JP5858699B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus that uses an imaging element in which smear is generated as a photometric sensor.

  2. Description of the Related Art Conventionally, an imaging apparatus using a linear sensor such as a CCD or CMOS as a photometric sensor is known. For example, Patent Document 1 proposes a digital still camera that includes a main image sensor and a sub image sensor and performs photometric control using an output signal of the sub image sensor.

JP 2001-346095 A

  However, when a CCD is used as a photometric sensor, smearing occurs when attempting to meter a high-luminance subject, and a correct photometric value cannot be obtained due to smearing. FIG. 10 is a diagram for explaining a difference generated between an ideal photometric value and an actual photometric value due to the effect of smear. An ideal photometric value refers to a photometric value that is supposed to be originally obtained.

  As shown in FIG. 10, until the ambient light BV value indicating the brightness of ambient light is close to BV9, there is almost no smear effect, and the ideal and actual photometric values match. On the other hand, from the vicinity of BV10, the effect of smear begins to appear and the actual photometric value becomes larger than the ideal photometric value, and the difference gradually increases between the ideal photometric value and the actual photometric value.

  Therefore, when exposure control is performed based on an actual photometric value that is larger than the ideal photometric value, the brightness of the external light is estimated brightly, resulting in underexposure.

  Accordingly, an object of the present invention is to enable exposure control with reduced influence of smear in a situation where smear occurs in a photometric sensor.

In order to achieve the above object, an imaging apparatus according to the present invention photoelectrically converts an object image, accumulates charges, outputs a signal corresponding to the accumulated charges, and outputs the signals according to the metering means. A setting means for setting a control value for controlling the photometry means so that a signal value becomes a target value; a calculation means for calculating a photometric value based on a signal output from the photometry means; and the calculation means Exposure control means for performing exposure control based on the photometric value calculated by the step, wherein the setting means, when the control value exceeds a predetermined range where smear does not affect the photometric value, the target value It is characterized by increasing.

  ADVANTAGE OF THE INVENTION According to this invention, the exposure control which reduced the influence of a smear can be performed in the condition where a smear generate | occur | produces in a photometry sensor.

1 is a configuration diagram of a camera according to an embodiment of the present invention. The figure which shows the control value correction process of the AE sensor 108 for reducing the influence of a smear. The figure which shows the photometry area | region of the AE sensor. The figure which shows an example of the relationship between the accumulation | storage time T (APEX value) and the actual accumulation | storage time t (ms). The figure which shows an example of the relationship between sensor output Y (APEX value) and actual sensor output y (count). The figure which shows an example of the correction value LensYij which correct | amends the peripheral light amount fall of a lens. The figure which shows an example of the relationship between photometric value BV (APEX value) and an actual bv value. The figure which shows an example of the relationship between the accumulation | storage time T, the amount of smears s (count), sensor output y, and the BV value at that time The figure which shows the influence of the smear after control value correction | amendment. The figure which shows the shift | offset | difference of the photometry value by the influence of smear.

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

  FIG. 1 is a diagram illustrating a configuration of a camera that is an imaging apparatus according to an embodiment of the present invention. The camera in the present embodiment includes the camera body 100 and the lens 200, but the camera body 100 and the lens 200 may be integrated.

  The internal structure of the camera body 100 and the lens 200 will be described.

  A microcomputer CPU (hereinafter referred to as camera microcomputer) 101 is a CPU that controls each part of the camera body 100, and a memory 102 is a memory such as a RAM and a ROM connected to the camera microcomputer 101.

  An imaging element 103 such as a CCD or CMOS including an infrared cut filter, a low-pass filter, and the like forms an image of a subject by the lens 200 during photographing. The shutter 104 shields the image sensor 103 when not photographing, and opens to guide the light beam to the image sensor 103 when photographing. The half mirror 105 reflects a part of the light incident from the lens 200 when not photographing, and forms an image on the focus plate 106. A display element 107 such as a PN liquid crystal is used to display an AF distance measurement frame, and indicates to the user where the focus adjustment is performed when looking through the optical viewfinder.

