An apparatus having image processing function performs image processing method. In the image processing method, a first portion of data is acquired as a data stream obtained from image data that has been sequentially converted and encoded, then the acquired data is decoded to obtain a two-dimensional image. The two-dimensional image is analyzed to determine a region of interest within the two-dimensional image. Then, a second portion of data is acquired as a data stream obtained from the image data based on the region of interest. Thus, areas that are useful to the diagnosis can be displayed promptly and in detail.