JP4054263B2 - Imaging device and imaging condition setting method for imaging device - Google Patents

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、デジタルカメラ１０のメモリ４８（図１参照）には、合成処理回路８０からＲ’、Ｇ’、Ｂ’の各合成データが入力され、当該Ｒ’、Ｇ’、Ｂ’の各合成データを格納する。
【００６９】
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８６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により合成されてメモリ４８に格納された合成データを当該メモリ４８から読み出して記録メディア８６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。
【００７０】
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。
【００７１】
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で実行される後述する撮影処理プログラム等の各種処理プログラムが記憶されている。また、ＲＡＭ６６には、Ａ／Ｄ変換器２２から制御回路６０に入力される高感度データ及び低感度データが各々互いに異なる領域に記憶される。
【００７２】
なお、デジタルカメラ１０では、ＣＣＤ１８により取得された画像データによって示される被写体像のコントラストが最大となるようにレンズの位置を設定する、所謂ＴＴＬ（Through The Lens）方式により合焦制御（所謂ＡＦ制御）を行う。
【００７３】
一方、本実施の形態に係るデジタルカメラ１０では、図４に示すように、ＣＣＤ１８によって得られた画像データ（本実施の形態では、高感度データ）により示される被写体像を水平方向及び垂直方向に複数の領域に分割し（ここでは縦方向に８分割、横方向に８分割の合計６４分割。）、当該画像データによって得られる被写体像の明るさを示す測光値をそれぞれの分割領域毎に検出することができる。
【００７４】
さらに、デジタルカメラ１０では、図４に示すように、被写体像の中央部（同図の太枠内）に位置する分割領域に大きな重み（同図では「６４」。）を付加し、被写体像の外周部に近い分割領域ほど重みを小さくして（外周に接する分割領域では「１」。）被写体全体としての測光を行う中央重点測光方式と、被写体像の中央部の分割領域のみに重みを付加し、その他の分割領域の重みを「０」として測光を行うスポット測光方式と、全ての分割領域の重みを同一として測光を行う平均測光方式と、の何れかの測光方式によって被写体像の明るさを示す測光データを取得することができる。
【００７５】
なお、デジタルカメラ１０では、これら３種類の測光方式のうち、何れか１つの測光方式が予めユーザによってカメラ操作部８４の操作により選択されるようになっており、ＣＰＵ６２では、予め選択されている測光方式により被写体像全体としての測光データを導出し、導出した測光データに応じてシャッタースピード及び絞りの状態を設定する露出制御（所謂ＡＥ制御）を行う。
【００７６】
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５に示すようなハニカムＣＣＤを採用することができる。
【００７７】
このＣＣＤ１８の撮像部は、図５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。
【００７８】
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。
【００７９】
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。
【００８０】
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。
【００８１】
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５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（開口部ＡＰの開口面積）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。
【００８２】
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。
【００８３】
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。
【００８４】
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。
【００８５】
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。
【００８６】
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がＲＡＭ６６に記憶されると共に、当該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。
【００８７】
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メモリ４８に格納される。
【００８８】
また、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を用いたＬＣＤ８２への画像表示のための処理を実行する。
【００８９】
ここで、本実施の形態に係るデジタルカメラ１０では、ユーザが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、ＣＰＵ６２において撮影処理プログラムが実行される。
【００９０】
図６は、当該撮影処理プログラムの処理の流れを示すフローチャートであり、以下、同図を参照して本実施の形態に係る撮影処理について説明する。なお、ここでは、露出制御に適用される測光方式がユーザによって予め選択されているものとして説明する。
【００９１】
まず、ステップ１００では、ＣＣＤ１８により取得された画像データ（ここでは、高感度データ）によって示される被写体像のコントラストが最大となるようにレンズの位置を決定するＡＦ制御を行う。
【００９２】
次のステップ１０２では、スポット測光方式による測光データ（以下、「ＥＶ＿ｓ」という。）と、中央部を除く分割領域（図４の太枠の外側に位置された分割領域）全体としての測光データ（以下、「ＥＶ＿ｂ」という。）とを取得し、その後にステップ１０４に移行してＥＶ＿ｂとＥＶ＿ｓの差（以下、「ΔＥＶ」という。）を導出する。なお、ＥＶ＿ｂは、中央部を除く各分割領域の測光データの平均値として導出する。
【００９３】
その後、ステップ１０６では、ΔＥＶが所定値以上であるか否かを判定する。当該判定が否定判定の場合は、逆光での撮影（ＣＣＤ１８による撮像）ではないものと判断してステップ１０８に移行して通常の撮影処理を実行し、その後に本撮影処理プログラムを終了する。
【００９４】
なお、逆光での撮影か否かを判定するための上記所定値は、中央部の分割領域と、中央部の分割領域を除く分割領域についての測光データの差ΔＥＶが当該所定値以上であれば被写体像に黒つぶれが発生するものと見なすことのできる値として、デジタルカメラ１０を用いた実機による実験や、デジタルカメラ１０の設計仕様に基づくコンピュータ・シミュレーション等によって予め得られた値等を適用することができる。
【００９５】
一方、ステップ１０６で肯定判定された場合は、ステップ１１０に移行してユーザにより、「ストロボ強制ＯＦＦモード」が設定されているか否かを判定する。当該判定が否定判定である場合、撮影時にストロボ８９を発光させて被写体の明るさを増加させるものと判断し、ユーザによって予め選択された測光方式によって通常のＡＥ制御を行い、その後にステップ１２２に移行する。
【００９６】
また、ステップ１１０において肯定判定された場合、ストロボ８９が発光されることはなく、被写体の明るさを増加させることはできないものと判断し、ステップ１１４に移行して、露出制御に適用する測光方式としてユーザによって予め選択された測光方式が「スポット測光方式」であるか否かを判定し、当該判定が否定判定の場合は測光方式を切換える必要があると判断してステップ１１６に移行し、露出制御に適用する測光方式を「スポット測光方式」に強制的に切換え、その後にステップ１１８に移行する。一方、ステップ１１４で肯定判定となった場合には、上記ステップ１１６の処理を実行することなくステップ１１８に移行する。
【００９７】
ステップ１１８では、スポット測光方式により測光データＥＶ＿ｓを取得する。そして、次のステップ１２０では、取得したＥＶ＿ｓに応じてシャッタスピード及び絞りを設定することによりＡＥ制御を行い、その後にステップ１２２に移行する。
【００９８】
以上の処理により、逆光での撮影時で、かつストロボ強制ＯＦＦモードが設定されておらず、ストロボ８９が発光される条件となっている場合には、当該ストロボ８９の発光によって主要被写体の明るさが増加するため、主要被写体の黒つぶれは発生しないものと見なして、ユーザにより設定された測光方式にて通常通りにＡＥ制御を行う。
【００９９】
一方、逆光での撮影時で、かつストロボ８９が発光されない条件となっている場合には、強制的にスポット測光方式に切換え、一般に被写体像の中央部に位置される主要被写体の明るさに応じたＡＥ制御を行うことにより、被写体全体としての明るさが逆光でないときより増加するようにしている。これによって、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像することが可能となる。
【０１００】
ステップ１２２では、シャッタスイッチが半押し状態から全押し状態に移行されたか否かを判定し、否定判定である場合はステップ１２４に移行して、シャッタスイッチがオフ状態とされたか否かを判定する。当該判定が肯定判定の場合は、ユーザによる撮影が中止されたものと判断して本撮影処理プログラムを終了し、当該判定が否定判定の場合は上記ステップ１２２に戻る。
【０１０１】
一方、ステップ１２２で肯定判定となった場合にはユーザによって撮影が指示されたものと判断してステップ１２６に移行し、ユーザによって「ストロボ強制ＯＦＦモード」が設定されているか否かを判定する。そして、当該判定が肯定判定の場合はステップ１２８に移行して、ΔＥＶに応じて上述した合成データのダイナミックレンジを決定する係数（以下、「合成に関する係数」という。）である閾値ｔｈ及びゲインｐの少なくとも一方を設定し、その後ステップ１４４に移行する。
