A new combinatorial characterization of a gray-tone image called Euler Vector is proposed. Euler number of a binary image is a well-known topological feature, which remains invariant under translation, rotation, scaling, and rubber-sheet transformation of the image. Euler vector comprises of a 4-tuple, where each element is an integer representing the Euler number of the partial binary image formed by the four most significant bit planes of the graytone image. Experimental results demonstrate

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... bustness of Euler vector under compression and inclusion of noise followed by filtering. The vector is topologically invariant and can be used for image indexing and retrieval. Index Terms-Euler number, digital image processing.