JP4891647B2 - camera - Google Patents

Description

  The present invention relates to a camera, and more particularly to a camera capable of obtaining an image subjected to appropriate background processing.

  In the field of digital images, it is widely performed to create one image by combining a plurality of images by image processing. For example, a technique has been proposed in which background processing is combined with background and person photos to make background processing appropriate (Patent Document 1).

There is also a proposal for synthesizing the foreground in-focus image and the distant view in-focus image to generate a focused image for both. For example, in Patent Document 2, when creating a single image by combining the results obtained from images taken at two focal positions, a double outline is generated at the boundary by adjusting the amount of blurring at the boundary. Techniques for preventing this are described.
Japanese Patent Laid-Open No. 11-224324 JP 2002-279401 A

  One of the problems in digital cameras is that the blur effect is difficult to obtain because the size of the image sensor is generally smaller than the size of the film screen of an old film camera in terms of efficiency in semiconductor manufacturing. That is, when the screen size is reduced, the focal length for obtaining the same angle of view is shortened, so that the subject depth is increased. This makes the background less blurry.

  And, when trying to blur the background by the method as in Patent Document 1, there is a problem that it takes time to shoot. In the method as described in Patent Document 2, complicated image processing is required to synthesize two images.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a camera capable of performing photographing with simple depiction and having excellent depictability.

In order to achieve the above object, the camera according to the first invention is focused on the aperture control unit for controlling the aperture position of the photographing optical system and the low-luminance main subject against the background of the night scene, and does not cause the flash to emit light. In the state, a determination unit that determines a change in a plurality of image data obtained by shooting with the aperture position changed, and according to an output result of the determination unit, the changed portion is classified as a light spot portion of the night view And an addition process for the light spot portion of the night scene that has been classified for each image obtained by changing the aperture position, and the strobe image that has been subjected to the addition process for the light spot part of the night scene is captured. And an image processing unit that combines the image that has not been photographed and the image that has been photographed with the flash while the main subject is in focus .

  ADVANTAGE OF THE INVENTION According to this invention, the camera which can be image | photographed excellent in descriptiveness by simple imaging | photography can be provided.

The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
The first embodiment will be described with reference to FIGS. 1 to 5 and FIG. 13. As described above, a digital camera is generally less blurred than a film camera. Therefore, in the first embodiment, background processing is performed so as to produce an effect of raising the main subject from the background. As a result, a beautiful and clear image can be obtained.

  FIG. 1 is an overall block diagram of a camera 1 to which the present invention is applied. The camera 1 includes a lens unit 2, a diaphragm unit 3, an image sensor 4, an image processing unit 5, and a memory 8. The lens unit 2 forms an image of the incident subject 20 on the image sensor 4. The image sensor 4 is composed of a CCD or a CMOS, and converts the formed subject image into an electrical signal.

  The image processing unit 5 performs various processes on the image data and records them in the memory 8. The image processing unit 5 includes a compression unit, an expansion unit, and the like, and performs various processes such as color correction, smoothing processing, contrast enhancement processing, signal compression, and expansion on the image data. The memory 8 records the image data that has undergone image processing. The image processing unit 5 includes a circuit for detecting a contrast value. A contrast value is output from the image processing unit 5 to the MPU 10. Further, the image processing unit 5 is provided with an image data comparison unit 15 as one feature of the invention. The image data comparison unit 15 will be described later.

  The camera 1 is provided with a display control unit 6 and a display unit 7. The display control unit 6 performs control for displaying the image processed by the image processing unit 5 on the display unit 7. The display unit 7 is composed of, for example, an LCD, and displays a monitor image at the time of shooting, and displays a decompressed recorded image at the time of reproduction.

  Further, the camera 1 is provided with a lens position control unit 13, a diaphragm unit 3, a diaphragm control unit 12, and a flash unit 14. The lens position control unit 13 includes an actuator and a position encoder, and controls the movement of the lens unit 2. The lens position control unit 13 detects the in-focus position based on the contrast value of the image output from the image processing unit 5 and moves the lens. The diaphragm unit 3 is provided between the lens units 2 and throttles the amount of light incident on the image sensor 4. The aperture control unit 12 controls the aperture amount of the aperture unit 3 based on the instruction. The strobe unit 14 irradiates the subject when it is dark.

