JP4392384B2 - Automatic exposure control device - Google Patents

Description

  The present invention relates to an automatic exposure control device for optical equipment such as a digital video camera and a digital still camera.

  Conventionally, methods such as average photometry, center-weighted photometry, spot photometry, and multi-pattern photometry are known as automatic exposure determination methods for exposure control devices. In either case, a plurality of evaluation areas are set in advance in the area of the captured image, and the exposure is determined using the average luminance information of each evaluation area. FIG. 1 shows an example of the conventional automatic exposure determination method. In this example, the evaluation area of a captured image is divided into 10 × 10 100 small areas. A plurality of evaluation areas are set for the entire photographed image and the like, and the minimum unit is referred to as a small area here. An evaluation area formed by combining a plurality of small areas is referred to as a middle area. Areas 1 to 6 surrounded by a thick line in FIG.

  For example, in center-weighted metering, exposure control is performed using metering data from the middle area of area 3 and area 4. In center-weighted metering, exposure control is generally performed by weighting the area 3 existing in the center of the two areas 3 and 4 with weight.

  In spot photometry, exposure control is performed using photometric data from an area that is the same as or narrower than the area 3 existing in the center.

  By the way, it is desirable to place the middle region at the center of the image area under shooting conditions with a small luminance difference, but under shooting conditions with a large luminance difference, a correction process called high luminance processing is required. Become.

  For example, as shown in FIG. 2, when photographing a landscape such as a sky at the top and a mountain or the ground at the bottom, the sky with much higher brightness than the brightness of the mountain or ground at the bottom is almost from the center of the screen. The shooting condition is located above. In such a case, since the high-luminance sky is located at the center of the screen, when center-weighted metering or spot metering is performed, the brightness of the sky greatly affects, resulting in a dark image as a whole.

  In automatic exposure control, exposure control such as shutter time and aperture is performed so that the average brightness at the time of shooting is approximately at the center of the shooting brightness range, so some correction is necessary to obtain a bright image suitable for mountains and the ground. Necessary.

  Here, a correction method has been proposed in which a small area having high luminance equal to or higher than a certain threshold (referred to as a high luminance limit threshold) is replaced with a high luminance limit value. Such a correction method is called high luminance processing.

  For example, in the technique disclosed in Japanese Patent Laid-Open No. 5-122600, which is similar to the present invention, a luminance signal having a preset clip level or higher is converted into a luminance signal having a clip level as an upper limit threshold (high luminance limit threshold). ing. Two types of clip levels are set in advance, and are selected based on photometric information.

  Further, according to the technique disclosed in Japanese Patent Laid-Open No. 7-298131 similar to the present invention, a high luminance signal exceeding a preset high luminance removal threshold is removed from the luminance signal (data), and the high luminance signal is removed. Exposure control is performed based on the remaining luminance signal.

  However, this type of conventional exposure control device still has the following problems.

 For example, the brightness histogram obtained when the upper part is empty, the lower part is a mountain, and the ground is as shown in FIG. Here, the horizontal axis is a partition number that is partitioned, for example, by 1 eV from the lower luminance to the higher luminance. The vertical axis represents the number of small areas having luminance existing in the section. The section number “4” corresponding to the sensitivity center of the CCD is the distribution center of the luminance histogram.

  In FIG. 3, the high luminance part (sky) is almost located at the center of the luminance histogram distribution. When this is removed or clipped by high luminance processing, the luminance histogram shown in FIG. 4 is obtained. In FIG. 4, the low luminance part (mountain or ground) is located almost at the center of the distribution of the luminance histogram. On the contrary, when the upper part is a forest, a mountain or the like and the lower part is a field, the distribution of the luminance histogram as shown in FIG. 5 is obtained.

  In FIG. 5, the high luminance part (field) is located almost at the center of the distribution of the luminance histogram. When this is corrected by adjusting the exposure to the low luminance part by high luminance processing, as shown in FIG. 6, the low luminance part (forest, mountain, etc.) becomes the center of the distribution of the luminance histogram, and the field is so bright. It becomes an image of whiteout.

Therefore, an automatic exposure control device that can select a high-intensity removal process that is optimal for removing the influence of a high-intensity captured image portion by obtaining a high-frequency section using a luminance histogram according to the situation. It has been proposed (see Patent Document 1).
JP 2002-372733 A

  However, the one disclosed in Japanese Patent Application Laid-Open No. 2002-372733 is able to select an optimum high-intensity removal process depending on the situation in order to remove the influence of a high-intensity photographed image portion. Although it has been possible to approach the luminance removal process one step, there are still aspects that are not sufficient from the viewpoint of obtaining appropriate automatic exposure.

  The present invention has been made in view of such a situation, and a captured image is divided into a plurality of rough middle areas each composed of a set of a plurality of small areas, and the middle area is determined according to the position of the middle area. By changing the threshold for determining whether or not the brightness of the small area is high brightness, and adopting a configuration that performs high brightness processing for each small area, to perform fine high brightness processing Therefore, it is an object of the present invention to provide an automatic exposure control device that can further contribute to obtaining a proper automatic exposure.

