JP2004215063A - Photographing device and outline correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a photographing device and an outline correction method by which a correction coefficient showing the degree of correction in outline correction processing is easily determined. <P>SOLUTION: The outline correction method comprises: acquiring high-sensitivity data showing an object image by photographing with high sensitivity an object by means of a CCD (Charge Coupled Device) 18; acquiring low-sensitivity data showing the object image by photographing with low sensitivity the object; applying gamma correction processing to the high-sensitivity data by means of a high-sensitivity side γ processing circuit 76 and applying the gamma correction processing to the low-sensitivity data by means of a low-sensitivity side γ processing circuit 78; generating composite data by composing the gamma correction-processed high-sensitivity data with the gamma correction-processed low-sensitivity data by means of a composite processing circuit 80; and setting the gain based on the gamma correction processing done by the high-sensitivity side γ processing circuit 76, when the outline correction processing is applied to the object image indicated by the composite data by using preset gain showing the degree of outline correction by means of an outline correction circuit 47. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００５３】
ここで、ｔｈは、高感度データと低感度データが１対１の割合で加算される閾値である。また、ｈｉｇｈは高感度データの値であり、ｌｏｗは低感度データの値である。更に、ｐは、加算データ全体に対するゲイン（通常は０．８〜０．９程度の値。）であり、これによってダイナミックレンジの制御を行う。このゲインｐが小さいほどダイナミックレンジは広く、大きいほどダイナミックレンジは狭くなる。具体的には、コントラストの高いシーン（真夏の晴天等）では０．８、曇りや日陰では０．８６、室内蛍光灯下では０．９といったようにシーンに応じてこの値を変化させることにより、階調値を有効に使用することが可能となる。
【００５４】
図２には、ゲインｐによってダイナミックレンジが変化する様子が示されている。なお、ここで適用したゲインｐの範囲における最小値に対応するものが破線で示されたものであり、最大値に対応するものが２点鎖線で示されたものである。同図に示すように、この場合、ゲインｐの値を小さくするほどダイナミックレンジは広くなることになる。
【００５５】
ここで、上記（１）式について、次の（２）式に示されるように一般化して更に説明する。
【００５６】
【数２】

【００５７】
上記（２）式におけるＭＩＮ（ｈｉｇｈ／ｔｈ，１）の部分における変化の様子を図３（Ａ）に示す。同図に示されるように、高感度データが閾値ｔｈとなったときに高感度データと低感度データが１対１で加算されることになる。
【００５８】
また、上記（２）式におけるＭＡＸ（−ｋ×ｈｉｇｈ／ｔｈ＋１，ｐ）の部分において係数ｋを０．２とした場合の変化の様子を図３（Ｂ）に示す。
【００５９】
なお、（２）式における係数ｋは、次の（３）式で示されるように、高感度信号の信号電荷飽和量Ｓｈと、低感度信号の信号電荷飽和量Ｓｌとによって定まる係数である。
【００６０】
【数３】

【００６１】
例えば、高感度信号と低感度信号の信号電荷飽和量の比が４対１であった場合には、ｋ＝０．２（＝１−４／（４＋１））となる。
【００６２】
また、（２）式におけるｐは前述したように加算データ全体に対するゲインであり、可変の値であるが、この下限値ｐ_ｍｉｎも、次の（４）式で示されるように、高感度信号と低感度信号の信号電荷飽和量の比によって定められる。
【００６３】
【数４】

【００６４】
予め高感度データの最大値が入力されたときに最終出力が最大値となるような系となっている場合に、高感度データと低感度データの合成データを出力する場合には、ゲイン操作が必要となる。
【００６５】
つまり、高感度信号と低感度信号の飽和量分だけ信号が入力された場合に、出力値に対してｐ_ｍｉｎ（＜１）分だけゲインをかけて、最終出力が最大値となるように変換をする必要がある。
【００６６】
例えば、高感度信号と低感度信号の信号電荷飽和量の比が４対１であった場合には、ｐ_ｍｉｎ＝０．８（＝４／（４＋１））となる。
【００６７】
そして、コントラストが高いようなシーンではｐ＝ｐ_ｍｉｎとすればよく、あまりコントラストの高くないようなシーンではｐをｐ_ｍｉｎよりも大きな値に設定することにより、有効に出力階調を使用することができるようになる。
【００６８】
一方、ＹＣ処理回路４９（図１参照）は、合成処理回路８０から入力されたＲ’、Ｇ’、Ｂ’の各合成データに対して全ての画素でＲ、Ｇ、Ｂ３面のデータが揃うように補間処理した後に、当該３面分のデータを用いて輝度信号Ｙとクロマ信号Ｃｒ、Ｃｂを生成する。
【００６９】
また、輪郭補正回路４７は、ＹＣ処理回路４９から入力された輝度信号Ｙに対して、高感度側γ処理回路７６によるガンマ補正処理に基づいて設定された輪郭補正の度合いを示すゲイン（本発明の「補正係数」に相当。）を用いて輪郭補正処理を行い、メモリ４８に格納する。
【００７０】
なお、ＹＣ処理回路４９において生成されたクロマ信号Ｃｒ、Ｃｂもメモリ４８に格納される。
【００７１】
また、記録制御部５０は、スマートメディアとして構成された記録メディア８０をデジタルカメラ１０に装着するための役割を有するものであり、合成処理回路８０により合成されて各種処理後にメモリ４８に格納された合成データ（輝度信号Ｙ及びクロマ信号Ｃｒ、Ｃｂ）を当該メモリ４８から読み出して記録メディア８０に記録する処理を行う。また、表示制御部５２は、メモリ４８に記憶された合成データを読み出し、当該合成データを用いた液晶ディスプレイ（以下、「ＬＣＤ」という。）８２への画像表示のための処理を行う。
【００７２】
上記構成に加え、デジタルカメラ１０は、ＣＰＵ（中央演算処理装置）６２と、ＲＯＭ６４と、ＲＡＭ６６と、を備えたマイクロ・コンピュータで構成された制御回路６０を備えている。
【００７３】
制御回路６０は、デジタルカメラ１０全体の動作を制御する。また、ＲＯＭ６４には、ＣＰＵ６２で実行される各種処理ルーチンのプログラムが記憶されている。
【００７４】
更に、デジタルカメラ１０は、被写体までの距離を検出する測距センサ３２を備えている。測距センサ３２で検出された被写体までの距離を示す信号は、制御回路６０に入力される。シャッタスイッチが半押しされると、制御回路６０により、測距センサ３２で得られた被写体までの距離に基づいてＡＦ（Ａｕｔｏ Ｆｏｃｕｓ、自動合焦）機能が働いて合焦制御される。
【００７５】
ここで、本実施の形態に係るＣＣＤ１８の構造について説明する。ＣＣＤ１８には、図４に示すようなハニカムＣＣＤを採用することができる。
【００７６】
このＣＣＤ１８の撮像部は、図４に示すように、１画素の１色について１つずつ割り当てられると共に、所定の配列ピッチ（水平配列ピッチ＝Ｐｈ（μｍ）、垂直配列ピッチ＝Ｐｖ（μｍ））で、かつ隣接する受光素子ＰＤ１が垂直方向及び水平方向にずらされて２次元配置された複数の受光素子ＰＤ１と、この受光素子ＰＤ１の前面に形成された開口部ＡＰを迂回するように配置され、かつ受光素子ＰＤ１からの信号（電荷）を取り出して垂直方向に転送する垂直転送電極ＶＥＬと、垂直方向最下に位置する垂直転送電極ＶＥＬの垂直方向下側に配置され、垂直転送電極ＶＥＬから転送されてきた信号を外部へ転送する水平転送電極ＨＥＬと、を備えている。なお、同図に示す例では、開口部ＡＰを八角形のハニカム形状に形成している。
【００７７】
ここで、水平方向に直線状に並んで配置された複数の垂直転送電極ＶＥＬにより構成される垂直転送電極群には、各々垂直転送駆動信号Ｖ１、Ｖ２、・・・、Ｖ８の何れか１つを同時に印加することができるように構成されている。なお、同図に示す例では、１段目の垂直転送電極群に対して垂直転送駆動信号Ｖ３が、２段目の垂直転送電極群に対して垂直転送駆動信号Ｖ４が、３段目の垂直転送電極群に対して垂直転送駆動信号Ｖ５が、４段目の垂直転送電極群に対して垂直転送駆動信号Ｖ６が、５段目の垂直転送電極群に対して垂直転送駆動信号Ｖ７が、６段目の垂直転送電極群に対して垂直転送駆動信号Ｖ８が、７段目の垂直転送電極群に対して垂直転送駆動信号Ｖ１が、８段目の垂直転送電極群に対して垂直転送駆動信号Ｖ２が、各々印加できるように構成されている。
【００７８】
一方、各受光素子ＰＤ１は隣接する１つの垂直転送電極ＶＥＬに対し転送ゲートＴＧを介して電気的に接続されるように構成されている。同図に示す例では、各受光素子ＰＤ１が右下に隣接する垂直転送電極ＶＥＬに転送ゲートＴＧを介して接続されるように構成されている。
【００７９】
なお、同図において‘Ｒ’が記入された受光素子ＰＤ１の前面に形成された開口部ＡＰは赤色の光を透過する色分離フィルタ（カラーフィルタ）で覆われており、‘Ｇ’が記入された受光素子ＰＤ１の前面に形成された開口部ＡＰは緑色の光を透過する色分離フィルタで覆われており、‘Ｂ’が記入された受光素子ＰＤ１の前面に形成された開口部ＡＰは青色の光を透過する色分離フィルタで覆われている。すなわち、‘Ｒ’が記入された受光素子ＰＤ１は赤色光を、‘Ｇ’が記入された受光素子ＰＤ１は緑色光を、‘Ｂ’が記入された受光素子ＰＤ１は青色光を、各々受光し、受光した光量に応じたアナログ信号を各々出力する。
【００８０】
ＣＣＤ１８は、更に、上述の受光素子ＰＤ１に比較して低感度な受光素子ＰＤ２を備えている。受光素子ＰＤ２は図４に示される如く、複数の受光素子ＰＤ１間に設けられている。この受光素子ＰＤ２も受光素子ＰＤ１と同様に、その前面に受光素子ＰＤ１の開口部より面積が小さい開口部ＡＰが形成され、隣接する１つの垂直転送電極ＶＥＬに対して転送ゲートＴＧにより電気的に接続されている。また、この受光素子ＰＤ２には、その前面に形成された開口部ＡＰに、受光素子ＰＤ１と同様にＲ、Ｇ、Ｂ何れかのカラーフィルタが装着されている。このように、受光素子ＰＤ２の受光面積を受光素子ＰＤ１の受光面積より小さくしているので、受光素子ＰＤ１に比較して低感度なＲ、Ｇ、Ｂ信号が得られる。
【００８１】
なお、受光素子ＰＤ２の転送ゲートＴＧが接続される電極は、隣接する受光素子ＰＤ１の転送ゲートＴＧが接続される電極とは異なるように設けられている。また、本実施の形態においては、先に受光素子ＰＤ１の電荷を読み出してから受光素子ＰＤ２の電荷を読み出すようにしている。
【００８２】
次に、図５を参照して、本実施の形態に係る輪郭補正回路４７の構成について説明する。同図に示すように、輪郭補正回路４７は、予め定められた高周波数帯域を通過させるバンド・パス・フィルタ（以下、「ＢＰＦ」という。）４７Ａと、乗算器４７Ｂと、乗算器４７Ｃと、加算器４７Ｄと、ＹＣ処理回路４７Ｊと、設定手段としての補正係数発生部４７Ｅ及びリミッタ４７Ｆと、を含んで構成されている。
【００８３】
ＢＰＦ４７Ａは、入力端がＹＣ処理回路４９の輝度信号Ｙを出力する出力端に接続されており、ＹＣ処理回路４９から出力された輝度信号Ｙから所定高周波帯域の成分を抽出して乗算器４７Ｂに出力する。例えば、ＹＣ処理回路４９から出力された輝度信号Ｙが図６（Ａ）に示すような状態である場合、ＢＰＦ４７Ａから乗算器４７Ｂに、図６（Ｂ）に示すような輝度信号Ｙのエッジの位置に対応するパルス（以下、「エッジ・パルス」という。）が出力される。すなわち、ＢＰＦ４７Ａは、輝度信号Ｙにより示される被写体像の輪郭を抽出する役割を有している。
【００８４】
乗算器４７Ｂでは、ＢＰＦ４７Ａから入力されたエッジ・パルスに対してリミッタ４７Ｆから入力された後述するゲインを乗算して、一方の入力端に予め定められたゲインが入力されている乗算器４７Ｃの他方の入力端に出力する。
【００８５】
ここで、乗算器４７Ｃの一方の入力端に入力されているゲインは、輪郭補正回路４７の全体のゲインを調整するためのものであり、乗算器４７Ｃでは、乗算器４７Ｂから入力されたエッジ・パルスに対して当該ゲインを乗算し、一方の入力端がＹＣ処理回路４９の輝度信号Ｙを出力する出力端に接続された加算器４７Ｄの他方の入力端に出力する。
【００８６】
従って、加算器４７Ｄでは、ＹＣ処理回路４９から出力された輝度信号Ｙに対して、乗算器４７Ｂ及び乗算器４７Ｃによって増幅されたエッジ・パルスが加算されて、一例として図６（Ｃ）に示すような、被写体像の輪郭が強調された状態の輝度信号Ｙが生成され、メモリ４８に記憶される。
【００８７】
すなわち、本実施の形態に係る輪郭補正回路４７は、ＹＣ処理回路４９によって生成された合成データの輝度信号Ｙに対して行う輪郭補正処理を、補正の度合いを示すゲインを用いて行うものとして構成されている。
【００８８】
一方、ＹＣ処理回路４７Ｊは、入力端が高感度側γ処理回路７６の出力端に接続されており、高感度側γ処理回路７６から入力された高感度データに対して全ての画素でＲ、Ｇ、Ｂ３面のデータが揃うように補間処理した後に、当該３面分のデータを用いて輝度信号Ｙとクロマ信号Ｃｒ、Ｃｂを生成する。
【００８９】
また、補正係数発生部４７Ｅは、入力端がＹＣ処理回路４７Ｊの輝度信号Ｙを出力する出力端に接続されており、ＹＣ処理回路４７Ｊから入力された輝度信号Ｙにより示される被写体像のそれぞれの画素に対して、高感度側γ処理回路７６によるガンマ補正処理におけるガンマ補正曲線の、それぞれの上記画素の信号レベルにおける微分係数の逆数を乗算器４７Ｂで用いるゲイン（本発明の「補正係数」に相当。）としてリミッタ４７Ｆに出力する。
【００９０】
図７（Ａ）にはガンマ補正曲線の一例が示されている。同図に示されるガンマ補正曲線における微分係数の分布は図７（Ｂ）に示されるものとなり、当該微分係数の逆数の分布は図７（Ｃ）に示されるものとなる。すなわち、当該微分係数の逆数の分布は、上記ガンマ補正曲線の傾斜の度合いが大きいほど傾斜の度合いが小さなものとされる。
【００９１】
本実施の形態に係る補正係数発生部４７Ｅは、乗算器４７Ｂで用いるゲインとして、このようなガンマ補正曲線の微分係数の逆数を適用しているので、ガンマ補正処理に起因する被写体像の暗部におけるノイズの発生を抑制することができる。
【００９２】
