JP2014027466A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a plurality of images differing in exposure amount which are assumed to have been photographed at the same time.SOLUTION: A set bracket width (±2EV or ±nEV) is checked (S100), and a number of images 16 (=2(n=2)) successively photographed is calculated from the bracket width. Sixteen images are successively photographed with a -2EV exposure (S104 to S106). A sum of the 16 photographed images ΣIm is made to be a +2EV image, and arithmetic averages thereof ΣIm/16 and 4ΣIm/16 are made to be a -2EV image and a ±0EV image, respectively. The -2EV, ±0EV and +2EV images are displayed on monitor (S110) and are also recorded in memory (S112).

Description

  The present invention relates to a digital camera capable of continuously capturing a plurality of images that are substantially continuous in time.

  As one of the shooting techniques using continuous shooting, for example, automatic exposure that automatically captures multiple images with different exposure values centered on the exposure value obtained by automatic exposure, thereby preventing loss of shooting at proper exposure Bracketing is known. As another example, when shooting a subject with a large contrast ratio, the subject is shot sequentially with different exposure times, and a composite image with an expanded dynamic range is obtained by combining a plurality of shot images. Range synthesis is known. However, in such a shooting technique using continuous shooting, a shift occurs in the position of the subject between the images, such as when the subject moves. In particular, there is a problem when the position of the subject is shifted in the high dynamic range (HDR) composition. For such a problem, the composition of the image is performed after performing coordinate conversion corresponding to the positional displacement between the images over time. An imaging method has been proposed (Patent Document 1).

JP 05-007336 A

  However, even in the method of Patent Document 1, the time taken for each image is different, and the images are still not taken simultaneously.

  An object of the present invention is to obtain a plurality of images having different exposure amounts that can be considered to have been photographed simultaneously.

  An imaging apparatus according to the present invention includes a continuous shooting unit that continuously captures and stores a plurality of images, an image combining unit that adds a plurality of images to combine the first images, and a first image from the first image or the plurality of images. And a second image generating means for generating a second image having a different exposure.

When the total number of the plurality of images is N, each pixel value of the second image is obtained by multiplying each pixel value of the first image or the plurality of images by a coefficient α of 1 / N ≦ α <1. preferable. When exposed width among a plurality of images of ± NEV, it is preferred that the total number of the plurality of images is 2 ²ⁿ sheets. An arithmetic average of a plurality of images may be used for the second image. Further, it is preferable that the continuous shooting is executed by electronic shutter control, and a plurality of images are taken substantially continuously. The first image and the second image are, for example, exposure bracket images. Further, the imaging apparatus may include an HDR synthesizing unit that performs HDR synthesis based on the first image and the second image.

  According to the present invention, it is possible to obtain a plurality of images having different exposure amounts that can be considered to have been shot simultaneously.

1 is a block diagram of an imaging apparatus to which an image acquisition method according to an embodiment of the present invention is applied. It is a flowchart which shows the flow of the imaging and image composition process (image acquisition method) in exposure bracket mode of this embodiment. The sequence of the imaging process in bracket imaging is shown. The structure of the synthesized image obtained by the calculation of ΣIm is schematically shown. It is a flowchart which shows the flow of the imaging and image composition process (image acquisition method) in the HDR mode of this embodiment. 6 is a flowchart of a modified example of the imaging / image composition processing (image acquisition method) in the HDR mode shown in FIG. 5.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an imaging apparatus to which an image acquisition method according to an embodiment of the present invention is applied.

  The imaging apparatus is, for example, a digital camera 10, and the digital camera 10 includes an imaging device 11, an image signal processing unit 12, a control unit 13 that drives the imaging device 11 and controls the entire camera, a through image, a captured image, or various setting screens. A monitor 14 such as an LCD for displaying the image, an operation unit 15 including an operation switch such as a release switch, and a removable external recording medium 16 such as a memory card.

  The image sensor 11 is controlled based on, for example, a drive signal from the control unit 13, and an image signal detected by the image sensor 11 is converted into a digital signal and input to the image signal processing unit 12. The image signal processing unit 12 includes, for example, a digital signal processor (DSP) 17 and an image memory 18.

  The image memory 18 can store images continuously captured by the image sensor 11, and the DSP 17 performs various types of conventionally known image processing and uses the images stored in the image memory 18 to perform the present embodiment described later. Form image processing is performed. The image processed by the DSP 17 can be output to the monitor 14 and is stored in the external recording medium 16 as necessary.

