JP2004361498A - Image display device, image display method, and image display program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform color matching of image data by taking the display characteristics of an image display element of an image display device of a personal digital assistant, such as a cellular phone, into consideration and simultaneously to reduce the amount of the data to be transferred to a display device. <P>SOLUTION: The image display device can be mounted on, for example, the cellular phone or the portable digital assistant and the like and processes and displays the image data etc., transferred from the outside. A CPU 216 first performs color subtraction processing to reduce the amount of the data of the acquired image data. Next, the CPU performs RGB to YUV conversion processing accompanied by hue matching taking the display characteristics of a display panel into consideration. Simultaneously at this time, sampling can also be performed by a YUV 4:2:2 format. Thereby, the image which is matched in colors with the display characteristics of the display panel and is free of the sense of incongruity can be displayed. Also, the amount of the data to be transferred to the display device 212 is reduced and therefore the number of clocks can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

式１によってＹＵＶ変換された画像データが、ＬＣＤなどの表示パネル２２７に表示される場合、図２（ａ）に示すＣＩＥ表現の色空間において、実線で表したＴ２を外形線とする三角形の領域内の色が表示される。一方、原画像は破線Ｔ１を外形線とする三角形の領域内の色を有している。これより、図２（ａ）の矢印のようにＴ１とＴ２で表した三角形の頂点が一致しておらず、特に青色を表わす領域（図の左下に位置する領域）において、Ｔ２を外形線とする三角形がＴ１を外形線とする三角形よりも大幅にはみ出していることが見て取れる。これは、先に述べたように、携帯端末装置のＬＣＤの特性が青色に偏ったものになっていることに起因する。
【００５１】
そこで本実施形態においては、表示パネル２２７に表示される画像の色が原画像の色に近づくように、ＣＰＵ２１６が画像データに対して色合わせの画像処理を行う。具体的には、式１を改良した式２を用いてＲＧＢ→ＹＵＶ変換処理を行う。
【００５２】
【数２】

式２は、青の色差を表すＵにおいては、赤色の階調を表すＲと緑色の階調を表すＧに対して、上式とは異なる定数αが付け加えられた係数が掛けられる。また、赤の色差を表すＶにおいては、緑色の階調を表すＧと青色の階調を表すＢに対して、定数βが付け加えられた係数が掛けられる。
【００５３】
式２を用いて、ＲＧＢ→ＹＵＶ変換を行った結果が、図２（ｂ）において太い実線で表したＴ２ａを外形線とする三角形である。ここで、白色を表す点Ｃ１（以下、白色点と呼ぶ。）と三角形Ｔ１の頂点を結ぶ線分を引いたとき、これらの線分上において白色点Ｃ１からの距離は、原画像の赤、青、緑の３原色の階調を表している。式２において適切なαとβを設定してＲＧＢ→ＹＵＶ変換処理を行うと、表示パネル２２７の出力特性であるＴ２を外形線とする三角形が白色点Ｃ１を中心に回転して、Ｔ２ａを外形線とする三角形のように頂点が上述した階調を表す線分上にほぼ重なるように移動する。また、この変換により、三角形Ｔ２ａは三角形Ｔ１内に入るようになる。なお、三角形Ｔ２ａの頂点は、表示パネル２２７の物理的特性を表しているので、変換しても元の三角形Ｔ２の外形線上に載る。
【００５４】
以上のように、本実施形態に係るＲＧＢ→ＹＵＶ変換処理においては、完全に色合わせをするような色変換を行ってないので、ＣＰＵ２１６に負荷を与えずに処理を行うことができる。また、完全な色合わせを行うと、入力された画像データの色域が広い場合には、色合わせ処理後の階調値がクリップしてしまい、階調がつぶれてしまうことがある。この点、本実施形態においては、色相を変換しているだけなので、色としては明度（明るさ）や彩度（濃さ）は一致していないが色相を正しく合わせることができ、かつ、上記のように変換後の階調値がクリップして階調がつぶれてしまうことがない。
【００５５】
さらに本実施形態に係るＹＵＶ変換は、ＳＴＮ（Ｓｕｐｅｒ Ｔｗｉｓｔｅｄ Ｎｅｍａｔｉｃ）やＴＦＤ（Ｔｈｉｎ Ｆｉｌｍ Ｄｉｏｄｅ）やＬＴＰＳ（Ｌｏｗ Ｔｅｍｐｅｒｔｕｒｅ Ｐｏｌｙ−Ｓｉ）などの様々な特性の液晶表示装置の表示する色を合わせる上で効果的である。例えば、ＳＴＮでは、液晶特性上の原理的な制約として、コントラストを上げることが困難であり、色域を広げることができない。このような場合、一番の違和感は、色がずれることであり（例えば、赤色が黄色っぽく見えてしまうこと）、色の明度や彩度は、あまり違和感を覚えない。むしろ、明度や彩度を無理やり合わせると、画像の階調特性を損なってしまう。このため、コスト低減や消費電力低減のためにＳＴＮを選択する場合にも、コントラストが高く、色域の広いＴＦＤやＬＴＰＳなどのアクティブ素子を搭載するＬＣＤパネルとの色合わせが容易にできる。
【００５６】
また、ＬＥＤのバックライトは製造上のばらつきが大きいため、このばらつきを吸収するためにも本発明に係る色変換は有効である。
【００５７】
本発明においては、上記のＲＧＢ→ＹＵＶ変換が行われる際、同時に図３に示すようなＹＵＶ４：２：２フォーマットでサンプリングの処理を行うことができる。この方法は、水平方向４画素を基準として考え、輝度は画素ごとにサンプリングし、色差は２画素ごとに平均してサンプリングする方法である。図３の例は、１画素２４ビットのＲＧＢ形式の画像データを減色処理して１画素１８ビットとした後、上記のＹＵＶ４：２：２フォーマットでサンプリング処理が行われたものを示している。その結果、１画素１２ビットのＹＵＶ形式の画像データが得られる。つまり、ＲＧＢ→ＹＵＶ変換後の画像データは元の画像データの１／２のデータ量となる。
【００５８】
さらに本発明では、上記とは別の方法として、図４に示すようなＹＵＶ４：２：０フォーマットでもサンプリングの処理を行うことができる。この方法は、ＹＵＶ４：２：２サンプリングを行った後に、さらに垂直２画素の色差情報を平均化する方法である。例えば、減色処理して１画素１２ビットになった画像データは、ＹＵＶ４：２：０フォーマットによりサンプリングの処理を行うと１画素６ビットになる。よってこの場合は、ＲＧＢ→ＹＵＶ変換後の画像データは元の画像データの１／４のデータ量になる。このサンプリング方法は、前記の方法よりもデータ量をより多く削減するため、表示装置２１２への転送速度がさらに速くなるという長所がある。但し、その分画質の劣化は大きくなる。
【００５９】
なお、表示する画像の画質を優先する場合（静止画などを表示する場合）は、上記のＹＵＶ４：２：２のサンプリング処理もＹＵＶ４：２：０のサンプリング処理も用いないで処理することもできる。この場合は、ＹＵＶ４：４：４フォーマットでサンプリングの処理を行うことになる。この方法では、画像データのデータ量が削減されないので、高画質な画像を表示することができる。
【００６０】
［表示装置での画像処理］
次に、表示装置２１２で行われるＹＵＶ→ＲＧＢ変換処理について説明する。
【００６１】
