Implementation of a fixed-point MPEG-4 scalable lossless coding encoder

Abstract

In this paper, we propose four fixed-point nonlinear functions to develop a fixed-point MPEG-4 scalable lossless coding (SLS) encoder: the square-root function, the logarithmic function, the exponential function, and the trigonometric function. The accuracy and complexity of the proposed fixed-point functions can be controlled by setting the required number of iterations to process a fixed-point function. A fixed-point square-root function is implemented based on the long-hand decimal division, and the complexity of the function is reduced by scaling the input so that the most significant bit (MSB) of the input can be processed at the first iteration. For the fixed-point logarithmic function, a piece of input is converted into an exponent and a mantissa. Then, the output of the function is obtained by independent operations using the exponent and mantissa. A fixed-point exponential function is implemented through the multiplication of the output range and scale factors that are generated from a characteristic of the exponential function. A fixed-point trigonometric function is proposed by designing the output table that has different step size according to input because the function has a different slope at each input. The fixed-point MPEG-4 SLS encoder is implemented using the proposed fixed-point nonlinear functions so that it can be developed on a chip or a fixed-point digital signal processor (DSP) at low-cost. To evaluate the performance of the implemented fixed-point MPEG-4 SLS encoder, two bit-streams, one encoded by a fixed-point MPEG-4 SLS encoder and the one by a floating-point encoder, are decoded using a floating-point MPEG-4 SLS decoder. Then, the root mean square (RMS) is measured from two decoded sounds. The RMS of the fixed-point MPEG-4 SLS encoder is less than -77.35 dB, and both the decoded sounds are identical by 77.2%.