Figure 3. Sparsity measures for three different coordinate system origins ().

Sparsity as measured with respect to different coordinate system origins (), as a function of the relative size of the active region. Remark that for a relative size of zero, only background samples are present and, thus, the mean of the mixture model coincides with the mean of the background (and the two sparsity measures correspond at this point). An analogous observation can be made for a relative size of one, now with respect to the activity (signal samples).