An image processing apparatus includes an acquisition unit configured to acquire a first medical image and a second medical image that are three-dimensional images obtained by imaging a subject, a determination unit configured to determine a first resolution based on a resolution of the first medical image and determine a second resolution based on a predetermined resolution, a first generation unit configured to generate a first subtraction image having the first resolution by performing a first subtraction process between the first and second medical images, and generate a second subtraction image having the second resolution by performing a second subtraction process between the first and second medical images, and a second generation unit configured to generate a projection image using the second subtraction image.