表示装置２１２は、ＣＰＵ２１６でＲＧＢ→ＹＵＶ変換された画像データを受け取り、ＹＵＶ→ＲＧＢ変換処理する。ここでは、上述のＲＧＢ→ＹＵＶ変換処理とは逆の変換を行い、式３により変換がなされる。
【００６２】
【数３】

また本発明においては、例えばＹＵＶ４：２：２フォーマットでサンプリングされて１画素１２ビットになった画像データを、図５に示す方法で１画素１８ビットのＲＧＢ形式の画像データに復元することができる。この方法では、図５の上段のＹＵＶ４：２：２フォーマットの画像データを、図５の下段に示すようにしてＹＵＶ４：４：４フォーマットとなるように色差成分を補完する処理を行う。
【００６３】
［表示制御処理］
次に、上述の画像処理を含んだ本発明に係る表示制御処理の実施例について説明する。
【００６４】
図６に、本発明に係る表示制御処理のフローチャートを示す。なお、以下に説明する表示制御処理は、図１に示す携帯端末装置２１０のＣＰＵ２１６と表示装置２１２が、上述したような画像処理に関するプログラムを実行することにより行われる。
【００６５】
本発明に係る画像表示装置においては、静止画を表示する静止画モードと、動画を表示する動画モードのモード選択が可能となっている。前述したような減色処理と、ＹＵＶ４：２：２フォーマットやＹＵＶ４：２：０フォーマットに従うＲＧＢ→ＹＵＶ変換を行うと、表示画像の画質はどうしても粗くなる。動画を表示する場合には、この画質で問題はないのだが、利用者が注視して観察する静止画像の場合は、画質の粗さが際立ってしまう。そこで、本発明では、静止画モードと動画モードを利用者が選択できるようにし、その選択結果に応じて前記のデータ量を削減する画像処理を行うか行わないかが決定されるようにした。
【００６６】
具体的には、静止画モードの場合は、画像データに対して減色処理を行わず、画像データを単に上位ビット及び下位ビットに分割（ビットスライス）し、２フレーム周期に渡って順に表示装置２１２へ転送する。即ち、元の画像データがＲＧＢ形式で１画素２４ビット（ＲＧＢ各色８ビット）であるので、各色の上位４ビット、合計１２ビットを最初のフレーム画像転送周期で表示装置２１２へ転送し、残りの各色下位４ビット、合計１２ビットを次のフレーム画像転送周期で表示装置２１２へ転送する。これにより、静止画モードの場合は、２フレーム画像転送周期により１画素２４ビットの高画質な静止画データを転送し、表示装置２１２に表示することができる。
【００６７】
なお、このビットスライス処理は、図１に示すプログラムＲＯＭ２２０内に予め用意されたビットスライス処理プログラムをＣＰＵ２１６が実行することにより行われる。
【００６８】
さらに本発明では、前記の動画モードにおいて、高速なフレームレートを持つ動画を表示するための高速動画モードの選択が可能になっている。テレビ等の情報媒体から受信した動画像データを表示装置２１２に転送する場合は、インターフェイスであるＣＰＵ２１６と表示装置２１２との間のデータレートの高速化が要求される。そのため、本発明では、動画モードにおいて高速動画モードと標準動画モードを利用者が選択できるようにし、その選択結果に応じて適切に画像データ量を削減する画像処理方法が選択されるようにした。具体的には、標準動画モードの場合はＣＰＵ２１６内でのＲＧＢ→ＹＵＶ変換はＹＵＶ４：２：２フォーマットに従うものとする。一方、高速動画モードの場合はＣＰＵ２１６内でのＲＧＢ→ＹＵＶ変換をＹＵＶ４：２：０フォーマットに従うものとし、データ量をさらに削減して表示装置２１２への動画像データの高速転送を可能とする。
【００６９】
なお、携帯端末装置２１０が静止画モード、標準動画モード及び高速動画モードのいずれにあるかの判定は、前述のように利用者の入力部２１８への入力に基づいてＣＰＵ２１６が行うことができる。ＣＰＵ２１６は、モード判定結果に基づいてＣＰＵ２１６内での処理を行うとともに、モード判定結果Ｓ２を表示装置２１２へ供給する。
【００７０】
次に、図６のフローチャートを参照して、本実施形態による表示制御処理について説明する。
【００７１】
まず、ステップＳ１１では、携帯端末装置２１０が外部のサーバその他から、表示の対象となる画像データを受信する。なお、この画像データはＲＧＢ形式の画像データであるとする。
【００７２】
次に、ＣＰＵ２１６は、利用者が静止画モードを選択しているか否かを判定する（ステップＳ１２）。動画モードと判定された場合（ステップＳ１２；Ｎｏ）は、ステップＳ１３に進み、利用者が高速動画モードを選択しているか否かがさらに判定される。
【００７３】
ここで、高速動画モードではない、即ち標準動画モードであると判定された場合（ステップＳ１３；Ｎｏ）は、ＣＰＵ２１６の減色処理部２３１は上述した減色処理を行う（ステップＳ１４）。具体的には、１画素２４ビットの画像データを受け取り、このデータをビットスライスし、ＬＵＴテーブル変換を行い１画素１８ビットの画像データに変換する。
【００７４】
次に、ステップＳ１５では、ＣＰＵ２１６のＲＧＢ→ＹＵＶ変換部２３２は、ＲＧＢ形式の画像データに対して、上述した式２を用いてＲＧＢ→ＹＵＶ変換処理を行う。この変換処理は、ＹＵＶ４：２：２のサンプリング方法で処理が行われる。この処理により、上記の１画素１８ビットのデータは、１画素１２ビットにまで削減される（元のデータ量の１／２になる）。このようにＣＰＵ２１６でデータ量削減の処理がされた画像データは、表示装置２１２に転送される。なお、式２には、あらかじめ表示パネル２２７の表示特性に適合するように画像データの色相を変換するためのαとβが代入されており、ＣＰＵ２１６はそれに基づき処理を行う。また、利用者の設定により、αとβを変更できるものとしても良い。この場合は、ＲＡＭ２２４などにαとβを記録しておき、ＣＰＵ２１６がこの値を読み出してＲＧＢ→ＹＵＶ変換処理を行う。
【００７５】
一方、高速動画モードと判定された場合（ステップＳ１３；Ｙｅｓ）では、ＣＰＵ２１６は例えば１画素２４ビットの画像データを受け取ったとき、このデータをビットスライスし、ＬＵＴテーブル変換を行い、１画素１２ビットの画像データに変換する（ステップＳ１６）。
【００７６】
次に、ステップＳ１７では、ＣＰＵ２１６のＲＧＢ→ＹＵＶ変換部２３２において、同様に上述の式２用いてＲＧＢ→ＹＵＶ変換処理を行う。ステップＳ１７においては、ＹＵＶ４：２：０のサンプリング方法で処理が行われる。これにより、上記の１画素１２ビットのデータは、１画素６ビットにまで削減される。高速動画モードでは、元のデータ量の１／４のデータ量になり、表示装置２１２に転送するデータを標準動画モードと比べてさらに高速に画像データを転送することができる。このようにしてＣＰＵ２１６で処理された画像データは、表示装置２１２に転送される。
【００７７】
一方、ステップＳ１２で静止画モードと判定された場合（ステップＳ１２；Ｙｅｓ）、静止画の画質を低下させないために、上述のような減色処理やデータ量削減を伴うＲＧＢ→ＹＵＶ変換は行わない。よって、ステップＳ１８において、単純にＲＧＢ形式の画像データを上述のようにビットスライスする処理を行う。例えば、１画素２４ビットの画像データをビットスライスして、下位１２ビットの画像データはＲＡＭ２２４に一時記憶させておく。そして、上位１２ビットの画像データは、ステップＳ１９において前述の式２を用いてＹＵＶ４：４：４フォーマットのサンプリング方法でＲＧＢ→ＹＵＶ変換される。このＹＵＶ４：４：４フォーマットに従うＹＵＶ形式の画像データは、表示装置２１２に転送されて処理が行われる。
【００７８】
なお、ＲＡＭ２２４に一時的に記憶されていた下位１２ビットの画像データは、上記の上位１２ビットの画像データがＹＵＶ変換処理後に表示装置２１２に転送された後、次のフレーム画像転送周期でＲＡＭ２２４から取り出されてＲＧＢ→ＹＵＶ変換され、表示装置２１２に転送される。このように、データを上位ビットと下位ビットに分割（ビットスライス）して表示装置２１２に転送するので、クロック数を低減することが可能である。また、完全な元画像データの復元には２倍のフレーム画像転送周期を必要とするものの、画像データの削減が行われないので、高画質の静止画を表示することができる。
【００７９】
さて、ＣＰＵ２１６において上述のステップＳ１４、Ｓ１６又はＳ１８のいずれかの処理がなされた画像データＳ１とモード判定結果Ｓ２はＣＰＵ２１６から表示装置２１２へ転送される。表示装置２１２は受け取った画像データＳ１とモード判定結果Ｓ２に基づいて以下の処理を行う。まず、ステップＳ２０で、ＹＵＶ→ＲＧＢ変換部２３３により画像データに対してＹＵＶ→ＲＧＢ変換が行われる。そして、ＲＧＢ形式に変換された画像データは、ステップＳ２１において、ドライバ２２６に供給され、表示パネル２２７に表示される。
【００８０】
