Stereoscopic image display apparatus

A stereoscopic image display apparatus according an embodiment includes: an elemental image display unit having a display face in which pixels having sub-pixels are arranged in a matrix form, the display face being divided into a plurality of elemental images for display; and an optical plate provided on a viewer side of the elemental image display unit, the optical plate having a plurality of lenses arranged periodically with respect to the display face to be respectively associated with the plurality of elemental images, each of the lenses controlling light rays from the pixels which display an associated elemental image. In each lens, the sub-pixels which display an elemental image associated with the lens differing in isolation degree between adjacent sub-pixels depending upon whether a location is in a central portion of the lens or in a peripheral portion of the lens.

FIELD

Embodiments described herein relate generally to a stereoscopic image display apparatus.

BACKGROUND

As for the stereoscopic image display apparatus capable of displaying a stereoscopic moving picture, which is the so-called three-dimensional display, various schemes are known. Especially, in recent years, a stereoscopic image display scheme which is the flat panel type, which does not need dedicated glasses or the like, and which generates parallax in a viewer by controlling light rays supplied from a display panel having fixed pixel positions in a plane display apparatus, with an optical plate is known. As the plane display apparatus, a liquid crystal display apparatus, a plasma display apparatus or the like of direct view type or projection type is used.

The optical plate (called parallax barrier as well) controls light rays to make different images visible according to the angle even in the same position on the optical plate. For example, when giving the lateral disparity (horizontal disparity), a lenticular sheet (cylindrical lens array) is used. When giving also the up-and-down disparity (vertical disparity), a lens array is used. In addition, the schemes using the optical plate are classified into the binocular scheme, multiview scheme, supermultiview scheme (supermultiview condition of the multiview scheme), and integral photography (hereafter referred to as IP as well).

Use of the lens sometimes expands a pixel part including an wiring pattern in the liquid crystal display apparatus and causes unevenness of brightness and darkness of luminance (moiré). In order to solve this problem, a method of providing a pixel overlapping part between adjacent sub-pixels by providing each pixel with a shape of a parallelogram or “<” is proposed.

If a pixel overlapping part is provided between adjacent sub-pixels, however, the parallax crosstalk quantity which makes it possible to visually recognize a plurality of parallax images becomes greater than a definite quantity in some cases. In this case, a double image or defocusing feeling becomes unallowable and it appears as a display obstruction sometimes. In addition, aberration is unavoidable from the lens characteristics. As the number of parallaxes increases and the viewing zone becomes wide, the parallax crosstalk quantity in the central portion of the lens differs from that in the peripheral portion. And if it is attempted to decrease the parallax crosstalk quantity in the lens central portion, the parallax crosstalk quantity in the peripheral portion increases. On the other hand, if it is attempted to decrease the parallax in the lens peripheral portion, the parallax crosstalk quantity in the central portion increases. In other words, the parallax crosstalk quantity in the lens central portion and that in the peripheral portion are in a trade-off relation.

According to the conventional art, it is impossible in a multi-parallax wide viewing zone stereoscopic display apparatus of lens type to generally reduce the difference in parallax crosstalk quantity between the lens central portion and the peripheral portion in this way.

DETAILED DESCRIPTION

A stereoscopic image display apparatus according to an embodiment includes: an elemental image display unit having a display face in which pixels having sub-pixels are arranged in a matrix form, the display face being divided into a plurality of elemental images for display; and an optical plate provided on a viewer side of the elemental image display unit, the optical plate having a plurality of lenses arranged periodically with respect to the display face to be respectively associated with the plurality of elemental images, each of the lenses controlling light rays from the pixels which display an associated elemental image. In each lens, the sub-pixels which display an elemental image associated with the lens differing in isolation degree between adjacent sub-pixels depending upon whether a location is in a central portion of the lens or in a peripheral portion of the lens.

Hereafter, embodiments will be described in detail with reference to the drawings.

