JP3792555B2 - Brightness adjustment method and imaging apparatus - Google Patents

Description

これに対して、累積度数が総度数Ｔａの７０％に達する明度の指標明度Ｌｈは、総度数Ｔａと同様に度数が負数となる明度については度数０とみなして明度の低い側から積算し、積算度数が０．７×Ｔａを満たす初めての明度として定義する。定義式は下記式（５）、
【数２】

を満たす最小のＬｘが指標明度Ｌｈということになる。
このようにして求められた指標明度Ｌｈと、予め定められた目標明度Ｌ０を比較し、指標明度Ｌｈが目標明度Ｌ０よりも大きい場合は、タイミングジェネレータ１９を制御し、電荷蓄積時間Ｓがより小さくなるよう調整するか、Ｄ／Ａコンバータ１８を制御し、ＡＧＣ回路１４のゲインＧがより小さくなるように調整する。
また、逆に目標明度Ｌ０が指標明度Ｌｈよりも大きい場合は、タイミングジェネレータ１９を制御し、電荷蓄積時間Ｓがより大きくなるよう調整するか、Ｄ／Ａコンバータ１８を制御し、ＡＧＣ回路１４のゲインＧがより大きくなるように調整する。
なお、明度調整の手段は、上記方法に限定されるものではなく、必ず画像の明度を上げる一連の操作と、必ず画像の明度を下げる一連の操作を組み合わせたものであれば、どのようなものであっても構わない。
【００３７】
以上のように、この実施の形態３によれば、度数加重係数による加重付き明度度数分布を計測するため、画像の中で各明度の画素がどの位置に分布しているかによって処理に変化を持たせた画像の明度調整を行う撮像装置を構成することが可能である。
また、度数加重係数に負数を含めることによって、特定領域の画素についてはその影響を排除することができ、被写体の背後から照明が当たる逆光状態や、逆に被写体のみに強い光が当たり主要被写体の信号レベルが飽和してしまう過順光状態においても、主要被写体部分で信号レベルが低くなってしまう黒潰れや逆に信号レベルが飽和する白飛びの現象が発生するのを緩和することが可能である。
これは背景が暗く主要被写体のみに照明が当たっている過順光状態においても同様であり、背景部に当たる輝度値の低い部分の度数が加重なしの場合と比較して減少するため、暗い背景部に引きずられて主要被写体部分が白く飛んでしまうのを防ぐことが可能である。
【００３８】
実施の形態４．
図１０はこの発明の実施の形態４による撮像装置を示す構成図であり、図において、２０はレンズ系１１における絞り機構を制御し、固体撮像素子１２に入射する光量を調節する絞り制御手段であり、撮像制御手段１７によって制御されるものである。
４ａ〜４ｃは互いに異なる度数加重係数が設定された複数の加重係数設定テーブル、５は複数の加重係数設定テーブル４ａ〜４ｃを動的に変更するテーブル切り替え手段である。２１は被写体確認のためにファインダを覗く撮影者の視線方向を検知し、検知された視線方向に応じてテーブル切り替え手段５を制御する視点検出手段である。その他の構成については、ＡＧＣ回路１４、Ｄ／Ａコンバータ１８、およびタイミングジェネレータ１９が含まれていない以外、図９と同一である。
図１１は視点位置に応じて互いに異なる度数加重係数が設定された複数の加重係数設定テーブルを示す説明図である。
【００３９】
次に動作について説明する。
撮像した画像をデジタルの映像信号に変換し、度数分布計測手段１６に入力する所までは、上記実施の形態３と同様であるが、度数加重係数の参照に用いる加重係数設定テーブルを複数持つ所が異なる。
この実施の形態４では、複数の加重係数設定テーブル４ａ〜４ｃのうちのいずれを使用するかはテーブル切り替え手段５によって決定される。テーブル切り替え手段５は、視点検出手段２１によって制御されており、撮影者の視線方向によって度数分布計測手段１６で用いる加重係数設定テーブルが決定される。
図１１は図７と共に、視点検出手段２１と組み合わせて用いられる複数の加重係数設定テーブルの一例となる組合せを示したものである。視線が画面中央部を注視している場合には図７に示した加重係数設定テーブルを使用し、画面内左方向を注視している場合には図１１（ａ）の加重係数設定テーブル、画面内右方向を注視している場合には図１１（ｂ）の加重係数設定テーブルを使用する。
【００４０】
以上のように、この実施の形態４によれば、画面内で視線が注視している方向の画素について度数加重係数値を大きく設定することで、例え被写体が中央部に存在しない構図であっても、使用者の撮影しようとする部分を主要被写体とする明度制御を行う撮像装置を構成することができる。
また、撮像制御手段１７において絞り制御手段２０を制御し、絞りの調節によって指標明度Ｌｈを目標明度Ｌ０に一致させる構成をとっている。この構成では指標明度Ｌｈが目標明度Ｌ０よりも大きい場合は、絞り制御手段２０によってより絞りを閉じ、固体撮像素子１２に入射する光量を減少させる。目標明度Ｌ０が指標明度Ｌｈよりも大きい場合は、絞り制御手段２０によってより絞りを開き、固体撮像素子１２に入射する光量を増加させる。
もちろん、固体撮像素子１２の蓄積時間を変更可能なシステムやＡＧＣ回路１４の利得変更可能なシステムでは、実施の形態３と同様の明度調整方法も可能であり、あるいは２つの手法を組み合わせて用いることも可能である。
さらに、画像をエリア毎のブロックに分割し、各エリアの度数加重係数のみを加重係数設定テーブルとして記録しておく場合には、各画素の度数加重係数を全て加重係数設定テーブルとして用意する場合と比較し、加重係数設定テーブルのために用意すべきデータサイズを大幅に削減することが可能である。
【００４１】
実施の形態５．
図１２はこの発明の実施の形態５による撮像装置を示す構成図であり、図において、２２は撮像制御手段１７において、指標明度Ｌｈおよび目標明度Ｌ０を対数値に変換する際に参照する対数値変換テーブルである。その他の構成については、図９と同一である。
図１３は対数値変換テーブルを示す説明図、図１４は被写体照度対数値、ゲイン設定値および蓄積時間設定値を対応させたテーブルを示す説明図である。
【００４２】
次に動作について説明する。
撮像した画像をデジタルの映像信号に変換し、度数分布計測手段１６によって加重付き明度度数分布を得る所までは、上記実施の形態３と同様であるが、指標明度Ｌｈを算出後、目標明度Ｌ０に一致させる制御を行う部分が異なる。
この実施の形態５ににおいては、飽和領域を除いてゲインや蓄積時間を２倍にすると、指標明度Ｌｈについてもほぼ２倍となり、ゲインや蓄積時間といった明度調整用のパラメータと調整指標値との間の線形性が保持されるという特長がある。このため指標明度Ｌｈを対数化して同じく対数化された目標明度Ｌ０との間の差分を求めることにより、高速安定かつ簡潔な明度補正処理を行うことができる。
具体的には、図１３に示すような対数値変換テーブル２２を用意し、そのテーブルの参照によって指標明度Ｌｈおよび目標明度Ｌ０の対数変換値を求める。二つの対数値の差分が目標明度Ｌ０に対する指標明度Ｌｈの比率を表すことになる。次に、図１４のテーブルを参照する。図１４のテーブルは、被写体照度の対数値と、その被写体照度に適した蓄積時間Ｓの設定値、およびゲインＧの設定値を対応させたものになっている。このテーブルにおいても、左列の値の差分が被写体照度の比率を表すことになるため、指標明度Ｌｈを算出する際に用いた蓄積時間Ｓの設定値、およびゲインＧの設定値に対して、先に求めた指標明度Ｌｈおよび目標明度Ｌ０の対数変換値の差分の分だけ、図１４の左列の値が変化するようにテーブルを移動させれば、指標明度Ｌｈを目標明度Ｌ０に一致させることが可能である。この際テーブルの移動量が計算で容易に求められるように、テーブル左列の値は一段毎の差分が一定となる等差級数を構成するようにしておく。
【００４３】
また、上述の方法では、蓄積時間Ｓの設定値およびゲインＧの設定値の変化と指標明度Ｌｈの変化が完全に線形に対応することを前提としているが、実際のシステムでは固体撮像素子１２の特性ばらつきや被写体条件の変動によって厳密な線形性は保たれないことが多い。この場合には、時定数Ｔ（Ｔ＜１）を導入することによって、より安定性を重視した制御を行うことも可能である。
具体的には上記で求めた指標明度Ｌｈおよび目標明度Ｌ０の対数変換値の差分Ｄに対してＤ×Ｔを求め、Ｄ×Ｔの分だけ、図１４の左列の値が変化するようにテーブルを移動させる。Ｔの値を小さくするほど、より安定した制御が可能であり、逆にＴの値を大きくするとより、高速に指標明度Ｌｈを目標明度Ｌ０に収束させることが可能である。
【００４４】
以上のように、この実施の形態５によれば、指標明度Ｌｈを対数化して、同じく対数化された目標明度Ｌ０との間の差分を求めることにより、高速安定かつ簡潔な明度補正処理を行うことができる。
【００４５】
【発明の効果】
以上のように、この発明によれば、画像データ取得工程によって取得された画像データにおける全ての画素の明度を算出すると共に、予め設定された画素の位置に対応する負値または正値の度数加重係数に基づき、各画素の位置に対応した度数を当該画素の度数として、明度の等しい画素の度数を累積して明度度数分布を計測し、かつ、累積値が負値となった明度は累積値を０度数とする度数分布計測工程と、度数分布計測工程によって計測された明度度数分布における指標明度が予め設定された目標明度に一致するように画像データ取得工程によって取得される画像データを調整する撮像制御工程とを備えるように構成したので、画像における主要被写体の位置を考慮した明度調整を行うことができると共に、逆光や過順光時にも画像の白飛び、黒潰れが発生しにくく、階調性のある画像を撮影することができる効果がある。
特に、この発明によれば、度数加重係数として負数を含み、かつ、累積値が負値となった明度は累積値を０度数とするよう構成したので、特定領域の画素についてはその影響を排除することができ、被写体の背後から照明が当たる逆光状態や、逆に被写体のみに強い光が当たり主要被写体の信号レベルが飽和してしまう過順光状態においても、主要被写体部分で信号レベルが低くなってしまう黒潰れや逆に信号レベルが飽和する白飛びの現象が発生するのを緩和することができる効果がある。
【００４６】
この発明によれば、度数分布計測工程において、画素の位置に対応する度数加重係数が予め設定された加重係数設定テーブルから度数加重係数を参照するように構成したので、加重係数設定テーブルを用いることによって、容易に該当する度数加重係数を参照することができる効果がある。
【００４７】
この発明によれば、度数分布計測工程において、撮像画面をそれぞれが複数の画素から成るブロックに分割し、各ブロックに対応する度数加重係数が予め設定された加重係数設定テーブルを用いるように構成したので、加重係数設定テーブルのために用意しなくてはならないデータサイズを大幅に削減することができる効果がある。
【００４８】
この発明によれば、度数分布計測工程において、互いに異なる度数加重係数が予め設定された複数の加重係数設定テーブルを動的に変更して使用するように構成したので、使用者の意図を反映した明度調整を行うことができる効果がある。
【００４９】
この発明によれば、撮像制御工程において、度数分布計測工程によって計測された明度度数分布における指標明度および予め設定された目標明度を、明度に対応する対数値が設定された対数値変換テーブルから参照し、それら参照した２つの対数値の差分に応じて画像データ取得工程によって取得される画像データを調整するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【００５０】
この発明によれば、撮像制御工程において、算出した対数値の差分と時定数との積を利用して画像データ取得工程によって取得される画像データを調整するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【００５１】
この発明によれば、固体撮像素子から出力される信号を利得制御自在に増幅する利得制御手段と、利得制御手段から出力される信号における全ての画素の明度を算出すると共に、予め設定された画素の位置に対応する負値または正値の度数加重係数に基づき、各画素の位置に対応した度数を当該画素の度数として、明度の等しい画素の度数を累積して明度度数分布を計測し、かつ、累積値が負値となった明度は累積値を０度数とする度数分布計測手段と、度数分布計測手段により計測された明度度数分布における指標明度が予め設定された目標明度に一致するように固体撮像素子の電荷蓄積時間または利得制御手段の利得値を制御する撮像制御手段とを備えるように構成したので、画像における主要被写体の位置を考慮した明度調整を行うことができると共に、逆光や過順光時にも画像の白飛び、黒潰れが発生しにくく、階調性のある画像を撮影することができる効果がある。
