1. A parallel correlation method, adapted for an optical navigation device, the method comprising: a) generating a reference array corresponding to a reference image and a compare array corresponding to a first compare image captured; b) storing the reference array in a first memory bank in a manner that the reference pixel values of an ith column of the reference array are indexed by the ith column; storing the compare array in a second memory bank in a manner that the compare pixel values of a jth column of the compare array are indexed by the jth column; and c) fetching the compare pixel values from the second memory bank and the corresponding reference pixel values from the first memory bank with column indexing to simultaneously compute the correlation between the reference array and the compare array for a L×M correlation array, wherein each correlation value in the L×M correlation array corresponds to an indexing movement of the reference array over the compare array; wherein L, M, i, and j are integers.