  A photometric sensor (hereinafter also referred to as an AE sensor) 108 uses a CCD, photoelectrically converts a subject image, accumulates charges, and outputs a signal corresponding to the accumulated charges. Since the AE sensor 108 uses a CCD, smearing occurs when photometry is performed on a high-luminance subject.

  The pentaprism 109 guides the subject image on the focusing screen 106 to the AE sensor 108 and the optical viewfinder. The AE sensor 108 expects a subject image formed on the focus plate 106 via a pentaprism 109 from an oblique position.

  The AF sensor 110 is used for automatic focus adjustment (AF), and a light beam incident from the lens 200 and passing through the half mirror 105 is reflected by the AF mirror 111 and guided.

An image processing / calculation CPU (hereinafter referred to as AECPU) 112 of the AE sensor 108 performs photometry calculation, control value correction processing of the AE sensor 108, and the like based on a signal output from the AE sensor 108.
The memory 113 is a memory such as a RAM or a ROM connected to the AECPU 112.

  In the present embodiment, a configuration having the AECPU 112 as a CPU dedicated to the AE sensor will be described. However, the camera microcomputer 101 may perform processing performed by the AECPU 112.

  In addition, the camera body 100 has an operation unit (not shown), and starts a shooting preparation operation and a shooting operation when a user operates a release switch in the operation unit.

  A CPU (hereinafter referred to as LCPU) 201 in the lens sends lens information including distance information to the subject, focal length information, and the like to the camera microcomputer 101. The LCPU 201 receives the result of the distance measurement calculation and the result of the photometry calculation from the camera microcomputer 101, and drives the lens and the aperture.

  Next, a control value correction process of the AE sensor 108 for reducing the effect of smear on the photometric value when smear occurs in the AE sensor 108 will be described with reference to FIG.

  When a power switch included in an operation unit (not shown) is operated and the camera is turned on, the AE sensor 108 performs the first photometry in step S101. At this time, the AECPU 112 sets the accumulation time of the AE sensor 108 to a predetermined accumulation time T0, and the AE sensor 108 performs accumulation at the set accumulation time T0.

  In step S102, the AECPU 112 calculates a photometric value from the output of the AE sensor 108 obtained by performing photometry in step S101 or step S107.

  The photometric value is obtained by dividing the effective pixel area of the photometric sensor into a plurality of photometric areas as shown in FIG. 3, first calculating the photometric value of each photometric area, and then, based on the photometric value of each photometric area, the final photometric value To decide. For example, the final photometric value is determined by performing a weighted average obtained by weighting the photometric value of each photometric region, or the final photometric value is determined by averaging the photometric value of a predetermined photometric region.

The photometric value BVij of each photometric area can be calculated by the following formula 1.
BVij = Yij + LensYij-P (Formula 1)
(Ij is a parameter indicating the position of the photometric area, i = 0 to 9, j = 0 to 6)
In Expression 1, Yij is a sensor output of each photometric area, LensYij is a correction value for correcting a peripheral light amount drop of the lens 200, P is a control value of the AE sensor 108, and in this embodiment, P = Let T (accumulation time). Note that the control value of the AE sensor 108 may include factors such as the pixel addition number and gain in addition to the accumulation time.

  Here, the accumulation time T (APEX value) in Equation 1 and the actual accumulation time t (ms) are set as shown in FIG. 4, for example. Further, the sensor output Yij (APEX value) and the actual sensor output yij (count) are set as shown in FIG. 5 assuming that the AE sensor 108 is a 14-bit output sensor, for example. Furthermore, FIG. 6 shows an example of the correction value LensYij that corrects the peripheral light amount drop of the lens 200. LensYij has a different value for each lens type. The lens correction value may be determined by determining the type of lens mounted through communication between the LCPU 201 and the camera microcomputer 101 and selecting appropriate data from data stored in the memory 102 in advance.

  The final photometric value BV can be obtained from BVij of each photometric area obtained from Equation 1 as described above.

  FIG. 7 is a diagram showing an example of the relationship between the photometric value BV (APEX value) obtained by Equation 1 and the actual bv value. The relationship between the photometric value BV (APEX value) and the actual bv value varies depending on the sensitivity of the AE sensor 108, the photometric optical system of the camera, and the like.