【０１０２】
なお、上記閾値ｔｈ及びゲインｐの設定は、被写体の明るさの増加の度合いを示すΔＥＶが大きくなるほどダイナミックレンジが拡大されるように設定する。
【０１０３】
すなわち、本撮影処理では、逆光での撮影時で、かつユーザにより「ストロボ強制ＯＦＦモード」が設定されている場合、ユーザによって予め選択された測光方式にかかわらず、スポット測光方式により露出制御を行い、被写体の明るさを増加させて中央部の主要被写体を黒つぶれさせることなく撮影できるようにすると共に、被写体の明るさの増加の度合い（ここでは、ΔＥＶ）に応じて閾値ｔｈ及びゲインｐを設定してダイナミックレンジを拡大することにより、主要被写体以外の領域における白とびの発生を防止できるようにしている。
【０１０４】
一方、ステップ１２６で否定判定となった場合にはステップ１３０に移行し、この時点でのスポット測光による測光データＥＶ＿ｓ１を取得し、その後にステップ１３２に移行してストロボ８９を発光させ、次のステップ１３４でストロボ８９を発光させたときのスポット測光による測光データＥＶ＿ｓ２を取得する。
【０１０５】
なお、合成処理回路８０では、ストロボ８９を発光させた状態でＣＣＤ１８を介して取得されたガンマ補正処理後の高感度データ及び低感度データを、内蔵された不図示のメモリの所定領域に記憶しておく。
【０１０６】
次のステップ１３６では、ストロボ８９の発光の前後でのスポット測光による測光データの変化量Ｘ（＝ＥＶ＿ｓ２−ＥＶ＿ｓ１）を導出し、その後にステップ１３８に移行して、被写体の明るさが所定量を超えて増加したか否かを判断すべく、変化量Ｘが所定値を超えているか否かを判定する。
【０１０７】
なお、上記所定値は、変化量Ｘが当該所定値を超えていれば、ストロボ８９からの光が主要被写体に十分に照射されているものと見なすことのできる値として、デジタルカメラ１０を用いた実機による実験や、デジタルカメラ１０の設計仕様に基づくコンピュータ・シミュレーション等によって予め得られた値等を適用することができる。
【０１０８】
ステップ１３８で否定判定となった場合、ストロボ８９からの光が主要被写体に十分には照射されていないものと見なしてステップ１４０に移行し、閾値ｔｈ及びゲインｐの少なくとも一方を、ダイナミックレンジが予め定められた上限レンジとするように予め定められた最小値に設定し、その後にステップ１４４に移行する。なお、上記最小値は、上述した高感度データ及び低感度データの飽和比等により決定されるものである。
【０１０９】
一方、ステップ１３８で肯定判定となった場合には、ストロボ８９からの光が主要被写体に十分に照射されているものと見なしてステップ１４２に移行し、閾値ｔｈ及びゲインｐを、ダイナミックレンジが上記上限レンジよりも狭くなるように予め定められた中間値に設定した後にステップ１４４に移行する。
【０１１０】
なお、上記中間値は、閾値ｔｈ及びゲインｐが当該中間値であれば被写体像を示すために充分なダイナミックレンジとなり、被写体に白とびが発生しないと見なすことのできる値として、デジタルカメラ１０を用いた実機による実験や、デジタルカメラ１０の設計仕様に基づくコンピュータ・シミュレーション等によって予め得られた値等を適用することができる。
【０１１１】
すなわち、本撮影処理では、逆光での撮像であると判断されたとき、強制的にストロボ８９が発光されるようにしている。これによって、ストロボ８９からの発光光が主要被写体に照射されることにより、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像することが可能となる。
【０１１２】
しかしながら、このとき、主要被写体にストロボ光が十分に照射されていない場合には、逆光での撮像時においてはコントラストが高い（主要被写体と他の領域との間の明るさの差が大きい）状態のまま撮像されることになるので、合成データにおけるダイナミックレンジを可能な限り拡大することが好ましい。
【０１１３】
このため、本撮影処理では、ストロボ８９の発光による被写体の明るさの増加の度合いが所定レベル以下である場合は、主要被写体にストロボ光が十分に照射されていないものと見なして、ダイナミックレンジが予め定められた上限レンジとなるように閾値ｔｈ及びゲインｐを設定しており、これによって、主要被写体の黒つぶれの発生を抑制しつつ、主要被写体以外の領域における白とびの発生を防止するようにしている。
【０１１４】
一方、主要被写体にストロボ光が十分に照射されている場合には、主要被写体の明るさは増加するものの、被写体像全体の明るさが増加するのではないため、主要被写体以外の領域において白とびが発生する可能性は低く、ダイナミックレンジを必要以上に拡大させないことが好ましい。ダイナミックレンジを必要以上に拡大させることは、合成データにおける階調数が多くなり過ぎてしまい、合成情報にノイズが発生し易くなるためである。
【０１１５】
このため、本撮影処理では、ストロボ８９の発光による被写体の明るさの増加の度合いが所定レベルを超えた場合には、主要被写体にストロボ光が十分に照射されているものと見なして、ダイナミックレンジが上記上限レンジよりも狭くなるように閾値ｔｈ及びゲインｐを設定するようにしている。
【０１１６】
ステップ１４４では、設定した閾値ｔｈ及びゲインｐを合成処理回路８０に出力し、その後にステップ１４６に移行し、合成処理回路８０に対して上記不図示のメモリに記憶しておいた高感度データ及び低感度データを閾値ｔｈ及びゲインｐを用いて合成させてメモリ４８に記憶させた後、記録制御部５０に対してメモリ４８に記憶された合成データを記録メディア８６へ記憶させることにより撮影を行い、本撮影処理プログラムを終了する。
【０１１７】
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によれば、ＣＣＤ１８により取得された画像データに基づいて逆光での撮像か否かを判断し、逆光での撮像であると判断したとき、被写体の明るさが他のときより増加するように予め定められた条件を設定する（ここでは、スポット測光方式への強制的な切換え）と共に、このときの被写体の明るさの増加の度合いが大きくなるほどダイナミックレンジが拡大されるように感度の異なる画像データ（高感度データ及び低感度データ）を合成するときに用いられる係数（閾値ｔｈ及びゲインｐ）を設定しているので、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像でき、かつ主要被写体以外の領域における白とびの発生を防止できる。
【０１１８】
また、本実施の形態に係るデジタルカメラ１０によれば、逆光での撮像であると判断されたとき、ＡＥ制御で適用される測光方式を、被写体像の中央部が含まれ、かつ外周部が除かれた所定分割領域のみの測光結果が用いられるスポット測光方式に強制的に切換えることにより、逆光時の撮像であるため著しく暗い状態となっている主要被写体の明るさが適正となるようにＡＥ制御を行ない、被写体全体としての明るさが逆光でないときより増加するようにしているので、測光方式の切換えのみにより容易に逆光での撮像時における主要被写体の黒つぶれの発生を防止することができる。
【０１１９】
さらに、本実施の形態に係るデジタルカメラ１０によれば、逆光での撮像であるときにストロボ８９を強制的に発光させることで被写体の明るさが他のときより増加するように設定すると共に、当該ストロボ８９の発光による被写体の明るさの増加の度合いが所定レベル以下である場合は、ダイナミックレンジが予め定められた上限レンジとなるように閾値ｔｈ及びゲインｐを設定し、他の場合には、ダイナミックレンジが上記上限レンジよりも狭くなるように閾値ｔｈ及びゲインｐを設定しているので、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像でき、かつ主要被写体以外の領域における白とびの発生を防止できる。
【０１２０】
（第２の実施の形態）
上記第１の実施の形態では、逆光での撮影であると判断され、かつユーザによって「ストロボ強制ＯＦＦモード」が設定されている場合、測光方式をスポット測光方式としてＡＥ制御を行うと共に、閾値ｔｈ及びゲインｐをΔＥＶに応じて設定する場合の形態について説明したが、本第２の実施の形態では、ユーザによって予め設定された測光方式による測光結果を、スポット測光方式による測光結果に応じて補正すると共に、当該補正による被写体の明るさの増加の度合いに応じて閾値ｔｈ及びゲインｐを設定する場合の形態について説明する。
【０１２１】
なお、本第２の実施の形態に係るデジタルカメラは、その構成及び作用が上記第１の実施の形態に係るデジタルカメラ１０（図１参照。）と同一であるので、ここではその説明を省略する。
【０１２２】
図７は、本第２の実施の形態に係る撮影処理プログラムの処理の流れを示すフローチャートであり、以下、同図を参照して本第２の実施の形態に係るデジタルカメラ１０の撮影処理について説明する。なお、同図において、図６と同一の処理を行うステップについては同一のステップ番号を付してその説明を省略する。
【０１２３】
本実施の形態では、撮影処理において逆光での撮影（ＣＣＤ１８による撮像）であると判断され、ステップ１１０で肯定判定となった場合には、ユーザによりストロボ８９の発光が禁止されているため、測光データを補正して被写体の明るさを増加させるべく、ステップ１１５に移行する。
【０１２４】
このステップ１１５では、ユーザにより予め選択された測光方式にて測光データ（以下、「ＥＶ＿ｓｅｔ」という。）を取得し、次のステップ１１７では、取得したＥＶ＿ｓｅｔと、スポット測光方式による測光データであるＥＶ＿ｓの差（以下、「ΔＥＶ＿ｓ」という。）を導出する。
【０１２５】
次のステップ１１９では、ΔＥＶ＿ｓ及び補正係数ａを用いて、次の（５）式に示すようにＥＶ＿ｓｅｔを補正して、実際にＡＥ制御に用いる測光データであるＥＶ＿ｃを導出する。
【０１２６】
【数５】

【０１２７】
なお、補正係数ａは、予め定められた範囲内の値であり（本実施の形態では、０＜ａ≦１）、この補正係数ａは、ユーザにより逆光補正の度合いを示す条件として予め設定されるようになっている。
【０１２８】
このようにしてＥＶ＿ｃが導出されるとステップ１２１に移行して、導出したＥＶ＿ｃに基づき、シャッタスピード及び絞りを設定することによりＡＥ制御を行った後、ステップ１２２に移行する。
【０１２９】
ここで、上記（５）式を用いてＥＶ＿ｓｅｔを補正し、当該補正により得られたＥＶ＿ｃを適用してＡＥ制御を行う場合、補正係数ａの値が大きくなるほど被写体の明るさの増加の度合いが大きくなる。例えば、補正係数ａが「１」である場合、ＥＶ＿ｃ＝ＥＶ＿ｓとなり、スポット測光方式による測光結果と一致し、中央部の被写体の明るさを基準としてＡＥ制御が行われ、上記第１の実施の形態の撮影処理におけるＡＥ制御と同様の効果が得られる。また、補正係数ａが「１」よりも小さい場合には、スポット測光方式によるよりも中央部の被写体の明るさの増加の度合いは少なくなるものの、中央部以外の被写体についての白とびの発生は、より抑制することができる。
