JP2004180165A

JP2004180165A - Method and device for exposure control

Info

Publication number: JP2004180165A
Application number: JP2002346341A
Authority: JP
Inventors: Pascal Goge; パスカルゴゲ; Yuzo Kawahara; 雄三川原
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 2002-11-28
Filing date: 2002-11-28
Publication date: 2004-06-24

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for exposure control, which can reduce the processing loads. <P>SOLUTION: The method and device comprise a histogram creating means 2 for creating a histogram of the values of each pixel of an imaging device C, which is equipped with an image sensor having a plurality of pixels and can adjust exposure; a histogram edge removing means 3 for removing parts of the histogram; a centroid calculation means 4 for calculating the centroid of the histogram; a comparison means 5 for calculating the direction and the size of the shifting of the histogram's centroid from a predetermined reference range; and an exposure control means 6 for controlling the exposure so that the centroid falls within the reference range, based on the direction and size calculation. Since the frequencies of the operations required for calculating the centroid can be made fewer than those required for calculating the average value of pixel output for one screen, processing loads can be reduced, as compared with the case where the average value of pixel output for one screen is used for control. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御方法及び露出制御装置に関するものである。
【０００２】
【従来の技術】
従来から、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御方法として、画素が出力する輝度信号（以下、単に「画素の出力」と呼ぶ）の一画面分の平均が基準値に近付くように露出を制御する露出制御方法が提案されている（例えば、特許文献１及び特許文献２参照）。
【０００３】
一画面の画素の出力の平均Ｉａｖｅｒａｇｅは、例えば演算装置を用いて下式１で算出していた。
【０００４】
【数１】

