JP2020088802A - Imaging apparatus and control method therefor, program, storage medium - Google Patents

Abstract

To provide an imaging apparatus allowing for higher accurate photometric arithmetic operation in a scanning type photometric arithmetic operation.SOLUTION: The imaging apparatus comprises: an imaging part that captures a subject image; an image control part that causes the imaging part to perform photographing at each of a plurality of preset different exposure values, and generates a plurality of photographed images having different exposure; a detection part that detects a halation quantity or quantity of loss of shadow detail in each of the plurality of photographed images; and a calculation part that selects at least two photographed images from among the plurality of photographed images on the basis of the halation quantity or the quantity of loss of shadow detail, and calculates an exposure value at a regular exposure on the basis of the exposure value of the selected photographed image.SELECTED DRAWING: Figure 2

Description

The present invention relates to an exposure control technique in an image pickup apparatus such as a digital camera.

In an imaging device such as a digital camera, as one of methods for determining exposure, a plurality of images are captured with a plurality of preset exposures, and an optimum exposure is obtained based on brightness data of the plurality of images. There is known a scan type exposure determining method for determining.

In this method, a plurality of images are photographed at a plurality of exposure values, and an exposure difference value, which is the difference between the image brightness value and the target brightness value at each exposure value, is obtained. At least two first and second images, the image having the smallest absolute value of the exposure difference value and the image having the second smallest absolute value, are selected from the plurality of images. Then, the exposure value at the time of main exposure is determined based on the exposure value and the exposure difference value of the first image and the exposure value and the exposure difference value of the second image.

For example, Patent Document 1 discloses a scan-type photometric technique for determining the optimum exposure by such a method.

JP, 2002-277918, A

In the above-mentioned Patent Document 1, scan photometry calculation is performed as follows.

The exposure difference values (ΔBv0, ΔBv1, ΔBv2) with respect to the target exposure value are set as follows for each of the three different exposure values from the image data shot with the three different preset exposure values ScanBv0, ScanBv1, and ScanBv2. To calculate.

First, the average luminance value Y(i, j) (i=0 to 23, j=0 to 15) for each 24×16 block obtained by dividing the image data into vertical 24×horizontal 16 blocks is calculated. Then, the exposure difference value is calculated from the average luminance value Y(i, j) for each 24×16 block based on the following arithmetic expression. However, Yref is a target luminance value of the image, and Weight(i,j) is a weighting coefficient for each block.

ΔBv=log ₂ (Σ(Y(i, j)×Weight(i, j))/(ΣWeight(i, j)×Yref))
As a result, the exposure difference values ΔBv0, ΔBv1, and ΔBv2 with respect to the target exposure value are calculated for each of the three image data captured with the three different exposure values ScanBv0, ScanBv1, and ScanBv2.

Here, it is assumed that the absolute value ABS(ΔBv0), ABS(ΔBv1), and ABS(ΔBv2) of ΔBv0, ΔBv1, and ΔBv2 are, for example, ABS(ΔBv0)>ABS(ΔBv1)>ABS(ΔBv2). In this case, the exposure value Bv at the time of the main exposure is calculated using the exposure values ScanBv1 and ScanBv2 and the exposure difference values ΔBv1 and ΔBv2 as in the following formula.

Bv=ScanBv1×ΔBv2/(ΔBv1+ΔBv2)+
ScanBv2×ΔBv1/(ΔBv1+ΔBv2)
In this method, the exposure value (ScanBv1) of the image with the smallest absolute value of the exposure difference value and its exposure difference value (ΔBv1), and the exposure value (ScanBv2) of the image with the second smallest absolute value of the exposure difference value are used. The exposure value Bv during the main exposure is calculated using the exposure difference value (ΔBv2). Specifically, the exposure values ScanBv1 and ScanBv2 are weighted and averaged based on the absolute values of the exposure difference values ΔBv1 and ΔBv2, and the value of the exposure value ScanBv of the image with the smaller exposure difference value ΔBv is emphasized. Is becoming

However, in the case of performing the scan photometric calculation as in the above-described conventional technique, the accuracy of the scan photometric calculation may decrease depending on the saturation characteristics of the image sensor.

For example, when the exposure value Bv at the time of the main exposure is calculated, the exposure value ScanBv of the image with the smaller exposure difference value ΔBv is more emphasized in the calculation. There are cases where there are many pixels in which “blackout” or “blackout” occurs. Here, "whiteout" and "blackout" are defined as follows. That is, when the brightness value of each pixel of the image is calculated with, for example, a resolution of 8 bits, a pixel having a brightness value of 255 is “blurred” and a pixel having a brightness value of 0 is “black out”. ".

