Fixed-slope near-lossless context-based image compression

This paper generalizes trellis based near-lossless image compression schemes, in order to satisfy two constraints: a local one, which enforces an upper bound /spl epsiv/ for the reconstruction error at every pixel, and a global one, which penalizes the quantity R+/spl lambda/D (the rate and distortion over each line of the image). By changing /spl lambda/ we obtain gradual changes from lossless coding (/spl lambda//spl infin/) to DPCM near-lossless coding (/spl lambda/=0), resulting in a distinct rate-distortion curve for each tolerance /spl epsiv/. We propose here a trellis-based fixed-slope near-lossless compression approach, that fits the adaptive context coding scheme ASBOSC introduced in 1997. The experimental results over a set of test images in near-lossless mode are better than the results obtained with other near-lossless techniques.