JP2005136760A - Digital still camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent image shake due to hand photographing from being made conspicuous without loading any expensive optical image shake correcting mechanism. <P>SOLUTION: This digital still camera is configured to photograph in shutter seconds based on photometric results, and to obtain electric image data, and is provided with a shake sensor which detects camera shake quantity, a shutter second changing device for, when the image shake quantity based on the output of the shake sensor exceeds a predetermined critical value, changing the shutter seconds to a high speed side in order to set it within the critical value, a photographing controller for, when the shutter seconds are changed to a high speed, continuously executing the number of photographing corresponding to the degree of the change and an image compositing device for compositing a plurality of image data generated by the continuous photographing, and for outputting the image data. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital still camera that obtains electrical image data by photographing, and more particularly to a device that is devised so that image data with inconspicuous image blur can be obtained.

  2. Description of the Related Art Conventionally, taking a picture with a camera fixed on a tripod to prevent camera shake has been performed. Various cameras and interchangeable lenses equipped with an optical image blur correction mechanism have been proposed and put into practical use. The optical image shake correction mechanism detects camera shake and corrects the image shake by driving the shake correction lens in a direction orthogonal to the optical axis of the photographing lens based on the detection result (for example, Patent Document 1).

Japanese Patent Laid-Open No. 4-76525 JP-A-11-164189 JP-A-5-7336

  However, tripods are heavy and bulky, making them inconvenient to carry, and because they are inferior in speed, they often miss photo opportunities. On the other hand, the optical image blur correction mechanism has a complicated structure and is expensive. Therefore, there is a demand for a digital still camera that can make image blur inconspicuous by hand-held shooting without mounting an expensive optical image blur correction mechanism.

The invention of claim 1 is applied to a digital still camera that takes an image at a shutter speed based on a photometric result and obtains electrical image data. And a shake sensor that detects the camera shake amount, and a shutter second that changes the shutter speed to the high speed side so that it falls within the limit value when the image shake amount based on the output of the shake sensor exceeds a predetermined limit value When the time change device and the shutter speed are changed at high speed, a shooting control device that continuously performs the number of shots corresponding to the degree of the change, and a plurality of image data generated by the continuous shooting And an image composition device that synthesizes and outputs by an addition method.
According to the second aspect of the present invention, when a shake sensor for detecting a camera shake amount and an image shake amount based on the output of the shake sensor are within a predetermined limit value, normal shooting is performed. And a photographing control device that performs continuous photographing and selects and outputs data having the smallest image shake amount from a plurality of image data generated by continuous photographing.
The invention of claim 3 is a shake sensor for detecting the camera shake amount, and when the image shake amount based on the output of the shake sensor at the time of shooting exceeds a predetermined limit value, for the image data obtained by the shooting, And an image processing apparatus that performs contour enhancement processing according to the amount of image blur.

According to the first aspect of the present invention, when the image blur amount exceeds a predetermined limit value, the shutter speed is changed to the high speed side so as to be within the limit value, and the number of images corresponding to the degree of the change is photographed. Is performed continuously, and multiple image data generated by continuous shooting are combined and output, so image blurring is reduced by increasing the shutter speed, and multiple image data are combined. By doing so, a properly exposed image can be obtained (exposure underexposure due to the increased shutter speed).
According to the second aspect of the present invention, when the image blur amount exceeds a predetermined limit value, a plurality of images are continuously captured, and the image blur amount of the most from the plurality of image data generated by the continuous shooting is determined. Since a small amount of data is selected and output, image blur reduction can be achieved as in the first aspect. Further, since continuous shooting and image selection as described above are performed only when the image blur amount exceeds a predetermined limit value, useless continuous shooting is not performed when the image blur amount is within the limit value. .
According to the invention of claim 3, when the image shake amount based on the output of the shake sensor at the time of shooting exceeds a predetermined limit value, contour enhancement corresponding to the image shake amount is performed on the image data obtained by the shooting. Since the processing is performed, it is possible to obtain an image that is visually inconspicuous by performing necessary minimum edge enhancement.

-First embodiment-
An embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a block diagram of a digital still camera according to the present embodiment, and only a portion related to the present invention is shown. The CPU 1 receives the detection result of the photometry circuit 2 that detects the luminance of the subject and the detection result of the shake sensor 3 that detects the amount of camera shake caused by camera shake and the like, and is linked to the half-press operation of the release button. The on / off status of the half-press switch SW1 that is turned on and the release switch SW2 that is turned on in conjunction with the full-press operation (release operation) of the release button are input. The shake sensor 3 may be, for example, an angular velocity sensor used in a known optical image shake correction apparatus, or may be another type. Further, the shake sensor 3 may be built in the camera or may be built in the interchangeable lens.

