JP3903095B2 - White balance control method and digital camera - Google Patents

Description

【００４１】
但し、ｉは、分割エリアの各々を示す添え字であり、上記の場合、０〜６３の値を取り得る。Ｎは、分割エリア数を示し、上記の場合は８×８＝６４である。ΔＥＶｉｓｏは、所定の感度（例えばＩＳＯ２００）を基準としてＥＶ値補正量であり、感度が変更されても、ＥＶ’が一定となるように調整するための値である。Ｗｉは、各分割エリアごとの重み係数であり、例えば図５に示すように中央重点測光方式の重み係数を用いる。
【００４２】
上記のように算出したＥＶ’に対し、更に、次式に示すように撮影モードに応じた露出補正ΔＥＶを行って撮影ＥＶ値を求める。求めた撮影ＥＶ値は、メモリ３９に記憶される。
【００４３】
ＥＶ＝ＥＶ’−ΔＥＶ …（２）
なお、ΔＥＶは、例えば、人物モードの場合にはΔＥＶ＝０、風景モード、夜景モードの場合にはΔＥＶ＝０．３とする。
【００４４】
上記のようにして求めた撮影ＥＶ値に基づいて撮影時の絞り値とシャッタスピードを最終的に決定する。
【００４５】
そして、シャッタボタンの全押し時に前記決定した絞り値になるように絞り駆動部４４を介して絞り１２を駆動し、また、決定したシャッタスピードとなるように電子シャッタによって電荷の蓄積時間を制御する。
【００４６】
次に、図６に示すフローチャートを参照しながらオートホワイトバランス制御方法について説明する。
【００４７】
図６に示したホワイトバランス制御は、予め定めた撮影モード及びストロボモードの場合で、かつストロボ発光すると判断した場合に実行される。
【００４８】
以下の表に、図６に示したホワイトバランス制御が実行される撮影モード及びストロボモードの組み合わせを示す。例えばオート撮影モードで、ＥＶ値が所定閾値以下の場合等に、以下のホワイトバランス制御が実行され、その他の場合には、通常のホワイトバランス制御が行われる。
【００４９】
【表１】

【００５０】
まず、ＥＶ値や撮影モード及びストロボモードからストロボ発光するか否かが判断され、ストロボ発光される場合は、撮影モード及びストロボモードが上記の表の○で示される組み合わせであるか否かが判断される。そして、ストロボ発光すると判断し、かつ撮影モード及びストロボモードが上記の表の○で示される組み合わせでないと判断された場合には、周知の方法により通常のストロボ発光時のホワイトバランス制御を行うためのホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇが設定され、ホワイトバランス調整回路３０に加えられる。また、ストロボ発光しないと判断された場合には、周知の方法によりストロボ光を発光しない場合に適したホワイトバランス制御を行うためのホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇが設定され、ホワイトバランス調整回路３０に加えられる。
【００５１】
そして、ストロボ発光すると判断し、かつ撮影モード及びストロボモードが上記の表の○で示される組み合わせであると判断された場合には、ＣＰＵ３８は、シャッタボタンの半押し時に求めた被写体までの距離データを取得する（ステップＳ１０）。
【００５２】
次に、シャッタボタンの半押し時に求めた撮影ＥＶ値をメモリ３９から読み込む（ステップＳ１１）。
【００５３】
次に、シャッタボタンの全押し時にストロボ発光されて撮像された画像のＲ、Ｇ、Ｂ信号は一旦メモリ２４に格納されているが、この１画面を複数のエリア（例えば８×８）に分割し、各分割エリアごとにＲ、Ｇ、Ｂ信号の色別の積算値を積算回路４８によって求める（ステップＳ１２）。
【００５４】
Ｒ，Ｇ，Ｂ信号の積算値Ｒｔ，Ｇｔ，Ｂｔは、積算回路４８とＣＰＵ３８との間に設けられた乗算器（乗算手段）５０Ｒ、５０Ｇ、５０Ｂに出力され、乗算器５０Ｒ、５０Ｇ、５０Ｂによって予め定められた基準ＷＢ（ホワイトバランス）ゲイン値（基準制御値）Ｒｓｔ，Ｇｓｔ、Ｂｓｔが掛けられる（ステップＳ１４）。なお、基準ＷＢゲイン値Ｒｓｔ，Ｇｓｔ、Ｂｓｔは、予めメモリ３９に記憶されている。
【００５５】
基準ＷＢゲイン値Ｒｓｔ，Ｇｓｔ，Ｂｓｔが掛けられたＲ，Ｇ，Ｂ信号の積算値Ｒｔ’，Ｇｔ’，Ｂｔ’は、ＣＰＵ３８に入力される。
【００５６】
この基準ＷＢゲイン値Ｒｓｔ，Ｇｓｔ，Ｂｓｔは、ストロボ光が被写体に十分に到達した場合のように、光源としてストロボ光が支配的な場合にホワイトバランスが適正となるように調整するためのゲイン値である。
【００５７】
そして、ＣＰＵ３８は、入力されたＲ信号の積算値Ｒｔ’とＧ信号の積算値Ｇｔ’との比Ｒｔ’／Ｇｔ’、及びＢ信号の積算値とＧ信号の積算値との比Ｂｔ’／Ｇｔ’を求める（ステップＳ１６）。なお、この処理は、本発明の取得手段に相当する。
【００５８】
上記のようにして各分割エリアごとに求められるＲｔ’／Ｇｔ’、Ｂｔ’／Ｇｔ’は、その分割エリアが、図７に示すグラフ上に表された検出枠のうちの、どの検出枠内に入るかを判別するために使用される。なお、図７における各検出枠は、ストロボ光以外の環境光源などの色分布の範囲を規定するものである。
【００５９】
図７に示すように、検出枠には、青空検出枠、日陰−曇り検出枠、昼光色（の蛍光灯）検出枠、緑検出枠、昼白色（の蛍光灯）検出枠、ストロボ検出枠、タングステン電球検出枠があり、日陰−曇り検出枠は、日陰−曇り検出枠ＣＬＤ１〜ＣＬＤ４を含み、昼光色検出枠は、昼光色検出枠ＥＸＤ１〜ＥＸＤ４を含み、昼白色検出枠は、昼白色検出枠ＥＸＮ１〜ＥＸＮ４を含み、タングステン電球検出枠は、タングステン電球検出枠ＴＮＧ１−１〜ＴＮＧ１−４，ＴＮＧ２−１〜ＴＮＧ２−４、ＴＮＧ３を含んでいる。
【００６０】
そして、ＣＰＵ３８は、Ｒｔ’／Ｇｔ’＝Ｘ’、Ｂｔ’／Ｇｔ’＝Ｙ’として、各分割エリアごとに求められたＲｔ’／Ｇｔ’、Ｂｔ’／Ｇｔ’で表される（Ｘ_i’、Ｙ_i’）が、これらの検出枠のうちの、どの検出枠内に入るかを判別し、その個数をカウントする（ステップＳ１８）。なお、この処理は、本発明の色分布検出手段に相当する。
【００６１】
次に、各検出枠内に存在する（Ｘ_i’、Ｙ_i’）の平均値（Ｘａ_j’Ｙａ_j’）を求める（ステップＳ２０）。ここで、ｊは、各検出枠の各々を示す添え字である。なお、平均値でなく、重心値でもよい。
【００６２】
次に、各検出枠に対応して設けられたメンバシップ関数により、色に関する光源らしさ（日陰−曇りらしさ等）を表す評価値Ｆｃ（）を算出する（ステップＳ２２）。メンバシップ関数は、検出枠内の個数を変数として色に関する光源らしさを表す評価値Ｆｃ（）を出力する関数である。すなわち、評価値が高ければ、その検出枠に対応する光源（環境光源）の可能性が高くなる。
【００６３】
Ｆｃ（ＣＬＤ１）〜Ｆｃ（ＣＬＤ４）は、図８に示すように、日陰−曇り検出枠内に入る分割エリアの個数を変数とした日陰−曇りらしさを表すメンバシップ関数の値である。
【００６４】
Ｆｃ（ＳＫＹ）は、図９に示すように、青空検出枠内に入る分割エリアの個数を変数とした青空らしさを表すメンバシップ関数の値である。同様に、Ｆｃ（ＧＲＮ）は、図９に示すように、緑検出枠内に入る分割エリアの個数を変数とした緑らしさを表すメンバシップ関数の値である。
【００６５】
Ｆｃ（ＥＸＤ１）〜Ｆｃ（ＥＸＤ４）は、図１０に示すように、昼光色検出枠内に入る分割エリアの個数を変数とした昼光色の蛍光灯らしさを表すメンバシップ関数である。Ｆｃ（ＥＸＮ１）〜Ｆｃ（ＥＸＮ４）、Ｆｃ（ＴＮＧ１−１）〜Ｆｃ（ＴＮＧ３）は、図１０に示したＦｃ（ＥＸＤ１）〜Ｆｃ（ＥＸＤ４）と同様であり、Ｆｃ（ＥＸＮ１）〜Ｆｃ（ＥＸＮ４）は、昼白色検出枠内に入る分割エリアの個数を変数とした昼白色の蛍光灯らしさを表すメンバシップ関数の値であり、Ｆｃ（ＴＮＧ１−１）〜Ｆｃ（ＴＮＧ３）は、タングステン電球検出枠内に入る分割エリアの個数を変数とした昼白色の蛍光灯らしさを表すメンバシップ関数の値である。
