JP2009177399A - Automatic exposure controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform stable exposure control which is not influenced by transfer of an object in a screen, and to appropriately control exposure of a target object in a backlight state or in an excess follow light state. <P>SOLUTION: An arithmetic processing part 132 integrates imaging signals for every divided area weighted by a center part important photometry system to calculate evaluation values for a preset object total area and a background area except the object total area, and compares the evaluation values to detect whether the object is in the backlight state or in the excess follow light state. The arithmetic processing part 132 further calculates evaluation values for each of a plurality of object division areas obtained by further subdividing the object total area, compares the evaluation values with an evaluation value of the background area, and sets an excess follow light flag or a backlight flag according to a comparison result. An input/output control part 131 performs control for reducing exposure when the excess follow light flag is set and performs control for raising the exposure when the backlight flag is set to an iris 12, a CCD 15, and an amplifier 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an automatic exposure control device, and more particularly to an automatic exposure control device for a video camera that performs exposure control by center-weighted metering.

  In a video camera, an object (subject) to be photographed is usually located near the center of the screen. Therefore, in general, the automatic exposure control device of a video camera suppresses the influence of the luminance distribution scattered in the peripheral portion (background) other than the subject and brings the exposure of the subject closer to correction in FIG. Use a table as shown to increase the weight of metering near the center of the screen, and decrease the weight as you go to the left and right of the screen. The exposure is controlled by the center-weighted metering method, with a light weight set to eliminate the effects of. Note that the weighting table shown in FIG. 4 shows the weighting values of the photometric values of each block when the screen is divided into eight blocks in the horizontal direction and seven blocks (areas) in the vertical direction.

  FIG. 5 is a flowchart for explaining the operation of an example of a conventional automatic exposure control apparatus. In this conventional automatic exposure control device, basically, each parameter of automatic exposure control is used so that the evaluation value of brightness obtained by center-weighted metering is used and it approaches a preset target value. (Iris, AGC, electronic shutter) are controlled.

  That is, first, the screen area of one screen is divided into a plurality of preset areas, and the luminance distribution data of the imaging signal is acquired for each divided area (step S1). Subsequently, weighting processing is performed on the divided luminance distribution data based on the center-weighted photometry method (step S2). Subsequently, an evaluation value of luminance is calculated (step S3). Here, the evaluation value is an integrated value of weighted luminance levels.

  Next, it is determined whether or not the target value is larger than the evaluation value (step S4). Here, the target value is a set value that provides proper exposure. When it is determined in step S4 that the target value is not larger than the evaluation value, it is determined that the light is excessively forward and control is performed to reduce the exposure (step S5). As control for lowering the exposure, iris control for increasing the iris diaphragm value (thinning the iris), automatic gain control (AGC control) for keeping the signal level of the imaging signal output from the image sensor, and shutter of the electronic shutter There is a shutter control for increasing the speed.

  On the other hand, when it is determined in step S4 that the target value is larger than the evaluation value, it is determined that the target light is backlit and control is performed to increase exposure (step S6). As control for increasing the exposure, iris control for reducing the iris diaphragm value (opening the iris), automatic gain control (AGC control) for keeping the signal level of the image pickup signal output from the image pickup device, shutter of the electronic shutter There is a shutter control for reducing the speed.

  Further, some conventional automatic exposure control devices for video cameras perform exposure control with emphasis on a dark portion within a frame set at the center during backlighting (see, for example, Patent Document 1). There is also an automatic exposure control device that performs exposure correction by pattern recognition. For example, as shown in FIG. 6, the subject portion 2 and the other background portion 3 so that the subject portion 2 located at the center of the screen 1 receives sunlight from the other background portion 3 from behind. If there is a large difference in brightness, the exposure of the entire screen is determined in a manner affected by the brightness level of the background portion 3, so that the exposure of the subject portion 2 that is the shooting target is not necessarily appropriate. Occurs (backlight of underexposure or overorder of overexposure).

  In order to avoid this, in exposure correction by pattern recognition, the luminance level of the subject portion 2 and the luminance level of the background portion 3 are compared to recognize that there is a backlight or over-order light state and correct it. In order to achieve this, an exposure shift is performed to optimize the exposure of the subject portion 2.