なお、本実施の形態に係る補正係数発生部４７Ｅは、一例として図８に示されるような、ＹＣ処理回路４７Ｊから入力された画素毎の高感度データの輝度信号Ｙの値と、それに対応する高感度側γ処理回路７６のガンマ補正曲線の微分係数の逆数（乗算器４７Ｂで用いるゲイン）と、を関連付けたルック・アップ・テーブルＬＵＴとして構成されている。
【００９３】
リミッタ４７Ｆでは、対応する画素の高感度データの輝度信号Ｙの値が予め定められた閾値より大きな場合、補正係数発生部４７Ｅから入力されたゲインを予め定められた値に置き換えて乗算器４７Ｂに出力し、他の場合は補正係数発生部４７Ｅから入力されたゲインをそのまま乗算器４７Ｂに出力する。
【００９４】
すなわち、リミッタ４７Ｆは、対象とする画素の信号レベルが所定レベルより大きな場合に乗算器４７Ｂで用いるゲインを制限する役割を有しており、これによって被写体像の明部における過度のエッジ強調を抑制することができるようにしている。
【００９５】
以下、このような構成のデジタルカメラ１０の撮影時における作用を説明する。
【００９６】
まず、光学レンズ１２、絞り１４、及びシャッタ１６を通過した被写体像を示す入射光は、ＣＣＤ１８の感度の異なる受光素子ＰＤ１及びＰＤ２の双方により受光され、被写体像を示すアナログ画像信号としてアナログ信号処理部２０に出力される。また、ユーザがデジタルカメラ１０にて被写体を撮影するためにカメラ操作部８４のシャッタスイッチを半押しすると、このとき測距センサ３２から入力された信号に基づいて被写体までの距離Ｔが導出され、駆動部２４の制御の下にＡＦ機能が働いて合焦制御される。
【００９７】
アナログ信号処理部２０は、ＣＣＤ１８から入力された高感度及び低感度の双方のアナログ画像信号に対して所定のアナログ信号処理を施す。これらのアナログ画像信号は、Ａ／Ｄ変換器２２により各々高感度データ及び低感度データに変換される。Ａ／Ｄ変換器２２から出力された高感度データ及び低感度データは、デジタル信号処理回路３４及び制御回路６０に入力される。
【００９８】
制御回路６０では、Ａ／Ｄ変換器２２から入力された高感度データ及び低感度データに基づいて高感度データ及び低感度データの各々のホワイトバランスを制御するためのゲイン値Ｒｇ、Ｇｇ、Ｂｇが導出され、対応する高感度側ＷＢ調整処理回路７２及び低感度側ＷＢ調整処理回路７４に出力される。
【００９９】
一方、デジタル信号処理回路３４に入力された高感度データ及び低感度データは、高感度側ＷＢ調整処理回路７２及び低感度側ＷＢ調整処理回路７４により、制御回路６０から入力されたゲイン値を用いてホワイトバランス調整が行われ、更に高感度側γ処理回路７６及び低感度側γ処理回路７８によりそれぞれガンマ補正処理が行われて合成処理回路８０に出力される。そして、合成処理回路８０では、入力された高感度データ及び低感度データが対数加算方式を用いて前述のように合成され、これによって得られた合成データがＹＣ処理回路４９に出力される。
【０１００】
ＹＣ処理回路４９では、合成処理回路８０から入力された合成データに基づいて、前述したように輝度信号Ｙ及びクロマ信号Ｃｒ、Ｃｂが生成され、当該輝度信号Ｙは輪郭補正回路４７に出力され、クロマ信号Ｃｒ、Ｃｂはメモリ４８の所定領域に記憶される。
【０１０１】
そして、輪郭補正回路４７では、前述のように、ＢＰＦ４７ＡにおいてＹＣ処理回路４９から出力された輝度信号Ｙから所定高周波帯域の成分（エッジ・パルス）が抽出されて乗算器４７Ｂに出力され、乗算器４７Ｂにおいて、ＢＰＦ４７Ａから入力されたエッジ・パルスに対してリミッタ４７Ｆから出力されたゲインが乗算されて乗算器４７Ｃに出力される。
【０１０２】
そして、乗算器４７Ｃでは、乗算器４７Ｂから入力されたエッジ・パルスに対して所定のゲインが乗算されて加算器４７Ｄに出力され、加算器４７Ｄにおいて、当該エッジ・パルスがＹＣ処理回路４９から出力された輝度信号Ｙに対して加算されることにより被写体像の輪郭が強調された状態の輝度信号Ｙが生成され、メモリ４８に格納される。
【０１０３】
一方、ＹＣ処理回路４７Ｊでは、高感度側γ処理回路７６から入力された高感度データに基づいて輝度信号Ｙ及びクロマ信号Ｃｒ、Ｃｂが前述したように生成され、このうちの輝度信号Ｙが補正係数発生部４７Ｅに出力される。
【０１０４】
そして、補正係数発生部４７Ｅでは、ＹＣ処理回路４７Ｊから入力された高感度データの輝度信号Ｙにより示される被写体像のそれぞれの画素に対して、高感度側γ処理回路７６によるガンマ補正処理におけるガンマ補正曲線の、それぞれの上記画素の信号レベルにおける微分係数の逆数が乗算器４７Ｂで用いるゲインとしてリミッタ４７Ｆに出力される。
【０１０５】
そして、リミッタ４７Ｆでは、対応する画素の高感度データの輝度信号Ｙの値が予め定められた閾値より大きな場合、補正係数発生部４７Ｅから入力されたゲインが予め定められた値に置き換えられて乗算器４７Ｂに出力され、他の場合は補正係数発生部４７Ｅから入力されたゲインがそのまま乗算器４７Ｂに出力される。
【０１０６】
従って、乗算器４７Ｂでは、当該ゲインがＢＰＦ４７Ａから入力されたエッジ・パルスに対して乗算されることになり、この結果として合成データにより示される被写体像の暗部におけるノイズの発生を抑制すると共に、明部における過度のエッジ強調を抑制することができる。
【０１０７】
一方、表示制御部５２は、メモリ４８に記憶された各種処理後の合成データ（輝度信号Ｙ及びクロマ信号Ｃｒ、Ｃｂ）を用いたＬＣＤ８２への画像表示のための処理を実行する。また、記録制御部５０は、カメラ操作部８４のシャッタスイッチが全押しされたときに制御回路６０から入力された指示信号に応じて、メモリ４８に記憶された合成データの記録メディア８０への記録を行う。これによって撮影がなされる。
【０１０８】
以上詳細に説明したように、本実施の形態に係るデジタルカメラ１０は、ＣＣＤ１８によって被写体を高感度で撮像して被写体像を示す高感度データを取得すると共に、上記被写体を低感度で撮像して上記被写体像を示す低感度データを取得し、高感度側γ処理回路７６により高感度データに対してガンマ補正処理を行うと共に低感度側γ処理回路７８により低感度データに対してガンマ補正処理を行い、合成処理回路８０によりガンマ補正処理後の高感度データと低感度データとを合成して合成データを生成し、輪郭補正回路４７によって輪郭補正の度合いを示す予め設定されたゲインを用いて上記合成データにより示される被写体像に対して輪郭補正処理を行うに際し、高感度側γ処理回路７６によるガンマ補正処理に基づいて上記ゲインを設定しているので、当該ゲインを容易に定めることができる。
【０１０９】
また、本実施の形態に係るデジタルカメラ１０では、被写体像のそれぞれの画素に対して、高感度側γ処理回路７６によるガンマ補正処理におけるガンマ補正曲線の、それぞれの上記画素の信号レベルにおける微分係数の逆数に基づき上記ゲインを設定しているので、被写体像の暗部におけるノイズの発生を抑制することができる。
【０１１０】
更に、本実施の形態に係るデジタルカメラ１０では、画素の信号レベルが予め定められた閾値より大きな場合、上記ゲインを予め定められた値に置き換えているので、当該ゲインの上限値を制限することができ、この結果として、被写体像の明部における過度のエッジ強調を抑制することができる。
【０１１１】
なお、本実施の形態では、ＹＣ処理回路４７Ｊ及び補正係数発生部４７Ｅにおいて、高感度側γ処理回路７６から出力された高感度データを入力として乗算器４７Ｂで用いるゲインを出力する場合について説明したが、本発明はこれに限定されるものではなく、例えば、高感度側ＷＢ調整処理回路７２から出力された高感度データを入力として当該ゲインを出力する形態とすることもできる。
【０１１２】
この場合、高感度側ＷＢ調整処理回路７２から入力された高感度データの輝度信号Ｙにより示される被写体像のそれぞれの画素に対して、高感度側γ処理回路７６によるガンマ補正処理におけるガンマ補正曲線の、それぞれの上記画素の信号レベルにおける微分係数の逆数を乗算器４７Ｂで用いるゲインとしてリミッタ４７Ｆに出力することになる。この場合も、本実施の形態と同様の効果を奏することができる。
【０１１３】
また、本実施の形態では、リミッタ４７Ｆにおいて、対応する画素の高感度データの輝度信号Ｙの値が予め定められた閾値より大きな場合、補正係数発生部４７Ｅから入力されたゲインを予め定められた値に置き換えて乗算器４７Ｂに出力する場合について説明したが、本発明はこれに限定されるものではなく、例えば、補正係数発生部４７Ｅから入力されたゲインが予め定められた閾値より大きな場合、当該ゲインを予め定められた値に置き換えて乗算器４７Ｂに出力する形態とすることもできる。この場合も、本実施の形態と同様の効果を奏することができる。
【０１１４】
〔第２実施形態〕
本第２実施形態では、高感度データと、高感度信号及び低感度信号の感度比とに基づいて低感度データを演算により導出し、当該低感度データ及び高感度データの合成データに基づいて輪郭補正の度合いを示すゲイン（補正係数）を設定する場合の形態、すなわち、請求項３に係る発明の実施の形態について説明する。
【０１１５】
まず、図９を参照して、本実施の形態に係るデジタルカメラ１０Ｂの構成を説明する。なお、図９における図１と同一の構成要素については図１と同一の符号を付して、その説明を省略する。
【０１１６】
図９に示されるように、本第２実施形態に係るデジタルカメラ１０Ｂは、輪郭補正回路４７に代えて、高感度側ＷＢ調整処理回路７２の出力端及び高感度側γ処理回路７６に接続された輪郭補正回路４７’が設けられている点のみが、上記第１実施形態に係るデジタルカメラ１０と異なっている。
【０１１７】
以下、図１０を参照して、本第２実施形態に係る輪郭補正回路４７’の構成について説明する。なお、図１０における図５と同一の構成要素については図５と同一の符号を付して、その説明を省略する。
【０１１８】
本第２実施形態に係る輪郭補正回路４７’は、入力されたデータに対してＣＣＤ１８の高感度信号と低感度信号の感度比を乗算する演算器４７Ｇと、低感度側γ処理回路７８と同一の構成とされた低感度側γ処理回路４７Ｈと、合成処理回路８０と同一の構成とされた合成処理回路４７Ｉと、が新たに設けられている点と、補正係数発生部４７Ｅに代えて補正係数発生部４７Ｅ’が設けられている点が、上記第１実施形態に係る輪郭補正回路４７と異なっている。
【０１１９】
演算器４７Ｇの入力端は高感度側ＷＢ調整処理回路７２の出力端に接続されており、演算器４７Ｇは高感度側ＷＢ調整処理回路７２から入力された高感度データに対して上記感度比を乗算して低感度側γ処理回路４７Ｈに出力する。
【０１２０】
ここで、上記感度比は、低感度信号の感度を高感度信号の感度で除算することによって得るものとされている。すなわち、演算器４７Ｇでは、低感度データにノイズが発生しないものと仮定し、上記感度比を高感度側ＷＢ調整処理回路７２から入力された高感度データに乗算することによって当該低感度データを導出している。
【０１２１】
低感度側γ処理回路４７Ｈでは、演算器４７Ｇから入力された低感度データに対して低感度側γ処理回路７８と同様にガンマ補正処理を行って、一方の入力端に高感度側γ処理回路７６の出力端が接続された合成処理回路４７Ｉの他方の入力端に出力する。
【０１２２】
従って、合成処理回路４７Ｉでは、低感度側γ処理回路４７Ｈから入力された低感度データと高感度側γ処理回路７６から入力された高感度データとを、合成処理回路８０と同様の手法で合成し、合成データとしてＹＣ処理回路４７Ｊに出力する。従って、ＹＣ処理回路４７Ｊでは、合成処理回路４７Ｉから入力された合成データに対して全ての画素でＲ、Ｇ、Ｂ３面のデータが揃うように補間処理した後に、当該３面分のデータを用いて輝度信号Ｙとクロマ信号Ｃｒ、Ｃｂを生成し、これらのうちの輝度信号Ｙを補正係数発生部４７Ｅ’に出力することになる。
【０１２３】
一方、本第２実施形態に係る補正係数発生部４７Ｅ’は、ＹＣ処理回路４７Ｊから入力された合成データの輝度信号Ｙにより示される被写体像のそれぞれの画素に対して、当該合成データに作用された高感度側γ処理回路７６及び低感度側γ処理回路４７Ｈの各々のガンマ補正処理における各ガンマ補正曲線の組み合わせの、それぞれの上記画素の信号レベルにおける微分係数の逆数を乗算器４７Ｂで用いるゲイン（本発明の「補正係数」に相当。）としてリミッタ４７Ｆに出力する。
【０１２４】
ここで、上記微分係数の逆数の分布は、上記各ガンマ補正曲線の組み合わせにおける傾斜の度合いが大きいほど傾斜の度合いが小さなものとされる。
【０１２５】
従って、本第２実施形態に係る補正係数発生部４７Ｅ’も、乗算器４７Ｂで用いるゲインとして、このようなガンマ補正曲線の微分係数の逆数を適用しているので、ガンマ補正処理に起因する被写体像の暗部におけるノイズの発生を抑制することができる。
【０１２６】
なお、本実施の形態に係る補正係数発生部４７Ｅ’も、上記第１実施形態に係る補正係数発生部４７Ｅと同様に、ＹＣ処理回路４７Ｊから入力された画素毎の輝度信号Ｙの値と、それに対応する上記微分係数の逆数（乗算器４７Ｂで用いるゲイン）と、を関連付けたルック・アップ・テーブルＬＵＴとして構成されている。
【０１２７】
一方、リミッタ４７Ｆでは、対応する画素の合成データの輝度信号Ｙの値が予め定められた閾値より大きな場合、補正係数発生部４７Ｅ’から入力されたゲインを予め定められた値に置き換えて乗算器４７Ｂに出力し、他の場合は補正係数発生部４７Ｅ’から入力されたゲインをそのまま乗算器４７Ｂに出力する。
【０１２８】
このように、本第２実施形態に係るリミッタ４７Ｆは、上記第１実施形態に係る輪郭補正回路４７で用いられているものと同一のものであり、被写体像の明部における過度のエッジ強調を抑制するためのものである。
【０１２９】
演算器４７Ｇが本発明の乗算手段に、低感度側γ処理回路４７Ｈが本発明の第３ガンマ補正手段に、合成処理回路４７Ｉが本発明の第２合成手段に、補正係数発生部４７Ｅ’が本発明の設定手段に、各々相当する。
【０１３０】
なお、輪郭補正回路４７’における演算器４７Ｇから補正係数発生部４７Ｅ’に至る部分以外のデジタルカメラ１０Ｂの作用は、上記第１実施形態に係るデジタルカメラ１０と同様であるので、ここでの説明は省略する。
【０１３１】
以上詳細に説明したように、本実施の形態に係るデジタルカメラ１０Ｂは、ＣＣＤ１８によって被写体を高感度で撮像して被写体像を示す高感度データを取得すると共に、上記被写体を低感度で撮像して上記被写体像を示す低感度データを取得し、高感度側γ処理回路７６により高感度データに対してガンマ補正処理を行うと共に低感度側γ処理回路７８により低感度データに対してガンマ補正処理を行い、合成処理回路８０によりガンマ補正処理後の高感度データと低感度データとを合成して合成データを生成し、輪郭補正回路４７’によって輪郭補正の度合いを示す予め設定されたゲインを用いて上記合成データにより示される被写体像に対して輪郭補正処理を行うに際し、高感度側γ処理回路７６によるガンマ補正処理に基づいて上記ゲインを設定しているので、当該ゲインを容易に定めることができる。
【０１３２】
また、本実施の形態に係るデジタルカメラ１０Ｂでは、高感度側γ処理回路７６によるガンマ補正処理前の高感度データに対し、高感度信号の感度に対する低感度信号の感度の割合を乗算して得られた低感度データに対して低感度側γ処理回路７８と同様のガンマ補正処理を行い、ガンマ補正処理後の高感度データと、低感度側γ処理回路４７Ｈから出力されたガンマ補正処理後の低感度データとを合成処理回路８０と同様に合成して合成データを生成し、被写体像のそれぞれの画素に対して、当該合成データに作用された高感度側γ処理回路７６及び低感度側γ処理回路４７Ｈの各々のガンマ補正処理における各ガンマ補正曲線の組み合わせの、それぞれの上記画素の信号レベルにおける微分係数の逆数に基づき上記ゲインを設定しているので、被写体像の暗部におけるノイズの発生を抑制することができる。
【０１３３】