The invention according to claim 1 is a luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
The high luminance removal threshold as a reference value for determining that the luminance of the small area extracted by the high luminance area extracting means should be high luminance and the luminance of the small area extracted by the high luminance area extracting means are used for exposure evaluation. A high brightness limit threshold value as a reference value for determining whether or not to replace the high brightness limit value to be used, and when the brightness for each small area is greater than the high brightness removal threshold value, the brightness is used for exposure evaluation. The luminance of the remaining small area excluded from the target for use is used as luminance information for exposure evaluation, and when the luminance of each small area is smaller than the high luminance removal threshold and larger than the high luminance limitation threshold, High luminance processing means for executing high luminance removal processing by replacing luminance with the high luminance limit value to obtain luminance information for exposure evaluation;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions composed of a set of a plurality of small regions, and the calculation means sets the high luminance removal threshold value, the high luminance limitation threshold value, and the high luminance limitation value for each middle region. Each has
The high brightness processing means executes the high brightness removal process based on the high brightness removal threshold, the high brightness restriction threshold, and the high brightness restriction value for each middle region.

  The invention according to claim 2 is characterized in that the relationship between the thresholds satisfies the following magnitude relationship.

High brightness extraction threshold ≦ High brightness limit threshold ≦ High brightness removal threshold The invention according to claim 3, wherein a middle area formed by a set of a plurality of small areas obtained by dividing the captured image is an upper middle area. It consists of remaining middle regions other than the upper middle region.

  The invention described in claim 4 is characterized in that the high luminance removal threshold value of the upper middle region is equal to the high luminance extraction threshold value.

  According to a fifth aspect of the present invention, a middle area composed of a set of a plurality of small areas obtained by dividing the photographed image comprises a middle middle area and a remaining middle area other than the middle middle area. The high brightness removal threshold value in the central middle region is larger than the high brightness removal threshold value in the remaining middle region.

  According to a sixth aspect of the present invention, a middle area composed of a set of a plurality of small areas obtained by dividing the photographed image comprises a middle middle area and a remaining middle area other than the middle middle area. The high luminance limit threshold value in the central middle region is greater than the high luminance limit threshold value in the remaining middle region.

The invention according to claim 7 is a luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
Having a high luminance removal threshold value as a reference value for determining that the luminance of the small region extracted by the high luminance region extracting means should be high luminance, and the luminance for each small region is higher than the high luminance removal threshold value A high-intensity processing means for performing high-intensity removal processing in which the luminance is excluded from the use target for exposure evaluation and the luminance of the remaining small area is set as luminance information for exposure evaluation when it is large;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions composed of a set of a plurality of small regions, and the calculation means has the high luminance removal threshold value for each middle region,
The high-intensity processing means executes the high-intensity removal processing based on the high-intensity removal threshold value for each middle region.

  According to an eighth aspect of the present invention, in the automatic exposure control apparatus according to the seventh aspect, a middle region composed of a set of a plurality of small regions obtained by dividing the photographed image is an upper middle region and the upper middle region. It consists of the remaining middle region other than the region.

  According to a ninth aspect of the present invention, in the automatic exposure control apparatus according to the seventh aspect of the present invention, a middle area formed by a set of a plurality of small areas obtained by dividing the captured image is a middle middle area and the middle area. It consists of a remaining middle region other than the middle region, and the high luminance removal threshold value of the central middle region is larger than the high luminance removal threshold value of the remaining middle region.

The invention according to claim 10 is a luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
Having a high brightness limit threshold value as a reference value for determining whether or not to replace the brightness of the small area extracted by the high brightness area extracting means with a high brightness limit value used for exposure evaluation; High luminance processing means for executing a high luminance removal process by replacing the luminance with the high luminance limitation value to obtain luminance information for exposure evaluation when the luminance is larger than the high luminance limitation threshold;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions consisting of a set of a plurality of small regions, and the computing means has the high brightness limit threshold and the high brightness limit value for each middle region,
The high brightness processing means executes the high brightness removal process based on the high brightness limit threshold and the high brightness limit value for each of the middle regions.

  According to an eleventh aspect of the present invention, a middle area composed of a set of a plurality of small areas obtained by dividing the photographed image includes a middle middle area and a remaining middle area other than the middle middle area. The high luminance limit threshold value in the central middle region is greater than the high luminance limit threshold value in the remaining middle region.

  As described above, the automatic exposure control apparatus according to the present invention divides a photographed image into a plurality of rough middle areas composed of a set of a plurality of small areas, and depending on the position of the middle area, The threshold for determining whether or not the brightness of a small area in the area is high brightness has been changed, and a configuration that performs high brightness processing for each small area has been adopted, so fine high brightness processing must be performed It is possible to make a further contribution to obtaining an appropriate automatic exposure.

  Hereinafter, an embodiment in which an automatic exposure control apparatus according to the present invention is applied to a digital camera will be described with reference to the drawings.

Example 1
7 to 9 are external views showing an example of a digital camera as an imaging apparatus to which the automatic exposure control apparatus according to the present invention is applied. FIG. 10 is a block circuit diagram of the digital camera shown in FIGS.

  7 to 10, reference numeral 7 denotes a lens barrel unit. The lens barrel unit 7 includes a zoom optical system 71, a focus optical system 72, a diaphragm unit 73, and a mechanical shutter unit 74.

  The zoom optical system 71 is roughly composed of a zoom lens 71a for capturing an optical image of a subject and a zoom drive motor 71b for driving the zoom lens 71a. The focus optical system 72 is roughly composed of a focus lens 72a and a focus drive motor 72b for driving the focus lens 72a.

  The diaphragm unit 73 is roughly composed of a diaphragm 73a and a diaphragm motor 73b that drives the diaphragm 73a. The mechanical shutter unit 74 includes a mechanical shutter 74a and a mechanical shutter motor 74b that drives the mechanical shutter 74a. The lens barrel unit 7 has a motor driver 75 that drives these motors.

