Image display apparatus combining three-in-one with single color light-emitting elements

An image display apparatus comprising a display section provided by pixels arranged in a grid pattern, each of the pixels being formed of a light-emitting element, in which basic grids are repeatedly arranged in a grid pattern, each of the basic grids consisting of four pixels of a 2 by 2 matrix, each of the basic grids having a pattern in which one or two pixels of the four pixels being assigned a three-in-one element including three primary colors of R, G, and B and the remaining pixels being assigned a single-color light-emitting element, and the apparatus comprises processor for correcting a first color reproduction range provided by chromaticities of the three primary colors of R, G, and B to a second color reproduction range by light-emission intensity of the single-color light-emitting element and shifting chromaticity points for the three colors.

TECHNICAL FIELD

The present invention relates to an image display apparatus in which a light-emitting element such as a light-emitting diode (LED) is used for a pixel.

BACKGROUND ART

A typical image display apparatus includes a display section formed of a number of display units arranged vertically and horizontally, and each of the display units is provided by arranging, in a grid pattern, pixels each formed of a light-emitting element such as an LED. To increase the resolution of the image display apparatus, it is necessary to reduce the pitch of the arranged pixels to arrange the pixels at a higher density. A large image display apparatus with a high resolution tends to have a higher cost due to the use of an increased number of LED elements per unit area.

An example of the large image display apparatus displays full-color images by having a display section formed such that pixels at least including an LED element for R (red), an LED element for G (green), and an LED element for B (blue) are arranged in a grid pattern on a basic grid (square grid) consisting of four pixels of a 2 by 2 matrix. For example, in the four pixels of the basic grid (square grid) consisting of the 2 by 2 matrix, an LED element for each of R, G, and B is assigned to three pixels, and G or R is assigned to the remaining one pixel.

The LED element allows arbitrary design of arrangement of three primary colors or arrangement pitch, which contributes to a recent selection of image display apparatuses with various resolution and luminance levels appropriate for different applications.

In another display type used in recent years, a three-in-one LED element (three-in-one element) including LED chips for three colors of R, G, and B put in a single LED lamp is used, and such three-in-one elements are arranged in a grid pattern.

When LED elements of the three-in-one type are arranged as pixels, one pixel emits light of three primary colors and thus the three colors are easily mixed as compared with a type in which single-color LED elements for R, G, and B are arranged. This provides a characteristic in which a viewer recognizes a mixed color at a shorter distance.

Various types of LED arrangement include the following ones including the LED element of the three-in-one type.

In recent years, applications requiring viewing at a shorter distance or applications requiring display with a higher resolution have increasingly employed a three-in-one element in which an LED pellet for three colors R, G, and B constitutes a single pixel (see, for example, Patent Document 1).

When the three-in-one element is used, an application requiring display of high-resolution contents with high image quality, for example Hi-Vision, involves a higher density of arrangement of LED elements, so that the cost is drastically increased and consumed power tends to be increased.

A proposed approach to reducing the cost is to reduce the number of LED elements while a reduction in image quality is minimized (see, for example, Patent Document 2).

Another proposed approach is to replace some of three-in-one LED elements with inexpensive white-color LED elements in a display having an array of three-in-one LED elements (see, for example, Patent Document 3).

As another example of the use of the white-color LED element, a recently proposed approach in the field of liquid crystal displays is to use four sub-pixels for colors of R, G, B, and W for a representative LED pixel arrangement of liquid crystal consisting of three colors of R, G, and B (see, for example, Patent Document 4).

CITATION LIST

Patent Literatures

SUMMARY OF INVENTION

Technical Problems

The approach of replacing some of the three-in-one elements with inexpensive white-color LED elements in the display including the array of three-in-one elements, however, has a problem in which the addition of the other color (white) to the three primary colors changes the proportion of the colors of R, G, and B and changes the hue of an image accordingly.

The present invention has been made in view of the above problem, and it is an object thereof to provide an image display apparatus capable of display with high image quality with a limited cost increase. Particularly, in a display having three-in-one elements including three primary colors of R, G, and B arranged in a grid pattern, some of pixels are replaced with single-color light-emitting elements to cut the cost and to reduce a hue change due to the influence of a single-color element.