  The exposure control circuit 4 drives a shutter and a diaphragm in accordance with an instruction from the CPU 1 and performs exposure (photographing) by causing the image sensor 11 to receive a subject light flux that has passed through a photographing lens (not shown). The image sensor 11 is composed of a CCD, for example, and photoelectrically converts the received light beam to generate an electrical image signal. The image signal from the image pickup device 11 is subjected to various image processing by the image processing circuit 12, compressed to, for example, the Jpeg format by the compression circuit 13, and then image recording medium (not shown) as image data by the recording circuit 14. (For example, a memory card). The image processing circuit 12, the compression circuit 13, and the recording circuit 14 perform each process in accordance with an instruction from the CPU 1. Reference numeral 15 denotes a buffer memory for temporarily storing an image signal (data) in the process described above.

  In the camera configured as described above, when the release switch SW2 is turned on, the CPU 1 reads the camera shake amount, which is the detection output of the shake sensor 3, prior to photographing, and converts it into the image shake amount at the time of exposure. The image blur amount is compared with a shake limit value, and if it is within the limit value, one exposure is performed as usual, and the generated image data is recorded on a recording medium. For the aperture value and the shutter speed at the time of exposure, values calculated by the camera based on the photometric result are used, thereby obtaining image data with appropriate exposure.

  On the other hand, when the image blur amount exceeds the limit value, the image becomes noticeable as it is, so that the shutter speed is reset to a high speed, and exposure is performed a plurality of times during the shutter time. Then, a plurality of obtained image data is combined to generate one image data, which is recorded on a recording medium. That is, by increasing the shutter speed, the image blur is suppressed within the limit value. However, if only the shutter speed is increased without changing the aperture value, the exposure is underexposed in only one exposure. End up. Therefore, exposure is performed a plurality of times in succession, and a plurality of image data are combined by an addition method to obtain image data with proper exposure. According to this method, it is possible to reduce image blur without providing an expensive optical image blur correction device, and it is not necessary to use a tripod.

The above control will be described in more detail with reference to the flowchart of FIG.
The CPU 1 determines that the release button has been half-pressed when the half-press switch SW1 is turned on, and starts the program of FIG. First, in step S1, photometry is performed by the photometry circuit 2, and in step S2, an exposure calculation is performed based on the photometry result, and an aperture value and a shutter time for obtaining an appropriate exposure are obtained. This photometry and exposure calculation are repeated until the half-press is released in step S4 or a release operation is performed in step S3 (until SW2 is turned on). When the half-press is released, the process ends. On the other hand, when a release operation is performed, the process proceeds to step S5.

  In step S5, the camera shake amount that is the output of the shake sensor 3 is read. In step S6, the image shake amount is calculated based on the camera shake amount. The image shake amount is an amount representing how much the subject image is shaken on the imaging surface (the light receiving surface of the image sensor 11) during exposure. In order to obtain this, in addition to the camera shake amount, the shutter speed and The focal length of the photographic lens is required as a parameter. This is because even if the sensor output is constant, the amount of image blur increases as the shutter speed is slower and the focal length is longer. When the shutter speed is a parameter, the value obtained by the exposure calculation in step S2 is used, and information from a detector (not shown) is used for the focal length.

  In the next step S7, the calculated image blur amount is compared with a predetermined blur limit value. Here, in general, image blur is considered not to be recognized as image blur on a normal photograph if the blur amount on the imaging plane is suppressed to 30 μm or less. If this theory is adopted, the blur limit value is set to 30 μm. do it. If the calculated image shake amount is within the shake limit value, exposure is performed with the aperture value and shutter time calculated in step S2 (step S8), and image processing is performed on the image signal obtained by the exposure. Compressed and recorded (steps S9 and S10).

  On the other hand, if the image blur amount exceeds the limit value, it is determined that the image blur is so large that it cannot be ignored. In step S11, the shutter speed is reset to a high speed value based on the image blur amount. The shutter time set here is such a value that the image blur amount falls within the limit value. Therefore, it is necessary to increase the shutter speed as the image blur amount calculated in step S6 increases. Subsequently, in step S12, the number of exposures N in the following continuous shooting is determined. The number of exposures N is determined by the difference between the shutter time initially set in step S2 and the shutter time reset in step S11. For example, if the initially set shutter speed is 1/30 seconds and the reset shutter time is 1/60 seconds, the difference is one stage (1/2 in light quantity), so N = 2. If the initially set shutter speed is 1/60 seconds and the reset shutter time is 1/250 seconds, the difference is two steps (1/4 in terms of light quantity), so N = 4 It becomes.

  Then, exposure is continuously performed in step S13 until it is determined in step S14 that the number of exposures has reached N. Each of the N pieces of image data is temporarily stored in the buffer memory 15, synthesized (added) after normal image processing (step S15), and then recorded (step S10). As a result, an image with proper exposure and no image blur is obtained.

-Second Embodiment-
Next, a second embodiment of the present invention will be described.
In the present embodiment, when the calculated image shake amount exceeds the shake limit value, continuous shooting is performed while the release operation is performed, and the most image shake amount among the obtained plurality of image data. The camera selects the one with less and records it on the recording medium.

The magnitude of image blur can be determined by compressing the obtained plurality of image data by the compression circuit 13 and comparing the sizes of the compressed image data. This is because the outline portion in the image becomes ambiguous as the image blur increases, and the data size of the compressed data inevitably increases. Therefore, if the plurality of image data obtained by the continuous shooting are all data of the same scene, the image with the smallest data size can be said to be the image with the least image blur, and this can be selected and recorded on the recording medium. Record. According to this method, there is an increased possibility of obtaining image data with less image blur as compared to the case where the image is taken only once.
Incidentally, in the case of an image that is not compressed, the size of the image data is constant (data size for one pixel × number of pixels) regardless of the magnitude of image blur.

