JP4334707B2 - Image display device - Google Patents

Description

【０１３６】
ここにＣ1 は正規化するための係数であり、記号＊はコンボリューションを表している。
【０１３７】
干渉項Ｈ１のグラフのシャープさは、高周波数成分の多い画像信号の場合ほどデルタ関数的にシャープになり、低周波数成分が支配的な画像信号ではシャープさがない周期関数となるが、ここでは標準的な画像信号を想定して適宜の関数を用いている。この表示素子のＭＴＦとしては、例えば、ナイキスト周波数ｆN が約２７［本／ｍｍ］であり、サンプリングノイズが約５４［本／ｍｍ］に存在したものとなる。
【０１３８】
次に、図２６（Ｂ）は、ローパスフィルタのＭＴＦを示したものである。
【０１３９】
ローパスフィルタを回折格子とした場合、さらに２次光以上の高次光の強度が有意でないとすると、ローパスフィルタのＭＴＦは、像面上での回折による画素（１次光の像（−１次光でも同様））と正規の画素（０次光の像）との距離と回折効率から求めることができる。
【０１４０】
すなわち、ローパスフィルタの垂直方向のＭＴＦであるＭＴＦＹ［ｖ］は、０次光強度をα［０］、１次光強度（０次光により正規化した強度比）をα［１］、０次光の像と１次光の像との距離をｙ［１］とすると、以下の数式３に示すようになる。
【０１４１】
【数３】

【０１４２】
ここにＣ2 は、正規化するための係数である。
【０１４３】
この数式３において、例えば０次光強度α［０］＝１、１次光強度α［１］＝１、０次光の像と１次光の像との距離をｙ［１］＝０．００６２［ｍｍ］などとした場合には、表示素子のサンプリングノイズの周波数約５４［本／ｍｍ］付近に、第１の遮断空間周波数ｆ1Cが位置する図示のＭＴＦＹ１となる。
【０１４４】
接眼窓（Ｒ窓）方式のローパスフィルタの場合には、接眼光学系の焦点距離ｆを２５［ｍｍ］とすると、０次光の像と１次光の像との距離δ＝０．００６１［ｍｍ］を実現するためには、上記数式１を用いると、ε＝２．４×１０＾（−４）［ｒａｄ］（ここに、記号＾はべき乗を表す）となる。
【０１４５】
この回折角εを有する回折格子のピッチＰは、１次回折角の一般的な式である次の数式４を用いれば、
【数４】

格子ピッチＰ＝２［ｍｍ］と算出される。ただし波長λとして、比視感度の強い波長λ＝０．５［μｍ］を用いている。
【０１４６】
続いて、図２６（Ｃ）は、上記図２６（Ａ）に示したような表示素子と、上記図２６（Ｂ）に示したようなローパスフィルタとを組み合わせたときのＭＴＦを示したものである。
【０１４７】
表示素子のＭＴＦであるＭＬＣＤ１と、ローパスフィルタのＭＴＦであるＭＴＦＹ１の積が、ローパスフィルタを配置したときの表示素子のＭＴＦであるＭＴＦ１となる。
【０１４８】
図示のように、表示素子が元々備えていたサンプリングノイズの強度が、ローパスフィルタの第１遮断空間周波数ｆ1Cによって低減されている様子を読み取ることができる。
【０１４９】
続いて、図２７は、上記図２４（Ｂ）に示したような格子ピッチが細かい場合のＭＴＦグラフ（ＬＰＦ例）を示したものである
図２７（Ａ）は、表示素子のＭＴＦを示したものであり、表示素子のＭＴＦであるＭＬＣＤ０、回折項Ｍ０、干渉項Ｈ０は、上記図２６（Ａ）に示したＭＬＣＤ１、回折項Ｍ１、干渉項Ｈ１と、それぞれ同様である。
【０１５０】
また、図２７（Ｂ）は、ローパスフィルタのＭＴＦを示したものである。
【０１５１】
ローパスフィルタの垂直方向のＭＴＦであるＭＴＦＹ［ｖ］は、上記数式３に示したようになる。
【０１５２】
ここで、例えば０次光強度α［０］＝１、１次光強度α［１］＝１，０次光の像と１次光の像との距離ｙ［１］＝０．０１２３［ｍｍ］などとした場合には、表示素子のサンプリングにノイズの周波数約５４［本／ｍｍ］付近に、第２の遮断空間周波数ｆ2Cが位置する図示のＭＴＦＹ０となる。
【０１５３】
これが上記図２６に示したような粗い回折格子と異なるのは、０次光の像と１次光の像との距離であり、回折効率は同様である。０次光の像と１次光の像との距離を異ならせることにより、回折角、すなわちローパスフィルタの格子ピッチを異ならせて、より細かい回折格子を実現するように工夫したものである。
【０１５４】
この例の場合のローパスフィルタの格子ピッチＰは、以下のようにして求められる。
【０１５５】
すなわち、接眼光学系の焦点距離を上述した例と同様に２５［ｍｍ］とすると、０次光の像と１次光の像との距離δ＝０．０１２３［ｍｍ］を実現するためには、上記数式１から、ε＝４．９×１０＾（−４）［ｒａｄ］（ここに、記号＾はべき乗を表す）となる。
【０１５６】
この回折角εを有する回折格子のピッチＰは、１次回折角の一般的な式である上記数式４を用いれば、格子ピッチＰ＝１．０［ｍｍ］と算出される。ここで、波長λとして、比視感度の強い波長λ＝０．５［μｍ］を用いているのは上述と同様である。
【０１５７】
上記図２４等において述べたように、ローパスフィルタを接眼窓やその近傍に配置する本実施形態の光学系のような場合には、観察者の瞳径は一般的に３〜５［ｍｍ］程度と限られているために、格子ピッチが小さい方が画面内の回折ムラがなく、良好な画像を表示することができる。
【０１５８】
そのために、上記図２４（Ａ）および図２６に示したような粗い回折格子のローパスフィルタよりも、上記図２４（Ｂ）および図２７に示したような細かい回折格子のローパスフィルタを好適に用いることができる。
【０１５９】
続いて、図２７（Ｃ）は、上記図２７（Ａ）に示したような表示素子と、上記図２７（Ｂ）に示したようなローパスフィルタとを組み合わせたときのＭＴＦを示したものである。
【０１６０】
表示素子のＭＴＦであるＭＬＣＤ０と、ローパスフィルタのＭＴＦであるＭＴＦＹ０の積が、ローパスフィルタを配置したときの表示素子のＭＴＦであるＭＴＦ０となる。
【０１６１】
図示のように、表示素子が元々備えていたサンプリングノイズの強度が、ローパスフィルタの第２遮断空間周波数ｆ2Cによって低減されている様子を読み取ることができる。
【０１６２】
なお、ウォブリングを行ったときの表示素子のＭＴＦは、ウォブリングした結果の画素配列を有する表示素子のＭＴＦとしてとらえることができるのは上述と同様である。
【０１６３】
ここで、表示素子が有するナイキスト周波数ｆN とローパスフィルタが有する遮断空間周波数ｆC との関係について説明する。
【０１６４】
サンプリング周波数は、画素ピッチの逆数から求められ、一番低周波数のサンプリングノイズの周波数はおよそこの値である。ナイキスト周波数ｆN は、該サンプリング周波数の約１／２の周波数である。
【０１６５】
また、ローパスフィルタの遮断空間周波数ｆC は、ＭＴＦが０となる周波数であるから、上述した数式３の左辺を０とした式から求めることができ、
【数５】

となる。
【０１６６】
ここで、第２遮断空間周波数ｆ2Cはｎ＝１とした周波数として求められる。
【０１６７】
この例では、ナイキスト周波数ｆN ＝２７、第２遮断空間周波数ｆ2C＝５４であり、ｆ2C／ｆN ＝２である。
【０１６８】
これに対して、上記図２４（Ａ）や図２６に示したような回折格子の粗いローパスフィルタの場合には、ｆ2C／ｆN ≒４となる。
【０１６９】
なお、ここでは、１次元（垂直方向）に限って説明してきたが、２次元でも考え方は同様であり、第２遮断空間周波数ｆ2Cの、表示素子のナイキスト周波数ｆN に対する比が、上記値２を挟んだ１．５〜２．５程度となるように、ローパスフィルタを構成することによって、回折ムラのない良好な画像を得ることが可能となる。
【０１７０】
続いて、ウォブリング素子（画素飛ばし光学素子）の構成やその作用について説明する。まず、図２８は、ウォブリングにおいて画素を斜め方向に飛ばす原理を説明するための図である。
【０１７１】
なお、ここでは２枚の複屈折板を用いる例について説明するが、これに限るものではなく、例えば旋光板等を用いて構成しても構わない。
【０１７２】
図２８において、第１の複屈折板５ｄは光の出射位置を水平方向にずらすもの、つまり水平方向に飛ばすものであり、一方、第２の複屈折板５ｅは、光の出射位置を垂直方向にずらすもの、つまり垂直方向に飛ばすものである。
【０１７３】
これら２枚の複屈折板５ｄ，５ｅを光軸方向に重ね合わせて組み合わせることにより、光の出射位置を斜め方向にずらすこと、つまり斜め方向に飛ばすことが可能となっている。
【０１７４】
すなわち、図２８（Ａ）に示すように、画素飛ばし光学素子の後述する第２のＴＮ液晶セル５ｃ（図２９参照）から水平方向に偏光した光が第１の複屈折板５ｄに入射したとすると、画素位置は水平方向に飛ばされて出射する。続く第２の複屈折板５ｅは、偏光方向が横方向の光に対しては何も作用しないために、そのまま通過して、画素位置は横方向に飛んだ状態で出射される（黒丸印参照）。
【０１７５】
次に、図２８（Ｂ）に示すように、上記第２のＴＮ液晶セル５ｃから縦方向に偏光した光が第１の複屈折板５ｄに入射したとすると、偏光方向が縦方向の光に対しては何も作用しないために、そのまま通過して第２の複屈折板５ｅに入射する。そして、この第２の複屈折板５ｅにおいては、縦方向に画素位置がずらされて出射する（黒丸印参照）。
【０１７６】
従って、図２８（Ａ）における第２の複屈折板５ｅからの出射状態から、図２８（Ｂ）における第２の複屈折板５ｅからの出射状態を見ると、黒丸で示した画素位置は、横方向にずらされた位置から縦方向にずらされた位置へ移動したことになり、これは結局、斜め方向にずらされた状態を実現したことになる。このように、第２のＴＮ液晶セル５ｃから出射される偏光方向が水平方向および垂直方向の光に対して、２枚の組み合わせ複屈折板を介在させることにより、光出射位置すなわち画素位置を斜め方向に飛ばすことが可能となる。
【０１７７】
次に、このような原理を用いて構成した、画素位置を４つの位置にずらす画素飛ばし光学素子（画素位置変位手段）の例について、図２９を参照して説明する。図２９は画素飛ばし光学素子の主要な構成を示す斜視図である。
【０１７８】
この画素飛ばし光学素子（ウォブリング素子５）は、第１のＴＮ液晶セル５ａと第１の複屈折板５ｂとを有してなる横方向の画素飛ばし素子と、第２のＴＮ液晶セル５ｃと第２の複屈折板５ｄと第３の複屈折板５ｅとを有してなる斜め方向の画素飛ばし素子とを備えて構成されている。
【０１７９】
ここで、上記第２の複屈折板５ｄは、図３０に示すような画素飛ばし位置におけるＰｘ／４に相当する厚さを有しており、上記第３の複屈折板５ｅは同図３０におけるＰｙ／２に相当する厚さを有している。また、上記第１の複屈折板５ｂの厚みは、Ｐｘ／２に相当する厚さを有している。なお、図３０は画素飛ばし素子により飛ばされる画素の位置関係を示す図である。
【０１８０】
次に、このように構成されている画素飛ばし光学素子の動作について説明する。
【０１８１】
この画素飛ばし光学素子においては、液晶表示素子４として、矢印で示すような横方向（水平方向）の偏光方向の光を射出するものが用いられているものとする。
【０１８２】
上記第１のＴＮ液晶セル５ａは、印加電圧をオン／オフすることにより、出射する光の偏光方向を９０°変化させるようになっている。
【０１８３】
また、第１の複屈折板５ｂは、その結晶軸が図示のように横方向に４５°傾いており、上記第１のＴＮ液晶セル５ａの印加電圧をオンとしたときの偏光方向が横方向の光は、矢印で示すように横方向にずれて出射される。一方、上記第１のＴＮ液晶セル５ａの印加電圧をオフとしたときの偏光方向が縦方向の光は、作用を受けることなくそのまま矢印で示すように通過する。従って、第１のＴＮ液晶セル５ａと第１の複屈折板５ｂとを有してなる画素ずらし素子への印加電圧をオン／オフすることにより、液晶表示素子４から出射された光は、そのまま通過されたり、あるいは横方向（水平方向）にずらされたりしてから出射される。
【０１８４】
次に、上記第２のＴＮ液晶セル５ｃに入射した光は、上述した第１のＴＮ液晶セル５ａと同様に、印加電圧をオン／オフすることにより、出射する光の偏光方向を９０°変化させる。すなわち、印加電圧がオンのときは偏光方向が変わらず、ＯＮ−ＯＮの矢印およびＯＦＦ−ＯＮの矢印に示すように、偏光方向は変化することなくそのまま通過する。一方、印加電圧がオフのときは、偏光方向は、９０°回転して、ＯＮ−ＯＦＦの矢印およびＯＦＦ−ＯＦＦの矢印に示すように、偏光方向が９０°回転して出射される。
【０１８５】
続いて、上記第２のＴＮ液晶セル５ｃから出射した光は、結晶軸を横方向に傾けた第２の複屈折板５ｄと、結晶軸を縦方向に傾けた第３の複屈折板５ｅと、の２枚の複屈折板を通過させることにより、上記図２８においてその原理を説明したように、第３の複屈折板５ｅからは、偏光方向が横方向の光はＯＮ−ＯＮの矢印およびＯＦＦ−ＯＦＦの矢印に示すように、横方向に少しずらされて出射する。一方、偏光方向が縦方向の光は、ＯＮ−ＯＦＦの矢印およびＯＦＦ−ＯＮの矢印に示すように、縦方向に少しずらされて出射する。こうして、偏光方向が縦方向の光は、偏光方向が横方向の光に対して、斜め方向にずらされた位置から出射されることになる。
【０１８６】
以上のように、第１および第２のＴＮ液晶セル５ａ，５ｃに対する印加電圧のオン／オフを、表１に示すような組み合わせ順とすることにより、液晶表示素子４からの出射位置（画素位置）を、図３０の番号１〜４に示すような画素位置に制御することができる。
【０１８７】
【表１】

【０１８８】
次に、図３１は、ウォブリングを行ったときの画素の光量の分配の割合を時間軸に沿って示す図である。
【０１８９】
上述したようなウォブリングを行って、画素の見かけの位置を、ある位置から次の位置にシフトさせる際には、画素位置が瞬間的に切り換わるわけではなく、元の画素の輝度が徐々に低下すると同時に、次の画素の輝度が徐々に上昇するという動作を行うことになる。
【０１９０】
このときの画素の光量の移り変わりの様子を示したのがこの図３１である。図示のように、例えば、第４の画素位置の光量が低下すると、次の第１の画素位置の光量が上昇するという動作を繰り返し行っている。
【０１９１】
このようなウォブリング動作により表示された画像を観察する際に、例えば符号Ａで示す時点の像と、この時点から約１６．６７［ｍｓ］経過した後の符号Ｂで示す時点の像との繰り返しが人間の眼に観察されてしまうことがある。
【０１９２】
図３２は、ウォブリングを行ったときに観察され得る画像の様子を示す図である。
【０１９３】
上記符号Ａで示すタイミングのときには、位置４の画素と位置１の画素が適宜の輝度をもっており、位置２の画素と位置３の画素は輝度が低く観察されない状態となっていて、このときの画像の様子を示すのが図３２（Ａ）である。
