1. A method comprising: obtaining spectral computed tomography (CT) information via an acquisition unit comprising an X-ray source and a CT detector; generating, with one or more processing units, using at least one image transform, a first basis image and a second basis image using the spectral CT information; performing, with the one or more processing units, guided processing on the second basis image using the first basis image as a guide to provide a modified second basis image; performing a first inverse image transform using the first basis image and the modified second basis image to provide a first modified image; and performing a second inverse image transform using the first basis image and the modified second basis image to provide a second modified image.