JP2012204952A - Exposure control apparatus, and camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure control apparatus and a camera capable of suitably performing exposure.SOLUTION: This exposure control apparatus 105 includes a luminance value acquiring part 105a for acquiring a luminance difference deltaBv between the maximum luminance value BvMax and the minimum luminance value BvMin of an object, a bracket amount calculating part 105b for finding a bracket amount HDRBKT in accordance with the luminance difference deltaBv between the maximum luminance value BvMax and the minimum luminance value BvMin when performing bracket photographing, a first exposure value calculating part 105c for determining an automatic exposure value EvAuto automatically found as proper exposure when photographing the object, and a second exposure value calculating part 105d for finding an overside exposure value EvAuto-ExCompPlus when performing overside photographing and an underside exposure value EvAuto+ExCompMinus when performing underside photographing by the maximum luminance value BvMax, the minimum luminance value BvMin, the bracket amount HDRBKT, and the automatic exposure value EvAuto.

Description

  The present invention relates to an exposure control device and a camera.

  When photographing a subject, if the luminance range of the subject exceeds the output dynamic range of the image sensor, whiteout or blackout occurs, and the image quality deteriorates. For this reason, bracket photography is performed, a captured image with a large exposure amount and a captured image with a small exposure amount are acquired, and a high dynamic range (HDR) is obtained by combining these images. . Conventionally, a technique for automatically performing this bracket photography has also been disclosed (see, for example, Patent Document 1).

JP 2008-104209 A

  However, the conventional technique takes time to determine the HDR exposure process while changing the actual exposure conditions several times. The patent document describes that the time can be shortened by estimating the brightness difference from the cumulative histogram and determining the exposure, but this lacks the accuracy of the HDR bracket.

  The subject of this invention is providing the exposure control apparatus and camera which can perform exposure suitably.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected and demonstrated, it is not limited to this.

According to the first aspect of the present invention, the luminance value acquisition unit (105a) for acquiring the maximum luminance value (BvMax) and the minimum luminance value (BvMin) of the subject, and the bracket amount (HDRBKT) when performing bracket shooting, A bracket amount calculation unit (105b) obtained according to a luminance difference (deltaBv) between the maximum luminance value (BvMax) and the minimum luminance value (BvMin), and automatic exposure automatically obtained as appropriate exposure when the subject is photographed A first exposure value calculation unit (105c) for determining a value (EvAuto), an over-side exposure value (EvAuto-ExCompPlus) when performing the bracket-side over-shooting, and an under-side exposure value (EvAuto + ExCompMinus) during under-shooting ) For the maximum luminance value (BvMax) and the minimum luminance value (B Min), which is the bracket amount (HDRBKT) and said automatic exposure value (comprise second exposure value calculation section for obtaining from EvAuto) and (105d), the exposure control device according to claim (105).
The invention according to claim 2 is the exposure control device (105) according to claim 1, wherein the maximum brightness value (BvMax) and the automatic exposure value (EvAuto) with respect to the brightness difference (deltaBv). An exposure control device (105) characterized in that a difference ratio is equal to a difference ratio between the over-exposure value (EvAuto-ExCompPlus) and the automatic exposure value (EvAuto) with respect to the bracket amount (HDRBKT). ).
According to a third aspect of the present invention, an over-side image is obtained with the exposure control device (105) according to the first or second aspect and an over-side exposure value (EvAuto-ExCompPlus) determined by the exposure control device (105). An imaging unit (104) that captures an image of the under side with the under side exposure value (EvAuto + ExCompMinus), and an image composition unit (105e) that combines the over side image and the under side image to obtain a high dynamic image. A camera (100) characterized by comprising:
According to a fourth aspect of the present invention, in the camera according to the third aspect, the luminance value acquisition unit is configured to detect a maximum luminance value (BvMax) and a minimum luminance of the subject from an image captured by the imaging unit. The camera is characterized by obtaining a value (BvMin).
The invention according to claim 5 is the camera (100) according to claim 3, wherein the luminance value acquisition unit (105a) is imaged by an imaging unit (112) different from the imaging unit (104). The camera (100) is characterized in that a maximum luminance value (BvMax) and a minimum luminance value (BvMin) of the subject are obtained from a captured image.
A sixth aspect of the present invention is the camera (100) according to any one of the third to fifth aspects, wherein the imaging unit (104) has a shutter speed at the time of imaging and an ISO sensitivity at the time of imaging. The camera (100) is characterized in that an exposure value is changed to capture the over-side image and the under-side image by changing at least one of them.
A seventh aspect of the present invention is the camera according to the sixth aspect of the invention, further comprising a scene determination unit that determines a shooting scene, and the imaging unit is a shutter at the time of imaging according to the determined shooting scene. The camera is characterized by selecting speed, ISO sensitivity at the time of imaging, or changing both shutter speed and ISO sensitivity.
Note that the configuration described with reference numerals may be modified as appropriate, and at least a part of the configuration may be replaced with another component.