【０１９４】
一方、上記符号Ｂで示すタイミングのときには、位置２の画素と位置３の画素が適宜の輝度をもっており、位置１の画素と位置４の画素は輝度が低く観察されない状態となり、図３２（Ｂ）に示すような画像が観察されることになる。
【０１９５】
こうした図３２（Ａ）に示すような画像と図３２（Ｂ）に示すような画像とが繰り返して観察されると、人間の眼には左上から右下にかけての斜めの縞模様が、左下から右上の方向に、または右上から左下の方向に移動するように見えてしまうことがある。
【０１９６】
同様に、上記図３１の符号ａで示す時点の像と、符号ｂで示す時点の像との繰り返しが人間の眼に観察されることもあり、この場合には、水平方向の縞模様が上から下の方向、または下から上の方向に移動するように見えてしまうことになる。
【０１９７】
このようにウォブリングを行うと、縞模様が移動して観察される現象があることを本出願人は発見したが、上述したようなローパスフィルタを用いることにより、こうした縞模様が観察されにくくなるという利点があることが、実験により確かめられている。
【０１９８】
従来は表示素子の近傍に配設されるローパスフィルタであるが、ウォブリング素子を用いる場合には、成形された樹脂等でなる該ローパスフィルタによって偏光方向が乱れることがあるために、そのまま従来の配置を適用することはできない。やむを得ず、ローパスフィルタを配設しない構成を採用すると、上述したようにウォブリングによって縞模様が観察される現象が発生してしまう。従って、本実施形態に示したように、接眼光学系よりも光路上後方となる例えば接眼窓部分にローパスフィルタを配置することで、上述したような縞模様が観察されるのを有効に抑制することができるのである。
【０１９９】
このような実施形態によれば、表示素子とローパスフィルタの虚像位置に距離差があるために、観察者の眼のピントが両方に同時に合うことはほとんどなく、ゴミや異物等が付着していたとしても観察されにくいという利点がある。従って、製造時の規格を緩和することが可能となり、製造コストの低減を図ることができる。
【０２００】
また、表示素子とローパスフィルタを離隔して配設することにより、モアレ等が発生し難くくなるという利点がある。
【０２０１】
さらに、ローパスフィルタを、画像表示装置の防塵や保護を行うための接眼窓として用いることにより、部品を共通化することができるために、部品点数を削減してコストを低減することができる。
【０２０２】
そして、ウォブリング光学系においては、接眼光学系の表示素子側の面と表示素子との間にウォブリング素子を配置するが、接眼光学系のワーキングディスタンス（接眼光学系の表示素子側の面と表示素子との間隔）の大きさは倍率に関係して一般的に制限があるために、ローパスフィルタの配設スペースにも制限がある。これに対して、上述したように接眼光学系よりも光路上後方に配設することで、ローパスフィルタの配設位置や配設スペースに制限が少なくなり、設計等が容易となる。
【０２０３】
また、接眼窓方式ではウォブリング素子よりも光路上後方にローパスフィルタを配置するために、ウォブリング素子を通過する偏光が乱れることはなく、正確なウォブリングを維持して画質を保つことができる。
【０２０４】
さらに、第２の遮断空間周波数でサンプリングノイズを遮断する構成とすることにより、回折格子のピッチを細かくすることが可能となって、単純に第１の遮断空間周波数によりサンプリングノイズを遮断する場合に比して、回折ムラが発生し難くくなるという利点がある。
【０２０５】
こうして本実施形態の画像表示装置によれば、ざらつき感やちらつきの少ない見やすい画像を観察することができる。
【０２０６】
なお、本発明は上述した実施形態に限定されるものではなく、発明の主旨を逸脱しない範囲内において種々の変形や応用が可能であることは勿論である。
【０２０７】
【発明の効果】
以上説明したように請求項１による本発明の画像表示装置によれば、接眼光学系と観察者の眼球との間に光学フィルタ手段を配置し、その第２の遮断空間周波数のナイキスト周波数に対する比を１．５と２．５の間となるようにしたために、画素ピッチを細かくすることが可能となって回折ムラを低減することができ、ざらつき感やちらつきの少ない見易い画像を観察することができる。
【０２０８】
また、請求項２による本発明の画像表示装置によれば、回折格子を有する光学フィルタ手段によって、請求項１に記載の発明と同様の効果を奏することができる。
【０２０９】
さらに、請求項３による本発明の画像表示装置によれば、請求項２に記載の発明と同様の効果を奏するとともに、回折格子を光学フィルタ手段の接眼光学系に対向する面に形成することにより、接眼窓と兼用させることが可能となり、部材点数を減らしてコストを削減することが可能となる。
【０２１０】
請求項４による本発明の画像表示装置によれば、表示素子と接眼光学系の間に第１の光学フィルタ手段を配置し、接眼光学系と観察者の眼球との間に第２の光学フィルタ手段を配置したために、ざらつき感やちらつきの少ない見易い画像を観察することができる。
【０２１１】
請求項５による本発明の画像表示装置によれば、請求項４に記載の発明と同様の効果を奏するとともに、第２の光学フィルタ手段の第２の遮断空間周波数の、ナイキスト周波数に対する比を１．５と２．５の間となるようにしたために、画素ピッチを細かくすることが可能となって回折ムラを低減することができる。
【０２１２】
請求項６による本発明の画像表示装置によれば、表示素子の画素位置を４点の位置で繰り返して変位させる画素位置変位手段を備えた構成において、請求項４に記載の発明と同様の効果を奏することができる。
【０２１３】
請求項７による本発明の画像表示装置によれば、回折格子が形成された光学ローパスフィルタまたは複屈折板でなる光学ローパスフィルタを備えた構成において、請求項４に記載の発明と同様の効果を奏することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態におけるＬＣＤの画素配列の一例を示す図。
【図２】上記図１に示したようなデルタ配列のＬＣＤの内の、Ｇ画素のみの配列を示す図。
【図３】上記実施形態における縦方向１次元ローパスフィルタによる画素配列の第１例を示す図。
【図４】上記実施形態における縦方向１次元ローパスフィルタによる画素配列の第２例を示す図。
【図５】上記実施形態における斜め方向の１次元ローパスフィルタによる画素配列を示す図。
【図６】上記実施形態における縦横方向２次元ローパスフィルタによる画素配列を示す図。
【図７】上記実施形態における、第１の縦方向１次元ローパスフィルタと第２の縦方向１次元ローパスフィルタとを組み合わせてなされる画素配列を示す図。
【図８】上記実施形態において、ウォブリングする前のカラーＬＣＤの画素配列を示す図。
【図９】上記図８に示したようなＬＣＤのウォブリング後の見かけの画素配列について、Ｇのみを抜き出して示す図。
【図１０】上記実施形態において、１次元ローパスフィルタに形成したストライプ状の回折格子の各種の例を示す図。
【図１１】上記実施形態における２次元ローパスフィルタの回折格子の第１例を示す斜視図。
【図１２】上記実施形態における２次元ローパスフィルタの回折格子の第２例を示す斜視図。
【図１３】上記実施形態における２次元ローパスフィルタの回折格子の第３例および第４例を示す斜視図。
【図１４】上記実施形態における２次元ローパスフィルタの回折格子の第５例を示す平面図。
【図１５】上記図１０（Ａ）に示したような矩形状の断面を有する回折格子の詳細な構成を示す図。
【図１６】上記図１４に示したような斜方向の回折格子を有してなる２次元ローパスフィルタの形状を示す図。
【図１７】上記実施形態における画像表示装置の光学系の第１の構成例を示す図。
【図１８】上記実施形態における画像表示装置の光学系の第２の構成例を示す図。
【図１９】上記実施形態におけるＲ窓方式の画像表示装置の光学系の第１の基本構成例を示す図。
【図２０】上記実施形態におけるＲ窓方式の画像表示装置の光学系の第２の基本構成例を示す図。
【図２１】上記実施形態におけるＲ窓方式の画像表示装置の光学系の第３の基本構成例を示す図。
【図２２】上記実施形態におけるＲ窓方式の画像表示装置の光学系の第４の基本構成例を示す図。
【図２３】上記実施形態において、ローパスフィルタに施すハードコート処理の各種の例を示す図。
【図２４】上記実施形態において、画像を使用者の眼球に結像させる際に格子ピッチの異なるローパスフィルタを通過させる様子を示す図。
【図２５】上記実施形態において、テレセントリック光学系を例に取ったときの回折角と分離幅の関係を示す図。
【図２６】上記図２４（Ａ）に示したような格子ピッチが粗い場合のＭＴＦグラフ。
【図２７】上記図２４（Ｂ）に示したような格子ピッチが細かい場合のＭＴＦグラフ。
【図２８】上記実施形態のウォブリングにおいて、画素を斜め方向に飛ばす原理を説明するための図。
【図２９】上記実施形態における画素飛ばし光学素子の主要な構成を示す斜視図。
【図３０】上記実施形態の画素飛ばし素子により飛ばされる画素の位置関係を示す図。
【図３１】上記実施形態において、ウォブリングを行ったときの画素の光量の分配の割合を時間軸に沿って示す図。
【図３２】上記実施形態において、ウォブリングを行ったときに観察され得る画像の様子を示す図。
【図３３】従来方式の画像表示装置の光学系の構成例を示す図。
【符号の説明】
１…筐体
３…バックライト
４…ＬＣＤ（表示装置、表示素子）
５…ウォブリング素子（画素位置変位手段）
６，８…接眼光学系
7,7B,7C,7D,7E,7l,7s,10,11,12,13,14,15,16,17,18,19,20…光学ローパスフィルタ（光学フィルタ手段）
３１…ハードコート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display device, and more particularly to an image display device that enlarges an image displayed on a display device by an eyepiece optical system and forms an image on an eyeball of an observer.
[0002]
[Prior art]
In recent years, image display devices for enlarging an image displayed on a display device by an eyepiece optical system to form an image on an observer's eyeball have been actively commercialized, and are displayed on the optical system of such an image display device. In general, a configuration in which an optical low-pass filter is interposed in order to remove a rough feeling of an image and make it easy to see.
[0003]
An example of the optical system of the image display apparatus using such an optical low-pass filter will be described with reference to FIG. FIG. 33 is a diagram illustrating a configuration example of an optical system of a conventional image display apparatus.
[0004]
This image display device includes a backlight 3 that emits illumination light, an LCD 4 that displays an image as a set of regularly arranged pixels, and an optical image emitted from the LCD 4. An optical low-pass filter 7 disposed in the vicinity of the LCD 4 to remove components, an eyepiece optical system 6 that forms an image of a light beam emitted from the optical low-pass filter 7 toward an observer's eyeball, and the housing And an eyepiece window (R window) 9 having a dustproof function and a protective function fitted in one eyepiece window position.
[0005]
Here, the conventional method refers to a device in which the optical low-pass filter 7 is disposed on or near the surface of the LCD 4 serving as a display element, and is currently most widely used. It is of the type.
[0006]
As an example of such an arrangement, Japanese Patent Laid-Open No. 63-114475 discloses an image display device having an image display having dot-shaped display segments arranged two-dimensionally. An image display device is disclosed in which an optical low-pass filter that passes a spatial frequency component lower than a predetermined spatial frequency determined accordingly is disposed on a display surface of an image display or in its finder optical system. Describes an example in which an optical low-pass filter is disposed between the image display and the eyepiece optical system.