JP-A-5-207361

  However, even when the video camera is fixed, the subject is rarely stationary at the center of the screen. This is the biggest point that a video camera differs from a still camera, and the video camera mainly records transitional motion. For the purpose of optimizing the exposure of the subject that is assumed to be near the center of the screen, if the ratio of weighting near the center of the screen in center-weighted metering is increased, the amount of exposure deviation when the subject is off the center of the screen will be Expanding. This becomes more conspicuous as the size of the subject occupying the entire screen becomes smaller, and under the situation of backlight or over-order light (spot light). Conversely, if the weighting ratio of the central portion of the screen in the center-weighted metering is reduced in order to suppress the amount of exposure shift due to the position change of the subject, the exposure control is easily influenced by the brightness of the background.

  In addition, in the conventional automatic exposure control device that performs exposure correction by pattern recognition, for example, as shown in FIG. 7A, the subject portion at the center of the screen is a planted portion including a person and the luminance is low. When the exposure control is performed on an image in which the background portion occupying most of the screen is mostly occupied by the high-luminance sky around it, an appropriate image cannot be obtained by the exposure control.

  That is, the conventional automatic exposure control apparatus recognizes the backlight state based on the result of the luminance difference between the subject portion and the background portion, and corrects it for the image shown in FIG. As shown in FIG. 7B, when the exposure shift is performed, the exposure of the subject portion that tends to sink is lifted as shown in FIG. 7B, but the face or the like of the person who is the main subject becomes an overexposed image. End up.

  The present invention has been made in view of the above points, and enables stable exposure control that is not affected by movement of the subject in the screen, and appropriately controls the exposure of the target subject in the backlit state or the overfronted state. An object is to provide an automatic exposure control device to obtain.

In order to achieve the above object, the present invention divides the imaging screen area of the imaging device of the video camera into a plurality of parts, and weights the divided areas in the central part of the imaging screen more than the weights of the divided areas in the peripheral part of the imaging screen In the automatic exposure control device based on the center-weighted photometry method that controls the exposure by the exposure control unit based on the imaging signal for each divided area set to a large weight,
The imaging screen is divided into a predetermined subject total area consisting of a plurality of divided areas and a background area other than that, and the image signals for each divided area weighted by the center-weighted metering method are added to each area. The evaluation value calculating means for calculating the evaluation value in the first place, the first comparing means for comparing the evaluation value of the subject general area calculated by the evaluation value calculating means and the evaluation value of the background area, and the subject comprehensive area respectively. Subdivided into a plurality of subject division areas composed of a plurality of division regions, subject division area evaluation value calculation means for calculating subject division area evaluation values for each subject division area by integrating the imaging signals for each subject division area; When the first comparison means obtains a comparison result in which the evaluation value of the subject comprehensive area is greater than the evaluation value of the background area, For each area evaluation value, a first difference obtained by subtracting the evaluation value of the background area from the subject division area evaluation value is obtained, and a state in which one or more first differences are larger than the first threshold is set. When the over-order light flag setting means for setting the over-order light flag when the time continues and the first comparison means obtain a comparison result in which the evaluation value of the subject comprehensive area is equal to or less than the evaluation value of the background area, a plurality of comparison results are obtained. For each of the subject division area evaluation values, a second difference obtained by subtracting the subject division area evaluation value from the evaluation value of the background area is obtained, and one or more second differences are larger than the second threshold value. Backlight flag setting means for setting a backlight flag when the state continues for a set time, and when the over-order light flag is set, the exposure control unit evaluates the evaluation value of the subject division area and the evaluation value of the background area When the backlight control is set so that the exposure is reduced by the exposure correction amount according to the difference and the backlight flag is set, the exposure correction according to the difference between the evaluation value of the subject division area and the evaluation value of the background area And first control means for performing control to increase exposure by an amount.