【００６６】
Ｆｃ（ＴＹＰ）は、ストロボ検出枠内に入る分割エリアの個数を変数としたストロボらしさ、すなわちストロボ光が支配的であるか否かを表すメンバシップ関数の値であり、このメンバシップ関数は、図１０に示す蛍光灯らしさを表すメンバシップ関数と同様である。
【００６７】
次に、各検出枠に対応して設けられたメンバシップ関数により、輝度に関する光源らしさ（屋内らしさ、屋外らしさ）を表す評価値Ｆｙ（）を算出する（ステップＳ２４）。メンバシップ関数は、ステップＳ１１で取得したＥＶ値を変数として輝度に関する光源らしさを表す評価値を出力する関数である。
【００６８】
Ｆｙ（屋外らしさＤＡＹ）は、図１１に示すように、ＥＶ値を変数としたデーライトの屋外らしさを表すメンバシップ関数の値である。
【００６９】
Ｆｙ（屋外らしさＣＬＤ）は、図１２に示すように、ＥＶ値を変数とした日陰又は曇りの屋外らしさを表すメンバシップ関数の値である。
【００７０】
Ｆｙ（屋内らしさＥＸＤ）、Ｆｙ（屋内らしさＥＸＮ）、Ｆｙ（屋内らしさＴＮＧ）は、図１３に示すように、それぞれＥＶ値を変数とした昼光色の蛍光灯の屋内らしさ又は昼白色の蛍光灯の屋内らしさ又はタングステン電球の屋内らしさを表すメンバシップ関数の値である。
【００７１】
次に、色に関する光源らしさを表す評価値及び輝度に関する評価値を表す評価値から各検出枠について総合的な光源らしさの評価値Ｈ_jを求める（ステップＳ２６）。
【００７２】
評価値Ｈ₁〜Ｈ₂₂は、以下の式によって求められる。
【００７３】
Ｈ₁（日陰−曇りらしさの評価値）＝Ｆｃ（ＣＬＤ１）×Ｆｙ（屋外らしさ）×Ｆｃ（ＳＫＹ） …（３）
Ｈ₂（日陰−曇りらしさの評価値）＝Ｆｃ（ＣＬＤ２）×Ｆｙ（屋外らしさ）×Ｆｃ（ＳＫＹ） …（４）
Ｈ₃（日陰−曇りらしさの評価値）＝Ｆｃ（ＣＬＤ３）×Ｆｙ（屋外らしさ）…（５）
Ｈ₄（日陰−曇りらしさの評価値）＝Ｆｃ（ＣＬＤ４）×Ｆｙ（屋外らしさ）…（６）
Ｈ₅（昼光色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＤ１）×Ｆｙ（屋内らしさＥＸＤ） …（７）
Ｈ₆（昼光色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＤ２）×Ｆｙ（屋内らしさＥＸＤ） …（８）
Ｈ₇（昼光色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＤ３）×Ｆｙ（屋内らしさＥＸＤ） …（９）
Ｈ₈（昼光色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＤ４）×Ｆｙ（屋内らしさＥＸＤ） …（１０）
Ｈ₉（昼白色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＮ１）×Ｆｙ（屋内らしさＥＸＮ） …（１１）
Ｈ₁₀（昼白色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＮ２）×Ｆｙ（屋内らしさＥＸＮ） …（１２）
Ｈ₁₁（昼白色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＮ３）×Ｆｙ（屋内らしさＥＸＮ）×Ｆｃ（ＧＲＮ） …（１３）
Ｈ₁₂（昼光色の蛍光灯らしさの評価値）＝Ｆｃ（ＥＸＮ４）×Ｆｙ（屋内らしさＥＸＮ）×Ｆｃ（ＧＲＮ） …（１４）
Ｈ₁₃（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ１−１）×Ｆｙ（屋内らしさＴＮＧ） …（１５）
Ｈ₁₄（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ１−２）×Ｆｙ（屋内らしさＴＮＧ） …（１６）
Ｈ₁₅（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ１−３）×Ｆｙ（屋内らしさＴＮＧ） …（１７）
Ｈ₁₆（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ１−４）×Ｆｙ（屋内らしさＴＮＧ） …（１８）
Ｈ₁₇（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ２−１）×Ｆｙ（屋内らしさＴＮＧ） …（１９）
Ｈ₁₈（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ２−２）×Ｆｙ（屋内らしさＴＮＧ） …（２０）
Ｈ₁₉（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ２−３）×Ｆｙ（屋内らしさＴＮＧ） …（２１）
Ｈ₂₀（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ２−４）×Ｆｙ（屋内らしさＴＮＧ） …（２２）
Ｈ₂₁（タングステン電球らしさの評価値）＝Ｆｃ（ＴＮＧ３）×Ｆｙ（屋内らしさＴＮＧ） …（２３）
Ｈ₂₂（ストロボ光らしさの評価値）＝Ｆｃ（ＴＹＰ）×Ｆｙ（屋外らしさＤＡＹ） …（２４）
ここで、０≦Ｆｃ（）、Ｆｙ（）≦１であるため、０≦Ｈ_j≦１である。なお、Ｆｃ（ＳＫＹ）、Ｆｃ（ＧＲＮ）は、図９に示すように、青空検出枠又は緑検出枠内に入る分割エリアの個数が多い程、日陰−曇りらしさ又は昼白色検出枠の評価値を下げる方向に作用する値をとる。
【００７４】
また、Ｆｙ（屋内らしさ）は、図１３に示すように、ＥＶ値が高い程、それらの検出枠の評価値を下げる方向に作用する値をとる。このように、光源らしさの評価値Ｈ_jは、色分布だけでなく輝度も考慮して決定されるため、適正に光源を特定することが可能となる。例えば、蛍光灯が点灯した室内と室外とで同じ色の被写体を撮影した場合に、色分布のみで光源を特定した場合には、光源の特定を誤ってしまい、カラーフェリアが発生してしまう場合がある。
【００７５】
しかしながら、本実施の形態では、輝度が低い場合、すなわち室内で撮影されたような場合には、Ｆｙ（室内らしさ）が高くなり、輝度が高い場合、すなわち室外で撮影されたような場合には、Ｆｙ（室内らしさ）が低くなるため、光源を正確に特定することができ、カラーフェリアが発生するのを防ぐことができる。
【００７６】
そして、上記のように各検出枠に対応した光源らしさの評価値が算出されると、これらの評価値のうち予め定めた所定閾値以上の（例えば０．４以上）か否かを判別する（ステップＳ２８）。そして、評価値が所定閾値以上のものが存在する場合には、評価値が所定閾値以上のものを環境光源の候補として選択する。なお、この処理は、本発明の設定手段に相当する。
【００７７】
次に、選択された環境光源の各々について、以下の式に従ってストロボ光と環境光源とが混合された混合光源の色が白色となるようにホワイトバランス制御を行うための制御値（ゲイン値）Ｇ_R、Ｇ_B、Ｇ_Gを算出する（ステップＳ３０）。なお、この処理は、本発明の算出手段に相当する。
【００７８】
Ｇ_R＝｛Σ（ｇｒ_j×Ｈ_j）／ΣＨ_j｝×｛Σ（Ｇ_j×Ｈ_j）／ΣＨ_j｝
…（２５）
Ｇ_B＝｛Σ（ｇｂ_j×Ｈ_j）／ΣＨ_j｝×｛Σ（Ｇ_j×Ｈ_j）／ΣＨ_j｝
…（２６）
Ｇ_G＝Σ（Ｇ_j×Ｈ_j）／ΣＨ_j …（２７）
