1. An image producing apparatus comprising: a reconstructing unit configured to use a first reconstruction filter to reconstruct an image based on projection data collected by a scan on a subject to be imaged using a radiation source and a detector; a difference-calculating unit configured to calculate a difference between two images based on said projection data, said two images being reconstructed using second and third reconstruction filters respectively having spatial frequency characteristics such that degrees of enhancement in a mid-/low-frequency region are substantially identical to each other and degrees of enhancement in a high-frequency region are different from each other; and an image production unit configured to produce an image having reduced aliasing artifacts using said image reconstructed using said first reconstruction filter, and said difference.