  ADVANTAGE OF THE INVENTION According to this invention, the exposure control apparatus and camera which can perform exposure suitably can be provided.

It is a block diagram which shows the camera of one Embodiment of this invention. It is a flowchart at the time of obtaining an HDR image. The second image pickup unit is schematically shown. 3 schematically shows a state in which a subject image is formed on the second imaging unit. It is a flowchart explaining step S104 of FIG. 2 in detail. It is a graph which shows the relationship between a luminance difference and the bracket amount of HDR.

  FIG. 1 is a block diagram showing a camera 100 according to an embodiment of the present invention. In the present embodiment, a single-lens reflex camera 100 including a camera body 100a and a lens barrel 100b that is detachably attached to the camera body 100a will be described.

  The lens barrel 100b includes a plurality of lens groups on which subject light is incident, but is represented by a single lens 102 in FIG.

  The camera body 100 a includes a mirror 110, a display unit 103, a prism 108, an eyepiece unit 109, and a photometric unit 130. The camera body 100 a further includes a shutter 111, a first imaging unit 104, a control unit 105, a monitor 107, a memory card slot 106, and an operation unit 101. Hereinafter, each part will be described.

  The mirror 110 is a rotatable quick return mirror, is provided at a position where light from the lens 102 is incident, and causes subject light to be incident on the display unit 103, the photometric unit 130, or the shutter 6 or the imaging unit 7.

  The display unit 103 is, for example, a polymer dispersed liquid crystal, and is disposed above the mirror 110. The subject light reflected by the mirror 110 is projected onto the display unit 103 to form a subject image. The display provided on the display unit 103 is superimposed on the light guided by the mirror 110 through the lens 102. The light superimposed with this display is guided to the eyepiece 109 by the prism 108, and the photographer can observe the subject image. The subject image projected on the display unit 103 is also guided to the photometric unit 130 by the pentaprism 108.

The photometric unit 130 includes a photometric lens 113 and a second imaging unit 112.
The second imaging unit 112 is an image sensor including a plurality of pixels such as a CMOS and a CCD. The image picked up by the second image pickup unit 112 is sent to the control unit 105, and based on this image, the control unit 105 performs known automatic exposure and determines the exposure.

The shutter 111 is disposed behind the mirror 110. Subject light is incident on the shutter 111 when the mirror 110 is rotated upward and becomes ready for photographing.
The shutter 111 includes a plurality of shutter blades (not shown). The shutter 111 opens and closes shutter blades according to a shooting instruction by a release button or the like, and makes subject light enter the first imaging unit 104.

  The first imaging unit 104 is an image sensor such as a CMOS or CCD. During imaging, the mirror 110 is raised, the shutter 111 is opened, and the subject image formed by the lens 102 is captured with the exposure determined by the control unit 105. The image signal obtained by the imaging is output to the control unit 105.

The control unit 105 includes a CPU, a memory, and other peripheral circuits, and controls the camera 100.
The control unit 105 generates image data in a predetermined image format, for example, JPEG format (hereinafter, main image data) based on the image signal input from the first imaging unit 104. Further, the control unit 105 creates display image data, for example, thumbnail image data, based on the generated image data. Then, the control unit 105 generates an image file that includes the generated main image data and thumbnail image data, and further includes header information, and outputs the image file to the memory card slot 106.
Further, the control unit 105 includes a luminance difference calculation unit 105a, a bracket amount calculation unit 105b, a first exposure value calculation unit 105c, a second exposure value calculation unit 105d, and an image composition unit 105e, which will be described later.

