JP4265033B2 - Color correction method, recording medium storing program for executing color correction method, color correction device, and display device - Google Patents

Description

図３は、画像中の人肌部分の信号値の例を示し、図４は画像中のチュ−リップ部分の信号値の例を示す。
【００６５】
また、表１は、それぞれの画像に対するＲ、Ｇ、Ｂ信号値と色差信号値の例である。尚、ディジタル信号処理において演算を行う場合、信号値は、ディジタル値で示されるが、以降の説明では、簡単の為、相対値として記載している。
【００６６】
図３（ａ）は、画像の人肌の領域のＲ、Ｇ、Ｂ信号値を示す。それぞれの信号値は表１に示すように、Ｒ＝０．８１、Ｇ＝０．５７、Ｂ＝０．４７である。
【００６７】
図３（ｂ）は、［式１］をもとに計算された色差信号Ｒ−Ｙ，Ｇ−Ｙ，Ｂ−Ｙを示し、それぞれの値は、表１に示すようにＲ−Ｙ＝０．１８、Ｇ−Ｙ＝−０．０６、Ｂ−Ｙ＝−０．１６となる。また、輝度信号Ｙは、［式１］より０．６３となる。
【００６８】
ここで、上記の色差信号と、上記の部分的に強調された色差信号の変換特性として、ユーザが図１８（ａ）の変換特性を選択したものとし、しきい値ｐ点、ｑ点としては、赤の色差信号Ｒ−Ｙに対してＲｐ，Ｒｑ、緑の色差信号Ｇ−Ｙに対してＧｐ，Ｇｑ、青の色差信号Ｂ−Ｙに対してＢｐ，Ｂｑとし、例えば以下の値をとるものとする。
［式５］
Ｒｐ＝０．２、Ｒｑ＝−０．１３
Ｇｐ＝０．０３、Ｇｑ＝−０．１
Ｂｐ＝０．２、Ｂｑ＝−０．３
各色差信号におけるｐ点、ｑ点のレベルは、図３（ｂ）において破線で示される。また、変換特性の乗算係数（変換特性における傾き）は、各色差信号の変換特性に対してｐ点からｑ点までを１、その範囲外を２とする。尚、上記の例では、ｐ、ｑの各々について定義したが、特にｐ、ｑの両方を指定する必要はなく、ｐ、又はｑの片方のみを定義するようにしてもよい。
【００６９】
この場合、人肌部分の色差信号値Ｒ−Ｙ、Ｇ−Ｙ，Ｂ−Ｙは、上記のｐ点とｑ点の間にあるので、乗算係数は１である。
【００７０】
即ち、強調された色差信号値(Ｒ−Ｙ)'，(Ｇ−Ｙ)'，(Ｂ−Ｙ)'は、図３（ｃ）に示すように、
(Ｒ−Ｙ)'＝０．１８
(Ｇ−Ｙ)'＝−０．０６
(Ｂ−Ｙ)'＝−０．１６
となり、各々（Ｒ−Ｙ），（Ｇ−Ｙ），（Ｂ−Ｙ）と等しい値となる。
【００７１】
強調された色信号Ｒ"，Ｇ"，Ｂ"の値は、［式１］より以下に示すように計算される。
Ｒ"＝０．８１
Ｇ"＝０．５７
Ｒ"＝０．４７
即ち、Ｒ、Ｇ、Ｂの値と等しいものとなり、色強調処理は、実質的に施されていないことがわかる。
【００７２】
一方、図４は、画像のチュ−リップの領域の信号値の例であり、図４（ａ）は、同領域のＲ、Ｇ、Ｂの信号値を示す。それぞれの信号値は、表１に示されるように、Ｒ＝０．８１、Ｇ＝０．２７、Ｂ＝０．３３である。
【００７３】
図４（ｂ）は、［式１］をもとに計算された色差信号Ｒ−Ｙ，Ｇ−Ｙ，Ｂ−Ｙを示し、それぞれの値は、表１に示すように
Ｒ−Ｙ＝０．３７、Ｇ−Ｙ＝−０．１７、Ｂ−Ｙ＝−０．１１
となる。また、輝度信号Ｙは、［式１］より０．４４となる。
【００７４】
ここで、上記の色差信号と、上記の部分的に強調された色差信号の変換特性が、上記と同様の変換特性とすると、例えば、赤の色差信号値Ｒ−ＹがＲｐ＝０．２より高くなっており、図１８（ａ）よりわかるように、Ｒｐからの超過分０．１７が乗算係数２で乗算されて、強調された色差信号値(Ｒ−Ｙ)'は０．５４となる。
【００７５】
また、図４（ｂ）に示す緑の色差信号値Ｇ−Ｙは、Ｇｑ＝−０．１より負の方向にレベルが高い。従って、強調された色差信号値(Ｇ−Ｙ)'は、図４（ｃ）に示すように、Ｇｑからの超過分−０．０７が乗算係数２で乗算されて、−０．２４となる。
【００７６】
一方、青の色差信号値Ｂ−Ｙは、しきい値ＢｐとＢｑの間にあるので、強調された色差信号値(Ｂ−Ｙ)'は−０．１１のままとなる。
【００７７】
図４（ｄ）に強調された色信号値Ｒ"、Ｇ"、Ｂ"を示す。
【００７８】
Ｒ"は、強調された色差信号値(Ｒ−Ｙ)'＝０．５４に輝度信号値Ｙ＝０．４４が加算されて０．９８となり、Ｇ"は、強調された色差信号値(Ｇ−Ｙ)'＝−０．２４に輝度信号値Ｙ＝０．４４が加算されて０．２となる。一方、Ｂ"は、強調された色差信号値(Ｂ−Ｙ)'＝−０．１１に輝度信号値Ｙ＝０．４４が加算され、色信号値Ｂと同じ、即ち０．３３となる。
【００７９】
このように、図１８（ａ）の変換特性の場合、人肌のように画像の色差が小さい場合、即ちＲ、Ｇ、Ｂの信号値が近接しており、無彩色に近い色に関しては、信号値は変わらない。
【００８０】
一方、チュ−リップのように画像の色差が大きい場合、即ちＲ、Ｇ、Ｂ信号値の差が大きく、有彩色に近い色に関しては、その色が強調されることがわかる。
【００８１】
次に、図１８（ａ）のしきい値ｐ，ｑについて説明する。
【００８２】
表１に示す被写体が１枚の画像の中に存在する場合について考える。
【００８３】
例えば、色差信号Ｒ−Ｙの上記画像のヒストグラムは、図１２に示すようなものとなる。横軸は、色差信号値、縦軸は、画素数を示している。ここで、画像中の被写体領域の大きさ、各被写体領域の単色性によって、各領域のヒストグラムの拡がり、高さが異なってくる。
【００８４】
しきい値ｐの値は、強調したい色の領域と、ヒストグラム上でその隣の領域の間に設定する。例えば、Ｒの色について、チュ−リップの赤のみを強調したい場合には、図１２のチュ−リップと人肌の領域の間のある値に設定する。
【００８５】
一方、しきい値ｑの値は、その量を減らしたい領域と、ヒストグラム上でその隣の領域の間に設定する。例えば、Ｒの色について、青空の領域のみ、その量を若干減らしたいような場合には、図１２の青空の領域と晴天時日陰雪の領域の間のある値に設定する。
【００８６】
ここで、上記の領域が明確に分離していない場合には、図１８（ａ）のような不連続な変換特性よりも、図１８（ｂ）に示されるような連続的な変換特性のほうが適している。
【００８７】
また、図１８（ｃ）に示すような色差信号から、強調された色差信号への変換特性とすることで、無彩色に近い部分のホワイトバランスのみを若干ずらして、有彩色部の色特性はそのままとしたい場合についても対応することができる。但し、この特性では、不連続な部分が存在する為、図１８（ｄ）に示すような変換特性とすることが望ましい。また、この場合は、後述のように、再度色強調処理を行う場合には、入出力の関係が１：１で定まらない為、色補正処理を施す前の画像デ−タを記憶しておかないと、不都合となる場合がある。
【００８８】
上記の色強調処理を行うシステムのブロックダイアグラムを図１７に示す。
【００８９】
端子５０８，５０９，５１０より入力される、アナログＲ、Ｇ、Ｂの映像信号は、Ａ／Ｄ変換器５０１でディジタル信号に変換される。制御部５１６は、端子５１４，５１５から入力される水平（ＨＤ）、垂直（ＶＤ）同期信号をもとに、ＰＬＬを構成し、各ブロックを制御する。
【００９０】
Ａ／Ｄ変換器５０１でディジタル化されたＲ、Ｇ、Ｂ映像信号は、メモリ部５０２に書き込まれる。また、メモリ部５０２は、Ｄ／Ａ変換器５０３に接続される。メモリ部５０２より読み出されたディジタル映像信号は、Ｄ／Ａ変換器５０３でＲ、Ｇ、Ｂアナログ映像信号に変換され、不図示の表示装置、画像形成装置等に出力される。
【００９１】
ここで、メモリ部５０２は、ＣＰＵ５０４により制御部５１６を介して、メモリ部５０２のフリーズ、スル−制御が可能である。具体的には、制御部５１６は、ＣＰＵ５０４の指令により、メモリ部５０２へのデータの書き込みを禁止することで、出力画像をフリーズ(freeze)し、メモリ部５０２への書き込みを連続的に許可することで出力画像をスルー(through)とする。尚、メモリ部５０２からの画像デ−タの読み出しは常に行われている。
【００９２】
Ｄ／Ａ変換器５０３は、オーバーレイメモリ５１７に接続される。オーバーレイメモリ５１７には、オンスクリーンディスプレイデータが記憶される。ＣＰＵ５０４の指令に基づいて、記憶されたオンスクリーンデータはＤ／Ａ変換器５０３に出力される。このようにして、ディジタル映像信号とオーバーレイメモリ５１７に記憶されるオンスクリーンディスプレイデータが、Ｄ／Ａ変換器５０３で混合される。
【００９３】
メモリ部５０２は、ＣＰＵ５０４のワーキングメモリであるＲＡＭ５０６にも接続されている。ＣＰＵ５０４には、キーボード５０５、上記色補正処理を行うプログラム等の格納される記憶媒体５０７も接続されている。
【００９４】
図１３は、上記の色補正処理を行う動作を示すフローチャートである。
【００９５】
まず、ステップＳ１０１で、キーボード５０５からのＣＰＵ５０４に画像をフリーズするコマンドを入力する。ＣＰＵ５０４は、このコマンドにより、制御部５１６にフリーズ制御信号を送出する。制御部５１６は、メモリ部５０２へのディジタルデータの書き込みを禁止する。
【００９６】
ステップＳ１０２で、上記の、色差信号から強調された色差信号への変換特性が、例えば図１９に示すような形でオンスクリーンディスプレイされ、キーボード５０５や、不図示のマウス等のポインティングデバイスにより、このうちの１つを選択する。尚、この際、パラメータの設定が必要な場合には、同パラメータについても、キーボード５０５や、マウス等のポインティングデバイスにより設定する。
【００９７】
ステップＳ１０３では、メモリ部５０２よりＲＡＭ５０６に、ディジタル画像データを転送する。ステップＳ１０３’でＣＰＵ５０４は、ＲＡＭ５０６に転送されたディジタル画像データを用いて［式１０］の演算を１画面について順次行い、演算結果をＲＡＭ５０６に書き込む。
［式１０］
Ｒ"＝ｈ（Ｒ−Ｙ）＋Ｙ
Ｇ"＝ｊ（Ｇ−Ｙ）＋Ｙ
Ｂ"＝ｋ（Ｂ−Ｙ）＋Ｙ
（ｈ（Ｒ−Ｙ）、ｊ（Ｇ−Ｙ）、ｋ（Ｂ−Ｙ）は、各々（Ｒ−Ｙ）、(Ｇ−Ｙ）、（Ｂ−Ｙ）の関数を示す）
尚、この際、輝度（Ｙ）デ−タについても、必要に応じて、ＲＡＭ５０６に記憶する。ＲＡＭ５０６への記憶は、輝度（Ｙ）デ−タを圧縮しても構わないが、再度、色強調処理を行う場合の、再生画像を高画質化する為には、可逆変換可能（Lossless)な圧縮とすることが望ましい。
【００９８】
ステップＳ１０４で、［式１０］によるＲＡＭ５０６に記憶された演算結果をメモリ部５０２に転送する。
【００９９】
尚、上記ではＲＡＭ５０６に１画面分のデータの記憶容量を持たせる構成としたが、ＲＡＭ５０６を小容量として、メモリ部５０２より１画面分のデータ量より少ない所定容量の画像データをＲＡＭ５０６に転送し、ＣＰＵ５０４で、所定容量の画像データについての演算が終了後、メモリ部５０２にデータを転送するようにしてもよい。この処理を１画面分の画像データについて繰り返す。
【０１００】
ステップＳ１０５では、出力画像の確認を行い、所望の効果が得られれば、色強調処理を終了する。この際、所望の効果が得られない等の場合には、上記の色補正処理を再度行う為に、上記の１回目の色補正処理を施す前の画像デ−タが必要となる。この画像デ−タを得る為には、キーボード５からの入力により、フリ−ズ状態を解除して、一度スルー状態に戻して（ステップＳ２０１）から再度フリーズ状態として（ステップＳ１０１）、色強調処理を施す前の画像デ−タを取得すればよい。
【０１０１】
また、色補正処理を再度行う為に、メモリ部５０２、又はＲＡＭ５０６に色補正処理を施す前の画像データを記憶する記憶領域を確保して、この領域に、色補正処理を施す前の画像デ−タ（Ｒ、Ｇ、Ｂ、又はＲ−Ｙ、Ｇ−Ｙ，Ｂ−Ｙ）を記憶し、２回目以降の変換特性、パラメータの設定後の処理（ステップＳ１０３〜）に使用してもよい。この場合の動作を図１４のフローチャートに示す。
【０１０２】
図１４において、Ｓ１０１、Ｓ１０２は図１３と同様であり、ステップＳ１０３ａにおいて、メモリ部５０２よりＲＡＭ５０６に転送されたディジタル画像データをＲＡＭ５０６に記憶する。２回目以降のステップＳ１０３ｂにおいて、ＣＰＵ５０４による演算に用いられるデータは、前の色補正処理の際にメモリ部５０２から転送されたデータ（すなわち前回のステップＳ１０３ｂで記憶しておいた画像データ）である。Ｓ１０３’Ｓ１０４、Ｓ１０５は図１３と同様である。
【０１０３】