更に、本実施の形態に係るデジタルカメラ１０Ｂでは、画素の信号レベルが予め定められた閾値より大きな場合、上記ゲインを予め定められた値に置き換えているので、当該ゲインの上限値を制限することができ、この結果として、被写体像の明部における過度のエッジ強調を抑制することができる。
【０１３４】
なお、本実施の形態では、リミッタ４７Ｆにおいて、対応する画素の合成データの輝度信号Ｙの値が予め定められた閾値より大きな場合、補正係数発生部４７Ｅ’から入力されたゲインを予め定められた値に置き換えて乗算器４７Ｂに出力する場合について説明したが、本発明はこれに限定されるものではなく、例えば、補正係数発生部４７Ｅ’から入力されたゲインが予め定められた閾値より大きな場合、当該ゲインを予め定められた値に置き換えて乗算器４７Ｂに出力する形態とすることもできる。この場合も、本実施の形態と同様の効果を奏することができる。
【０１３５】
また、上記各実施の形態では、補正係数発生部をルック・アップ・テーブルとして構成した場合について説明したが、本発明はこれに限定されるものではなく、例えば、補正係数発生部の入力データと出力データとの関係を示す数式を予め記憶しておき、当該数式を用いて出力データを演算により導出する形態とすることもできる。この場合は、当該演算にかかる負荷が増加するものの、ルック・アップ・テーブルを記憶するための記憶容量を削減することができる。
【０１３６】
また、上記各実施の形態では、高感度の受光素子ＰＤ１と低感度の受光素子ＰＤ２の各々を設け、高感度信号及び低感度信号を得る例について説明したが、図１１に示されるように、１つの受光素子ＰＤの受光領域をチャネルストッパ９４により高感度の受光を行う受光面積が広い高感度受光領域９２と低感度の受光を行う受光面積が狭い低感度受光領域９０とに分割し、それぞれの領域により高感度信号及び低感度信号が得られるような構成としてもよい。なお、受光素子ＰＤにはチャネルストッパ９４が設けられているため、高感度で受光された信号と低感度で受光された信号とが混合されずに、双方の信号を別々に受光することができる。
【０１３７】
また、上記各実施の形態では、合成データの輝度信号Ｙに対して輪郭補正を行う場合について説明したが、本発明はこれに限定されるものではなく、合成データに対して輪郭補正を行う形態とすることもできる。この場合は、上記各実施の形態で必要とされたＹＣ処理回路４９及びＹＣ処理回路４７Ｊは必要がなくなる。この場合も、本実施の形態と同様の効果を奏することができる。
【０１３８】
また、上記各実施の形態に係るデジタルカメラ１０、１０Ｂの構成（図１及び図９参照）は一例であり、本発明の主旨を逸脱しない範囲内において適宜変更可能であることは言うまでもない。
【０１３９】
更に、本発明は上記デジタルカメラに限られるものではなく、様々な撮像装置に適用可能である。
【０１４０】
【発明の効果】
以上説明した如く本発明によれば、撮像素子によって被写体を第１の感度で撮像して被写体像を示す第１画像信号を取得すると共に、上記被写体を第１の感度より低い第２の感度で撮像して上記被写体像を示す第２画像信号を取得し、第１ガンマ補正手段により第１画像信号に対してガンマ補正処理を行うと共に第２ガンマ補正手段により第２画像信号に対してガンマ補正処理を行い、合成手段によりガンマ補正処理後の第１画像信号と第２画像信号とを合成して合成信号を生成し、輪郭補正手段によって輪郭補正の度合いを示す予め設定された補正係数を用いて上記合成信号により示される被写体像に対して輪郭補正処理を行うに際し、第１ガンマ補正手段によるガンマ補正処理に基づいて上記補正係数を設定しているので、当該補正係数を容易に定めることができる、という効果が得られる。
【図面の簡単な説明】
【図１】第１実施形態に係るデジタルカメラの構成を示すブロック図である。
【図２】実施の形態に係る（１）式において、ゲインｐによりダイナミックレンジが変化する様子を示す光量対合成データ（最終画像８ｂｉｔＱＬ）のグラフである。
【図３】実施の形態に係る（１）式の説明に供するグラフである。
【図４】実施の形態に係るデジタルカメラで適用されているＣＣＤの構成を示す概略図である。
【図５】第１実施形態に係る輪郭補正回路４７の構成を示すブロック図である。
【図６】実施の形態に係る輪郭補正回路４７の動作の説明に供する波形図である。
【図７】ガンマ補正曲線における微分係数の逆数の説明に供するグラフである。
【図８】第１実施形態に係る補正係数発生部４７Ｅの構成を示す模式図である。
【図９】第２実施形態に係るデジタルカメラの構成を示すブロック図である。
【図１０】第２実施形態に係る輪郭補正回路４７’の構成を示すブロック図である。
【図１１】高感度と低感度の信号の双方を受光することができる受光素子が設けられたＣＣＤの構成を示す概略図である。
【符号の説明】
１０、１０Ｂ デジタルカメラ
１８ ＣＣＤ（撮像素子）
４７、４７’ 輪郭補正回路（輪郭補正手段）
４７Ｅ、４７Ｅ’ 補正係数発生部（設定手段）
４７Ｆ リミッタ（設定手段）
４７Ｇ 演算器（乗算手段）
４７Ｈ 低感度側γ処理回路（第３ガンマ補正手段）
４７Ｉ 合成処理回路（第２合成手段）
６０ 制御回路
７６ 高感度側γ処理回路（第１ガンマ補正手段）
７８ 低感度側γ処理回路（第２ガンマ補正手段）
８０ 合成処理回路（合成手段）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus and a contour correction method, and in particular, includes an image sensor that can acquire image signals with different sensitivities, and performs contour correction on an image obtained by imaging with the image sensor. The present invention relates to an imaging device capable of performing the same and a contour correction method in the imaging device.
[0002]
[Prior art]
Conventionally, when contour correction is performed on a given image, gamma correction is performed on the image and then contour correction is performed, or contour correction is performed on the given image and then gamma correction is performed. Had gone. Such a method has a problem that a gain in a region where a signal level of a given image is low is large, and noise in a dark portion of the image is noticeable. In addition, since the gain is uniformly applied to the luminance of the image, the effect of the contour correction in the bright part of the image is deteriorated.
[0003]
In order to solve such problems, conventionally, a contour correction signal is generated based on the video signal extracted from the previous stage of the gamma correction circuit, and the contour correction signal is superimposed on the video signal that has been gamma corrected by the gamma correction circuit. There is a technique for performing contour compensation (see, for example, Patent Document 1).
[0004]
Also, a contour correction unit that performs a contour correction process on the video input signal, a gamma correction unit that performs a gamma correction process on the video input signal, an addition unit that adds the video output signals from the contour correction unit and the gamma correction unit to each other, There is also a technique provided with (for example, refer to Patent Document 2).
[0005]
[Patent Document 1]
JP 55-92083 A
[Patent Document 2]
JP-A 63-209373
[0006]
[Problems to be solved by the invention]
However, the former technique generates a contour correction signal based on an image after gamma correction, and thus has a problem that noise in a dark part of the image is greatly noticeable. Further, the latter technique has a problem that excessive edge enhancement is applied in a bright part of an image.
[0007]
Therefore, in order to solve these problems, in Japanese Patent Application No. 2002-44044 by the applicant of the present invention, a correction coefficient based on gamma correction processing is generated, and the correction coefficient is extracted from the image after gamma correction processing. There has been proposed a technique for performing contour correction by multiplying image data of a contour portion and then adding the image data to the image data of the image after the gamma correction processing.
[0008]
In this technique, the reciprocal of the differential coefficient of the gamma correction curve in the gamma correction process is applied to each pixel of the image to be processed as the correction coefficient, and a limiter for limiting the upper limit value of the correction coefficient is provided. As a result, generation of noise in the dark part of the image can be suppressed, and excessive edge enhancement in the bright part of the image can be suppressed.
[0009]
On the other hand, in recent years, the demand for digital cameras has increased rapidly with the increase in the resolution of imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) image sensors.
[0010]
By the way, the dynamic range of an image pickup element in an image pickup apparatus such as a digital camera that is widely spread at present is generally narrower than that of a photographic film. For this reason, when photographing a high-luminance subject, the amount of received light exceeds the dynamic range, the output signal of the image sensor is saturated, and subject information may be lost.
[0011]
In order to solve such problems, there has conventionally been a technique for expanding the dynamic range by synthesizing a high-sensitivity image signal obtained by photographing and a low-sensitivity image signal (Japanese Patent Laid-Open No. 2000-2007). 307963). In this technique, a high-sensitivity image is replaced with a low-sensitivity image for each part in one image using a mask to generate a composite image.
[0012]
However, in this technique, when attention is paid to each pixel of the image, since only one of the high-sensitivity image signal and the low-sensitivity image signal is used, the dynamic range cannot always be effectively expanded. There was a problem.
[0013]