[0007]
When designing the optical low-pass filter as described above, there is a concept that the cutoff spatial frequency of the optical low-pass filter substantially matches the frequency of the first noise in the sampling noise determined by the pixel arrangement of the display element. is there.
[0008]
As a conventional example that limits the range of such a cut-off spatial frequency, for example, Japanese Patent Application Laid-Open No. 8-122710 discloses an image display body in which a plurality of pixels are periodically arranged two-dimensionally, and the above image display An optical low-pass filter disposed in front of the body, wherein two cutoff spatial frequencies in at least one direction of the optical low-pass filter have a specific sampling frequency (of a sampling frequency determined by a pixel arrangement of the image display body ( The image display device set in the range of 1/4 or more and 3/4 or less and 3/4 or more and 5/4 or less is described, where (the one having the second lowest frequency) is 1. Yes.
[0009]
In recent years, a technique for increasing the number of apparent pixels has been proposed by a technique called pixel skipping (or wobbling).
[0010]
As an example of such a technique, Japanese Patent Application Laid-Open No. 7-36054 discloses that a plurality of transparent substrates in an optical system in which an optically transparent electrode and an alignment film are provided in this order include the electrode and the light distribution film. At least one liquid crystal selected from a ferroelectric liquid crystal, an antiferroelectric liquid crystal, and a smectic liquid crystal exhibiting an electroclinic effect is injected into the gap. There is described an optical apparatus configured by combining a plurality of elements each including a phase modulation optical element and an optically transparent birefringent medium.
[0011]
[Problems to be solved by the invention]
However, in the conventional configuration as shown in FIG. 33, since a low-pass filter is arranged in the vicinity of the display element, it becomes easy to observe when dust or the like is attached. In order to cope with this, the standard at the time of manufacture had to be strict, and the manufacturing cost would increase. Further, when the pixel pitch of the display element and the pitch of the diffraction grating constituting the low-pass filter are close to an integer ratio, there has been a problem that moire or the like is likely to occur.
[0012]
Furthermore, in the image display device to which the pixel skipping technique as described above is applied, the pixel skipping element is arranged in the vicinity of the display element. However, in consideration of productivity, it is made by molding a resin by a stamper or the like. Since the low-pass filter may disturb the polarization direction, the configuration as shown in FIG. 33 cannot be applied as it is. However, when an image display apparatus using a pixel skip technique is used without using a low-pass filter, as will be described in detail in an embodiment described later, a striped pattern that should not originally exist in the image appears to move. The applicant has found through experimentation that there is a possibility of being lost.
[0013]
In addition, in an optical low-pass filter that matches the cutoff spatial frequency to the frequency of the first sampling noise, the pixel separation amount by the optical low-pass filter on the LCD virtual image plane becomes smaller as the display element becomes higher in definition. As a result, the grating pitch of the filter increases. On the other hand, in an optical system that presents a virtual image to the observer, the light beam diameter when passing through the optical low-pass filter is about the pupil diameter of the observer, so the number of sampled gratings is reduced and diffraction is performed within the screen. Unevenness may occur, causing the image to flicker or appear blurred or sharp when the eye is moved.
[0014]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image display device capable of observing an easy-to-view image with less roughness and flicker.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, an image display device according to a first aspect of the present invention includes a display device in which pixels are regularly arranged, and an image displayed on the display device is enlarged and connected to an eyeball of an observer. An eyepiece optical system for imaging, and an optical filter means for separating the light from the eyepiece optical system disposed between the eyepiece optical system and the eyeball of the observer into a plurality of lights, and the optical filter means , Having a first cut-off spatial frequency and a second cut-off spatial frequency which is higher than the first cut-off spatial frequency, and the second cut-off spatial frequency f2C depends on the pixel pitch of the display device. For the determined Nyquist frequency fN,
1.5 <f2C / fN <2.5
Satisfy the relationship.
[0016]
An image display device according to a second invention is the image display device according to the first invention, wherein the optical filter means has a diffraction grating.
[0017]
Furthermore, an image display device according to a third invention is the image display device according to the second invention, wherein the diffraction grating of the optical filter means is formed on a surface of the optical filter means facing the eyepiece optical system. It is.
[0018]
According to a fourth aspect of the present invention, there is provided an image display device comprising: a display element having regularly arranged pixels; an eyepiece optical system for enlarging an image displayed on the display element to form an image on an observer's eyeball; and the display A first optical filter means for separating or switching light from the display element disposed between the element and the eyepiece optical system into a plurality of lights, and disposed between the eyepiece optical system and the eyeball of the observer. And second optical filter means for separating the light from the eyepiece optical system into a plurality of lights.
