JP4731845B2 - Imaging apparatus and control method thereof - Google Patents

Description

The present invention relates to an imaging apparatus and an imaging method , and particularly relates to exposure control.

  A shooting mode preset by a CPU (central processing unit) installed in the camera (for example, an aperture priority shooting mode in which exposure control is performed with priority given to the aperture set by the operator, or a shutter speed set by the operator). There is provided a camera in which the exposure amount is automatically determined according to the shutter speed priority shooting mode that performs exposure control with priority and the portrait mode that performs exposure control suitable for shooting a person). ing.

  Also provided is a camera with an exposure compensation function that allows the operator to set an arbitrary exposure compensation by operating an exposure compensation setting dial or switch for the appropriate exposure value automatically calculated from the obtained luminance signal. Has been.

  Some electronic cameras using a photoelectric conversion element that converts light such as a CCD or CMOS into an electric signal as an image sensor also serve as the photometric sensor for measuring the luminance of a subject.

  Data such as the luminance signal, color signal, and sharpness of the subject is extracted from the output of the image sensor. Based on these data, automatic exposure control (hereinafter referred to as AE), white balance control (hereinafter referred to as AWB) and auto Focus control (hereinafter referred to as AF) is performed.

  The output of the image sensor is processed as an image signal, and is displayed as an image that can be visually recognized by an operator using an electronic viewfinder (hereinafter referred to as EVF) such as an LCD (see, for example, Patent Document 1).

By displaying an image subjected to exposure control on the output of the image sensor at the time of actual photographing on the EVF, it is possible to estimate whether the exposure state of the image obtained at the time of actual photographing is good or bad.

  In the automatic exposure control, first, the image sensor is exposed in a state in which the exposure control is performed in accordance with an already set aperture value (hereinafter referred to as Av) and shutter speed value (hereinafter referred to as Tv). The output of the image sensor is amplified by an imaging sensitivity value (hereinafter referred to as Sv) determined by controlling the gain that has been set, and input to the image processing apparatus. The CPU takes in the luminance signal of the image extracted by the image processing apparatus, compares it with the appropriate signal level that is the reference value, and sets the exposure value again by reflecting the difference in the currently set exposure value.

  Hereinafter, an example of an automatic exposure control and exposure correction method in a conventional camera will be described with reference to the flowchart of FIG.

  First, when the exposure correction control mode is entered in step S200, the EVF display update is stopped so that the image from the image sensor is not updated to EVF.

  Next, the process proceeds to step S201, and in order to start photometry, since +2 steps of exposure correction are currently set, the exposure correction value is set to 0 and appropriate exposure is set. At this time, although the exposure condition of the image sensor changes, since the update of the EVF display is stopped in step S200, the brightness change is not recognized by the operator.

  In step S202, the image sensor is exposed under the exposure condition where the exposure correction is zero. In step S205, when the exposure is completed, the image signal is read from the image sensor, and in step S206, the luminance of the subject is detected by the image signal processing circuit. A signal is extracted and its luminance value is obtained. Then, a difference between the obtained luminance value and a luminance value at which the luminance signal of the subject is appropriate is calculated.

In step S207, the brightness difference is converted into an exposure difference, and it is determined whether the exposure difference is within an appropriate range. If it is not within the appropriate range, the process proceeds to step S208, exposure is changed based on the exposure difference, and exposure for photometry is performed again in step S202.

If it is within the appropriate range, the process proceeds to step S203, the exposure value is added to the exposure value at this time, the exposure value is changed, and the image obtained from the image sensor is updated to EVF in step S204. Thus, the EVF display update is restarted, and photometry and exposure control are repeated until an interrupt operation such as release is entered.

  In the conventional example, assuming that the exposure correction setting is +2 steps, the initial exposure value is Ev8, the proper exposure value after exposure correction is Ev10, and the proper exposure value of the subject is Ev15, the target exposure value reflecting the exposure correction Becomes Ev13.

  FIG. 7 shows the relationship between the exposure of the image sensor, the reading of the image signal from the image sensor, the photometry calculation, the exposure control, and the EVF display when the operation based on the flowchart is performed. FIG. 8 shows the state of convergence. The alphabetical characters in the figure indicate the order of image signals exposed by the image sensor.

  As shown in FIG. 7, in the EVF display update stop period, the exposure exposure of 14 times from exposure b to o is not displayed on the EVF, and only the exposure exposure of a remains displayed. For example, in the case of a frame rate of 30 frames per second, one exposure and readout period is 1/30 second, and in the example of FIG. 7, 14 × (1/30) ≈0.47 (seconds). Become.