特にこの発明によれば、度数分布計測手段は、度数加重係数として負数を含み、かつ、累積値が負値となった明度は累積値を０度数とするよう構成したので、特定領域の画素についてはその影響を排除することができ、被写体の背後から照明が当たる逆光状態や、逆に被写体のみに強い光が当たり主要被写体の信号レベルが飽和してしまう過順光状態においても、主要被写体部分で信号レベルが低くなってしまう黒潰れや逆に信号レベルが飽和する白飛びの現象が発生するのを緩和することができる効果がある。
【００５２】
この発明によれば、固体撮像素子への入射光量を制御する絞り制御手段と、固体撮像素子から出力される画像データにおける全ての画素の明度を算出すると共に、予め設定された画素の位置に対応する負値または正値の度数加重係数に基づき、各画素の位置に対応した度数を当該画素の度数として、明度の等しい画素の度数を累積して明度度数分布を計測し、かつ、累積値が負値となった明度は累積値を０度数とする度数分布計測手段と、度数分布計測手段により計測された明度度数分布における指標明度が予め設定された目標明度に一致するように絞り制御手段を制御する撮像制御手段とを備えるように構成したので、画像における主要被写体の位置を考慮した明度調整を行うことができると共に、逆光や過順光時にも画像の白飛び、黒潰れが発生しにくく、階調性のある画像を撮影することができる効果がある。
特にこの発明によれば、度数分布計測手段は、度数加重係数として負数を含み、かつ、累積値が負値となった明度は累積値を０度数とするよう構成したので、特定領域の画素についてはその影響を排除することができ、被写体の背後から照明が当たる逆光状態や、逆に被写体のみに強い光が当たり主要被写体の信号レベルが飽和してしまう過順光状態においても、主要被写体部分で信号レベルが低くなってしまう黒潰れや逆に信号レベルが飽和する白飛びの現象が発生するのを緩和することができる効果がある。
【００５３】
この発明によれば、画素の位置に対応する度数加重係数が予め設定された加重係数設定テーブルを備えるように構成したので、加重係数設定テーブルを用いることによって、容易に該当する度数加重係数を参照することができる効果がある。
【００５４】
この発明によれば、加重係数設定テーブルにおいて、撮像画面をそれぞれが複数の画素から成るブロックに分割し、各ブロックに対応する度数加重係数が予め設定されるように構成したので、加重係数設定テーブルのために用意しなくてはならないデータサイズを大幅に削減することができる効果がある。
【００５５】
この発明によれば、互いに異なる度数加重係数がそれぞれ予め設定された複数の加重係数設定テーブルと、複数の加重係数設定テーブルのうちの使用する加重係数設定テーブルを動的に変更するテーブル切り替え手段とを備えるように構成したので、使用者の意図を反映した明度調整を行うことができる効果がある。
【００５６】
この発明によれば、視点位置に応じて互いに異なる度数加重係数がそれぞれ予め設定された複数の加重係数設定テーブルと、撮影者の視点位置を検出する視点検出手段と、視点検出手段によって検出された視点位置に応じて複数の加重係数設定テーブルのうちの使用する加重係数設定テーブルを動的に変更するテーブル切り替え手段とを備えるように構成したので、撮影者の撮影しようとする部分を主要被写体として、明度調整を行うことができる効果がある。
【００５７】
この発明によれば、明度に対応する対数値が設定された対数値変換テーブルを備え、撮像制御手段は、度数分布計測手段により計測された明度度数分布における指標明度の対数値を対数値変換テーブルから参照すると共に、予め設定された目標明度の対数値を対数値変換テーブルから参照し、それら参照した２つの対数値の差分に応じて固体撮像素子の電荷蓄積時間または利得制御手段の利得値を制御するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【００５８】
この発明によれば、明度に対応する対数値が設定された対数値変換テーブルを備え、撮像制御手段は、度数分布計測手段により計測された明度度数分布における指標明度の対数値を対数値変換テーブルから参照すると共に、予め設定された目標明度の対数値を対数値変換テーブルから参照し、それら参照した２つの対数値の差分に応じて絞り制御手段を制御するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【００５９】
この発明によれば、撮像制御手段において、算出した対数値の差分と時定数との積を利用して固体撮像素子の電荷蓄積時間または利得制御手段の利得値を制御するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【００６０】
この発明によれば、撮像制御手段において、算出した対数値の差分と時定数との積を利用して絞り制御手段を制御するように構成したので、高速かつ簡潔に明度調整を行うことができる効果がある。
【図面の簡単な説明】
【図１】 この発明の実施の形態１による明度調整方法を示すブロック図である。
【図２】 画素の位置に対応する度数加重係数を示す説明図である。
【図３】 度数加重係数を付加した明度度数分布からの明度調整方法を示す説明図である。
【図４】 度数加重係数を付加した明度度数分布に負数が存在する場合を示す説明図である。
【図５】 黒潰れや白飛びに対する効果を示す説明図である。
【図６】 この発明の実施の形態２による明度調整方法を示すブロック図である。
【図７】 複数の画素から成る各ブロックに対応する度数加重係数を示す説明図である。
【図８】 この発明の実施の形態２による他の明度調整方法を示すブロック図である。
【図９】 この発明の実施の形態３による撮像装置を示す構成図である。
【図１０】 この発明の実施の形態４による撮像装置を示す構成図である。
【図１１】 視点位置に応じて互いに異なる度数加重係数が設定された複数の加重係数設定テーブルを示す説明図である。
【図１２】 この発明の実施の形態５による撮像装置を示す構成図である。
【図１３】 対数値変換テーブルを示す説明図である。
【図１４】 被写体照度対数値、ゲイン設定値および蓄積時間設定値を対応させたテーブルを示す説明図である。
【図１５】 従来のデジタルスチルカメラを示す構成図である。
【図１６】 従来の明度度数分布を示す特性図である。
【符号の説明】
１ 画像データ取得工程、２ 度数分布計測工程、３ 撮像制御工程、４，４ａ〜４ｃ 加重係数設定テーブル、５ テーブル切り替え手段、１１ レンズ系、１２ 固体撮像素子、１３ プリアンプ、１４ ＡＧＣ回路（利得制御手段）、１５ Ａ／Ｄコンバータ、１６ 度数分布計測手段、１７ 撮像制御手段、１８ Ｄ／Ａコンバータ、１９ タイミングジェネレータ、２０ 絞り制御手段、２１ 視点検出手段、２２ 対数値変換テーブル、３１ 撮像手段、３２ 明度解析手段、３３ 露出制御手段。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a brightness adjustment method and an imaging apparatus in a digital color imaging apparatus.
[0002]
[Prior art]
FIG. 15 is a block diagram showing a conventional digital still camera disclosed in, for example, Japanese Patent Application Laid-Open No. 11-69372. In FIG. 15, reference numeral 31 denotes an imaging means such as a lens or a CCD, and 32 denotes the brightness of an image obtained by photographing. Brightness analysis means 33 for creating a frequency distribution, and exposure control means 33 for adjusting the aperture and shutter speed based on the created brightness frequency distribution.
FIG. 16 is a characteristic diagram showing a conventional brightness frequency distribution.
[0003]
Next, the operation will be described.
There is a lightness adjustment method that uses a lightness frequency distribution and performs lightness correction so that the saturation level of pixels becomes a fixed number. This uses human visual characteristics, and the impression of the brightness that humans receive from the image is determined by the frequency of the highlight part rather than the overall average value, so the frequency of the maximum brightness of the brightness frequency distribution Processing is performed based on the idea of managing
In FIG. 15, brightness analysis means 32 creates a brightness frequency distribution for the image obtained by the imaging means 31, and exposure control means 33 adjusts the aperture and shutter speed based on the created brightness frequency distribution.
FIG. 16 shows an example of the brightness frequency distribution of the properly exposed negative film. In the figure, in the brightness frequency distribution Y appropriately exposed to the brightness frequency distribution X, the maximum brightness (255) is around 1%. It is known that clipping always occurs.
According to such a digital still camera, for example, even if the photographed image is overexposed and the ratio of the pixels having the maximum brightness (255) in the brightness frequency distribution is about 5%, the gain is 5%. The brightness can be controlled to fall to 1%, and if the image is taken again with the reset exposure value, image data having a maximum brightness of 1%, that is, appropriate brightness Image data can be acquired.