  The motor driver 75 is driven and controlled by a drive command from a CPU block 1043 in the digital still camera processor 104, which will be described later, based on an input from the remote control light receiving unit 6 and an operation input of each operation switch SW1 to SW13 of the operation unit key unit. Is done. In addition, since the function of each operation switch SW1-SW13 is well-known, only a name is attached | subjected to drawing and the detailed description is abbreviate | omitted.

  The ROM 108 stores a control program and control parameters described by codes readable by the CPU block 1043. When the power SW 13 of the digital camera is turned on, the control program is loaded into the main memory (not shown), and the CPU block 1043 controls the operation of each part of the apparatus according to the control program, and the data necessary for the control, etc. Are temporarily stored in the RAM 107 and a local SRAM 1044 in the digital still camera processor 104 described later. By using a rewritable flash ROM for the ROM 108, the control program and control parameters can be changed, and the function can be easily upgraded.

  The CCD 101 is a solid-state image sensor for photoelectric conversion of an optical image. The F / E (front end) -IC 102 includes a CDS 1021, an AGC 1022, an A / D 1023, and a TG 1024. The CDS 1021 performs correlated double sampling for image noise removal. The AGC 1022 performs gain adjustment. The A / D 1023 performs digital signal conversion. The TG 1024 is supplied with a vertical synchronizing signal (hereinafter referred to as VD) and a horizontal synchronizing signal (hereinafter referred to as HD) from the CCD1 signal processing block 1041 and is controlled by the CPU block 1043, the CCD 101 and the F / E-IC 102. A drive timing signal is generated.

  The digital still camera processor 104 includes a CCD1 signal processing block 1041, a CCD2 signal processing block 1042, a CPU block 1043, a local SRAM 1044, a USB block 1045, a serial block 1046, a JPEG CODEC block 1047, a RESIZE block 1048, a TV signal display block 1049, and a memory. A card controller block 10410 is included.

  The CCD1 signal processing block 1041 performs white balance setting and gamma setting on the output data of the F / E-IC 102 from the CCD 101, and supplies a VD signal and an HD signal. The CCD2 signal processing block 1042 performs conversion into luminance data and color difference data by filtering processing. The CPU block 1043 controls the operation of each part of the device. The local SRAM 1044 temporarily stores data necessary for the above-described control. The USB block 1045 performs USB communication with an external device such as a personal computer. The serial block 1046 performs serial communication with an external device such as a personal computer. The JPEG CODEC block 1047 performs JPEG compression / decompression. The RESIZE block 1048 enlarges / reduces the size of the image data by interpolation processing. The TV signal display block 1049 converts the image data into a video signal for display on an external display device such as a liquid crystal monitor or a TV. A memory card controller block 10410 controls a memory card that records captured image data.

  The SDRAM 103 temporarily stores image data when the digital still camera processor 104 performs various processes on the image data. The image data to be stored is, for example, “RAW-RGB image data” in which the CCD 1 signal processing block 1041 takes in the white balance setting and gamma setting from the CCD 101 via the F / E-IC 102. “YUV image data” in which luminance data / color difference data conversion has been performed in the CCD2 signal processing block 1042, “JPEG image data” compressed in JPEG by the JPEG CODEC block 1047, and the like.

  The memory card throttle 121 is a throttle for mounting a removable memory card. The built-in memory 120 is a memory for storing captured image data even when no memory card is attached to the memory card throttle 121 described above. The LCD driver 117 is a drive circuit that drives the LCD monitor 10 described later, and also has a function of converting the video signal output from the TV signal display block 1049 into a signal for displaying on the LCD monitor 10.

  The LCD monitor 10 is used for monitoring the state of a subject before shooting, checking a shot image, displaying image data recorded in a memory card or the built-in memory 120 described above, and the like. The video AMP 118 is used for impedance conversion of the video signal output from the TV signal display block 1049 by 75Ω. The video jack 119 is used to connect to an external display device such as a TV. The USB connector 122 is used for USB connection with an external device such as a personal computer. The serial driver circuit 1231 is used for voltage conversion of the output signal of the serial block 1046 described above in order to perform serial communication with an external device such as a personal computer, and the RS-232C connector 1232 is serially connected to an external device such as a personal computer. Used to do.

  The SUB-CPU 109 is a CPU in which ROM / RAM is built in one chip, and outputs the operation signals SW1 to SW13 of the operation key unit and the output signal of the remote control light receiving unit 6 to the CPU block 1043 as user operation information. In addition, a signal indicating the state of the camera output from the CPU block 1043 is converted into a control signal for the sub LCD 1, AF LED 8, strobe LED 9, and buzzer 113, which will be described later, and output.

  The sub LCD 1 is a display unit that displays, for example, the number of shootable images, and the LCD driver 111 is a drive circuit that drives the sub LCD 1 based on an output signal of the SUB-CPU 109. The AF LED 8 is used to display a focus state at the time of shooting, and the strobe LED 9 is used to indicate a strobe charging state. Note that the AF LED 8 and the strobe LED 9 may be used for other purposes such as when a memory card is being accessed. The operation switches SW1 to SW13 of the operation key unit constitute a part of the key circuit operated by the user, and the remote control light receiving unit 6 is a signal receiving unit of the remote control transmitter operated by the user.

  The audio recording unit 115 is roughly composed of a microphone 1153 to which a user inputs an audio signal, a microphone AMP 1152 for amplifying the input audio signal, and an audio recording circuit 1151 for recording the amplified audio signal. The audio reproduction unit 116 includes an audio reproduction circuit 1161 that converts the recorded audio signal into a signal that can be output from the speaker, an audio AMP 1162 that amplifies the converted audio signal, and drives the speaker, and a speaker 1163 that outputs the audio signal. It is abbreviated.

