A digital signal processor such as a watermark detector (12-18) operating with integer arithmetic circuits has a certain accuracy. Each processing step (multiplication, addition) increases the number of bits (the word length). For example, the Fast Fourier Transform (12) having a butterfly structure requires a plurality of such processing steps to be performed. In practical implementations, the processing steps are recursively performed by a single integer arithmetic circuit having a given word length, say N. After each step, the word length of the signal is reduced to the given word length N by rounding, truncation, or some other smart form of quantization. In order to prevent quantization errors, the signal is pre-processed by a pre-processor (19) which reduces the word length and which is invariant with respect to the subsequent process.; This means that if the pre-processor operated with infinite accuracy, it would have no effect on the subsequent process. If such a pre-processor operates with finite accuracy, it will reduce the quantization noise.
|Published - 6 Apr 2005