ここで、上記（２５）〜（２７）式は、評価値が所定閾値以上のものについて算出され、例えば所定閾値以上の評価値がＨ₁₁〜Ｈ₁₄である場合には、Ｈ₁₁〜Ｈ₁₄の光源についてｇｒ_j，ｇｂ_jが算出され、算出されたｇｒ_j，ｇｂ_j、Ｈ₁₁〜Ｈ₁₄を用いて各Σ内の計算が行われる。また、ｇｒ_j，ｇｂ_jは、各検出枠における光源の色を所定色とするために必要なゲインであり、次式で示される。なお、Ｇ_jは、この場合Ｇｓｔであり、固定値である。
【００７９】
ｇｒ_j＝Ｘｓｔ／Ｘａ_j’×Ｔｘ_j …（２８）
ｇｂ_j＝Ｙｓｔ／Ｙａ_j’×Ｔｙ_j …（２９）
ここで、Ｘｓｔ＝Ｒｓｔ／Ｇｓｔ、Ｙｓｔ＝Ｂｓｔ／Ｇｓｔである。また、Ｔｘ_j、Ｔｙ_jは、基準ＷＢゲイン値が掛けられていない元の画像データのＲ，Ｇ，Ｂの積算値について求めたＸ_i、Ｙ_iの平均値をＸａ_j（＝Ｘａ_j’／Ｘｓｔ）、Ｙａ_j（＝Ｙａ_j’／Ｙｓｔ）とした場合における、Ｘａ_j、Ｙａ_jの目標値であり、所定色に対応する。すなわち、ｇｒ_j，ｇｂ_jは、元の画像データのＲ，Ｇ，Ｂの積算値についてＸａ_j、Ｙａ_jを求めた場合に、このＸａ_j、Ｙａ_jで示される光源（ストロボ光と環境光源との混合光源）の色を所定色とするために必要なゲインである。なお、Ｔｘ_j、Ｔｙ_jは、例えば１である。
【００８０】
従って、上記（２５）、（２６）式の第１項は、評価値Ｈ_jを重みとしたｇｒ_j，ｇｂ_jはの加重平均値をそれぞれ表している。また、第２項は、明るさを補正するための項であるが、Ｇ_jが固定値であるため、この場合は明るさは補正されない。
【００８１】
なお、ストロボ検出枠の評価値Ｈ₂₂が所定閾値以上であるとして選択されている場合には、ｇｒ₂₂＝Ｘｓｔ、ｇｂ₂₂＝Ｙｓｔとする。
【００８２】
このようにして、ストロボ光とストロボ光以外の環境光源とが混合された混合光源の色を所定色にするための制御値Ｇ_R、Ｇ_B、Ｇ_Gが算出されると、これらの制御値が、基準ＷＢゲイン値との間の値で、かつ混合光源に適した値となるように、距離センサ４７により検出した被写体までの距離に応じて調整される（ステップＳ３２）。なお、この処理は、本発明の調整手段に相当する。調整後の制御値は、ホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇとして表され、次式により得られる。
【００８３】
Ｒｇ＝（Ｇ_R−Ｒｓｔ）×Ｌｄ＋Ｒｓｔ …（３０）
Ｇｇ＝（Ｇ_G−Ｇｓｔ）×Ｌｄ＋Ｇｓｔ …（３１）
Ｂｇ＝（Ｇ_B−Ｂｓｔ）×Ｌｄ＋Ｂｓｔ …（３２）
ここで、Ｌｄは、被写体までの距離に応じた補正係数であり、例えば図１４に示すように、距離が０から予め定めた閾値ｔｈ１までの区間と、距離が予め定めた閾値ｔｈ２以上の区間は一定の値となり、閾値ｔｈ１〜閾値ｔｈ２の区間では、距離が大きくなるに従って大きくなる値をとる。従って、ホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇは、距離が小さくなるに従って基準ＷＢゲイン値Ｒｓｔ，Ｇｓｔ，Ｂｓｔに近づき、距離が大きくなるに従って制御値Ｇ_R、Ｇ_B、Ｇ_Gに近づく。すなわち、被写体までの距離が近い場合には、ストロボ光を光源とした場合に適したホワイトバランス制御が行われるように制御値が調整され、距離が遠い場合には、混合光源に適したホワイトバランス制御が行われるように制御値が調整される。これにより、被写体までの距離に応じて最適にホワイトバランス制御を行うことができる。
【００８４】
このように算出されたホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇは、ホワイトバランス調整回路３０へ出力され、元の画像データのＲ、Ｇ、Ｂの各信号がホワイトバランス調整される（ステップＳ３４）。補正後の信号をＲ’、Ｇ’、Ｂ’とすると、Ｒ’、Ｇ’、Ｂ’は、次式で表される。
【００８５】
Ｒ’＝Ｒｇ×Ｒ …（３３）
Ｇ’＝Ｇｇ×Ｇ …（３４）
Ｂ’＝Ｂｇ×Ｂ …（３５）
一方、所定閾値以上の評価値Ｈ_jが１つもない場合には、ホワイトバランス補正値Ｒｇ、Ｇｇ、ＢｇをそれぞれＲｓｔ、Ｇｓｔ、Ｂｓｔに設定して（ステップＳ３６）、ホワイトバランス調整を行う（ステップＳ３４）。
【００８６】
このように、本実施形態では、環境光源の色だけでなくＥＶ値をも考慮して環境光源を定めるため、環境光源を正確に定めることができる。また、環境光源の色は、ストロボ光が発光された状態での撮像画像の画像データ、すなわち本撮影での撮像画像の画像データから求めているため、撮像シーケンスを複雑にすることなく環境光源を正確に定めることができる。
【００８７】
そして、ホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇは、基準ＷＢゲイン値から混合光源の色を所定色にするための制御値Ｇ_R、Ｇ_B、Ｇ_Gとの間の値で、かつ被写体までの距離に適したホワイトバランス制御を行うことができる値となるため、被写体までの距離に応じて適正にホワイトバランス制御することができ、カラーフェリアの発生を抑えることができる。
【００８８】
また、ホワイトバランス補正値Ｒｇ、Ｇｇ、Ｂｇは、専用センサによらずに求めているため、コストを抑えることができると共に、装置を小型化することができる。
【００８９】
【発明の効果】
以上説明したように本発明によれば、ホワイトバランス制御のための制御値が、この制御値と基準制御値との間の値で、かつ混合光源に適した値となるように、被写体までの距離に応じて調整されるため、ストロボ発光下の撮影でも適正にホワイトバランス制御を行うことができると共に、カラーフェリアの発生を抑えることができる、という効果を有する。
【図面の簡単な説明】
【図１】 本発明に係るデジタルカメラの背面図である。
【図２】 デジタルカメラの上面に設けられたモードダイヤルの平面図である。
【図３】 デジタルカメラの内部構成を示すブロック図である。
【図４】 ＥＶ値の求め方について説明するための図である。
【図５】 測光方式について説明するための図である。
【図６】 ホワイトバランス制御方法のフローチャートである。
【図７】 光源の色分布の範囲としての検出枠を示すグラフである。
【図８】 日陰−曇りらしさを表すメンバシップ関数を示すグラフである。
【図９】 青空のメンバシップ関数を示すグラフである。
【図１０】 蛍光灯らしさ等を表すメンバシップ関数を示すグラフである。
【図１１】 デーライトの屋外らしさを表すメンバシップ関数を示すグラフである。
【図１２】 屋外らしさを表すメンバシップ関数を示すグラフである。
【図１３】 屋内らしさを表すメンバシップ関数を示すグラフである。
【図１４】 被写体までの距離と補正係数との関係を示す線図である。
【符号の説明】
１０ 撮影レンズ
１６ 駆動回路
１８ ＣＤＳ回路
２０ Ａ／Ｄ変換器
２４ メモリ
２６ デジタル信号処理回路
２８ 同時化回路
３０ ホワイトバランス調整回路
３０Ｒ、３０Ｇ、３０Ｂ 乗算器
３２ ガンマ補正回路
３４ ＹＣ信号作成回路
３６ メモリ
３９ メモリ
４０ カメラ操作部
４２ 駆動部
４４ 絞り駆動部
４７ 距離センサ
４８ 積算回路
５０Ｒ、５０Ｇ、５０Ｂ 乗算器[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a white balance control method and a digital camera, and more particularly to a white balance control method and a digital camera for performing appropriate white balance control in accordance with a light source when shooting with strobe light.
