In this paper, based on a careful investigation on the calibration (downsample) technique, we improve two detectors for detecting LSB matching: Calibrated HCF COM and Calibrated Adjacency HCF COM. Instead of using the COM (center of mass) of the HCF (histogram characteristic function), we consider the ratio of the histogram's DFT coefficients of the image to the corresponding coefficients of the downsampled image. Moreover, we propose to downsample only for non-oscillating pixels. With a same level of computational complexity, the new detectors thus obtained are better than the old ones, especially for uncompressed images.