Aiming at the defects of the PSI (Pixel Shape Index) algorithm, this algorithm has been modified accordingly, and an improved PSI algorithm of adaptive spectral
threshold (Improved Pixel Shape Index of Adaptive Spectral Threshold, IPSIAST) is proposed in this paper. The main advantages of the new algorithm are following: 1) In order to
enhance the rationality of direction line generation, the differences existed in the spectral feature homogeneity between the bands have been considered adequately. The
direction line on each band layer is extended independently. 2) Length of each direction line is defined as the weighted sum of the lengths about all direction lines along the
same orientation on all band layers. The differences existed in the spectral feature homogeneity between the bands are further reflected by this way, and the accuracy of PSI
about each pixel is improved. 3) Spectral threshold T1 can be adjusted adaptively according to the spectral homogeneity of the local region, and the influence of the
contrast on the edge of the surface feature will be reduced during the computing process of the PSI. Finally, by using visual comparison analysis and five quantitatively
evaluating indexes, the results of experiments showed that compared with the PSI, the imagery segmentation accuracy was further improved through associating with the IPSIAST.