BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image capturing apparatus, a method for driving the image capturing apparatus and a storage medium, and more specifically to detecting a change in external light (flicker) that occurs during shooting.

Description of the Related Art

With the recent increase in ISO of digital cameras, high-speed shutters can be released even under an artificial light source that generates flicker. While there is an advantage that pictures without blurring can be taken when shooting indoor sports, etc., in shooting with high-speed shutter under a flicker light source, due to the influence of flicker, exposure and color unevenness may occur between frames of images or even within an image of one frame.

To solve such a problem, there is a method of reducing the influence of flicker by detecting flicker and performing exposure at the peak position of flicker, where the change in brightness is smallest. In particular, regarding the detection of flicker and its frequency, the following method is disclosed in Japanese Patent Laid-Open No. 2017-11352. First, photometry is performed a plurality of times in a fixed cycle, and among the obtained multiple photometric values, a first evaluation value is obtained from the photometric values acquired at a first interval whose phase is close to the phase of the flicker, and a second evaluation value is obtained from the photometric values acquired at a second interval whose phase is close to the opposite phase of the flicker. Then, the presence or absence of flicker and the frequency of the flicker are determined from the obtained first evaluation value and the second evaluation value.

However, in the prior art disclosed in Japanese Patent Laid-Open No. 2017-11352, it is necessary to acquire images for flicker detection at a high frame rate, so that the images for flicker detection are actually obtained by performing processing such as thinning and addition of pixels. Therefore, there is a problem from the viewpoint of image quality to use the images for flicker detection as images viewed by the user as in a live view display. In particular, in a camera having only one image sensor, such as a mirrorless camera, images for live view display and images for flicker detection are acquired using the same image sensor. Therefore, when flicker detection is performed in such a camera, the live view display will be temporarily blacked out or frozen.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the above situation, and flicker can always be detected even during displaying a live view without blackout or freezing of the live view display.

According to the present invention, provided is an image capturing apparatus comprising: an image sensor; a drive control unit that drives the image sensor; and a detection unit that calculates an evaluation value based on a plurality of second images and detects flicker based on the evaluation value, wherein the drive control unit controls to perform, during a first cycle of a display device: a first operation for reading out a first image to be displayed on the display device; and a second operation for reading out the plurality of second images at a second cycle which is shorter than the time taken to read out the first image at timings different from a timing of reading out the first image in a predetermined period in which the first image is read out from the image sensor, and wherein, upon calculating the evaluation value based on the plurality of second images, the detection unit detects flicker by using different pairs of images from among the plurality of second images for calculation of the evaluation value according to the first cycle, wherein each unit is implemented by one or more processors, circuitry or a combination thereof.

Further, according to the present invention, provided is a control method of an image capturing apparatus having an image sensor, the method comprising: a drive control step of driving the image sensor; and a detection step of calculating an evaluation value based on a plurality of second images and detecting flicker based on the evaluation value, wherein, in the drive control step, it is controlled so as to perform, during a first cycle of a display device: a first operation for reading out a first image to be displayed on the display device; and a second operation for reading out the plurality of second images at a second cycle which is shorter than the time taken to read out the first image at timings different from a timing of reading out the first image in a predetermined period in which the first image is read out from the image sensor, and wherein, in the detection step, upon calculating the evaluation value based on the plurality of second images, flicker is detected by using different pairs of images from among the plurality of second images for calculation of the evaluation value according to the first cycle.

Furthermore, according to the present invention, provided is a non-transitory computer-readable storage medium storing a program that when executed by a computer causes the computer to perform the method of an image capturing apparatus having an image sensor, the method comprising: a drive control step of driving the image sensor; and a detection step of calculating an evaluation value based on a plurality of second images and detecting flicker based on the evaluation value, wherein, in the drive control step, it is controlled so as to perform, during a first cycle of a display device: a first operation for reading out a first image to be displayed on the display device; and a second operation for reading out the plurality of second images at a second cycle which is shorter than the time taken to read out the first image at timings different from a timing of reading out the first image in a predetermined period in which the first image is read out from the image sensor, and wherein, in the detection step, upon calculating the evaluation value based on the plurality of second images, flicker is detected by using different pairs of images from among the plurality of second images for calculation of the evaluation value according to the first cycle.

Furthermore, according to the present invention, provided is a non-transitory computer-readable storage medium storing a program that when executed by a computer causes the computer to perform the above control method.

Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