ここで、画像が静止画である場合は、前述のように上位１２ビットと下位１２ビットが異なるフレーム画像転送周期で順にＣＰＵ２１６から転送される。よって、例えば最初に送られてきた上位１２ビットの画像データを表示装置２１２に内蔵されているＲＡＭなどに記憶させておき、残りの下位１２ビットのデータが転送され終わったときに、完全な画像を作成して表示させることができる。また、その代わりに、上位１２ビットの画像データが転送された時点で直ちにその画像データを表示することもできる。その場合には、最初のフレーム画像転送周期では上位１２ビットのみの画像データしかないため、表示画像は粗くなるが、利用者は画像自体の概要程度は把握することができる。
【００８１】
なお、ＣＰＵ２１６から表示装置２１２へ供給されるモード判定結果Ｓ２は、ＣＰＵ２１６側でどのような画像処理が行われたかを示す情報である。例えば高速動画モードのモード判定結果を受け取ると、表示装置２１２は、ＣＰＵ２１６内で減色処理及びＹＵＶ４：２：０フォーマットによるＲＧＢ→ＹＵＶ変換処理されて作成された１画素６ビットの画像データが転送されることを知る。また、静止画モードのモード判定結果を受け取ると、表示装置２１２は、ＣＰＵ２１６内において上位１２ビットと下位１２ビットにビットスライスして得られる静止画データが転送されることを知る。よって、表示装置２１２は、モード判定結果Ｓ２に基づいて、対応する方法でＹＵＶ→ＲＧＢ変換処理を行うことができる。
【００８２】
このように、本実施形態では、携帯端末装置２１０における画像表示モードを、静止画モードと高速動画モードと標準動画モードに分けたので、表示装置２１２までのインターフェイスでの画像処理を、表示画像の種類に合った適切な方法で行うことができる。具体的には、動画モードにおいては、表示装置に転送する情報を削減するようにしたため、インターフェイス部分であるコネクタの接点数を減らし、クロック数を低減することが可能となる。また、高速動画モードを別に設けたことにより、さらに高速に表示装置に情報を転送することが可能となる。一方、静止画モードの場合は、分割してデータを転送するので元の画像データがは失われることはなく、高画質の静止画像を表示することができる。
【００８３】
また、いずれのモードにおいても、式２を用いたＲＧＢ→ＹＵＶ変換を行うことにより、表示すべき画像データの色相を、表示パネルの特性に合わせることができる。
【図面の簡単な説明】
【図１】本発明の画像処理を適用した携帯端末装置の概略構成を示す。
【図２】本発明に係る色変換を説明するための図である。
【図３】ＹＵＶ４：２：２フォーマットを説明するための図である。
【図４】ＹＵＶ４：２：０フォーマットを説明するための図である。
【図５】ＹＵＶ４：２：２フォーマットからＹＵＶ４：４：４フォーマットへの変換方法を説明する図である。
【図６】本発明に係る表示制御処理のフローチャートである。
【符号の説明】
２１０ 携帯端末装置、 ２１２ 表示装置、 ２１４ 送受信部、 ２１６ＣＰＵ、 ２１８ 入力部、 ２２０ プログラムＲＯＭ、 ２２４ ＲＡＭ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a liquid crystal display panel and other image display devices including an image display unit, performing color matching of image data to be displayed in consideration of display characteristics of the image display unit, and reducing the data amount of the image data. The present invention relates to a method of transferring data to an image display unit.
[0002]
[Background Art]
2. Description of the Related Art In a mobile terminal device such as a mobile phone or a PDA (Personal Digital Assistant), a display device such as an LCD (Liquid Crystal Display) is used. Generally, a white LED is used for the backlight of the LCD. Since the white LED is manufactured by covering the blue LED with a yellow phosphor, the image display characteristics of the LCD are strongly affected by the blue LED.
[0003]
A specific example will be described with reference to FIG. FIG. 2 is a color space represented by an XYZ color system based on an international standard system of the International Commission on Illumination CIE, and a broken line L1 is an outline (spectrum locus) of the color space. The coordinates of a point in the area having L1 as an outline represent a specific color. In the color space of the CIE expression system, in order to further unify the difference in color reproduction characteristics between devices of a display device, an international standard color space which defines colors and saturations is standardized as sRGB. In FIG. 2A, a triangular outline T1 indicated by a broken line represents the sRGB characteristics. That is, the color of the original image data received by the mobile terminal device belongs to a triangle having the outer shape of T1. On the other hand, in the output characteristics of the LCD of the portable terminal device, for example, a color in a triangle whose outline is T2 represented by a solid line is expressed. As indicated by the arrow in the figure, the vertices of the triangles T1 and T2 do not match, and it can be seen that T2 protrudes significantly more than T1 particularly in the region representing blue (the region located at the lower left of the diagram). . This is because the characteristics of the LCD of the portable terminal device are biased toward blue.
[0004]
As a means for coping with such a situation, there has been proposed a method of performing correction by performing hue conversion on an input image in an image display device. For example, Patent Literature 1 discloses a system that performs color correction by adjusting device characteristics according to a display device, a setting situation, and a use environment.
