of the present invention.

FIG. 18 is an explanatory diagram of a brightness index distribution of the display device configured in the third embodiment of the present invention.

FIG. 19 is an explanatory diagram of gradation in a display device configured in Embodiment 3 of the present invention.

FIG. 20 is an explanatory diagram of a brightness index improvement of the display device configured in Embodiment 3 of the present invention.

FIG. 21 is a block diagram illustrating a specific configuration of a signal processing unit of the display device according to the third embodiment.

FIG. 22 is a schematic diagram showing a storage state of a first lookup table.

FIG. 23 is a schematic diagram showing a storage state of a second lookup table.

FIG. 24 is a diagram illustrating a method for determining a second multiplication gain.

FIG. 25 is a diagram for explaining signal conversion processing when all signal levels of a scanning line have a luminance of 100%.

FIG. 26 is a diagram for explaining signal conversion processing when all signal levels of a scanning line have a luminance of 50%.

FIG. 27 is a diagram for explaining signal conversion processing when the signal level in the first half of the scanning line is 50% luminance and the signal level in the second half is 100% luminance.

FIG. 28 is a block diagram illustrating a configuration of a signal processing unit of a display device according to the fourth embodiment.

FIG. 29 is a schematic diagram showing a storage state of a third lookup table.

FIG. 30 is a block diagram illustrating a configuration of a signal processing unit of the display device according to the fifth embodiment.

FIG. 31 is a block diagram illustrating a configuration of a signal processing unit of a display device according to a sixth embodiment.

FIG. 32 is a configuration diagram of a conventional display device.

FIG. 33 is an explanatory diagram of a luminance gradient in a conventional display device.

FIG. 34 is a block diagram of driving means in a conventional display device.

[Explanation of symbols]

Reference Signs List 10: light source 12: luminance gradient forming means 13: image display means 16: minute scattering dots 17: backlight 19: transparent light guide plate 30: video signal decoding means 31: signal correction means 32: display element interface means 33: gradation Adjusting means 40: Extraction voltage varying means 41: Substrate 42: Phosphor 43: Anode electrode 44: Extraction electrode 45: Electron gun 46: Extraction voltage 47: Acceleration voltage 50: Decoder means 51: Position detection means 52: Brightness level detecting means 53: first look-up table 54: second look-up table 55: first multiplying means 56: second multiplying means 57: external light detecting means 58: third look-up table 59: Operating time detecting means 60: fourth look-up table 61: temporal change detecting means 62: Fifth lookup table

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 5/06 H04N 5/66 B H04N 5/66 G02F 1/1335 530 (72) Inventor Akifumi Ogihara Osaka Prefecture 1006 Kadoma, Kadoma Matsushita Electric Industrial Co., Ltd. (72) Inventor Junko Asayama 1006 Kadoma, Kadoma, Osaka Prefecture F-term (reference) in Sangyo Co., Ltd. 2H091 FA23Z FA41Z FD04 GA11 LA18 2H093 NA52 NC49 ND03 ND06 ND07 ND09 ND39 NE06 5C058 AA01 AA07 AA08 AA11 AA12 AA13 BA05 BA07 BA26 BB14 5C080 AA05 EJ05 EJ05 EJ05 BB05 BB51 CA11 CB03 DA51 DA71 MM10

Claims (60)