[0002]
[Prior art]
In digital cameras equipped with a strobe device, the white balance is adjusted so that white objects are reproduced in white regardless of the color temperature of the light source. Regardless of the type of light source, white balance adjustment was performed in accordance with the color temperature of the strobe light. Therefore, the white balance may not be appropriate when the strobe light does not reach enough.
[0003]
In order to solve this problem, Japanese Patent Application Laid-Open No. 9-322191 discloses a white balance control value by obtaining color temperature information of external light by performing pre-exposure in a state where the strobe does not emit light, and this is determined in advance. A device is described that determines the white balance control value during strobe emission from proportional distribution with the white balance control value of the strobe light, and controls the white balance during strobe emission according to this control value during main exposure. .
[0004]
Japanese Patent Application Laid-Open No. 7-301842 discloses a technique for providing a dedicated sensor for white balance adjustment and obtaining a white balance control value when no strobe light is emitted using the output result of the dedicated sensor. Yes.
[0005]
[Problems to be solved by the invention]
However, in the technique described in Japanese Patent Application Laid-Open No. 9-322191, color temperature information is detected when the strobe does not emit light during pre-exposure. There is a problem that the color temperature may not be detected correctly due to the effect of smear.
[0006]
In order to solve this problem, for example, it is necessary to operate a mechanical shutter for eliminating the influence of smear not only at the time of main exposure but also at the time of preliminary exposure, so that there is a problem that the imaging sequence becomes complicated.
[0007]
Also, when shooting a chromatic subject that does not include an achromatic color, such as green leaves, the color of the light source cannot be detected accurately, and the light source is obtained from the color information obtained from the captured image. When the white balance control corresponding to the detected color of the light source is performed, a color feria that rotates around the subject's complementary color occurs, and in this case, the color of the green tree leaves withered. There is also a problem such as.
[0008]
Further, the technique described in Japanese Patent Laid-Open No. 7-301842 has a problem that a dedicated sensor is required, which increases costs and makes it difficult to reduce the size.
[0009]
The present invention has been made in consideration of the above-described facts, and an object of the present invention is to provide a white balance control method and a digital camera capable of appropriately performing white balance control even in shooting under strobe light emission.
[0010]
[Means for Solving the Problems]
To achieve the above object, according to a first aspect of the present invention, in the white balance control method in a digital camera capable of emitting strobe light, a step of detecting a distance to a subject and a captured image when the subject is imaged are detected. A step of detecting a luminance level, and white balance in the image data of the captured image in a state in which the strobe light is emitted so that the color of the reference light source becomes a predetermined color using the strobe light as a reference light source. Multiply the reference control value for control To correct the image data to which white balance control is applied when the strobe light is used as the light source. Dividing the captured image into a plurality of areas, obtaining each color information from the image data multiplied by the reference control value belonging to each area, and based on the obtained color information for each area, Detecting a color distribution of an area, determining an environmental light source based on the detected luminance level and the color distribution, and setting a color of a mixed light source of the environmental light source and the reference light source to be the predetermined color A step of calculating a control value for performing white balance control, and the distance so that the control value is a value between the control value and the reference control value and suitable for the mixed light source. According to Depending on the adjustment factor Adjusting the control value.
[0011]
According to the present invention, the distance to the subject is detected, and the brightness level of the captured image when the subject is imaged is detected. The luminance level can be obtained from each color data of R, G, B of the captured image, for example, but may be detected by a dedicated sensor.
[0012]
A reference control value for performing white balance control on image data of a captured image in a state where the strobe light is emitted, using the strobe light as a reference light source so that the color of the reference light source is a predetermined color, for example, white. Multiply That is, the image data of the captured image is corrected to image data subjected to white balance control when strobe light is used as a light source.
[0013]
Then, the captured image is divided into a plurality of areas, and each piece of color information is acquired from the image data multiplied by the reference control value belonging to each area. The color information can be, for example, the ratio R / G, B / G of R, G, B signals in the area.
[0014]
Based on the acquired color information for each area, the color distribution of each area is detected. The color distribution can be obtained by, for example, applying each area to a detection frame indicating a range of color distribution corresponding to a plurality of predetermined environmental light sources, and obtaining the number of areas that apply to each detection frame. The detection frame may be a frame defined by, for example, an R / G range and a B / G range.
[0015]
Next, an environmental light source is determined based on the detected luminance level and color distribution. The color distribution is based on the image data obtained by multiplying the reference control value by the image data of the captured image captured by the mixed light source in which the strobe light is emitted, that is, the strobe light and the environmental light source other than the strobe light. Since it is calculated | required from the acquired color information, only an environmental light source can be defined. An environmental light source refers to a light source other than strobe light, for example, a light source such as a daylight light, a fluorescent lamp, or a light bulb. The environmental light source can be determined based on, for example, an evaluation value indicating the degree of environmental lightness that is calculated by a predetermined formula provided corresponding to each of a plurality of predetermined environmental light sources. The predetermined formula can be determined by a formula that calculates an evaluation value representing the degree of environmental light source from the brightness level, color distribution, that is, the number of areas that apply to each detection frame, and the like.
[0016]
In this way, since the environmental light source is determined in consideration of not only the color distribution but also the luminance level, the environmental light source can be accurately determined. In addition, since the color distribution is obtained from the image data of the captured image in a state in which the strobe light is emitted, that is, the image data of the captured image in actual shooting, the environmental light source can be accurately determined without complicating the imaging sequence. Can be determined.
[0017]
Then, a control value for performing white balance control is calculated so that the color of the mixed light source of the environmental light source and the reference light source becomes a predetermined color. This control value is, for example, whether or not an evaluation value representing the degree of environmental lightness that is calculated by a predetermined formula provided corresponding to each of a plurality of predetermined environmental light sources is equal to or greater than a predetermined threshold. Determining a corresponding control value corresponding to each of the evaluation values equal to or greater than the predetermined threshold, and a weighted average value of the corresponding control values with the evaluation value equal to or greater than the predetermined threshold as a weight. And the step of calculating as follows.
[0018]
That is, it is determined that an evaluation value representing the degree of environmental lightness is equal to or higher than a predetermined threshold is high, and a corresponding control value corresponding to each environmental light source determined to be equal to or higher than the predetermined threshold is obtained. These weighted average values are used as control values. Thereby, the control value can be determined in a balanced manner.
