Levels of knowledge for object extraction

A paradigm for image interpretation and object extraction that deals explicitly with the levels of abstraction of such processes is described. The central new feature of this paradigm is two intermediate-level processes that deal with construction of symbolic image tokens and with symbolic descriptions of quantities. These intermediate-level processes have access to digital data but produce symbolic, abstract tokens and descriptions. The object extraction system is controlled by a higher-level symbolic process that uses knowledge-based reasoning. To demonstrate this paradigm of reasoning according to levels of abstraction, we present its description in the limited domain of road-finding on aerial photographs. This example is followed in detail from the construction of line segments and uniform blobs, which are intermediate-level tokens, to the construction of contextual road segments from these tokens.