A stereoscopic image display apparatus according to an embodiment is shown inFIG. 1.FIG. 1is a horizontal section view of a stereoscopic image display apparatus according to the present embodiment. The stereoscopic image display apparatus according to the present embodiment includes an elemental image display unit2and a parallax generating lens40which functions as an optical plate for generating a parallax in left and right eyes of a viewer. In the present embodiment, the parallax generating lens40is a cylindrical lens array. The cylindrical lens array40has a configuration in which a plurality of cylindrical lenses40aeach having a major axis extending in a vertical direction (a direction perpendicular to paper) are arranged in a horizontal direction (a direction parallel to the paper). The cylindrical lenses40ahave a pitch PL. The elemental image display unit2displays images (elemental images) associated with respective cylindrical lenses40a. In the present embodiment, a liquid crystal panel is used as the elemental image display unit2. The elemental image display unit2includes a first transparent substrate20using, for example, a glass substrate, a first transparent electrode21provided on the first transparent substrate20and having a plurality of wiring patterns, a second transparent electrode23provided over the first transparent electrode21and having a plurality of wiring patterns, a liquid crystal layer22interposed between the first transparent electrode21and the second transparent electrode23, and a sub-pixel unit24provided on the second transparent electrode23and having R (red), G (green) and B (blue) color filters arranged in an array form, a second transparent substrate25provided on the sub-pixel unit24and using, for example, a glass substrate, a first sheet polarizer26aprovided on an opposite side of the first transparent substrate20from the first transparent electrode21, a second sheet polarizer26bprovided on an opposite side of the second transparent substrate25from the sub-pixel unit24, and a back light27which is provided on an opposite side of the first sheet polarizer26afrom the first transparent substrate20and which emits light. In the liquid crystal layer22, initial orientations of liquid crystal molecules are aligned in one direction. The first and second sheet polarizers26aand26bare constituted to transmit light vibrating respectively in predetermined directions in which directions of transmitted light (polarized directions) are perpendicular to each other.

In the present embodiment, a cylindrical lens array is used as the parallax generating lens40. However, a fly eye lens can be used. The lens convex part of the parallax generating lens40can be located on either of the elemental image display unit2side and the viewer side (opposite side of the parallax generating lens40from the elemental image display unit2). In a structure having a wide viewing zone, however, it is desirable that the lens convex part of the parallax generating lens40is located on the elemental image display unit side.

As the first and second sheet polarizers26aand26b, linearly sheet polarizers, circularly sheet polarizers, elliptically sheet polarizers, or the like can be used. The back light27may be a typical fluorescent tube, a LED back light, or a combination of a light guiding panel and a diffuser.

In the present embodiment, the sub-pixel unit24has a structure in which an isolation degree in the central portion of the parallax generating lens40is different from that in the peripheral portion. Here, the isolation degree indicates a ratio of a part overlapping an adjacent sub-pixel in the vertical direction to an area of the original sub-pixel.

As a comparative example, a stereoscopic image display apparatus having the same configuration as that of the stereoscopic image display apparatus according to the present embodiment except that the isolation degree in the central portion of the parallax generating lens is the same as that in the peripheral portion will now be considered. Dependence of a parallax crosstalk quantity upon the parallax number in the stereoscopic image display apparatus according to the comparative example is shown inFIG. 2. InFIG. 2, the parallax crosstalk quantity is normalized by a maximum parallax crosstalk quantity. In the present specification, the parallax crosstalk quantity refers to a luminance ratio of an adjacent parallax to the main parallax which can be visually recognized at an arbitrary viewing distance. If in the case of an image a quantity of crossing of adjacent parallaxes exceeds an allowable value, then a double image or feeling of defocusing is brought about in some cases. A graph “a” inFIG. 2indicates a lens design example in which the parallax crosstalk quantity of the central parallax (parallax in the lens central portion) is minimized. A graph “b” indicates a lens design example in which the parallax crosstalk quantity of the peripheral parallax (parallax in the lens peripheral portion) is minimized. In the case of the graph “a”, the parallax crosstalk quantity of the peripheral parallax becomes greater than the parallax crosstalk quantity of the central parallax. In the case of the graph “b”, the parallax crosstalk quantity of the central parallax becomes greater than the parallax crosstalk quantity of the peripheral parallax. This is because of the aberration characteristics of the lens. The parallax crosstalk quantity in the lens central portion and the parallax crosstalk quantity in the peripheral portion are in a relation of trade off. InFIG. 2, parallax number 0 corresponds to the lens central portion.

The graph a′ and the graph b′ respectively indicate improvement target examples of the graph “a” and the graph “b” in the lens design example in the comparative example in the stereoscopic image display apparatus according to the present embodiment.

Luminance distribution of light rays emitted from each sub-pixel in the lens pitch width in the stereoscopic image display apparatus according to the present embodiment is shown inFIG. 3.FIG. 3schematically shows the case where the isolation degree of sub-pixels in 9 parallaxes differs depending upon whether the location is in the central portion of the lens or in the peripheral portion. A peak part of each parallax is a point where each parallax image is visually recognized with accuracy. A shaded area shown inFIG. 3represents a parallax crosstalk quantity between adjacent parallaxes. As the isolation degree of sub-pixels becomes high, the parallax crosstalk quantity decreases.