  In the present invention, based on the comparison result between the evaluation value of the subject general area and the evaluation value of the background area by the first comparison means, it is roughly determined whether the subject is over-ordered or back-lit. The over-order light flag or the back-order light flag is determined based on the difference between the evaluation value of each of the plurality of subject division areas obtained by dividing the general subject area based on the determination result and the evaluation value of the background area. A backlight flag is set, and exposure control is performed according to the over-order light flag or the backlight flag.

  In order to achieve the above object, in a second invention according to the first invention, a luminance evaluation value calculating means for calculating a luminance evaluation value by integrating luminance signals for each divided region; For each divided region, a peak histogram obtained by counting the number of pixels having a luminance level that is larger or smaller than a preset third threshold value among a plurality of pixels constituting the divided region is obtained, and from the peak histogram The detection means for detecting the presence or absence of blackout or overexposure of the subject, the second comparison means for comparing the evaluation value of the brightness with the target value that is the set value for appropriate exposure, and the target value by the second comparison means Is smaller than the luminance evaluation value, and when the detection unit does not detect blackening of the subject, the exposure control unit calculates the difference between the evaluation value of the subject division area and the evaluation value of the background area. According When control is performed to lower the exposure by the exposure correction amount, a comparison result in which the target value is larger than the luminance evaluation value is obtained by the second comparison means, and the overexposure of the subject is not detected by the detection means The exposure control unit further includes second control means for performing control to increase exposure by an exposure correction amount corresponding to a difference between the evaluation value of the subject division area and the evaluation value of the background area.

  In the present invention, by utilizing the position variation of the subject in reverse, the difference between the target value and the evaluation value of the changing luminance can be used only for the control for correcting the backlight and the control for correcting the overorder light. Thus, the direction of exposure control is limited. Also, in the present invention, the situation of overexposure and underexposure is monitored based on the peak histogram, and when there is no overexposure and underexposure, the exposure control is continuously increased or decreased.

  Furthermore, in order to achieve the above object, in a third invention, in the second invention described above, the comparison result in which the target value obtained by the second comparison means is smaller than the evaluation value of the luminance, When either one of the detection results without blackout is not obtained, the exposure control by the exposure control unit is maintained without being changed or the processing for increasing the exposure is performed, and the target by the second comparison unit If either of the comparison result whose value is larger than the luminance evaluation value or the detection result of the subject without whiteout by the detection means cannot be obtained, the exposure control by the exposure control unit is not changed. It further has the 3rd control means to perform processing which maintains or lowers exposure.

  In the present invention, when blackout or overexposure occurs, the exposure control is controlled in the opposite direction to the previous one, or the exposure control is maintained as it is.

  According to the present invention, by performing exposure control by separating the subject and the background, stable exposure control that is not affected by the position variation of the subject can be realized. In addition, according to the present invention, stable exposure can be obtained even if subject fluctuation occurs during backlighting or over-order light, and the performance of exposure correction during backlight or exposure correction during over-order light can be improved. Furthermore, according to the present invention, it is possible to control the target subject to an appropriate exposure by monitoring the situation of overexposure and underexposure and reflecting the monitoring result in the exposure control.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a block diagram of an embodiment of an automatic exposure control apparatus according to the present invention. As shown in the figure, an automatic exposure control device 10 of this embodiment is mounted on a video camera, and includes a lens 11, an iris 12, a microcomputer 13, and a CCD driving IC (Integrated Circuit: semiconductor integrated circuit) 14. , A CCD (Charge Coupled Device) 15 as an example of a solid-state imaging device, an amplifier 16, an A / D converter 17, and a signal processing process LSI (Large Scale Integrated circuit) 18. The The signal processing process LSI is configured by a DSP (Digital Signal Processor).

  The microcomputer 13 includes an input / output control unit 131 and an arithmetic processing unit 132. The input / output control unit 131 (1) iris control for controlling the iris value of the iris 12, and (2) CCD driving for controlling the shutter speed of the electronic shutter by controlling the operation of the CCD 15 via the CCD driving IC 14. And (3) AGC (Auto Gain Control) control for controlling the gain of the amplifier 16 so that the output signal level of the amplifier 16 becomes constant, and (4) a signal for controlling the operation of the signal processing process LSI 18. Processing process control is performed based on an automatic exposure control program.