In this case, since the exposure difference value ΔBv is not accurately calculated, even if the exposure difference value ΔBv is small, if the exposure value Bv in the main exposure is calculated by giving more importance to the value of the exposure value ScanBv of the image, In some cases, the exposure value Bv at that time cannot be obtained accurately.

The present invention has been made in view of the above-described problems, and an object thereof is to provide an imaging device capable of performing more accurate photometric calculation in scan-type photometric calculation.

An image pickup apparatus according to the present invention includes an image pickup unit for picking up a subject image, and an image pickup control for causing the image pickup unit to perform image pickup at a plurality of preset different exposure values to generate a plurality of photographed images having different exposures. Means for detecting the amount of blown-out highlights or the amount of blown-out shadows in each of the plurality of picked-up images, and at least two of the plurality of picked-up images are shot based on the amount of blown-out highlights or the amount of blown-out blacks. Calculating means for selecting an image and calculating an exposure value at the time of main exposure based on the exposure value of the selected photographed image.

According to the present invention, it is possible to perform more accurate photometric calculation in scan-type photometric calculation.

FIG. 1 is a block diagram showing a schematic configuration of an image pickup device according to an embodiment of the present invention. 6 is a flowchart showing an exposure determining operation according to the embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a schematic configuration of an image pickup apparatus 100 according to an embodiment of the present invention.

In FIG. 1, a photographing optical system 101 collects incident light and forms a subject image. The mechanical shutter 102 opens and closes the optical path of the photographing optical system 101 and controls the exposure time of the image sensor 103. The image pickup element 103 photoelectrically converts the subject image formed by the photographing optical system 101 and outputs an analog image signal. The CDS circuit 104 performs analog signal processing on the image signal. The A/D converter 105 converts an analog image signal into a digital image signal. The timing signal generation circuit 106 generates a signal for operating the CDS circuit 104 and the A/D converter 105. The drive circuit 107 drives the photographing optical system 101, the mechanical shutter 102, and the image sensor 103. The signal processing circuit 108 performs signal processing necessary for image data. The image memory 109 temporarily stores the signal-processed image data. The recording medium 110 is arranged so as to be removable from the imaging device 100 and records image data. The recording circuit 111 performs a process of recording the image data that has been subjected to signal processing on the recording medium 110. The image display device 112 displays the image data subjected to signal processing. The display circuit 113 drives the image display device 112 to display an image. The system control unit 114 controls the entire imaging device 100. The ROM 115 stores a program executed by the system control unit 114 to control the entire imaging device 100. The program stored in the ROM 115 is expanded in the RAM 116 and executed by the system control unit 114. The RAM 116 is also used as a work area of the system control unit 114.

Hereinafter, a shooting operation in the image pickup apparatus 100 configured as described above will be described.

First, the photographing optical system 101 drives the optical system in response to a control signal from the system control unit 114 to form a subject image having an appropriate brightness on the image sensor 103. Next, the mechanical shutter 102 is driven by the control signal from the system control unit 114 so as to shield the image sensor 103 in accordance with the operation of the image sensor 103 so that the required exposure time is obtained. At this time, when the image sensor 103 has an electronic shutter function, it may be used together with the mechanical shutter 102 to secure a necessary exposure time.

The image sensor 103 is driven based on the operation pulse generated by the timing signal generation circuit 106 controlled by the system control unit 114, photoelectrically converts the subject image into an electric signal, and outputs the electric signal as an analog image signal. The clock synchronism noise of the analog image signal output from the image sensor 103 is removed by the CDS circuit 104 based on the operation pulse generated by the timing signal generation circuit 106 controlled by the system control unit 114. Then, it is converted into a digital image signal by the A/D converter 105. The digital image signal output from the A/D converter 105 is subjected to image processing such as color conversion processing, white balance processing, gamma correction processing, resolution conversion processing, and image compression processing in the signal processing circuit 108.

The image memory 109 is used to temporarily store a digital image signal that is being signal-processed or to store image data that is a signal-processed digital image signal. The image data signal-processed by the signal processing circuit 108 and the image data stored in the image memory 109 are converted into data (for example, file system data having a hierarchical structure) suitable for the recording medium 110 in the recording circuit 111 and recorded. It is recorded on the medium 110. Alternatively, after the resolution conversion processing is performed by the signal processing circuit 108, the signal is converted into a signal suitable for the image display device 112 (for example, an analog signal of NTSC system) in the display circuit 113 and displayed on the image display device 112.