この場合、２回目以降の色補正処理においては、メモリ部５０２からＲＡＭ５０６へのデータの転送は行われない。この、ＲＡＭ５０６に記憶されている色補正処理を施す前の画像データは、ステップＳ１０５が肯定された時点で不要となる。
【０１０４】
また、色補正処理がなされた画像データ（Ｒ"、Ｇ"，Ｂ"）より、［式１０］の逆の演算を行い、色補正処理の施される前の画像デ−タ（Ｒ，Ｇ，Ｂ、又はＲ−Ｙ，Ｇ−Ｙ，Ｂ−Ｙ）を求め、この画像デ−タ（Ｒ、Ｇ、Ｂ、又はＲ−Ｙ，Ｇ−Ｙ，Ｂ−Ｙ）を、２回目以降の色補正処理に使用してもよい。但し、この逆演算においては、前の色補正処理における変換特性、及びパラメ−タ、輝度（Ｙ）のデ−タが必要となるので、前回の色強調処理における変換特性、及びパラメ−タ、輝度デ−タ（Ｙ）を、例えばＲＡＭ５０６に記憶しておく必要がある。この場合の動作を図１５のフローチャートに示す。
【０１０５】
図１５において、Ｓ１０１、Ｓ１０２、１０３’、Ｓ１０４、Ｓ１０５は図１３と同様である。ステップＳ１０３ｃにおいて、色強調処理における変換特性、及びパラメ−タ、輝度デ−タ（Ｙ）をＲＡＭ５０６に記憶しておく。
【０１０６】
上記の逆演算は、ステップＳ２０３において行われる。具体的には、前回の色補正処理により得られた色補正されたＲ"、Ｇ"、Ｂ"より、ＲＡＭ５０６に記憶されている輝度（Ｙ）デ−タを減算し、ｈ（Ｒ−Ｙ）、ｊ（Ｇ−Ｙ），ｋ（Ｂ−Ｙ）を求める。色強調処理の各変換特性において、部分的に強調された色差信号は、色差信号により１対１の関係で決定される為、Ｒ−Ｙ、Ｇ−Ｙ，Ｂ−Ｙを求めることができる（但し、前回の色補正処理において、図１８（ｃ），図１８（ｄ）の特性を選択した場合は、出力と入力が１対１に対応しない場合があるから、１つの出力に対して１つの入力を定義できないことがある。そのため、このような手法は用いることはできない）。
このようにして求められたＲ−Ｙ，Ｇ−Ｙ，Ｂ−Ｙは、ＲＡＭ５０６に記憶され、次の色補正処理に用いられる。（ステップＳ１０３’ｃ）
この、ＲＡＭ５０６に記憶されている色補正処理を施す前の輝度（Ｙ）の画像データ、変換特性、及びパラメ−タは、ステップＳ１０５が肯定された時点で不要となる。
【０１０７】
上記説明では、再度色強調処理を行う際に、一度等価的に前回の色強調処理を施す前の画像デ−タを復元する例について示している。
【０１０８】
これとは別に、一度色補正処理された画像デ−タに対して、さらに別、又は同じ変換特性、及び／又はパラメ−タの色補正処理を施す場合には、特に、前回の色補正処理を施す前の画像デ−タの記憶、復元は不要である。この場合の動作は図１６のフロ−チャ−トに示す。
【０１０９】
出力画像の確認のステップＳ１０５において、再度、追加で色補正処理を施す必要がある場合には、ステップＳ２０４により、追加で施す色補正処理における変換特性、及び／又はパラメ−タを設定する。ステップ１０３’では、前回の色補正処理で得られた結果に対して、ステップＳ２０４での設定に基づいた色補正処理が行われる。他のステップは図１３と同様である。
【０１１０】
図１７中の記憶媒体５１８は、例えばＰＣカード、サ−バ−のメモリなどの記憶媒体であり、必要に応じて圧縮された画像データと、上記ステップＳ１０２で設定された変換特性、及び必要に応じて設定されたパラメ−タが記憶される。
【０１１１】
この画像データを再び再生する場合には、必要に応じて圧縮された画像データは解凍され、一緒に記憶されていた、変換特性、パラメ−タに基づいて、ＣＰＵ５０４により色強調処理が行われる。この場合、画像デ−タが記憶されているのは、記憶媒体５１８であり、ＣＰＵ５０４により演算された結果がＲＡＭ５０６から、メモリ部５０２に転送される。
【０１１２】
上記の圧縮は、再生画像を高画質化する為に、可逆再生可能（Lossless)とすることが望ましい。
【０１１３】
但し、上記の記憶媒体５１８に記憶する画像デ−タが、色補正処理後の画像デ−タの場合には、特にこの限りではなく、また、変換特性、パラメ−タ等の記憶も不要となる。
【０１１４】
尚、上記の実施の形態では、画面の全領域について、同じ変換特性、パラメ−タで色強調処理を行うようにしたが、画面を複数の領域に分割し、各分割領域について異なる変換特性、及び／又はパラメ−タで色強調処理を行うようにしてもよい。この場合、前述のように、各領域毎に、変換特性，及び／又はパラメ−タの記憶が必要となる場合がある。
【０１１５】
上記説明では、Ｒ、Ｇ、Ｂの信号値が与えられて、これより各色差信号を算出する例について示したが、各色差信号、コンポジット信号等のその他の信号が与えられる場合についても、本発明を適用することができる。
【０１１６】
以上説明した色補正方法の手順は、ＣＰＵ５０４が読み取り可能なコンピュータプログラムとして、記憶媒体５０７に記憶されており、ＣＰＵ５０４がこのプログラムを記憶媒体５０７から読み出して実行される。
本発明の別の実施の形態について図面に従って説明する。図１は、本発明の実施の形態の色補正装置の構成例である。
【０１１７】
マトリクス回路１は、入力信号であるＲ信号、Ｇ信号、Ｂ信号から、式１に示す輝度信号Ｙと色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙとを生成し、色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙを色差信号強調回路４に出力する。
【０１１８】
色差信号強調回路４は、入力される色差信号のレベルに応じて異なる増幅度を有する増幅器で、色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙを部分的に強調した色差信号(Ｒ−Ｙ)'、(Ｇ−Ｙ)'、(Ｂ−Ｙ)'を出力する。
【０１１９】
部分的に強調された色差信号(Ｒ−Ｙ)'、(Ｇ−Ｙ)'、(Ｂ−Ｙ)'は、それぞれ加算器３に入力され、マトリクス回路１から出力される輝度信号Ｙと加算される。加算器３は、それらの信号から部分的に強調された色信号Ｒ"、Ｇ"、Ｂ"を出力する。この部分的に強調された色信号Ｒ"、Ｇ"、Ｂ"は式４に基づいて得られる。
【０１２０】
図２は、本発明の実施の形態の色差信号強調回路４の入出力特性例で、赤の色差信号Ｒ−Ｙが入力される場合を示す。図２において、横軸は入力の赤の色差信号Ｒ−Ｙを示し、縦軸は出力である強調された色差信号(Ｒ−Ｙ)'を示す。また、横軸のｐ、ｑは増幅度が変化するしきい値を示し、この場合はｐ＝０．３、ｑ＝−０．３である。
【０１２１】
色差信号強調回路４は、図２に示すように色差信号Ｒ−Ｙが正であればしきい値ｐより高い部分、負であればしきい値ｑより低い部分の増幅度が大きくなる。即ち、ｐ〜ｑ間の増幅度はＡ（例えば、１）であるが、その範囲外の増幅度はＢ（例えば、２）となる。従って、画面の中で色の鮮やかな部分の画像がより鮮やかになり、鮮やかでない部分はそのままとなり自然な画像が得られる。
【０１２２】
次に、本実施の形態の色補正装置で具体的な被写体の色を補正する場合について、図３、図４及び表１を用いて説明する。図３は、人肌を撮影する場合の信号例を示し、図４はチューリップを撮影する場合の信号例を示す。また、表１は、それぞれの被写体に対するＲ、Ｇ、Ｂ信号と色差信号の値の例である。
【０１２３】
図３（ａ）は、被写体が人肌の場合に色補正装置に入力されるＲ、Ｇ、Ｂ信号を示す。それぞれの信号の値は表１に示すように、
Ｒ＝０．８１、Ｇ＝０．５７、Ｂ＝０．４７
である。
【０１２４】
図３（ｂ）は、色補正装置のマトリクス回路１から出力される色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙを示し、それぞれの値は表１に示すように、
Ｒ−Ｙ＝０．１８、Ｇ−Ｙ＝−０．０６、Ｂ−Ｙ＝−０．１６
となる。なお、輝度信号Ｙは、式１より０．６３となる。
【０１２５】
ここで、図２のしきい値であるｐ点、ｑ点として、赤の色差信号Ｒ−Ｙに対してＲｐ、Ｒｑ、緑の色差信号Ｇ−Ｙに対してＧｐ、Ｇｑ、青の色差信号Ｂ−Ｙに対してＢｐ、Ｂｑとし、例えば式５に示した値をとるものとする。
【０１２６】
各色差信号におけるｐ点、ｑ点のレベルは、図３（ｂ）における点線で示される。また、色差信号強調回路４は、図２と同様に各色差信号に対してｐ点からｑ点間での増幅度を１、その範囲外の増幅度を２とする。
【０１２７】
ｐ点、ｑ点のレベルが図３（ｂ）の場合、人肌の各色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙは、上記の各ｐ点とｑ点の間にあるので、増幅度１で色差信号強調回路４から出力される。
【０１２８】
即ち、色差信号強調回路４の出力である色差信号(Ｒ−Ｙ)'、(Ｇ−Ｙ)'、(Ｂ−Ｙ)'は、図３（ｃ）に示すように、
(Ｒ−Ｙ)'＝０．１８
(Ｇ−Ｙ)'＝−０．０６
(Ｂ−Ｙ)'＝−０．１６
となり、入力である色差信号（Ｒ−Ｙ）、（Ｇ−Ｙ）、（Ｂ−Ｙ）と等しい。
【０１２９】
色差信号(Ｒ−Ｙ)'、(Ｇ−Ｙ)'、(Ｂ−Ｙ)'は、加算器３により輝度信号Ｙ＝０．６３と加算される。従って、色補正装置の出力である色信号Ｒ"、Ｇ"、Ｂ"は、図３（ｄ）に示すように、
Ｒ"＝０．８１
Ｇ"＝０．５７
Ｂ"＝０．４７
となり、入力の色信号Ｒ、Ｇ、Ｂがそのまま出力される。
【０１３０】
図４は、被写体がチューリップの場合の信号例であり、図４（ａ）は、マトリクス回路１に入力されるＲ、Ｇ、Ｂ信号を示す。それぞれの信号の値は表１に示すように、
Ｒ＝０．８１、Ｇ＝０．２７、Ｂ＝０．３３
である。
【０１３１】
図４（ｂ）は、マトリクス回路１から出力される色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙを示し、それぞれの値は、
Ｒ−Ｙ＝ ０．３７
Ｇ−Ｙ＝−０．１７
Ｂ−Ｙ＝−０．１１
である。なお、輝度信号Ｙは式１より０．４４となる。
【０１３２】
ここで、色差信号強調回路４のしきい値であるｐ点、ｑ点を式５の値とすると、赤の色差信号Ｒ−ＹがＲｐ＝０．２よりレベルが高い。従って、色差信号強調回路４の出力は、図４（ｃ）に示すようにＲｐからの超過分０．１７が増幅度２で増幅されて０．３４となり、増幅度１で出力される０．２と加算されて、強調された色差信号（Ｒ−Ｙ）’は０．５４となる。
【０１３３】
また、図４（ｂ）に示す緑の色差信号Ｇ−Ｙは、Ｇｑ＝−０．１より負の方向にレベルが高い。従って、強調された色差信号(Ｇ−Ｙ)'は、図４（ｃ）に示すように、Ｇｑからの超過分−０．０７が増幅度２で増幅されて−０．１４となり、増幅度１で出力される−０．１と加算されて−０．２４となる。
【０１３４】
一方、青の色差信号Ｂ−ＹはＢｐとＢｑの間にあるから、色差信号強調回路４の出力である色差信号(Ｂ−Ｙ)'は−０．１１のままである。
【０１３５】
図４（ｄ）は色補正装置の出力を示す。色信号Ｒ"は、色差信号(Ｒ−Ｙ)'＝０．５４に輝度信号Ｙ＝０．４４が加算されて０．９８となり、色信号Ｇ"は、色差信号(Ｇ−Ｙ)'＝−０．２４に輝度信号Ｙ＝０．４４が加算されて０．２となる。一方、色信号Ｂ"は、色差信号(Ｂ−Ｙ)'＝−０．１１に輝度信号Ｙ＝０．４４が加算され、入力される色信号Ｂと同じレベル即ち０．３３で出力される。
【０１３６】
このように本実施の形態の色補正装置では、人肌のように被写体の色差が小さい場合、即ちＲ、Ｇ、Ｂ信号のレベルが近接しており、淡い印象を与える色に関しては入力レベルと同じレベルで出力される。一方、チューリップのように被写体の色差が大きい場合、即ちＲ、Ｇ、Ｂ信号のレベル差が大きく、比較的鮮やかな印象を与える色に関しては、その色が強調されて出力される。
【０１３７】
図２の色差信号強調回路４の入出力特性例では、ｐ点、ｑ点において増幅度が異なる場合を示したが、色差信号の入力レベルに応じて増幅度が連続的に変わるようにしてもよい。即ち、
〔式６'〕
(Ｒ−Ｙ)'＝（Ｒ−Ｙ）^3
(Ｇ−Ｙ)'＝（Ｇ−Ｙ）^3
(Ｂ−Ｙ)'＝（Ｂ−Ｙ）^3
（ａ^3は、ａの3乗を示す）
のように、入力信号の３乗を出力する特性としてもよい。この場合は、強調される色の度合いが徐々に変化し、より自然な画像が得られる。
【０１３８】
図５は、図１に示した色差信号強調回路４の具体例で、赤の色差信号Ｒ−Ｙを強調する場合を示す。色差信号Ｒ−Ｙは、コアリング回路６と色差信号Ｒ−Ｙに所定の遅延時間を与えるディレイライン５とに入力される。
【０１３９】
