1. Field of the Invention
The present invention relates to an image-capturing apparatus and a method of controlling the same and, more particularly, to an image-capturing apparatus which performs photometry using a charge-accumulation type image sensor, and a method of controlling the same.
2. Description of the Related Art
The photometric range required for an image-capturing apparatus such as a digital camera or a digital video camera is generally Bv values of about −5 to +15 in APEX units. That is, the dynamic range of the photometric range is about 20 steps. On the other hand, the dynamic range in which photometry can be performed by one-time accumulation using a charge-accumulation type image sensor is narrower than 20 steps.
Hence, with a known technique, a charge-accumulation type image sensor is used to combine image signals obtained by capturing images of the same scene by a plurality of times using different exposure amounts, thereby generating an image having a dynamic range wider than that which can be attained by one-time accumulation (image capturing). Such a technique is so-called HDR (High Dynamic Range) imaging.
Widening of the dynamic range of a photometric device which employs a charge-accumulation type light-receiving element in the same way has also been proposed. In, for example, Japanese Patent Laid-Open No. 6-130462, a photometric device which employs a charge-accumulation type light-receiving element alternately performs photometry that uses a long accumulation period and photometry that uses a short accumulation period, thereby obtaining photometric values from a low-luminance region to a high-luminance region even if the difference in luminance in the field is very large.
However, the method described in Japanese Patent Laid-Open No. 6-130462 requires a long exposure time to perform image capturing for photometry in a low-luminance region, thus prolonging the time required for photometry.
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