JP2019193314A - Imaging apparatus - Google Patents

Abstract

To perform gain setting of an image.SOLUTION: A camera 100 includes: distance information acquiring means for acquiring information on distance to a subject illuminated with illumination light from an environmental illumination and with illumination light from a flash device; gain setting means for setting gains different for each distance to the subject on the basis of the information on distance to the subjects acquired by the distance information acquiring means; and image generation means for generating images by applying gains set by the gain setting means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an imaging apparatus.

  The following flash photography apparatuses are known. In this strobe photographing device, the light emission amount is controlled so that the brightness of a specific subject existing at a certain distance is appropriate (for example, Patent Document 1).

JP 2009-288657 A

  However, in the conventional strobe shooting device, if an auxiliary light such as a strobe is used at the time of shooting, the subject at the distance that the camera tried to reproduce at the proper exposure will be at the proper exposure, but the subject at the front side will be overexposed. Therefore, there is a problem that the subject on the rear side is underexposed.

  An imaging device according to the present invention is an imaging device that images a first subject and a second subject, and is based on a distance from the imaging device to the first subject and a distance from the imaging device to the second subject. Thus, the first signal of the imaged first subject and the imaged of the imaged first subject so that the difference between the brightness of the first subject and the brightness of the second subject is reduced within a range up to a predetermined upper limit value. A setting unit that sets different gains for the second signal of the second subject, and a signal processing unit that processes the first signal and the second signal according to the gain set by the setting unit. .

  According to the present invention, it is possible to obtain appropriate exposure for subjects with different distances.

It is a block diagram which shows the structure of one Embodiment of a camera. It is a figure which shows the relationship between a to-be-photographed object distance and the brightness at the time of flash photography which shoots by making the illuminating device 200 light-emit. It is a figure which shows the method of the gain control according to the distance to a to-be-photographed object. It is the figure which showed typically the difference in the brightness of the to-be-photographed object before and behind correction | amendment. It is a figure which shows the specific example of the correction method and a picked-up image. It is a figure which shows the specific example at the time of applying a gain correction | amendment to imaging | photography in a regular light illumination environment.

  FIG. 1 is a block diagram illustrating a configuration of an embodiment of a camera according to the present embodiment. The camera 100 includes an imaging device 1 and 2, a polarization separation prism 3, a pupil division filter 4, an objective lens 5, an AF driving unit 6, a position sensor 7, an imaging driving unit 8, and an image processing unit 9. The camera control unit 10, the storage medium 11, the operation member 12, and the display element 13 are provided. The camera 100 is connected to an illumination device 200 that is a flash device that illuminates the subject, for example, a strobe. The lighting device 200 includes a power source 201, a light emission driving unit 202, and a lighting control unit 203. Here, an example in which the lighting device 200 is detachably attached to the camera 100 via a connection unit (not shown) will be described. However, the present invention can also be applied to the case where the camera 100 includes the lighting device 200. is there.

  In the camera 100 according to the present embodiment, the pupil division filter 4 having transmission characteristics whose transmission polarization axes are orthogonal to each other is disposed at the pupil position of the objective lens 5. Each light transmitted through the pupil division filter 4 is separated into two directions by the polarization separation prism 3 and forms images on the imaging devices 1 and 2, respectively. Since the images picked up by the image pickup devices 1 and 2 are transmitted through different pupil regions, if the focal point is deviated, the imaging position is deviated, and the distance information of the object scene is acquired from the deviation amount. Can do.

  The parallax images captured by the two imaging elements 1 and 2 are transmitted to the imaging drive unit 8 and then input to the image processing unit 9. In the image processing unit 9, the input image is subjected to image processing so as to be displayed on the display element 13, and at the same time, an image shift between the two images is detected to calculate a defocus amount of the objective lens 5. Based on the defocus amount, the position of the objective lens 5 is adjusted by the AF driving unit 6 to perform a focusing operation. By detecting the lens position of the objective lens 5 at this time by the position sensor 7, the absolute distance of the focused object can be calculated.

  The camera control unit 10 calculates the distance distribution of the entire screen from the defocus amount with reference to this absolute distance. Then, the camera control unit 10 determines the light emission amount of the illumination device 200 based on the subject distance specified by the calculated distance distribution. The determined light emission amount data is transmitted from the camera control unit 10 to the illumination control unit 203, and the illumination control unit 203 controls the light emission drive unit 202 to emit light.