[0005]
[Patent Document 1]
JP-A-7-56549
[0006]
[Problems to be solved by the invention]
However, in the above-described method, since the characteristics of the input image are forcibly matched with the device characteristics, the amount of calculation required for image processing increases, and it is difficult to perform the same calculation on the mobile terminal device.
[0007]
In recent years, display devices mounted on mobile terminal devices such as mobile phones and PDAs (Personal Digital Assistants) have been increasing in screen size and resolution, and high-resolution image data having a larger number of pixels than before has been used. It can be displayed on a larger screen.
[0008]
However, high-resolution image data corresponding to such a large-screen display or high-resolution display has a large data amount. In the data transfer to the display device, the number of clocks can be reduced by increasing the number of data lines (data lines), but there is a drawback that the power consumption increases accordingly.
[0009]
Further, a liquid crystal driver IC which is a semiconductor circuit has an upper limit of the number of operation clocks due to its nature. For example, in the case where the number of data lines is one, in order to transfer a total of 18 bits of moving image data of 6 bits each for RGB, a total of 18 bits, according to QCIF (Quarter Common Intermediate Format) having a resolution of 176 × 208 pixels, 60 frames per second. Requires a dot clock of 39.5 MHz (176 × 208 × 18 × 60). On the other hand, when the number of data lines is three, the dot clock is 13.2 MHz, which is 1/3 of the above case. With this level, the read / write speed of the built-in circuit of the liquid crystal driver IC manufactured by the current semiconductor process, particularly the RAM, can be sufficiently supported.
[0010]
However, in the case of CIF (Common Intermediate Format) having a resolution of 352 × 416 pixels, similarly to the above, in order to transfer moving image data of 6 bits each of RGB and a total of 18 bits per pixel, 60 frames per second, The dot clock requires 158.1 MHz. In this case, even if the number of data lines is three, the dot clock becomes 52.7 MHz, which makes it impossible to cope with the current read / write speed of the RAM. Further, when transferring image data of 24 bits (full color: 8 bits for each of RGB) with higher image quality, the dot clock is 210 MHz, and even if the number of data lines is three, it becomes 70.3 MHz. Therefore, the current capability of the liquid crystal driver IC cannot cope.
[0011]
As described above, it is theoretically possible to reduce the dot clock by increasing the number of data lines, but the mobile terminal device has a limited mounting area, and the signal input / output unit of the liquid crystal driver IC is It has to be small connectors and small contacts. Therefore, an increase in the number of data lines may lead to a decrease in the reliability of the connector due to a shock or a temperature change when the portable terminal device is carried. That is, there is a limit to the increase in the number of data lines.
[0012]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an image display device for a portable terminal device such as a mobile phone in which image display characteristics of an image display unit are taken into consideration. An object of the present invention is to provide an image display device, an image display method, and an image display program capable of reducing the amount of data of an image to be transferred to a display device while performing data color matching.
[0013]
[Means for Solving the Problems]
According to one aspect of the present invention, an image display device including an image display unit includes: an image data acquisition unit configured to acquire image data in RGB format to be displayed; and a color reduction process configured to perform a color reduction process on the acquired image data to reduce a data amount. Processing means, YUV conversion means for converting the color-reduced image data to YUV format image data with hue conversion, and transfer means for transferring the YUV-converted image data to the image display unit. Prepare.
[0014]
The above-described image display device can be various terminal devices such as a mobile phone and a portable terminal including a liquid crystal display panel as an image display unit. The image data acquisition means acquires image data in RGB format from, for example, an external server or the like. This image data includes both still image data and moving image data. The acquired image data is converted into YUV format image data after the data amount is reduced by the color reduction processing. The image data with the reduced data amount is transferred to the image display unit and displayed. Therefore, it is possible to reduce the load of the process of transferring the image data to the image display unit and to speed up the transfer. When the image data is converted into YUV format image data, hue conversion is performed simultaneously so as to match the display characteristics of the image display unit, so that image data having characteristics suitable for the image display unit can be displayed. .
[0015]
In one aspect of the above-described image display device, the color reduction processing unit can perform a bit slice of a predetermined number of bits on the image data. Thereby, the data amount of the image data to be transferred to the image display unit can be reduced.
[0016]
In another aspect of the above-described image display device, the YUV conversion unit can reduce the amount of converted image data. In this case, the YUV conversion can be performed according to, for example, the YUV 4: 2: 2 format or the YUV 4: 2: 0 format. Thus, the data amount can be further reduced during the YUV conversion, in addition to the data amount reduction by the color reduction processing.
[0017]
In another aspect of the above-described image display device, the YUV conversion unit can perform YUV conversion according to a conversion formula including a constant for the hue conversion. In this aspect, if the above constant is determined in consideration of the display characteristics of the image display unit, hue conversion can be performed by a simple calculation.
[0018]
In another aspect of the above-described image display device, the image display unit displays the RGB-converted image data by converting the image data transferred by the transfer unit into image data in RGB format. A display panel. According to this aspect, the image data transferred to the image display unit with the data amount reduced is converted from the YUV format to the RGB format and displayed in the image display unit.
[0019]
In a similar aspect of the present invention, an image display method performed in an image display device including an image display unit includes an image data obtaining step of obtaining image data in RGB format to be displayed, and performing a color reduction process on the obtained image data. A color reduction processing step of reducing the amount of data by using the image data, a YUV conversion step of converting the image data subjected to the color reduction processing into YUV format image data with hue conversion, and the YUV-converted image data to the image display unit. And a transfer step of transferring.
[0020]
In a similar aspect of the present invention, the image display program is executed in an image display device having an image display unit, so that the image display device acquires image data in RGB format to be displayed. Means for reducing the amount of data by performing color reduction processing on acquired image data, YUV conversion means for converting the image data subjected to color reduction processing into image data in YUV format with hue conversion, and YUV conversion Transfer means for transferring the input image data to the image display unit.
[0021]
According to the image display method and the image display program, it is possible to reduce the data amount and transfer the data to the image display unit as in the above-described image display device.
[0022]
According to another aspect of the present invention, an image display device including an image display unit includes: an image data acquisition unit that acquires image data in RGB format to be displayed; and a color reduction process that performs a color reduction process on the acquired image data to reduce a data amount. Processing means; YUV conversion means for converting the color-reduced image data into YUV format image data with hue conversion; and determining whether the image display device is in a still image display mode or a moving image display mode. Determining mode determination means, and transferring the image data not subjected to the color reduction processing by the color reduction processing means to the image display unit when the image display device is in the still image display mode, and setting the image display device to the moving image display mode. Transfer means for transferring the image data subjected to the color reduction processing by the color reduction processing means to the image display unit at one time.
[0023]
The above-described image display device can be various terminal devices such as a mobile phone and a portable terminal including a liquid crystal display panel as an image display unit. The image data acquisition means acquires image data in RGB format from, for example, an external server or the like. This image data includes both still image data and moving image data. The acquired image data is converted into YUV format image data after the data amount is reduced by the color reduction processing. When the image data is converted into YUV format image data, hue conversion is performed simultaneously so as to match the display characteristics of the image display unit, so that image data having characteristics suitable for the image display unit can be displayed. .
[0024]
Further, it is determined whether the image display device is in the still image display mode or the moving image display mode. When the image display device is in the still image display mode, the image data that has not been subjected to the color reduction processing by the color reduction processing means is transferred to the image display unit. In the moving image display mode, the image data after the color reduction processing by the color reduction processing means is transferred to the image display unit. Therefore, when in the moving image display mode, the image data whose data amount has been reduced is transferred to the image display unit and displayed, so that the load of the process of transferring the image data to the image display unit is reduced and the transfer speed is increased. can do. On the other hand, in the still image display mode, high-quality image data can be transferred and displayed.
