Image pickup apparatus and method of picking up image

1. An image pickup apparatus that synthesizes a plurality of images with different exposures and that are obtained through bracketing, and generates an image signal having a wide dynamic range, comprising:

an exposure calculation unit to calculate a plurality of exposures necessary for bracketing on the basis of shutter speeds;

an image pickup possibility determination unit to determine whether or not respective shutter speeds corresponding to the plurality of exposures calculated by the exposure calculation unit are equal to or higher than a first threshold value, and to permit pickup of an image at an exposure when a shutter speed corresponding to that exposure is determined to be equal to or higher than the first threshold value;

an image pickup setting unit to set the number of images to be picked up at the exposure at which image pickup has been permitted by the image pickup possibility determination unit in such a manner that the total number of images that have to be picked up to generate the image signal having a wide dynamic range using image signals obtained at the exposure at which image pickup has been permitted by the image pickup possibility determination unit is a minimum;

an image obtainment unit to obtain the number of image signals set by the image pickup setting unit; and

an image signal synthesis unit to synthesize the plurality of image signals obtained by the image obtainment unit so as to generate an image signal having a wide dynamic range.

2. The image pickup apparatus according to claim 1 , wherein:

an image pickup possibility determination unit increases a sensitivity of an image sensing device and a shutter speed at an exposure when a shutter speed corresponding to the exposure is determined to be not equal to or higher than the first threshold value, and thereafter permits pickup of an image at that exposure when a sensitivity after the change is determined to be equal to or lower than a second threshold value and a shutter speed after the change is equal to or higher than the first threshold value.

3. The image pickup apparatus according to claim 1 , wherein:

the first threshold value is a slowest shutter speed that does not cause camera shaking.

4. The image pickup apparatus according to claim 2 , wherein:

the second threshold value is a highest sensitivity of the image sensing device that allows obtainment of an image signal with reduced noise.

5. An image pickup apparatus that synthesizes a plurality of images with different exposures and that are obtained through bracketing, and that generates an image signal having a wide dynamic range, comprising:

an exposure calculation unit to calculate a plurality of exposures necessary for bracketing on the basis of shutter speeds;

a number-of-picked-up-images setting unit to set the number of images to be picked up at each of the plurality of exposures calculated by the exposure calculation unit, the setting being done in such a manner that the total number of images that have to be picked up to generate the image signal having a wide dynamic range is a minimum;

an image obtainment unit to obtain the number of images set by the number-of-picked-up-images setting unit starting sequentially from a lowest exposure among the plurality of exposures calculated by the exposure calculation unit;

a camera shake detection unit to detect camera shaking;

an image pickup possibility determination unit to change a current exposure to a lower exposure, to change the number of images to be picked up in such a manner that image signals at each exposure calculated by the exposure calculation unit can be obtained using an exposure after the change, and to make the image obtainment unit obtain image signals again when the camera shake detection unit has detected camera shaking; and

an image signal synthesis unit to synthesize the plurality of image signals obtained by the image obtainment unit so as to generate the image signal having a wide dynamic range.

6. The image pickup apparatus according to claim 5 , wherein:

the camera shake detection unit detects camera shaking on the basis of a plurality of obtained image signals.

7. The image pickup apparatus according to claim 5 , wherein:

the camera shake detection unit is a sensor that detects movement of the image pickup apparatus.

8. An image pickup method of synthesizing a plurality of images with different exposures and that are obtained through bracketing, and of generating an image signal having a wide dynamic range, comprising:

calculating a plurality of exposures necessary for bracketing on the basis of shutter speeds;

determining whether or not respective shutter speeds corresponding to the plurality of exposures are equal to or higher than a threshold value, and permitting pickup of an image at an exposure when a shutter speed corresponding to that exposure is determined to be equal to or higher than the threshold value;

setting the number of images to be picked up at the exposure at which image pickup has been permitted in such a manner that the total number of images that have to be picked up to generate the image signal having a wide dynamic range using image signals obtained at the exposure at which image pickup has been permitted is a minimum;

obtaining the set number of image signals; and

synthesizing the plurality of obtained image signals so as to generate the image signal having a wide dynamic range.

9. An image pickup method of synthesizing a plurality of images with different exposures and that are obtained through bracketing, and of generating an image signal having a wide dynamic range, comprising:

calculating a plurality of exposures necessary for bracketing on the basis of shutter speeds;

setting the number of images to be picked up at each of the plurality of calculated exposures in such a manner that the total number of images that have to be picked up to generate the image signal having a wide dynamic range is a minimum;

obtaining the set number of images starting sequentially from a lowest exposure among the plurality of calculated exposures;

changing a current exposure to a lower exposure, changing the number of images to be picked up in such a manner that image signals at each calculated exposure can be obtained using an exposure after the change, and obtaining image signals again when camera shaking has been detected; and

synthesizing the plurality of obtained image signals so as to generate the image signal having a wide dynamic range.