  FIG. 2 is a diagram illustrating a relationship between the distance to the subject (subject distance) and the brightness at the time of flash photography in which the illumination device 200 emits light to perform photography. Here, it is assumed that four subjects 2a to 2d are arranged on the optical axis of the camera 100 as shown in FIG. Here, for the sake of simplification of description, the case where the entire exposure is based on the strobe light illuminated from the illumination device 200 is considered without considering the influence of the ambient light.

  The amount of strobe light from the illumination device 200 attached to the camera 100 decreases in inverse proportion to the square of the distance from the camera 100. For this reason, as shown in FIG. 2B, when the amount of strobe light is determined so that the subject 2b at the distance X from the camera 100 is properly exposed, the subject 2a at the distance of 0.7X. Since the amount of light is approximately doubled, the exposure is one step over (+1 EV). Since the subject 2c at a distance of 1.4X has a light amount approximately ½ times, the exposure is one step under (-1 EV). Since the subject 2d located at a distance of 2.0X has a light amount that is about 1/4 times, the exposure is two-stage under (-2EV). As a result, as shown in FIG. 2B, in the captured image, the subject becomes darker as the shooting distance increases, and the object at a short distance becomes brighter. For this reason, when photographing people or the like arranged in the depth direction, the brightness of the subject varies depending on the distance from the camera 100.

  Therefore, in the present embodiment, the image processing unit 9 reduces the above-described change in the brightness of the subject by applying different gains according to the distance to the subject during flash photography. Specifically, processing is performed as follows.

  FIG. 3 is a diagram showing a method of gain control (distance-specific gain control) according to the distance to the subject in the present embodiment. FIG. 3A shows the relationship between the amount of strobe light and the subject distance during conventional strobe photography. That is, from FIG. 3A, as described above, when the subject 2b at the distance X is photographed so as to have proper exposure (100%), the amount of light is inversely proportional to the square of the distance. It turns out that it falls.

  FIG. 3B shows the density (vertical axis) of the image and the subject distance (horizontal) generated when the subject 2b at the distance X is photographed with a strobe so that the proper exposure (100%) is obtained. It is a figure which shows the relationship with an axis | shaft. In FIG. 3B, the solid line shows an example of the case where the brightness of the subject differs depending on the conventional gradation before applying the present invention, that is, the subject distance. Here, the density at the time of proper exposure at the distance X is assumed to be a level 128 that is the middle of 8-bit 256 gradations. When the subject distance is 1.4X, the amount of light is ½ of the distance X, so the image density is reproduced as a level 64 that is half of the distance X. When the subject distance is 2X, the amount of light is ¼ of the distance X, so the image density is level 32 which is ¼. However, this is only an example, and changes depending on the tone reproduction characteristics (= gamma setting) of the image.

  Here, if the distance of the subject is known, it is possible to prevent the brightness from varying depending on the distance by changing the gain (amplification magnification) according to the distance. For example, the image density can be corrected to the same level 128 as the image density at the distance X by applying a double gain to the subject at the distance 1.4X. Further, by giving a fourfold gain to the subject at the distance 2X, the image density can be corrected to the same level 128 as the image density at the distance X.

  Specifically, when the setting sensitivity of the camera is ISO400, ISO800 is applied to a subject with a distance of 1.4X, and ISO1600 is applied to a subject with a distance of 2X. It can be corrected. In this example, all exposure is performed with strobe light. However, when exposure is performed with a mixture of steady light, the steady light does not change depending on the distance between the subject and the camera, so only the contribution of the strobe light is considered. Gain adjustment may be performed. For example, when the mixing ratio of the steady light and the strobe light at the distance X is 1: 1 and appropriate, the distance 2X is 1: 1/4, so if the gain is increased by 3/4 of the exposure difference from the distance X, Good. On the other hand, if the entire exposure amount including the steady light is corrected, a long-distance subject is corrected excessively brightly, and a preferable result cannot be obtained.

  The image processing unit 9 thus applies different gains depending on the subject distance, thereby correcting the image density to level 128 at all subject distances as indicated by the dotted line in FIG. As a result, it is possible to reduce a change in brightness according to the subject distance.

  FIG. 4 is a diagram schematically showing the difference in brightness of the subjects 2a to 2d before and after the correction described above. In the image before correction, the brightness of the subjects 2a to 2b is different as shown in FIG. The gradation corresponding to the subject distance in FIG. 4 (a) is shown in FIG. 5 (a), and a specific example of the image taken at that time is shown in FIG. 5 (b). The gradation shown in FIG. 5A is the same as the gradation shown by the solid line in FIG. 3B, and the image example shown in FIG. 5B is the image shown in FIG. Same as example. In FIG. 5B, +1 EV or the like displayed on each subject represents a difference in exposure from the subject 2b at the distance X. The same applies to FIGS. 5D, 5F, and 5H described later.