The CCD1 signal processing block 1041 functions as a luminance value calculation means, and performs luminance integration processing for each small evaluation area. This is performed by converting RGB signal data included in the image signal of each evaluation small area into luminance data (brightness value) and integrating the luminance value for each evaluation small area.

  The integrated luminance value for each small evaluation area is processed by a control program (ROM: 108) as a histogram generating means, and a luminance histogram based on the luminance distribution is generated by the control program. Based on the brightness histogram and the exposure conditions at the time of shooting, each threshold value for high brightness and a high brightness processing method are determined.

  Each threshold value of high luminance here is determined based on the distribution of the high frequency sections of the luminance histogram. The high brightness processing thus determined is executed, and an exposure control value for exposure control is obtained, and the exposure control is performed by controlling the F / E-IC 102 and the aperture motor 73b based on the exposure control value. .

  Hereinafter, the high luminance processing will be described. FIG. 11 is a flowchart of high luminance processing.

First, the CCD 1 signal processing block (exposure control unit) 1041 creates a luminance histogram in consideration of the difference in exposure conditions up to the previous time (S.801). Here, the luminance histogram is created from the luminance information (exposure evaluation information) of each small region obtained by dividing the captured image region G into 100 of 10 × 10 as shown in FIG. Note that the exposure evaluation information is a general term for information used for determining exposure in addition to luminance information which is a luminance signal of each small region.

  In the example shown in FIG. 12, since the number of small regions used in the histogram is only 100, the width per section of the horizontal axis (corresponding to the luminance) of the luminance histogram cannot be made too small. This is because if the width per section is narrowed, the total number of sections increases, and the number (frequency number) in which the luminance of each small area enters per section decreases. Therefore, considering that the sensitivity of the CCD 101 is around ± 3 ev (Expousure Value), the width per section is set to 1.0 ev. Alternatively, the width per section may be 0.5 ev, and the adjacent sections may be 1.0 ev. The number of sections is set to seven sections in consideration of corrections such as exposure correction. Note that it is known that the unit of the section is set to the ev unit, so that it is less affected by the high luminance image portion.

  When the exposure evaluation information of each small region is output as a linear value, the threshold value for each section when creating the histogram is converted from the ev value to the linear value, and the histogram is created. For example, when the linear data at the target exposure (luminance as the central section of the luminance histogram) is 1000, the histogram sections (shown by the center value in Table 1) shown in Table 1 below are set.

図１３はこのようにして得られた輝度ヒストグラムの一例である。ＣＣＤ１信号処理ブロック（露出制御部の演算手段）１０４１は輝度ヒストグラムの作成後、輝度ヒストグラムの平均値（頻度平均値＝輝度平均値）を求める（Ｓ.８０２）。頻度平均値（輝度平均値）の計算式は以下の通りである。
頻度平均値（輝度平均値）＝（区画番号×各区画毎の頻度）の総和／小領域の総個数
なお、ここでは、小領域の総個数は１００であり、その図１３において、符号Ｚ１は頻度平均値（輝度平均値）を示す。

FIG. 13 is an example of the luminance histogram obtained in this way. The CCD 1 signal processing block (calculation means of the exposure control unit) 1041 obtains an average value (frequency average value = luminance average value) of the luminance histogram after creating the luminance histogram (S.802). The calculation formula of the frequency average value (luminance average value) is as follows.
Frequency average value (luminance average value) = (sum of partition number × frequency for each partition) / total number of small regions Here, the total number of small regions is 100, and in FIG. The frequency average value (luminance average value) is shown.

Next, the CCD 1 signal processing block (exposure control unit) 1041 determines a frequency threshold value from the created luminance histogram (S.803). In FIG. 13, reference numeral Z2 indicates the frequency threshold.

  Incidentally, when the luminance is concentrated, as shown in FIG. 14A, the frequency of the luminance histogram exceeds the frequency threshold Z2, but when the luminance on the screen is dispersed, for example, As shown in FIG. 14B, the frequency of the luminance histogram is divided into two, and the phenomenon occurs that the frequency threshold Z2 is not exceeded.

  Therefore, it is conceivable to prepare two frequency threshold values, a high frequency threshold value Z2H and a low frequency threshold value Z2L, as shown in FIG. 15. However, as shown in FIG. If the frequency histogram is fixed to the high frequency threshold Z2H in the luminance histogram obtained from the above, a section with a frequency higher than the frequency threshold Z2H cannot be obtained. In such a case, it is desirable to set a low frequency threshold Z2L.

  On the other hand, as shown in FIG. 15B, if the frequency histogram is fixed to a low frequency threshold Z2L in the case of a luminance histogram obtained from a photographed image in which the luminance distribution is concentrated, a non-high frequency section is also set as a high frequency. In such a case, it is desirable to set a high frequency threshold Z2H.

That is, since it is not desirable anyway if the frequency threshold value Z2 is fixed, the CCD 1 signal processing block (exposure control unit) 1041 sets a minimum frequency threshold value Z2MIN as an empirical value. The number N of partitions having a frequency equal to or higher than the minimum frequency threshold Z2MIN is counted, and the dynamic frequency threshold ZT is determined from the reciprocal thereof. That is, an empirically obtained value P is set, and the dynamic frequency threshold ZT is obtained by the following equation.
ZT = P / N
When such processing is performed, N is increased when the luminance distribution of the captured image is substantially uniform, so that the frequency threshold ZT is decreased, and it is possible to prevent a high-frequency section higher than the frequency threshold ZT from being present. In addition, when the luminance distribution is locally concentrated, N is small, so the frequency threshold ZT is large, so that a partition with a frequency that is not high can be removed, and a higher-frequency partition can be extracted (S.804). .