Therefore, in order to solve this problem, a technique of combining and using a high-sensitivity image signal and a low-sensitivity image signal for each pixel of the image can be considered.
[0014]
Then, to this technique, a technique for applying the contour correction technique in the above-mentioned Japanese Patent Application No. 2002-44044, that is, a high-sensitivity image signal and a low-sensitivity image signal are synthesized for each pixel, and an image obtained thereby A technique of applying the contour correction technique to a signal (synthetic signal) is also conceivable. As a result, generation of noise in the dark part of the image indicated by the composite signal can be suppressed, and excessive edge enhancement in the bright part of the image can be suppressed.
[0015]
However, in this technique, each of the high-sensitivity image signal and the low-sensitivity image signal is individually subjected to gamma correction processing, and then the respective image signals are combined and obtained based on the resultant composite signal. When contour correction is performed using a correction coefficient (the reciprocal of the differential coefficient of the gamma correction curve in gamma correction processing), there are two systems of gamma correction processing, so that the correction coefficient cannot be easily determined. was there.
[0016]
That is, in this case, the synthesized signal is a high-sensitivity image signal and a low-sensitivity image signal in which the signal-to-noise ratio (Signal to Noise Ratio) is low and noise is more likely to occur than the image signal. On the other hand, it is obtained by synthesizing each image signal after performing gamma correction processing with a predetermined gamma characteristic individually, and it is not easy to determine a correction coefficient for such a synthesized signal.
[0017]
The present invention has been made to solve the above-described problems, and an object thereof is to provide an imaging apparatus and a contour correction method that can easily determine a correction coefficient indicating the degree of correction in contour correction processing.
[0018]
[Means for Solving the Problems]
In order to achieve the above object, an imaging apparatus according to claim 1 captures a subject with a first sensitivity to obtain a first image signal indicating a subject image, and sets the subject to a first sensitivity lower than the first sensitivity. An image sensor that captures an image with a sensitivity of 2 to obtain a second image signal indicating the subject image, a first gamma correction unit that performs a gamma correction process on the first image signal, and a second gamma correction signal for the second image signal. Second gamma correction means for performing gamma correction processing, combining means for generating a composite signal by combining the first image signal after gamma correction processing and the second image signal after gamma correction processing, and contour correction Contour correction means for performing contour correction processing on the subject image indicated by the composite signal using a preset correction coefficient indicating the degree of the correction, and the correction coefficient based on the gamma correction processing by the first gamma correction means Set up It includes setting means for, the.
[0019]
According to the imaging device of the first aspect, the first image signal indicating the subject image is acquired by the imaging device by imaging the subject with the first sensitivity, and the subject is lower than the first sensitivity. A second image signal indicating the subject image is acquired with a sensitivity of 2 and a gamma correction process is performed on the first image signal by the first gamma correction unit, and the second image is output by the second gamma correction unit. A gamma correction process is performed on the signal, and the first image signal after the gamma correction process and the second image signal after the gamma correction process are combined by the combining unit to generate a combined signal. By this synthesis, the dynamic range of the image sensor can be expanded.
[0020]
Note that the first image signal and the second image signal synthesized by the synthesizing unit may be analog signals or digital signals. Further, the image pickup device can include a solid-state image pickup device such as a CCD or a CMOS image sensor.
[0021]
In the present invention, the contour correction unit performs contour correction processing on the subject image indicated by the composite signal using a preset correction coefficient indicating the degree of contour correction.
[0022]
Here, in the present invention, the correction coefficient is set by the setting means based on the gamma correction processing by the first gamma correction means.
[0023]
That is, according to the present invention, the high-sensitivity image signal and the low-sensitivity image signal are individually subjected to gamma correction processing, and then the respective image signals are combined to generate a combined signal. Since there are two correction processes, the correction coefficient cannot be easily determined as described above.
[0024]
Therefore, in the present invention, the correction coefficient is not obtained based on the synthesized signal, but is the first image on the high sensitivity side, which is the image signal before synthesis and is the dominant signal of the resultant synthesized signal. The correction coefficient is obtained based on the gamma correction processing by the first gamma correction means for performing gamma correction processing on the signal. As a result, the correction coefficient can be easily obtained as compared with the case where the correction coefficient is obtained based on the synthesized signal.
[0025]
As described above, according to the imaging apparatus of the first aspect, the subject is imaged with the first sensitivity by the imaging element to obtain the first image signal indicating the subject image, and the subject is detected based on the first sensitivity. A second image signal indicating the subject image is obtained by imaging with a low second sensitivity, a gamma correction process is performed on the first image signal by the first gamma correction means, and a second image is obtained by the second gamma correction means. Gamma correction processing is performed on the signal, the first image signal after the gamma correction processing and the second image signal are synthesized by the synthesizing unit to generate a synthesized signal, and the contour correction unit presets the degree of contour correction When the contour correction process is performed on the subject image indicated by the composite signal using the corrected correction coefficient, the correction coefficient is set based on the gamma correction process by the first gamma correction unit. It can be determined the correction coefficient easily.
