The figure below compares the theoretical minimum data rate e with the measured data rate E3 for a common redundancy reduction scheme that consists of differential pulse code modulation (DPCM) and entropy coding as shown below. The DPCM encoder first predicts the acquired sample so based on some previous samples s1, s2, ..., sn, and it then subtracts this prediction from the actual value. The decoder reverses this process by adding the prediction to the received signal. The entropy (Huffman) coding, which follows the DPCM, deals with the efficient assignment of binary code words. The efficiency is gained by letting the length of the binary code word for a quantization level be inversely related to its frequency of occurrence. The measurements E3 are the average of 30 trials with different realization of the random-polygon scene. The actual data rate E3 for non-Gaussian signals can be lower than e, which is defined only for a Gaussian signal.