Image retrieval based on tolerable difference of direction

This paper proposes two polynomial algorithms for similar image retrieval on the basis of tolerable difference of direction. A user can freely determine the tolerable difference of direction to meet his requirements. This paper then proposes an algorithm to recognize rotational invariance images. In the modified algorithm, it is unnecessary for a user to specify where the rotation center is. Experimental results show that the rotational angle estimated by this algorithm is close to the actual rotational angle if the required parameter value is well determined