Solution to Problem

An image display apparatus according to the present invention includes a display section provided by pixels arranged in a grid pattern, each of the pixels being formed of a light-emitting element, in which basic grids (square grids) are repeatedly arranged in a grid pattern, each of the basic grids consisting of four pixels of a 2 by 2 matrix, each of the basic grids having a pattern in which one or two pixels of the four pixels being assigned a three-in-one element including three primary colors of R, G, and B and the remaining pixels being assigned a single-color light-emitting element, and the apparatus comprises color reproduction range correcting means for correcting a first color reproduction range provided by chromaticities of the three primary colors of R, G, and B to a second color reproduction range through adjustment of light-emission intensity of the single-color light-emitting element.

Advantageous Effects of Invention

In the image display apparatus according to the present invention, some of the pixels can be replaced with the single-color light-emitting elements to cut the cost, and the light-emission intensity of the single-color light-emitting element can be adjusted to reduce a hue change due to the influence of the single-color light-emitting element.

Other objects, characteristics, aspects, and advantages of the present invention will be apparent from the following detailed description of the present invention with reference to the accompanying drawings.

DESCRIPTION OF EMBODIMENTS

First Embodiment

First, the basic configuration of an image display apparatus is described.FIG. 1Ais a diagram showing the configuration of the image display apparatus necessary for describing the present invention. An image display apparatus10is, for example, a large display apparatus such as Aurora Vision®, and includes a display section (screen)4formed of a number of display units5arranged vertically and horizontally.FIG. 1Bis an enlarged view of some pixels3in each display unit5. The display unit5is formed such that pixels2each consisting of a light-emitting element such as an LED are arranged in a grid pattern, and for example, four pixels2of a 2 by 2 matrix constitute a single basic grid (square grid)1. The display units5are arranged in a grid pattern to constitute the display section4. For convenience, the pixels2constituting the basic grid1are in contact with adjacent pixels2in this example, but they are generally spaced from each other.

Next, a typical pixel arrangement in the image display apparatus10is described with reference toFIG. 2.FIGS. 2A, 2B, and 2Cshow exemplary pixel arrangements in one basic grid1. For example, when three single-color light-emitting elements (single-color LED elements2b) for three primary colors of R, G, and B are regularly arranged on pixels2as shown inFIGS. 2A and 2B, single-color LED elements2bfor R, G, and B are assigned to three of the four pixels2of the 2 by 2 matrix in the basic grid (square grid), and G or R is assigned to the remaining one pixel. Alternatively, as shown inFIG. 2C, a three-in-one LED element (hereinafter referred to simply as a three-in-one element) is assigned to all the pixels2in a grid pattern.

FIG. 3is a diagram showing a typical arrangement of pixels2to which coordinates are added for describing the operation of the present invention. Each box represents one pixel2inFIG. 3.FIG. 4shows spatial frequency resolutions of an image in which horizontal and vertical resolutions of an image signal inFIG. 3are shown two-dimensionally (the horizontal axis represents the horizontal resolution (Cycle/cm) and the vertical axis represents the vertical resolution (Cycle/cm)). As shown inFIG. 4, assuming that pitches of arranged pixels in a horizontal direction x and a vertical direction y are represented by x0and y0, respectively, and that the sampling frequency of the image signal in the horizontal direction corresponds to the pixel pitch x0(y0for the vertical direction), the highest frequency of a restorable image signal is represented by 1/2x0, and the highest frequency of a restorable image signal in the vertical direction is represented by 1/2y0. InFIG. 4, the spatial frequency characteristic of a representable image is shown by a square area surrounded by a straight line including a point at 1/2x0from the center on the horizontal axis and a point at 1/2y0from the center on the vertical axis.