  The camera 1 is provided with an MPU 10, a ROM 11, and an operation unit 16. An MPU (microcontroller) 10 is a control unit that controls the entire camera 1 such as shooting and reproduction according to a program. Further, the MPU 10 is provided with an area division unit 10a as a processing function. The area division unit 10a will be described later. The ROM 11 is a non-volatile and recordable memory such as a flash ROM, and stores a control program for performing camera processing. The operation unit 16 notifies the MPU 10 of the photographer's instruction. As a representative example of the operation unit 16, switches 16a, 16b, and 16c are provided. The switch 16a is a release switch, and the switches 16b and 16c are mode changeover switches. As described above, the MPU 10 detects user instructions such as shooting and display with the switches 16a, 16b, and 16c, and controls these units connected to perform smooth, speedy and beautiful image shooting.

  A series of operations at the time of photographing by the above functions will be described. The subject image 20 enters the image sensor 4 through the lens unit 2. When the lens position control unit 13 performs focusing, this incident image can be focused. Focusing is performed by detecting the output contrast of the image sensor 4 and moving the lens, and stopping the lens at the point where the contrast becomes highest. Then, shooting is performed. A contrast value is output from the contrast value detection circuit of the image processing unit 5 to the MPU 10. The MPU 10 controls the lens unit 2 via the lens position control unit 13 while monitoring this result (contrast value).

  3A and 3B are graphs showing the focusing operation. FIG. 3A shows the position of the lens unit 2 that moves with time. The image is captured while moving the position of the lens unit 2 little by little. The image processing unit 5 calculates a contrast value for the captured image. FIG. 3B is a graph plotting the contrast values at that time. The point where the contrast reaches its peak (maximum) is the focus point. If the in-focus point is found, the lens unit 2 is returned to that position, and the focus position at the time of photographing is determined.

  Further, the image processing unit 5 performs the correction of the color and the gradation using the output from the image sensor 4 in addition to the determination of the image, performs the image compression, and records it in the memory 8. An appropriately thinned signal is sent to the display control unit 6 in real time. The composition of the subject is displayed on the display unit 7 such as an LCD.

  Further, the image data comparison unit 15 which is one characteristic part of the present invention determines changes in a plurality of image data obtained by changing the optical characteristics at the time of photographing or at a timing preceding the photographing. The image data comparison unit 15 determines an image change pattern based on the contrast value of the image output from the image processing unit 5. The image data comparison unit 15 is also called a determination unit. Based on the comparison determination result, the area classification unit 10a of the MPU 10 classifies the image into the main subject and the background area. Then, the image processing unit 5 performs different image processing on the divided background and main subject areas as necessary for each area. Examples of image processing include smooth (low-pass filter) processing, contrast enhancement processing, and addition processing. That is, here, the image processing unit 5 operates as an image enhancement unit. The MPU 10 controls these.

  Further, at the time of photographing, it is necessary to make the amount of light of the subject image 20 appropriate by controlling the exposure other than focusing on the subject. The MPU 10 controls the diaphragm unit 3 with the diaphragm control unit 12 or controls the light emission of the strobe unit 14 so that appropriate exposure can be obtained.

  FIG. 2 is an external view of the camera 1. FIG. 2A is a view of the camera 1 as viewed from the front. Windows for the lens unit 2 and the strobe unit 14 are arranged. On the upper surface of the camera 1, a release switch 16a and other mode changeover switches 16b are arranged. FIG. 2B is a view of the camera 1 as seen from the back. A display unit 7 such as an LCD panel and other mode switches 16c are arranged. The user can determine the composition of the subject or determine the photo opportunity while viewing the monitor image displayed on the display unit 7.

  FIG. 5 is a diagram for explaining the principle of the background processing. 5A and 5B are diagrams for explaining that the amount of blur changes due to the difference in the diameter of the light beam passing through the lens. In both (A) and (B), the lens unit 2 is in focus at a short distance. The light that has passed through the lens unit 2 and the diaphragm unit 3 forms an image on the image sensor 4. An object at a short distance is imaged (focused) at one point on the image sensor 4, while an object at a long distance is imaged (blurred) with a certain width. On the right is the contrast curve. The vertical direction is the width direction of the screen.

