Each frame image is acquired as an input image. An image obtained by emphasizing high frequency components in the input image is generated as a high frequency component emphasized image, a composite image is generated by compositing the input image and an input image of a previous frame before the input image, and an image including low frequency components in the composite image is generated as a low frequency component image. Then, the high frequency component emphasized image and low frequency component image are alternately output as images of sub-frames of the input image.