FIG. 5andFIG. 7show exemplary pixel arrangements of the basic grid1in the image display apparatus10according to the present invention.FIG. 5shows an exemplary pixel arrangement in which one three-in-one element2aand three single-color LED elements2bare placed in the 2-by-2 pixel basic grid1.FIG. 7shows an exemplary pixel arrangement in which two three-in-one elements2aand two single-color LED elements2bare alternately placed in the basic grid1. As shown in those exemplary pixel arrangements, in the image display apparatus10according to First Embodiment of the present invention, some of the three-in-one elements2aof the pixels2arranged in the grid pattern are replaced with inexpensive white-color LED elements2b. The spatial frequency characteristic of a representable image is shown by a double structure as shown inFIG. 6.

InFIG. 6, the spatial frequency characteristic of a representable image in the three-in-one element2aof the pixels2is represented by a square area surrounded by straight lines including a point at 1/4x0from the center on the horizontal axis and a point at 1/4y0from the center on the vertical axis. On the other hand, the spatial frequency characteristic of a representable image through control of both the white-color single-color LED element2band the three-in-one element2aof the pixels2is represented by a square area surrounded by a straight line including a point at 1/2x0from the center on the horizontal axis and a point at 1/2y0from the center on the vertical axis, similarly to the example inFIG. 4. In other words, the spatial frequency characteristic of a displayable image in the pixel arrangement including one three-in-one element2ain the basic grid1as shown inFIG. 5is shown by the double structure consisting of an inner area represented by the square including the points at 1/4x0and 1/4y0inFIG. 6and achieving full-color display with the arrangement of the pixel of the three-in-one element2aand an outer area represented by the square including the points at 1/2x0and 1/2y0and achieving display through the control of both the three-in-one element2aand the white-color single-color LED element2b. The outer area does not necessarily have sufficient color information for full-color representation, but at least displays information about brightness/darkness.

Since human vision is less sensitive to color changes than to brightness/darkness characteristics, the region of higher resolutions is served by the white-color single-color LED element2bwhich is the monochrome light-emitting element, and the region of lower resolutions is served by the three-in-one element2acapable of color display, thereby achieving the effective representation capability suitable for the visual properties of humans.

In this case, the three-in-one element2aincluding the three primary colors of R, G, and B is assigned to some pixels2of the four display pixels of the basic grid1, and the single-color light-emitting element2b, for example the white-color single-color LED element2b, is assigned to the remaining pixels. When the screen is viewed at an extremely short distance, a distinct noise in a grid pattern due to the pixel structure may be found since the white-color LED lamp and three-in-one element2aare mixed in the basic grid1, but such a noise is not perceived when the screen is viewed at a proper distance at which the discrete pixels appear to be continuous.

As a result, the inexpensive white-color single-color LED elements2bcan be arranged at a high density to form the display section4with a high resolution. Specifically, the resolution of display is ensured through the use of the inexpensive white-color single-color LED element2b, and the colors necessary for full-color display are provided by the three-in-one element2a, thereby making it possible to achieve the full-color image display apparatus10at a low cost and a high resolution.

The exemplary pixel arrangement inFIG. 7shows the case in which the three-in-one element2aincluding the three primary colors of R, G, and B is assigned to two pixels2located diagonally, and the white-color single-color LED element2b, for example, is assigned to the remaining two pixels2in the basic grid1consisting of four pixels of a 2 by 2 matrix. InFIG. 7, the pitches of the arranged pixels in the horizontal direction x and the vertical direction y are set to x0and y0, respectively.

FIG. 8shows the spatial frequency characteristic representing the resolution of an image in the grid pixel arrangement inFIG. 7. InFIG. 8, assuming that the horizontal axis represents the horizontal resolution (Cycle/cm) and the vertical axis represents the vertical resolution (Cycle/cm), the spatial frequency characteristic of a representable image when the white-color single-color LED element2bis used for the pixel2is represented by a square area surrounded by a straight line including a point at 1/2x0from the center on the horizontal axis and a point at 1/2y0from the center on the vertical axis, similarly to the case inFIG. 6. The spatial frequency characteristic of a representable image in the three-in-one element2ais represented by a square area having apexes corresponding to a point at 1/2x0from the center on the horizontal axis and a point at 1/2y0from the center on the vertical axis.

