Efficient image coding for access to pixel ranges

Technical imaging applications such as coding "images" of digital elevation maps, require extracting regions of compressed images with the pixel values within a pre-defined range, without having to decompress the whole image. Previously, we introduced a class of nonlinear transforms which are small modifications of linear transforms to facilitate a search for the regions with pixel values below (above) a given \´threshold\´, without incurring any penalty in coding efficiency. However, coding efficiency had to be somewhat compromised when searching for regions with a given pixel \´range\´, especially at high coding rates. In this paper, we propose an improved method of pixel \´range\´ coding to deal with the aforementioned problem. Results show significant improvements in coding efficiency.