JP2002099250A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device which enables to enlarge a dynamic range even for a picture having large brightness inclination in a screen and displaying a high definition picture. SOLUTION: This display device is provided with picture displaying parts 11, 22, an illuminating part 12 which has plural illuminating regions which illuminate the inside of the picture displaying parts, luminous brightness controlling parts 14-18 which control the brightness of the respective illuminating regions of the illuminating part on the basis of an input picture signal and picture signal converting parts 19-21 which convert the input picture signal on the basis of brightness information with respect to the respective illuminating regions of the illuminating part which is obtained on the luminous brightness controlling parts and supplies the transferred picture signal toward the picture displaying parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a display device such as a liquid crystal display device.

[0002]

2. Description of the Related Art A non-light emitting type represented by a liquid crystal display (LCD), that is, a display pixel itself does not emit light,
A display device that controls transmittance or reflectance in accordance with image information includes an illumination device that illuminates a display screen, except for some reflective display devices that use ambient light. Normally, the lighting device is normally lit, and illuminates the liquid crystal display (liquid crystal panel) with a constant luminance.

In a direct-view LCD in which a liquid crystal display section is directly viewed, an illuminating device is a planar light emitting element, and a cold cathode fluorescent tube is mainly used as a light source. Such a flat backlight is classified into a direct type and a sidelight type according to the arrangement of fluorescent tubes. The former has a structure in which a plurality of fluorescent tubes are arranged directly below a liquid crystal panel, and the latter employs a method in which a light guide plate is arranged directly below a liquid crystal panel, and a fluorescent tube is arranged on an end face of the light guide plate for illumination. Since the direct type can increase the brightness,
Mainly used for LCDs for in-vehicle and large-sized PC monitors, the sidelight type is widely used for LCDs for small and medium-sized PCs for mobile use because it consumes less power and can be made thinner. In both methods, a uniform luminance distribution can be obtained over the entire light emitting surface by inserting a plurality of transmissive diffusion plates directly below the liquid crystal panel so as to prevent luminance unevenness on the liquid crystal display screen.

In recent years, for LCDs for mobile phones,
White LE that does not require an inverter for the backlight source
A method using D has also been proposed.

On the other hand, a proposal has been made to extend the dynamic range of display by making the luminance of a backlight, which was conventionally constant over time, variable over time according to image information. That is, the backlight is darkened for an image in which a large amount of black information is displayed, and the backlight is brightly lit for an image in which a large amount of white information is displayed.
That is.

The above-described method of temporally controlling the backlight luminance is effective as a method of expanding the dynamic range of an LCD, which is said to be narrower than that of a conventional CRT. However, since the backlight brightness is controlled collectively over the entire screen, the backlight brightness is temporally constant for an image including many highlight portions that cause a large brightness gradient in the screen. The dynamic range is the same as a certain conventional method,
The problem that the dynamic range is lower than T cannot be solved.

[0007]

As described above, in a conventional non-light emitting type display device represented by a liquid crystal display device, the CR
There is a problem that the dynamic range is narrower than T, and as a solution to this problem, a method has been proposed in which the luminance of the backlight is temporally changed according to image information.
Since the backlight brightness is controlled collectively for the entire screen, it has been difficult to widen the dynamic range for an image having a large brightness gradient in the screen.

The present invention has been made to solve the above-mentioned conventional problems, and can expand the dynamic range even for an image having a large luminance gradient in a screen.
It is an object to provide a display device capable of displaying a high-quality image.

[0009]

A display device according to the present invention illuminates an image display section, an image display area of the image display section, and includes an illumination section having a plurality of illumination areas, and an input image. An illumination luminance control unit that controls the luminance of each illumination region of the illumination unit based on the signal; and converting the input image signal based on luminance information for each illumination region of the illumination unit obtained by the illumination luminance control unit. And an image signal conversion unit for supplying the converted image signal to the image display unit.

It is preferable that the image signal conversion section has a function of converting the gradation of the input image signal based on the luminance information.

In the present invention, since the brightness of each illumination area of the illumination section is controlled based on the input image signal, the display portion of the entire screen that contains a lot of bright image information is provided with illumination light. On the other hand, the luminance of the illumination light can be reduced for a display portion having a high luminance and containing a lot of dark image information, and the dynamic range of the entire screen can be expanded. However, since the luminance of the illumination light is changed for each illumination area, if the input image signal is supplied to the image display unit with the same gradation, the luminance of the display image is shifted between the illumination areas. In the present invention, since the input image signal is converted according to the luminance of the illumination light for each illumination area, the display image between each illumination area is converted according to the appropriate gradation converted according to the luminance of the illumination light of each illumination area. It is possible to obtain an appropriate image with no deviation in luminance.

