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Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment.

Abstract：

:The superimposition of a face photograph with that of a skull for identification purposes necessitates the use of comparable photographic parameters between the two image acquisition sessions, so that differences in optics and consequent recording of images does not thwart the morphological analysis. Widely divergent, but published, speculations about the thresholds at which perspective distortion becomes negligible (0.5 to >13.5 m) must be resolved and perspective distortion (PD) relationships quantified across their full range to judge tolerance levels, and the suitability of commonly employed contemporary equipment (e.g., 1 m photographic copy-stands). Herein, basic trigonometry is employed to map PD for two same sized 179 mm linear lengths - separated anteroposteriorly by 127 mm - as a function of subject-to-camera distance (SCD; 0.2-20 m). These lengths approximate basic craniofacial heights (e.g., tr-n) and widths (e.g., zy-zy), while the latter approximates facial depth (e.g., n-t). As anticipated, PD decayed in logarithmic and continuous manner with increasing SCD. At SCD of 12 m, the within-image PD was negligible (<1%). At <2.5 m SCD, it exceeded 5% and increased sharply as SCD decreased. Since life size images of skulls and faces are commonly employed for superimposition, a relative 1% perspective distortion difference is recommended as the ceiling standard for craniofacial comparison (translates into a ≤2 mm difference in physiognomical face height). Since superimposition depends on relative comparisons of a photographic pair (not one photograph), there is practically no scenario in superimposition casework where SCDs should be ignored and no single distance at which PD should be considered negligible (even if one image holds >12 m SCD).

journal_name

Forensic Sci Int

journal_title

Forensic science international

authors

Stephan CN

doi

10.1016/j.forsciint.2015.09.009

subject

Has Abstract

pub_date

2015-12-01 00:00:00

pages

520.e1-520.e8

eissn

0379-0738

issn

1872-6283

pii

S0379-0738(15)00381-3

journal_volume

257

pub_type

杂志文章

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Perspective distortion in craniofacial superimposition: Logarithmic decay curves mapped mathematically and by practical experiment.