InFIG. 8, as compared withFIG. 6, the area displayable through control of both the three-in-one element2aand the white-color single-color LED element2bsurrounded by the line including the points at 1/2x0on the horizontal axis and at 1/2y0on the vertical axis is identical to that inFIG. 6. In contrast, the central area representable in full color with the arrangement of the three-in-one element2ahas twice the area of that inFIG. 6since the number of the three-in-one elements2ais increased to be twice as compared with the characteristic inFIG. 6. In addition, the three-in-one elements2aare arranged alternately in a staggered form, so that the resulting shape provides horizontal and vertical resolutions with a higher priority than a diagonal resolution. Since a typical image includes more horizontal and vertical components than a diagonal component, the spatial frequency characteristic inFIG. 8matches the typical image characteristics as well as the human visual properties. Thus, as compared with an arrangement in which the three-in-one element2ais assigned to all the pixels2as shown inFIG. 2C, the pixel arrangement inFIG. 7allows a significant cost reduction with a limited reduction in image quality since some of the three-in-one elements2aare replaced with the inexpensive single-color LED elements2b.

When the arrangement as shown inFIG. 5andFIG. 7is utilized in which some pixels of the basic grid1are replaced with the single-color pixels while the use of the three-in-one element2ais maintained, the use of the three-in-one element2aenables the full-color display, and simultaneously, the advantage of cost reduction can be achieved. In addition, the noise in the grid pattern due to the pixel structure can also be reduced on condition that the screen is viewed at a proper distance. For the hue, however, the color balance is adjusted on the basis of the three primary colors in the three-in-one element2a, so that the addition of the other color to the three primary colors changes the hue of an image according to the change in the proportion of the colors of R, G, and B.

In view of the context described above, in First Embodiment of the present invention, description is made of the image display apparatus10capable of reducing the cost by replacing some of the pixels2with the single-color light-emitting elements and of reducing the hue change due to the influence of the single-color light-emitting element in the display4(which may be a screen or a display) having the three-in-one elements2aincluding the three primary colors of R, G, and B arranged in the grid pattern.

FIG. 9is a diagram showing the configuration of the image display apparatus10and illustrates the image display apparatus10including color reproduction range correcting means (color converting section40) for adjusting the light-emission intensity (or luminance) of the white-color light-emitting element to correct a first color reproduction range formed of chromaticity of the three primary colors of R, G, and B in the present invention to a second color reproduction range.

As shown inFIG. 9, an image signal is input to an RGB decoder31. The RGB decoder31decodes and separates the input image signal into three primary colors of R, G, and B to output signals for the respective colors of R, G, and B. The R, G, and B signals in analog form output from the RGB decoder31are input to an A/D converter32for analog/digital conversion followed by output as Rd, Gd, and Bd signals in digital form. The Rd, Gd, and Bd signals output from the A/D converter32are input to an image memory33. The image memory33also receives the input of signals such as text or computer graphics from a computer interface and a first timing signal from a timing producing section (sampling control)34. In a recent digital TV, image information is stored into the image memory33via a demultiplexing section for extracting video from packetized signals or an MPEG decoding section for decoding encoded images, rather than the RGB decoder31and the A/D converter32, but common processing is performed after the image memory33. The image memory33outputs the Rd, Gd, and Bd signals to a color converting section (color reproduction range correcting means)40in accordance with the timing signal. The color converting section40performs computation of the input signals with a predetermined color conversion function or the like and outputs Rd2, Gd2, and Bd2signals after the color conversion processing together with a second timing signal. The output signals are input to display units (unit11to unit mn)5of the display section44via an image data bus and buffer memories (BM1to BMm) and are used to adjust the light-emission intensity of the three-in-one element2aor the white-color single-color LED element2bconstituting each pixel2.