【０１３０】
その後、ステップ１２６で肯定判定された場合はＥＶ＿ｃに基づいてＡＥ制御が行われたものとしてステップ１２９に移行し、上記測光データの補正量（ａ×ΔＥＶ＿ｓ）に応じて閾値ｔｈ及びゲインｐを設定し、被写体の明るさの増加の度合いに応じてダイナミックレンジを拡大する。
【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１０によれば、ＣＣＤ１８により取得された画像データに基づいて逆光での撮像か否かを判断し、逆光での撮像であると判断したとき、被写体の明るさが他のときより増加するように予め定められた条件を設定する（ここでは、スポット測光方式への強制的な切換え）と共に、このときの被写体の明るさの増加の度合いが大きくなるほどダイナミックレンジが拡大されるように感度の異なる画像データ（高感度データ及び低感度データ）を合成するときに用いられる係数（閾値ｔｈ及びゲインｐ）を設定しているので、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像でき、かつ主要被写体以外の領域における白とびの発生を防止できる。
【０１３２】
また、本実施の形態に係るデジタルカメラ１０によれば、逆光での撮像であると判断されたとき、分割測光による測光結果が、被写体像の中央部が含まれ、かつ外周部が除かれた所定分割領域のみの測光結果（スポット測光方式による測光結果）に応じて補正されることにより、被写体全体としての明るさが逆光でないときより増加するようにしているので、測光結果の補正のみにより容易に逆光での撮像時における主要被写体を黒つぶれの発生を防止することができる。
【０１３３】
さらに、本実施の形態に係るデジタルカメラ１０によれば、逆光での撮像であるときにストロボ８９を強制的に発光させることで被写体の明るさが他のときより増加するように設定すると共に、当該ストロボ８９の発光による被写体の明るさの増加の度合いが所定レベル以下である場合は、ダイナミックレンジが予め定められた上限レンジとなるように閾値ｔｈ及びゲインｐを設定し、他の場合には、ダイナミックレンジが上記上限レンジよりも狭くなるように閾値ｔｈ及びゲインｐを設定しているので、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像でき、かつ主要被写体以外の領域における白とびの発生を防止できる。
【０１３４】
なお、第２の実施の形態では、撮影処理において測光データを補正するための補正係数ａの範囲が（０＜ａ≦１）である形態について説明したが、本発明はこれに限らず、補正後の測光データＥＶ＿ｃが、これに基づき露出状態を設定できる範囲であれば、ａ＞１としてもよい。
【０１３５】
また、上記各実施の形態では、合成前にホワイトバランス調整及びガンマ補正を高感度データ及び低感度データのそれぞれに対して行い、その後に対数加算方式により合成処理する形態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、合成処理回路によってＡ／Ｄ変換器から入力された高感度データ及び低感度データを、ホワイトバランス調整やガンマ補正を行う前に合成する形態とすることもできる。
【０１３６】
図８は、この形態に係るデジタル信号処理部３４Ｂの構成を示している。デジタル信号処理回路３４Ｂは、合成手段としての合成処理回路４０と、Ｋｎｅｅ処理回路４２と、ホワイトバランス（ＷＢ）調整回路４４と、ガンマ処理回路４６と、メモリ４８と、記録制御部５０と、表示制御部５２と、を含んで構成されている。
【０１３７】
図８の構成によれば、合成処理回路４０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を、真数加算方式を用いて次の（６）式に示すように合成する。
【０１３８】
【数６】

【０１３９】
ここで、Ｓは、高感度信号と低感度信号の比（感度比）を示すものであり、その値は１以上となる。ｔｈは、画像形成において合成データｄａｔａの合成開始レベルを示す閾値である。また、ｈｉｇｈは、高感度データの値であり、ｗ_hは、高感度データの重みを示す値である。ｌｏｗは、低感度データの値であり、ｗ_lは、低感度データの重みを示す値である。なお、上記（６）式を簡略化するために、本実施の形態では、重みｗ_hと重みｗ_lの合計値を１とするものとされている。
【０１４０】
なお、上記閾値ｔｈは、高感度データにより示される階調値が当該値未満であれば当該高感度データにより示される被写体像に白とびが発生しないと見なすことのできる値として、実際のＣＣＤ１８を用いた実験や、ＣＣＤ１８の設計仕様に基づくコンピュータ・シミュレーション等によって予め得られた値等を適用する。
【０１４１】
図９は、このとき、合成処理回路４０によって、被写体からの光を受光して得られた高感度データと、その高感度データに低感度データを上述のように合成して得られた合成データとの関係を示した図である。図中の細線が合成前の高感度データであり、太線が合成処理により得られた合成データである。また、被写体輝度において、Ｘ₁は合成処理を行わない場合に表現可能な被写体輝度の最大値を示しており、Ｘ₂は合成後に表現可能となった被写体輝度の最大値を示している。この場合の撮影対象である被写体の輝度Ｘ₂はＸ₁のレベルより高い。なお、本図は、Ｒ、Ｇ、Ｂ何れか１色についてのデータを示している。
【０１４２】
図から明らかなように、上述した合成処理により表現可能な被写体輝度のレベルはＸ₁からＸ₂まで拡大されている。このため、被写体がＸ₁のレベルより高い輝度を有する場合には、合成処理を施すことにより好適にダイナミックレンジが拡大され、表現可能な領域を拡大することができる。
【０１４３】
そして、この場合、低輝度データの重みｗ_lの値が大きくなるほどダイナミックレンジは拡大されることになる。従って、この場合は、図６に示される撮影処理のステップ１２８、１４０及び１４２と、図７に示される撮影処理のステップ１２９、１４０及び１４２における閾値ｔｈ及びゲインｐの設定に代えて、重みｗ_lの値を設定することになる。
【０１４４】
そして、設定された重みｗ_lを適用して合成処理回路４０により得られた合成データはＫｎｅｅ処理回路４２に出力され、Ｋｎｅｅ処理回路４２での予め設定されたＫｎｅｅ特性に応じた処理後、ＷＢ調整処理回路４４及びガンマ処理回路４６で所定の処理が行われた後、メモリ４８の所定領域に記憶される。
【０１４５】
そして、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８６への記録を行う。これによって撮影がなされる。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。
【０１４６】
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１０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。
【０１４７】
また、上記各実施の形態で説明した撮影処理プログラム（図６及び図７参照）の処理の流れは一例であり、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。
【０１４８】
また、本実施の形態に係るデジタルカメラ１０の構成（図１参照）も一例であり、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。
【０１４９】
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。
【０１５０】
【発明の効果】
以上説明したように、本発明によれば、撮像素子により取得された画像情報に基づいて逆光での撮像か否かを判断し、逆光での撮像であると判断したとき、被写体の明るさが他のときより増加するように予め定められた条件を設定すると共に、このときの被写体の明るさの増加の度合いが大きくなるほどダイナミックレンジが拡大されるように感度の異なる画像情報を合成するときに用いられる係数を設定しているので、逆光での撮像時においても主要被写体を黒つぶれすることなく撮像でき、かつ主要被写体以外の領域における白とびの発生を防止できる、という効果が得られる。
【図面の簡単な説明】
【図１】実施の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（２）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（２）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測光方式のうち、中央重点測光方式での各分割領域の重みを示す模式図である。
【図５】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６】第１の実施の形態に係る撮影処理プログラムの処理の流れを示すフローチャートである。
【図７】第２の実施の形態に係る撮影処理プログラムの処理の流れを示すフローチャートである。
【図８】デジタル信号処理回路の他の構成例を示すブロック図である。
【図９】合成前の高感度データと、合成処理されて得られた合成データとの関係を示すグラフである。
【図１０】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 デジタルカメラ
１８ ＣＣＤ（撮像素子）
６２ ＣＰＵ（逆光判断手段、条件設定手段、係数設定手段、露出制御手段）
８０ 合成処理回路（合成手段）
８９ ストロボ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging device and a shooting condition setting method for the imaging device, and particularly includes an imaging device that can acquire image information with different sensitivities and combines and uses image information obtained by the imaging device. The present invention relates to an imaging device and a shooting condition setting method for the imaging device.
