The present invention relates to a method, apparatus and computer program product enabling at least identification the presence data symbols that have been embedded in a media signal. A transmitted media signal is obtained (step 22), which comprises a possibly distorted version of a host signal in which data symbols have been embedded by quantisation using a certain quantisation step size and to which dither with a set of dither values has been added. Several dither value intervals within the set are provided, where each interval corresponds to one dither value (step 26). A histogram is determined for each interval (step 30), where a histogram is determined for all sample values of a set of signal samples of the transmitted media signal and having a dither value in the corresponding interval. The separate histograms are combined and a rescaling factor is determined based on the combined histogram (step 32) in order to estimate the quantisation step size.
展开▼