[0019]
The final control value is a value between this control value and the reference control value, and depends on the detected distance to the subject so as to be a value suitable for the mixed light source. Depending on the adjustment factor Adjusted. For example, as described in claim 2, the control value is adjusted so as to approach the reference control value as the distance decreases. That is, since the strobe light is dominant when the distance to the subject is short, the control value is adjusted so that white balance control suitable for the case where the strobe light is used as a light source is performed. Thereby, the white balance can be optimally adjusted according to the distance of the subject.
[0020]
In the above-described white balance control method, as described in claim 3, in a digital camera capable of emitting strobe light, distance detection means for detecting a distance to a subject, and a luminance level of a captured image when the subject is imaged Brightness level detecting means for detecting the image and image data of the captured image in a state in which the strobe light is emitted, white light so that the color of the reference light source is a predetermined color using the strobe light as a reference light source. Multiply the reference control value for balance control To correct the image data to which white balance control is applied when the strobe light is used as the light source. Multiplying means, obtaining means for dividing the captured image into a plurality of areas, and obtaining each color information from the image data multiplied by the reference control value belonging to each area, and based on the obtained color information for each area A color distribution detecting means for detecting a color distribution in each area; a setting means for determining an environmental light source based on the detected luminance level and the color distribution; and a color of a mixed light source of the environmental light source and the reference light source A calculating means for calculating a control value for performing white balance control so as to obtain a predetermined color, and the control value is a value between the control value and the reference control value, and a value suitable for the mixed light source Depending on the distance so that Depending on the adjustment factor It can be realized by a digital camera comprising adjusting means for adjusting the control value.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.
[0022]
FIG. 1 is a rear view of a digital camera according to the present invention, and FIG. 2 is a plan view of a mode dial provided on the upper surface of the camera.
[0023]
As shown in FIG. 2, the mode dial 1 is rotated so that the icons 1A to 1F on the dial are aligned with the mark M, so that the continuous shooting / bracketing mode, aperture and shutter speed for shooting at a plurality of levels of exposure are set. Suitable for manual shooting modes that can be set, auto shooting mode suitable for shooting various subjects, portrait mode suitable for shooting people, landscape mode suitable for shooting landscapes, and shooting night scenes The camera can be set to a shooting mode such as night view mode. In FIG. 2, a landscape mode is set.
[0024]
In addition to these shooting modes, you can select a combination of aperture and shutter speed, P (program) mode, you can select an aperture, A (aperture priority) mode in which the shutter speed is automatically selected, and shutter speed It is possible to set a photographing mode such as an S (shutter speed priority) mode in which an aperture is automatically selected. In addition, for each shooting mode, auto mode that automatically fires the flash, red-eye reduction mode to reduce red-eye when a person is shot, flash forced flash mode that forces the flash to fire, and flash light emission At the same time, it is possible to set a flash mode such as a slow sync mode for shooting a person and a night scene in a balanced manner by increasing the shutter speed.
[0025]
In the center of the mode dial 1, a shutter button 2 having a switch S1 that is turned on when half-pressed and a switch S2 that is turned on when fully pressed is provided.
[0026]
On the back of the digital camera, as shown in FIG. 1, a viewfinder eyepiece 3, a shift key 4, a display key 5, a shooting mode / playback mode switching lever 6, a cancel key 7, an execution key 8, and a multifunction cross key 9 And a liquid crystal monitor 52 are provided.
[0027]
FIG. 3 is a block diagram showing an internal configuration of the digital camera shown in FIG.
[0028]
In the figure, a subject image formed on a light receiving surface of a solid-state image sensor (CCD) 14 through a photographing lens 10 and a diaphragm 12 is converted into a signal charge in an amount corresponding to the amount of incident light by each sensor. . The signal charges accumulated in this way are read out to the shift register by a read gate pulse applied from the CCD drive circuit 16, and sequentially read out as a voltage signal corresponding to the signal charge by a register transfer pulse. The CCD 14 has a so-called electronic shutter function that can sweep out the accumulated signal charge by a shutter gate pulse and thereby control the charge accumulation time (shutter speed).
[0029]
The voltage signal sequentially read out from the CCD 14 is applied to a correlated double sampling circuit (CDS circuit) 18, where R, G, B signals for each pixel are sampled and held and applied to an A / D converter 20. It is done. The A / D converter 20 converts the R, G, and B signals sequentially added from the CDS circuit 18 into, for example, 10-bit (0 to 1023) digital R, G, and B signals and outputs the signals. The CCD drive circuit 16, the CDS circuit 18, and the A / D converter 20 are driven in synchronization with a timing signal applied from a timing generation circuit (TG) 22.
[0030]
The R, G, and B signals output from the A / D converter 20 are temporarily stored in the memory 24, and then the R, G, and B signals stored in the memory 24 are added to the digital signal processing circuit 26. The digital signal processing circuit 26 includes a synchronization circuit 28, a white balance adjustment circuit 30, a gamma correction circuit 32, a YC signal creation circuit 34, and a memory 36.
[0031]
The synchronization circuit 28 converts the dot-sequential R, G, B signals read from the memory 24 into simultaneous equations and outputs the R, G, B signals to the white balance adjustment circuit 30 simultaneously. The white balance adjustment circuit 30 includes multipliers 30R, 30G, and 30B for increasing and decreasing the digital values of the R, G, and B signals. The R, G, and B signals are respectively multiplied by the multipliers 30R, 30G, and 30G, respectively. Added to 30B.
[0032]
White balance correction values (gain values) Rg, Gg, and Bg for white balance control from the central processing unit (CPU) 38 are added to other inputs of the multipliers 30R, 30G, and 30B. , 30G, and 30B each multiply two inputs, and output R ′, G ′, and B ′ signals subjected to white balance adjustment by this multiplication to the gamma correction circuit 32. The details of the white balance correction values Rg, Gg, and Bg applied from the CPU 38 to the white balance adjustment circuit 30 will be described later.
[0033]
The gamma correction circuit 32 changes the input / output characteristics so that the white balance adjusted R ′, G ′, B ′ signals have the desired gamma characteristics, and the 10-bit signal becomes an 8-bit signal. And output to the YC signal generation circuit 34. The YC signal creation circuit 34 creates a luminance signal Y and chroma signals Cr and Cb from the gamma-corrected R, G, and B signals. The luminance signal Y and chroma signals Cr and Cb (YC signal) are stored in the memory 36 in the same memory space as the memory 24.
[0034]
Here, by reading the YC signal in the memory 36 and outputting it to the liquid crystal monitor 52, a moving image or a still image can be displayed on the liquid crystal monitor 52. The YC signal after photographing is compressed into a predetermined format by the compression / decompression circuit 54 and then recorded on a recording medium such as a memory card by the recording unit 56. Further, in the reproduction mode, the image data recorded on the memory card or the like is decompressed by the compression / decompression circuit 54 and then output to the liquid crystal monitor 52 so that the reproduced image is displayed on the liquid crystal monitor 52. .
[0035]
The CPU 38 controls each circuit based on inputs from the camera operation unit 40 including the mode dial 1 and the shutter button 2 shown in FIG. 1, and performs control such as autofocus, automatic exposure control, and auto white balance. Do. This autofocus control is, for example, contrast AF that moves the taking lens 10 so that the high-frequency component of the G signal is maximized, and the drive unit 42 so that the high-frequency component of the G signal is maximized when the shutter button 2 is half-pressed. Then, the photographing lens 10 is moved to the in-focus position.
[0036]
The CPU 38 also includes a memory 39 for storing various data such as an EV value and distance data to the subject, a strobe 46 for emitting strobe light, and a distance sensor (distance detection for detecting the distance to the subject). (Means) 47 is connected, and these are controlled. Note that the distance to the subject is detected by the distance sensor 47 when the shutter button 2 is half-pressed and stored in the memory 39.