  In addition, the arithmetic processing unit 132 performs (1) center portion emphasis processing, (2) brightness / darkness determination processing, (3) subject / background separation processing, and (4) exposure control amount determination processing based on the automatic exposure control program. . In the microcomputer 13, the input / output control unit 131 acquires the screen division luminance information created by the signal processing process LSI 18, and the input / output control unit 131 controls the iris 12 according to the exposure control amount calculated by the arithmetic processing unit 132. The value, the electronic shutter speed based on the CCD drive control signal, and the AGC control signal to the amplifier 16 are varied to obtain an appropriate exposure.

  In this embodiment, incident light from a subject (not shown) converged by the lens 11 is imaged on the light receiving surface of the CCD 15 and photoelectrically converted by the iris 12 with the amount of light limited by the aperture value. The The electronic shutter speed of the CCD 15 is controlled by the charge transfer operation and the like being controlled by a drive signal from the CCD drive IC 14. The image pickup signal output from the CCD 15 is amplified by the amplifier 16, further converted into a digital signal by the A / D converter 17, and then supplied to the signal processing process LSI 18 for known predetermined signal processing. The signal processing process LSI 18 generates screen division luminance information based on the input signal. The automatic exposure control apparatus according to this embodiment automatically controls the incident exposure amount of the CCD 15 that is an image sensor of a video camera in accordance with the incident light amount.

  Next, the automatic exposure control operation in the present embodiment will be described in detail with reference to the flowcharts of FIGS. The microcomputer 13 starts automatic exposure (AE) control at a constant cycle (for example, one field cycle) (step S11 in FIG. 2). Thereby, first, the input / output control unit 131 acquires the screen division luminance information created by the signal processing process LSI 18 (step S12 in FIG. 2). Here, the screen division luminance information is obtained by dividing the screen area of one screen into a plurality of preset division areas, and data for one screen composed of luminance information for each division area, that is, divided luminance distribution data. That is.

  Subsequently, based on the divided luminance distribution data, the arithmetic processing unit 132 divides the imaging screen into a preset “subject total area” where the subject is predicted to be located and other “background areas”. Further, an evaluation value is calculated based on the divided luminance distribution data weighted by the center-weighted photometry method for each area (step S13 in FIG. 2). Here, the “subject overall area” is an area composed of a plurality of predetermined divided areas in the central portion of the imaging screen. The “background area” is an area composed of a plurality of divided areas other than the subject general area. These areas are all fixed regardless of the actual subject position. The evaluation value is an integrated value of the divided luminance distribution data weighted by the center-weighted photometry as described above.

  Subsequently, the arithmetic processing unit 132 compares the evaluation value of the subject general area (subject evaluation value) calculated in step S13 with the evaluation value of the background area (background evaluation value) calculated in step S13 (FIG. 2). Step S14). When the comparison result that the subject evaluation value is larger than the background evaluation value is obtained in step S14, the arithmetic processing unit 132 determines that the subject is over-ordered and further includes a plurality of subjects in the subject general area. An evaluation value is calculated based on the divided luminance distribution data that is subdivided into divided areas and weighted by the center-weighted metering method for each of the subject divided areas (step S15 in FIG. 2). Here, each subject division area is a region formed by a plurality of the above-described division regions. Note that a part of adjacent subject division areas may overlap.

  Subsequently, the arithmetic processing unit 132 calculates the difference obtained by subtracting the background evaluation value from the evaluation value of each subject division area for each evaluation value that is an integrated value of the divided luminance distribution data for each subject division area calculated in step S15. Further, it is determined whether or not there is even one of the differences that is greater than a preset threshold value (step S16 in FIG. 2). When there is one or more of the above differences (Y in step S16 in FIG. 2) and the state has continued for, for example, 2 seconds (Y in step S17 in FIG. 2), the arithmetic processing unit 132 performs overorder light. And the over-order light flag is set (step S18 in FIG. 2).

