An image is picked up through sampling in a predetermined sampling pattern to acquire an image signal representing the image. Sampling information, which concerns the predetermined sampling pattern, is appended to the image signal, which has been acquired. The sampling information is information for discriminating checkered sampling and square sampling from each other. Different sharpness enhancement processing is performed on the image signal and in accordance with the sampling information to obtain a processed image signal. The different sharpness enhancement processing may be a processing in accordance with frequency characteristics of the image signal, which has been acquired, due to the sampling pattern.