[0019]
An image display device according to a fifth invention is the image display device according to the fourth invention, wherein the second optical filter means has a first cut-off spatial frequency and a frequency higher than the first cut-off spatial frequency. The second cutoff spatial frequency f2C is Nyquist frequency fN determined by the pitch of the pixels generated by the display element and the first optical filter means.
1.5 <f2C / fN <2.5
Satisfy the relationship.
[0020]
The image display device according to a sixth invention is the image display device according to the fourth invention, wherein the first optical filter means repeatedly displaces the pixel position of the display element at four positions. It is.
[0021]
An image display device according to a seventh invention is the image display device according to the fourth invention, wherein the first optical filter means is an optical low-pass filter or a birefringent plate formed with a diffraction grating. .
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 32 show an embodiment of the present invention, and FIG. 1 is a view showing an example of a pixel array of an LCD.
[0023]
First, with reference to FIG. 1, a delta arrangement will be described as an example of an LCD pixel arrangement.
[0024]
In this delta arrangement, pixels are arranged cyclically in the order of, for example, R (red), G (green), and B (blue) in the same column, the even columns are the same, and the odd columns are the same. In this case, the even-numbered columns and the odd-numbered columns are arranged so as to be out of phase by 3/2 pixels.
[0025]
More specifically, taking G of these as an example, it is composed of two adjacent G pixels in the even-numbered column 2n and two G pixels in the same phase in the next even-numbered column 2n + 2. The odd row 2n + 1 G pixels are positioned so as to be positioned approximately at the center of the rectangle.
[0026]
Similarly, even columns are arranged so as to be located at substantially the center of a rectangle formed by two G pixels adjacent to each other in the odd column 2n + 1 and two G pixels having the same phase in the next odd column 2n + 3. It is configured such that 2n + 2 G pixels are located.
[0027]
Here, the delta arrangement is taken as an example, but of course, a stripe arrangement, a mosaic arrangement, or the like may be used.
[0028]
Further, here, a color LCD is given as an example of the display element, but the technology described later can be applied almost as it is even for a monochrome LCD.
[0029]
FIG. 2 is a diagram showing an arrangement of only G pixels in the delta arrangement LCD as shown in FIG.
[0030]
As described above, the G pixels are alternately arranged in even columns and odd columns. For the sake of simplicity, the following description will be given mainly with respect to the G pixel, but the contents of the description are also applied to the R pixel and the B pixel in substantially the same manner.
[0031]
Next, with reference to FIG. 3 and subsequent figures, the state of light separation when using an optical low-pass filter (hereinafter, abbreviated as a low-pass filter as appropriate) as an optical filter means will be described.
[0032]
Note that the low-pass filter includes a type in which a diffraction grating that gives a phase difference is formed, and a type that uses a birefringent plate formed of, for example, quartz crystal, but a diffraction grating is formed here. A case where a low-pass filter is applied will be described.
[0033]
First, FIG. 3 is a diagram illustrating a first example of a pixel array using a vertical one-dimensional low-pass filter.
[0034]
This vertical one-dimensional low-pass filter forms a diffraction grating having a horizontal stripe shape and separates pixel images in the vertical direction. FIG. 3 shows an apparent pixel array realized by this low-pass filter. Is shown.
[0035]
More specifically, the low-pass filter splits the + 1st order light and the −1st order light at a position shifted by 1/3 of the vertical pitch between pixels in even columns or between pixels in odd columns. Yes.
[0036]
As a result, the image of each pixel is separated into three parts of 0th-order light, + 1st-order light, and −1st-order light, which are arranged at equal intervals, and the number of images that is three times the number of pixels is formed. become.
[0037]
The light intensity of each image at this time is configured such that, for example, the intensity of the 0th-order light and the 1st-order light are substantially equal, and the intensity of the secondary light and the 3rd-order light is negligible. Has been. In order to ignore the secondary light and below, an optical filter having a stripe having a sinusoidal cross section may be used as will be described later.
[0038]
Next, FIG. 4 is a diagram illustrating a second example of a pixel array using a vertical one-dimensional low-pass filter.
[0039]
This low-pass filter is only half the vertical pitch between even-numbered pixels or odd-numbered pixels, that is, only the vertical pitch between pixels of even-numbered columns and odd-numbered columns adjacent to the even-numbered columns. This is an example of a low-pass filter in which a diffraction grating for separating + 1st order light and −1st order light is formed at a shifted position.
[0040]
As a result, the image of each pixel is separated into three parts of 0th order light, + 1st order light, and −1st order light. For example, −1st order light of 2n columns of pixels is divided into + 1st order light of 2n + 2 columns of pixels. Similarly, since the −1st order light of the 2n + 1 column pixels overlaps with the + 1st order light of the 2n + 3 column pixels, an image twice as many as the number of pixels is formed and arranged at equal intervals.
[0041]
Regarding the light intensity of each image at this time, for example, if the intensity of the primary light is approximately half the intensity of the 0th-order light, the even-numbered columns or the odd-numbered columns are adjacent to each other vertically. The + 1st order light and the −1st order light of the pixel are superposed to obtain almost uniform light intensity.
[0042]
Next, FIG. 5 is a diagram illustrating a pixel array by a one-dimensional low-pass filter in an oblique direction.
[0043]
This low-pass filter has a distance of 1 between the even-numbered column and the odd-numbered column adjacent to the even-numbered column, for example, in the direction toward the pixel at a position different by 3/2 of the horizontal pitch. This is an example of a low-pass filter in which a diffraction grating in an oblique direction that separates + 1st order light and −1st order light is formed at a position shifted by / 3.
[0044]
As a result, the image of each pixel is separated into three directions of zero-order light, + 1st-order light, and −1st-order light in an oblique direction, and each of them is arranged at equal intervals to form an image that is three times the number of pixels. Will be.
[0045]
In the example of FIG. 5, a low pass is applied in the upper left-lower right direction. However, a low pass may be applied in the lower left-upper right direction, or a two-dimensional two-dimensional low pass filter. However, if the pixel separation amount is large, the same pixel arrangement as in FIG. 5 can be realized.
[0046]
FIG. 6 is a diagram showing a pixel arrangement by a two-dimensional low-pass filter in the vertical and horizontal directions.
[0047]
This low-pass filter has a left (-1, 0) centered on the original pixel image when coordinates are taken in the horizontal (horizontal) direction and the vertical (vertical) direction with the original pixel image as the center position (0, 0). ), Right (1, 0), top (0, 1), bottom (0, -1), top right (1, 1), bottom right (1, -1), top left (-1, 1), bottom left ( In this example, the diffraction images are arranged in a grid pattern with equal intervals in (-1, -1).
[0048]
At this time, the coordinates represent the orders of the diffracted light, and display (the order in the horizontal direction and the order in the vertical direction), respectively.
[0049]
As a result, the image of each pixel is separated into nine, but since the pixel image other than the original pixel image (0, 0) is superimposed on the separated image of other pixels, the number is four times the number of pixels. The image of is formed.
[0050]
FIG. 7 is a diagram illustrating a pixel array formed by combining the first vertical one-dimensional low-pass filter and the second vertical one-dimensional low-pass filter.
[0051]
Here, two diffraction images are generated in the vertical direction by the first low-pass filter (vertical one-dimensional low-pass filter) made of a birefringent optical crystal such as quartz disposed between the display element and the eyepiece optical system. Furthermore, these two diffracted images are longitudinally converted by a second low-pass filter (similarly a vertical one-dimensional low-pass filter) composed of a stripe-shaped diffraction grating disposed between the eyepiece optical system and the observer's eyeball. By separating each into three, a total of six diffraction images are generated (see FIG. 22 described later).
[0052]
In FIG. 7, the order of the diffracted light (the first low-pass filter image (shift or through), the second low-pass filter order) is represented.
[0053]
That is, by passing through the first low-pass filter, the image at the position (T, 0) in the figure is also separated into the position (S, 0), and further passing through the second low-pass filter, The image at the position (T, 0) and the image at the position (S, 0) are represented by the position (T, 1), the position (S, 1), the position (T, -1), and (S , -1), and a total of six images are generated as described above.
[0054]
Next, FIG. 8 is a diagram showing a pixel arrangement of the color LCD before wobbling.
[0055]
In the example shown in FIG. 8, pixels are arranged in the order of G, R, and B from the left to the right in the same column, and the order is reverse to that shown in FIG. However, the principle described above is applied as it is to the diffraction pattern generated by the low-pass filter.
[0056]
Further, in FIG. 1 and the like, the shape of each pixel is illustrated as a substantially square in order to simplify the display. However, in practice, for example, as illustrated in FIG.
[0057]
Next, FIG. 9 is a diagram showing only the G extracted from the apparent pixel arrangement after wobbling of the LCD as shown in FIG.
[0058]
As shown in the figure, four-point wobbling for moving each vertex of the parallelogram is performed by changing the apparent position of the pixel by moving in the horizontal direction and moving in the oblique direction. . The principle of such wobbling by the wobbling element will be described later.
[0059]
Also, here, in order to make the wobbling result easier to understand and to avoid complicating the appearance, only the result for G is shown, but other R and B are also moved by wobbling in the same way. Of course.
[0060]
FIG. 10 is a diagram showing various examples of stripe-shaped diffraction gratings formed in a one-dimensional low-pass filter.
[0061]
First, the low-pass filter 10 shown in FIG. 10A is obtained by forming a diffraction grating 10a having a rectangular cross section on the upper surface of a plate-like member.
[0062]
Further, the low-pass filter 11 shown in FIG. 10B has a diffraction grating 11a having a triangular wave cross section formed on the upper surface of a plate-like member.
[0063]
Furthermore, in the low-pass filter 12 shown in FIG. 10C, a diffraction grating 12a having a sine wave cross section is formed on the upper surface of the plate-like member.
[0064]
In FIG. 10, diffraction gratings having various cross-sectional shapes are given as examples. However, when selecting the diffraction grating shape, attention must be paid to image flare due to higher-order diffracted light.
[0065]
That is, when calculating the diffraction efficiency, the second-order or higher-order diffracted light is often ignored because the light intensity is weak, but such higher-order diffracted light is actually present even if it is weak in intensity. May cause flare in the image. Even though the flare in the image is very weak, it may be annoying to the observer, and since it is related to the quality of the image, care should be taken to reduce unnecessary high-order diffracted light as much as possible. It is desirable to do.
