In recent years, with the increase of the resolution of solid-state imaging devices such as CCD (charge-coupled device) image sensors and CMOS (complementary metal-oxide-semiconductor) image sensors, the demand for information apparatus having a shooting function, such as digital still cameras, digital video cameras, cell phones (e smartphones), and PDAs (personal digital assistants) has been increasing. Such information apparatus having a shooting function are referred to as imaging apparatus.
In such imaging apparatus, a contrast AF (autofocus) method and a phase difference AF method are employed as focus control methods for focusing the apparatus on a major subject. Since the contrast AF method and the phase difference AF method have respective advantages, imaging apparatus have been proposed which employ both methods (refer to Patent document 1, for example).
Under such light sources as fluorescent lamps, a light quantity variation occurs due to what is called flickering. If such a light quantity variation occurs in the contrast AF method, the peak portion of an evaluation value curve for evaluation of a focusing state may get out of shape depending on the timing of acquisition of an image, resulting in reduction in focusing accuracy.
In view of the above, in Patent document 1, in an imaging apparatus that increases the accuracy of phase difference autofocusing using both of phase difference autofocusing and contrast autofocusing, reduction of AF accuracy due to a flicker is prevented by changing an evaluation value calculation algorithm of contrast autofocusing when a flicker is detected.
Patent documents 2 and 3 disclose methods for suppressing a flicker by elongating the pixel exposure time in an imaging device when the flicker is detected.
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USPTO Backgrounds