[0025]
In one aspect of the image display device, the mode determination unit determines whether the video mode is a standard video mode or a high-speed video mode, and the YUV conversion unit determines that the image display device is in the standard video mode. When the image display device is in the high-speed moving image mode, the YUV conversion can be performed according to the YUV 4: 2: 0 format. Thus, in the high-speed moving image mode, the data amount is further reduced as compared with the standard moving image mode, and high-speed data transfer becomes possible.
[0026]
In another aspect of the image display device, in the still image display mode, the transfer unit transfers the image data whose data amount has not been reduced in a plurality of data transfer cycles. In this aspect, in the still image mode in which high image quality is required, image data whose data amount has not been reduced by color reduction processing or the like is transferred in a plurality of data transfer cycles. Therefore, although a long time is required for data transfer, a high-quality still image can be displayed.
[0027]
In another aspect of the above-described image display device, the transfer unit transfers upper bits of the image data in a first data transfer cycle, and transfers remaining lower bits of the image data in a second data transfer cycle. Forward. In this aspect, the upper bits of the still image to be displayed are transferred in the first data transfer cycle, so that the entire still image can be displayed immediately, although the image itself is coarse. Then, by receiving the image data of the remaining lower bits in the next data transfer cycle, a complete still image can be displayed.
[0028]
In a similar aspect of the present invention, an image display method performed in an image display device including an image display unit includes an image data obtaining step of obtaining image data in RGB format to be displayed, and performing a color reduction process on the obtained image data. A color reduction processing step of reducing the amount of data by using the image display apparatus, a YUV conversion step of converting the image data subjected to the color reduction processing into image data of a YUV format together with a hue conversion, and the image display device displays a still image display mode and a moving image display. A mode determining means for determining which of the modes the image display device is in, and transferring the image data that has not been subjected to the color reduction processing to the image display unit when the image display device is in the still image display mode, and Transferring the image data after the color reduction processing to the image display unit in the mode.
[0029]
Further, according to a similar aspect of the present invention, an image display program executed in an image display device including an image display unit includes: an image data acquisition unit configured to acquire image data in RGB format to be displayed; Color reduction processing means for reducing the amount of data by performing color reduction processing on the converted image data; YUV conversion means for converting the image data subjected to the color reduction processing into YUV format image data with hue conversion; A mode determining unit that determines whether the image display device is in a display mode or a moving image display mode; and, when the image display device is in a still image display mode, image data that has not been subjected to the color reduction processing by the color reduction processing unit. When the image display device is in the moving image display mode, the image data after the color reduction processing by the color reduction processing means is displayed in the image display mode. Transfer means for transferring to, to function as a.
[0030]
According to the image display method and the image display program, it is possible to reduce the data amount and transfer the data to the image display unit as in the above-described image display device.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0032]
[Configuration of mobile terminal device]
FIG. 1 shows a schematic configuration of a portable terminal device according to an embodiment of the present invention. In FIG. 1, a mobile terminal device 210 is, for example, a terminal device such as a mobile phone or a PDA. The mobile terminal device 210 includes a display device 212, a transmission / reception unit 214, a CPU 216, an input unit 218, a program ROM 220, and a RAM 224. The display device 212 includes a driver 226 and a display panel 227.
[0033]
The transmission / reception unit 214 receives image data from outside. The reception of the image data is performed, for example, when the user operates the mobile terminal device 210 to connect to a server device that provides a content providing service, and inputs an instruction to download desired image data. The received image data includes moving image data and still image data. The image data received by the transmission / reception unit 214 can be stored in the RAM 224. Here, it is assumed that, for example, image data of RGB 24 bits (full color) per pixel is received.
[0034]
The input unit 218 can be configured with various operation buttons or the like for a mobile phone, or a tablet or the like for detecting contact with a touch pen or the like for a PDA, and is used when a user performs various instructions and selections. . Instructions, selections, and the like input to the input unit 218 are converted into electric signals and sent to the CPU 216.
[0035]
The program ROM 220 stores various programs for executing various functions of the mobile terminal device 210, and particularly in the present embodiment, a color reduction processing program for performing color reduction processing on image data transmitted from the transmission / reception unit 214, It stores an RGB → YUV conversion program for performing RGB → YUV conversion (also referred to as YUV conversion) according to the present invention.
[0036]
The RAM 224 is used as a working memory when processing image data according to a program such as a color reduction processing program or a YUV conversion program. Further, as described above, external image data received by the transmission / reception unit 214 can be stored as needed.
[0037]
The CPU 216 executes various functions of the portable terminal device 210 by executing various programs stored in the program ROM 220. In the present embodiment, first, the color reduction processing program stored in the program ROM 220 is read and executed, thereby functioning as the color reduction processing unit 231 and reducing the amount of image data.
[0038]
The CPU 216 also functions as an RGB → YUV conversion unit 232 by reading and executing an RGB → YUV conversion program also stored in the program ROM 220, and converts RGB format image data into YUV format image data. I do. In the present embodiment, when performing the YUV conversion processing, the display characteristics of the display panel 227 are taken into account, and color matching is performed on the image data so that the color of the image displayed on the display panel 227 approaches the color of the original image. Hue conversion for (hue adjustment) is performed. Note that the RGB → YUV conversion processing can also be performed by a sampling method that reduces the data amount.
[0039]
The CPU 216 determines whether the mobile terminal device 210 is in the still image display mode or the moving image display mode based on the input to the input unit 218 by the user, and sends the mode determination result S2 to the display device 212. Supply. The CPU 216 detects whether the image data supplied from the transmission / reception unit 214 is still image data or moving image data in addition to performing the input based on the user's input, and automatically determines the mode based on the result. It may be configured to make a determination.
[0040]
As described above, in the CPU 216, the data amount of the image data is reduced by the color reduction process and the RGB → YUV conversion process, so that the data transfer speed of the image data to the display device 212 can be increased, and low power consumption can be realized. . Note that the CPU 216 realizes various functions of the portable terminal device 210 by executing various programs other than the above, but these are not directly related to the present invention, and thus description thereof is omitted.
[0041]
The display device 212 is a lightweight and thin display device such as an LCD (Liquid Crystal Display), and includes a liquid crystal display panel 227 and a driver 226 which is a semiconductor. The display device 212 includes a YUV → RGB conversion unit 233 as a processing unit for the image data received from the CPU 216. Note that these processing units can be realized by, for example, a processor in the display device executing a predetermined YUV → RGB conversion program, and can also be provided inside the driver 226.
[0042]
In the display device 212, the YUV-to-RGB conversion unit 233 converts the YUV image data S1 subjected to the YUV conversion in the CPU 216 into RGB image data. This is because the driver built in the display device 212 is generally compatible with RGB format image data. At this time, if necessary, processing for restoring the data reduced in the above-mentioned RGB → YUV conversion can be performed.
[0043]
Thus, the image data on which the necessary processing has been performed is supplied to the driver 226. The driver 226 drives the display panel 227 according to the input image data, and displays an image in the display area of the display panel 227. The display device 212 is capable of high-resolution display with, for example, the above-described 352 × 416 pixels (CIF size) in the horizontal direction and the vertical direction.