As described above, according to the present invention, it is possible to display a high-contrast, high-definition appropriate image having a wide dynamic range even for an image having a large luminance gradient in the screen. Become.

[0013] By configuring the illuminating section using a plurality of types of light emitting elements having different light emitting principles, for example, the entire screen is illuminated by a certain light emitting element, and the luminance of each illumination area is illuminated by another light emitting element. Control according to the suitability of each light emitting element, such as changing, can be performed.

When a plurality of types of light emitting elements are used,
Generally, the emission color differs depending on the type of light emitting element (spectral distribution differs), but by providing a color compensator that performs color compensation according to the difference in emission color, a high-quality image with little color shift can be obtained. Becomes possible.

Further, by dividing each illumination area of the illumination section by a partition, mutual interference of illumination light between adjacent illumination areas can be suppressed, and a higher quality image can be obtained. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an outline of a display device according to an embodiment of the present invention will be described.

The present display device can be roughly divided into a non-light-emitting type display device, a lighting device having a plurality of divided lighting regions, a lighting control circuit capable of independently controlling the brightness of each lighting region, and a conversion of an image signal. Image conversion circuit.

A transmissive liquid crystal panel is most suitable as a non-emissive display element. The transmission type liquid crystal panel may be of any type as long as it can display multiple gradations, and may be an active matrix type or a passive matrix type having a switching element such as a TFT. As for the liquid crystal display mode, smectic liquid crystals such as antiferroelectric liquid crystals as well as nematic liquid crystals such as TN, VA, IPS, and OCB which are currently in practical use can be used. SSFLs that cannot be electrically displayed in multiple gradations
C and the like can also be used because pseudo grayscale display is possible by performing temporal switching.

In order to spatially control the brightness, a plurality of light sources may be provided, or a shutter capable of blocking and transmitting light from the light source for each area may be provided. In the case where a plurality of light sources are provided, it is effective to provide a plurality of rows of fluorescent tubes and independently control the light emission thereof or to combine LEDs. In particular, the brightness of the fluorescent tube is controlled when the brightness of the entire screen is collectively controlled, and the LE is controlled when the brightness of a specific area is controlled.
It is desirable to use D. When the gradation is uniform over the entire screen, such as in raster display, it is desirable that the luminance of the backlight be uniform in the plane. When light and dark occur in the screen, a continuous luminance change will occur according to the image information. Is desirable.

The image conversion circuit is a circuit for converting the image information input to the liquid crystal panel based on the luminance distribution information of the backlight so that a correct gradation reproduction can be obtained in the screen. The backlight brightness control and the image information conversion are performed, for example, by the following procedure.

First, the input image information is analyzed for each control area of the backlight, and the average or most frequent gradation, the maximum gradation and the minimum gradation are extracted. The luminance distribution of the backlight is determined based on the image information. That is, when the image information includes a lot of bright luminance information, the luminance of the backlight is set high, and when the image information includes a lot of dark luminance information, the luminance of the backlight is set low.

Next, based on the result of the backlight control,
A gradation shift amount is determined for each image area having a smaller area. At this time, even if the backlight luminance control values for illuminating the image area are the same, the gradation shift amounts are not necessarily the same. This is because even if the brightness control value for directly illuminating the image area is the same, the brightness control value around the image illumination area changes due to surrounding image information, and the image area is illuminated by crosstalk between the backlight illumination areas. This is because the luminance value changes. Therefore, an appropriate gradation shift amount is determined based on the matrix information of the luminance control value for illuminating the image. The gray scale shift amount is also generally not linear, but is shifted non-linearly according to a γ characteristic relating the gray scale to the display luminance level.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a diagram showing a configuration example of a display device main body of this embodiment. The display device body is
It is composed of a transmissive liquid crystal light valve (LCD 11) and a backlight unit (backlight 12), and an image is displayed by illumination from the back of the LCD.

The LCD 11 and the backlight 12 are each divided into a plurality of regions. In the LCD 11, the RGB signals are modulated and controlled for each pixel based on the RGB gradation conversion data for each region. In the backlight 12, L
Brightness control is performed based on image brightness information for each area of the CD 12. In the present embodiment, as shown in FIG.
The LCD 11 was divided into a 6 × 8 area (FIG. 2A), and the backlight 12 was divided into a 3 × 4 area (FIG. 2B). For convenience,
The area on the LCD 11 is (i, j), and the backlight 1
The area in 2 is denoted by [i, j].

