The invention provides an image processing method in a diagnostic apparatus of diagnosing a disease using a captured image of an affected area, comprising the steps of: (i) separating the captured image memorized into a brightness component and a color information component (Step S131); (ii) separating the brightness component into a base component and a detail component (Step S132); (iii) performing a highlighting process on the base component and/or the detail component (Step S133-S140); and (iv) restoring a brightness component from a highlighted base component and the detail component, and/or from the base component and a highlighted detail component, and using the restored brightness component and the color information component to generate a highlighted image (Step S141).