コアリング回路６は、例えば図６に示す入出力特性を有しており、入力信号が所定のレベル範囲、即ちコアリングレベルであるｐ点とｑ点の間にある場合は入力信号を遮断し、入力信号が所定のレベル範囲外、即ちｐ点とｑ点の範囲外にある場合は信号を出力する。この場合、コアリングレベルｐ、ｑを外部から設定できるようにすれば、強調する色差信号のレベルを変えることができる。例えば、ｐ点のレベルを低く設定すると、比較的淡い色でも強調することができる。コアリング回路６を通った信号は、増幅度Ａの増幅回路７により増幅され、加算器８によりディレイライン５を通った色差信号Ｒ−Ｙと加算されて強調された色差信号(Ｒ−Ｙ)'となる。
【０１４０】
また、図５に示すコアリング回路６、増幅回路７、加算器８の機能をルックアップテーブル（Look Up Table）を用いて実現してもよい。この場合、ディレイライン５の機能は不要となる。ルックアップテーブルを、例えば、書き換え可能なメモリで構成し、メモリの各アドレスには、（Ｒ−Ｙ）の値が入力され、メモリの対応するアドレスの各データ部には、（Ｒ−Ｙ）を入力した場合の(Ｒ−Ｙ)'の計算結果が書き込まれる。
【０１４１】
例えば、（Ｒ−Ｙ）が８ビットのディジタルデータ、(Ｒ−Ｙ)'が８ビットのディジタルデータであると仮定すると、ルックアップテーブルを構成するメモリの容量としては、アドレス８ビット、データ８ビットが必要となる。
【０１４２】
ここで、図５に示されるｐ、ｑ、Ａを変える場合には、上記ルックアップテーブルを構成するメモリのデータ部書き換えればよい。
【０１４３】
さらに、上記容量の整数倍の容量を持つメモリを用いて、メモリのデータ部に上記のｐ、ｑ、Ａを変えた場合のデータをいくつか記憶しておき、メモリのアドレスの一部を用いて、これを選択してもよい。
【０１４４】
メモリのデータ部を書き換える場合には、例えば、データの計算をＣＰＵ、ＤＳＰ等で行い、この計算結果を、メモリのデータ部に書き込めばよい。
【０１４５】
ルックアップテーブルを用いて、上記機能を達成する場合には、後述の高周波成分のもれは発生しないという利点がある。
【０１４６】
また、増幅回路７の増幅度Ａを外部から設定できるようにしてもよい。この場合は、色を強調したくない場合、例えば、輝度が高く強調すると鮮やかになりすぎる色に関しては増幅度Ａを低く設定することができる。
【０１４７】
図７は、図５に示した色差信号強調回路４を使用した場合の信号例である。ここで図７（ａ）、（ｂ）は、図４（ａ）、（ｂ）と同様に被写体がチューリップの場合のＲ、Ｇ、Ｂ信号及び色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙを示す。なお、図７（ｂ）において、コアリングレベルＲｐ、Ｒｑ等は式５に示す値と同じとする。
【０１４８】
色差信号Ｒ−Ｙ、Ｇ−Ｙ、Ｂ−Ｙがコアリング回路６に入力されると、コアリング回路６は、図７（ｃ）に示すようにコアリングレベルの範囲外の信号を出力する。即ち、色差信号Ｒ−Ｙは０．１７となり、色差信号Ｇ−Ｙは−０．０７となる。一方、色差信号Ｂ−Ｙはコアリングレベルの範囲内であり０となる。
【０１４９】
コアリング回路６の出力は、例えば増幅度２の増幅回路７で図７（ｄ）に示すように増幅され、色差信号Ｒ−Ｙは０．３４となり色差信号Ｇ−Ｙは−０．１４となる。一方、色差信号Ｂ−Ｙは０のままである。
【０１５０】
増幅回路７の出力は、加算器８によりディレイライン５を通った入力の色差信号と加算される。従って、色差信号強調回路４の出力は、図７（ｅ）に示すように、色差信号(Ｒ−Ｙ)'が０．７１となり色差信号(Ｇ−Ｙ)'が−０．３１となる。一方、色差信号(Ｂ−Ｙ)'は図７（ｂ）と変わらず−０．１１のままである。
【０１５１】
図７（ｆ）は色補正装置の出力を示す。色補正装置の出力は、図１に示すように色差信号強調回路４の出力と輝度信号Ｙ＝０．４４とが加算され、色信号Ｒ"、Ｇ"、Ｂ"はそれぞれ１．１５、０．１３、０．３３となる。
【０１５２】
このようにコアリング回路６を使用した色補正装置においても、被写体の色差が小さい場合は入力レベルと同じレベルで出力され、被写体の色差が大きい場合は、その色が強調されて出力される。
【０１５３】
図８は、本実施の形態のコアリング回路６の回路例を示す。ここでコアリング回路６の入力端子１５へ入力される電圧をＶ１、コアリング回路６の出力端子３４から出力される電圧をＶ４とする。また、コアリング回路６内の演算増幅器２２の出力電圧をＶ２、演算増幅器２９の出力電圧をＶ３、ダイオード１７、ダイオード２４（以下Ｄ１７、Ｄ２４とする。）の順方向電圧Ｖｆを０．７Ｖとする。
【０１５４】
演算増幅器２２のプラス端子の電圧をＶａ’とすると、Ｄ１７がオンとなるのは入力電圧Ｖ１が（Ｖａ’＋０．７）以上のときであり、そのときの演算増幅器２２のゲインは、Ｒ１９／Ｒ１８で与えられる。
【０１５５】
また、入力電圧Ｖ１が（Ｖａ’＋０．７）より小さいときＤ１７はオフしており演算増幅器２２のゲインは０となるので、演算増幅器２２は、入力電圧Ｖ１の（Ｖａ’＋０．７）より大きい部分を取り出すことができる。
【０１５６】
一方、演算増幅器２９のプラス端子の電圧をＶｂ’とすると、Ｄ２４がオンとなるのは入力電圧Ｖ１が（Ｖｂ’−０．７）以下のときであり、そのときのゲインは、Ｒ２６／Ｒ２５で与えられる。
【０１５７】
また、入力電圧Ｖ１が（Ｖｂ’−０．７）より高いときＤ２４はオフしており演算増幅器２９のゲインは０となるので、演算増幅器２９は、入力電圧Ｖ１の（Ｖｂ’−０．７）より小さい部分を取り出すことができる。
【０１５８】
更に、演算増幅器２２、２９の出力電圧Ｖ２、Ｖ３は、入力電圧Ｖ１に対し極性が反転しているので、演算増幅器３３によって、Ｖ２、Ｖ３を加算しながら反転させると、図６に示す入出力特性が得られる。
【０１５９】
なお、演算増幅器２２、２９のプラス端子の電圧Ｖａ’、Ｖｂ’は、電源電圧Ｖａ、Ｖｂを端子１６、２３に供給し、抵抗Ｒ２０、２１、２７、２８で分圧することにより得る。この場合は、Ｖａ’、Ｖｂ’は固定値となる。
【０１６０】
一方、Ｖａ’、Ｖｂ’を外部から可変する場合は、端子１６、２３に任意の電圧を発生する制御手段を接続する。あるいは、この制御手段を演算増幅器２２、２９のプラス端子に直接接続しても良い。
【０１６１】
以上の手段により図２に示すｐ点、ｑ点を設定するが、図８のコアリング回路６において、（Ｖａ’＋０．７）がｐ点となり、（Ｖｂ’−０．７）がｑ点となる。
【０１６２】
図９は、本発明の実施の形態の色差信号強調回路４の別の具体例である。図５の色差信号強調回路４に使用されるコアリング回路６は、信号を部分的に切り取るため、色差信号の高周波成分が漏れることが多い。
【０１６３】
その漏れた高周波成分をキャンセルするため、図９に示すようにコアリング回路６と増幅回路７の間に高周波成分を遮断するローパスフィルタ９を入れる。人の視覚においては高周波における色の分解能は低いことから、ローパスフィルタ９を入れることにより、表示効果を落とさずに画質を低下させるノイズ成分を除くことができる。
【０１６４】
図１０は、本発明の実施の形態のローパスフィルタ９の効果例である。図１０（ａ）は、コアリング回路６に入力される色差信号を示す。また、図１０（ｂ）は、コアリング回路６の出力を示す。このようにコアリング回路６は、信号が急激に変化する信号のエッジ部分で高周波信号の漏れを生じる。
【０１６５】
図１０（ｃ）は、ローパスフィルタ９の出力を示す。ローパスフィルタ９は、信号の高周波成分を遮断するので、色差信号に含まれる高周波成分が外部に漏れることを防止し、高画質の画像を表示させることができる。
【０１６６】
図１１は、本発明が適用できるプロジェクタ２００のブロック図を撮像装置１００のブロック図と共に示す。図１１において、撮像装置１００は、おもに静止画を撮像する書画撮像装置であり、被写体３０１からの光をレンズ１０１を通して集光する。レンズ１０１を通った光は、赤、緑、青のフィルタ部分に３分割された色分解フィルタ１０２で１フィールドごとに赤、緑、青の各色の光に色分解され、ＣＣＤ１０３で光電変換される。
【０１６７】
ＣＣＤ１０３で電気信号に変換されたＲ信号、Ｇ信号、Ｂ信号は信号処理回路１０４でホワイトバランス、ガンマ変換等の処理が施されて、Ａ／Ｄ変換器１０５に入力されＡ／Ｄ変換される。
【０１６８】
ここまでは、時系列でＲ、Ｇ、Ｂ信号が発生しているので、フレームメモリ１０６で、通常の映像信号の形式である３チャンネルの信号に変換する。フレームメモリ１０６からの信号は、Ｄ／Ａ変換器１０７でアナログＲＧＢ信号に変換されて出力され、ケーブル１０８を介してプロジェクタ２００に入力される。
【０１６９】
プロジェクタ２００は、本実施の形態の色補正回路２０１を入力段に設け、撮像装置１００から出力されるアナログＲＧＢ信号を受ける。色補正回路２０１で色補正された信号は、Ａ／Ｄ変換器２０２でＡ／Ｄ変換され、駆動回路２０３に入力される。駆動回路２０３は、Ａ／Ｄ変換器２０２からの信号により空間光変調素子２０４〜２０６、例えば、反射型の液晶パネルを駆動する。
【０１７０】
一方、空間光変調素子２０４〜２０６にはミラー２０８およびダイクロイックミラー２０９、２１０を介して光源２０７からの光が投射される。空間光変調素子２０４〜２０６は、光源２０７からの光を駆動回路２０３からの信号で変調し、ミラー２０８およびダイクロイックミラー２０９、２１０に戻し、レンズ２１１を介して、外部のスクリーン３０２に被写体３０１の像を投影する。
【０１７１】
このように本実施の形態のプロジェクタ２００は、強調させた方が望ましい被写体の色だけを強調する色補正装置２０１を使用しているので、表示効果の高い画像を投影することができる。
【０１７２】
上記例では、色補正画像をプロジェクタを用いて表示する場合について記載したが、特にこれに限定されず、モニタ、テレビジョン受像機、プラズマディスプレイ等、種々の表示装置に適用できることは言うまでもない。
【０１７３】
さらには、図１１より、容易に理解できるように、本発明は、撮像装置に対しても適用できる。この場合も、上記と同様に、撮像装置は、図１１に記載した面順次カメラに限定されず、電子スチルカメラ等その他の撮像装置であってもよい。
【０１７４】
さらには、本発明は、上記のような表示手段、撮像手段以外の、例えば、画像処理装置、パーソナルコンピュータ等のデータ処理装置に対しても適用できる。
【０１７５】
また、上記実施の形態においては、色差信号のレベルによる処理において、色差信号のレベルが大きいときの増幅度が、色差信号のレベルが小さい時の増幅度に比べて大きくなるような場合について説明したが、例えば、被写体が人物とチューリップの場合、チューリップの色はあまり変えないで、人肌を赤くしたいような場合には、上記説明とは逆に、色差信号のレベルが大きい時の増幅度を、色差信号のレベルが小さい時の増幅度に比べて小さくすればよい。これは、上記ルックアップテーブルを用いれば容易に実現することができる。この場合は、ホワイトバランス補正装置として機能させることもできる。
【０１７６】
以上、具体的な実施の形態について説明したが、かかる実施の形態が本発明の技術的範囲を限定するものではない。
【０１７７】
以上のような実施の形態によれば、色差信号を色差信号のレベルに応じて異なる増幅度で増幅する色差信号強調手段を有するので、色信号を部分的に増幅して出力することができる。従って、被写体の色を強調する場合に、強調させた方が望ましい被写体の色だけを強調することができる。即ち、淡い色の被写体で、そのままの色の方が望ましい場合はもとの色で出力され、色の濃い被写体はより強調されて出力される。
【０１７８】
また、本実施の形態によれば、増幅度又はしきい値は外部から可変できるので、強調する色差信号のレベルを変えることができる。従って、強調する度合いを、被写体の色や状況に応じて選択でき、表示効果を著しく向上させることができる。
【０１７９】
また、本実施の形態によれば、所定のレベル範囲の色差信号の通過を阻止し、所定のレベル範囲外の色差信号を通過させるコアリング回路を有するので、被写体の色差が小さい場合は入力レベルと同じレベルで出力し、被写体の色差が大きい場合は、その色を強調して出力することができる。
【０１８０】
また、本実施の形態によれば、コアリング回路の出力に含まれる高周波成分を遮断するローパスフィルタを有するので、表示する画像の画質を低下させるノイズ成分を除くことができる。
【０１８１】
本実施の形態のプロジェクタによれば、強調させた方が望ましい被写体の色だけを強調する色補正装置を使用しているので、表示効果の高い画像を投影することができる。
【０１８２】
【発明の効果】