  Note that the memory constituting the control unit 105 includes SDRAM and flash memory. The SDRAM is a volatile memory, and is used as a work memory for the CPU to develop a program when the program is executed, and as a buffer memory for temporarily recording data. The flash memory is a non-volatile memory in which data of a program executed by the control unit 105, various parameters read at the time of program execution, and the like are recorded.

  The monitor 107 is a liquid crystal monitor mounted on the back surface of the camera 100, and the monitor 107 displays an image stored in a memory card, a setting menu for setting the camera 100, and the like.

  The operation unit 101 includes input members operated by the user, such as a power switch, a release button, a zoom button, a cross key, an enter button, a play button, and a delete button. In the operation unit 101, it is possible to select whether or not to perform a high dynamic range (HDR), which will be described later, and to select an adaptation amount thereof.

In the present embodiment, it is assumed that both the main image data and the thumbnail image data are image data represented by, for example, an RGB color system.
The memory card slot 106 is a slot for inserting a memory card as a storage medium, and records and records the image file output from the control unit 105 on the memory card.
Further, the memory card slot 106 reads an image file stored in the memory card based on an instruction from the control unit 105.

  The camera 100 of this embodiment operates as follows. The subject light reflected by the mirror 110 through the lens 102 is guided to the display unit 103 and the photometry unit 130. Then, the image captured by the second imaging unit 112 of the photometry unit 130 is sent to the control unit 105. And based on this image, the 1st exposure value calculating part 105c of the control part 105 performs well-known automatic exposure, and determines exposure.

  When shooting is instructed by fully pressing the release switch included in the operation unit 101, the mirror 110 is rotated upward to enter a shooting enabled state, the shutter 111 is opened, and the first imaging unit 104 is illuminated with subject light. Is incident. The subject image picked up by the first image pickup unit 104 is converted into an electrical signal by the control unit 105 and is output to the memory card slot 106 as image information.

Here, when photographing a subject, if the subject has a large luminance difference, the subject's luminance range may exceed the dynamic range of the imaging unit. In this case, whiteout or blackout occurs, and the image quality deteriorates.
For this reason, in the present embodiment, bracket shooting is performed to acquire a captured image with an increased exposure amount and a captured image with a reduced exposure amount, and these images are combined to obtain an HDR image.

FIG. 2 is a flowchart for obtaining an HDR image.
First, in step S <b> 101, a subject image that has passed through the lens 102, the mirror 110, and the display unit 103 is captured by the second imaging unit 112. Then, the captured image is sent to the control unit 105.

  In step S102, the luminance value acquisition unit 105a of the control unit 105 converts the output of the second imaging unit 112 into a luminance value, and detects the maximum luminance value and the minimum luminance value. The detection of the maximum luminance value and the minimum luminance value will be described with reference to FIGS.

FIG. 3 schematically shows the second imaging unit 112. In the present embodiment, the number of pixels 200 of the second imaging unit 112 is 15, and in FIG. 3, each pixel 200 is indexed from 0 to 14. In the following description, each pixel is referred to as a 0th pixel to a 15th pixel.
In the present embodiment, the number of pixels 200 is 15. However, each pixel 200 may further include a plurality of pixels.

FIG. 4 schematically illustrates a state in which a subject image is formed on the second imaging unit 112. As shown in FIG. 4, for example, when a subject image of the sun and a person is formed on the second imaging unit 112, the pixel luminance value of the second imaging unit 112 is maximized at the 0th pixel and is the eighth pixel. The thirteenth pixel is the smallest.
Here, it is assumed that the maximum luminance value in the pixel of the second imaging unit 112 is MaxBv, and the minimum luminance value is MinBv.
Returning to FIG. 2, in step S103, the first exposure value calculation unit 105c of the control unit 105 performs a known automatic exposure. In this automatic exposure, an appropriate automatic exposure value in the subject image of FIG. 4 is determined by setting. Let this automatic exposure value be EvAuto.

In step S104, an exposure value when bracket shooting is performed using the MaxBv, MinBv, and EvAuto is obtained.
FIG. 5 is a flowchart for explaining step S104 in detail.