[0044]
As described above, in the present embodiment, after the data amount of the original image data is reduced by performing the color reduction process or the RGB → YVU conversion process in the CPU 216, the image data is supplied to the display device 212. Therefore, the data transfer speed of image data to the display device 212 can be increased, and low power consumption can be realized.
[0045]
[Image processing by CPU]
Next, the color reduction processing and the RGB → YUV conversion processing performed by the CPU 216 will be described in detail.
[0046]
(Color reduction processing)
First, the color reduction processing performed by the color reduction processing unit 231 in the CPU 216 will be described. In the present embodiment, a color reduction process is performed in which the data amount of an image is bit sliced to reduce the data amount. Specifically, the lower bits of the original image data are discarded, and the CPU 216 refers to a look-up table (LUT) storing the display characteristics of the display device 212 for each of R, G, and B colors, and generates a new gradation value. (LUT table conversion). Thus, when image data of, for example, 24 bits per pixel is received from the transmission / reception unit 214, the CPU 216 can perform the color reduction processing to reduce the data amount to 18 bits or 12 bits per pixel.
[0047]
(RGB → YUV conversion processing)
Next, an RGB → YUV conversion process performed by the CPU 216 will be described. This conversion is for converting image data in RGB format received from the outside into YUV format. Here, the RGB format refers to red (red), green (green), and blue (blue) three primary color gradations of light. On the other hand, in the YUV format, Y represents luminance, and U and V represent blue color difference (Cb) and red color difference (Cr), respectively. The image data in the RGB format sent from the transmission / reception unit 214 to the CPU 216 is converted into the YUV format by the RGB → YUV conversion unit 232.
[0048]
In the present embodiment, when RGB image data is converted to YUV format, color conversion is performed so that the hue of the image data is converted. Hereinafter, the specific method and its effect will be described in detail.
[0049]
Equation 1 is a general equation used for RGB → YUV conversion processing.
[0050]
(Equation 1)

When the image data YUV-converted according to Equation 1 is displayed on a display panel 227 such as an LCD, a triangular area having a T2 represented by a solid line as an outline in a CIE-expressed color space shown in FIG. The color inside is displayed. On the other hand, the original image has a color in a triangular area whose outline is the broken line T1. As a result, the vertices of the triangles represented by T1 and T2 do not coincide with each other as shown by the arrow in FIG. 2A, and in particular, in an area representing blue (an area located at the lower left of the figure), T2 is regarded as the outline. It can be seen that the triangular shape protrudes significantly more than the triangle whose outline is T1. This is because, as described above, the characteristics of the LCD of the portable terminal device are biased toward blue.
[0051]
Therefore, in the present embodiment, the CPU 216 performs image processing for color matching on the image data so that the color of the image displayed on the display panel 227 approaches the color of the original image. Specifically, the RGB → YUV conversion processing is performed using Expression 2 obtained by improving Expression 1.
[0052]
(Equation 2)

In Equation 2, in U representing the blue color difference, R representing the red gradation and G representing the green gradation are multiplied by a coefficient obtained by adding a constant α different from the above expression. In V representing red color difference, G representing green gradation and B representing blue gradation are multiplied by a coefficient to which a constant β is added.
[0053]
The result of performing RGB → YUV conversion using Equation 2 is a triangle having T2a represented by a thick solid line in FIG. Here, when a line segment connecting a point C1 representing white color (hereinafter, referred to as a white point) and the vertex of the triangle T1 is drawn, the distance from the white point C1 on these line segments is red, It represents the gradation of three primary colors, blue and green. When RGB → YUV conversion processing is performed by setting appropriate α and β in Expression 2, a triangle having an outer line of T2 which is an output characteristic of the display panel 227 rotates around a white point C1, and an outer shape of T2a becomes The vertices are moved so that the vertices substantially overlap the above-mentioned line segment representing the gradation like a triangle as a line. In addition, this conversion causes the triangle T2a to fall within the triangle T1. Note that the vertices of the triangle T2a represent the physical characteristics of the display panel 227, and therefore, are placed on the outline of the original triangle T2 even after conversion.
[0054]
As described above, in the RGB → YUV conversion processing according to the present embodiment, since the color conversion that completely matches the colors is not performed, the processing can be performed without imposing a load on the CPU 216. Further, when complete color matching is performed, if the color gamut of the input image data is wide, the tone value after the color matching process is clipped, and the tone may be lost. In this regard, in the present embodiment, since only the hue is converted, the lightness (brightness) and the saturation (darkness) do not match as a color, but the hue can be correctly adjusted. As described above, there is no possibility that the converted gradation value is clipped and the gradation is lost.
[0055]
Further, the YUV conversion according to the present embodiment is effective in matching colors displayed by liquid crystal display devices having various characteristics such as STN (Super Twisted Nematic), TFD (Thin Film Diode), and LTPS (Low Temperature Poly-Si). It is a target. For example, in STN, it is difficult to increase the contrast and the color gamut cannot be expanded as a principle restriction on the liquid crystal characteristics. In such a case, the most uncomfortable feeling is that the color is shifted (for example, red looks yellowish), and the lightness and saturation of the color do not feel very uncomfortable. Rather, if the lightness and the saturation are forcibly combined, the gradation characteristics of the image will be impaired. Therefore, even when STN is selected for cost reduction and power consumption reduction, color matching with an LCD panel having an active element such as TFD or LTPS having a high contrast and a wide color gamut can be easily performed.
[0056]
In addition, since the LED backlight has a large variation in manufacturing, the color conversion according to the present invention is effective for absorbing the variation.
[0057]
In the present invention, when the above RGB → YUV conversion is performed, sampling processing can be simultaneously performed in the YUV 4: 2: 2 format as shown in FIG. This method is a method in which luminance is sampled for each pixel and color difference is averaged and sampled for every two pixels, considering four pixels in the horizontal direction as a reference. In the example of FIG. 3, the image data in the RGB format of 24 bits per pixel is subjected to color reduction processing to 18 bits per pixel, and then subjected to the sampling process in the above-described YUV 4: 2: 2 format. As a result, YUV format image data of 12 bits per pixel is obtained. That is, the image data after the RGB → YUV conversion has a data amount of １ ／ of the original image data.
[0058]
Further, in the present invention, as another method, the sampling process can be performed even in the YUV 4: 2: 0 format as shown in FIG. In this method, after performing YUV 4: 2: 2 sampling, the color difference information of two more vertical pixels is averaged. For example, image data that has been reduced to 12 bits per pixel by color reduction processing has 6 bits per pixel when subjected to sampling processing in the YUV 4: 2: 0 format. Therefore, in this case, the image data after the RGB → YUV conversion has a data amount of １ ／ of the original image data. This sampling method has an advantage that the transfer rate to the display device 212 is further increased because the data amount is reduced more than the above method. However, the image quality deteriorates accordingly.
[0059]
When the image quality of the displayed image is prioritized (when a still image or the like is displayed), the processing can be performed without using the sampling process of YUV 4: 2: 2 or the sampling process of YUV 4: 2: 0. . In this case, sampling processing is performed in the YUV 4: 4: 4 format. In this method, a high-quality image can be displayed since the data amount of the image data is not reduced.
[0060]
[Image processing on display device]
Next, the YUV → RGB conversion process performed by the display device 212 will be described.