[0066]
Other than the triangular wave, rectangular wave, and sine wave as shown in FIGS. 10A, 10B, and 10C, the lattice shape used for the low-pass filter is not shown, but a trapezoidal wave. A typical example is given.
[0067]
There is a difference in the intensity of the high-order diffracted light generated by the diffraction gratings of these shapes, and when comparing them, a sine wave as shown in FIG. The intensity of the higher-order diffracted light increases in the order of a triangular wave as shown in FIG. 10B, a trapezoidal wave (not shown), and a rectangular wave as shown in FIG. Therefore, when high-order diffracted light is considered, it is desirable to use a low-pass filter having a diffraction grating having a shape as shown in FIG.
[0068]
The two-dimensional low-pass filter is the same as the one-dimensional low-pass filter as described above, and a low-pass filter having a sinusoidal cross section is used to prevent flare due to higher-order diffracted light. desirable.
[0069]
FIG. 11 is a perspective view showing a first example of a diffraction grating of a two-dimensional low-pass filter.
[0070]
This two-dimensional low-pass filter is a combination of two one-dimensional low-pass filters 13 and 14 superimposed so that the directions of the stripes are orthogonal.
[0071]
That is, the stripe-shaped diffraction grating 13a formed in one low-pass filter 13 and the stripe-shaped diffraction grating 14a formed in the other low-pass filter 14 are disposed so as to be orthogonal to each other.
[0072]
On the other hand, FIG. 12 is a perspective view showing a second example of the diffraction grating of the two-dimensional low-pass filter.
[0073]
This two-dimensional low-pass filter 15 forms a striped diffraction grating 15a on one side of a plate-like member, and forms a striped diffraction grating 15b on the other side, and the direction of these diffraction gratings 15a and 15b Are orthogonal to each other.
[0074]
If the low-pass filter as shown in FIG. 12 is used, there is an advantage that a function equivalent to that in FIG. 11 can be realized only by a single member.
[0075]
FIG. 13 is a perspective view showing a third example and a fourth example of a diffraction grating of a two-dimensional low-pass filter.
[0076]
First, FIG. 13A shows a third example of a diffraction grating of a two-dimensional low-pass filter. The two-dimensional low-pass filter 16 is formed by cutting a stripe-shaped groove twice in a direction orthogonal to one side of a plate-like member. For example, the stripe-shaped mask can be formed twice, and the mask direction can be orthogonalized between the first masking and the second masking.
[0077]
As a result, the low-pass filter 16 is cut only once when it is not masked by masking only one of the convex portions 16c that are not cut by masking twice. Middle step portions 16a and 16b and a recess portion 16d which is cut twice by being not masked twice are formed.
[0078]
Unlike the one shown in FIG. 12, the low-pass filter as shown in FIG. 13 has an advantage that it is easy to form because only one side of the plate-like member needs to be processed.
[0079]
FIG. 13B shows a fourth example of the diffraction grating of the two-dimensional low-pass filter. The two-dimensional low-pass filter 17 is realized by cutting a mosaic groove on one surface of a plate-like member. For example, this is performed by applying a mosaic mask.
[0080]
Thus, the low-pass filter 17 is formed with a mosaic of convex portions 17a that are not cut by masking and concave portions 17b that are cut by non-masking.
[0081]
FIG. 14 is a plan view showing a fifth example of the diffraction grating of the two-dimensional low-pass filter.
[0082]
The low-pass filter 18 is configured as shown in FIG. 13 (A) or 13 (B), but the two diffraction directions are not orthogonal to each other, and are obliquely crossed at an appropriate angle θ. It is configured.
[0083]
That is, the low-pass filter 18 has a convex portion 18a having a parallelogram shape and a concave portion 18b having a similar parallelogram shape formed in a mosaic shape, and diffraction in the direction of arrow a and diffraction in the direction of arrow b. And come to do.
[0084]
At this time, the angle formed by these diffraction directions, that is, the angle θ formed by the arrow a and the arrow b is not a right angle, but an appropriate angle. Further, the pitch Pa of the diffraction grating in the arrow a direction, The pitch is different from the pitch Pb of the diffraction grating in the arrow b direction.
[0085]
Accordingly, for example, it is possible to suitably cope with the case of four-point wobbling in a parallelogram shape as shown in FIG.
[0086]
FIG. 15 is a diagram showing a detailed configuration of a diffraction grating having a rectangular cross section as shown in FIG.
[0087]
The low-pass filter 19 has, for example, a convex that forms a striped diffraction grating along the longitudinal direction on one surface side of a rectangular plate member having a long side and a short side as shown in FIG. A plurality of portions 19a are formed in parallel along the short direction, and a portion 19d indicated by a dotted line is an effective range.
[0088]
More specifically, the diffraction grating having the rectangular convex portion 19a as shown in FIG. 15B has a width 0.5P which is half the pitch P of the diffraction grating, as shown in FIG. 15C. The height, that is, the groove depth when viewed from the convex portion 19a is d.
[0089]
Of the optical performance of the low-pass filter 19 configured as such a diffractive optical element, the pixel position (or diffraction angle) shifted by diffraction is mainly determined by the pitch P of the diffraction grating, and the intensity of diffracted light ( That is, the diffraction efficiency is determined mainly by the groove depth d. Of course, these diffraction angles and diffraction efficiencies also depend on the wavelength of light to be diffracted.
[0090]
Next, FIG. 16 is a diagram showing the shape of a two-dimensional low-pass filter having a diagonal diffraction grating as shown in FIG. 14, for example.
[0091]
As shown in FIG. 16A, the low-pass filter 20 is configured such that one diffraction grating from the upper left to the lower right intersects with the long side of the plate member at an appropriate angle θ. The diffraction grating from the upper right to the lower left of the plate intersects with the short side of the plate member at an appropriate angle θ ′, and the portion 20d indicated by the dotted line is within the effective range.
[0092]
FIG. 16B shows the shape of these diffraction gratings viewed from the direction indicated by arrow 16B, and FIG. 16C shows the shape viewed from the direction indicated by arrow 16C. As shown in FIGS. 16B and 16C, a plurality of convex portions 20a are formed with the concave portions interposed therebetween. For example, as in the example shown in FIG. 15, half the pitch in each direction is formed. It is formed as a convex part having a width.
[0093]
Next, FIG. 17 is a diagram illustrating a first configuration example of the optical system of the image display apparatus.
[0094]
In FIG. 17, the diffraction angle is shown deformed in order to clarify how the light diffracted by the low-pass filter is separated.
[0095]
This image display device includes a backlight 3 that emits illumination light inside a housing 1, an LCD 4 that is a display device that displays an image as a set of regularly arranged pixels, and an LCD 4. A wobbling element 5 as pixel position displacement means for changing the apparent position of an image displayed in time series in synchronization with the LCD 4 and a light beam emitted from the wobbling element 5 are directed toward an eyeball of an observer. An eyepiece optical system 6 composed of, for example, a single lens to be imaged, and a high-frequency component are removed from an optical image emitted from the eyepiece optical system 6, and are fitted into a position of an eyepiece window (R window) of the housing 1. And a low-pass filter 7 as optical filter means.
[0096]
The low-pass filter 7 is, for example, a one-dimensional low-pass filter in which a stripe diffraction grating as described above is formed. As shown in the figure, an image of a pixel emitted from the eyepiece optical system 6 is converted into zero-order light, The light is separated into + 1st order light and −1st order light.
[0097]
FIG. 18 is a diagram illustrating a second configuration example of the optical system of the image display apparatus.
[0098]
In FIG. 18, similarly, the diffraction angle of the light diffracted by the low-pass filter is shown deformed.
[0099]
This image display apparatus is an example using a free-form surface prism as an eyepiece optical system.
[0100]
That is, a backlight 3 that emits illumination light in order from the top to the bottom inside the housing 1, an LCD 4 that displays an image as a set of regularly arranged pixels, and the LCD 4 chronologically. The wobbling element 5 that changes the apparent position of the image displayed on the LCD 4 in synchronization with the LCD 4, and the light beam emitted from the wobbling element 5 is internally reflected and formed toward the observer's eyeball a plurality of times. An eyepiece optical system 8 made of, for example, a free-form surface prism, and removes high-frequency components from the optical image emitted from the eyepiece optical system 8 at a position to be an eyepiece window (R window) of the housing 1 The low pass filter 7 to be fitted is inserted.
[0101]
The low-pass filter 7 separates the pixel image emitted from the eyepiece optical system 8 into 0th order light, + 1st order light, and −1st order light as described above.
[0102]
Next, FIG. 19 is a diagram illustrating a first basic configuration example of an optical system of an R window type image display apparatus.
[0103]
Here, the R window method is an anti-dust protection R disposed on the eyeball side of the observer with respect to the optical system of the conventional image display apparatus as shown in FIG. A low-pass filter is disposed at or near the window (eyepiece window). Alternatively, as a broader definition, any position may be included in the R window method as long as a low-pass filter is disposed on the eyeball side of the observer from the eyepiece optical system.
[0104]
This image display device includes a backlight 3 that emits illumination light, an LCD 4 that displays an image as a set of regularly arranged pixels, and an optical image emitted from the LCD 4 inside the housing 1. An eyepiece optical system 6 made of, for example, a single lens that forms an image toward a person's eyeball, and a low-pass filter 7 that removes an optical high-frequency component that is fitted into the eyepiece window of the housing 1. Configured.
[0105]
More specifically, the low-pass filter 7 also has a function as an eyepiece window for dust prevention and protection. The surface on which the diffraction grating is formed is disposed on the inner side toward the eyepiece optical system 6 to perform diffraction. The surface on which no lattice is formed is disposed outside.
[0106]
FIG. 20 is a diagram illustrating a second basic configuration example of the optical system of the R window type image display apparatus.
[0107]
The configuration of this image display apparatus is almost the same as that shown in FIG. 19 except that an eyepiece window 9 is separately provided and the low-pass filter 7 is provided between the eyepiece window 9 and the eyepiece optical system 6 as a separate element. It is arranged as.
[0108]
In this case, since the low-pass filter 7 does not have to be dustproof or protective, the surface on which the diffraction grating is formed may be on the eyepiece window 9 side or on the eyepiece optical system 6 side. Absent.
[0109]
FIG. 21 is a diagram showing a third basic configuration example of the optical system of the R window type image display apparatus.
[0110]
The configuration of this image display device is substantially the same as that shown in FIG. 19 except that a first diffraction grating is formed between the LCD 4 and the eyepiece optical system 6 and performs separation in the horizontal direction (horizontal direction). The first one-dimensional low-pass filter 7B is disposed, and a second one-dimensional diffraction grating is formed that separates the eyepiece window 6 between the eyepiece optical system 6 and the observer's eyeball in the vertical direction. A low-pass filter 7C is arranged.