[0002]
[Prior art]
In recent years, the demand for digital cameras has increased rapidly with the increase in resolution of imaging devices such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) image sensors.
[0003]
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 imaging a high-brightness subject, the amount of light received exceeds the dynamic range, the output signal of the image sensor saturates, and so-called whiteout occurs where information about the subject is lost was there.
[0004]
On the other hand, in conventional imaging devices, since exposure conditions are generally set so that a subject with high brightness does not exceed the dynamic range, in imaging with backlight, the main subject generally located at the center of the subject image In some cases, the luminance level is extremely lower than the luminance level of other subjects such as the background, and the main subject is crushed black in the subject image obtained by imaging.
[0005]
Therefore, conventionally, in a video camera, the level of the imaging signal in the center of the imaging screen and the level of the imaging signal in the peripheral area excluding the center of the imaging screen are detected and subjected to predetermined calculation processing. Based on the result, it is determined whether or not shooting is performed with backlighting, and the gain is corrected so that the central portion of the image has an appropriate signal level by continuously controlling the gain of the gain control unit according to the determination result. (For example, see Patent Document 1).
[0006]
Further, in the video camera, it is determined whether or not the image data that is captured and input is obtained by imaging in the backlight state. If the image data is obtained in the backlight state, the backlight type ( For example, true backlight, halation, etc.) are determined, and the main subject is properly exposed by performing light quantity control after selectively switching the metering method to point metering method or center-weighted metering method according to the identified backlight type. There has been a technique for controlling (see, for example, Patent Document 2).
[0007]
[Patent Document 1]
JP-A-62-110369
[Patent Document 2]
JP 2002-204388 A
[0008]
[Problems to be solved by the invention]
However, in backlit imaging, the brightness level of the main subject located in the center is significantly lower than in other areas. With each of the above technologies, exposure control is performed so that the main subject is properly exposed. As a result, the amount of received light exceeds the dynamic range and is likely to be saturated in a region other than the main subject. As a result, there is a problem in that whiteout is likely to occur in an area other than the main subject.
[0009]
The present invention has been made to solve the above-described problems, and can capture a main subject without being blacked out even during backlight imaging, and can prevent overexposure in a region other than the main subject. An object of the present invention is to provide an imaging apparatus and an imaging condition setting method for the imaging apparatus.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a plurality of first light receiving elements that receive light from a subject with a first sensitivity and acquire first image information according to the received light quantity. An imaging device comprising: a plurality of second light receiving elements that receive light from the subject with a second sensitivity lower than the first sensitivity and obtain second image information according to the received light quantity; Combining means for combining the first image information and the second image information so as to change the dynamic range according to a preset coefficient to generate combined information, and the image information acquired by the image sensor A backlight determining unit that determines whether or not the image is captured by backlighting, and when the backlight determining unit determines that the image is captured by backlighting, the brightness of the subject is determined in advance to be higher than at other times. Condition setting means for setting Coefficient setting means for setting the coefficient so that the dynamic range is expanded as the degree of increase in the brightness of the subject by the condition setting means increases when it is determined by the backlight determination means that the image is captured with backlight. And.
[0011]
According to the first aspect of the present invention, light from the subject is received by the first light receiving element with the first sensitivity by the imaging element, and first image information corresponding to the received light quantity is acquired, Light from the subject is received by the second light receiving element with a second sensitivity lower than the first sensitivity, and second image information corresponding to the received light amount is acquired. Thereby, image information with different sensitivities can be acquired.
[0012]
Note that the image pickup device can include a solid-state image pickup device such as a CCD or a CMOS image sensor.
[0013]
In the present invention, the first image information and the second image information acquired by the image sensor are combined by the combining unit so that the dynamic range is changed according to a preset coefficient, thereby generating combined information. The As described above, in the present invention, image information having different sensitivities are combined to form combined information. Therefore, the dynamic range can be effectively expanded by using the combined information as image information indicating a subject image.
[0014]
The first image information and the second image information synthesized by the synthesizing unit may be analog information or digital information.
[0015]
Here, in the present invention, the backlight determining unit determines whether or not the image is captured with backlight based on the image information acquired by the image sensor. As a result, when it is determined that the image is captured with backlight, A predetermined condition is set by the condition setting means so that the brightness of the subject increases compared to other times, and the coefficient is set so that the dynamic range is expanded as the degree of increase in the brightness of the subject at this time increases. It is set by coefficient setting means.
[0016]
That is, in the present invention, attention is paid to the fact that the main subject is significantly darker than other times when imaging with backlight, and when it is determined that imaging is performed with backlight, the brightness of the subject is increased compared to other times. This prevents the main subject from being blacked out in the subject image obtained by imaging with backlight.
[0017]
However, in this case, although the black shadow of the main subject can be prevented, the area other than the main subject, such as the background portion, becomes too bright, and overexposure may occur.
[0018]
Therefore, in the present invention, the coefficient used when combining the image information is set by the combining means so that the dynamic range is expanded as the degree of increase in the brightness of the subject increases, and thereby, the region other than the main subject is set. This prevents the occurrence of overexposure.
[0019]
As described above, according to the imaging apparatus of the first aspect, it is determined whether or not the imaging is performed with the backlight based on the image information acquired by the imaging device. Image information with different sensitivities so that the dynamic range is expanded as the degree of increase in the brightness of the subject at this time increases. Since the coefficients used for the composition are set, the main subject can be imaged without being blacked out even during imaging with backlight, and the occurrence of overexposure in areas other than the main subject can be prevented.
[0020]
The invention according to claim 2 further includes exposure control means for performing exposure control according to photometry results by split photometry using the first image information in the invention according to claim 1, wherein the condition setting is performed. The means uses the photometric result of only the predetermined divided area including the center part of the subject image and excluding the outer peripheral part for the divided photometry applied by the exposure control means, so that the brightness of the subject is increased. It is set to increase from other times.
[0021]
According to the second aspect of the present invention, the exposure control unit performs exposure control according to the photometry result by the division photometry using the first image information of the present invention. Thereby, the brightness of the subject can be grasped for each of the plurality of divided areas, and exposure control according to the partial photometric result can be performed.
[0022]
Further, in the present invention, when it is determined that the imaging is performed with backlighting, the above-mentioned divided photometry is performed by the condition setting unit only in a predetermined divided area including the central portion of the subject image and excluding the outer peripheral portion. The result shall be used.
[0023]
That is, in the present invention, focusing on the point that the main subject is generally located at the center of the subject image, exposure control using the photometric result of only the predetermined divided area including the center and excluding the outer periphery. By performing the exposure control, exposure control is performed so that the brightness of the main subject that is extremely dark because it is imaging in backlight is appropriate, and the brightness of the entire subject is increased compared to when it is not backlit. ing. As a result, the main subject can be imaged without being blacked out even during imaging with backlight.
[0024]
Also in the present invention, the coefficient is set by the coefficient setting means so that the dynamic range is expanded as the degree of increase in the brightness of the subject by the condition setting means increases. The occurrence of jumps can be prevented.
[0025]
The invention according to claim 3 further includes exposure control means for performing exposure control according to photometric results by split photometry using the first image information in the invention according to claim 1, wherein the condition setting is performed. The means corrects the photometry result by the division photometry according to the photometry result of only the predetermined divided area including the center portion of the subject image and excluding the outer peripheral portion, so that the brightness of the subject is higher than in other cases. It is set to increase.
[0026]
According to the invention described in claim 3, in the invention described in claim 1, exposure control according to the photometry result by the division photometry using the first image information of the present invention is performed by the exposure control means. Thereby, the brightness of the subject can be grasped for each of the plurality of divided areas, and exposure control according to the partial photometric result can be performed.