Further, a reproducing operation when image data is recorded on the recording medium 110 will be described. The recording circuit 111 reads image data from the recording medium 110 in response to a control signal from the system control unit 114. Similarly, in response to a control signal from the system control unit 114, the signal processing circuit 108 performs image expansion processing when the image data is a compressed image, and stores it in the image memory 109. The image data stored in the image memory 109 is subjected to resolution conversion processing in the signal processing circuit 108, converted into a signal suitable for the image display device 112 in the display circuit 113, and displayed on the image display device 112.

Next, FIG. 2 is a flowchart showing the operation of the exposure control processing in the present embodiment. The exposure control in this embodiment is performed by the system control unit 114 executing a program stored in the ROM 115.

First, in step S201, the system control unit 114 captures (generates) a plurality of image data (captured images) a plurality of times by using a plurality of exposure values preset for scan photometry. The imaging control is performed. When performing scanning photometry using three exposure values, three image data captured with three different exposure values ScanBv0, ScanBv1, ScanBv2 are acquired. The Bv indicating the exposure value is defined by an APEX (ADDITIVE SYSTEM OF PHOTOGRAPHIC EXPOSURE) system.

Next, in step S202, the system control unit 114 controls the signal processing circuit 108 to calculate (detect) a brightness value for each block when each image is divided into blocks. In the present embodiment, an average luminance value Y(i,j) (i=0 to 23, j=0 to 15) is calculated for each block of 24×16 obtained by dividing an image into blocks of 24×16.

In step S203, the system control unit 114, based on the average luminance value Y(i,j) of each 24×16 block obtained in step S202, blows out white or black in a block of 24×16. The ratio (ratio) of the number of existing blocks to the total number of blocks is calculated. That is, the ratios Ratio0, Ratio1, and Ratio2 of the numbers of blocks that are overexposed or blackened are calculated for each of the three image data captured with the exposure values ScanBv0, ScanBv1, and ScanBv2.

Finally, in step S204, the system control unit 114 calculates the exposure value at the time of main exposure based on the three different exposure values ScanBv0, ScanBv1, ScanBv2, and Ratio0, Ratio1, and Ratio2 calculated in step S203.

Specifically, the exposure value Bv at the time of main exposure is calculated as follows. If the magnitude relationship between the ratios Ratio0, Ratio1, and Ratio2 is, for example, Ratio0> Ratio1> Ratio2, the exposure value Bv is calculated using two images in which the ratio of the number of blocks with overexposure or blackout is small. .. That is, the exposure values ScanBv1 and ScanBv2, and the ratios Ratio1 and Ratio2 are used to calculate as in the following equation.

Bv=ScanBv1×Rtio2/(Ratio1+Ratio2)+
ScanBv2×Ratio1/(Ratio1+Ratio2)
In this method, the exposure value (ScanBv1) of the image having the smallest ratio (Ratio) of the number of blocks that are overexposure or underexposure in the 24×16 block and the overexposure or underexposure at that time. The ratio of the number of blocks (Ratio1) is used. At the same time, the exposure value (ScanBv2) of the image having the second smallest ratio of the number of blocks that are overexposed or blackened and the ratio of the number of blocks that are overexposed or blackened (Ratio2) at that time are used. The exposure value Bv at the time of main exposure is calculated using all of these. Specifically, the exposure values ScanBv1 and ScanBv2 are weighted averaged (weighted and averaged) based on the values of the ratios Ratio1 and Ratio2, and the value of the exposure value ScanBv of the image with the smaller ratio Ratio is emphasized more. It is a calculation. In other words, the weighted average is performed based on the reciprocal of the ratio Ratio.

As described above, in the related art, when calculating the exposure value Bv during the main exposure from the two different exposure values ScanBv, the exposure value ScanBv of the image with the smaller exposure difference value ΔBv should be more emphasized. The calculation is done. However, even if the exposure difference value ΔBv is small, if there are many pixels that are blown out or blacked out in the captured image data, the exposure difference value ΔBv itself is likely to be inaccurate. As a result, even if the calculation is performed so that the value of the exposure value ScanBv of the image with the smaller exposure difference value ΔBv is more emphasized, the exposure value Bv at the time of the main exposure will not be accurately calculated as a result.

Therefore, in the present embodiment, when the exposure value Bv at the time of main exposure is calculated from the two different exposure values ScanBv, the exposure of the image with the smaller ratio (Ratio) of the number of blocks that are overexposed or blackened. The calculation is performed so that the value of the value ScanBv is more important. The exposure value ScanBv of an image with a small ratio Ratio is more likely to be accurate as the exposure value. Therefore, the exposure value Bv at the time of main exposure is more likely to be calculated more accurately by performing a calculation that gives more importance to the value of the exposure value ScanBv of the image with the smaller ratio Ratio.