  Thus, by determining the dynamic frequency threshold value ZT from the distribution state of the luminance histogram, it is possible to stably extract a high luminance small region.

  Therefore, when the frequency threshold is fixed to a certain value, the exposure histogram changes, or the angle of view changes, the luminance histogram distribution is changed, and the section where the ratio of the high luminance small area is larger than the frequency threshold Z2 changes. The problem of instability is resolved, the frequency threshold value can be determined more finely, and a small area with high brightness can be extracted stably according to the distribution state of the brightness histogram.

  Next, for each section of the luminance histogram, a section having a frequency greater than the frequency threshold Z2 is obtained (S.805). Hereinafter, the section obtained in this way is referred to as a high-frequency section. In FIG. 13, section number 2 and section number 6 are high-frequency sections.

  Next, among the obtained high-frequency partitions, a partition having the largest partition number (referred to as the highest-frequency partition) and a partition having the smallest partition number (referred to as the minimum-frequency partition) are determined. In FIG. 13, section number 2 corresponds to the minimum high-frequency section, and section number 6 corresponds to the maximum high-frequency section. When only one section has a frequency greater than the frequency threshold Z2 (ZT), the maximum high frequency section and the minimum high frequency section are naturally the same.

  Next, the CCD1 signal processing block 1041 compares whether or not the number of the minimum high-frequency section is larger than a certain section number (S.806). For example, a certain partition number is “4”. The CCD1 signal processing block 1041 resets the minimum high-frequency section when the minimum high-frequency section number is larger than the fixed section number (S.807).

  First, the frequency is sequentially added from the low-luminance side division of the luminance histogram toward the high-luminance side division, and the addition value is compared with the frequency threshold value Z2 (ZT) for each addition. The section at the time when the added value exceeds the frequency threshold value Z2 is newly set as the minimum high-frequency section.

  This resetting process improves that it is difficult to obtain sections having a frequency higher than the frequency threshold Z2 (ZT) when the luminance of a landscape image or the like is dispersed.

  Next, the CCD1 signal processing block 1041 compares whether or not the difference between the section number of the maximum frequent section and the section number of the least frequent section is a certain value or more (S.808). If the difference is greater than or equal to a certain value, the high-brightness extraction threshold Z3 is set when the luminance difference is large (S.809). That is, a value obtained by adding a constant value to the evaluation value (luminance value) corresponding to the minimum high frequency section is set as the high luminance extraction threshold. If the difference is equal to or smaller than a certain value, the high luminance extraction threshold value Z3 'when the luminance difference is small is set (S.810). That is, a value obtained by adding a constant value to the frequency average value (average luminance value) is set as the high luminance extraction threshold value Z3 '. Here, a value obtained by adding a constant value to the evaluation value corresponding to the minimum high-frequency section is shown as a high-frequency extraction threshold Z3 in FIG.

  Next, the high luminance removal process (S. 811) will be described. Here, the high luminance removal processing refers to processing including replacement.

  Here, as shown in FIG. 12, the rectangular captured image G is composed of an upper middle region G1 composed of a set of a plurality of small regions and a remaining middle region G2 other than the upper middle region G1.

  FIG. 16 is a flowchart of the high luminance removal process.

The CCD 1 signal processing block 1041 executes high luminance extraction for each small region, and executes high luminance removal processing for the extracted high luminance small region.

The CCD1 signal processing block 1041 has an upper middle area G1
High luminance removal threshold = high luminance restriction threshold = high luminance extraction threshold. For the upper middle region G1, all of the extracted high-intensity small regions are to be removed. In the end, not all of the small areas to be removed are removed due to the limited number of removed areas.

  As a result, the influence of the sky part can be reduced for a luminance pattern such as a photographed image whose upper part corresponds to the sky part.

For the remaining middle region G2,
High luminance removal threshold = High luminance extraction threshold + 1.5 Ev
High luminance limit threshold = High luminance extraction threshold + 0.5 Ev
High luminance limit value (Yclip) = high luminance limit threshold value.

  The reason for using each threshold value as a reference for the high brightness extraction threshold value derived from the brightness distribution is to follow the change in brightness, and to influence the hunting effect that the image display for monitoring becomes brighter or darker. This is to reduce it.

  Also, the middle region G2 other than the upper middle region G1 is removed, replaced by a limit value, and switched to use as it is according to the luminance value, so that it is possible to remove strange high luminance such as a point light source, Further, the replacement with +0.5 Ev suppresses the shift to the high luminance side and makes it possible to reduce the overexposure phenomenon.

  The CCD1 signal processing block 1041 acquires the luminance value of the target small region (S.601), and determines whether it is larger than the high luminance extraction threshold value determined from the distribution state of the luminance histogram (S.602).

  If it is smaller, the normal area number Nn is counted as a normal luminance area (S.603). Further, the integrated luminance value Yn of the luminance values in the normal area is obtained (S.604).

  If it is larger, it is next determined whether or not this small region belongs to the upper area (upper middle region G1) (S.605).

  In the case of the upper middle region G1, the number of upper high luminance removal regions Nhu is counted as a high luminance removal region of the upper middle region G1 (S.606). Further, the integrated luminance value Yhu of the upper high luminance removal region of the upper middle region G1 is obtained (S.607).

  In the case of the middle region G2 other than the upper middle region G1, it is next determined whether or not the luminance value of the target small region is larger than the high luminance removal threshold (S.608).

