1. An image processing method comprising the steps of: obtaining an image generated by an image pickup system; and performing correction processing for the image by performing convolution of an image restoration filter on the image, the image restoration filter being generated or selected based on an optical transfer function of the image pickup system, wherein the image restoration filter is configured to reduce, of a phase degradation component and an amplitude degradation component of the image, the phase degradation component, which is an asymmetric image component corresponding to an asymmetric point spread function of the image pickup system, without reducing the amplitude degradation component, the reduction of the phase degradation component increasing symmetry of the phase degradation component.