[0026]
By the way, the generation of noise in the dark part of the image can be suppressed by applying the inverse of the differential coefficient of the gamma correction curve in the gamma correction process to each pixel of the image to be processed as the correction coefficient of the present invention. It is as follows.
[0027]
In view of this, the imaging device according to claim 2 is the gamma correction curve in the gamma correction processing by the first gamma correction unit for each pixel of the subject image. The correction coefficient is set based on the reciprocal of the differential coefficient at the signal level of each of the pixels.
[0028]
According to the imaging apparatus of the second aspect, the signal of each pixel of the gamma correction curve in the gamma correction processing by the first gamma correction unit is performed on each pixel of the subject image by the setting unit of the present invention. The correction coefficient of the present invention is set based on the reciprocal of the differential coefficient at the level.
[0029]
As described above, according to the image pickup apparatus of the second aspect, the same effect as that of the first aspect of the invention can be achieved, and the first gamma correction means is used for each pixel of the subject image. Since the correction coefficient of the present invention is set based on the reciprocal of the differential coefficient at the signal level of each pixel of the gamma correction curve in the gamma correction process, it is possible to suppress the occurrence of noise in the dark part of the subject image.
[0030]
On the other hand, an imaging apparatus according to a third aspect is the invention according to the first aspect, wherein the second image with respect to the first sensitivity with respect to the first image signal before the gamma correction processing by the first gamma correction means. Multiplication means for multiplying the ratio of the sensitivity and outputting a third image signal, third gamma correction means for performing gamma correction processing similar to the second gamma correction means on the third image signal, and gamma correction Second setting means for generating a second combined signal by combining the processed first image signal and the third image signal after gamma correction processing in the same manner as the combining means; and the setting means Is a combination of each gamma correction curve in each gamma correction process of each of the first gamma correction means and the third gamma correction means applied to the second composite signal for each pixel of the subject image. That In which the signal level of the pixel sets said correction coefficient on the basis of the reciprocal of the differential coefficient.
[0031]
According to the imaging apparatus of claim 3, the multiplication unit multiplies the first image signal before the gamma correction processing by the first gamma correction unit by the ratio of the second sensitivity to the first sensitivity. A third image signal is output. That is, the multiplication means assumes that no noise occurs in the image signal on the low sensitivity side, and multiplies the first image signal, which is the image signal on the high sensitivity side, by the above ratio, thereby obtaining the image signal on the low sensitivity side. (Third image signal) is derived.
[0032]
In the present invention, the third gamma correction unit performs gamma correction processing similar to the second gamma correction unit on the third image signal, and the second synthesis unit performs first gamma correction processing after the first gamma correction processing. The image signal and the third image signal after the gamma correction processing are combined in the same manner as the combining means of the present invention to generate a second combined signal. Therefore, the second synthesized signal generated here is the same as the synthesized signal generated by the synthesizing means of the present invention when no noise occurs in the second image signal on the low sensitivity side.
[0033]
Here, in the present invention, each gamma correction in each of the gamma correction processes of the first gamma correction unit and the third gamma correction unit applied to the second composite signal is performed on each pixel of the subject image by the setting unit. The correction coefficient of the present invention is set based on the reciprocal of the differential coefficient at the signal level of each pixel of the combination of curves.
[0034]
As described above, according to the imaging apparatus of the third aspect, the same effect as that of the first aspect of the invention can be obtained, and the first image signal before the gamma correction processing by the first gamma correction unit can be obtained. On the other hand, the third image signal obtained by multiplying the ratio of the second sensitivity to the first sensitivity is subjected to gamma correction processing similar to the second gamma correction means, and the first image signal after the gamma correction processing is performed. And the third image signal after the gamma correction processing are synthesized in the same manner as the synthesis means to generate a second synthesized signal, and the first gamma correction applied to the second synthesized signal for each pixel of the subject image The correction coefficient of the present invention is set based on the reciprocal of the differential coefficient at the signal level of each pixel of the combination of the respective gamma correction curves in the respective gamma correction processes of the means and the third gamma correction means. of The generation of noise can be suppressed in the section.
[0035]
By the way, as described above, it is possible to suppress excessive edge enhancement in the bright part of the image by limiting the upper limit value of the correction coefficient of the present invention.
[0036]
In view of this, in the imaging device according to claim 4, in the invention according to claim 2 or claim 3, the setting unit performs the correction when the signal level of the pixel or the correction coefficient is larger than a predetermined threshold. The coefficient is replaced with a predetermined value.
[0037]
According to the imaging apparatus of the fourth aspect, when the signal level of the pixel or the correction coefficient of the present invention is larger than a predetermined threshold, the correction coefficient is replaced with a predetermined value by the setting means. Thereby, the upper limit value of the correction coefficient of the present invention can be limited.
[0038]
As described above, according to the imaging device of the fourth aspect, the same effect as that of the second or third aspect of the invention can be achieved, and the pixel signal level or the correction coefficient of the present invention is previously set. If the threshold value is larger than the predetermined threshold value, the correction coefficient is replaced with a predetermined value, so that the upper limit value of the correction coefficient can be limited. As a result, excessive edge enhancement in the bright part of the subject image is performed. Can be suppressed.
[0039]
On the other hand, in order to achieve the above object, the contour correction method according to claim 5 captures a subject with a first sensitivity to obtain a first image signal indicating a subject image, and the subject has a first sensitivity. An image sensor that acquires a second image signal indicating the subject image by imaging with a lower second sensitivity, a first gamma correction unit that performs gamma correction processing on the first image signal, and the second image Second gamma correction means for performing gamma correction processing on the signal, and combining means for generating a composite signal by combining the first image signal after the gamma correction processing and the second image signal after the gamma correction processing; A contour correction method for an imaging apparatus comprising: a correction coefficient indicating a degree of contour correction based on a gamma correction process by the first gamma correction means, and indicated by the composite signal using the correction coefficient. Subject image And performs contour correction processing for.
[0040]
Therefore, according to the contour correcting method of the fifth aspect, since it operates in the same manner as the first aspect of the invention, the same effect as the first aspect of the invention can be achieved.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, a case where the present invention is applied to a digital camera will be described.
[0042]
[First Embodiment]
First, the configuration of the digital camera 10 according to the present embodiment will be described with reference to FIG. As shown in the figure, the digital camera 10 includes an optical lens 12, a diaphragm 14 for adjusting the amount of light passing through the optical lens 12, a shutter 16 for adjusting the passage time of light, the optical lens 12, and a diaphragm. 14 and R (red), G (green), and B (blue) indicating the subject image obtained by imaging the subject with respective high-sensitivity and low-sensitivity light receiving elements based on incident light indicating the subject image that has passed through the shutter 16. And a CCD 18 for outputting color analog image signals of three colors.
[0043]
The CCD 18 includes an analog signal processing unit 20 that performs predetermined analog signal processing on high-sensitivity and low-sensitivity signals input from the CCD 18, and high-sensitivity and low-sensitivity analog signals input from the analog signal processing unit 20. Are sequentially connected to an analog / digital converter (hereinafter referred to as “A / D converter”) 22 for converting each of the signals into digital data. The high-sensitivity digital data (hereinafter referred to as “high-sensitivity data”) output from the A / D converter 22 corresponds to the “first image signal” of the present invention, and the low-sensitivity digital data. (Hereinafter referred to as “low sensitivity data”) corresponds to the “second image signal” of the present invention.
[0044]
The digital camera 10 includes a drive unit 24 for driving the optical lens 12, a drive unit 26 for driving the aperture 14, a drive unit 28 for driving the shutter 16, and a CCD 18 during shooting. A CCD control unit 30 that performs timing control and a camera operation unit 84 that includes various operation switches such as a shutter switch are provided.
[0045]
The high sensitivity data and low sensitivity data (digital data of R, G, B signals) output from the A / D converter 22 are input to the control circuit 60 (details will be described later) and also to the digital signal processing circuit 34. Entered.
[0046]
The digital signal processing circuit 34 includes a high sensitivity side WB (white balance) adjustment processing circuit 72 for adjusting white balance on the high sensitivity data side, and a low sensitivity side WB adjustment processing circuit 74 for adjusting white balance on the low sensitivity data side. The high sensitivity side WB adjustment processing circuit 72 is connected to the high sensitivity side γ processing circuit 76 for performing gamma correction processing on the high sensitivity data side, and the low sensitivity side WB adjustment processing circuit 74 is connected to the low sensitivity data side. A low-sensitivity side γ processing circuit 78 for performing gamma correction processing, a synthesis processing circuit 80, a YC processing circuit 49, a contour correction circuit 47, a memory 48, a recording control unit 50, and a display control unit 52. It is configured to include.
[0047]
The CCD 18 is an image pickup device of the present invention, the high sensitivity side γ processing circuit 76 is a first gamma correction unit of the present invention, and the low sensitivity side γ processing circuit 78 is a second gamma correction unit of the present invention. 80 corresponds to the synthesizing means of the present invention, and the contour correction circuit 47 corresponds to the contour correcting means of the present invention.
[0048]
The high-sensitivity side WB adjustment processing circuit 72 and the low-sensitivity side WB adjustment processing circuit 74 respectively multiply the input R, G, and B image data (high-sensitivity data or low-sensitivity data) by a gain. The image forming apparatus includes three multipliers (not shown) for increasing / decreasing, and R, G, and B image data are respectively input to the multipliers. Further, gain values Rg, Gg, and Bg for controlling white balance are input to the multiplier from the control circuit 60, and each of the multipliers multiplies these two inputs. The R ′, G ′, and B ′ image data whose white balance is adjusted by this multiplication are output to the high sensitivity side γ processing circuit 76 or the low sensitivity side γ processing circuit 78.
[0049]
The high-sensitivity side γ processing circuit 76 and the low-sensitivity side γ processing circuit 78 have input / output characteristics so that the input white balance adjusted R ′, G ′, and B ′ image data have predetermined gamma characteristics. Is changed so that the 10-bit signal becomes an 8-bit signal, and is output to the synthesis processing circuit 80.
[0050]
The synthesis processing circuit 80 synthesizes the input high sensitivity data and low sensitivity data of R ′, G ′, and B ′ for each color as follows, and generates the composite data (corresponding to the “synthesis signal” of the present invention). Output as.
[0051]
That is, the synthesis processing circuit 80 synthesizes the input high sensitivity data and low sensitivity data as shown in the following equation (1) using a logarithmic addition method.
[0052]
[Expression 1]

[0053]
Here, th is a threshold value at which high sensitivity data and low sensitivity data are added at a ratio of 1: 1. Further, high is a value of high sensitivity data, and low is a value of low sensitivity data. Furthermore, p is a gain (usually a value of about 0.8 to 0.9) with respect to the entire added data, and thereby the dynamic range is controlled. The smaller the gain p, the wider the dynamic range, and the larger the gain p, the narrower the dynamic range. Specifically, by changing this value depending on the scene, such as 0.8 for high-contrast scenes (midsummer sunny weather, etc.), 0.86 for cloudy or shaded, 0.9 for indoor fluorescent lighting, etc. Therefore, the gradation value can be used effectively.
[0054]
FIG. 2 shows how the dynamic range changes depending on the gain p. The one corresponding to the minimum value in the range of the gain p applied here is indicated by a broken line, and the one corresponding to the maximum value is indicated by a two-dot chain line. As shown in the figure, in this case, the dynamic range becomes wider as the value of the gain p is reduced.
[0055]
Here, the above equation (1) is further generalized as shown in the following equation (2).
