Quantifying interpretability for motion imagery with applications to image compression

For still imagery, the national imagery interpretability rating scale (NIIRS) has served as a community standard for quantifying interpretability. No comparable scale exists for motion imagery. This paper summarizes a series of user evaluations to understand and quantify the effects of critical factors affecting the perceived interpretability of motion imagery. These evaluations provide the basis for relating perceived image interpretability to image parameters, including ground sample distance (GSD) and frame rate. The first section of this paper presents the key findings from these studies. The second part of the paper applies these methods to quantifying information loss due to compression of motion imagery. We consider several methods for video compression (JPEG2000, MPEG-2, and H.264) at various bitrates. A set of objective image quality metrics were computed for the parent video clip and the various compressed products. The metrics are compared to subjective ratings provided by trained imagery analysts. The imagery analysts rated each clip relative to image interpretability tasks. Both the objective metrics and the ratings by analysts indicate the interpretability loss arising from the compression. The findings indicate the compression rates at which image interpretability declines significantly, with implications for sensor system design, systems architecture, and mission planning.