The final metering value BV may be obtained by weighting according to each metering mode (evaluation metering, center-weighted average metering, spot metering, etc.) and performing a weighted average. Then, the final photometric value BV, which is an average value, is obtained by the following formula 2.
BV = ΣBVij / 70 (Formula 2)
Subsequently, in step S103, the AECPU 112 calculates a control value Tnext of the AE sensor 108 when performing the next photometry.

  When calculating the accumulation time Tnext, the AECPU 112 first obtains a difference ΔBV between the sensor output and the target value (target value). If the brightness of the object field is stable and a sufficient time has passed (if metering is performed a sufficient number of times while the object field is stable), the difference ΔBV between the sensor output and the target value is 0.

  The AECPU 112 sets a control value (accumulation time in this embodiment) in each photometry so that the output of the AE sensor 108 becomes a target value. In normal times, the target value Yt is preferably in the vicinity of a value having a sufficient dynamic range above and below, and in FIG. 5, it is preferably in the vicinity of Yij = 78 (yij = 1000).

Here, ΔBV is obtained by the following Equation 3.
ΔBV = ΣYij / 70−Yt (Formula 3)
The next accumulation time Tnext can be obtained from the following equation 4 from ΔBV obtained in equation 3 and the current accumulation time T.
Tnext = T−ΔBV (Formula 4)
In step S104, the AECPU 112 compares the next control value (next accumulation time Tnext) obtained in step S103 with a threshold value used to determine whether or not to apply control value correction. Although the case where the next control value is compared with the threshold value will be described here, the current control value may be compared with the threshold value. Moreover, as long as the photometry is performed twice or more, the control value and the threshold value may be compared before this time. Data is previously stored for the control value at which the smear effect starts to appear on the photometric value, and the control value is determined based on the data.

  As a method of determining the accumulation time at which the smear influence starts to appear in the photometric value, for example, taking the photometric value and accumulation time data while changing the BV value of a uniform luminance surface such as a luminance box, the ideal photometric value and the actual photometric value It can be determined that the accumulation time at which the offset starts to shift is the accumulation time at which the effect of smear begins to appear. Here, the BV value on the uniform luminance surface corresponds to the ideal photometric value.

  FIG. 8 shows an example of the relationship between the accumulation time T, the smear amount s (count), the sensor output y, and the BV value at that time. The BV value is a value when the lens having the correction value shown in FIG. 6 is attached. Further, regarding the BV value, an actual photometric value (BV value) and an ideal photometric value (external light BV value) are shown.

  From FIG. 8, it can be considered that the accumulation time at which the smear effect starts to appear in the photometric value is T = 13 when the actual photometric value (BV value) and the ideal photometric value (external light BV value) start to shift. it can.

  The accumulation time for starting the control value correction from the data shown in FIG. 8, that is, the threshold used for the comparison in step S104 is, for example, Ts = 32 that can be corrected sufficiently when T = 13.

  As described above, the smaller the accumulation time T, the greater the effect of smear. Therefore, when the next accumulation time Tnext is smaller than the threshold value Ts, the process proceeds to step S105, and when it is greater than or equal to the threshold value Ts, the process proceeds to S107.

In step S105, the AECPU 112 calculates a control correction value for suppressing the effect of smear. The calculation of the control correction value Δsmear can be calculated by, for example, the following formula 5.
Δsmear = (Ts−T) × A (Formula 5)
In Equation 5, Ts is an accumulation time at which control value correction starts to be applied, A is a coefficient that determines how much correction is to be applied, and in this embodiment, Ts = 32 and A = 1/2. The values of Ts and A can be changed as appropriate and are not limited to these.

In step S106, the AECPU 112 corrects the next control value as shown in Equation 6 below, taking into account the control correction value calculated in S105.
Tnext ′ = Tnext + Δsmear (Formula 6)
FIG. 9 is a diagram showing the effect of smear when control value correction is performed. The BV value is a value when the lens having the correction value shown in FIG. 6 is attached.

  As shown in FIG. 9, by increasing the accumulation time by the control correction value Δsmear, that is, by increasing the target value of the sensor (increasing the target value), the effect of smear on the sensor output is reduced and actual photometry is performed. The difference between the value and the ideal photometric value is reduced. For example, in the case of Tnext = 13, if the control value is not corrected, the smear amount s = 97 with respect to the target value y = 1000. By doing so, the relative ratio of the smear amount to the target value becomes small.