[0056]
[Expression 2]

[0057]
FIG. 3A shows the state of change in the MIN (high / th, 1) portion in the above equation (2). As shown in the figure, when the high sensitivity data reaches the threshold th, the high sensitivity data and the low sensitivity data are added on a one-to-one basis.
[0058]
FIG. 3B shows the change when the coefficient k is 0.2 in the portion of MAX (−k × high / th + 1, p) in the above equation (2).
[0059]
The coefficient k in the equation (2) is a coefficient determined by the signal charge saturation amount Sh of the high sensitivity signal and the signal charge saturation amount S1 of the low sensitivity signal, as shown by the following equation (3).
[0060]
[Equation 3]

[0061]
For example, when the ratio of the signal charge saturation amount between the high sensitivity signal and the low sensitivity signal is 4: 1, k = 0.2 (= 1−4 / (4 + 1)).
[0062]
Further, p in the equation (2) is a gain for the whole added data as described above, and is a variable value. _min Is also determined by the ratio of the signal charge saturation amount between the high sensitivity signal and the low sensitivity signal, as shown by the following equation (4).
[0063]
[Expression 4]

[0064]
When the system is such that the final output is the maximum value when the maximum value of the high sensitivity data is input in advance, the gain operation is performed when outputting the combined data of the high sensitivity data and the low sensitivity data. Necessary.
[0065]
That is, when the signal is input by the saturation amount of the high sensitivity signal and the low sensitivity signal, the output value is p. _min It is necessary to convert so that the final output becomes the maximum value by multiplying the gain by (<1).
[0066]
For example, when the ratio of the signal charge saturation amount between the high sensitivity signal and the low sensitivity signal is 4: 1, p _min = 0.8 (= 4 / (4 + 1)).
[0067]
And in a scene with high contrast, p = p _min P in the scene where contrast is not so high _min By setting a larger value than this, the output gradation can be used effectively.
[0068]
On the other hand, the YC processing circuit 49 (see FIG. 1) has R, G, and B3 plane data for all the pixels for the R ′, G ′, and B ′ combined data input from the combining processing circuit 80. After the interpolation processing as described above, the luminance signal Y and the chroma signals Cr and Cb are generated using the data for the three surfaces.
[0069]
Further, the contour correction circuit 47 is a gain indicating the degree of contour correction set based on the gamma correction processing by the high sensitivity side γ processing circuit 76 for the luminance signal Y input from the YC processing circuit 49 (present invention). The contour correction process is performed using the correction coefficient and stored in the memory 48.
[0070]
The chroma signals Cr and Cb generated in the YC processing circuit 49 are also stored in the memory 48.
[0071]
The recording control unit 50 has a role for mounting the recording medium 80 configured as a smart medium on the digital camera 10, and is synthesized by the synthesis processing circuit 80 and stored in the memory 48 after various processing. The combined data (luminance signal Y and chroma signals Cr, Cb) is read from the memory 48 and recorded on the recording medium 80. Further, the display control unit 52 reads the composite data stored in the memory 48 and performs a process for displaying an image on a liquid crystal display (hereinafter referred to as “LCD”) 82 using the composite data.
[0072]
In addition to the above configuration, the digital camera 10 includes a control circuit 60 configured by a microcomputer including a CPU (Central Processing Unit) 62, a ROM 64, and a RAM 66.
[0073]
The control circuit 60 controls the operation of the entire digital camera 10. The ROM 64 stores various processing routine programs executed by the CPU 62.
[0074]
Furthermore, the digital camera 10 includes a distance measuring sensor 32 that detects the distance to the subject. A signal indicating the distance to the subject detected by the distance measuring sensor 32 is input to the control circuit 60. When the shutter switch is half-pressed, the control circuit 60 performs an AF (Auto Focus) function based on the distance to the subject obtained by the distance measuring sensor 32 and performs focus control.
[0075]
Here, the structure of the CCD 18 according to the present embodiment will be described. As the CCD 18, a honeycomb CCD as shown in FIG. 4 can be adopted.
[0076]
As shown in FIG. 4, the imaging unit of the CCD 18 is assigned one by one for one color of one pixel, and has a predetermined arrangement pitch (horizontal arrangement pitch = Ph (μm), vertical arrangement pitch = Pv (μm)). The adjacent light receiving elements PD1 are arranged so as to bypass the plurality of light receiving elements PD1 which are two-dimensionally arranged by being shifted in the vertical and horizontal directions, and the opening AP formed on the front surface of the light receiving element PD1. In addition, a vertical transfer electrode VEL that takes out a signal (charge) from the light receiving element PD1 and transfers it in the vertical direction and a vertical transfer electrode VEL that is positioned at the lowest in the vertical direction are arranged on the lower side in the vertical direction, and from the vertical transfer electrode VEL A horizontal transfer electrode HEL for transferring the transferred signal to the outside. In the example shown in the figure, the opening AP is formed in an octagonal honeycomb shape.
[0077]
Here, each of the vertical transfer electrode groups constituted by a plurality of vertical transfer electrodes VEL arranged in a straight line in the horizontal direction has one of the vertical transfer drive signals V1, V2,. Can be applied simultaneously. In the example shown in the figure, the vertical transfer drive signal V3 is applied to the first-stage vertical transfer electrode group, and the vertical transfer drive signal V4 is applied to the second-stage vertical transfer electrode group. The vertical transfer drive signal V5 for the transfer electrode group, the vertical transfer drive signal V6 for the fourth vertical transfer electrode group, and the vertical transfer drive signal V7 for the fifth vertical transfer electrode group are 6 The vertical transfer drive signal V8 for the vertical transfer electrode group at the stage, the vertical transfer drive signal V1 for the vertical transfer electrode group at the seventh stage, and the vertical transfer drive signal for the vertical transfer electrode group at the eighth stage. V2 can be applied to each.
[0078]
On the other hand, each light receiving element PD1 is configured to be electrically connected to one adjacent vertical transfer electrode VEL via a transfer gate TG. In the example shown in the figure, each light receiving element PD1 is configured to be connected to a vertical transfer electrode VEL adjacent to the lower right via a transfer gate TG.
[0079]
In the figure, the opening AP formed on the front surface of the light receiving element PD1 in which “R” is entered is covered with a color separation filter (color filter) that transmits red light, and “G” is entered. The opening AP formed on the front surface of the light receiving element PD1 is covered with a color separation filter that transmits green light, and the opening AP formed on the front surface of the light receiving element PD1 on which “B” is written is blue. It is covered with a color separation filter that transmits light. That is, the light receiving element PD1 in which “R” is written receives red light, the light receiving element PD1 in which “G” is written receives green light, and the light receiving element PD1 in which “B” is written receives blue light. Each analog signal corresponding to the amount of received light is output.
[0080]
The CCD 18 further includes a light receiving element PD2 that is less sensitive than the light receiving element PD1 described above. As shown in FIG. 4, the light receiving element PD2 is provided between the plurality of light receiving elements PD1. Similarly to the light receiving element PD1, the light receiving element PD2 is formed with an opening AP having a smaller area than the opening of the light receiving element PD1, and is electrically connected to one adjacent vertical transfer electrode VEL by the transfer gate TG. It is connected. In addition, in the light receiving element PD2, an R, G, or B color filter is mounted in an opening AP formed on the front surface thereof, similarly to the light receiving element PD1. Thus, since the light receiving area of the light receiving element PD2 is smaller than the light receiving area of the light receiving element PD1, R, G, and B signals having lower sensitivity than the light receiving element PD1 can be obtained.
[0081]
The electrode to which the transfer gate TG of the light receiving element PD2 is connected is provided to be different from the electrode to which the transfer gate TG of the adjacent light receiving element PD1 is connected. In the present embodiment, the charge of the light receiving element PD1 is read out first, and then the charge of the light receiving element PD2 is read out.
[0082]
Next, the configuration of the contour correction circuit 47 according to the present embodiment will be described with reference to FIG. As shown in the figure, the contour correction circuit 47 includes a band-pass filter (hereinafter referred to as “BPF”) 47A that passes a predetermined high frequency band, a multiplier 47B, a multiplier 47C, An adder 47D, a YC processing circuit 47J, a correction coefficient generation unit 47E as a setting means, and a limiter 47F are included.
[0083]
The BPF 47A has an input terminal connected to an output terminal that outputs the luminance signal Y of the YC processing circuit 49. The BPF 47A extracts a component in a predetermined high frequency band from the luminance signal Y output from the YC processing circuit 49, and supplies it to the multiplier 47B. Output. For example, when the luminance signal Y output from the YC processing circuit 49 is in a state as shown in FIG. 6A, the edge of the luminance signal Y as shown in FIG. 6B is transferred from the BPF 47A to the multiplier 47B. A pulse corresponding to the position (hereinafter referred to as “edge pulse”) is output. That is, the BPF 47A has a role of extracting the contour of the subject image indicated by the luminance signal Y.
[0084]
In the multiplier 47B, the edge pulse input from the BPF 47A is multiplied by a later-described gain input from the limiter 47F, and the other of the multiplier 47C in which a predetermined gain is input to one input terminal. Output to the input end of.
[0085]
Here, the gain input to one input terminal of the multiplier 47C is for adjusting the overall gain of the contour correction circuit 47. In the multiplier 47C, the edge input from the multiplier 47B The pulse is multiplied by the gain, and one input terminal is output to the other input terminal of the adder 47D connected to the output terminal that outputs the luminance signal Y of the YC processing circuit 49.
[0086]
Therefore, in the adder 47D, the edge pulse amplified by the multiplier 47B and the multiplier 47C is added to the luminance signal Y output from the YC processing circuit 49, and an example is shown in FIG. The luminance signal Y in such a state that the contour of the subject image is emphasized is generated and stored in the memory 48.
[0087]
That is, the contour correction circuit 47 according to the present embodiment is configured to perform the contour correction processing performed on the luminance signal Y of the composite data generated by the YC processing circuit 49 using a gain indicating the degree of correction. Has been.
[0088]
On the other hand, the input end of the YC processing circuit 47J is connected to the output end of the high-sensitivity side γ processing circuit 76, and R, After performing interpolation processing so that the data of the G and B3 planes are aligned, the luminance signal Y and the chroma signals Cr and Cb are generated using the data for the three planes.
[0089]
The correction coefficient generation unit 47E is connected to the output terminal for outputting the luminance signal Y of the YC processing circuit 47J at the input terminal, and each of the subject images indicated by the luminance signal Y input from the YC processing circuit 47J. For a pixel, a gain (in the “correction coefficient” of the present invention) that uses the reciprocal of the differential coefficient at the signal level of each pixel of the gamma correction curve in the gamma correction processing by the high sensitivity side γ processing circuit 76 in the multiplier 47B. To the limiter 47F.
[0090]
FIG. 7A shows an example of a gamma correction curve. The distribution of the differential coefficient in the gamma correction curve shown in FIG. 7 is as shown in FIG. 7B, and the reciprocal distribution of the differential coefficient is as shown in FIG. 7C. That is, in the distribution of the reciprocal of the differential coefficient, the degree of inclination becomes smaller as the degree of inclination of the gamma correction curve becomes larger.
[0091]
Since the correction coefficient generation unit 47E according to the present embodiment applies the reciprocal of the differential coefficient of such a gamma correction curve as the gain used in the multiplier 47B, in the dark part of the subject image resulting from the gamma correction process. Generation of noise can be suppressed.
[0092]
Note that the correction coefficient generation unit 47E according to the present embodiment corresponds to the value of the luminance signal Y of the high-sensitivity data for each pixel input from the YC processing circuit 47J as shown in FIG. 8 as an example. It is configured as a look-up table LUT in which the reciprocal of the differential coefficient of the gamma correction curve of the high sensitivity side γ processing circuit 76 (gain used in the multiplier 47B) is associated.