  On the other hand, in the image after correction, the brightness of the subjects 2a to 2b is the same as shown in FIG. The gradation corresponding to the subject distance in FIG. 4B is shown in FIG. 5C, and a specific example of the image taken at that time is shown in FIG. 5D. Note that the gradation indicated by the dotted line in FIG. 5C is the same as the gradation indicated by the dotted line in FIG. In this case, as shown in FIG. 5D, there is no difference in exposure between the subjects 2a to 2b, and the brightness of all the subjects is the same.

  In the above-described processing, as shown in FIG. 5C, the image processing unit 9 applies a gain according to the distance so that the brightness of the subjects at all the subject distances is constant. However, the change in the brightness of the subject due to the distance may be reduced by applying a gain so as to obtain a gradation as shown in FIG. 5 (e) or FIG. 5 (g). For example, as shown in FIG. 5C, when the exposure amount difference due to the distance is completely corrected, the difference in image brightness due to the distance can be corrected, but the far distance is set to an excessively high sensitivity setting. Noise may be noticeable. In addition, there is a possibility that the feeling of depth is reduced by making the brightness of the entire image uniform. If this is not desirable, correction may be performed as shown in FIGS. 5 (e) and 5 (g).

  The correction method shown in FIG. 5E shows a method in which the distance for performing the brightness correction is limited. As shown in FIG. 5 (e), the correction is performed up to a certain distance in the same manner as in FIG. 5 (c), but the sensitivity setting is not further increased beyond this distance. FIG. 5F shows a specific example of an image obtained as a result of performing gain correction in this way. In this way, if the gain is set for a predetermined distance range and the increase in sensitivity on the far side is limited, the generation of noise can be suppressed. Further, by making the far side slightly darker, a sense of depth can be given to the image. Alternatively, an upper limit sensitivity may be set, correction may be performed up to a distance reaching the sensitivity, and the sensitivity may not be increased beyond the upper limit sensitivity at a distance longer than that. Since the same effect can be obtained by such a method, the photographer may be able to select which is to be prioritized and restricted.

  The correction method shown in FIG. 5G shows a method of correcting the difference in brightness due to distance at a constant rate. Specifically, in order to give a sense of the depth of the subject depending on the distance, the distance difference between the brightnesses is not completely corrected, and the ratio is smaller than the gain that makes the brightness of the subject shown in FIG. 5C constant. The gain is set so as to be corrected. As a result, while maintaining a sense of depth of the subject, it is possible to suppress overexposure and underexposure due to distance, and it is possible to suppress the use of excessively high sensitivity setting at a long distance. FIG. 5H shows a specific example of an image obtained as a result of performing gain correction in this way.

  FIG. 6 is a diagram illustrating a specific example in the case where the gain correction according to the subject distance in the present embodiment is applied to photographing in a steady light illumination environment. FIG. 6A shows a specific example in the case where still image shooting is performed by causing the illumination device 200 to emit light in a steady light illumination environment, and FIG. 6B shows the illumination in the steady light illumination environment. A specific example in which the apparatus 200 emits light to shoot a moving image is shown.

  When still image shooting is performed by causing the lighting device 200 (strobe) to emit light in a constant light illumination environment, as shown in FIG. 6A, the release button is pressed halfway until it is fully pressed (half-pressed). During the period from ON to release ON), constant light is measured. After that, when the shutter release is detected, the flash is pre-flashed, the flash light at that time is metered, the flash output is determined based on the pre-flash photometry result, and the flash is fired. Take a picture.

  On the other hand, when shooting a moving image by causing the lighting device 200 to emit light in a constant light illumination environment, it is necessary to continuously illuminate the lighting device 200 during shooting of a moving image (during recording). However, when photometry is performed while the illumination device 200 emits light in a steady light illumination environment, it is not possible to determine the state and ratio of the ambient light and the illumination light. Therefore, in this embodiment, as shown in FIG. 6B, illumination light is stopped (OFF) for a short time during recording, and ambient light is measured during that time. As a result, the state of steady light can be measured, and an appropriate white balance can be set. In this case, the illumination used as the strobe needs to be capable of blinking at high speed such as an LED.