[0061]
The display device 212 receives the image data subjected to RGB → YUV conversion by the CPU 216 and performs YUV → RGB conversion processing. Here, a conversion reverse to the above-described RGB → YUV conversion processing is performed, and conversion is performed by Expression 3.
[0062]
[Equation 3]

In the present invention, for example, image data sampled in the YUV 4: 2: 2 format and having 12 bits per pixel can be restored to image data in the RGB format with 18 bits per pixel by the method shown in FIG. . In this method, a process of complementing the color difference components so that the image data in the YUV 4: 2: 2 format in the upper part of FIG. 5 is in the YUV 4: 4: 4 format as shown in the lower part of FIG.
[0063]
[Display control processing]
Next, an embodiment of the display control processing according to the present invention including the above-described image processing will be described.
[0064]
FIG. 6 shows a flowchart of the display control processing according to the present invention. Note that the display control process described below is performed by the CPU 216 and the display device 212 of the portable terminal device 210 illustrated in FIG. 1 executing a program related to the above-described image processing.
[0065]
In the image display device according to the present invention, it is possible to select a mode between a still image mode for displaying a still image and a moving image mode for displaying a moving image. If the above-described color reduction processing and the RGB → YUV conversion according to the YUV 4: 2: 2 format or the YUV 4: 2: 0 format are performed, the image quality of the displayed image is inevitably coarse. When displaying a moving image, there is no problem with this image quality. However, in the case of a still image that is watched and observed by the user, the image quality is noticeably rough. Therefore, in the present invention, the user can select the still image mode or the moving image mode, and it is determined whether or not to perform the image processing for reducing the data amount according to the selection result.
[0066]
Specifically, in the case of the still image mode, the image data is not subjected to the color reduction processing, the image data is simply divided into upper bits and lower bits (bit slice), and the display device 212 is sequentially switched over two frame periods. Transfer to That is, since the original image data is 24 bits per pixel (8 bits for each color of RGB) in RGB format, the upper 4 bits of each color, that is, a total of 12 bits, are transferred to the display device 212 in the first frame image transfer cycle, and the remaining The lower 4 bits of each color, a total of 12 bits, are transferred to the display device 212 in the next frame image transfer cycle. Thus, in the still image mode, high-quality still image data of 24 bits per pixel can be transferred at a two-frame image transfer cycle and displayed on the display device 212.
[0067]
This bit slice processing is performed by the CPU 216 executing a bit slice processing program prepared in advance in the program ROM 220 shown in FIG.
[0068]
Further, according to the present invention, in the moving image mode, a high-speed moving image mode for displaying a moving image having a high frame rate can be selected. When transferring moving image data received from an information medium such as a television to the display device 212, it is required to increase the data rate between the CPU 216 as an interface and the display device 212. Therefore, in the present invention, the high-speed moving image mode and the standard moving image mode can be selected by the user in the moving image mode, and an image processing method for appropriately reducing the image data amount is selected according to the selection result. Specifically, in the case of the standard moving image mode, the RGB → YUV conversion in the CPU 216 follows the YUV 4: 2: 2 format. On the other hand, in the case of the high-speed moving image mode, the RGB → YUV conversion in the CPU 216 is performed in accordance with the YUV 4: 2: 0 format, and the data amount is further reduced so that high-speed transfer of moving image data to the display device 212 is enabled.
[0069]
The CPU 216 can determine whether the mobile terminal device 210 is in the still image mode, the standard moving image mode, or the high-speed moving image mode, based on the user's input to the input unit 218 as described above. The CPU 216 performs processing in the CPU 216 based on the mode determination result, and supplies the mode determination result S2 to the display device 212.
[0070]
Next, a display control process according to the present embodiment will be described with reference to the flowchart in FIG.
[0071]
First, in step S11, the mobile terminal device 210 receives image data to be displayed from an external server or the like. Note that this image data is assumed to be RGB format image data.
[0072]
Next, the CPU 216 determines whether or not the user has selected the still image mode (step S12). If it is determined that the mode is the moving image mode (Step S12; No), the process proceeds to Step S13, and it is further determined whether or not the user has selected the high-speed moving image mode.
[0073]
Here, when it is determined that the mode is not the high-speed moving image mode, that is, the mode is the standard moving image mode (Step S13; No), the color reduction processing unit 231 of the CPU 216 performs the above-described color reduction processing (Step S14). Specifically, image data of 24 bits per pixel is received, this data is bit sliced, and LUT table conversion is performed to convert the image data to image data of 18 bits per pixel.
[0074]
Next, in step S15, the RGB → YUV conversion unit 232 of the CPU 216 performs an RGB → YUV conversion process on the image data in the RGB format using the above equation (2). This conversion process is performed by a sampling method of YUV 4: 2: 2. By this processing, the above-described data of 18 bits per pixel is reduced to 12 bits per pixel (1/2 of the original data amount). The image data subjected to the data amount reduction process by the CPU 216 is transferred to the display device 212. Note that α and β for converting the hue of the image data so as to conform to the display characteristics of the display panel 227 are substituted in Equation 2 in advance, and the CPU 216 performs processing based on the values. Further, α and β may be changed according to the setting of the user. In this case, α and β are recorded in the RAM 224 or the like, and the CPU 216 reads these values and performs RGB → YUV conversion processing.
[0075]
On the other hand, when it is determined that the mode is the high-speed moving image mode (step S13; Yes), when the CPU 216 receives, for example, image data of 24 bits per pixel, the CPU 216 slices the data, performs LUT table conversion, and performs 12 bits per pixel. (Step S16).
[0076]
Next, in step S17, the RGB → YUV conversion processing is similarly performed by the RGB → YUV conversion unit 232 of the CPU 216 using the above-described equation (2). In step S17, processing is performed by the sampling method of YUV 4: 2: 0. Thus, the data of 12 bits per pixel is reduced to 6 bits per pixel. In the high-speed moving image mode, the data amount becomes 1/4 of the original data amount, and the image data can be transferred to the display device 212 at a higher speed than in the standard moving image mode. The image data processed by the CPU 216 in this manner is transferred to the display device 212.
[0077]
On the other hand, if it is determined in step S12 that the image mode is the still image mode (step S12; Yes), the RGB → YUV conversion involving the above-described color reduction processing and data amount reduction is not performed in order not to lower the image quality of the still image. Therefore, in step S18, a process of simply bit-slicing the RGB format image data as described above is performed. For example, image data of 24 bits per pixel is bit sliced, and image data of lower 12 bits is temporarily stored in the RAM 224. Then, the image data of the upper 12 bits is subjected to RGB → YUV conversion by the sampling method of the YUV 4: 4: 4 format using the above equation 2 in step S19. The image data in the YUV format according to the YUV 4: 4: 4 format is transferred to the display device 212 and processed.
[0078]
Note that the lower 12-bit image data temporarily stored in the RAM 224 is transferred from the RAM 224 at the next frame image transfer cycle after the upper 12-bit image data is transferred to the display device 212 after the YUV conversion processing. The data is taken out, RGB → YUV converted, and transferred to the display device 212. As described above, since the data is divided into upper bits and lower bits (bit slice) and transferred to the display device 212, the number of clocks can be reduced. Although the restoration of the complete original image data requires twice the frame image transfer cycle, the image data is not reduced, so that a high-quality still image can be displayed.