Thus, conventionally, the purpose is to determine whether or not the brightness of an image is appropriate based on the brightness frequency distribution, and to perform adjustment so that the brightness frequency distribution satisfies the above conditions, Rather than assuming that the captured image satisfies some condition, focusing only on what is necessary for an image with appropriate brightness, and processing to satisfy that condition, Regardless of the content of the image, it always seeks good results.
[0004]
[Problems to be solved by the invention]
Since the conventional brightness adjustment method is configured as described above, only 1% of all pixels in the bright background portion are saturated in a so-called backlit state where illumination is applied from behind the subject. In order to control the brightness, the subject portion has a low signal level, and there is a problem that it is impossible to avoid the phenomenon of black crushing that results in a black image.
Further, if there is a saturated pixel at the end portion or the center portion of the screen, it is counted in the same manner, and there is a problem that the brightness control cannot be performed with emphasis on the image at the center portion of the screen.
Furthermore, from the brightness frequency distribution, the occurrence of a backlit state or an over-ordered light state where the signal level of the main subject is saturated due to strong light only on the subject is detected. For example, there is a brightness adjustment method in which bright correction is performed to increase the signal level of the main subject, and dark correction is performed in the case of excessive forward light. However, in this case, switching between the backlit mode and the over-ordered mode occurs, so automatic brightness is continuously applied during imaging with a digital video camera or during operation of the liquid crystal finder in the digital camera. When processing, there existed problems, such as processing becoming unstable.
[0005]
The present invention has been made to solve the above-described problems, and can perform brightness adjustment in consideration of the position of the main subject in the image, and can also cause whiteout and blackout of the image even during backlighting and excessive light. It is an object of the present invention to obtain a brightness adjustment method and an imaging apparatus that are capable of capturing an image having a gradation property, which is less likely to occur.
[0006]
[Means for Solving the Problems]
  The brightness adjustment method according to the present invention calculates the brightness of all pixels in the image data acquired by the image data acquisition process.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0A frequency distribution measuring step, and an imaging control step of adjusting the image data acquired by the image data acquiring step so that the index lightness in the lightness frequency distribution measured by the frequency distribution measuring step matches a preset target lightness; It is equipped with.
[0007]
  In the brightness adjustment method according to the present invention, in the frequency distribution measurement step,Divide the imaging screen into blocks each consisting of multiple pixels.Frequency weighting factor from the weighting factor setting table in which the frequency weighting factor corresponding toAdd toIt is what you do.
[0009]
In the brightness adjustment method according to the present invention, in the frequency distribution measurement step, a plurality of weighting factor setting tables in which different frequency weighting factors are set in advance are dynamically changed and used.
[0010]
The brightness adjustment method according to the present invention is a logarithmic value conversion in which a logarithmic value corresponding to a lightness is set to an index lightness and a preset target lightness in the lightness frequency distribution measured by the frequency distribution measurement step in the imaging control step. The image data acquired by the image data acquisition process is adjusted according to the difference between the two logarithmic values referred to from the table.
[0011]
  The brightness adjustment method according to the present invention adjusts the image data acquired by the image data acquisition step using a product of the calculated logarithmic difference and a time constant in the imaging control step.The
[0012]
  An image pickup apparatus according to the present invention calculates gain values of all pixels in a signal output from a gain control means, and gain control means for amplifying a signal output from a solid-state image pickup element in a gain-controllable manner.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0The charge accumulation time of the solid-state imaging device or the gain value of the gain control means is controlled so that the index brightness in the brightness frequency distribution measured by the frequency distribution measuring means and the brightness frequency distribution measured by the frequency distribution measuring means matches a preset target brightness. Imaging control means.