  FIG. 5A shows a state in which the aperture 3 is opened. When the subject is in focus at a short distance, the image of a subject at a long distance is widened and blurred, and the contrast of the image signal is also reduced. On the other hand, in FIG. 5B, since the aperture is closed, even when the focus is close to the distance, the spread of the light beam is small and the blur is small, and the contrast of the subject at a long distance is also (A). Larger than That is, in a digital camera, since the lens diameter tends to be small and tends to be as shown in FIG. 5B, it can be said that the background at a long distance is troublesome and tends to appear on the screen. In this example, the state is as shown in FIG. 5A, but it is still assumed that the background blur is insufficient.

Then, it is assumed that the image is obtained twice in the state as shown in FIGS. 5A and 5B with the exposure of the main subject portion being appropriate. FIG. 5C is a diagram in which the contrast curves of the two obtained images are superimposed. In (C), the graph is rotated 90 degrees from the curve (A) (B). When comparing the contrasts of the two images as shown in FIG. 5 (C), there is no difference in the main subject portion at a short distance, but the background portion has contrast and blur as described in FIGS. 5 (A) and 5 (B). It can be seen that there is a difference in quantity. The main subject portion and the background are determined using the difference portion. Doing more smoothed image processing such as decreasing the contrast of (like low-pass filtering) to the image of the background portion, as shown in FIG. 5 (D), the contrast of the main subject as it was blurred background only You can get an image. For the main subject (where there is no difference in contrast between the two images), the image is used as is. As a result, even in a camera having a small lens diameter, it is possible to obtain an image in which the subject is clearly lifted from the background by effectively using image processing.

  Some cameras combine with the background while shifting the focus, but with these cameras, the magnification of the image changes when the focus is shifted, the size of the main subject on the screen changes, and the outline with the background when combining Some parts may become unnatural. In the present embodiment, since the lens position is not changed, there is no problem, and efficient image acquisition can be performed with a simple configuration.

  FIG. 4 is a flowchart for explaining the procedure of the photographing process of the camera 1. This photographing process is mainly executed by the MPU 10 according to the program, the area sorting unit 10a, the image processing unit 5, and the image data comparison unit 15.

  First, focus is performed (step S11). Focusing is the method as described in FIG. After the focusing is completed, shooting is performed at the aperture position 1 (for example, open), and an image obtained by this shooting is set as an image 1 (step S12). Next, photographing is performed at the aperture position 2 (for example, the minimum), and an image obtained by this photographing is defined as an image 2. Imaging is performed with the aperture position changed as described with reference to FIGS. The degree of coincidence of the contrast between the two images obtained in this way is compared by the image data comparison unit 15 (step S14). This is a comparison as shown in FIG. The matched portion is used as it is as shown in FIG. 5D, and this is used as image 3 (step S15). Image 3 becomes the main subject portion.

  For the unmatched portion, the amount of change is emphasized, and this is set as an image 4 (step S16). Here, as shown in FIG. 5D, the contrast is reduced (smoothed). As a method for reducing the contrast, for example, there is a method of applying a low-pass filter to an image signal to obtain a smooth signal. FIG. 13 is a diagram schematically illustrating how the contrast signal is smoothed by applying a low-pass filter. Then, the image 3 and the image 4 are combined by the image processing unit 5 (step S17). This completes the shooting. Then, this image is recorded in the memory 8.

  As described above, according to the present embodiment, by using the change in the background image caused by the change in the aperture and performing the image processing in which the blur is emphasized more than the actually obtained blur amount, the description that is the size or the spec limit of the camera is described. It is possible to obtain an image that exceeds power.

(Second Embodiment)
In the first embodiment, an example has been described in which the background blur is enhanced by suppressing the contrast. Of course, it is also possible to enhance the contrast and draw more effective. For example, when a person is photographed in front of a night view, the point light source of each night view is dark, and it is also an extension of the idea of the present invention to add and emphasize the light of these point light sources separated as a background. On the line. In the second embodiment, such an example will be described. A block diagram of a camera to which the present invention is applied is the same as that shown in FIG.