[0079]
The CPU 216 transfers the image data S1 and the mode determination result S2 subjected to any one of the above-described steps S14, S16, and S18 from the CPU 216 to the display device 212. The display device 212 performs the following processing based on the received image data S1 and the mode determination result S2. First, in step S20, the YUV → RGB conversion is performed on the image data by the YUV → RGB conversion unit 233. Then, the image data converted into the RGB format is supplied to the driver 226 and displayed on the display panel 227 in step S21.
[0080]
If the image is a still image, the upper 12 bits and the lower 12 bits are sequentially transferred from the CPU 216 at different frame image transfer cycles as described above. Therefore, for example, the upper 12-bit image data transmitted first is stored in a RAM or the like built in the display device 212, and when the remaining lower 12-bit data has been transferred, a complete image is transferred. Can be created and displayed. Alternatively, the image data can be displayed immediately when the upper 12-bit image data is transferred. In this case, the display image becomes coarse because there is only the upper 12 bits of image data in the first frame image transfer cycle, but the user can grasp the outline of the image itself.
[0081]
The mode determination result S2 supplied from the CPU 216 to the display device 212 is information indicating what kind of image processing has been performed on the CPU 216 side. For example, when receiving the mode determination result of the high-speed moving image mode, the display device 212 transfers the image data of 6 bits per pixel created by the color reduction process and the RGB → YUV conversion process in the YUV 4: 2: 0 format in the CPU 216. Know that Further, when receiving the mode determination result of the still image mode, the display device 212 knows that the still image data obtained by bit slicing the upper 12 bits and the lower 12 bits in the CPU 216 is transferred. Therefore, the display device 212 can perform the YUV → RGB conversion process by a corresponding method based on the mode determination result S2.
[0082]
As described above, in the present embodiment, the image display mode of the portable terminal device 210 is divided into the still image mode, the high-speed moving image mode, and the standard moving image mode. It can be done in a manner appropriate for the type. Specifically, in the moving image mode, information to be transferred to the display device is reduced, so that it is possible to reduce the number of contacts of the connector, which is the interface portion, and the number of clocks. In addition, the separate provision of the high-speed moving image mode makes it possible to transfer information to the display device at a higher speed. On the other hand, in the still image mode, since the data is divided and transferred, the original image data is not lost, and a high-quality still image can be displayed.
[0083]
In any mode, the hue of the image data to be displayed can be adjusted to the characteristics of the display panel by performing the RGB → YUV conversion using Expression 2.
[Brief description of the drawings]
FIG. 1 shows a schematic configuration of a portable terminal device to which the image processing of the present invention is applied.
FIG. 2 is a diagram for explaining color conversion according to the present invention.
FIG. 3 is a diagram for explaining a YUV 4: 2: 2 format.
FIG. 4 is a diagram for explaining a YUV 4: 2: 0 format.
FIG. 5 is a diagram illustrating a conversion method from a YUV 4: 2: 2 format to a YUV 4: 4: 4 format.
FIG. 6 is a flowchart of a display control process according to the present invention.
[Explanation of symbols]
210 portable terminal device, 212 display device, 214 transmitting / receiving section, 216 CPU, 218 input section, 220 program ROM, 224 RAM

Claims (13)

In an image display device including an image display unit,
Image data acquisition means for acquiring image data in RGB format to be displayed;
Color reduction processing means for performing color reduction processing on the acquired image data to reduce the data amount;
YUV conversion means for converting the color-reduced image data to YUV format image data with hue conversion;
Transfer means for transferring the YUV-converted image data to the image display unit. The image display device according to claim 1, wherein the color reduction processing means performs a bit slice of a predetermined number of bits on the image data. 3. The image display device according to claim 1, wherein the YUV conversion unit reduces a data amount of the converted image data. The image display device according to claim 1, wherein the YUV conversion unit performs the YUV conversion according to a conversion formula including a constant for the hue conversion. The image display unit,
RGB conversion means for converting the image data transferred by the transfer means into image data in RGB format;
The image display device according to claim 1, further comprising: a display panel configured to display image data subjected to RGB conversion. In an image display device including an image display unit,
Image data acquisition means for acquiring image data in RGB format to be displayed;
Color reduction processing means for performing color reduction processing on the acquired image data to reduce the data amount;
YUV conversion means for converting the color-reduced image data to YUV format image data with hue conversion;
Mode determining means for determining whether the image display device is in a still image display mode or a moving image display mode,
When the image display device is in the still image display mode, the image data that has not been subjected to the color reduction processing by the color reduction processing unit is transferred to the image display unit, and when the image display device is in the moving image display mode, the color reduction processing unit And a transfer unit for transferring the image data after the color reduction processing to the image display unit. The mode determination means determines whether the video mode is a standard video mode or a high-speed video mode,
The YUV conversion means performs YUV conversion according to the YUV 4: 2: 2 format when the image display device is in the standard moving image mode, and performs the YUV 4: 2: 0 format when the image display device is in the high speed moving image mode. The image display device according to claim 6, wherein the YUV conversion is performed according to the following. 7. The image display device according to claim 6, wherein in the still image display mode, the transfer unit transfers image data whose data amount has not been reduced in a plurality of data transfer cycles. 9. The image forming apparatus according to claim 8, wherein the transfer unit transfers upper bits of the image data in a first data transfer cycle, and transfers remaining lower bits of the image data in a second data transfer cycle. Image display device. In an image display method executed in an image display device including an image display unit,
An image data acquisition step of acquiring image data in RGB format to be displayed;
A color reduction process for reducing the amount of data by performing color reduction on the acquired image data;
A YUV conversion step of converting the color-reduced image data into YUV format image data with hue conversion;
Transferring the YUV-converted image data to the image display unit. By being executed in an image display device including an image display unit, the image display device,
Image data acquisition means for acquiring image data in RGB format to be displayed;
Color reduction processing means for performing color reduction processing on the acquired image data to reduce the data amount;
YUV conversion means for converting the color-reduced image data into YUV format image data with hue conversion, and
An image display program functioning as transfer means for transferring YUV-converted image data to the image display unit. In an image display method executed in an image display device including an image display unit,
An image data acquisition step of acquiring image data in RGB format to be displayed;
A color reduction process for reducing the amount of data by performing color reduction on the acquired image data;
A YUV conversion step of converting the color-reduced image data into YUV format image data with hue conversion;
Mode determining means for determining whether the image display device is in a still image display mode or a moving image display mode,
When the image display device is in the still image display mode, the image data that has not been subjected to the color reduction processing is transferred to the image display unit, and when the image display device is in the moving image display mode, the image data after the color reduction processing is transferred to the image Transferring the image data to a display unit. By being executed in an image display device including an image display unit, the image display device,
Image data acquisition means for acquiring image data in RGB format to be displayed;
Color reduction processing means for performing color reduction processing on the acquired image data to reduce the data amount;
YUV conversion means for converting the color-reduced image data into YUV format image data with hue conversion,
Mode determining means for determining whether the image display device is in a still image display mode or a moving image display mode, and
When the image display device is in the still image display mode, the image data that has not been subjected to the color reduction processing by the color reduction processing unit is transferred to the image display unit, and when the image display device is in the moving image display mode, the color reduction processing unit An image display program functioning as transfer means for transferring the image data after the color reduction processing to the image display unit.

Images