【０００５】
ただし、図４に示すように、Ｋｍａｘは撮像素子の縦に並んだ画素数、Ｍｍａｘは撮像素子の横に並んだ画素数、Ｉ（ｋ，ｍ）は上からｋ番目、左からｍ番目の画素Ｐの出力である。つまり、画素の出力を加算し、画素数Ｋｍａｘ×Ｍｍａｘで割ることによって一画面の画素の出力の平均Ｉａｖｅｒａｇｅを算出している。なお、例えばカメラ付ドアホンで一般的に使用されている撮像装置（ＣＣＤカメラ）の撮像素子（ＣＣＤ素子）では、Ｋｍａｘ＝２４０、Ｍｍａｘ＝３２０である。
【０００６】
【特許文献１】
特開平５−２０７３６１号公報（第４頁）
【特許文献２】
特開平６−４６３２５号公報（第６頁）
【０００７】
【発明が解決しようとする課題】
しかし、上記従来の露出制御方法においては、一画面の画素の出力の平均を算出するために、画素数と同じ回数の演算を行う必要がある。上で例に挙げた撮像装置の場合、加算が（２４０×３２０−１）回と除算が１回とで、合計７６８００回もの演算が必要となる。従って、演算装置に大きな負荷がかかり、露出の制御が遅くなって画像の変化への追従性が悪くなっていた。
【０００８】
本発明は上記事由に鑑みてなされたものであり、その目的は、処理負荷を軽減することができる露出制御方法及び露出制御装置を提供することにある。
【０００９】
【課題を解決するための手段】
請求項１の発明は、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御方法であって、撮像素子の画素値のヒストグラムを作成し、前記ヒストグラムの重心を算出し、予め設定された基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとに基づいて前記ヒストグラムの重心が前記基準範囲内に入るように露出を制御することを特徴とする。
【００１０】
請求項２の発明は、請求項１記載の発明において、前記ヒストグラムの重心を算出する前に、画素値の撮像装置において決まる最大値から一定幅の範囲と、画素値が０から一定幅の範囲との少なくとも一方を前記ヒストグラムから除去することを特徴とする。
【００１１】
請求項３の発明は、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御装置であって、撮像素子の画素値のヒストグラムを作成するヒストグラム作成手段と、前記ヒストグラムの重心を算出する重心算出手段と、予め設定された基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとを算出する比較手段と、前記基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとに基づいて前記ヒストグラムの重心が前記基準範囲内に入るように露出を制御する露出制御手段とを備えることを特徴とする。
【００１２】
請求項４の発明は、請求項３記載の発明において、画素値の撮像装置において決まる最大値から一定幅の範囲と画素値が０から一定幅の範囲との少なくとも一方を前記ヒストグラムから除去するヒストグラム端除去手段を備え、前記重心算出手段は前記ヒストグラム端除去手段が出力した前記ヒストグラムの重心を算出することを特徴とする。
【００１３】
【発明の実施の形態】
以下、本発明の実施の形態を図面に基づいて説明する。
【００１４】
本実施形態は、図１に示すように、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置Ｃ（例えばＣＣＤカメラ）の露出を制御するものであって、撮像装置Ｃの各画素の出力をＡ／Ｄ変換するＡ／Ｄ変換手段１と、Ａ／Ｄ変換手段１の出力に基づいてヒストグラムを作成するヒストグラム作成手段２と、ヒストグラムの一部を除去するヒストグラム端除去手段３と、ヒストグラムの重心を算出する重心算出手段４と、予め設定された基準範囲に対するヒストグラムの重心のずれの向きと大きさとを算出する比較手段５と、基準範囲に対するヒストグラムの重心のずれの向きと大きさとに基づいてヒストグラムの重心が基準値に近付くように露出を制御する露出制御手段６とを備える。ヒストグラム作成手段２と、ヒストグラム端除去手段３と、重心算出手段４と、比較手段５と、露出制御手段６とはそれぞれマイコンのような演算装置によって実現される。
【００１５】
詳しく説明すると、Ａ／Ｄ変換部１は各画素の出力をＡ／Ｄ変換して画素値を生成する。画素値は、０から撮像装置Ｃにおいて決まる画素の出力の最大値までに対応する離散値であって、例えば０〜２５５の整数値をとる。ヒストグラム作成手段２は、図２（ａ）に示すように画素値に対する画素数を示すヒストグラムを作成する。
【００１６】
ヒストグラム端除去手段３には、予め第１の閾値Ｌと、第１の閾値Ｌよりも大きな第２の閾値Ｈとが設定されており、図２（ｂ）に示すように画素値が０から第１の閾値Ｌまでの範囲と、第２の閾値Ｈから画素値の最大値（例えば２５５）までの範囲とをヒストグラムから除去する。ここで、第１の閾値Ｌと第２の閾値Ｈとは、被写体に対応する可能性の高い画素値の範囲が除去されずに残るように、撮像装置Ｃの設置場所の状況等に合わせて設定される。
【００１７】
なお、第１の閾値Ｌと第２の閾値Ｈとを予め設定する代わりに、撮影毎に又は定期的に、除去する範囲を自動的に設定する構成としてもよい。例えば、最も画素値が低い位置にあるピークよりも画素値が高い位置にある谷の位置を第１の閾値Ｌとし、最も画素値が高い位置にあるピークよりも画素値が低い位置にある谷の位置を第２の閾値Ｈとする。
【００１８】
重心算出手段４は、ヒストグラム端除去手段３が出力したヒストグラムの重心Ｉ_０（図２（ｃ）参照）を、下式２によって算出する。
【００１９】
【数２】