  If larger, the high brightness removal area count Nh3 is counted as the high brightness removal area (S.609). Further, the luminance integrated value Yh3 of the high luminance removal area is obtained (S.610).

  If it is smaller, it is next determined whether or not the luminance value of the target small area is larger than the high luminance limit threshold (S.611).

  If larger, the number Nh2 of high-luminance restricted areas is counted as the high-luminance restricted area (S.612). Further, the integrated luminance value Yh2 of the high luminance limited area is obtained (S.613).

  If it is smaller, the number of high luminance areas Nh1 is counted as high luminance areas (S.614). Further, the luminance integrated value Yh1 of the high luminance region is obtained (S.615).

  After the count and integration of the target small region are completed, it is determined whether the count and integration of all the small regions has been completed (S.616). If not completed, the next small region is acquired and compared. The counting and integration process is repeated (S.601 to S.616).

  When all the small areas are completed, the effective area number Ne is calculated (S.617). That is, the high luminance removal region number Nh3 and the upper high luminance removal region number Nhu, which are the number of removal regions to be removed from the total region number (Nall), are subtracted.

  Next, the effective luminance integrated value Ye is calculated (S.618). The effective luminance integrated value Ye is the luminance integrated value Yn of the normal region, the luminance integrated value Yh1 of the high luminance region, and the luminance integrated value obtained by clipping the high luminance limiting region with the high luminance limiting value (= high luminance limiting region number Nh2 × high luminance). It is the sum of the limit value Yclip).

Finally, the final luminance value Y is calculated (S.619). The final luminance value Y is obtained by dividing the effective luminance integrated value Ye by the effective area number Ne. CCD1 signal processing block 1041, based-out in this final luminance value Y, and calculates the exposure will control value.

  FIG. 17 is a flowchart of the high luminance removal process when the high luminance removal threshold is not used for the remaining middle region G2 other than the upper middle region G1. In the flowchart of the high luminance removal process, steps S.608 to S.610 of the flowchart of the high luminance removal process of FIG. 16 are omitted. Since the processing other than the processing of steps S.608 to S.610 is the same as the flow of the high luminance removal processing of FIG. 16, the same processing as that corresponding to FIG. Description is omitted.

  FIG. 18 is a flowchart of the high luminance removal process when the high luminance removal threshold and the high luminance restriction threshold are not used in the remaining middle region G2 other than the upper middle region G1.

In the flowchart of the high luminance removal process, steps S.608 to S.613 in the flowchart of the high luminance removal process of FIG. 16 are omitted. Since the processing other than the processing of steps S.608 to S.613 is the same as the flow of the high luminance removal processing of FIG. 16, the same processing as that corresponding to FIG. Description is omitted.
(Example 2)
Next, another embodiment of the high-intensity removal process will be described with reference to a flowchart of the high-intensity removal process shown in FIG. 19 and a segmented example of the captured image G shown in FIG.

  In this embodiment, as shown in FIG. 20, the captured image G is a part of the upper middle region G1, the middle middle region G2 ′, and the remainder that surrounds the middle middle region G2 ′ in cooperation with the upper middle region G1. It consists of a region G3.

For the upper middle region G1,
High luminance removal threshold = high luminance restriction threshold = high luminance extraction threshold, and all the extracted high luminance small areas are set as removal targets, and finally, all of the targeted areas are limited by the number of removal areas. This region is not removed as in the previous embodiment.

For the central middle region G2 ′,
High luminance removal threshold = High luminance extraction threshold + 2 Ev
High luminance limit threshold = High luminance extraction threshold + 1 Ev
High luminance limit value (Yclip) = high luminance limit threshold value.

For the remaining middle region G3,
High luminance removal threshold = High luminance extraction threshold + 1.5 Ev
High luminance limit threshold = High luminance extraction threshold + 0.5 Ev
High luminance limit value (Yclip) = high luminance limit threshold value.

  The reason why the threshold value of the central middle region G2 ′ is set to be larger than the threshold values of the middle regions G1 and G3 other than the central central region G2 ′ is that the reproducibility of the high luminance portion of the central central region G2 ′ is determined. This is to make it possible to increase.

  The CCD1 signal processing block 1041 first acquires a target integration area (middle area). In this embodiment, it is the upper middle region G1, the middle middle region G2 ', or the remaining middle region G3.

Next, the threshold value of the target integration area is set. As shown above, in the case of the central middle region G2 ′,
High luminance removal threshold = High luminance extraction threshold + 2 Ev
High luminance limit threshold = High luminance extraction threshold + 1 Ev
High luminance limit value (Yclip) = high luminance limit threshold value.

  The CCD1 signal processing block 1041 executes high-intensity extraction for each small area, and performs high-intensity removal processing on the extracted high-intensity small area.

  First, a middle region as a processing target is acquired (S.601 '). Next, a high luminance removal threshold value, a high luminance limit threshold value, and a high luminance limit value are set as threshold values for each middle region (S.602 ').

  Subsequently, the CCD1 signal processing block 1041 counts the small areas and integrates the luminance values for the small areas in each middle area.

  Next, the luminance value of the small area to be processed is acquired (S.603 ′), and it is determined whether or not the luminance value is larger than the high luminance extraction threshold value determined from the distribution state of the luminance histogram (S.604 ′). .

  When the luminance value of the small area to be processed in the middle area to be processed is smaller than the high luminance extraction threshold, the normal area number Nn is counted as the normal luminance area (S.605 '). Further, the integrated luminance value Yn of the luminance values in the normal region is obtained (S.606 ').

  If the luminance value of the small region to be processed in the middle region of the processing target is larger than the high luminance extraction threshold, it is next determined whether or not the luminance value of the small region is larger than the high luminance removal threshold ( S.607 ').