  On the other hand, when it is determined in step S16 that there is no difference greater than the preset threshold value, or when it is determined in step S17 that it will not continue for more than 2 seconds, or in step S18, the over-order light flag is set. When it is set, it is then determined whether or not the state where there is no over-order light continues for, for example, 2 seconds or longer (step S19 in FIG. 2). When it is determined in step S19 that the operation has continued for 2 seconds or longer, the over-order light flag is cleared (step S20 in FIG. 2). Further, when it is determined in step S19 that the operation does not continue for two seconds or more, or when the over-order light flag is cleared in step S20, the arithmetic processing unit 132 subsequently starts the automatic exposure control shown in FIG. 3 (FIG. 2). Step S27).

  On the other hand, when the comparison result in which the subject evaluation value is equal to or smaller than the background evaluation value is obtained in step S14, the arithmetic processing unit 132 determines that the subject is backlit and further divides the subject total area into a plurality of subject division areas. The evaluation value is calculated based on the divided luminance distribution data weighted by the center-weighted photometry method for each of the subject divided areas (step S21 in FIG. 2).

  Subsequently, the arithmetic processing unit 132 calculates, for each evaluation value for each subject division area calculated in step S21, a difference obtained by subtracting the evaluation value for each subject division area from the background evaluation value, and further, for those differences. Among these, it is determined whether or not there is at least one difference larger than a preset threshold value (step S22 in FIG. 2). When there is one or more of the above differences and the state continues for 2 seconds or longer (Y in step S23 in FIG. 2), the arithmetic processing unit 132 determines that the backlight is back and sets the back light flag. (Step S24 in FIG. 2).

  On the other hand, when it is determined in step S22 that there is no difference larger than the preset threshold value, or when it is determined in step S23 that it will not continue for more than 2 seconds, or the backlight flag is set in step S24. Then, it is determined whether or not the non-backlight state continues for 2 seconds or longer (step S25 in FIG. 2). When it is determined in step S25 that the operation has continued for 2 seconds or more, the backlight flag is cleared (step S26 in FIG. 2). In addition, when it is determined in step S25 that the operation does not continue for 2 seconds or more, or when the backlight flag is cleared in step S26, the arithmetic processing unit 132 starts the automatic exposure control shown in FIG. 3 (step in FIG. 2). S27).

  Next, the arithmetic processing unit 132 determines whether both the backlight flag and the over-order light flag are not set (the L level) (step S28 in FIG. 3). When both the backlight flag and the over-order light flag are not set, the arithmetic processing unit 132 determines that there is no backlight or over-order light above a certain level, and even if the subject position changes slightly, the exposure is not performed. Therefore, the exposure is not intentionally corrected, and the process proceeds to step S2 in FIG. 5 to perform exposure control by the conventional center-weighted photometry method.

  On the other hand, when it is determined in step S28 that either the backlight flag or the over-order light flag is set, the arithmetic processing unit 132 weights the divided luminance distribution data based on the center-weighted metering method as in the past. After the processing is performed (step S29 in FIG. 3), a luminance evaluation value is calculated (step S30 in FIG. 3). Here, the evaluation value is an integrated value of luminance levels weighted as described above.

  Subsequently, it is determined whether or not the backlight flag is set (step S31 in FIG. 3). When it is determined that the backlight flag is not set, it is a case where the over-order light flag is set. Therefore, it is determined that the over-order light state is present, and it is determined whether or not the determination is the first time (FIG. 3). In step S32), if it is the first time, the first exposure control according to the degree of excessive forward light is performed (step S33 in FIG. 3). That is, at the time of the first exposure control with respect to over-order light, control to lower the exposure (control to reduce the iris, control of the electronic shutter speed to the high speed side, AGC gain down control) is performed. The exposure correction amount is increased or decreased according to the difference between the evaluation value of the subject division area and the evaluation value of the background area (the larger the difference is, the more the correction amount is increased).

  On the other hand, when it is determined in step S31 that the backlight flag is set, it is determined that the backlight is in the backlight state, and it is determined whether this determination is the first time (step S38 in FIG. 3). First exposure control according to the degree is performed (step S39 in FIG. 3). That is, at the time of the first exposure control with respect to the backlight, control for increasing the exposure (control to open the iris, control to the low speed side of the electronic shutter speed, gain increase control of AGC) is performed. The exposure correction amount is increased or decreased according to the difference between the evaluation value of the subject division area and the evaluation value of the background area (the larger the difference is, the more the correction amount is increased).