The color reproduction range correcting means corresponding to the color converting section40converts a wide color reproduction range into a practical color reproduction range by using the fact that the LED provides a higher color purity for a single color of R, G, or B than that of the three-in-one element2aand a wider color reproduction range than that in the specifications for image signals of high image quality such as for Hi-Vision (HDTV). In the present invention, some of the three-in-one elements2aare replaced with the inexpensive single-color LED elements and the inexpensive single-color LED element2bis used, so that the present invention can compensate for reduced luminance in single-color display and a hue change caused since the proportion of the three primary colors is changed from that when only the three-in-one elements are used, thereby realizing the display apparatus at a low cost and with high image quality.

FIG. 10is a diagram for describing the color reproduction range of the image display apparatus10according to First Embodiment and is a chromaticity diagram showing representative chromaticities of three primary colors in the LED (thick broken line, black circles) and chromaticities in the Hi-Vision specifications (HDTV) (dash-dotted line, black rhombus). A triangular area surrounded by the thick broken line connecting the chromaticity points of R, G, and B (R1, G1, and B1(black circles)) corresponds to the color reproduction range of the LED (first color reproduction range). R2, G2, and B2represent the chromaticity points of the respective colors after the color conversion. A triangular area surrounded by the chromaticity points of R2, G2, and B2(the triangular shape is shown inFIG. 11as later described) corresponds to the second color reproduction range in the present invention.

FIG. 11is a diagram showing the conversion of the color reproduction range, in which the second color reproduction range obtained by the conversion of the color reproduction range is represented as a triangular range surrounded by a chain double-dashed line with R2, G2, and B2located at apexes.

As shown inFIG. 11, the color converting section40performs control such that, for the single color R, R1is converted into R2by lighting of W, and similarly, colors (R1, C11, C21, . . . C51, G1) located on a line R1-G1are converted into colors (R2, C12, C22, . . . C52, G2) located on a line R2-G2. More particularly, the color converting section40performs control such that the color located on a C11-W1line is converted into a color located on a C12-W1line, for example.

FIG. 12is a diagram for describing colors and shows the chromaticity diagram three-dimensionally. The three primary colors are represented by vectors R, G, and B in a three-dimensional color space, and x and y components in a plane x+y+z=1 correspond to the chromaticity diagram inFIG. 10. X and y components at intersections R1, G1, and B1of the vectors R, G, and B and the plane x+y+z=1 correspond to the chromaticity coordinates of the three primary colors (R, G, and B), respectively. In the display, for example including the white-color (W) single-color LED element2bin addition to the three-in-one element2aas shown inFIG. 5andFIG. 7, a W vector is added to the vectors of R, G, and B, and the addition of the white color of the white-color LED element to the combined colors of the three primary colors increases the overall luminance.

In the display including the arranged three-in-one elements2a, the proportion of the luminance of R, G, and B can be adjusted for each pixel2. In general, the adjustment of the luminance proportion of R, G, and B is performed such that the combined color is white when all the three primary colors R, G, and B are emitted. In this case, the resultant vector W of the R, G, and B vectors passes through a white chromaticity point W1.

Referring toFIG. 13, color representation is described.FIG. 13Ashows the same pixel arrangement as the pixel arrangement inFIG. 2C(the grid arrangement formed only of the three-in-one elements2a), andFIG. 13Cshows an example of single-color display in which only G is displayed in that arrangement. Similarly,FIG. 13Bshows the same pixel arrangement as the pixel arrangement inFIG. 7(the arrangement in which the white-color single-color LED2bis placed diagonally in the basic grid1of the 2-by-2 matrix), andFIG. 13Dshows an example in which only G is displayed in a single color in that arrangement. InFIGS. 13C and 13D, a reference sign2aashows a three-in-one element2aain which only G is lit. R and B are not lit in the three-in-one element2aa. G is included in the three-in-one element2abut not included in the white (W) single-color LED element2b. Thus, in the single-color display of G, as compared withFIG. 13Cin which G is lit in all the pixels, half of the pixels are the W pixels which are not lit and thus the number of element corresponding to the lit G is reduced by half in the arrangement inFIG. 13D. This means not only a reduced luminance in the single-color display of G but also a reduced resolution.