  When the luminance value to be processed is larger than the high luminance removal threshold, the small region is determined as a high luminance removal region, and the number of high luminance removal regions Nh3 is counted (S.608 '). Next, the integrated luminance value Yh3 of the high luminance removal area is obtained (S.609 ').

  On the other hand, when the brightness of the small area is smaller than the high brightness removal threshold, it is determined whether the brightness value of the small area is larger than the high brightness limit threshold (S.610 ').

  When the brightness value of the small area is larger than the high brightness limit threshold, it is determined as a high brightness limit area and the number of high brightness limit areas Nh2 is counted (S.611 '). Next, the integrated luminance value Yh2 of the high luminance limited area is obtained (S.612 ').

  When the brightness value of the small area is smaller than the high brightness limit threshold, the number of high brightness areas Nh1 is counted as the high brightness area (S.613 '). Next, a luminance integrated value Yh1 in the high luminance region is obtained (S.614 ').

  After the count and integration of the corresponding small region are completed, it is determined whether the count and integration of all the small regions in the target middle region is completed (S.615 ′). The target small area is acquired, and the comparison process, the count process, and the integration process are repeated until all the small areas in the middle area are completed (S.601 ′ to S.615 ′).

  The CCD1 signal processing block 1041 calculates the number Ne of effective areas when the counting and integration in the middle area is completed (S.616 '). Subsequently, the effective luminance integrated value Ye is calculated (S.617 ').

  Here, the number Ne of effective areas is obtained by subtracting the number Nh3 of high luminance removal areas, which is the number of removal areas to be removed, from the number of all small areas (Nall = 100).

  The effective luminance integrated value Ye is a luminance integrated value obtained by clipping the luminance integrated value Yn of the normal region, the luminance integrated value Yh1 of the high luminance region, and the luminance of the high luminance limiting region with the high luminance limiting value (= number of high luminance limiting regions). (Nh2) × high luminance limit value (Yclip)).

Then, each middle region luminance value (Yi: i = 1 to 3) is calculated (S.618 ′). This middle region luminance value is obtained by dividing the effective luminance integrated value Ye by the number Ne of effective regions. This is repeated for all middle regions M1 to M3 (S.619 ').
When the luminance value calculation for all the middle regions is completed, final luminance value calculation (Y) is performed (S.620 ′). This final luminance value Y is obtained by dividing the sum of the luminance values (Y1 to Y3) of each middle region by the number of middle regions (Narea = 3).

CCD1 signal processing block 1041, based-out in this final luminance value Y, and calculates the exposure will control value.

  The processing according to the present invention can be performed by a program. The program including this processing is stored in an external storage medium such as a memory card, and the processing according to the present invention is performed by rewriting the camera program as necessary. It may be.

  In the second embodiment, the setting of the evaluation small area and the evaluation middle area is described as the three-divided mode shown in FIG. 20, but the present invention is not limited to this.

  In the first and second embodiments of the present invention, the luminance histogram used for exposure control is described as having a width per section of 1 ev and nine sections as shown in FIG. The section width and the number of sections are not limited to this.

  Furthermore, in the first and second embodiments of the present invention, it has been described that the captured image is stored in the memory card. However, the present invention is not limited to the memory card. For example, a video tape may be used as the storage medium. . At this time, the memory card storing the control program is set in the video camera separately from the storage medium storing the image.

  In the embodiment of the present invention, the exposure control device of the optical device has been described as the exposure control device of a digital still camera. However, the present invention is not limited to this as long as it is an optical device using an image sensor. It can also be applied to a scope using a camera or a CCD.

It is explanatory drawing which shows an example of the division area of the conventional picked-up image. It is a figure which shows an example of a to-be-photographed object typically. It is a figure which shows the brightness | luminance of the picked-up image obtained when image | photographing the to-be-photographed object shown in FIG. 2 with a brightness | luminance histogram. It is a figure which shows the brightness | luminance histogram obtained when performing a high brightness | luminance process about the sky part of the picked-up image which has a brightness | luminance histogram shown in FIG. It is a figure which shows the brightness | luminance of the picked-up image obtained when image | photographing the scenery of a mountain on the upper part and a field on the lower part with a luminance histogram. It is a figure which shows the brightness | luminance histogram obtained when a high-intensity process is performed about the field of the picked-up image which has a brightness | luminance histogram shown in FIG. It is a front view which shows an example of the digital camera to which the automatic exposure control apparatus concerning this invention was applied. It is a rear view of the digital camera shown in FIG. FIG. 8 is a top view of the digital camera shown in FIG. 7. FIG. 8 is a block circuit diagram of the digital camera shown in FIG. 7. It is a high-intensity processing flow figure concerning this invention. It is explanatory drawing which shows an example of the division | segmentation of the small area | region and middle area | region of the picked-up image concerning this invention. It is explanatory drawing which shows an example of the brightness | luminance histogram obtained by the automatic exposure control apparatus concerning this invention. It is explanatory drawing which illustrates typically the malfunction by the luminance concentration of a luminance histogram, dispersion | distribution, Comprising: (a) is explanatory drawing which shows the malfunction when luminance concentrates, (b) is a case where luminance is disperse | distributing It is explanatory drawing which shows this malfunction. It is explanatory drawing which shows an example of the solution method of the malfunction by preparing two frequency threshold values and luminance concentration and dispersion | distribution, Comprising: (a) is explanatory drawing which shows typically the case where luminance distribution is disperse | distributed, (b) These are explanatory drawings schematically showing a case where the luminance distribution is concentrated. FIG. 13 is a flowchart showing a high luminance removal process according to the present invention, and shows an example applied to the middle region division shown in FIG. 12. It is a flowchart for demonstrating the modification of the high-intensity removal process flow shown in FIG. FIG. 17 is a flowchart for explaining another modified example of the high-luminance removal processing flow shown in FIG. 16. FIG. 21 is a flowchart of a high luminance removal process according to the present invention, showing an example applied to the middle region division shown in FIG. 20. It is explanatory drawing which shows the other example of the division | segmentation of the middle area | region concerning this invention.