(Calculation of luminance difference between maximum luminance and minimum luminance)
First, in step S201, the bracket amount calculation unit 105b of the control unit 105 calculates a luminance difference deltaBv between the maximum luminance and the minimum luminance in the screen of the second imaging unit 112.
deltaBv = BvMax−BvMin

(Bracket amount calculation)
In step S202, the bracket amount calculation unit 105b of the control unit 105 obtains a bracket amount for HDR from the obtained luminance difference deltaBv.
FIG. 6 is a graph showing the relationship between the luminance difference and the HDR bracket amount, where the horizontal axis represents the luminance difference deltaBv and the vertical axis represents the HDR bracket amount HDRBKT.
HDRLimit1 shown on the vertical axis in FIG. 6 is the minimum exposure difference during HDR imaging. This HDRLimit 2 is the maximum exposure difference that can be combined with HDR without a sense of incongruity. DeltaBvTh1 and deltaBvTh2 on the horizontal axis in FIG. 6 are values obtained in advance through experiments or the like.

As shown,
(1) When the luminance difference is equal to or less than deltaBvTh1, the bracket amount is constant at HDRLimit1. Here, HDRLimit1 may be set to 0 because it is the minimum exposure difference during HDR shooting. This is because the difference in brightness is small and the necessity for bracketing is low.
(2) When the luminance difference is greater than or equal to deltaBvTh2, the bracket amount is constant at HDRLimit2. This is because if the bracket amount is increased further, an unnatural image is obtained.

In other words, when expressed in mathematical formulas:
deltaBv ≦ deltaBvTh1 → HDRBKT = HDRLimit1
deltaBv ≧ deltaBvTh2 → HDRBKT = HDRLimit2

(3) In other ranges, the bracket amount changes linearly according to the luminance difference and satisfies the following expression.
HDRBKT =
{(HDRLimit2-HDRLimit1) * dBv + (HDRLimit1 * deltaBvTh2-HDRLimit2 * deltaBvTh1)}
/ (DeltaBvTh2-deltaBvTh1)

In step S203, the second exposure value calculation unit 105d of the control unit 105 calculates an exposure correction value ExCompPlus for the automatic exposure value EvAuto obtained by automatic exposure in order to obtain an overexposed image from the bracket amount obtained in step S202. .
This exposure correction amount is calculated by the following equation.
ExCompPlus = HDRBKT × (MaxBv−EvAuto) / deltaBv

In step S204, in order to obtain an underexposed image from the bracket amount obtained in step S202, a correction value ExCompMinus for the automatic exposure value EvAuto obtained by automatic exposure is calculated.
This correction amount is calculated by the following equation.
ExCompMinus = HDRBKT × (EvAuto−MinBv) / deltaBv

Alternatively, the exposure correction value ExCompMinus for obtaining an underexposed image may be calculated from the BKT amount HDRBKT as follows.
ExCompMinus = HDRBKT-ExCompPlus

As described above, an exposure correction value for photographing two images having an exposure difference for creating an HDR image is obtained.
As a result, in the actual imaging operation, the exposure correction is added to EvAuto calculated by a known automatic exposure. The exposure for taking an under image is EvAuto + ExCompMinus, and the exposure for taking an over image is EvAuto-ExCompPlus.

Returning to the flowchart of FIG. 2, the release operation is determined in step S105.
When the release is performed in step S105, a bracket (BKT) imaging operation is performed by the first imaging unit in step S106.
The BKT imaging operation is to perform imaging twice continuously. In the first imaging, an under image is captured with the exposure value EvAuto + ExCompMinus, and in the second imaging, an over image is captured with the exposure value EvAuto-ExCompPlus. Or vice versa.
Note that when performing the imaging operation twice in succession, a mechanical shutter or an electronic shutter may be used.

Here, the imaging unit changes the exposure value by changing at least one of the shutter speed at the time of imaging and the ISO sensitivity at the time of imaging, and images the over side image and the under side image.
Through the above processing, two images with an exposure difference are obtained. In step S107, the image composition unit 105e of the control unit 105 combines the two images to obtain a high dynamic range image.

  As described above, according to the present embodiment, the difference between the maximum luminance value and the automatic exposure value of the subject, the ratio of the difference between the automatic exposure value and the minimum luminance value, and the difference between the HDR over-side exposure value and the automatic exposure value. And the ratio of the difference between the automatic exposure value and the under exposure value. As a result, when the difference between the maximum brightness value and the automatic exposure value is larger than the difference between the minimum brightness value and the automatic exposure value and the degree of white stripes is likely to increase, the white exposure difference is allocated to ExCompMinus. Tobi can be suppressed.