  FIG. 8 is a flowchart showing a processing procedure of night-time emphasized photographing. It is mainly executed by the MPU 10, the image processing unit 5, and the image data comparison unit 15 according to the program. Steps S41 to S44 are the same as steps S11 to S14 in FIG. FIG. 9 shows an example of an image at each timing to be processed.

  First, focus is performed (step S41). After the focusing is completed, shooting is performed at the aperture position 1 (for example, open), and an image obtained by this shooting is set as an image 1 (step S42). Next, photographing is performed at the aperture position 2 (for example, the minimum), and an image obtained by this photographing is defined as an image 2. Imaging is performed with the aperture position changed as described with reference to FIGS. The degree of coincidence of the two images thus obtained is compared by the image data comparison unit 15 (step S44). This comparison is a comparison as shown in FIG. FIGS. 9A and 9B show images 1 and 2 obtained in this way. It is assumed that the main subject is not captured because the strobe is not used yet in these two shootings.

  For the part that does not match due to the background partial information conversion, the image processing unit 5 performs pixel addition processing (step S45). By this processing, an emphasized image of the background portion as shown in FIG. 9C is obtained. Thereafter, the aperture is opened and flash photography is performed to obtain image 4 (step S46). Then, image 3 is added to image 4 (step S47). Then, an image in which both the main subject and the background are clearly expressed as shown in FIG. 9D is obtained. As described above, it is possible to obtain a night view photo with a rich atmosphere that clearly depicts the night view that tends to be dark.

  FIG. 10 is a diagram illustrating light spot addition processing. At this time, addition is performed for each light spot as shown in FIGS. 10 (A), (B), and (C). The horizontal axis indicates the position of the pixel, and the vertical axis indicates the amount of optical signal obtained therefrom. When the light distribution as shown in FIGS. 10 (A) and 10 (B) is obtained by photographing in step S42 and step S43, FIGS. 10 (A) and 10 (B) are simply added to obtain the light distribution as shown in (C). The distribution may be expressed on an image. This is an example of the addition emphasis shown in step S47 of FIG.

  In addition, when two images as shown in FIGS. 10A and 10B are overlapped and compared as shown in FIG. It can be judged as a clear signal. This clear light spot can be emphasized with a gain as shown in FIG. 11B, and a night scene description with contrast enhancement as shown in FIG. 12 can be drawn. With such emphasis depiction, it is possible to make an image rich in atmosphere that reproduces the dark background, which used to be dark in the dark.

(Third embodiment)
In the first embodiment, a highlighted image is obtained by synthesizing a plurality of images with different aperture positions. In the third embodiment, an example in which similar processing is performed by changing the focus position will be described. A block diagram of a camera to which the present invention is applied is the same as that shown in FIG.

  In this embodiment, a background detection / separation method by photographing with a shifted focus position will be described using the principle that a subject at a long distance is less affected by a change in focus than a short distance. FIG. 7 is a diagram for explaining the state of blur due to the focus position. FIGS. 4A and 4B schematically show a state in which a subject image is formed on the image sensor 4 by the lens unit 2 and a contrast curve of the image obtained on the right side. FIG. 7A shows a case where the focus is set to a long distance. A background image at a long distance tends to output an image with a clear contrast, but the main subject at a short distance (near side) has a low contrast.

  FIG. 7B shows a case where the focus is adjusted to a short distance. Even when focusing on the main subject in the foreground, the background is not so blurred due to the depth of field. For example, a slight difference in focus position during macro shooting is greatly blurred, but in the case of a landscape, even if the focus position is brought to the front, it will not be greatly blurred.

  FIG. 7C is a diagram in which the contrasts of the images (A) and (B) are superimposed. When the image signals obtained in FIGS. 7A and 7B are compared with each other as shown in FIG. 7C based on such a principle, a place where the blur difference is small depending on the focus position is considered as the background (far distance). be able to. By applying this concept, it is possible to take a photo with the same background as described with reference to FIGS. That is, as shown in FIG. 7C, the main subject position at a short distance can be regarded as a place where the focus is shifted and there is a large change and a difference occurs. A place where the difference is small can be considered as a background position at a long distance.