FIG. 3 is a block diagram mainly showing signal processing in the display device of the present embodiment.

The RGB input image signals are temporarily stored in the frame memory 13 and then read out for each LCD area.
A luminance value for each LCD area is calculated by the image luminance calculation circuit 14 based on the read data, and the calculated luminance data for each LCD area is sent to the image luminance data holding unit 15. Based on the brightness data for each LCD area from the image brightness data holding unit 15, the backlight brightness level for each backlight area is changed to a B / L (backlight) brightness calculation circuit 16.
The calculated brightness data for each backlight area is sent to the backlight brightness data holding unit 17. The backlight brightness control circuit 18 controls the backlight brightness for each area based on the calculation result of the backlight brightness calculation circuit 16.

On the other hand, the R stored in the frame memory 13
The GB input image signal is sequentially read out for each pixel, and the backlight 1 illuminates the pixel area by the gradation conversion circuit 19.
2 undergoes gradation modulation based on the luminance data. Further, based on the backlight luminance information around the pixel area,
Using the data of the gradation correction LUT (look-up table) 20, the gradation correction circuit 21 receives an appropriate gradation correction, and the RGB signals finally input to the LCD driver 22.
The sequence is converted into a signal (R "G" B ").

FIG. 4 is a diagram showing the correspondence between the luminance level of the backlight, the luminance and the gradation signal in the present embodiment.

In this embodiment, the brightness level of the backlight is controlled in three stages. The LCD according to the present embodiment has a contrast of 200, an input signal level to the driver of 8 bits each for RGB, and a γ value (input signal level versus transmittance) of 2.2 which is the same as that of a CRT. As a white luminance obtained when a white display signal (R = G = B = 255) is input to the LCD, a white display luminance 250c at level 2 is obtained.
With d / m ² as a reference (gain 1), the backlight luminance at level 1 was set to 0.2 times and that at level 3 was set to 3.0 times.

At this time, the luminance of the input RGB signal versus the luminance at each backlight luminance level is represented by B = G {K + [W−K] × (S _{RGB / 255} ) ^γ } (1) Here, B: backlight luminance (cd / m
² ), G: gain, W: white display luminance at gain 1,
K: black display luminance (= W / contrast) at gain 1, S _RGB : input signal (0 to 255), γ: gamma value. FIGS. 5A and 5B are diagrams showing the relationship between the input RGB signal level and the screen luminance at each backlight luminance level.

FIGS. 6A and 6B show the relationship between the gradation signal R'G'B 'and the screen luminance when 8-bit display is performed using the entire range of the backlight levels 1 to 3. It is a figure showing a relation.

The relationship between screen brightness B 'level S _R'G'B' of gradation signals R'G'B _{is, B = K min + [W} max -K min] × (S R'G'B _' / 255) ^γ (2) Here, W _max is the maximum white display luminance, K _min
Is the minimum black display luminance. In the present embodiment, the white display luminance at level 3 (750 cd / m ² ) and the black display luminance at level 1 (0.25 cd / m ² ), respectively. From the white and black display luminances of each level, the gradation signal R'G '
The displayable signal range of each level at B ′ can be obtained. 0 to 74 at level 1 and 12 to 1 at level 2
54, level 3 is 22-255.

In the present invention for controlling the backlight luminance, since the input signal RGB is nothing but the gradation signal R'G'B ', the gradation to be inputted to the LCD driver is obtained by using the equations (1) and (2). The signal R "G" B "can be obtained.
Input gradation signal R'G'B 'and LCD output gradation signal R "
FIG. 7 shows the relationship with G "B". When the γ value is not 1, the two have a non-linear relationship. However, since the two can be approximated by a substantially linear relationship as shown in FIG. 7, the gradation conversion process can be realized by a small-scale circuit.

Next, a gradation correction method performed after the gradation conversion processing will be specifically described together with the above-described method of determining the backlight luminance level.

FIG. 8 shows the input RGB signal levels corresponding to the images stored in the frame memory in FIG.
FIG. 9 is a diagram showing an example of a result of calculating an average luminance gradation for each pixel region. The relationship between the RGB signal and the signal luminance level Y can be expressed as Y = 0.30R + 0.59G + 0.11B (3) in consideration of the visibility of each RGB signal. The coefficients in equation (3) are RGB
Each chromaticity point and white point are determined by the specifications of the display system. In addition, although the error increases, it is also possible to substitute a G value with high visibility in order to reduce the calculation load.

