1. A method for detecting a pattern from an image of an over-sampled datapage, comprising: detecting a detection image of the datapage by over-sampling the datapage; comparing the detection image with a reference image by a covariance, the reference image is an imagae of over-sampling for the pattern by a covariance; and, calculating a pixel of the pattern over-sampled by values of the reference image and the detection image compared by the covariance.