[0013]
  An image pickup apparatus according to the present invention calculates aperture control means for controlling the amount of light incident on a solid-state image sensor and the brightness of all pixels in image data output from the solid-state image sensor.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0A frequency distribution measuring unit that controls the aperture control unit so that the index lightness in the lightness frequency distribution measured by the frequency distribution measuring unit matches a preset target lightness.
[0014]
  An imaging apparatus according to the present invention isDivide the imaging screen into blocks each consisting of multiple pixels.Is provided with a weighting coefficient setting table in which the frequency weighting coefficient corresponding to is preset.
[0016]
The imaging apparatus according to the present invention includes a plurality of weighting factor setting tables in which different frequency weighting factors are set in advance, and table switching for dynamically changing a weighting factor setting table to be used among the plurality of weighting factor setting tables. Means.
[0017]
The imaging apparatus according to the present invention is detected by a plurality of weighting coefficient setting tables in which different frequency weighting coefficients are set in advance according to the viewpoint position, a viewpoint detection means for detecting the photographer's viewpoint position, and a viewpoint detection means. Table switching means for dynamically changing a weighting factor setting table to be used among a plurality of weighting factor setting tables according to the viewpoint position.
[0018]
The imaging apparatus according to the present invention includes a logarithmic value conversion table in which a logarithmic value corresponding to lightness is set, and the imaging control means logarithmically expresses the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means. Reference is made from the conversion table and a logarithmic value of a preset target brightness is referred to from the logarithmic value conversion table, and the charge accumulation time of the solid-state imaging device or the gain of the gain control means is determined according to the difference between the two logarithmic values referred The value is controlled.
[0019]
The imaging apparatus according to the present invention includes a logarithmic value conversion table in which a logarithmic value corresponding to lightness is set, and the imaging control means logarithmically expresses the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means. In addition to referring to the conversion table, the logarithmic value of the preset target brightness is referred to from the logarithmic value conversion table, and the aperture control means is controlled in accordance with the difference between the two logarithmic values referred to.
[0020]
In the imaging apparatus according to the present invention, in the imaging control means, the charge accumulation time of the solid-state imaging device or the gain value of the gain control means is controlled by using the product of the calculated logarithmic difference and the time constant. It is.
[0021]
  In the imaging apparatus according to the present invention, the aperture control unit is controlled by using the product of the calculated logarithmic difference and a time constant in the imaging control unit.The
[0022]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing a brightness adjustment method according to Embodiment 1 of the present invention. In FIG. 1, 1 is an image data acquisition step, 2 is a frequency distribution measurement step, and 3 is an imaging control step.
FIG. 2 is an explanatory diagram showing the frequency weighting coefficient corresponding to the pixel position.
FIG. 3 is an explanatory diagram showing a lightness adjustment method from a lightness frequency distribution to which a frequency weighting coefficient is added.
FIG. 4 is an explanatory diagram showing a case where a negative number exists in the brightness frequency distribution to which the frequency weighting coefficient is added.
FIG. 5 is an explanatory diagram showing the effect against black crushing and whiteout.
[0023]
Next, the operation will be described.
In FIG. 1, in an image data acquisition step 1, a signal output from a solid-state image sensor or a signal output from a data reader that reads image data once recorded on a medium is read.
The image data referred to here is expressed as a set of three elements in which the pixel values of each pixel are independent from each other, and “a set of three elements independent from each other” is a color image such as RGB, CMY, etc. A three-color color system that is used to represent is generally used. However, there are many other methods for expressing pixel values by a set of three independent elements, such as the XYZ color system, and in the first embodiment, the present invention is not limited to any specific color system. Absent.
[0024]
Next, with respect to the image data obtained in the image data acquisition step 1, in the frequency distribution measurement step 2, first, the brightness defined based on the three elements is calculated.
As the definition of brightness, for example, in the RGB color system, brightness L and pixel value are (R, G, B),
L = 0.2989 · R + 0.5866 · G + 0.1145 · B (1)
The calculation formula is known.
However, the definition of the lightness in the lightness adjustment method of the present invention is not necessarily limited to the above formula (1), and the largest pixel value among the RGB pixel values is used as the lightness.
L = max (R, G, B) (2)
Or simply using the G pixel value as the brightness,
L = G (3)
Such a definition method is also conceivable.
[0025]
  If the R, G, and B values of each pixel are represented as 8-bit data, the brightness obtained based on the above equation (1) can also be represented as 8-bit data. In this case, the value that brightness can take is a value between 0 and 255.
  A brightness frequency distribution (brightness histogram) in the entire image is created from the brightness value for each pixel obtained as described above. In a normal brightness frequency distribution, one pixel always corresponds to one frequency, and the operation of adding one by one to the frequency corresponding to the brightness of each pixel is repeated over the entire screen. In this method, as shown in FIG. 2, a frequency weighting coefficient corresponding to the pixel position is set in advance, and the frequency weighting coefficient corresponding to each pixel is set to a frequency corresponding to the brightness of each pixel.AsAdditionTo do. At this time, if a negative frequency weighting coefficient value is set, the frequency is subtracted instead of added.
  Here, FIG. 2 shows the relationship between the position of the pixel and the frequency weighting coefficient, and represents that the frequency weighting coefficient of the pixel included in each area is a numerical value written in that area. For example, if the brightness of the pixel A in FIG. 2 is 100, the value of the region including the pixel A is −0.2.Assuming that the frequency of the pixel A is -0.2,Frequency of pixel with brightness 100Cumulative value ofThe process of subtracting 0.2 from. Similarly, assuming that the lightness of the pixel B and the pixel C is 50 and 150, respectively, the frequency of the pixel having a lightness of 50 for the pixel BCumulative value of4.0 is added to pixel number C, and pixel C has a brightness of 150 pixelsFrom the cumulative value ofSubtract 0.4.
[0026]
In the imaging control step 3, using the weighted lightness frequency distribution created in this way, the lightness at which the cumulative frequency from lightness 0 in the weighted lightness frequency distribution is a constant ratio with respect to the power of all pixels is obtained. This brightness is set as the index brightness, and the image data acquisition process 1 is adjusted so that the index brightness approaches the target brightness that is a predetermined value.
Regarding this adjustment means, when the image data acquisition step 1 outputs a signal from the solid-state image sensor, a method of changing the amount of light incident on the solid-state image sensor, or a signal amplifying device provided in the solid-state image sensor A method of changing the amplification factor of the first, a time from the start of charge accumulation to reading, that is, a method of changing the shutter speed of a so-called electronic shutter, or the like can be considered.
Further, when the image data acquisition step 1 outputs a signal from a data reading device that reads the image data once recorded on the medium, the amplification factor of the device that amplifies the signal with respect to the read image data is changed. A method etc. can be considered.
However, the brightness adjustment unit of the first embodiment is not limited to the above method, and any combination of a series of operations that always increase the brightness of an image and a series of operations that always decrease the brightness of the image. Anything can be used.
[0027]
FIG. 3 specifically shows a method of adjusting brightness from weighted brightness frequency distribution data. Assuming that a weighted brightness frequency distribution D is obtained in FIG. 3, first, the frequencies are accumulated from the low brightness side, and the brightness with a constant ratio to the total frequency is obtained. In FIG. 3, this fixed ratio is assumed to be 70% of the total frequency, and this is used as the index brightness. In the weighted brightness frequency distribution D, the index brightness is different from the preset target brightness, and the index brightness needs to be raised to the target brightness level.
Here, when the image data acquisition step 1 outputs a signal from the solid-state image sensor and the index lightness is adjusted by changing the amplification factor of the signal amplification device provided in the solid-state image sensor, amplification is performed. The rate is increased step by step, and the increase is stopped when the indicator brightness reaches the target brightness. By performing such processing, a frequency distribution in which the index brightness as shown in the weighted brightness frequency distribution E matches the target brightness is obtained.
