I. Introduction
Image segmentation is to segment an image into several regions which inner pixels are with a same homogeneous feature. The features of still image in spatial domain can be categorized into three types: intensity, colors distribution and texture. In general, the dominant criterion in image segmentation is described as follows [1].
Each segmented region must be with a single identity and represents a same characterization.
The original image is composed of the segmented regions.
The structure of segmented region must be possibly simplified to avoid over-segmentation.
There must be significant different characterizations during the adjacent regions.
The edge of segmented region must be clear and easily recognized.