In this embodiment, the 2 × 2 pixel area corresponds to the backlight unit area (see FIG. 2), and the average luminance is calculated for each backlight area from FIG. 8 as shown in FIG. it can. Similarly, the maximum value and the minimum value of the RGB signal on the backlight area can be calculated from the maximum value and the minimum value of the signal level for each pixel area.

The luminance level of each area of the backlight is determined from the average, maximum and minimum luminance signal levels in a procedure as shown in FIG.

That is, for example, an appropriate backlight luminance level is selected based on the average luminance signal level, and other parameters (here, maximum and minimum values) are set to the displayable signal level range at the selected backlight luminance level. Determine if it fits. When any of the parameters is out of the range, the backlight luminance level is selected by the repetitive processing. If all parameters are not included in the displayable signal level range at any of the backlight luminance levels, a backlight luminance level that includes either the minimum value or the maximum value is selected.
Which of the maximum value and the minimum value is preferentially within the range is arbitrary, and the criterion may be switched automatically or manually. One policy for automatically switching is to select a backlight luminance level such that the average luminance signal level is closest to the center of the displayable signal level range,
And the like. In the case of fixed, it is generally desirable to give priority to the minimum value side that is sensitive to luminosity, but it cannot be said unconditionally because it depends on the picture of the display image.

In the present embodiment, the backlight luminance level as shown in FIG. 10B is selected from the RGB display average luminance signal levels for each backlight area as shown in FIG.

RG sequentially read from the frame memory
The B signal level is subjected to gradation conversion based on the backlight luminance level information of each illumination area (see FIG. 10B) based on the relationship shown in FIG. However, it is necessary to perform a gradation correction process for the following reasons.

FIG. 11 shows an area [2, 2] in which the luminance level 1 is selected in FIG. 10B and an area [3, 2] located on the lower side of the screen of [2, 2] and having the luminance level 3 selected. 2] is a diagram schematically illustrating a spatial distribution of luminance during white display in [2].

When the backlight luminance is modulated for each area,
Due to crosstalk between the illumination regions, not only the backlight region luminance immediately below but also the luminance of an adjacent illumination region is superimposed on the backlight luminance for illuminating a certain pixel region. That is, the phenomenon that the actual backlight luminance deviates from the backlight luminance used for gradation conversion (illumination error) occurs due to the wraparound of the illumination light from the adjacent area.

In FIG. 11, the slosh talk between the two regions is shown for simplicity. However, in actuality, as shown in FIG. 10B, the region around the [2, 2] region, ie, [1, 1] ,
[1,2], [1,3], [2,1], [2,3],
The actual backlight luminance distribution is determined by the combination of the luminance levels selected in [3, 1], [3, 2], and [3, 3]. The number of divisions of the illumination area, area area,
Since the crosstalk is determined by the design of the backlight and the like, depending on the conditions, the crosstalk may be affected by a change in the luminance level in the illumination area other than the adjacent area. For example, when the actual luminance of the backlight in which the luminance level 1 is selected for a certain pixel region includes an error of 20% with respect to the luminance data at the time of gradation conversion (20% luminance is high),
As shown in FIG. 12, a gradation conversion error of about 2 to 5 gradations occurs, which is visually recognized as a disturbance such as a false contour between pixel regions or gradation inversion.

In order to compensate for a gradation conversion error due to an illumination error, in this embodiment, as shown in FIG.
The final LC is obtained by the gradation correction circuit 21 using T20.
The D driver signal R "G" B "is output.
The gradation correction LUT 20 stores, for each pixel region, gradation correction table data corresponding to a combination of a luminance level of a certain backlight illumination region and a luminance level of a backlight illumination region adjacent thereto. The gradation correction amount is determined with reference to the luminance level information of the image.

As described above, by performing the gradation correction according to the backlight luminance level, it is possible to perform a display without interference. In contrast to the conventional display (white luminance 250 cd / m ² , contrast 200) in which backlight luminance control is not performed, in the present embodiment, white luminance 750 cd / m ² ,
High-quality display with an effective contrast of 3000 can be performed.

Next, a specific configuration for controlling the brightness of the backlight for each area in this embodiment will be described.

FIG. 13 is a diagram schematically showing mainly the structure of the backlight 12 in FIG. In this example,
It has a direct-type structure in which a plurality of cold cathode fluorescent tubes 101 are arranged immediately below the LCD 11.