以上説明した通り、本発明によれば、色信号を部分的に強調して出力することができる。従って、被写体の色を強調する場合に、強調させた方が望ましい被写体の色だけを強調することができる。
【０１８３】
また、本発明の表示装置は、強調させた方が望ましい被写体の色だけを強調する色補正装置を使用しているので、表示効果の高い画像を投影することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態の色補正装置の構成例である。
【図２】本発明の実施の形態の色差信号強調回路の入出力特性例である。
【図３】本発明の実施の形態で人肌を撮影する場合の信号例である。
【図４】本発明の実施の形態でチューリップを撮影する場合の信号例である。
【図５】本発明の実施の形態の色差信号強調回路の具体例である。
【図６】本発明の実施の形態のコアリング回路の入出力特性例である。
【図７】本発明の実施の形態のコアリング回路を使用する場合の信号例である。
【図８】本発明の実施の形態のコアリング回路の回路例である。
【図９】本発明の実施の形態の色差信号強調回路の別の具体例である。
【図１０】本発明の実施の形態のローパスフィルタの効果例である。
【図１１】本発明の実施の形態のプロジェクタの使用例である。
【図１２】本発明の実施の形態における被写体像の色差信号のヒストグラムである。
【図１３】本発明の実施の形態における色補正処理を行う動作を示すフローチャートである。
【図１４】本発明の実施の形態における色補正処理を行う動作を示すフローチャートである。
【図１５】本発明の実施の形態における色補正処理を行う動作を示すフローチャートである。
【図１６】本発明の実施の形態における色補正処理を行う動作を示すフローチャートである。
【図１７】本発明の実施の形態の色補正方法を用いる色補正装置の構成を示すブロック図である。
【図１８】本発明の実施の形態における色差信号と強調された色差信号の変換特性の例を示す図である。
【図１９】本発明の実施の形態における色差信号から強調された色差信号への変換特性がオンスクリーンディスプレイされた状態を示す図である。
【図２０】従来の色補正装置の構成図である。
【符号の説明】
１：マトリクス回路、３：加算器、４：色差信号強調回路４、５：ディレイライン、６：コアリング回路、７：増幅回路、８：加算器、５０１：Ａ／Ｄ変換器、５０２：メモリ部、５０３：Ｄ／Ａ変換器、５０４：ＣＰＵ、５０５：キーボード、５０６：ＲＡＭ、５０７：記憶媒体、５０８，５０９，５１０：端子、５１６：制御部、５１４，５１５：端子、５１７：オーバーレイメモリ、５１８：記憶媒体。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color correction method for correcting a color signal, a recording medium storing a program for executing the color correction method, a color correction device, and a display device.
[0002]
[Prior art]
In an imaging device that captures an image of a subject and outputs a video signal, or a display device that displays an input video signal on a monitor or screen, the red, green, and blue color signals included in the video signal are used to increase the display effect. A color correction device is used to correct the above.
[0003]
In this case, for example, if the red color signal is simply amplified in order to emphasize the red color of the tulip that is the subject, the red component of the other subject is also emphasized in the same way, and a white color is used to make the white subject appear white. The balance will be lost.
[0004]
Therefore, the following color correction device is used for white and black achromatic colors in order to emphasize the chromatic colors such as red and green without changing the white balance.
[0005]
FIG. 20 shows a configuration example of a conventional color correction apparatus. The matrix circuit 1 converts color difference signals RY and GI from three color signals that are input signals, that is, signals including red, green, and blue components (hereinafter referred to as R signal, G signal, and B signal). , B-Y and the luminance signal Y are generated.
[0006]
Here, the luminance signal Y is a signal obtained by weighting and adding the R signal, the G signal, and the B signal, and the color difference signals RY, G-Y, and BY are the respective color signals and luminance signals. This is the difference from Y. The luminance signal Y and the color difference signals R-Y, G-Y, and B-Y are expressed, for example, by Equation 1 shown below.
[Formula 1]
Y = 0.3R + 0.59G + 0.11B
RY = 0.7R-0.59G-0.11B
G-Y = -0.3R + 0.41G-0.11B
BY = -0.3R-0.59G + 0.89B
The color difference signals R-Y, G-Y, and B-Y obtained by the matrix circuit 1 are respectively input to the amplifier 2 and multiplied by appropriate coefficients a, b, and c. The color difference signals a (R−Y), b (G−Y), and c (B−Y) multiplied by a, b, and c are input to the adder 3 and output from the matrix circuit 1 respectively. And the enhanced color signals R ′, G ′, and B ′ are output. The emphasized color signals R ′, G ′, and B ′ at this time are shown in Equation 2.
[Formula 2]
R ′ = a (R−Y) + Y
G ′ = b (G−Y) + Y
B ′ = c (BY) + Y
Considering a case where a video signal of a reddish subject is input to the color correction apparatus, if the red color difference signal RY is positive and the amplification degree a of the amplifier 2 is greater than 1, the color is corrected. The signal R ′ is larger than the input color signal R and is emphasized. That is, when the difference between the color signal R ′ and the color signal R in Equation 2 is obtained,
[Formula 3]
R′−R = (a−1) (R−Y)
If RY> 0 and a> 1, then R ′> R, and the color signal R ′ is larger than the input color signal R and is emphasized.
[0007]
On the other hand, if the amplification signals a, b, and c of the amplifier 2 are larger than 1, the color signals R ′, G ′, and B ′ are input if the color signals R, G, and B are equal, that is, if they are achromatic colors. Equal to color signals R, G, B. That is, when R = G = B, the color difference signals RY, GY, BY are 0 from Equation 1, and the color signals R ′, G ′, B ′ are equal to the luminance signal Y. As described above, in the color correction apparatus of FIG. 20, when an achromatic color is input, an achromatic color equal to the luminance signal is output, and the white balance is not lost.
[0008]
[Problems to be solved by the invention]
However, the conventional color correction apparatus shown in FIG. 20 amplifies the color difference signal by multiplying it by a predetermined coefficient (amplification degree) regardless of the magnitude of the color difference signal. Emphasizes the color.
[0009]
For this reason, when both a tulip and a person are photographed as subjects, if the amplification degree a of the amplifier 2 is increased in order to emphasize the red color of the tulip, the red color of the tulip is emphasized but the human skin becomes too red. Become.