[0027]
Further, in the present invention, when it is determined that the image is captured with backlighting, the condition setting unit includes a predetermined divided area in which the photometric result of the divided photometry includes the center portion of the subject image and the outer peripheral portion is excluded. Only the photometric result is corrected.
[0028]
That is, also in the present invention, paying attention to the point that the main subject is generally located at the center of the subject image, split metering is performed according to the metering result of only the predetermined divided area including the center and excluding the outer periphery. By correcting the photometry results, exposure control is performed so that the brightness of the main subject, which is extremely dark because it is imaged during backlighting, is appropriate, so that the brightness of the subject as a whole is not backlit. Try to increase. As a result, the main subject can be imaged without being blacked out even during imaging with backlight.
[0029]
Also in the present invention, the coefficient is set by the coefficient setting means so that the dynamic range is expanded as the degree of increase in the brightness of the subject by the condition setting means increases. The occurrence of jumps can be prevented.
[0030]
Further, the invention according to claim 4 further includes a strobe for compensating for a shortage of ambient light amount at the time of imaging by the image sensor in the invention according to claim 1, wherein the condition setting means emits the strobe. The coefficient setting means sets the dynamic range when the degree of increase in the brightness of the subject due to the flash emission is equal to or less than a predetermined level. Is set to a predetermined upper limit range, and in other cases, the coefficient is set so that the dynamic range is narrower than the upper limit range.
[0031]
According to the invention described in claim 4, in the invention described in claim 1, the strobe for compensating for the shortage of ambient light amount at the time of imaging by the image sensor is included, and the ambient light amount at the time of imaging is insufficient. Even if it is a case, imaging becomes possible.
[0032]
In the present invention, the strobe is emitted by the condition setting means when it is determined that the image is taken with the backlight using the strobe. Thus, the main subject is irradiated with the light emitted from the strobe, so that the main subject can be imaged without being blacked out even during backlight imaging.
[0033]
However, at this time, if the main subject is not sufficiently irradiated with strobe light, the contrast is high (the brightness difference between the main subject and other areas is large) during imaging with backlight. Since the image is captured as it is, it is preferable to expand the dynamic range in the composite information as much as possible.
[0034]
Therefore, in the present invention, when the degree of increase in the brightness of the subject due to the flash emission is equal to or less than a predetermined level, the dynamic range is determined in advance assuming that the main subject is not sufficiently irradiated with the flash light. The coefficient of the present invention is set by the coefficient setting means so that the upper limit range is set, thereby preventing the occurrence of overexposure in an area other than the main subject while suppressing the occurrence of blackout of the main subject. I am doing so.
[0035]
On the other hand, when the main subject is sufficiently irradiated with strobe light, the brightness of the main subject increases, but the brightness of the entire subject image increases as in the inventions according to claims 2 and 3. Therefore, it is unlikely that overexposure occurs in a region other than the main subject, and it is preferable not to increase the dynamic range more than necessary. The reason why the dynamic range is expanded more than necessary is that the number of gradations in the combined information becomes too large, and noise is easily generated in the combined information.
[0036]
For this reason, in the present invention, when the degree of increase in the brightness of the subject due to the flash emission exceeds a predetermined level, it is assumed that the main subject is sufficiently irradiated with the flash light, and the dynamic range is The coefficient of the present invention is set by the coefficient setting means so as to be narrower than the upper limit range.
[0037]
As described above, according to the present invention, the brightness of the subject is set to be increased by causing the strobe to emit light when shooting with backlight, and the brightness of the subject due to the light emission of the strobe. When the degree of increase is less than a predetermined level, the coefficient of the present invention is set so that the dynamic range is a predetermined upper limit range. In other cases, the dynamic range is narrower than the upper limit range. Since the coefficients are set as described above, the main subject can be imaged without being blacked out even during imaging with backlight, and the occurrence of overexposure in a region other than the main subject can be prevented.
[0038]
On the other hand, in order to achieve the above-described object, the invention according to claim 5 is configured to receive a light from a subject with a first sensitivity, and to obtain a plurality of first light receptions for obtaining first image information corresponding to the received light quantity. An imaging device comprising: an element; and a plurality of second light receiving elements that receive light from the subject with a second sensitivity lower than the first sensitivity and obtain second image information according to the received light quantity; An imaging condition setting of an imaging apparatus, comprising: a synthesis unit configured to synthesize the first image information and the second image information so that a dynamic range is changed according to a preset coefficient to generate synthesis information In this method, it is determined whether or not the image is captured with backlight based on the image information acquired by the image sensor, and when it is determined that the image is captured with backlight, the brightness of the subject increases compared to other times. And set the predetermined conditions as As the dynamic range degree of increase in brightness is large subject of this case is to set the coefficient as is enlarged.
[0039]
Therefore, according to the imaging condition setting method of the imaging device according to claim 5, the imaging device can be operated similarly to the invention according to claim 1, so that, similarly to the invention according to claim 1, Even when shooting with backlight, the main subject can be picked up without being blacked out, and overexposure in areas other than the main subject can be prevented.
[0040]
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.
[0041]
(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 the high-sensitivity and low-sensitivity light receiving elements based on the incident light indicating the subject image that has passed through the shutter 16. A CCD 18 for outputting three color analog image signals, and a strobe 89 for compensating for a shortage of ambient light during imaging by the CCD 18 are provided.
[0042]
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. Note that high-sensitivity digital data (hereinafter referred to as “high-sensitivity data”) output from the A / D converter 22 corresponds to “first image information” of the present invention, and low-sensitivity digital data. (Hereinafter referred to as “low sensitivity data”) corresponds to the “second image information” of the present invention.
[0043]
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, a light emission control unit 88 that controls the light emission amount of the strobe 89, control of light emission timing, and the like, and a camera operation unit 84 that includes various operation switches such as a shutter switch are provided. It has been.
[0044]
Here, in the digital camera 10 according to the present embodiment, the “strobe forced OFF mode”, which is a mode for prohibiting the flash 89 from emitting light regardless of the state of the subject, can be set by operating the camera operation unit 84. ing.
[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. The low-sensitivity side γ processing circuit 78 for performing the gamma correction processing, the synthesis processing circuit 80, the memory 48, the recording control unit 50, and the display control unit 52 are included.
[0047]
The CCD 18 corresponds to the image sensor of the present invention, and the composition processing circuit 80 corresponds to the composition 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, 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 “composition information” 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 composite data R ′, G ′, and B ′ is input from the composite processing circuit 80 to the memory 48 (see FIG. 1) of the digital camera 10, and the composite data of the R ′, G ′, and B ′ is input. Is stored.
[0069]
The recording control unit 50 has a role for mounting the recording medium 86 configured as a smart medium on the digital camera 10. The recording data synthesized by the synthesis processing circuit 80 and stored in the memory 48 is stored in the recording control unit 50. A process of reading from the memory 48 and recording on the recording medium 86 is performed. 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.
[0070]
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.
[0071]
The control circuit 60 controls the operation of the entire digital camera 10. Further, the ROM 64 stores various processing programs such as a photographing processing program described later executed by the CPU 62. The RAM 66 stores high sensitivity data and low sensitivity data input from the A / D converter 22 to the control circuit 60 in different areas.
[0072]
In the digital camera 10, focusing control (so-called AF control) is performed by a so-called TTL (Through The Lens) method in which the lens position is set so that the contrast of the subject image indicated by the image data acquired by the CCD 18 is maximized. )I do.
[0073]
On the other hand, in the digital camera 10 according to the present embodiment, as shown in FIG. 4, the subject image indicated by the image data (high sensitivity data in the present embodiment) obtained by the CCD 18 is horizontally and vertically oriented. It is divided into a plurality of areas (here, a total of 64 divisions, 8 divisions in the vertical direction and 8 divisions in the horizontal direction), and a photometric value indicating the brightness of the subject image obtained from the image data is detected for each division region. can do.
[0074]
Further, in the digital camera 10, as shown in FIG. 4, a large weight (“64” in the figure) is added to the divided area located in the center of the subject image (inside the thick frame in the figure), and the subject image is obtained. The weight of the divided area closer to the outer periphery of the subject is reduced (“1” in the divided area in contact with the outer periphery). In addition, the brightness of the subject image can be determined by any one of the spot metering method in which metering is performed with the weights of the other divided regions set to “0” and the average metering method in which metering is performed with all the segment regions having the same weight. Photometric data indicating the accuracy can be acquired.
[0075]
In the digital camera 10, any one of these three types of metering methods is selected in advance by an operation of the camera operation unit 84 by the user, and is selected in advance in the CPU 62. Exposure control (so-called AE control) is performed in which photometry data for the entire subject image is derived by the photometry method, and the shutter speed and aperture state are set according to the derived photometry data.
[0076]
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. 5 can be adopted.