Returning to the explanatory diagram for colors inFIG. 12, the resultant vector of the single-color G and white (W) passes through a straight line connecting G1and W1. While the passing point is shifted toward W1as the luminance of white (W) is increased, G can be adjusted to a desired appropriate chromaticity value G2by adjusting the luminance of W. In the chromaticity diagram inFIG. 11, G2has a color purity lower than that of G1, but the area of the color reproduction range (triangle of a chain double-dashed line delimited by chromaticity points R2, G2, and B2) is equal to the area of the triangle of the dash-dotted line for HDTV, which means that the adjustment can be performed to ensure the range comparable to that for the Hi-Vision specifications. As a result, the white luminance for shifting G1to G2is added to the luminance value for obtaining G1, so that the luminance in the single-color display of G is improved.

InFIG. 13B, since the white (W) single-color LED element2bis lit as well as the single color G included in the three-in-one element2a, the resolution is increased to improve reduced luminance and reduced resolution in single-color display which are the problems in replacing some of the three-in-one elements2awith the inexpensive white (W) elements, resulting in improved representation of image outlines and fine lines.

Similarly, since the resultant vector of the single color B and white (W) is located on a straight line connecting B1and W1, B can be adjusted to a desired appropriate chromaticity value B2by adjusting the luminance of white (W). The single color R can also be adjusted to a desired appropriate chromaticity value R2by adjusting the luminance of white (W). In any case, R2, G2, and B2are obtained from the chromaticity points R1, G1, and B1of the single color R, G, and B by adjusting the luminance of W. In the single-color display for R, G, and B, the addition of the luminance of W to the luminance of the three primary colors included in the three-in-one element2aincreases the luminance and the resolution.

As shown inFIG. 14, the color converting section40may be formed of a first color converting section41and a second color converting section42.FIG. 15shows an example for describing the color converting section40inFIG. 9. Data input to the color converting section40is Rd, Gd, and Bd shown inFIG. 15Aand does not contain any white (W) component. Based on the data, the first color converting section41extracts a white (W) component Wd1from the color data Rd, Gd, and Bd for the three primary colors. The result of the extraction of the white component Wd1from the original data Rd, Gd, and Bd for three primary colors is Rd1, Gdl, and Bd1shown inFIG. 15B. The conversion from Rd, Gd, and Bd into Rd1, Gd1, and Bd1is the subtraction of the white component (Wd1component). Next, the second color converting section42performs color conversion computation for obtaining desired hues Rd2, Gd2, and Bd2shown inFIG. 15Cbased on the data Rd1, Gd1, and Bd1.

The principles of the color conversion for obtaining Rd2, Gd2, and Bd2from Rd1, Gd1, and Bd1can be described in the following expression:

In the expression, a to j represent constants for color conversion. The constant are set to be variable to allow arbitrary setting, so that arbitrary display devices with different chromaticities can be controlled. In addition, the hue can be set in accordance with illumination in the environments and the like to provide the image display apparatus with high image quality.

In the chromaticity diagram inFIG. 10, the chromaticity points R2, G2, and B2are located on straight lines (fine broken lines) connecting the chromaticity point W1for W and the chromaticity points R1, G1, and B1for the three primary colors R, G, and B in the LED. The positions of the chromaticity points R2, G2, and B2on the chromaticity diagram may be adjusted to have a certain margin on the straight lines connecting to the chromaticity points R1, G1, and E1for the three primary colors R, G, and B. Such color conversion involving the adjustment focused on W allows efficient conversion of chromaticity to effectively reduce consumed power. As shown inFIG. 11, although the chromaticity points R2, G2, and B2are slightly displaced from the specifications for image signals with high quality such as for Hi-Vision, the area of the color reproduction range surrounded by the chain double-dashed line with the chromaticity points R2, G2, and B2located at the apexes can be comparable to the area of the triangle for the Hi-Vision specifications surrounded by the dash-dotted line. Thus, display with low power consumption and high image quality can be achieved with a small influence in practical use such as a feeling of strangeness due to a different hue. Particularly, an efficient LED element such as an LED for illumination can be used for white (W) to reduce the power consumed by the display.