Each illumination area of the backlight 12 is shown in FIG.
As shown in FIG. 1, a cold cathode fluorescent tube 101 is partitioned by an opaque partition wall 102 also serving as a reflection plate, and penetrates the partition wall. Although not particularly shown, when the fluorescent tubes 101 are lit in a steady state, the LCD 11 is almost uniformly illuminated in the plane without the shadows of the partition walls 102 being generated. In addition, an LED for adjusting brightness is provided below the space 102 between the fluorescent lights.
(Not shown) are arranged in each area.

FIG. 14 is a diagram showing a sectional structure of the backlight 12. In this example, a cold cathode fluorescent tube is disposed above a reflector and a first light source for uniforming luminance is further disposed above the reflector, as in a normal direct-type backlight structure.
Diffusion sheet, prism sheet for improving front luminance gain,
A second diffusion sheet is arranged, and a white LED chip 103 is arranged immediately below the fluorescent tube. This LED10
3 is not a lens type having a high front luminous intensity, but a so-called oval type LED having a wide viewing angle.

As described above, by disposing the LED directly under the fluorescent tube, which has conventionally been poor in light extraction efficiency, a decrease in the light use efficiency of the fluorescent tube is suppressed, and the shadow of the LED and the like are reduced to uniform brightness. Influence is prevented. Further, since the light emission from the LED has an emission distribution suppressed in the normal direction where the fluorescent tube exists, the light use efficiency of both can be maximized.

FIG. 15 is a diagram showing a lighting method of the fluorescent tube 101 and the LED 103. In this example, as shown in FIG. 15, the fluorescent tube 101 is turned on by the inverter circuit 104 in a steady state, and the LED 1 is turned on by the B / L luminance control circuit 105 (corresponding to the B / L luminance control circuit 18 in FIG. 3).
03, the brightness control is performed. The brightness control of the LED 103 is performed according to a control signal, and is controlled segmentally for each illumination area. At the backlight luminance level 1 having the lowest illumination luminance, only the fluorescent tube 101 is lit, and L
ED does not emit light. By controlling the amount of current to the LED 103 at the luminance level 2 and the luminance level 3, the emission intensity of the LED 103 is controlled in two stages, and a desired backlight luminance can be obtained.

By adopting such a lighting method, it is possible to make the entire illumination uniform by using a fluorescent tube having excellent illumination uniformity and chromaticity uniformity. No circuit is required. Also,
An LED having excellent responsiveness and excellent controllability by DC lighting can be effectively used for the purpose of improving luminance. Further, since it is easy to switch between the main lighting method and the conventional backlight steady lighting method, it is possible to appropriately select a display method according to the purpose of use.

Although not explicitly shown in FIG. 15,
By individually adjusting the amount of current of the LEDs in the illumination area, it is possible to improve the brightness uniformity in the illumination area when the LEDs are turned on.

FIG. 16 shows a white LED (NS made by Nichia Chemical).
PW300PS) and cold cathode fluorescent tubes (Harrison Electric 2
FIG. 3 is a diagram showing a light emission spectrum distribution in the case of combination with a 25L3PFJ and a spectral transmittance characteristic of a representative color filter provided in a TFT-LCD.

In general, the emission spectra of the cold cathode fluorescent tube and the white LED are significantly different. When the luminance gain is changed by the white LED, the white point and the RGB chromaticity point shift.

FIG. 17 is a diagram showing a white point and RGB chromaticity points when the luminance gain of the white LED shown in FIG. 16 is changed according to FIG. If the chromaticity shift is extremely large, a color reproduction error occurs between illumination areas having different luminance levels, which is recognized as block noise, and CM.
An obstacle to accurate color reproduction in S (color management system).

In order to reduce the chromaticity shift, the white L
By adjusting the spectra of the ED and the fluorescent tube, the white point is made to match as much as possible. In FIG. 16, the cutoff characteristic of the bull color filter is 500 nm.
Such as not including the phosphor emission spectrum component in the green wavelength region of the white LED,
It is effective to increase the color purity of the color filter.

However, when the effect of reducing the chromaticity shift is insufficient even if such measures are taken, it is possible to eliminate the chromaticity shift by the following example. FIG.
FIG. 2 is a block diagram showing an example of the above.