[0093]
In the limiter 47F, when the value of the luminance signal Y of the high-sensitivity data of the corresponding pixel is larger than a predetermined threshold value, the gain input from the correction coefficient generation unit 47E is replaced with a predetermined value and the multiplier 47B In other cases, the gain input from the correction coefficient generator 47E is output to the multiplier 47B as it is.
[0094]
That is, the limiter 47F has a role of limiting the gain used in the multiplier 47B when the signal level of the target pixel is higher than a predetermined level, thereby suppressing excessive edge enhancement in the bright part of the subject image. To be able to.
[0095]
Hereinafter, the operation of the digital camera 10 having such a configuration at the time of shooting will be described.
[0096]
First, incident light indicating a subject image that has passed through the optical lens 12, the diaphragm 14, and the shutter 16 is received by both the light receiving elements PD1 and PD2 having different sensitivity of the CCD 18, and analog signal processing is performed as an analog image signal indicating the subject image. Is output to the unit 20. Further, when the user half-presses the shutter switch of the camera operation unit 84 to photograph the subject with the digital camera 10, the distance T to the subject is derived based on the signal input from the distance measuring sensor 32 at this time. Under the control of the drive unit 24, the AF function works to control the focus.
[0097]
The analog signal processing unit 20 performs predetermined analog signal processing on both high-sensitivity and low-sensitivity analog image signals input from the CCD 18. These analog image signals are respectively converted into high sensitivity data and low sensitivity data by the A / D converter 22. The high sensitivity data and the low sensitivity data output from the A / D converter 22 are input to the digital signal processing circuit 34 and the control circuit 60.
[0098]
In the control circuit 60, gain values Rg, Gg, and Bg for controlling the white balance of each of the high sensitivity data and the low sensitivity data based on the high sensitivity data and the low sensitivity data input from the A / D converter 22 are set. Derived and output to the corresponding high sensitivity side WB adjustment processing circuit 72 and low sensitivity side WB adjustment processing circuit 74.
[0099]
On the other hand, the high sensitivity data and the low sensitivity data input to the digital signal processing circuit 34 use the gain values input from the control circuit 60 by the high sensitivity side WB adjustment processing circuit 72 and the low sensitivity side WB adjustment processing circuit 74. The white balance is adjusted, and further, the high sensitivity side γ processing circuit 76 and the low sensitivity side γ processing circuit 78 respectively perform gamma correction processing and output to the synthesis processing circuit 80. In the synthesis processing circuit 80, the input high sensitivity data and low sensitivity data are synthesized as described above using the logarithmic addition method, and the resultant synthesized data is output to the YC processing circuit 49.
[0100]
In the YC processing circuit 49, as described above, the luminance signal Y and the chroma signals Cr and Cb are generated based on the combined data input from the combining processing circuit 80, and the luminance signal Y is output to the contour correcting circuit 47. Chroma signals Cr and Cb are stored in a predetermined area of the memory 48.
[0101]
In the contour correction circuit 47, as described above, a component (edge pulse) in a predetermined high frequency band is extracted from the luminance signal Y output from the YC processing circuit 49 in the BPF 47A, and is output to the multiplier 47B. In 47B, the edge pulse input from the BPF 47A is multiplied by the gain output from the limiter 47F and output to the multiplier 47C.
[0102]
The multiplier 47C multiplies the edge pulse input from the multiplier 47B by a predetermined gain and outputs the result to the adder 47D. The adder 47D outputs the edge pulse from the YC processing circuit 49. The luminance signal Y in a state in which the contour of the subject image is emphasized is generated by being added to the luminance signal Y, and is stored in the memory 48.
[0103]
On the other hand, the YC processing circuit 47J generates the luminance signal Y and the chroma signals Cr and Cb based on the high sensitivity data input from the high sensitivity side γ processing circuit 76 as described above, and the luminance signal Y of these is corrected. It is output to the coefficient generator 47E.
[0104]
Then, the correction coefficient generation unit 47E applies gamma in the gamma correction processing by the high sensitivity side γ processing circuit 76 to each pixel of the subject image indicated by the luminance signal Y of the high sensitivity data input from the YC processing circuit 47J. The reciprocal of the differential coefficient at the signal level of each pixel of the correction curve is output to the limiter 47F as a gain used in the multiplier 47B.
[0105]
Then, in the limiter 47F, when the value of the luminance signal Y of the high sensitivity data of the corresponding pixel is larger than a predetermined threshold, the gain input from the correction coefficient generation unit 47E is replaced with a predetermined value and multiplied. In other cases, the gain input from the correction coefficient generator 47E is output to the multiplier 47B as it is.
[0106]
Therefore, in the multiplier 47B, the gain is multiplied by the edge pulse input from the BPF 47A. As a result, the occurrence of noise in the dark part of the subject image indicated by the composite data is suppressed, and the Excessive edge enhancement in the part can be suppressed.
[0107]
On the other hand, the display control unit 52 executes processing for image display on the LCD 82 using the combined data (luminance signal Y and chroma signals Cr and Cb) after various processing stored in the memory 48. In addition, the recording control unit 50 records the composite data stored in the memory 48 on the recording medium 80 in accordance with an instruction signal input from the control circuit 60 when the shutter switch of the camera operation unit 84 is fully pressed. I do. As a result, shooting is performed.
[0108]
As described above in detail, the digital camera 10 according to the present embodiment captures a subject with high sensitivity by the CCD 18 to acquire high sensitivity data indicating a subject image, and captures the subject with low sensitivity. The low sensitivity data indicating the subject image is acquired, the gamma correction processing is performed on the high sensitivity data by the high sensitivity side γ processing circuit 76 and the gamma correction processing is performed on the low sensitivity data by the low sensitivity side γ processing circuit 78. The composite processing circuit 80 generates high-sensitivity data and low-sensitivity data after the gamma correction processing to generate composite data, and the contour correction circuit 47 uses the preset gain indicating the degree of contour correction. When performing the contour correction process on the subject image indicated by the composite data, the gain is based on the gamma correction process by the high sensitivity side γ processing circuit 76. Since the set can be determined the gain easily.
[0109]
Further, in the digital camera 10 according to the present embodiment, the differential coefficient at the signal level of each pixel of the gamma correction curve in the gamma correction processing by the high sensitivity side γ processing circuit 76 for each pixel of the subject image. Since the gain is set on the basis of the reciprocal number, the generation of noise in the dark part of the subject image can be suppressed.
[0110]
Furthermore, in the digital camera 10 according to the present embodiment, when the signal level of the pixel is larger than a predetermined threshold value, the gain is replaced with a predetermined value, so that the upper limit value of the gain is limited. As a result, excessive edge enhancement in the bright part of the subject image can be suppressed.
[0111]
In the present embodiment, a case has been described in which the YC processing circuit 47J and the correction coefficient generation unit 47E output the gain used by the multiplier 47B using the high sensitivity data output from the high sensitivity side γ processing circuit 76 as an input. However, the present invention is not limited to this, and for example, the gain can be output with the high sensitivity data output from the high sensitivity side WB adjustment processing circuit 72 as an input.
[0112]
In this case, a gamma correction curve in the gamma correction processing by the high sensitivity side γ processing circuit 76 is performed for each pixel of the subject image indicated by the luminance signal Y of the high sensitivity data input from the high sensitivity side WB adjustment processing circuit 72. The reciprocal of the differential coefficient at the signal level of each of the pixels is output to the limiter 47F as a gain used in the multiplier 47B. Also in this case, the same effects as in the present embodiment can be obtained.
[0113]
In the present embodiment, when the value of the luminance signal Y of the high sensitivity data of the corresponding pixel is larger than a predetermined threshold in the limiter 47F, the gain input from the correction coefficient generation unit 47E is determined in advance. Although the case where the value is output to the multiplier 47B has been described, the present invention is not limited to this. For example, when the gain input from the correction coefficient generation unit 47E is larger than a predetermined threshold value, The gain may be replaced with a predetermined value and output to the multiplier 47B. Also in this case, the same effects as in the present embodiment can be obtained.
[0114]
[Second Embodiment]
In the second embodiment, the low sensitivity data is derived by calculation based on the high sensitivity data and the sensitivity ratio of the high sensitivity signal and the low sensitivity signal, and the contour is based on the combined data of the low sensitivity data and the high sensitivity data. An embodiment in which a gain (correction coefficient) indicating the degree of correction is set, that is, an embodiment of the invention according to claim 3 will be described.
[0115]
First, the configuration of the digital camera 10B according to the present embodiment will be described with reference to FIG. In FIG. 9, the same components as those in FIG. 1 are denoted by the same reference numerals as those in FIG. 1, and description thereof is omitted.
[0116]
As shown in FIG. 9, the digital camera 10 </ b> B according to the second embodiment is connected to the output terminal of the high sensitivity side WB adjustment processing circuit 72 and the high sensitivity side γ processing circuit 76 instead of the contour correction circuit 47. The only difference from the digital camera 10 according to the first embodiment is that a contour correction circuit 47 'is provided.
[0117]
Hereinafter, the configuration of the contour correction circuit 47 ′ according to the second embodiment will be described with reference to FIG. 10 that are the same as in FIG. 5 are assigned the same reference numerals as in FIG. 5 and descriptions thereof are omitted.
[0118]
The contour correction circuit 47 ′ according to the second embodiment is the same as the calculator 47G that multiplies the input data by the sensitivity ratio of the high sensitivity signal and the low sensitivity signal of the CCD 18 and the low sensitivity side γ processing circuit 78. The low-sensitivity side γ processing circuit 47H configured as described above and the synthesis processing circuit 47I configured the same as the synthesis processing circuit 80 are newly provided, and correction is performed instead of the correction coefficient generation unit 47E. The difference from the contour correction circuit 47 according to the first embodiment is that a coefficient generator 47E ′ is provided.
[0119]
The input terminal of the computing unit 47G is connected to the output terminal of the high sensitivity side WB adjustment processing circuit 72, and the computing unit 47G calculates the sensitivity ratio for the high sensitivity data input from the high sensitivity side WB adjustment processing circuit 72. Multiply and output to the low sensitivity side γ processing circuit 47H.
[0120]
Here, the sensitivity ratio is obtained by dividing the sensitivity of the low sensitivity signal by the sensitivity of the high sensitivity signal. That is, the computing unit 47G assumes that no noise is generated in the low sensitivity data, and derives the low sensitivity data by multiplying the high sensitivity data input from the high sensitivity side WB adjustment processing circuit 72 by the sensitivity ratio. doing.
[0121]
The low-sensitivity side γ processing circuit 47H performs gamma correction processing on the low-sensitivity data input from the computing unit 47G in the same manner as the low-sensitivity side γ processing circuit 78, and at one input terminal, the high-sensitivity side γ processing circuit The output is output to the other input terminal of the synthesis processing circuit 47I to which the output terminal 76 is connected.
[0122]
Accordingly, in the synthesis processing circuit 47I, the low sensitivity data input from the low sensitivity side γ processing circuit 47H and the high sensitivity data input from the high sensitivity side γ processing circuit 76 are synthesized by the same method as the synthesis processing circuit 80. Then, it is output as composite data to the YC processing circuit 47J. Therefore, the YC processing circuit 47J uses the data for the three surfaces after interpolation processing is performed on the combined data input from the combining processing circuit 47I so that the data of the R, G, and B3 surfaces are aligned in all pixels. Thus, the luminance signal Y and the chroma signals Cr and Cb are generated, and the luminance signal Y of these is output to the correction coefficient generator 47E ′.