Since a negative number may be used as the frequency weighting coefficient as described above, the weighted lightness frequency distribution obtained by the frequency distribution measurement step 2 may have a lightness with a negative frequency as shown by the hatched portion in FIG. There is sex. In this case, if the calculation is performed as it is, the cumulative frequency from the low brightness side does not increase monotonously, and the index brightness may not be uniquely determined. In order to avoid this, the lightness area where the frequency is a negative number is regarded as the frequency 0, and the total frequency and the cumulative frequency from the low lightness side may be calculated.
[0028]
As described above, according to the first embodiment, since the weighted brightness frequency distribution by the frequency weighting coefficient is measured, there is a change in processing depending on where the pixels of each brightness are distributed in the image. Is possible.
In addition, by including a negative number in the frequency weighting coefficient, the influence of the pixels in a specific area can be eliminated, and the backlight is illuminated from behind the subject, or conversely, only the subject is exposed to strong light and the main subject It is possible to mitigate the occurrence of blackout that causes the signal level to be low in the main subject and the occurrence of whiteout that causes the signal level to be saturated, even in an over-ordered light state where the signal level is saturated. is there.
[0029]
FIG. 5 shows the effect against black crushing and whiteout. When the background is bright and the subject is dark as shown in FIG. 5 (a), the frequency weighting coefficient added to the frequency is small or negative for the pixels in the background portion. The frequency of the main subject portion existing in the central portion is increased, and the frequency of the brightness corresponding to the bright background portion is decreased as compared with the case of creating the image.
Here, it is assumed that the lightness (which corresponds to the index lightness in FIG. 5) having a cumulative frequency of 70% from the low lightness side is matched with the lightness level of 70% (corresponding to the target lightness in FIG. 5). When the brightness adjustment is performed, since the frequency of the background portion is counted low, it is possible to realize exposure control that increases the contrast of the central portion.
This is the same in an over-ordered state where only the main subject is illuminated as shown in FIG. 5B, and the frequency of the low-lightness portion corresponding to the background portion is reduced as compared with the case of no weighting. Therefore, it is possible to prevent the main subject portion from being whitened by being dragged by the dark background portion.
[0030]
Embodiment 2. FIG.
FIG. 6 is a block diagram showing a brightness adjustment method according to Embodiment 2 of the present invention. In FIG. 6, 4 is a weighting coefficient setting table. Other configurations are the same as those in FIG.
FIG. 7 is an explanatory diagram showing the frequency weighting coefficient corresponding to each block composed of a plurality of pixels.
FIG. 8 is a block diagram showing another brightness adjustment method according to Embodiment 2 of the present invention. In FIG. 8, 4a to 4c are a plurality of weighting factor setting tables in which different frequency weighting factors are set, and 5 is a plurality of weighting factor setting tables. This is table switching means for dynamically changing the weighting coefficient setting tables 4a to 4c. Other configurations are the same as those in FIG.
[0031]
Next, the operation will be described.
In FIG. 6, the processing of the image data acquisition step 1, the frequency distribution measurement step 2, and the imaging control step 3 is the same as that in the first embodiment, and the weighting coefficient setting table 4 is set for each pixel in the frequency distribution measurement step 2. The frequency weighting coefficient to be added to or subtracted from is table data set in advance.
As shown in FIG. 2, the table data may be a record of the frequency weighting coefficient corresponding to each pixel as it is. In order to save the data size required for the table, the image is divided into areas as shown in FIG. It is also possible to divide the data into blocks and record the values for each area as a table on the assumption that the frequency weighting coefficient is constant in each area.
Further, as shown in FIG. 8, a plurality of weighting coefficient setting tables 4 a to 4 c can be prepared and switched by the table switching means 5. The table switching timing may be switch switching by the user, the user's line-of-sight direction detected by the line-of-sight input device, or the like.
[0032]
As described above, according to the second embodiment, the frequency weighting coefficients are held as the weighting coefficient setting tables 4a to 4c, thereby enabling a flexible usage method such as dynamically using a plurality of frequency weighting coefficients. ing.
Further, in changing the weighting factor setting tables 4a to 4c by the user's switch switching, for example, a weighting factor setting table for performing backlight correction and a weighting factor setting table for performing less backlighting are prepared, and the user is in a backlight state. It is possible to perform a brightness adjustment process that reflects the user's intention by leaving a rough decision as to whether or not the image has occurred or whether or not to perform backlight correction.
Further, when the weighting coefficient setting tables 4a to 4c are switched by the line-of-sight input device, the direction of the image being watched by the user is detected in the finder of the digital still camera or digital video camera, and that portion is used as the main subject. It is possible to increase the weighting factor setting. Thereby, even if the composition does not exist in the central portion, it is possible to perform brightness control with the main subject as the portion to be photographed by the user.
Further, when the image is divided into blocks for each area and only the frequency weighting coefficient of each area is set as the weighting coefficient setting table 4, all the frequency weighting coefficients of each pixel are prepared as the weighting coefficient setting table 4. Compared to the case, the data size to be prepared for the weighting coefficient setting table 4 can be greatly reduced.
[0033]
Embodiment 3 FIG.
FIG. 9 is a block diagram showing an image pickup apparatus according to Embodiment 3 of the present invention. In FIG. 9, reference numeral 11 denotes a lens system for forming a subject image on the image pickup surface of the image pickup element, and reference numeral 12 photoelectrically converts an incident light image. This is a solid-state imaging device that can change the charge accumulation time S for outputting an electric video signal.
Reference numeral 13 denotes a preamplifier that amplifies the video signal from the solid-state imaging device 12, reference numeral 14 denotes an AGC circuit (gain control means) that amplifies the video signal from the preamplifier 13, and gain can be changed. Reference numeral 15 denotes a video signal from the AGC circuit 14. An A / D converter 16 for converting to a digital video signal calculates the brightness of each pixel from the pixel value of the digital video signal for one frame from the A / D converter 15 and accumulates the frequency of pixels having the same brightness. At the same time, the frequency weighting coefficient corresponding to the pixel position preset in the weighting coefficient setting table 4 is referred to, and the frequency weighting coefficient is added to or subtracted from the corresponding accumulated frequency to measure the weighted lightness frequency distribution. It is a frequency distribution measuring means.
17 obtains the index lightness Lh based on the weighted lightness frequency distribution calculated by the frequency distribution measuring means 16, and controls the D / A converter 18 and the timing generator 19 to thereby determine the index lightness Lh in advance. Imaging control means for performing control to match the lightness L0, 18 is a D / A converter that outputs an analog control signal for controlling the gain G of the AGC circuit 14, and 19 is a drive for controlling the charge accumulation time S of the solid-state imaging device 12. It is a timing generator that supplies pulses.
[0034]
Next, the operation will be described.
In FIG. 9, an optical image incident on the imaging device is formed on the imaging surface of the solid-state imaging device 12 by the lens system 11, converted into an electric video signal by the solid-state imaging device 12, and then the preamplifier 13 and the AGC circuit. 14 and amplified by the A / D converter 15 to be converted into a digital video signal. In this digital video signal, the brightness of each pixel is calculated by the frequency distribution measuring means 16, and the brightness calculated for each pixel from the pixel value for one frame and the frequency weighting coefficient corresponding to the position of the pixel are referred to. From the value of the weighting coefficient setting table 4 to be used, it is used to measure the weighted brightness frequency distribution.
Here, the pixel value of each pixel is assumed to be composed of a set of three independent elements of RGB, but other values represented as a set of three elements whose pixel values are independent of each other, such as the CMY color system. Any arbitrary color system may be used.
In addition, the lightness is calculated by the definition of the above formula (1) where the lightness is L and the pixel value is (R, G, B), but an arbitrary calculation formula that can be created by a combination of three elements is lightness. It can be used as a definition of L.
[0035]
A weighted brightness frequency distribution is sequentially calculated based on the combination of the brightness of each pixel included in the frame and the pixel position in the screen. For example, if each of the three elements of the pixel value has a data width of 8 bits, each of R, G, and B takes a value in the range from 0 to 255. Therefore, the lightness L is also a value in the range from 0 to 255. It becomes. In order to calculate the brightness frequency distribution, 256 variables from H (0) to H (255) are prepared, and the frequency weighting of the corresponding pixel position is applied to H (L) according to the brightness L calculated for each pixel. Add the coefficient K. However, the frequency weighting coefficient K may take a negative number, in which case subtraction is performed.