[0010]
On the other hand, if the amplification degree a is reduced in order to prevent the human skin from becoming red, the red of the tulip is not emphasized and the display effect is not improved.
[0011]
Further, in the case where the subject is a landscape and the image includes snow and lawn in the shade on a sunny day, or blue sky, it is preferable to emphasize the green of the lawn or blue of the blue sky, but the snow is preferably as white as possible. For this reason, it is better not to emphasize the green or blue component contained in the snow white, even though the green of the lawn or the blue of the blue sky is emphasized.
[0012]
Therefore, the present invention provides a color correction method capable of enhancing only the color of a subject that is desired to be emphasized when the color of the subject is emphasized, a recording medium storing a program for executing the color correction method, An object is to provide a color correction device and a display device.
[0013]
[Means for Solving the Problems]
In order to solve the above problems, the color correction method of the present invention is:
A first step of performing a non-linear operation with different multiplication coefficients on a plurality of color difference signals indicating a difference between the color signal and the luminance signal at at least two levels of the color difference signal;
A second step of adding the luminance signal to the result of the nonlinear calculation to obtain a corrected color signal;
including.
[0014]
Furthermore, a step of inputting conversion characteristics of the non-linear operation and / or parameters of the non-linear operation may be included.
[0015]
Further, a step of obtaining a color signal before correction after completion of the second step may be included.
[0016]
Further, the step of obtaining the color signal before correction may be based on any of the following (A) to (C).
(A) Acquire a color signal or a color difference signal again.
(B) Obtained by storing and reading out the color signal or color difference signal data before correction.
(C) The conversion characteristics, parameters, and luminance data at the time of correction are stored, and the result of color correction processing is reversed using the conversion characteristics, parameters, and luminance data. Perform the operation.
[0017]
Further, the luminance signal data is stored, and after the first color correction processing, the luminance signal data, the conversion characteristics and parameters in the first color correction processing are used to determine the luminance signal data. A step of obtaining a color difference signal before the first color correction processing and performing the second color correction processing based on the conversion characteristics and / or parameters in the second color correction processing based on the result is also included. Good.
[0018]
A step of storing data of the luminance signal;
After performing the first color correction processing, equivalently, color difference signal data before the first color correction is obtained based on the luminance signal data, and is the same as or different from the first color correction processing. A second color correction process having conversion characteristics and / or parameters may be performed.
[0019]
Further, the conversion characteristics and / or parameters of the nonlinear calculation may be set to be different depending on the area on the display screen of the display device.
[0020]
Further, the method may include a step of generating the color difference signal from the input image data, and a step of fixing the input image data before the step.
[0021]
The image data before color correction processing and the conversion characteristics and parameters in the color correction processing may be transferred to a removable storage medium or an external storage device.
[0022]
Further, the luminance signal or the image data may be compressed and stored in a reversible form.
[0033]
The color correction apparatus of the present invention is
First means for performing a non-linear operation with a different multiplication coefficient on at least two levels of the color difference signal on a plurality of color difference signals indicating a difference between the color signal and the luminance signal;
And a second means for adding the luminance signal to the result of the nonlinear calculation to obtain a corrected color signal.
[0034]
Furthermore, it may be configured to include means for inputting conversion characteristics of the nonlinear calculation and / or parameters of the nonlinear calculation.
[0035]
Further, it may be configured to have means for obtaining a color signal before correction after completion of the processing in the second means.
[0036]
The means for obtaining the color signal before correction may be any one of the following (A) to (C).
(A) Acquire a color signal or a color difference signal again.
(B) Obtained by storing and reading out the color signal or color difference signal data before correction.
(C) The conversion characteristics, parameters, and luminance data at the time of correction are stored, and the result of color correction processing is reversed using the conversion characteristics, parameters, and luminance data. Perform the operation.
[0037]
And a storage means for storing the luminance signal data. After the first color correction processing, the luminance signal data, conversion characteristics and parameters in the first color correction processing are provided. Thus, the color difference signal before the first color correction processing is obtained, and based on this result, the second color correction processing is performed by the conversion characteristics and / or parameters in the second color correction processing. It is good also as a structure which has 3 means.
[0038]
And storage means for storing data of the luminance signal,
After performing the first color correction processing, equivalently, color difference signal data before the first color correction is obtained based on the luminance signal data, and is the same as or different from the first color correction processing. A second color correction process having conversion characteristics and / or parameters may be performed.
[0039]
Further, the non-linear calculation conversion characteristics and / or parameters in the first means may be set differently depending on the area on the display screen of the display device.
[0040]
Further, it may have a color difference signal generating means for generating the color difference signal from the input image data, and a means for fixing the input image data before generating the color difference signal by the color difference signal generating means. .
[0041]
Further, the image data before the color correction process and the conversion characteristics and parameters in the color correction process may be provided with a transfer unit that transfers the data to a removable storage medium or an external storage device.
[0042]
The luminance signal or the image data may be stored after being compressed in a reversible transformable form.
[0043]
The color correction apparatus of the present invention is
A color correction device that receives three types of color signals including red, green, and blue components, and amplifies and outputs at least one type of the color signals,
Matrix means for outputting a luminance signal and at least one color difference signal obtained by subtracting the luminance signal from the color signal;
Color difference signal enhancement means for amplifying the color difference signal with a different amplification degree according to the level of the color difference signal;
An addition unit that adds the output from the color difference signal enhancement unit and the luminance signal is provided.
[0044]
The color correction apparatus of the present invention is
Color difference signal enhancement means for amplifying the color difference signal at different amplification levels according to the levels of a plurality of color difference signals indicating differences between three color signals including red, green, and blue components and a luminance signal, and the color difference signal enhancement Adding means for adding the output from the means and the luminance signal to output an amplified color signal;
It is the structure which has.
[0046]
Further, the color difference signal emphasizing means may have a configuration in which the degree of amplification differs at at least two levels of the color difference signal.
[0048]
Further, the color difference signal emphasizing means prevents corrosion of the color difference signal in a predetermined level range, and allows coring means to pass the color difference signal outside the predetermined level range;
Amplifying means for amplifying the output of the coring means;
It is good also as a structure which has the 2nd addition means which adds the output of the said amplification means, and the said color difference signal.
[0052]
The display device of the present invention is a display device that receives an image signal of a captured subject and displays the image of the subject, and includes any one of the color correction devices described above.
[0053]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0054]
The color difference signals RY, G-Y, and BY are multiplied by different coefficients depending on their levels, and the color difference signals R-Y, G-Y, BY are partially enhanced (R--). Y) ′, (G−Y) ′, and (B−Y) ′ are obtained.
[0055]
The partially enhanced color difference signals (R−Y) ′, (G−Y) ′, and (B−Y) ′ are added to the luminance signal Y, respectively, and the partially enhanced color signals R ″ and G Find ", B".
[0056]
The partially emphasized color signals R ″, G ″, B ″ are shown in [Formula 4].
[0057]
[Formula 4]
R ″ = (R−Y) ′ + Y
G "= (G−Y) ′ + Y
B "= (BY) '+ Y
18A to 18D show the color difference signals R-Y, G-Y, and BY and the partially enhanced color difference signals (R-Y) 'and (G-Y). It is a figure which shows the example of the conversion characteristic of ', (BY)'. In FIG. 18, the horizontal axis indicates the color difference signal (for example, RY) of each color, and the vertical axis indicates the color difference signal (for example, (RY) ′) of each color that is partially enhanced.
[0058]
In FIG. 18A, p and q on the horizontal axis indicate points at which the coefficient (gradient of the graph) at the time of multiplication is changed. If the color difference signal RY is positive, it is higher than the threshold value p. If the part is negative, the multiplication coefficient is larger in the part lower than the threshold value q. Note that the absolute values of p and q need not be equal.
[0059]
That is, the multiplication coefficient between p and q is A (for example, 1), but the multiplication coefficient outside the range is B (for example, 2). Accordingly, the image of the brightly colored part becomes more vivid, and the non-vivid part remains as it is and a natural image can be obtained.
[0060]
FIG. 18B has conversion characteristics in which the multiplication coefficient changes continuously according to the color difference signal level. That is,
[Formula 6]
(R−Y) ′ = C (R−Y) ^ X
(G−Y) ′ = C (G−Y) ^ X
(BY) '= C (BY) ^ X
(^ Indicates a power, a ^ X indicates a to the X power. X is a number other than 1 or 0. However, when X is an even number, (R−Y), (G−Y), (B− When Y) is negative, C = −1, when (R−Y), (G−Y), and (B−Y) are positive, C = 1, and when X is an odd number, C = 1)
As described above, the conversion characteristic of outputting the X power of the color difference signal is provided. In this case, the degree of the emphasized color gradually changes, and a natural image can be obtained from FIG.
[0061]
For example, when a plurality of conversion characteristic examples of the color difference signal and the partially emphasized color difference signal are prepared as described above, one of the conversion characteristics is selected, and the threshold is selected. The values p and q and the slope of the conversion characteristic graph, or the value of X are set. This setting may be selected from those set as defaults even if the user sets numerical values.
[0062]
Thereby, the conversion characteristic from the color difference signal to the partially enhanced color difference signal is determined.
[0063]
Next, the case of actually correcting the color of an image will be described with reference to FIGS. 3 and 4 and Table 1. FIG.
[0064]
[Table 1]

FIG. 3 shows an example of the signal value of the human skin portion in the image, and FIG. 4 shows an example of the signal value of the tulip portion in the image.
[0065]
Table 1 is an example of R, G, B signal values and color difference signal values for each image. Note that, when performing computation in digital signal processing, the signal value is represented by a digital value, but in the following description, it is described as a relative value for simplicity.
[0066]
FIG. 3A shows R, G, and B signal values of the human skin region of the image. As shown in Table 1, the respective signal values are R = 0.81, G = 0.57, and B = 0.47.
[0067]
FIG. 3B shows color difference signals RY, G-Y, and BY calculated based on [Equation 1], and the respective values are represented by RY = 0 as shown in Table 1. .18, GY = −0.06, BY = −0.16. The luminance signal Y is 0.63 from [Equation 1].
[0068]
Here, it is assumed that the user has selected the conversion characteristics shown in FIG. 18A as the conversion characteristics of the color difference signal and the partially emphasized color difference signal. Rp and Rq for the red color difference signal RY, Gp and Gq for the green color difference signal GY, and Bp and Bq for the blue color difference signal BY, for example, take the following values: Shall.
[Formula 5]
Rp = 0.2, Rq = −0.13
Gp = 0.03, Gq = −0.1
Bp = 0.2, Bq = −0.3
The levels of the points p and q in each color difference signal are indicated by broken lines in FIG. Also, the multiplication factor (gradient in the conversion characteristic) of the conversion characteristic is 1 for the conversion characteristic of each color difference signal from the point p to the point q, and 2 outside that range. In the above example, each of p and q is defined. However, it is not necessary to specify both p and q, and only one of p or q may be defined.
[0069]
In this case, the color difference signal values RY, GY, and BY of the human skin portion are between the above points p and q, and thus the multiplication coefficient is 1.
[0070]
That is, the emphasized color difference signal values (R−Y) ′, (G−Y) ′, and (B−Y) ′ are expressed as shown in FIG.
(R−Y) ′ = 0.18
(G−Y) ′ = − 0.06
(BY) ′ = − 0.16
And become values equal to (R−Y), (G−Y), and (B−Y), respectively.
[0071]
The values of the emphasized color signals R ″, G ″, B ″ are calculated as shown below from [Equation 1].
R "= 0.81
G "= 0.57
R "= 0.47
That is, it becomes equal to the values of R, G, and B, and it can be seen that the color enhancement processing is not substantially performed.
[0072]
On the other hand, FIG. 4 shows an example of signal values in the tulip region of the image, and FIG. 4A shows R, G, and B signal values in the region. As shown in Table 1, the respective signal values are R = 0.81, G = 0.27, and B = 0.33.
[0073]
FIG. 4B shows the color difference signals RY, G-Y, and BY calculated based on [Equation 1], and the respective values are as shown in Table 1.
R−Y = 0.37, G−Y = −0.17, B−Y = −0.11
It becomes. The luminance signal Y is 0.44 from [Equation 1].