[Claims] An image display unit; and a luminance gradient forming unit configured to form a luminance gradient by substantially monotonically decreasing luminance from a substantially center of a display screen of the image display unit to a peripheral portion when displaying an all white signal. An image display device comprising: 2. The image display device according to claim 1, wherein the luminance gradient is a luminance gradient that decreases substantially monotonically in a horizontal direction and a vertical direction from a substantially center of the display screen. 3. The image display device according to claim 1, wherein the luminance gradient is a luminance gradient that is substantially symmetric with respect to a horizontal axis passing through a substantially center of the display screen. 4. The image display device according to claim 1, wherein the brightness gradient is a brightness gradient that is substantially symmetric with respect to a vertical axis passing through a substantially center of the display screen. 5. The luminance B at a point in the screen at a distance x in the horizontal direction and a distance y in the vertical direction from the approximate center of the display screen as an origin, is substantially represented by a luminance gradient function f (x, y). The image display device according to claim 1, wherein the values are equal. 6. The brightness gradient function f (x, y) is calculated by a brightness distribution shape function r (x, y) defining a distribution shape.
6. The image display device according to claim 5, wherein (x, y) = f (r). 7. The luminance distribution shape function r is r = (x ² +
y ²⁾ (image display apparatus according to claim 6, characterized in that the ^1/2). 8. The luminance distribution shape function r is such that when a and b are positive constants, r = ((x / a) ² + (y / b) ² ) ^(1/2)
The image display device according to claim 6, wherein 9. The image display device according to claim 8, wherein the ratio of the positive constants a and b is substantially equal to one of 4: 3, 16: 9, and 5: 4. 10. The luminance distribution shape function r is represented by h when the total length in the horizontal direction of the display image is h and the total length in the vertical direction is v.
7. The image display device according to claim 6, wherein: = rect (1 / h × x, 1 / v × y). 11. The luminance distribution shape function r is represented by r when the total length in the horizontal direction of the display image is h and the total length in the vertical direction is v.
= Rect (1 / (h × (x × cos θ−y × sin θ)), 1 / (v × (xx
7. sin θ + y × cos θ)))
An image display device according to claim 1. 12. The image display device according to claim 6, wherein the brightness distribution shape function r is r = x or r = y. 13. The image display device according to claim 6, wherein the luminance gradient function f (r) decreases substantially monotonically with r. 14. The luminance gradient function f (r) is a and b
14. The image display device according to claim 13, wherein when is a positive constant, f (r) = − a × r + b. 15. The brightness gradient function f (r) is a and b
14. The image display apparatus according to claim 13, wherein when is a positive constant, f (r) = a × exp (−b × r). 16. The luminance gradient function f (r) is a and b
Is a positive constant, f (r) = a × exp ｛− (r / b) ² /
The image display device according to claim 13, wherein the image display device is represented by 2｝. 17. The method according to claim 13, wherein the luminance gradient function f (r) is represented by f (r) = − a × r ＾ b + c when a, b, and c are positive constants. The image display device as described in the above. 18. The luminance gradient function f (r) is f (r) = a × cos (2π / λ ×) when a, b and λ are positive constants.
The image display device according to claim 13, wherein the image display device is represented by (b × r). 19. The brightness gradient function f (r) is represented by a,
When b, c, and d are positive constants, f (r) = a / (b × r
The image display device according to claim 13, wherein the image display device is represented by + c) + d. 20. The image display device according to claim 1, wherein the luminance ratio between the luminance at the 0.9 diagonal angle of view and the central part when displaying the all-white signal is the boundary luminance. 21. The boundary value luminance is 54%, 30%, 1
21. The image display device according to claim 20, wherein the value is substantially equal to any one of 5%. 22. The image display device according to claim 1, wherein said image display means is a light receiving type display means. 23. The image display device according to claim 1, wherein said light receiving type display means is a liquid crystal panel. 24. The light receiving type means is a liquid crystal panel,
23. The image display device according to claim 22, wherein the image on the liquid crystal panel is enlarged and projected to display the image. 25. The image display device according to claim 1, wherein said image display means is a self-luminous display means. 26. The image display apparatus according to claim 1, wherein said image display means displays an image by emitting a phosphor by scanning a cathode ray. 27. The image display device according to claim 26, comprising a plurality of cathode ray sources. 28. The image display device according to claim 1, wherein said image display means is a plasma display. 29. The image display device according to claim 1, wherein said image display means emits light by electroluminescence. 30. The image display device according to claim 1, wherein the luminance gradient forming means has a transparent light guide and a plurality of fine scatterers formed on a back surface. 