[0036]
Next, based on the weighted brightness frequency distribution calculated by the frequency distribution measuring means 16, the imaging control means 17 obtains the index brightness Lh. Here, the index lightness Lh is defined as a point in the weighted lightness frequency distribution where the frequencies are accumulated from the lightness side and the cumulative frequency reaches 70% of the total frequency. Of course, the ratio of the cumulative frequency used for determining the index lightness Lh to the total frequency may take any value.
Specifically, first, the total frequency Ta of the weighted lightness frequency distribution is obtained. At this time, the weighted lightness frequency distribution may include a lightness whose frequency is a negative number, but such lightness is integrated as a frequency of zero. Therefore, the defining formula is as shown in the following formula (4).
[Expression 1]

On the other hand, the lightness index lightness Lh at which the cumulative frequency reaches 70% of the total frequency Ta is regarded as the frequency 0 for the lightness having a negative power as in the case of the total frequency Ta, and is integrated from the low lightness side. It is defined as the first brightness that satisfies a cumulative frequency of 0.7 × Ta. The definition formula is the following formula (5),
[Expression 2]

The minimum Lx that satisfies the condition is the index lightness Lh.
The index lightness Lh obtained in this way is compared with a predetermined target lightness L0. When the index lightness Lh is larger than the target lightness L0, the timing generator 19 is controlled to make the charge accumulation time S shorter. Or the D / A converter 18 is controlled to adjust the gain G of the AGC circuit 14 to be smaller.
Conversely, when the target lightness L0 is larger than the index lightness Lh, the timing generator 19 is controlled to adjust the charge accumulation time S to be longer, or the D / A converter 18 is controlled, and the AGC circuit 14 Adjustment is made so that the gain G becomes larger.
The lightness adjustment means is not limited to the above method, and any method may be used as long as it combines a series of operations that always increase the brightness of an image and a series of operations that always decrease the brightness of the image. It does not matter.
[0037]
As described above, according to the third embodiment, since the weighted lightness frequency distribution by the frequency weighting coefficient is measured, there is a change in processing depending on where the pixels of each lightness are distributed in the image. It is possible to configure an imaging apparatus that adjusts the brightness of the displayed image.
In addition, by including a negative number in the frequency weighting coefficient, the influence of the pixels in a specific area can be eliminated, and the backlight is illuminated from behind the subject, or conversely, only the subject is exposed to strong light and the main subject It is possible to mitigate the occurrence of blackout that causes the signal level to be low in the main subject and the occurrence of whiteout that causes the signal level to be saturated, even in an over-ordered light state where the signal level is saturated. is there.
This is also the case in the over-forward lighting state where the background is dark and only the main subject is illuminated, and the frequency of the low-brightness portion hitting the background is reduced compared to the case of no weighting. It is possible to prevent the main subject portion from flying white by dragging.
[0038]
Embodiment 4 FIG.
FIG. 10 is a block diagram showing an image pickup apparatus according to Embodiment 4 of the present invention. In the figure, reference numeral 20 denotes a stop control means for controlling the stop mechanism in the lens system 11 and adjusting the amount of light incident on the solid-state image pickup device 12. Yes, and controlled by the imaging control means 17.
Reference numerals 4a to 4c denote a plurality of weighting coefficient setting tables in which different frequency weighting coefficients are set, and reference numeral 5 denotes table switching means for dynamically changing the plurality of weighting coefficient setting tables 4a to 4c. Reference numeral 21 denotes a viewpoint detection unit that detects the line of sight of a photographer looking into the viewfinder for subject confirmation and controls the table switching unit 5 in accordance with the detected line of sight. Other configurations are the same as those in FIG. 9 except that the AGC circuit 14, the D / A converter 18, and the timing generator 19 are not included.
FIG. 11 is an explanatory diagram showing a plurality of weighting factor setting tables in which different frequency weighting factors are set according to the viewpoint position.
[0039]
Next, the operation will be described.
The process up to converting the captured image into a digital video signal and inputting it to the frequency distribution measuring means 16 is the same as in the third embodiment, but has a plurality of weighting coefficient setting tables used for referring to the frequency weighting coefficient. Is different.
In the fourth embodiment, which one of the plurality of weighting factor setting tables 4a to 4c is used is determined by the table switching means 5. The table switching means 5 is controlled by the viewpoint detection means 21, and the weighting coefficient setting table used in the frequency distribution measurement means 16 is determined according to the direction of the sight line of the photographer.
FIG. 11 together with FIG. 7 shows a combination as an example of a plurality of weighting coefficient setting tables used in combination with the viewpoint detection means 21. When the line of sight is looking at the center of the screen, the weighting coefficient setting table shown in FIG. 7 is used. When the line of sight is looking at the left direction in the screen, the weighting coefficient setting table shown in FIG. When the inner right direction is watched, the weighting coefficient setting table of FIG. 11B is used.
[0040]
As described above, according to the fourth embodiment, the frequency weighting coefficient value is set to be large for the pixel in the direction in which the line of sight is gazing in the screen, so that the subject does not exist in the center portion. In addition, it is possible to configure an image pickup apparatus that performs brightness control using a portion to be photographed by the user as a main subject.
Further, the imaging control means 17 controls the aperture control means 20 so that the index brightness Lh matches the target brightness L0 by adjusting the aperture. In this configuration, when the index lightness Lh is larger than the target lightness L0, the diaphragm control means 20 closes the diaphragm more, and the amount of light incident on the solid-state image sensor 12 is reduced. When the target lightness L0 is larger than the index lightness Lh, the diaphragm control means 20 opens the diaphragm more, and the amount of light incident on the solid-state image sensor 12 is increased.
Of course, in a system capable of changing the accumulation time of the solid-state imaging device 12 and a system capable of changing the gain of the AGC circuit 14, the same brightness adjustment method as in the third embodiment is possible, or two methods are used in combination. Is also possible.
Furthermore, when the image is divided into blocks for each area and only the frequency weighting coefficient of each area is recorded as a weighting coefficient setting table, the frequency weighting coefficient of each pixel is prepared as a weighting coefficient setting table. In comparison, the data size to be prepared for the weighting factor setting table can be greatly reduced.
[0041]
Embodiment 5. FIG.
FIG. 12 is a block diagram showing an image pickup apparatus according to Embodiment 5 of the present invention. In the figure, reference numeral 22 denotes a logarithmic value that is referred to when the image control means 17 converts the index lightness Lh and the target lightness L0 into logarithmic values. It is a conversion table. Other configurations are the same as those in FIG.
FIG. 13 is an explanatory diagram illustrating a logarithmic value conversion table, and FIG. 14 is an explanatory diagram illustrating a table in which a subject illuminance logarithmic value, a gain setting value, and an accumulation time setting value are associated with each other.
[0042]
Next, the operation will be described.
The processing up to converting the captured image into a digital video signal and obtaining the weighted brightness frequency distribution by the frequency distribution measuring means 16 is the same as in the third embodiment, but after calculating the index brightness Lh, the target brightness L0 is calculated. The part that performs control to match is different.
In the fifth embodiment, when the gain and the accumulation time are doubled except for the saturation region, the index lightness Lh is also almost doubled, and the brightness adjustment parameters such as the gain and the accumulation time and the adjustment index value There is a feature that the linearity between them is maintained. Therefore, by calculating the index lightness Lh logarithmically and obtaining the difference from the logarithmized target lightness L0, high-speed stable and simple lightness correction processing can be performed.
Specifically, a logarithmic value conversion table 22 as shown in FIG. 13 is prepared, and logarithmic conversion values of the index lightness Lh and the target lightness L0 are obtained by referring to the table. The difference between the two logarithmic values represents the ratio of the index lightness Lh to the target lightness L0. Next, the table in FIG. 14 is referred to. The table of FIG. 14 associates the logarithm value of the subject illuminance with the set value of the accumulation time S and the set value of the gain G suitable for the subject illuminance. Also in this table, since the difference between the values in the left column represents the ratio of the subject illuminance, with respect to the setting value of the accumulation time S and the setting value of the gain G used for calculating the index lightness Lh, If the table is moved so that the value in the left column of FIG. 14 changes by the difference between the logarithm conversion values of the previously obtained index lightness Lh and target lightness L0, the index lightness Lh matches the target lightness L0. It is possible. At this time, the values in the left column of the table are configured to form an equality series in which the difference at each stage is constant so that the movement amount of the table can be easily obtained by calculation.