It should be noted that the above-described embodiment is an example, and the present invention is not limited to this. In the present embodiment, the exposure scan is performed using three exposure values, but the number is not limited to three, and any number other than three may be set as long as the number is set to two or more.
Further, when the image is divided into blocks, it is divided into vertical 24×horizontal 16; however, any other number of divisions may be used.

In addition, when the ratio (Ratio) of the number of blocks that are overexposed or blackened in the block of the image data captured with the first exposure value is 0 or the ratio is very small (predetermined (Less than the value), shooting at the second and third exposure values planned may be canceled. In that case, the exposure value Bv at the time of the main exposure is calculated using only the image data captured with the first exposure value.

The exposure value Bv at this time is calculated by the following equation using the exposure difference value ΔBv1 and the exposure value ScanBv1 obtained from the image data captured with the first exposure value.

Bv=ScanBv1+ΔBv1
In this way, the ratio (Ratio) of the number of blocks with whiteout or blackout is 0 or very small among the blocks of the image data captured with the first (first) exposure value. In this case, there is a high possibility that the value of ΔBv obtained from the image data captured with the first exposure value is accurate. Therefore, it is considered that there is no need to mix and use information from two exposure values as in the above-described embodiment. This eliminates the need to capture the second and subsequent (second and subsequent) images, which has the effect of shortening the photometric time.

Further, the exposure value of the image data in which the ratio (Ratio) of the number of blocks with overexposure or blackout is not less than a predetermined value may not be used in the calculation of the exposure value during the main exposure. As a result, it is possible to reduce the calculation error of the exposure value during the main exposure.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof.

(Other embodiments)
The present invention also supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read the program. It can also be realized by executing processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

100: imaging device, 101: photographing optical system, 103: imaging element, 105: A/D converter, 108: signal processing circuit, 114: system control unit

Claims (10)

An image pickup means for picking up a subject image,
Imaging control means for causing the imaging means to perform photography with a plurality of preset different exposure values, respectively, and generating a plurality of photographed images with different exposures;
A detection unit that detects the amount of whiteout or the amount of blackout in each of the plurality of captured images,
At least two captured images are selected from the plurality of captured images based on the whiteout amount or the blackout amount, and the exposure value at the time of main exposure is calculated based on the exposure value of the selected captured images. Calculating means to
An imaging device comprising: 2. The detection unit detects the whiteout amount or blackout amount by dividing the captured image into a plurality of blocks and calculating an average luminance value for each block. Imaging device. The detection means obtains the number of blocks that are whiteout or blackout based on the average luminance value of each block, and the ratio of the number of whiteout or blackened blocks to the number of the plurality of blocks. The image pickup apparatus according to claim 2, wherein is calculated as the amount of whiteout or the amount of blackout. The calculating means calculates the exposure value at the time of the main exposure by weighting and adding the exposure values of the plurality of photographed images and averaging the exposure values based on the ratio of the number of blocks that are whiteout or blackout. The image pickup apparatus according to claim 3, wherein The calculating means weights and adds the exposure values of the plurality of photographed images at a ratio based on the reciprocal of the ratio of the number of blocks that have been blown out or blacked out to obtain the exposure at the time of the main exposure. The imaging device according to claim 4, wherein a value is calculated. In the first captured image, the calculating unit does not capture the second and subsequent images when the ratio of the number of whiteout or blackout blocks is smaller than a predetermined value, and the first captured image The image pickup apparatus according to claim 4, wherein the exposure value at the time of the main exposure is calculated using only the exposure value of. For the photographed image in which the ratio of the number of blocks that are blown out or blackened is a predetermined value or more, the calculating unit does not use the exposure value of the photographed image for calculating the exposure value during the main exposure. The image pickup apparatus according to claim 4 or 5, characterized in that. A method for controlling an image pickup apparatus including an image pickup unit for picking up a subject image, comprising:
An image capturing control step of causing the image capturing unit to perform image capturing with a plurality of different exposure values set in advance, and generating a plurality of captured images with different exposures,
A detection step of detecting the amount of whiteout or the amount of blackout in each of the plurality of captured images;
At least two captured images are selected from the plurality of captured images based on the whiteout amount or the blackout amount, and the exposure value at the time of main exposure is calculated based on the exposure value of the selected captured images. The calculation process to
A method for controlling an imaging device, comprising: A program for causing a computer to execute each step of the control method according to claim 8. A computer-readable storage medium storing a program for causing a computer to execute each step of the control method according to claim 8.

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