[0111]
In this way, the combination of the first one-dimensional low-pass filter 7B and the second one-dimensional low-pass filter 7C realizes the two-dimensional low-pass filter as shown in FIG.
[0112]
FIG. 22 is a diagram illustrating a fourth basic configuration example of the optical system of the R window type image display apparatus.
[0113]
The configuration of this image display device is substantially the same as that shown in FIG. 21 above, but instead of the one-dimensional low-pass filter 7B made of a diffraction grating, the first longitudinal one-dimensional low-pass filter made of a birefringent material 7D is arranged.
[0114]
On the other hand, the second longitudinal one-dimensional low-pass filter 7E disposed between the eyepiece optical system 6 and the observer's eyeball is configured of a diffraction grating type as in the example of FIG.
[0115]
FIG. 23 is a diagram illustrating various examples of hard coat processing performed on the low-pass filter.
[0116]
As described above, when the low-pass filter is attached to the eyepiece window for dust prevention and protection, the hard coat process is performed so that the low-pass filter itself is not damaged.
[0117]
As this hard coat treatment, for example, as shown in FIG. 23A, the hard coat 31 is formed by spraying only the surface of the low-pass filter 7 where the diffraction grating is not formed, or FIG. As shown in FIG. 23B, only the surface of the low-pass filter 7 on which the diffraction grating is formed is formed by spraying a hard coat 31 having a refractive index different from that of the material constituting the filter, as shown in FIG. C) As shown in FIG. 23D, the entire low pass filter 7 is formed by immersing the entire low pass filter 7 in a hard coat material having a refractive index different from that of the material constituting the filter. A hard coat 31 is formed by immersing the entire low-pass filter in a hard-coat material so as not to fill in the recesses constituting the diffraction grating of the low-pass filter 7 Those for the refractive index of the hard coating material which is adapted may in what appropriate, and the like Some examples.
[0118]
FIG. 24 is a diagram illustrating a state in which images are passed through low-pass filters having different lattice pitches when an image is formed on the user's eyeball.
[0119]
When the low-pass filter is disposed closer to the eyeball of the observer than the eyepiece optical system, for example, at the position of the eyepiece window (R window), the pitch of the diffraction grating is increased as compared with the case of being disposed near the LCD. I need to take it. FIG. 24A schematically shows such an example.
[0120]
That is, FIG. 24A shows a state where the light beam passes through the low-pass filter 7l in which the pitch of the diffraction grating 35 is coarser than the pupil diameter. At this time, the diameter of the light beam reaching the exit pupil 32 is considered to be approximately the same as the pupil diameter because the distance between the low-pass filter 7l disposed at the eyepiece window position and the eyeball is relatively short. For example, the light beam 33 from the center of the screen reaches the eyeball as having been affected by, for example, three diffraction gratings, while the light beam 34 from the upper right of the screen is only having the effect of, for example, two diffraction gratings. The diffraction unevenness such as reaching the eyeball is likely to occur in the screen.
[0121]
Therefore, as described later, by adjusting to the second cutoff spatial frequency, the pitch of the diffraction grating 35 can be made fine even though it is disposed at the position of the eyepiece window (R window). FIG. 24B shows the state of the light beam reaching the exit pupil at that time.
[0122]
That is, FIG. 24B shows a state in which the light beam passes through the low-pass filter 7s in which the pitch of the diffraction grating 35 is finer than the pupil diameter. At this time, for example, the number of diffraction gratings that are effected when the light beam 33 from the center of the screen passes and the number of diffraction gratings that are effected when the light beam 34 from the upper right of the screen pass are respectively the above figures. The number is larger than that in the case of 24 (A). When these are compared, even if there is a difference of about one, the ratio is almost the same, so the difference in effect due to the diffraction grating does not occur so much. There is an advantage that diffraction unevenness hardly occurs in the screen.
[0123]
FIG. 25 is a diagram showing the relationship between the diffraction angle and the separation width when a telecentric optical system is taken as an example.
[0124]
Here, the relationship between the diffraction angle ε and the separation width δ of the diffraction image (primary light) on the object plane when a substantially telecentric optical system is employed as the optical system will be described.
[0125]
The display element 4 and the eyepiece optical system 6 are disposed via a distance f (here, f is the focal length of the eyepiece optical system 6), and the distance between the eyepiece optical system 6 and the eyeball of the observer is almost the same. f.
[0126]
Further, when the width of the effective range of the display element 4 is Y and the separation width in the display element 4 is δ, f · tan ε = δ, f · tan θy = Y / 2 (where the angles ε and θy are the optical axes) (The angle from O), and approximating the former with ε being small,
[Expression 1]
δ = fε
It becomes.
[0127]
Formula 1 is used as a relational expression for determining the grating pitch when designing a low-pass filter.
[0128]
Next, FIG. 26 is an MTF (Modulation Transfer Function: light transmission characteristic with respect to spatial frequency) graph (LPF example) when the grating pitch is coarse as shown in FIG.
[0129]
In the following, for the sake of simplicity, it is assumed that the display element is a monochrome type, and the description is limited to the pixel pitch in the vertical direction (referred to as the v direction). Assuming pixels of the same color, the same can be considered.
[0130]
Further, the following description can be applied in the same manner when wobbling is performed, and in this case, it may be considered as an MTF of a display element having a pixel array as a result of wobbling.
[0131]
First, FIG. 26A shows the MTF of the display element.
[0132]
The MLCD 1 that is the MTF of the display element is represented by a convolution of a diffraction term M1 determined from the shape and size of the pixel aperture and an interference term H1 determined from the pixel pitch.
[0133]
The diffraction term M1 is obtained by Fourier transformation of a function representing the pixel aperture, and one interference term H1 is obtained from Fourier transformation of a function representing the pixel pitch.
[0134]
For example, assuming that the vertical pixel pitch is Py = 0.185 and the vertical size of the pixel opening is Dy = 0.024, the vertical interference term H [v shown by a thin solid line in FIG. ], The vertical diffraction term M [v] indicated by the dotted line in the figure, and MLCD [v] which is the MTF of the display element indicated by the thick solid line in the figure, as shown in Equation 2 below, respectively: Become.
[0135]
[Expression 2]

[0136]
Here, C1 is a coefficient for normalization, and the symbol * represents convolution.
[0137]
The sharpness of the graph of the interference term H1 becomes a delta function sharper in the case of an image signal with many high frequency components, and becomes a periodic function without sharpness in an image signal in which the low frequency component is dominant. An appropriate function is used assuming a standard image signal. As the MTF of this display element, for example, the Nyquist frequency fN is about 27 [lines / mm] and the sampling noise is present at about 54 [lines / mm].
[0138]
Next, FIG. 26 (B) shows the MTF of the low-pass filter.
[0139]
If the low-pass filter is a diffraction grating, and if the intensity of the second-order or higher-order light is not significant, the MTF of the low-pass filter is a pixel (first-order light image (even -1st-order light) due to diffraction on the image plane. The same)) and the regular pixel (0th-order light image) and the diffraction efficiency.
[0140]
That is, MTFY [v], which is the MTF in the vertical direction of the low-pass filter, has the 0th-order light intensity α [0], the first-order light intensity (intensity ratio normalized by the 0th-order light) α [1], and the 0th-order light intensity. Assuming that the distance between the light image and the primary light image is y [1], the following Expression 3 is obtained.
[0141]
[Equation 3]

[0142]
Here, C2 is a coefficient for normalization.
[0143]
In Equation 3, for example, the 0th-order light intensity α [0] = 1, the first-order light intensity α [1] = 1, and the distance between the 0th-order light image and the first-order light image is y [1] = 0. In the case of 0062 [mm] or the like, the MTFY1 shown in the figure is located where the first cut-off spatial frequency f1C is located near the sampling noise frequency of about 54 [lines / mm] of the display element.
[0144]
In the case of an eyepiece window (R window) type low-pass filter, if the focal length f of the eyepiece optical system is 25 [mm], the distance δ = 0.0061 [0th order light image and first order light image] In order to realize [mm], when the above Equation 1 is used, ε = 2.4 × 10 ^ (− 4) [rad] (here, the symbol ^ represents a power).
[0145]
The pitch P of the diffraction grating having the diffraction angle ε is expressed by the following formula 4, which is a general formula of the first-order diffraction angle:
[Expression 4]

The lattice pitch P is calculated as 2 [mm]. However, as the wavelength λ, a wavelength λ = 0.5 [μm] having a high specific visibility is used.
[0146]
Next, FIG. 26C shows the MTF when the display element as shown in FIG. 26A is combined with the low-pass filter as shown in FIG. is there.
[0147]
The product of MLCD1 that is the MTF of the display element and MTFY1 that is the MTF of the low-pass filter is MTF1 that is the MTF of the display element when the low-pass filter is arranged.
[0148]
As shown in the figure, it can be read that the intensity of the sampling noise originally provided in the display element is reduced by the first cut-off spatial frequency f1C of the low-pass filter.
[0149]
Next, FIG. 27 shows an MTF graph (LPF example) when the lattice pitch is fine as shown in FIG.
FIG. 27A shows the MTF of the display element. The MLCD0, the diffraction term M0, and the interference term H0, which are the MTFs of the display element, are the same as the MLCD1, diffraction term M1, and the like shown in FIG. The same applies to the interference term H1.
[0150]
FIG. 27B shows the MTF of the low-pass filter.
[0151]
MTFY [v], which is the MTF in the vertical direction of the low-pass filter, is as shown in Equation 3 above.
[0152]
Here, for example, the 0th-order light intensity α [0] = 1, the first-order light intensity α [1] = 1, the distance y [1] between the 0th-order light image and the 1st-order light image = 0.0123 [mm] ], The second cutoff spatial frequency f2C is located in the vicinity of the noise frequency of about 54 [lines / mm] for sampling of the display element.
[0153]
This differs from the coarse diffraction grating shown in FIG. 26 in the distance between the zero-order light image and the first-order light image, and the diffraction efficiency is the same. By varying the distance between the 0th-order light image and the 1st-order light image, the diffraction angle, that is, the grating pitch of the low-pass filter is varied to devise a finer diffraction grating.
[0154]
The lattice pitch P of the low-pass filter in this example is obtained as follows.
[0155]
That is, when the focal length of the eyepiece optical system is 25 [mm] as in the above-described example, in order to realize the distance δ = 0.123 [mm] between the 0th-order light image and the 1st-order light image. From the above Equation 1, ε = 4.9 × 10 ^ (− 4) [rad] (here, the symbol ^ represents a power).