In FIG. 18, the gradation conversion circuit 1 shown in FIG.
9, the chromaticity calculation circuit 31 and the chromaticity correction LUT 20 for expanding the gradation correction LUT 20 and the gradation correction circuit 21 to perform gradation conversion and correction for not only the luminance level but also the chromaticity value.
UT 32, color correction circuit 33, and RGB signal conversion circuit 34
Is provided.

In FIG. 18, in the chromaticity calculation circuit 31,
A tristimulus value XYZ is calculated based on the RGB input signal and the backlight luminance level determined from the input signal value. The corrected XYZ is obtained by converting the tristimulus values predicted in this manner into a correction value and a color correction amount due to the backlight illumination distribution using the color correction LUT 32. Further, the signal level R "G" B "to be applied to the LCD driver 22 is calculated by inverse conversion from (X, Y, Z) to (R, G, B).

For example, when the luminance level is 1, that is, under the illumination condition of only the cold cathode fluorescent lamp, the tristimulus value for the RGB output signal (R ′, G ′, B ′) considering the γ characteristic with respect to the RGB input signal is represented by (X ', Y', Z '). (R ',
G ′, B ′) to (X ′, Y ′, Z ′) is 3
Using a × 3 linear matrix M, it is expressed as (X ′, Y ′, Z ′) ^t = M (R ′, G ′, B ′) ^t (4) Where (X ′, Y ′, Z ′) ^t is
Represents the transpose of (X ′, Y ′, Z ′). Matrix M
Elements are represented by RGB, (1, 0, 0), (0,
(1,0) and (0,0,1) are the XYZ tristimulus values when RGB output signals are given.

On the other hand, it is possible to similarly define a linear matrix that relates the tristimulus values XYZ obtained under the illumination condition of only the white LED and the RGB output signals.
If this matrix is M ', the cold cathode tube and the white LED
(R ′,
The relational expression for conversion from (G ′, B ′) to (X ′, Y ′, Z ′) is: (X ′, Y ′, Z ′) ^t = M (R ′, G ′, B ′) ^t + gM '(R', G ', B') ^t = (M + gM ') (R', G ', B') ^t = N (R ', G', B ') ^t (5) N = M + gM' (6 ). Here, g is a constant and is given from the gain, that is, the luminance level of the white LED.

Now, as the RGB output signals (R ₀ ′, G ₀ ′,
If you give B ₀ '), the color correction RGB output signal to be obtained ^{_{(R 0 ", G 0"}} , B 0 ") , the cold cathode fluorescent tube lighting and the cold cathode fluorescent tube lighting + chromaticity values in the white LED lighting (Tristimulus values)
Conditions are equal _{sM (R 0 ', G 0} ', B 0 ') t = N (R 0 ", G 0", B 0 ") from the _{^{t (7), (R 0}} ", G 0 ", B ^{_{0 ") t = sN -1 M}} (R 0 ', G 0', B 0 ') can be obtained by ^t (8). Here, s is a proportionality constant assuming that the same luminance as that of the cold cathode fluorescent tube illumination + white LED illumination is obtained under the illumination condition of only the cold cathode fluorescent tube illumination, and N ⁻¹ is an inverse matrix of N It is.

In addition, the present method uses not only white LEDs but also white LEDs.
This is also effective when the RGB LEDs are arranged. FIG. 19 shows emission spectra of LEDs of each color of RGB.
FIG. 3 is a diagram illustrating an emission spectrum of a cold cathode tube and a spectral transmittance of an RGB color filter. In this configuration, since the emission intensity of each color LED can be controlled independently, FIG.
As shown in (1), it is easy to match the white point of the LED with the white point of the fluorescent tube.

In this method, since the color difference between the two illumination conditions in the halftone display is not so large, as shown in FIG.
By providing the UT 42, it is also possible to perform color compensation on a signal having a saturation of a certain level or more by gradation conversion processing in which simple color correction is added. In this case, since compensation is performed on the RGB signal level having a certain luminance and saturation,
The memory and the signal conversion circuit can be simplified.

(Embodiment 2) FIG. 22 is a diagram showing a configuration of a main part in a second embodiment of the present invention. In the present embodiment, as shown in FIG. 23, a direct type structure using only the cold cathode fluorescent tubes 111 as the backlight 12 is adopted, and each cold cathode fluorescent tube 111 is separated by a partition wall 112. Also, as shown in FIG. 22, a plurality of inverter circuits 113 for lighting each of the cold cathode tubes are independently provided, and the inverter circuits 113 correspond to the B / L luminance control circuit 114 (corresponding to the B / L luminance control circuit 18 in FIG. 3). )It is connected to the.