[0074]
Here, assuming that the conversion characteristics of the color difference signal and the partially enhanced color difference signal are the same as those described above, for example, the red color difference signal value RY is Rp = 0.2. As shown in FIG. 18A, the excess color 0.17 from Rp is multiplied by the multiplication coefficient 2, and the emphasized color difference signal value (RY) ′ is 0.54. .
[0075]
Also, the green color difference signal value G−Y shown in FIG. 4B has a higher level in the negative direction than Gq = −0.1. Therefore, as shown in FIG. 4C, the emphasized color difference signal value (G−Y) ′ is −0.24 by multiplying the excess −0.07 from Gq by the multiplication coefficient 2. .
[0076]
On the other hand, since the blue color difference signal value BY is between the threshold values Bp and Bq, the enhanced color difference signal value (BY) ′ remains −0.11.
[0077]
FIG. 4D shows the emphasized color signal values R ″, G ″, and B ″.
[0078]
R ″ is 0.98 by adding the luminance signal value Y = 0.44 to the enhanced color difference signal value (R−Y) ′ = 0.54, and G ″ is the enhanced color difference signal value (G The luminance signal value Y = 0.44 is added to −Y) ′ = − 0.24 to be 0.2. On the other hand, the luminance signal value Y = 0.44 is added to the emphasized color difference signal value (B−Y) ′ = − 0.11 and B ″ is the same as the color signal value B, that is, 0.33.
[0079]
As described above, in the case of the conversion characteristics shown in FIG. 18A, when the color difference of the image is small, such as human skin, that is, the signal values of R, G, and B are close to each other, The signal value does not change.
[0080]
On the other hand, when the color difference of the image is large as in the case of Tulip, that is, the difference between the R, G, and B signal values is large, it can be seen that the color is emphasized for a color close to a chromatic color.
[0081]
Next, the threshold values p and q in FIG.
[0082]
Consider the case where the subject shown in Table 1 exists in one image.
[0083]
For example, the histogram of the image of the color difference signal RY is as shown in FIG. The horizontal axis indicates the color difference signal value, and the vertical axis indicates the number of pixels. Here, the histogram of each region expands and the height varies depending on the size of the subject region in the image and the monochromaticity of each subject region.
[0084]
The value of the threshold value p is set between a color area to be emphasized and an adjacent area on the histogram. For example, when only the red of the tulip is desired to be emphasized for the R color, it is set to a certain value between the tulip and the human skin region of FIG.
[0085]
On the other hand, the value of the threshold value q is set between an area whose amount is to be reduced and an adjacent area on the histogram. For example, when it is desired to slightly reduce the amount of the R color only in the blue sky region, a certain value between the blue sky region and the sunny shaded snow region in FIG. 12 is set.
[0086]
Here, when the above regions are not clearly separated, the continuous conversion characteristic as shown in FIG. 18B is more preferable than the discontinuous conversion characteristic as shown in FIG. Is suitable.
[0087]
Further, by converting the color difference signal as shown in FIG. 18C to an enhanced color difference signal, only the white balance of the portion close to the achromatic color is slightly shifted, and the color characteristic of the chromatic color portion is The case where it is desired to keep it as it is can be dealt with. However, since there are discontinuous portions in this characteristic, it is desirable to have a conversion characteristic as shown in FIG. In this case, as will be described later, when the color enhancement process is performed again, since the input / output relationship is not determined at 1: 1, the image data before the color correction process is stored. Otherwise, it may be inconvenient.
[0088]
FIG. 17 shows a block diagram of a system that performs the above color enhancement processing.
[0089]
Analog R, G, and B video signals input from terminals 508, 509, and 510 are converted into digital signals by an A / D converter 501. The control unit 516 configures a PLL and controls each block based on horizontal (HD) and vertical (VD) synchronization signals input from terminals 514 and 515.
[0090]
The R, G, B video signals digitized by the A / D converter 501 are written in the memory unit 502. The memory unit 502 is connected to the D / A converter 503. The digital video signal read from the memory unit 502 is converted into an R, G, B analog video signal by a D / A converter 503 and output to a display device, an image forming device, etc. (not shown).
[0091]
Here, the memory unit 502 can be subjected to freeze and through control of the memory unit 502 via the control unit 516 by the CPU 504. Specifically, the control unit 516 prohibits the writing of data to the memory unit 502 according to a command from the CPU 504, thereby freezing the output image and continuously allowing the writing to the memory unit 502. This makes the output image through. Note that image data is always read from the memory unit 502.
[0092]
The D / A converter 503 is connected to the overlay memory 517. The overlay memory 517 stores on-screen display data. The stored on-screen data is output to the D / A converter 503 based on a command from the CPU 504. In this manner, the digital video signal and the on-screen display data stored in the overlay memory 517 are mixed by the D / A converter 503.
[0093]
The memory unit 502 is also connected to a RAM 506 that is a working memory of the CPU 504. The CPU 504 is also connected to a keyboard 505 and a storage medium 507 for storing a program for performing the color correction process.
[0094]
FIG. 13 is a flowchart showing the operation for performing the color correction process.
[0095]
First, in step S101, a command for freezing an image is input from the keyboard 505 to the CPU 504. In response to this command, the CPU 504 sends a freeze control signal to the control unit 516. The control unit 516 prohibits writing of digital data to the memory unit 502.
[0096]
In step S102, the conversion characteristic from the color difference signal to the emphasized color difference signal is displayed on the screen as shown in FIG. 19, for example, and this is displayed by a keyboard 505 or a pointing device such as a mouse (not shown). Select one of them. At this time, if it is necessary to set a parameter, the parameter is also set by a keyboard 505 or a pointing device such as a mouse.
[0097]
In step S103, the digital image data is transferred from the memory unit 502 to the RAM 506. In step S <b> 103 ′, the CPU 504 sequentially performs the calculation of [Equation 10] for one screen using the digital image data transferred to the RAM 506 and writes the calculation result in the RAM 506.
[Formula 10]
R ″ = h (R−Y) + Y
G ″ = j (G−Y) + Y
B "= k (BY) + Y
(H (R−Y), j (G−Y), and k (B−Y) represent functions of (R−Y), (G−Y), and (B−Y), respectively)
At this time, luminance (Y) data is also stored in the RAM 506 as necessary. The storage in the RAM 506 may compress the luminance (Y) data. However, in order to improve the quality of the reproduced image when the color enhancement process is performed again, it can be reversibly converted (Lossless). It is desirable to use compression.
[0098]
In step S104, the calculation result stored in the RAM 506 according to [Equation 10] is transferred to the memory unit 502.
[0099]
In the above description, the RAM 506 has a storage capacity for one screen of data. However, the RAM 506 has a small capacity, and the memory unit 502 transfers a predetermined amount of image data smaller than the data amount of one screen to the RAM 506. The CPU 504 may transfer the data to the memory unit 502 after completing the calculation for the predetermined amount of image data. This process is repeated for image data for one screen.
[0100]
In step S105, the output image is confirmed, and if a desired effect is obtained, the color enhancement process is terminated. At this time, if a desired effect cannot be obtained, image data before the first color correction process is required to perform the color correction process again. In order to obtain this image data, the freeze state is canceled by an input from the keyboard 5, and once returned to the through state (step S201) and then again frozen (step S101), color enhancement processing is performed. What is necessary is just to acquire the image data before performing.
[0101]
In order to perform color correction processing again, a storage area for storing image data before color correction processing is secured in the memory unit 502 or the RAM 506, and image data before color correction processing is stored in this area. -Data (R, G, B, or RY, G-Y, BY) may be stored and used for the second and subsequent conversion characteristics and processing after parameter setting (steps S103-). . The operation in this case is shown in the flowchart of FIG.
[0102]
14, S101 and S102 are the same as those in FIG. 13, and the digital image data transferred from the memory unit 502 to the RAM 506 is stored in the RAM 506 in step S103a. In the second and subsequent steps S103b, the data used for the calculation by the CPU 504 is the data transferred from the memory unit 502 during the previous color correction process (that is, the image data stored in the previous step S103b). . S103′S104 and S105 are the same as those in FIG.
[0103]
In this case, no data is transferred from the memory unit 502 to the RAM 506 in the second and subsequent color correction processes. The image data before color correction processing stored in the RAM 506 becomes unnecessary when step S105 is affirmed.
[0104]
Further, the inverse calculation of [Equation 10] is performed from the image data (R ″, G ″, B ″) that has been subjected to color correction processing, and image data (R, G before being subjected to color correction processing). , B, or R-Y, G-Y, B-Y), and this image data (R, G, B, or R-Y, G-Y, B-Y) However, this inverse operation requires conversion characteristics, parameters, and luminance (Y) data in the previous color correction process, so that the previous color enhancement is performed. The conversion characteristics, parameters, and luminance data (Y) in the processing must be stored in, for example, the RAM 506. The operation in this case is shown in the flowchart of FIG.
[0105]
15, S101, S102, 103 ′, S104, and S105 are the same as those in FIG. In step S103c, the conversion characteristics, parameters, and luminance data (Y) in the color enhancement process are stored in the RAM 506.
[0106]
The above inverse operation is performed in step S203. More specifically, the luminance (Y) data stored in the RAM 506 is subtracted from the color-corrected R ″, G ″, B ″ obtained by the previous color correction process, and h (R−Y ), J (G−Y), k (B−Y) Since the color difference signal partially enhanced in each conversion characteristic of the color enhancement processing is determined in a one-to-one relationship by the color difference signal. , R-Y, G-Y, and BY can be obtained (however, if the characteristics shown in FIGS. 18C and 18D are selected in the previous color correction process, the output and input are Since there is a case where there is no one-to-one correspondence, there is a case where one input cannot be defined for one output, and therefore such a method cannot be used.
RY, GY, and BY obtained in this way are stored in the RAM 506 and used for the next color correction process. (Step S103′c)
The luminance (Y) image data, conversion characteristics, and parameters before the color correction processing stored in the RAM 506 are not required when step S105 is affirmed.
[0107]
In the above description, when color enhancement processing is performed again, an example in which image data before the previous color enhancement processing is equivalently restored once is shown.
[0108]
Apart from this, when the image data that has been subjected to color correction processing is subjected to another or the same conversion characteristic and / or parameter color correction processing, the previous color correction processing is particularly important. It is not necessary to store and restore the image data before performing the operation. The operation in this case is shown in the flowchart of FIG.
[0109]
In step S105 for confirming the output image, if additional color correction processing needs to be performed again, conversion characteristics and / or parameters in the additional color correction processing are set in step S204. In step 103 ′, color correction processing based on the setting in step S204 is performed on the result obtained in the previous color correction processing. Other steps are the same as those in FIG.
[0110]
A storage medium 518 in FIG. 17 is a storage medium such as a PC card or a server memory, for example. The image data compressed as necessary, the conversion characteristics set in step S102, and the necessity. The parameters set accordingly are stored.
[0111]
When this image data is reproduced again, the compressed image data is decompressed as necessary, and color enhancement processing is performed by the CPU 504 based on the conversion characteristics and parameters stored together. In this case, image data is stored in the storage medium 518, and the result calculated by the CPU 504 is transferred from the RAM 506 to the memory unit 502.
[0112]
The above compression is desirably lossless in order to improve the quality of the reproduced image.
[0113]
However, when the image data stored in the storage medium 518 is image data after color correction processing, this is not particularly limited, and storage of conversion characteristics, parameters, and the like is not necessary. Become.
[0114]
In the above embodiment, the color enhancement processing is performed with the same conversion characteristics and parameters for the entire area of the screen. However, the screen is divided into a plurality of areas, and different conversion characteristics for each divided area. And / or color enhancement processing may be performed using parameters. In this case, as described above, it may be necessary to store conversion characteristics and / or parameters for each region.
[0115]
In the above description, an example in which R, G, and B signal values are given and the respective color difference signals are calculated from the R, G, and B signal values has been shown. However, the present invention also applies to cases where other signals such as the respective color difference signals and composite signals are given. The invention can be applied.
[0116]
The procedure of the color correction method described above is stored in the storage medium 507 as a computer program readable by the CPU 504, and the CPU 504 reads this program from the storage medium 507 and executes it.
Another embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a configuration example of a color correction apparatus according to an embodiment of the present invention.