31. The two-dimensional distribution of the density or opening area of the fine scatterers is a luminance distribution obtained when the density or opening area of the fine scatterers is equal over the entire rear surface of the transparent light guide, and is a desired distribution. 31. The image display device according to claim 30, wherein the value is substantially equal to a value obtained by dividing the luminance distribution. 32. The image according to claim 1, wherein said luminance gradient forming means comprises a plurality of light sources, and the distribution of the light sources is sparse from a substantially central portion of the screen to a peripheral portion of the screen. Display device. 33. The image display device according to claim 1, wherein said luminance gradient forming means modulates an input signal to form a luminance distribution in a screen. 34. The image display apparatus according to claim 1, wherein said luminance gradient forming means has a look-up table for defining at least the gradation of each pixel in the image. 35. The image display apparatus according to claim 1, wherein said luminance gradient forming means has at least a display element interface means and changes a gain of a level shift. 36. The image display device according to claim 1, wherein said luminance gradient forming means has a drawing voltage varying means. 37. An image display device comprising: an image display unit; and a luminance gradient forming unit that forms a luminance gradient, wherein the luminance gradient forming unit detects a signal level of each pixel of a video signal. Means, position detecting means for detecting two-dimensional coordinate information in an image of a video signal, different gamma curves are set for different positions, and a second multiplication gain determined according to a signal level based on the gamma curve is calculated. A second look-up table for storing two-dimensional coordinate information from the position detecting means and luminance level information from the luminance level detecting means, and outputting a second multiplication gain according to the input information; And first multiplying means for multiplying a signal level of the video signal by a second multiplication gain output from the second look-up table. Image display device. 38. An image display device comprising: an image display unit; and a luminance gradient forming unit that forms a luminance gradient, wherein the luminance gradient forming unit detects a signal level of each pixel of a video signal. Means, an external light detecting means for detecting an external light level on the screen, and a third multiplication gain determined by the external light level and the signal level to compensate for a γ value caused by a change in contrast due to the external light. The external light level indicator information from the external light detecting means and the luminance level information from the luminance level detecting means are input, and a third level corresponding to the input information is stored.
And a third multiplying means for multiplying the signal level of the video signal by the third multiplication gain output from the third lookup table. Image display device. 39. An image display device comprising: an image display unit; and a luminance gradient forming unit that forms a luminance gradient, wherein the luminance gradient forming unit detects a signal level of each pixel of a video signal. Means for detecting an image display time; and a fourth means determined by an image display time and a signal level to compensate for a γ value caused by a change in peak luminance due to aging.
And the image display time information from the operation time detecting means and the luminance level information from the luminance level detecting means are input, and a fourth multiplying gain corresponding to the input information is output. And a fourth multiplying means for multiplying a signal level of the video signal by a fourth multiplication gain output from the fourth lookup table. 40. An image display device comprising: an image display unit; and a luminance gradient forming unit that forms a luminance gradient, wherein the luminance gradient forming unit detects a signal level of each pixel of a video signal. Means, a time-dependent change detecting means for detecting the time-dependent change level of the luminance, and a fifth multiplication gain determined by the time-dependent change level and the signal level so as to compensate for the γ value caused by the change in the peak luminance due to the time change. A fifth look-up for inputting the temporal change level information from the temporal change detecting means and the luminance level information from the luminance level detecting means and outputting a fifth multiplication gain according to the input information. And a fifth multiplying means for multiplying a signal level of the video signal by a fifth multiplication gain output from the fifth look-up table. An image display device comprising: 41. A luminance gradient forming unit comprising: a position detecting unit for detecting two-dimensional coordinate information in an image of a video signal; a luminance level detecting unit for detecting a signal level of each pixel of the video signal; A first multiplication gain corresponding to the two-dimensional coordinate information is stored in order to modulate the luminance so as to have a predetermined luminance gradient from a substantially central part toward a peripheral part, and the two-dimensional coordinate from the position detecting means is stored. A first look-up table for inputting information and outputting a first multiplication gain according to the input information; and a different gamma curve set for each different position and determined corresponding to a signal level based on the gamma curve. 