According to the present embodiment, a plurality of inverter circuits 113 are provided in a conventional LCD having a direct backlight structure.
And a simple structure in which only a B / L luminance control circuit and a gradation conversion circuit as shown in FIG. 3 are provided. As shown in FIG. 24, the illumination luminance according to the image luminance information in the fluorescent tube arrangement direction. It is possible to have a distribution. The effect that the circuit size can be reduced is that the backlight structure can be used with almost the same structure as the conventional one and the number of screen divisions is small, so that the gradation correction data corresponding to the combination of the luminance levels is reduced.

(Embodiment 3) FIG. 25 is a diagram showing a configuration of a main part in a third embodiment of the present invention. The present embodiment is characterized in that a plurality of illumination areas are constituted only by the white LED 121 without using a cold cathode tube as a backlight light source. In this embodiment, since the cold cathode tube and the inverter are not used, the light source can be reduced in weight and simplified.

FIG. 26 is a diagram showing the relationship between the arrangement of the LEDs in the screen, the effective illumination area by each LED, and the pixel area subjected to the gradation conversion process when the illumination area is not partitioned by a partition wall or the like. In this configuration, the LEDs are densely arranged to make the luminance uniform. In such a configuration, since there is no clear illumination area as in the first embodiment, a plurality of effective illumination areas corresponding to each LED serve as a reference for selecting a luminance level. Further, for gradation correction, a gradation correction table corresponding to a combination of luminance levels in a plurality of LED chips that illuminate the pixel area dominantly is provided.

(Embodiment 4) FIG. 27 is a diagram schematically showing a configuration of a backlight section according to a fourth embodiment of the present invention. The present embodiment is characterized in that the backlight is constituted by an electroluminescent (EL) backlight and an LED.

In the present embodiment, as shown in FIG. 27, the illumination area is divided into four areas, and the EL light emitting surface is of a direct type and illuminates from the rear side of the LCD. As shown in FIG. 28, the EL backlight 131 has a configuration in which an EL light emitting layer is interposed between a reflective electrode layer and a transparent electrode layer. Since the reflective electrode or the transparent electrode is divided for each illumination area, it is possible to independently illuminate segmentally. LED 132
Has a sidelight type arrangement in which illumination light is incident from an end face of a light guide plate arranged on the upper surface of the EL backlight 131. Make a notch in the light guide plate to make LE
The independence of each region of the D illumination light is enhanced. The notch of the light guide plate is preferably formed in a zigzag shape so that light vertically incident on the end face of the light guide plate is totally reflected. Thus, in the present embodiment, the LEDs 132, E
The illumination area of each of the L backlights 131 is divided, and has a structure in which both can be modulated in luminance.

By adopting the above configuration, the effects of the present invention can be achieved even in a combination of an EL backlight and an LED. Also, although not specifically shown, E
Various light sources can be used in combination, such as a backlight having a configuration in which LEDs are embedded in the L light emitting surface, and a configuration in which an EL backlight is disposed in a reflector portion of a cold cathode. In addition, among the different types of light sources, not only is one brightness fixed and the other is modulated,
Both can also control the luminance level by performing luminance modulation.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and can be variously modified and implemented without departing from the gist thereof. Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining the disclosed constituent elements. For example, even if some constituent elements are deleted from the disclosed constituent elements, they can be extracted as an invention as long as a predetermined effect can be obtained.

[0075]

According to the present invention, it is possible to display a high-quality image having a wide dynamic range.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a display device main body according to a first embodiment of the present invention.

FIG. 2 is a view showing an example of area division of a screen and a backlight according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration example of a display device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a correspondence relationship between a luminance level of a backlight, luminance, and a gradation signal in the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between an input RGB signal level and a screen luminance at each backlight luminance level in the first embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between an input gradation signal R′G′B ′ and screen luminance in the first embodiment of the present invention.

FIG. 7 is a diagram illustrating a relationship between an input gray scale signal R′G′B ′ and an LCD output gray scale signal R ″ G ″ B ″ in the first embodiment of the present invention.

FIG. 8 is a diagram showing an example of a result of calculating an average luminance gradation of an input signal level for each pixel region in the first embodiment of the present invention.

FIG. 9 is a view showing a method of selecting a backlight luminance level according to the first embodiment of the present invention.

FIG. 10 is a diagram showing an example of a result of calculating an average luminance gradation of an input signal level for each backlight illumination region in the first embodiment of the present invention.

