In this paper we present a robust focus measure for unsupervised au to-focusing based on optimum discrete cosine transform (DCT) coefficients. The focusing window of an input image is divided into non-overlapping 8×8 sub-images, and the focusing measure is computed from the appropriately chosen mid frequency band. Be cause of low complexity in computing the DCT coefficients, the proposed focusing measure can be applied to the real-time auto-focusing. Experimental results show that the proposed method is more effective than the traditional methods based on comparison with well-known autofocusing uncertainty measure (AUM).
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