【００２０】
ここで、Ｎ（ｉ）は画素値ｉをとる画素の数である。
【００２１】
比較手段５は、図２（ｄ）に示すように、予め下限値Ａ１と上限値Ａ２とが設定された基準範囲に対する重心Ｉ_０のずれの向きと大きさとを算出する。例えば重心Ｉ_０が基準範囲の下限値Ａ１よりも低かった場合、下限値Ａ１と重心Ｉ_０との差Ｗを算出する。
【００２２】
露出制御手段６は、重心Ｉ_０が基準範囲内に入るように撮像装置Ｃの絞り量やシャッタースピードを制御することによって露出を制御する。
【００２３】
発明者が行った実験において、図３（ａ）に示すヒストグラムの両端部を除去して画素数の最大値を１とするように規格化して整形した図３（ｂ）に示すヒストグラムの重心Ｉ_０に基づいて制御を行った結果、図３（ｃ）に示すヒストグラムが得られ、露出の適正化が確認された。
【００２４】
上記構成によれば、結局、重心算出手段４としての演算装置が重心の算出のために行う演算は、式２の分子に対して画素値に設定した数程度の乗算と、式２の分子と分母とに対してそれぞれ画素値に設定した数程度の加算と、１回の除算とであるので、必要な演算の回数は合計で画素値に設定した数の高々３倍程度となる。また、発明者が行った実験の結果、画素値には０〜２５５の２５６段階程度を設定すれば、一画面の画素の出力を平均する従来の方法と同等の露出制御効果が得られることが分かっている。つまり、例えばテレビ付ドアホンで用いられる撮像装置に搭載される撮像素子のようにおよそ１０万〜３０万の画素を有する撮像素子の場合、一画面の画素の出力を平均する従来の方法ではおよそ１０万回〜３０万回もの演算を行う必要があるのに対し、本発明に用いられる演算装置が重心算出手段４として行う演算は合計で１０００回にも満たないことになる。また、ヒストグラム作成は安価な演算装置でも行うことのできる程度の軽い処理であるから、総合的には処理負荷が軽減される。
【００２５】
従って、演算装置への負担が減少することにより露出の制御が高速化し、画像の明るさの変化への追従性が向上するから、マンションなどの集合住宅の玄関に設置されるカメラや、テレビ付きドアホンのカメラや、監視カメラなど、画像の明るさが変化しやすい環境に設置される撮像装置に好適である。または、従来と同等の追従性を維持しながらも従来用いられた演算装置よりも安価な低速の演算装置を用いてコストを下げることができる。また、処理負荷が軽減されることにより、必要なメモリが少なくなる。
【００２６】
また、ヒストグラム端除去手段３が設けられているから、画面内に極端に明るい領域が存在するときに被写体が黒つぶれする現象や、画面内に極端に暗い領域が存在するときに被写体が白とびする現象などが防止され、より適切な露出制御が可能となる。その上、ヒストグラム端除去手段３を設けない場合に比べ、ヒストグラムの幅が狭くなることにより、ヒストグラムの重心を算出するための演算の回数が減るから、さらに処理負荷が軽減される。
【００２７】
【発明の効果】
請求項１の発明は、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御方法であって、撮像素子の画素値のヒストグラムを作成し、前記ヒストグラムの重心を算出し、予め設定された基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとに基づいて前記ヒストグラムの重心が前記基準範囲内に入るように露出を制御するので、ヒストグラムの重心の算出に必要な演算の回数は一画面の画素の出力の平均値の算出に必要な演算の回数よりも少なくすることができ、かつヒストグラム作成は安価な演算装置でも行うことのできる程度の軽い処理であるから、一画面の画素の出力の平均値を制御に用いる場合に比べ、総合的な処理負荷を軽減することができる。
【００２８】
請求項２の発明は、請求項１記載の発明において、前記ヒストグラムの重心を算出する前に、画素値の撮像装置において決まる最大値から一定幅の範囲と、画素値が０から一定幅の範囲との少なくとも一方を前記ヒストグラムから除去するので、画面内に極端に明るい領域が存在するときに被写体が黒つぶれする現象や、画面内に極端に暗い領域が存在するときに被写体が白とびする現象などが防止され、より適切な露出制御が可能となる。その上、ヒストグラムの幅が狭くなることにより、ヒストグラムの重心を算出するための演算の回数が減るから、さらに処理負荷が軽減される。