Second Embodiment

Second Embodiment of the present invention is described with reference to a diagram for describing color reproduction ranges inFIG. 16. The color reproduction range in Second Embodiment is characterized in that the chromaticity points R2, G2, and B2for the three primary colors described in First Embodiment are shifted to new chromaticity points R3, G3, and B3by controlling the light-emission intensity of the LED for the three primary colors included in the three-in-one element2ain addition to the light-emission intensity of white. The chromaticity points R3, G3, and B3obtained in Second Embodiment correspond to points shifted from R2, G2, and B2toward the apexes of a triangle representing the Hi-Vision specifications (HDTV) and are located within a circle indicated by hatch lines inFIG. 16. The shift of the chromaticity points R2, G2, and B2to R3, G3, and B3can be performed by changing the constants a to j for color conversion of the expression (1) in the second color converting section42. The second color converting section42may refer to the extracted white component Wd1as required.

As a result, the second color reproduction range can include not only the area on the chromaticity diagram but also the chromaticity points at substantially the same levels as those of the Hi-Vision specifications to achieve image display with high image quality. Human vision is less sensitive to color changes than to brightness/darkness characteristics. As long as the second color reproduction range generally satisfies chromaticity values for the three primary colors defined in the specifications for television signals, it is not essential that the chromaticity points exactly match the chromaticity points defined in the specifications in practical use.

As described above, First Embodiment and Second Embodiment have shown the use of the white-color LED in the example of replacing some of the three-in-one elements2aarranged in the grid form with the inexpensive single-color light-emitting elements2b. Various specifications are possible for the single-color light-emitting element2b. To seek a significant cost reduction with a limited reduction in image quality, yellow-color or green-color (greenish yellow) LED elements or inexpensive elements for other colors can be used, not limited to the white-color LEDs. In this case, the first color converting section41extracts a common component from color data Rd, Gd, and Bd for three primary colors in accordance with the inexpensive color in use and obtains desired hues Rd2, Gd2, and Bd2in cooperation with the second color converting section42in the subsequent stage. When the inexpensive color in use includes no component common to another color like green (G), the first color converting section41may be skipped to allow the second color converting section42to obtain the desired hues Rd2, Gd2, and Bd2. The color conversion processing in this case may be performed such that the chromaticity points R2, G2, and B2may be corrected to have wide adjustment ranges as indicated by hatched ovals inFIG. 10as long as the correction is uniform with small variations. The chromaticity points R3, G3, and B3may be corrected at the equivalent level to that for R3, G3, and B3inFIG. 16since the three primary colors included in the three-in-one element2acan be used for the correction.

Third Embodiment

In the three-in-one element2adescribed in First Embodiment and Second Embodiment, the LED chips for the three primary colors of R, G, and B are included in a single LED package. The three-in-one element2ais provided by using a material with a high transmittance for the surface of the package and a material with a high reflectance for the inner face in order to enhance the light-emission efficiency of the LED. As a result, the three-in-one element2aappears to be whitish when viewed from the display face, which contributes to a reduced contrast. Third Embodiment of the present invention provides the image display apparatus10including a filter on the face of the light-emitting element for suppressing the transmission of light other than emitted light color in order to limit the reduced contrast.

FIG. 17is a sectional side view of a single-color LED element20provided with such a filter. The image display apparatus10according to Third Embodiment includes the basic grid of four pixels of a 2 by 2 matrix according to First Embodiment or Second Embodiment, in which some of the three-in-one elements2aincluding three primary colors of R, G, and B arranged in a grid pattern are replaced with single-color light-emitting elements.FIG. 17shows a single-color LED element2bserving as such a single-color light-emitting element. A gray-color filter21is formed as a color filter for emitted light color on the front face (light-emitting face) of the white-color single-color LED element2b. For the three-in-one element2a, it is difficult to form the filter efficiently passing three primary colors at different wavelengths, and when the filter is formed on the front face, the luminance tends to be reduced. For the single-color light-emitting element, however, the filter21passing the emitted light color of the LED can be formed on the light-emitting face to suppress the transmission of light other than the emitted light color, thereby limiting a reduction in luminance and suppressing reflection of external light from an area with a high reflectance on the package face or inside the package.

