Patent ID: 7110567

Claim:
A method of detecting a watermark in the form of a set of coefficients in an information signal, the method including the steps of: configuring, intended to configure said watermark in the form of a matrix of size M*M, and said information signal in the form of at least one matrix of size M*M, calculating the coefficients of the Fourier transform matrix of the signal matrix, calculating the coefficients of the Fourier transform matrix of the watermark matrix, calculating the inverse transform matrix of the multiplication of the transform matrix of the signal and the transform matrix of the watermark, detecting the watermark by detection of peaks in the coefficients of the inverse transform matrix of the multiplication, characterized in that the calculation step of the inverse transform matrix of the multiplication is carried out in sequences which each result in obtaining I columns of the inverse transform matrix of the multiplication, M being a multiple of I and different from I, said I columns being stored in a memory called internal memory, and in that the detection step of the watermark is carried out with each sequence by a detection of peaks in each set of the I columns, white said I columns are present in the internal memory.