[0117]
The matrix circuit 1 generates the luminance signal Y and the color difference signals RY, G-Y, and BY shown in Expression 1 from the R signal, the G signal, and the B signal that are input signals, and the color difference signal RY. , G-Y and BY are output to the color difference signal enhancement circuit 4.
[0118]
The color difference signal enhancement circuit 4 is an amplifier having different amplification degrees depending on the level of the input color difference signal, and a color difference signal (RY) in which the color difference signals RY, GY, BY are partially enhanced. ) ′, (G−Y) ′, and (B−Y) ′.
[0119]
The partially enhanced color difference signals (R−Y) ′, (G−Y) ′, and (B−Y) ′ are respectively input to the adder 3 and added to the luminance signal Y output from the matrix circuit 1. Is done. The adder 3 outputs partially emphasized color signals R ″, G ″, B ″ from these signals. These partially enhanced color signals R ″, G ″, B ″ are expressed in Equation 4. Obtained on the basis.
[0120]
FIG. 2 shows an example of input / output characteristics of the color difference signal emphasizing circuit 4 according to the embodiment of the present invention, in which a red color difference signal RY is input. In FIG. 2, the horizontal axis represents the input red color difference signal RY, and the vertical axis represents the enhanced color difference signal (RY) ′ that is the output. Further, p and q on the horizontal axis indicate threshold values at which the amplification degree changes. In this case, p = 0.3 and q = −0.3.
[0121]
As shown in FIG. 2, the color difference signal emphasizing circuit 4 has a higher degree of amplification in a portion higher than the threshold value p if the color difference signal RY is positive and in a portion lower than the threshold value q if it is negative. That is, the amplification degree between p and q is A (for example, 1), but the amplification degree outside the range is B (for example, 2). Therefore, the image of the brightly colored part in the screen becomes more vivid, and the natural part of the image is obtained without changing the non-brilliant part.
[0122]
Next, a case where a specific subject color is corrected by the color correction apparatus according to the present embodiment will be described with reference to FIGS. 3 and 4 and Table 1. FIG. FIG. 3 shows a signal example when photographing human skin, and FIG. 4 shows a signal example when photographing a tulip. Table 1 is an example of R, G, B signal and color difference signal values for each subject.
[0123]
FIG. 3A shows R, G, and B signals input to the color correction apparatus when the subject is human skin. The value of each signal is shown in Table 1,
R = 0.81, G = 0.57, B = 0.47
It is.
[0124]
FIG. 3B shows the color difference signals R-Y, G-Y, BY output from the matrix circuit 1 of the color correction apparatus, and the respective values are as shown in Table 1.
R−Y = 0.18, G−Y = −0.06, B−Y = −0.16
It becomes. Note that the luminance signal Y is 0.63 from Equation 1.
[0125]
Here, the threshold values p and q which are the threshold values in FIG. 2 are Rp and Rq for the red color difference signal RY, and Gp, Gq and blue color difference signals for the green color difference signal G-Y. For B−Y, Bp and Bq are assumed, for example, the values shown in Equation 5 are assumed.
[0126]
The levels at points p and q in each color difference signal are indicated by dotted lines in FIG. Similarly to FIG. 2, the color difference signal emphasizing circuit 4 sets the amplification degree between points p and q to 1 for each color difference signal, and sets the amplification degree outside the range to 2.
[0127]
When the levels of the p point and the q point are as shown in FIG. 3B, the color difference signals RY, GY, and BY of the human skin are between the p point and the q point described above. It is output from the color difference signal enhancement circuit 4 at a degree of 1.
[0128]
That is, the color difference signals (R−Y) ′, (G−Y) ′, and (B−Y) ′ that are the outputs of the color difference signal enhancement circuit 4 are as shown in FIG.
(R−Y) ′ = 0.18
(G−Y) ′ = − 0.06
(BY) ′ = − 0.16
It is equal to the input color difference signals (R−Y), (G−Y), and (B−Y).
[0129]
The color difference signals (R−Y) ′, (G−Y) ′, and (B−Y) ′ are added by the adder 3 to the luminance signal Y = 0.63. Therefore, the color signals R ″, G ″, B ″, which are the outputs of the color correction device, are as shown in FIG.
R "= 0.81
G "= 0.57
B "= 0.47
Thus, the input color signals R, G, and B are output as they are.
[0130]
FIG. 4 is an example of a signal when the subject is a tulip, and FIG. 4A shows R, G, and B signals input to the matrix circuit 1. The value of each signal is shown in Table 1,
R = 0.81, G = 0.27, B = 0.33
It is.
[0131]
FIG. 4B shows the color difference signals RY, GY, and BY output from the matrix circuit 1, and the respective values are as follows.
RY = 0.37
G−Y = −0.17
BY = −0.11
It is. The luminance signal Y is 0.44 from Equation 1.
[0132]
Here, if the p point and the q point, which are threshold values of the color difference signal enhancement circuit 4, are the values of Expression 5, the red color difference signal RY has a higher level than Rp = 0.2. Therefore, the output of the color difference signal emphasizing circuit 4 is obtained by amplifying the excess 0.17 from Rp with an amplification factor of 2 to 0.34 as shown in FIG. When added with 2, the enhanced color difference signal (RY) ′ is 0.54.
[0133]
Further, the green color difference signal G-Y shown in FIG. 4B has a higher level in the negative direction than Gq = −0.1. Therefore, as shown in FIG. 4C, the emphasized color difference signal (G−Y) ′ is obtained by amplifying an excess −0.07 from Gq with an amplification factor of −2 to −0.14. -0.1 output at 1 is added to -0.24.
[0134]
On the other hand, since the blue color difference signal BY is between Bp and Bq, the color difference signal (BY) ′ that is the output of the color difference signal enhancement circuit 4 remains −0.11.
[0135]
FIG. 4D shows the output of the color correction apparatus. The color signal R ″ becomes 0.98 by adding the luminance signal Y = 0.44 to the color difference signal (RY) ′ = 0.54, and the color signal G ″ becomes the color difference signal (G−Y) ′ = The luminance signal Y = 0.44 is added to −0.24 to become 0.2. On the other hand, the luminance signal Y = 0.44 is added to the color difference signal (BY) ′ = − 0.11 and the color signal B ″ is output at the same level as the input color signal B, that is, 0.33. .
[0136]
As described above, in the color correction apparatus according to the present embodiment, when the color difference of the subject is small, such as human skin, that is, the levels of the R, G, and B signals are close to each other, and the color that gives a light impression is the input level. Output at the same level. On the other hand, when a subject has a large color difference, such as a tulip, that is, a color that has a large level difference between R, G, and B signals and gives a relatively vivid impression, the color is emphasized and output.
[0137]
In the example of the input / output characteristics of the color difference signal emphasizing circuit 4 in FIG. 2, the amplification degree is different at the p point and the q point. However, the amplification degree may be continuously changed according to the input level of the color difference signal. Good. That is,
[Formula 6 ']
(R−Y) ′ = (R−Y) ^ 3
(G−Y) ′ = (G−Y) ^ 3
(BY) '= (BY) ^ 3
(A ^ 3 indicates the cube of a)
As in the above, it may be a characteristic that outputs the cube of the input signal. In this case, the degree of the emphasized color gradually changes, and a more natural image can be obtained.
[0138]
FIG. 5 is a specific example of the color difference signal enhancement circuit 4 shown in FIG. 1 and shows a case where the red color difference signal RY is enhanced. The color difference signal RY is input to the coring circuit 6 and the delay line 5 that gives a predetermined delay time to the color difference signal RY.
[0139]
The coring circuit 6 has, for example, the input / output characteristics shown in FIG. 6, and cuts off the input signal when the input signal is within a predetermined level range, that is, between the p point and the q point that are the coring level. When the input signal is outside the predetermined level range, that is, outside the range between the p point and the q point, a signal is output. In this case, if the coring levels p and q can be set from the outside, the level of the color difference signal to be emphasized can be changed. For example, if the p point level is set low, even a relatively light color can be emphasized. The signal passing through the coring circuit 6 is amplified by the amplification circuit 7 having the amplification degree A, and is added to the color difference signal RY passing through the delay line 5 by the adder 8 to enhance the color difference signal (RY). 'Become.
[0140]
Further, the functions of the coring circuit 6, the amplifier circuit 7, and the adder 8 shown in FIG. 5 may be realized using a look-up table. In this case, the function of the delay line 5 becomes unnecessary. For example, the look-up table is composed of a rewritable memory. A value of (R−Y) is input to each address of the memory, and each data part of the corresponding address of the memory has (R−Y). (R−Y) ′ calculation result is input.
[0141]
For example, assuming that (R−Y) is 8-bit digital data and (R−Y) ′ is 8-bit digital data, the capacity of the memory constituting the lookup table is 8 bits of address, 8 bits of data. A bit is required.
[0142]
Here, when p, q, and A shown in FIG. 5 are changed, the data portion of the memory constituting the lookup table may be rewritten.
[0143]
Further, using a memory having a capacity that is an integral multiple of the above capacity, some data when the above p, q, and A are changed are stored in the data portion of the memory, and a part of the address of the memory is used. This may be selected.
[0144]
When the data portion of the memory is rewritten, for example, the calculation of data is performed by a CPU, DSP, etc., and the calculation result is written into the data portion of the memory.
[0145]
When the above function is achieved using a look-up table, there is an advantage that leakage of high frequency components described later does not occur.
[0146]
Further, the amplification degree A of the amplifier circuit 7 may be set from the outside. In this case, when it is not desired to emphasize the color, for example, the amplification degree A can be set low for a color that becomes too bright when emphasized with high luminance.
[0147]
FIG. 7 is a signal example when the color difference signal enhancement circuit 4 shown in FIG. 5 is used. Here, FIGS. 7A and 7B are similar to FIGS. 4A and 4B in that the R, G, and B signals and the color difference signals RY, GY, and B− when the subject is a tulip are used. Y is shown. In FIG. 7B, the coring levels Rp, Rq, etc. are the same as the values shown in Equation 5.
[0148]
When the color difference signals R-Y, G-Y, and BY are input to the coring circuit 6, the coring circuit 6 outputs a signal outside the range of the coring level as shown in FIG. 7C. . That is, the color difference signal R-Y is 0.17, and the color difference signal G-Y is -0.07. On the other hand, the color difference signal BY is within the range of the coring level and becomes zero.
[0149]
The output of the coring circuit 6 is amplified as shown in FIG. 7D by the amplification circuit 7 having an amplification factor of 2, for example, so that the color difference signal RY becomes 0.34 and the color difference signal G-Y becomes -0.14. Become. On the other hand, the color difference signal BY remains 0.
[0150]
The output of the amplifier circuit 7 is added to the input color difference signal that has passed through the delay line 5 by the adder 8. Therefore, as shown in FIG. 7E, the output of the color difference signal enhancement circuit 4 has a color difference signal (RY) ′ of 0.71 and a color difference signal (G−Y) ′ of −0.31. On the other hand, the color difference signal (BY) ′ remains at −0.11 as in FIG. 7B.
[0151]
FIG. 7F shows the output of the color correction apparatus. As shown in FIG. 1, the output of the color correction device is obtained by adding the output of the color difference signal enhancement circuit 4 and the luminance signal Y = 0.44, and the color signals R ″, G ″, B ″ are 1.15, 0, respectively. .13, 0.33.
[0152]
As described above, even in the color correction apparatus using the coring circuit 6, when the color difference of the subject is small, it is output at the same level as the input level, and when the color difference of the subject is large, the color is emphasized and output.
[0153]
FIG. 8 shows a circuit example of the coring circuit 6 of the present embodiment. Here, the voltage input to the input terminal 15 of the coring circuit 6 is V1, and the voltage output from the output terminal 34 of the coring circuit 6 is V4. The output voltage of the operational amplifier 22 in the coring circuit 6 is V2, the output voltage of the operational amplifier 29 is V3, and the forward voltage Vf of the diode 17 and the diode 24 (hereinafter referred to as D17 and D24) is 0.7V. To do.
[0154]
When the voltage at the positive terminal of the operational amplifier 22 is Va ′, D17 is turned on when the input voltage V1 is equal to or higher than (Va ′ + 0.7), and the gain of the operational amplifier 22 at that time is R19 / Given by R18.