  Next, after the start of the first exposure control of over-order light in step S33 or when the arithmetic processing unit 132 determines that the exposure control is being performed instead of the first exposure control in step S32, the following exception processing is performed. I do. In the exception process, first, it is determined from the peak histogram data whether the subject is blacked out (step S34 in FIG. 3). Here, the peak histogram data is data that the arithmetic processing unit 132 generates for each divided region based on the divided luminance distribution data acquired from the signal processing process LSI 18 via the input / output control unit 131. The threshold value is set, and the number of pixels having a luminance level equal to or higher than (or lower than) the threshold value is counted.

  From this peak histogram data, the magnitude of the brightness level above or below the threshold (or less than the threshold) and the area within the screen at that brightness level can be determined. Based on the peak histogram data, the required subject on the screen An overexposed (under) part can be recognized. By appropriately setting the threshold value of the brightness level, it is possible to grasp the situation in which the subject (for example, a part of a person's face) is whiteout (blackout).

  Subsequently, the arithmetic processing unit 132 determines whether or not the evaluation value calculated in step S30 is larger than the target value and there is no blackout (step S35 in FIG. 3). When the evaluation value is larger than the target value and there is no blackout, overexposure light exposure is being controlled, but there is no blackout, so further overexposure exposure control is possible. Then, control for reducing the exposure (control for iris reduction, control for increasing the electronic shutter speed, and gain reduction control for AGC) is performed (step S37 in FIG. 3). The exposure correction amount is increased or decreased according to the difference between the evaluation value of the subject division area and the evaluation value of the background area (the larger the difference is, the more the correction amount is increased).

  On the other hand, when the arithmetic processing unit 132 determines in step S35 that the evaluation value is equal to or lower than the target value and the luminance level has reached a level predicted to shift to blackout of the subject by over-order light exposure control. The exposure control at that time is maintained for the purpose of not increasing the overcorrected light exposure correction (step S36 in FIG. 3). In addition, when it is determined in step S35 that the subject is blacked out within the range of the peak histogram data within a specified level due to a change in the light source, the angle of view, and the like, it is assumed that the overcorrected light exposure correction is performed transiently. Judgment and control to increase the exposure in the direction to reduce the over-order light correction operation (control to open the iris, control of the electronic shutter speed to the low speed side, AGC gain increase control) are performed (step S36 in FIG. 3). .

  On the other hand, the arithmetic processing unit 132 performs the following exception processing even after the start of the first exposure control at the time of backlighting in step S39 or when it is determined that the exposure control is being performed instead of the first exposure control in step S38. . In the exception processing at this time, first, it is determined from the peak histogram data whether or not the subject is whiteout (step S40 in FIG. 3).

  Subsequently, the arithmetic processing unit 132 determines whether or not the evaluation value calculated in step S30 is smaller than the target value and there is no whiteout (step S41 in FIG. 3). When the evaluation value is smaller than the target value and there is no whiteout, backlight exposure control is in progress, but there is no whiteout. Control (control to open the iris, control of the electronic shutter speed to the low speed side, AGC gain increase control) is performed (step S43 in FIG. 3). The exposure correction amount is increased or decreased according to the difference between the evaluation value of the subject division area and the evaluation value of the background area (the larger the difference is, the more the correction amount is increased).

  On the other hand, when the arithmetic processing unit 132 determines in step S41 that the evaluation value is equal to or higher than the target value and the luminance level has reached a level predicted to shift to the overexposure of the subject by the backlight exposure control, the backlight is backlit. In order not to increase the exposure correction, the current exposure control is maintained (step S42 in FIG. 3). Further, if it is determined in step S41 that the subject has whiteout within the range of the specified peak histogram data due to changes in the light source, the angle of view, etc., it is determined that the backlight exposure correction is being performed transiently. Then, the control for reducing the exposure in the direction of reducing the backlight correction operation (the control for reducing the iris, the control for increasing the electronic shutter speed, the gain reduction control for AGC) is performed (step S42 in FIG. 3).