[0077]
As shown in FIG. 5, the image pickup 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)). And adjacent light receiving elements PD1 are arranged so as to bypass a plurality of light receiving elements PD1 that are two-dimensionally shifted in the vertical direction and the horizontal direction, and an opening AP formed in 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.
[0078]
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.
[0079]
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.
[0080]
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.
[0081]
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. 5, 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 (opening area of the opening AP) is made smaller than the light receiving area of the light receiving element PD1, R, G, and B signals that are less sensitive than the light receiving element PD1 are obtained. It is done.
[0082]
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.
[0083]
Hereinafter, the operation of the digital camera 10 having such a configuration at the time of shooting will be described.
[0084]
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.
[0085]
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.
[0086]
In the control circuit 60, the high sensitivity data and the low sensitivity data input from the A / D converter 22 are stored in the RAM 66, and each of the high sensitivity data and the low sensitivity data is based on the high sensitivity data and the low sensitivity data. Gain values Rg, Gg, and Bg for controlling the white balance are derived and output to the corresponding high sensitivity side WB adjustment processing circuit 72 and low sensitivity side WB adjustment processing circuit 74, respectively.
[0087]
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 synthesized data obtained thereby is stored in the memory 48.
[0088]
In addition, the display control unit 52 executes a process for displaying an image on the LCD 82 using the combined data after various processes stored in the memory 48.
[0089]
Here, in the digital camera 10 according to the present embodiment, when the user half-presses the shutter switch of the camera operation unit 84 in order to shoot a subject, a shooting process program is executed in the CPU 62.
[0090]
FIG. 6 is a flowchart showing the flow of processing of the photographing processing program. Hereinafter, photographing processing according to the present embodiment will be described with reference to FIG. Here, a description will be given assuming that the photometry method applied to the exposure control is selected in advance by the user.
[0091]
First, in step 100, AF control is performed to determine the lens position so that the contrast of the subject image indicated by the image data (here, high sensitivity data) acquired by the CCD 18 is maximized.
[0092]
In the next step 102, photometric data (hereinafter referred to as “EV_s”) based on the spot photometry method, and photometric data (divided area located outside the thick frame in FIG. 4) excluding the central part ( (Hereinafter referred to as “EV_b”), and then the process proceeds to step 104 to derive the difference between EV_b and EV_s (hereinafter referred to as “ΔEV”). EV_b is derived as an average value of the photometric data of each divided area except for the central portion.
[0093]
Thereafter, in step 106, it is determined whether or not ΔEV is equal to or greater than a predetermined value. If the determination is negative, it is determined that the image is not captured with backlight (imaged by the CCD 18), and the process proceeds to step 108 to execute the normal image capturing process, and then the image capturing process program is terminated.
[0094]
It should be noted that the predetermined value for determining whether or not shooting is performed with backlight is as long as the difference ΔEV between the photometric data in the central divided area and the divided areas excluding the central divided area is equal to or greater than the predetermined value. As a value that can be considered to cause blackout in the subject image, a value obtained in advance by an experiment using an actual machine using the digital camera 10 or a computer simulation based on a design specification of the digital camera 10 is applied. be able to.
[0095]
On the other hand, when an affirmative determination is made in step 106, the process proceeds to step 110 to determine whether or not the “strobe forced OFF mode” is set by the user. If the determination is negative, it is determined that the strobe 89 is caused to emit light at the time of shooting to increase the brightness of the subject, and normal AE control is performed by a photometric method selected in advance by the user, and then the process proceeds to step 122. Transition.
[0096]
If the determination in step 110 is affirmative, it is determined that the strobe 89 is not fired and the brightness of the subject cannot be increased, and the process proceeds to step 114 where the photometry method is applied to exposure control. It is determined whether or not the metering method selected in advance by the user is the “spot metering method”. If the determination is negative, it is determined that the metering method needs to be switched, and the process proceeds to step 116 to perform exposure. The metering method applied to the control is forcibly switched to the “spot metering method”, and then the process proceeds to step 118. On the other hand, if the determination in step 114 is affirmative, the process proceeds to step 118 without executing the process in step 116.
[0097]
In step 118, photometric data EV_s is acquired by spot photometry. In the next step 120, AE control is performed by setting the shutter speed and the aperture according to the acquired EV_s, and then the process proceeds to step 122.
[0098]
With the above processing, when shooting with backlighting and when the forced flash OFF mode is not set and the flash 89 is in a condition to emit light, the brightness of the main subject is emitted by the flash 89. Therefore, AE control is performed as usual using the photometry method set by the user, assuming that blackening of the main subject does not occur.
[0099]
On the other hand, when shooting with backlighting and when the flash 89 does not emit light, it is forcibly switched to the spot metering method, and generally according to the brightness of the main subject located at the center of the subject image. By performing the AE control, the brightness of the entire subject is increased compared to when the backlight is not backlit. As a result, the main subject can be imaged without being blacked out even during imaging with backlight.
[0100]
In step 122, it is determined whether or not the shutter switch has been shifted from the half-pressed state to the fully-pressed state. If the determination is negative, the process proceeds to step 124 to determine whether or not the shutter switch has been turned off. . If the determination is affirmative, it is determined that shooting by the user has been stopped, and the shooting processing program is terminated. If the determination is negative, the process returns to step 122 above.
[0101]
On the other hand, if an affirmative determination is made in step 122, it is determined that photographing has been instructed by the user, the process proceeds to step 126, and it is determined whether or not the “flash forced OFF mode” is set by the user. If the determination is affirmative, the process proceeds to step 128, where a threshold th and a gain p, which are coefficients that determine the dynamic range of the combined data described above in accordance with ΔEV (hereinafter referred to as “combining coefficients”). Is set, and then the process proceeds to step 144.
[0102]
The threshold th and the gain p are set so that the dynamic range is expanded as ΔEV indicating the degree of increase in the brightness of the subject increases.
[0103]
In other words, in this shooting process, when shooting with backlighting and the “Flash forced-off mode” is set by the user, exposure control is performed using the spot metering method regardless of the metering method selected in advance by the user. The brightness of the subject is increased so that the central main subject can be photographed without being blacked out, and the threshold th and the gain p are set according to the degree of increase in the brightness of the subject (here, ΔEV). By setting and expanding the dynamic range, it is possible to prevent overexposure in areas other than the main subject.
[0104]
On the other hand, if a negative determination is made in step 126, the process proceeds to step 130, and photometry data EV_s1 by spot metering at this time is acquired, and then the process proceeds to step 132 to cause the strobe 89 to emit light. In step 134, photometric data EV_s2 by spot photometry when the strobe 89 is caused to emit light is acquired.
[0105]
Note that the synthesis processing circuit 80 stores the high sensitivity data and the low sensitivity data after the gamma correction processing acquired through the CCD 18 in a state where the strobe 89 is caused to emit light in a predetermined area of a built-in memory (not shown). Keep it.
[0106]
In the next step 136, a photometric data change amount X (= EV_s2-EV_s1) by spot photometry before and after the flash 89 is emitted is derived, and then the process proceeds to step 138, where the brightness of the subject reaches a predetermined amount. In order to determine whether or not the increase has been exceeded, it is determined whether or not the change amount X exceeds a predetermined value.
[0107]
Note that the digital camera 10 is used as the predetermined value as a value that can be considered that the light from the strobe 89 is sufficiently irradiated to the main subject if the amount of change X exceeds the predetermined value. Values obtained in advance by experiments with actual machines or computer simulations based on design specifications of the digital camera 10 can be applied.
[0108]
If a negative determination is made in step 138, it is assumed that the light from the strobe 89 is not sufficiently irradiated to the main subject, and the routine proceeds to step 140, where at least one of the threshold th and the gain p is determined in advance if the dynamic range is preset. The predetermined minimum value is set so as to be within the predetermined upper limit range, and then the process proceeds to step 144. The minimum value is determined by the saturation ratio of the high sensitivity data and the low sensitivity data described above.
[0109]
On the other hand, if an affirmative determination is made in step 138, it is assumed that the light from the strobe 89 is sufficiently applied to the main subject, and the routine proceeds to step 142 where the threshold th and gain p are set to the above dynamic range. After setting to a predetermined intermediate value so as to be narrower than the upper limit range, the routine proceeds to step 144.
[0110]
The intermediate value has a dynamic range sufficient to show the subject image if the threshold value th and the gain p are the intermediate values, and the digital camera 10 can be regarded as a value that can be regarded as no overexposure to the subject. Values obtained in advance by experiments with the actual machine used, computer simulations based on the design specifications of the digital camera 10, or the like can be applied.
[0111]
That is, in this photographing process, the strobe 89 is forcibly emitted when it is determined that the image is captured with backlight. As a result, the main subject is irradiated with the light emitted from the strobe 89, so that the main subject can be imaged without being blacked out even during backlight imaging.