2 and the two-dimensional coordinate information from the position detecting means and the luminance level information from the luminance level detecting means are input, and a second multiplication is performed according to the input information. A second look-up table for outputting a signal, a first multiplying means for multiplying a signal level of the video signal by a second multiplication gain output from the second look-up table, and the first look-up table. And a second multiplication means for multiplying the multiplication result of the first multiplication means by the first multiplication gain output from the second multiplication means. The image display means displays an image according to an output of the second multiplication means. 2. The image display device according to claim 1, wherein the image is displayed. 42. A luminance gradient forming means, a position detecting means for detecting two-dimensional coordinate information in an image of a video signal, a luminance level detecting means for detecting a signal level of each pixel of a video signal, External light detecting means for detecting an external light level; and first multiplication according to two-dimensional coordinate information for modulating luminance so as to have a predetermined luminance gradient from a substantially central portion of the display screen toward the peripheral portion. A first look-up table for storing the gain, inputting the two-dimensional coordinate information from the position detecting means, and outputting a first multiplication gain according to the input information, and a change in contrast caused by external light. In order to compensate for the γ value, a third multiplication gain determined by the external light level and the signal level is stored, and the external light level indicator information from the external light detection means and the third multiplication gain from the luminance level detection means are stored. A third lookup table for inputting luminance level information and outputting a third multiplication gain according to the input information; and a third multiplication gain output from the third lookup table as a signal level of a video signal. And a sixth multiplying means for multiplying a multiplication result of the third multiplying means by a first multiplication gain output from the first look-up table, wherein the image The image display device according to claim 1, wherein the display means displays an image in accordance with an output of the sixth multiplication means. 43. A luminance gradient forming means, a position detecting means for detecting two-dimensional coordinate information in an image of a video signal, a luminance level detecting means for detecting a signal level of each pixel of the video signal, and an image display time. And a first multiplication gain corresponding to the two-dimensional coordinate information for modulating the luminance so as to have a predetermined luminance gradient from a substantially central part of the display screen toward the peripheral part. And a first look-up table for inputting two-dimensional coordinate information from the position detecting means and outputting a first multiplication gain according to the input information, and a change in peak luminance due to a change with time. γ
In order to compensate for the values, a fourth multiplication gain determined by the image display time and the signal level is stored, and image display time information from the operation time detection means and luminance level information from the luminance level detection means are input. A fourth lookup table for outputting a fourth multiplication gain according to the input information; and a fourth lookup table for multiplying the signal level of the video signal by a fourth multiplication gain output from the fourth lookup table. Multiplying means, and seventh multiplying means for multiplying a multiplication result of the fourth multiplying means by a first multiplication gain output from the first look-up table, wherein the image display means comprises: 2. The image display device according to claim 1, wherein an image is displayed according to an output of the seventh multiplication means. 44. A luminance gradient forming means, a position detecting means for detecting two-dimensional coordinate information in an image of a video signal, a luminance level detecting means for detecting a signal level of each pixel of the video signal, A temporal change detecting means for detecting a change level; and a first multiplication gain corresponding to two-dimensional coordinate information for modulating luminance so as to have a predetermined luminance gradient from a substantially central portion to a peripheral portion of the display screen. And a first look-up table for inputting the two-dimensional coordinate information from the position detecting means and outputting a first multiplication gain according to the input information. Γ caused
In order to compensate the values, the fifth multiplication gain determined by the aging level and the signal level is stored, and
Input the temporal change level information from the temporal change detecting means and the luminance level information from the luminance level detecting means,
A fifth look-up table for outputting a fifth multiplication gain according to input information, and a fifth multiplication means for multiplying the signal level of the video signal by the fifth multiplication gain output from the fifth look-up table And an eighth multiplying means for multiplying a multiplication result of the fifth multiplying means by a first multiplication gain output from the first look-up table, wherein the image display means comprises: 2. The image display device according to claim 1, wherein an image is displayed according to an output of said multiplication means. 45. The luminance at the time of an all white signal is L, the contrast in a bright place is CR, the contrast in a dark place is Cr, and the gradation coefficient is γ