[0037]
In the automatic exposure control, as shown in FIG. 4, the R, G, B signals are fetched up to four times at predetermined exposures (1) to (4), and these R, G, B signals are integrated. The subject luminance (shooting EV value) is obtained based on the value. This is executed when the shutter button 2 is half-pressed. Note that the process for obtaining the photographing EV value corresponds to the luminance level detecting means of the present invention.
[0038]
Next, details of the measurement of the photographing EV value will be described.
[0039]
As shown in FIG. 5, one screen is divided into a plurality of areas (8 × 8), the luminance signals obtained from the R, G, and B signals are integrated for each divided area, and each division is performed based on the integrated value. The EV value (EVi) of the area is obtained. Subsequently, as shown in FIG. 5, the EV value of each divided area is weighted corresponding to the shooting mode, and the EV ′ value of the entire screen is calculated by the following equation.
[0040]
[Expression 1]

[0041]
However, i is a subscript indicating each of the divided areas, and can take a value of 0 to 63 in the above case. N indicates the number of divided areas. In the above case, 8 × 8 = 64. ΔEViso is an EV value correction amount based on a predetermined sensitivity (for example, ISO 200), and is a value for adjusting EV ′ to be constant even when the sensitivity is changed. Wi is a weighting factor for each divided area. For example, as shown in FIG. 5, the weighting factor of the center-weighted metering method is used.
[0042]
The EV ′ calculated as described above is further subjected to exposure correction ΔEV corresponding to the shooting mode as shown in the following equation to obtain the shooting EV value. The obtained shooting EV value is stored in the memory 39.
[0043]
EV = EV′−ΔEV (2)
Note that ΔEV is, for example, ΔEV = 0 in the portrait mode, and ΔEV = 0.3 in the landscape mode and the night view mode.
[0044]
The aperture value and shutter speed at the time of shooting are finally determined based on the shooting EV value obtained as described above.
[0045]
Then, when the shutter button is fully pressed, the diaphragm 12 is driven through the diaphragm driving unit 44 so that the determined diaphragm value is obtained, and the charge accumulation time is controlled by the electronic shutter so that the determined shutter speed is achieved. .
[0046]
Next, an auto white balance control method will be described with reference to the flowchart shown in FIG.
[0047]
The white balance control shown in FIG. 6 is executed in the case of a predetermined shooting mode and strobe mode and when it is determined that strobe light is emitted.
[0048]
The following table shows combinations of shooting modes and strobe modes in which the white balance control shown in FIG. 6 is executed. For example, in the auto shooting mode, the following white balance control is executed when the EV value is equal to or less than a predetermined threshold value, and in other cases, normal white balance control is performed.
[0049]
[Table 1]

[0050]
First, it is determined whether or not strobe light is emitted from the EV value, shooting mode, and strobe mode. If strobe light is emitted, it is determined whether or not the shooting mode and strobe mode are a combination indicated by a circle in the above table. Is done. If it is determined that the flash fires, and the shooting mode and the flash mode are determined not to be a combination indicated by a circle in the above table, white balance control during normal flash firing is performed by a well-known method. White balance correction values Rg, Gg, and Bg are set and applied to the white balance adjustment circuit 30. If it is determined that the strobe light is not emitted, white balance correction values Rg, Gg, and Bg for performing white balance control suitable for a case where the strobe light is not emitted are set by a known method, and a white balance adjustment circuit is set. 30.
[0051]
If it is determined that the flash is emitted and the shooting mode and the flash mode are determined to be a combination indicated by a circle in the above table, the CPU 38 obtains the distance data to the subject obtained when the shutter button is half-pressed. Is acquired (step S10).
[0052]
Next, the photographing EV value obtained when the shutter button is half-pressed is read from the memory 39 (step S11).
[0053]
Next, the R, G and B signals of the image captured by the flash emission when the shutter button is fully pressed are temporarily stored in the memory 24. This one screen is divided into a plurality of areas (for example, 8 × 8). Then, an integrated value for each color of the R, G, and B signals is obtained by the integrating circuit 48 for each divided area (step S12).
[0054]
The integrated values Rt, Gt, Bt of the R, G, B signals are output to multipliers (multiplier means) 50R, 50G, 50B provided between the integrating circuit 48 and the CPU 38, and the multipliers 50R, 50G, 50B are output. Is multiplied by a predetermined reference WB (white balance) gain value (reference control value) Rst, Gst, Bst (step S14). The reference WB gain values Rst, Gst, and Bst are stored in the memory 39 in advance.
[0055]
The integrated values Rt ′, Gt ′, Bt ′ of the R, G, B signals multiplied by the reference WB gain values Rst, Gst, Bst are input to the CPU 38.
[0056]
The reference WB gain values Rst, Gst, and Bst are gain values for adjusting the white balance to be appropriate when the strobe light is dominant as a light source, such as when the strobe light sufficiently reaches the subject. It is.
[0057]
Then, the CPU 38 has a ratio Rt ′ / Gt ′ between the integrated value Rt ′ of the input R signal and the integrated value Gt ′ of the G signal, and a ratio Bt ′ / Gt of the integrated value of the B signal and the integrated value of the G signal. Gt ′ is obtained (step S16). This process corresponds to an acquisition unit of the present invention.
[0058]
Rt ′ / Gt ′ and Bt ′ / Gt ′ obtained for each divided area as described above are the detection frames in which the divided area is detected from the detection frames represented on the graph shown in FIG. Used to determine whether to enter. Note that each detection frame in FIG. 7 defines a range of color distribution of an environmental light source other than strobe light.
[0059]
As shown in FIG. 7, the detection frame includes a blue sky detection frame, a shade-clouding detection frame, a daylight color (fluorescent light) detection frame, a green detection frame, a daylight white (fluorescent light) detection frame, a strobe detection frame, tungsten. There is a light bulb detection frame, the shade-cloud detection frame includes shade-cloud detection frames CLD1 to CLD4, the daylight color detection frame includes daylight color detection frames EXD1 to EXD4, and the daylight white detection frame includes a daylight white detection frame EXN1. The tungsten light bulb detection frame includes EXN4, and includes tungsten light bulb detection frames TNG1-1 to TNG1-4, TNG2-1 to TNG2-4, and TNG3.
[0060]
Then, the CPU 38 represents Rt ′ / Gt ′ = X ′, Bt ′ / Gt ′ = Y ′, and Rt ′ / Gt ′, Bt ′ / Gt ′ obtained for each divided area (X _i ', Y _i ') Discriminates which detection frame of these detection frames is included, and counts the number (step S18). This process corresponds to the color distribution detecting means of the present invention.
[0061]
Next, it exists in each detection frame (X _i ', Y _i ') Average value (Xa _j 'Ya _j ') Is obtained (step S20). Here, j is a subscript indicating each detection frame. The center of gravity value may be used instead of the average value.
[0062]
Next, an evaluation value Fc () representing the light source likeness (shade-cloudiness etc.) regarding the color is calculated by the membership function provided corresponding to each detection frame (step S22). The membership function is a function that outputs an evaluation value Fc () representing the light source likeness with respect to the color using the number in the detection frame as a variable. That is, if the evaluation value is high, the possibility of a light source (environment light source) corresponding to the detection frame increases.
[0063]
As shown in FIG. 8, Fc (CLD1) to Fc (CLD4) are membership function values representing shade-cloudiness as variables with the number of divided areas falling within the shade-cloudiness detection frame.
[0064]
As shown in FIG. 9, Fc (SKY) is a value of a membership function that represents the likelihood of a blue sky with the number of divided areas falling within the blue sky detection frame as a variable. Similarly, as shown in FIG. 9, Fc (GRN) is a membership function value representing the greenness with the number of divided areas falling within the green detection frame as a variable.
