Embedded still image coder with rate-distortion optimization

It is well known that the fixed rate coder achieves optimality when all coefficients are coded with the same rate-distortion (R-D) slope. In this paper, we show that the performance of the embedded coder can be optimized in a rate-distortion sense by coding the coefficients with decreasing R-D slope. We denote such coding strategy as rate-distortion sense by coding the coefficients with decreasing R-D slope. We denote such coding strategy as rate-distortion optimized embedding (RDE). RDE allocates the available coding bits first to the coefficient with the steepest R-D slope, i.e. the largest distortion decrease per coding bit. The resultant coding bitstream can be truncated at any point and still maintain an optimal R-D performance. To avoid the overhead of coding order transmission, we use the expected R-D slope which can be calculated from the coded bits and are available in both the encoder and the decoder. With the probability estimation table of the QM- coder, the calculation of the R-D slope can be just a look- up table operation. Experimental results show that the rate- distortion optimization significantly improves the coding efficiency in a wide range of coding rates.