As a technique for supporting a diagnosis based on a tissue sample image of a biological tissue, a method in which a diagnosis is made through staining a section of a biological tissue and then observing the state of the staining is known. It is important for the diagnosis to separate a stromal part from the tissue sample image after the staining. The patent document 1 describes a classification of stroma from a biological tissue through hematoxylin-eosin staining (HE staining). Specifically, the paragraph [0073] of the patent document 1 describes the following. “Tissue stroma is dominated by the color red. The intensity difference d, “red ratio” r=R/(R+G+B) and the red channel standard deviation σR of image objects may be used to classify stroma objects.” That is, stroma is stained red with eosin, and therefore, the stroma objects are classified by the color thereof.