[0065]
As shown in FIG. 10, Fc (EXD1) to Fc (EXD4) are membership functions representing the daylight-colored fluorescent lamps with the number of divided areas entering the daylight color detection frame as variables. Fc (EXN1) to Fc (EXN4) and Fc (TNG1-1) to Fc (TNG3) are the same as Fc (EXD1) to Fc (EXD4) shown in FIG. 10, and Fc (EXN1) to Fc (EXN4) ) Is a value of a membership function representing the nature of a fluorescent white light with the number of divided areas falling within the natural white detection frame as a variable. Fc (TNG1-1) to Fc (TNG3) are tungsten light bulb detections. This is a membership function value representing the characteristic of daylight fluorescent light with the number of divided areas falling within the frame as a variable.
[0066]
Fc (TYP) is a strobe characteristic with the number of divided areas falling within the strobe detection frame as a variable, that is, a membership function value indicating whether or not strobe light is dominant. This is the same as the membership function representing the fluorescent lightness shown in FIG.
[0067]
Next, an evaluation value Fy () representing the light source-likeness (indoorness, outdoorness) relating to the luminance is calculated by a membership function provided corresponding to each detection frame (step S24). The membership function is a function that outputs an evaluation value representing the light source-likeness related to the luminance using the EV value acquired in step S11 as a variable.
[0068]
As shown in FIG. 11, Fy (outdoor likelihood DAY) is a value of a membership function that represents the outdoorness of the daylight with the EV value as a variable.
[0069]
As shown in FIG. 12, Fy (outdoor likelihood CLD) is a value of a membership function representing shaded or cloudy outdoor appearance with the EV value as a variable.
[0070]
As shown in FIG. 13, Fy (indoorness EXD), Fy (indoorness EXN), and Fy (indoorness TNG) are respectively the indoorness of daylight fluorescent lamps with the EV value as a variable or the whiteness of daylight fluorescent lamps. This is a membership function value representing the indoorness or the indoorness of a tungsten light bulb.
[0071]
Next, an overall evaluation value H of the light source likeness for each detection frame from the evaluation value showing the light source likeness relating to the color and the evaluation value showing the evaluation value relating to the luminance. _j Is obtained (step S26).
[0072]
Evaluation value H ₁ ~ H _{twenty two} Is obtained by the following equation.
[0073]
H ₁ (Evaluation value of shade-cloudiness) = Fc (CLD1) × Fy (outdoorness) × Fc (SKY) (3)
H ₂ (Evaluation value of shade-cloudiness) = Fc (CLD2) × Fy (outdoorness) × Fc (SKY) (4)
H _Three (Evaluation value of shade-cloudiness) = Fc (CLD3) × Fy (outdoorness) (5)
H _Four (Evaluation value of shade-cloudiness) = Fc (CLD4) × Fy (outdoorness) (6)
H _Five (Evaluation value of daylight color fluorescent light) = Fc (EXD1) × Fy (indoor quality EXD) (7)
H ₆ (Evaluation value of daylight color fluorescent light) = Fc (EXD2) × Fy (indoor quality EXD) (8)
H ₇ (Evaluation value of daylight color fluorescent light) = Fc (EXD3) × Fy (indoor quality EXD) (9)
H ₈ (Evaluation value of daylight color fluorescent light) = Fc (EXD4) × Fy (indoor quality EXD) (10)
H ₉ (Evaluation value of daylight white fluorescent light) = Fc (EXN1) × Fy (indoor quality EXN) (11)
H _Ten (Evaluation value of daylight white fluorescent light) = Fc (EXN2) × Fy (indoor quality EXN) (12)
H ₁₁ (Evaluation value of daylight white fluorescent light) = Fc (EXN3) × Fy (indoorness EXN) × Fc (GRN) (13)
H ₁₂ (Evaluation value of daylight color fluorescent lamp) = Fc (EXN4) × Fy (indoorness EXN) × Fc (GRN) (14)
H ₁₃ (Evaluation value of tungsten bulb-likeness) = Fc (TNG1-1) × Fy (indoor-likeness TNG) (15)
H ₁₄ (Evaluation value of tungsten bulb-likeness) = Fc (TNG1-2) × Fy (indoor-likeness TNG) (16)
H ₁₅ (Evaluation value of tungsten bulb-likeness) = Fc (TNG1-3) × Fy (indoorness-likeness TNG) (17)
H ₁₆ (Evaluation value of tungsten bulb-likeness) = Fc (TNG1-4) × Fy (indoor-likeness TNG) (18)
H ₁₇ (Evaluation value of tungsten bulb-likeness) = Fc (TNG2-1) × Fy (indoor-likeness TNG) (19)
H ₁₈ (Evaluation value of tungsten bulb-likeness) = Fc (TNG2-2) × Fy (indoor-likeness TNG) (20)
H ₁₉ (Evaluation value of tungsten bulb-likeness) = Fc (TNG2-3) × Fy (indoor-likeness TNG) (21)
H ₂₀ (Evaluation value of tungsten bulb-likeness) = Fc (TNG2-4) × Fy (indoor-likeness TNG) (22)
H _{twenty one} (Evaluation value of tungsten bulb-likeness) = Fc (TNG3) × Fy (indoor-likeness TNG) (23)
H _{twenty two} (Evaluation value of strobe lightness) = Fc (TYP) × Fy (outdoor likeness DAY) (24)
Here, since 0 ≦ Fc () and Fy () ≦ 1, 0 ≦ H _j ≦ 1. As shown in FIG. 9, Fc (SKY) and Fc (GRN) are the evaluation values of the shade-cloudiness or neutral white detection frame as the number of divided areas that fall within the blue sky detection frame or the green detection frame increases. Takes a value that acts in the direction of lowering.
[0074]
Further, as shown in FIG. 13, Fy (indoorness) takes a value that acts in the direction of lowering the evaluation value of the detection frames as the EV value is higher. Thus, the evaluation value H of the light source quality _j Is determined in consideration of not only the color distribution but also the luminance, so that the light source can be specified appropriately. For example, when shooting a subject of the same color in a room where the fluorescent lamp is lit, and when the light source is specified only by the color distribution, the light source is incorrectly specified and a color failure occurs. There is.
[0075]
However, in this embodiment, when the luminance is low, that is, when the image is taken indoors, Fy (appearance of the room) is high, and when the luminance is high, that is, when the image is taken outdoor. , Fy (likeness in the room) is reduced, so that the light source can be specified accurately and the occurrence of color feria can be prevented.
[0076]
When the evaluation value of the light source corresponding to each detection frame is calculated as described above, it is determined whether or not the evaluation value is not less than a predetermined threshold value (for example, not less than 0.4) among these evaluation values ( Step S28). If there is an evaluation value that is equal to or greater than a predetermined threshold value, an evaluation value that is equal to or greater than the predetermined threshold value is selected as an environmental light source candidate. This process corresponds to setting means of the present invention.
[0077]
Next, for each selected environmental light source, a control value (gain value) G for performing white balance control so that the color of the mixed light source in which the strobe light and the environmental light source are mixed according to the following formula is white. _R , G _B , G _G Is calculated (step S30). This process corresponds to the calculation means of the present invention.
[0078]
G _R = {Σ (gr _j × H _j ) / ΣH _j } × {Σ (G _j × H _j ) / ΣH _j }
... (25)
G _B = {Σ (gb _j × H _j ) / ΣH _j } × {Σ (G _j × H _j ) / ΣH _j }
... (26)
G _G = Σ (G _j × H _j ) / ΣH _j ... (27)
Here, the above formulas (25) to (27) are calculated for evaluation values that are equal to or higher than a predetermined threshold value. ₁₁ ~ H ₁₄ If H ₁₁ ~ H ₁₄ About light source of gr _j , Gb _j Is calculated and the calculated gr _j , Gb _j , H ₁₁ ~ H ₁₄ Is used to calculate within each Σ. Gr _j , Gb _j Is a gain necessary for setting the color of the light source in each detection frame to a predetermined color, and is expressed by the following equation. G _j In this case, Gst is a fixed value.