  If it is determined from the state of the image being recorded that the screen has changed significantly and the ambient light state has changed, the ambient light metering frequency may be increased more than usual to accommodate the change. For example, in FIG. 6B, this is dealt with by increasing the number of times the lighting is stopped only during the period indicated as “illumination state fluctuation”. Thereby, when the illumination state of environmental light changes, the photometry timing of environmental light can be increased and the photometric accuracy of environmental light can be improved. In addition, since the illumination state changes at the ambient light metering timing, the frames taken while the illumination light is turned off to measure ambient light are not left in the recorded image, or are interpolated from the frames before and after that. Therefore, it is necessary to make the influence of the illumination light OFF inconspicuous.

According to the present embodiment described above, the following operational effects can be obtained.
(1) The distance information to the subject illuminated with the illumination light from the illumination device 200 is acquired, and the change in the brightness of the subject according to the distance is reduced based on the acquired distance information to the subject. A different gain is set for each distance to the subject, and an image is generated by applying the set gain. Thereby, a change in the brightness of the subject in the image can be reduced.

(2) As shown in FIG. 5C, a gain corresponding to the distance is applied so that the brightness of the subjects at all the subject distances is constant. Thereby, the brightness of the subject in the image can be made constant.

(3) The gain is set within a range up to a predetermined upper limit value. As a result, the generation of noise can be suppressed by limiting the increase in sensitivity on the long distance side. Further, if the far side is slightly darkened, a sense of depth can be given to the image.

(4) As shown in FIG. 5E, the gain is set within a predetermined distance range. As a result, the generation of noise can be suppressed by limiting the increase in sensitivity on the long distance side. Further, if the far side is slightly darkened, a sense of depth can be given to the image.

(5) As shown in FIG. 5G, the gain is set and corrected so that the ratio becomes smaller than the gain that makes the brightness of the subject constant. Accordingly, it is possible to suppress overexposure / underexposure due to distance while maintaining a sense of depth of the subject, and to suppress use of an excessively high sensitivity setting at a long distance.

(6) When illuminating the subject from the illumination device 200 continuously during moving image shooting, the illumination from the illumination device 200 is stopped at a predetermined timing, and the subject is measured based on the result of photometry while the illumination is stopped. The distance information was acquired. This makes it possible to set the gain according to the distance to the subject with high accuracy even during shooting of a moving image.

(7) When the illumination state of the ambient light changes, the number of times to stop the illumination from the illumination device 200 is changed. Thereby, when the illumination state of environmental light changes, the photometry timing of environmental light can be increased and the photometric accuracy of environmental light can be improved.

-Modification-
The camera according to the above-described embodiment can be modified as follows.
(1) In the example shown in FIG. 6B, the example in which the illumination light is stopped (OFF) for a short time during recording and the ambient light is measured during that time has been described. However, photometry may be continuously performed during recording, and ambient light metering may be performed using only photometry data while illumination light is stopped.

(2) In the above-described embodiment, the example in which gain correction is performed by the method shown in FIGS. 5C, 5E, and 5G has been described. However, you may make it use combining the method shown to FIG.5 (c), (e), (g). For example, as shown in FIG. 5G, correction may be performed at a constant rate, and excessive high sensitivity may be avoided by setting the upper limit sensitivity.

(3) In the above-described embodiment, the example in which the present invention is applied to the camera 100 has been described. However, the present invention can also be applied to other photographing apparatuses including a lighting device.

  Note that the present invention is not limited to the configurations in the above-described embodiments as long as the characteristic functions of the present invention are not impaired. Moreover, it is good also as a structure which combined the above-mentioned embodiment and a some modification.

DESCRIPTION OF SYMBOLS 100 Camera, 1, 2 Image pick-up element, 3 Polarization separation prism, 4 Pupil division filter, 5 Objective lens, 6 AF drive part, 7 Position sensor, 8 Imaging drive part, 9 Image processing part, 10 Camera control part, 11 Storage medium , 12 Operation member, 13 Display element, 200 Illumination device, 201 Power source, 202 Light emission drive unit, 203 Illumination control unit

Claims (1)

An imaging device for imaging a first subject and a second subject,
Based on the distance from the imaging device to the first subject and the distance from the imaging device to the second subject, the brightness of the first subject and the brightness of the second subject in a range up to a predetermined upper limit value. A setting unit that sets different gains for the first signal of the captured first subject and the second signal of the captured second subject, respectively, so that the difference between
A signal processing unit for processing the first signal and the second signal with the gain set by the setting unit;
An imaging apparatus comprising:

Images