1. Field of the Invention
The present invention relates generally to an image capturing apparatus and method, and more particularly to an image capturing apparatus such as a digital camera and method thereof that are able to obtain a preferable image of a subject with a broad brightness range.
2. Description of Related Art
An image capturing apparatus such as a digital camera uses a solid state image sensor such as a charge-coupled device (CCD), of which dynamic range is narrower than that of a silver halide film. Then, if an image of a subject with a broad brightness range is captured by the CCD, the image is partially blackened or whitened.
To enlarge the dynamic range of the digital camera, there has been proposed an apparatus that captures a plurality of images with different exposures in the same scene and combines the plurality of images to compose one image of a broad brightness range (Japanese Patent Provisional Publication Nos. 8-214211 and 9-275527).
The apparatus of Japanese Patent Provisional Publication No. 8-214211 automatically determines whether the dynamic range must be enlarged in accordance with the first captured image. Only when the apparatus determines that the dynamic range must be enlarged, another image is captured with a different exposure. If the apparatus determines that there is no need for enlarging the dynamic range, the image is captured only once so that the image can be captured within a short period. This apparatus captures the images twice whenever it determines that the dynamic range must be enlarged. Thus, a main subject in the second captured image may be out of the position of the main subject in the first image due to the movement of the main subject or the movement of the camera between the two image capturing operations. This deteriorates the quality of the composed image.
The apparatus of Japanese Patent Provisional Publication No. 9-275527 has a plurality of CCDs. The CCDs capture a plurality of images in different exposures, respectively, at the same time, and the captured images are combined. This apparatus, however, is relatively expensive and large because it must have the plurality of CCDs.
In view of the foregoing, it is an object of the present invention to provide an image capturing apparatus, which can combine a plurality of images in which a main subject is at almost the same position even if the plurality of images are not captured at the same time, and which can obtain a preferable image with a broad dynamic range.
To achieve the above-mentioned object, the present invention is directed to an image capturing apparatus, comprising: an imaging device for obtaining image data representing a subject; an exposure controller for controlling an exposure in the imaging device in accordance with brightness of the subject; a determination part for determining whether, if a plurality of images are sequentially captured at a predetermined time interval, the subject will be at the same position in the plurality of images; and a controlling part for controlling the imaging device to sequentially capture the plurality of images at the predetermined time interval while controlling the exposure controller to change exposures for the plurality of images, respectively, when the determination part determines that the subject will be at the same position in the plurality of images.
Preferably, the image capturing apparatus according to the present invention further comprises an image composition part for receiving image data with different exposures, obtained by the imaging device, and combining the image data to compose image data representing one image.
According to the present invention, the image capturing apparatus of the present invention captures the images multiple times while changing the exposure to enlarge the dynamic range only when it is determined that the main subject hardly moves and that the main subject will be at the same position in the images. It is therefore possible to satisfactorily combine the captured images to obtain an image with a broad dynamic range.
Preferably, the determination part comprises at least one of the following detection parts: a detection part for detecting that the image capturing apparatus is mounted on a tripod; a detection part for detecting a selection of a self-timer mode; a detection part for detecting a selection of a remote control mode; a detection part for detecting a selection of a macro image capturing mode; a detection part for detecting a selection of a distant view image capturing mode; a detection part for detecting that a shutter speed is lower than a predetermined threshold; and a detection part for detecting a selection of a multiple-time image capturing mode for capturing the plurality of images. The image capturing apparatus may further comprise: a body; and an imaging head including the imaging device, the imaging head being attached on the body and capable of rotating with respect to the body. In this case, the determination part may comprise a detection part for detecting that the imaging head is rotated by at least a predetermined angle with respect to the body and that the imaging device is ready to capture an image of a user.
Upon the detection by the detection part, it is determined that the image capturing apparatus is fixed or placed steadily and is unmoved, or that the main subject hardly moves.