  The digital camera 10 includes, for example, an HDR mode in which a plurality of images are taken as a shooting mode and high dynamic range composition is performed based on the images, and an exposure bracket mode in which automatic exposure bracket shooting is performed. Each mode is selected by the user operating the operation unit 15, and when the release switch is turned on, as described below, for example, a plurality of images are continuously taken by an electronic shutter operation and the image memory 18 is operated. And predetermined image processing for each mode is performed.

  FIG. 2 is a flowchart showing a flow of imaging / image composition processing (image acquisition method) in the exposure bracket mode of the present embodiment. When the release switch is turned on in the exposure bracket mode, this processing is executed mainly by the control unit 13 and the DSP 17.

  In step S100, the setting of the bracket width is confirmed. The bracket width is stored in the memory based on, for example, a default or a user setting, and the exposure is the best among a plurality of images photographed around an appropriate exposure value obtained by automatic exposure or an exposure value set by the user. It shows the difference between the under exposure value and the over exposure value. In the example of FIG. 2, the exposure width of 4EV (4 exposure levels), that is, ± 2EV (up and down 2 steps) centered on the set exposure value is set as the bracket width.

In step S102, the number of images that are continuously shot is calculated based on the acquired bracket width. That is, when the bracket width is ± NEV is the number of images is set to 2 ²ⁿ sheets. In the example of FIG. 2, since n = 4, 16 images are captured. In steps S104 and S106, 16 (2 ²ⁿ ) images are continuously captured with an exposure of −2EV (−nEV). That is, each image is shot at a shutter speed that is 1/16 (1/2 ²ⁿ ) of the shutter speed assumed in shooting at + 2EV (+ nEV) and stored in the image memory 18. FIG. 3 shows a sequence of imaging processing at this time. That is, in FIG. 3, the horizontal axis represents time, and the vertical axis represents the exposure amount, which shows the change in exposure amount over time in each image capture when 16 images are continuously captured. The period from t0 to t1 corresponds to the exposure period of the first image, t1 to t2 corresponds to the exposure period of the second image, and t15 to t16 correspond to the exposure period of the 16th image.

  In step S108, three images corresponding to, for example, +2 EV, ± 0 EV (set exposure value), and −2 EV are created from the 16 images captured at −2 EV. That is, the average value ΣIm / N of all 16 (N) images captured by bracket shooting is used for the −2 EV image. Here, Im represents the mth image among the 16 (N) captured images (m: 1 to 16 (N)). Similarly, 4ΣIm / N obtained by quadrupling a −2EV image is used as an image of ± 0 EV (set exposure value), and ΣIm obtained by adding all the images is used as an image of + 2EV. The calculated −2 EV, ± 0 EV, and +2 EV images are stored in, for example, the image memory 18.

  FIG. 4 schematically shows an image obtained by the calculation of ΣIm. For example, when the subject is moving, the positions of the subject in the 16 images are different. However, the image of ΣIm obtained by adding these corresponds to an image photographed with t0 to t16 in FIG. 3 as an exposure period, and the subject appears as a sum of subjects that appear in all 16 images. Further, since the images of −2EV and ± 0EV are also calculated as pixel values of the image obtained by ΣIm being 1/16 (N), 4/16 (N), similarly to the + 2EV image, t0 to t16. Corresponds to an image taken as an exposure period.

  In step S110, the images of −2EV, ± 0EV, and + 2EV synthesized in step S108 are displayed on the monitor 14. These images may be displayed side by side, or may be configured to be sequentially compared and displayed one by one through key operations. In step S112, −2EV, ± 0EV, + 2EV images temporarily stored in the image memory 18 are recorded on the external recording medium 16, for example. Thus, the image acquisition process in the exposure bracket mode is completed.

  FIG. 5 is a flowchart showing a flow of imaging / image composition processing (image acquisition method) in the HDR mode of the present embodiment. That is, when the release switch is turned on in the HDR mode, this processing is executed mainly by the control unit 13 and the DSP 17.