【００２９】
請求項３の発明は、複数の画素を有する撮像素子を備え露出の調整が可能な撮像装置の露出を制御する露出制御装置であって、撮像素子の画素値のヒストグラムを作成するヒストグラム作成手段と、前記ヒストグラムの重心を算出する重心算出手段と、予め設定された基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとを算出する比較手段と、前記基準範囲に対する前記ヒストグラムの重心のずれの向きと大きさとに基づいて前記ヒストグラムの重心が前記基準範囲内に入るように露出を制御する露出制御手段とを備えるので、ヒストグラムの重心の算出に必要な演算の回数は一画面の画素の出力の平均値の算出に必要な演算の回数よりも少なくすることができ、かつヒストグラム作成は安価な演算装置でも行うことのできる程度の軽い処理であるから、一画面の画素の出力の平均値を制御に用いる場合に比べ、総合的な処理負荷を軽減することができる。
【００３０】
請求項４の発明は、請求項３記載の発明において、画素値の撮像装置において決まる最大値から一定幅の範囲と画素値が０から一定幅の範囲との少なくとも一方を前記ヒストグラムから除去するヒストグラム端除去手段を備え、前記重心算出手段は前記ヒストグラム端除去手段が出力した前記ヒストグラムの重心を算出するので、画面内に極端に明るい領域が存在するときに被写体が黒つぶれする現象や、画面内に極端に暗い領域が存在するときに被写体が白とびする現象などが防止され、より適切な露出制御が可能となる。その上、ヒストグラムの幅が狭くなることにより、ヒストグラムの重心を算出するための演算の回数が減るから、さらに処理負荷が軽減される。
【図面の簡単な説明】
【図１】本発明の実施形態を示すブロック図である。
【図２】同上を示す動作説明図である。
【図３】同上の実験結果を示す説明図である。
【図４】従来例において画素の出力の平均を求める方法を示す説明図である。
【符号の説明】
２ヒストグラム作成手段
３ヒストグラム端除去手段
４重心算出手段
５比較手段
６露出制御手段
Ｃ撮像装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure control method and an exposure control apparatus for controlling an exposure of an imaging device having an imaging element having a plurality of pixels and capable of adjusting the exposure.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an exposure control method for controlling exposure of an imaging device including an imaging element having a plurality of pixels and capable of adjusting exposure, one of luminance signals (hereinafter, simply referred to as “pixel output”) output from pixels is used as an exposure control method. An exposure control method has been proposed in which exposure is controlled so that the average of screens approaches a reference value (for example, see Patent Documents 1 and 2).
[0003]
The average Iaverage of the output of the pixels on one screen was calculated by the following equation 1 using, for example, an arithmetic unit.
[0004]
(Equation 1)