  Further, as shown in FIG. 8, Ev8 at the start of control is displayed in EVF, but EVF is not updated as described above, and the next display is the final exposure value Ev13 and the brightness changes abruptly. End up.

  As described above, when metering is performed with appropriate exposure, the EVF display screen is not updated until the image reflecting the exposure correction value from the start of control to the end of control is displayed during the metering period. Since the brightness of the display screen changes, there is a drawback that the operator feels uncomfortable.

  Even if the display is updated every time in FIG. 8, the control is started with the corrected exposure value Ev8, and the target value is Ev13. Although the value finally converges at p, assuming that the display is updated every time from a, the exposure correction setting is +2 steps, so finally, from n which is Ev15, p which is Ev13 which is the target value It is necessary to correct the exposure until the display is once darkened and brightened.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an EVF display that avoids a sudden luminance change of the EVF display and does not give the operator a sense of incongruity.

In order to solve the above-described problems and achieve the object, an imaging apparatus according to the present invention includes an imaging unit that captures an image of a subject and acquires an image signal, and brightness of the subject based on the image signal acquired by the imaging unit. A photometric means for measuring a value, an exposure control means for performing exposure control so that an exposure value based on a luminance value measured by the photometric means becomes a target exposure value, and an exposure correction value for changing the target exposure value Exposure correction means for setting and display means for displaying and updating an image based on the image signal acquired by the imaging means at a predetermined interval, and the exposure control means when acquiring said imaging means an image signal is use to measure the brightness values, the exposure compensation line exposure control without considering the value Utotomoni, the measurement of the luminance value of the subject by the light measuring means An image signal not when the imaging unit is acquired, have the line exposure control going stepwise converging the exposure value on the target exposure value the exposure correction value is taken into account, the display means, the metering An image based on an image signal used for measuring the luminance value of the subject by means is not displayed.

In order to solve the above-described problems and achieve the object, a control method for an imaging apparatus according to the present invention includes an imaging step of capturing an image of a subject and acquiring an image signal , and the image signal acquired in the imaging step A photometric step for measuring the luminance value of the subject, an exposure control step for performing exposure control so that an exposure value based on the luminance value measured in the photometric step becomes a target exposure value, and for changing the target exposure value An exposure correction step for setting an exposure correction value, and a display step for updating and displaying an image based on the image signal acquired in the imaging step at a predetermined interval. In the exposure control step, the photometry step when obtaining an image signal is use to measure the brightness value of the subject in the imaging step, the exposure correction value line exposure control without considering the Utotomoni, measurement of the luminance value of the object in the photometric process Not used for When obtaining an image signal by the image pickup step, it has rows exposure control going stepwise converging the exposure value on the target exposure value the exposure correction value is taken into account, in the display step, the metering step Thus, an image based on an image signal used for measuring the luminance value of the subject is not displayed.

  According to the present invention, the display update of EVF is stopped only at the time of metering, and the result obtained by adding exposure correction to the appropriate exposure is displayed step by step on the EVF, thereby rapidly changing the brightness of the display image. Can be prevented.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

(First embodiment)
FIG. 5 is a block diagram of a camera embodying the present invention.

  In the figure, 100 is a lens, 101 is a control motor for driving the lens, 102 is a motor driver for the lens, 103 is an aperture, 104 is a motor for control for driving the aperture, 105 is its motor driver, and 106 is An electronic shutter driving circuit that controls the accumulation time of charge that is photoelectrically converted by the imaging device, 107 is an imaging device that photoelectrically converts incident light, and 108 is a signal amplification circuit such as AGC that changes the gain of a signal output from the imaging device. , 109 is an image signal processing circuit, 110 is an image output device such as EVF or video output for displaying an image processed in the signal processing circuit, and 111 is a CPU for performing arithmetic processing.

  In the above configuration, the optical signal that has passed through the lens group is converted into an electrical signal by the image sensor, and is input to the image signal processing circuit via the signal amplification circuit. At this time, the image signal processing circuit outputs the image signal to the image output device and extracts data such as the luminance signal, color signal, and sharpness of the image signal at this time. AWB and AF are performed.

  Next, exposure control is performed from the CPU.

  First, the diaphragm is controlled, and the CPU 104 drives the motor driver 105 by Av to drive the motor 104 to perform opening / closing control of the diaphragm 103.

  The electronic shutter speed is controlled by controlling the amount of charge accumulated in the image sensor 107 by controlling the electronic shutter driving circuit from the CPU by Tv.

  Gain of signal amplification is performed by amplifying a signal from the image sensor by controlling the signal amplification circuit 108 from the CPU by Sv.

