Dense scale selection over space, time and space-time

TL;DR

This paper introduces a methodology for dense scale selection across space, time, and space-time domains, enabling local characteristic scale estimation at every point and moment in images, signals, and videos.

Contribution

It proposes a novel approach for dense scale selection using local extrema detection of a quasi quadrature measure, addressing phase dependency issues in scale estimates.

Findings

Results show local scale estimates reflect variations in characteristic structures.

Method achieves reasonable and consistent scale detection across diverse data types.

Addresses phase dependency in scale estimation for more accurate local scale detection.

Abstract

Scale selection methods based on local extrema over scale of scale-normalized derivatives have been primarily developed to be applied sparsely --- at image points where the magnitude of a scale-normalized differential expression additionally assumes local extrema over the domain where the data are defined. This paper presents a methodology for performing dense scale selection, so that hypotheses about local characteristic scales in images, temporal signals and video can be computed at every image point and every time moment. A critical problem when designing mechanisms for dense scale selection is that the scale at which scale-normalized differential entities assume local extrema over scale can be strongly dependent on the local order of the locally dominant differential structure. To address this problem, we propose a methodology where local extrema over scale are detected of a quasi quadrature measure involving scale-space derivatives up to order two and propose two independent mechanisms to reduce the phase dependency of the local scale estimates by: (i) introducing a second layer of post-smoothing prior to the detection of local extrema over scale and (ii) performing local phase compensation based on a model of the phase dependency of the local scale estimates depending on the relative strengths between first- vs. second-order differential structure. This general methodology is applied over three types of domains: (i) spatial images, (ii) temporal signals and (iii) spatio-temporal video. Experiments show that the proposed methodology leads to intuitively reasonable results with local scale estimates that reflect variations in the characteristic scales of locally dominant structures over space and time.