[0005]
However, as shown in FIG. 4, Kmax is the number of pixels arranged vertically in the image sensor, Mmax is the number of pixels arranged horizontally in the image sensor, and I (k, m) is the k-th pixel from the top and the m-th pixel from the left. This is the output of the pixel P. That is, the average Iaverage of the outputs of the pixels of one screen is calculated by adding the outputs of the pixels and dividing the sum by the number of pixels Kmax × Mmax. For example, in an image pickup device (CCD device) of an image pickup device (CCD camera) generally used in a door phone with a camera, Kmax = 240 and Mmax = 320.
[0006]
[Patent Document 1]
JP-A-5-207361 (page 4)
[Patent Document 2]
JP-A-6-46325 (page 6)
[0007]
[Problems to be solved by the invention]
However, in the above-described conventional exposure control method, it is necessary to perform the same number of calculations as the number of pixels in order to calculate the average of the output of the pixels on one screen. In the case of the image pickup apparatus described above, addition (240 × 320-1) and division are performed once, and a total of 76800 operations are required. Therefore, a heavy load is applied to the arithmetic unit, and the control of the exposure is delayed, so that the ability to follow the change of the image is deteriorated.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exposure control method and an exposure control device capable of reducing a processing load.
[0009]
[Means for Solving the Problems]
The invention according to claim 1 is an exposure control method for controlling the exposure of an image pickup apparatus including an image pickup device having a plurality of pixels and capable of adjusting the exposure, wherein a histogram of pixel values of the image pickup device is created, A center of gravity is calculated, and exposure is controlled based on a direction and a magnitude of a shift of the center of gravity of the histogram with respect to a preset reference range so that the center of gravity of the histogram falls within the reference range.
[0010]
According to a second aspect of the present invention, in the first aspect of the present invention, before calculating the center of gravity of the histogram, the pixel value ranges from a maximum value determined by the imaging device to a fixed width, and the pixel value ranges from 0 to a fixed width. At least one of the above is removed from the histogram.
[0011]
The invention according to claim 3 is an exposure control device that controls the exposure of an imaging device that includes an imaging device having a plurality of pixels and that can adjust the exposure, wherein a histogram creating unit that creates a histogram of pixel values of the imaging device. A center of gravity calculating means for calculating the center of gravity of the histogram; a comparing means for calculating the direction and magnitude of the shift of the center of gravity of the histogram with respect to a preset reference range; and the direction of the shift of the center of gravity of the histogram with respect to the reference range. And exposure control means for controlling exposure such that the center of gravity of the histogram falls within the reference range based on the size and the size.
[0012]
According to a fourth aspect of the present invention, in the third aspect of the present invention, at least one of a range of a fixed width from a maximum value determined in the imaging device for pixel values and a range of a pixel value of 0 to a fixed width is removed from the histogram. The image processing apparatus further comprises edge removing means, wherein the center of gravity calculating means calculates a center of gravity of the histogram output by the histogram edge removing means.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0014]
The present embodiment, as shown in FIG. 1, controls the exposure of an imaging device C (for example, a CCD camera) having an imaging device having a plurality of pixels and capable of adjusting the exposure. A / D conversion means 1 for A / D converting the output of a pixel, histogram creation means 2 for creating a histogram based on the output of A / D conversion means 1, and histogram edge removal means 3 for removing a part of the histogram A center of gravity calculating means 4 for calculating the center of gravity of the histogram; a comparing means 5 for calculating the direction and magnitude of the shift of the center of gravity of the histogram with respect to a preset reference range; An exposure control means for controlling the exposure so that the center of gravity of the histogram approaches the reference value based on the size. The histogram creating means 2, the histogram edge removing means 3, the center-of-gravity calculating means 4, the comparing means 5, and the exposure controlling means 6 are each realized by an arithmetic device such as a microcomputer.
[0015]
More specifically, the A / D converter 1 performs A / D conversion on the output of each pixel to generate a pixel value. The pixel value is a discrete value corresponding to a range from 0 to the maximum value of the pixel output determined in the imaging device C, and takes an integer value of, for example, 0 to 255. The histogram creating means 2 creates a histogram indicating the number of pixels with respect to the pixel value as shown in FIG.
[0016]
A first threshold value L and a second threshold value H that is larger than the first threshold value L are set in the histogram edge removing unit 3 in advance, and as shown in FIG. The range from the first threshold L and the range from the second threshold H to the maximum pixel value (for example, 255) are removed from the histogram. Here, the first threshold value L and the second threshold value H are adjusted according to the situation of the installation location of the imaging device C and the like so that a range of pixel values likely to correspond to the subject remains without being removed. Is set.
[0017]
Instead of setting the first threshold value L and the second threshold value H in advance, the configuration may be such that the range to be removed is automatically set for each photographing or periodically. For example, the position of the valley where the pixel value is higher than the peak where the pixel value is the lowest is set as the first threshold L, and the valley where the pixel value is lower than the peak where the pixel value is the highest. Is the second threshold value H.
[0018]
The center-of-gravity calculating means 4 calculates the center of gravity I ₀ (see FIG. 2C) of the histogram output from the histogram edge removing means 3 by the following equation 2.
[0019]
(Equation 2)

