**3. User-based evaluation of compression**

To quantify image interpretability, subjective rating scale was developed by Irvine *et al.* (2007c), based on consistent ratings by trained imagery analysts. The scale assigns the values 0 to a video clip of no utility and 100 to clips that could support any of the analysis tasks under consideration (Fig. 3). Three additional clips identified in this study formed markers to evenly divide the subjective interpretability space. Thus, reference clips were available at subjective rating levels of 0, 25, 50, 75, and 100.

Fig. 3. NIIRS Development Functional Decomposition

A set of specific image exploitation tasks were reviewed by imagery analysts and rated relative to these marker video clips. In this way, these analysis tasks were calibrated to the subjective rating scale. A subset of these "calibrated" analysis tasks were used to evaluate the compressed video products (Table 2). Note that some of these tasks do not require analysis of temporal activity and could be performed with still imagery. We label these as "static" tasks. A second set of tasks are "dynamic" because they require direct observation or inference about movements of objects.

Image analysts rated their confidence in performing each image exploitation task with respect to each compression product, including the original (uncompressed) clip. We calculated an overall interpretability rating from each analyst for each clip.