[0079]
gr _j = Xst / Xa _j '× Tx _j ... (28)
gb _j = Yst / Ya _j '× Ty _j ... (29)
Here, Xst = Rst / Gst and Yst = Bst / Gst. Tx _j , Ty _j X obtained from the integrated values of R, G, B of the original image data not multiplied by the reference WB gain value _i , Y _i The average value of Xa _j (= Xa _j '/ Xst), Ya _j (= Ya _j '/ Yst), Xa _j , Ya _j Which corresponds to a predetermined color. That is, gr _j , Gb _j Xa for the integrated values of R, G, B of the original image data _j , Ya _j Xa _j , Ya _j Is a gain necessary to set the color of the light source (mixed light source of strobe light and environmental light source) to a predetermined color. Tx _j , Ty _j Is 1, for example.
[0080]
Therefore, the first term of the above equations (25) and (26) is the evaluation value H _j Gr with weight _j , Gb _j Represents the weighted average of each. The second term is a term for correcting the brightness. _j Since is a fixed value, the brightness is not corrected in this case.
[0081]
The evaluation value H of the strobe detection frame _{twenty two} Is selected as being greater than or equal to a predetermined threshold, gr _{twenty two} = Xst, gb _{twenty two} = Yst.
[0082]
In this way, the control value G for setting the color of the mixed light source in which the strobe light and the environmental light source other than the strobe light are mixed to a predetermined color. _R , G _B , G _G Is calculated according to the distance to the subject detected by the distance sensor 47 so that these control values are values between the reference WB gain value and a value suitable for the mixed light source. (Step S32). This process corresponds to the adjusting means of the present invention. The adjusted control values are expressed as white balance correction values Rg, Gg, and Bg, and are obtained by the following equations.
[0083]
Rg = (G _R −Rst) × Ld + Rst (30)
Gg = (G _G −Gst) × Ld + Gst (31)
Bg = (G _B −Bst) × Ld + Bst (32)
Here, Ld is a correction coefficient corresponding to the distance to the subject. For example, as shown in FIG. 14, a section where the distance is from 0 to a predetermined threshold th1 and a section where the distance is equal to or greater than the predetermined threshold th2. Becomes a constant value, and takes a value that increases as the distance increases in the interval from the threshold th1 to the threshold th2. Accordingly, the white balance correction values Rg, Gg, and Bg approach the reference WB gain values Rst, Gst, and Bst as the distance decreases, and the control values G as the distance increases. _R , G _B , G _G Get closer to. That is, when the distance to the subject is short, the control value is adjusted so that white balance control suitable for the case where strobe light is used as the light source, and when the distance is long, the white balance suitable for the mixed light source is adjusted. The control value is adjusted so that control is performed. Thereby, white balance control can be optimally performed according to the distance to the subject.
[0084]
The white balance correction values Rg, Gg, Bg calculated in this way are output to the white balance adjustment circuit 30, and the R, G, B signals of the original image data are white balance adjusted (step S34). Assuming that the corrected signals are R ′, G ′, and B ′, R ′, G ′, and B ′ are expressed by the following equations.
[0085]
R ′ = Rg × R (33)
G ′ = Gg × G (34)
B ′ = Bg × B (35)
On the other hand, the evaluation value H equal to or greater than a predetermined threshold _j If there is no single, the white balance correction values Rg, Gg, and Bg are set to Rst, Gst, and Bst, respectively (step S36), and white balance adjustment is performed (step S34).
[0086]
Thus, in this embodiment, since the environmental light source is determined in consideration of not only the color of the environmental light source but also the EV value, the environmental light source can be accurately determined. Also, since the color of the environmental light source is obtained from the image data of the captured image in a state where the strobe light is emitted, that is, the image data of the captured image in actual shooting, the environmental light source can be selected without complicating the imaging sequence. It can be determined accurately.
[0087]
The white balance correction values Rg, Gg, and Bg are control values G for setting the color of the mixed light source to a predetermined color from the reference WB gain value. _R , G _B , G _G And a value that enables white balance control suitable for the distance to the subject, so that white balance control can be performed appropriately according to the distance to the subject, and the occurrence of color feria Can be suppressed.
[0088]
Further, since the white balance correction values Rg, Gg, and Bg are obtained without using a dedicated sensor, the cost can be reduced and the apparatus can be downsized.
[0089]
【The invention's effect】
As described above, according to the present invention, the control value for white balance control is a value between the control value and the reference control value, and a value suitable for the mixed light source. Since it is adjusted according to the distance, it is possible to appropriately control white balance even in shooting under strobe light emission and to suppress the occurrence of color feria.
[Brief description of the drawings]
FIG. 1 is a rear view of a digital camera according to the present invention.
FIG. 2 is a plan view of a mode dial provided on the upper surface of the digital camera.
FIG. 3 is a block diagram showing an internal configuration of the digital camera.
FIG. 4 is a diagram for explaining how to obtain an EV value;
FIG. 5 is a diagram for explaining a photometric method.
FIG. 6 is a flowchart of a white balance control method.
FIG. 7 is a graph showing a detection frame as a range of color distribution of a light source.
FIG. 8 is a graph showing a membership function representing shade-cloudiness.
FIG. 9 is a graph showing a blue sky membership function.
FIG. 10 is a graph showing a membership function representing the likelihood of a fluorescent lamp and the like.
FIG. 11 is a graph showing a membership function representing the outdoorness of daylight.
FIG. 12 is a graph showing a membership function representing outdoorness.
FIG. 13 is a graph showing a membership function representing indoorness.
FIG. 14 is a diagram showing a relationship between a distance to a subject and a correction coefficient.
[Explanation of symbols]
10 Shooting lens
16 Drive circuit
18 CDS circuit
20 A / D converter
24 memory
26 Digital signal processing circuit
28 Synchronization circuit
30 White balance adjustment circuit
30R, 30G, 30B multiplier
32 Gamma correction circuit
34 YC signal generation circuit
36 memory
39 memory
40 Camera control unit
42 Drive unit
44 Aperture drive
47 Distance sensor
48 Integration circuit
50R, 50G, 50B multiplier

Claims (3)

In a white balance control method in a digital camera capable of emitting strobe light,
Detecting the distance to the subject;
Detecting the brightness level of the captured image when the subject is imaged;
A reference control value for performing white balance control on the image data of the captured image in a state where the strobe light is emitted, using the strobe light as a reference light source so that the color of the reference light source becomes a predetermined color. To correct the image data subjected to white balance control when the strobe light is used as the light source ,
Dividing the captured image into a plurality of areas, and obtaining each color information from the image data multiplied by the reference control value belonging to each area;
Detecting the color distribution of each area based on the acquired color information for each area;
Determining an ambient light source based on the detected brightness level and the color distribution;
Calculating a control value for performing white balance control so that a color of a mixed light source of the environmental light source and the reference light source becomes the predetermined color;
Adjusting the control value by a coefficient for adjustment according to the distance so that the control value is a value between the control value and the reference control value and suitable for the mixed light source. When,
A white balance control method comprising:   The white balance control method according to claim 1, wherein the control value is adjusted to approach the reference control value as the distance decreases. In digital cameras that can emit strobe light,
Distance detection means for detecting the distance to the subject;
Brightness level detection means for detecting the brightness level of the captured image when the subject is imaged;
A reference control value for performing white balance control on the image data of the captured image in a state where the strobe light is emitted, using the strobe light as a reference light source so that the color of the reference light source becomes a predetermined color. Multiplying means for correcting the image data subjected to white balance control when the strobe light is used as a light source ,
An acquisition unit that divides the captured image into a plurality of areas and acquires color information from image data multiplied by the reference control value belonging to each area;
Color distribution detection means for detecting the color distribution of each area based on the acquired color information for each area;
Setting means for determining an environmental light source based on the detected luminance level and the color distribution;
Calculating means for calculating a control value for performing white balance control so that a color of a mixed light source of the environmental light source and the reference light source becomes the predetermined color;
Adjustment that adjusts the control value by a coefficient for adjustment according to the distance so that the control value is a value between the control value and the reference control value and is a value suitable for the mixed light source Means,
A digital camera characterized by including:

Images