[0020]
Here, N (i) is the number of pixels having the pixel value i.
[0021]
Comparison means 5, as shown in FIG. 2 (d), to calculate the direction and magnitude of the deviation of the center of gravity I ₀ with respect to a reference range and advance a lower limit value A1 and the upper limit value A2 is set. For example, when the center of gravity I ₀ is lower than the lower limit value A1 of the reference range, it calculates a difference W between the lower limit value A1 and the center of gravity I _0.
[0022]
Exposure control means 6 controls the exposure by controlling the aperture amount and a shutter speed of the imaging device C as the center of gravity I ₀ falls within the reference range.
[0023]
In an experiment conducted by the inventor, the center of gravity I of the histogram shown in FIG. 3B, which was shaped by removing both ends of the histogram shown in FIG. 3A and normalizing the maximum number of pixels to be 1, was formed. As a result of performing control based on ₀ , a histogram shown in FIG. 3C was obtained, and it was confirmed that exposure was optimized.
[0024]
According to the configuration described above, the calculation performed by the arithmetic device as the center of gravity calculation means 4 for calculating the center of gravity is multiplied by the number of pixels set to the numerator of Equation 2 and the numerator of Equation 2 Since the number of additions to the denominator is about the number set for the pixel value, and one division is performed, the number of necessary operations is at most about three times the number set for the pixel value in total. Further, as a result of an experiment conducted by the inventor, if the pixel value is set to about 256 levels from 0 to 255, an exposure control effect equivalent to the conventional method of averaging the output of the pixels of one screen can be obtained. I know it. That is, for example, in the case of an image pickup device having about 100,000 to 300,000 pixels such as an image pickup device mounted on an image pickup device used in a door phone with a television, the conventional method of averaging the output of the pixels of one screen is about 10 While it is necessary to perform the operation as many as 10,000 to 300,000 times, the operation performed by the arithmetic device used in the present invention as the center of gravity calculation means 4 is less than 1000 in total. In addition, since the histogram creation is a light process that can be performed by an inexpensive arithmetic device, the processing load is reduced overall.
[0025]
Accordingly, exposure control is speeded up by reducing the burden on the arithmetic unit, and the ability to follow changes in the brightness of images is improved. It is suitable for an imaging device installed in an environment where the brightness of an image is easily changed, such as a door phone camera or a surveillance camera. Alternatively, the cost can be reduced by using a low-speed arithmetic device that is less expensive than a conventionally used arithmetic device while maintaining the same tracking performance as the conventional one. In addition, as the processing load is reduced, the required memory is reduced.
[0026]
Further, since the histogram edge removing means 3 is provided, the phenomenon in which the subject is lost in the image when an extremely bright area exists in the screen, or the phenomenon in which the subject is overexposed when the extremely dark area exists in the screen. Is prevented, and more appropriate exposure control becomes possible. In addition, as compared with the case where the histogram edge removing means 3 is not provided, the width of the histogram is narrowed, so that the number of calculations for calculating the center of gravity of the histogram is reduced, so that the processing load is further reduced.
[0027]
【The invention's effect】
The invention according to claim 1 is an exposure control method for controlling the exposure of an image pickup apparatus including an image pickup device having a plurality of pixels and capable of adjusting the exposure, wherein a histogram of pixel values of the image pickup device is created, The center of gravity is calculated, and the exposure is controlled based on the direction and magnitude of the shift of the center of gravity of the histogram with respect to a preset reference range, so that the exposure is controlled so that the center of gravity of the histogram falls within the reference range. The number of operations required for the calculation can be made smaller than the number of operations required for calculating the average value of the output of the pixels of one screen, and the histogram creation is a light process that can be performed by an inexpensive arithmetic device. Therefore, the overall processing load can be reduced as compared with the case where the average value of the output of the pixels of one screen is used for control.
[0028]
According to a second aspect of the present invention, in the first aspect of the present invention, before calculating the center of gravity of the histogram, the pixel value ranges from a maximum value determined by the imaging device to a fixed width, and the pixel value ranges from 0 to a fixed width. Is removed from the histogram, so that the subject will be overexposed when an extremely bright area exists in the screen, or the subject will be overexposed when an extremely dark area exists on the screen. Is prevented, and more appropriate exposure control can be performed. In addition, since the width of the histogram is reduced, the number of operations for calculating the center of gravity of the histogram is reduced, and the processing load is further reduced.
[0029]
The invention according to claim 3 is an exposure control device that controls the exposure of an imaging device that includes an imaging device having a plurality of pixels and that can adjust the exposure, wherein a histogram creating unit that creates a histogram of pixel values of the imaging device. A center of gravity calculating means for calculating the center of gravity of the histogram; a comparing means for calculating the direction and magnitude of the shift of the center of gravity of the histogram with respect to a preset reference range; and the direction of the shift of the center of gravity of the histogram with respect to the reference range. And exposure control means for controlling the exposure so that the center of gravity of the histogram falls within the reference range based on the size of the histogram and the size of the histogram. The number of calculations required for calculating the average value can be reduced, and the creation of the histogram can be performed by an inexpensive calculation device. Since degrees of a lighter treatment, compared with the case of using the control average value of the output of one screen of pixel, it is possible to reduce the overall processing load.
[0030]
According to a fourth aspect of the present invention, in the third aspect of the present invention, at least one of a range from a maximum value determined by the imaging device for pixel values to a certain width and a range from 0 to a fixed width from the pixel value is removed from the histogram. Edge removing means, and the center of gravity calculating means calculates the center of gravity of the histogram output by the histogram edge removing means.Therefore, when an extremely bright area exists in the screen, the subject may be overexposed or black. When an extremely dark area exists, the phenomenon in which the subject is overexposed is prevented, and more appropriate exposure control can be performed. In addition, when the width of the histogram is reduced, the number of operations for calculating the center of gravity of the histogram is reduced, so that the processing load is further reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is an operation explanatory view showing the above.
FIG. 3 is an explanatory diagram showing the results of the above experiment.
FIG. 4 is an explanatory diagram showing a method for obtaining an average of pixel outputs in a conventional example.
[Explanation of symbols]
2 Histogram creation means 3 Histogram edge removal means 4 Center of gravity calculation means 5 Comparison means 6 Exposure control means C Imaging device