[0156]
The pitch P of the diffraction grating having the diffraction angle ε is calculated as the grating pitch P = 1.0 [mm] by using the above-described formula 4, which is a general formula of the first-order diffraction angle. Here, as the wavelength λ, the wavelength λ = 0.5 [μm] having high specific visibility is used as described above.
[0157]
As described in FIG. 24 and the like, in the case of the optical system according to the present embodiment in which the low-pass filter is arranged in the eyepiece window or in the vicinity thereof, the observer's pupil diameter is generally about 3 to 5 [mm]. Therefore, when the grating pitch is smaller, there is no diffraction unevenness in the screen, and a good image can be displayed.
[0158]
Therefore, a low-pass filter having a fine diffraction grating as shown in FIGS. 24B and 27 is preferably used rather than a low-pass filter having a coarse diffraction grating as shown in FIGS. 24A and 26. be able to.
[0159]
Next, FIG. 27C shows the MTF when the display element as shown in FIG. 27A is combined with the low-pass filter as shown in FIG. 27B. is there.
[0160]
The product of MLCD0, which is the MTF of the display element, and MTFY0, which is the MTF of the low-pass filter, is MTF0, which is the MTF of the display element when the low-pass filter is arranged.
[0161]
As shown in the figure, it can be read that the intensity of the sampling noise originally provided in the display element is reduced by the second cutoff spatial frequency f2C of the low-pass filter.
[0162]
Note that the MTF of the display element when wobbling is performed can be regarded as the MTF of the display element having the pixel arrangement as a result of wobbling, as described above.
[0163]
Here, the relationship between the Nyquist frequency fN that the display element has and the cutoff spatial frequency fC that the low-pass filter has will be described.
[0164]
The sampling frequency is obtained from the reciprocal of the pixel pitch, and the lowest sampling noise frequency is approximately this value. The Nyquist frequency fN is about a half of the sampling frequency.
[0165]
Further, since the cutoff spatial frequency fC of the low-pass filter is a frequency at which the MTF is 0, it can be obtained from an equation in which the left side of Equation 3 is 0,
[Equation 5]

It becomes.
[0166]
Here, the second cut-off spatial frequency f2C is obtained as a frequency where n = 1.
[0167]
In this example, the Nyquist frequency fN = 27, the second cutoff spatial frequency f2C = 54, and f2C / fN = 2.
[0168]
On the other hand, in the case of a low-pass filter having a rough diffraction grating as shown in FIG. 24A or FIG. 26, f2C / fN≈4.
[0169]
Here, the description is limited to one dimension (vertical direction), but the idea is the same in two dimensions. By configuring the low-pass filter so as to be about 1.5 to 2.5 sandwiched, it is possible to obtain a good image without diffraction unevenness.
[0170]
Next, the configuration and operation of the wobbling element (pixel skipping optical element) will be described. First, FIG. 28 is a diagram for explaining the principle of skipping pixels in an oblique direction in wobbling.
[0171]
Here, an example in which two birefringent plates are used will be described. However, the present invention is not limited to this. For example, an optical rotation plate or the like may be used.
[0172]
In FIG. 28, the first birefringent plate 5d shifts the light emission position in the horizontal direction, that is, moves it in the horizontal direction, while the second birefringent plate 5e moves the light emission position in the vertical direction. It is a thing to move in the vertical direction.
[0173]
By combining these two birefringent plates 5d and 5e so as to overlap each other in the optical axis direction, it is possible to shift the light emission position in the oblique direction, that is, in the oblique direction.
[0174]
That is, as shown in FIG. 28A, when light polarized in the horizontal direction is incident on the first birefringent plate 5d from a second TN liquid crystal cell 5c (see FIG. 29) described later of the pixel skipping optical element. Then, the pixel position is skipped in the horizontal direction and emitted. The subsequent second birefringent plate 5e does not act on the light whose polarization direction is in the lateral direction, and therefore passes as it is and is emitted with the pixel position flying in the lateral direction (see black circles). ).
[0175]
Next, as shown in FIG. 28B, assuming that light polarized in the vertical direction from the second TN liquid crystal cell 5c is incident on the first birefringent plate 5d, the polarization direction is changed to light in the vertical direction. On the other hand, since nothing acts, it passes as it is and enters the second birefringent plate 5e. The second birefringent plate 5e emits light with the pixel position shifted in the vertical direction (see black circles).
[0176]
Therefore, when the emission state from the second birefringent plate 5e in FIG. 28B is viewed from the emission state from the second birefringent plate 5e in FIG. 28A, the pixel position indicated by the black circle is: This means that the position is shifted from the position shifted in the horizontal direction to the position shifted in the vertical direction, and this eventually realizes a state shifted in the oblique direction. As described above, the light emitting position, that is, the pixel position is inclined by interposing the two combined birefringent plates with respect to the light whose polarization direction is emitted from the second TN liquid crystal cell 5c in the horizontal direction and the vertical direction. It is possible to fly in the direction.
[0177]
Next, an example of a pixel skipping optical element (pixel position displacement means) configured using such a principle and shifting the pixel position to four positions will be described with reference to FIG. FIG. 29 is a perspective view showing the main configuration of the pixel skipping optical element.
[0178]
The pixel skip optical element (wobbling element 5) includes a horizontal pixel skip element including a first TN liquid crystal cell 5a and a first birefringent plate 5b, a second TN liquid crystal cell 5c, and a second TN liquid crystal cell 5c. The second birefringent plate 5d and the third birefringent plate 5e are provided with an oblique pixel skip element.
[0179]
Here, the second birefringent plate 5d has a thickness corresponding to Px / 4 at the pixel skip position as shown in FIG. 30, and the third birefringent plate 5e is shown in FIG. It has a thickness corresponding to Py / 2. The first birefringent plate 5b has a thickness corresponding to Px / 2. FIG. 30 is a diagram showing the positional relationship of pixels skipped by the pixel skip element.
[0180]
Next, the operation of the pixel skipping optical element configured as described above will be described.
[0181]
In this pixel skipping optical element, a liquid crystal display element 4 that emits light in the horizontal (horizontal) polarization direction as indicated by an arrow is used.
[0182]
The first TN liquid crystal cell 5a is configured to change the polarization direction of the emitted light by 90 ° by turning on and off the applied voltage.
[0183]
The first birefringent plate 5b has its crystal axis inclined by 45 ° in the horizontal direction as shown in the figure, and the polarization direction when the applied voltage of the first TN liquid crystal cell 5a is turned on is the horizontal direction. This light is emitted with a lateral shift as indicated by arrows. On the other hand, the light whose polarization direction is vertical when the applied voltage of the first TN liquid crystal cell 5a is turned off passes as shown by the arrow without being affected. Therefore, by turning on / off the voltage applied to the pixel shifting element having the first TN liquid crystal cell 5a and the first birefringent plate 5b, the light emitted from the liquid crystal display element 4 remains as it is. The light is emitted after being passed or shifted in the horizontal direction (horizontal direction).
[0184]
Next, the light incident on the second TN liquid crystal cell 5c is changed by 90 ° in the polarization direction of the emitted light by turning on / off the applied voltage in the same manner as the first TN liquid crystal cell 5a described above. Let That is, when the applied voltage is on, the polarization direction does not change, and as shown by the ON-ON arrow and OFF-ON arrow, the polarization direction passes without change. On the other hand, when the applied voltage is OFF, the polarization direction is rotated by 90 °, and the polarization direction is rotated by 90 ° and emitted as indicated by the ON-OFF arrow and the OFF-OFF arrow.
[0185]
Subsequently, the light emitted from the second TN liquid crystal cell 5c includes a second birefringent plate 5d whose crystal axis is tilted in the horizontal direction, and a third birefringent plate 5e whose crystal axis is tilted in the vertical direction. By passing the two birefringent plates, as described in FIG. 28, the third birefringent plate 5e emits light whose polarization direction is transverse from the ON-ON arrow and As indicated by the OFF-OFF arrow, the light is emitted with a slight shift in the horizontal direction. On the other hand, light whose polarization direction is vertical is emitted with a slight shift in the vertical direction as indicated by the ON-OFF arrow and the OFF-ON arrow. In this way, light whose polarization direction is vertical is emitted from a position shifted in an oblique direction with respect to light whose polarization direction is horizontal.
[0186]
As described above, by turning on / off the applied voltage to the first and second TN liquid crystal cells 5a and 5c in the combination order as shown in Table 1, the emission position (pixel position) from the liquid crystal display element 4 is obtained. ) Can be controlled to pixel positions as indicated by numbers 1 to 4 in FIG.
[0187]
[Table 1]

[0188]
Next, FIG. 31 is a diagram showing the distribution ratio of the light amount of the pixel when wobbling is performed along the time axis.
[0189]
When the apparent position of a pixel is shifted from one position to the next by performing wobbling as described above, the pixel position does not change instantaneously, and the brightness of the original pixel gradually decreases. At the same time, the operation of gradually increasing the luminance of the next pixel is performed.
[0190]
FIG. 31 shows how the amount of light of the pixel changes at this time. As illustrated, for example, when the amount of light at the fourth pixel position decreases, the operation of increasing the amount of light at the next first pixel position is repeatedly performed.
[0191]
When observing an image displayed by such a wobbling operation, for example, an image at a time point indicated by a symbol A and an image at a time point indicated by a symbol B after about 16.67 [ms] have elapsed since this time point are repeated. May be observed in the human eye.
[0192]
FIG. 32 is a diagram illustrating a state of an image that can be observed when wobbling is performed.
[0193]
At the timing indicated by the symbol A, the pixel at the position 4 and the pixel at the position 1 have appropriate luminance, and the pixel at the position 2 and the pixel at the position 3 are in a state where the luminance is low and is not observed. This is shown in FIG.
[0194]
On the other hand, at the timing indicated by the symbol B, the pixel at the position 2 and the pixel at the position 3 have appropriate luminance, and the pixels at the position 1 and the pixel at the position 4 are in a state where the luminance is low and is not observed. An image as shown in FIG.
[0195]
When such an image as shown in FIG. 32 (A) and an image as shown in FIG. 32 (B) are repeatedly observed, an oblique stripe pattern from the upper left to the lower right is observed in the human eye from the lower left. It may appear to move in the upper right direction or from the upper right to the lower left direction.
[0196]
Similarly, repetition of the image at the time point indicated by the symbol a in FIG. 31 and the image at the time point indicated by the symbol b may be observed by human eyes. In this case, the horizontal stripe pattern is It will appear to move from down to up or down to up.
