Abstract
It is well established that natural scenes have a 1/f drop off of spatial and temporal frequencies. The exponent or slope of this drop off has often been reported as being equal to 1. However, more recent work in the spatial domain has revealed that only a few natural scenes conform to this value. Instead, photographs of natural scenes on average have a slope ~1.2, and can range between 0.8 to 1.4. It is currently unknown whether this is also the case in the temporal domain, as to the best of our knowledge, an analysis of a wider range of natural movies has yet to be conducted. Here we measure the 1/f spatiotemporal amplitude spectrum of movies in the DynTex database—a freely available dynamic texture database. We manually labelled a subset of movies across three categories: 1) Natural – containing mostly natural objects, 2) Mixed – containing a roughly equal mix of natural and man-made objects, 3) Unnatural – containing mostly man-made objects. Across the three categories, we found large variance in both spatial and temporal slope measurements. In the spatial domain, our findings closely correspond to past research where the slope in the Natural category was ~1.1 on average, but had a wider range between ~0.6 to 1.9. In the temporal domain we found that the slope in the Natural category was ~0.5 on average, and ranged between ~0.0 to 1.1. Mixed and Unnatural categories had significantly different spatial and temporal slope measurements, where slopes on average were steeper spatially (~1.3) and shallower temporally (~0.4). The temporal slope measurements in the Natural category notably differ from past research. This finding may be unique to the database analysed, and as such further research is needed to confirm the extent to which 1/f slope in the temporal domain varies in nature.