  Although omitted in FIG. 3, when the peak histogram data generates a numerical value of overexposure or underexposure that exceeds a specified level and this continues for a certain period of time, a series of backlight correction or over-order light correction operations are canceled. To do.

  As described above, in the present embodiment, when the backlight flag or the over-order light flag is set, the exposure correction is first performed according to the degree of the backlight or over-order light that is first determined to be the backlight or the over-order light. carry out. The weighting of the central part and the evaluation value created from it are the same as in the conventional control algorithm, but the difference between the target value and the changed evaluation value is corrected for backlight by using the subject's position variation in reverse. The direction of the exposure control is limited so that it can be used only for the control of the direction to perform and the control of the direction for correcting the excessive forward light. That is, when the over-order light flag is set, the process for lowering the exposure is not performed even if the luminance evaluation value becomes equal to or lower than the target value thereafter (steps S35 and S36 in FIG. 3), and the backlight flag is set. In the case where it is determined that the exposure is not increased even if the luminance evaluation value becomes equal to or higher than the target value thereafter (steps S41 and S42 in FIG. 3).

  As a result, the exposure level of the backlight compensation or the over-order light compensation once balanced does not return to the decreasing direction, and the control for stabilizing the target exposure is achieved even if the position of the subject fluctuates thereafter. The exposure correction amount is increased or decreased according to the difference between the evaluation value of the subject division area and the evaluation value of the background area (the larger the difference is, the more the correction amount is increased).

  In addition, according to the present embodiment, since the exposure control is performed sequentially based on the comparison result between the target value and the evaluation value during the backlight correction or over-order light correction, the subject changes during backlight or over-order light. Even if there is, stable exposure can be obtained, and it is possible to improve the performance of exposure compensation during backlighting and exposure compensation during over-order lighting.

  Furthermore, according to the present embodiment, the situation of overexposure and underexposure is monitored based on the peak histogram, and exposure control is performed based on the monitoring result. In other words, even if the over-order light flag is set, if it is detected that blackout has occurred thereafter, processing for increasing exposure and reducing exposure correction is performed (steps S35 and S36 in FIG. 3). Further, even when the backlight flag is set, when it is detected that the overexposure has occurred thereafter, processing for reducing exposure and reducing exposure correction is performed (steps S41 and S42 in FIG. 3).

  As a result, as shown in FIG. 7 (A), it is difficult to distinguish between a subject such as a person who actually wants to perform exposure compensation and other subjects and mechanical compensation makes excessive exposure compensation control. Even in such a case, the subject's face or the like as shown in FIG. 7B will not be overexposed, and exposure control can be performed so that the target subject has an appropriate exposure.

  In the above embodiment, the evaluation value and the peak histogram by the pixels in the horizontal direction of the screen have been described. However, the present invention is also based on the evaluation value and the peak histogram by the pixels in the vertical direction of the screen. Perform automatic exposure control.

  Further, the present invention is not limited to the above-described embodiment. For example, in steps S17, S19, S26, and S25 in FIG. 2, whether or not a predetermined state is continued for 2 seconds is monitored. The determination time can be arbitrarily set, and is not limited to 2 seconds. Further, the comparison determination in step S14 may be performed after the processing in step S15 (S21) in FIG. 2 is performed first. Further, as means for controlling the exposure, the control of the iris value, the control of the shutter speed of the electronic shutter, and the gain control of the amplifier 16 have been described. However, these three controls are not performed, and one or two of these are not performed. This control may be performed.

It is a block diagram of one embodiment of an automatic exposure control device according to the present invention. FIG. 3 is a flowchart (part 1) for explaining the operation of FIG. 1; FIG. FIG. 3 is a flowchart (part 2) for explaining the operation of FIG. 1; It is a figure which shows an example of the weighting table in a center part weighted metering system. It is a flowchart for operation | movement description of an example of the conventional automatic exposure control apparatus. It is explanatory drawing of an example of the backlight determination by pattern recognition. It is a figure which shows an example of the malfunction of the backlight determination by pattern recognition utilization.