Claims

An exposure control method for controlling an exposure of an image pickup apparatus including an image pickup device having a plurality of pixels and capable of adjusting the exposure, wherein a histogram of pixel values of the image pickup device is created, a center of gravity of the histogram is calculated, and the histogram is set in advance. An exposure control method for controlling exposure such that the center of gravity of the histogram falls within the reference range based on the direction and magnitude of the shift of the center of gravity of the histogram with respect to the reference range.

Before calculating the center of gravity of the histogram, at least one of a range of a fixed width from a maximum value determined by an imaging device of a pixel value and a range of a fixed width from 0 to a pixel value is removed from the histogram. The exposure control method according to claim 1.

What is claimed is: 1. An exposure control apparatus for controlling exposure of an image pickup apparatus having an image pickup element having a plurality of pixels and capable of adjusting exposure, comprising: a histogram creating means for creating a histogram of pixel values of the image pickup element; and calculating a center of gravity of the histogram. A calculating means for calculating a direction and a magnitude of a shift of the center of gravity of the histogram with respect to a predetermined reference range; and Exposure control means for controlling exposure so that the center of gravity of the histogram falls within the reference range.

A histogram edge removing unit that removes at least one of a range of a fixed width from a maximum value determined in the imaging device for pixel values and a range of a pixel value of 0 to a constant width from the histogram; 4. The exposure control device according to claim 3, wherein a center of gravity of the histogram output by the means is calculated.