[0112]
However, at this time, if the main subject is not sufficiently irradiated with strobe light, the contrast is high (the brightness difference between the main subject and other areas is large) during imaging with backlight. Since the image is captured as it is, it is preferable to expand the dynamic range in the combined data as much as possible.
[0113]
For this reason, in this photographing process, when the degree of increase in the brightness of the subject due to the light emission of the strobe 89 is equal to or less than a predetermined level, it is assumed that the main subject is not sufficiently irradiated with the strobe light, and the dynamic range is The threshold th and the gain p are set so as to be in a predetermined upper limit range, thereby preventing occurrence of overexposure in a region other than the main subject while suppressing occurrence of blackout of the main subject. I have to.
[0114]
On the other hand, when the main subject is sufficiently exposed to strobe light, the brightness of the main subject increases, but the brightness of the entire subject image does not increase. It is preferable that the dynamic range is not increased more than necessary. The reason why the dynamic range is increased more than necessary is that the number of gradations in the combined data becomes too large, and noise is easily generated in the combined information.
[0115]
For this reason, in the main photographing process, when the degree of increase in the brightness of the subject due to the light emission of the strobe 89 exceeds a predetermined level, it is assumed that the main subject is sufficiently irradiated with the strobe light, and the dynamic range is reached. The threshold value th and the gain p are set so that is narrower than the upper limit range.
[0116]
In step 144, the set threshold value th and gain p are output to the synthesis processing circuit 80. Thereafter, the process proceeds to step 146, where the high sensitivity data stored in the memory (not shown) and the synthesis processing circuit 80 are stored. The low sensitivity data is combined using the threshold th and the gain p and stored in the memory 48, and then the combined data stored in the memory 48 is stored in the recording medium 86 in the recording control unit 50 to perform shooting. Then, this photographing processing program is terminated.
[0117]
As described above in detail, according to the digital camera 10 according to the present embodiment, it is determined based on the image data acquired by the CCD 18 whether or not the image is captured with backlight, and is determined to be image with backlight. In this case, a predetermined condition is set so that the brightness of the subject increases compared to other times (in this case, forced switching to the spot metering method), and the increase in the brightness of the subject at this time The coefficients (threshold th and gain p) used when combining image data (high sensitivity data and low sensitivity data) with different sensitivities are set so that the dynamic range is expanded as the degree is increased. Even during imaging, the main subject can be imaged without being blacked out, and overexposure in areas other than the main subject can be prevented.
[0118]
Further, according to the digital camera 10 according to the present embodiment, when it is determined that the image is captured with backlight, the photometry method applied in the AE control includes the center portion of the subject image and the outer peripheral portion. By forcibly switching to the spot metering method in which the photometric result of only the predetermined divided area is used, the AE is adjusted so that the brightness of the main subject that is extremely dark due to imaging at the time of backlighting is appropriate. Control is performed so that the brightness of the entire subject is increased compared to when the backlight is not backlit. Therefore, it is possible to easily prevent blackout of the main subject during imaging using backlight only by switching the metering method. .
[0119]
Furthermore, according to the digital camera 10 according to the present embodiment, the brightness of the subject is set to increase compared to other times by forcibly causing the strobe 89 to emit light when imaging with backlight. When the degree of increase in the brightness of the subject due to the light emission of the strobe 89 is below a predetermined level, the threshold th and the gain p are set so that the dynamic range becomes a predetermined upper limit range, and in other cases Since the threshold value th and the gain p are set so that the dynamic range is narrower than the upper limit range, the main subject can be captured without being blacked out even in imaging with backlight, and in areas other than the main subject. The occurrence of overexposure can be prevented.
[0120]
(Second Embodiment)
In the first embodiment, when it is determined that shooting is performed under backlighting and the “strobe forced OFF mode” is set by the user, the AE control is performed with the photometry method as the spot photometry method, and the threshold value th In the second embodiment, the photometry result obtained by the photometry method preset by the user is corrected according to the photometry result obtained by the spot photometry method. At the same time, a mode in which the threshold th and the gain p are set according to the degree of increase in the brightness of the subject due to the correction will be described.
[0121]
Note that the configuration and operation of the digital camera according to the second embodiment are the same as those of the digital camera 10 (see FIG. 1) according to the first embodiment, and thus the description thereof is omitted here. To do.
[0122]
FIG. 7 is a flowchart showing a flow of processing of the shooting processing program according to the second embodiment. Hereinafter, shooting processing of the digital camera 10 according to the second embodiment will be described with reference to FIG. explain. In the figure, steps that perform the same processing as in FIG. 6 are denoted by the same step numbers and description thereof is omitted.
[0123]
In the present embodiment, if it is determined that shooting is performed under backlighting (imaging by the CCD 18) in the shooting process and an affirmative determination is made in step 110, light emission of the strobe 89 is prohibited by the user. In order to correct the data and increase the brightness of the subject, the process proceeds to step 115.
[0124]
In this step 115, photometric data (hereinafter referred to as “EV_set”) is acquired by a photometric method selected in advance by the user, and in the next step 117, the acquired EV_set and EV_s which is photometric data by the spot photometric method. Difference (hereinafter referred to as “ΔEV_s”).
[0125]
In the next step 119, EV_set is corrected using ΔEV_s and the correction coefficient a as shown in the following equation (5) to derive EV_c that is photometric data actually used for AE control.
[0126]
[Equation 5]

[0127]
The correction coefficient a is a value within a predetermined range (0 <a ≦ 1 in the present embodiment), and the correction coefficient a is set in advance as a condition indicating the degree of backlight correction by the user. It has become so.
[0128]
When EV_c is derived in this way, the process proceeds to step 121. After performing AE control by setting the shutter speed and the aperture based on the derived EV_c, the process proceeds to step 122.
[0129]
Here, when EV_set is corrected using the above equation (5) and AE control is performed by applying EV_c obtained by the correction, the degree of increase in the brightness of the subject increases as the value of the correction coefficient a increases. growing. For example, when the correction coefficient a is “1”, EV_c = EV_s, which matches the photometry result by the spot photometry method, and AE control is performed based on the brightness of the subject in the center, and the first embodiment is performed. The same effect as that of the AE control in the form photographing processing can be obtained. When the correction coefficient a is smaller than “1”, the degree of increase in the brightness of the subject in the central portion is smaller than that in the spot metering method, but overexposure occurs in subjects other than the central portion. Can be suppressed more.
[0130]
Thereafter, if an affirmative determination is made in step 126, it is assumed that AE control has been performed based on EV_c, and the flow proceeds to step 129, where the threshold value th and gain p are set according to the photometric data correction amount (a × ΔEV_s). Then, the dynamic range is expanded according to the degree of increase in the brightness of the subject.
[0131]
As described above in detail, according to the digital camera 10 according to the present embodiment, it is determined based on the image data acquired by the CCD 18 whether or not the image is captured with backlight, and is determined to be image with backlight. In this case, a predetermined condition is set so that the brightness of the subject increases compared to other times (in this case, forced switching to the spot metering method), and the increase in the brightness of the subject at this time The coefficients (threshold th and gain p) used when combining image data (high sensitivity data and low sensitivity data) with different sensitivities are set so that the dynamic range is expanded as the degree is increased. Even during imaging, the main subject can be imaged without being blacked out, and overexposure in areas other than the main subject can be prevented.
[0132]
Further, according to the digital camera 10 according to the present embodiment, when it is determined that the image is captured with backlight, the photometry result by the division photometry includes the center portion of the subject image and the outer peripheral portion is excluded. Since the brightness of the subject as a whole is increased compared to when it is not backlit by correcting it according to the photometric result of only a predetermined area (photometric result of spot photometry), it is easy only by correcting the photometric result In addition, it is possible to prevent blackout of the main subject during imaging with backlight.
[0133]
Furthermore, according to the digital camera 10 according to the present embodiment, the brightness of the subject is set to increase compared to other times by forcibly causing the strobe 89 to emit light when shooting with backlight. When the degree of increase in the brightness of the subject due to the light emission of the strobe 89 is below a predetermined level, the threshold th and the gain p are set so that the dynamic range becomes a predetermined upper limit range, and in other cases Since the threshold value th and the gain p are set so that the dynamic range is narrower than the upper limit range, the main subject can be captured without being blacked out even in imaging with backlight, and in areas other than the main subject. The occurrence of overexposure can be prevented.
[0134]
In the second embodiment, the mode in which the range of the correction coefficient a for correcting the photometric data in the photographing process is (0 <a ≦ 1) has been described. However, the present invention is not limited to this, and correction is performed. If the subsequent photometric data EV_c is within a range in which the exposure state can be set based on this, a> 1 may be set.