A concrete example for obtaining a structure in which the isolation degree of sub-pixels differs depending upon whether the location is in the central portion of the parallax generating lens40or in the peripheral portion in the stereoscopic image display apparatus according to the present embodiment will now be described.

First Concrete Example

A pixel structure in each lens in a stereoscopic image display apparatus according to a first concrete example is shown inFIG. 4(a).FIG. 4(b) is a diagram obtained by plotting vertical aperture areas of respective pixels in the stereoscopic image display apparatus according to the first concrete example having the pixel structure shown in.FIG. 4(a). Additional lines inFIG. 4(a) represent a one horizontal sub-pixel width and one third vertical sub-pixel width.

In the first concrete example and a second concrete example which will be described later, the sub-pixel takes a different shape depending upon whether the location is in the lens central portion or in the peripheral portion although the sub-pixel pitch Ppsuband an aperture ratio of sub-pixels are constant, in order to cause the isolation degree of the sub-pixels to differ depending upon whether the location is in the lens central portion or in the peripheral portion. In other words, the inclination of the sub-pixel differs depending upon whether the location is in the lens central portion or in the peripheral portion in order to change the isolation degree between adjacent sub-pixels when attention is paid to the vertical aperture ratio. Here, the isolation degree of the sub-pixel indicates a ratio of a part overlapping an adjacent sub-pixel in the vertical direction to an area of the original sub-pixel.

The first concrete example shown inFIG. 4(a) andFIG. 4(b) has a configuration in which the sub-pixel isolation degree in the lens central portion becomes greater than the sub-pixel isolation degree in the peripheral portion. As appreciated fromFIG. 4(a), in the first concrete example, an inclination angle (inclination angle from the vertical direction) θ of the sub-pixel decreases as the location advances from the lens central portion to the peripheral portion. Denoting an inclination angle of a pixel in the lens central portion by θC, an inclination angle of a pixel at the right end of the lens by θR, and an inclination angle of a pixel at the left end of the lens by θL, a pixel structure satisfying a relation θR=θL<θCis formed. In other words, in this case, a lens designed to minimize the condensing width at the central parallax position which is the sub-pixel position in the lens central portion is used. However, all aperture areas of sub-pixels in respective pixels are constant.

Second Concrete Example

A pixel structure in each lens in a stereoscopic image display apparatus according to a second concrete example is shown inFIG. 5(a).FIG. 5(b) is a diagram obtained by plotting vertical aperture areas of respective pixels in the stereoscopic image display apparatus according to the second concrete example having the pixel structure shown inFIG. 5(a). Additional lines inFIG. 5(a) represent a one horizontal sub-pixel width and one third vertical sub-pixel width.

The stereoscopic image display apparatus according to the second concrete example has a sub-pixel structure obtained when using a lens designed to minimize the parallax crosstalk quantity in the lens peripheral portion. The inclination of the sub-pixel increases as the location advances to the lens peripheral portion, and the isolation degree of the left and right pixels increases. Denoting an inclination angle of a pixel in the lens central portion by θC, an inclination angle of a pixel at the right end of the lens by θR, and an inclination angle of a pixel at the left end of the lens by θL, a pixel structure satisfying a relation θR=θL>θCis formed.

Incidentally, in the first and second concrete examples, moiré5can be prevented by providing sub-pixels in an even numbered row in the vertical direction with shapes obtained by inverting shapes of sub-pixels in an odd numbered row about a horizontal axis, that is, by forming a pixel shape of one “<” character in two rows.

Third Concrete Example

A pixel structure in each lens in a stereoscopic image display apparatus according to a third concrete example is shown inFIG. 6(a).FIG. 6(b) is a diagram obtained by plotting vertical aperture areas of respective pixels in the stereoscopic image display apparatus according to the third concrete example having the pixel structure shown inFIG. 6(a). Additional lines inFIG. 6(a) represent a one horizontal sub-pixel width and one third vertical sub-pixel width.

In the third concrete example and a fourth concrete example which will be described later, the parallax crosstalk quantity in luminance distribution of light rays illuminated from each sub-pixel changes depending upon the width of the black matrix, that is, the horizontal aperture ratio of the sub-pixel. The stereoscopic image display apparatus according to the third concrete example shown inFIGS. 6(a) and6(b) has a pixel shape in the case where a lens designed to minimize the condensing width of parallax in the lens central portion is used. The horizontal aperture width of a sub-pixel located in the lens central portion is wide, and the horizontal aperture width decreases as the location advances to the peripheral portion. Denoting a horizontal aperture width in the lens central portion by WC, a horizontal aperture width at the lens left end by WL, and a horizontal aperture width at the lens right end by WR, the pixel structure satisfies a relation WL=WR<WC.