  FIG. 6 is a flowchart showing the procedure of the photographing process by the camera 1 based on the above principle. It is mainly executed by the MPU 10, the area sorting unit 10a, the image processing unit 5, and the image data comparison unit 15 according to the program. Shift (movement) of the focus position is started (step S21). First, the variable n is reset to 1 (step S22). Photographing is performed at the focus position n to acquire image data, and the image processor 5 obtains or detects a contrast value (see FIG. 3) for this image data (step S23). Next, it is determined whether or not the focus position shift is finished (step S24). The end determination is made based on whether the contrast of the obtained image is maximized. In other words, the image data contrast acquisition is continued while shifting the focus position until the contrast of the main subject is maximized.

If the contrast is not maximum (step S24 NO), n is incremented (step S25).
Returning to step S23, the contrast is acquired and determined at the next focus position, and this loop is circulated. If it is determined that the contrast of the main subject has become maximum (step S24 YES), the focus position shift is terminated (step S26). Then, the image data comparison unit 15 compares the contrast of the first image (n = 1) with the contrasted image having the maximum contrast (step S27). A portion having a high degree of coincidence is considered as a background, and image enhancement processing is performed by the image processing unit 5. As the image enhancement processing, the blurring processing by the low-pass filter processing described with reference to FIG. 4 or the background contrast enhancement processing and addition processing shown in FIGS. The processed image is used as a background image.

  Further, a portion where the contrast does not match (a portion with a large difference) is considered as the main subject. This portion of the maximum contrast image, that is, the focused image is employed (step S29). Then, the image processing unit 5 combines the portion subjected to the image enhancement processing as the background in step S28 and the portion set as the main subject in step S29 (step S30).

  In this way, instead of simply using one image with high contrast, an image in which only the background is blurred can be obtained by adopting each of the plurality of images with high contrast.

  As described in the first to third embodiments, a plurality of images photographed under a plurality of different photographing conditions are used, and those that are easily affected by differences in photographing conditions due to switching of the photographing optical system are difficult to be performed. It was possible to separate the main subject and the background by analyzing them with electrical signals.

The background image thus obtained has various meanings depending on the situation with respect to a main subject such as a person. First, in portrait photography and the like, if there are various backgrounds, the image becomes noisy, and the subject matter tends to be ununiform. However, in the case of snaps etc., if the background is not clearly captured, it will not be possible to know where the picture was taken, and it will completely lose its meaning as a record. In this way, it is a case-by-case basis for which processing (whether to blur or clarify) the background depiction is better. Therefore, switching is possible according to the user's intention to shoot. That is, by operating the camera mode switching switch 16b, the user can select the background blur mode and the background clear mode, and the contrast of the background portion is lowered or increased according to the result.
(Fourth embodiment)
In the above, the selection of the background blur mode and the background clear mode is made by the user. The fourth embodiment is an example of automatically selecting background blurring and background sharpness. A fourth embodiment will be described with reference to FIGS. 14 and 15. A block diagram of a camera to which the present invention is applied is the same as that shown in FIG. First, an example will be described in which such processing is switched depending on the proportion of the subject in the screen or the composition of the photograph. FIG. 14 is a flowchart illustrating a procedure of photographing processing by the camera 1. The following processing is mainly executed by the MPU 10, the area division unit 10a, the image processing unit 5, and the image data comparison unit 15 according to a program.

  First, it is determined whether the ratio of the main subject to the entire screen is large (step S51). When the proportion of the main subject is large (YES in step S51), it is considered as a portrait photograph, for example, and photographing is performed by the above-described process of blurring the background (step S52). If the proportion of the main subject is not large (NO in step S51), it is next determined whether the composition is vertical (step S53). If it is a vertical composition (step S53 YES), the background is blurred and imaged (step S52) as described above. If it is not a vertical composition (NO in step S53), shooting is performed with a background enhancement process (step S54).

  Next, an example will be described in which processing is further switched depending on the background situation. This is because it can be switched from the background depending on the situation of the background because it can be separated from the background. FIG. 15 is a flowchart showing the procedure of this shooting by the camera 1.