  Steps S200 to S208 in this process correspond to steps S100 to S108 in the exposure bracket mode, and the processing content is the same as that in the exposure bracket mode. Therefore, in step S208, the image memory 18 stores images taken at -2EV, ± 0EV, and + 2EV. The HDR mode is different from the exposure bracket mode in that, in step S210, high dynamic range (HDR) composition is performed using images taken with these three different EV values, -2EV, ± 0EV, and + 2EV. . In this embodiment HDR mode, an electronic shutter is used to ensure the continuity of the composite image, and under and over images are created by synthesizing the same image in order to ensure the synchronism of the composite image. The In step S212, the synthesized HDR image is displayed on the monitor 14, and the synthesized HDR image in step S214 is recorded on the external recording medium 16, and the image acquisition process in the HDR mode is completed. Note that the HDR synthesis in step S210 is performed by a conventionally known method.

  FIG. 6 shows a flowchart of a modified example of the HDR mode. In the image acquisition process in the HDR mode of FIG. 5, the bracket width is set by the user or by default, but in the modification of FIG. 6, the bracket width is automatically set according to the shooting environment.

That is, when the release switch is turned on in the HDR mode, the luminance distribution of the subject is determined in step S300, and the bracket width ± nEV (n may not be an integer) is determined. In step S302, the number of images to be continuously captured based on the acquired bracket width ± NEV is calculated as 2 ²ⁿ sheets. In step S304, ^{S306, 2 2n} images are taken with exposure -nEV continuously, is stored in the image memory 18.

In step S308, from ^{2 2n} images taken by -NEV, e.g. -nEV, ± 0EV (set exposure value), + NEV is three images corresponding are created and stored in the image memory 18. In step S310, a conventionally known HDR synthesis process is executed using the three images -nEV, ± 0EV, and + nEV having different exposures. In step S312, the synthesized HDR image is displayed on the monitor 14. In step S314, the HDR image is recorded on, for example, the external recording medium 16, and the image acquisition process in the HDR mode ends.

  As described above, according to this embodiment, it is possible to obtain a plurality of identical images that differ only in the exposure amount using the same exposure period (t0 to t16). That is, a plurality of images having the same simultaneity with different exposures are acquired. This makes it possible to move the subject during bracket shooting, or to cause a temporal change within the shooting angle of view, particularly in HDR synthesis where a single image is obtained by combining a plurality of images. Although the change over time has been an obstacle to improving the image quality of the generated composite image, such a problem can be solved by applying the image acquisition method of the present embodiment.

  Further, in this embodiment, since the dynamic range is expanded by adding a plurality of images taken with a short exposure time, noise may be expanded unlike when an image signal is multiplied by a gain. Absent.

  In this embodiment, the bracket images are continuously captured using the electronic shutter. However, even when the bracket images are slightly separated, for example, when a mechanical shutter is used, the interval can be sufficiently short. The present embodiment can be applied.

  In this embodiment, an arithmetic average is used. However, it is also possible to use a weighted average by weighting each bracket image. For example, a light weight may be given to a frame in which a flash is emitted, or a new image may be weighted larger.

  In this embodiment, three images with different exposures are created. However, the number of images to be created is not limited to this as long as it is two or more, and may be four or more. In that case, an arbitrary coefficient α of 1 / N ≦ α <1 is multiplied by ΣIm. In addition, when a large number of images are added to synthesize an image with a large exposure amount, as is well known in the art, a method such as sequentially performing addition is used to prevent missing digits.

DESCRIPTION OF SYMBOLS 10 Digital camera 11 Image sensor 12 Image signal processing part 13 Control part 14 Monitor 15 Operation part 16 External recording medium 17 DSP
18 Image memory

Claims (7)

Continuous shooting means for continuously shooting and storing a plurality of images;
Image synthesizing means for synthesizing the first image by adding the plurality of images;
An imaging apparatus comprising: a second image generation unit configured to generate a second image having a different exposure from the first image from the first image or the plurality of images.   When the total number of the plurality of images is N, each pixel value of the second image is obtained by multiplying each pixel value of the first image or the plurality of images by a coefficient α of 1 / N ≦ α <1. The imaging apparatus according to claim 1, wherein: When said exposure width between a plurality of images of ± NEV, imaging apparatus according to any one of claims 1 or claim 2 total number of the plurality of images characterized in that it is a 2 ²ⁿ sheets.   The imaging apparatus according to claim 1, wherein the second image includes an arithmetic average of the plurality of images.   The imaging apparatus according to any one of claims 1 to 4, wherein the continuous shooting is executed by electronic shutter control, and the plurality of images are captured substantially continuously.   The imaging apparatus according to claim 1, wherein the first image and the second image are exposure bracket images.   The imaging apparatus according to claim 1, further comprising an HDR synthesizing unit that performs HDR synthesis based on the first image and the second image.

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