Conversely, if the difference between the minimum brightness and the automatic exposure is larger than the difference between the maximum brightness and the automatic exposure and the level of blackout is likely to increase, the black exposure is suppressed by assigning more HDR exposure differences to ExCompPlus. I can do it.
Therefore, according to the present embodiment, it is possible to determine the optimum HDR exposure.

(Deformation)
The present invention is not limited to the above-described embodiment, and various modifications and changes as described below are possible, and these are also within the scope of the present invention.
(1) In the present embodiment, use with a camera generally called a single lens reflex has been described. However, a compact digital camera or a mobile phone with a camera function may be used as long as the minimum luminance and the maximum luminance in the screen can be detected.
In the above-described embodiment, since a single-lens reflex camera is used, the first imaging unit 104 that captures the subject image and the second imaging unit 112 that obtains the luminance of the subject are used. However, the present invention is not limited to this. For example, in the case of a compact camera or the like, the imaging unit that captures the subject image and the imaging unit for obtaining the luminance of the subject may be the same.
(2) In addition, the camera may include a scene determination unit that determines a shooting scene. In this case, the imaging unit determines the shutter speed at the time of imaging, the ISO sensitivity at the time of imaging, or the It may be selected whether to change both the shutter speed and the ISO sensitivity.
In addition, although embodiment and a deformation | transformation form can also be used in combination as appropriate, detailed description is abbreviate | omitted. Further, the present invention is not limited to the embodiment described above.

  100: camera, 105: control unit, 105a: luminance value acquisition unit, 105b: bracket amount calculation unit, 105c: first exposure value calculation unit, 105d: second exposure value calculation unit, 105e: image composition unit, BvMax: maximum Luminance value, BvMin: Minimum luminance value, deltaBv: Luminance difference, HDRBKT: Bracket amount, EvAuto: Automatic exposure value, EvAuto-ExCompPlus: Over side exposure value, Under side exposure value: EvAuto + ExCompMinus

Claims (7)

A luminance value acquisition unit for acquiring the maximum luminance value and the minimum luminance value of the subject;
A bracket amount calculation unit for obtaining a bracket amount when performing bracket shooting according to a luminance difference between the maximum luminance value and the minimum luminance value;
A first exposure value calculation unit that determines an automatic exposure value that is automatically obtained as an appropriate exposure when shooting the subject;
The second exposure obtained from the maximum brightness value, the minimum brightness value, the bracket amount, and the automatic exposure value for the over-side exposure value during over-shooting of the bracket shooting and the under-side exposure value during under-shooting. A value calculation unit,
An exposure control device characterized by. The exposure control device according to claim 1,
A ratio of the difference between the maximum brightness value and the automatic exposure value to the brightness difference;
The ratio of the difference between the over-side exposure value and the automatic exposure value to the bracket amount is equal;
An exposure control device characterized by. An exposure control device according to claim 1 or 2,
An imaging unit that captures an over-side image with an over-side exposure value determined by the exposure control device, and that captures an under-side image with the under-side exposure value;
An image composition unit that combines the over image and the under image to obtain a high dynamic image,
Camera characterized by. The camera according to claim 3,
The luminance value acquisition unit acquires a maximum luminance value and a minimum luminance value of the subject from an image captured by the imaging unit;
Camera characterized by. The camera according to claim 3,
The luminance value acquisition unit acquires a maximum luminance value and a minimum luminance value of the subject from an image captured by an imaging unit different from the imaging unit;
Camera characterized by. The camera according to any one of claims 3 to 5,
The imaging unit changes the exposure value by changing at least one of the shutter speed at the time of imaging and the ISO sensitivity at the time of imaging, and captures the over-side image and the under-side image;
Camera characterized by. The camera according to claim 6,
A scene determination unit for determining a shooting scene;
The imaging unit selects whether to change the shutter speed at the time of imaging, the ISO sensitivity at the time of imaging, or both the shutter speed and the ISO sensitivity according to the determined shooting scene,
Camera characterized by.

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