  First, it is determined whether there are few contrast change portions in the background portion (step S61). When there is little contrast change in the background (YES in step S61), shooting is performed with processing that emphasizes the background (step S62). On the other hand, when the contrast change is not small in the background (NO in step S61), it is also determined whether the contrast of the main subject is high (step S63). When the contrast of the main subject is high, shooting is performed by blurring the background (step S64). If there are many changing parts in the background, an annoying effect is produced for the main subject. However, when the contrast of the main subject is low (NO in step S63), the process proceeds to step S62. This is because if the background blur processing is further performed on an image with a low contrast of the main subject, the whole picture becomes sleepy.

  As described above, according to each of the embodiments described above, the background processing is appropriately performed even for a camera that captures images with a relatively small aperture with an excellent speed and a high mobility, without taking a photo opportunity. It is possible to provide a camera that can depict the main subject with a beautiful blur effect. In addition, it is possible to enhance the background contrast according to the situation, and to perform shooting that makes use of the features of the scene.

  In the above-described embodiment, a part or all of the MPU 10 processing described in the above embodiments may be configured by hardware. Conversely, the image data comparison unit 15 may be configured by software. The specific configuration is a design matter. Each control process by the MPU 10 is realized by a software program stored in the ROM 11 being supplied to the MPU and operating according to the supplied program. Therefore, the software program itself realizes the functions of the MPU 10, and the program itself constitutes the present invention. A recording medium for storing the program also constitutes the present invention. As a recording medium, besides a flash memory, an optical recording medium such as a CD-ROM or DVD, a magnetic recording medium such as an MD, a tape medium, a semiconductor memory such as an IC card, or the like can be used. Similarly, the playback selection unit 38 may be entirely or partially configured by software. Moreover, although each embodiment demonstrated the example which applied this invention to the digital camera, you may apply not only to this but the camera part of a mobile telephone, for example.

  Furthermore, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is an overall block diagram of a camera 1 to which the present invention is applied in a first embodiment. 1 is an external view of a camera 1 in the first embodiment. The figure which graphed the operation | movement of focusing in 1st Embodiment. 5 is a flowchart for explaining a procedure of photographing processing of the camera 1 in the first embodiment. The figure explaining the principle of a background process in 1st Embodiment. 9 is a flowchart illustrating a procedure of photographing processing by a camera according to a third embodiment. The figure for demonstrating the condition of the blurring by a focus position in 3rd Embodiment. The flowchart which shows the process sequence of night emphasis photography in 2nd Embodiment. In 2nd Embodiment, the example of the image in each timing processed is shown. The figure which shows the addition process of a light spot in 2nd Embodiment. The figure which shows the addition process of the further emphasized light spot in 2nd Embodiment. The figure which shows the night view image | photographed by contrast emphasis without a blur in 2nd Embodiment. The figure which shows a mode that a contrast signal becomes smooth by applying a low-pass filter in 1st Embodiment. 14 is a flowchart illustrating a procedure of photographing processing by the camera 1 in the fourth embodiment. 14 is a flowchart illustrating a procedure of photographing processing by the camera 1 in the fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Camera, 2 ... Lens part, 3 ... Diaphragm part, 4 ... Image pick-up element, 5 ... Image processing part, 6 ... Display control part,
DESCRIPTION OF SYMBOLS 7 ... Display part, 8 ... Memory, 10 ... MPU, 10a ... Area division part, 11 ... ROM, 12 ... Aperture control part, 13 ... Lens position control part, 14 ... Strobe part, 15 ... Image data comparison part,
16 ... operation unit, 16a ... release switch, 16b, 16c ... mode switch, 20 ... subject,

Claims (2)

An aperture controller for controlling the aperture position of the photographic optical system;
A determination unit that determines a change in a plurality of image data obtained by shooting with the aperture position changed in a state where a low-luminance main subject with a night view as a background is in focus and a strobe is not emitted ;
In accordance with the output result of the determination unit, an area classification unit that classifies a portion with a change as a light spot portion of the night view ,
For each image obtained by changing the aperture position, an addition process is performed on the light spot portion of the divided night view, and an image that has not been subjected to flash photography that has been subjected to the addition process for the light spot portion of the night scene, and the main image An image processing unit that synthesizes an image captured with a flash with the subject in focus and produces a captured image
A camera characterized by that. The camera according to claim 1, wherein the aperture control unit controls the aperture to an open position when performing strobe shooting with the main subject in focus .