Hierarchical Description of Textures

A system is proposed which analyzes various textures statistically or structurally, depending on the nature of the textures. The system first describes a texture globally by both gray level first order statistics and edge statistics to roughly classify it. Next, the system extracts homogeneous gray level regions to try to describe the texture structurally. However, if too many regions are extracted or if regions cannot be easily extracted, this indicates the existence of micro-textures. In such a case, the system extract regions based on local gray level first order statistics and local edge statistics. Then figure regions are distinguished from ground regions and are decomposed into atomic texture elements of simple shape. The system then describes the structure of the atomic texture elements. If there are locally ordered texture elements, they are grouped into subpatterns and their structure are described. This process results in a hierarchical description of the texture. I Introduction Texture carries useful information with which a vision system may discriminate objects and identify them. Thus It Is necessary to describe textures compactly, for example, for scene analysis, analysis of aerial photographs, or diagnosis of medical images. Texture has been studied on at least two levels: statistical and structural [1], On the statistical level, a texture is defined by a set of statistics extracted from a large ensemble of local picture properties. On the structural level, a texture is considered to be defined by elements which occur repeatedly according to placement rules. Roughly speaking, statistical methods are suitable for micro-textures and structural methods are suitable for macro-textures. There are at least four types of textures from the view of analysis. The model texture patterns are shown in Fig.1. Pattern A has many small texture elements in the image. So it can be described by global statistics without regard to the texture elements. Pattern B also has many small texture elements but they form local clusters. It is reasonable to regard clustered texture elements as regions and to describe the structure of those regions. Pattern C has comparatively large texture elements; it is reasonable to describe the structure of the fexture elements. Pattern D also has large texture elements but they constitute subpatterns. It is reasonable to group such locally ordered texture elements and describe the structure of the subpatterns. In this paper, a system is proposed which analyzes textures statistically or structurally depending on their natures. Hierarchical descriptions …