  In order to perform AE, a luminance level signal indicating the luminance signal level at that time is extracted from a signal input to the signal processing circuit, and is input to the CPU, and photometric calculation is performed based on this signal to perform subject luminance (hereinafter referred to as Bv). 4), and Av, Tv, and Gain are obtained from a program diagram such as FIG. 4 showing the relationship between Bv, Sv, Av, Tv, and Gain. This is done by controlling the speed and gain.

  The signal from the image sensor subjected to exposure control in this way is processed into a video signal by a signal processing circuit and output to an image output device such as an electronic viewfinder or a video output.

  At this time, in this embodiment, as in the conventional example, the case where the exposure correction setting is +2 steps, the initial exposure value is Ev8, and the appropriate exposure value of the subject is Ev15 will be described.

  FIG. 1 shows a flowchart according to an embodiment of the present invention.

An embodiment of the present invention will be described using this flowchart. Before entering this flowchart, it is assumed that the exposure control is performed with the exposure value reflecting the exposure correction value, and is a state of CCD exposure a in FIG.

First, at step S100, it does not update the image from an imaging element on the EVF as to stop the EVF display update.

Next, in order to start photometry in step S101, since +2 steps of exposure correction are currently set, the exposure correction value is set to 0 and appropriate exposure is set. This state corresponds to the state b of CCD exposure in FIG. At this time, although not described in the flowchart, reading of the signal from the CCD is started immediately before the CCD exposure b state is entered, and the read signal is subjected to image processing and displayed on the EVF. This is the state of CCD readout a and EVF display a, and the CCD signal read out at this time is an exposure state image in which exposure correction is reflected and is displayed on the EVF. That is, in the state of CCD exposure b, the EVF display is in the state a. Further, since step S100 and step S101 are performed in parallel, the display update of the image displayed in the EVF state in the CCD exposure state c is stopped, and the EVF display is in the state a.

At this time, in the CCD exposure b state, the exposure conditions of the image sensor change from the CCD exposure a state, but since the update of the EVF display is stopped in step S100, the brightness change is not recognized by the operator.

In step S102, the image sensor is exposed under the exposure condition where the exposure correction is zero , that is, in the state of CCD exposure b. When the exposure is completed, the exposure correction value is added to the current exposure value in step S103. It performs exposure changes Te (state of c of the CCD exposure), to update the image from the imaging device at step 104 the EVF, EVF display update resumes. Since the EVF display update is restarted, the brightness of the image displayed on the EVF in the CCD exposure d state is the same as the exposure value at the time of step S100, so that the brightness does not change. .

In step S103, the image signal exposed for photometry from the image sensor is read in step S105. In step S106, the luminance signal of the subject is extracted by the image signal processing circuit, and the luminance value is obtained. As described above, the signal starts to be read from the CCD immediately before entering the CCD exposure c state. Then, a luminance difference between the obtained luminance value and a luminance value at which the luminance signal of the subject is appropriate is calculated.

In step S107, the brightness difference is converted into an exposure difference, and it is determined whether the exposure difference is within an appropriate range. If it is not within the appropriate range, the process proceeds to step S108, the exposure is changed based on the exposure difference, and the EVF display is updated based on the exposure value in step S109.

If the exposure value reaches the target appropriate exposure value, the process returns to the first step, and the photometry and exposure control are repeated. If not, the exposure is changed until the target appropriate exposure value is reached. Repeat the display update operation.

In this embodiment, the exposure is changed step by step because the digital camera with a high-pixel imaging device has a narrow dynamic range, unlike the silver halide camera using negative film, so the appropriate exposure range is also This is because it is difficult to reach the proper exposure of the subject with a single exposure change . In this case, the target exposure value is set between the current exposure value and the appropriate exposure value, and if the exposure value changes to reach the target exposure value, the photometric calculation is performed. If it is difficult, set the target exposure value again. Further, since the EVF display cycle is sufficiently faster than the processing time of one exposure control, the display is updated in a plurality of times.

  FIG. 2 shows the relationship between the exposure of the image sensor, the reading of the image signal from the image sensor, the photometric calculation, the exposure control, and the EVF display when the operation based on the flowchart of the present embodiment is performed. FIG. 3 shows how automatic exposure control converges. The numbers in the figure indicate the order of image signals exposed by the image sensor.

  As shown in FIG. 2, the EVF display update stop period is only for exposures of b, g, and l, and only the previous exposures remain displayed on the EVF. Similar to the conventional example, in the case of a frame rate of 30 frames per second, for example, one exposure and readout period is 1/30 seconds. In the example of FIG. 2, 3 × (1/30) = 0 .1 (second) is the EVF display update stop period, which is suppressed to about 21% compared to the conventional example. Moreover, the EVF display update stop period is intermittent, and one EVF display update stop period is 0.03 (= 1/30) second, which is the shortest period, which is improved to the extent that the operator does not notice. Yes.