Explanation of symbols

101 ... CCD (imaging device)
108 ... ROM (histogram creation means)
1041... CCD1 signal processing block (calculation means)

Claims (11)

Luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
The high luminance removal threshold as a reference value for determining that the luminance of the small area extracted by the high luminance area extracting means should be high luminance and the luminance of the small area extracted by the high luminance area extracting means are used for exposure evaluation. A high brightness limit threshold value as a reference value for determining whether or not to replace the high brightness limit value to be used, and when the brightness for each small area is greater than the high brightness removal threshold value, the brightness is used for exposure evaluation. The luminance of the remaining small area excluded from the target for use is used as luminance information for exposure evaluation, and when the luminance of each small area is smaller than the high luminance removal threshold and larger than the high luminance limitation threshold, High luminance processing means for executing high luminance removal processing by replacing luminance with the high luminance limit value to obtain luminance information for exposure evaluation;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions composed of a set of a plurality of small regions, and the calculation means sets the high luminance removal threshold value, the high luminance limitation threshold value, and the high luminance limitation value for each middle region. Each has
The automatic exposure control apparatus, wherein the high luminance processing means executes the high luminance removal processing based on the high luminance removal threshold, the high luminance limitation threshold, and the high luminance limitation value for each middle region. 2. The automatic exposure control apparatus according to claim 1, wherein the relationship between the threshold values satisfies the following magnitude relationship.
High brightness extraction threshold ≤ High brightness limit threshold ≤ High brightness removal threshold   2. The middle region composed of a set of a plurality of small regions obtained by dividing the photographed image includes an upper middle region and a remaining middle region other than the upper middle region. 2. The automatic exposure control apparatus according to 2.   The automatic exposure control apparatus according to claim 1, wherein the high luminance removal threshold value of the upper middle region is equal to the high luminance extraction threshold value.   A middle region composed of a set of a plurality of small regions obtained by dividing the photographed image is composed of a middle middle region and a remaining middle region other than the middle middle region, and the central middle region has high brightness. The automatic exposure control apparatus according to claim 1, wherein the removal threshold value is larger than the high brightness removal threshold value in the remaining middle region.   A middle region composed of a set of a plurality of small regions obtained by dividing the photographed image is composed of a middle middle region and a remaining middle region other than the middle middle region, and the central middle region has high brightness. 2. The automatic exposure control device according to claim 1, wherein the limit threshold is larger than the high brightness limit threshold of the remaining middle region. Luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
Having a high luminance removal threshold value as a reference value for determining that the luminance of the small region extracted by the high luminance region extracting means should be high luminance, and the luminance for each small region is higher than the high luminance removal threshold value A high-intensity processing means for performing high-intensity removal processing in which the luminance is excluded from the use target for exposure evaluation and the luminance of the remaining small area is set as luminance information for exposure evaluation when it is large;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions composed of a set of a plurality of small regions, and the calculation means has the high luminance removal threshold value for each middle region,
The automatic exposure control apparatus, wherein the high luminance processing means executes the high luminance removal processing based on the high luminance removal threshold value for each of the middle regions.   8. The middle area composed of a set of a plurality of small areas obtained by dividing the captured image includes an upper middle area and a remaining middle area other than the upper middle area. Automatic exposure control device.   A middle region composed of a set of a plurality of small regions obtained by dividing the photographed image is composed of a middle middle region and a remaining middle region other than the middle middle region, and the central middle region has high brightness. The automatic exposure control device according to claim 7, wherein the removal threshold value is larger than the high brightness removal threshold value in the remaining middle region. Luminance value calculation means for dividing a captured image into a plurality of small areas based on image data from the image sensor and calculating a luminance value for each small area;
Histogram creation means for creating a brightness histogram by dividing the brightness value for each small area into sections;
A high-brightness region extraction means for extracting a high-brightness region from each of the small regions by a high-brightness extraction threshold determined according to the distribution state of the luminance histogram;
Having a high brightness limit threshold value as a reference value for determining whether or not to replace the brightness of the small area extracted by the high brightness area extracting means with a high brightness limit value used for exposure evaluation; High luminance processing means for executing a high luminance removal process by replacing the luminance with the high luminance limitation value to obtain luminance information for exposure evaluation when the luminance is larger than the high luminance limitation threshold;
In an automatic exposure control apparatus having a calculation means for calculating an exposure control value based on luminance information of each small area obtained based on the processing of the high luminance processing means,
The photographed image is divided into a plurality of middle regions consisting of a set of a plurality of small regions, and the computing means has the high brightness limit threshold and the high brightness limit value for each middle region,
The automatic exposure control device, wherein the high brightness processing means executes the high brightness removal process based on the high brightness limit threshold and the high brightness limit value for each of the middle regions.   A middle region composed of a set of a plurality of small regions obtained by dividing the photographed image is composed of a middle middle region and a remaining middle region other than the middle middle region, and the central middle region has high brightness. 11. The automatic exposure control apparatus according to claim 10, wherein the limit threshold is larger than the high brightness limit threshold of the remaining middle region.

Images