Fourth Concrete Example

A pixel structure in each lens in a stereoscopic image display apparatus according to a fourth concrete example is shown inFIG. 7(a).FIG. 7(b) is a diagram obtained by plotting vertical aperture areas of respective pixels in the stereoscopic image display apparatus according to the fourth concrete example having the pixel structure shown inFIG. 7(a). Additional lines inFIG. 7(a) represent a one horizontal sub-pixel width and one third vertical sub-pixel width.

The stereoscopic image display apparatus according to the fourth concrete example has a pixel shape in the case where a lens designed to minimize the condensing width of the peripheral parallax is used. As shown inFIGS. 7(a) and7(b), the horizontal aperture ratio of the sub-pixel increases as the location advances from the lens central portion to the peripheral portion. In other words, the horizontal aperture width of the sub-pixel located in the lens central portion is narrow, and the horizontal aperture width increases as the location advances to the peripheral portion.

Denoting a horizontal aperture width in the lens central portion by WC, a horizontal aperture width at the lens left end by WL, and a horizontal aperture width at the lens right end by WR, the pixel structure satisfies a relation WL=WR>WC.

Incidentally, in the third and fourth concrete examples, a diffusion film28should be provided between the second sheet polarizer26band the parallax generating lens40as shown inFIG. 8in order to eliminate moiré5in which the luminance varies periodically caused by the black matrix of the sub-pixel resulting from the lens effect.

Relations among inclination angles of the color filter arrangement (sub-pixel arrangement) with respect to a ridgeline (major axis) of the lens will now be described with reference toFIGS. 9(a) to10(b). In the case of a pixel shape in which the inclination angle of the pixel differs depending upon the location is in the lens central portion or in the peripheral portion as described above, it will be indicated that the inclination angle of the lens also has a general purpose property.FIGS. 9(a) and9(b) show examples of a mosaic arrangement in which R, G and B pixels forming color filters are arranged alternately both in the horizontal direction and the vertical direction. AndFIGS. 9(a) and9(b) show examples in the case where sub-pixels have pixel shapes shown inFIG. 4(a) andFIG. 5(a), respectively. In this case, a vertical lens having a ridge line direction of the lens which is vertical is used. AlthoughFIGS. 9(a) and9(b) show the examples of the mosaic arrangement, a lateral stripe arrangement in which R, G and B are arranged in the same way may also be used.

FIGS. 10(a) and10(b) show examples using a stripe arrangement in which the same colors are arranged in the vertical direction. AndFIGS. 10(a) and10(b) show examples in the case where sub-pixels have pixel shapes shown inFIG. 4(a) andFIG. 5(a), respectively. In the examples shown inFIGS. 10(a) and10(b), an oblique lens in which the lens ridgeline direction has an inclination depending upon the number of parallaxes is used. It is possible to conduct color display with resolution lowering suppressed and parallax crosstalk quantity suppressed.

Incidentally, inFIGS. 9(a) to10(b), moiré5can be prevented by providing sub-pixels in an even numbered row in the vertical direction with shapes obtained by inverting shapes of sub-pixels in an odd numbered row about a horizontal axis, that is, by forming a pixel shape of one “<” character in two rows.

FIGS. 11(a) and11(b) are diagrams showing results obtained by conducting a simulation of the parallax crosstalk quantity in nine parallaxes with sub-pixel shapes shown in FIG.4(a) andFIG. 5(a). Normalized parallax crosstalk for each parallax number is shown. Triangular points indicate the conventional case in which all pixel structures are the same. Rhomb points indicate results obtained by using pixel shapes in the present embodiment. In the case ofFIG. 11(a), the lens is designed to minimize the parallax crosstalk quantity of the central parallax, and consequently the pixel shape in which the inclination angle of the sub-pixel becomes great as the location approaches the central portion of the lens is used. Since the isolation degree of the sub-pixel in the lens peripheral portion is high, the parallax crosstalk quantity of luminance is improved by at least 10% as compared with the conventional case. In the case ofFIG. 11(b), the lens is designed to minimize the parallax crosstalk quantity of the peripheral parallax, and consequently the pixel shape in which the inclination angle of the sub-pixel becomes small as the location approaches the central portion of the lens is used. In this case, the parallax crosstalk quantity is improved by at least 7% as compared with the conventional case. It should be noted that the improved parallax crosstalk quantity differs according to a change of panel specifications such as the pixel shape and the sub-pixel width. However, it is apparent that the pixel shape in the present embodiment brings about a great effect in reduction of the parallax crosstalk quantity as compared with the conventional pixel shape.

According to the present embodiment, the difference in parallax crosstalk quantity can be reduced as described heretofore.