  In addition, as shown in FIG. 3, Ev8 at the start of control is displayed in EVF. In the conventional example, EVF is not updated, and the next display is the final exposure value Ev13, and the brightness changes abruptly. However, in this embodiment, when attention is paid to the photometry before and after a to c, f to h, and k to m, there is no change in the exposure value between them, so that no change in luminance occurs. Moreover, since the state of the image approaching convergence is also reflected in the EVF display, it looks very natural for the operator.

  In the conventional example and the example, in order to simplify the explanation, the feedback gain is set to 1 time, in which the difference between the luminance at the time of photometry and the luminance at the time of appropriateness is set to the exposure change value as it is. However, in reality, exposure devices such as apertures, shutters, and gains often do not have linearity, and subject brightness changes. Therefore, if the gain of feedback is 1, automatic exposure control Hunting sometimes occurs and it is easily assumed that the control does not converge. Therefore, in practice, the feedback gain is reduced to 0.5 times, for example. In this case, in the prior art and the present invention, it means that the time for convergence to the final exposure is extended. In the prior art, the EVF display update stop period is further prolonged. In the invention, since the EVF display update stop period is the shortest period, the operator is not stressed.

It is the flowchart which showed the exposure control method in the Example of this invention. It is a timing chart of the exposure control method in the Example of this invention. It is the figure which showed the transition state of the exposure of the exposure control method in the Example of this invention. It is a program diagram at the time of photometry of the automatic exposure control in the Example of this invention. It is a program diagram in the Example of this invention. It is the flowchart which showed the exposure control method in a prior art example. It is a timing chart of the exposure control method in a prior art example. It is the figure which showed the transition state of the exposure of the exposure control method in a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Lens 101 Control motor which drives a lens 102 Motor driver 103 Diaphragm 104 Control motor which drives a diaphragm 105 Motor driver 106 Electronic shutter drive circuit 107 Image sensor 108 Signal amplification circuit 109 Image signal processing circuit 110 Image output device 111 CPU

Claims (4)

Imaging means for capturing an image of a subject and acquiring an image signal;
Photometric means for measuring the luminance value of the subject based on the image signal acquired by the imaging means;
Exposure control means for performing exposure control so that an exposure value based on the luminance value measured by the photometry means becomes a target exposure value;
Exposure correction means for setting an exposure correction value for changing the target exposure value;
Display means for displaying and updating an image based on the image signal acquired by the imaging means at a predetermined interval;
Said exposure control means, the image signal is use to measure the brightness values of the subject by the photometry means when the imaging means to acquire the row Utotomoni exposure control without consideration of the exposure correction value, the When the imaging unit obtains an image signal that is not used for measuring the luminance value of the subject by the photometric unit, an exposure that gradually converges the exposure value to the target exposure value with the exposure correction value added. control stomach line,
The imaging apparatus according to claim 1, wherein the display means does not display an image based on an image signal used for measuring the luminance value of the subject by the photometry means.   The display means is acquired immediately before an image signal used for measuring the luminance value of the subject by the photometric means, instead of an image based on an image signal used for measuring the luminance value of the subject by the photometric means. The image pickup apparatus according to claim 1, wherein an image based on the image signal is displayed. An imaging process for capturing an image of a subject and obtaining an image signal;
A photometric step of measuring a luminance value of the subject based on the image signal acquired in the imaging step;
An exposure control step of performing exposure control so that an exposure value based on the luminance value measured in the photometry step becomes a target exposure value;
An exposure correction step for setting an exposure correction value for changing the target exposure value;
A display step of displaying and updating an image based on the image signal acquired in the imaging step at a predetermined interval;
Wherein the exposure control step, when obtaining an image signal is use in the imaging process to measure the luminance value of the object in the photometric process, the exposure correction value line exposure control without consideration of Utotomoni, the When acquiring an image signal that is not used for measuring the luminance value of the subject in the photometry step in the imaging step, an exposure that gradually converges the exposure value to the target exposure value in consideration of the exposure correction value. control stomach line,
In the display step, an image based on an image signal used for measuring the luminance value of the subject in the photometry step is not displayed.   In the display step, instead of the image based on the image signal used for measuring the luminance value of the subject in the photometric step, the image is acquired immediately before the image signal used for measuring the luminance value of the subject in the photometric step. The method according to claim 3, wherein an image based on the image signal is displayed.

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