1. An image processing method in a diagnostic apparatus for diagnosing a lesion using a captured image of an affected area to be diagnosed, the method comprising: performing an image conversion processing corresponding to a first state of disease on the captured image to generate a converted image, wherein the image conversion processing comprises a structure clarifying conversion process corresponding to the first state of disease, wherein the structure clarifying conversion process comprises: performing a first separation process of separating the captured image into a brightness component and a color information component; performing a second separation process of separating the brightness component into a base component and a detail component; performing highlighting processing on the base component; and performing a generation process of restoring a brightness component based on a highlighting-processed base component and the detail component, and using the color information component to generate a highlighted image, and wherein in the generation process, the highlighting-processed base component is added to the detail component to restore the brightness component, and a conversion to a second color space is performed based on the restored brightness component and the color information component corresponding to a direction of a red-based color and a direction of a blue-based color in a first color space so as to generate the highlighted image.