Comparison of Software Tools for Analysis of Hemispherical Photographs

A question of particular interest is which software program should be used for processing of hemispherical photographs (HP) of forest canopies? While a few studies have attempted to address this question, varying approaches to comparing different HP software have not resulted in conclusive evidence as to which software is best. Our objective was to select from available software and to conduct a functional analysis of software features and capabilities, followed by a quantitative analysis of photographs representing a range of forest canopies at four sites, to provide an improved basis for software selection. Four criteria encompassing availability, maintenance, documentation and active use were used to select among available HP programs for assessment. Six programs were selected (Gap Light Analyzer (GLA) , HemiView , CAN-EYE , CIMES , WinSCANOPY , SOLARCALC ), but one (WinSCANOPY) was not made available by the manufacturer for further assessment. The programs were used to estimate three structural-canopy and two light-regime attributes. There was a high degree of agreement among some of the attributes evaluated, and statistically significant differences among others. Differences were attributed, in part, to variations in the algorithm selected and in its implementation in the software for a given attribute. Identifying which software to select is a function of many factors governing interoperability, availability, software functionality, user experience and intended application. The decision depends on knowledge of these factors, of the algorithms used by the programs, and of the potential for error in image acquisition and processing.