[0123]
On the other hand, the correction coefficient generator 47E ′ according to the second embodiment operates on the combined data for each pixel of the subject image indicated by the luminance signal Y of the combined data input from the YC processing circuit 47J. The multiplier 47B uses the inverse of the differential coefficient at the signal level of each pixel of the combination of the gamma correction curves in the gamma correction processing of the high sensitivity side γ processing circuit 76 and the low sensitivity side γ processing circuit 47H. (Corresponding to “correction coefficient” of the present invention) and output to the limiter 47F.
[0124]
Here, in the distribution of the reciprocal of the differential coefficient, the degree of inclination becomes smaller as the degree of inclination in the combination of the respective gamma correction curves becomes larger.
[0125]
Accordingly, the correction coefficient generation unit 47E ′ according to the second embodiment also uses the reciprocal of the differential coefficient of such a gamma correction curve as the gain used in the multiplier 47B. Generation of noise in the dark part of the image can be suppressed.
[0126]
The correction coefficient generation unit 47E ′ according to the present embodiment also has the value of the luminance signal Y for each pixel input from the YC processing circuit 47J, similarly to the correction coefficient generation unit 47E according to the first embodiment, It is configured as a look-up table LUT in which the reciprocal of the differential coefficient corresponding thereto (gain used in the multiplier 47B) is associated.
[0127]
On the other hand, in the limiter 47F, when the value of the luminance signal Y of the combined data of the corresponding pixel is larger than a predetermined threshold value, the gain input from the correction coefficient generation unit 47E ′ is replaced with a predetermined value. In other cases, the gain input from the correction coefficient generator 47E ′ is output to the multiplier 47B as it is.
[0128]
As described above, the limiter 47F according to the second embodiment is the same as that used in the contour correction circuit 47 according to the first embodiment, and performs excessive edge enhancement in the bright part of the subject image. It is for suppressing.
[0129]
The computing unit 47G is the multiplication unit of the present invention, the low sensitivity side γ processing circuit 47H is the third gamma correction unit of the present invention, the synthesis processing circuit 47I is the second synthesis unit of the present invention, and the correction coefficient generator 47E ′ is Each corresponds to the setting means of the present invention.
[0130]
The operation of the digital camera 10B other than the portion from the computing unit 47G to the correction coefficient generation unit 47E ′ in the contour correction circuit 47 ′ is the same as that of the digital camera 10 according to the first embodiment, and will be described here. Is omitted.
[0131]
As described above in detail, the digital camera 10B according to the present embodiment captures a subject with high sensitivity by the CCD 18 to obtain high sensitivity data indicating a subject image, and captures the subject with low sensitivity. The low sensitivity data indicating the subject image is acquired, the gamma correction processing is performed on the high sensitivity data by the high sensitivity side γ processing circuit 76 and the gamma correction processing is performed on the low sensitivity data by the low sensitivity side γ processing circuit 78. The synthesized processing circuit 80 synthesizes the high-sensitivity data and the low-sensitivity data after the gamma correction processing to generate synthesized data, and the contour correction circuit 47 ′ uses a preset gain indicating the degree of contour correction. When the contour correction process is performed on the subject image indicated by the composite data, the gain is based on the gamma correction process by the high sensitivity side γ processing circuit 76. Therefore, the gain can be easily determined.
[0132]
In the digital camera 10B according to the present embodiment, the high sensitivity data before the gamma correction processing by the high sensitivity side γ processing circuit 76 is multiplied by the ratio of the sensitivity of the low sensitivity signal to the sensitivity of the high sensitivity signal. The low-sensitivity data is subjected to the same gamma correction processing as that of the low-sensitivity side γ processing circuit 78, and the high-sensitivity data after the gamma correction processing and the gamma correction process output from the low-sensitivity side γ processing circuit 47H. The low-sensitivity data and the low-sensitivity side γ processing circuit 76 and the low-sensitivity side γ are applied to each pixel of the subject image, and the low-sensitivity side γ processing circuit 76 and the low-sensitivity side γ are combined. Since the gain is set based on the reciprocal of the differential coefficient at the signal level of each pixel of the combination of each gamma correction curve in each gamma correction process of the processing circuit 47H. The generation of noise in the dark part of the subject image can be suppressed.
[0133]
Furthermore, in the digital camera 10B according to the present embodiment, when the pixel signal level is larger than a predetermined threshold value, the gain is replaced with a predetermined value, so that the upper limit value of the gain is limited. As a result, excessive edge enhancement in the bright part of the subject image can be suppressed.
[0134]
In the present embodiment, when the value of the luminance signal Y of the combined data of the corresponding pixel is larger than a predetermined threshold in the limiter 47F, the gain input from the correction coefficient generation unit 47E ′ is determined in advance. The case where the value is replaced with a value and output to the multiplier 47B has been described. However, the present invention is not limited to this. For example, when the gain input from the correction coefficient generation unit 47E ′ is larger than a predetermined threshold value. The gain may be replaced with a predetermined value and output to the multiplier 47B. Also in this case, the same effects as in the present embodiment can be obtained.
[0135]
In each of the above embodiments, the case where the correction coefficient generation unit is configured as a look-up table has been described. However, the present invention is not limited to this, for example, the input data of the correction coefficient generation unit and A mathematical expression indicating the relationship with the output data may be stored in advance, and the output data may be derived by calculation using the mathematical expression. In this case, although the load applied to the calculation increases, the storage capacity for storing the look-up table can be reduced.
[0136]
Further, in each of the above embodiments, an example in which each of the high sensitivity light receiving element PD1 and the low sensitivity light receiving element PD2 is provided to obtain a high sensitivity signal and a low sensitivity signal has been described, but as shown in FIG. A light receiving region of one light receiving element PD is divided into a high sensitivity light receiving region 92 having a large light receiving area for receiving high sensitivity light by a channel stopper 94 and a low sensitivity light receiving region 90 having a small light receiving area for receiving low sensitivity light. It is good also as a structure from which a high sensitivity signal and a low sensitivity signal are obtained by this area | region. Since the light receiving element PD is provided with the channel stopper 94, the signal received with high sensitivity and the signal received with low sensitivity are not mixed, and both signals can be received separately. .
[0137]
Further, in each of the above embodiments, the case where the contour correction is performed on the luminance signal Y of the composite data has been described. However, the present invention is not limited to this, and the form in which the contour correction is performed on the composite data. It can also be. In this case, the YC processing circuit 49 and the YC processing circuit 47J required in the above embodiments are not necessary. Also in this case, the same effects as in the present embodiment can be obtained.
[0138]
Further, the configurations of the digital cameras 10 and 10B according to the above-described embodiments (see FIGS. 1 and 9) are merely examples, and it goes without saying that they can be appropriately changed without departing from the gist of the present invention.
[0139]
Furthermore, the present invention is not limited to the above digital camera, and can be applied to various imaging devices.
[0140]
【The invention's effect】
As described above, according to the present invention, a subject is imaged with a first sensitivity by an imaging device to obtain a first image signal indicating a subject image, and the subject is captured with a second sensitivity lower than the first sensitivity. A second image signal indicating the subject image is obtained by imaging, and the first gamma correction unit performs gamma correction processing on the first image signal and the second gamma correction unit performs gamma correction on the second image signal. Processing is performed, a synthesized signal is generated by synthesizing the first image signal and the second image signal after the gamma correction processing by the synthesizing unit, and a preset correction coefficient indicating the degree of contour correction is used by the contour correcting unit. When the contour correction process is performed on the subject image indicated by the composite signal, the correction coefficient is set based on the gamma correction process by the first gamma correction unit. Can easily be determined, the effect is obtained that.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a digital camera according to a first embodiment.
FIG. 2 is a graph of light quantity versus combined data (final image 8 bitQL) showing how the dynamic range changes according to the gain p in the expression (1) according to the embodiment.
FIG. 3 is a graph for explaining the expression (1) according to the embodiment.
FIG. 4 is a schematic diagram showing a configuration of a CCD applied in the digital camera according to the embodiment.
FIG. 5 is a block diagram showing a configuration of a contour correction circuit 47 according to the first embodiment.
FIG. 6 is a waveform diagram for explaining the operation of the contour correction circuit 47 according to the embodiment;
FIG. 7 is a graph for explaining the reciprocal of a differential coefficient in a gamma correction curve.
FIG. 8 is a schematic diagram showing a configuration of a correction coefficient generation unit 47E according to the first embodiment.
FIG. 9 is a block diagram illustrating a configuration of a digital camera according to a second embodiment.
FIG. 10 is a block diagram showing a configuration of a contour correction circuit 47 ′ according to the second embodiment.
FIG. 11 is a schematic diagram showing a configuration of a CCD provided with a light receiving element capable of receiving both high sensitivity and low sensitivity signals.
[Explanation of symbols]
10, 10B Digital camera
18 CCD (imaging device)
47, 47 'Contour correction circuit (contour correction means)
47E, 47E 'correction coefficient generator (setting means)
47F limiter (setting means)
47G computing unit (multiplication means)
47H Low sensitivity side γ processing circuit (third gamma correction means)
47I Synthesis processing circuit (second synthesis means)
60 Control circuit
76 High sensitivity side γ processing circuit (first gamma correction means)
78 Low sensitivity side γ processing circuit (second gamma correction means)
80 Composition processing circuit (composition means)

Claims (5)

A first image signal indicating a subject image is acquired by imaging the subject with a first sensitivity, and a second image signal indicating the subject image is acquired by imaging the subject with a second sensitivity lower than the first sensitivity. An image sensor to obtain;
First gamma correction means for performing gamma correction processing on the first image signal;
Second gamma correction means for performing gamma correction processing on the second image signal;
Combining means for combining the first image signal after the gamma correction processing and the second image signal after the gamma correction processing to generate a combined signal;
Contour correcting means for performing contour correction processing on the subject image indicated by the composite signal using a preset correction coefficient indicating the degree of contour correction;
Setting means for setting the correction coefficient based on gamma correction processing by the first gamma correction means;
An imaging apparatus comprising: The setting means sets the correction coefficient for each pixel of the subject image based on the reciprocal of the differential coefficient at the signal level of each pixel of the gamma correction curve in the gamma correction processing by the first gamma correction means. The imaging device according to claim 1 to set. Multiplying means for multiplying the first image signal before the gamma correction processing by the first gamma correction means by the ratio of the second sensitivity to the first sensitivity to output a third image signal;
Third gamma correction means for performing gamma correction processing similar to the second gamma correction means on the third image signal;
Second combining means for combining the first image signal after the gamma correction processing and the third image signal after the gamma correction processing in the same manner as the combining means to generate a second combined signal;
Further comprising
The setting means applies each gamma correction curve in each gamma correction process of the first gamma correction means and the third gamma correction means applied to the second composite signal to each pixel of the subject image. The imaging apparatus according to claim 1, wherein the correction coefficient is set based on a reciprocal of a differential coefficient at a signal level of each pixel of the combination. The imaging apparatus according to claim 2 or 3, wherein the setting means replaces the correction coefficient with a predetermined value when the signal level of the pixel or the correction coefficient is larger than a predetermined threshold. A first image signal indicating a subject image is acquired by imaging the subject with a first sensitivity, and a second image signal indicating the subject image is acquired by imaging the subject with a second sensitivity lower than the first sensitivity. An imaging device to be acquired, first gamma correction means for performing gamma correction processing on the first image signal, second gamma correction means for performing gamma correction processing on the second image signal, and after gamma correction processing A contour correcting method for an imaging apparatus, comprising: a combining unit configured to combine the first image signal and the second image signal after the gamma correction process to generate a combined signal;
Setting a correction coefficient indicating the degree of contour correction based on the gamma correction processing by the first gamma correction means;
A contour correction method for performing contour correction processing on a subject image indicated by the composite signal using the correction coefficient.

Images