ROI coding with integer wavelet transforms and unbalanced spatial orientation trees

In this paper, we present region-based coding of medical images using integer wavelet transforms and the modified SPIHT algorithm. Our method differs from previously reported region-of- interest (ROI) coders in such a way that the region-based integer wavelet transform is used to obtain the representation of the partitioned image plane rather than differentiating the coefficients associated with each region after using the conventional wavelet decomposition. In fact, this region-based representation retains the properties of the conventional wavelet transform, and thereby facilitates the use of conventional wavelet coefficient plane coders for region-based coding. We propose a novel region-based coder based on the SPIHT algorithm. Previous region-based SPIHT coders employ conventional one-to-four parent-child binding, which accumulates coefficients from different regions within a spatial orientation tree. Alternatively, we present the unbalanced spatial orientation tree structure, which prevents the aforementioned heterogeneity in the tree, and size of which adapts to the size of the region being encoded. In addition to its superior rate-distortion (R-D) performance, the proposed coder offers region-size insensitive coding of the partitioned wavelet coefficient plane.