  In this embodiment, since the camera automatically determines whether to perform the above continuous shooting or the single frame shooting according to the degree of image blur, the photographer does not need to pay attention to the selection. When continuous shooting is not required (when image blur is negligibly small), continuous shooting is not wasted.

  Note that the method for selecting the image with the least image blur from a plurality of image data is not limited to the above-described method, and for example, a method as disclosed in JP-A-11-164189 may be used.

FIG. 3 shows a flowchart for realizing the control of this embodiment in software, and the same steps as those in FIG. 2 are given the same step numbers.
If it is determined in step S7 that the image blur amount exceeds the limit value, the first exposure is performed in step S51, and the obtained image data is subjected to image processing and compression in step S52. Then, the image data compressed in step S53 is temporarily stored in the area A of the buffer memory 15 (hereinafter referred to as buffer A). Eventually, the data stored in the buffer A is recorded.

  Next, the processes in steps S55 to S59 are repeated until it is determined in step S54 that the release switch SW2 is turned off. In steps S55 and S56, exposure, image processing and compression are performed in the same manner as described above, and the compressed image data is stored in the buffer B in step S57. In step S58, the sizes of the compressed image data in the buffers A and B are compared. If A ≦ B, the process directly returns to step S54. If A> B, the image data in the buffer B is overwritten in the buffer A in step S59. Then, the process returns to step S54. If it is determined in step S54 that the release switch SW2 is off, the process proceeds to step S60. At this time, the buffer A has the smallest data size (image blurring) among a plurality of image data obtained by a plurality of exposures. Is stored in memory. Accordingly, in step S60, the image data in the buffer A is recorded on the recording medium.

-Third embodiment-
A third embodiment of the present invention will be described.
In this embodiment, imaging is performed as usual regardless of the magnitude of the image blur. However, when the image blur amount exceeds the blur limit value, contour enhancement processing according to the image blur amount is performed on the generated image data. Apply. The contour enhancement function is used to increase or decrease the sharpness of the image as used in commercially available image retouching software, etc., and does not correct image blurring. It is possible to make the runout inconspicuous.

Therefore, in the present embodiment, as shown in FIG. 4, only normal image processing is performed if the image blur amount is within the limit value, but when the image blur amount exceeds the limit value, contour enhancement is performed in addition to the normal image processing. (Step S70). The contour enhancement needs to be strongly applied when the image blur amount is large, but does not need to be so strong when the image blur amount is small. Rather, if the edge enhancement is too strong, there is a problem that the photograph becomes hard. Therefore, based on the calculated image blur amount, the edge enhancement is more strongly applied as the image blur amount is larger. This can be realized, for example, by storing in advance a table in which the image blur amount and the edge enhancement strength are associated with each other. According to this, it is possible to always perform the minimum necessary contour enhancement, and in addition to making the image blur inconspicuous, it is not necessary to impair the atmosphere of the photograph more than necessary.
Note that the relationship between the amount of image blur and the strength of edge enhancement in the table varies depending on whether importance is attached to image blur reduction or the image atmosphere.

The block diagram of the control system of the digital still camera in an embodiment. The flowchart which shows the process sequence of 1st Embodiment. The flowchart which shows the process sequence of 2nd Embodiment. The flowchart which shows the process sequence of 3rd Embodiment.

Explanation of symbols

1 CPU
2 Photometry circuit 3 Shake sensor 4 Exposure control circuit 11 Image sensor 12 Image processing circuit 13 Compression circuit 14 Recording circuit 15 Buffer memory SW1 Half-press switch SW2 Release switch

Claims (3)

In a digital still camera that takes an image at the shutter speed based on the photometric result and obtains electrical image data,
A shake sensor for detecting camera shake amount;
A shutter time changing device that changes the shutter time to a high speed side so that the image shake amount based on the output of the shake sensor exceeds a predetermined limit value,
When the shutter speed is changed at high speed, a shooting control device that continuously performs shooting of the number of sheets according to the degree of the change;
A digital still camera comprising: an image composition device that composes and outputs a plurality of image data generated by the continuous photographing by an addition method. In a digital still camera that obtains electrical image data by shooting,
A shake sensor for detecting camera shake amount;
If the image blur amount based on the output of the shake sensor is within a predetermined limit value, normal shooting is performed. If the image blur amount exceeds the limit value, a plurality of images are continuously shot and generated by the continuous shooting. A digital still camera comprising: a photographing control device that selects and outputs data having the smallest image blur amount from the plurality of image data. In a digital still camera that obtains electrical image data by shooting,
A shake sensor for detecting camera shake amount;
An image processing device that performs contour enhancement processing according to the image shake amount on image data obtained by the shooting when the image shake amount based on the output of the shake sensor at the time of shooting exceeds a predetermined limit value; A digital still camera comprising:

Images