[0155]
Further, when the input voltage V1 is smaller than (Va ′ + 0.7), D17 is off and the gain of the operational amplifier 22 is 0. Therefore, the operational amplifier 22 is less than (Va ′ + 0.7) of the input voltage V1. A large part can be taken out.
[0156]
On the other hand, when the voltage at the plus terminal of the operational amplifier 29 is Vb ′, D24 is turned on when the input voltage V1 is (Vb′−0.7) or less, and the gain at that time is R26 / R25. Given in.
[0157]
Further, when the input voltage V1 is higher than (Vb′−0.7), D24 is off and the gain of the operational amplifier 29 becomes 0. Therefore, the operational amplifier 29 has (Vb′−0.7) of the input voltage V1. ) A smaller part can be taken out.
[0158]
Furthermore, since the polarities of the output voltages V2 and V3 of the operational amplifiers 22 and 29 are inverted with respect to the input voltage V1, if the operational amplifier 33 inverts while adding V2 and V3, the input / output shown in FIG. Characteristics are obtained.
[0159]
The voltages Va ′ and Vb ′ at the positive terminals of the operational amplifiers 22 and 29 are obtained by supplying the power supply voltages Va and Vb to the terminals 16 and 23 and dividing them by the resistors R20, 21, 27, and 28. In this case, Va ′ and Vb ′ are fixed values.
[0160]
On the other hand, when Va ′ and Vb ′ are varied from the outside, control means for generating an arbitrary voltage is connected to the terminals 16 and 23. Alternatively, this control means may be directly connected to the plus terminals of the operational amplifiers 22 and 29.
[0161]
The points p and q shown in FIG. 2 are set by the above means. In the coring circuit 6 of FIG. 8, (Va ′ + 0.7) becomes p point and (Vb′−0.7) becomes q point. It becomes.
[0162]
FIG. 9 is another specific example of the color difference signal enhancement circuit 4 according to the embodiment of the present invention. Since the coring circuit 6 used in the color difference signal enhancement circuit 4 in FIG. 5 partially cuts out the signal, the high frequency components of the color difference signal often leak.
[0163]
In order to cancel the leaked high-frequency component, a low-pass filter 9 for blocking the high-frequency component is inserted between the coring circuit 6 and the amplifier circuit 7 as shown in FIG. Since the color resolution at high frequencies is low in human vision, the noise component that degrades the image quality can be removed without degrading the display effect by inserting the low-pass filter 9.
[0164]
FIG. 10 shows an effect example of the low-pass filter 9 according to the embodiment of the present invention. FIG. 10A shows a color difference signal input to the coring circuit 6. FIG. 10B shows the output of the coring circuit 6. As described above, the coring circuit 6 leaks a high-frequency signal at the edge portion of the signal where the signal rapidly changes.
[0165]
FIG. 10C shows the output of the low-pass filter 9. Since the low-pass filter 9 blocks the high-frequency component of the signal, the high-frequency component included in the color difference signal is prevented from leaking to the outside, and a high-quality image can be displayed.
[0166]
FIG. 11 shows a block diagram of a projector 200 to which the present invention can be applied, together with a block diagram of the imaging apparatus 100. In FIG. 11, an image capturing apparatus 100 is a document image capturing apparatus that mainly captures a still image, and condenses light from a subject 301 through a lens 101. The light that has passed through the lens 101 is color-separated into red, green, and blue light for each field by a color separation filter 102 that is divided into three red, green, and blue filter portions, and photoelectrically converted by the CCD 103. .
[0167]
The R signal, the G signal, and the B signal converted into electric signals by the CCD 103 are subjected to processing such as white balance and gamma conversion by the signal processing circuit 104, and input to the A / D converter 105 for A / D conversion. .
[0168]
Up to this point, since R, G, and B signals have been generated in time series, the frame memory 106 converts the signals into a three-channel signal that is a normal video signal format. A signal from the frame memory 106 is converted into an analog RGB signal by the D / A converter 107 and output, and then input to the projector 200 via the cable 108.
[0169]
The projector 200 is provided with the color correction circuit 201 of this embodiment in the input stage, and receives an analog RGB signal output from the imaging apparatus 100. The signal color-corrected by the color correction circuit 201 is A / D converted by the A / D converter 202 and input to the drive circuit 203. The drive circuit 203 drives the spatial light modulation elements 204 to 206, for example, a reflection type liquid crystal panel, with a signal from the A / D converter 202.
[0170]
On the other hand, light from the light source 207 is projected onto the spatial light modulation elements 204 to 206 via the mirror 208 and the dichroic mirrors 209 and 210. The spatial light modulators 204 to 206 modulate the light from the light source 207 with the signal from the drive circuit 203, return it to the mirror 208 and the dichroic mirrors 209 and 210, and pass the object 301 onto the external screen 302 via the lens 211. Project an image.
[0171]
As described above, since the projector 200 according to the present embodiment uses the color correction device 201 that emphasizes only the color of the subject that should be emphasized, an image with a high display effect can be projected.
[0172]
In the above example, the case where the color correction image is displayed using a projector has been described. However, the present invention is not particularly limited thereto, and it goes without saying that the present invention can be applied to various display devices such as a monitor, a television receiver, and a plasma display.
[0173]
Furthermore, as can be easily understood from FIG. 11, the present invention can also be applied to an imaging apparatus. Also in this case, as described above, the imaging device is not limited to the frame sequential camera described in FIG. 11, and may be other imaging devices such as an electronic still camera.
[0174]
Furthermore, the present invention can also be applied to data processing apparatuses such as an image processing apparatus and a personal computer other than the above display means and imaging means.
[0175]
Further, in the above embodiment, in the processing based on the color difference signal level, a case has been described in which the amplification factor when the color difference signal level is large is larger than the amplification factor when the color difference signal level is small. However, for example, if the subject is a person and a tulip, and you want to make the human skin red without changing the color of the tulip very much, contrary to the above explanation, the amplification factor when the level of the color difference signal is large is used. What is necessary is just to make it small compared with the amplification degree when the level of the color difference signal is small. This can be easily realized by using the lookup table. In this case, it can function as a white balance correction device.
[0176]
Although specific embodiments have been described above, such embodiments do not limit the technical scope of the present invention.
[0177]
According to the embodiment as described above, since the color difference signal emphasizing means for amplifying the color difference signal with different amplification degrees according to the level of the color difference signal is provided, the color signal can be partially amplified and output. Accordingly, when the color of the subject is emphasized, only the color of the subject that is desired to be emphasized can be emphasized. In other words, if the subject is a light color, and the original color is desirable, the original color is output, and the dark subject is output with more emphasis.
[0178]
In addition, according to the present embodiment, the amplification degree or threshold value can be varied from the outside, so that the level of the color difference signal to be emphasized can be changed. Therefore, the degree of emphasis can be selected according to the color and situation of the subject, and the display effect can be significantly improved.
[0179]
In addition, according to the present embodiment, since the coring circuit that prevents the color difference signal in the predetermined level range from passing and passes the color difference signal outside the predetermined level range is provided, the input level is set when the subject color difference is small. When the color difference of the subject is large, the color can be emphasized and output.
[0180]
Further, according to the present embodiment, since the low-pass filter that blocks high-frequency components included in the output of the coring circuit is provided, noise components that degrade the image quality of the displayed image can be removed.
[0181]
According to the projector of the present embodiment, since the color correction device that emphasizes only the color of the subject that is desired to be emphasized is used, an image with a high display effect can be projected.
[0182]
【The invention's effect】
As described above, according to the present invention, a color signal can be partially emphasized and output. Accordingly, when the color of the subject is emphasized, only the color of the subject that is desired to be emphasized can be emphasized.
[0183]
In addition, since the display device of the present invention uses a color correction device that emphasizes only the color of a subject that should be emphasized, an image with a high display effect can be projected.
[Brief description of the drawings]
FIG. 1 is a configuration example of a color correction apparatus according to an embodiment of the present invention.
FIG. 2 is an example of input / output characteristics of a color difference signal enhancement circuit according to an embodiment of the present invention.
FIG. 3 is a signal example when human skin is photographed in the embodiment of the present invention.
FIG. 4 is a signal example when photographing a tulip in the embodiment of the present invention.
FIG. 5 is a specific example of a color difference signal enhancement circuit according to an embodiment of the present invention.
FIG. 6 is an example of input / output characteristics of the coring circuit according to the embodiment of the present invention.
FIG. 7 is a signal example when using the coring circuit according to the embodiment of the present invention;
FIG. 8 is a circuit example of a coring circuit according to the embodiment of the present invention.
FIG. 9 is another specific example of the color difference signal enhancement circuit according to the embodiment of the present invention.
FIG. 10 is an effect example of the low-pass filter according to the embodiment of the present invention.
FIG. 11 is a usage example of the projector according to the embodiment of the invention.
FIG. 12 is a histogram of a color difference signal of a subject image in the embodiment of the present invention.
FIG. 13 is a flowchart showing an operation for performing color correction processing in the embodiment of the present invention;
FIG. 14 is a flowchart showing an operation for performing color correction processing in the embodiment of the present invention;
FIG. 15 is a flowchart showing an operation of performing color correction processing in the embodiment of the present invention.
FIG. 16 is a flowchart showing an operation for performing color correction processing in the embodiment of the present invention;
FIG. 17 is a block diagram showing a configuration of a color correction apparatus using the color correction method according to the embodiment of the present invention.
FIG. 18 is a diagram illustrating an example of conversion characteristics between a color difference signal and an enhanced color difference signal in the embodiment of the present invention.
FIG. 19 is a diagram showing a state in which a conversion characteristic from a color difference signal to an enhanced color difference signal is on-screen displayed in the embodiment of the present invention.
FIG. 20 is a configuration diagram of a conventional color correction apparatus.
[Explanation of symbols]
1: Matrix circuit, 3: Adder, 4: Color difference signal enhancement circuit 4, 5: Delay line, 6: Coring circuit, 7: Amplifier circuit, 8: Adder, 501: A / D converter, 502: Memory 503: D / A converter, 504: CPU, 505: keyboard, 506: RAM, 507: storage medium, 508, 509, 510: terminal, 516: control unit, 514, 515: terminal, 517: overlay memory 518: Storage medium.

Claims (6)

A first step of performing a non-linear operation for multiplying a plurality of color difference signals indicating a difference between a color signal and a luminance signal by a different coefficient according to the level of the color difference signal;
A second step of adding the luminance signal to the result of the non-linear operation to obtain a corrected color signal ;
In order that the slope of the coefficient changes between the case where the level of the color difference signal is within the range of two threshold values and the case where it is outside the range of the two threshold values in the first step. A color correction method, wherein two threshold values are set according to a subject to be photographed . The color correction method according to claim 1,
The luminance signal, the color correction method characterized in that it is stored in compressed reversible transform form. First means for performing a non-linear operation for multiplying a plurality of color difference signals indicating a difference between a color signal and a luminance signal by a different coefficient according to the level of the color difference signal;
A second means for adding the luminance signal to the result of the nonlinear calculation to obtain a corrected color signal;
In the first means, the slope of the coefficient changes between when the level of the color difference signal is within the range of two threshold values and when the level is outside the range of the two threshold values. A color correction apparatus, wherein two threshold values are set according to a subject to be photographed . The color correction device according to claim 3,
The luminance signal, the color correction apparatus characterized in that it is stored in compressed reversible transform form. Color difference signal enhancement means for amplifying the color difference signals with different amplification degrees according to the levels of a plurality of color difference signals indicating the difference between the three color signals including red, green and blue components and the luminance signal;
Possess an adding means for outputting an output and the luminance signal and the color signal amplified by adding from the color difference signal enhancement means,
In the color difference signal emphasizing means, the two degrees of amplification are changed so that the level of the color difference signal varies between the case where the level of the color difference signal is within the range of the two threshold values and the case where the level is outside the range of the two threshold values. A color correction apparatus, characterized in that a threshold value is set according to a subject to be photographed . The color correction apparatus according to claim 5 ,
The color difference signal enhancing means prevents the color difference signal from passing through a predetermined level range;
Coring means for passing the color difference signal outside the predetermined level range;
Amplifying means for amplifying the output of the coring means;
2. A color correction apparatus comprising: a second addition unit that adds the output of the amplification unit and the color difference signal.

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