FIG. 11 is a diagram showing an illumination error due to crosstalk between backlight regions in the first embodiment of the present invention.

FIG. 12 is a diagram showing an example of a gradation error caused by an illumination error in the first embodiment of the present invention.

FIG. 13 is a diagram showing an example of the structure of the backlight unit according to the first embodiment of the present invention.

FIG. 14 is a diagram illustrating a cross-sectional configuration of an example of a backlight unit according to the first embodiment of the present invention.

FIG. 15 is a view showing a backlight lighting method according to the first embodiment of the present invention.

FIG. 16 is a diagram showing a light emission intensity distribution of a backlight light source and a transmittance characteristic of a color filter in the first embodiment of the present invention.

FIG. 17 shows a white LE according to the first embodiment of the present invention.
The figure which showed the white point and RGB chromaticity point at the time of changing the brightness gain of D.

FIG. 18 is a block diagram showing a modified example of the display device according to the first embodiment of the present invention.

FIG. 19 is a diagram showing a light emission intensity distribution of a backlight light source and a transmittance characteristic of a color filter in the first embodiment of the present invention.

FIG. 20 is a view showing the relationship between each color LE in the first embodiment of the present invention;
The figure which showed the white point and RGB chromaticity point at the time of controlling the light emission intensity of D.

FIG. 21 is a block diagram showing a modified example of the display device according to the first embodiment of the present invention.

FIG. 22 is a view showing a backlight lighting method according to the second embodiment of the present invention.

FIG. 23 is a diagram showing a configuration example of a display device main body according to a second embodiment of the present invention.

FIG. 24 is a diagram showing an illumination area of a backlight according to the second embodiment of the present invention.

FIG. 25 is a diagram showing a configuration example of a display device main body according to a third embodiment of the present invention.

FIG. 26 is a diagram showing an illumination area of a backlight according to a third embodiment of the present invention.

FIG. 27 is a diagram illustrating a configuration of a backlight unit according to a fourth embodiment of the present invention.

FIG. 28 is a diagram illustrating a cross-sectional configuration of a backlight unit according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... LCD 12 ... Backlight 13 ... Frame memory 14 ... Image brightness calculation circuit 15 ... Image brightness data holding part 16 ... Backlight brightness calculation circuit 17 ... Backlight brightness data holding part 18 ... Backlight brightness control circuit 19 ... Grayscale Conversion circuit 20: gradation correction LUT 21: gradation correction circuit 22: LCD driver 31: chromaticity calculation circuit 32: color correction circuit 33: color correction LUT 34: RGB signal conversion circuit 41: saturation prediction color correction judgment Section 42: LUTs 101 and 111 for saturation correction Cold cathode fluorescent tubes 102 and 112 Partition walls 103, 121 and 132 LED 104 and 113 Inverter circuits 105 and 114 Backlight luminance control circuit 131 EL backlight

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09F 9/00 337 G09G 3/20 642J G09G 3/20 642 642B G02F 1/1335 530 F term (reference) 2H091 FA42Z FA44Z FA45Z FD22 GA11 LA17 2H093 NA52 NC29 NC42 NC49 NC59 NC62 ND04 ND07 NE06 NH18 5C006 AA16 AA22 AF13 AF44 AF46 AF51 AF53 AF63 AF85 BB11 BF02 EA01 FA18 FA22 FA56 5C080 AA10 BB05 CC03 DD05 EE29 EE30 JJ02 AJ12 JJ05 JJ02 AJ12 JJ05 JJ02 JJ05 JJ05 EE29 EE30 FF03 FF13 GG23 GG24 GG25 GG26 GG27

Claims (5)

[Claims] An image display unit; an illumination unit having a plurality of illumination regions for illuminating the inside of the image display unit; and an illumination luminance control unit for controlling luminance of each illumination region of the illumination unit based on an input image signal. An image signal conversion unit that converts the input image signal based on luminance information for each illumination region of the illumination unit obtained by the illumination luminance control unit, and supplies the converted image signal to the image display unit. A display device, comprising: 2. The display device according to claim 1, wherein said image signal conversion unit has a function of converting a gradation of said input image signal based on said luminance information. 3. The display device according to claim 1, wherein the illuminating section is configured using a plurality of types of light emitting elements having different light emitting principles. 4. The display device according to claim 3, further comprising a color compensator for performing color compensation according to a difference in emission color of the plurality of types of light emitting elements. 5. The display device according to claim 1, wherein each illumination area of the illumination section is divided by a partition.