Improved delta modulation algorithm for image coding

In a delta modulation (DM) system, the difference between two consecutive pixel intensities is coded by an one-bit quantizer. The performance of a basic DM system depends only on two quantities: sampling rate and quantization step size. In order to reach low bit-rate while preserving the decoded image quality, these two quantities have to be designed carefully. The performance of the DM system can be improved by using a delayed coding scheme and/or adapting the step size. However, such a DM system becomes so complex that it loses the advantage of simplicity. In this paper, we propose a modified DM algorithm to keep the advantage of simplicity while improving the performance of the DM system. Based on the characteristics of the human visual system, we introduce a nonlinear DM scheme by adapting a relative step size, in which the Robert's pseudo-noise technique is employed to make the proposed system stable. In addition, we show that the proposed system with a 2D predictor improves the subjective quality of the decoded image.