M indicates the luminance of the all black display when there is no influence of external light.
F. An image display device characterized in that when the brightness increase due to the influence of external light is BG, the brightness index BI represented by (Equation 1) is substantially equal in the screen when all white signals are displayed. (Equation 1) BI = a × L + b × CR + d × γM + g = a × L + b × L / (OFF + BG) + d × γM + g = a × L + b / (1 / Cr + BG / L) + d × γM + g 46. The value of a is 0.00423339-0.002671539.
≦ a ≦ 0.00423339 + 0.002671539, and b is 0.007648902−0.005754385 ≦ b ≦ 0.007648902
+0.005754385, and d is −79.52542076−18.92439144 ≦ d ≦ −79.52542
076 + 18.92439144, wherein the g is -0.7131531895-0.16046239 ≦ g ≦ −0.713153
The pixel display device according to claim 45, wherein the value is 1895 + 0.16046239. 47. An external light detecting means for detecting an external light level on a screen, and a sixth multiplication gain for compensating a lightness index fluctuated by the external light so that the lightness index becomes constant in the screen. A third look-up table for outputting a third multiplication gain according to the outside light level information from the outside light detection means, and a third multiplication gain output from the third look-up table as a video signal. 46. The image display device according to claim 45, further comprising: third multiplication means for multiplying the signal level of the third multiplication means; and image display means for displaying an image according to an output of the third multiplication means. 48. An operation time detecting means for detecting an image display time, and a fourth multiplication gain for compensating for a lightness index fluctuated by the operation time so that the lightness index becomes constant in a screen, and
A fourth operation mode according to the operation time information from the operation time detecting means.
A fourth look-up table for outputting a multiplication gain of the fourth multiplication gain, a fourth multiplication means for multiplying the signal level of the video signal by a fourth multiplication gain output from the fourth lookup table, and the fourth multiplication. The image display device according to claim 45, further comprising: image display means for displaying an image according to an output of the means. 49. A temporal change detecting means for detecting a temporal change level of luminance, and a fifth multiplying gain for compensating for a lightness index fluctuated due to the temporal change so that the lightness index becomes constant in a screen, is stored.
Fifth according to the temporal change information from the temporal change detecting means.
A fifth look-up table that outputs a multiplication gain of the fifth multiplication gain; a fifth multiplication unit that multiplies the signal level of the video signal by a fifth multiplication gain output from the fifth look-up table; The image display device according to claim 45, further comprising: image display means for displaying an image according to an output of the means. 50. A display device comprising a luminance gradient forming means and an image display means, wherein the luminance gradient forming means displays a brightness index BI represented by (Equation 1) when displaying an all-white signal in a display image. An image display device characterized in that the density is reduced substantially monotonously from a center to a peripheral portion. (Equation 1) BI = a × L + b × CR + d × γM + g = a × L + b × L / (OFF + BG) + d × γM + g = a × L + b / (1 / Cr + BG / L) + d × γM + g where L is the value when all white signals are used. Brightness, CR is bright place contrast, Cr is dark place contrast, γM is gradation coefficient, OF
F indicates the luminance at the time of full black display without the influence of external light, and BG indicates the luminance increase due to the influence of external light. 51. The a is 0.00423339-0.002671539.
≦ a ≦ 0.00423339 + 0.002671539, and b is 0.007648902−0.005754385 ≦ b ≦ 0.007648902
+0.005754385, and d is −79.52542076−18.92439144 ≦ d ≦ −79.52542
076 + 18.92439144, wherein the g is -0.7131531895-0.16046239 ≦ g ≦ −0.713153
The pixel display device according to claim 50, wherein 1895 + 0.16046239. 52. The image display apparatus according to claim 50, further comprising a brightness index improving unit, wherein said brightness index improving unit changes the gradation in a screen. 53. The image display device according to claim 52, wherein said brightness index improving means has a look-up table for defining the gradation of each pixel in the image. 54. An image display apparatus according to claim 52, wherein said brightness index improving means has at least a display element interface means and changes a gain of a level shift. 55. The image display device according to claim 52, wherein said brightness index improving means has a drawing voltage varying means. 56. The image display apparatus according to claim 52, wherein said brightness index improving means compensates said brightness index substantially uniformly over the entire area of the screen. 57. The image display apparatus according to claim 52, wherein said brightness index improving means compensates said brightness index substantially uniformly over the entire area of 0.5 diagonal angles of view. 58. The brightness index improving unit corrects a distribution shape of the brightness index in a screen.
3. The image display device according to 2. 59. The image display apparatus according to claim 52, wherein said brightness index improving means corrects a gradient of the brightness index. 60. The apparatus according to claim 52, wherein the brightness index improving means corrects a substantially periodic change in luminance in the screen.
An image display device according to claim 1.