[0135]
In each of the above embodiments, the white balance adjustment and the gamma correction are performed on each of the high sensitivity data and the low sensitivity data before the synthesis, and then the synthesis process is performed using the logarithmic addition method. Is not limited to this, and high sensitivity data and low sensitivity data input from the A / D converter by the synthesis processing circuit may be combined before white balance adjustment or gamma correction. .
[0136]
FIG. 8 shows a configuration of the digital signal processing unit 34B according to this embodiment. The digital signal processing circuit 34B includes a synthesis processing circuit 40, a knee processing circuit 42, a white balance (WB) adjustment circuit 44, a gamma processing circuit 46, a memory 48, a recording control unit 50, and a display. And a control unit 52.
[0137]
According to the configuration of FIG. 8, in the synthesis processing circuit 40, the high sensitivity data and the low sensitivity data input from the A / D converter 22 are expressed by the following formula (6) using a true number addition method. Synthesize.
[0138]
[Formula 6]

[0139]
Here, S indicates the ratio (sensitivity ratio) between the high sensitivity signal and the low sensitivity signal, and the value thereof is 1 or more. “th” is a threshold value indicating a synthesis start level of the synthesis data “data” in image formation. Further, high is a value of high sensitivity data, and w _h Is a value indicating the weight of the high sensitivity data. low is the value of low sensitivity data, w _l Is a value indicating the weight of the low sensitivity data. In order to simplify the above equation (6), in this embodiment, the weight w _h And weight w _l It is supposed that the total value of 1 is 1.
[0140]
Note that the threshold th is a value that can be regarded as no over-exposure in the subject image indicated by the high sensitivity data if the gradation value indicated by the high sensitivity data is less than the value. Values obtained in advance by experiments used, computer simulations based on the design specifications of the CCD 18, and the like are applied.
[0141]
FIG. 9 shows the high sensitivity data obtained by receiving the light from the subject by the synthesis processing circuit 40 and the synthesized data obtained by synthesizing the low sensitivity data with the high sensitivity data as described above. It is the figure which showed the relationship. The thin line in the figure is the high sensitivity data before synthesis, and the thick line is the synthesized data obtained by the synthesis process. In the subject brightness, X ₁ Indicates the maximum value of the subject brightness that can be expressed when the composition processing is not performed. ₂ Indicates the maximum value of the subject brightness that can be expressed after synthesis. In this case, the luminance X of the subject to be photographed ₂ Is X ₁ Higher than the level. This figure shows data for one of R, G, and B colors.
[0142]
As is apparent from the figure, the level of subject brightness that can be expressed by the above-described combining process is X ₁ To X ₂ Has been expanded to. Therefore, the subject is X ₁ When the luminance is higher than this level, the dynamic range is suitably expanded by performing the synthesis process, and the area that can be expressed can be expanded.
[0143]
In this case, the weight w of the low luminance data _l As the value of increases, the dynamic range is expanded. Therefore, in this case, instead of setting the threshold value th and the gain p in steps 128, 140, and 142 of the shooting process shown in FIG. 6 and steps 129, 140, and 142 of the shooting process shown in FIG. _l Will be set.
[0144]
And the set weight w _l Is output to the knee processing circuit 42, and after processing according to preset knee characteristics in the knee processing circuit 42, the WB adjustment processing circuit 44 and the gamma processing circuit are applied. After predetermined processing is performed at 46, it is stored in a predetermined area of the memory 48.
[0145]
Then, the display control unit 52 executes a process for displaying an image on the LCD 82 using the combined data after various processes 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 86 in response to 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. Also in this case, the same effects as in the present embodiment can be obtained.
[0146]
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. The light receiving area of one light receiving element PD is divided into a high sensitivity light receiving area 92 having a large light receiving area for receiving high sensitivity light by a channel stopper 94 and a low sensitivity light receiving area 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. .
[0147]
Further, the flow of processing of the photographing processing program (see FIGS. 6 and 7) described in the above embodiments is merely an example, and it goes without saying that it can be appropriately changed without departing from the gist of the present invention.
[0148]
Further, the configuration of the digital camera 10 according to the present embodiment (see FIG. 1) is also an example, and it is needless to say that the configuration can be appropriately changed without departing from the gist of the present invention.
[0149]
Furthermore, the present invention is not limited to the above digital camera, and can be applied to various imaging devices.
[0150]
【The invention's effect】
As described above, according to the present invention, it is determined whether the image is captured with backlight based on the image information acquired by the image sensor, and the brightness of the subject is determined when it is determined that the image is captured with backlight. When setting predetermined conditions so as to increase more than other times, and combining image information with different sensitivities so that the dynamic range is expanded as the degree of increase in the brightness of the subject at this time increases. Since the coefficient to be used is set, it is possible to obtain an effect that the main subject can be imaged without being blacked out even during imaging with backlighting, and overexposure in an area other than the main subject can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a digital camera according to an 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 (2) according to the embodiment.
FIG. 3 is a graph for explaining the expression (2) according to the embodiment.
FIG. 4 is a schematic diagram showing the weight of each divided area in the center-weighted photometry method among the photometry methods applied in the digital camera according to the embodiment.
FIG. 5 is a schematic diagram showing a configuration of a CCD applied in the digital camera according to the embodiment.
FIG. 6 is a flowchart showing a flow of processing of a photographing processing program according to the first embodiment.
FIG. 7 is a flowchart showing a flow of processing of a photographing processing program according to the second embodiment.
FIG. 8 is a block diagram illustrating another configuration example of the digital signal processing circuit.
FIG. 9 is a graph showing a relationship between high-sensitivity data before synthesis and synthesized data obtained by synthesis processing.
FIG. 10 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 Digital camera
18 CCD (imaging device)
62 CPU (backlight judgment means, condition setting means, coefficient setting means, exposure control means)
80 Composition processing circuit (composition means)
89 Strobe

Claims (5)

A plurality of first light receiving elements that receive light from the subject with a first sensitivity and acquire first image information according to the received light amount, and a second light that is lower than the first sensitivity and that emits light from the subject. An image sensor including a plurality of second light receiving elements that receive light with sensitivity and acquire second image information according to the received light quantity;
A synthesizing unit that synthesizes the first image information and the second image information so as to change a dynamic range according to a preset coefficient, and generates synthesis information;
Back light judgment means for judging whether or not imaging with back light is based on image information acquired by the image sensor;
A condition setting means for setting a predetermined condition so that the brightness of the subject increases when compared with other times when it is determined by the backlight determination means that the image is captured with backlight;
Coefficient setting means for setting the coefficient so that the dynamic range is expanded as the degree of increase in the brightness of the subject by the condition setting means increases when it is determined by the backlight determination means that the image is captured with backlight. When,
An imaging apparatus including: Exposure control means for performing exposure control according to a photometric result by split photometry using the first image information,
The condition setting means uses the photometric result of only the predetermined divided area including the center part of the subject image and excluding the outer peripheral part for the divided photometry applied by the exposure control means. The imaging apparatus according to claim 1, wherein the brightness is set so as to increase compared to other times. Exposure control means for performing exposure control according to a photometric result by split photometry using the first image information,
The condition setting means corrects the photometry result by the division photometry according to the photometry result of only a predetermined divided area including the center portion of the subject image and excluding the outer peripheral portion, thereby changing the brightness of the subject. The imaging device according to claim 1, wherein the imaging device is set so as to increase from the time of (1). Further comprising a strobe for making up for a lack of ambient light at the time of imaging by the imaging device,
The condition setting means sets the brightness of the subject to be increased compared to other times by causing the strobe to emit light,
The coefficient setting means sets the coefficient so that the dynamic range is a predetermined upper limit range when the degree of increase in brightness of the subject due to light emission of the strobe is equal to or lower than a predetermined level. The imaging apparatus according to claim 1, wherein the coefficient is set so that the dynamic range is narrower than the upper limit range. A plurality of first light receiving elements that receive light from the subject with a first sensitivity and acquire first image information according to the received light amount, and a second light that is lower than the first sensitivity and that emits light from the subject. An image sensor having a plurality of second light receiving elements that receive light with sensitivity and acquire second image information according to the received light quantity, and a coefficient that is set in advance for the first image information and the second image information An imaging condition setting method for an imaging apparatus, comprising: a synthesis unit configured to generate synthesis information by combining the dynamic range so as to change according to
Determining whether or not imaging with backlight based on image information acquired by the imaging element;
When it is determined that the image is captured by backlighting, a predetermined condition is set so that the brightness of the subject increases compared to other times, and the dynamic degree increases as the degree of increase in the brightness of the subject at this time increases. Set the coefficient so that the range is expanded,
Shooting condition setting method.

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