[0043]
In the above-described method, it is assumed that the change in the set value of the accumulation time S and the set value of the gain G and the change in the index lightness Lh correspond completely linearly. In many cases, strict linearity is not maintained due to variations in characteristics and variations in subject conditions. In this case, by introducing a time constant T (T <1), it is possible to perform control with more importance on stability.
Specifically, D × T is obtained for the difference D between the logarithmic transformation values of the index lightness Lh and the target lightness L0 obtained above, and the value in the left column of FIG. 14 changes by the amount of D × T. Move the table. The smaller the value of T, the more stable control is possible. Conversely, the larger the value of T, the faster the index lightness Lh can converge to the target lightness L0.
[0044]
As described above, according to the fifth embodiment, the index lightness Lh is logarithmically obtained, and the difference between the logarithmically obtained target lightness L0 is obtained, thereby performing high-speed stable and simple lightness correction processing. be able to.
[0045]
【The invention's effect】
  As described above, according to the present invention, the brightness of all pixels in the image data acquired by the image data acquisition process is calculated.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0A frequency distribution measuring step, and an imaging control step of adjusting the image data acquired by the image data acquiring step so that the index lightness in the lightness frequency distribution measured by the frequency distribution measuring step matches a preset target lightness; The brightness can be adjusted in consideration of the position of the main subject in the image. There is an effect that an image can be taken.
  In particular, according to the present invention, since the lightness including a negative number as the frequency weighting coefficient and the accumulated value becomes a negative value is configured such that the accumulated value is set to 0 degrees, the influence is excluded for the pixels in the specific region. The signal level is low in the main subject even in a backlit state where the light is illuminated from behind the subject, or in an over-ordered state where the signal level of the main subject is saturated due to strong light only on the subject. There is an effect that it is possible to mitigate the occurrence of blackouts that occur and conversely the occurrence of whiteout phenomenon in which the signal level is saturated.
[0046]
According to the present invention, in the frequency distribution measurement step, the frequency weighting coefficient corresponding to the pixel position is configured to refer to the frequency weighting coefficient from the preset weighting coefficient setting table, so that the weighting coefficient setting table is used. Therefore, it is possible to easily refer to the corresponding frequency weighting coefficient.
[0047]
According to the present invention, in the frequency distribution measurement step, the imaging screen is divided into blocks each composed of a plurality of pixels, and a weighting coefficient setting table in which the frequency weighting coefficient corresponding to each block is set in advance is used. As a result, the data size that must be prepared for the weighting factor setting table can be greatly reduced.
[0048]
According to the present invention, in the frequency distribution measurement step, a plurality of weighting factor setting tables in which different frequency weighting factors are set in advance are dynamically changed and used, so that the intention of the user is reflected. There is an effect that the brightness can be adjusted.
[0049]
According to this invention, in the imaging control process, the index brightness and the preset target brightness in the brightness frequency distribution measured by the frequency distribution measurement process are referred to from the logarithmic value conversion table in which the logarithmic value corresponding to the brightness is set. And since it comprised so that the image data acquired by an image data acquisition process might be adjusted according to the difference of these two logarithm values referred, there exists an effect which can perform brightness adjustment quickly and simply.
[0050]
  According to the present invention, in the imaging control process, the image data acquired by the image data acquisition process is adjusted using the product of the calculated logarithmic difference and the time constant. The effect of adjusting the brightnessThe
[0051]
  According to the present invention, the gain control means for amplifying the signal output from the solid-state imaging device so that the gain can be controlled, and the brightness of all pixels in the signal output from the gain control means is calculated.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0The charge accumulation time of the solid-state imaging device or the gain value of the gain control means is controlled so that the index brightness in the brightness frequency distribution measured by the frequency distribution measuring means and the brightness frequency distribution measured by the frequency distribution measuring means matches a preset target brightness. Since it is configured to include an imaging control unit, it is possible to perform brightness adjustment in consideration of the position of the main subject in the image, and it is difficult for whiteout and blackout of the image to occur even in backlight or over-order light. There is an effect that an image having a tonality can be taken.
  In particular, according to the present invention, the frequency distribution measuring means is configured to include a negative number as the frequency weighting coefficient, and the brightness when the cumulative value becomes a negative value is set to the cumulative value as 0 degree. The main subject part can be removed even in a backlit state where the light is illuminated from behind the subject, or in an over-ordered state where the signal level of the main subject is saturated due to strong light only on the subject. Thus, it is possible to alleviate the occurrence of blackout that causes the signal level to become low and the occurrence of whiteout phenomenon that the signal level is saturated.
[0052]
  According to this invention, the aperture control means for controlling the amount of light incident on the solid-state image sensor, and the brightness of all pixels in the image data output from the solid-state image sensor are calculated.In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is set as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The lightness frequency distribution is measured, and the lightness of which the cumulative value is negative is the cumulative value of 0The frequency distribution measuring means to perform and the imaging control means for controlling the aperture control means so that the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means coincides with the preset target lightness. In addition, it is possible to perform brightness adjustment in consideration of the position of the main subject in the image, and it is possible to capture an image with gradation, with less occurrence of whiteout and blackout of the image even in backlighting or excessively forward lighting. effective.
  In particular, according to the present invention, the frequency distribution measuring means is configured to include a negative number as the frequency weighting coefficient, and the brightness when the cumulative value becomes a negative value is set to the cumulative value as 0 degree. The main subject part can be removed even in a backlit state where the light is illuminated from behind the subject, or in an over-ordered state where the signal level of the main subject is saturated due to strong light only on the subject. Thus, it is possible to alleviate the occurrence of blackout that causes the signal level to become low and the occurrence of whiteout phenomenon that the signal level is saturated.
[0053]
According to the present invention, the frequency weighting coefficient corresponding to the position of the pixel is configured to have the weighting coefficient setting table set in advance, so that the corresponding frequency weighting coefficient can be easily referred to by using the weighting coefficient setting table. There is an effect that can be done.
[0054]
According to the present invention, in the weighting coefficient setting table, the imaging screen is divided into blocks each consisting of a plurality of pixels, and the frequency weighting coefficient corresponding to each block is set in advance. Therefore, there is an effect that the data size that must be prepared for the data can be greatly reduced.
[0055]
According to the present invention, a plurality of weighting factor setting tables in which different frequency weighting factors are set in advance, and a table switching means for dynamically changing a weighting factor setting table to be used among the plurality of weighting factor setting tables, Therefore, there is an effect that it is possible to perform brightness adjustment reflecting the user's intention.
[0056]
According to the present invention, a plurality of weighting coefficient setting tables in which different frequency weighting coefficients are set in advance according to the viewpoint position, the viewpoint detection means for detecting the photographer's viewpoint position, and the viewpoint detection means are detected. Since the table switching means for dynamically changing the weighting coefficient setting table to be used among a plurality of weighting coefficient setting tables according to the viewpoint position is provided, the portion to be photographed by the photographer is set as the main subject. There is an effect that the brightness can be adjusted.
[0057]
According to this invention, the logarithmic value conversion table in which the logarithmic value corresponding to the lightness is set is provided, and the imaging control means converts the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means to the logarithmic value conversion table. The logarithmic value of the preset target brightness is referred to from the logarithmic value conversion table, and the charge storage time of the solid-state image sensor or the gain value of the gain control means is determined according to the difference between the two logarithmic values referred to. Since it is configured to be controlled, there is an effect that the brightness adjustment can be performed quickly and simply.
[0058]
According to this invention, the logarithmic value conversion table in which the logarithmic value corresponding to the lightness is set is provided, and the imaging control means converts the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means to the logarithmic value conversion table. In addition, the logarithmic value of the preset target brightness is referred to from the logarithmic value conversion table, and the aperture control means is controlled in accordance with the difference between the two logarithmic values referred to. There is an effect that the brightness can be adjusted.