Explanation of symbols

10 Automatic Exposure Control Device 12 Iris 13 Microcomputer 14 CCD Drive IC
15 CCD
16 Amplifier 17 A / D Converter 18 Signal Processing Process LSI (DSP)
131 I / O controller 132 Arithmetic processor

Claims (3)

Each divided area obtained by dividing the imaging screen area of the imaging device of the video camera into a plurality of weights and setting the weight of the divided area in the central part of the imaging screen to be larger than the weight of the divided area in the peripheral part of the imaging screen In the automatic exposure control device by the center-weighted metering method that controls the exposure by the exposure control unit based on the imaging signal for each,
The imaging screen is divided into a preset subject total area composed of a plurality of the divided areas and a background area other than the predetermined area, and each area is weighted by the center-weighted metering method for each area. Evaluation value calculation means for calculating an evaluation value by integrating signals;
First comparison means for comparing the evaluation value of the subject comprehensive area calculated by the evaluation value calculation means with the evaluation value of the background area;
The subject total area is subdivided into a plurality of subject division areas each composed of a plurality of the divided regions, and the image pickup signals for each subject division area are integrated to calculate a subject division area evaluation value for each subject division area. Subject division area evaluation value calculating means;
When the first comparison means obtains a comparison result in which the evaluation value of the subject comprehensive area is larger than the evaluation value of the background area, subject division is performed for each of the plurality of subject division area evaluation values. A first difference obtained by subtracting the evaluation value of the background area from the area evaluation value is obtained, and when one or more of the first differences are larger than the first threshold value continues for a set time, the order is excessive. An over-order light flag setting means for setting a light flag;
When the first comparison means obtains a comparison result in which the evaluation value of the subject comprehensive area is equal to or less than the evaluation value of the background area, the evaluation value of the background area for each of the plurality of subject division area evaluation values A second difference obtained by subtracting the subject division area evaluation value is obtained, and a backlight flag is set when one or more of the second differences are larger than a second threshold for a set time. A backlight flag setting means;
When the over-order light flag is set, the exposure control unit controls the exposure to be reduced by an exposure correction amount corresponding to the difference between the evaluation value of the subject division area and the evaluation value of the background area, When the backlight flag is set, the exposure control unit controls the exposure to be increased by an exposure correction amount corresponding to the difference between the evaluation value of the subject division area and the evaluation value of the background area. And an automatic exposure control device. A luminance evaluation value calculating means for calculating a luminance evaluation value by integrating the luminance signal for each of the divided areas weighted by the center-weighted photometry;
For each of the divided regions, a peak histogram is obtained by counting the number of pixels having a luminance level that is larger or smaller than a preset third threshold value among a plurality of pixels constituting the divided region, and the peak histogram Detection means for detecting the presence or absence of blackout or whiteout of the subject from,
A second comparing means for comparing the evaluation value of the brightness with a target value which is a set value for appropriate exposure;
When the comparison result that the target value is smaller than the evaluation value of the luminance is obtained by the second comparison unit, and the blackout of the subject is not detected by the detection unit, the exposure control unit detects the subject. Control is performed to reduce the exposure by an exposure correction amount corresponding to the difference between the evaluation value of the divided area and the evaluation value of the background area, and the target value is greater than the evaluation value of the luminance by the second comparison unit. When a certain comparison result is obtained and when the detection unit does not detect overexposure of the subject, exposure according to the difference between the evaluation value of the subject division area and the evaluation value of the background area is performed by the exposure control unit. The automatic exposure control apparatus according to claim 1, further comprising: a second control unit that performs control to increase exposure by a correction amount.   When either one of the comparison result that the target value by the second comparison unit is smaller than the evaluation value of the luminance and the detection result by the detection unit that the subject is not blacked out cannot be obtained. The exposure control state is maintained by the exposure control unit or the process of increasing the exposure is performed, and the comparison result that the target value by the second comparison unit is larger than the evaluation value of the brightness and the detection unit A third control unit for maintaining the exposure control state by the exposure control unit or performing a process of reducing the exposure when either one of the detection results of no overexposure of the subject cannot be obtained; The automatic exposure control device according to claim 2, wherein the automatic exposure control device is provided.