  Further, since the control correction value Δsmear increases as the smear effect increases, the control correction value Δsmear increases and the sensor target value increases as the smear effect increases.

  In step S107, the AECPU 112 performs photometry using the next control value (next accumulation time Tnext or next accumulation time Tnext ') determined in step S103 or step S106. Then, it returns to step S102 and repeats said step S102-S107.

  When control value correction is performed, both the storage time Tnext before correction and the storage time Tnext ′ after correction are stored in the memory 113. In the next step S102, the photometric value BVij may be calculated using the accumulation time Tnext 'stored in the memory 113 as P. Further, in the next steps S104 and S105, new Tnext and Δsmear may be calculated using the accumulation time Tnext stored in the memory 113 as T.

  When shooting, exposure control is performed by calculating the aperture value, shutter speed, shooting sensitivity, and the like by the camera microcomputer 101 or the AECPU 112 based on the photometric value calculated before shooting.

  As described above, by setting the target value of the average output of the AE sensor 108 at a higher level than at the normal time when the luminance is high, it is possible to reduce the effect of smear on the output of the AE sensor 108, and to perform exposure control that reduces the effect of smear. It can be carried out.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  For example, in the above-described embodiment, the control value P of the AE sensor 108 is set to the accumulation time T, but a value based on factors such as the number of added pixels and gain in addition to the accumulation time may be used as the control value.

  Further, if the control value P = accumulation time T, the smaller the accumulation time T, the greater the effect of smear. Therefore, the control value correction is performed when the control value P is smaller than the threshold value, but depending on the definition of the control value It can be considered that the larger the control value, the greater the effect of smear. In such a case, the control value correction may be performed when the control value is equal to or greater than the threshold value. That is, if the control value does not exceed the predetermined range, the control value is not corrected. If the control value exceeds the predetermined range, the target value is increased (the target value is increased). That's fine. The target value may be increased (the target value is increased) as the control value is far from the predetermined range.

DESCRIPTION OF SYMBOLS 100 Camera 101 Camera microcomputer 103 Image pick-up element 108 Photometric sensor 112 AECPU

Claims (7)

Photometric means for photoelectrically converting a subject image to accumulate charges and outputting a signal corresponding to the accumulated charges;
Setting means for setting a control value for controlling the photometric means so that the value of the signal output by the photometric means becomes a target value;
Calculating means for calculating a photometric value based on a signal output by the photometric means;
Exposure control means for performing exposure control based on the photometric value calculated by the calculation means,
The setting device increases the target value when the control value exceeds a predetermined range where smear does not affect the photometric value . The setting means calculates the control value based on the photometric value calculated by the calculation means,
When the calculated control value exceeds the predetermined range, the target value is increased and the calculated control value is corrected so that the value of the signal output from the photometry means becomes the increased target value. The imaging apparatus according to claim 1.   The imaging apparatus according to claim 1, wherein the setting unit increases the target value as the control value is far from a predetermined range.   The imaging apparatus according to claim 1, wherein the control value is at least one of an accumulation time, a pixel addition number, and a gain of the photometry unit.   The setting means sets the control value such that an average value obtained by weighting and averaging each of signals output from a plurality of photometry areas of the photometry means becomes the target value. Item 5. The imaging device according to any one of Items 1 to 4.   The said setting means sets the said control value so that the average value of the signal output from the several photometry area | region of the said photometry means may become the said target value, The any one of Claim 1 thru | or 4 characterized by the above-mentioned. The imaging device described in 1. A method for controlling an imaging apparatus having photometric means for photoelectrically converting a subject image to accumulate charges and outputting a signal corresponding to the accumulated charges,
A setting step for setting a control value for controlling the photometric means so that the value of the signal output by the photometric means becomes a target value;
A calculation step of calculating a photometric value based on a signal output by the photometric means;
An exposure control step for performing exposure control based on the photometric value calculated in the calculation step,
The method of controlling an image pickup apparatus, wherein the setting step increases the target value when the control value exceeds a predetermined range where smear does not affect the photometric value .

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