FIG. 18is a diagram showing an exemplary pixel arrangement for describing how a display screen appears in the image display apparatus10to which Third Embodiment is applied.FIG. 18Ashows an exemplary pixel arrangement in which only the three-in-one element2ais used.FIG. 18Bshows an exemplary pixel arrangement in which half of the pixels inFIG. 18Aare replaced with single-color LED elements20having the gray-color filter21and the single-color LED elements20alternate with the three-in-one elements2a.FIG. 18Cshows an exemplary pixel arrangement in which the three-in-one element2ais used for one pixel2in the basic grid1of the 2 by 2 matrix and the single-color LED element20having the gray-color filter21is used for the remaining three pixels2.

The filter21can be formed with various methods such as a film affixing method and an ink applying or printing method. The transmittance of light through the filter21formed on the front face of the white-color single-color LED element2bcan be arbitrarily adjusted, for example.

As compared with the arrangement of the three-in-one elements2ain a grid pattern shown inFIG. 18A, in the image display apparatus10in which some of the elements are replaced with the single-color LED elements20having the gray-color filter as shown inFIG. 18B, reflection of light (external light) is limited from the outside of the image display apparatus10when it is not lit, and thus the screen appears to be blackish. The color reproduction range in this case is represented as the triangle delimited by R1, G1, and B1shown inFIG. 12. When external light is applied to the screen in bright environments, the chromaticity points for three primary colors are shifted inward of the triangle under the influence of color vectors of the reflected light, and the color reproduction range tends to be narrowed. When the color filter for the single-color light-emitting element is formed on the light-emitting face to reduce the reflection on the surface, the color reproduction range is maintained to allow the reproduction of clear colors with high fidelity to the color conversion technology.

Although the above example shows the white-color light-emitting element used for the single-color LED element2b, a yellow-color or green-color (greenish yellow) LED element can also be used. In addition, an inexpensive single-color LED element can be used other than white, yellow, and green (greenish yellow) LED elements. Since the luminosity factor of humans is high for colors from greenish yellow to green, display with a high resolution is expected. When some of the whitish three-in-one elements2aare replaced with the inexpensive LED elements having the color filter formed on the light-emitting face, the pixel structure may be recognized as a distinct noise when the screen is viewed at an extremely short distance, but this type of noise can be avoided when the screen is viewed at a proper distance. As a result, the inexpensive image display apparatus10with high image quality can be provided even when the inexpensive yellow or green light-emitting element is used.

The embodiments of the present invention can be combined freely, or modified or omitted as appropriate within the spirit or scope of the present invention. For example, when the three-in-one element2ais placed diagonally in the basic grid1as shown inFIG. 19, a green-color LED element (G) may be placed as the single-color LED element2bas shown inFIG. 19A, or two types including a green-color LED element (G) and a red-color LED element (R) may be placed in combination in a grid pattern as shown inFIG. 19B. When the three-in-one element2ais placed as one element of the basic grid1as shown inFIG. 20, three types including green-color, red-color, and blue-color LED elements (G, R, and B) can be used in combination as the single-color LED element2b.FIG. 20Ashows an example in which the basic grids1are staggered, andFIG. 20Bshows an example in which the basic grids1are placed vertically and horizontally in a matrix pattern. As shown inFIG. 19B, the single-color LED elements2of different colors may be arranged alternately in a staggered form. When two or more types of single-color LED elements2bare used, the color reproduction range correcting means adjusts the light-emission intensity for each color of the single-color LED elements2bor for all the colors together. Although the above embodiments have been described in conjunction with the LED element used for the light-emitting element, another light-emitting element may be used. Although the pixel2is indicated by the circle or the square in Figures, this is for illustrative and does not limit the shape of the light-emitting element.