[0059]
According to the present invention, the imaging control means is configured to control the charge accumulation time of the solid-state imaging device or the gain value of the gain control means using the product of the calculated logarithmic difference and the time constant. There is an effect that the brightness can be adjusted quickly and simply.
[0060]
  According to this invention, since the imaging control means is configured to control the aperture control means using the product of the calculated logarithmic difference and the time constant, the brightness adjustment can be performed quickly and simply. EffectiveThe
[Brief description of the drawings]
FIG. 1 is a block diagram showing a brightness adjustment method according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory diagram showing a frequency weighting coefficient corresponding to a pixel position.
FIG. 3 is an explanatory diagram showing a lightness adjustment method from a lightness frequency distribution to which a frequency weighting coefficient is added.
FIG. 4 is an explanatory diagram showing a case where a negative number exists in a brightness frequency distribution to which a frequency weighting coefficient is added.
FIG. 5 is an explanatory diagram showing effects on black crushing and whiteout.
FIG. 6 is a block diagram showing a brightness adjustment method according to Embodiment 2 of the present invention.
FIG. 7 is an explanatory diagram showing a frequency weighting coefficient corresponding to each block composed of a plurality of pixels.
FIG. 8 is a block diagram showing another brightness adjustment method according to Embodiment 2 of the present invention.
FIG. 9 is a block diagram showing an imaging apparatus according to Embodiment 3 of the present invention.
FIG. 10 is a block diagram showing an imaging apparatus according to Embodiment 4 of the present invention.
FIG. 11 is an explanatory diagram showing a plurality of weighting factor setting tables in which different frequency weighting factors are set according to viewpoint positions.
FIG. 12 is a block diagram showing an imaging apparatus according to Embodiment 5 of the present invention.
FIG. 13 is an explanatory diagram showing a logarithmic value conversion table.
FIG. 14 is an explanatory diagram showing a table in which a subject illuminance logarithmic value, a gain setting value, and an accumulation time setting value are associated with each other.
FIG. 15 is a block diagram showing a conventional digital still camera.
FIG. 16 is a characteristic diagram showing a conventional brightness frequency distribution.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image data acquisition process, 2 Frequency distribution measurement process, 3 Imaging control process, 4, 4a-4c Weighting coefficient setting table, 5 Table switching means, 11 Lens system, 12 Solid-state image sensor, 13 Preamplifier, 14 AGC circuit (gain control) Means), 15 A / D converter, 16 frequency distribution measuring means, 17 imaging control means, 18 D / A converter, 19 timing generator, 20 aperture control means, 21 viewpoint detection means, 22 logarithmic value conversion table, 31 imaging means, 32 brightness analysis means, 33 exposure control means.

Claims (14)

An image data acquisition process for acquiring image data;
The brightness of all the pixels in the image data is calculated , and the frequency corresponding to the position of each pixel is set as the frequency of the pixel based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position. A frequency distribution measurement step of measuring the brightness frequency distribution by accumulating the frequencies of pixels having the same brightness, and the brightness having a negative cumulative value ;
Brightness adjustment comprising: an imaging control step of adjusting the image data acquired by the image data acquisition step so that the index brightness in the brightness frequency distribution measured by the frequency distribution measurement step matches a preset target brightness Method. The frequency distribution measurement step divides the imaging screen into blocks each composed of a plurality of pixels, and the frequency weighting coefficient corresponding to the position of the corresponding pixel from the weighting coefficient setting table in which the frequency weighting coefficient corresponding to each block is preset. The brightness adjustment method according to claim 1, wherein the frequency weighting coefficient is added to the corresponding accumulated frequency as the frequency of the pixel . Frequency distribution measuring step, the brightness adjustment method of claim 2 Symbol mounting, characterized in that it uses to dynamically change the plurality of weighting coefficient setting table different frequency weighting coefficients are set in advance to each other. The imaging control step refers to the index lightness and the preset target lightness in the lightness frequency distribution measured by the power distribution measurement step from the logarithmic value conversion table in which logarithmic values corresponding to the lightness are set, and 2 The brightness adjustment method according to any one of claims 1 to 3 , wherein the image data acquired by the image data acquisition step is adjusted according to a difference between two logarithmic values. The image data acquisition step captures a plurality of continuous images, and the imaging control step uses the product of the calculated logarithmic difference and a time constant to obtain image data acquired by the image data acquisition step. The brightness adjustment method according to claim 4 , wherein the brightness is adjusted. A solid-state image sensor that photoelectrically converts an incident light image and outputs image data of an electrical signal, gain control means that amplifies image data output from the solid-state image sensor in a gain-controllable manner, and all of the image data While calculating the brightness of a pixel, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is used as the frequency of the pixel, and pixels of equal brightness The lightness frequency distribution is measured by accumulating the frequency, and the lightness whose cumulative value is negative is a frequency distribution measuring unit in which the cumulative value is 0 frequency, and the lightness frequency distribution measured by the frequency distribution measuring unit. Imaging control for controlling at least one of the charge accumulation time of the solid-state imaging device and the gain value of the gain control means so that the index brightness matches a preset target brightness An image pickup apparatus having a stage. Calculated and the solid-state image sensor for outputting image data of an electrical signal an optical image incident through photoelectric conversion, a diaphragm control means for controlling the amount of light entering the solid-state imaging device, the brightness of all pixels in the image data In addition, based on a negative or positive frequency weighting coefficient corresponding to a preset pixel position, the frequency corresponding to the position of each pixel is used as the frequency of the pixel, and the frequency of pixels having the same brightness is accumulated. The brightness of which the frequency distribution is measured and the accumulated value is negative is set in advance as a frequency distribution measuring means in which the accumulated value is 0 degrees, and an index brightness in the brightness frequency distribution measured by the frequency distribution measuring means is preset. An image pickup apparatus comprising image pickup control means for controlling the aperture control means so as to coincide with the target brightness. The imaging screen is divided into blocks each composed of a plurality of pixels, and a weighting coefficient setting table in which a frequency weighting coefficient corresponding to each block is set in advance is provided, and the frequency distribution measuring unit includes the corresponding pixels from the weighting coefficient setting table. with reference to frequency weighting factor corresponding to the position, the frequency weighting coefficient corresponding accumulated imaging device according to claim 6 or claim 7, wherein adding the frequency as the frequency of the pixel. A plurality of weighting factor setting tables in which different frequency weighting factors are set in advance, and table switching means for dynamically changing a weighting factor setting table to be used among the plurality of weighting factor setting tables. The imaging apparatus according to claim 8, characterized in that: A plurality of weighting factor setting tables in which different frequency weighting factors are set in advance according to the viewpoint position, viewpoint detection means for detecting the photographer's viewpoint position, and according to the viewpoint position detected by the viewpoint detection means. 9. The imaging apparatus according to claim 8, further comprising table switching means for dynamically changing a weighting coefficient setting table to be used among the plurality of weighting coefficient setting tables. A logarithmic value conversion table in which a logarithmic value corresponding to the lightness is set, the imaging control means refers to the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means from the logarithmic value conversion table, The logarithmic value of the preset target brightness is referred to from the logarithmic value conversion table, and at least one of the charge accumulation time of the solid-state imaging device and the gain value of the gain control means according to the difference between the two logarithmic values referred to. claim 6, characterized in that control whether the imaging apparatus according to any one of claims 10 claim 8. A logarithmic value conversion table in which a logarithmic value corresponding to the lightness is set, the imaging control means refers to the logarithmic value of the index lightness in the lightness frequency distribution measured by the frequency distribution measuring means from the logarithmic value conversion table, the logarithm of a preset target brightness reference from the logarithm conversion table, claim 7, characterized in that to control the diaphragm control means in accordance with the difference of the two logarithmic values and their references of claim 10 The imaging device of any one of them. The imaging apparatus is an imaging apparatus that captures a plurality of consecutive images, and the imaging control means controls the charge accumulation time and gain of the solid-state imaging device using a product of the calculated logarithmic difference and a time constant. 12. The imaging apparatus according to claim 11 , wherein at least one of the gain values of the means is controlled. The imaging apparatus is an imaging apparatus that captures a plurality of continuous images, and the imaging control means controls the aperture control means by using a product of a calculated logarithmic difference and a time constant. The imaging device according to claim 12 .

Images