[0197]
Although the present applicant has found that there is a phenomenon in which the striped pattern moves and is observed when wobbling is performed in this way, it is difficult to observe such a striped pattern by using the low-pass filter as described above. Experiments have confirmed that there are advantages.
[0198]
Conventionally, it is a low-pass filter arranged in the vicinity of the display element. However, when a wobbling element is used, the polarization direction may be disturbed by the low-pass filter made of molded resin or the like. Cannot be applied. If a configuration in which a low-pass filter is not provided is unavoidable, a phenomenon in which a stripe pattern is observed by wobbling as described above occurs. Therefore, as shown in the present embodiment, by arranging a low-pass filter at, for example, an eyepiece window portion that is rearward on the optical path than the eyepiece optical system, it is possible to effectively suppress the observation of the stripe pattern as described above. It can be done.
[0199]
According to such an embodiment, since there is a distance difference between the virtual image positions of the display element and the low-pass filter, the eyes of the observer are rarely in focus at the same time, and dust, foreign matter, etc. are attached. However, there is an advantage that it is difficult to observe. Therefore, it is possible to relax the standard at the time of manufacturing, and it is possible to reduce the manufacturing cost.
[0200]
In addition, by arranging the display element and the low-pass filter apart from each other, there is an advantage that moire or the like is hardly generated.
[0201]
Further, by using the low-pass filter as an eyepiece window for dust-proofing and protecting the image display device, it is possible to share the components, so that the number of components can be reduced and the cost can be reduced.
[0202]
In the wobbling optical system, the wobbling element is arranged between the display element side surface of the eyepiece optical system and the display element. However, the working distance of the eyepiece optical system (the display element side surface of the eyepiece optical system and the display element) Is generally limited in relation to the magnification, there is also a limitation in the space for arranging the low-pass filter. On the other hand, as described above, by disposing behind the eyepiece optical system on the optical path, there are less restrictions on the disposition position and disposition space of the low-pass filter, and design and the like are facilitated.
[0203]
In the eyepiece window method, since the low-pass filter is arranged behind the wobbling element in the optical path, the polarization passing through the wobbling element is not disturbed, and the image quality can be maintained while maintaining the accurate wobbling.
[0204]
Furthermore, by adopting a configuration in which the sampling noise is cut off at the second cut-off spatial frequency, it becomes possible to make the pitch of the diffraction grating fine, and when the sampling noise is cut off simply by the first cut-off spatial frequency. Compared to this, there is an advantage that uneven diffraction is less likely to occur.
[0205]
Thus, according to the image display apparatus of the present embodiment, it is possible to observe an easy-to-see image with less roughness and flicker.
[0206]
It should be noted that the present invention is not limited to the above-described embodiments, and various modifications and applications can be made without departing from the spirit of the invention.
[0207]
【The invention's effect】
As described above, according to the image display apparatus of the present invention according to claim 1, the optical filter means is disposed between the eyepiece optical system and the eyeball of the observer, and the ratio of the second cut-off spatial frequency to the Nyquist frequency. Since the pixel pitch is between 1.5 and 2.5, it is possible to reduce the pixel pitch, reduce the unevenness of diffraction, and observe an easy-to-view image with little roughness and flicker. it can.
[0208]
Further, according to the image display device of the present invention according to claim 2, the same effect as that of the invention of claim 1 can be obtained by the optical filter means having the diffraction grating.
[0209]
Further, according to the image display device of the present invention of claim 3, the same effect as that of the invention of claim 2 is obtained, and the diffraction grating is formed on the surface of the optical filter means facing the eyepiece optical system. It becomes possible to share the eyepiece window, and the number of members can be reduced to reduce the cost.
[0210]
According to the image display device of the present invention according to claim 4, the first optical filter means is disposed between the display element and the eyepiece optical system, and the second optical filter is disposed between the eyepiece optical system and the eyeball of the observer. Since the means is arranged, it is possible to observe an easy-to-see image with less roughness and flicker.
[0211]
According to the image display device of the present invention of claim 5, the same effect as that of the invention of claim 4 is achieved, and the ratio of the second cutoff spatial frequency of the second optical filter means to the Nyquist frequency is 1. Since it is set between .5 and 2.5, it is possible to reduce the pixel pitch and reduce diffraction unevenness.
[0212]
According to the image display device of the present invention according to claim 6, in the configuration including the pixel position displacement means for repeatedly displacing the pixel position of the display element at four positions, the same effect as the invention according to claim 4 is provided. Can be played.
[0213]
According to the image display device of the present invention according to claim 7, in the configuration including the optical low-pass filter formed with the diffraction grating or the optical low-pass filter made of a birefringent plate, the same effect as the invention according to claim 4 is obtained. Can play.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a pixel array of an LCD according to an embodiment of the present invention.
FIG. 2 is a diagram showing an arrangement of only G pixels in the delta arrangement LCD as shown in FIG. 1;
FIG. 3 is a diagram showing a first example of a pixel array by a vertical one-dimensional low-pass filter in the embodiment.
FIG. 4 is a diagram showing a second example of a pixel array using a vertical one-dimensional low-pass filter in the embodiment.
FIG. 5 is a diagram showing a pixel arrangement by a one-dimensional low-pass filter in an oblique direction in the embodiment.
FIG. 6 is a diagram showing a pixel arrangement by a vertical and horizontal two-dimensional low-pass filter in the embodiment.
FIG. 7 is a diagram showing a pixel arrangement formed by combining the first vertical one-dimensional low-pass filter and the second vertical one-dimensional low-pass filter in the embodiment.
FIG. 8 is a diagram showing a pixel arrangement of a color LCD before wobbling in the embodiment.
9 is a diagram showing only G extracted from the apparent pixel arrangement after wobbling of the LCD as shown in FIG.
FIGS. 10A and 10B are diagrams showing various examples of a stripe diffraction grating formed in a one-dimensional low-pass filter in the embodiment.
FIG. 11 is a perspective view showing a first example of a diffraction grating of the two-dimensional low-pass filter in the embodiment.
12 is a perspective view showing a second example of the diffraction grating of the two-dimensional low-pass filter in the embodiment. FIG.
FIG. 13 is a perspective view showing a third example and a fourth example of the diffraction grating of the two-dimensional low-pass filter in the embodiment.
FIG. 14 is a plan view showing a fifth example of the diffraction grating of the two-dimensional low-pass filter in the embodiment.
FIG. 15 is a diagram showing a detailed configuration of a diffraction grating having a rectangular cross section as shown in FIG.
16 is a view showing the shape of a two-dimensional low-pass filter having a diffraction grating in the oblique direction as shown in FIG.
FIG. 17 is a diagram showing a first configuration example of an optical system of the image display device in the embodiment.
FIG. 18 is a diagram showing a second configuration example of the optical system of the image display device in the embodiment.
FIG. 19 is a diagram showing a first basic configuration example of an optical system of an R window type image display device in the embodiment.
FIG. 20 is a diagram illustrating a second basic configuration example of an optical system of the R window type image display apparatus according to the embodiment.
FIG. 21 is a diagram showing a third basic configuration example of the optical system of the R window type image display device in the embodiment.
FIG. 22 is a diagram showing a fourth basic configuration example of the optical system of the R window type image display device in the embodiment.
FIG. 23 is a diagram showing various examples of hard coat processing performed on the low-pass filter in the embodiment.
FIG. 24 is a diagram illustrating a state in which an image is passed through a low-pass filter having a different lattice pitch when an image is formed on the user's eyeball in the embodiment.
FIG. 25 is a diagram showing a relationship between a diffraction angle and a separation width when a telecentric optical system is taken as an example in the embodiment.
FIG. 26 is an MTF graph when the lattice pitch is coarse as shown in FIG.
FIG. 27 is an MTF graph when the lattice pitch is fine as shown in FIG.
FIG. 28 is a view for explaining the principle of skipping pixels in an oblique direction in the wobbling of the embodiment.
FIG. 29 is a perspective view showing the main configuration of a pixel skipping optical element in the embodiment.
30 is a diagram showing a positional relationship of pixels skipped by the pixel skip element of the embodiment. FIG.
FIG. 31 is a diagram showing a distribution ratio of the light amount of the pixel along the time axis when wobbling is performed in the embodiment.
FIG. 32 is a diagram showing a state of an image that can be observed when wobbling is performed in the embodiment.
FIG. 33 is a diagram showing a configuration example of an optical system of a conventional image display apparatus.
[Explanation of symbols]
1 ... Case
3 ... Backlight
4 ... LCD (display device, display element)
5 ... Wobbling element (pixel position displacement means)
6, 8 ... Eyepiece optical system
7,7B, 7C, 7D, 7E, 7l, 7s, 10,11,12,13,14,15,16,17,18,19,20 ... Optical low-pass filter (optical filter means)
31 ... Hard coat

Claims (7)

A display device in which pixels are regularly arranged;
An eyepiece optical system for enlarging an image displayed on the display device and forming an image on an observer's eyeball;
An optical filter means disposed between the eyepiece optical system and the eyeball of the observer, for separating light from the eyepiece optical system into a plurality of lights;
Comprising
The optical filter means has a first cutoff spatial frequency and a second cutoff spatial frequency higher than the first cutoff spatial frequency, and the second cutoff spatial frequency f2C For the Nyquist frequency fN determined by the pixel pitch of
1.5 <f2C / fN <2.5
An image display device characterized by satisfying the following relationship. The image display device according to claim 1, wherein the optical filter means includes a diffraction grating. 3. The image display device according to claim 2, wherein the diffraction grating of the optical filter means is formed on a surface of the optical filter means facing the eyepiece optical system. A display element in which pixels are regularly arranged;
An eyepiece optical system for enlarging an image displayed on the display element and forming an image on an eyeball of an observer;
A first optical filter means disposed between the display element and the eyepiece optical system for separating or switching light from the display element into a plurality of lights;
A second optical filter means disposed between the eyepiece optical system and the eyeball of the observer for separating light from the eyepiece optical system into a plurality of lights;
An image display device comprising: The second optical filter means has a first cutoff spatial frequency and a second cutoff spatial frequency that is higher than the first cutoff spatial frequency, and the second cutoff spatial frequency f2C is: For the Nyquist frequency fN determined by the pitch of the pixels generated by the display element and the first optical filter means,
1.5 <f2C / fN <2.5
The image display device according to claim 4, wherein the relationship is satisfied. 5. The image display device according to claim 4, wherein the first optical filter means is pixel position displacement means for repeatedly displacing the pixel position of the display element at four positions. 5. The image display device according to claim 4, wherein the first optical filter means is an optical low-pass filter formed with a diffraction grating or an optical low-pass filter made of a birefringent plate.

Images