Pixel mixing device and method for controlling operation of same

The present invention enables knowing whether a pixel is of a high-frequency prior to pixel mixing. In a partial image (11) obtained from an imaging element having a Bayer array, Gr pixels representing the green component in rows having R pixels representing the red component are distinguished from Gb pixels representing the green component in rows having B pixels representing the blue component. The distinguished Gr pixels and Gb pixels are separately subjected to pixel mixing. If the pre-mixing image is a high-frequency component, the levels of the post-pixel-mixing Gr pixels and Gb pixels differ. It is known whether the pre-pixel-mixing image is of a high-frequency component from the levels of the Gr pixels and the levels of the Gb pixels after pixel mixing.